RETAINING RING FOR A CHEMICAL MECHANICAL POLISHING TOOL

Abstract

A retaining ring for a chemical mechanical polishing tool comprises a pad side surface. The pad side surface has an edge portion adjacent its outer circumference. A surface normal of the edge portion and a surface normal of the pad side surface include an acute angle. Additionally, or alternatively, the retaining ring may comprise at least one groove extending from an inner circumference of the pad side surface to the outer circumference of the pad side surface. The groove comprises at least one edge portion adjacent the pad side surface. A surface normal of the at least one edge portion and a surface normal of the pad side surface include an acute angle.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to the field of fabrication of integrated circuits, and, more particularly, to a retaining ring for a chemical mechanical polishing tool.

2. Description of the Related Art

In integrated circuits, a large number of circuit elements, such as transistors, capacitors and resistors, are fabricated on a single substrate by depositing semiconductive, conductive and insulating material layers and patterning these layers by photolithography and etch techniques. The individual circuit elements are electrically connected by means of metal lines. In the formation of these metal lines, a so-called interlayer dielectric is deposited. Thereafter, vias and trenches are formed in the interlayer dielectric. The vias and trenches are then filled with a metal, e.g., copper, to provide electrical contact between the circuit elements. In modern integrated circuits, a plurality of such metallization layers comprising metal lines are stacked on top of each other to maintain the required functionality. The repeated patterning of material layers, however, creates a non-planar surface topography, which may deteriorate subsequent patterning processes, especially for integrated circuits including features with minimum dimensions in the submicron range.

The surface of the substrate may be planarized between the formation of subsequent layers. A planar surface of the substrate is desirable for various reasons, one of them being the limited optical depth of focus in photolithography which is used to pattern the material layers of micro structures. Chemical mechanical polishing is an appropriate and widely used process to achieve global planarization of a substrate.

FIG. 1 shows a schematic sketch of a conventional chemical mechanical polishing tool 100. The chemical mechanical polishing tool 100 comprises a platen 101 on which a polishing pad 102 is mounted. Frequently, polishing pads are formed of a cellular microstructure polymer material having numerous voids, such as polyurethane. A polishing head 130 comprises a body 104 and a substrate holder 105 for receiving and holding a substrate 103. The polishing head 130 is coupled to a drive assembly 106. The chemical mechanical polishing tool 100 further comprises a slurry supply 112 and a pad conditioner 131. The pad conditioner 131 comprises a conditioning head 107 and a conditioning pad 108 attached to the conditioning head 107. The conditioning head 107 is coupled to a drive assembly 109.

A retaining ring 120 is attached to the body 104. The retaining ring 120 has an inner diameter which is greater than the diameter of the substrate 103. Thus, the substrate 103 may be provided inside the retaining ring 120 such that the retaining ring 120 circumferentially surrounds the substrate 103.

In operation, the platen 101 rotates. The slurry supply 112 supplies slurry to a surface of the polishing pad 102 where it is dispensed by centrifugal forces. The slurry comprises a chemical compound reacting with the material or materials on the surface of the substrate 103. The reaction product is removed by abrasives contained in the slurry and/or the polishing pad 102. The polishing head 130, and thus also the substrate 103, is rotated by the drive assembly 106 in order to substantially compensate for the effects of different angular velocities of parts of the polishing pad 102 at different radii. In advanced chemical mechanical polishing tools 100, the rotating polishing head 130 is additionally moved across the polishing pad 102 to further optimize the relative motion between the substrate 103 and the polishing pad 102 and to maximize pad utilization. The drive assembly 109 rotates the conditioning head 107 and thus also the conditioning pad 108 attached to it. The conditioning pad 108 may comprise an abrasive component, e.g., diamonds embedded in a matrix. Thus, the surface of the polishing pad 102 is abraded and densified slurry, as well as particles that have been polished away from the surface of the substrate, are removed from voids in the porous polishing pad 102. This process is denoted as conditioning.

Without conditioning, densified slurry and particles abraded from the substrate 103 might clog pores in the polishing pad 102. Thus, the polishing pad 102 would lose its absorbency such that most of the slurry would flow off the polishing pad 102 too quickly. Due to this degradation of the polishing pad 102, the removal rate in the polishing process would steadily decrease.

Conditioning may be performed after the polishing of one or more substrates 103. This, however, leads to significant variations of the removal rate due to the difference between the reworked surface of a freshly conditioned polishing pad 102 compared to the exhausted surface present immediately before the conditioning. Alternatively, the pad conditioner 131 may be continuously in contact with the polishing pad 102 while the substrate 103 is polished. Thus, a more uniform rate of removal of substrate material is achieved.

Various designs of chemical mechanical polishing devices are known in the art. For example, the rotating platen 101 may be replaced with a continuous belt kept in tension by rollers moving at high speed, or slurry may be injected through the polishing pad 102 in order to deliver slurry directly to the interface between the polishing pad 102 and the substrate 103.

In the operation of the chemical mechanical polishing tool 100, the retaining ring 120 may prevent or reduce the chance of the substrate 203 becoming disengaged from the body 104 of the polishing head 130. In some examples of chemical mechanical polishing tools 100 according to the state of the art, the retaining ring 120 may contact the polishing pad 102 during the chemical mechanical polishing process. In particular, the retaining ring 120 can be configured to exhibit a different pressure to the polishing pad 102 than the substrate 103, for example a smaller pressure.

The pressure exhibited to the polishing pad 102 by the retaining ring 120 may help to avoid an uneven distribution of pressure across the surface of the substrate 103 which may occur in chemical mechanical polishing tools 100 wherein the retaining ring 120 does not contact the polishing pad 102, and which may lead to different rates of material removal in portions of the substrate 103.

One problem of chemical mechanical polishing tools according to the state of the art is that, during the polishing process, mechanical friction between the polishing pad 102 and the substrate 103 and/or the retaining ring 120 may induce moderately strong shear forces in the polishing pad 102. The shear forces may be particularly high in chemical mechanical polishing tools wherein the retaining ring 120 contacts the polishing pad 102. Additionally, friction may lead to a reduction of the thickness of the polishing pad 102, due to an abrasion of the polishing pad 102, and to generation of frictional heat which may lead to an increase of the temperature of the polishing pad 102.

The shear forces may be strong enough to create mechanical damage to the polishing pad 102. Such damage may include rip out of the polishing pad 102, holes in the polishing pad 102 and/or a local thinning of the polishing pad 102. Damage to the polishing pad 102 may adversely affect the substrate 103. For example, the substrate 103 may be scratched or may even be broken.

A further problem of chemical mechanical tools according to the state of the art is that the retaining ring 120 may be ground during the chemical mechanical polishing process. Thus, in the course of the operating lifetime of the retaining ring 120, the retaining ring 120 may obtain sharp edges. The sharp edges may cut the polishing pad 102, thus leading to damage to the polishing pad 102.

The present disclosure is directed to various methods and devices that may avoid, or at least reduce, the effects of one or more of the problems identified above.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

According to one illustrative embodiment disclosed herein, a retaining ring for a chemical mechanical polishing tool comprises a pad side surface having an edge portion adjacent an outer circumference thereof. A surface normal of the edge portion and a surface normal of the pad side surface include an acute angle.

According to another illustrative embodiment disclosed herein, a retaining ring for a chemical mechanical polishing tool comprises a pad side surface. The pad side surface comprises at least one groove extending from an inner circumference of the pad side surface to an outer circumference of the pad side surface. The at least one groove comprises at least one edge portion adjacent the pad side surface. A surface normal of the at least one edge portion and a surface normal of the pad side surface include an acute angle.

According to yet another illustrative embodiment disclosed herein, a method of chemical mechanical polishing comprises providing a retaining ring comprising a pad side surface. The pad side surface comprises at least one groove extending from an inner circumference of the pad side surface to an outer circumference of the pad side surface. The at least one groove comprises an edge portion wherein a surface normal of the edge portion and a surface normal of the pad side surface include an acute angle. The retaining ring is rotated relative to a polishing pad. The direction of rotation is adapted such that the at least one groove moves ahead of the edge portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

FIG. 1 shows a schematic view of a chemical mechanical polishing tool according to the state of the art;

FIG. 2a shows a schematic bottom view of a retaining ring according to an embodiment disclosed herein;

FIGS. 2b and 2c show schematic cross-sectional views of the retaining ring shown in FIG. 2a; and

FIGS. 3a and 3b show schematic cross-sectional views of a retaining ring according to another embodiment disclosed herein.

While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Various illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

In one embodiment disclosed herein, a retaining ring for a chemical mechanical polishing tool comprises an edge portion adjacent a pad side surface. In case the retaining ring is mounted in a chemical mechanical polishing tool, the pad side surface faces the polishing pad. The edge portion may be provided at an outer or inner circumference of the retaining ring and/or may be provided at a groove formed in the pad side surface.

A surface normal of the edge portion and a surface normal of the pad side surface include an acute angle. To this end, the edge portion may have a chamfered configuration or may be rounded. Thus, the occurrence of sharp edges at the circumference of the retaining ring and/or the grooved may be reduced or avoided. Even if the retaining ring is ground during the course of the chemical mechanical polishing process, a portion of the edge in the vicinity of the surface of the polishing pad has an acute angle relative to the polishing pad surface. Therefore, a sharpness of the edge may be reduced compared to retaining rings according to the state of the art comprising edge portions which are substantially perpendicular to the pad side surface of the retaining ring. Additionally, as the retaining ring moves across the surface of the polishing pad, the polishing pad may be guided by the edge portion such that the polishing pad slips smoothly under the retaining ring. This may help reducing friction between the retaining ring and the polishing pad.

Thus, the subject matter disclosed herein reduces friction, which may lead to damage to the polishing pad and an undesirable increase of the temperature of the polishing pad. Additionally, damage to the polishing pad resulting from the polishing pad being cut or ripped by sharp edges of the retaining ring may be reduced.

FIG. 2a shows a schematic bottom view of a retaining ring 200 according to one illustrative embodiment disclosed herein. The retaining ring 200 may be adapted for use in a chemical mechanical polishing tool similar to the chemical mechanical polishing tool 100 described above with reference to FIG. 1. For example, the retaining ring 200 may be used instead of the retaining ring 120 according to the state of the art shown in FIG. 1.

The retaining ring 200 comprises a pad side surface 201 (see FIG. 2b). In the operation of a chemical mechanical polishing tool comprising the retaining ring 200, the retaining ring 200 may be mounted such that the pad side surface 201 contacts a polishing pad of the chemical mechanical polishing tool. The retaining ring 200 may comprise a central opening 223. In the operation of the chemical mechanical polishing tool, a substrate holder similar to the substrate holder 105 described above and/or a substrate to be polished may be provided in the central opening 223 such that the retaining ring 200 circumferentially surrounds the substrate to be polished.

In other embodiments, the retaining ring 200 may be formed integrally with a substrate holder and/or a body of a polishing head. In such embodiments, a recess adapted to receive the substrate to be polished and/or a substrate holder may be provided instead of the central opening 223.

The pad side surface 201 of the retaining ring 200 may comprise an edge portion 202 which is provided adjacent an outer circumference of the pad side surface 201, and may further comprise one or more grooves 203-210 extending from an inner circumference of the pad side surface 201 to the outer circumference of the pad side surface 201.

FIG. 2b shows a schematic cross-sectional view of the retaining ring 200 along a plane 219 (FIG. 2a) running through a center 224 of the retaining ring 200 and being substantially perpendicular to the plane of drawing of FIG. 2a. The edge portion 202 of the retaining ring 200 may be chamfered or rounded. Thus, the pad side surface 201 and the surface of the edge portion 202 may include an angle which is different from a right angle.

The relative orientation between the pad side surface 201 and the surface of the edge portion 202 may be characterized by an angle 232 between a surface normal 230 of the pad side surface 201 and a surface normal 231 of the edge portion 202.

As persons skilled in the art know, a surface normal of a surface is a vector of unit length which is perpendicular to the surface, pointing away from the surface. Thus, the surface normal 230 is perpendicular to the pad side surface 201 and the surface normal 231 is perpendicular to the surface of the edge portion 202. The surface normals 230, 231 point away from the retaining ring 200. The angle 232 may be an acute angle, having a value of less than 90 degrees. In some embodiments, the angle 232 may have a value in a range from approximately 35-55 degrees.

FIG. 2c shows a schematic cross-sectional view of the retaining ring 200 along a plane 220 which runs through the groove 203 of the pad side surface 201 and is substantially perpendicular to a length direction of the groove 203 as well as to the plane of drawing of FIG. 2a.

The groove 203 comprises a first edge portion 211 and a second edge portion 225. The first edge portion 211 may be chamfered or rounded. Thus, a surface of the first edge portion 211 and the pad side surface 201 may include an angle which is different from a right angle.

Similar to the edge portion 202 of the pad side surface 201, the relative orientation between the first edge portion 211 of the groove 203 and the pad side surface 201 may be characterized by an angle 242 between a surface normal 240 of the pad side surface 201 and a surface normal 241 of the first edge portion 211. The surface normal 241 is substantially perpendicular to the surface of the edge portion 211, pointing away from the retaining ring 200.

The angle 242 may be an acute angle having a value less than 90 degrees. In some embodiments, the angle 242 may have a value in a range from about 35-55 degrees. In further embodiments, the angle 242 may be substantially equal to the angle 232 (FIG. 2b).

In one illustrative embodiment, the second edge portion 225 of the groove 203 may be substantially perpendicular to the pad side surface 201. Thus, a surface normal 250 of the pad side surface 201 and a surface normal 251 of the second edge portion 225 may be substantially perpendicular to each other.

In the operation of a chemical mechanical polishing tool comprising the retaining ring 200, the retaining ring 200 may be rotated in a predetermined direction of rotation, as indicated by arrow 222 in FIGS. 2a and 2c. The direction of rotation 222 may be adapted such that the groove 203 moves ahead of the first edge portion 211. The groove 203 may be further angled forwardly in the direction of rotation 222. Slurry which is supplied to a polishing pad over which the retaining ring 200 is rotated may pass through the groove 203, entering the central opening 223 inside the retaining ring 200 to contact the semiconductor structure to be polished. The groove 203, when inclined forwardly in the direction of rotation, may advantageously improve an exchange of slurry between the opening 223 and portions of the polishing pad outside the opening 223 compared to a groove 203 being substantially radial or inclined backwardly.

The inclination of the groove 223 may be characterized by an angle 221 (see FIG. 2a) between the groove 203 and a radius 226 of the retaining ring 200 running through an end 227 of the groove 223 at the inner circumference of the retaining ring 200. The angle 221 may have a value greater than zero. In some embodiments, the angle 221 may have a value in a range from about 35-55 degrees, in particular a value of about 45 degrees. The first edge portion 211 may be provided on a side of the groove 203 which is nearer to the radius 226 than the second edge portion 225 of the groove 203. Thus, the groove 203 can move ahead of the first edge portion 211 in case the retaining ring is rotated in the direction of rotation 222 being adapted such that the groove 203 is inclined forwardly in the direction of rotation 222.

The other grooves 204-210 may have a configuration similar to that of the groove 203. In particular, each of the grooves 204 may comprise an edge portion wherein a surface normal of the edge portion and a surface normal of the pad side surface 201 include an acute angle. In FIG. 2a, reference numeral 212 denotes an edge portion of the groove 204, reference numeral 213 denotes an edge portion of the groove 205, and reference numerals 214-218 denote edge portions of the grooves 206-210.

In the operation of the chemical mechanical polishing tool, the retaining ring 200 may be rotated relative to a polishing pad in the direction of rotation 222. This can be done by rotating a polishing head to which the retaining ring 200 is attached, similar to the polishing head 130 described above with reference to FIG. 1. Thereby, the pad side surface 201 may contact the polishing pad.

The edge portion 202 of the pad side surface 201 and the polishing pad include an acute angle which is substantially equal to the angle 232. Thus, as the retaining ring 200 moves over the polishing pad, the edge portion 202 may move over any unevenness of the polishing pad surface. Thus, the edge portion 202 and the pad side surface 201 may slide over the unevenness rather than abut upon the unevenness. Thus, the edge portion 202 may help reduce friction between the retaining ring 200 and the polishing pad.

Furthermore, since the pad side surface 201 and the edge portion 202 include an obtuse angle 270 at the interface between the pad side surface 201 and the edge portion 202, a formation of sharp edges may be substantially avoided or at least reduced, even if the pad side surface 201 is ground during the chemical mechanical polishing process. Therefore, a likelihood of damage to the polishing pad, such as cutting and/or ripping the pad, may be advantageously reduced.

In embodiments wherein the pad side surface includes grooves 203-210, the edge portions 211-218 of the grooves 203-210 may help reduce friction between the polishing pad and the retaining ring 200 and may further reduce a risk of damage to the polishing pad, similar to the edge portion 202 of the pad side surface 201.

The present invention is not restricted to embodiments wherein the edge portion 202 of the pad side surface 201 and the edge portions 211-218 of the grooves 203-210 are chamfered. In other embodiments, some or all of the edge portions 202, 211-218 may be rounded.

FIG. 3a shows a schematic cross-sectional view of the retaining ring 200 along the plane 219 running through the center 224 of the retaining ring 200 in an embodiment wherein the edge portion 202 of the pad side surface 201 is rounded. In FIG. 3a, reference numeral 330 denotes a surface normal of the pad side surface 201 and reference numeral 331 denotes a surface normal at a point 334 of the edge portion 202. The surface normals 330, 331 include an angle 332.

In embodiments wherein the edge portion 202 is rounded, the angle 332 between the surface normal 330 of the pad side surface 201 and the surface normal 331 of the edge portion 202 may depend on the location of the point 334. A surface normal of the edge portion 202 in the vicinity of the interface between the edge portion 202 and the pad side surface 201 may have a smaller angle relative to the surface normal 330 than a surface normal of the edge portion 202 at a greater distance to the interface between the edge portion 202 and the pad side surface 201.

The edge portion 202 may comprise at least one surface normal having an acute angle relative to the surface normal 330 of the pad side surface 201. For example, the angle 332 between the surface normal 330 and the surface normal 331 at the point 334 may have a value less than 90 degrees. In some embodiments, the surface normal 330 of the pad side surface 201 and any surface normal at any point on the edge portion 202 may include an acute angle.

In some embodiments, a cross-section of the edge portion 202 along a radial plane of the retaining ring 200 such as the plane 219 may comprise a substantially elliptical arc section. In some embodiments, one of a major axis and a minor axis of the elliptical arc section may be substantially parallel to the surface normal 330 of the pad side surface 330. Thus, a smooth transition between the pad side surface 201 and the edge portion 202 may be provided. This may help to further reduce a likelihood of damage to the polishing pad when the retaining ring 200 is used in a chemical mechanical polishing tool.

In further embodiments, a cross-section of the edge portion 202 along a radial plane of the retaining ring 200 may comprise a substantially circular arc section. In FIG. 3a, reference numeral 333 denotes a radius of the arc section. The radius 333 may have a value in a range from about 0.5-5 mm, in particular a value of about 2 mm.

In some embodiments, the edge portions 211-218 of the grooves 203-210 may also have a rounded shape. FIG. 3b shows a schematic cross-sectional view of the retaining ring 200 along the plane 220 in such an embodiment. A surface normal 340 of the pad side surface 201 and a surface normal 341 of the first edge portion 211 of the groove 203 at a point 344 include an acute angle 342. Additionally, surface normals at a plurality of points at the edge portion 211 may include an acute angle with the surface normal 340 of the pad side surface 201.

In some embodiments, a cross-section of the groove 203 along a plane substantially perpendicular to a length direction of the groove 203 such as the plane 203 may comprise a substantially elliptical arc section. A major axis of the elliptical arc section or a minor axis of the elliptical arc section may be substantially parallel to the surface normal 340 of the pad side surface 201. Thus, a smooth transition between the pad side surface 201 and the first edge portion 211 of the groove 203 may be provided, which may help to further reduce a risk of the polishing pad being damaged. In some embodiments, the first edge portion 211 of the groove 203 may comprise a substantially circular cross-section having a radius 343. The radius 343 may have a value in a range from about 0.5-5 mm, in particular a value of about 2 mm.

The edge portions 212-218 of the other grooves 204-210 of the retaining ring 200 may have a shape similar to that of the first edge portion 211 of the groove 203.

The present invention is not restricted to embodiments wherein each of the grooves 203-210 comprises only one edge portion having a surface normal which includes an acute angle with a surface normal of the pad side surface 201. In other embodiments, each of the grooves 203-211 may comprise two edge portions wherein a surface normal of each edge portion and a surface normal of the pad side surface 201 include an acute angle. In some embodiments, each of the grooves 203-210 may comprise two chamfered edge portions. In other embodiments, each of the grooves 203-210 may comprise two rounded edge portions wherein a cross-section of each edge portion perpendicular to a length direction of the respective groove 203-210 may comprise an elliptical and/or circular arc section.

Advantageously, providing grooves comprising two edge portions wherein each edge portion has a surface normal including an acute angle with a surface normal of the pad side surface 201 may help reduce a likelihood of damage to the polishing pad in case the direction of rotation of the retaining ring is reversed during the chemical mechanical polishing process.

Furthermore, the present invention is not restricted to embodiments wherein both edge portions of the grooves 203-210 and the edge portion 202 of the pad side surface 201 comprise a surface normal including an acute angle with a surface normal of the pad side surface. In other embodiments, one of the edge portions of the grooves 203-210 or the edge portion 202 of the pad side surface 201 may be substantially perpendicular to the pad side surface.

Moreover, the number of grooves 203-210 of the retaining ring 200 need not be eight, as shown in FIG. 2a. In other embodiments, a different number of grooves 203-210 may be provided. The number of grooves 203-210 may be greater than eight or smaller than eight. In further embodiments, the grooves 203-210 may be omitted.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modifled and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.

Claims

1. A retaining ring for a chemical mechanical polishing tool comprising a pad side surface, said pad side surface having an edge portion adjacent an outer circumference thereof, wherein a surface normal of said edge portion and a surface normal of said pad side surface include an acute angle.

2. The retaining ring of claim 1, wherein said edge portion is chamfered.

3. The retaining ring of claim 2, wherein said surface normal of said edge portion and said surface normal of said pad side surface include an angle in a range from about 35-55 degrees.

4. The retaining ring of claim 1, wherein said edge portion has a rounded shape.

5. The retaining ring of claim 4, wherein a cross-section of said edge portion along a radial plane comprises a substantially elliptical arc section.

6. The retaining ring of claim 5, wherein said cross-section of said edge portion along said radial plane comprises a substantially circular arc section.

7. The retaining ring of claim 6, wherein said substantially circular arc section has a radius in a range from about 0.5 mm to about 5 mm.

8. The retaining ring of claim 1, wherein said pad side surface comprises at least one groove extending from an inner circumference of said pad side surface to an outer circumference of said pad side surface, said groove comprising at least one edge portion adjacent said pad side surface, wherein a surface normal of said at least one edge portion and a surface normal of said pad side surface include an acute angle.

9. The retaining ring of claim 8, wherein said angle between said surface normal of said at least one edge portion of said groove and said pad side surface has a value in a range from about 35-55 degrees.

10. A retaining ring for a chemical mechanical polishing tool comprising a pad side surface, wherein said pad side surface comprises at least one groove extending from an inner circumference of said pad side surface to an outer circumference of said pad side surface, said at least one groove comprising at least one edge portion adjacent said pad side surface, wherein a surface normal of said at least one edge portion and a surface normal of said pad side surface include an acute angle.

11. The retaining ring of claim 10, wherein said at least one edge portion is chamfered.

12. The retaining ring of claim 10, wherein said surface normal of said at least one edge portion and said surface normal of said pad side surface include an angle in a range from about 35-55 degrees.

13. The retaining ring of claim 12, wherein said at least one edge portion is rounded.

14. The retaining ring of claim 13, wherein a cross-section of said groove along a plane substantially perpendicular to a length direction of said groove comprise a substantially elliptical arc section.

15. The retaining ring of claim 14, wherein said arc section is substantially circular.

16. The retaining ring of claim 15, wherein said arc section has a radius in a range from about 0.5 mm to about 5 mm.

17. The retaining ring of claim 10, wherein said at least one groove is inclined relative to a radius of said retaining ring running through an end of said groove at an inner circumference of said retaining ring, and wherein each of said grooves comprises one edge portion wherein a surface normal of said edge portion and said surface normal of said pad side surface include an acute angle, said edge portion being provided on a first side of said groove nearer to said radius than a second side of said groove.

18. The retaining ring of claim 17, wherein a surface normal of another edge portion of said groove and said surface normal of said pad side surface are substantially perpendicular to each other.

19. A chemical mechanical polishing tool, comprising:

a retaining ring according to claim 17; and

a drive unit adapted to rotate said retaining ring in a direction of rotation, wherein said direction of rotation is adapted such that said at least one groove is inclined forwardly in said direction of rotation.

20. A method of chemical mechanical polishing, comprising:

providing a retaining ring comprising a pad side surface, said pad side surface comprising at least one groove extending from an inner circumference of said pad side surface to an outer circumference of said pad side surface, said at least one groove comprising an edge portion, wherein a surface normal of said edge portion and a surface normal of said pad side surface include an acute angle; and

rotating said retaining ring relative to a polishing pad in a direction of rotation, wherein said direction of rotation is adapted such that said at least one groove moves ahead of said edge.