Photomask Assist Pattern Shifting for Resolution and Transfer Control
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Solution Overview
Problem
In current photomask structure design methods, assist patterns can be inadvertently transferred to the photoresist layer during lithography due to close proximity, leading to unexpected pattern generation.
Innovation Solution
A design method for a photomask structure where an assist pattern is initially placed close to a layout pattern, and after optical proximity correction (OPC), the adjacent portion is shifted to increase the distance between them to a safety distance greater than or equal to the minimum specified by the mask rule check, preventing assist pattern transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the assist pattern is placed close to the layout pattern to improve resolution, then the resolution is improved, but the assist pattern is transferred to the photoresist layer during lithography, generating unexpected patterns
Solution Approach 1:
The patent applies preliminary action by performing optical proximity correction (OPC) before lithography to pre-adjust the layout pattern. The OPC process calculates and applies compensation for optical effects, ensuring that when the assist pattern is placed close to the layout pattern, the final printed pattern remains accurate and the assist pattern does not inadvertently transfer to the photoresist layer.
Solution Approach 2:
The patent applies parameter changes by modifying the geometric parameters of the layout pattern through OPC. Specifically, the patent adjusts the position, size, and shape parameters of the layout pattern features based on optical proximity calculations. This allows the assist pattern to be positioned at optimal distances that balance resolution improvement with prevention of unwanted pattern transfer.
2Reliability
If the distance between the assist pattern and the layout pattern is increased to prevent assist pattern transfer, then the reliability is improved, but the resolution improvement from the assist pattern is reduced
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the distance parameter between the assist pattern and layout pattern based on OPC calculations. The system determines optimal distances that are close enough to provide resolution improvement but far enough to prevent pattern transfer, using corrected geometric parameters derived from optical proximity analysis.
Solution Approach 2:
The patent applies dynamics by making the assist pattern positioning adaptive rather than fixed. The distance between the assist pattern and layout pattern is dynamically determined through OPC calculations, allowing optimization for each specific design case. This dynamic positioning enables the system to achieve both close proximity for resolution improvement and sufficient separation to prevent transfer.
Data Source
AI summary
A design method of a photomask structure including the following steps is provided. A first layout pattern is provided. An assist pattern is added aside the first layout pattern. An optical proximity correction (OPC) is performed to convert the first layout pattern into a second layout pattern, wherein the assist pattern has an adjacent portion adjacent to the second layout pattern, a first distance between the adjacent portion and the second layout pattern is less than a safety distance, and the safety distance is a distance to prevent the assist pattern from being transferred to a photoresist layer during a lithography process. After the OPC is performed, the adjacent portion is shifted to increase the first distance to a second distance, wherein the second distance is greater than or equal to the safety distance.