The reason why pore characteristics of resulting pSi structures depend upon doping type and its level of silicon wafer is that pore formation mechanism relies on se parameters.

Dry etching is removal of material in absence of solvent. Here, etchant gases are primary medium for removal of material. There are three main types of dry etching-
1. Plasma etch
2. Ion beam milling
3. Reactive ion etch.

In plasma etch, chemical etchant is introduced in gas phase. For etching silicon oxide, CF4 (tetrafluoromethane) is used. The chamber is first evacuated before introducing gas. Radio frequency (RF) electrodes are n used to generate plasma that ionizes gas.

In deposition, Si from wafer is not consumed and wafer can be maintained at room temperature or at elevated temperatures.

It is critical to consider resistance of metal used as a contact towards corrosion since a continuous exposure to etching electrolyte can degrade its integrity with use and thus its performance. Typically, noble metals such as platinum or gold are best choice as y are inert. Or materials such as stainless steel, brass, tungsten or aluminium can also be used.

Silicon dioxide etch rate at 90 °C using 30 % KOH is ~ 1 µm/hr. So, using silicon oxide as a mask for Si etching will not be good enough or a very thick oxide layer is required.

The space-charge limited mechanism is associated with pore formation in ?pSi structures, which results when n-type silicon wafers are electrochemically etched in HF solutions.

pSi structures can be divided into three categories: (i) microporous silicon (?pSi) with dp < 2 nm, mesoporous silicon (mpSi) with 2 nm < dp < 50 nm and macroporous silicon (MpSi) with dp > 50 nm.

There is a chemical reaction between wafer surface and etchants that helps in material removal. Eir a photoresist layer or a hard mask like oxide or nitride layer is used to protect rest of wafer.

If etching conditions are not controlled, period length, which is defined as distance between two consecutive pore modulations, decreases with pore depth due to diffusion limitations (i.e. lower concentration of HF at pore bottom tips). As a result, critical current density decreases and pore growth rate becomes slower.