Plasma Etching
of Silicon
- Single-crystal etch is required to form
shallow trench isolation which is used in sub-half micron IC chips.
- Single crystal silicon etch normally employs
silicon dioxide or, both silicon dioxide and silicon nitride hard mask.
- It uses the blocking mechanism, with HBr as
the main etchant and O2 as the sidewall passivation agent.
- In plasma, HBr dissociates and releases free
bromine radicals, which can react with silicon to form volatile silicon
tetra bromide.
- Oxygen oxidizes silicon on the sidewall to
form silicon dioxide, which protects silicon from free bromine radicals.
- At the bottom of the trench, ion bombardment
keeps oxide from growing, thus the etch process continues only in the
normal direction.
- The main chemical reaction of the
single-crystal silicon plasma etching process is:
HBr ® H + Br (plasma)
4Br + Si ® SiBr4 (plasma)