Semiconductor Wafer Thickness Measurement With Reference Wafer Compensation
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Solution Overview
Problem
Existing measurement methods for semiconductor wafer thickness are affected by changes in ambient temperature, leading to fluctuations in measurement accuracy.
Innovation Solution
A method and apparatus that simultaneously irradiate a sample wafer and a reference wafer with light, perform frequency analysis of interference signals, and calculate the sample wafer's thickness using peak positions and a proportional formula, while adjusting for temperature changes using correction factors and temperature control mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurement is performed using light irradiation on semiconductor wafer, then thickness measurement can be performed, but measurement accuracy deteriorates when ambient temperature changes
Solution Approach 1:
The patent introduces a reference wafer with uniform thickness that copies the temperature-dependent optical properties of the sample wafer. By measuring both the sample wafer and reference wafer under identical temperature conditions, the system creates a controlled comparison that isolates the thickness measurement from temperature-induced optical variations, thereby maintaining measurement accuracy despite ambient temperature changes.
Solution Approach 2:
The reference wafer acts as an intermediary element that mediates between the sample wafer and the measurement system. It provides a baseline that accounts for temperature effects, allowing the system to differentiate between actual thickness changes and temperature-induced measurement artifacts through comparative analysis of interference patterns from both wafers.
2Ease of operation
If single wafer measurement method is used, then measurement process is simple, but measurement accuracy is affected by temperature-dependent optical properties
Solution Approach 1:
The patent merges the measurement of the sample wafer with the measurement of a reference wafer into a single operational process. Both wafers are irradiated with light simultaneously, and their interference patterns are captured and processed together. This combined approach maintains operational simplicity while improving accuracy by using the reference wafer to compensate for temperature-dependent optical property variations.
Solution Approach 2:
The reference wafer serves as a copy with known uniform thickness that replicates the sample wafer's temperature response characteristics. By measuring both copies under the same conditions, the system can distinguish between actual sample thickness variations and temperature-induced measurement changes, thereby maintaining simplicity while enhancing precision.
3Measurement precision
If reference wafer with uniform thickness is introduced, then temperature effect can be compensated, but device complexity increases
Solution Approach 1:
The patent combines the sample wafer and reference wafer into a single measurement chamber and optical path, allowing both to be measured simultaneously using the same light source and detection system. This merging approach compensates for temperature effects through comparative measurement while avoiding the need for separate temperature-controlled environments or complex additional instrumentation, thus limiting the increase in device complexity.
Solution Approach 2:
By using a reference wafer that is identical in material and structure to the sample wafer but with known uniform thickness, the system creates a simple copy that can be measured alongside the sample. This copying approach enables temperature compensation through ratio calculations without requiring complex temperature sensors, actuators, or environmental control systems, thereby minimizing the added complexity.
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 and apparatus reduce the impact of ambient temperature changes on measurement accuracy, enabling precise and accurate thickness measurement of semiconductor wafers.
Implementation Method 1
interference signals of the light reflected on front and back surfaces of the sample wafer and the reference wafer are received
Data Source
AI summary
A measurement apparatus for measuring a thickness of a semiconductor wafer includes: an optical system configured to perpendicularly irradiate a sample wafer and a reference wafer with light, and receive interference signals of the light reflected on front and back surfaces of the respective wafers; a signal processor configured to perform frequency analysis of the interference signals received by the optical system to obtain peak positions of a point spread function of the respective wafers; and a calculator configured to calculate a thickness “tsample” of the sample wafer based on the peak position “x” of the sample wafer and the peak position “y” of the reference wafer obtained by the signal processor, and a thickness “treference” of the reference wafer.