Paper PS-TuP12
Silicon Micro-Channel Definition Via ICP Plasma Etching Process Using Different Hard Masks

Tuesday, October 22, 2019, 6:30 pm, Room Union Station B

Alumina, pieces of silicon wafers, lithographed aluminum (Al) and aluminum nitride (AlN) were used as mechanical hard masks materials for micro-channel etching in silicon (Si) using a high-density inductively coupled plasma - Reactive Ion Etching (ICP-RIE) reactor. The mechanical masks of alumina and silicon, with thickness of 1 mm and 0.35 mm, respectively, were positioned manually on the Si substrates, where the silicon micro-channels (SiMCs) were etched. In the case of Alumina, two rectangular masks were spaced 0.7 mm between them in the Si substrate, resulting in only one micro-channel. For Si mask, six Si pieces with rectangular shapes were positioned in the Si substrate with different spacing between them. The Al films with thickness of 500 nm were evaporated and wet etched using a two lithographed masks patterns: i) parallel lines with width of 0.8 mm and 0.2 mm spaced ; ii) parallel lines with width of 0.2 mm and 0.8 mm spaced. This second sample was carried out to an ICP plasma nitridation (for 30 minutes) to result an AlN/Al structure. AlN material is considered a hard mask especially for the RIE plasma etching based on SF6 gas. The ICP-RIE processes to fabricate the SiMC and to characterize the mask resistance under the plasma etching were carried out using these fixed parameters: 10 sccm of SF₆ + 15sccm of Ar, 15 mTorr of process pressure, 1200W of ICP and 40W of RIE powers. The SiMC profiles, obtained by scan profiler system. indicate that: (i) with alumina mechanical masks, SiMC was obtained the maximum depth value of 108 µm, for the width of 0.7 mm. As in this case, it has only one channel, the unprotected silicon region was small when this sample is compared with others. Small silicon region to etch, highest etch rate can be obtained; (ii) with silicon mechanical masks, it was obtained the depth values between 53 and 87 µm. Furthermore, it can be observed that there is a dependence between the width and the depth of channel. (iii) with Al mask defined by lithography and etching, the SiMC profiles are uniform, with the same width and depth of about 0.24 mm and 80 µm, respectively. The spacing regions with width of 0.76 mm are with surface roughness (up to 5 µm), indicating that the Al mask has not supported the plasma etching for 2 hours; (v) with AlN/Al mask defined by lithography, etching and plasma nitridation, the SiMC profiles are uniform, with the same width and depth of about 0.33 mm and 90 µm, respectively. The spacing regions with width of 0.66 mm have not presented the surface roughness, indicating that the Al mask has supported the plasma etching for 2 hours. However, at the end of plasma etching, this mask was very thinner.