Simultaneous Optimization of Lithography Mask and Illumination
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Solution Overview
Problem
The challenge lies in efficiently determining exposure conditions and mask patterns to achieve high accuracy in pattern formation on substrates, particularly due to the separate optimization of illumination shape and mask pattern, which can lead to suboptimal results and increased time for convergence in complex device patterns.
Innovation Solution
A method involving a computer-based process that sets evaluation positions and items, and iteratively adjusts pattern and illumination shape parameters to optimize both simultaneously, utilizing proximity effects and symmetry characteristics to reduce the number of optimization variables and enhance convergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If separate optimization of illumination shape and mask pattern is performed sequentially, then the optimization process is simpler to implement, but the convergence time increases and manufacturing precision deteriorates
Solution Approach 1:
The patent combines the illumination shape optimization and mask pattern optimization into a single simultaneous optimization process. The evaluation function considers both the illumination parameters (σ_inner, σ_outer) and mask pattern parameters together, allowing the system to find the optimal combination of both parameters at the same time rather than sequentially. This merging resolves the contradiction by maintaining simplicity while improving convergence speed and pattern formation accuracy.
2Manufacturing precision
If the number of optimization variables is increased to handle complex device patterns, then the optimization accuracy improves, but the convergence time increases significantly
Solution Approach 1:
The patent introduces a unified evaluation function that changes the parameter representation from separate optimization variables to a combined set of illumination parameters (σ_inner, σ_outer) and mask pattern parameters. This parameter transformation allows the system to efficiently handle complex device patterns by optimizing all parameters simultaneously within a unified mathematical framework, thereby improving convergence speed without sacrificing accuracy.
3Ease of operation
If OPC is executed after illumination shape determination, then the process follows conventional workflow, but the illumination shape may no longer be optimal after mask pattern changes
Solution Approach 1:
The patent performs preliminary simultaneous optimization of both illumination shape and mask pattern together before the actual lithography process. By determining the optimal illumination parameters and mask pattern parameters in a single unified optimization step, the system eliminates the need for subsequent iterative adjustments that would be required in the conventional sequential approach, thereby maintaining workflow simplicity while achieving superior pattern formation accuracy.
Data Source
AI summary
A determining method includes the steps of setting a first parameter to define the shape of the plurality of pattern elements of the mask, setting a second parameter to define the effective light source distribution; and repeating the process of calculation of the image of the mask pattern and calculation of a value of an evaluation item while varying the value of the first parameter and the second parameter to thereby determine the effective light source distribution and the mask pattern, wherein parameters of pattern elements are set as one parameter by using a value of an index representing the proximity effect.