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

Abstract

Anisotropic wet etching is a most widely employed for the fabrication of MEMS/NEMS structures using silicon bulk micromachining. The use of Si{110} in MEMS is inevitable when a microstructure with vertical sidewall is to be fabricated using wet anisotropic etching. In most commonly employed etchants (i.e. TMAH and KOH), potassium hydroxide (KOH) exhibits higher etch rate and provides improved anisotropy between Si{111} and Si{110} planes. In the manufacturing company, high etch rate is demanded to increase the productivity that eventually reduces the cost of end product. In order to modify the etching characteristics of KOH for the micromachining of Si{110}, we have investigated the effect of hydroxylamine (NH 2 OH) in 20 wt% KOH solution. The concentration of NH 2 OH is varied from 0 to 20% and the etching is carried out at 75 °C. The etching characteristics which are studied in this work includes the etch rates of Si{110} and silicon dioxide, etched surface morphology, and undercutting at convex corners. The etch rate of Si{110} in 20 wt% KOH + 15% NH 2 OH solution is measured to be four times more than that of pure 20 wt% KOH. Moreover, the addition of NH 2 OH increases the undercutting at convex corners and enhances the etch selectivity between Si and SiO 2 .

Material selection for optimum design of MEMS pressure sensors

“…The findings of our current study and the past literature (Kanda and Yasukawa 1997) suggest that Si(110) has a good potential to increase the sensitivity of a diaphragm pressure sensor, which has yet not been exploited. It is worth mentioning that Si(110) is an active research area (Rao et al 2017;Dutta et al 2011;Hölke and Henderson 1999;Singh et al 2017;Swarnalatha et al 2018) and already being used for fabrication of various micro-machined/MEMS devices. Examples of Si(110) wafer based micro-machined devices include a high aspect ratio comb actuator (Kim et al 2002), a high sensitivity vertical hall sensor (Chiu et al 2001), a capacitive accelerometer for air bag application (Tsugai et al 1997), an opto-mechanical accelerometer based on strain sensing by a Bragg grating in a planar waveguide (Storgaard-Larsen et al 1996), a vertical-membrane optical-fiber pressure sensor (Tu and Zemel 1993), a micro-channel (Singh et al 2008) and an optical Fabry-Perot modulator (Chaffey et al 2004) etc.…”

Electron Diagnostics for Extreme High Brightness Nano-Blade Field Emission Cathodes

“…In addition, any non-uniformity on the surface creates potential hot spots which must be experimentally determined before they are used in further experiments [5]. One possible alternative is the class of precision machined nano-structures [6]. We thus seek to identify and characterize such a structure for future use as an extremely high brightness photocathode.…”

“…The wet-etch acid bath is then used to cut away at the now exposed areas of silicon. The anistropy refers to the etch itself which for the given silicon layering leads to a trapezoidal cross section rather than a circular cross-section as would be the case for an isotropic etch [6]. A chemical bath is used to remove the remaining photoresist.…”

Determination of precise crystallographic directions on Si{111} wafers using self-aligning pre-etched pattern

“…Wet anisotropic etching, which is low cost and best suitable for batch process, is a well-established technique in silicon bulk micromachining [1][2][3][4][5][6][7][8]. Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are most commonly used etchant in wet anisotropic etching [9][10][11][12][13][14][15][16][17]. In wet anisotropic etching, the sidewalls of the stable etched profile are formed by {111} planes.…”