Abstract
A method of conditioning a surface of a polishing pad is used for conditioning a polishing pad on a polishing table for polishing a thin film formed on a surface of a substrate. The conditioning method includes bringing a dresser into contact with the polishing pad, and conditioning the polishing pad by moving the dresser between a central part of the polishing pad and an outer circumferential part of the polishing pad. A moving speed of the dresser at a predetermined area of the polishing pad is higher than a standard moving speed of the dresser at the predetermined area of the polishing pad.
Claims
1. A method of conditioning a polishing pad on a polishing table for polishing a thin film formed on a surface of a substrate, the polishing pad to be brought into contact with the thin film to perform the polishing, said method comprising: bringing a dresser into contact with the polishing pad, the dresser being capable of wearing down an entire surface of the polishing pad uniformly when the dresser is moved at an identified standard moving speed, the standard moving speed being defined as a moving speed of the dresser preset at each of a plurality of areas identified in a radial direction of the polishing pad to obtain the identical wear rate over the entire surface of the polishing pad; and conditioning the polishing pad by moving the dresser between a central part of the polishing pad and an outer circumferential part of the polishing pad; wherein a moving speed of the dresser at a predetermined area of the polishing pad is lower than the standard moving speed of the dresser preset for the predetermined area of the polishing pad; and wherein the predetermined area of the polishing pad is defined as the area of the polishing pad to be brought into contact with a portion of the surface of the substrate whereat a polishing rate will be higher than a polishing rate of any other portion of the surface of the substrate if the predetermined area of the polishing pad was conditioned by moving the dresser at the standard moving speed.
2. The method of conditioning a polishing pad according to claim 1, wherein said moving speed of the dresser is an oscillating speed of the dresser which is oscillated about a swing shaft located outside the polishing table.
3. The method of conditioning a polishing pad according to claim 1, wherein the polishing pad comprises a polishing pad having a plurality of holes in a surface thereof.
4. The method of conditioning a polishing pad according to claim 1, further comprising polishing the thin film on the substrate using a polishing liquid containing ceria particles.
5. The method of conditioning a polishing pad according to claim 1, further comprising polishing the thin film on the substrate and cooling the polishing pad by blowing a cooling gas on the polishing pad when the thin film on the substrate is polished.
6. The method of conditioning a polishing pad according to claim 1, wherein the predetermined area of the polishing pad is an area which is to be brought into contact with a central area of the substrate during polishing of the substrate.
7. An apparatus for conditioning a polishing pad on a polishing table for polishing a thin film formed on a surface of a substrate, the polishing pad to be brought into contact with the thin film to perform the polishing, said apparatus comprising: a dresser configured to be brought into contact with the polishing pad, said dresser to be moved between a central part of the polishing pad and an outer circumferential part of the polishing pad for conditioning the polishing pad, the dresser being configured to wear down an entire surface of the polishing pad uniformly when the dresser is moved at an identified standard moving speed, the standard moving speed being defined as a moving speed of the dresser preset at each of a plurality of areas identified in a radial direction of the polishing pad to obtain the identical wear rate over the entire surface of the polishing pad; and a controller configured to control said dresser such that a moving speed of said dresser at a predetermined area of the polishing pad is lower than the standard moving speed of said dresser preset for the predetermined area of the polishing pad; wherein the predetermined area of the polishing pad is defined as the area of the polishing pad to be brought into contact with a portion of the surface of the substrate whereat a polishing rate will be higher than a polishing rate of any other portion of the surface of the substrate if the predetermined area of the polishing pad was conditioned by moving the dresser at the standard moving speed.
8. The apparatus for conditioning a polishing pad according to claim 7, wherein the moving speed of said dresser is an oscillating speed of said dresser which is oscillated about a swing shaft located outside of said polishing table.
9. The apparatus for conditioning a polishing pad according to claim 7, wherein the polishing pad comprises a polishing pad having a plurality of holes in a surface thereof.
10. The apparatus for conditioning a polishing pad according to claim 7, further comprising a polishing liquid containing ceria particles to be used when the thin film on the substrate is polished.
11. The apparatus for conditioning a polishing pad according to claim 7, further comprising a cooling nozzle for cooling the polishing pad by blowing a cooling gas on the polishing pad when the thin film on the substrate is polished.
12. The apparatus for conditioning a polishing pad according to claim 7, wherein said predetermined area of said polishing pad is an area which is to be brought into contact with a central area of the substrate during polishing of the substrate.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 is a schematic view showing an entire structure of a polishing apparatus having a conditioning apparatus of a polishing pad according to an embodiment of the present invention;
(2) FIG. 2 is a plan view showing a top ring positioned on a polishing table and a moving locus of a dresser when the dresser dresses the surface (polishing surface) of the polishing pad;
(3) FIG. 3 is a plan view showing the relationship between the polishing pad on the polishing table, the top ring holding the substrate, and the dresser and showing areas on the polishing pad; and
(4) FIGS. 4A and 4B are graphs showing experimental results obtained by conditioning the polishing pad in such a manner that the oscillating speed of the dresser is changed in each of the areas and by polishing substrates using the polishing pad which has been conditioned with the changed oscillating speed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(5) A conditioning method and apparatus of a polishing pad according to embodiments of the present invention will be described below with reference to FIGS. 1 through 4. Similar or corresponding parts are denoted by similar or corresponding reference numerals in FIGS. 1 through 4 and will not be described below repetitively.
(6) FIG. 1 is a schematic view showing an entire structure of a polishing apparatus having a conditioning apparatus of a polishing pad according to an embodiment of the present invention. As shown in FIG. 1, the polishing apparatus comprises a polishing table 1, and a top ring 10 for holding a substrate W such as a semiconductor wafer as an object to be polished and pressing the substrate against a polishing pad 2 on the polishing table 1. The polishing table 1 is coupled via a table shaft 1a to a polishing table rotating motor (not shown) disposed below the polishing table 1. Thus, the polishing table 1 is rotatable about the table shaft 1a. A polishing pad 2 is attached to an upper surface of the polishing table 1. An upper surface of the polishing pad 2 constitutes a polishing surface 2a for polishing the substrate W. The polishing pad 2 comprising IC-1000/SUBA400 (two-layer cloth) manufactured by the Dow Chemical Company is used. The IC-1000 comprises a pad having a large number of fine holes formed in its surface and is also called a perforated pad. A polishing liquid supply nozzle 3 is provided above the polishing table 1 to supply a polishing liquid (slurry) onto the polishing pad 2 on the polishing table 1.
(7) The top ring 10 is connected to a top ring shaft 11, and the top ring shaft 11 is vertically movable with respect to a top ring head 12. When the top ring shaft 11 moves vertically, the top ring 10 is lifted and lowered as a whole for positioning with respect to the top ring head 12. The top ring shaft 11 is configured to be rotated by operating a top ring rotating motor (not shown). The top ring 10 is rotated about the top ring shaft 11 by rotation of the top ring shaft 11.
(8) The top ring 10 is configured to hold the substrate W such as a semiconductor wafer on its lower surface. The top ring head 12 is configured to be pivotable about a top ring head shaft 13. Thus, the top ring 10, which holds the substrate W on its lower surface, is movable from a position at which the top ring 10 receives the substrate to a position above the polishing table 1 by pivotable movement of the top ring head 12. Then, the top ring 10 is lowered to press the substrate W against the surface (polishing surface) of the polishing pad 2. At this time, while the polishing table 1 and the top ring 10 are respectively rotated, a polishing liquid is supplied onto the polishing pad 2 from the polishing liquid supply nozzle 3 provided above the polishing table 1. The polishing liquid containing ceria (CeO.sub.2) as abrasive particles is used. In this manner, while the polishing liquid is supplied onto the polishing pad 2, the substrate W is pressed against the polishing pad 2 and is moved relative to the polishing pad 2 to polish an insulating film, a metal film or the like on the substrate. Examples of the insulating film include SiO.sub.2, and examples of the metal film include a Cu film, a W film, a Ta film and a Ti film.
(9) As shown in FIG. 1, the polishing apparatus has a conditioning apparatus 20 for conditioning (dressing) the polishing pad 2. The conditioning apparatus 20 comprises a dressing arm 21, a dresser 22 which is rotatably attached to a forward end of the dresser arm 21, a swing shaft 23 coupled to the other end of the dresser arm 21, and a motor 24 serving as a driving mechanism for oscillating (swinging) the dresser arm 21 about the swing shaft 23. The lower part of the dresser 22 comprises a dressing member 22a, and the dressing member 22a has a circular dressing surface. Hard particles are fixed to the dressing surface by electrodeposition or the like. Examples of the hard particles include diamond particles, ceramic particles and the like. A motor (not shown) is provided in the dresser arm 21, and the dresser 22 is rotated by the motor. The swing shaft 23 is coupled to a lifting and lowering mechanism (not shown), and the dresser arm 21 is lowered by the lifting and lowering mechanism to allow the dressing member 22a to be pressed against the polishing surface 2a of the polishing pad 2. Equipment including the polishing table 1, the top ring 10, the conditioning apparatus 20 and the like are connected to a controller 40, and the rotational speed of the polishing table 1, the rotational speed and the polishing pressure of the top ring 10, the oscillating speed of the dresser 22 in the conditioning apparatus 20, and the like are controlled by the controller 40.
(10) FIG. 2 is a plan view showing the top ring 10 positioned on the polishing table 1 and a moving locus of the dresser 22 when the dresser 22 dresses the surface (polishing surface) of the polishing pad 2. As shown in FIG. 2, the dresser arm 21 is longer than a radius of the polishing pad 2, and the swing shaft 23 is positioned radially outwardly of the polishing pad 2. When the polishing surface of the polishing pad 2 is dressed, the polishing pad 2 is rotated and the dresser 22 is rotated by the motor, and then the dresser arm 21 is lowered by the lifting and lowering mechanism to bring the dressing member 22a provided at the lower surface of the dresser 22 into sliding contact with the polishing surface of the rotating polishing pad 2. In this state, the dresser arm 21 is oscillated (swung) about the swing shaft 23 by the motor 24. During dressing of the polishing pad 2, pure water (deionized water) as a dressing liquid is supplied onto the polishing surface of the polishing pad 2 from the polishing liquid supply nozzle 3 (see FIG. 1). By swing motion of the dresser arm 21, the dresser 22 located at the forward end of the dresser arm 21 can move transversely from the outer circumferential end to the central part of the polishing surface of the polishing pad 2. By this swing motion, the dressing member 22a can dress the polishing surface of the polishing pad 2 over the entire surface including the central part.
(11) Further, as shown in FIG. 2, the polishing apparatus has a cooling nozzle 30 serving as a gas ejection unit which is installed parallel to the polishing surface of the polishing pad 2 and extends along the substantially radial direction of the polishing pad 2. Gas ejection ports 30a communicating with the interior of the cooling nozzle 30 are provided at the lower part of the cooling nozzle 30 to eject a cooling gas such as compressed air toward the polishing pad 2. The location of the cooling nozzle 30 and the number of gas ejection ports 30a provided in the cooling nozzle 30 are set arbitrarily in accordance with the process condition or the like.
(12) FIG. 3 is a plan view showing the relationship between the polishing pad 2 on the polishing table 1, the top ring 10 holding the substrate W, and the dresser 22. In FIG. 3, the symbol C.sub.T represents a rotation center of the polishing table 1, and the symbol C.sub.W represents a center of the substrate W held on the lower surface of the top ring 10. Further, the symbol C.sub.D represents a center of the dresser 22. During polishing, the polishing table 1 rotates in a clockwise direction about the rotation center C.sub.T, and the top ring 10 rotates in a clockwise direction about the center C.sub.W. During polishing, the top ring 10 is not moved in the horizontal direction, and thus the substrate W held by the top ring 10 remains at the position shown in FIG. 3. Concentric circles C1, C2, C3, C4 and C5 described about the center C.sub.T on the polishing pad 2 represent loci in the case where the polishing pad 2 passes through predetermined positions on the surface, being polished, of the substrate W by the rotation of the polishing table 1. Specifically, the concentric circle C3 on the polishing pad 2 passes through the center C.sub.W of the substrate W, and the concentric circle C2 on the polishing pad 2 passes through a central area of the substrate W spaced by a distance L from the center C.sub.W of the substrate W to a radially inner side of the polishing table, and the concentric circle C4 on the polishing pad 2 passes through a central area of the substrate W spaced by a distance L from the center C.sub.W of the substrate W to a radially outer side of the polishing table. Further, the concentric circle C1 on the polishing pad 2 passes through the neighborhood of the outer circumferential edge of the substrate W in the vicinity of the rotation center C.sub.T of the polishing table 1, and the concentric circle C5 on the polishing pad 2 passes through the neighborhood of the outer circumferential edge of the substrate W in the vicinity of the outer circumferential edge of the polishing table 1. If the diameter of the substrate W is 300 mm, the distance L is about 20 to 140 mm.
(13) On the other hand, the dresser 22 is swung about the swing shaft 23 on the polishing pad 2, and thus the dresser 22 is radially reciprocated between the central part of the polishing pad 2 and the outer circumferential edge of the polishing pad 2. The outer diameter of the dresser 22 is set to be smaller than the diameter of the substrate W to be polished. Specifically, in the case where the diameter of the dresser 22 is d and the diameter of the substrate W to be polished is D, d is set in the range of ( 1/15) D to 1D, i.e., d=( 1/15) D to 1D. Then, the oscillating speed (swing speed) of the dresser 22 can be adjusted in each of the areas on the polishing pad 2 when the dresser 22 is oscillated between the outer circumferential edge of the polishing pad 2 and the central part of the polishing pad 2. Specifically, when the dresser 22 is swung from the center of the polishing pad 2 toward the outer circumferential edge of the polishing pad 2, the oscillating speed of the dresser 22 is set such that the oscillating speed is low at the area A1 from the concentric circle C1 to the concentric circle C2, high at the area A2 from the concentric circle C2 to the concentric circle C4, and low at the area A3 from the concentric circle C4 to the concentric circle C5. Conversely, when the dresser 22 is swung from the outer circumferential edge of the polishing pad 2 toward the center of the polishing pad 2, the oscillating speed of the dresser 22 is set such that the oscillating speed is low at the area A3 from the concentric circle C5 to the concentric circle C4, high at the area A2 from the concentric circle C4 to the concentric circle C2, and low at the area A1 from the concentric circle C2 to the concentric circle C1. In this manner, the oscillating speed of the dresser 22 is changed in each of the areas, and this change of the oscillating speed is performed by setting an oscillating recipe in the controller 40, and the conditioning apparatus 20 is controlled on the basis of the oscillating recipe by the controller 40. The controller 40 may be installed in the conditioning apparatus 20. In each of the cases where the dresser 22 is moved from the center of the polishing pad 2 toward the outer circumferential edge of the polishing pad 2 one time, the dresser 22 is moved from the outer circumferential edge of the polishing pad 2 toward the center of the polishing pad 2 one time, the dresser 22 is oscillated between the center of the polishing pad 2 and the circumferential edge of the polishing pad 2 one time, and the dresser 22 is oscillated between the center of the polishing pad 2 and the outer circumferential edge of the polishing pad 2 several times, the moving speed or the oscillating speed of the dresser 22 is controlled in each of the areas in the same manner as the above.
(14) As shown in FIG. 3, the area A1 from the concentric circle C1 to the concentric circle C2 in the polishing pad 2 is brought into contact with the outer circumferential area (edge area) of the substrate W, the area A2 from the concentric circle C2 to the concentric circle C4 in the polishing pad 2 is brought into contact with the central area (center area) of the substrate W, and the area A3 from the concentric circle C4 to the concentric circle C5 in the polishing pad 2 is brought into contact with the outer circumferential area (edge area) of the substrate W. The pad scratching distance by the dresser is small in the area A2 where the oscillating speed of the dresser is high, and the pad scratching distance by the dresser is large in the areas A1 and A3 where the oscillating speed of the dresser is low. Thus, the amount of slurry remaining in the area A2 on the polishing pad 2 becomes large, and the amount of slurry remaining in the areas A1 and A3 becomes small. Therefore, during polishing, the central area of the substrate W is brought into sliding contact with the area A2 where the amount of residual slurry is large on the polishing pad 2, and the outer circumferential area of the substrate W is brought into sliding contact with the areas A1 and A3 where the amount of residual slurry is small on the polishing pad 2. In this manner, in the case where the substrate W is polished by the polishing pad 2 where there is a difference in the amount of slurry remaining in each of the areas, the polishing rate is prevented from lowering in the center area where the amount of residual slurry is large, thus improving in-plane uniformity of the polishing rate. In this case, making the oscillating speed of the dresser 22 high or making the oscillating speed of the dresser 22 low means that while the oscillating speed of the conventional dresser in each of the areas is set to a standard oscillating recipe in which the entire surface of the polishing pad is uniformly worn down, the oscillating speed of the dresser 22 is made higher or lower than the conventional oscillating speed in the same area (same section).
(15) Although the case where the polishing pad 2 is divided into three dressing areas and the oscillating speed of the dresser 22 is changed in each of the areas has been described, the polishing pad 2 may be divided further into six dressing areas, twelve dressing areas or the like, and the oscillating speed of the dresser 22 may be changed in each of the areas.
(16) Next, experimental results obtained by conditioning the polishing pad in such a manner that the oscillating speed of the dresser 22 is changed in each of the areas and by polishing substrates using the polishing pad which has been conditioned with the changed oscillating speed will be described with reference to FIGS. 4A and 4B. FIG. 4A is a graph showing the relationship between the radial position on the polishing pad and the oscillating speed ratio of the dresser. FIG. 4B is a graph showing the relationship between the radial position on the substrate and the polishing rate when the substrates are polished by the polishing pad which has been conditioned using the oscillating speed of the dresser shown in FIG. 4A. The substrates having a diameter of 300 mm were used. Further, during polishing of the substrates using the polishing pad which has been conditioned, a cooling gas is blown from the cooling nozzle 30 to the polishing pad to cool the polishing surface of the polishing pad 2.
(17) In FIG. 4A, the straight line (std) represented by black rhombuses represents the recipe (standard moving recipe) in which the oscillating speed of the dresser in each of the areas is adjusted to obtain the identical cutting rate (wear rate) over the entire surface of the polishing pad, and this case is referred to as standard oscillation. In FIG. 4A, the horizontal axis represents radial position on the polishing pad, and the vertical axis represents the speed ratio to the standard oscillating speed in each of the areas in this recipe. Therefore, the speed ratio of the standard oscillation becomes 1 over the entire area of the polishing pad. The curve (tune 24) represented by X marks represents the case where the speed ratio is increased from the position of about 80 mm to the position of about 180 mm from the center of the polishing pad in a radial direction of the polishing pad, and is decreased from the position of about 220 mm to the position of about 350 mm from the center of the polishing pad in the radial direction of the polishing pad. The speed ratio to the standard oscillation increases gradually from 0.6 (position of about 80 mm) to 3.1 (position of about 180 mm) and decreases gradually from 3.1 (the position of about 220 mm) to 0.4 (position of about 350 mm).
(18) Here, the standard oscillating speed in the radial position of about 80 mm is 11 mm/sec, the standard oscillating speed in the radial position of about 180 mm is 21 mm/sec, the standard oscillating speed in the radial position of about 220 mm is 21 mm/sec, and the standard oscillating speed in the radial position of about 350 mm is 13 mm/sec.
(19) In FIG. 4A, the oscillating speed pattern shown by std represents the standard oscillation in which the oscillating speed of the dresser in each of the areas is adjusted to obtain the identical cutting rate (wear rate) over the entire surface of the polishing pad. This conditioning method is the same as the conventional conditioning method. In the oscillating speed pattern shown by tune 24, the oscillating speed of the dresser is low in the central part (area A1 of FIG. 3) and the outer circumferential part (area A3 of FIG. 3), and the oscillating speed of the dresser is high in the intermediate part (area A2 of FIG. 3) between the central part of the polishing pad and the outer circumferential part of the polishing pad. This conditioning method is the same as the conditioning method shown in FIG. 3. Other dressing conditions such as the rotational speed of the dresser are the same in both of std and tune 24.
(20) In FIG. 4B, the polishing rate (std) represented by black rhombuses is low at the central area of the substrate and is high at the outer circumferential area of the substrate. Therefore, it is understood that in the case where the polishing pad conditioned by the standard oscillating recipe was used, the central area of the substrate was polished insufficiently. The polishing rate (tune 24) represented by the X marks is substantially uniform over the entire surface of the substrate with no difference in the central area and the outer circumferential area of the substrate. Thus, it is understood that in the case where the polishing pad conditioned by the recipe in which the oscillating speed of the dresser in the area A2 of the polishing pad is higher than that in the standard oscillating recipe was used, the substrate was uniformly polished over the entire surface of the substrate. Other polishing conditions such as the rotational speed of the polishing table, the rotational speed of the top ring, the polishing pressure and the like are the same in both of std and tune 24.
(21) From the above experimental results, the following has been confirmed: In the case where the polishing pad conditioned by the recipe in which the oscillating speed of the dresser in the area A2 of the polishing pad is higher than that in the standard oscillating recipe is used, the amount of slurry remaining on the polishing pad 2 is large at the central area of the substrate and is small at the outer circumferential area of the substrate. Thus, when the substrate is polished by the polishing pad having different amounts of residual slurry in each of the areas, the polishing rate is prevented from lowering in the central area where the amount of residual slurry is large, thus improving in-plane uniformity of the polishing rate.
(22) Although the case where the dresser 22 is swung has been described in the embodiments shown in FIGS. 1 through 4, the dresser 22 may be moved linearly in the radial direction of the polishing pad 2. Further, the case where the oscillating speed of the dresser 22 is changed in each of the areas of the polishing pad 2 has been described. However, the amount of residual slurry may differ in each of the areas of the polishing pad 2 by changing the dressing load, the rotational speed of the dresser, the dressing time, the rotational speed of the polishing table, and the like. Further, although the case where the perforated pad is used as a polishing pad has been described, a grooved pad having grooves formed in a surface of the pad may be used.
(23) By using the above-described conditioning method and apparatus of the polishing pad, the polishing apparatus can planarize a surface, being polished, of a substrate such as a semiconductor wafer over the entire surface of the substrate.
(24) Although the embodiments of the present invention have been described herein, the present invention is not intended to be limited to these embodiments. Therefore, it should be noted that the present invention may be applied to other various embodiments within a scope of the technical concept of the present invention.
