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(11) | EP 0 769 350 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and apparatus for dressing polishing cloth |
| (57) A polishing cloth mounted on a turntable is dressed by a dresser for restoring polishing
capability of the polishing cloth. The dresser comprises a dresser body and an annular
diamond grain layer provided on the dresser body, and the annular diamond grain layer
is made of diamond grains which are electrodeposited. Alternatively, the dresser comprises
a dresser body and a SiC layer provided on the dresser body. The dressing of the polishing
cloth is performed by bringing the diamond grain layer or the SiC layer into contact
with the polishing cloth while the turntable and the dresser are rotating. |
BACKGROUND OF THE INVENTION
Field of the Invention:
[0001] The present invention relates to a method and apparatus for dressing a polishing cloth, and more particularly to a method and apparatus for dressing a polishing cloth for restoring polishing capability of the polishing cloth to thereby polish a semiconductor wafer to a flat mirror finish.
Description of the Related Art:
[0002] Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 µm wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of the optical system is relatively small.
[0003] It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus.
[0004] Conventionally, a polishing apparatus has a turntable and a top ring which rotate at respective individual speeds. A polishing cloth is attached to the upper surface of the turntable. A semiconductor wafer to be polished is placed on the polishing cloth and clamped between the top ring and the turntable. An abrasive liquid containing abrasive grains is supplied onto the polishing cloth and retained on the abrasive cloth. During operation, the top ring exerts a certain pressure on the turntable, and the surface of the semiconductor wafer held against the polishing cloth is therefore polished to a flat mirror finish while the top ring and the turntable are rotating. In the conventional polishing apparatus, a nonwoven fabric cloth is often used as a polishing cloth for polishing the semiconductor wafer having a device pattern thereon.
[0005] However, the recent higher integration of IC or LSI demands more and more planarized finish of the semiconductor wafer. In order to satisfy such a demand, harder materials, such as polyurethane foam, are recently used as the polishing cloth.
[0006] After, for example, one or more workpieces have been polished, the polishing cloth is processed to recover its original polishing capability. Various processes have been and are being developed for restoring the polishing cloth, and are collectively called "dressing". The polishing cloth is dressed in order to enable the polishing apparatus to perform a good polishing function at all times without undesired degradation of a polishing performance.
[0007] When the polishing cloth is made of a nonwoven fabric cloth, a nylon brush is generally used for dressing the polishing cloth to restore its polishing capability. When the polishing cloth is made of polyurethane foam, a polishing amount per unit time corresponding to a polishing rate, i.e. the amount of a material removed from the workpiece per unit time tends to be decreased in each polishing process, as shown in FIG. 14. In FIG. 14, the horizontal axis represents the number of semiconductor wafers which have been polished, and the vertical axis represents a polishing rate (Å/min). In an example of FIG. 14, although the polishing cloth was dressed by the dresser made of nylon brush after each polishing process, the polishing rate was rapidly lowered after polishing several semiconductor wafers.
[0008] There has been proposed a dresser having diamond grains for dressing a polishing cloth made of polyurethane foam to restore the polishing capability thereof. The polishing capability of the polishing cloth made of polyurethane foam, once dressed by the diamond grain dresser, tends to be effectively restored and not to be rapidly decreased.
[0009] However, the polishing amount per unit time is decreased depending on a polishing time unless an appropriate size of diamond grains is used to form the proper surface roughness of the polishing cloth, as shown in FIG. 15. In FIG. 15, the horizontal axis represent a size of the diamond grains according to Japanese Industrial Standard JISB4130 and JISB4131 defining a grain size of diamond and cubic crystal of boron nitride, and the vertical axis represents a polishing rate (Å/min) and a polishing amount (Å).
[0010] When the polishing cloth is dressed by the diamond dresser, the polishing cloth is slightly scraped off. Unless the polishing cloth is linearly scraped off in any vertical cross section, i.e. is linearly scraped off in a radial direction of the polishing cloth, the semiconductor wafer which is a workpiece to be polished cannot be uniformly polished as the number of dressing processes increases.
SUMMARY OF THE INVENTION
[0011] It is therefore an object of the present invention to provide a method and apparatus for dressing a polishing cloth which can prevent the polishing amount per unit time from being decreased in each polishing process, form the proper surface roughness of the polishing cloth, and dress the polishing cloth linearly in any vertical cross section so that a workpiece such as a semiconductor wafer having a device pattern is uniformly polished.
[0012] According to one aspect of the present invention, there is provided a method of dressing a polishing cloth mounted on a turntable, comprising the steps of: providing a dresser comprising a dresser body and an annular diamond grain layer provided on the dresser body, the annular diamond grain layer being made of diamond grains which are electrodeposited; and dressing the polishing cloth by pressing the annular diamond grain layer against the polishing cloth while the turntable and the dresser are rotating.
[0013] According to another aspect of the present invention, there is provided an apparatus for dressing a polishing cloth mounted on a turntable, comprising: a dresser comprising a dresser body and an annular diamond grain layer provided on the dresser body, the annular diamond grain layer being made of diamond grains which are electrodeposited; a first actuator for rotating the dresser about a central axis of the dresser; and a second actuator for pressing the annular diamond grain layer of the dresser against the polishing cloth.
[0014] According to the above method and apparatus, the surface of the polishing cloth is linearly scraped off in any vertical cross section thereof, and the surface roughness of the polishing cloth which suffers the degradation of the polishing performance can be restored to a good polishing condition.
[0015] According to still another aspect of the present invention, there is provided a method of dressing a polishing cloth mounted on a turntable, comprising the steps of: providing a dresser comprising a dresser body and a SiC layer provided on the dresser body; and dressing the polishing cloth by pressing the SiC layer against the polishing cloth while the turntable and the dresser are rotating.
[0016] According to still another aspect of the present invention, there is provided an apparatus for dressing a polishing cloth mounted on a turntable, comprising: a dresser comprising a dresser body and a SiC layer provided on the dresser body; a first actuator for rotating the dresser about a central axis of the dresser; and a second actuator for pressing the dresser against the polishing cloth.
[0017] According to the above method and apparatus, the surface of the polishing cloth is linearly scraped off in any vertical cross section thereof, and the surface roughness of the polishing cloth which suffers the degradation of the polishing performance can be restored to a good polishing condition. Further, since the dresser has the SiC layer, a thickness of material removed from the polishing cloth is minimized by the dressing process. In case of dressing the polishing cloth by the dresser having diamond grains, the diamond grains fall off from the dresser, and the semiconductor wafer may possibly be scratched or damaged in the polishing process by the diamond grains which have fallen off from the dresser during the dressing process. However, in case of dressing the polishing cloth by the dresser having a SiC layer, there is no fear of scratches or damages on the semiconductor wafer. Further, even if acidic abrasive liquid is used, the SiC layer of the dresser is not eroded by the acidic abrasive liquid.
[0018] The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]
FIG. 1 is a vertical cross-sectional view of a polishing apparatus having a dressing apparatus according to the present invention;
FIG. 2A is a bottom view showing a dresser of a first embodiment of the present invention;
FIG. 2B is a cross-sectional view taken along the line A-A of FIG. 2A;
FIG. 2C is an enlarged view showing the section B of FIG. 2B;
FIG. 3 is a plan view showing an arrangement of the dresser and a polishing cloth mounted on a turntable according to the first embodiment of the present invention;
FIG. 4 is a graph showing a scratch length of the dresser in the first embodiment of the present invention and the conventional apparatus;
FIG. 5 is a graph showing a contour of the polishing cloth which has been dressed by the dresser of the first embodiment of the present invention;
FIG. 6A is a graph showing a surface roughness of an unused polishing cloth;
FIG. 6B is a graph showing a surface roughness of the polishing cloth which has been dressed by the dresser of the first embodiment of the present invention;
FIG. 6C is a graph showing a surface roughness of the polishing cloth after the polishing process;
FIG. 7 is a graph showing a polishing rate of an oxide layer of the semiconductor wafer after the polishing cloth is dressed by the dresser of the first embodiment of the present invention;
FIG. 8A is a perspective bottom view showing a dresser of a second embodiment of the present invention;
FIG. 8B is a bottom view showing the dresser of the second embodiment of the present invention;
FIG. 8C is a cross-sectional view taken along the line A-A of FIG. 8B;
FIG. 9 is an enlarged view showing the section B of FIG. 8C;
FIG. 10A is an enlarged plan view showing a SiC layer;
FIG. 10B is a cross-sectional view taken along the line C-C of FIG. 10A;
FIG. 11 is a graph showing a scratch length of the dresser in the second embodiment of the present invention and the conventional apparatus;
FIG. 12 is a graph showing a contour of the polishing cloth which has been dressed by the dresser of the second embodiment of the present invention;
FIG. 13 is a graph showing a polishing rate of an oxide layer of the semiconductor wafer after the polishing cloth is dressed by the dresser of the second embodiment of the present invention;
FIG. 14 is a graph showing the relationship between the number of semiconductor wafers and polishing rates of the semiconductor wafers in the conventional apparatus; and
FIG. 15 is a graph showing the relationship between polishing rates and the diamond grain size.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] A dressing apparatus according to a first embodiment of the present invention will be described below with reference to FIGS. 1 through 7.
[0021] A dressing apparatus is installed in a polishing apparatus in FIG. 1. As shown in FIG. 1, the polishing apparatus comprises a turntable 1, and a top ring 3 positioned above the turntable 1 for holding a semiconductor wafer 2 against the turntable 1. The top ring 3 is located in an off-center position with respect to the turntable 1. The turntable 1 is rotatable about its own axis as indicated by the arrow A by a motor (not shown) which is coupled through a shaft 1a to the turntable 1. A polishing cloth 4 is attached to an upper surface of the turntable 1.
[0022] The top ring 3 is coupled to a motor (not shown) and also to a lifting/lowering cylinder (not shown). The top ring 3 is vertically movable and rotatable about its own axis as indicated by the arrows B, C by the motor and the lifting/lowering cylinder. The top ring 3 can therefore press the semiconductor wafer 2 against the polishing cloth 4 under a desired pressure. The semiconductor wafer 2 is attached to a lower surface of the top ring 3 under a vacuum or the like. A guide ring 6 is mounted on the outer circumferential edge of the lower surface of the top ring 3 for preventing the semiconductor wafer 2 from being disengaged from the top ring 3.
[0023] An abrasive liquid supply nozzle 5 is disposed above the turntable 1 for supplying an abrasive liquid onto the polishing cloth 4 attached to the turntable 1.
[0024] A dressing apparatus comprises a dressing head 8 which is positioned above the turntable 1 in diametrically opposite relation to the top ring 3. The polishing cloth 4 is supplied with a dressing liquid such as water from a dressing liquid supply nozzle 9 extending over the turntable 1. The dressing head 8 is coupled to a motor 15 and also to a lifting/lowering cylinder 16. The dressing head 8 is vertically movable and rotatable about its own axis as indicated by the arrows D, E by the motor 15 and the lifting/lowering cylinder 16.
[0025] The dressing head 8 is of a disk shape having a certain diameter, and holds a dresser 10 on its lower surface. The lower surface of the dressing head 8, to which the dresser 10 is attached, has holes (not shown) defined therein which are connected to a vacuum source for attaching the dresser 10 under vacuum to the lower surface of the dressing head 8. The dresser 10 may be also attached to the dressing head 8 by bolts or the like. The dressing head 8 can be oscillated so that the dressing head 8 is movable in a radial direction of the polishing cloth 4. The motor 15 constitutes a first actuator for rotating the dresser 10 about a central axis thereof, and the lifting/lowering cylinder 16 constitutes a second actuator for pressing the dresser 10 against the polishing cloth 4.
[0026] The abrasive liquid supply nozzle 5 and the dressing liquid supply nozzle 9 extend to a region near the central axis of the turntable 1 above the upper surface thereof for supplying an abrasive liquid and a dressing liquid such as water, respectively, to the polishing cloth 4 at a predetermined position thereon.
[0027] The polishing apparatus operates as follows: The semiconductor wafer 2 is held on the lower surface of the top ring 3, and pressed against the polishing cloth 4 on the upper surface of the turntable 1. The turntable 1 and the top ring 3 are rotated relatively to each other for thereby bringing the lower surface of the semiconductor wafer 2 in sliding contact with the polishing cloth 4. At this time, the abrasive liquid nozzle 5 supplies the abrasive liquid to the polishing cloth 4. The lower surface of the semiconductor wafer 2 is now polished by a combination of a mechanical polishing action of abrasive grains in the abrasive liquid and a chemical polishing action of an alkaline solution in the abrasive liquid.
[0028] The polishing process comes to an end when the semiconductor wafer 2 is polished by a predetermined thickness of a surface layer thereof. When the polishing process is finished, the polishing properties of the polishing cloth 4 is changed and the polishing performance of the polishing cloth 4 deteriorates. Therefore, the polishing cloth 4 is dressed to restore its polishing properties.
[0029] In a first embodiment of the present invention, an apparatus for dressing a polishing cloth has a dresser 10, which is attached to the dressing head 8, shown in FIGS. 2A through 2C. FIG. 2A is a bottom view of the dresser 10, FIG. 2B is a cross-sectional view taken along the line A-A of FIG. 2A, and FIG. 2C is an enlarged view showing a portion B of FIG. 2B.
[0030] The dresser 10 comprises a dresser body 11 of a circular plate, an annular projecting portion 12 which projects from an outer circumferential portion of the dresser body 11, and an annular diamond grain layer 13 on the annular projecting portion 12. The annular diamond grain layer 13 is made of diamond grains which are electrodeposited on the annular projecting portion 12. The diamond grains are deposited on the annular projecting portion 12 by nickel plating.
[0031] One example of the dresser 10 is as follows. The dresser body 11 has a diameter of 250 mm. The annular diamond grain layer 13 having a width of 6 mm is formed on the circumferential area of the lower surface of the dresser body 11. The annular diamond grain layer 13 comprises a plurality of sectors (eight in this embodiment).
[0032] The polishing cloth is dressed by the dresser in a manner shown in FIG. 3. The polishing cloth 4 made of polyurethane foam to be dressed is attached to the upper surface of the turntable 1 which rotates in a direction indicated by the arrow A. The dresser 10 which rotates in a direction indicated by the arrow B is pressed against the polishing cloth so that the annular diamond grain layer 13 is brought in contact with the polishing cloth 4. The turntable 1 and the dresser 10 are rotated relatively to each other for thereby bringing the lower surface of the diamond grain layer 13 in sliding contact with the polishing cloth 4.
[0033] FIG. 4 is a graph showing a scratch length of the dresser of the present invention. The amount of a material removed from the polishing cloth by dressing, which is carried out with the dresser, depends on the scratch length.
[0034] The scratch length is defined, per a certain small area of the polishing cloth, as the total length which is the product of the relative speed between said area and each point of the surface of the dresser and the dressing time during which said area and the dresser contact to each other. That is, the scratch length is defined as the length in which said area is scratched by the dresser. The scratch lengths differ with the distance from the center of the rotation of the polishing cloth mounted on the turntable to said area. In the case where the effective area of the dresser is disk-shaped, the scratch length has the following feature.
[0035] In the area of the polishing cloth which is located in the same distance from the center of the polishing cloth as the distance between the center of the dresser and the center of the polishing cloth, the scratch length is relatively long. In the area of the polishing cloth which is located in the same distance from the center of the polishing cloth as the distance between the edge of the dresser and the center of the polishing cloth, the scratch length is relatively short. This is because the arc length of the dresser at a radial position from the center of the polishing cloth differs with the radial position from the center of the polishing cloth.
[0036] As described above, the amount of a material removed from the polishing cloth by dressing with the dresser is proportional to the scratch length. Therefore, in case of using a disk-shaped dresser, the polishing cloth is scratched excessively at the location of the same distance as the distance between the center of the dresser and the center of the polishing cloth, and the cross-sectional view of the dressed area of the polishing cloth has a recess, the depth of which is deeper as the location in the recess is nearer to the center of the recess.
[0037] In the case where the workpiece is polished with the polishing cloth having the recess, the sufficient flatness of the polished surface of the workpiece cannot be obtained.
[0038] In the present invention, the effective area of the dresser is arranged to be annular. That is, the diamond grain layer 13 is annular.
[0039] By reducing the effective area of the inner portion of the dresser, the amount of a material removed from the polishing cloth by dressing is decreased at the inner area of said recess, and the irregularity of the depth of said recess is improved. Thus, the flatness of the surface of the dressed area of the polishing cloth is improved, and more effective dressing is obtained.
[0040] In FIG. 4, the horizontal axis represents a radial position on the polishing cloth (mm), and the vertical axis represents a scratch length (mm) of the dresser 10. The curve A represents the relationship between scratch lengths and radial positions on the polishing cloth when the polishing cloth was dressed by the dresser 10 which has the annular diamond grain layer 13 on the dresser body 11, and the curve B represents the relationship between scratch lengths and radial positions on the polishing cloth when the polishing cloth was dressed by the dresser which has a circular diamond grain layer which is formed by electrodepositing diamond grains on the entire lower surface of a circular plate. As shown in FIG. 4, the upper surface of the polishing cloth was substantially uniformly contacted by the diamond grain layer 13, and was linearly scraped off in any vertical cross section. This means that the scratch lengths are substantially uniform at all radial positions of the polishing cloth in a radical direction of the polishing cloth. In FIG. 4, the dressing length L1 represents a polishing range of an 8-inch wafer which is not oscillated during polishing process, and the dressing length L2 represents a polishing range of a 6-inch wafer which is not oscillated during polishing process.
[0041] FIG. 5 is a graph showing a contour of the polishing cloth which has been dressed by the dresser 10 of the present invention. A 6-inch semiconductor wafer was polished by pressing the semiconductor wafer against the polishing cloth by the top ring 3 shown in FIG. 1 at a pressure of 400 gf/cm2 for 176 minutes and 30 seconds. After the above polishing process, the polishing cloth was dressed by the dresser 10 of the present invention by pressing the dresser 10 against the polishing cloth 4 at a pressure of 57 gf/cm2 for 43 minutes and 49 seconds. In FIG. 5, the horizontal axis represents a radial position of the polishing cloth, and the vertical axis represents a thickness of the polishing cloth. Further, Ld represents a region over which the dresser contacts the polishing cloth, and Lt represents a region over which the top ring is movable. FIG. 5 shows that the polishing cloth is linearly scraped off in any vertical cross section by the dressing process. The center of the top ring is located at the radial position of 170 mm during polishing process.
[0042] Further in the present invention, the annular dressing area of the dresser is formed in such a manner that the inner diameter of the annular dressing area is larger than the diameter of the workpiece by the following reason.
[0043] In the case where the effective area of the dresser is annular, the scratch length of the polishing cloth by dressing with said dresser changes irregularly at the circular positions where the distance of the area from the center of the polishing cloth is the same as the shortest distance between the inner edge of the annular dressing area of the dresser and the center of the polishing cloth or the same as the longest distance between the inner edge of the annular dressing area of the dresser and the center of the polishing cloth. That is, at said circular positions, the scratch length has improper values.
[0044] These unsmoothness of the scratch length impairs the flatness of the surface of the dressed polishing cloth, and then the flatness of the surface of the polished workpiece.
[0045] In order to deviate these positions of unsmoothness of the scratch length out of the area of the polishing cloth used for polishing, the annular dressing area of the dresser is formed in such a manner that the inner diameter of the annular dressing area of the dresser is larger than the diameter of the workpiece.
[0046] FIGS. 6A through 6C show a surface roughness of the polishing cloth. In FIGS. 6A through 6C, the horizontal axis represents a radial position of the polishing cloth, and the vertical axis represents a surface roughness of the polishing cloth. FIG. 6A shows an unused polishing cloth, FIG. 6B shows the polishing cloth which has been dressed by the dresser of the present invention, and FIG. 6C shows the polishing cloth after polishing semiconductor wafers. As shown in FIGS. 6A through 6C, the surface roughness of the polishing cloth was substantially restored to the unused state by the dressing process of the present invention. In this case, the sizes of the diamond grains in the annular diamond grain layer 13 were in the range of 10 to 25 µm. The observation of the surface roughness of the polishing cloth before and after the dressing process proved that when the surface roughness of the polishing cloth was maintained in the range of 10 to 40 µm, good polishing results were obtained.
[0047] FIG. 7 shows a polishing rate of an oxide layer formed on the semiconductor wafer which have been polished by the polishing cloth. The polishing cloth has been dressed by the dresser of the present invention after each polishing process. In FIG. 7, the horizontal axis represents the number of semiconductor wafers which have been polished, and the vertical axis represents a polishing rate (Å/min.) and a uniformity across the wafer (standard deviation %). As shown in FIG. 7, the polishing rate (Å/min.) is an average of 2250, a maximum of 2290 and a minimum of 2210. The standard deviation (%) is an average of 4.0, a maximum of 4.7 and a minimum of 3.0. As is apparent from the above results, in the case where polishing of the semiconductor wafer is performed by the polishing cloth which has been dressed by the dresser 10 of the present invention, a stable polishing rate is obtained, and an excellent uniformity across the wafer is obtained.
[0048] According to the first embodiment of the present invention, the surface of the polishing cloth is linearly scraped off in any vertical cross section thereof, and the surface roughness of the polishing cloth which suffers the degradation of the polishing performance can be restored to a good polishing condition.
[0049] FIGS. 8A through 8C shows a dresser according to a second embodiment of the present invention. FIG. 8A is a perspective bottom view of the dresser, FIG. 8B is a bottom view of the dresser and FIG. 8C is a cross-sectional view taken along the line A-A of FIG. 8B.
[0050] The dresser 20 comprises a dresser body 21, and an annular SiC (silicon carbide) layer 22 provided on a circumferential portion of the dresser body 21. The SiC layer 22 comprises a plurality of SiC sectors 22a (eight in this embodiment) having a circular arc shape. The SiC layer 22 is fixed to the lower surface of the dresser body 21 by an adhesive 23 made of epoxy resin, as shown in FIG. 9 which is an enlarged view showing the section B of FIG. 8C. The dresser body 21 is made of stainless steel in this embodiment.
[0051] The SiC sector 22a has a plurality of projections 22b arranged in equal intervals and a lattice of grooves 22c on its surface, as shown in FIGS. 10A and 10B. The projection 22b is in the form of a quadrangular pyramid. FIG. 10A is a fragmentary enlarged plan view of the SiC sector 22a, and FIG. 10B is a cross-sectional view taken along the line C-C of FIG. 10A. In one example of the dresser, the dresser body 21 has a diameter of 248 mm, and the SiC layer 22 has a width of 6 mm. The projection 22b has a height h ranging from 60 to 65 µm, the pitch p between the two projections 22b is 300 µm, and the width w of the groove 22c is 100 µm.
[0052] The polishing cloth is dressed by the dresser in a manner as shown in FIG. 3. The polishing cloth made of polyurethane foam to be dressed is attached to the upper surface of the turntable 1 which rotates in a direction indicated by the arrow A. The dresser 20 which rotates in a direction indicated by the arrow B is pressed against the polishing cloth so that the SiC layer 22 is brought into contact with the polishing cloth 4. The turntable 1 and the dresser 20 are rotated relatively to each other for thereby bringing the lower surface of the SiC layer 22 in sliding contact the polishing cloth 4.
[0053] FIG. 11 is a graph showing a scratch length of the dresser 20 of the present invention. In FIG. 11, the horizontal axis represents a radial position on the polishing cloth (mm), and the vertical axis represents a scratch length (mm) of the dresser. The curve A represents the relationship between scratch lengths and radial positions on the polishing cloth when the polishing cloth was dressed by the dresser 20 which has the annular SiC layer 22 on the dresser body 21, and the curve B represents the relationship between scratch lengths and radial positions on the polishing cloth when the polishing cloth was dressed by the dresser which has a circular diamond grain layer which is formed by electrodepositing diamond grains on the entire lower surface of a circular plate. As shown in FIG. 11, the upper surface of the polishing cloth was substantially uniformly contacted by the SiC layer 22, and was linearly scraped off in any vertical cross section. This means that the scratch lengths are substantially uniform at all radial positions of the polishing cloth in a radial direction of the polishing cloth. In FIG. 11, the dressing length L1 represents a polishing range of an 8-inch wafer which is not oscillated during polishing process, and the dressing length L2 represents a polishing range of a 6-inch wafer which is not oscillated during polishing process.
[0054] FIG. 12 is a graph showing a contour of the polishing cloth which has been dressed by the dresser 20 of the present invention. In FIG. 12, the horizontal axis represents a radial position (mm) of the polishing cloth, and the vertical axis represents a thickness (mm) of the polishing cloth. Further, Ld represents a region over which the dresser contacts the polishing cloth. The polishing cloth was dressed by the dresser 20 of the present invention by pressing the dresser 20 against the polishing cloth at a pressure of 450 gf/cm2 for 300 seconds in each dressing process, and the dressing process was repeated 20 times. Thus, the total dressing time was 6000 seconds. As shown in FIG. 12, a maximum thickness of material removed from the polishing cloth was as little as 0.007 mm, and the polishing cloth is radially linearly scraped off by the dressing process.
[0055] It was confirmed that when the height h of the projections 22b of the SiC layer 22 was in the range of 60 to 65 µm, good polishing results were obtained without lowering the polishing rate. Further, the observation of the surface roughness of the polishing cloth before and after the dressing process proved that when the surface roughness was maintained in the range of 10 to 40 µm, good polishing results were obtained.
[0056] FIG. 13 shows a polishing rate of an oxide layer formed on the semiconductor wafer which has been polished by the polishing cloth. The polishing cloth has been dressed by the dresser of the present invention. In FIG. 13, the line A shows a polishing rate of a polishing cloth which has been dressed by the dresser 20 of the second embodiment in FIG. 8, and the line B shows a polishing rate of the polishing cloth which has been dressed by the dresser 10 of the first embodiment in FIG. 2. In FIG. 13, the horizontal axis represents a polishing time performed by the polishing cloth, and the vertical axis represents a thickness (Å) of material removed from the semiconductor wafer. As shown in FIG. 13, the polishing cloth which has been dressed by the dresser 20 of the second embodiment has substantially the same polishing capability as the polishing cloth which has been dressed by the dresser 10 of the first embodiment. In this case, the rotational speeds of the turntable and the dresser were 13 rpm, and the dressing time was 17 seconds.
[0057] According to the second embodiment of the present invention, the surface of the polishing cloth is linearly scraped off in any vertical cross section thereof, and the surface roughness of the polishing cloth which suffers the degradation of the polishing performance can be restored to a good polishing condition.
[0058] Further, according to the second embodiment of the present invention, since the dresser has the SiC layer, a thickness of material removed from the polishing cloth is minimized by the dressing process.
[0059] In case of dressing the polishing cloth by the dresser having diamond grains, the diamond grains fall off from the dresser, and the semiconductor wafer may possibly be scratched or damaged in the polishing process by the diamond grains which have fallen off from the dresser during the dressing process. However, in case of dressing the polishing cloth by the dresser having a SiC layer, there is no fear of scratches or damages on the semiconductor wafer. Further, even if acidic abrasive liquid is used, the SiC layer of the dresser is not eroded by the acidic abrasive liquid.
[0060] In the embodiments, although the annular diamond grain layer and the annular SiC layer have a circular outer shape and a circular inner shape, respectively, they may have an elliptical outer shape and an elliptical inner shape, respectively, or a circular outer shape and a heart-shaped inner shape, or any other shapes.
[0061] Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims. It should be noted that the objects and advantages of the invention may be attained by means of any compatible combination(s) particularly pointed out in the items of the following summary of the invention and the appended claims.
SUMMARY OF THE INVENTION
[0062]
1. A method of dressing a polishing cloth mounted on a turntable, comprising the steps of:
providing a dresser comprising a dresser body and an annular diamond grain layer provided on said dresser body, said annular diamond grain layer being made of diamond grains which are electrodeposited; and
dressing said polishing cloth by pressing said annular diamond grain layer against said polishing cloth while said turntable and said dresser are rotating.
2. A method wherein said polishing cloth comprises polyurethane foam.
3. A method wherein said annular diamond grain layer has a number of diamond grains whose sizes are in the range of 10 to 40 µm.
4. A method wherein said polishing cloth is dressed to a surface roughness ranging from 10 to 40 µm.
5. A method wherein said polishing cloth has a surface which contacts a workpiece during a polishing process and is radially linearly scraped off by said annular diamond grain layer.
6. A method wherein said diamond grain layer has an inner diameter larger than a diameter of a workpiece polished by said polishing cloth.
7. A method of dressing a polishing cloth mounted on a turntable, comprising the steps of:
providing a dresser comprising a dresser body and a SiC layer provided on said dresser body; and
dressing said polishing cloth by pressing said SiC layer against said polishing cloth while said turntable and said dresser are rotating.
8. A method wherein said SiC layer is annular.
9. A method wherein said SiC layer has an inner diameter larger than a diameter of a workpiece polished by said polishing cloth.
10. A method wherein said polishing cloth comprises polyurethane foam.
11. A method wherein said SiC layer has a plurality of projections formed thereon, and said polishing cloth is dressed to a surface roughness ranging from 10 to 40 µm.
12. A method wherein said polishing cloth has a surface which contacts a workpiece during a polishing process and is radially linearly scraped off by said SiC layer.
13. A method wherein said workpiece comprises a semiconductor wafer having a device pattern and is polished by supplying acidic abrasive liquid onto said polishing cloth.
14. An apparatus for dressing a polishing cloth mounted on a turntable, comprising:
a dresser comprising a dresser body and an annular diamond grain layer provided on said dresser body, said annular diamond grain layer being made of diamond grains which are electrodeposited;
a first actuator for rotating said dresser about a central axis of said dresser; and
a second actuator for pressing said annular diamond grain layer of said dresser against said polishing cloth.
15. An apparatus wherein said polishing cloth comprises polyurethane foam.
16. An apparatus wherein said annular diamond grain layer has a number of diamond grains whose sizes are in the range of 10 to 40 µm.
17. An apparatus wherein said polishing cloth is dressed to a surface roughness ranging from 10 to 40 µm.
18. An apparatus wherein said polishing cloth has a surface which contacts a workpiece during a polishing process and is radially linearly scraped off by said annular diamond grain layer.
19. An apparatus wherein said diamond grain layer has an inner diameter larger than a diameter of a workpiece polished by said polishing cloth.
20. An apparatus for dressing a polishing cloth mounted on a turntable, comprising:
a dresser comprising a dresser body and a SiC layer provided on said dresser body;
a first actuator for rotating said dresser about a central axis of said dresser; and
a second actuator for pressing said SiC layer of said dresser against said polishing cloth.
21. An apparatus wherein said SiC layer is annular.
22. An apparatus wherein said SiC layer has an inner diameter larger than a diameter of a workpiece polished by said polishing cloth.
23. An apparatus wherein said polishing cloth comprises polyurethane foam.
24. An apparatus wherein said SiC layer has a plurality of projections formed thereon, and said polishing cloth is dressed to a surface roughness ranging from 10 to 40 µm.
providing a dresser comprising a dresser body and an annular diamond grain layer provided on said dresser body, said annular diamond grain layer being made of diamond grains which are electrodeposited; and
dressing said polishing cloth by pressing said annular diamond grain layer against said polishing cloth while said turntable and said dresser are rotating.
providing a dresser comprising a dresser body and a SiC layer provided on said dresser body; and
dressing said polishing cloth by pressing said SiC layer against said polishing cloth while said turntable and said dresser are rotating.
a dresser comprising a dresser body and an annular diamond grain layer provided on said dresser body, said annular diamond grain layer being made of diamond grains which are electrodeposited;
a first actuator for rotating said dresser about a central axis of said dresser; and
a second actuator for pressing said annular diamond grain layer of said dresser against said polishing cloth.
a dresser comprising a dresser body and a SiC layer provided on said dresser body;
a first actuator for rotating said dresser about a central axis of said dresser; and
a second actuator for pressing said SiC layer of said dresser against said polishing cloth.