Wafer Thickness Measurement Using Interferometer Phase Referencing
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Solution Overview
Problem
Existing wafer thickness measurement devices rely on sample pieces with uniform thickness for accuracy, limiting the measurement precision and not fully utilizing the performance of optical interferometers.
Innovation Solution
A wafer thickness measurement device utilizing a pair of optical interferometers and distance meters to measure a reference point on a reference piece and the wafer, calculating thickness based on phase differences and absolute distances to achieve high accuracy without relying on the uniformity of the sample piece.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sample piece with uniform thickness is used as a reference for measurement, then the measurement can be performed using addition or subtraction of displacement amounts, but the measurement accuracy is limited by the uniformity of the sample piece thickness
Solution Approach 1:
The invention extracts the reference measurement process from the actual wafer measurement process. By separately measuring a reference surface (z1) and the wafer surface (z2) using the same optical interferometer, the system eliminates the need for a physical sample piece with uniform thickness. The thickness is calculated as the difference between these two measurements, thereby removing the constraint of sample piece uniformity while maintaining high measurement accuracy.
Solution Approach 2:
The invention introduces a reference surface as an intermediary element between the optical interferometer and the wafer measurement. This reference surface serves as a stable baseline (z1) against which the wafer thickness is measured (z2). By using this intermediary reference surface instead of a sample piece, the system achieves high measurement accuracy without being constrained by the uniformity of any physical sample piece.
2Measurement precision
If an optical heterodyne interferometer is used to measure wafer thickness, then high measurement sensitivity is achieved, but the measurement process becomes complex and requires sample pieces with high uniformity
Solution Approach 1:
The invention extracts the reference measurement (z1) from the wafer measurement (z2) as a separate, independent process. This allows the optical interferometer to be used in its full capability for both measurements without requiring complex sample piece preparation. The system complexity is reduced by eliminating the need for specialized sample pieces with high uniformity, while maintaining the high sensitivity of the optical heterodyne interferometer.
3Measurement precision
If a sample piece with high accuracy and uniform thickness is required, then measurement accuracy can be maintained, but the device cannot fully utilize the performance of the optical interferometer
Solution Approach 1:
The invention extracts the measurement process from dependence on sample piece properties. By measuring a reference surface (z1) and the wafer surface (z2) separately with the optical interferometer, the system fully utilizes the interferometer's performance capabilities without being limited by sample piece uniformity. The thickness calculation (z2 - z1) maintains high accuracy while enabling full utilization of the optical interferometer's measurement capabilities.
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
Enables precise measurement of wafer thickness with an accuracy of several nanometers by leveraging the performance of optical interferometers, independent of the sample piece's uniformity, and allowing for high-speed and vibration-resistant measurements.
Implementation Method 1
an optical heterodyne interference measurement device, a thickness of a wafer
Data Source
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AI summary
A wafer thickness measurement device of the present invention obtains, based on: first and second interferometer reference measurement results obtained by measuring, with an A-surface optical interferometer and a B-surface optical interferometer, a reference measurement point on a reference piece having the reference measurement point at which the reference piece has a known thickness; first and second distance meter reference measurement results obtained by measuring the reference measurement point with an A-surface distance meter and a B-surface distance meter; first and second interferometer measurement results obtained by measuring a measurement point of the wafer with the A-surface optical interferometer and the B-surface optical interferometer; and first and second distance meter measurement results obtained by measuring the measurement point with the A-surface distance meter and the B-surface distance meter, a number of phases between a reference displacement based on the first and second interferometer reference measurement results and a displacement based on the first and second interferometer measurement results, and obtains a thickness, of the wafer, at the measurement point.