Fabrication of a multi-level lens using independent-exposure lithography and FAB plasma etching

Design and Fabrication of Diffractive Light-Collecting Microoptical Device with 1D and 2D Lamellar Grating Structures

“…Next, E-beam exposed silicon substrate was developed in ZEP 520 developer for 5 min and washed in the rinse-filled beaker (methyl isobutyl ketone) for 30 sec in the water pool at a temperature of 23 ∘ C and then postbaked for 3 min at 110 ∘ C. As seen in Figure 5(d), the PR patterned 1D and 2D DOEs (300 m by 300 m) on the silicon substrate were fabricated. FAB etching has a good directionality and a constant etching ratio (1 : 1) between the silicon and PR [10,13,18,19]. The FAB etching ratio, 21.0 nm/min, was calibrated under an etching condition as shown in Figure 6.…”

“…The diffractive optical elements (DOEs) can overcome such problems. Recently, a great deal of research in DOEs has been performed [6][7][8][9][10][11][12][13]. The DOEs play an important role in many optical applications, including optical telecommunications components, multiple imaging, light-collecting, and spectroscopy applications, because of their high uniformity, light weight, and miniaturization in size [1][2][3][4].…”

“…Many fabrication methods have been proposed to produce Fresnel lenses. Fugita et al fabricated the stepwise Fresnel lens on a Si substrate by using Ebeam lithography [9,10]. Yan et al fabricated the continuous Fresnel lens on a germanium (Ge) substrate by using ultraprecision machining [11], and Joo et al fabricated the continuous Fresnel lens on polymeric substrate by using ultraprecision machining [12].…”

“…Yan et al fabricated the continuous Fresnel lens on a germanium (Ge) substrate by using ultraprecision machining [11], and Joo et al fabricated the continuous Fresnel lens on polymeric substrate by using ultraprecision machining [12]. However, MEMS-based fabrication methods such as E-beam lithography, photolithography, and holography are limited to machining circularly curved facets and low material removal efficiency [6][7][8][9][10]. On the other hand, 2 International Journal of Manufacturing Engineering ultraprecision machining-based fabrication methods rely on more complicated mechanisms depending on the degree of the size effect due to small ratio of depth of cut to the tool edge radius.…”

“…An evident disadvantage of using a lens with grooves is the possibility of losing light due to incidence on the draft facet. Making the facet perfectly vertical (i.e., perpendicular to the incident plane of light) works to minimize the optical loss (draft loss) [9][10][11][12]. However there is little work regarding thin film-type Fresnel lens for microoptics light-collecting applications.…”