TECHNICAL FIELD

[0001] The present disclosure applies broadly to the field of plasma processing equipment. More specifically, systems and methods for providing spatially uniform plasma processing on a workpiece are disclosed.

BACKGROUND

[0002] Integrated circuits and other semiconductor products are often fabricated on surfaces of substrates called "wafers." Sometimes processing is performed on groups of wafers held in a carrier, while other times processing and testing are performed on one wafer at a time. When single wafer processing or testing is performed, the wafer may be positioned on a wafer chuck. Other workpieces may also be processed on similar chucks.

SUMMARY

[0003] In an embodiment, a wafer chuck assembly includes a puck, a shaft and a base. The puck includes an electrically insulating material that defines a top surface of the puck, a heater element embedded within the electrically insulating material, and an electrically conductive plate disposed proximate to the electrically insulating material. The shaft includes an electrically conductive shaft housing that is electrically coupled with the plate, and a plurality of connectors, including electrical connectors for the heater element and electrical connectors for the electrodes. The base includes an electrically conductive base housing that is electrically coupled with the shaft housing, and an electrically insulating terminal block disposed within the base housing, the plurality of connectors passing through the terminal block.

[0004] In an embodiment, a method of plasma processing includes loading a workpiece onto a chuck having an electrically insulating top surface, providing a DC voltage differential across two spatially separated electrodes within the electrically insulating top surface, to clamp the workpiece to the chuck, and heating the chuck and the workpiece by passing current through heater elements embedded in the chuck. The method further includes providing process gases in a chamber surrounding the chuck, and providing an RF voltage between a conductive plate beneath the chuck, and one or more walls of the chamber, to ignite a plasma from the process gases.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 schematically illustrates major elements of a wafer processing system, according to an embodiment.

[0006] FIG. 2 is a schematic illustration of a wafer chuck shown in FIG. 1, showing exemplary component parts thereof, according to an embodiment.

[0007] FIG. 3 is a schematic illustration of a plasma wafer processing system including a wafer chuck, showing exemplary component parts thereof, according to an embodiment. [0008] FIG. 4 is a schematic illustration of part of the plasma wafer processing system of

FIG. 3, including portions of a wafer chuck and a diffuser therein, and illustrating exemplary power supply connections thereto.

[0009] FIG. 5 illustrates a portion of a wafer in process, according to an embodiment.

[0010] FIG. 6 illustrates a hypothetical result when the wafer portion of FIG. 5 is exposed to a plasma that does not steer ions.

[0011] FIG. 7 illustrates the result when the wafer of FIG. 5 is exposed to a plasma that steers ions, according to an embodiment.

DETAILED DESCRIPTION

[0012] The present disclosure may be understood by reference to the following detailed description taken in conjunction with the drawings described below, wherein like reference numerals are used throughout the several drawings to refer to similar components. It is noted that, for purposes of illustrative clarity, certain elements in the drawings may not be drawn to scale. Specific instances of an item may be referred to by use of a numeral in parentheses (e.g., connectors 230(1), 230(2), etc.) while numerals without parentheses refer to any such item (e.g., connectors 230). In instances where multiple instances of an item are shown, only some of the instances may be labeled, for clarity of illustration. [0013] Embodiments herein provide new and useful functionality for wafer processing systems. Semiconductor wafer sizes have increased while feature sizes have decreased significantly over the years, so that more integrated circuits with greater functionality can be harvested per wafer processed. Typical wafer diameters increased from about 2 or 3 inches in the 1970s to 12 inches or more in the 2010s. Over the same time frame, typical minimum feature sizes of commercial integrated circuits decreased from about 5 microns to about 0.015 microns. Processing smaller features while wafers grow larger requires significant improvements in processing uniformity. Because chemical reaction rates are often temperature sensitive, point to point temperature control across wafers during processing is becoming more important. For example, in certain types of processing, point to point temperature differences within a wafer of a few degrees Celsius may have been acceptable in the past, but now such differences may need to be held to about a degree or less. Certain materials used in fabrication of integrated circuits and other devices may also require very high temperature processing in very corrosive plasma environments. Plasma processing of workpieces other than wafers may also benefit from improved processing uniformity, and are considered within the scope of the present disclosure. Thus, characterization of the chucks herein as "wafer chucks" for holding "wafers" should be understood as equivalent to chucks for holding workpieces of any sort, and "wafer processing systems" as similarly equivalent to processing systems.

[0014] FIG. 1 schematically illustrates major elements of a wafer processing system 100. System 100 is depicted as a single wafer, semiconductor wafer processing system, but it will be apparent to one skilled in the art that the techniques and principles herein are applicable to plasma processing systems of any type (e.g., systems that process workpieces of other types, not necessarily semiconductors or wafers). It should also be understood that FIG. 1 only

schematically illustrates selected, major elements of system 100; an actual processing system will accordingly look different and likely contain additional elements as compared with system 100.

[0015] Wafer processing system 100 is serviced by one or more utilities such as process fluid(s) 10, external power 20, and vacuum 30. Wafer processing system 100 includes a housing 110 and a wafer interface 115 that receives wafers 50 from external sources and positions them within a processing location 160. Wafer processing system 100 may also include a user interface 145, and a controller 135 that typically includes a microprocessor, memory and the like, may take input from user interface 145 and/or other sources, and provides computer based control over the hardware elements of wafer processing system 100. Controller 135 may interface with external networks and/or computers over one or more data links 40 that may be physical (wires or optical connectors) or wireless connections. Wafer processing system 100 may also include one or more internal power supplies 150 that transform or condition power supplied by external power 20 for use by the hardware elements of the system.

[0016] Processing location 160 receives each wafer 50 onto a wafer chuck 170 that, in embodiments, includes three portions: a puck 175, a shaft 180 that supports puck 175, and a base 185 that supports shaft 180. Wafer 50 is physically positioned on, and in embodiments is heated, cooled and/or mechanically held by, puck 175. Wafer chuck 170 is also configured to couple radio frequency (RF) and/or direct current (DC) voltages to wafer 50, for electrostatic clamping of wafer 50 to puck 175, for generating a plasma within processing location 160 and/or for directing reactive ions from the plasma to wafer 50. Processing location 160 thus exposes wafer 50 to "plasma products," defined herein as any material that is, or has at one time been, part of a plasma. Plasma products may include any or all of ions, radicals, molecular fragments of source gases, other activated species, and/or source gas atoms or molecules that were part of a plasma but were not transformed into ions, radicals and so forth. Gases that have not formed part of a plasma at any time are defined herein as "unactivated gases."

[0017] Puck 175 and/or shaft 180 are also, in embodiments, configured to manipulate wafer 50 for access to wafer handling tools. For example, in embodiments, shaft 180 may raise puck 175 for a wafer 50 to be received thereon, and subsequently lower puck 175 to another height for processing, or the reverse. In these or other embodiments, puck 175 and/or shaft 180 may include actuators that raise or lower wafer 50 relative to a top surface of puck 175, such as lift pins that can extend from or retract within puck 175, such that a wafer tool may be inserted between wafer 50 and the top surface. Shaft 180 may also facilitate electrical and/or fluid connections with puck 175. Base 185 mechanically anchors shaft 180 within housing 110 and, in embodiments, provides interfaces for electrical utilities and/or fluids to shaft 180. Portions of base 185, shaft 180 and puck 175, or any combination thereof, may be formed monolithically with one another, or may be assembled partially or completely from component parts, as further described below.

[0018] FIG. 2 is a schematic illustration of wafer chuck 170, showing exemplary component parts thereof. FIG. 2 is not drawn to scale, certain components of wafer chuck 170 are exaggerated or diminished in size, not every instance of each component is labeled, and not all internal connections among components are shown, for illustrative clarity. Regions of wafer chuck 170 are identified as puck 175, shaft 180 and base 185, as per FIG. 1, although certain components of wafer chuck 170 may overlap two or more of these regions. Puck 175 includes an insulating top 205 in which are embedded electrodes 210 and heater elements 215. Top 205 may be formed of ceramic or other electrically insulating material; for example, in embodiments, top 205 is formed of aluminum nitride or alumina. Electrodes 210 and heater elements 215 may be formed of conductive and/or resistive materials that can withstand high temperatures, such as tungsten oxide, for example. An optional channel 207 within top 205 brings a heat transfer gas such as helium into contact with the backside of wafer 50 to improve heat transfer between top 205 and wafer 50. The improved heat transfer can help in cases where a wafer is not perfectly flat, and thus is not in uniform contact with the top surface of top 205, and/or to improve thermal uniformity from the range of a few degrees point-to-point on a wafer, to the range of one degree or less. Optional channels 208 interconnect with channel 207 and with one another within a top surface of top 205, so that the heat transfer gas can spread between the bottom surface of wafer 50 and top 205 until the gas passes an outer edge of wafer 50.

[0019] An electrically conductive plate 220 that may be formed of metal, for example, of aluminum or alloys thereof, is disposed beneath and proximate to top 205. In embodiments, top 205 and plate 220 are separated by a gap 217 to allow for differing thermal expansion of the two across a wide temperature range (e.g., from room temperature when chuck 170 is out of use, up to about 450C for certain processes). It is not necessary for gap 217 to be continuous, that is, top 205 and/or plate 220 may form ridges or channels for mechanical support therebetween, with a gap being considered to exist even if such ridges or channels are present. Gap 217 is thus exposed to process gases and/or plasma products at outer edges of top 205 and plate 220. An inert gas such as nitrogen or helium may be provided as a purge gas for gap 217, providing positive pressure within gap 217 with respect to the surrounding process chamber, to keep the gases and/or plasma products away from internal surfaces of top 205, plate 220 and

corresponding surfaces within shaft 180. In embodiments, gap 217 separates top 205 and plate 220 by about 0.5 to 1.5 millimeters. [0020] In shaft 180, an electrically conductive shaft housing 222 is below top 205 and forms a housing for shaft 180. Shaft housing 222 may also be made, for example, of aluminum; plate 220 and shaft housing 222 are electrically coupled and may be integrally formed, as shown in FIG. 2, or assembled by fastening or joining component parts. Shaft housing 222 houses an optional insulating liner 225, made for example of a ceramic material such as AIN or A1 ₂ 0 ₃ , that helps keep internal components from shorting or arcing to shaft housing 222. Insulating liner 225 may, optionally, be flushed with inert gases such as helium or nitrogen to remove heat or to dilute and remove process gases that may enter the chuck surface as wafers are transferred to and from chuck 170.

[0021] Shaft 180 also houses a variety of connectors 230 among power supplies and other facilities of equipment in which chuck 170 is located, and features of puck 175. Exemplary connectors 230 shown in FIG. 2 include radio-frequency/direct current (RF/DC) terminals 230(1), 230(2); a direct current (DC) probe center-tap terminal 230(3); inner zone heater terminals 230(4), 230(5); outer zone heater terminals 230(6), 230(7); and a thermocouple (TC) or resistance temperature detector (RTD) wire 230(8) (e.g., a two-element wire, shown schematically as a single connector in FIG. 2). Other connectors 230 are possible, in embodiments. Connectors 230 may be single or twisted pair wires, rods, coaxial or other connectors, and may be insulated or uninsulated. In embodiments, coaxial connectors 230 may include an inner conductor, an insulating layer about the inner conductor, a ground tube about the insulating layer, and a ceramic tube about the ground tube. TCs or RTDs may be implemented in any number and may optionally be organized for sensitivity to temperature variations caused by operation of various heater zones, heating by plasma or plasma products, heating or cooling caused by interaction with flowing gases or plasma products, or other causes. In embodiments, characterization of chuck 170 may determine that temperature is uniform across a given configuration of chuck 170, such that a single TC or RTD accurately represents the temperature of chuck 170. In other embodiments, multiple TCs or RTDs can be used to monitor temperatures across chuck 170, providing information that can be used to automatically and/or manually adjust operation of heater zones or other aspects of a plasma processing system in which chuck 170 is located, to promote temperature uniformity.

[0022] Connectors 230 may also be fluid conduits. Additionally, or instead of connectors 230 being configured as fluid conduits, shaft housing 222, insulating liner 225 and/or spaces between them may be configured with fluid passages. For example, FIG. 2 shows gap 217, discussed above, between shaft housing 222 and insulating liner 225, as discussed above, connected to a purge gas source 285(1) of base 185. Also, a backside gas source 285(2) supplies He or other inert gas to channel 207, for improved thermal control across wafer 50.

[0023] The number and arrangement of connectors 230 in FIG. 2 is schematic only; connectors 230 may, and usually will, be arranged differently for purposes such as minimizing size of shaft 180, maximizing space between adjacent connectors 230, improving temperature uniformity and/or heat dissipation, and other reasons.

[0024] Base 185 of chuck 170 includes an electrically conductive base housing 270 that may be made of metal (for example, of aluminum) and may be may be integrally formed with shaft housing 222 or assembled to it by fasteners, welding or the like. In embodiments, base housing 270 includes an electrically insulating terminal block 275 through which connectors

230-265 pass. Terminal block 275 serves to align connectors 230-265 such that their respective distal ends are arranged to mate with corresponding sockets within puck 175. Terminal block 275 may be formed of an insulator such as polyether ether ketone (PEEK) or ceramic, which both provide good electrical resistance and stability at high temperatures. [0025] Base housing 270 may include channels such as channel 280 therein for heating/cooling fluids, as shown. Heating/cooling fluids passed through channel 280 may be either gases or liquids. In embodiments, a heating/cooling fluid passed through channel 280 is a mixture of water and ethylene glycol or propylene glycol, having a mix ratio of approximately 50% water, 50% glycol. In embodiments, cooling provided through channel 280 cools not only base housing 270, but also shaft housing 222 and conductive plate 220 mechanically connected therewith. Advantageously, gap 217 and the purge gas provided therein serve to insulate plate 220 from the highest temperatures reached within top 220; also, metal of shaft housing 222 may be thicker than would be required for mechanical purposes only, to provide high heat transfer from plate 220 down to base housing 270, where the heat is removed by the cooling fluids passed through channel 280. For example, in embodiments, shaft housing 222 may be 1.5mm, 2.0mm, 2.5mm or thicker.

[0026] Base 185 may be fixed within an associated piece of wafer processing equipment, or may be movably mounted using slides, hinges, stages or other devices to position puck 175 to send or receive a wafer or other workpiece, and/or to align the wafer or workpiece as needed. [0027] FIG. 3 is a schematic illustration of a plasma wafer processing system 300 including wafer chuck 170, showing exemplary component parts thereof. FIG. 3 is not drawn to scale, certain components of plasma wafer processing system 300 are exaggerated or diminished in size, not every instance of each component is labeled, and not all internal connections among components are shown, for illustrative clarity. Plasma wafer processing system 300 is an example of wafer processing system 100, FIG. 1. Plasma wafer processing system 300 processes a wafer 50 within a process chamber 305 using plasma products and/or unactivated gases; FIG. 3 shows flows of plasma products as open arrows and of unactivated gases as solid arrows. An optional remote plasma source 310 generates a first plasma (not shown) from a first input gas stream 10(1) and optionally mixes resulting plasma products with a second input gas stream 10(2), passing the plasma products toward a diffuser 320. The plasma products may pass through other, optional diffusers 320, 325 and 340 that serve at least to distribute the plasma products uniformly before they are introduced into process chamber 305. In the configuration shown, a first power supply 150(1) provides RF energy across a space 330 between diffusers 325 and 340, forming a second plasma 335 in space 330. Plasma products from the first and second plasmas may optionally mix with a further input gas stream 10(3) through a further diffuser 350 (sometimes referred to as a "showerhead"). Diffuser 350 is configured with large ports for passing the plasma products therethrough, and gas passages 360 that transmit input gas stream 10(3) through only the side of diffuser 350 that faces process chamber 305. It will be appreciated that the use of any or all of remote plasma source 310 and diffusers 320, 325, 340 and 350 is optional.

[0028] A second power supply 150(2) is controllably configured to provide RF energy and/or DC bias to electrodes 210(1) and 210(2) within chuck 170, through connectors 230(1) and 230(2), as schematically shown, and to other parts of processing system 300. Specific connections of the RF energy and/or DC bias may vary, as discussed further below. Power supply 150(2) may provide, for example, DC bias across electrodes 210(1) and 210(2), and may provide RF energy and/or DC bias between electrodes 210(1) and 210(2) and other parts of processing system 300, as indicated by connection 151 between power supply 150(2) and diffuser 350. Providing both RF energy and DC bias is especially useful for both electrostatically clamping wafer 50 (or any other workpiece) to chuck 170, for generating a plasma within process chamber 305, and for directing ions of the plasma to certain processing sites on wafer 50, as discussed further below. Typical DC clamping voltages are ±200V delivered to opposite electrodes 210(1) and 210(2), while typical RF voltages are ±75V across process chamber 305 (RF power applied to the plasma is about 100W-500W). A portion of processing system 300 is shown in greater detail in FIG. 4.

[0029] FIG. 4 is a schematic illustration of part of plasma wafer processing system 300 including portions of wafer chuck 170 and diffuser 350, and illustrating exemplary power supply connections thereto. FIG. 4 is not drawn to scale, certain components of plasma wafer processing system 300 are exaggerated or diminished in size, not every instance of each component is labeled, and not all internal connections among components are shown, for illustrative clarity. FIG. 4 shows a portion of process chamber 305 bounded by respective portions of diffuser 350 and chuck 170, wafer 50, a plasma 355 within process chamber 305, and exemplary details of power supply 150(2). Plasma 355 is generated from gas streams 10(1), 10(2) and/or 10(3), either in their original, unactivated forms or as plasma products formed in remote plasma source 310 or within space 330 (FIG. 3). RF energy for forming plasma 355 is supplied by RF source 390 within power supply 150(2). In the configuration shown in FIG. 4, power supply 150(2) also provides a DC bias 370 across electrodes 210(1) and 210(2), that serves to electrostatically clamp wafer 50 to wafer chuck 170. DC electric fields are shown in FIG. 4 with dotted arrows. The embodiment shown in FIG. 4 also includes an optional DC bias 380 between electrodes 210 and diffuser 350. DC bias 380 can steer ions formed in plasma 355 (or existing in plasma products from other locations, as discussed above) toward wafer 50 to influence directionality of plasma processing on wafer 50 (see FIGs. 5-7). [0030] FIG. 4 also shows a center tap DC probe 395 that can be monitored to determine the actual backside DC voltage of wafer 50. Voltage measured on DC probe 395 can be measured and used to control DC bias 380, in order to control and optimize process results on wafer 50. For example, when plasma processing is performed, reactive species within the plasma products are often negatively charged ions, which can transfer negative charge to wafer 50 when they react. This leads to charging of wafer 50; a typical DC voltage acquired by wafer 50 during processing may be about -50V. Center tap DC probe 395 allows this voltage to be sensed and thus compensated by adjusting DC bias 380 accordingly. Thus, DC probe 395 couples with a high impedance circuit 398 that measures the voltage on DC probe 395 and provides appropriate information for power supply 150(2) to adjust DC bias 380. [0031] All of the components of, and integrated with, wafer chuck 170 are compatible with very high temperature operation, in contrast to earlier systems that may utilize materials that are not compatible with high temperatures, such as certain polymers or plastics, rubber, and the like. The components that are exposed to plasma are also capable of surviving very harsh plasma environments, such as H* or F* radicals, and others, produced when H ₃ or F ₃ respectively are utilized as source gases. 0 ₂ is also commonly added as a source gas (to supply electrons, facilitating plasma initiation) creating further ionic species and radicals. Earlier systems often used stainless steel chucks, but stainless generally corrodes in such environments, causing particulate contamination. The arrangement of wafer chuck 170 within processing system 300 is unique in that it allows for processing to take place at a uniform, high temperature while also providing firm electrostatic clamping for heat transfer, and the ability to steer reactive ionic species toward the workpiece, without corrosion or thermal degradation. For example, with proper sizing of components (e.g., thickness of shaft housing 222, and flow rate of purge gas within gap 217) embodiments herein are capable of operating up to 500C, facilitating plasma etching of certain metallic and/or ceramic materials on wafer 50.

[0032] FIGS. 5, 6 and 7 illustrate exemplary processing results obtainable with the wafer chucks and wafer processing systems described herein. FIG. 5 illustrates a portion of a wafer 50(1) in process. Wafer 50(1) has already been processed to form deep trenches 410 therein, and a film 400(1) has been deposited on both top surfaces of wafer 50(1) and in trenches 410.

Subsequent processing is intended to remove film 400(1) from certain regions of wafer 50(1) but leave film 400(1) on other regions; photoresist 420 is therefore provided in the regions where film 400(1) is to remain.

[0033] FIG. 6 illustrates a hypothetical result when wafer 50(1) is exposed to a plasma that does not steer ions, for example by exposing wafer 50(1) to a plasma where reactive species are simply directed randomly by diffusion. Surfaces of film 400(1) that are readily exposed to the reactive species are etched, while wafer 50(1) does not react with the reactive species. This process leaves the resulting wafer 50(2) with film 400(4) protected by photoresist 420, but also leaving residual material 400(3) within trenches 410. This occurs because the reactive species simply travel until they meet something, then react where they land. Few reactive species happen to be traveling in the exact direction required to penetrate deeply into trenches 410. It may or may not be possible, and is usually impractical, to etch wafer 50(1) long enough to remove residual material 400(3) using randomly directed reactive species.

[0034] FIG. 7 illustrates the result when wafer 50(1) is exposed to a plasma that steers ions by providing an electric field that directs ions toward wafer 50(1); that is, as shown in FIGS. 3 and 4 using wafer chuck 170. The electric field indicated in FIG. 4 directs negatively charged reactive species downward in the orientation of FIG. 7, such that more of the reactive species reach lower regions of film 400(1) within trenches 410. The resulting wafer 50(3) retains film 400(4) only in locations where original film 400(1) is protected by photoresist 420, as shown.

[0035] The design and types of materials used in wafer chucks described herein are not those that would be normally considered for wafer chucks. In the past, wafer chucks have often been quite simple affairs ranging from mere slabs of metal to slightly more complicated systems that provide vacuum or electrostatic clamping, adjustable wafer alignment/positioning, and the like. Designs that retain all of these functions and yet operate at very high temperatures in highly corrosive plasma environments without degradation, are not known. [0036] Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention. [0037] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included. [0038] As used herein and in the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a process" includes a plurality of such processes and reference to "the electrode" includes reference to one or more electrodes and equivalents thereof known to those skilled in the art, and so forth. Also, the words "comprise," "comprising," "include," "including," and "includes" when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.