US20090088050A1

US20090088050A1 - Conductive polishing article for electrochemical mechanical polishing

Info

Publication number: US20090088050A1
Application number: US11/863,878
Authority: US
Inventors: Wei-Yung Hsu; Alain Duboust; Liang-Yuh Chen; Feng Q. Liu
Original assignee: Individual
Current assignee: Applied Materials Inc
Priority date: 2007-09-28
Filing date: 2007-09-28
Publication date: 2009-04-02

Abstract

A conductive polishing article is provided. The conductive polishing article at least has a polishing pad, cathodes and anodes. Cathodes and anodes are disposed below the polishing surface of the polishing pad, and an ion exchange membrane at least partially covers the anodes.

Description

BACKGROUND OF THE INVENTION

DESCRIPTION OF THE RELATED ART

Sub-quarter micron multi-level metallization is one of the key technologies for the next generation of ultra large-scale integration (ULSI). The multilevel interconnects that lie at the heart of this technology require planarization of interconnect features formed in high aspect ratio apertures, including contacts, vias, lines and other features. Reliable formation of these interconnect features is very important to the success of ULSI and to the continued effort to increase circuit density and quality on individual substrates and die.
As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization. Planarizing a surface, or “polishing” a surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization is also useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even surface for subsequent levels of metallization and processing.
One material increasingly utilized in integrated circuit fabrication is copper due to its desirable electrical properties. However, for planarizing copper, conventional chemical mechanical polishing (CMP) encountered some problems such as that the interface between the conductive material and the barrier layer is generally non-planar and residual copper material is retained in irregularities formed by the non-planar interface. Further, the conductive material and the barrier materials are often removed from the substrate surface at different rates, both of which can result in excess conductive material being retained as residues on the substrate surface. Additionally, the substrate surface may have different surface topography, depending on the density or size of features formed therein. Copper material is removed at different removal rates along the different surface topography of the substrate surface, which makes effective removal of copper material from the substrate surface and final planarity of the substrate surface difficult to achieve.
One solution for polishing copper in low dielectric materials with reduced or minimal defects formed thereon is polishing copper by electrochemical mechanical polishing (ECMP) techniques. ECMP techniques remove the conductive material from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion compared to conventional CMP processes. The electrochemical dissolution is performed by applying a bias between a cathode and substrate surface to remove conductive materials from a substrate surface into a surrounding electrolyte. In one embodiment of an ECMP system, the bias is applied by a ring of conductive contacts in electrical communication with the substrate surface. However, the contact ring has been observed to exhibit non-uniform distribution of current over the substrate surface, which results in non-uniform dissolution. Mechanical abrasion is performed by positioning the substrate in contact with conventional polishing pads and providing relative motion therebetween. However, conventional polishing pads often limit electrolyte flow to the surface of the substrate. Additionally, the polishing pad may be composed of insulative materials that may interfere with the application of bias to the substrate surface and result in non-uniform or variable dissolution of material from the substrate surface.
Therefore, there is a need for an improved polishing article for the removal of conductive material on a substrate surface.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a polishing article is provided. The polishing article comprises a polishing pad, a first electrode, a second electrode, and a membrane. The polishing pad has a polishing surface adapted to contact a substrate surface. The first electrode disposes below the polishing surface at a first distance, and the second electrode disposes below the polishing surface at a second distance. The second distance is substantially shorter than the first distance. The membrane disposes at least partially covering the second electrode. The membrane is permeable to ions to allow ionic communication between the second electrode and the substrate.
According to another embodiment of this invention, a conductive polishing article is provided. The conductive polishing article comprises a polishing pad, plural cathodes, plural anodes, plural ion exchange membranes, and a sub pad. The polishing pad has a polishing surface for polishing a substrate and a mounting surface located oppositely, wherein the polishing pad has a plurality of first perforations and second perforations distributed evenly. The cathodes are located in the first perforations, and the anodes are located in the second perforations. A first distance between a top surface of the cathodes and the polishing surface is greater than a second distance between the top surface of the anodes and the polishing surface. The ion exchange membranes, which are comprised of an ion exchange material, respectively encapsulate the anodes to prevent oxygen gas contacting the substrate. The sub pad is located adjacent to the mounting surface of the polishing pad.
According to another embodiment of this invention, a conductive polishing article for electrochemical mechanical polishing is provided. The conductive polishing article comprises a polishing pad, at least one cathode, plural anodes, plural ion exchange membranes, and a sub pad. The polishing pad has a polishing surface adapted to polish a substrate, wherein the polishing pad has plural perforations and plural grooves cut into the polishing pad from the polishing surface. The at least one cathode is located in or behind the polishing pad, wherein at least a part of the cathode is exposed to the substrate by the perforations. The anodes are located in the grooves. A first distance between the exposed surface of the cathodes and the polishing surface is greater than a second distance between the top surface of the anodes and the polishing surface. The ion exchange membranes respectively encapsulate the anodes to prevent oxygen gas contacting the substrate, the ion exchange membranes being comprised of an ion exchange material. The sub pad is located behind the polishing pad to support the polishing pad.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

FIG. 1A is an isometric view of a conductive polishing article according to an embodiment of the invention;

FIG. 1B is a sectional view along the line I-I′ in FIG. 1A;

FIG. 1C is a sectional view showing another arrangement of the anode electrode encapsulated in an ion exchange membrane;

FIG. 1D is a sectional view showing the conductive polishing article in FIGS. 1A and 1B polishing a substrate.

FIG. 2A is an isometric view of a conductive polishing article according to another embodiment of the invention;

FIG. 2B is a partial enlarged plan view of the conductive polishing article in FIG. 2A;

FIG. 2C is a sectional view along the line II-II′ in FIG. 2B;

FIG. 3A is an isometric view of a conductive polishing article according to another embodiment of the invention;

FIG. 3B is a sectional view along the line III-III′ in FIG. 3A; and

FIG. 3C is a sectional view along the line III-III′ in FIG. 3A showing another cathode arrangement.

DETAILED DESCRIPTION

Embodiments of the present invention are generally directed to a conductive polishing article, which can be used in electrochemical mechanical polishing (ECMP). The introduction and details of an ECMP system are disclosed in U.S. Pat. No. 7,066,800, which is incorporated here entirely by reference. In embodiments of this invention, no conductive element such as an electrode is needed to contact with a wafer during ECMP process. The wafer electrically contacts with the conductive polishing article through an electrolyte solution. Further, an ion exchange membrane at least partially covering the anodes is used to prevent undesired species, such as oxygen gas generated near the anodes, from contacting a surface of the wafer.

Embodiment 1

FIG. 1A is an isometric view of a conductive polishing article according to an embodiment of the invention. In FIG. 1A, a conductive polishing article 100, from bottom to top, generally comprises a rigid support 105, a sub pad 110, and a polishing pad 115. The polishing pad 115 has a polishing surface 116 thereon and a mounting surface 117 thereunder (please refer to FIG. 1B). A plurality of concentric circular perforations 120 a and 120 b may be formed in the polishing paid 115. The width of the perforations 120 a is about 1-10 mm, and the width of the perforations 120 b is about 3-10 mm. The sub pad 110 located on the rigid support 105 is used to support the polishing pad 115 and may have a printed circuit adjacent to the mounting surface 117 of the polishing pad 115 to bias electrodes in the polishing pad 115. The rigid support 105 may couple with an ECMP system. An electrolyte supplier 125 is disposed over the conductive polishing article 100 for supplying an electrolyte solution during the ECMP process.
A sectional view along line I-I′ in FIG. 1A is shown in FIG. 1B. In FIG. 1B, cathodes 130 and anodes 135 are respectively located on the bottoms of the perforations 120 a and 120 b. The top surfaces of the cathodes 130 and the anodes 135 are all below the polishing surface 116 of the polishing pad 115, and the top surfaces of the cathodes 130 are lower than the top surfaces of the anodes 135. The distance between the top surfaces of the cathodes 130 and the polishing surface 116 is about 1 mm to about 5 mm. The distance between the top surfaces of the anodes 135 and the polishing surface 116 is about 0.1 mm to about 1 mm. Since the top surface of the anodes 135 is very close to the polishing surface 116 of the polishing pad 115, the electrical potential of the wafer on the polishing surface 116 is almost the same as the anodes 135.
A ratio of the total top surfaces of the cathodes 130 over the total top surfaces of the anodes 135 is about 0.01 to about 100. For example, the ratio is about 3 in one embodiment of this invention.
In FIG. 1B, each anode 135 has an ion exchange membranes 140 a covering thereon. The ion exchange membranes 140 a are permeable to ions to allow electrical communication between the anodes 135 and the conductive layer of the wafer through ions in the electrolyte solution disposed on the polishing pad 115. The ion exchange membrane 140 a can further confine the oxygen gas, which is generated on surfaces of the anodes 135 due to higher voltage applied, under the ion exchange membrane 140 a. Therefore, the oxygen gas cannot contact the conductive layer on the wafer to reduce defect formation and stabilize current density between the anodes 135 and the conductive layer on the wafer. Another embodiment of the anodes 135 and the ion exchange membrane 140 b is shown in FIG. 1C. In FIG. 1C, the anodes 135 can be encapsulated in the ion exchange membrane 140 b, and the oxygen gas is hence confined in the ion exchange membrane 140 b.
For some other purposes, such as anode activation, catalyst isolation, and particle reduction, the ion exchange membrane 140 a and 140 b can be used to retain an anolyte solution 145 having a composition different from the electrolyte solution supplied by the electrolyte supplier 125. In one embodiment, an anolyte source 147 (FIG. 1B) may be connected to the conductive polishing article 100 to circulate the anolyte solution 145 around the anodes 135. In one embodiment, the anolyte solution 145 may be recycled during processing. The anolyte source 147 may comprise a regenerator (not shown) that removes bubbles generated around the anodes 135 and reimburse consumed species in the anolyte solution 145. The anolyte source 147 may connect to the anodes 135 through inlets 147 a and outlets 147 b located in a space between the ion exchange membrane 140 a, 140 b and the anode 135, i.e. the space occupied by the anolyte solution 145.
The material of the ion exchange membrane 140 a and 140 b comprises an ion exchange material for transporting cations in electrolyte solution through the ion exchange membrane 140 a or 140 b. In one embodiment, the ion exchange membrane 140 a and 140 b may comprise cation exchange material. Thus, a certain current density between the anodes 135 and the wafer can be maintained. The ion exchange material can be, for example, a fluorinated polymer matrix having at least an anionic functional group, such as NAFION® membrane manufactured by Dupont Corporation. The anionic functional group described above can be, for example, sulfonate, carboxylate, phosphate or a combination thereof.
FIG. 1D is a sectional view showing the conductive polishing article in FIGS. 1A and 1B polishing a substrate. In FIG. 1D, during an ECMP process, a wafer 150 having a conductive layer 155 thereon is placed on the polishing pad 115, and the conductive layer 155 faces the polishing surface 116 of the polishing pad 115. The anolyte solution 145 is retained in the ion exchange membrane 140 a. A polishing solution 160, which has different electrolyte composition from that of the anolyte solution 145, is above the cathodes 130 and the ion exchange membranes 140 a. In one embodiment, the conductive layer 155 may be in contact with the polishing surface 116 during polishing.

Embodiment 2

FIG. 2A is an isometric view of a conductive polishing article according to another embodiment of the invention. In FIG. 2A, a conductive polishing article 200, from bottom to top, generally comprises a rigid support 205, a sub pad 210, and a polishing pad 215. The polishing pad 215 has a polishing surface 216 thereon and a mounting surface 217 thereunder (please refer to FIG. 2C). The sub pad 210 located on the rigid support 205 is used to support the polishing pad 215 and may have a printed circuit adjacent to the mounting surface 217 of the polishing pad 215 to bias electrodes in the polishing pad 215. The rigid support 205 may couple with an ECMP system.
Some linear perforations 220 and some circle perforations 225 are distributed in the polishing pad 215. The linear perforations 220 constitute a grid pattern, and the circle perforations 225 located on intersects of the linear perforations 220. The width of the linear perforations 220 is about 1-6 mm. The diameter of the circle perforations 225 is about 5-15 mm.
FIG. 2B is a partial enlarged plan view of the conductive polishing article in FIG. 2A. In FIG. 2B, cathodes 230 and the anodes 235 are alternatively located in the perforations 225. Electrolyte solutions can flow between the perforations 225 through the linear perforations 220. The shape of the perforations 225 is not limited to circle, the shape of the perforations 225 can be, for example, square or polygon.
The sectional view along line II-II′ is shown in FIG. 2C. In FIG. 2C, similar to Embodiment 1, cathodes 230 and anodes 235 are respectively located on the bottoms of the perforations 225. The top surfaces of the cathodes 230 and the anodes 235 are also all below the polishing surface 216 of the polishing pad 215, and the top surfaces of the cathodes 230 are lower than the top surfaces of the anodes 235. The distance between the top surfaces of the cathodes 230 and the polishing surface 216 is about 1 mm to about 5 mm. The distance between the top surfaces of the anodes 235 and the polishing surface 216 is about 0.1 mm to about 1 mm, and the voltage of the wafer on the polishing surface 116 is hence almost the same as the anodes 135. In one embodiment, the distance between the top surfaces of the anodes 235 and the polishing surface 216 approximate the thickness of the ion exchange membrane 240 a. Similarly, a ratio of the total top surfaces of the cathodes 230 over the total top surfaces of the anodes 235 is also about 0.01 to about 100.
There is an ion exchange membrane 240 a located above each of the anode 235 and below the polishing surface 216. The anodes 235 can also be encapsulated in the ion exchange membrane, as depicted in FIG. 1C. The material and the function of the ion exchange membrane 240 a has been discussed in Embodiment 1 and hence omitted here.
In one embodiment, an anolyte source 247 (FIG. 1C) may be connected to the conductive polishing article 200 and circulate an anolyte solution 245 around the anodes 235. The anolyte source 247 may comprise a regenerator (not shown) that removes bubbles generated around the anodes 235 and reimburse consumed species in the anolyte solution 245. The anolyte source 247 may circylate the anolyte solution 245 through inlets 247 a and outlets 247 b located in a space between the ion exchange membrane 240 a and the anode 235, i.e. the space occupied by the anolyte solution 245.

Embodiment 3

FIG. 3A is an isometric view of a conductive polishing article according to another embodiment of the invention. In FIG. 3A, a conductive polishing article 300, from bottom to top, generally comprises a rigid support 305, a sub pad 310, and a polishing pad 315. The polishing pad 315 has a polishing surface 316 thereon and a mounting surface 317 thereunder (please refer to FIG. 3B). Some linear grooves 320 and perforations 325 are distributed in the polishing pad 315. The linear grooves 320 are distributed radially, and the perforations 325 are distributed evenly between the linear grooves 320. The width of the linear grooves 320 is about 2 mm to about 8 mm. The diameter of the perforations 325 is about 4 mm to about 14 mm.
The sub pad 310 located on the rigid support 305 is used to support the polishing pad 315 and may have a printed circuit adjacent to the mounting surface 317 of the polishing pad 315 to bias electrodes in the polishing pad 315. The rigid support 305 may couple with an ECMP system.
A sectional view along line III-III′ in FIG. 3A is shown in FIG. 3B. In FIG. 3B, cathodes 330 a and anodes 335 are respectively located on the bottoms of the perforations 325 and the linear grooves 320. Similar to Embodiment 1, the top surfaces of the cathodes 330 a and the anodes 335 are also all below the polishing surface 316 of the polishing pad 315, and the top surfaces of the cathodes 330 a are lower than the top surfaces of the anodes 335. The distance between the top surfaces of the cathodes 330 a and the polishing surface 316 is about 1 mm to about 5 mm. The distance between the top surfaces of the anodes 335 and the polishing surface 316 is about 0.1 mm to about 1 mm, and the voltage of the wafer on the polishing surface 116 is hence almost the same as the anodes 135. Similarly, a ratio of the total top surfaces of the cathodes 330 a over the total top surfaces of the anodes 335 is also about 0.01 to about 100. An ion exchange membrane 340 encapsulates each of the anodes 335. The material and the function of the ion exchange membrane 340 has been discussed in Embodiment 1 and hence omitted here.
In one embodiment, an anolyte source 347 may be connected to the conductive polishing article 300 and circulate an anolyte solution 345 around the anodes 335. The anolyte source 347 may comprise a regenerator (not shown) that removes bubbles generated around the anodes 335 and reimburse consumed species in the anolyte solution 345. The anolyte source 347 may circulate the anolyte solution 345 through inlets 347 a and outlets 347 b located in a space between the ion exchange membrane 340 and the anode 335, i.e. the space occupied by the anolyte solution 345.
FIG. 3C is a sectional view along the line III-III′ in FIG. 3A showing another cathode arrangement. In FIG. 3C, the cathode 330 b is located under the polishing pad 315 instead of on the bottom of the perforations 325 as shown in FIG. 3B. In this case, a ratio of the total exposed surfaces of the cathodes 330 b over the total top surfaces of the anodes 335 is also about 0.01 to about 100.
According to the forgoing embodiments, the present invention has the advantages of no conductive electrode is contact with a wafer on the polishing pad, since top surfaces of both cathodes and anodes are below the polishing surface of the polishing pad. Hence, no scratch defects caused by the contact of conductive electrodes are generated. At least, polishing defects can thus be minimized. Moreover, an ion exchange membrane covers each of the anodes to prevent oxygen gas contact the wafer, the polishing defects can be further reduced.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A polishing article comprising:

a polishing pad having a polishing surface adapted to contact a substrate surface;

a first electrode disposed below the polishing surface at a first distance;

a second electrode disposed below the polishing surface at a second distance, wherein the second distance is substantially shorter than the first distance; and

an ion exchange membrane disposed at least partially covering the second electrode, wherein the membrane is permeable to ions and allows ionic communication between the second electrode and the substrate surface.

2. The polishing article of claim 1, wherein the ion exchange membrane is comprised of an ion exchange material.

3. The conductive polishing article of claim 1, wherein the membrane is configured to retain an electrolyte solution therein.

4. The conductive polishing article of claim 1, wherein the first distance is about 1 to 5 millimeters.

5. The conductive polishing article of claim 1, wherein the second distance is about 0.1 to 1 millimeters.

6. The conductive polishing article of claim 1, wherein a ratio of the total exposed surfaces of the first electrode over the total exposed surfaces of the second electrode is about 0.01 to about 100.

7. The conductive polishing article of claim 1, wherein a ratio of the total exposed surfaces of the first electrode over the total exposed surfaces of the second electrode is about 3.

8. A conductive polishing article for electrochemical mechanical polishing, comprising:

a polishing pad having a polishing surface for polishing a substrate and a mounting surface located oppositely, wherein the polishing pad has a plurality of first perforations and second perforations distributed evenly;

a plurality of cathodes located in the plurality of first perforations;

a plurality of anodes located in the second perforations, wherein a first distance between a top surface of the cathodes and the polishing surface is greater than a second distance between the top surface of the anodes and the polishing surface;

a plurality of ion exchange membranes respectively encapsulating the anodes to prevent oxygen gas contacting the substrate, the ion exchange membranes being comprised of an ion exchange material; and

a sub pad located adjacent to the mounting surface of the polishing pad.

9. The conductive polishing article of claim 8, wherein the ion exchange material is based on a fluorinated polymer matrix having at least an anionic functional group.

10. The conductive polishing article of claim 8, wherein the ion exchange membrane is configured to retain an electrolyte solution therein.

11. The conductive polishing article of claim 8, wherein the first distance is about 1 mm to about 5 mm.

12. The conductive polishing article of claim 8, wherein the second distance is about 0.1 mm to about 1 mm.

13. The conductive polishing article of claim 8, wherein a ratio of the total top surfaces of the cathodes over the total top surfaces of the anodes is from about 0.01 to about 100.

14. The conductive polishing article of claim 8 wherein a ratio of the total top surfaces of the cathodes over the total top surfaces of the anodes is about 3.

15. A conductive polishing article for electrochemical mechanical polishing, comprising:

a polishing pad having a polishing surface adapted to polish a substrate, wherein the polishing pad has plural perforations and plural grooves cut into the polishing pad from the polishing surface;

at least one cathode located in or behind the polishing pad, wherein at least a part of the cathode is exposed to the substrate by the perforations;

a plurality of anodes located in the grooves, wherein a first distance between the exposed surface of the cathodes and the polishing surface is greater than a second distance between the top surface of the anodes and the polishing surface;

a sub pad located behind the polishing pad to support the polishing pad.

16. The conductive polishing article of claim 15 wherein the ion exchange material is based on a fluorinated polymer matrix having at least an anionic functional group.

17. The conductive polishing article of claim 15 wherein the ion exchange membrane is configured to retain an electrolyte solution therein.

18. The conductive polishing article of claim 15 wherein the first distance is about 1 to 2 millimeters.

19. The conductive polishing article of claim 15 wherein the second distance is about 0.1 to 0.5 millimeters.

20. The conductive polishing article of claim 15, wherein a ratio of the total exposed surfaces of the cathode over the total top surfaces of the anodes is about 3.