Photomask Reticle Transmissivity Gradient for Resist Thinning
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Solution Overview
Problem
Conventional photomask reticles with dense and isolated light shield patterns suffer from significant thinning of resist patterns due to insufficient diffraction control, leading to shallow depth of focus and inability to maintain uniform line thickness in dense and isolated patterns.
Innovation Solution
A photomask reticle design with specific transmissivity relationships between areas, including a first area with high transmissivity, a second area with intermediate transmissivity, a third area with lower transmissivity, and a fourth area with even lower transmissivity, along with micro light shields in the third and fourth areas, to control light diffraction and reduce pattern thinning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photomask reticles with dense and isolated light shield patterns are used, then manufacturing simplicity is maintained, but resist pattern thinning occurs due to insufficient diffraction control
Solution Approach 1:
The reticle is divided into multiple functional areas (first area with light shield pattern, second area with intermediate transmissivity, third area with lower transmissivity, and fourth area with even lower transmissivity) to control light diffraction at different zones, thereby preventing resist pattern thinning while maintaining manufacturing feasibility
Solution Approach 2:
Different areas of the reticle are assigned different transmissivity characteristics to address local diffraction problems. The first area has high transmissivity for main pattern formation, while the second through fourth areas have progressively lower transmissivity to control stray light and prevent thinning in specific regions
2Manufacturing precision
If bar-shaped auxiliary patterns are added to restrain light diffraction, then some diffraction control is achieved, but the restraint on straying-in light ray is insufficient and thinning remains significant
Solution Approach 1:
The invention changes the transmissivity parameter across different reticle areas to control light diffraction. By creating a gradient of transmissivity values (first area > second area > third area > fourth area), the system effectively restrains straying-in light rays and prevents pattern thinning without requiring complex auxiliary structures
3Manufacturing precision
If multiple areas with different transmissivity are introduced, then light diffraction is effectively controlled and pattern accuracy is enhanced, but reticle structure becomes more complex
Solution Approach 1:
The reticle is segmented into four distinct areas with progressively different transmissivity characteristics, allowing precise control of light diffraction at each zone to achieve uniform pattern accuracy and enhanced depth of focus
Solution Approach 2:
Each area of the reticle is assigned a specific transmissivity quality appropriate for its function: the first area for main pattern transmission, and the second through fourth areas for progressive diffraction control, optimizing overall pattern formation
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
The reticle effectively restrains light diffraction, minimizing resist pattern thinning and enhancing pattern accuracy and depth of focus, allowing for consistent line thickness in both dense and isolated patterns.
Implementation Method 1
the restraint on the straying-in of light ray due to diffraction is not yet sufficient
Data Source
AI summary
A photomask reticle for use in projection exposure to form a resist pattern on a workable film formed over a semiconductor substrate, includes a first area in which a light shield is formed, a second area formed around said first area, a third area formed around said second area; and a fourth area formed around said third area, the areas being formed over a substrate, a relationship between transmissivities of said areas being second area transmissivity>fourth area transmissivity>third area transmissivity>first area transmissivity.