In Search of Perfection: Understanding the Highly Defect-Selective Chemistry of Anisotropic Etching

Abstract

Anisotropic etchants selectively reveal a specific crystallographic plane. Although prized industrially, these etchants are poorly understood because they target specific defect sites on a surface. New methods, which rely on a combination of scanning tunneling microscopy, kinetic Monte Carlo simulations, and infrared spectroscopy, have been developed to quantify these reactions. By correlating the measured reaction rates with the structure of the defects, information about reaction mechanisms can be obtained. These techniques have also been extended to allow for the quantification of impurity reactions such as the reaction of dissolved O2, and of nonetching additives, such as alcohols. A complementary macroscopic technique, which utilizes microfabricated arrays of miscut surfaces to measure orientation-dependent kinetics, is also described.

Investigation of the Chemical Purity of Silicon Surfaces Reacted with Liquid Methanol

“…Si(111) samples were hydrogen-terminated by a 30 s dip in 10-20% HF(aq) followed by a 2.5 min dip in 40% NH 4 F(aq), and a final rinse in H 2 O for 10 s. This latter procedure produces an atomically smooth (111)-oriented surface for tens to hundreds of nanometers. 54,61,62 Oxides were chemically grown on an atomically flat hydrogen-terminated Si(111) surface using either the SC1/SC2 procedure outlined above or a 10 min exposure to 100°C solution of 4:1 concentrated (18 M) H 2 SO 4 :30% H 2 O 2 (aq) (hereafter referred to as piranha solution). Oxide surfaces grown from the piranha clean typically produced FTIR spectra that exhibited less hydrocarbon contamination.…”

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

“…are mono-hydride steps. This means that each atom in the step is triply bonded to the crystal surface and has only one dangling bond, which is saturated by an hydrogen atom [8,12,13]. As a measure for pit triangularity, we here introduce a parameter R ab ¼ a/b, where a is the distance, projected on the (111) plane, between the pit center and the pit edges /2 1 1 S, while b represents the projection of the distance between the pit center and the pit corners opposite to the just-mentioned edges (Figs.…”

First-principles calculations of Cu adsorption on an H-terminated Si surface

“…6 According to wet etching experiments in alkaline solutions, [24][25][26] Cu has a dramatic impact on the etch rate, the surface morphology, and the surface roughness of ͑110͒ and ͑100͒. During KOH etching, the surface is mostly H terminated, 27,28 although it includes a small fraction of OH terminations, 29 whose number is expected to increase with increasing KOH concentration. As compared to other metal impurities, copper seems to have a particular preference to adsorb on the H-terminated surface during etching, presumably acting as a blocking agent ͑"micromask"͒ once it has been attached, locally reducing the etching probability.…”