Lithographic Projection System Aberration Calibration
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Solution Overview
Problem
Current lithographic apparatuses face challenges in accurately predicting and mitigating aberrations in projection systems, particularly due to heat-induced distortions, which affect the quality of pattern projection onto substrates, and existing calibration methods are inadequate for fast heating effects with limited measurement frequency and noise.
Innovation Solution
A method and apparatus for calibrating a projection system heating model by rapidly measuring aberrations during exposure and cooling phases with frequent data points, using temporal and amplitude modulation of the radiation beam, and maintaining consistent numerical aperture, to accurately model and correct heat-induced aberrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurements are taken frequently to capture fast heating effects, then measurement precision improves, but the time required for calibration increases
Solution Approach 1:
The system performs preliminary actions by continuously monitoring aberrations during normal exposure operations and storing this data for later analysis. This allows the calibration process to utilize pre-collected measurement data rather than requiring dedicated calibration time, thereby improving measurement precision without increasing calibration time.
Solution Approach 2:
The measurement system operates continuously during exposure fields, collecting aberration data throughout the exposure process rather than taking discrete measurements. This continuous data collection captures fast heating effects effectively while utilizing otherwise wasted time during normal operations, improving precision without extending calibration duration.
2Measurement precision
If the measurement time period is reduced to capture fast heating effects, then measurement precision improves, but productivity decreases
Solution Approach 1:
The system merges the measurement function with the normal exposure operation by collecting aberration data during routine substrate exposure. This integration allows precise measurements of fast heating effects to be obtained without adding separate measurement steps that would reduce productivity, as the same infrastructure serves dual purposes.
Solution Approach 2:
The measurement system serves itself by utilizing the existing exposure radiation and optical path to perform aberration measurements during normal operations. The system automatically collects and stores data without requiring additional resources or time, achieving high measurement precision while maintaining full substrate exposure throughput.
3Manufacturing precision
If aberrations are measured during exposure fields, then the heating model calibration accuracy improves, but device complexity increases
Solution Approach 1:
The measurement system is designed with multi-functionality, using the same optical path and detection infrastructure for both normal substrate exposure and aberration measurement. This universal approach allows accurate heating model calibration without requiring separate dedicated measurement equipment, thereby improving calibration accuracy while minimizing device complexity.
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 enables precise prediction and correction of aberrations, improving the accuracy of pattern projection and reducing calibration time, thereby enhancing the availability and efficiency of lithographic apparatuses.
Implementation Method 1
The projection system which is used to image the pattern onto the substrate will induce some aberrations in the wavefront of the projected image
Implementation Method 2
passing exposure radiation through a projection system to expose one or more exposure fields on a substrate provided on a substrate table; and making measurements of the aberration in the projection system caused by the exposure radiation
Data Source
AI summary
A method of calibrating a projection system heating model to predict an aberration in a projection system in a lithographic apparatus, the method comprising passing exposure radiation through a projection system to expose one or more exposure fields on a substrate provided on a substrate table, making measurements of the aberration in the projection system caused by the exposure radiation, wherein the time period between measurements is less than the time period that would be taken to expose all exposure fields on the substrate.