1.5D Spatial Light Modulator for Lithography
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Solution Overview
Problem
Optically-based micro lithographic systems using one-dimensional micro-mirror arrays suffer from asymmetrical image characteristics along and across the direction of sweep, leading to less favorable image quality and increased complexity and cost due to the need for high computation and complex data paths to drive numerous micro mirrors.
Innovation Solution
The implementation of a 1.5D SLM with a long and narrow configuration, utilizing partially coherent light along the long axis and coherent light along the narrow axis, allows for improved diffraction effects and symmetrical image characteristics by controlling the phase of multiple mirrors as a single pixel unit, enabling interference and enhancing image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a one-dimensional micro-mirror array is used for lithography, then high throughput and good utilization of optical field are achieved, but image characteristics along the narrow axis become less favorable due to lack of diffraction effects
Solution Approach 1:
The patent transitions from a 1D micro-mirror array to a 2D micro-mirror array configuration. This dimensional change enables diffraction effects to occur along both the long axis and the narrow axis of the array, thereby improving image characteristics in previously problematic directions while maintaining the high throughput benefits of swept-beam lithography
2Adaptability or versatility
If a 2D SLM with one million or more micro mirrors is used, then comprehensive pattern coverage is achieved, but system complexity and cost increase due to enormous computation requirements
Solution Approach 1:
The patent segments the 2D SLM into a specific configuration with a first dimension having a larger number of micro mirrors and a second dimension having a smaller number. This segmentation strategy, combined with selective illumination, reduces the total number of actively controlled mirrors compared to fully addressing a million-element array, thereby reducing computation complexity while maintaining adequate pattern coverage capability
Solution Approach 2:
The patent applies local quality by using partially coherent or locally coherent radiation that illuminates only specific regions or subsets of the micro-mirror array at different times. This approach allows comprehensive pattern coverage to be achieved through sequential scanning and stitching, rather than requiring simultaneous control of all million mirrors, thus reducing the computation burden
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 results in more symmetrical and cost-effective image patterning with improved resolution and depth of focus, reducing the complexity and expense of the system while maintaining high throughput and efficient use of optical fields.
Implementation Method 1
The SLM disclosed works in a diffractive mode with a continuous or quasi-continuous radiation source. It uses a long and narrow SLM and takes advantage of diffractive effects along the narrow axis of the SLM to improve writing characteristics along that axis.
Implementation Method 2
Image characteristics along the length of the array benefit from use of diffraction effects between adjoining mirrors illuminated with partially coherent or locally coherent radiation.
Data Source
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AI summary
This invention relates to an improved micro lithographic writer that sweeps a modulated pattern across the surface of a workpiece. The SLM disclosed works in a diffractive mode with a continuous or quasi-continuous radiation source. It uses a long and narrow SLM and takes advantage of diffractive effects along the narrow axis of the SLM to improve writing characteristics along that axis.