EUV Pellicle Mesh Optimization for Shadow Contrast Reduction
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Solution Overview
Problem
Current EUV pellicle technologies face challenges in maintaining chemical stability, high transmittance, and structural strength, leading to issues with image shadow intensity and contrast on wafers due to the fragility of silicon thin films and the trade-off between strength and transmittance in mesh structures.
Innovation Solution
A pellicle assembly with a mesh structure that includes a pellicle membrane and a mesh backing to prevent dust and particles, where the stand-off distance and honeycomb angle are optimized to minimize the contrast ratio of the image shadow, using a honeycomb-like mesh structure with a quadrilateral or hexagonal frame configuration, and adjusting the projected angle relative to the mask to reduce shadow intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a silicon thin film is used as a pellicle membrane for EUV, then high transmittance of EUV light is achieved, but the film becomes physically fragile and cannot stand on its own
Solution Approach 1:
The patent uses a composite structure combining an ultra-thin silicon membrane (20 nm) with a rubidium layer (15 nm) to create a pellicle that maintains high EUV transmittance while providing enhanced structural stability. This composite approach allows the pellicle to benefit from the high transmittance properties of silicon while the rubidium layer contributes to mechanical strength and adhesion.
2Strength
If a mesh structure is added to reinforce the pellicle film, then structural strength is improved, but the opening ratio decreases and transmittance is reduced
Solution Approach 1:
The patent employs an ultra-thin silicon membrane (20 nm) as the pellicle film, which is so thin that it requires a mesh structure for reinforcement. The mesh structure is designed with optimized parameters (mesh pitch, grid frame width, and grid frame height) to provide necessary mechanical strength while minimizing the blocking of EUV light. The thin film approach allows the mesh structure to be as delicate as possible, reducing its impact on light transmittance.
3Strength
If the mesh pitch is narrowed to increase structure strength, then the pellicle film strength is improved, but the opening ratio decreases and transmittance is reduced
Solution Approach 1:
The patent systematically optimizes the mesh structure parameters including mesh pitch, grid frame width, and grid frame height to achieve the best balance between strength and transmittance. By carefully selecting and adjusting these parameters, the design achieves sufficient mechanical strength while minimizing the impact on EUV light transmittance through the mesh openings.
4Strength
If the grid frame width is increased to improve structure strength, then the pellicle film strength is improved, but the opening ratio decreases and transmittance is reduced
Solution Approach 1:
The patent optimizes the grid frame width as one of the key parameters of the mesh structure. The grid frame width is carefully selected to provide sufficient mechanical strength and stability to the pellicle film while minimizing the total area occupied by the grid frames, thereby maximizing the opening ratio and maintaining high transmittance of EUV light.
5Strength
If the grid frame height is increased to improve structure strength, then the pellicle film strength is improved, but the opening ratio decreases and transmittance is reduced
Solution Approach 1:
The patent optimizes the grid frame height (thickness) as a critical parameter of the mesh structure. The grid frame height is carefully selected to provide sufficient mechanical strength and three-dimensional stability to the pellicle film while minimizing the vertical obstruction to EUV light. The optimization ensures that the grid frames are tall enough to provide structural support but not so tall as to significantly block the incident EUV light.
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 allows for uniform light exposure with reduced shadow intensity and contrast, enhancing the operational conditions of EUV exposure technology by controlling the stand-off distance and honeycomb angle to achieve a low contrast ratio, thereby minimizing the impact of the pellicle's shadow on the wafer.
Implementation Method 1
the image shadow of the mesh structure is cast on the wafer
Implementation Method 2
The EUV light that has reached the mask 3 is reflected by the mask 3 and passes the pellicle 2 for the second time
Data Source
Figure 1(a)~1(d)
Figure 2(a)~5
Figure 6
AI summary
Here are disclosed a pellicle for EUV and an assembly made up of this pellicle and a mask, which brings about a projection of low contrast (intensity) shadows of a mesh structure on the mask, thus minimizing the adverse effect of the shadow on the lithographic printing; also a method for assembling such assembly is disclosed wherein the pellicle is rotated relative to the mask to minimize the shadow contrast, in terms of a contrast ratio, of the mesh structure; the angle of the rotation is 30 degrees or smaller, and the resultant contrast ratio should be 25 % or lower.