Methods of making chemical mechanical polishing layers having improved uniformity
The present invention provides methods of manufacturing a chemical mechanical polishing (CMP polishing) layer for polishing substrates, such as semiconductor wafers comprising providing a composition of a plurality of liquid-filled microelements having a polymeric shell; classifying the composition via centrifugal air classification to remove fines and coarse particles and to produce liquid-filled microelements having a density of 800 to 1500 g/liter; and, forming the CMP polishing layer by (i) converting the classified liquid-filled microelements into gas-filled microelements by heating them, then mixing them with a liquid polymer matrix forming material and casting or molding the resulting mixture to form a polymeric pad matrix, or (ii) combining the classified liquid-filled microelements directly with the liquid polymer matrix forming material, and casting or molding.
1. A method of manufacturing a chemical mechanical polishing (CMP polishing) layer for polishing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate, comprising:
providing a raw composition of a plurality of liquid-filled microelements having a polymeric shell, the raw composition forming 100 μm blowout holes when casting in polyurethane and a coarse fraction of the new composition forming interconnected pores when casting in polyurethane;
classifying the raw composition via a Coanda block air classifier to remove fines and coarse particles from the raw composition of the plurality of liquid-filled microelements to produce classified liquid-filled microspheres, and the classified liquid-filled microspheres having a density of 800 to 1500 g/liter and an average particle size of 3 to 30 μm and to lower an open cell content in the polishing layer, the open cell content defined as follows:
Open
cell
content
=
(
1
-
Pycnometer
volume
Dimensional
volume
)
×
100
%
=
(
1
-
Dimensional
density
Pycnometer
density
)
×
100
%
;
and,
forming the CMP polishing layer by
combining the classified liquid-filled microspheres with a liquid polymer matrix forming material having a gel time of from 1 to 30 minutes at a casting or molding temperature of from 25 to 125° C. to form a pad forming mixture and casting or molding the pad forming mixture to form a polymeric pad matrix at the casting or molding temperature, and allowing the reaction exotherm to convert the liquid-filled microspheres to gas-filled microspheres and the gas-filled microelements have a density of 10 to 100 g/liter and the polishing layer is free of 100 μm blowout holes and interconnected pores.
2. The method as claimed in claim 1 , wherein the classified liquid-filled microspheres have a density of from 950 to 1300 g/liter.
3. The method as claimed in claim 1 , wherein the classifying removes from 2 to 20 wt. % from the raw composition of the plurality of the liquid-filled microspheres, comprising from 1 to 10 wt. % of the composition as fine particles and from 1 to 10 wt. % of the composition as coarse particles.
4. The method as claimed in claim 1 , wherein the classifying removes from 2 to 12 wt. % of the composition from the raw composition of the plurality of liquid-filled microspheres, comprising from 1 to 6 wt. % of the composition as fine particles and from 1 to 6 wt. % of the composition as coarse particles.
5. The method as claimed in claim 1 , wherein the resulting composition of classified liquid-filled microspheres is substantially free of silica, magnesia and other alkaline earth metal oxides.
6. The method as claimed in claim 1 , wherein the polymeric shell of the liquid-filled microspheres comprises polymers chosen from poly(meth)acrylonitrile, poly(vinylidene chloride), poly(methyl methacrylate), poly (isobornyl acrylate), polystyrene, copolymers thereof with each other, copolymers thereof with vinyl halide monomers, copolymers thereof with C 1 to C 4 alkyl (meth)acrylates, copolymers thereof with C 2 to C 4 hydroxyalkyl (meth)acrylates, or acrylonitrile-methacrylonitrile copolymers.