Silicon Wafer Polishing via Dual-Stage Temperature Control
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Solution Overview
Problem
Current polishing methods for silicon wafers face a trade-off between achieving higher flatness and reducing surface roughness, as the rotation rate of the turntable affects both properties, and existing techniques fail to improve both simultaneously.
Innovation Solution
A method involving two polishing stages with a first stage using an aqueous alkaline solution containing abrasive grains and a second stage using a polymer solution without abrasive grains, where the polishing pad's surface temperature in the second stage is controlled to be at least 2°C higher than in the first stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If constant polishing conditions are used in both stages, then process simplicity is maintained, but both flatness and surface roughness cannot be improved simultaneously
Solution Approach 1:
The polishing process is segmented into two distinct stages with different slurry compositions and optimized conditions for each stage. The first stage uses a slurry containing abrasive grains optimized for flatness improvement, while the second stage uses a slurry without abrasive grains optimized for surface roughness reduction. This segmentation allows simultaneous improvement of both properties despite increased process complexity.
Solution Approach 2:
The invention changes multiple parameters between stages including slurry composition (presence/absence of abrasive grains), rotation rate of the turn table, and other polishing conditions. These parameter changes enable optimization for different objectives in each stage, allowing both flatness and surface roughness to be improved simultaneously rather than being constrained by constant conditions.
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
This approach allows for improved flatness and reduced surface roughness of silicon wafers by precisely controlling the polishing pad's temperature, enabling both properties to be enhanced simultaneously.
Implementation Method 1
a first polishing step of polishing a surface of the silicon wafer by bringing the silicon wafer held by a polishing head into sliding contact with a polishing pad attached to a turn table while supplying an aqueous alkaline solution containing an abrasive grain onto the polishing pad
Implementation Method 2
a second polishing step of polishing the surface of the silicon wafer by bringing the silicon wafer into sliding contact with the polishing pad while supplying an aqueous alkaline solution containing a polymer without containing an abrasive grain onto the polishing pad
Implementation Method 3
the polishing pad is controlled to have a surface temperature in such a way that the surface temperature of the polishing pad in the second polishing step is higher than the surface temperature of the polishing pad in the first polishing step by 2° C. or more
Data Source
AI summary
A method for polishing a silicon wafer, including: a first polishing step of polishing a silicon wafer surface by bringing the wafer held by a polishing head into sliding contact with a polishing pad attached to a turn table while supplying an aqueous alkaline solution containing abrasive grains onto the polishing pad, and a second polishing step of polishing the silicon wafer surface by bringing the wafer into sliding contact with the polishing pad while supplying an aqueous alkaline solution containing a polymer without containing abrasive grains onto the polishing pad, wherein the surface temperature of the polishing pad is controlled such that the surface temperature of the polishing pad in the second polishing step is higher than the surface temperature of the polishing pad in the first polishing step by 2° C. or more. This successfully achieves both of higher flatness and reduction in surface roughness.