Study on the Mechanism of Silicon Etching in HNO₃-Rich HF/HNO₃ Mixtures

Abstract

The wet chemical etching of silicon using HNO 3 -rich HF/HNO 3 mixtures has been studied. The effect of different parameters on the etch rate of silicon, for example, the HF/HNO 3 mixing ratio, the silicon content of the etchant, temperature, and stirring speed in these solutions, has been examined and discussed in light of a previous study on etching in HF-rich HF/HNO 3 mixtures. Nitrogen(III) intermediates are generated owing to the dissolution of silicon and the decomposition if the solution is exposed to air. The nitrite ion concentration, measured in diluted etchant solution by ion chromatography, acts as a sum parameter for the reactive N(III) species in the concentrated etchant. The etch rate shows two different correlations to the nitrite concentration. In the region of high nitrite concentrations, the etch rate decreases slightly with decreasing nitrite concentration, whereas at lower nitrite concentrations, the etch rate increases linearly with further decreasing nitrite concentration. Stirring experiments and the determination of activation energies show that the etching of silicon in HNO 3 -rich etchants is controlled by diffusion. X-ray photoelectron spectroscopy measurements of the silicon surface after etching revealed a hydrogen termination independent of the concentration of reactive species and the content of HNO 3 in the etchant. Si-O containing surface species were not found. A combined electrochemical (injection of holes into the valence band of silicon) and chemical (Si-Si back-bond breaking by an attack of HF) reaction mechanism of silicon etching without generation of SiO 2 is proposed.

On The Mechanism of the Anisotropic Dissolution of Silicon in Chlorine Containing Hydrofluoric Acid Solutions

“…13 To replace nitric acid, alternative oxidants as ammonium peroxodisulfate (NH 4 ) 2 S 2 O 8 , ozone O 3 , and hydrogen peroxide H 2 O 2 were tested. 1,[14][15][16] In these solutions the reactivity is very low, for example in HF-O 3 -mixtures a dissolution rate of silicon of 0.6 nm s −1 is observed.…”

Chemical etching of isolation grooves in high-power silicon devices

“…On the one hand, recent studies have shown [8] that during the etching in acid mixtures, the injection of holes into semiconductor valence band occurs due to reduction of nitric acid on Si surface. This process indicates the electrochemical origin of the reaction.…”

HF-HNO 3 -H 2 SO 4 /H 2 O Mixtures for Etching Multicrystalline Silicon Surfaces: Formation of NO2+${\rm{N}}{{\rm{O}}_{{2^ + }}}$ , Reaction Rates and Surface Morphologies

“…However, several further species including NO2, N2O, and H2 were detected as additional reaction products of HF-HNO3-H2O etching solutions [6,7], and the formation of an intermediate silicon dioxide layer was excluded by means of XPS measurements [8,9]. Instead, after etching in HF-containing solutions silicon surfaces are completely hydrogen-terminated, and in a few cases F atoms have been detected on the silicon surface.…”