Development of a Deep Silicon Phase Fresnel Lens using Gray-scale Lithography and Deep Reactive Ion Etching

A phase Fresnel lens (PFL) could achieve higher sensitivity and angular resolution in astronomical observations than the current generation of gamma and hard x-ray instruments. For ground tests of a PFL system, silicon lenses must be fabricated on the micro-scale with controlled profiles…

1 Introduction
1.1 Astronomical Imaging Systems
1.2 Fresnel Lenses
1.2.1 Fresnel Lens Derivatives
1.2.2 The proposed Fresnel Lens-based Telescope
1.3 Test Lens Considerations
1.3.1 Material Selection
1.3.2 Dimensions
1.4 Micro-Electro-Mechanical Systems (MEMS) Fabrication
1.4.1 Planar Fabrication Photolithography Surface Micromachining Bulk Micromachining Planar micro-scale Fresnel Lenses
1.4.2 3-Dimensional MEMS Fabrication
2 Gray-scale Technology
2.1 Introduction
2.2 Gray-scale Lithography
2.2.1 Gray-scale Mask Design
2.2.2 Lithography Processing Photoresist Selection Exposure Development
2.2.3 Calibration Mask
2.2.4 Standardized Lithography Process
2.3 Dry-anisotropic Etching
2.3.1 Deep Reactive Ion Etching
2.3.2 Gray-scale Pattern Transfer
2.3.3 Selectivity Control Experiments
2.4 Summary
3 Optical Mask Design
3.1 Introduction
3.2 PFL Equations
3.3 PFL Mask Design considerations
3.3.1 Pitch Selection
3.3.2 Pixel Constraints
3.3.3 Choice of Gray Levels
3.3.4 Multiple Phase Depths
3.4 Gaussian Approximation Method
3.4.1 Experiment
3.4.2 Integration into C Program Design
3.5 PFL Device Design Parameters
3.6 Summary
4 PFL Fabrication and Evaluation
4.1 Introduction
4.2 Lithography Results
4.2.1 Photoresist PFL Structures
4.2.2 PFL Metrology (Photoresist)
4.2.3 Gaussian Approximation Confirmation
4.3 Dry Etching Results
4.3.1 General DRIE Results
4.3.2 DRIE with Oxygen-only Step
4.3.3 Aspect Ratio Dependent Etching
4.4 Profile Evaluation
4.4.1 Method
4.4.2 Profile Measurements
4.4.3 Lens Design Comparison
4.5 Summary
5 Summary and Future Work
5.1 Summary
5.2 Future Work
5.2.1 ARDE Compensation
5.2.2 Bulk Silicon Removal
5.3 Conclusion

Author: Morgan, Brian

Source: University of Maryland

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