Wafer Thickness Measurement Using Dual Single-Shot Interferometers
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Solution Overview
Problem
Existing methods for measuring semiconductor wafer thickness and shape variation are prone to errors due to vibration and air turbulence, and require multiple data acquisitions, making them inefficient and sensitive to environmental changes.
Innovation Solution
The use of two single-shot phase shift interferometers that acquire data simultaneously on both sides of the wafer, allowing for fast shutter speed and phase averaging techniques to minimize vibration and air turbulence effects, enabling accurate thickness and shape measurement in a single data acquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple data acquisitions are used to improve measurement accuracy, then measurement precision is improved, but measurement time increases and productivity decreases
Solution Approach 1:
The measurement system is divided into two independent interferometers that simultaneously measure opposite surfaces of the wafer. This segmentation allows parallel data acquisition, eliminating the need for multiple sequential measurements while maintaining measurement accuracy through simultaneous capture of both surface profiles.
Solution Approach 2:
The system performs continuous measurement by using two interferometers that operate simultaneously and continuously on both wafer surfaces. The fast shutter speed enables the measurement to be completed within a fraction of a camera frame time, ensuring continuous operation without interruption or repeated acquisitions.
2Reliability
If fast shutter speed is used to reduce vibration effects, then measurement reliability is improved, but the ability to capture sufficient phase information may be compromised
Solution Approach 1:
The system applies preliminary phase shifting to the interferometric fringes before capture. By pre-modulating the phase information and using phase averaging techniques on the captured fringes, the system can extract accurate phase data even from single-shot measurements with fast shutter speeds, thereby maintaining both reliability and precision.
Solution Approach 2:
The system uses phase averaging techniques that effectively provide feedback by comparing and averaging multiple phase measurements. This feedback mechanism allows the system to maintain high measurement reliability and accuracy even when using fast shutter speeds that capture only a single moment in time.
3Productivity
If two interferometers are used to measure both sides of the wafer simultaneously, then productivity is improved, but device complexity increases
Solution Approach 1:
The two interferometers used in the system are identical and perform the same function of measuring wafer surfaces. This universality simplifies the overall system design and operation, as both instruments can be calibrated and operated using the same procedures, reducing operational complexity despite the increased number of components.
Solution Approach 2:
The system combines the measurement functions of two interferometers into a single integrated measurement process. By merging the data acquisition and processing workflows of both interferometers, the system achieves simultaneous two-sided measurement while managing complexity through unified control and analysis procedures.
4Productivity
If single-shot measurement is used to improve throughput, then productivity is improved, but measurement precision deteriorates due to vibration and air turbulence
Solution Approach 1:
The system converts the harmful effects of vibration and air turbulence into beneficial measurement conditions. By using fast shutter speeds to freeze motion and phase averaging techniques to filter out turbulence effects, the system transforms environmental disturbances into manageable factors that do not compromise measurement precision while maintaining single-shot productivity.
Solution Approach 2:
The system applies preliminary phase shifting and uses fast shutter speeds to capture fringes before vibration and turbulence can significantly affect the measurement. This preliminary capture of stable phase information enables single-shot measurement with high precision, eliminating the need for multiple acquisitions while maintaining accuracy.
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 approach provides robust and accurate simultaneous measurement of wafer thickness and shape variation, reducing measurement errors caused by vibration and air turbulence, while improving throughput by completing data acquisition within a fraction of a camera frame time.
Implementation Method 1
two single-shot phase-shifting interferometers to simultaneously measure wafer shape and thickness variation
Data Source
AI summary
A method and system is disclosed for utilizing two single-shot phase shift interferometers to simultaneously measure wafer shape and thickness variation of two sides of a wafer.This system is able to extract the front height, the back height, and the thickness variation of a wafer in a single data acquisition.This system, when utilized with a fast shutter speed, decreases the insensitivity to vibration. Algorithms are introduced that extract the true thickness variation of a wafer even when the wafer is vibrating.The effects of air turbulence can be reduced by a phase averaging technique.