US20050022931A1

US20050022931A1 - Chemical mechanical polishing apparatus

Info

Publication number: US20050022931A1
Application number: US10/899,178
Authority: US
Inventors: Chung-Ki Min; Yong-Sun Ko; Kyung-hyun Kim
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2003-07-28
Filing date: 2004-07-27
Publication date: 2005-02-03
Also published as: KR100546355B1; KR20050013436A

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 of FIG. 1;
FIG. 3 is an exploded perspective view of the CMP apparatus of FIG. 1;
FIG. 4 is a plane view of an embodiment of an insert pad for the CMP apparatus of FIG. 1;
FIG. 5 is a cross-sectional view of a wafer and the polishing station of the CMP apparatus of FIG. 4;
FIG. 6A is a top view of another embodiment of an insert pad installed in the CMP apparatus of FIG. 1;
FIG. 6B is a magnified cross-sectional view taken along the line VIb-VIb′ in FIG. 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 of FIG. 7; and
FIG. 9 is a cross-sectional view of a wafer and a polishing station of the CMP apparatus of FIG. 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 a polishing station 10 and a polishing head 50 of a chemical mechanical polishing (CMP) apparatus according to a first embodiment of the present invention.
Referring to FIG. 1, the polishing station 10 comprises a platen 12, which is disk-shaped and can rotate, and a polishing pad assembly 20, which is disposed on an upper surface of the platen 12. Any conventional polishing pad assembly may be used as the polishing pad assembly 20. For example, the polishing pad assembly 20 may be a composite polishing pad which is formed of soft and hard polishing pads.
The platen 12 is connected to a driver 15, such as a motor. The platen 12 receives torque from the driver 15 during a CMP process and rotates about a central axis X in a direction A. The platen 12 may rotate in the direction A or in the opposite direction.
An insert pad 30 is interposed between the platen 12 and the polishing pad assembly 20 in order to form a local step in the polishing pad assembly 20 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, the insert pad 30 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, the insert pad 30 may be formed of ceramic or metal and is adhered to the upper surface of the platen 12 by a bonding means, such as an adhesive.
As illustrated in FIG. 1, the step formed by the insert pad 30 has a convex shape in a portion of the polishing pad assembly 20 that corresponds to a central portion of the wafer W. The structure of the insert pad 30 will be explained in detail later. Together, the insert pad 30 and the polishing pad assembly 20 form a polishing pad structure.
As further shown in FIG. 1, a polishing head 50, which may be formed of one or more components, is mounted above the polishing station 10. The polishing head 50 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 the polishing pad assembly 20.
In order to carry out the CMP process, the polishing head 50 applies pressure to the polishing pad assembly 20 and polishes the polishing target on the wafer W when the wafer W is chucked. At this time, the polishing head 50 and the wafer W rotate in the direction of arrow B with a speed set by a polishing head displacement device 52. However, the polishing head 50 and the wafer W may rotate in the opposite direction to the direction B.
A polishing slurry with a desirable composition is supplied by a slurry supplying system 60 during the CMP process. Because the insert pad 30 forms a step in the polishing pad assembly 20, a relatively large pressure is applied to the central portion, as compared to an outer portion, of the wafer W by the polishing pad assembly 20 during a polishing process.
FIG. 2 is a top view of the platen 12, which is installed in the CMP apparatus according to the first embodiment of the present invention.
Referring to FIG. 2, the platen 12 rotates in the direction A and the wafer W rotates in the same direction as the polishing head 50, that is, in the direction B. An upper surface 12 a of the platen 12 has a polishing area 14, which is the area below the wafer W when the polishing pad assembly 20 rotates during the CMP process. The polishing area 14 has an annular shape with a first width Wp in a radial direction. The polishing area 14 is divided into a central polishing area 14 a, which is located under the polishing pad assembly 20 and faces a central portion of the wafer W, and outer polishing areas 14 b, which are located under the polishing pad assembly 20 and faces an outer portion of the wafer W. The central polishing area 14 a has an annular or donut shape, and the outer polishing areas 14 b extend a radial distance respectively from inner and outer circumferences of the central polishing area 14 a. A width or scope of the central and outer polishing areas 14 a and 14 b may 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 the insert pad 30 of the CMP apparatus.
Referring to FIGS. 3 and 4, the insert pad 30 is interposed between the platen 12 and the polishing pad assembly 20 and covers the central polishing area 14 a of the upper surface 12 a of the platen 12. Therefore, the insert pad 30 has an annular shape almost equal in size with the central polishing area 14 a.
In FIG. 3, the polishing pad assembly 20 is a composite polishing pad formed of a soft polishing pad 22 and a hard polishing pad 24; however, any conventional polishing pads may be used as the polishing pad assembly 20. In one embodiment, a groove (not shown) is formed on an upper surface of the hard polishing pad 24, 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 polishing station 10 in FIG. 3, the insert pad 30 is adhered to the platen 12, and the soft polishing pad 22 and the hard polishing pad 24 are sequentially deposited on the insert pad 30.
FIG. 5 is a cross-sectional view of the wafer W disposed on the polishing station 10 of the CMP apparatus of FIG. 3. As shown, since the insert pad 30 is interposed between the platen 12 and the polishing pad assembly 20 and covers only the upper surface 12 a of the platen 12 in the central polishing area 14 a, a step is formed with a convex shape in the portion of the polishing pad assembly 20 that corresponds to the central portion of the wafer W. As will be appreciated, the insert pad 30 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 the polishing pad assembly 20, 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, the insert pad 30 has a rectangular cross-section and vertical sidewalls at the inner and outer radii of the insert pad 30. As shown, these sidewalls are exposed—not covered by the polishing pad assembly 20. This structure of the insert pad is particularly suitable when the desired step size is small. For example, the insert pad 30 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 an insert pad 40 and FIG. 6B is a magnified cross-sectional view taken along the line VIb-VIb′ of FIG. 6A.
Referring to FIGS. 6A and 6B, the insert pad 40 includes inner and outer circumferential portions which have a slope. This structure of the insert pad is suitable when a relatively large step in the polishing pad assembly 20 is desired. For example, in this embodiment, the insert pad 40 may have a thickness of 2˜300 mm. If the insert pad 30, which has a rectangular shape is too thick, the conformity of the polishing pad assembly 20 to the insert pad 30 may be poor, and thus, an adhesive property between the polishing pad assembly 20 and the insert pad 30 may be degraded. However, if the insert pad 40 has the trapezoid sectional shape as illustrated in FIG. 6, an excellent adhesive property between the insert pad 40 and the polishing pad assembly 20 can be maintained, even if the thickness of the insert pad 40 is increased.
When the CMP apparatus according to the embodiments of the present invention is used, the insert pad 30 covers only the central polishing area 14 a in the polishing area 14 on the platen 12. 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 the insert pad 130 of FIG. 7.
Referring to FIGS. 7 and 8, the insert pad structure 130 is interposed between the platen 12 and the polishing pad assembly 20 and covers the upper surface 12 a of the platen 12 on the outer polishing areas 14 b of the platen 12 (see FIG. 2). For this purpose, the insert pad structure 130 comprises a first insert pad 130 a that covers a central or inner circular portion of the platen 12 and a second insert pad 130 b that covers an outer circumferential portion of the platen 12. The first insert pad 130 a is illustrated with a circular shape in FIGS. 7 and 8. However, the first insert pad 130 a may be formed to have an annular shape that covers only a central portion of the outer polishing area 14 b disposed towards the center of the platen 12. The second insert pad 130 b has an annular shape as illustrated. The first and second insert pads 130 a and 130 b are separated by the width of the central polishing area 14 a. The composition and shape of the first and second insert pads 130 a and 130 b are not restricted to the aforementioned case and they may be formed to have any shape that covers only the outer polishing areas 14 b of the polishing area 14. That is, the first and second insert pads 130 a and 130 b do not cover the central polishing area 14 a.
FIG. 9 is a cross-sectional view of the wafer W disposed on the polishing station 10 of the CMP apparatus of FIG. 7 according to an embodiment of the present invention. More specifically, FIG. 9 is a cross-sectional view taken along the line IX-IX′ of FIG. 8.
Referring to FIG. 9, the insert pads 130 a and 130 b are interposed between the platen 12 and the polishing pad assembly 20 and cover only the outer polishing areas 14 b in the polishing area 14, 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, the insert pads 130 a and 130 b forming 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 the polishing pad assembly 20 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.
In FIG. 9, the insert pads 130 a and 130 b are illustrated with a rectangular sectional shape and vertical sidewalls of the insert pads 130 a and 130 b near the inner and outer radii of the central polishing area 14 a are exposed. This composition is suitable when the insert pads 130 a and 130 b are formed of a relatively thin film. However, the respective outer portions of insert pads 130 a 130 b may be formed to have the cross-sectional shape of FIG. 6 that the sidewalls of the insert pads 130 a and 130 b near the inner and outer radii of the central polishing area 14 a are 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, the insert pad 130 covers only the outer polishing areas 14 b in the polishing area 14 on the platen 12, 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

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 of claim 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 of claim 1, wherein the insert pad structure is 0.5˜300 mm thick.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

21. The apparatus of claim 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 of claim 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 of claim 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 of claim 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 of claim 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 of claim 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 of claim 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.