DMD Exposure Optics With Elliptical Pupil Distortion Correction
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Solution Overview
Problem
Existing exposure apparatuses using spatial light modulating elements like DMDs suffer from image distortion due to the diffraction grating effect when oblique illumination is used for fine pattern projection, leading to degraded image forming states.
Innovation Solution
A pattern exposure apparatus with a spatial light modulating element, an illumination unit that condenses and obliquely irradiates light at a predetermined incidence angle, and a projection unit that corrects distortion by deforming the outline of the surface light source into an elliptical shape using a correcting optical member.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If oblique illumination is used for fine pattern projection, then the resolution for fine patterns is improved, but image distortion occurs due to the diffraction grating effect of the DMD
Solution Approach 1:
The patent changes the geometric parameters of the light source by deforming it from a circular shape to an elliptical shape. This parameter change compensates for the diffraction grating effect caused by oblique illumination, allowing fine pattern projection with improved resolution while maintaining image forming quality. The elliptical light source has a major axis and minor axis with a specific aspect ratio that counteracts the distortion introduced by the oblique illumination angle.
Solution Approach 2:
The patent introduces asymmetry by using an elliptical light source instead of a symmetric circular light source. This asymmetric light source distribution is specifically designed to counterbalance the asymmetric diffraction grating effect that occurs during oblique illumination of the DMD, thereby resolving the contradiction between achieving fine pattern resolution and maintaining image quality.
2Device complexity
If a circular light source is used with oblique illumination, then the illumination is simple, but the light source image on the pupil plane becomes distorted
Solution Approach 1:
The patent modifies the geometric parameters of the light source from a circular shape to an elliptical shape with a specific aspect ratio. This parameter change pre-compensates for the distortion that will occur on the pupil plane during oblique illumination, ensuring that the light source image maintains the correct shape and position for accurate pattern projection without increasing system complexity.
3Adaptability or versatility
If the DMD is used as a spatial light modulating element, then mask pattern flexibility is improved, but diffraction grating effects degrade the image forming state
Solution Approach 1:
The patent converts the harmful diffraction grating effect into a beneficial correction mechanism. By using an elliptical light source with specifically designed geometric parameters, the patent exploits the diffraction grating effect to counteract itself, thereby maintaining the flexibility of the DMD for various mask patterns while eliminating the image degradation caused by diffraction.
Solution Approach 2:
The patent changes the geometric parameters of the illumination system by using an elliptical light source instead of a circular one. This parameter change is specifically tailored to counteract the diffraction grating effect produced by the DMD's pixel structure during oblique illumination, thereby preserving image forming quality while maintaining the adaptability benefits of using a DMD.
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 effectively corrects image distortion and enhances the image forming state during oblique illumination, improving the precision of pattern projection on substrates.
Implementation Method 1
a condensing optical member that is configured to condense light from a surface light source having a predetermined shape which is a source of the illumination light so as to obliquely irradiate the light to the spatial light modulating element
Implementation Method 2
a projection unit configured to project reflected light from selected micro mirrors of the spatial light modulating element in an ON state
Implementation Method 3
a correcting optical member configured to deform a shape of an outline of the surface light source so as to correct distortion of an outline of an image of the surface light source, which is formed on the pupil of the projection unit
Implementation Method 4
a spatial light modulating element including a plurality of micro mirrors selectively driven based on drawing data
Data Source
AI summary
A pattern-exposure-apparatus includes: spatial-light-modulating-element including a plurality of micro-mirrors selectively driven based on drawing data, illumination-unit that irradiates spatial-light-modulating-element with illumination-light at predetermined-incidence-angle, and projection-unit that projects reflected-light from selected micro-mirrors of spatial-light-modulating-element in ON-state to substrate, and pattern-exposure-apparatus projects and exposes pattern corresponding to drawing data to substrate, illumination-unit including condensing-optical-member that condenses light from surface-light-source having predetermined shape so as to obliquely irradiate light to spatial-light-modulating-element and that is disposed along optical-axis which is inclined at incidence-angle with respect to optical-axis of projection-unit so as to optically conjugate surface-light-source with pupil of projection-unit, and correcting-optical-member that deforms shape of outline of the surface-light-source so as to correct distortion of outline of image of the surface-light-source, which is formed on pupil of the projection-unit by reflected-light from micro-mirrors of the spatial-light-modulating-element in ON-state, into elliptical-shape according to incidence-angle.