Substrate Height Measurement Correction for Lithography
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Solution Overview
Problem
Conventional lithographic apparatuses face challenges in obtaining accurate height maps of substrates due to dynamic effects caused by non-uniform substrate velocities, leading to measurement inaccuracies and potential defocus during exposure.
Innovation Solution
A method and system for calculating a corrected substrate height map by subtracting a correction map from the initial height map. The correction map is derived from the difference between height maps obtained at different substrate velocities, allowing for compensation of acceleration-induced deformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If measurement samples are taken at constant sampling rate while substrate moves at non-constant velocity, then measurement duration is reduced, but measurement precision deteriorates due to non-uniform sample distribution and acceleration-induced deformations
Solution Approach 1:
The patent applies parameter changes by adjusting the sampling rate dynamically based on the substrate velocity. Instead of using a constant sampling rate, the system varies the sampling interval according to the instantaneous velocity of the substrate, ensuring that samples are taken at equidistant positions along the measurement trajectory even when the substrate accelerates or decelerates. This resolves the contradiction by maintaining measurement precision while allowing non-constant substrate velocity.
Solution Approach 2:
The system implements feedback by continuously monitoring the substrate velocity and using this information to adjust the sampling timing. The measured velocity signal feeds back to the sampling control mechanism, which then modifies the sampling rate in real-time to compensate for velocity variations. This feedback loop ensures that acceleration-induced deformations do not compromise measurement accuracy, while still enabling reduced measurement duration through non-constant velocity operation.
2Productivity
If substrate velocity is increased to reduce measurement time, then productivity improves, but measurement precision deteriorates due to acceleration-induced deformations
Solution Approach 1:
The patent changes the parameter of sampling rate to match the substrate velocity profile. By increasing the sampling rate during high-velocity phases and decreasing it during low-velocity phases, the system maintains equidistant sampling along the measurement path. This allows the substrate to move at higher average velocities (improving productivity) while preserving measurement precision through adaptive sampling.
Solution Approach 2:
The system transitions from static constant-rate sampling to dynamic velocity-adaptive sampling. The sampling mechanism becomes dynamic, adjusting its operation in real-time according to the substrate's motion state. This dynamic approach enables the system to exploit higher substrate velocities for faster measurements while automatically compensating for acceleration effects, thus resolving the contradiction between measurement speed and precision.
Data Source
AI summary
The present invention provides a method for calculating a corrected substrate height map of a first substrate using a height level sensor. The method comprises: sampling the first substrate by means of the height level sensor with the first substrate moving with a first velocity, wherein the first velocity is a first at least partially non-constant velocity of the first substrate with respect to the height level sensor, to generate a first height level data, generating a first height map based on the first height level data, and calculating a corrected substrate height map by subtracting a correction map from the first height map, wherein the correction map is calculated from the difference between a first velocity height map and a second velocity height map.