Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-01-21
2002-03-12
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S548000, C451S527000, C451S036000
Reexamination Certificate
active
06354915
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, memory disks or the like. More particularly, the polishing pads of the present invention comprise a base substrate which supports a thin hydrophilic polishing layer, the polishing layer having an particular surface texture and topography.
2. Discussion of the Related Art
High precision chemical-mechanical polishing is often required in the manufacture of integrated circuits and memory disks. Such polishing is generally accomplished, using a polishing pad in combination with a polishing fluid. However, unwanted “pad to pad” variation in polishing performance is quite common, and therefore a need exists for polishing pads which exhibit more predicable performance.
U.S. Pat. No. 4,927,432 describes a polishing pad comprising a porous thermoplastic resin which is reinforced with a fibrous network such as a felted mat, the polishing material is modified by coalescing the resin among the fibers, preferably by heat treatment, to increase the porosity and hardness of the material as well as increasing the surface activity of the resin.
SUMMARY OF INVENTION
The present invention is directed to polishing pads having: 1. a base substrate; and 2. a thin hydrophilic polishing layer. The polishing layer has a particular surface texture and topography. “Texture” is intended to mean surface characteristics on a scale of less than 10 microns, and “surface topography” is intended to mean surface characteristics of 10 microns of more.
The base substrates of the present invention can comprise a single layer or multiple layers and can comprise a combination of layers that are bonded together. What is critical is that at least a portion of the base layer defines a planarity even when a non-uniform pressure of 10 pounds per square inch is applied against the base layer. In one embodiment, a base layer is bonded to a polishing layer and the combination is slid over a rigid component such as a platen or plate during polishing. A preferred base layer comprises a resilient layer of plastic, particularly an engineering plastic, such as a polyamide, polyimide, and/or polyester, particularly poly(ethylene terephthalate) or “PET”. The layer is preferably a flexible web capable of being pulled from a roll or easily wound into a roll.
The base substrate of the present invention preferably has a thickness of less than 1 millimeter. In a preferred embodiment, the support layer has a thickness of less than 0.5 millimeters, more preferably less than 300 microns.
In a preferred embodiment, the thin polishing layers of the present invention are less than 500 microns, more preferably less than 300 microns and yet more preferably less than 150 microns and comprise a random surface texture comprising pores and/or micro-voids of varying sizes and dimensions. A preferred method of forming the thin polishing layer is by coagulation of a polymer onto the support (base) layer, such as in accordance with the “Process For Producing Microporous Films and Coatings” described in U.S. Pat. No. 3,100,721 which is hereby incorporated into this specification by reference. In an alternative embodiment, the thin polishing layer is, printed, sprayed, cast, molded, ink-jet printed or otherwise coated onto the support layer and thereafter solidified by cooling or by a curing reaction.
It has been surprisingly discovered that the combination of a thin base layer and a thin polishing layer can provide ultra high performance polishing, due to a more precise and predictable polishing interaction when a rigid support presses the thin polishing pad against (and the pad is moved in relation to) a substrate to be polished. This polishing pad can be manufactured to very tight tolerances and (together with the rigid support) can provide predictable compressibility and planarization length. “Planarization length” is intended to mean the span across the surface of a polishing pad which lies substantially in a single plane and remains in a single plane during polishing, such that as high features on a wafer surface are polished, features of lesser height do not polish unless or until the higher features are diminished to the height of the shorter features.
It has been surprisingly discovered that polishing pads having a thickness greater than 1.5 millimeters have a much higher propensity for unpredictable warping or otherwise deviations from their original shape. Such warping and/or deviations are generally more detrimental to ultra precision polishing performance than pads having a thin base substrate in accordance with the present invention.
It has also been surprisingly discovered that thin polishing layers in accordance with the present invention are less susceptible to unpredictable polishing performance due to material fatigue during the polishing operation. For the polishing layers of the present invention, fatigue effects are much more predictable and generally have a diminished affect on polishing performance. Furthermore, thin polishing layers will tend to fully saturate and reach a steady state equilibrium with a polishing slurry much more quickly and predictably than conventional polishing pads.
In a preferred embodiment, the polishing layer is substantially free of macro-defects. “Macro-defects” are intended to mean burrs or other protrusions from the polishing surface of the pad which have a dimension (either width, height or length) of greater than 25 microns.
Macro-defects should not be confused with “micro-asperities.” Micro-asperities are intended to mean burrs or other protrusions from the polishing surface of the pad which have a dimension (either width, height or length) of less than 10 microns. It has been surprisingly discovered that micro-asperities are generally advantageous in ultra precision polishing, particularly in the manufacture of semi-conductor devices, and in a preferred embodiment, the polishing layer provides a large number of micro-asperities at the polishing interface.
Furthermore, the polishing layers of the present invention comprise a hydrophilic material. The polishing layer preferably has: 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 15 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 MeaPascal); 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. Soft domains may possibly be a polymer. Hard domains may possibly be ceramic particles. Particles which may be incorporated into the polishing layer include; alumina, silicon carbide, chromia, alumina-zirconia, silica, diamond, iron oxide, ceria, boron nitride, boron carbide, garnet, zirconia, magnesium oxide, titania, and combinations thereof.
Pads of the present invention may be manufactured to be placed on a rigid platen such as the circular platen of a typical semiconductor planarization apparatus. They may also be manufactured for use in linear-type planarization apparatus in the form of a rolled web which can be indexed over a platen which provides rigid planarity for the pad during polishing. Another possible form for the pad is that of a continuous belt.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to an improved polishing pad useful in the polishing or planarizing of substrates, particularly substrates for the manufacture of semiconductor devices, memory disks 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 materials, including but not limited to silicon, silicon dioxide, metal (including, but not limited to tungsten, copper, and aluminum), dielectrics
Baker Arthur Richard
Cook Lee Melbourne
James David B.
Banks Derris H.
Benson Kenneth
Kaeding Konrad
Kita Gerald
Rodel Holdings Inc.
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