Reflective Mask Data Correction for EUV Lithography
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Solution Overview
Problem
The EUV lithography technique faces challenges in achieving sufficient positional precision due to image shifts caused by mask surface unevenness and non-telecentric exposure systems, leading to inaccuracies in pattern transfer on the wafer.
Innovation Solution
A method is developed to generate writing pattern data for reflective masks by measuring and calculating the vertical position profile of the mask substrate, accounting for unevenness and local surface gradients, and correcting the design pattern data based on calculated image position shifts and optics parameters to achieve precise positional alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a non-telecentric reflective exposure system is used for EUV lithography, then the lithography technique can be implemented, but image shift occurs on the wafer due to mask surface unevenness
Solution Approach 1:
The patent measures the vertical position profile of the mask substrate before pattern writing, calculates the image shift caused by surface unevenness in advance, and corrects the writing pattern data beforehand. This preliminary correction action eliminates the image shift problem during actual exposure without requiring changes to the non-telecentric exposure system.
2Reliability
If the distance between mask and wafer is controlled to be constant, then depth of focus is secured, but image shift still occurs due to local unevenness in the irradiation region
Solution Approach 1:
The patent measures the vertical position at multiple discrete points across the mask substrate surface to obtain a detailed position profile. By analyzing local unevenness at each measurement point and calculating corresponding image shifts, the method applies localized corrections to the writing pattern data, ensuring positional precision is maintained across the entire irradiation region while preserving constant depth of focus.
3Manufacturing precision
If mask surface unevenness is measured and writing pattern data is corrected, then image shift is minimized, but additional measurement and calculation steps are required
Solution Approach 1:
The patent utilizes the existing non-telecentric exposure system's optical path and geometry to calculate image shifts based on measured mask surface profiles. The correction methodology leverages the system's inherent characteristics (angle of incidence, reduction ratio) to automatically compute and apply corrections, making the exposure system itself contribute to the correction process rather than requiring entirely separate correction equipment.
Data Source
AI summary
A method of generating writing pattern data of a reflective mask for use in a non-telecentric exposure tool comprises obtaining a vertical position profile by measuring vertical positions of a plurality of X, Y coordinates arbitrarily set on the surface of a blank mask substrate when mounted on a mask stage, or by measuring and calculating a flatness profile, calculating unevenness of the blank mask substrate surface from the vertical position profile, calculating a shift amount of an image position, generated in a wafer mounted on a wafer stage of the exposure tool, in accordance with the unevenness of the blank mask substrate and parameters of a non-telecentric optics of the exposure tool, and obtaining corrected writing pattern data by correcting design pattern data of the reflective mask based on the shift amount of the image position and a reduction ratio of a projection optics of the exposure tool.