Double-Side Polishing Method for Wafer Flatness Control
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Solution Overview
Problem
Conventional double-side polishing methods struggle to achieve high flatness of the entire wafer, particularly the outer circumference, due to limitations in measuring and adjusting for variations in carrier thickness and wear, leading to issues like sag and rise, which affect yield and productivity.
Innovation Solution
A double-side polishing method that includes a high-speed polishing step followed by a low-speed step, with precise measurement of the wafer's cross-sectional shape using optical reflection interferometry and adjustment of polishing conditions based on quantified flatness, allowing for targeted thickness adjustments to improve flatness across the entire wafer, including the outermost circumference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the polishing rate is increased to improve productivity, then the polishing efficiency is improved, but the flatness precision deteriorates
Solution Approach 1:
The invention performs preliminary measurement of the wafer's outer circumference flatness before the polishing process using a confocal microscope. This preliminary measurement allows the system to pre-calculate target thickness values that will achieve desired flatness, enabling high-speed polishing to proceed with pre-determined parameters that ensure both speed and precision.
Solution Approach 2:
The system implements feedback control by measuring the actual outer circumference flatness after polishing and comparing it with target values. The measured data is used to adjust polishing parameters for subsequent wafers, creating a closed-loop control system that maintains high precision even at high polishing rates.
2Device complexity
If conventional measurement methods are used to measure wafer flatness, then the measurement process is simple, but the measurement precision of the outer circumference deteriorates
Solution Approach 1:
The invention introduces a confocal microscope as an intermediary measurement device specifically for measuring the outer circumference region. This intermediary device provides high-precision measurement of the critical outer circumference area without replacing the standard interferometry system used for general flatness measurement, thus maintaining overall system simplicity while enhancing local measurement capability.
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 method enables precise measurement and improvement of the wafer's flatness up to the outermost circumference without reducing productivity, effectively addressing the challenges of sag and rise, thereby enhancing the yield of semiconductor devices.
Implementation Method 1
precise measurement of the wafer's cross-sectional shape using optical reflection interferometry
Implementation Method 2
double-side polishing process simultaneously polishing both surfaces of a wafer that is held with a carrier and interposed between polishing pads
Data Source
AI summary
The invention provides a double-side polishing method including first polishing at a high polishing rate, second polishing at a low polishing rate, dividing a straight line extending between the outermost circumferences of the wafer through the center into prescribed sections, and optically measuring a cross-sectional shape of the sections; applying a weight predetermined for each section to the cross-sectional shape to quantify flatness of each section; and determining polishing conditions of the first and second polishing in subsequent polishing on a basis of the quantified flatness, wherein a beam diameter of a measurement apparatus used to measure the cross-sectional shape of outermost sections is smaller than that used to measure the cross-sectional shape of the other section. The method can measure the shape of the wafer up to its outermost circumference with high precision without reducing productivity, and improve the flatness of the entire wafer including its outermost circumference.