Fabrication and Characterization of Smooth Si Mold for Hot Embossing Process

Abstract

In this paper, we propose a fabrication and characterization of silicon mold for PMMA hot embossing process. Silicon molds were fabricated from silicon wafer with thickness of 500µm. First, DRIE technique was performed after optimized etching time and deposition (passivation) time to obtain a depth of 30µm with positive tapered sidewall of 1°. This is very important for de-molding process while hot embossing. Second, in order to reduce scalloping steps on the sidewall after DRIE, silicon molds were soaked in the TMAH solution 20% at 80°C for 10 minutes without magnetic stirrer. Third, to further reduce the friction coefficient between sidewall surface and PMMA substrate while de-molding, the post-passivation technique was applied to create a thin layer of Teflon-like material on the surface of the sidewall of silicon mold. These smooth silicon molds were used to emboss several models of PMMA patterns and comb-drive actuators, as well as applications in Micro Conveyer System. The PMMA patterns obtained after hot embossing process had very sharp edge and aspect ratio of 15 with minimum feature sized of 2µm.

Highly Manufacturable Deep (Sub‐Millimeter) Etching Enabled High Aspect Ratio Complex Geometry Lego‐Like Silicon Electronics

“…Hiroaki et al demonstrated that introducing O 2 plasma to the DRIE process results in smoother sidewalls, and Mukherjee et al also achieved 7 nm surface roughness on sidewalls introducing O 2 into the DRIE chamber . Pham et al used tetramethylammonium hydroxide (TMAH) at 80 °C to achieve a feature size of 2 µm and smooth sidewalls . Smooth sidewalls/edges are critical for applications involving electronic transport as the rough edges would scatter electrons and reduce overall current.…”

Development of polymer electrostatic comb-drive actuator using hot embossing and ultraprecision cutting technology

“…ICP-RIE conditions were investigated carefully to guarantee the positive taper on the sidewall of the mold. 6 Last, a lubricating agent ͑3M Novec Electronic Coating EGC-1720͒ for easier demolding was applied to the Si mold before going to the embossing process. Figure 4 shows the fabricated silicon mold ͑upper image͒ and a close-up image of the comb fingers ͑lower image͒.…”

Development of a Monolithic PMMA Comb-Drive Micro Actuator Utilizing Hot Embossing and Ultra-Precision Machining

“…Next, photoresist is removed and the second ICP-RIE process is performed (with the etching mask is SiO2) to a depth of 70 ptm, and the patterns of the movable part are created (figure 4d). ICP-RIE conditions was investigated carefully to guarantee the positive taper of the side wall of the mold [6]. Finally lubricating agent for easier de-molding is applied to the Si mold before perfroming embossing process.…”