Variable Intensity Threshold for Lithography Topography Compensation
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Solution Overview
Problem
Current Optical Proximity Correction (OPC) techniques fail to compensate for topography variations during optical lithography, leading to critical dimension (CD) variations in semiconductor manufacturing, which decrease yield and performance due to shrinking usable depth of focus (UDOF) and increased sensitivity to defocus caused by wafer surface topography.
Innovation Solution
A system that computes a variable intensity threshold based on the area densities of n-type, p-type, and field oxide features in the proximity of an evaluation point, using a statistical model fitted to process data, to accurately determine the critical dimension by comparing aerial-image intensity with a dynamically adjusted threshold instead of a constant threshold, thereby compensating for topography variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If constant intensity threshold is used in OPC, then the OPC process is simple, but topography variations cause CD variations that decrease yield
Solution Approach 1:
The patent transforms the static constant intensity threshold into a dynamic variable intensity threshold that adapts to local topography conditions. The threshold is adjusted based on the aerial-image intensity at each evaluation point, allowing the OPC process to compensate for topography-induced defocus variations while maintaining manufacturing feasibility through automated computation.
Solution Approach 2:
The patent applies different intensity thresholds to different regions of the layout based on local topography characteristics. By evaluating the aerial-image intensity at each evaluation point and computing a location-specific threshold, the method enables localized compensation for topography variations, ensuring each region is corrected according to its specific conditions rather than applying a uniform threshold.
2Manufacturing precision
If wavelength decreases and NA increases to improve integration density, then lithography resolution improves, but usable depth of focus decreases making the process more sensitive to topography variations
Solution Approach 1:
The patent changes the threshold parameter from a constant value to a variable value that depends on the local aerial-image intensity. This parameter transformation allows the system to adapt to the reduced depth of focus by dynamically adjusting the comparison threshold based on the actual intensity conditions at each evaluation point, thereby compensating for the increased sensitivity to focus variations.
Solution Approach 2:
The patent implements a feedback mechanism where the aerial-image intensity computed from the layout and optical model is used to determine the appropriate intensity threshold. This feedback loop allows the system to respond to actual intensity conditions caused by topography variations and adjust the threshold accordingly, improving reliability under high-NA, short-wavelength conditions.
Data Source
AI summary
One embodiment of the present invention provides a system that accurately determines a critical dimension of a feature in a layout by compensating for the effects of topography variation on the performance of an optical lithography process. During operation, the system first receives a layout. Next, the system computes and aerial-image intensity at an evaluation point in the layout using and optical lithography model that models the optical lithography process. Note that the aerial-image intensity is typically compared with a constant intensity threshold to determine a critical dimension of a feature in the layout. The system then computes an intensity threshold based on features in the proximity of the evaluation point, which compensates for the effects of topography variations on the performance of the optical lithography process. Next, the system determines the critical dimension of the feature by comparing the aerial-image intensity with the computed intensity threshold, instead of comparing the aerial-image intensity with the constant intensity threshold.