YOUN KYUNG SOO (KR)
| US20070049164A1 | 2007-03-01 | |||
| US6293854B1 | 2001-09-25 | |||
| US5989405A | 1999-11-23 |
| A method of manufacturing a conditioning disc for a polishing pad, which is integrally formed with a plurality of protrusions, comprising: forming a feedstock having ceramic powder and a thermoplastic resin binder uniformly distributed therein by mixing and crushing the ceramic powder and the thermoplastic binder; injection molding to form an injection molded body by injecting and solidifying the feedstock into a cavity of an injection mold while heating and softening the feedstock; debinding to remove the thermoplastic resin binder from the injection molded body; and sintering the debinded injection molded body. |
| The method according to claim 1, wherein the ceramic powder and the thermoplastic resin binder of the feedstock have a ratio by volume of 1:0.3 ~0.7. |
| The method according to claim 1, wherein the forming a feedstock comprises three-dimensionally mixing (rotational-torsion mixing) and then crushing the ceramic powder and the thermoplastic resin binder to form the feedstock. |
| The method according to claim 3, wherein the forming a feedstock comprises: three-dimensionally mixing a mixture of the ceramic powder and the thermoplastic resin binder at room temperature under vacuum conditions; performing the three-dimensional mixing while increasing temperature to a first preset temperature at which fluidity can be imparted to the thermoplastic resin binder; maintaining the first preset temperature for a predetermined duration, followed by performing the three-dimensional mixing and solidification while slowly cooling to a second preset temperature; and crushing the solidified mixture, wherein the second preset temperature is lower than the first preset temperature. |
| The method according to claim 1, wherein, when injecting the feedstock into the cavity of the injection mold during the injection molding, pressure for injecting the feedstock is uniformly distributed. |
| The method according to claim 1, wherein the injection mold has the cavity defined therein, and comprises a first mold formed with a plurality of injection ports and a second mold formed with an engraved pattern, the cavity of the injection mold being larger than a required size of the conditioning disc. |
| The method according to claim 1, wherein the ceramic powder comprises zirconia powder. |
| The method according to claim 7, wherein the ceramic powder comprises partially stabilized zirconia powder. |
| The method according to claim 1, wherein the thermoplastic resin binder comprises a binding agent, a swelling agent and a plasticizer. |
| The method according to claim 1, wherein the forming a feedstock comprises adding a fluidity additive. |
| The method according to claim 10, wherein the fluidity additive comprises urethane. |
| The method according to claim 1, wherein the ceramic powder comprises particles having different sizes, and the thermoplastic resin binder comprises particles having different sizes. |
The present invention relates to a conditioning disc for a polishing pad, and more particularly to a method of manufacturing a conditioning disc, which can be used to more precisely machine a plurality of protrusions formed on the conditioning disc.
In the late of 1980s, International Business Machines (IBM) Corporation of the United States developed a new polishing process called a Chemical-Mechanical Polishing (hereinafter, referred to as “CMP”) process, where a mechanical removal process and a chemical removal process are combined into a single process.
Together with Plasma Enhanced Chemical Vapor Deposition (PECVD) and Reaction Ion Etching (RIE), the CMP process is necessarily used in fabrication of a chip on a submicron scale. In particular, interlayer dielectric (ILD) CMP and metal CMP have to be continuously applied to the entire surface of a device layer in order to widely flatten each layer to obtain a three-dimensional shape. CMP is a polishing process wherein a mechanical action and a chemical action are applied simultaneously to achieve cooperation therebetween.
In CMP, a wafer is polished by a polishing pad and slurry while a polishing table having the polishing pad mounted thereon is simply rotated. Further, a head unit presses the wafer with a certain pressure while rotating and shaking.
The wafer is mounted on the head unit by surface tension or vacuum and contacts the polishing pad by the weight of the head unit and the applied pressure. The slurry provided as a processing liquid flows through a minute gap in the contact and/or through pores of the polishing pad. Then, mechanical removal is obtained by polishing particles in the slurry and protrusions on the polishing pad, while chemical removal is obtained by chemical substances in the slurry.
In CMP, the pressure between the polishing pad and the wafer causes the contact at the top of a protrusion of a device and is thus concentrated on this portion, thereby polishing the surface at a relatively high speed. As the process continues, the protrusion is gradually lowered and is uniformly removed on the overall surface.
A conventional mechanical polishing process is liable to form a deformed layer, which becomes a defect of a semiconductor chip. Further, a chemical polishing process does not form the deformed layer but cannot provide a planar shape, i.e., shape precision. As a result, the chemical polishing method is limited to the formation of a simple smooth surface. On the contrary, CMP has an advantage of providing high shape precision without forming the deformed layer.
On the other hand, the polishing pad for use in CMP undergoes a decrease in surface roughness while polishing the surface of a target such as a wafer. If the surface roughness of the polishing pad is not restored to an original state, removal rate and uniformity will be deteriorated in a subsequent polishing process.
Accordingly, a conditioning process is necessary for supplying new slurry while restoring the surface roughness of the polishing pad. In the conditioning process, a conditioning disc is employed for conditioning and is compressed against the surface of the polishing pad by a certain pressure while the new slurry is supplied to the polishing pad.
Through the conditioning process, the polishing pad can maintain a constant porosity and the surface roughness thereof can be restored; non-uniformity deformation can be suppressed to thereby maintain flatness; and the slurry can be smoothly supplied into the pores thereof.
As for a conditioning disc, a diamond disc is commonly used and is fabricated using diamond particles having a size of 100~250㎛ and a metal binder. However, the diamond disc has disadvantages in that the diamond particles can be easily separated the disc by abrasion or corrosion at binding portions due to the slurry. Then, the separated diamond particles tend to be attached to the surface of the polishing pad and scratch the wafer surface. Further, the separated diamond particles can act as a main cause of metal ion contamination which causes short-circuit or the like on the wafer surface.
To minimize the separation of the diamond particles, there has been proposed a method of coating a corrosion resistant material composed of chrome, palladium or the like onto the surface of the metal binder used for binding the diamond particles. However, this method cannot solve the separation problem of the diamond particles.
In recent years, various research has been conducted into alternatives to the metal binder. Instead of using the diamond particles, there have been proposed a method of forming a plurality of protrusions by mechanically processing a surface of a ceramic material (Korean Patent No. 10-0387954, Document 1), a method of spraying to a surface of a ceramic material (Korean Patent No. 10-0678303, Document 2), etc.
In Document 1, a ceramic plate of a predetermined shape is sintered to prepare a sintered body, and both surfaces of the sintered body are subjected to primary rough machining, secondary semi-rough machining, and tertiary finish-grinding, thereby providing a ceramic body. Then, a plurality of protrusions is formed on one side of the ceramic body through mechanical machining using a diamond tool.
However, Document 1 has disadvantages in that machining takes considerable time and mass production is not easy. Further, grinding shock due to the mechanical machining causes non-uniform formation of unverifiable internal cracks, so that the protrusion on the internal cracks can be easily separated.
In Document 2, the spraying method is used to integrally form the plurality of protrusions on the surface of the ceramic body.
However, Document 2 has disadvantages in that the heights of the sprayed protrusions are uneven and irregular pores are formed in the ceramic body. Thus, adhesion strength is not uniform throughout the surface of the ceramic body, so that the strength of the ceramic body can be partially lower than the ceramic’s inherent strength and the plurality of protrusions can be separated by a micro size.
Further, the overall heights of the plural protrusions on the surface of the conditioning disc must be uniform to facilitate uniform conditioning of the polishing pad.
Further, height uniformity (deviation) of the protrusions must be maintained within at least 30㎛, so that not only an optimal current condition, i.e., a grinding force of 2.5~3.5㎛ per minute can be kept but also precise control of the grinding force, number control of protrusions, and the like can be made easier.
However, the conventional conditioning disc has a disadvantage in that it cannot precisely maintain the height uniformity of the protrusions due to difference in shrinkage (10~30%) or warp of the ceramic body according to region after sintering as compared with that before sintering
Therefore, the present invention is conceived in light of the foregoing problems, and an aspect of the present invention is to provide a conditioning disc for a polishing pad, which can fundamentally prevent particle separation due to abrasion or chemical corrosion that occurs during a conditioning process of the polishing pad.
Another aspect of the present invention is to provide a conditioning disc for a polishing pad, which can maintain more precise height uniformity of protrusions through significant improvement in machining precision.
In accordance with an aspect of the present invention, a method of manufacturing a conditioning disc for a polishing pad, which is integrally formed with a plurality of protrusions, includes: forming a feedstock having ceramic powder and a thermoplastic resin binder uniformly distributed therein by mixing and crushing the ceramic powder and the thermoplastic binder; injection molding to form an injection molded body by injecting and solidifying the feedstock into a cavity of an injection mold while heating and softening the feedstock; debinding to remove the thermoplastic resin binder from the injection molded body; and sintering the debinded injection molded body.
The ceramic powder and the thermoplastic resin binder of the feedstock may have a ratio by volume of 1:0.3 ~0.7.
According to one embodiment, the thermoplastic resin is employed instead of metal as a binder for binding the ceramic powder, thereby fundamentally preventing the protrusions of the conditioning disc from being separated by physical abrasion, chemical corrosion or the like.
The forming a feedstock includes three-dimensionally mixing and then crushing the ceramic powder and the thermoplastic resin binder to form the feedstock.
That is, according to one embodiment, the ceramic powder and the thermoplastic resin binder are mixed through a three-dimensional mixing process so that they can be uniformly distributed, thereby precisely maintaining height uniformity of the protrusions.
The forming a feedstock may include: a first mixing operation of three-dimensionally mixing a mixture of the ceramic powder and the thermoplastic resin binder at room temperature under vacuum conditions; a second mixing operation of performing the three-dimensional mixing while increasing temperature to a first preset temperature at which fluidity can be imparted to the thermoplastic resin binder; a third mixing operation of maintaining the first preset temperature for a predetermined duration, followed by performing the three-dimensional mixing and solidification while slowly cooling to a second preset temperature; and a crushing operation of crushing the solidified mixture, wherein the second preset temperature is lower than the first preset temperature.
During the injection molding, pressure for injecting the feedstock may be uniformly distributed.
The injection mold may have the cavity defined therein and may include a first mold formed with a plurality of injection ports and a second mold formed with an engraved pattern, and the cavity of the injection mold may be larger than a required size of the conditioning disc.
The ceramic powder may include zirconia powder.
The ceramic powder may include partially stabilized zirconia powder.
The thermoplastic resin binder may include a binding agent, a swelling agent and a plasticizer.
The forming a feedstock may include adding a fluidity additive.
The fluidity additive may include urethane.
The ceramic powder may include particles having different sizes, and the thermoplastic resin binder may include particles having different sizes. As a result, a vacant space between contacting parts when mixed can be minimized.
According to embodiments of the present invention, the method can fundamentally prevent particle separation by abrasion or chemical corrosion that occurs during a conditioning process of a polishing pad, thereby preventing metal ion contamination, short-circuit of a wafer or the like due to the particle separation.
Further, the method can significantly improve machining precision, so that the shape and number of protrusions can be freely designed, thereby improving a removal rate thereof.
The above and other aspects, features and advantages of the present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings, in which:
Fig. 1 is a flowchart of a method of manufacturing a conditioning disc according to one embodiment of the present invention;
Fig. 2 is a detailed flowchart of a feedstock forming operation of the method according to the embodiment of the present invention;
Fig. 3 shows injection molding of the method according to the embodiment of the present invention; and
Fig. 4 shows examples of a conditioning disc manufactured by a method of manufacturing a conditioning disc according to an embodiment of the present invention.
Exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings.
Figs. 1 to 3 show a method of manufacturing a conditioning disc according to one embodiment of the present invention.
The present invention is directed to manufacture a conditioning disc 100 that is formed at one side thereof with a plurality of protrusions 110, and examples thereof are illustrated in Fig. 4. However, it should be noted that the conditioning disc 100 according to the present invention is not limited to the shapes shown in Fig. 4 and can be modified into various shapes.
The conditioning disc 100 may be mounted on a main body 200. The main body 200 may be made of Teflon, stainless steel or other materials, which have good corrosion and chemical resistance and permit easy shape processing. The main body 200 is not indispensable in light of its function, and simply serves to connect the conditioning disc 100 to a motor shaft of conditioning equipment.
First, a feedstock for injection molding is formed in operation S1. The feedstock is formed by mixing ceramic powder, a thermoplastic resin binder, and other additives, followed by cooling and crushing the mixture.
Since the ceramic powder, the thermoplastic resin binder, and the additives, have different specific gravities, they cannot be fully uniformly dispersed due to gravity. Further, since they are different in pore or air content, it is difficult to precisely control height uniformity of protrusions 110 on the condition disc 100.
To solve these problems, according to an embodiment of the present invention, the ceramic powder, the thermoplastic resin binder and the like are fully uniformly dispersed and mixed through three-dimensional mixing (rotational-torsion mixing) under vacuum conditions.
However, it should be noted that the present invention is not limited to the three-dimensional mixing. Alternatively, two-dimensional mixing requiring a long running time of 12 hours or more, or various other processes may be employed as long as the ceramic powder, the thermoplastic resin binder, and the like can be uniformly dispersed and mixed.
Next, the operation S1 of forming the feedstock will be described in detail with reference to Fig. 2.
First, in operation S1-1, the mixture of the ceramic powder, the thermoplastic resin binder, the additives, etc. is injected into a container, which in turn is evacuated to a vacuum and is then mounted on a three-dimensional mixer. Here, the inner space of the container is evacuated to a vacuum in order to prevent bubbles or air from being contained in the mixture when mixing the mixture, thereby enhancing dispersion efficiency of the mixture.
Then, the three-dimensional mixer is driven to three-dimensionally mix the mixture at room temperature for a predetermined duration in operation S1-2.
In operation S1-3, the three-dimensional mixing is continued while increasing the temperature of the container up to a first preset temperature. The first preset temperature is about 150℃, at which fluidity can be imparted to the thermoplastic resin binder.
When the temperature of the container reaches the first preset temperature, the first preset temperature is maintained for a predetermined duration, e.g., for about 10 ~ 30 minutes, and then the three-dimensional mixing and solidification are carried out while slowly cooling the container to a second preset temperature in operation S1-4. The second preset temperature is about 50℃ or less, which is enough to decrease the fluidity of the thermoplastic resin binder.
Thus, the mixture having the ceramic powder and the thermoplastic resin binder uniformly dispersed and solidified therein is prepared and crushed, thereby forming a feedstock in operation S1-5.
Here, the particles of the ceramic powder and the thermoplastic resin binder may have the same size or different sizes (for example, a zirconia particle of 0.5㎛ and a zirconia particle of 0.3㎛, and so on). In particular, if the different sized particles are mixed with each other, a vacant space between contacting particles can be advantageously minimized.
The feedstock formed as described above is heated and softened, and is then injected into a cavity 10a of an injection mold 10, where the feedstock is solidified by cooling or the like, as shown in Figs. 3(a) and 3(b), thereby forming an injection molded body 20, in operation S2.
The injection mold 10 includes a first mold 11 formed with a plurality of injection ports 11a, and a second mold 12 in which a plurality of grooves 12a is engraved.
In the first mold 11, the plural injection ports 11a are spaced apart at regular intervals so that pressure for injecting the feedstock can be uniformly distributed, thereby making the density of the Fmolten feedstock uniform in the cavity 10a.
On an inner surface of the second mold 12, the plurality of grooves 12a is formed to have shapes corresponding to the shape of the protrusions 110 of the conditioning disc 100.
The cavity 10a of the injection mold 10 may be larger than the designed conditioning disc 100. This is determined in consideration of shrinkage (20 ~ 35%) of the injection molded body 20 upon sintering.
The injection molding operation S2 may be performed through an automatic injection molding press. If the automatic injection molding press is used, pressure can be properly adjusted according to the size of the conditioning disc not only to minimize the shrinkage of the injection molded body 20 upon sintering, but also to stabilize deformation due to density. Furthermore, the conditioning disc 100 having the plurality of protrusions 110 need not undergo post-processing.
Then, the thermoplastic resin binder is removed from the injection molded body 20 through a debinding process in operation S3, and the injection molded body 20 with no thermoplastic resin binder (see Fig. 3(c)) is sintered through a sintering process to thereby form the conditioning disc 100 having a desired-shape in operation S4.
Particularly, according to this embodiment, the feedstock in which the thermoplastic resin binder is uniformly dispersed through the three-dimensional mixing is used, so that the injection molded body 20 can have uniform shrinkage (20 ~ 35%) on the overall surface thereof upon sintering. As a result, the plurality of protrusions 110 can precisely maintain the height uniformity of no more than about 20~30㎛, and therefore there is no need for post-processing for planarizing the protrusions 110 or the surface of the conditioning disc 100 after sintering. Accordingly, the present invention facilitates mass production by minimizing equipment and manpower.
Further, according to this embodiment of the invention, the thermoplastic resin binder is employed instead of the metal binder in manufacturing the conditioning disc 100, so that the manufactured conditioning disc 100 can minimize separation of the protrusions 110 or the particles due to abrasion, corrosion or the like.
According to an embodiment of the present invention, zirconia powder, which has excellent corrosion resistance, acid resistance, heat resistance, etc. may be used as the ceramic powder. Further, a partial stabilizer such as Y 2 O 3 or the like may be added to the zirconia powder so as to facilitate molding.
An example of the partially stabilized zirconia is as follows.
ZrO 2 +Y 2 O 3 +HfO 2 +Al 2 O 3 wt%: >99.7
Y 2 O 3 wt%: <5.15
Al 2 O 3 wt%: <0.25
SiO 2 wt%: <0.02
The partially stabilized zirconia has a crystal structure varied depending on temperature, and thus has a monoclinic structure at room temperature. The monoclinic structure is transformed into a tetragonal structure at about 1,200℃ or more, and such phase transformation is called martensite. To obtain a dense zirconia sintered body, various oxidized substances such as CaO, MgO, CeO 2 , Y 2 O 3 , and the like may be added as a stabilizer. As the stabilizer is added, the monoclinic structure stabilized at room temperature is changed into the tetragonal or cubic structure and thus there is no phase transformation during cooling, thereby avoiding deformation or cracks. Accordingly, the ceramic powder according to this embodiment may be the partially stabilized zirconia (PSZ). Further, the molding density may be increased by adjusting the amount of partial stabilizer such as Y 2 O 3 .
In this embodiment, the binder is made of a material that has sufficient fluidity during injection molding, can be easily separated from the mold, and has good debinding properties. Since it is difficult for a single thermoplastic resin to simultaneously exhibit these properties, combination of various kinds of resins may be used. Here, the binder is composed of a binding agent, a swelling agent, a plasticizer, etc.
Examples of the binding agent include polyethylene, polypropylene, ethylene acetic acid vinyl copolymers, ethylene acryl copolymers, polystyrene, etc., which exhibit good fluidity when heated, and also include polystyrene, atactic polypropylene, methacrylic resin, polyacetal, etc., which have good debinding properties.
Examples of the swelling agent include paraffin wax, microcrystalline wax, stearic acid, amide wax, etc.
An example of the plasticizer includes butyl ester.
In the injection molding operation S2, since fluidity is obtained through the binder, the composition and the additive amount of the binder may be combined in consideration of fluidity, releasing properties, debinding properties, etc. If an excessive amount of binder is added, fluidity is improved but debinding properties deteriorates, or the shrinkage increases during sintering to thereby deteriorate the precision of the sintered body. For example, the ceramic powder and the binder may be in the ratio of 1 to 0.3~0.7.
Further, a resin component, such as polypropylene (PP), polyethylene (PE) and the like, may be added as a fluidity additive for facilitating flux. The fluidity additive may adjust the molding density according to the amount thereof. As more of the fluidity additive of the resin is added, the fluidity becomes better and the injection molding is smoothly carried out. However, when shrinkage occurs during a sintering process after molding, warpage may occur. Here, warping due to the shrinkage can be minimized by controlling the content of the resin in the range of 3~25 wt% according to the size of a product.
In this embodiment, urethane may be used as the fluidity additive. Nothing can secure greater fluidity than a small amount of urethane. Further, urethane is excellent in keeping the shape and thus can easily overcome differences in molding density.
The following is an example of a composition of the feedstock according to the present invention.
Partially stabilized zirconia (ZrO 2 +Y 2 O 3 +HfO 2 +Al 2 O 3 )--- 84.10 wt%
Urethane -------------------------------------------- 5.17 wt%
Polystyrene ----------------------------------------- 3.20 wt%
Atactic polypropylene-------------------------------- 2.93 wt%
Stearic acid ---------------------------------------- 0.42 wt%
Nonionic surface active agent ----------------------- 4.18 wt%
Here, the content of Y2O3 may be varied in the range of about 2 ~ 6% in consideration of the size of the conditioning disc 100.
<Experimentation 1>
Through a physical method, a conditioning disc manufactured by a method according to one embodiment of the present invention was compared with a conventional example in terms of particle separation.
A water jet having an orifice diameter of 0.3mm was used. The water jet was separated a distance of about 30mm from target products (inventive and conventional examples), and pressure of water was 40,000psi (i.e. 2.812kgf/cm 2 ). Further, an orifice head was moved at speeds of 1,000mm/min, 800mm/min, 500mm/min, and 300mm/min.
Table 1 shows results of this experimentation.
Table 1
It can be seen from the above results that particles were not easily separated by an external force from the conditioning disc manufactured by the method according to the embodiment of the present invention.
<Experimentation 2>
After lapse of a certain time from when a conditioning disc manufactured by a method according to one embodiment of the present invention and a conventional example were dipped into an undiluted solution of HCl, it was observed whether the protrusions or the particles were separated or not.
First, it was observed that bubbles or air started to occur as soon as the conventional example was dipped into the undiluted solution of HCL, and that corrosion also began. After four hours, reaction with acid caused all diamond particles to break away.
On the other hand, the conditioning disc made of a ceramic material according to the embodiment of the invention absolutely did not react with acid in the undiluted solution of HCl. Therefore, it could be seen that the conditioning disc according to the embodiment of the present invention was chemically stable.