Creep-Resistant Polyurethane Window for Semiconductor Polishing
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Solution Overview
Problem
Current polyurethane windows used in polishing pads for semiconductor manufacturing lack sufficient optical transmission, durability, and are prone to bulging, which leads to defects during chemical mechanical polishing processes, especially with the increasing complexity and miniaturization of semiconductor devices.
Innovation Solution
A cross-linked polyurethane window formed with an aliphatic or cycloaliphatic isocyanate and a polyol in a prepolymer mixture, reacted with a chain extender having OH or NH2 groups, with a stoichiometry less than 95%, providing a creep-resistant and optically transparent window with a Shore D hardness of 45 to 80 and optical double pass transmission of at least 15% at 400 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyurethane windows are formed by casting polyurethane polishing material around a solid polyurethane window, then the window provides structural support, but it causes bulging during polishing which increases polishing defects
Solution Approach 1:
The patent changes the physical and chemical parameters of the polyurethane window material, specifically controlling the cross-section thickness (0.5mm to 2.0mm) and using specific polyol combinations (polyester polyol and polyether polyol in specific ratios) to achieve optimal mechanical properties that prevent bulging while maintaining structural support
Solution Approach 2:
The patent uses a composite polyurethane system combining polyester polyol and polyether polyol in specific weight ratios (30-70% polyester, 70-30% polyether) to create a material with balanced properties that provides both structural support and resistance to bulging during polishing
2Illumination intensity
If aliphatic polyurethane windows are used to improve light transmission, then optical transmission is enhanced, but durability is reduced
Solution Approach 1:
The patent employs a composite polyurethane system combining aliphatic polyester polyol and aliphatic polyether polyol, where the polyester component provides durability and the polyether component contributes to optical transmission and flexibility, achieving both required properties simultaneously
Solution Approach 2:
The patent optimizes the molecular weight ratios and composition of the polyol components, using polyester polyol with Mn of 500-2000 and polyether polyol with Mn of 1000-5000 in specific weight ratios to balance optical transmission and durability
3Strength
If the OH or NH2 to unreacted NCO stoichiometry is increased to improve cross-linking, then durability increases, but optical transmission decreases
Solution Approach 1:
The patent precisely controls the stoichiometry of the chain extender to unreacted isocyanate groups to be between 90-105%, optimizing the cross-linking density to provide durability while maintaining optical transmission by avoiding excessive cross-linking that would reduce light transmission
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 solution achieves a polyurethane window with reduced time-dependent strain, maintaining optical transmission and durability, preventing bulging and defects during polishing, thus enhancing the accuracy and reliability of endpoint detection in semiconductor manufacturing.
Implementation Method 1
a cross-linked structure formed with an aliphatic or cycloaliphatic isocyanate and a polyol in a prepolymer mixture, the prepolymer mixture being reacted with a chain extender having OH or NH2 groups
Implementation Method 2
an optical double pass transmission of at least 15% at a wavelength of 400 nm
Data Source
AI summary
The polishing pad is useful for polishing at least one of magnetic, optical and semiconductor substrates. The polishing pad includes a polishing layer having a polyurethane window. The polyurethane window has a cross-linked structure formed with an aliphatic or cycloaliphatic isocyanate and a polyol in a prepolymer mixture. The prepolymer mixture is reacted with a chain extender having OH or NH2 groups and having an OH or NH2 to unreacted NCO stoichiometry less than 95%. The polyurethane window has a time dependent strain less than or equal to 0.02% when measured with a constant axial tensile load of 1 kPa at a constant temperature of 60° C. at 140 minutes, a Shore D hardness of 45 to 90 and an optical double pass transmission of at least 15% at a wavelength of 400 nm for a sample thickness of 1.3 mm.