US20050022931A1 - Chemical mechanical polishing apparatus - Google Patents

Abstract

The chemical mechanical polishing (CMP) apparatus includes an insert pad that forms a local step on an upper surface of a polishing pad assembly. The insert pad is interposed between a rotatable platen and the polishing pad assembly.

Description

BACKGROUND OF THE INVENTION
• This application claims the priority of Korean Patent Application No. 2003-52091, filed on Jul. 28, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
• 1. Field of the Invention
• The present invention relates to a polishing apparatus for polishing a wafer to form a semiconductor device, and more particularly, to a chemical mechanical polishing (CMP) apparatus.
• 2. Description of the Related Art
• In a semiconductor manufacturing process using chemical mechanical polishing (CMP) technology, a wafer is polished by rotating a wafer and rotating a polishing pad against one another while a slurry is supplied. It is very difficult to uniformly polish an area on a wafer and to planarize a die to a desired level in a CMP process. A difference in uniformity occurs because of different polishing rates applied to different portions of the wafer. A polishing rate of the CMP process is a speed at which polishing target material is removed from the wafer. Accordingly, if the distribution of polishing rates is poor (i.e., not uniform), then planarizing of the wafer is poor. As the degree of integration of semiconductor devices increases, less and less deviations in the distribution of polishing rates can be tolerated.
• Therefore, it is required to exactly and flexibly control the polishing rate. The planarity of the wafer is influenced by a structure of a CMP apparatus, the slurry used, and an attritional material, such as, a polishing pad used.
• In particular, a polishing pad, which is generally used in the CMP process, requires a proper balance between strength and flexibility. Strength is necessary for obtaining uniformity in a die, but sufficient flexibility is essential for obtaining uniformity over the entire target on the wafer. Although a soft polishing pad, which is now used commercially, is advantageously elastically transformable and obtains a uniform polishing rate regardless of whether a step exists on a wafer, it is difficult to remove the step. On the other hand, a hard polishing pad can guarantee excellent planarity regardless of steps on the wafer, but it is difficult to remove a polishing target membrane with a uniform polishing rate over the entire surface of the wafer. Therefore, a composite polishing pad, in which soft and hard polishing pads are sequentially deposited on a platen, is widely used in order to obtain polishing characteristics of both the soft and hard polishing pads together.
• However, even if the composite polishing pad including sequentially deposited soft and hard polishing pads is used, it is extremely difficult to exactly and flexibly control the polishing rate since the polishing rate.
• In fact, the distribution of the polishing rate of the CMP process is largely influenced by a structure of a polishing head, chemical characteristics of a slurry, operating conditions of the CMP apparatus, and characteristics of a polishing target membrane. When an oxide layer is polished using a common silica slurry and a CMP apparatus with a fixed retainer ring, that is, when a mechanical element has a large influence on the polishing rate, the polishing rate at an outer portion of the wafer is greater than a central portion of a wafer. Accordingly, a poor distribution of the polishing rate occurs. Yet, if a chemical element has a large influence on the polishing rate, for example, a poly slurry or a ceria slurry with a high selectivity is used, the polishing rate in the central portion of the wafer is greater than the outer portion of the wafer, and thus, a poor distribution of the polishing rate occurs. As a consequence, a poor distribution of the polishing rate on the wafer is very difficult to overcome by only adjusting operating conditions of the CMP apparatus.
SUMMARY OF THE INVENTION
• The present invention provides a chemical mechanical polishing apparatus having a rotatable platen and a polishing pad structure disposed on the rotatable platen. The polishing pad structure has portions with different thickness. As such differing amounts of stress will be applied to a wafer being polished such that a more uniform distribution of polishing rates may be achieved.
• In one exemplary embodiment, the polishing pad structure includes a polishing pad assembly and an insert pad structure disposed between the polishing pad assembly and the platen.
• In one embodiment, the insert pad structure includes an insert pad disposed on an area of the platen corresponding to a central area of the wafer to be polished. Here, the polishing pad structure has a thick portion corresponding to the central area of the wafer to be polished and thin portions corresponding to outer areas of the wafer to be polished.
• In another embodiment, the insert pad structure includes insert pads disposed on areas of the platen corresponding to the outer areas of the wafer to be polished. Here, the polishing pad structure has thick portions corresponding to the outer areas of the wafer to be polished and a thin portion corresponding to a central area of the wafer to be polished.
BRIEF DESCRIPTION OF THE DRAWINGS
• The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
• FIG. 1 is a view of a polishing station and a polishing head of a chemical mechanical polishing (CMP) apparatus according to an embodiment of the present invention;
• FIG. 2 is a top view of a platen included in the CMP apparatus ofFIG. 1;
• FIG. 3 is an exploded perspective view of the CMP apparatus ofFIG. 1;
• FIG. 4 is a plane view of an embodiment of an insert pad for the CMP apparatus ofFIG. 1;
• FIG. 5 is a cross-sectional view of a wafer and the polishing station of the CMP apparatus ofFIG. 4;
• FIG. 6A is a top view of another embodiment of an insert pad installed in the CMP apparatus ofFIG. 1;
• FIG. 6B is a magnified cross-sectional view taken along the line VIb-VIb′ inFIG. 6A;
• FIG. 7 is an exploded perspective view of main elements of a CMP apparatus according to another embodiment of the present invention;
• FIG. 8 is a plane view of an insert pad ofFIG. 7; and
• FIG. 9 is a cross-sectional view of a wafer and a polishing station of the CMP apparatus ofFIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
• The present invention will now be described more fully with reference to the attached drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the forms of elements are exaggerated for clarity. To facilitate understanding, identical reference numerals are used, where possible, to identify identical elements throughout the figures.
• FIG. 1 is a view of apolishing station10 and a polishinghead50 of a chemical mechanical polishing (CMP) apparatus according to a first embodiment of the present invention.
• Referring toFIG. 1, thepolishing station10 comprises aplaten12, which is disk-shaped and can rotate, and apolishing pad assembly20, which is disposed on an upper surface of theplaten12. Any conventional polishing pad assembly may be used as thepolishing pad assembly20. For example, thepolishing pad assembly20 may be a composite polishing pad which is formed of soft and hard polishing pads.
• Theplaten12 is connected to adriver15, such as a motor. Theplaten12 receives torque from thedriver15 during a CMP process and rotates about a central axis X in a direction A. Theplaten12 may rotate in the direction A or in the opposite direction.
• Aninsert pad30 is interposed between theplaten12 and thepolishing pad assembly20 in order to form a local step in thepolishing pad assembly20 to a thickness of 0.5˜300 mm and is formed of a film, which is made of a strong and hard material that has no elasticity and flexibility. For instance, theinsert pad30 may be formed of hard plastic, such as an acryl resin, a polyolefine series resin, a polybutyleneterephthalate (PBT) resin, a polystyrene series resin, or a polycarbonate. Furthermore, theinsert pad30 may be formed of ceramic or metal and is adhered to the upper surface of theplaten12 by a bonding means, such as an adhesive.
• As illustrated inFIG. 1, the step formed by theinsert pad30 has a convex shape in a portion of thepolishing pad assembly20 that corresponds to a central portion of the wafer W. The structure of theinsert pad30 will be explained in detail later. Together, theinsert pad30 and thepolishing pad assembly20 form a polishing pad structure.
• As further shown inFIG. 1, a polishinghead50, which may be formed of one or more components, is mounted above the polishingstation10. The polishinghead50 comprises a vacuum device in order to chuck or hold the wafer W in a stable state when a polishing target on the wafer W faces the upper surface of thepolishing pad assembly20.
• In order to carry out the CMP process, the polishinghead50 applies pressure to thepolishing pad assembly20 and polishes the polishing target on the wafer W when the wafer W is chucked. At this time, the polishinghead50 and the wafer W rotate in the direction of arrow B with a speed set by a polishinghead displacement device52. However, the polishinghead50 and the wafer W may rotate in the opposite direction to the direction B.
• A polishing slurry with a desirable composition is supplied by aslurry supplying system60 during the CMP process. Because theinsert pad30 forms a step in thepolishing pad assembly20, a relatively large pressure is applied to the central portion, as compared to an outer portion, of the wafer W by thepolishing pad assembly20 during a polishing process.
• FIG. 2 is a top view of theplaten12, which is installed in the CMP apparatus according to the first embodiment of the present invention.
• Referring toFIG. 2, theplaten12 rotates in the direction A and the wafer W rotates in the same direction as the polishinghead50, that is, in the direction B. Anupper surface12aof theplaten12 has a polishingarea14, which is the area below the wafer W when thepolishing pad assembly20 rotates during the CMP process. The polishingarea14 has an annular shape with a first width Wp in a radial direction. The polishingarea14 is divided into acentral polishing area14a, which is located under thepolishing pad assembly20 and faces a central portion of the wafer W, andouter polishing areas14b, which are located under thepolishing pad assembly20 and faces an outer portion of the wafer W. Thecentral polishing area14ahas an annular or donut shape, and theouter polishing areas14bextend a radial distance respectively from inner and outer circumferences of thecentral polishing area14a. A width or scope of the central andouter polishing areas14aand14bmay be adjusted according to a diameter of the wafer W used in the CMP process.
• FIG. 3 is an exploded perspective view of the CMP apparatus according to the first embodiment of the present invention.FIG. 4 is a plane view of theinsert pad30 of the CMP apparatus.
• Referring toFIGS. 3 and 4, theinsert pad30 is interposed between theplaten12 and thepolishing pad assembly20 and covers thecentral polishing area14aof theupper surface12aof theplaten12. Therefore, theinsert pad30 has an annular shape almost equal in size with thecentral polishing area14a.
• InFIG. 3, thepolishing pad assembly20 is a composite polishing pad formed of asoft polishing pad22 and ahard polishing pad24; however, any conventional polishing pads may be used as thepolishing pad assembly20. In one embodiment, a groove (not shown) is formed on an upper surface of thehard polishing pad24, that faces the wafer W. With this structure, the slurry flows into the groove in the CMP process, and thus, polishing efficiency is enhanced.
• In order to obtain the structure of the polishingstation10 inFIG. 3, theinsert pad30 is adhered to theplaten12, and thesoft polishing pad22 and thehard polishing pad24 are sequentially deposited on theinsert pad30.
• FIG. 5 is a cross-sectional view of the wafer W disposed on the polishingstation10 of the CMP apparatus ofFIG. 3. As shown, since theinsert pad30 is interposed between theplaten12 and thepolishing pad assembly20 and covers only theupper surface12aof theplaten12 in thecentral polishing area14a, a step is formed with a convex shape in the portion of thepolishing pad assembly20 that corresponds to the central portion of the wafer W. As will be appreciated, theinsert pad30 causes the polishing pad structure to have a thicker portion corresponding to the central portion of the wafer W and thinner portions corresponding to outer portions of wafer W. Stress is concentrated at this protruded portion more than the other portions of thepolishing pad assembly20, and a relatively large pressure is applied to the central portion of the wafer W. Accordingly, the central portion of the wafer W is polished at a higher rate.
• Also, theinsert pad30 has a rectangular cross-section and vertical sidewalls at the inner and outer radii of theinsert pad30. As shown, these sidewalls are exposed—not covered by thepolishing pad assembly20. This structure of the insert pad is particularly suitable when the desired step size is small. For example, theinsert pad30 may have a thickness of less than 2 mm.
• FIGS. 6A and 6B illustrate an example of an insert pad installed in the CMP apparatus according to another embodiment of the present invention. Specifically,FIG. 6A is a plane view of aninsert pad40 andFIG. 6B is a magnified cross-sectional view taken along the line VIb-VIb′ ofFIG. 6A.
• Referring toFIGS. 6A and 6B, theinsert pad40 includes inner and outer circumferential portions which have a slope. This structure of the insert pad is suitable when a relatively large step in thepolishing pad assembly20 is desired. For example, in this embodiment, theinsert pad40 may have a thickness of 2˜300 mm. If theinsert pad30, which has a rectangular shape is too thick, the conformity of thepolishing pad assembly20 to theinsert pad30 may be poor, and thus, an adhesive property between the polishingpad assembly20 and theinsert pad30 may be degraded. However, if theinsert pad40 has the trapezoid sectional shape as illustrated inFIG. 6, an excellent adhesive property between theinsert pad40 and thepolishing pad assembly20 can be maintained, even if the thickness of theinsert pad40 is increased.
• When the CMP apparatus according to the embodiments of the present invention is used, theinsert pad30 covers only thecentral polishing area14ain the polishingarea14 on theplaten12. Pressure, which is applied to the central portion of the wafer W, is increased along with the polishing speed of the central portion of the wafer W. Consequently, the distribution of the polishing rate on the wafer W is improved.
• FIG. 7 is an exploded perspective view of a CMP apparatus according to another embodiment of the present invention.FIG. 8 is a plane view of theinsert pad130 ofFIG. 7.
• Referring toFIGS. 7 and 8, theinsert pad structure130 is interposed between theplaten12 and thepolishing pad assembly20 and covers theupper surface12aof theplaten12 on theouter polishing areas14bof the platen12 (seeFIG. 2). For this purpose, theinsert pad structure130 comprises afirst insert pad130athat covers a central or inner circular portion of theplaten12 and asecond insert pad130bthat covers an outer circumferential portion of theplaten12. Thefirst insert pad130ais illustrated with a circular shape inFIGS. 7 and 8. However, thefirst insert pad130amay be formed to have an annular shape that covers only a central portion of theouter polishing area14bdisposed towards the center of theplaten12. Thesecond insert pad130bhas an annular shape as illustrated. The first andsecond insert pads130aand130bare separated by the width of thecentral polishing area14a. The composition and shape of the first andsecond insert pads130aand130bare not restricted to the aforementioned case and they may be formed to have any shape that covers only theouter polishing areas14bof the polishingarea14. That is, the first andsecond insert pads130aand130bdo not cover thecentral polishing area14a.
• FIG. 9 is a cross-sectional view of the wafer W disposed on the polishingstation10 of the CMP apparatus ofFIG. 7 according to an embodiment of the present invention. More specifically,FIG. 9 is a cross-sectional view taken along the line IX-IX′ ofFIG. 8.
• Referring toFIG. 9, theinsert pads130aand130bare interposed between theplaten12 and thepolishing pad assembly20 and cover only theouter polishing areas14bin the polishingarea14, and thus, a step is formed to have a convex shape in a portion corresponding to the outer portion of the wafer W among a portion of the polishing pad assembly facing the wafer W. As will be appreciated, theinsert pads130aand130bforming the insert pad structure cause the polishing pad structure to have thicker portions corresponding to the outer portions of the wafer W and a thinner portion corresponding to a central portion of the wafer W. As a result, stress is concentrated on a high step area of thepolishing pad assembly20 and relatively large pressure is applied to the outer portion of the wafer W. This causes the polishing speed of the outer portion of the wafer W to increase.
• InFIG. 9, theinsert pads130aand130bare illustrated with a rectangular sectional shape and vertical sidewalls of theinsert pads130aand130bnear the inner and outer radii of thecentral polishing area14aare exposed. This composition is suitable when theinsert pads130aand130bare formed of a relatively thin film. However, the respective outer portions ofinsert pads130a130bmay be formed to have the cross-sectional shape ofFIG. 6 that the sidewalls of theinsert pads130aand130bnear the inner and outer radii of thecentral polishing area14aare sloped.
• Where a chemical element, for example, slurry that provides a high selectivity has a large influence on a polishing rate, a poor distribution of a polishing rate occurs since the polishing rate of the central portion of the wafer W is greater than the polishing rate of the outer portion of the wafer W. However, when the CMP apparatus according to the this embodiment of the present invention is used, theinsert pad130 covers only theouter polishing areas14bin the polishingarea14 on theplaten12, and pressure applied to the outer portion of the wafer W and the polishing speed of the outer portion of the wafer W increase. Consequently, the distribution of the polishing rate of the wafer W is improved.
• As described above, the CMP apparatus according to the example embodiments of the present invention includes an insert pad that is formed of a hard material and is interposed between the platen and the polishing pad assembly. When a poor distribution of the polishing rate would occur due to a higher polishing rate at the outer portion of the wafer than the central portion of the wafer, the inclusion of the insert pad that covers only the central polishing area increases the polishing speed in the central portion of the wafer thereby improving the polishing rate distribution. Furthermore, when a poor distribution of the polishing rate would occur due to a higher polishing rate at the central portion of the wafer than at the outer portion of the wafer, the inclusion of the insert pad that covers only the outer polishing areas increases the polishing speed in the outer portion of the wafer, thereby improving the polishing rate distribution.
• The distribution of the polishing rate is improved due to a step that is formed on the polishing pad assembly. The step created by the insert pad causes an increase in the pressure applied to the wafer by the polishing pad at appropriate locations, thereby compensating for the uneven polishing rate.
• While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. For example, while the polishing pad structure has been shown as formed of the polishing pad assembly and one or more insert pads, an integral structure may be used.

Claims (28)

1. A chemical mechanical polishing (CMP) apparatus comprising:

a rotatable platen;

a polishing pad assembly disposed on the platen; and

an insert pad structure disposed between the platen and the polishing pad assembly.

2. The apparatus ofclaim 1, wherein the polishing pad assembly is a composite polishing pad formed of a soft polishing pad and a hard polishing pad.

3. The apparatus ofclaim 1, wherein the insert pad structure is 0.5˜300 mm thick.

4. The apparatus ofclaim 1, wherein the insert pad structure is formed of plastic, ceramic, or metal.

5. The apparatus ofclaim 1, wherein the insert pad is adhered to an upper surface of the platen by an adhesive.

6. The apparatus ofclaim 1, wherein

the platen includes an upper surface with an annular-shaped polishing area that corresponds to a location where a wafer faces the polishing pad assembly during a CMP process;

the polishing area includes a central polishing area, which is located under the polishing pad assembly and faces a central portion of the wafer, and outer polishing areas, which are located under the polishing pad assembly and face an outer portion of the wafer.

7. The apparatus ofclaim 6, wherein the insert pad structure includes an insert pad covering only the central polishing area.

8. The apparatus ofclaim 7, wherein the insert pad is formed of an annular-shaped film having inner and outer edges.

9. The apparatus ofclaim 8, wherein the insert pad has vertical sidewalls at the inner and outer edges.

10. The apparatus ofclaim 9, wherein the insert pad is 0.5˜2 mm thick.

11. The apparatus ofclaim 8, wherein the insert pad has sloped sidewalls at the inner and outer edges.

12. The apparatus ofclaim 11, wherein the insert pad is 2˜300 mm thick.

13. The apparatus ofclaim 6, wherein the insert pad structure covers only the outer polishing areas.

14. The apparatus ofclaim 13, wherein the insert pad structure comprises:

a first insert pad that covers a central portion of the upper surface of the platen and a second insert pad that covers an outer portion of the upper surface of the platen.

15. The apparatus ofclaim 14, wherein the first insert pad is formed of a circular or annular-shaped film.

16. The apparatus ofclaim 14, wherein the second insert pad is formed of an annular-shaped film.

17. The apparatus ofclaim 14, wherein the first and second insert pads are separated from each other at a distance corresponding to the central polishing area.

18. The apparatus ofclaim 14, wherein the first and second insert pads have a vertical sidewall at each edge thereof.

19. The apparatus ofclaim 18, wherein the insert pad is 0.5˜2 mm thick.

20. The apparatus ofclaim 14, wherein the first and second insert pads insert pads have at least one sloped sidewall at an edge thereof.

21. The apparatus ofclaim 12, wherein the insert pad is 2˜300 mm thick.

22. A chemical mechanical polishing apparatus, comprising:

a rotatable platen; and

a polishing pad structure having a non-planar surface disposed on the platen.

23. The apparatus ofclaim 22, wherein the polishing pad structure has at least one thick portion and at least one thin portion, the thick portion having a greater thickness than the thin portion.

24. The apparatus ofclaim 22, wherein the thick portion is over an area of the platen corresponding to central portion of a wafer to be polished.

25. The apparatus ofclaim 24, wherein the thin portions are over an area of the platen corresponding to outer portions of the wafer to be polished.

26. The apparatus ofclaim 23, wherein the thick portions are over an area of the platen corresponding to output portions of a wafer to be polished.

27. The apparatus ofclaim 26, wherein the thin portion is over an area of the platen corresponding to a central portion of the wafer to be polished.

28. The apparatus ofclaim 22, wherein the polishing pad structure comprises:

a polishing pad assembly; and

an insert pad structure disposed between the polishing pad assembly and the platen.

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