Etching Mechanism Of Silicon Research Articles

Effect of wafer resistivity and HF concentration on the formation of vertically aligned porous silicon

In this study, the mechanism of vertically aligned porous silicon formation was examined. Silicon wafers with various resistivities and electrolytes containing different HF concentrations were used to explain porous silicon formation by the reaction at the silicon/electrolyte interface. Total pore volume increased proportionally to the current applied and anodization time. As the concentration of HF increased, pore depth and total pore volume formed in silicon anodization increased, then decreased beyond the optimum point. At a given applied current, total pore volume formed by anodization increased with an increase in resistivity of silicon wafer, but then decreased. From the mechanism of silicon etching and schematic isoetch contour of silicon suggested in this study, it is concluded that the formation of porous silicon is determined by an accumulation of F − near the silicon/electrolyte interface in silicon anodization.

Investigations on the mechanism of silicon etching with chlorine-trifluoride

We investigated chlorine trifluoride (ClF3) etching of silicon with a patterned oxide mask layer prepared by e-beam lithography. The mask apertures varied from 0.1μmto300μm. This enables to adjust the flow rate of ClF3 molecules into the etched cavity leading to a strong variation of the ClF3 abundance at the silicon surface. A crucial dependence of the etch rate on the aperture area was observed revealing a maximum of the etch rate for a specific ClF3 abundance. A physical description of the etch process is developed in order to distinguish between different mechanisms within the etching process. At low ClF3 abundance the etch rate is limited due to a lack of ClF3. For high abundance the etch rate is assumed to be hampered by a diffusion like transport of ClF3 molecules through a fluorosilyl layer formed on the silicon surface. It can be shown that the etch rate of silicon with ClF3 is not limited by the chemical reaction at high ClF3 abundance. Additionally, we observed a change in etching behavior from isotropic to anisotropic with a strong correlation to the etching regime.

Mechanism of silicon etching in the presence of CF2, F, and Ar+

Molecular dynamics simulations of CF2, F, and Ar+ impacting silicon surfaces reveal the spontaneous formation of segregated layers of Si-C and SiFx, formed due to Ar+ ion impact and ion-induced mixing. The mechanisms of steady-state etching under these conditions involve a leading front of SiFx that fluorinates the Si substrate, followed by a region or zone of Si-C. The SiFx and Si-C layers move through the substrate Si during steady-state etching. Si is generally etched from the surface of the Si-C layer by an ion impact. Carbon reaction with Si in the Si-C zone raises the total atomic density in the Si-C layer to nearly three times the value observed in undisturbed Si and reduces the Si etch rate by limiting ion mixing. Etching stops completely if the Si-C layer becomes so impervious that ions cannot reach the SiFx front. The importance of the depth profile of ion energy deposition in sustaining etching is very clearly observed in the simulations.

Kinetic isotopic effects in the anisotropic etching of p-Si〈100〉 in alkaline solutions

The etching mechanism of silicon has been investigated by measuring the H/D-kinetic isotopic effect on dissolution rate. The etching rate of p-Si〈100〉 was measured using optical profilometry. It was found that in 2 M KOH + H2O and 2 M NaOH + H2O it was approximately twice as large as in 2 M KOD + D2O and 2 M NaOD + D2O. The existence of a H/D-isotopic effect shows that the cleavage of the SiH bond represents the rate determining step in silicon etching. Calculations of the activation barriers from IR data for the SiH and SiD vibrations show that the observed isotopic effect reflects the nature of the transition state, in which the SiH bond is not completely broken. Both the chemical and electrochemical pathways for the dissolution process of silicon in alkaline solutions are discussed on the basis of the results presented.

Mechanism of silicon etching in HF-KMnO4-H2O solution

The etching reaction of silicon in HF-KMnO4-H2O mixed solution has been studied under various experimental conditions. The etch rates were measured as a function of agitation speed, HF and KMnO4 concentrations, and etching temperature and time. A comprehensive mechanism for the silicon etching and insoluble solid-phase film (K2SiF6) formation has been proposed. The holes formed at silicon surface accelerated not only the etch rate of silicon but also the formation rate of K2SiF6. With the increase of hole concentration at lower HF concentrations the etch rates decreased because of the deposition of K2SiF6 on etched silicon surface. Under the condition of sufficiently high HF concentration, the rate increased with the increase of hole formation and the formation of holes at silicon surface was the rate limiting step of the silicon etching reaction in HF-KMnO4-H2O solution. High HF concentration enough for dissolving K2SiF6 was apparently essential to obtain high etch rate in the silicon etching reaction.

The Band Model and the Etching Mechanism of Silicon in Aqueous KOH

The energy band diagram of n‐Si in aqueous 2M is constructed by the measured open‐circuit potential and the flatband voltage. A photocurrent susceptivity method was proposed to determine the flatband voltage. A flatband voltage of −1.04 (saturated calomel electrode) for the n‐Si in 2M was determined by this new method. The energy band diagram of the p‐Si in the same electrolyte is also constructed. Accumulation of carriers at the interface is predicted by the band diagram and confirmed by the ohmic‐contact‐like I‐V curve. Depletion of carriers at interface is predicted by the band diagram and confirmed by the rectifying I‐V characteristics. The passivation of Si under anodic bias is attributed to the formation of an oxide film. The competition between the oxidation rate and the diffusion rate of oxidation product determines whether the anodic oxidation is an etching or passivation process. The etching oxidation is assumed to be dominated by the electrochemical reaction. The transport of these carriers which participate in the electrochemical reaction can be explained by the energy band diagram. All etching or passivation phenomena are consistent with the prediction from the band diagram viewpoint. The etch stop for heavily doped Si is attributed to the enhanced growth rate of oxide film under high carrier concentration.

Mechanism of silicon etching by a CF 4 plasma

Mechanism of silicon etching by a CF 4 plasma

Mechanism of silicon etching by a CF4 plasma

The mechanisms for the reactive ion etching of silicon by CF4 plasma are investigated. A model is proposed whereby silicon is etched by chemical reaction with free fluorine to produce a volatile species, and also by physical sputtering. The chemical etching is shown to be enhanced by ion bombardment of the reacting surface. This etching process, together with a model for cracking CF4 in the plasma, is evaluated by comparison to actual etch rates. Experimentally, the silicon etch rate is observed to decrease with increasing silicon area, by what is called the loading effect. The functional form of the loading effect, as predicted by the model, is fitted to experimental loading curves. The contributions of the various etching components are separated, to yield empirical values for the enhancement of the chemical reaction by physical sputtering.