Fabrication of glass-like carbon molds to imprint on glass materials by MEMS processing technologies

Abstract

We processed a precise relief structure on the surface of a glass-like carbon (GC) substrate by applying micro-electro-mechanical-systems (MEMS) technologies, and made a high temperature resistant mold for thermal imprinting on glass materials. An attractive feature of GC is its chemical stability at high temperatures (above 1,000°C). The down side is its brittleness that makes microfabrication with GC a difficult task. We investigated to find if photolithography combined with reactive-ion-etching (RIE), which are generally used in MEMS fabrication, could be applied for the fabrication of GC molds. In our work with the RIE process, we made masking layers using Au and a positivetone photoresist. By taking advantage of the difference between the etching rates of the masking materials and GC, we fabricated convex mold patterns with vertical and curved sidewalls. From the experimental results imprinted on Pyrex glass and on quartz, the practicability of using both kinds of GC molds appeared to be quite promising. We believe that in the near future these techniques will be successfully applied in the fabrication of large-size GC molds.

Control of inclination angle of glass-like carbon mold by defocus UV exposure on Si-containing photoresist

“…These imprint conditions were determined based upon the result of a previous work. 21 Figures 5 and 6 show the results when the convex mold patterns (Fig. 4) were transferred on Pyrex glass and quartz substrates, respectively.…”

“…The details for preparation of GC wafers and the practicality of GC mold in thermal imprinting on glass materials have already been reported. 21,22 FH-SP3CL photoresist was spin-coated on polished GC wafers, and was then run through a 90 C prebake for 90 s to provide a 800 nm thick photoresist film on the wafer. 23 The detailed experimental conditions in the defocus UV exposure are shown in Table I.…”

“…In another previous work, a 450-nm-thick coat of a positive-tone photoresist S1830 was used as a masking layer. 21 In that case, the edges of convex microstructures on GC substrates were excessively etched, which led to curved sidewalls. Because the etching rates of GC and S1830 photoresist are 109 and 542 nm/min, respectively, which result in low selectivity (GC/S1830 photoresist ¼ 0.2), the mold pattern's height did not reach 1 lm.…”

“…Furthermore, a fabrication technique of a GC mold by MEMS manufacturing technologies was combined with a thermal imprinting on glass materials at high temperature. 21,22 A GC mold whose pattern's sidewalls were inclined at some angle was developed, and three-dimensional (3D) microstructures were transferred from the GC mold to Pyrex glass, and to quartz substrates by thermal imprinting.…”

Multilevel micro-structuring of glassy carbon molds for precision glass molding

“…They successfully used GC molds for imprinting Fused Silica, borosilicate glass and Al. Etching process based on O 2 /SF 6 were demonstrated for on-fiber devices [20] and microfluidics [21,19]. To the author's best knowledge the use of O 2 /SF 6 RIE microstructuring of GC has been scarcely investigated addressing precision glass molding of diffractive optical elements with its increased demand on surface quality.…”