Reference Spectrum Library for Variable-Rate Film Thickness Estimation
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Solution Overview
Problem
Conventional optical film-thickness measuring devices face inaccuracies in estimating film thickness due to variations in polishing rates that are not constant, leading to discrepancies between estimated and actual film thicknesses.
Innovation Solution
A method for producing a reference-spectrum library that involves measuring initial and final film thicknesses, generating reference spectra during polishing, calculating polishing index values, and determining a polishing-rate line to accurately reflect the actual polishing rate, thereby associating precise film thicknesses with the reference spectra.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a constant polishing rate is assumed to calculate reference film thicknesses, then the reference-spectrum library can be produced with simple linear calculations, but the accuracy of film thickness estimation deteriorates when actual polishing rates vary
Solution Approach 1:
The patent changes the parameter used for film thickness calculation from a constant polishing rate to a variable polishing rate that is calculated based on actual measured film thicknesses at different polishing times. This allows the system to adapt to varying polishing conditions and improve estimation accuracy without requiring complex pre-calibration for each possible polishing rate scenario
Solution Approach 2:
The patent implements a feedback mechanism where the actual film thicknesses measured at different polishing times are used to calculate the actual polishing rate, which then feeds back into the determination of reference film thicknesses. This closed-loop approach ensures that the reference-spectrum library reflects actual polishing behavior rather than assuming constant rates
2Measurement precision
If multiple intermediate film thickness measurements are taken during polishing to determine the polishing-rate line, then the accuracy of reference film thickness determination is improved, but the time and complexity of producing the reference-spectrum library increases
Solution Approach 1:
The patent takes measurements at multiple intermediate polishing times (excessive action) to ensure accurate determination of the polishing-rate line, rather than relying on just the initial and final measurements. This partial sampling approach provides sufficient data points to characterize the polishing rate variation without requiring continuous measurement
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 method improves the accuracy of film thickness estimation by accounting for variations in polishing rates, ensuring that the determined film thicknesses closely match the actual values.
Implementation Method 1
generate a measurement spectrum of reflected light from a workpiece
Implementation Method 2
polishing the reference workpiece with a polishing apparatus
Data Source
AI summary
A method of producing a reference-spectrum library that can improve an accuracy of film thicknesses corresponding to reference spectra is disclosed. The method includes: generating reference spectra of reflected light from the reference workpiece obtained at polishing times during polishing of the reference workpiece; calculating polishing index values indicative of a progress of polishing of the reference workpiece from the reference spectra; determining a polishing-rate line indicative of a relationship between film thickness and polishing time of the reference workpiece from the initial film thickness, the polishing index values, and the final film thickness; determining reference film thicknesses corresponding to the polishing index values based on the polishing-rate line; and producing the reference-spectrum library by associating the reference film thicknesses with the reference spectra, respectively.