Fabrication of multilevel silicon diffractive lenses for terahertz frequencies

Edward D. Walsby; R. Cheung; Richard J. Blaikie; David R. S. Cumming

doi:10.1117/12.360535

31 August 1999 Fabrication of multilevel silicon diffractive lenses for terahertz frequencies

Edward D. Walsby, R. Cheung, Richard J. Blaikie, David R. S. Cumming

Proceedings Volume 3879, Micromachine Technology for Diffractive and Holographic Optics; (1999) https://doi.org/10.1117/12.360535
Event: Symposium on Micromachining and Microfabrication, 1999, Santa Clara, CA, United States

Abstract

Multilevel diffractive lenses give much higher efficiencies than simple binary structures by introducing a blaze. We have developed a novel micro-machining process that allows complex multi-level optics to be fabricated in silicon for use at terahertz frequencies. In this paper we demonstrate the fabrication of a four level (quaternary) lens designed for use at 1 THz. The process required two highly anisotropic dry etch stages that both used a SF₆/O₂ plasma at 173 K. The etch produced smooth etch surfaces with a vertical etch rate of 1 micrometers /min. The lithography for the first etch stage used a conventional positive photoresist process followed by NiCr deposition and lift-off to form an etch mask. For the second etch step the substrate was planarized and over-coated using SU-8, which was also used as a negative resist. The planarized specimen was then exposed to produce the etch mask for the next phase level etch of the lens. The process yielded a silicon:SU-8 etch selectivity of 4:1 which was more than adequate. Between the two etches a total etch depth of 115 micrometers was obtained, with steps at 38 and 77 micrometers and a minimum feature of 84 micrometers . It is anticipated that the process can be extended to give more phase levels with greater optical efficiency.

Citation Download Citation

Edward D. Walsby, R. Cheung, Richard J. Blaikie, and David R. S. Cumming "Fabrication of multilevel silicon diffractive lenses for terahertz frequencies", Proc. SPIE 3879, Micromachine Technology for Diffractive and Holographic Optics, (31 August 1999); https://doi.org/10.1117/12.360535

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