Abrading – Rigid tool – Rotary disk
Reexamination Certificate
2000-02-28
2001-09-11
Hail, III, Joseph J. (Department: 3723)
Abrading
Rigid tool
Rotary disk
C451S041000
Reexamination Certificate
active
06287185
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to polishing pads useful in the manufacture of semiconductor devices or the like. More particularly, the polishing pads of the present invention comprise an advantageous hydrophilic material having an innovative surface topography which generally improves predictability and polishing performance.
2. Discussion of the Related Art
Integrated circuit fabrication generally requires polishing of one or more substrates, such as silicon, silicon dioxide, tungsten or aluminum. Such polishing is generally accomplished, using a polishing pad in combination with a polishing fluid.
The semiconductor industry has a need for precision polishing to narrow tolerances, but unwanted “pad to pad” variations in polishing performance are quite common. A need therefore exists in the semiconductor industry for polishing pads which exhibit more predictable performance during high precision polishing operations.
SUMMARY OF INVENTION
The present invention is directed to thermoformed (or embossed) polishing pads having an innovative polishing surface formed from an innovative hydrophilic material. The pads of the present invention comprise a hydrophilic material having: i. a density greater than 0.5 g/cm
3
; ii. a critical surface tension greater than or equal to 34 milliNewtons per meter; iii. a tensile modulus of 0.02 to 5 GigaPascals; iv. a ratio of tensile modulus at 30° C. to tensile modulus at 60° C. of 1.0 to 2.5; v. a hardness of 25 to 80 Shore D; vi. a yield stress of 300-6000 psi (2.1-41.4 MegaPascal); vii. a tensile strength of 1000 to 15,000 psi (7-105 MegaPascal); and viii. an elongation to break up to 500%. In a preferred embodiment, the polishing layer further comprises a plurality of soft domains and hard domains.
The polishing materials of the present invention do not include felt-based polishing pads created by coalescing a polymer onto a fiber substrate, as described in U.S. Pat. No. 4,927,432 to Budinger, et al.
The polishing surface has a topography produced by a thermoforming process. The topography consists of large and small features that facilitate the flow of polishing fluid and facilitate smoothing and planarizing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to polishing pads formed from an innovative hydrophilic polishing material and having an innovative polishing surface. More specifically, the present invention is directed to an improved polishing pad useful in the polishing of substrates, particularly substrates for the manufacture of semiconductor devices or the like. The compositions and methods of the present invention may also be useful in other industries and can be applied to any one of a number of workpiece materials, including but not limited to silicon, silicon dioxide, metal, dielectrics, ceramics and glass. It should be noted that the term “polish” (and any form thereof) as used throughout this application, is intended to include “planarize” (and any corresponding forms).
The present invention is innovative because it; 1) recognizes the detrimental effect on precision polishing that occurs from damage caused by the incorporation of surface features into prior art pads; 2) recognizes how the damage is created during the fabrication of polishing pads; 3) teaches how to manufacture pads having low levels of damage; 4) teaches how to manufacture pads with highly reproducible surface features and therefore more predictable pad performance relative to conventional pads produced by cutting or skiving; and 5) teaches novel means to incorporate surface features into a pad during manufacture. None of these aspects of the present invention were heretofore appreciated in the art and are truly a significant contribution to the art of precision polishing. Some of the aspects of the present invention are described in U.S. Pat. No. 6,022,268 which is made a part of the present specification by reference.
The polishing pads of the present invention comprise a highly reproducible and advantageous surface topography with a minimum of surface damage such as indentations and protrusions often created during pad fabrication.
Pad fabrication that includes cutting or skiving creates damage that tends to vary from pad to pad. Prior art pad fabrication may include cutting sections of a polymer cake to form pads. As a blade cuts through the cake it typically leaves directional surface damage, including indentations and protrusions from the pad surface. The damage generally varies from pad to pad as the cutting edge dulls.
Another step in pad fabrication is the incorporation of channels or other features into the pad surface to facilitate polishing fluid flow. Prior art pads generally have these features cut or machined into the pad. This also generally, tends to leave damage on the pad surface and within the cuts. Other factors, such as temperature, humidity and line speed changes cause variations in the pad surface characteristics. These variations cause performance variations from pad to pad, making it difficult to delineate optimum polishing parameters.
The pads of the present invention are created with little or no cutting, machining or similar type fracturing of the polishing surface. Unwanted directional patterns such as those generated by skiving are generally eliminated. Surface features or a portion thereof are applied onto (or into) the pad, also without fracturing of the polishing surface. This eliminates the problems associated with prior art techniques.
According to the present invention, surface features incorporated after the formation of the pad are created, at least in part, by thermoforming. Thermoforming is any process whereby the surface of the pad is heated and is permanently deformed by some means such as pressure or stress. Thermoforming reduces the extent of damage relative to conventional pads. Thermoforming also provides more reproducible features than cutting or machining because of the consistency of the surface of the thermoforming die. Therefore, pads of the present invention exhibit more predictable performance and allow for optimum polishing parameters to be delineated.
In one embodiment, surface features are incorporated into the surface of the polishing pad, by heating the pad surface until it softens and then forming, or shaping it, utilizing a die and pressure. The features preferably comprise one or more indentations having an average depth and/or width of greater than about 0.05 millimeters and preferably greater than about 0.1 millimeters. These features facilitate the flow of polishing fluid and thereby enhance polishing performance.
In another embodiment pads are extruded to create a sheet of material. The material may be formed into a polishing belt by creating a seam from the two ends of the sheet, or in an alternative embodiment, the sheet may be cut to form pads of any shape or size. In another embodiment of the present invention, compression molding is employed whereby a pliable polymer is placed in a die. The polymer is then compressed which causes it to spread throughout the mold. It then solidifies and is released from the mold.
In another embodiment, the pad material is extruded upon a second solid or semi-solid material, thereby causing the extruded material to be bonded to the second material after it has solidified. The second material can provide reinforcement to the pad so that the solidified, extruded material need not be self-supporting. Alternatively or in addition, the second material can provide structural integrity to the pad, thereby providing improved performance, longevity and/or greater flexibility in manufacturing.
In a preferred embodiment of the present invention, surface features are embossed with a chilled roller employed to ensure that plastic flow subsequent to embossing is eliminated or significantly reduced. This creates very reproducible embossed indentations, generally reducing pad-to-pad variations typically found in pads produced by many conventional methods. This reproducibilit
Cook Lee Melbourne
James David B.
Jenkins Charles W.
Roberts John V. H.
Benson Kenneth A.
Hail III Joseph J.
Kaeding Konrad
Kita Gerald K.
Ojini Anthony
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