Halftone Photomask with Variable Transmittance for Process Margin
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Solution Overview
Problem
Achieving a large process margin in photomask manufacturing is challenging due to the varying optimal light transmittance rates required for different photomask patterns, which complicates the exposure of resist films and leads to suboptimal lithography results.
Innovation Solution
A photomask manufacturing method involving a halftone mask with regions of different light transmittance rates, where one region acts as a dark mask with a lower transmittance rate and another as a bright mask with a higher transmittance rate, allowing for simultaneous exposure under a single condition to enhance process margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single light transmittance rate is used for the photomask, then the manufacturing process is simple, but the process margin is reduced due to varying optimal transmittance rates for different patterns
Solution Approach 1:
The photomask is divided into multiple regions with different light transmittance rates tailored to specific pattern requirements. Each region's transmittance rate is locally optimized for its duty ratio, allowing high-density patterns to use lower transmittance rates while low-density patterns use higher transmittance rates, thereby maximizing process margin for each pattern type without requiring multiple separate masks
Solution Approach 2:
The photomask pattern layer is segmented into multiple duty ratio ranges, with each range assigned a specific light transmittance rate. This segmentation allows the photomask to handle diverse pattern densities within a single mask structure, achieving optimal exposure results for both high-density and low-density patterns simultaneously under unified exposure conditions
2Manufacturing precision
If different light transmittance rates are used for different regions, then lithography results are improved, but the photomask design becomes more complex
Solution Approach 1:
The light transmittance rate parameter is varied across different regions of the photomask based on pattern duty ratios. By establishing a correspondence between duty ratio ranges and optimal transmittance rates, the invention enables precise control of light exposure for different pattern densities, significantly improving lithography results while providing a systematic approach to managing design complexity
3Reliability
If multiple photomasks with different transmittance rates are used, then exposure conditions can be optimized for each pattern, but the exposure process becomes more complex requiring multiple conditions
Solution Approach 1:
Multiple photomask regions with different light transmittance rates are merged into a single photomask structure. This consolidation allows all regions to be exposed simultaneously under unified exposure conditions, eliminating the need for multiple separate exposure processes while maintaining optimal exposure parameters for each pattern type, thereby simplifying the overall exposure operation
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 increases the process margin by allowing both regions to be used under the same conditions, reducing design constraints and improving lithography results by setting distinct transmittance rates for different duty ratios within the photomask.
Implementation Method 1
A light transmittance rate of light through the substrate in the first region and the first mask pattern is different from a light transmittance rate of the light through the substrate in the second region and the second mask pattern
Data Source
AI summary
A method of manufacturing a photomask comprises forming a mask film on a surface of a substrate, and forming, with the mask film, a first mask pattern in a first region of the substrate and a second mask pattern in a second region of the substrate. A coverage ratio of the first mask pattern is different from a coverage ratio of the second mask pattern. A light transmittance rate of light through the substrate in the first region and the first mask pattern is different from a light transmittance rate of the light through the substrate in the second region and the second mask pattern.