[0001] End Effectors and End Effector Pads Having Crosslinked Polymers for Semiconductor Applications to Provide Improved Manufacturing Speed and Methods of Making and Using the Same

CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This U.S. Non-Provisional Patent Application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 63/306,270, filed February 3, 2022, entitled, “End Effectors and End Effector Pads Having Crosslinked Polymers for Semiconductor Applications to Provide Improved Manufacturing Speed and Methods of Making and Using the Same,” the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0003] The invention is related to the field of semiconductor applications and to providing desired frictional sliding characteristics to parts for use, for example, in wafer transfer including end effectors, and more particularly to incorporating crosslinked aromatic polymers into parts such as end effectors and end effector pads for use in semiconductor or other end applications where similar frictional sliding characteristics are desired.

DESCRIPTION OF RELATED ART

[0004] In the semiconductor manufacturing field, semiconductor wafer handling is an important step in the fabrication process of semiconductor wafers and semiconductor chips. Due to the need to keep such processes isolated, different steps are carried out in different reaction chambers, and semiconductor wafers (from which semiconductor chips are formed) are transported from chamber to chamber within the processing apparatus. For example, cluster tools with multiple processing chambers for carrying out key manufacturing steps as required to fabricate devices, such as layering, patterning, doping and heat treatment. A cluster tool typically includes chambers for loading and unloading a wafer, a central tool (such as a robotic apparatus) to transfer semiconductor wafers between processing chambers and various processing chambers in communication with the robotic apparatus. A robotic arm or similar device can move the semiconductor wafer into and out of the various processing chambers. Such cluster tool designs can shorten processing time and improve yield efficiency as well as to reduce instances of contamination.

[0005] Cluster tools may be used with the majority of types of processes employed in a wafer fabrication plant (“wafer fab”), including photolithography, etching, chemical vapor deposition (“CVD”) and physical vapor deposition, cleaning, thermal processing, and photoresist stripping. A sequence of these chemical and physical processing steps is typically performed repeatedly using different tools to build the required chip structure on a silicon wafer. One limiting factor in the efficiency of the overall wafer fabrication process is the speed at which a wafer is transported from one chamber to another in a cluster tool or other semiconductor manufacturing apparatus having various chambers and a wafer transportation apparatus. The wafer transfer operation in most wafer processes uses a robotic hand. The end of such robotic hand is commonly referred to as an end effector. The end effector is used when lifting the wafer and when moving it. However, due to the need to maintain the purity of a wafer and avoid damage to the wafer, semiconductor wafers in operation are typically positioned on the end effector without the use of any other robotic end effector fixture such as a pin, adhesive or gripping device. Instead, the wafer is positioned and held in place by friction acting as the force, and typically the sole force, to prevent the wafer from sliding while loading and in transit.

[0006] Thus, speed and acceleration of the process with respect to movement of the end effector is necessarily generally limited to the applicable friction force which must be present to avoid wafer displacement and/or misalignment. Thus, while some force is necessary for that purpose, the force must also be able to be overcome for the purpose of wafer transfer.

[0007] Prior art end effector “hands,” typically are positioned on a robot “arm” such as a blade, paddle, fork or plate-like device. End effectors are known to include pads positioned on the end effector that contact the wafer. The pads must be initially chemically clean, remain chemically clean during processing, release sufficiently low levels of particulates, and have a controllable static coefficient of friction that allows the robot to be programmed to operate successfully at a standard set of processing conditions.

[0008] Semiconductor wafers are often very hot, as they are subjected to process temperatures of 300°C and, in some cases as high as 400°C or more. The demands for further high temperature processing and increased process speed can be limited by end effectors which either cannot be used at such high temperatures or which do not have properties that allow for increases in processing speed. [0009] Elastomers, such as fluoroelastomers (FKM) or perfluoroelastomers (FFKM) have been used in transporting wafers in a wafer fab, since they typically are able to provide a high static coefficient of friction in comparison to most plastics, and are generally also soft, so they do not scratch the backside of the wafer. They also typically have low levels of particle generation which is desirable in such processes. However, most FKM and FFKM elastomers, have temperature limits that can range to about 200°C for FKMs and to about 350°C for FFKMs, depending on the polymer backbone, crosslinker used and elastomer formulation. This limits their applicability in end effector applications when considering effectiveness at even higher temperatures or when considering their use for long periods of time.

[0010] Ceramics such as alumina have also been employed in end effector pads, but they are very hard materials and can scratch the backside of the wafer. They also typically generate inorganic particles due to wear between the ceramic and the wafer silicon, which causes cleanliness issues in the process. Further, the static coefficient of friction of prior art ceramics used in end effectors, when mated with a silicon wafer is typically significantly lower than that of organic materials paired with a silicon wafer. Lower coefficients of friction translate to a lower speed of transport of the wafer from chamber to chamber, which limits throughput and efficiency of the overall process.

[0011] In U.S. Patent No. 9,698,035, microstructures or nanostructures such as nanohairs are provided to surfaces to modify the coefficient of friction through van der Waals forces to prevent sliding of a wafer on an end effector to improve processing speed. Such materials are complex and have to be formed using techniques such as nanoprinting or lithography.

[0012] U.S. Patent No. 8,276,959 discloses end effectors having end effector pads that are coupled to the end effector using magnetic force. Such mechanisms may incorporate carbon fiber reinforced polymers, alumina, metal matrix composites, an aluminum beryllium matrix or other ceramic materials.

[0013] International Publication No. WO 2018/157179 A2 discloses a modified design of an end effector to remove rougher edges of the pad to avoid wafer damage, and in which the end effector pad is formed from polyetherether ketone.

[0014] While there have been various attempts at forming end effector pads, there remains a need in the art for an end effector material that can withstand temperatures of 350°C to 400°C or higher, which is softer than a silicon wafer to avoid scratching, and that has a static coefficient of friction higher than ceramics such as alumina to maintain wafer position in transport so that processing speeds may be increased. BRIEF SUMMARY OF THE INVENTION [0015] The invention herein comprises an end effector pad and an end effector for use in robotic transfer. In an embodiment herein an end effector pad is provided that is for use in an end effector for robotic transfer. The end effector pad comprises a first portion for supporting an object to be moved and a second portion for positioning the end effector pad on an end effector body, an upper surface on the first portion of the end effector pad is configured for supporting an object, and at least the upper surface of the first portion of the end effector pad comprises at least one crosslinked aromatic polymer. In one embodiment, the at least one crosslinked polymer comprises a crosslinked polymer that is at least substantially amorphous or is fully amorphous and is operable at temperatures above the glass transition temperature of the crosslinked polymer. In another embodiment, the at least one crosslinked polymer comprises a crosslinked polymer that is semicrystalline and is operable at temperatures above the crystalline melting point of the crosslinked polymer.

[0016] The end effector pad is preferably operable in an end effector for robotic transfer at temperatures of about 300°C to about 450°C.

[0017] The second portion of the end effector pad may extend longitudinally from the first portion of the end effector pad, and the second portion of the end effector pad may be configured to connect the end effector pad to an end effector body. The second portion of the end effector pad may also comprise screw threads thereon for mating with receiving threads on an end effector body. In such an embodiment, the screw threads on the second portion of the end effector pad preferably extend circumferentially around at least a portion of the outer surface of the second portion of the end effector pad.

[0018] The upper surface of the first portion of the end effector pad may comprise at least one curved feature formed on the first portion of the end effector pad. The at least one curved feature of the upper surface of the first portion of the end effector pad in an embodiment herein is configured to have a generally convex dome shape and to extend outwardly from the first portion of the end effector pad so that at least a center point of the at least one curved feature is positioned to support an object placed thereon.

[0019] The least one curved feature may extend over all or substantially all of the upper surface of the first portion of the end effector pad. There may be two or more curved features on the upper surface of the first portion of the end effector pad. In such an embodiment, each of the two or more curved features may be configured as a convex dome shape and extend outwardly from the upper surface of the first portion of the end effector pad so that at least a center point of each of the convex dome-shaped curved features is positioned to support an object placed thereon. [0020] The two or more curved features may also be positioned around a central point of the upper surface of the first portion of the end effector pad, and optionally may be positioned so that some or all of the two or more curved features are equidistant from the central point of the upper surface. Further, the two or more curved features may be arranged in a pattern around the central point of the upper surface of the first portion of the end effector pad.

[0021] In other embodiments, there may be from two to about four, from about five to about 14 curved features or from about 15 to about 73 curved features on the upper surface of the first portion of the end effector pad.

[0022] In one embodiment, the entire first portion of the end effector pad comprises the at least one crosslinked aromatic polymer. The entire end effector pad may also comprise the at least one crosslinked aromatic polymer. Further, the end effector pad may include the at least one crosslinked aromatic polymer as an outer layer over the first portion and/or the second portion of the end effector pad.

[0023] The at least one crosslinked aromatic polymer noted above, in embodiments herein, may be selected from crosslinked aromatic polymers such as, but not limited to, polyarylenes, polysulfones, polyethersulfones, polyphenylene sulfides, polyphenylene oxides, polyimides, polyetherimides, thermoplastic polyimides, polybenzamide, polyamideimide, polyurea, polyurethane, polyphthalamide, polybenzimidazole, polyaramid, and blends, co-polymers, and alloys thereof. In preferred embodiments herein, the crosslinked aromatic polymer is formed from crosslinking a polyarylene selected from polyetherketone, polyetheretherketone, polyetherdiphenylether ketone, polyetherketone ketone, and blends, co-polymers and alloys thereof.

[0024] The at least one crosslinked aromatic polymer may be a crosslinked polyarylene selected from polyetherketone, polyetheretherketone, polyetherdiphenylether ketone, polyetherketone ketone, and blends, co-polymers and alloys thereof.

[0025] The least one crosslinked aromatic polymer may be formed by providing a composition comprising one or more crosslinkable aromatic polymers and crosslinking at least one of the crosslinkable aromatic polymers in the composition. The at least one crosslinkable aromatic polymer may comprise one or more functionalized groups for crosslinking.

[0026] The at least one crosslinkable polymer may be a polyarylene ether having repeating units along its backbone according to the structure of formula (I): wherein Ar ¹ , Ar ² , Ar ³ and Ar ⁴ are identical or different aryl radicals, m = 0 to 1, and n = 1- m.

[0027] The at least one crosslinkable aromatic polymer may have repeating units along its backbone having the structure of formula (II): (II); or formula (Ila):

(Ila).

[0028] The at least one crosslinkable aromatic polymer may comprise a blend of at least two different polymers, for example, those selected from, but not limited to, the group of polyphenylene sulfide and polyetherether ketone; polyphenylene oxide and polyphenylene sulfide; and polyetherimide and polyphenylene sulfide. In a blend, it one embodiment herein, the at least one crosslinkable aromatic polymer may comprise a first crosslinkable polymer that may be a polyphenylene sulfide and at least one second crosslinkable polymer that may be selected from a group consisting of (i) one or more polyarylenes selected from polyetherketone, polyetheretherketone, polyetherdiephenylether ketone, polyetherketone ketone, and blends, co-polymers and alloys thereof; (ii) one or more of polysulfone, polyphenyl sulfone, polyethersulfone, co-polymers and alloys thereof; and (iii) one or more of polyimide, thermoplastic polyimide, polyetherimide, and blends, co-polymers and alloys thereof. [0029] The composition noted above that comprises the at least one crosslinkable aromatic polymer as noted above may also comprise at least one crosslinking compound that has a structure according to one of the following formulae: wherein A is a bond, an alkyl, an aryl, or an arene moiety having a molecular weight less than about 10,000 g/mol; wherein R ¹ , R ² , and R ³ are the same or different and are independently selected from the group consisting of hydrogen, hydroxyl (-OH), amine (NH2), halide, ester, ether, amide, aryl, arene, or a branched or straight chain, saturated or unsaturated alkyl group of one to about six carbon atoms; wherein m is from 0 to 2, n is from 0 to 2, and m + n is greater than or equal to zero and less than or equal to two; wherein Z is selected from the group of oxygen, sulfur, nitrogen, and a branched or straight chain, saturated or unsaturated alkyl group of one to about six carbon atoms; and wherein x is about 1 to about 6.

[0030] The at least one crosslinking compound noted above may a structure according to formula (IV) and can be selected from the group consisting of

[0031] The at least one crosslinking compound may also have a structure according to formula (V) and can be selected from a group consisting of:

[0032] The at least one crosslinking compound may also have a structure according to formula (VI) and may be selected from the group consisting of:

[0033] In the above noted formulae, A may have a molecular weight of about 1,000 g/mol to about 9,000 g/mol.

[0034] The at least one crosslinking compound if used, may be present in the composition having the at least one aromatic crosslinkable polymer in an amount of about 1% by weight to about 50% by weight of an unfilled weight of the composition. The weight ratio of the aromatic polymer to the crosslinking compound in such as composition is about 1:1 to about 100:1. The composition for use in forming the end effector pad, at least in part, may further comprise in addition to a crosslinking compound(s), a crosslinking reaction control additive selected from a cure inhibitor or a cure accelerator. Such a crosslinking reaction control additive may be present in the composition in an amount of about 0.01% to about 15% by weight of the crosslinking compound. The crosslinking reaction control additive may be a cure inhibitor such as one comprising lithium acetate, or may be a cure accelerator, such as one comprising magnesium chloride.

[0035] The composition comprising the at least one crosslinkable aromatic polymer used to form the at least one crosslinked aromatic polymer of the end effector pad may comprise one or more additives selected from continuous or discontinuous, long or short, reinforcing fibers selected from carbon fibers, glass fibers, woven glass fibers, woven carbon fibers, aramid fibers, boron fibers, polytetrafluoroethylene fibers, ceramic fibers, polyamide fibers; and/or one or more fillers selected from carbon black, silicate, fiberglass, glass beads, glass spheres, milled glass, calcium sulfate, boron, ceramic, polyamide, asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, aluminum oxide, borax (sodium borax), activated carbon, pearlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, carbon nanotubes and fullerene tubes. If such additives and/or fillers are used, preferably they comprise about 0.5% by weight to about 65% by weight within the composition. Preferred additives include one or more of carbon fiber, glass fiber, PTFE, and graphite.

[0036] The end effector pad once formed preferably has on at least the upper surface thereof on the first portion of the end effector pad an average surface roughness (Rd) of about 12 p-in. to about 28 p-in. The at least upper surface of the first portion of the end effector pad preferably has a static coefficient of friction (//) of about 0.25 to about 0.5, and a low specific wear factor (k) under typical semiconductor end application conditions.

[0037] The invention also includes an end effector for robotic transfer that comprises an end effector body having at least one mounting area for receiving at least one end effector pad, wherein the end effector body is operably connected, directly or indirectly, to a robotic transfer apparatus; at least one end effector pad, each of the at least one end effector pad having a first portion for supporting an object to be moved and a second portion for positioning the end effector pad on the end effector body in the at least one mounting area, wherein each of the at least one end effector pad has an upper surface on the first portion thereof configured for supporting an object and at least the upper surface of the first portion of the end effector pad comprises a crosslinked aromatic polymer.

[0038] In one embodiment of the end effector, the at least one crosslinked polymer may comprise a crosslinked polymer that is substantially or fully amorphous and is operable at temperatures above the glass transition temperature of the crosslinked polymer. In another embodiment of the end effector, the at least one crosslinked polymer may comprise a crosslinked polymer that is semicrystalline and is operable at temperatures above the crystalline melting point of the crosslinked polymer. The end effector is preferably operable for robotic transfer at temperatures of about 300°C to about 450°C.

[0039] The invention further includes a method of making an end effector pad for use in an end effector for robotic transfer, comprising: providing a composition comprising at least one crosslinkable aromatic polymer; heat molding the composition to form at least a first portion of an end effector pad and to crosslink the at least one crosslinkable polymer, wherein the first portion of the end effector pad comprises an upper surface for supporting an object to be moved; forming a second portion of the end effector pad, wherein the second portion of the end effector pad is for positioning the end effector pad on an end effector body, and combining the first portion and the second portion of the end effector pad. In such a method, the first portion and the second portion may be formed and combined simultaneously. The first and second portion may also be formed and combined in a preformed mold.

[0040] In the method of making the end effector pad above, the at least one crosslinkable aromatic polymer may comprise a crosslinkable aromatic polymer that is substantially or fully amorphous and upon crosslinking is operable at temperatures above a glass transition temperature of the crosslinked aromatic polymer.

[0041] In another embodiment of method, the at least one crosslinkable aromatic polymer may comprise a crosslinkable aromatic polymer that is semicrystalline and that upon crosslinking is operable at temperatures above a crystalline melting point of the crosslinked polymer. In the embodiment using the semicrystalline aromatic crosslinkable polymer, crosslinking preferably occurs so as to minimize crystallinity in the crosslinked polymer. The method may further comprise incorporating the end effector pad in an end effector for robotic transfer at temperatures of about 300°C to about 450°C.

[0042] In a further aspect of the invention, the invention includes a method of making an end effector pad for use in an end effector for robotic transfer, comprising: providing a composition comprising at least one crosslinkable aromatic polymer; heat molding the composition and crosslinking the aromatic polymer to form an end effector pad, wherein the end effector pad has a first portion for supporting an object to be moved and a second portion for positioning the end effector pad on an end effector body. The crosslinking may occur during heat molding of the composition. The method may also further comprise incorporating the end effector pad in an end effector for robotic transfer at temperatures of about 300°C to about 450°C.

[0043] In a further method according to the invention, a method is provided for making an end effector pad for use in an end effector for robotic transfer, comprising: forming an end effector pad by heat molding a base material, wherein the end effector pad has a first portion for supporting an object to be moved and a second portion for positioning the end effector pad on an end effector body; and forming a layer of a crosslinked aromatic polymer on at least an upper surface of a first portion of the end effector pad from a composition comprising a crosslinkable aromatic polymer. The layer of the crosslinked aromatic polymer may be formed by heated insert molding, or by applying the composition in a liquid form to the base material on at least the upper surface of the first portion of the end effector pad. The end effector may also be dip-coated with the liquid composition over a portion or all of the end effector. In the method, the base material may be selected from ceramic materials, thermoplastic materials, metals, metal alloys, a crosslinked aromatic polymer of the same or different type from that used as the crosslinked aromatic polymer in the layer of the crosslinked aromatic polymer. Combinations of these base materials may be incorporated in one more portions of the end effector body in a layered or uniform manner. The end effector pad may further be incorporated in the method into an end effector for robotic transfer at temperatures of about 300°C to about 450°C.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) [0044] The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

[0045] Fig. 1 is a top elevational view of an end effector having an end effector pad according to one embodiment of the invention herein;

[0046] Fig. 2 is a longitudinal cross-sectional view of an enlarged portion of the end effector according to Fig. 1 supporting a silicon wafer;

[0047] Fig. 3 is a top elevational view of an end effector having an end effector pad according to a further embodiment of the invention herein;

[0048] Fig. 4 is a longitudinal cross-sectional view of an enlarged portion of the end effector of Fig. 3;

[0049] Fig. 5 is a perspective view of the end effector pad of Fig. 1;

[0050] Fig. 6 is a perspective view of the end effector pad of Fig. 3;

[0051] Fig. 7 is a perspective view of an end effector pad according to a further embodiment herein;

[0052] Fig. 8 is a perspective view of an end effector pad according to yet a further embodiment herein;

[0053] Fig. 9 is a graphical representation of the relationship between wafer displacement and lateral acceleration for various sample configurations in a simulation as described in Example 1;

[0054] Fig. 10 is a top, front perspective view of a modified version of an apparatus as described in ASTM-D1894 for testing static and kinetic coefficients of friction as employed in Example 1 herein;

[0055] Fig. 11 is a top elevational view of the apparatus of Fig. 10; [0056] Fig. 12 is a left-side elevational view of the apparatus of Fig. 10;

[0057] Fig. 13 is an enlarged portion of the apparatus as shown in Fig. 12;

[0058] Fig. 14 is an enlarged portion of a wafer and wafer pad installed in the apparatus of Fig. 10 without the attached frame portion of the apparatus;

[0059] Fig. 15 is a graphical representation of the elastic behavior of a crosslinked polyetherether ketone in comparison with a polybenzimidazole based on a dynamic mechanical analysis (DMA) curve of the storage modulus, G’, over a range of temperatures; [0060] Fig. 16 is a graphical representation of the DSC curve of the crosslinked aromatic polymer cured in Example 2 using a standard curing cycle, Cure 1 (profile B) and a modified high-temperature two-step curing cycle, Cure 2 (profile A); and [0061] Fig. 17 is a graphic representation of a DMA run on the same samples using Cure 1 (dashed line) and Cure 2 (solid line) from Example 2 showing the leathery region.

DETAILED DESCRIPTION OF THE INVENTION

[0062] The invention is directed to use of compositions including crosslinked aromatic polymers for forming articles having improved tribological and wear properties, as well as use of such compositions in elevated temperature processing to improve the frictional stability of objects supported on a surface for robotic transfer, particularly for use in forming end effector pads useful in end effectors for transport of silicon wafers in high temperature semiconductor manufacturing applications.

[0063] As used herein, words such as “inner” and “outer,” “upper” and “lower,” “top” and bottom,” “left” and “right,” “inwardly” and “outwardly,” “transversely” and “longitudinally” and “circumferentially” and words of similar import are intended to assist in understanding preferred embodiments of the invention with reference to the accompanying Figures and with respect to the orientation of the end effectors and end effector pad examples as shown in the Figures, and are not intended to be limiting to the scope of the invention or to limit the invention scope to the preferred embodiments shown in the Figures. The embodiments herein each use like reference numerals to refer to analogous features of the invention as described herein and as shown in the drawings, such that absent language to the contrary describing alternate configurations for a particular feature, one skilled in the art would understand, based on this disclosure and the drawings attached hereto, that description of one such feature is applicable to an analogous feature in another embodiment herein unless otherwise specified.

[0064] Further, as used herein, the terms “a” and “at least one” can mean “one or more” absent language to the contrary, such as language indicating a specific number. [0065] As used herein, “aromatic polymer” is a polymer that includes aromatic moieties either along its polymer backbone or attached thereto, preferably it is one that incorporates an aromatic moiety (a cyclic moiety derived from an aromatic compound) in the polymer backbone. Such aromatic moieties may be a single ring and/or a multiring structures and can be linked together directly on the backbone or connected through linking species or elements, such as oxygen, sulfur, hydrogen, alkyl or other groups.

[0066] As used herein, “crosslinkable polymer” means a polymer that has groups capable of reacting with each other (self-crosslinking), capable of reacting through application of heat, radiation or light, or capable of reacting with a crosslinking agent or compound. Such groups may exist on a polymer when formed through polymerization or may be provided to the polymer through functional groups or other crosslinking groups positioned along the length of the polymer chain, or along substituents extending from the polymer chain, including terminal groups.

[0067] An “end effector” as used herein refers to a portion of a tool, such as a robotic tool that extends from a robotic arm in the position where a “hand” would be for engaging in a robotic operation. In the context of a semiconductor transfer or cluster tool, as described in the Background hereof, the arm may be one of several extendable tools having an operable end (the end effector) that is used to transport a semiconductor wafer, such as a silicon wafer, from one reaction chamber to another as described further herein. Such end effectors may have a variety of designs, and may incorporate as is generally known, the use of one or more end effector pads in the upper portion of an end effector body to provide a supporting surface for an object such as a wafer that is to be transported from one location to another. Such cluster or transfer tools will each be referred to generally herein as a robotic transfer apparatus and the operation of such a robotic transfer apparatus as a robotic transfer. Thus, a robotic transfer apparatus may be considered broadly to be the operating apparatus that is operably connected to a robotic transfer arm for moving an object from one location to another. At the end of such a robotic transfer apparatus, including any robotic transfer arm employed, the end effector would be connected thereto for the physical contact with the object to be transferred.

[0068] Each of the end effectors according to the invention incorporates into the end effector at least one or more of an aromatic crosslinked polymer. The crosslinked polymer(s) may be used to form the entire end effector, including its end effector body and any end effector pad(s) or it may be used to form only a portion of the end effector, such as at least some aspect of the end effector pad(s). End effectors according to the invention may have only one end effector pad thereon for supporting an object to be transferred or may incorporate multiple such pads depending on the robotic design used. Further, either the end effector body or the end effector pad may have the crosslinked polymer(s) incorporated therein for use in the invention. Preferably, at least the upper surface of any part of the end effector, or end effector pads that is intended to contact an object to be transferred, incorporates or is formed from the at least one crosslinked aromatic polymer. Thus, the crosslinked polymer(s) may be included in an upper surface, an outer layer or throughout some or all of the end effector or its end effector pad(s).

[0069] Crosslinked polymers herein may be formed from a composition including at least one crosslinkable polymer, as well as one or more additives, crosslinking compounds, reaction control agents or other additives or fdlers. The compositions thus formed may be crosslinked using a variety of acceptable crosslinking techniques such as thermally induced crosslinking, radiation induced crosslinking, grafting crosslinkable groups on a polymer and reacting the polymer with one or more other materials and/or through chemically induced crosslinking reactions. The crosslinking may occur during and/or after molding or forming the crosslinkable aromatic polymer in the composition into a part or one or more features of an end effector. The crosslinkable aromatic composition may also be in solvent form and applied to an existing part or core formational structure as a formed outer layer or coating over the part or structure, which is then dried and cured on the part or structure.

[0070] The compositions useful for forming the end effectors or its parts, including particularly, end effector pads herein, include one or more crosslinkable aromatic polymer(s). Such crosslinkable aromatic polymers may be at least substantially or fully amorphous or may be semicrystalline.

[0071] The crosslinkable aromatic polymer(s) herein may be any of a variety of crosslinked aromatic polymers. In preferred embodiments, the crosslinkable aromatic polymer(s) are polyarylene polymers, such as a polyarylene ethers (PAE), polyarylene ketones (PAK) or polyarylene ether ketones (PAEK) and various co-polymers thereof known or to be developed in the art. The aromatic polymer compositions include an aromatic polymer that can be crosslinked and may optionally include at least one crosslinking compound.

[0072] The crosslinking of crosslinkable, aromatic polymers herein is preferably achieved either by modification of the polymer for grafted crosslinking and then exposing the aromatic polymer to sufficiently high temperatures to induce self-crosslinking of the polymer and/or by use of a crosslinkable aromatic polymer with the use of one or more crosslinking compound(s).

[0073] The aromatic polymer may be crosslinked, for example, by grafting functional groups onto the polymer backbone which can be thermally induced to crosslink the polymers, as further described in U.S. Patent No. 6,060,170, incorporated in relevant part herein by reference. Alternatively, the crosslinkable aromatic polymer may be crosslinked by thermal action at temperatures greater than about 350°C or more, as disclosed in U.S. Patent No. 5,658,994, incorporated herein, in relevant part, by reference. An example of a preferred material for use in thermal crosslinking is 1,2, 4, 5 tetra(phenylethynyl)benzene as shown below:

[0074] In a preferred embodiment of the present application, the crosslinkable polymer compositions to prepare the end effectors and, particularly end effector pads, include an aromatic polymer and at least one crosslinking compound capable of crosslinking the aromatic polymer either across chains or to itself within the polymer matrix. Such polymers may include, either through polymerization or through functionalization, groups that enable self-crosslinking. Grafted crosslinking may also be used, provided that the polymer formed is capable of being formed into an end effector, such as by molding or other part formation processes.

[0075] The crosslinkable aromatic polymer in the compositions used herein may be any of a variety of polyarylene homopolymers or copolymers, including polyarylene ethers and/or polyarylene ketones, such as polyetherketone (PEK), polyetherketone ketone (PEKK), polyetherether ketone (PEEK), polyetherdiephenylether ketone (PEDEK) and the like; polysulfones (PSU); polyethersulfones (PES); polyphenylene sulfides (PPS); polyphenylene oxides (PPO); polyphenyl sulfones (PPSU); polyimides (PI); poly etherimides (PEI) and thermoplastic polyimides (TPI); polybenzamides (PBA); polyamide-imides (PAI); aromatic polyureas; polyurethanes (PU); polyphthalamides (PPA); polybenzimidazoles (PBI); polyaramids or similar aromatic polymers known in the art or to be developed including various copolymers and functionalized or derivatized versions of such polymers. Examples of various polyketones and poly sulfone homopolymers and copolymers that are amenable to the method described herein are outlined in McGrail, “Polyaromatics,” Polymer International 41 (1996), pp. 103-120. [0076] The crosslinkable aromatic polymer(s) may be functionalized or nonfunctionalized as desired to achieve specific properties or as necessary for end effectors and end effector pads having specific operational uses or end applications, e.g., functional groups such as hydroxyl, mercapto, amine, amide, ether, ester, halogen, sulfonyl, aryl and functional aryl groups or other functional groups can be provided depending on intended end effects and properties. The aromatic polymer can also be a polymer blend, alloy, or copolymer or other multiple monomer polymerization of two or more of such aromatic polymers, provided that one such monomer enables formation of a polymer in each case that is crosslinkable or provided that in a blend, alloy or copolymerization, at least one of the polymers is crosslinkable. Preferably, when the aromatic polymer is a blend or alloy, the aromatic polymers are chosen so as to be processible in compatible processing temperature ranges.

[0077] In an embodiment of the method, in the composition used for forming end effectors and end effector pads herein, the crosslinkable aromatic polymer(s) may be a poly(arylene ether) including polymer repeating units along its backbone having a structure according to formula (I):

[0078] wherein Ar ¹ , Ar ² , Ar ³ and Ar ⁴ may be identical or different aryl radicals, m = 0 to 1, and n = -m, wherein such polymers may be of a variety of molecular weights and chain lengths depending on intended end use as is known in the relevant aromatic polymer art. Ar radicals in Formula (I) include but are not limited to biphenyl, terphenyl, Lanthracene, naphthyl, and other polyaromatic moieties. Larger aryl structures are known in the art in order to increase Tg so that polymers may be selected or modified to be more suitable as a polymer or copolymer structure depending on the end application service temperature for the end effector pads. See, McGrail, as noted above.

[0079] In one embodiment, the crosslinkable aromatic polymer(s) may be a poly(arylene ether) as in formula (I), wherein m is 1 and n is 0, and the aromatic polymer has repeating units along its backbone having a structure as shown below in formula (II) where x indicates a repeating unit that will vary with the desired chain length and molecular weight:

[0080] In another embodiment, the aromatic polymer has a standard polyetherether ketone repeating unit as noted below wherein from Formula (I), m is 1 and n is zero and x indicates a repeating unit that will vary depending on desired chain length of molecular weight:

[0081] In preferred embodiments, the crosslinkable aromatic polymer(s) are one or more of polyaryletherketones (PAEK), including polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), poly etherdiphenylether ketone (PEDEK) and polyetherketoneetherketoneketone (PEKEKK). The crosslinkable aromatic polymer may be a commercially available crosslinkable aromatic polymer as noted above. Preferred PAEKs for use in the invention are commercially available, for example as PEEK under the name Victrex™ PEEK, available from Victrex, pic; KetaSpire® PEEK from Solvay, and Vestakeep® from Evonik. Suitable copolymers of such materials including ketone and/or sulfones and other biphenyl, diphenyl and triphenyl derivatives may also be used.

[0082] In an embodiment herein in which an optional crosslinking compound(s) is/are used, such crosslinking compounds may be any such compounds which can initiate chemical crosslinking of aromatic polymers. Preferred crosslinking compounds for use with the crosslinkable aromatic polymers are described in applicant’s U.S. Patents Nos.

9,006,353 and 9,109,075, each of which is incorporated herein by reference, in relevant part, with respect to useful polymers and crosslinking compounds and crosslinking control additives which may be used herein. One such crosslinking compound is of the general structure: wherein R is OH, NH2, halide, ester, amine, ether or amide, and x is 1 to 6 and A is an arene moiety having a molecular weight of less than about 10,000 g/mol. When reacted with an aromatic polymer, such as a polyarylene ketone, such crosslinking compound forms a thermally stable, cross-linked oligomer or polymer.

[0083] Such crosslinking technology enables aromatic polymers, which are otherwise difficult to crosslink, to be formed in a crosslinkable form so as to be thermally stable up to temperatures greater than 260°C and even greater than 400°C, than about 450°C or more, depending on the polymer so modified, i.e., poly sulfones, polyimides, polyamides, polyetherketones and other polyarylene ketones, polyphenylene sulfides, polyureas, polyurethanes, polyphthalamides, polyamide-imides, aramids, and polybenzimidazoles.

[0084] Additional crosslinking compounds for crosslinking aromatic polymers are described in applicant’s co-pending, U.S. Patent Publications Nos. 2020-0172667 Al and 2020-0172669 Al which include one or more of the crosslinking compounds according to any of the following structures: , (V), and wherein Q is a bond and A may be Q, an alkyl, an aryl, or an arene moiety having a molecular weight less than about 10,000 g/mol. Each of R ¹ , R ² , and R ³ may be the same or different and may be independently selected from the group consisting of hydrogen, hydroxyl (-OH), amine (-NH2), halide, ester, ether, amide, aryl, arene, or a branched or straight chain, saturated or unsaturated alkyl group, preferably of one to about six carbon atoms. Formula (Illa) is substantially the same as formula (III) above, with the exception that the moiety A in formula (III) is replaced by Q (which represents a bond) and R ¹ of formula (Illa) is defined differently than R of formula (III).

[0085] In formula (V), m is preferably from 0 to 2, n is preferably from 0 to 2, and m + n is greater than or equal to zero and less than or equal to two. Further, in formula (V), Z is preferably selected from the group of oxygen, sulfur, nitrogen, and a branched or straight chain, saturated or unsaturated alkyl group of one to about six carbon atoms. In any of formulae (Illa), (V) and (VI), as with formula (III), x is also about 1 to about 6.

[0086] The compositions used in the articles and methods of the present invention to form end effectors and/or end effector pads may include aromatic crosslinkable polymer(s) and a blend of one or more crosslinking compounds. In another embodiment, the composition may be used that includes a single crosslinking compound that can be selected based upon the aromatic polymer in the composition including the at least one crosslinkable polymer.

[0087] In a further embodiment, crosslinking compounds may be added to the composition including the at least one crosslinkable polymer composition for use in forming an end effector and/or an end effector pad according to the present invention may include structures according to one of the following formulae:

[0088] In each of formulae (IV)-(VI), A may be a bond, an alkyl, an aryl, or an arene moiety preferably having a molecular weight less than about 10,000 g/mol. A molecular weight of less than about 10,000 g/mol permits the overall structure to be more miscible with the aromatic polymer, and permits uniform distribution, with few or no domains, within the composition including the aromatic polymer and crosslinking compound. More preferably, A has a molecular weight from about 1,000 g/mol to about 9,000 g/mol. Most preferably, A has a molecular weight from about 2,000 g/mol to about 7,000 g/mol.

[0089] The moiety A may be varied to have different structures, including, but not limited to the following:

[0090] Further, the moiety A may be functionalized, if desired, using one or more functional groups such as, e. ., and without limitation, sulfate, phosphate, hydroxyl, carbonyl, ester, halide or mercapto or the other functional groups noted above.

[0091] In formulas (IV) and (VI), R ¹ is preferably selected from the group consisting of hydrogen, hydroxyl (-OH), amine (NH2), halide, ester, ether, amide, aryl, arene, or a branched or straight chain, saturated or unsaturated alkyl group of preferably one to about six carbon atoms.

[0092] In formula (V), R ¹ , R ² , and R ³ may be the same or different and are preferably independently selected from the group consisting of hydrogen, hydroxyl (-OH), amine (NH2), halide, ester, ether, amide, aryl, arene, or a branched or straight chain, saturated or unsaturated alkyl group of preferably one to about six carbon atoms. Thus, R ¹ , R ² , and R ³ may each be different, two of R ¹ , R ² , and R ³ may be the same with the third being different, or each of R ¹ , R ² , and R ³ may be the same. Further, in formula (V), m is preferably from 0 to 2, n is preferably from 0 to 2, and m + n is preferably greater than or equal to zero and less than or equal to two. Thus, in formula (V), one or two R ² groups may be present, one or two R ³ groups may be present, one R ² group and one R ³ group may be present, or R ² and R ³ may both be absent. In formula (V), Z is preferably selected from the group of oxygen, sulfur, nitrogen, and a branched or straight chain, saturated or unsaturated alkyl group of one to about six carbon atoms. In any of formulas (IV)-(VI), x is preferably about 1 to about 6.

[0093] In embodiments having a crosslinking compound according to formula (IV), the crosslinking compound may have a structure according to one or more of the following preferred structures: 1

[0094] The above-listed crosslinking compounds are not intended to be limiting and are merely provided as examples of crosslinking compounds according to formula (IV). In the above crosslinking compounds of formula (IV), R ¹ is shown as being a hydroxyl group. The moiety, A, is shown as being any of various aryl groups, and x is shown as being either 2 or 4. [0095] In embodiments having a crosslinking compound of formula (V), the crosslinking compound may have a structure according to one or more of the following:

[0096] The above-listed crosslinking compounds are not intended to be limiting and are merely provided as examples of crosslinking compounds according to formula (V). In the above crosslinking compounds of formula (V), Z is shown as being an alkyl group with one carbon atom or O. R ¹ is shown as being a hydroxyl group. R ² and R ³ are shown as being the same, different or not present. The moiety A is shown as being a bond or an aryl group. Further, x is shown as being 1 or 2.

[0097] In embodiments in which the crosslinking compound has a structure according to formula (VI), the crosslinking compound may have one or more of the following structures:

[0098] The above-listed crosslinking compounds are not intended to be limiting and are merely provided as examples of crosslinking compounds according to formula (VI). In the above compounds of formula (VI), R ¹ is shown as a hydroxyl group. The moiety A is shown as being a bond or an aryl group. Further, x is shown as being 2.

[0099] The amount of crosslinking compound(s) for use with crosslinkable aromatic polymers in a composition to be used to form an end effector and/or an end effector pad as described herein is/are (collectively) preferably about 1% by weight to about 50% by weight, more preferably about 5% by weight to about 30% by weight or about 10% to about 35%, or most preferably about 8% by weight to about 24% by weight based on the total weight of an unfdled composition of the crosslinkable aromatic polymer and the crosslinking compound.

[0100] The compositions used herein may have a weight ratio of the crosslinkable aromatic polymer to the crosslinking compound that is preferably about 1 : 1 to about 100: 1. More preferably, the weight ratio of the aromatic crosslinkable polymer to the crosslinking compound in the composition is about 3:1 to about 10: 1.

[0101] The compositions may optionally further include crosslinking reaction additive(s) for controlling the cure reaction rate during formation of the end effector and/or end effector pads and during any post-treatment processing. Such additive(s) may be mixed into the composition in varying amounts depending on the end properties and cross-linking density desired for the end effector pads. The amount of the crosslinking compound typically impacts the degree of cross-linking such that use of particular levels of crosslinking compound can provide the desired degree of crosslinking and crosslink density. The use of a crosslinking reaction control additive for controlling cure reaction rate, i.e., crosslinking rate and extent, will also depend upon the cure reaction kinetics of a particular aromatic polymer and the crosslinking compound used, and so may be adjusted to help to control the reaction rate for a given composition. Thus the crosslinking reaction control additive included can be a cure inhibitor (a Lewis base agent), such as lithium acetate for reactions with a high reaction rate, or the crosslinking reaction additive may be a cure accelerator (a Lewis acid agent) when the cure reaction rate is too slow, such as magnesium chloride or other rare earth metal halides. When the composition includes a crosslinking reaction control additive, the amount of crosslinking reaction control additive in the composition is preferably about 0.01% to about 5% by weight based on the weight of the crosslinking compound, but may be adjusted depending on the reaction rate achieved in a given system.

[0102] The above compositions may be formed to have blends of crosslinkable aromatic polymers in the composition. Such blends include two or more such polymers. Providing control to the reaction by blending (and/or through use of additives as noted above) allows for the reaction to occur earlier or later in the end effector pad forming process to provide variations in physical properties such as strength. Blending and/or control additives may also be used, optionally with the crosslinking compound, to more specifically achieve desired properties for an end effector end application such as sufficient hardness, creep resistance and a lack of transfer of material from the end effector part, such as the end effector pad, to a wafer to be transferred. Aromatic or thermoplastic material that are not crosslinked, tend to melt and transfer to the wafer surface, causing contaminatio as wll as robot arm handling failure.

[0103] When using the blends of two or more crosslinkable aromatic polymers, if the aromatic polymers are self-crosslinkable and/or many be thermally crosslinked, a crosslinking compound may not be necessary and crosslinkable aromatic polymers that have different crosslinking reaction rates may be used together to modify or control the overall crosslinking rate. This is described in detail in applicant’s co-pending U.S. Patent Application Publication No. 2021-0388216 Al, incorporated herein by reference.

[0104] The composition for use in forming an end effector pad herein may further be filled or reinforced with one or more additives to improve or otherwise modify the modulus, impact strength, wear or tribology properties, bonding strength, dimensional stability, and heat resistance as well as potentially insulation properties of the end effector pads formed using the compositions described herein. Preferably, such additives is/are selected from one or more of continuous or discontinuous, long or short, reinforcing fibers selected from one or more of carbon fibers, glass fibers, woven glass fibers, woven carbon fibers, aramid fibers, boron fibers, polytetrafluoroethylene (PTFE) fibers, ceramic fibers, polyamide fibers, and/or one or more fillers selected from carbon black, silicate, fiberglass, glass beads, glass spheres, milled glass, calcium sulfate, boron, ceramic, polyamide, asbestos, fluorographite, aluminum hydroxide, barium sulfate, calcium carbonate, magnesium carbonate, silica, aluminum nitride, borax (sodium borax), activated carbon, pearlite, zinc terephthalate, graphite, graphene, talc, mica, silicon carbide whiskers or platelets, nanofillers, molybdenum disulfide, fluoropolymer fillers, carbon nanotubes and fullerene tubes.

Particularly preferred for use in forming end effector pads of such additives are carbon fiber, graphite and PTFE fillers. Additives may also be chosen in order to assist in modifying the coefficient of thermal expansion (CTE) for dimensional stability of the end effector pads, including fillers that would reduce the CTE of the polymer in the compositions for forming pads herein, e.g., glass fibers, milled glass, glass beads, mica, aluminum oxide and/or talc. [0105] The additives may additionally or alternatively include other thermal management fillers, including but not limited to, nanodiamonds and other carbon allotropes, polyhedral oligomeric silsesqui oxane (“POSS”) and variants thereof, silicon oxides, boron nitrides, and aluminum oxides. The additives may additionally or alternatively include flow modifiers, such as ionic or non-ionic chemicals.

[0106] The additive may include an optional CTE-reducing additive as noted above and/or an optional reinforcing fiber which is a continuous or discontinuous, long or short fiber, that is carbon fiber, PTFE fiber, glass fiber and/or graphite. Preferably, such additives provide properties that are more isotropic in nature, but other less isotropic or anisotropic properties may also be acceptable.

[0107] The crosslinkable polymer composition comprises about 0.5% to about 65% by weight of additives in the composition, and more preferably about 5% to about 40% by weight of additives in the composition. The crosslinkable polymer composition may further comprise one or more of stabilizers, tribological or rheological adjustment additives, flame retardants, pigments, colorants, plasticizers, surfactants, or dispersants.

[0108] Preferred additives in compositions herein for use in end effector or end effector pad end applications including but are not limited to a crosslinking compounds such as those of Formulae (IV), (V) or (VI) noted above, a crosslinking control additives such as, for example a lithium acetate or its hydrate, and optionally a fdler such as carbon black, although there are a wide variety of optional additives and components as noted above. [0109] The composition may be prepared by providing the crosslinkable aromatic polymer(s) and optionally a crosslinking compound capable of crosslinking the aromatic polymer(s) and combining the aromatic polymer and the crosslinking compound. If self- crosslinkable polymers or grafted polymers are used, the crosslinking compound may be omitted. If the crosslinking compound is used in the composition it is preferably combined with the aromatic polymer to form a preferably substantially homogeneous composition. [0110] Incorporation of the crosslinking compound(s) into the crosslinkable aromatic polymer(s) can be performed by various methods, such as by solvent precipitation, mechanical blending or melt blending. Preferably, the crosslinkable polymer composition is formed by dry powder blending of the crosslinking compound and aromatic polymer, such as by conventional non-crosslinked polymer compounding processes, including, for example, twin-screw compounding. The resulting composition can be extruded into fdaments or can be used as a powder or pellets for use in the method herein.

[0111] Blending (including blending of more than one crosslinkable aromatic polymer) may be accomplished further by use of an extruder, such as a twin-screw extruder, a ball mill, or a cryogrinder. Blending of the crosslinkable aromatic polymer(s) and crosslinking compound(s) is preferably conducted at a temperature during blending that does not exceed about 250°C so as to preferably avoid premature curing during the blending process. If a melt process is used, care should be taken to ensure thermal history and temperature exposure are minimized, i.e., it is preferred to use short residence times and/or as low temperature as feasible to achieve material flow. Alternatively, use of rate controlling additives as described above and/or the blending of crosslinkable aromatic polymers of differing reaction kinetics, may be used to inhibit curing and/or control the curing rate to minimize any crosslinking due to compounding and conversion into a pellet or fiber form. Depending on the polymer and components selected in the composition, the material may be introduced to an extruder as a powder, fiber, pellet or in some instances, as a liquid. Suitable crosslinking additives are known in the art and are described in U.S. Patent No. 9,109,080 noted above, which is incorporated herein, in relevant part, with respect to the cross-linking control additives.

[0112] As the blending process may be exothermic, it is necessary to control the temperature, which can be adjusted as necessary and to temperatures indicated depending upon the particular crosslinkable aromatic polymer(s) selected for use. In mechanical blending of the aromatic polymer and crosslinking compound, the resulting composition is preferably substantially homogenous in order to obtain uniform crosslinking.

[0113] When the composition is prepared, it can be cured by exposure to a temperature greater than 250°C, for example at a temperature of about 250°C to about 500°C. However, when and to what extent to subject the composition to heat and crosslinking during a forming process will depend upon the desired properties to be achieved in the end product. For example, greater crosslinking may create higher levels of mechanical strength, but could impact ductility. Crosslinking levels may range as noted above, but are preferably from about 5 molar percent to about 50 molar percent. Crosslinking levels may impact the static coefficient of friction of the base polymer, but more importantly, the crosslinking enables the aromatic base polymer to maintain structure and resist melting at high temperatures associated with many semiconductor end applications.

[0114] The crosslinked aromatic polymer compositions herein resist melting but also achieve a somewhat rubbery state and undergo an elastomer state transition to form a thermal stable rubbery surface layer during elevated operating temperatures. An Example of this is illustrated in Fig. 15 which shows the DMA curve for a commercial crosslinked polyetherether ketone (Arion® 3000XT). Also shown is a DMA curve for a polybenzimidazole (PBI), an uncrosslinked aromatic polymer. The softer and stable rubbery modulus of the crosslinked poly etherether ketone above its rubbery transition temperature (350°C) is shown in Fig. 15. It provides a stable operating state, whereas the comparative PBI material shows unstable and harder modulus as well as an instability in properties in the same temperature range and at the same temperatures. The softer, stable elastomeric surface of the crosslinked material give the ability to provide a better contact surface for receiving a wafer or other object to be transported, e g., on an end effector pad, and a stable and better static coefficient of friction. It also minimizes surface scratching of an object to be transferred (such as a silicon wafer) from contact with an end effector surface that is too hard.

[0115] The rubbery state transition is dependent upon the selected crosslinked polymer. For amorphous crosslinked polymers, the glass transition temperature is the rubbery state transition temperature. For semi-crystalline crosslinked polymers, the melting point of crystallization is the rubbery state transition temperature. When working with semicrystalline crosslinkable polymers, or substantially amorphous polymers that may have crystalline domains, in curing such materials, curing should occur so as to minimize the crystallinity in the resulting crosslinked polymer.

[0116] In a standard cure, crystallization can occur as well as chemical crosslinking. Formed crystallites can melt or soften above their melting temperature. Such melting results in both a phase change and can also impact or cause changes in the coefficient of friction. Such changes can be undesired in the end application, particularly if it involves higher end use temperature. Further such effects can vary from cycle to cycle during operation in the end application, depending on the end application cooling cycles, dwell time at temperature and thermal conductivity of the sample, i.e., the dimensions and coefficient of friction can be different in the end application from cycle 1 to cycle 500 to cycle 5000. The coefficient of friction of an amorphous polyetherether ketone is known to be approximately 30% higher than that of a semicrystalline polyetherether ketone. See, e.g., Moskalewicz, T. et al., “The Effect of the Polymer Structure in Composite Alumina/Polyetheretherketone Coatings on Corrosion Resistance, Micro-mechanical and Tribological Properties of the Ti-6A1-4V Alloy,” J. of Material Eng. and Perform., vol. 29, pp. 1426-1438 (2020).

[0117] To minimize the variations that can result from crystallinity using certain semicrystalline aromatic crosslinkable polymers when intended for use in an end application having a higher temperature and/or long cycle use, it is preferred to cure semicrystalline aromatic crosslinkable polymers herein so as to minimize the crystallinity in the resulting crosslinked polymer and thereby reduce the potential in such end high temperature or long cycle applications of dimensional changes or variability in frictional properties that could be induced if the surface of an end effector formed using the crosslinked polymer will be an application having a temperature above about 350°C and the crosslinkable aromatic polymer used is semicrystalline prior to curing. This may be carried out by either employing a standard curing cycle below the melting temperature of the polymer followed by a second higher temperature curing step at a temperature that is higher than the standard curing cycle temperature by an amount of about 5 °C to about 50°C (or more depending on the polymer), in effect, a second annealing step where a higher temperature is employed for some period of time. The time period and temperatures can be adjusted based on the aromatic polymer being crosslinked provided that the annealing step reaches a temperature that minimizes the crystallinity of the resulting cross-linked polymer.

[0118] Alternatively, instead of the above-mentioned two-step curing cycle, crystallinity of in the crosslinked aromatic polymer may also be reduced by crosslinking the aromatic polymer at a higher temperature curing cycle than would normally be employed (e.g., raising the standard curing temperature of the aromatic polymer by about 5°C to about 50°C or more throughout the curing process, provided that the higher temperature chosen for the curing cycle is one that would minimize the crystallinity of the resulting crosslinked aromatic polymer.

[0119] Thus, using the compositions herein, it is possible to form a desired article using a crosslinkable polymer in a composition as noted above and to crosslink during formation such as by heat molding, extrusion molding, or insert molding a part or portion of a part, and then further curing for shaping and to complete crosslinking. It is also possible to fully crosslink the material and then heat mold the part. Finally, it is possible to form a part of a different underlying core material that is preferably also able to perform in high temperature applications and apply the composition to an exterior of the core materials, such as by coating or molding a layer on an exterior thereof, or otherwise joining or molding parts or materials together.

[0120] With respect to the end effector pad properties, the degree of cross-linking (cross-link density) may be varied or adjusted to provide different properties and to avoid potential cracking and warping during use as well as to provide desired surface hardness, desired surface roughness, creep-resistance and frictional properties such as wear resistance and a desired static coefficient of friction. Cross-link density may be controlled when using compositions having a crosslinking compound by varying the concentration of the crosslinking compound and/or by controlling the amount of any optional crosslinking reaction additive used in conjuction with the crosslinking compound. The extent of cure, i.e., the completion of the crosslinking reaction, is related to both thermal activation of the reaction if driven by changes in temperature, as well as practical concerns involving the rate of cure.

[0121] In an embodiment using a blend of two crosslinkable polymers of different kinetics as described herein, the crosslinking rate may be controlled not only by modifying the amount of any cross-compound used, but also by altering the amount of the crosslinking polymer having the slower curing reaction rate used in the blend. The level of crosslinking may be adjusted for achieving desired mechanical end properties. Generally, higher levels of a crosslinking compound will tend to form a stiffer product with less ductility after a full cure cycle. For forming an end effector pad, the compositions herein may be used to balance the processability with a reduction in stiction and improved creep resistance. Higher levels of crosslinking will improve physical properties but at the expense of processibility as well as formability of end parts. Thus, depending on the physical properties of a given composition, if further processability is desired, the crosslinking level may be adjusted to balance the desired end effector part properties and/or reaction rate or additives may be used for minor modifications.

[0122] The composition may further be prepared by dissolving both the crosslinkable aromatic polymer and crosslinking compound in a common solvent and removing the common solvent via evaporation or by the addition of a non-solvent to cause precipitation of both the polymer and crosslinking compound from the solvent. For example, depending upon the aromatic polymer and crosslinking compound selected, the common solvent may be tetrahydrofuran, and the non-solvent may be water. An additional option for polymers and crosslinking additives that are soluble in the same solvent is the use of solvent casting or dip coating of a substrate such that, for example, an end effector pad may be formed wherein the interior or core of the end effector pad need not be a crosslinked aromatic polymer and the aromatic polymer may be applied to an exterior of a molded core in a thickness sufficient to provide desired wear and mechanical properties on the exterior of the end effector pad for high temperature operation and robotic transfer. In such a case, the crosslinkable polymer(s) and any crosslinking compounds and/or additives would be dissolved in a suitable solvent and then applied to a core molded end effector or end effector pad having a shape which may be the same or different from the outer dip coated portion of the end effector pad. The solvent would be removed in a controlled manner, and the uncured outer portion of the end effector pad could then be cured using various techniques such as application of heat or radiation, and/or by chemically induced cross-linking. For example, an inner molded core of any suitable shape may be formed of a different polymer and an outer coating of at least one crosslinked aromatic polymer may be formed around the core to provide the desired outer shape and curved features on the end effector pads herein. [0123] Core materials may be formed of other materials such as ceramics such as alumina, metals, metal alloys, organic or inorganic core materials, or various polymeric materials, such as non-crosslinked or crosslinked polymers, wherein the core material may have some desired properties for use, but lacks desired chemical-resistance when subjected to cleaning or solvents used in an end effector end application or another end application, or may have adequate strength and physical properties, but lack desirable surface or frictional properties for an end effector or other given end use. The crosslinked polymer compositions herein may be used to coat or encapsulate the core material to reduce or eliminate shedding of parties, or improve exterior surface particles and improve the frictional properties of the core material.

[0124] In preparing a composition for forming an end effector and/or an end effector pad herein, it is preferred that any optional additives are added to the composition along with or at the same time the crosslinking compound is combined with the crosslinkable aromatic polymer(s) to make the crosslinkable polymer composition. However, the specific manner of providing reinforcing fibers or fillers may be according to various techniques for incorporating such materials and should not be considered to limit the scope of the invention.

[0125] End effectors herein are now discussed more specifically and with respect to Figs 1-8. In a first embodiment, as shown in Figs. 1, 2 and 5, an end effector 100 is shown having an end effector body 102, which may be solid or open in a center area A thereof (such as with respect to concave parts). The end effector body 102 as shown has a generally rectangular shape and can be operably connected to robotic transfer apparatus RTA directly or indirectly, such as through a robotic arm (RA). At least one end effector pad 104 may be provided on an upper surface 106 of the end effector body 102. As shown in embodiment 100, in Fig. 1, there are four end effector pads 104a, 104b, 104c and 104d spaced around the periphery of the upper surface 106 of the end effector body 102 of the end effector 100. Each of such pads 104 is identical as shown. Each has an upper surface 108 positioned for receiving an object for transfer such as, for example, but not limited to, a silicon wafer or other semiconductor wafer.

[0126] As best shown in Fig. 2, a longitudinal cross-sectional view of one of the end effector pads 104a is shown in an enlarged view. A first portion 110 of the end effector pad 104a is shown which includes an upper surface 108 for supporting an object such as a silicon wafer W as shown for illustrative purposes. Preferably the wafer W or other object contacts the upper surface 108 at a location that includes at least one point of contact P. As shown, the upper surface 108 is configured so as to have a generally convex dome shape that extends outwardly from the first portion 110 of the end effector pad. This dome shape provides at least one curved feature 107 to the upper surface 108 of the end effector pad 104a. The curved feature 107 in this case covers the entire upper surface 108 of the end effector pad 104a, such that the center C of the dome-shaped, curved feature also forms the at least one point of contact P for an object to be situated on the upper surface 108 of the end effector pad. However, it should be understood that the at least one curved feature may extend over all, substantially all or only a portion of the upper surface.

[0127] Further, it is within the scope of the invention to include two, three, four or more such curved features on the upper surface 108 of the end effector pad. For example, there may be two or more curved features, some or all of which may have a generally convex dome shaped curved feature. The curved features may also be provided so as to be generally concave or as depressions. In such case, the at least one point of contact would not be on the curved feature, but on a point or point(s) of the upper surface which are not concave or depressed. If curved features are provided, it is preferred that there be at least one, but in some embodiments herein, there may be two or more such curved features, which may be preferably positioned around a central point C of the upper surface for stability. Such features may be arranged so as to be equidistant from the central point of contact or arranged in a patterned that is designed around the central point of contact so as to preferably give uniform support to an object placed thereon. If there are a large number of curved features, one of the curved features (as is the case with having only one such curved feature) can itself be positioned on the central point C so that its point of contact P is also the central point C of the end effector pad’s upper surface.

[0128] The first portion 110 of the end effector pad 104a is preferably an upper portion of the end effector. A second portion 112 of the end effector pas 104a is configured for positioning the end effector pad 104a on the end effector body 102. As shown, in one preferred embodiment, the second portion 112 of the end effector pad 104a includes, for example, mating threads 114, extending at least partially around the second portion 112 of the end effector body in a circumferential manner for connecting the end effector pad 104a securely to the end effector body 102. The end effector body is formed so as to preferably include at least one interior bore 118 into the end effector body that may be configured to define mating threads 116 for engaging threads 114 on the second portion 112 of the end effector pad 104a. While mating threads are shown, other methods of fastening such as snap fit caps that interact with the second portion of the end effector pad, mating tabs formed on the end effector pad and end effector body, seated snap fittings which may be positioned in a bore in the end effector body, adhesives or other fastening means known or to be developed in the art may be used to connect or seat the second portion 112 of the end effector pad 104a to the end effector body 102. The connection may be permanent or releasable and need not be air tight or hermetically sealed. However, seals, inserts or other stablizing parts may also be used if desired. As shown, the parts are solid and formed of a crosslinked aromatic polymer. It is also within the scope of the invention that the second portion of the end effector may be split or formed as a cam for fastening.

[0129] Figs. 3, 4 and 6 show a further embodiment, 200, of an end effector incorporating multiple curved features. As shown, the end effector 200 includes an end effector body 202, which may be solid or open in a center area A i thereof in the same manner as the first embodiment 100. The end effector body 202 as shown also has a generally rectangular shape and can be operably connected to a robotic transfer apparatus RTA in the same manner as shown with respect to Fig. 1, directly or indirectly, such as through a robotic arm (RA). At least one end effector pad 204 may be provided on an upper surface 206 of the end effector body 202. As shown in embodiment 200, in Fig. 3, there are four end effector pads 204a, 204b, 204c and 204d spaced around the periphery of the upper surface 206 of the end effector body 202 of the end effector 200. As is the case with both embodiments 100 and 200, there may be only one such end effector pad or multiple pads, although four are shown herein.

[0130] Each of such end effector pads 204 is identical as shown as was the case with embodiment 100, however, varying designs of such end effector pads may be used within the scope of the invention. Each end effector pad has an upper surface 208 positioned for receiving an object for transfer such as, for example, but not limited to, a silicon wafer or other semiconductor wafer.

[0131] As best shown in Fig. 4, a longitudinal cross-sectional view of one of the end effector pads 204a is shown in an enlarged view. A first portion 210 of the end effector pad 204a is shown which includes an upper surface 208 for supporting an object such as a silicon wafer W as shown for also in this embodiment for illustrative purposes. Preferably the wafer W or other object contacts the upper surface 208 at a location that includes at least one point of contact P. In this embodiment as shown in Fig. 3, there are four such points of contact (only two appear in full in the cross section of Fig. 4). As shown, the upper surface 208 has four dome shaped, curved features 207 (as shown enlarged in Fig. 4, two such features are shown as features 207a and 207b). Figs. 3 and 5 show all four such curved features. Such curved features 207 are formed on and are preferably integral with the upper surface 208 of the end effector pad 204a shown. It is possible to form such features out of a crosslinked polymer and adhere them or heat weld or otherwise attach the features to the upper surface 208, however, it is preferred that they are molded as part of the upper surface 208 of the end effector pad.

[0132] The curved features 207 in this case do not cover the entire upper surface 208 of the end effector pad 204a. However, they are arranged around and also equidistant from the center point C of the upper surface 208 as best shown in Fig. 6. Each of the curved features has its own point of contact^. As shown in the cross-sectional view of Fig. 4, curved features 207a, 207b each have respective points of contact Pi, P2. Identical such points of contact and curved features appear to form four such curved features 207 as shown in Fig. 3 which are arranged around central point C of the upper surface 208.

[0133] The first portion 210 of the end effector pad 204a is preferably an upper portion of the end effector. A second portion 212 of the end effector pad 204a is configured for positioning the end effector pad 204a on the end effector body 202. As shown, in one preferred embodiment, the second portion 212 of the end effector pad 204a includes, for example, mating threads 214, extending at least partially around the second portion 212 of the end effector body in a circumferential manner for connecting the end effector pad 204a securely to the end effector body 202. The end effector body is formed so as to preferably include at least one interior bore 218 into the end effector body 202 that may be configured to define mating threads 216 for engaging threads 214 on the second portion 212 of the end effector pad 204a. While mating threads are shown, other methods of fastening, connecting and permanently or releasably attaching the end effector pads as described above in embodiment 100 may be used in embodiment 200 as well.

[0134] To further illustrate the positioning and use of the at least one curved feature herein, further non-limiting examples are shown in alternative end effector pads 304 and 404 in Figs. 7 and 8, respectively. In these Figures, analogous numbers refer to analogous elements. Fig. 7 shows use of 14 curved features 307, all arranged around central point C of the upper surface 308 of a first portion 310 of the end effector pad 304. Fig. 8 shows 55 curved features 407 arranged on upper surface 408 of the first portion 410 of the end effector pad 404, wherein a central curved feature is formed on central point C which would also be a point of contact.

[0135] One will understand from this disclosure that the number, positioning, shape and extension or depression of curved features from one to four, from five to fourteen or from 15 to up to 73 or more such features is optional and may be used to modify the frictional release and retention of an object on the upper surface of an end effector pad. More features can provide more points of contact and also elevate the object off of a flat surface. This provides greater ability to move and relase the object and avoids too much contact between the upper surface and the object. However, it is within the scope of the invention that the upper surface of the end effector pad may also be flat or have non-curved features and operate within the scope of the invention, provided it also incorporates in some portion of the end effector and/or end effector pad that contacts and object for transport a crosslinked aromatic polymer as described herein.

[0136] The invention will now be described with respect to the following non-limiting Examples:

EXAMPLE 1

[0137] Various samples were formed according to the invention by heat molding a crosslinkable composition as noted herein using a commercial crosslinked aromatic polymer based on crosslinkable polyetherether ketone, z.e., Arion® 3000 XT.

[0138] Simulations were performed on concave 1,2,3 designs as well as single dome, 4 dome, and 14 dome.

[0139] Machined parts were prepared of single dome, 4 dome, 12 dome and 55 dome designs (See Figs. 5, 6, 7 and 8). Machined parts were polished in a tumbler with a slurry [0140] Injection molded parts were made of the single dome, 4 dome, 12 dome and 55 dome designs. The parts were injection molded, chemically cleaned by solvent washing in an ultrasonic bath with isopropyl alcohol to remove mold release or machining lubricant. [0141] While the parts as formed herein were formed by injection molding and are preferred, if desired for testing of additional designs, such parts may be machined from stock shapes, or molded directly to a final shape from alternate processes such as injection compression. Such parts may also be printed using three-dimensional printing techniques given a sufficient printer resolution. As the frictional properties of parts can be impacted by surface finish variations in the contact area of the end effector, optional polishing of parts by abrasive slurry, chemical polishing or other methods may be used to provide a desired surface and associated friction properties.

[0142] End effector pads having upper surfaces on the first portion thereof with varying types of curved features were prepared by injection molding. For comparison purposes, one sample having a single convex, dome-shaped curved feature across substantially all of the upper surface, as well as two samples with multiple domes, one with an upper surface having four domes and one with an upper surface having 14 domes were formed. Such sample designs are also shown in Fig. 9. [0143] A rectangular sample was prepared for dynamic mechanical analysis (DMA) testing at a temperature of 440°C for 2 hours in transient contact with a wafer which equated to about 2,000 to 5,000 cycles.

[0144] Fig. 9 depicts the change in lateral acceleration (G) for each of the designs as a wafer placed on the upper surface that is displaced (as this is a simulation and not a physical test) over a distance on each sample from a simulation using input coefficient of friction values measured via laboratory testing.

[0145] Static coefficient of friction for the Samples was measured using a modified ASTM D1894 (Standard Test Method for Static and Kinetic Coefficients of Friction of Plastic Film and Sheeting) apparatus Q as shown in Figs. 10-14. The apparatus Q included a hot plate HP and a fixture FX made of copper for retaining a one-inch diameter wafer W on a sample end effector pad EP. In use, single 1-inch wafers W were placed on the hot plate HP, which was heated to greater than 300°C. The copper fixture FX was used to hold the wafers W in place. A rectangular frame RF was used to mount four end effector pads EP and hold them in contact with the heated wafers W. An Instron® was used to apply force to the sled SL of the apparatus Q. The applied force was increased until the sled SL moved. The initial force (in grams force) required to move the sled was measured. The coefficient of friction was calculated by dividing the break loose force by the sled weight. [0146] The parts were molded in an injection molding machine (Arburg 270S All- Rounder 44 ton) at a temperature of about 665°F and at a molding pressure of 9500 psi. A surface roughness (Rd) of about 20 p-in. or greater was retained for these samples.

[0147] Testing of crosslinked polyetherether ketone end effector pads using Arion® 3000XT, was conducted and compared to another thermoplastic material, PBI (which was a Celazole U 60 stock shape rod machined into the end effector pad design and was in unfilled form), as well as to alumina (from Superior Technical Ceramics AL9980 (99.8% alumina). The test temperature was 300°C. The crosslinked Arion® 3000 XT showed 50% higher static coefficient of friction at room temperature, and a very similar coefficient of friction at high temperatures. This consistency at varied temperatures, along with the higher room temperature (RT) coefficient of friction (COF) shows that the crosslinked material has excellent stiction properties. The properties are shown below in Table 1. TABLE 1

[0148] Other materials were also tested by DMA for comparison using the same transient contact with a wafer at 440°C for two hours, using the same aromatic base polymer Arion® 3000 but that was not crosslinked (using Evonik 5000 grade PEEK) and polybenzimidazole (SCM 7000) from PBI Performance Products.

[0149] Additional testing was performed using DMA testing in a heated changer under an inert atmosphere. The crosslinked aromatic polymer sample in Fig. 9 was shown to be stable at 440°C for several hours. Through use of thermal simulation as well as Arrhenius’ Law, the data indicated that an effective thermal lifetime exceeding several thousand hours and tens of thousands of wafer transfer cycles for wafers may be made at temperatures of 400°C. This thermal stability, combined with the improved coefficient of friction would support faster wafer transfer speeds and consistent long-term performance of such compositions for making end effector pads and similar parts subjected to high temperatures and that required specific surface friction properties.

[0150] Crosslinked aromatic polymers as used herein were formed, and at high temperatures were dimensionally stable, had controlled dimensions, and a low surface roughness. It was further found that this performance could be enhanced by polishing the mold surfaces to ensure a lower surface roughness and an increased stiction for the upper surfaces so that the wafers were able to hold well in transfer but to release with increased acceleration to thereby allow for higher wafer processing speeds. Of the varying designs, while all were improvements, the best performance was indicated using a finite element analysis (FEA) simulations run on Abaqus® software based on the material indicated above at varying simulations as shown in Fig. 9. Through the simulations, the best performance was indicated by a design having four convex, dome-shaped curved features on the upper surface of the end effector pad sample.

[0151] Based on the above evaluation, sample end effector pads having four domes, 14 domes and 55 domes were made and their surface roughness evaluated using a 3D Laser Scanning Microscope and an ISO 4287 inspection method. The arithmetic mean roughness, Ra, was analyzed at the tip (point of contact) of each dome where a wafer or object would contact the upper surface of the end effector pad samples. The surface roughness for each design are shown below in Table 2, which also indicated that the 4-dome design had the best surface roughness capability of injection molded parts.

TABLE 2

[0152] Thus, the samples according to the invention were found to be softer than a silicon wafer, provide a static coefficient of friction which is higher than ceramics such as alumina and which can withstand temperatures of 350°C or 400°C and higher.

Accordingly, the samples provide the benefits and reduced particulation similar to use of fluoroelastomers, and which are sufficiently soft to avoid damage to wafers, but which are strong enough and provide preferred frictional properties that enable transfer of wafers safely but with increased acceleration in displacement to provide enhanced performance in a semiconductor environment.

[0153] The targeted performance of the materials was intended to be equal to or higher than the static coefficient of friction of comparative materials such as alumina (currently used in end effector applications) as well as to achieve a consistency and higher minimum coefficient of friction which would allow for higher transfer speeds at all temperatures. The lowest coefficient of friction is the limiting factor for how fast the end effector pad can transfer the wafers from chamber to chamber. It is also a goal that it would be best to achieve a very low wear factor. Less wear should provide a lower level of particulation.

The coefficient of friction is also expected to be correlated with, and able to be correlated to, the speed of transfer, that is, for example, a static coefficient of friction of 0.3 should yield a G-force acceleration of 0.3 before a wafer would move off its placement on a wafer arm due to momentum. In addition, particles released in transfer with the present invention would be organic in nature in comparison to inorganic particles that would be released in the use of prior art ceramic end effector pads.

EXAMPLE 2

[0154] In this experiment, differential scanning calorimetry (DSC) testing was used to evaluate the crystallinity of a crosslinked semicrystalline PEEK to illustrate that crosslinked polymers formed from a semicrystalline crosslinkable polymers can be prepared so as to minimize crystallization in those polymers for achieving improved performance in high temperature end applications. The DSC samples were run on a TA® Instruments QI 00 with 20°C/min heating rate. The melting points were determined by peak position, and peaks were integrated from an extrapolated flat baseline.

[0155] DMA testing was performed on a TA Instruments Ares G2 DMA using a rectangular torsion sample, heated at 5°C/min. Fig. 16 shows that by changing the cure cycle for the same PEEK polymer during crosslinking from a standard cure cycle to one in which a second step including a higher temperature cure cycle was employed, the standard cure curve A in Fig. 16 changes to cure curve B having a greatly reduced melting endotherm. Table 3 below provides the data as shown in Fig. 16. Cure 1 was carried out as a standard cure cycle which allows crystallization and crosslinking to occur during curing of the aromatic polymer and is carried out below the melting point of the polymer at approximately 310°C for a period of time. Cure 2 was carried out using the same initial curing cycle at the same temperature for the same time period, but an additional curing step was added after the initial curing cycle that was carried out above the melting temperature of the semicrystalline aromatic polymer by about 40°C and inhibited and minimized crystallization in the crosslinked polymer.

TABLE 3

[0156] In addition to the impact on the curing temperature profde as shown in Fig. 16, the DMA shows a reduction in the leathery region in a sample cured using the modified cure of Cure 2. Low crystallinity provided also a lower leathery region modulus (140°C to 320°C range, which is above the _g but below T _ra ). Of note, as shown in Fig. 17, is that the “rubbery plateau” (as shown in the enclosed box) starts at 320°C when using the modified Cure 2 (shown by the solid line) in comparison to the rubbery plateau from 350° to 360°C associated with the standard cure Cure 1 (shown by the dashed line). Thus, properties and dimensional stability can be more consistent from a range of 320°C to about 400°C or more if using the modified cure cycle Cure 2 in comparison to a standard cure as with Cure 1. Further, performance may be improved in a circumstance in which a thermal history for an end effector pad might be otherwise inconsistent from pad to pad due to incomplete contact of the pad with heated wafers (e.g., with warped wafers). [0157] The above testing and the material properties of the compositions herein indicate such properties are achieved and that the speed of transfer can be substantially improved while limiting transfer of material from the end effector pad to a transferred surface of a wafer. [0158] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.