Scheme of the laser lithography system showing the main optical components and the laser beam path; the dotted line denotes the center of the deflection cone while the full line visualizes the path of the first-order deflected beam. The AODs and the M.O. are placed in the focal planes of the Keplerian telescope formed by lenses and .
Measured intensity of the laser beam after the M.O. as a function of the driving rf (one AOD axis) at constant rf power (not compensated) and real-time compensated power.
SEM of two rings in SU-8 photoresist written by (a) the 40× and (b) the 100× objective. The rings with a radius of have the minimum achievable widths of 380 and 200 nm, respectively.
Schematics of the exposure strategy for rectangular (top) and circular structures (bottom) using acousto-optic deflection.
SEMs of photoresist ridges exposed by means of acousto-optic deflection and the 40× objective. The point spacings of the grid are [from (a) to (d)] 500, 400, 350, and 300 nm. The measured peak-to-peak roughness of the sidewalls are 100, 55, 35, and [from (a) to (d)].
SEMs of ridge structures in SU-8 exposed with different laser powers [(a)–(c)]: 4.2, 6.3, and .
Schematics of the two-step lithography procedure. (a) Application of photoresist and exposure of the straight waveguide. (b) Developing of the structure. (c) Application of another resist layer and exposure of the microring by AO-deflection. (d) Second development yields the combined structure.
(a) SEM of two microring resonators with a coupling port structured in diluted AZ 5214E photoresist by the two-step lithography method. The rings have a diameter of . (b) Enlarged picture of the coupling region showing a gap of about 100–150 nm.
(a) PhC structure in AZ 5214E photoresist with a lattice constant of and a hole-diameter 520 nm. (b) PhC structure in SU-8. The lattice constant is 450 nm, the diameter of the pillars about 200 nm.
Summary of the system components and their properties.
Characteristics of the two M.O.s used in the experiment and their impact on the performance of the lithography system.
Experimentally determined threshold dose at 375 nm for SU-8 ( thickness) and AZ 5214E ( thickness). In both cases, the UMPlanFL40× objective was used for the exposure.
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