Wafer Thickness Measurement Using Interferometer and Distance References
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Solution Overview
Problem
Existing wafer thickness measurement devices rely on the uniformity of a sample piece's thickness, limiting their accuracy, and do not fully utilize 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 sample piece's uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a sample piece with known uniform thickness is used as a reference, then the measurement process is simplified, but the measurement precision is limited by the uniformity of the sample piece
Solution Approach 1:
The invention extracts the reference function from a physical sample piece to a virtual reference plane defined by the inclined surface. Instead of relying on a physical reference piece with uniform thickness, the system uses an optically defined reference plane that can be precisely established through the interferometer, thereby eliminating the limitation of physical sample uniformity while maintaining measurement simplicity
Solution Approach 2:
The invention replaces the mechanical reference system (physical sample piece with uniform thickness) with an optical reference system (interferometer-based measurement). The optical interferometer creates a virtual reference plane that is not constrained by material uniformity, allowing measurement precision to reach the optical wavelength level while keeping the measurement process straightforward
2Measurement precision
If a sample piece with high accuracy and uniform thickness is used, then the measurement precision improves, but the device complexity increases and the full performance of the optical interferometer is not utilized
Solution Approach 1:
The invention replaces the complex mechanical reference system requiring high-precision uniform sample pieces with a simpler optical reference system. The interferometer generates a virtual reference plane through optical interference, eliminating the need for physically perfect reference samples and fully utilizing the optical interferometer's precision capabilities
Solution Approach 2:
The invention creates a virtual copy of the reference plane through optical interference patterns rather than using a physical reference piece. This optical copy can be precisely defined and reproduced without the manufacturing constraints of physical samples, reducing device complexity while maintaining or improving measurement precision
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.
Implementation Method 1
an optical heterodyne interferometer that measures a displacement of a wafer
Data Source
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, and obtains a thickness, of the wafer, at the measurement point.