Photomask Assist Pattern Placement via Evaluation Points
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Solution Overview
Problem
The existing photomask designing methods face challenges in efficiently placing assist patterns to enhance lithographic latitude and depth of focus, particularly when dealing with fine patterns approaching the resolution limit of exposure apparatuses, due to the complexity and cost associated with manual optimization and the potential reduction in lithographic performance from interactions among multiple assist patterns.
Innovation Solution
A method and program that utilize evaluation points and an approximately-coherent imaging optical system to determine optimal placement conditions for assist patterns by evaluating light intensity distributions and imaging properties, allowing for the placement of assist patterns based on specific regions to enhance lithographic latitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple assist patterns are simply placed around a design pattern, then the assist pattern placement can be achieved within practical time and cost, but the lithographic latitude (exposure latitude and depth of focus) may be reduced due to interaction among the assist patterns
Solution Approach 1:
The patent applies local quality by evaluating imaging properties at different local positions around the design pattern and placing assist patterns only in regions where they provide beneficial effects. The method divides the area around the design pattern into multiple evaluation points, calculates imaging properties (such as light intensity distribution and gradient) at each point, and selectively places assist patterns in regions where the evaluation index indicates improvement potential, rather than uniformly placing assist patterns everywhere.
Solution Approach 2:
The patent changes parameters by introducing an evaluation index that combines multiple imaging properties (light intensity, gradient, and other optical characteristics) to quantitatively assess the effect of potential assist pattern placements. By calculating and comparing evaluation indices at different positions, the method determines optimal assist pattern placement parameters (position, size, shape) that improve lithographic latitude while avoiding harmful interactions.
2Manufacturing precision
If a design is made according to an optimization method with trial-and-error placement of assist patterns based on designer experience, then a pattern layout including assist pattern can be determined, but the cost and time in designing increase
Solution Approach 1:
The patent applies self-service by creating an automated system that evaluates imaging properties and determines optimal assist pattern placement without requiring repeated manual trial-and-error by designers. The computer automatically calculates light intensity distributions, evaluates imaging properties at multiple points, and determines assist pattern parameters based on evaluation indices, enabling the system to optimize its own design decisions.
Solution Approach 2:
The patent replaces the mechanical trial-and-error process with an automated computational system. Instead of manually placing and evaluating assist patterns through iterative design cycles, the method uses computer-based optical modeling and evaluation algorithms to automatically determine optimal assist pattern configurations, substituting human designer effort with automated computational analysis.
3Manufacturing precision
If illumination conditions of an exposure apparatus are set to be suitable for transferring the densest pattern, then the resolution limit can be approached, but the exposure latitude and depth of focus for patterns other than the densest pattern decrease
Solution Approach 1:
The patent applies local quality by placing assist patterns selectively in specific regions around the design pattern where they can enhance imaging properties without interfering with the primary pattern transfer. The evaluation-based placement ensures that assist patterns are positioned to improve exposure latitude and depth of focus in critical areas while maintaining the resolution of the densest pattern.
Solution Approach 2:
The assist patterns act as intermediaries between the illumination system and the design pattern. By strategically placing these intermediate structures, the system mediates the optical interaction to improve the imaging of both the densest pattern and other patterns, effectively broadening the exposure latitude without compromising the resolution achieved by the optimized illumination conditions.
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 simplifies the placement of assist patterns, reduces design time and cost, and improves lithographic performance by allowing for independent evaluation of imaging properties at different positions on the photomask, resulting in enhanced exposure latitude and depth of focus.
Implementation Method 1
combining a light intensity distribution of the design pattern with light intensity distributions of the evaluation points to obtain a light intensity distribution of the design pattern on the imaging surface
Implementation Method 2
utilize evaluation points and an approximately-coherent imaging optical system to determine optimal placement conditions for assist patterns by evaluating light intensity distributions and imaging properties
Data Source
AI summary
In one embodiment, a photomask designing method for creating a pattern layout having an assist pattern placed around a design pattern is disclosed. The method can place a plurality of evaluation points around the design pattern and set an evaluation index for imaging properties of the design pattern on an imaging surface. The method can combine a light intensity distribution of the design pattern with light intensity distributions of the evaluation points to obtain a light intensity distribution on the imaging surface and evaluate the light intensity distribution on the imaging surface using the evaluation index to determine a region having an effective evaluation point placed. In addition, the method can determine a placement condition for the assist pattern based on the region where the effective evaluation point is placed and place the assist pattern around the design pattern based on the placement condition to create the pattern layout.