Electrochemical etching and the process of applying related principles are
important semiconductor material technologies, and are now also the key
technologies for fabricating nanostructures in nanotechnology. The key s
ubstance for the electrochemical etching chemical reaction is the hole (h
+), because the hole can enter the chemical bond connecting the solid sur
face atoms and weaken bond strength to result in etching.
Since the N-type silicon substrate lacks the element of anodic oxidation -
holes, this becomes the biggest obstacle in making the porous layer. The e
xisting method is to irradiate the surface or the back of the silicon substrat
e with strong light from a halogen lamp to generate holes to assist the etc
hing during etching. However, the hole density excited by projected light i
s easily affected by the intensity of the light source, distance, medium, wa
velength, etc., and is far less stable than anodic oxidation in a dark room.

This technology uses hydrophobic wafer bonding technology to bond P-t
ype silicon as an intermediary electrode on the back of N-type silicon to f
orm a detachable PN junction and then connect electrodes to form N-typ
e Si/P-type Si/ Electrode sandwich structure. The P-type silicon and N-typ
e silicon form a PN junction, which can convert the holes in the N-type sili
con from "secondary carrier flow" to "main control current", thus greatly i
mproving the anodic oxidation efficiency of the substrate surface . After t
he electrochemical etching process is completed, the P-type silicon used a
s the intermediary electrode can be easily separated from the N-type silic
on, so that the processed N-type silicon remains pure and free from pollut
ion. This technology has been successfully expanded from the application
of N-type silicon crystal materials to N-type silicon carbide materials. It is
expected to be extended and applied to other N-type semiconductor mat
erials.