Substrate Height Measurement Normalization
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Solution Overview
Problem
Existing substrate height measurement technologies in lithographic apparatuses face inaccuracies due to optical measurement errors and differences in sensor footprints, leading to incorrect focus control and product defects.
Innovation Solution
An apparatus comprising multiple sensors with different footprints, where a processor normalizes data from each sensor by convolving it with the footprint of the other sensor to minimize measurement discrepancies, allowing for accurate height mapping and focus adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple sensors with different footprints are used to measure substrate height, then measurement accuracy is improved, but measurement discrepancies due to footprint differences increase
Solution Approach 1:
The patent introduces an intermediary computational process (normalization algorithm) that mediates between measurements from sensors with different footprints. The processor normalizes the measurements by applying correction factors derived from the known footprint characteristics, enabling consistent comparison and combination of data from multiple sensor types without requiring identical sensor geometries
Solution Approach 2:
The patent changes the parameter representation of sensor measurements by applying normalization transformations. Instead of using raw measurements directly, the system transforms the measurement data by incorporating footprint information as a correction parameter, allowing measurements from different sensor footprints to be reconciled into a unified height map
2Speed
If optical sensors are used to measure substrate height, then measurement speed is improved, but optical measurement errors increase
Solution Approach 1:
The patent merges measurements from multiple sensor types (including optical sensors and non-optical sensors) into a unified height measurement. By combining the high-speed optical measurements with complementary measurements from other sensor types, the system achieves both high measurement rates and improved accuracy, as the complementary sensors help correct optical measurement errors
Solution Approach 2:
The patent implements a feedback mechanism where measurements from multiple sensors are cross-validated and used to correct each other. The processor compares measurements from different sensor types and uses discrepancies as feedback to refine the final height measurement, thereby reducing optical measurement errors while maintaining high measurement rates
Data Source
AI summary
An apparatus for measuring a height of a substrate for processing in a lithographic apparatus is disclosed. The apparatus comprises a first sensor for sensing a height of the substrate over a first area. The apparatus also comprises a second sensor for sensing a height of the substrate over a second area. The apparatus further comprises a processor adapted to normalize first data corresponding to a signal from the first sensor with a second sensor footprint to produce a first normalized height data, and to normalize second data corresponding to a signal from the second sensor with a first sensor footprint to produce a second normalized height data. The processor is adapted to determine a correction to a measured height of the substrate based on a difference between the first and second normalized height data.