New shapes in (100) Si using KOH and EDP etches

Abstract

Wet chemical etching in EDP, pure KOH and KOH with isopropyl alcohol (KOH/IPA) are known to etch different crystal planes with different etch rates. It is shown in this work that etching in EDP or KOH/IPA reverses the etch-rate ratios of (100) and (110) planes, as compared to etching in pure KOH. This can be used to reveal other relatively slow etching planes, other than (111), to be used in new structures. V-grooves, retro-reflector ridges and mesa structures were fabricated bounded by (110) planes with 45 degrees angles to the (100) surface. Also, by using a corner-compensated mask aligned in the (100) direction and etched in pure aqueous KOH, free-standing cubic studs bounded by (100) planes were fabricated.

Silicon 45° micromirrors fabricated by etching in alkaline solutions with organic additives

“…The {110} planes are patterned with stripes after etching in the KOH solution with isopropanol, whereas the striped pattern is considerably less pronounced in the TMAH/ Triton solution. These results are in a good agreement with those reported in the literature (Backlund and Rosengren 1992;Strandman et al 1995;Resnik et al 2005). The stripes almost do not appear on the {110} surface when 20 ppm of Triton is added to the KOH etchant.…”

“…The {110} sidewalls were obtained in ethylenediamine pyrocatechol (EDP) and potassium hydroxide/isopropyl alcohol [KOH/IPA (also called isopropanol)] mixtures, in which the etch rate ratio R(100)/R(110) [ 1 occurred (Backlund and Rosengren 1992;Strandman et al 1995). Although the smooth {110} surface was achieved in EDP, (Rola and Zubel 2011a, b;.…”

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

“…The anisotropic etchants etch materials much faster in one direction than in another, exposing the slowest etching crystal planes over time [1,2,4,10,[23][24][25][26][27]. Several kinds of aqueous alkaline solutions such as potassium hydroxide solution (KOH) [23][24][25][26][28][29][30][31][32][33][34][35], tetramethylammonium hydroxide (TMAH) [27,[36][37][38][39][40][41][42][43][44][45], ethylenediamine pyrocatechol water (EDP or EPW) [26,35,46,47], hydrazine [23,48,49], ammonium hydroxide [50], and cesium hydroxide (CsOH) [51] are employed for silicon wet anisotropic etching. Among these etchants, potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) are most frequently used.…”

Impact of alcohol additives concentration on etch rate and surface morphology of (100) and (110) Si substrates etched in KOH solutions

“…The etching processes were usually carried out in TMAH or KOH aqueous solutions, optionally with addition of surfactants or alcohols. The KOH solution saturated with isopropyl alcohol (also called isopropanol or IPA) was often used, because it provides high etch rate ratio R(100)/R(110), smooth (100) surface and reduction of convex corner undercut (Backlund and Rosengren 1992;Zubel 2001;Zubel and Kramkowska 2004). However, the {110} planes are patterned with stripes after etching in this solution (Backlund and Rosengren 1992;Zubel and Kramkowska 2004).…”

“…The KOH solution saturated with isopropyl alcohol (also called isopropanol or IPA) was often used, because it provides high etch rate ratio R(100)/R(110), smooth (100) surface and reduction of convex corner undercut (Backlund and Rosengren 1992;Zubel 2001;Zubel and Kramkowska 2004). However, the {110} planes are patterned with stripes after etching in this solution (Backlund and Rosengren 1992;Zubel and Kramkowska 2004). Although smooth {110} planes can be obtained in TMAH-based solution (Resnik et al 2005;Yagyu et al 2010;Xu et al 2011), it is quite expensive and usually provides lower etch rates than KOH.…”