Lithographic Calibration Using Multi-Focal Plane Interpolation
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Solution Overview
Problem
Current lithographic simulation calibration techniques are limited to a narrow range of conditions, leading to inaccurate predictions of manufacturing performance due to differences between ideal and actual photomask patterns caused by diffraction and optical-proximity effects, which complicates the design and manufacturing of smaller integrated circuit features.
Innovation Solution
A computer system determines calibration parameters for a lithographic process by analyzing images at multiple focal planes and using an interpolation function to provide accurate calibration parameters for arbitrary focal planes, incorporating critical-dimension scanning-electron-microscope images and quadratic functions to improve simulation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If calibration is performed only for a limited range of lithographic conditions, then the calibration process remains simple and quick, but the simulation accuracy deteriorates when applied to conditions outside the calibrated range
Solution Approach 1:
The patent extends calibration from a single focal plane to multiple focal planes (first, second, and third focal planes), adding the focal plane dimension to the calibration process. This multi-plane calibration approach enables accurate simulation across a broader range of lithographic conditions while maintaining a systematic calibration workflow
Solution Approach 2:
The patent performs calibration measurements at multiple focal planes in advance, storing the calibration parameters for later use. This preliminary multi-plane calibration eliminates the need to perform calibration during actual production, improving both accuracy and efficiency by preparing calibration data beforehand for the full range of conditions
2Measurement precision
If images are captured at multiple focal planes, then calibration accuracy across different conditions improves, but the measurement time and data processing complexity increase
Solution Approach 1:
The patent divides the calibration process into separate measurements at distinct focal planes (first, second, and third focal planes). Each focal plane is calibrated independently, allowing for systematic data collection and processing. This segmentation enables efficient use of calibration data by isolating measurements to specific planes rather than requiring continuous multi-plane monitoring
3Manufacturing precision
If the photo-mask pattern is designed to compensate for diffraction and optical-proximity effects, then the target wafer pattern can be achieved, but the photo-mask design becomes increasingly complex and difficult to manufacture
Solution Approach 1:
The patent uses lithographic simulation with calibrated parameters to predict the actual wafer pattern outcome before manufacturing. This feedback loop allows designers to adjust the photo-mask pattern iteratively, using the simulation results to guide design modifications and achieve the desired wafer pattern while managing photo-mask complexity
Solution Approach 2:
The patent employs calibrated parameters derived from multi-plane measurements to adjust and optimize photo-mask design parameters. By using accurate calibration data across multiple focal planes, the design process can systematically modify mask parameters to compensate for diffraction and optical-proximity effects, achieving target patterns with controlled complexity
Data Source
AI summary
A technique for determining a set of calibration parameters for use in a model of a photo-lithographic process is described. In this calibration technique, images of a test pattern that was produced using the photo-lithographic process are used to determine corresponding sets of calibration parameters. These images are associated with at least three different focal planes in an optical system, such as a photo-lithographic system that implements the photo-lithographic process. Moreover, an interpolation function is determined using the sets of calibration parameters. This interpolation function can be used to determine calibration parameters at an arbitrary focal plane in the photo-lithographic system for use in simulations of the photolithographic process, where the set of calibration parameters are used in a set of transmission cross coefficients in the model of the photo-lithographic process.