US20150283668A1

US20150283668A1 - Retaining ring assembly with inserts

Info

Publication number: US20150283668A1
Application number: US14/679,435
Authority: US
Inventors: George J. Frank, Jr.
Original assignee: SPM Technology Inc
Current assignee: SPM Technology Inc
Priority date: 2014-04-04
Filing date: 2015-04-06
Publication date: 2015-10-08

Abstract

A generally annular retaining ring assembly having a retaining ring and a backing ring, the backing ring having an upper portion, an inner portion, an outer portion and a lower portion, wherein the inner portion, outer portion and the lower portion form a receiving channel configured to receive a plurality of inserts. The backing ring may be made of a polymeric material and the inserts may be made of a material such as, for example, stainless steel, that provides additional rigidity and heat dissipation to the polymeric backing ring. The inserts absorb the deforming forces exerted when the retaining ring assembly is fastened to the carrier head of a polishing device. However, the inserts are secured within the retaining channel in the underside of the backing ring so that the inserts are isolated from the chemicals present during polishing.

Description

PRIORITY STATEMENT UNDER 35 U.S.C. §119 & 37 C.F.R. §1.78

This non-provisional application claims priority based upon prior U.S. Provisional Patent Application Ser. No. 61/975,319 filed Apr. 4, 2014 in the names of George J. Frank, Jr. and Nathan Brown entitled “THREE PART RING WITH INSERTS,” the disclosures of which are incorporated herein in their entirety by reference as if fully set forth herein.

BACKGROUND

Chemical mechanical polishing equipment can be used in several applications including the manufacture of integrated circuits in which the equipment polishes silicon wafer substrates to a smooth, flat finish prior to the deposition of conductive, semi-conductive and/or insulative layers. The semiconductor wafer is placed on a carrier head which holds the wafer using a combination of vacuum suction or other means to contact the rear side of the wafer.
During polishing, a retaining ring around the edge of the wafer retains the wafer on the carrier head. The front side of the wafer is then contacted by a rotating polishing pad that polishes the outermost surface of the wafer to a flat smooth surface. The carrier head and retaining ring assembly press against the substrate and the rotating polishing pad. The movement of the polishing pad across the surface of the substrate causes material to be mechanically and chemically removed from the face of the substrate.
In the polishing of semiconductor wafers, it is important that the equipment and materials used in the process, including the retaining ring and the materials used in the retaining ring, are compatible with each other and with the chemical and material constraints inherent to the semiconductor device. Those skilled in the art recognize that a silicon wafer with partially constructed devices, such as memory chips or microprocessors, are inherently vulnerable to negative chemical processes such as corrosion, electrostatic emission, physical damage by contact with foreign objects, contamination with foreign materials from equipment component wear and degradation, by-products from chemicals and materials used in processes, and other dilatory factors and processes inherent in chemical mechanical processing.
When polishing conductive materials such as tungsten, copper, conductive polymers, and the like, the process environment must be controlled to minimize the propensity of high-purity metals to degrade when exposed to surface contamination. One method of minimizing such contamination is the use of materials that are not chemically reactive in the construction of the polishing equipment. Because the polishing of conductive materials generally involves using chemicals that react with metal surfaces, it is desirable to minimize or eliminate exposure of any metallic components in the chemical mechanical polishing environment. Historically, this has partially accomplished by constructing components of the equipment from specially designated plastics that are non-reactive but provide near-metallic strength. This method has been successful where, for example, the physical properties of the plastics, such as the heat stability, durability, ability to withstand friction, etc., were suitable substitutes for metal in the polishing process and equipment. Where the substitution of plastic for metal has not sufficed, it has been necessary to design processes that allow for some inherent contamination during processing.
While the problems inherent in polishing conductive materials seem apparent, there are also significant difficulties in polishing non-conductive materials such as doped oxide materials, including tetraethyl orthosilicate (TEOS), borophosphosilicate glass (BPSG), and other layers deposited using chemical vapor deposition, electrodeposition, epitaxy and other deposition methods. As a result, the process environment must also be controlled during the polishing of these materials.
While non-conductive materials tend to be more stable than conductive materials, they are nonetheless subject to damage during processing, including surface damage, contamination by contact with foreign matter, chemical contamination and ionic contamination. In the case of ionic contamination, for example, the non-conductive layers, particularly those involving device isolation processes such as those occurring early in the semiconductor device creation process, must not be exposed to ionizing materials such as sodium, potassium, and the like These ions, sometimes called mobile ions, are extremely detrimental to semiconductor devices. To limit the exposure of the wafer surface to mobile ions, the process space is, where possible, constructed of materials that do not react to the chemicals used during processing. For example, when polishing non-conductive material, basic or high pH chemicals are typically used. Ideally, the chemical mechanical processing area would not have any exposed metallic equipment due to the inherently reactive nature of metallic materials to non-conductive polishing chemicals.
These issues have been addressed in the past with the use of a one piece polymer retaining ring. While this eliminates the negative effect of contamination from the stainless steel, it introduces new problems due to heat retention by the polymer ring due to its insulative properties and vibration induced by the polymer's lack of mass and rigidity. The present invention seeks to eliminate these issues while minimizing the exposure of steel to the process environment by encapsulating the insert within the polymer components limiting exposure to the process environment while enhancing rigidity and providing dissipation of heat generated by the polishing process.

SUMMARY

The invention is directed to various embodiments of a retaining ring assembly comprising a backing ring and a retaining ring, each having a generally annular body. The backing ring is configured with an upper portion, an inner portion, an outer portion and a lower portion, wherein the inner portion, the outer portion and the lower portion form a receiving channel configured to receive a plurality of inserts. The backing ring may be made of a polymeric material and the inserts may be made of a material such as, for example, stainless steel, which provides additional rigidity and heat dissipation to the polymeric backing ring. The inserts absorb the deforming forces exerted when the retaining ring assembly is assembled and fastened to the carrier head of the polishing device. However, because the inserts are isolated within the retaining channel in the underside of the backing ring and then covered with the retaining ring, the inserts are isolated from the chemicals present during polishing.
The foregoing has outlined rather broadly certain aspects of the present invention in order that the detailed description of the invention that follows may better be understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

DESCRIPTION OF DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows perspective views of a two-piece ring known in the art;

FIG. 2 is an expanded top perspective view of one embodiment of a retaining ring assembly with inserts as described in the present invention;

FIG. 3 is an expanded bottom perspective view of an alternate view of one embodiment of a retaining ring assembly and shows embodiments of inserts as described in the present invention;

FIG. 4 is a perspective view of one embodiment of an insert as described in the present invention;

FIG. 5 is a cross-sectional view of a retaining ring assembly showing one embodiment of inserts as described in the present invention; and

FIG. 6 is a close up cross-sectional view of a retaining ring assembly showing one embodiment of inserts as described in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an improved retaining ring assembly used in chemical mechanical polishing. The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
The present invention provides, in part, for specially designed inserts that increase rigidity and improve heat dissipation in retaining ring assemblies. Inserts that are more rigid, and that have better ability to conduct heat, are inserted into a retaining groove configured within the backing ring of a two part retaining ring assembly. Because the inserts are more rigid than the material used in the backing ring, they absorb the deforming forces present as a result of fastening the retaining ring assembly to a carrier head. Also, because they are better conductors than the material used in the body of the backing ring, the retaining ring assembly is better able to dissipate heat generated during the polishing process. Moreover, because the inserts are positioned within the groove in the backing ring and covered with the retaining ring, the inserts are not exposed to the polishing surface during polishing and, therefore, are less likely to react undesirably with the chemicals used during polishing.
Two-part retaining ring assemblies, such as that shown in FIG. 1, are known in the art. The backing ring 101 of the two part retaining ring assembly 100, is typically made of stainless steel which provides the necessary rigidity to accommodate the stresses of the chemical mechanical polishing process. The metal also serves to accelerate heat dissipation. While this added rigidity of the backing ring 101 is advantageous during polishing, there are also negative effects as discussed in the background section. These negative effects include exposure of the stainless steel backing ring 101 to basic and acidic chemicals that can degrade the metal and thereby contaminate the environment in which the polishing occurs. The retaining ring 102 of the two part ring assembly 100 is commonly made of a polymeric materials such as PET, PPS, and the like.
Referring now to FIGS. 2 and 3 which show exploded views of one embodiment of the retaining ring assembly of the present invention. In this embodiment, a retaining ring assembly 200 has a generally annular body comprising a backing ring 201 and a retaining ring 207. The backing ring 201 is configured with an upper portion 202, an inner portion 203, an outer portion 204 and a lower portion 205, wherein the inner portion 203, outer portion 204 and the lower portion 205 form a receiving channel configured to receive a plurality of inserts 210.
The backing ring 201 may be made from a polymeric material, which is a more cost effective material than most metals. For example, the backing ring 201 may be made from acrylonitrile butadiene styrene, polybutylene terepthalate, polycarbonate, polyamide, polypropylene, polyethylene or polyvinylchloride, among others. Each of these materials has sufficient chemical resistance characteristics for the chemical-mechanical processing process environment, but they can also be manufactured at a reasonable cost.
The backing ring 201 could be manufactured, for example, by injection molding, compression molding, conventional machining or additive manufacturing such as 3D printing or similar processes. In one embodiment, the backing ring 201 is an annular shaped ring made of polymeric materials ranging in durometer from approximately 80 to 120.
The inserts 210 may be made from any material that is dissimilar from the backing ring that would provide for an increase in the overall mass or rigidity of the retaining ring assembly. In some embodiments, it is desirable that the inserts 210 increase the overall mass by at least twenty percent. The inserts 210 may be made of materials that are not only more rigid but also more thermally conductive than the backing ring 201 material. This includes, but is not limited to, stainless steel.
The inserts 210 absorb the deforming forces exerted when the retaining ring assembly 200 is fastened to the carrier head of the polishing device. The presence of the inserts 210 in the retaining ring assembly 200 also increases the overall mass of the retaining ring assembly 200 which dampens harmonics and vibration during the polishing process. The benefit of this dampening effect is to decrease deflectivity on the surface of the wafer. The improvement in harmonics and vibration also provide for improved process consistency from one polish head to another and over the life of the retaining ring assembly 200.
As previously discussed, the inserts 210 are isolated within the retaining channel in the underside of the backing ring 201 and covered by the retaining ring 207 so that the inserts 210 are isolated from the chemicals present during polishing. The horizontal shape of the inserts 210 can be generally rectangular as shown in FIG. 4, or the shape can be elliptical or multi-sided depending upon the needs of the polishing process and cost effectiveness of manufacturing processes. In some embodiments, the vertical surface of the inserts 210 are configured so that they are readily bonded to and arranged in a fully annular configuration. The inserts 210 may be prepared, for example, using surface texturing using bead-blasting, surface structuring by machine tool, surface texturing and structuring by casting or molding.
The surface of the inserts 210 may be fashioned in a manner that will allow the insert 210 to be securely fastened in a rigid annular configuration within the backing ring 201, while allowing for the use of more cost effective manufacturing methods than can be used to produce a fully annular component. This can be accomplished by, but is not limited to; forging, casting, powdered metal technology, conventional machining or additive methods.
The inserts 210 could be fastened to the backing ring 201 using an adhesive, using press fit or snap fit technology, using mechanical fasteners such as screws, using injection molding techniques whereby the ring is injection molded about the inserts, using ultrasonic welding technique, or using other methods known in the art.
The retaining ring 207 may be made of any suitable engineering polymeric material commonly used in the chemical mechanical polishing process, such as, for example, PPS, PET, PEEK, and the like.
Referring now to FIGS. 5 and 6 which show a collapsed view of one embodiment of the retaining ring assembly 200 of the present invention. The retaining ring assembly 200 has a generally annular body comprising an backing ring 201 and a retaining ring 207. The inserts 210 are isolated within the retaining channel in the underside of the backing ring 201 and covered by the retaining ring 207 so that the inserts 210 are isolated from the chemicals present during polishing. In some embodiments, the backing ring 201 is secured to the retaining ring 207 through the inserts 210 using an attachment device 212. In other embodiments, the backing ring is secured to the retaining ring through a method known in the art, and the inserts 210 are affixed to the backing ring 201 using an attachment device 212.
While the present system and method has been disclosed according to the preferred embodiment of the invention, those of ordinary skill in the art will understand that other embodiments have also been enabled. Even though the foregoing discussion has focused on particular embodiments, it is understood that other configurations are contemplated. In particular, even though the expressions “in one embodiment” or “in another embodiment” are used herein, these phrases are meant to generally reference embodiment possibilities and are not intended to limit the invention to those particular embodiment configurations. These terms may reference the same or different embodiments, and unless indicated otherwise, are combinable into aggregate embodiments. The terms “a”, “an” and “the” mean “one or more” unless expressly specified otherwise. The term “connected” means “communicatively connected” unless otherwise defined.
When a single embodiment is described herein, it will be readily apparent that more than one embodiment may be used in place of a single embodiment. Similarly, where more than one embodiment is described herein, it will be readily apparent that a single embodiment may be substituted for that one device.
In light of the wide variety of methods for chemical mechanical polishing rings known in the art, the detailed embodiments are intended to be illustrative only and should not be taken as limiting the scope of the invention. Rather, what is claimed as the invention is all such modifications as may come within the spirit and scope of the following claims and equivalents thereto.
None of the description in this specification should be read as implying that any particular element, step or function is an essential element which must be included in the claim scope. The scope of the patented subject matter is defined only by the allowed claims and their equivalents. Unless explicitly recited, other aspects of the present invention as described in this specification do not limit the scope of the claims.

Claims

What is claimed is:

1. A retaining ring assembly for chemical mechanical polishing comprising:

a substantially annular backing ring having an upper portion, a lower portion, an inner portion and an outer portion, wherein the lower portion, the inner portion and the outer portion are configured with a retaining grove;

substantially annular inserts located within the retaining groove;

a substantially annular retaining ring configured to cover the retaining groove so that chemicals used during processing cannot enter the retaining grove.

2. The retaining ring assembly of claim 1, wherein the backing ring is secured to the retaining ring using an attachment device.

3. The retaining ring assembly of claim 1, wherein said backing ring is made from polycarbonate, polyethylene terpthalate, polyethersulphone, polyetheretherketone, or polyphenelynesulfide.

4. The retaining ring assembly of claim 1, wherein the backing ring is made of a material having a hardness between 80 and 120 durometers.

5. The retaining ring assembly of claim 1, wherein the backing ring is made of a material having durometer readings between 80 and 120.

6. The retaining ring assembly of claim 1, wherein said inserts are made of stainless steel.

7. The retaining ring assembly of claim 1, wherein said inserts are made from a material which deforms less during stress than the backing ring.

8. The retaining ring assembly of claim 1, wherein said inserts are affixed in said receiving groove through use of an adhesive, press-fit features, injection molding, over-molding, or ultrasonic welding.

9. The retaining ring assembly of claim 1, wherein the mass of the inserts is at least 20% greater than the mass of the backing ring.