Inhibition of pyramid formation in the etching of Si p(100) in aqueous potassium hydroxide-isopropanol

Abstract

Production of smooth, defect-free silicon surfaces is essential for the fabrication of precise three-dimensional devices. Micromachining usually involves anisot ropic etching in alkaline media such as potassium hydroxide-isopropanol mixtures (KOHIIPA). The quality of the etched surfaces is highly dependent on the etching conditions and surface inhomogeneities such as micropyramids or pits can present major problems. In the present investigation, the purity of the reagents used in the etchant and the effects of dissolved gases, such as oxygen and nitrogen, on surface finish have been evaluated for KOHIIPA baths. The purity of both the water and KOH used was found to be extremely important; the best surfaces were obtained with baths prepared with the lowest impurity content. Dissolved gases had marked effects on surface finish. Pyramid-free surfaces were obtained in oxygen-saturated etchants; this is attributed to the rapid reaction of oxygen with hydrogen produced at the surface during etching, thereby decreasing hydrogen bubble formation. The opposite was seen in solutions saturated with nitrogen where pyramid formation increased. The presence of IPA in the nitrogen-saturated bath improved the sudace finish but did not prevent pyramid formation whereas with oxygen and IPA, defects were completely eliminated and surfaces with a roughness of less than 5 nm were obtained.

Wet chemical etching of silicon {111}: Etch pit analysis by the Lichtfigur method

“…A similar zero etch rate in the absence of water has also been reported for silicon etched in water-free ethylinediamine with pyrocatechol as additive [15]. The water-free experiment once again demonstrates the essential role of H 2 O in the etching process as proposed in the literature [6]. The OH À ions only act as a catalyst in the reaction:…”

“…Ideally, a flat surface should be obtained, but the surface is roughened by etch hillocks (pyramids), etch pits and, at a smaller scale, steps and kinks. Numerous studies have been devoted to understand and control the roughness of the fast etching {1 0 0} faces [6,7]. The surface roughness of this face after etching was investigated using different purity grades of H 2 O and KOH, different organic additives, such as isopropanol (IPA), or by dissolving oxygen or nitrogen gas in the etchant solution.…”

Surface termination and hydrogen bubble adhesion on Si(100) surfaces during anisotropic dissolution in aqueous KOH

“…The overall reaction is [13,14] Si þ 2H 2 Etching defects and surface roughness can result if the hydrogen bubbles produced remain long enough on the surface to mask it from the etching solution [15][16][17][18][19]. The purpose of this work was to investigate the physicochemical aspects of bubble adhesion from measurements of bubble size, lifetime and IR spectroscopy of Si(1 0 0) surfaces in contact with aqueous KOH.…”

Ultrasonic Transducers

“…Wet etching of silicon wafer in alkaline aqueous has been extensively studied [7,21,[40][41][42][43], in following sections, we would like to make a brief introduction of the etch behaviors of different wafers. Possible structures that can be fabricated are presented, all these results are derived from the apparent simple relations showed in Tab.…”