Low-Density CMP Polishing Pads With Uniform Pore Structure
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Solution Overview
Problem
Existing polishing pads exhibit variability in properties such as pore size distribution and specific gravity, leading to inconsistent polishing performance.
Innovation Solution
A method involving the reaction of an isocyanate-terminated pre-polymer with a specific blend of curatives and pre-expanded polymeric microspheres, followed by curing and cutting a polymer block to form polishing layers with controlled specific gravity and unimodal pore size distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If pre-expanded and un-expanded fluid-filled polymeric microspheres are used to reduce specific gravity, then polishing pad density decreases, but pore size distribution becomes bi-modal leading to property variability
Solution Approach 1:
The patent changes the physical state parameter of the microspheres from a mixture of pre-expanded and un-expanded states to exclusively pre-expanded state. This parameter change ensures uniform pore size distribution while achieving the desired low specific gravity through controlled expansion ratios and microsphere selection.
Solution Approach 2:
The patent applies homogeneity by using only pre-expanded fluid-filled polymeric microspheres with controlled expansion ratios, eliminating the heterogeneity introduced by mixing different expansion states. This results in uniform pore size distribution throughout the polishing pad structure.
2Productivity
If multiple curatives are used to form the polymer matrix, then curing speed increases, but heat generation becomes difficult to control affecting microsphere expansion uniformity
Solution Approach 1:
The patent changes the chemical composition parameters of the curative blend, specifically using a polyamine curative with 2-10 aromatic rings and controlling the isocyanate index. These parameter changes optimize the balance between curing speed and heat generation, enabling controlled exothermic reaction that supports uniform microsphere expansion.
Solution Approach 2:
The patent uses a composite curative system comprising a polyamine curative with aromatic rings combined with specific isocyanate-functional pre-polymers. This composite material approach allows tuning of the curing reaction characteristics to achieve both high curing speed and controlled heat generation.
3Loss of time
If the mixture is cured at high temperature to accelerate the reaction, then curing time decreases, but the polymer matrix becomes too rigid preventing further microsphere expansion
Solution Approach 1:
The patent applies periodic action through a two-stage curing process: first curing the polymer matrix to establish structural integrity, then applying additional heat to enable further microsphere expansion. This sequential thermal treatment allows the matrix to transition from rigid to sufficiently compliant and back to rigid, achieving both fast curing and complete expansion.
Solution Approach 2:
The patent utilizes phase transitions of the polymer matrix through controlled thermal cycling. The matrix transitions from a rigid cured state to a more compliant state during the expansion phase, allowing microsphere expansion, then returns to rigid state upon final curing, achieving both speed and expansion completeness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method produces polishing layers with consistent properties, achieving lower specific gravity and improved polishing performance, enhancing removal rates of metals and oxides by up to 40% compared to single curative systems.
Implementation Method 1
heat being released from reaction of the isocyanate-functional pre-polymer and the curatives
Implementation Method 2
pores formed by further expansion of the pre-expanded fluid filled polymer microspheres the further expansion being caused by the heat from the cure and the heat released from the reaction
Data Source
AI summary
A polishing pad for chemical mechanical polishing comprises a polishing layer which comprises a polymer matrix which is the reaction product of an isocyanate terminated oligomer or polymer, with a curative blend comprising two or more polyamine curatives wherein pores are present in the polymer matrix, such pores being formed by expansion of pre-expanded fluid filled polymeric microspheres such expansion occurring during reaction of the isocyanate terminated oligomer or polymer with the two or more curatives, wherein the polishing layer is characterized by one or more of a ratio of viscous modulus (G″) at 104° C. to shear loss modulus (G″) at 150° C. of at least 5:1; and a specific gravity of the polishing layer is less than or equal to 95% of a calculated specific gravity for the isocyanate terminated oligomer or polymer, the curative blend and the pre-expanded fluid filled polymeric microspheres.