Aliphatic Polyurethane CMP Endpoint Detection Windows
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Solution Overview
Problem
Conventional CMP polishing pads with endpoint detection windows suffer from degradation when exposed to light wavelengths below 400 nm and have low transmittance at these wavelengths, leading to increased polishing defects and inadequate planarity in semiconductor fabrication.
Innovation Solution
Development of a CMP polishing pad with endpoint detection windows made from a reaction mixture of cycloaliphatic diisocyanates and a polyol mixture, featuring a UV cut-off at 325 nm or lower, which provides improved transmittance and durability, using a specific ratio of cycloaliphatic diisocyanates, polymeric diols, and triols with appropriate catalysts to maintain transparency and prevent degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional polymer endpoint detection windows are used, then the polishing pad provides structural integrity, but the windows exhibit degradation upon exposure to light with wavelength of 330 to 425 nm and have low transmittance below 400 nm
Solution Approach 1:
The patent changes the chemical composition parameters of the polyurethane resin by using aliphatic isocyanates instead of aromatic isocyanates, and by controlling the ratio of polyether polyol to polyester polyol (from 90:10 to 70:30), achieving both durability and UV transmittance below 400 nm
Solution Approach 2:
The endpoint detection window uses a composite polyurethane resin system combining aliphatic isocyanate with both polyether and polyester polyols in specific ratios, creating a material that integrates both durability and optical transparency properties
2Reliability
If aromatic groups are included in the resin for durability, then the endpoint detection window maintains structural stability, but the transmittance cut-off wavelength increases to too high a radiation wavelength
Solution Approach 1:
The patent changes the chemical structure parameter by replacing aromatic isocyanate groups with aliphatic isocyanate groups (such as hexamethylene diisocyanate, isophorone diisocyanate, or 4,4'-dicyclohexylmethane diisocyanate), which eliminates the UV absorption characteristic of aromatic rings and achieves a transmittance cut-off wavelength of 380 nm or lower while maintaining durability
3Object-generated harmful factors
If softer polishing layer material is used to reduce polishing defects, then micro-scratches and chatter marks are reduced, but conventional endpoint detection window materials do not pair well with softer materials, leading to increased polishing defectivity
Solution Approach 1:
The patent adjusts the hardness parameter of the endpoint detection window by controlling the polyol ratio and molecular weight, enabling the window to be softer and more compatible with soft polishing layers, thereby reducing polishing defects while maintaining endpoint detection functionality
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 ensures high transmittance at wavelengths below 400 nm, reduces polishing defects, and maintains durability, enabling accurate endpoint detection and improved planarity in semiconductor processing.
Implementation Method 1
the reaction mixture of (A) from 30 to 56 wt. % of one or more cycloaliphatic diisocyanates or polyisocyanates with (B) from 43 to 69.9999 wt. % of a polyol mixture
Implementation Method 2
which at a thickness of 2 mm would have a UV cut-off at a wavelength of 325 nm or lower and which are the product of a reaction mixture
Implementation Method 3
monitoring a reflected optical signal at a single wavelength, such as light from a laser source
Data Source
AI summary
The present invention provides a chemical mechanical (CMP) polishing pad for polishing, for example, a semiconductor substrate, having one or more endpoint detection windows (windows) which at a thickness of 2 mm would have a UV cut-off at a wavelength of 325 nm or lower which are the product of a reaction mixture of (A) from 30 to 56 wt. % of one or more cycloaliphatic diisocyanates or polyisocyanates with (B) from 43 to 69.9999 a polyol mixture of (i) a polymeric diol having an average molecular weight of from 500 to 1,500, such as a polycarbonate diol for hard windows and a polyether polyol for soft windows and (ii) a triol having an average to molecular weight of from 120 to 320 in a weight ratio of (B)(i) polymeric diol to (B)(ii) triol ranging from 1.6:1 to 5.2:1, and a catalyst, preferably a secondary or tertiary amine or bismuth neodecanoate, all weight percent's based on the total solids weight of the reaction mixture.