Micromirror Array Asymmetry for Illumination Uniformity
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Solution Overview
Problem
Multi-mirror arrays in projection exposure systems experience undesirable intensity fluctuations in the object plane due to design-related gaps between mirrors, which affect the uniformity of illumination in microlithography.
Innovation Solution
A micromirror array with non-rectangular, geometrically similar micromirrors arranged in a parallelogram shape, tiled without gaps, and capable of tilting and moving to suppress intensity fluctuations, ensuring a smooth edge and improved illumination uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multi-mirror arrays are used in projection exposure systems, then the illumination coverage and flexibility are improved, but intensity fluctuations occur due to gaps between mirrors
Solution Approach 1:
The patent applies asymmetry by using non-rectangular micromirror shapes (specifically parallelograms or trapezoids) instead of conventional rectangular mirrors. This asymmetric geometry allows the mirrors to be arranged in a tiled configuration that eliminates gaps between adjacent mirrors while maintaining the desired illumination coverage and angular distribution. The asymmetric shape enables seamless tiling that suppresses intensity fluctuations in the object plane.
Solution Approach 2:
The patent inverts the conventional approach by making the micromirrors geometrically similar to each other with identical non-rectangular shapes, rather than using rectangular mirrors of potentially varying sizes. This inversion of the design paradigm - where all mirrors share the same geometric form factor - enables gapless tiling and eliminates the intensity non-uniformities that arise from rectangular mirror arrangements.
2Ease of manufacture
If rectangular micromirrors are used, then manufacturing is simplified, but gaps between mirrors cause intensity fluctuations
Solution Approach 1:
The patent deliberately chooses asymmetric non-rectangular shapes (parallelograms or trapezoids) for the micromirrors. While this deviates from the simplest rectangular form, the geometric regularity and self-similarity of these shapes actually simplify the tiling and assembly process. The asymmetric geometry naturally fits together in a seamless pattern, eliminating the need for complex gap compensation mechanisms and simplifying the overall system integration.
3Ease of operation
If micromirrors are arranged in a grid pattern, then alignment is simplified, but jagged edges cause intensity losses
Solution Approach 1:
The patent uses asymmetric non-rectangular micromirror shapes that, when arranged in a grid pattern, produce smooth overall edges rather than jagged boundaries. The parallelogram or trapezoidal geometry allows the mirrors to tessellate perfectly, creating a continuous illuminated field without the stair-step effects that characterize rectangular mirror arrays. This eliminates intensity losses at the boundaries while maintaining the alignment simplicity of a grid arrangement.
Solution Approach 2:
The patent applies the principle of curvature in a generalized sense by creating smooth edges through the geometric arrangement of non-rectangular mirrors. The parallelogram or trapezoidal shapes, when tiled together, produce smoothly varying boundaries rather than sharp angular transitions, effectively creating a curved-like smooth edge profile that minimizes diffraction and intensity losses.
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 solution achieves illumination uniformity better than 0.1% in the object field, significantly improving the efficiency and uniformity of the illumination process by eliminating gaps and optimizing the arrangement of micromirrors.
Implementation Method 1
The micromirrors feature individual reflective surfaces that are reflective for radiation in the EUV range, particularly for radiation with wavelengths in the range of 5 nm to 30 nm
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The invention concerns a micromirror array (27) having the form of a sheared-off rectangle. When arranged in an illumination optics system (4), one side is aligned perpendicular to a scanning direction.