Overlay Measurement Method Using Three Predetermined Patterns
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Solution Overview
Problem
Current overlay measurement methods in photolithographic processes for semiconductor manufacturing suffer from measurement deviations due to errors in refractive index differences, leading to inaccurate reflection of real positions between successive layers.
Innovation Solution
A method involving three predetermined patterns on a wafer, where image points are obtained through inspection, and a real offset value is calculated using a computer system to correct overlay errors, eliminating detection errors caused by refractive index differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional overlay measurement methods are used, then measurement process is simple, but measurement precision deteriorates due to refractive index errors
Solution Approach 1:
The measurement system is segmented into multiple independent measurement points (first, second, and third measurement points) distributed across the wafer. Each point provides an independent measurement that contributes to the overall overlay calculation, allowing the system to eliminate refractive index errors through comparative analysis of multiple segmented measurements rather than relying on a single measurement point
Solution Approach 2:
The patent introduces predetermined patterns as intermediary elements between the measurement system and the actual overlay being measured. These patterns serve as reference markers that mediate the measurement process, enabling the calculation of real offset values by comparing the positions of image points relative to known pattern positions, thereby eliminating detection errors
2Measurement precision
If three predetermined patterns and calculation process are used, then overlay measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The three predetermined patterns are pre-defined and pre-positioned on the wafer before the actual overlay measurement is performed. This preliminary arrangement of reference patterns simplifies the measurement process by providing ready-made reference points that eliminate the need for complex real-time calculations or adjustments during the measurement itself
Solution Approach 2:
The system uses feedback from the measured image point positions to calculate real offset values that correct for refractive index errors. The measurement process incorporates feedback loops where the positions of image points relative to predetermined patterns are continuously measured and used to refine the overlay calculation, improving accuracy while managing complexity through iterative correction
Data Source
AI summary
An overlay measurement method includes providing three predetermined patterns, including a first predetermined pattern, a second predetermined pattern and a third predetermined pattern. An inspection process is then performed on said three predetermined patterns, to obtain three image points, including a first image point, a second image point and a third image point respectively. Next, a defining process is performed to define a default position, and a calculating process is performed to obtain a real offset value x=(p−q)*(c−a)/(a−b)+p.