US20070037486A1

US20070037486A1 - Polishing pad, method of manufacturing the polishing pad, and chemical mechanical polishing apparatus comprising the polishing pad

Info

Publication number: US20070037486A1
Application number: US11/500,512
Authority: US
Inventors: Kyoung-Moon Kang; Bong-su Ahn; Dong-jun Lee; Nam-Soo Kim; Jae-Hyun So
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2005-08-09
Filing date: 2006-08-08
Publication date: 2007-02-15
Also published as: JP2007049146A; KR20070018324A; KR100727485B1

Abstract

A polishing pad of a CMP apparatus has a plurality of pores. A characteristic associated with the pores, such as average size or pore density, varies substantially from region to region of the pad across the pad in a diametral direction of the pad. The polishing pad can be designed and manufactured using sample pads whose pore characteristics differ from each other. CMP test processes are performed in which the sample pads are used to polish test wafers, and the rates at which the test wafers are polished are measured and stored in a database. The polishing pad is fabricated using data from the database so that a chemical mechanical polishing apparatus employing the pad will polish wafers with a high degree of uniformity. The database can be used to select sample pads from a stockpile. Sections of the sample pads are cut out, respectively, and fastened to one another.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to the manufacturing of semiconductor devices. More particularly, the present invention relates to a chemical mechanical polishing apparatus, to the polishing pad of a chemical mechanical polishing apparatus and to a method of manufacturing a polishing pad of a chemical mechanical polishing apparatus.
2. Description of the Related Art
In general, the manufacturing of a semiconductor device includes a deposition process, a photolithography process and an etch process. The deposition process entails depositing conductive material on a wafer to form a thin film on the wafer. In the photolithography process, a resist is formed on the thin film, and the resist is exposed and developed to pattern the resist. In the etch process, the conductive thin film is etched using the patterned resist as a mask to form a fine circuit pattern from the conductive thin film. These processes are repeated until a number of circuit layers are formed on the wafer. However, the patterned conductive thin film provides many irregularities on the wafer. These irregularities would prevent the conductive material subsequently deposited on the wafer from forming a regular film on the wafer. An irregular conductive film would produce various errors in the subsequent processes such as a defocus error in a photolithography process.
Therefore, the wafer is planarized to remove irregularities from the surface thereof. To this end, chemical mechanical polishing (CMP) is mainly used to polish, i.e., planarize, a wafer. CMP is a global process meaning that it can provide a high degree of flatness over the entire surface of a substrate such as a semiconductor wafer. Therefore, CMP is currently the preferred process for planarizing semiconductor wafers because the diameter (surface area) of today's wafers tends be relatively large.
The CMP apparatus includes a rotary platen and a polishing pad mounted to the platen. The wafer is pressed against the polishing pad as the pad is rotated so that a surface of the wafer is polished by friction. The CMP apparatus also typically includes a polishing head that holds the wafer using suction. The polishing head is movable towards the polishing pad to press the wafer against the polishing pad. In this respect, the polishing head provides a controllable pressure on the back of the wafer to press the wafer against the polishing pad. In addition, the CMP apparatus supplies slurry between the polishing pad and the wafer surface so that the surface of the wafer is also polished by a chemical reaction produced by the slurry. The polishing pad includes grooves for guiding the slurry along the surface of the pad and fine pores for confining the slurry to the pad.
An important aim of the polishing process is to impart a high degree of flatness to the surface of the wafer. In this respect, characteristics of the polishing pad have been researched in an attempt to improve the uniformity of the polishing process. Characteristics of the polishing pad that are known to affect the rate at which the pad can be used to polish a wafer include the surface area, roughness, hardness, and compressibility of the pad. Furthermore, improvements in the structure of the polishing head and the composition of the slurry have been proposed as means to increase the rate at which a wafer can be polished by a CMP apparatus.
However, in spite of all the efforts so far, CMP still does not provide an optimal degree of uniformity in the polishing of a wafer.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a polishing pad by which a chemical mechanical polishing apparatus can polish a wafer at a rate having a desired profile across the wafer, such as at a rate having a high degree of uniformity across the wafer.
Likewise, another object of the present invention is to provide a chemical mechanical polishing apparatus, which employs such a polishing pad.
Another object of the present invention is to provide a method of manufacturing such a polishing pad.
According to one aspect of the present invention, there is provided a polishing pad of a CMP apparatus wherein the pad has pores and a characteristic associated with the pores varies substantially from region to region of the pad across the pad in a diametral direction of the pad, thereby demarcating the regions from one another. Some of the pores are isolated inside the polishing pad and other pores are exposed at an upper surface of the polishing pad. The characteristic associated with the pores that varies is either the average size of the pores or the pore density. The pore density refers to a ratio of the volume of all of the pores located in a region of the pad to the total volume of that region.
The polishing pad thus has plurality of sections that are disposed adjacent one another and constitute the various regions of the pad, respectively. Preferably, these sections include a central circular section, and at least one annular section surrounding the central section. The characteristic associated with the pores of each section of the pad, e.g. the pore density, is different from that of each section adjacent thereto. Also, the polishing pad may be sectioned only at an upper portion of the pad, only at a lower portion of the pad, or at both upper and lower portions of the pad.
According to another aspect of the invention, there is provided a chemical mechanical polishing apparatus that includes a rotatable platen, a dispensing system that dispenses a polishing medium such as a slurry, a polishing head, and a polishing pad having pores and attached to the platen, wherein a characteristic associated with the pores of the polishing pad varies substantially from region to region of the pad across the pad in a diametral direction of the pad. The polishing pad receives the polishing medium dispensed by the dispensing system, and the pores of the polishing pad exposed at the upper surface of the polishing pad confine the polishing medium to the pad. The polishing head has a chuck that holds a substrate, such as a semiconductor wafer, and presses a surface of the substrate against the polishing pad during a CMP process.
The polishing head can be movable in the apparatus to a polishing position at which the center of the surface of the substrate held by the chuck is disposed on the polishing pad at a location spaced a predetermined distance from the center of the polishing pad, i.e., the substrate is disposed eccentrically with respect to the polishing pad.
In this case, the diameter of the polishing pad will be at least about twice that of the substrate. Also, the polishing pad will have first and second sections dedicated to contact a peripheral area of the substrate held by the polishing head, and an intermediate section dedicated to contact a central region of the substrate held by the polishing head. The characteristics associated with the pores of the first and second sections of the pad are the same but are each different from the characteristic associated with the pores of the intermediate section of the pad.
Alternatively, the polishing head is movable in the apparatus to a polishing position at which the center of the surface of a substrate held by the chuck is disposed on the polishing pad at the center of the polishing pad, i.e. the substrate is centered on the polishing pad. In this case, the diameter of the substrate may be substantially the same as that of the polishing pad. Also, the polishing pad will have a peripheral section dedicated to contact a peripheral area of the substrate held by the polishing head, and a central section dedicated to contact a central area of the substrate held by the polishing head. The characteristic associated with the pores of the peripheral section of the pad will be different from that of the central section of the pad.
According to still another aspect of the present invention, there is provided a method of manufacturing a polishing pad of a chemical mechanical polishing apparatus, wherein the polishing pad is designed based on CMP test processes using sample pads whose pore characteristics are uniform within each sample pad but which characteristics differ from sample pad to sample pad. For example, the pore density of each of the sample pads may be uniform but the magnitude of the pore density may differ from sample pad to sample pad. The CMP test processes are carried out on substrates having films disposed thereon (test wafers), and the rates at which the films are polished by the sample pads are measured. A database is constructed which correlates the polishing rates to the characteristics of the sample pads used to effect such polishing rates.
The rate at which a film is polished using each of the sample pads may be measured at multiple locations across the substrate on which the film is disposed. In this case, the database can comprise data representative of the profile of the polishing rate across the substrate. Alternatively, the database can comprise the averages of the rates measured across each substrate.
Then, the polishing profile of a semiconductor wafer to be polished by a CMP process is predetermined. Specifically, rates at which several regions of a semiconductor wafer are to be polished, respectively, by an actual CMP process are predetermined.
Next, a polishing pad for use in the actual CMP process is designed by assigning characteristics in the database to sections of the polishing pad that will polish the regions of the semiconductor wafer, respectively. An actual polishing pad is then fabricated based on the design. That is, the polishing pad is fabricated such that sections of the polishing pad have the pore characteristics assigned thereto in the design process.
According to yet another aspect of the present invention, there is provided a method of manufacturing a polishing pad from several sample pads whose pore characteristics, e.g., average size or pore density, are uniform, respectively, but wherein the pore characteristics differ from sample pad to sample pad. Thus, the sample pads would polish similar wafers at different rates if used in carrying out a given CMP process on the wafers, respectively. Pad sections are cut out from the sample pads, respectively, and fastened to one another. Preferably, the sections include a circular section for the central region of the polishing pad and one or more annular sections fro the peripheral region of the pad.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiments thereof made with reference to the attached drawings in which:
FIG. 1 is a perspective view of a chemical mechanical polishing apparatus;
FIG. 2 is a perspective view of a polishing pad of the apparatus shown in FIG. 1 according to the present invention;
FIG. 3A is a graph of the rates at which locations along the surface of a wafer are polished by CMP apparatus according to the pore density of the polishing pad of the apparatus;
FIG. 3B is a graph of the average polishing rate according to pore density of the polishing pad in the CMP processes that produced the results shown in FIG. 3A;
FIG. 4A is another graph of rates at which locations along the surface of a wafer are polished by CMP apparatus according to pore density of the polishing pad of the apparatus;
FIG. 4B is a graph of the average polishing rate according to pore density of the polishing pad in the CMP processes that produced the results shown in FIG. 4A;
FIG. 5 is a chart of another set of results of the average polishing rate according to pore density of a polishing pad;
FIG. 6A is a cross-sectional view of several regions of a first embodiment of a polishing pad according to the present invention;
FIG. 6B is a cross-sectional view of several regions of another form of the first embodiment of a polishing pad according to the present invention;
FIG. 6C is a cross-sectional view of several regions of yet another embodiment of a polishing pad according to the present invention;
FIG. 7 is an exploded perspective view of the polishing pad of FIG. 2;
FIG. 8A is a plan view of the polishing pad according to the present invention with a wafer disposed thereon;
FIG. 8B is a sectional view taken along line A-A′ of FIG. 8A and also shows a polishing head assembly used to press the wafer against the polishing pad;
FIG. 9A is a plan view of another polishing pad according to the present invention with a wafer disposed thereon;
FIG. 9B is a sectional view taken along line B-B′ of FIG. 8A and also shows a polishing head assembly used to press the wafer against the polishing pad;
FIGS. 10A to 10C are cross-sectional views of various other embodiments of a polishing pad according to the present invention;
FIG. 11 is a flow chart of a method of manufacturing a polishing pad of a chemical mechanical polishing apparatus according to the present invention;
FIG. 12 is conceptual diagram illustrating the method of manufacturing a polishing pad according to the present invention; and
FIG. 13 is a graph of the rates at which locations along the surface of a wafer are polished using sample pads and a polishing pad fabricated according to test data derived using the sample pads.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a chemical mechanical apparatus 1 includes a polishing head assembly 10, a platen 20, a slurry dispensing system including a slurry supply arm 40 and a polishing pad 100. The platen 20 is cylindrical, and is supported by a rotary member (not shown) that is coupled to the bottom of the platen 20. A motor (also not shown) is coupled to the rotary member to rotate the member and hence, the platen 20 during a polishing process. The rotary member and the motor are disposed inside a base 50 of the apparatus. The polishing pad 100 is attached to the platen 20. A pad conditioner (not shown) and the slurry supply arm 40 are supported adjacent the platen 20. The pad conditioner maintains the condition of the polishing pad 100 during the polishing process. The slurry supply arm 40 provides a polishing medium, such as slurry, onto the surface of the polishing pad 100.
The polishing head assembly 10 is positioned above the platen 20 during the polishing process. The polishing head assembly 10 includes a polishing head 12 that holds the wafer (W, refer to FIG. 8 b) with suction such that the surface of the wafer to be polished faces the polishing pad 100, and presses the wafer (W) toward the polishing pad 100 during the polishing process. To this end, the polishing head 12 may comprise various components that are well known in the art per se. For instance, the polishing head 12 may have a vacuum chuck including plenum connected to a vacuum line, and a membrane to which the wafer (W) is adhered using a vacuum created in the plenum. The polishing head 12 may also include a retaining ring encircling the membrane to prevent the wafer (W) from migrating from the polishing head 12 during the polishing process.
In any case, the polishing head 12 is supported by a driving axle 14 at a position offset from the axis of rotation of the polishing pad 100. The driving axle 14 and hence, the polishing head 12, are rotated by a motor 16 during the polishing process. The driving axle 14 rotates in the same direction as the platen 20 during the polishing process. Also, the polishing head 12 may be oscillated in the radial direction of the polishing pad 100 during the polishing process.
The polishing pad 100 is circular and is disposed on the platen 20 and attached thereto by an adhesive. An upper surface of the polishing pad 100 contacts the surface of the wafer (W) to be polished and polishes the wafer (W) mechanically during the polishing process. The polishing pad 100 has a diameter that is at least twice that of the wafer (W) to be polished and thus, at least twice that of the retaining ring of the polishing head 12 as well. For instance, in the case in which the wafer (W) has a diameter of about 300 mm, the diameter of the polishing pad 100 is about 700 to 800 mm.
Referring to FIG. 2, grooves 102 are formed in an upper surface of the polishing pad 100. The slurry, supplied to the polishing pad 100 during the polishing process, flows along the grooves 102 and is thereby provided between the polishing pad 100 and the wafer (W). The grooves 102 may be annular and, in particular, may be circular.
The slurry supplied to the polishing pad 100 tends to flow radially outwardly along the polishing pad 100 due to centrifugal force caused by the rotation of the polishing pad 100. However, the slurry must remain on the upper surface of the polishing pad 100 and take part in the polishing process for best results. Accordingly, the polishing pad 100 has a plurality of pores 104 that are present inside the pad and are exposed at the upper surface of the pad. Particles of the slurry supplied to the polishing pad 100 are stored in the pores 104 exposed at the upper surface of the polishing pad 100. The slurry particles are extruded from the pores 104 and used in the polishing process when the wafer (W) is pressed against the polishing pad 100. Although the pores 104 located inside the polishing pad 100 do not store the slurry particles during the polishing process, these pores 104 become exposed as the surface of the polishing pad 100 becomes worn or after the pad is conditioned by the pad conditioner.
The ratio of the volume of the pores 104 in any region of the polishing pad 100 to the total volume of that region of the pad is a measure of the density of that region of the pad. Such a ratio will hereinafter be referred to as the pore density. Except as otherwise noted, the pore density of the polishing pad will take into account both the pores 104 exposed at the upper surface of the pad and the pores 104 isolated inside the pad. Also, the term polishing rate of a wafer (W) will hereinafter refer to the rate at which a film formed on the wafer (W) is polished.
The pore density of the polishing pad 100 has a significant effect on the polishing rate because the pore density of the polishing pad 100 has an influence on the area of the polishing pad 100 that will be in surface-to-surface contact with the wafer (W), the amount of slurry that will undergo a reaction with the wafer (W), the compressibility of the polishing pad 100, and the hardness of the polishing pad 100, etc. In this respect, the area of the polishing pad 100 that will be in surface-to-surface contact with the wafer (W), the compressibility of the polishing pad 100 and the hardness of the polishing pad 100 affect the mechanical action of the polishing process, whereas the amount of slurry that will undergo a reaction with the wafer (W) affects the chemical action of the polishing process.
A higher pore density results in a smaller surface area of the polishing pad. Also, the higher the pore density is, the greater the compressibility of the polishing pad and the lower the hardness of the polishing pad are. Also, the greater the volume of the pores exposed at the upper surface of the polishing pad is, the larger is the amount of slurry that can be stored at the surface of the polishing pad. Therefore, the mechanical action of the polishing process dominates for those polishing pads in which the pore density is comparatively small, and the chemical action of the polishing process dominates for those polishing pads in which the pore density is comparatively low.
FIGS. 3A and 3B show test results of CMP processes carried out on wafers each having an interlayer dielectric layer, and using a silica slurry for polishing the interlayer dielectric layers. The tests were conducted using polishing pads whose pore densities differed from one another. The differences in the pore densities were due to differences in the average distance between the pores 104 whereas the size of the pores 104 was nearly uniform throughout the polishing pads. On the other hand, FIGS. 4A and 4B show results of CMP processes carried out on wafers each having a shallow trench isolation film, and using a ceria slurry for polishing the shallow trench isolation films. These tests were also conducted using polishing pads of the type that were used in carrying out the CMP processes that produced the results shown in FIGS. 3A and 3B.
FIGS. 3A to 4B show lower polishing rates in connection with those polishing pads in which the average distance between the pores 104 is smaller (i.e., for those polishing pads having larger pore densities). This result can be explained by the fact that the films used in the tests are more readily polished (removed) by the mechanical action of the polishing process than by the chemical action of the polishing process. However, opposite results can be obtained when the same type of pads are used to polish a different type of film. For instance, although not shown, tests using polishing pads having the same pore densities as those shown in FIG. 3A showed that the rate at which a tungsten film can be polished is higher for pads which have higher pore densities, contrary to what is indicated in FIG. 3A.
Furthermore, as shown in FIG. 3A, the peripheral region (We) of a wafer (W) is polished at a higher rate than the central region (Wc) of the wafer (W) regardless of the type of film that is being polished, as long as a silica slurry is used as the polishing medium. However, whether the peripheral region (We) is polished at a higher rate than the central region (Wc) of the wafer (W) depends on the type of film that is being polished when a ceria slurry is used as the polishing medium.
FIG. 5 shows test results of CMP processes carried out on wafers each having a tungsten film disposed thereon, and using a silica slurry as the polishing medium. The tests were conducted using polishing pads in which the average size (diameter) of the pores 104 differed from each other but the pore densities were substantially the same. FIG. 5 shows that the polishing rate of the wafer (W) was higher for the polishing pads whose pores 104 had a smaller average size. That is, the test results shown in FIG. 5 indicate that the size of the pores 104 may also affect the polishing rate irrespective of the pore density.
The present invention is predicated on these test results, namely that the polishing rate of a CMP process generally varies across the surface of the wafer being polished, and is dependent on the pore density or the average size of the pores of the polishing pad used to carry out the process. Thus, in the polishing pad according to the present invention, the pore density or average size of the pores 104 varies amongst several different regions of the polishing pad to offset the variations in the polishing rate that would otherwise occur across the surface of a wafer if a uniform polishing pad were used instead, for example.
FIGS. 6A and 6B illustrate embodiments of polishing pads according to the present invention in which the pore density differs amongst several regions of the pad. These regions are laid out across the pad, i.e., in the diametral direction of the pad, and thus are demarcated at one (or more) interfaces located a given distance(s) from the center of the pad. The regions of the pad may correspond to the different regions of a wafer (W) that have been shown to experience different polishing rates when polished using a pad having a uniform pore density. FIG. 6A shows a polishing pad 100 a in which the pores 104 have substantially the same size in each of the regions of the pad but wherein the average distance between the pores 104 differs from region to region across the pad. FIG. 6B shows a polishing pad 100 b in which the average size of the pores 104 differs significantly from region to region across the pad whereas the average distance between the pores 104 in each region is the same from region to region across the pad. Furthermore, although not shown in the figures, a polishing pad according to the present invention can have pores 104 of about the same size but whose spacing in the depth-wise (vertical) direction of the pad differs from region to region across the pad, and whose spacing in the width-wise (horizontal) direction of the pad is substantially the same from region to region across the pad, such that the pore density of the pad varies from region to region across the pad.
On the other hand, FIG. 6C shows an embodiment of a polishing pad 100 c in which the pore densities of the various regions of the pad are substantially the same across the pad. In this embodiment, the average size of the pores 104 in each region differs from region to region across the polishing pad, but the volume of the pores 104 in each region is approximately the same from region to region across the pad.
The average size of the pores 104 in any region of a polishing pad 100 according to the present invention, i.e., the average diameter of the pores 104, may be between about 5 micrometers and about 500 micrometers. Also, the pores 104 in any region of the pad may have a volume of from about 0 percent to about 80 percent of the total volume of that region polishing pad 100. Still further, the pores 104 exposed at the surface of the polishing pad 100 in any region of the pad may make up 0 percent to 80 percent of the entire projected area of that region of the polishing pad 100. Of course, if the pores are said to make up 0 percent of the volume of a specific region of the polishing pad 100 that means that no pores exist in the specified region. Likewise, if the pores are said to make up 0 percent of the area of a specific region of the polishing pad 100 that means that no pores are exposed at the surface of the specified region of the pad.
FIG. 7 shows an embodiment in which the various regions of the polishing pad 100 are constituted by a plurality of discrete pad sections. Therefore, the respective pore densities of adjacent ones of the sections of the pad are different from one another (or the average size of the pores in each section of the pad is different from the average size of the pores in the adjacent section of the pad). The sections of the pad have complementary shapes that allow the sections of the pad to be combined. In this embodiment, the sections of the polishing pad 100 are circular and annular. More specifically, the polishing pad 100 has an inner portion and an outer portion 140. The inner portion is located at the center of the pad 100 and consists of a circular pad section 120. The outer pad portion 140 includes a first outer pad section 142 and a second outer pad section 144. Each of the first and second outer pad sections 142 and 144 is annular. The first outer pad section 142 surrounds the circular pad section 120 and the inner diameter of the first outer pad section 142 is substantially same as the diameter of the circular pad section 120. The second outer pad section 144 surrounds the first outer pad section 142 and the inner diameter of the second outer pad section 144 is substantially same as the outer diameter of the first outer pad section 142. The circular pad section 120, the first outer pad section 142 and the second outer pad section 144 may be combined using adhesive, mechanical fasteners, etc.
The embodiment described above has two outer pad sections 142 and 144 but the present invention is not so limited. For example, the outer portion 140 of the polishing pad may consist of one annular pad section, or three or more annular pad sections. In addition, the inner circular pad section 120 and the outer annular pad section(s) have been described as discrete but integral parts. However, the inner and outer portions of the polishing pad 100 may instead be unitary.
Hereinafter, the polishing of a wafer (W) using a polishing pad 200 according to the present invention will be described with respect to FIGS. 8A and 8B. In this polishing process, the diameter of the polishing pad 200 is at least twice that of the wafer (W). Hence, the diameter of the polishing pad 200 is at least twice that of the membrane of the polishing head 12 to which the wafer (W) adheres and is likewise at least twice the inner diameter of the retaining ring of the polishing head 12, as shown in FIG. 8B. The wafer (W) is positioned by the polishing head 12 in contact with but off-center with respect to the polishing pad 200 during the polishing process. The polishing pad 200 has one intermediate pad section 220 and two pad sections 240 between which the intermediate pad section lies. The intermediate pad section 220 is annular. The two pad sections 240 include a first pad section 242 that is circular and a second pad section 244 that is annular.
The first pad section 242 and the second pad section 244 have pores, and the pore density of the first pad section 242 is substantially the same as that of the second pad section 244. Also, the pore density of the central pad section 220 is different from that of the first and second pad sections 242 and 244.
The first pad section 242 is disposed at the center of the polishing pad 200. The second pad section 244 is disposed at the outer periphery of the polishing pad 200. More specifically, the intermediate pad section 220 has an inner diameter that is substantially the same as outer diameter of the first pad section 242, and surrounds the first pad section 242. The second pad section 244 has an inner diameter that is substantially the same as the outer diameter of the intermediate pad section 220, and surrounds the intermediate pad section 220. Thus, the pad sections 240 are in contact with the peripheral region of the wafer (W) during the polishing process, whereas the central pad section 220 is mostly in contact with the central region of the wafer (W).
FIGS. 9A and 9B show the polishing of a wafer (W) using another polishing pad 300 according to the present invention. Referring to FIGS. 9A and 9B, the polishing pad 300 has a diameter that is substantially the same as that of the wafer (W) and hence, that is substantially the same as the diameter of the membrane and inner diameter of the retaining ring of the polishing head 12. The polishing pad 300 has a central pad section 320 that is in contact with the central region (Wc) of the wafer (W) during the polishing process and a peripheral pad section 340 that is in contact with the peripheral region (We) of the wafer (W) during the polishing process. The central pad section 320 is circular shape, and the peripheral pad section 340 is annular. The peripheral pad section 340 thus has an inner diameter that is approximately the same as the diameter of the central pad section 320, and surrounds the central pad section 320.
In the case in which either of the methods shown in FIGS. 8A-9B is applied to the polishing of an interlayer dielectric layer on a wafer (W) using a silica slurry as the polishing medium, a polishing pad is used in which the pore density of those section(s) of the pad corresponding to the peripheral region (We) of the wafer (W) is higher than the pore density of the section of the pad that corresponds to the central region (Wc) of the wafer (W). Thus, the interlayer dielectric layer will be polished more evenly than if the polishing pad had a uniform pore density, i.e., the polishing rate will be more uniform than that depicted in any of the plots of FIG. 3A.
To the contrary, in the case in which either of the methods shown in FIGS. 8A-9B is applied to the polishing of a tungsten film on a wafer (W) using a silica slurry as the polishing medium, a polishing pad is used in which the pore density of those section(s) of the pad corresponding to the peripheral region (We) of the wafer (W) is lower than the pore density of the section of the pad that corresponds to the central region (Wc) of the wafer (W). Thus, the tungsten layer will be polished more evenly than if the polishing pad had a uniform pore density, i.e., the polishing rate will be more uniform.
Also, in the case in which either of the methods shown in FIGS. 8A-9B is applied to the polishing of a shallow trench isolation film on a wafer (W) using a ceria slurry, a polishing pad is used in which the pore density of those section(s) of the pad corresponding to the peripheral region (We) of the wafer (W) is lower than the pore density of the section of the pad that corresponds to the central region of the wafer (W). Thus, the shallow trench isolation film will be polished more evenly than if the polishing pad had a uniform pore density, i.e., the polishing rate will be more uniform.
FIGS. 10A to 10C illustrate various forms of another embodiment of a polishing pad 400 according to the present invention.
Referring to FIGS. 10A to 10C, a polishing pad 400 includes an upper portion 420 a, 420 b, 420 c and a lower portion 440 a, 440 b, 440 c. The upper portion 420 a, 420 b, 420 c is stacked on the lower portion 440 a, 440 b, 440 c, and the lower portion 440 a, 440 b, 440 c of the pad 400 is made of a softer material than the upper portion 420 a, 420 b, 420 c of the pad. The lower portion 440 a, 440 b, 440 c of the pad 400 is attached to the upper portion of the platen 20 by adhesive. Also, the upper portion 420 a, 420 b, 420 c of the pad 400 is attached to the lower portion 440 a, 440 b, 440 c of the pad 400 by adhesive.
As shown in FIG. 10A, the pore density of the upper portion 420 a of the pad 400 may be uniform, and the pore density of the lower portion of the pad 440 a may vary from region to region across the pad 400. Alternatively, as shown in FIG. 10B, the pore density of the upper portion 420 b of the pad 400 may vary from region to region across the pad 400, and the pore density of the lower portion 440 b of the pad 400 may be uniform. Furthermore, as shown in FIG. 10C, the pore density of both the upper portion 420 c and the lower portion 440 c of the pad 400 may vary from region to region across the pad. Variations in the pore density of the upper portion 420 b, 420 c of the polishing pad 400, as shown in FIG. 10B or 10C, create corresponding variations in the compressibility and hardness of the polishing pad 400, the amount of surface-to-surface contact between the polishing pad 400 and the wafer (W) and the amount of the slurry supplied to the various regions of the wafer (W). Variations in the pore density of the lower portion 440 a, 440 c of the pad 400, as shown in FIG. 10A or 10C, create corresponding variations in the compressibility of the polishing pad 400 but not in the other factors mentioned above.
A method of manufacturing a polishing pad 600 according to the present invention will now be described with reference to FIGS. 11 to 13.
Referring first to the flowchart of FIG. 11, sample pads each having pores therein and pores exposed at an upper surface thereof are fabricated. The respective pore densities of the sample pads, though, are different from one another (step S12). Then, each sample pad is used in a CMP process to polish a wafer and the polishing rate of the wafer is measured for each sample pad. Also, the sample pads are used to polish various types of films, respectively. The rates at which the wafers (films) are polished are stored in a database as correlated with the pore density of the polishing pads used to polish them (step S 14). Also, the rates may be measured at multiple locations across each of the wafers so that each measurement stored in the database m ay be representative of the polishing profile of a wafer, i.e., the rates at which the regions of the wafer are polished as shown in FIGS. 3A and 4A. Alternatively, each measurement stored in the database may be an average of the rates at which the regions of the wafer are polished.
Then, the polishing rate for each region of a wafer (W) to be polished is determined (step S16). The database is then used to design a polishing pad for polishing the wafer (W) based on the predetermined rates at which the regions of the wafer (W) are to be polished (step S18). Specifically, the sections of the polishing pad are designed to have the same pore density as respective ones of the sample pads. Finally, the polishing pad is fabricated according to the design made using the data derived from the sample pads (step S20). For example, the polishing pad can be fabricated from a stockpile of sample pads. That is, in the case in which the polishing pad is fabricated from discrete sections, these discrete sections are fabricated from sample pads and are combined with each other. For instance, circular and one or more annular sections are taken from sample pads and are combined.
FIG. 12 illustrates the concept behind the method of manufacturing a polishing pad according to the present invention. FIG. 13 is a graph of the rates at which locations along the surface of similar wafers are polished, respectively, using sample pads and a polishing pad fabricated according to test data derived using the sample pads. In FIG. 13, the plot ‘a’ and the plot ‘b’ show the rates at which a wafer are polished using a first sample pad 720 and a second sample pad 740, respectively. The plot ‘c’ shows the rate at which the wafer (W) is polished using a polishing pad 600 manufactured according to the present invention.
Referring to FIGS. 12 and 13, the rate at which a wafer is polished using the first sample pad 720 or the second sample pad 740 varies across the surface of the wafer. Thus, characteristics (e.g., pore density) of the sample pads 720, 740 are selected based on the data represented by plots ‘a’and ‘b’ and are incorporated to yield a polishing pad 600 that will uniformly polish a wafer (W) similar to the type of wafer polished by the sample pads. For example, in the case in which the polishing pad 600 is to be used in the manner shown in FIGS. 8A and 8B, the same pore density as the first sample pad 720 is selected for the section 620 of the polishing pad that will polish the central region (Wc) of the wafer (W). On the other hand, the same pore density of the second sample pad 740 is selected for those sections 642 and 644 of the polishing pad 600 that will polish the peripheral region (We) of the wafer (W). Then, the polishing pad 600 having integral or unitary sections 620, 642 and 644 is fabricated. For example, sample pads are combined by being cut into circular and annular sections 620, 642, 644 and the sections 620, 642 and 644 are fastened together using adhesive or other fastening means. The resulting polishing pad 600 will polish the wafer (W) with minimal variations in the polishing rate, i.e., with hardly any difference between the rate at which the central region (Wc) and the rate at which the peripheral region (We) of the wafer (W) are polished, as shown by plot ‘c’ in FIG. 13.
In the embodiments described above in connection with FIGS. 12 and 13, only two sample pads are combined to manufacture the polishing pad. However, the present invention is not so limited. Rather, three or more of the sample pads may be combined to manufacture the polishing pad. The uniformity of the polishing rate across the surface of the wafer (W) is generally improved as the number of sample pads combined with each other increases.
Further, the method of manufacturing a polishing pad according to the present invention has only been described in connection with improving the uniformity of the polishing rate across the surface of the wafer (W). However, the method of the present invention may also be applied to manufacture a polishing pad intended to produce variations in the polishing rate, i.e. predetermined differences in the polishing rate amongst several regions of the wafer (W).
Still further, the method of manufacturing a polishing pad according to the present invention has been described above as involving the selection of pore densities of the sample pads for incorporation into the sections of the polishing pad which correspond to the regions (We, Wc) of the wafer (W) to be polished. However, again, the present invention is not so limited. That is, the sample pads may be provided with different average pore sizes instead of different pore densities. In this case, the average pore size of the sample pads is selected, based on the data derived from testing the sample pads, and incorporated into a polishing pad to yield a polishing pad that will polish a wafer (W) according to a desired polishing profile.
Finally, although the present invention has been described in connection with the preferred embodiments thereof, various modifications of and changes to the preferred embodiments will be readily apparent to those of ordinary skill in the art. Therefore, variations of the disclosed embodiments are seen to be within the true spirit and scope of the invention as defined by the appended claims.

Claims

1. A chemical mechanical polishing apparatus comprising:

a platen supported in the apparatus so as to be rotatable;

a dispensing system that dispenses a polishing medium;

a polishing pad disposed on the upper surface of and attached to the platen to receive the polishing medium dispensed by the dispensing system, the polishing pad having a plurality of pores some of which are isolated inside the polishing pad and others of which are exposed at an upper surface of the polishing pad to confine the polishing medium to the pad,

wherein a characteristic associated with the pores varies substantially from region to region of the pad across the pad in a diametral direction of the pad, thereby demarcating the regions from one another; and

a polishing head having a chuck that holds a substrate to be polished and is movable in the apparatus to press a surface of a substrate held by the chuck against the polishing pad.

2. The chemical mechanical polishing apparatus of claim 1, wherein said characteristic associated with the pores is either the average size of the pores within the polishing pad or the pore density, the pore density corresponding to the ratio of the volume of all of the pores located in a region of the pad to the total volume of that region.

3. The chemical mechanical polishing apparatus of claim 1, wherein said characteristic associated with the pores is the average size of the pores within the polishing pad, whereby the average size of the pores within each of said regions varies from region to region across the pad in the diametral direction of the pad.

4. The chemical mechanical polishing apparatus of claim 1, wherein said characteristic associated with the pores is the pore density, whereby the pore density varies from region to region across the pad in the diametral direction of the pad.

5. The chemical mechanical polishing apparatus of claim 2, wherein the polishing pad has an inner section at a central region of the pad, and an outer section that is disposed radially outwardly of the inner section, said characteristic of the outer section of the pad being different from said characteristic of the inner section of the pad.

6. The chemical mechanical polishing apparatus of claim 5, wherein the inner section of the pad is circular, and the outer section of the pad is annular.

7. The chemical mechanical polishing apparatus of claim 2, wherein the polishing pad has a plurality of sections that are adjacent one another including an inner section at a central region of the pad, and a plurality of outer sections that are disposed radially outwardly of the inner section, and said characteristic of each of the sections of the pad is different from that of the section adjacent thereto.

8. The chemical mechanical polishing apparatus of claim 7, wherein the inner section of the pad is circular and each of the outer sections of the pad is annular.

9. The chemical mechanical polishing apparatus of claim 2, wherein the polishing pad has an upper portion that includes the upper surface at which pores of the pad are exposed, and a lower portion interposed between the upper portion and said platen, wherein said characteristic varies substantially from region to region of the upper portion of the pad across the pad in a diametral direction of the pad, thereby demarcating the regions of the upper portion of the pad from one another.

10. The chemical mechanical polishing apparatus of claim 2, wherein the polishing pad has an upper portion that includes the upper surface at which pores of the pad are exposed, and a lower portion interposed between the upper portion and said platen, wherein said characteristic varies substantially from region to region of the lower portion of the pad across the pad in a diametral direction of the pad, thereby demarcating the regions of the lower portion of the pad from one another.

11. The chemical mechanical polishing apparatus of claim 2, wherein the polishing head is movable in the apparatus to a polishing position at which the center of a surface of a substrate held by the chuck is disposed on the polishing pad at a location spaced a predetermined distance from the center of the polishing pad,

the polishing pad has first and second sections dedicated to contact a peripheral area of a substrate held by the polishing head at the polishing position during a polishing process, and an intermediate section dedicated to contact a central region of the substrate held by the polishing head at the polishing position during the polishing process, and

said characteristic of the first section of the pad and said characteristic of said second section of the pad are each different from said characteristic of the intermediate section of the pad.

12. The chemical mechanical polishing apparatus of claim 2, wherein the polishing head is movable in the apparatus to a polishing position at which the center of a surface of a substrate held by the chuck is disposed on the polishing pad at the center of the polishing pad,

the polishing pad has a peripheral section dedicated to contact a peripheral area of a substrate held by the polishing head at the polishing position during a polishing process, and a central section dedicated to contact a central area of the substrate held by the polishing head at the polishing position during the polishing process, and

said characteristic of the peripheral section of the pad is different from that of the central section of the pad.

13. The chemical mechanical polishing apparatus of claim 1, wherein said characteristic is the spacing of the pores, whereby the spacing of the pores varies substantially from region to region of the pad across the pad in a diametral direction of the pad.

14. The chemical mechanical polishing apparatus of claim 4, wherein the pore density of a peripheral region of the polishing pad less than the pore density of a central region of the polishing pad.

15. The chemical mechanical polishing apparatus of claim 4, wherein the pore density of a peripheral region of the polishing pad is greater than the pore density of a central region of the polishing pad.

16. A polishing pad of a chemical mechanical polishing apparatus, the polishing pad having a plurality of pores some of which are isolated inside the polishing pad and others of which are exposed at an upper surface of the polishing pad to confine a polishing medium to the pad,

wherein a characteristic associated with the pores varies substantially from region to region of the pad across the pad in a diametral direction of the pad, thereby demarcating the regions from one another.

17. The polishing pad of claim 16, wherein said characteristic associated with the pores is either the average size of the pores within the polishing pad or the pore density, the pore density corresponding to the ratio of the volume of all of the pores located in a region of the pad to the total volume of that region.

18. The polishing pad of claim 16, wherein said characteristic associated with the pores is the average size of the pores within the polishing pad, whereby the average size of the pores within each of said regions varies from region to region across the pad in the diametral direction of the pad.

19. The polishing pad of claim 16, wherein said characteristic associated with the pores is the pore density, whereby the pore density varies from region to region across the pad in the diametral direction of the pad.

20. The polishing pad of claim 17, wherein the polishing pad has an inner section at a central region of the pad, and an outer section that is disposed radially outwardly of the inner section, said characteristic of the outer section of the pad being different from said characteristic of the inner section of the pad.

21. The polishing pad of claim 20, wherein the inner section of the pad is circular, and the outer section of the pad is annular.

22. The polishing pad of claim 17, wherein the polishing pad has a plurality of sections that are adjacent one another including an inner section at a central region of the pad, and a plurality of outer sections that are disposed radially outwardly of the inner section, and said characteristic of each of the sections of the pad is different from that of the section adjacent thereto.

23. The polishing pad of claim 22, wherein the inner section of the pad is circular and each of the outer sections of the pad is annular.

24. The polishing pad of claim 17, wherein the polishing pad has an upper portion that includes the upper surface at which pores of the pad are exposed, and a lower portion interposed between the upper portion and said platen, wherein said characteristic varies substantially from region to region of the upper portion of the pad across the pad in a diametral direction of the pad, thereby demarcating the regions of the upper portion of the pad from one another.

25. The polishing pad of claim 17, wherein the polishing pad has an upper portion that includes the upper surface at which pores of the pad are exposed, and a lower portion interposed between the upper portion and said platen, wherein said characteristic varies substantially from region to region of the lower portion of the pad across the pad in a diametral direction of the pad, thereby demarcating the regions of the lower portion of the pad from one another.

26. The polishing pad of claim 16, wherein said characteristic is the spacing of the pores, whereby the spacing of the pores varies substantially from region to region of the pad across the pad in a diametral direction of the pad.

27. The polishing pad of claim 19, wherein the pore density of a peripheral region of the polishing pad less than the pore density of a central region of the polishing pad.

28. The polishing pad of claim 19, wherein the pore density of a peripheral region of the polishing pad is greater than the pore density of a central region of the polishing pad.

29. A method of manufacturing a polishing pad of a chemical mechanical polishing (CMP) apparatus, comprising:

providing sample pads each having a characteristic that influences the rate at which the sample pad can be used to polish a film of material in a CMP process;

performing CMP test processes using the sample pads on a plurality of substrates each having a film of material thereon to thereby polish the films, measuring the rates at which the films are polished using the sample pads, and constructing a database in which measurements of the rates at which the films were polished are correlated to said characteristics of the sample pads used to effect said rates;

predetermining rates at which each of several regions of a semiconductor wafer are to be polished using an actual CMP process;

designing a polishing pad by using the database to assign said characteristics in the database to sections of the polishing pad that will polish said several regions of the semiconductor wafer, respectively, when the polishing pad is used in the actual CMP process; and

fabricating a polishing pad in which the sections of the pad have the characteristics assigned thereto.

30. The method of claim 29, wherein each of the sections of the polishing pad to which said characteristics are assigned is a circular or annular section.

31. The method of claim 29, wherein the rate at which a film is polished using each of the sample pads is measured at multiple locations across the substrate on which the film is disposed, and each of said measurements in the database is data of a profile of the rate across the substrate.

32. The method of claim 29, wherein the rate at which a film is polished using each of the sample pads is measured at multiple locations across the substrate on which the film is disposed, and each of said measurements in the database is data of an average of the rates measured at said locations across the substrate.

33. The method of claim 29, wherein the characteristic is the average size of the pores within the sample pad or the pore density, the pore density corresponding to the ratio of the volume of all of the pores located in a region of the sample pad to the total volume of that region.

34. The method of claim 29, wherein the fabricating of the polishing pad comprises cutting out sections from several sample pads, and fastening the sections cut out from the sample pads to one another.

35. A method of manufacturing a polishing pad of a chemical mechanical polishing (CMP) apparatus, the method comprising:

providing several sample pads each having a plurality of pores some of which are isolated inside the sample pad and others of which are exposed at an upper surface of the sample pad to confine the polishing medium to the pad, and a characteristic associated with the pores that influences that the rate at which the sample pad can be used in a CMP process to polish a wafer,

wherein said characteristics of the sample pads are different from each other such that the sample pads if used in carrying out the CMP process on similar wafers, respectively, would polish the similar wafers at different rates;

cutting out sections from the sample pads, respectively; and

fastening the sections to one another in such a way as to fabricate a polishing pad in which the characteristic varies.

36. The method of claim 35, wherein the characteristic associated with the pores is either the average size of the pores within the sample pad or the pore density, the pore density corresponding to the ratio of the volume of all of the pores located in a region of the pad to the total volume of that region.

37. The method of claim 35, wherein said cutting comprises cutting out a circular section from one of the sample pads and an annular section from another of the sample pads.