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

Abstract

The formation and growth of hydrogen bubbles on a Si(1 0 0) surface during its anisotropic etching in aqueous KOH has been investigated. Quantitative data on bubble size, lifetime and density on the etching surface was obtained and their dependence on KOH concentration, applied potential and temperature were measured. In situ FTIR measurements demonstrated a strong dependence of bubble attachment on surface termination and hence on the hydrophilicity of the Si(1 0 0) surface during etching. The formation of surface defects and the geometry of bubble imprints have been directly characterised with scanning probe microscopy. The analysis of hillock formation and statistical considerations show that the adhesion of hydrogen bubbles during anisotropic etching of silicon is a source of surface roughness and pyramid formation.

Triton Surfactant as an Additive to KOH Silicon Etchant

“…Although the Si surface is primarily H-terminated during etching in alkaline solutions, a little number of -OH terminations also appears. These hydroxyl groups make the particular surface sites hydrophilic [31], [38], [39]. Moreover, the coverage of Si surface by -OH groups is reported to increase with the hydroxide concentration [38], [39].…”

“…These hydroxyl groups make the particular surface sites hydrophilic [31], [38], [39]. Moreover, the coverage of Si surface by -OH groups is reported to increase with the hydroxide concentration [38], [39]. Gosalvez et al claim that a small number of -OH terminations could even enhance the adsorption of Triton molecules on the Si surface by formation of hydration bridges between polyethylene oxide groups and -OH terminations of Si [28], which could account for the relatively low increase in the etch rates in the range of 2-4 M of KOH of the solution with Triton.…”

Acid Pickling/polishing of AZ31 Magnesium Alloy

“…The increased surface roughness is a combined result of high hydrogen evolution and hydrogen bubbles staying for long periods of times on the AZ31 Mg alloy surface as hydrogen bubbles staying long enough on the surface mask it from the etching solution [16]. Removal of hydrogen bubbles by mechanical means demonstrate that the final surface morphology is greatly affected by wetting of the dissolving surface by the gas bubbles.…”

“…Protruding microscopic surface irregularities are attacked more than the other lower peaks, hence simultaneous attack of higher peaks and masking of smaller peaks by hydrogen bubbles can lead to an increase in surface roughness. It is this effect of differential dissolution rates at the surface that results in increased surface roughness [16].…”

Development of etch hillocks on different Si(hkl) planes in silicon anisotropic etching

“…The problem of hillocks formation has been widely discussed in the literature concerning silicon etching in KOH and TMAH, especially in KOH solution saturated with isopropanol or other additives [1][2][3][4][5]. Among the reasons of hillocks formation, the following are most often mentioned in the literature: incomplete dissolution of reaction products remaining on the etched surface [1,3,[6][7][8], hydrogen bubbles created in the dissolution process [2,[8][9][10], oxygen precipitates in bulk crystal and stress following the thermal treatment of the substrates [2,4,11,12], metal impurities [7,[13][14][15]. It is evident that all heterogeneities coming from the bulk of crystal or encountered on its surface can disturb the homogeneity of etching process and cause its temporary stopping.…”