Angular Error Correction for Rotary Wafer Inspection
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Solution Overview
Problem
Rotary inspection systems for semiconductor wafers face angular errors due to misalignment of inspection spots with the axis of rotation, leading to incorrect data mapping and defective defect detection, especially as design rules and process windows shrink.
Innovation Solution
The implementation of an angular error correction method that calculates and applies a correction value based on the distance between the inspection spot and the axis of rotation, allowing for accurate data acquisition by shifting the timing of data collection or remapping data to corrected polar coordinates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If data acquisition is triggered by interpolation of encoder pulses from a rotary encoder, then the system can operate with simple timing control, but angular error is introduced causing data to be mapped to incorrect locations on the wafer surface
Solution Approach 1:
The system performs preliminary calculation of angular error correction values based on the known offset between the inspection spot and the axis of rotation. These correction values are pre-computed and stored, allowing the data acquisition system to apply the correct timing adjustment without complex real-time calculations, thus maintaining operational simplicity while achieving measurement precision.
2Adaptability or versatility
If the inspection spot is not aligned with the trajectory of the axis of rotation, then the system can inspect multiple locations, but angular error is introduced in the representation of the position of the inspection spot
Solution Approach 1:
The system changes the parameter of angular position representation by applying correction values that account for the offset between the inspection spot and the axis of rotation. The rotary encoder continues to provide angular positions relative to the axis of rotation, but the system transforms these into correct angular positions relative to the inspection spot by adding the pre-calculated correction values, thus maintaining manufacturing precision while preserving inspection location flexibility.
3Device complexity
If angular error correction is applied as a post-processing step, then the data collection process remains simple, but the correction must be applied to each sample individually
Solution Approach 1:
The system performs preliminary calculation of angular error correction values and stores them in a lookup table or memory structure. During data collection, the system simply retrieves the appropriate correction value based on the current angular position and applies it, rather than performing complex real-time calculations. This approach maintains data collection simplicity while improving processing efficiency through pre-computed corrections.
Data Source
AI summary
A wafer is moved under an inspection spot by a rotary inspection system. The system rotates the wafer about an axis of rotation and translates the wafer along a linear trajectory. When the inspection spot is not aligned with the trajectory of the axis of rotation, an angular error is introduced in the representation of the position of the inspection spot with respect to the wafer by the rotary encoder. The angular error is corrected based on an angular error correction value. The angular error correction value is determined based on the distance between the inspection spot and the trajectory of the axis of rotation, the radial distance between the axis of rotation and the inspection spot at a first instance of a particular angular position, and a second radial distance between the axis of rotation and the inspection location at a second instance of the angular position.