Halftone Phase Shift Photomasks with Variable Thickness Shift Layer
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Solution Overview
Problem
Conventional photolithography technologies face difficulties in forming fine patterns on semiconductor devices due to the increasing complexity and miniaturization of contact and interconnection patterns, where halftone phase shift photomasks are needed to improve resolution but struggle with maintaining optical density and phase difference as the light shielding layer thickness decreases.
Innovation Solution
The method involves forming halftone phase shift photomasks with a transparent substrate, a molybdenum silicon oxynitride shift layer, and a chromium light shielding layer, where the shift pattern in the blind area is thicker than in the pattern area to achieve an optical density greater than 2.5 and a phase difference of 180°, and the light shielding pattern is made thin to improve resolution by adjusting the thicknesses of the shift and light shielding layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the light shielding layer thickness is decreased to improve resolution, then the resolution of fine patterns is improved, but the optical density and phase difference are compromised
Solution Approach 1:
The patent applies local quality by creating different thicknesses of the shift layer in different regions of the photomask. The blind area has a thicker shift layer (first thickness) to ensure optical density greater than 2.5, while the pattern area has a thinner shift layer (second thickness) to maintain phase difference of 180°. This spatial variation in layer thickness allows each region to optimize its optical properties for its specific function, resolving the contradiction between resolution and optical performance.
Solution Approach 2:
The patent segments the photomask into distinct functional regions: a blind area with thicker shift layer for optical density optimization and a pattern area with thinner shift layer for phase shift optimization. This segmentation allows independent optimization of optical parameters in each region, enabling the light shielding layer to be thin overall while maintaining required optical density where needed.
2Manufacturing precision
If the light shielding layer is made thin to improve resolution, then the resolution is improved, but the optical density in the blind area decreases
Solution Approach 1:
The patent implements local quality by making the shift layer thickness location-dependent. In the blind area, the shift layer has a first thickness that provides optical density greater than 2.5, while in the pattern area, it has a second thickness that is thinner. This allows the light shielding layer to be thin overall for improved resolution while the blind area maintains sufficient optical density through its locally thicker shift layer.
Solution Approach 2:
The patent introduces a dimensional variation in the thickness of the shift layer across different spatial regions of the photomask. By transitioning from a uniform thickness to a non-uniform thickness distribution, the design achieves both thin film characteristics for resolution and sufficient optical density in the blind area through strategic thickening in that specific region.
3Reliability
If the shift layer thickness is varied to maintain optical density and phase difference, then the optical performance is maintained, but the manufacturing complexity increases
Solution Approach 1:
The patent segments the photomask manufacturing process into distinct steps: forming the shift layer with a first thickness in the blind area, then selectively removing material to create a second, thinner thickness in the pattern area. This segmentation allows systematic control of thickness variations through controlled etching processes, making the complexity manageable through standardized manufacturing steps.
Solution Approach 2:
The patent employs preliminary action by first forming the shift layer at a uniform first thickness across the entire photomask, then subsequently removing material only in the pattern area to create the second thickness. This sequential approach simplifies the manufacturing process compared to attempting to create different thicknesses simultaneously, as it breaks down the complex thickness variation into manageable steps.
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 enhances the optical density in the blind area, maintains a phase difference of 180° in the pattern area, and allows the light shielding pattern to become a thin film, improving the resolution of fine patterns and addressing the limitations of conventional photomask manufacturing technologies.
Implementation Method 1
a light shielding layer stacked on the shift layer
Implementation Method 2
maintains a phase difference of 180° in the pattern area
Data Source
AI summary
Halftone phase shift photomasks are provided including a substrate configured to transmit light; a shift pattern on the substrate, the shift pattern including a pattern area on a center portion of the substrate and a blind area disposed on a periphery of the substrate, the shift pattern of the blind area having a greater thickness than a thickness that of the pattern area, and being configured to partially transmit the light; and a light shielding pattern formed on the shift pattern in the blind area and being configured to shield the light. Related methods are also provided herein.