Transparent Microporous CMP Pad for Defect Reduction
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Solution Overview
Problem
Existing chemical-mechanical polishing pads suffer from high defectivity, dishing, and erosion due to wide pore size distributions and random pore morphologies, leading to issues like wafer scratches and inconsistent optical transmittance, particularly in advanced CMP applications for 65 nanometer or lower nodes.
Innovation Solution
A microporous polymeric foam polishing pad with a narrow pore size distribution of 0.05µm to 5µm and predominantly closed-cell structure, made from thermoplastic polyurethane, is developed, which is produced by combining a solid polymer sheet with a supercritical gas under elevated temperature and pressure, resulting in a substrate with controlled pore morphology and improved light transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a solid polyurethane window is used in the polishing pad, then the pad provides structural support and wear resistance, but the optical transmittance decreases steadily during the polishing pad's lifetime due to scratching
Solution Approach 1:
The patent replaces the solid polyurethane window with a microporous polymeric foam window having controlled pore sizes (0.05µm to 5µm) and predominantly closed-cell structure. The porous structure prevents residue deposition while maintaining optical transmittance, eliminating the scratching problem inherent in solid windows.
Solution Approach 2:
The patent uses a microporous polymeric foam composite material that combines the structural support and wear resistance needed for polishing pad windows with a pore structure that maintains optical transmittance. This composite material integrates multiple functions (structural integrity, wear resistance, and optical clarity) that cannot be achieved with solid polyurethane alone.
2Quantity of substance
If polishing pads have wide pore size distributions and random pore morphologies, then the pads provide high absorbency and slurry transport, but the pads generate high defectivity, dishing, and erosion
Solution Approach 1:
The patent specifies precise pore size parameters (0.05µm to 5µm) and closed-cell structure for the microporous polymeric foam window, changing the physical parameters from random/wide distribution to controlled/narrow distribution. This parameter control eliminates residue deposition while maintaining adequate slurry transport.
Solution Approach 2:
The patent applies different pore structure characteristics to different regions: the window region has controlled microporous structure (0.05µm to 5µm) for optical clarity and residue prevention, while the bulk polishing pad can have different porosity for slurry transport. This local differentiation optimizes both optical performance and polishing performance.
3Duration of action of stationary object
If the polishing pad window has slower wear rate than the remainder of the polishing pad, then the window provides durability, but a lump forms in the polishing pad leading to undesirable polishing defects
Solution Approach 1:
The microporous polymeric foam window material provides wear characteristics matched to the bulk polishing pad through its controlled pore structure. The porous nature allows the window to wear at a rate consistent with the surrounding pad material, preventing lump formation while maintaining structural integrity.
4Strength
If residue deposits in the polishing pad pores, then the pads provide mechanical polishing action, but the residue causes wafer scratches and increased defectivity
Solution Approach 1:
The patent controls pore size parameters (0.05µm to 5µm) and closed-cell structure to prevent residue deposition while maintaining mechanical polishing action. The specific pore size range is small enough to prevent residue entrapment but sufficient to maintain the necessary mechanical properties for effective polishing.
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 polishing pad achieves reduced defectivity, consistent light transmittance over its lifetime, and enhanced polishing performance by preventing residue deposition and maintaining uniformity, thus minimizing the need for endpoint detection system adjustments and reducing polishing defects.
Implementation Method 1
combining a solid polymer sheet with a supercritical gas under elevated temperature and pressure until the gas has saturated the polymer sheet
Implementation Method 2
releasing the pressure to afford a microporous polymeric foam from the gas saturated polymer sheet
Data Source
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AI summary
The invention is directed to a chemical-mechanical polishing pad substrate comprising a microporous closed-cell foam characterized by a narrow pore size distribution in the range of 0.01 microns to 10 microns. The polishing pad is produced by foaming a solid polymer sheet with a supercritical gas under an elevated temperature and pressure until the sheet is saturated with gas. The invention is further directed to a polishing pad comprising the polishing pad substrate, a method of polishing comprising the use of the polishing pad substrate, and a chemical-mechanical apparatus comprising the polishing pad substrate.