Fabrication methods based on wet etching process for the realization of silicon MEMS structures with new shapes

Abstract

In this paper, fabrication methods are developed in order to realize the silicon microelectromechanical systems components with new shapes in {100} Si wafers. Fabrication process utilizes wet etching with a single step of photolithography. The silicon etching is carried out in complementary metal oxide semiconductor process compatible pure and surfactant Triton-X-100 [C 14 H 22 O (C 2 H 4 O] n , n = 9-10) added tetramethylammonium hydroxide (TMAH) solutions. The fabricated structures are divided in two categories: fixed and freestanding. The fixed structures are realized in single oxidized silicon wafers, while freestanding are formed in silicon nitride-based silicon on insulator (SOI) wafers. The SOI wafers are prepared by bonding the oxidized and the nitride deposited wafers, followed by thinning and chemical mechanical polishing processes. The etching results such as {100} and {110}Si etch rates, undercutting at rounded concave and sharp convex corners and etched surface morphologies are measured in both pure and Triton added TMAH solutions. Different concentrations of TMAH are used to optimize the etching conditions for desired etched profiles.

A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

“…proof mass for accelerometer, mesa structures, chip isolation grooves, bent V-grooves, etc. as shown in Figure 10 [1,2, 39,57,70,92,95,118,120]. Thus, the undercutting is unwanted for the fabrication of these types of microstructures and it is highly anticipated to eliminate this problem by some means.…”

Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

“…It is a low cost technique and suitable for batch process. Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are the two main etchants used for wet anisotropic etching-based silicon bulk micromachining [6][7][8][9][10][11][12]. These etchants are thoroughly investigated under various etching conditions.…”

“…In the case of {100} wafer, four {111} planes making an angle of 54.7° with wafer surface expose at ⟨110⟩ directions. Hence {100} wafer is suitable to fabricate rectangular shaped cavities or suspended structures over rectangular shape cavity using wet anisotropic etching [3,6,12,21]. In the case of the wafer with {110} surface, two slanted planes making an angle of 35.5° with wafer surface and four vertical planes with respect to wafer surface appear along ⟨110⟩ and ⟨112⟩ directions, respectively.…”

Heterojunction of poly (o-toluidine) and silicon nanowires

“…These polymers are more commonly known as "synthetic metals." 1,2 Since most organic polymers do not have intrinsic charge carriers, the required charge carriers may be provided by partial oxidation (p-type redox doping) of the polymer chain with electron acceptors, or by partial reduction (n-type redox doping) with electron donors. Through such a doping process, charged defects (e.g., polaron, bipolaron, and soliton) are introduced, which could then be available as the charge carriers enabling conjugated polymers to gain high conductivities.…”