I'm not an expert in chemistry but I hope it to be a straight forward question.
The situation is, as shown in the figure below, I'm trying to etch a semiconductor in KOH solution (4M concentration) at room temperature. There is a negative sheet charge with a density of P (C/cm2) located at the bottom surface which repels the OH- from accessing the semiconductor. However, the etching can progress along the sidewall until the distance (d) is too close and the diffusion force and electric field reach an equilibrium. I'd like to know how to calculate this distance d. Thanks in advance.
There are few ways to do it. One is gravimetric determination, which follows equatation:
d = (m1-m2)/s*q
In this equatation d - is layer thickness, m1 - your semiconductor mass before etching and m2 - after etching, s - etching area and q - density of etched material. If the layer is not that thick you could do AFM on the intersection, or as other option you could take SEM image of cross section. I hope this will help.
Thanks Lina Dedelaite for the answer,
That's a interesting method using weight and density to convert to volume, and then thickness. However, the equation you have given is not possible in this case as the etching would be in nm scale and I doubt I can get the mass accurately. And also, the estimated size would be ~10-20 nm for both the trench length and the thickness. So it is too small for SEM, or even AFM (since the AFM tip can be bigger than the feature size which can give error).
I'm just wondering, if it is possible to calculate it in the electrochamical way such that the electric field balances with the diffusion force?
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