Effect of NH₂OH on Etching Characteristics of Si{100} in KOH Solution

Abstract

Potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are most extensively used etchants for wet anisotropic etching process. Amongst these two etchants, KOH is a low cost etchant and provides high etch rate anisotropy between Si{111} and Si{100} planes. Increasing the etch rate is an important research problem for both academic and industrial applications. In this research, we study the effect of hydroxylamine (NH2OH) in 20 wt% KOH on the etching characteristics of Si{100}. This type of wafer orientation (i.e. Si{100}) is selected owing to its popularity in fabricating planar semiconductor devices (e.g. diode, transistor, complementary metal oxide semiconductor (CMOS), etc.) and MEMS components (e.g. cantilever, diaphragm, etc.). A systematic parametric analysis of various concentrations of hydroxylamine (from 0 to 20% in step of 5%) added 20 wt% KOH is carried out and its effect on the etching characteristics is discussed. We have found that the etch rate of Si{100} is increased threefold when 15% NH2OH is added to 20 wt% KOH solution. Additionally, this concentration also exhibits improved etching characteristics including undercutting rate, etch selectivity, and surface morphology. We have obtained improved etching characteristics when NH2OH is added to 20 wt% KOH. Due to an improvement in etching characteristics, present research is very useful to pave the path toward application in microfabrication industries as well as academic research laboratories.

High speed etching of silicon in KOH + NH 2 OH solution at lower temperatures for the fabrication of through holes in silicon wafer

“…In order to overcome this problem, the etching is carried out at lower temperatures in the range of 50-60°C. However, at low temperatures, the KOH etch rate is very poor and this necessitates the addition of special additives such as hydroxylamine (NH 2 OH) [15,16].…”

“…The effect of different concentrations of NH 2 OH on the etching characteristics of Si{100} using 20 wt% KOH and 5 wt% TMAH is studied [15][16][17][18]. 15% NH 2 OH is found to be the optimal concentration in 20 wt% KOH to obtain improved etching characteristics.…”

“…15% NH 2 OH is found to be the optimal concentration in 20 wt% KOH to obtain improved etching characteristics. The etch rates, etched surface morphologies, and undercutting results in 15% NH 2 OH-added 20 wt% KOH are presented in the literature [15,16]. Etch rate of Si{100} in 15% NH 2 OH + 20 wt% KOH solution is nearly three times higher than that in pure KOH at the same temperature.…”

“…The etch selectivity, which is defined as the ratio of Si etch rate and SiO 2 etch rate, increases remarkably in NH 2 OH + KOH solution. The addition of NH 2 OH does not affect the etched surface roughness and morphology significantly [15,16]. For through hole fabrication, etching needs to be carried out for long durations.…”

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.…”