In: Physics
a)
Buffered oxide etch (BOE) is used to remove SiO2. BOE is a very
selective etchant, meaning that
it stops at Silicon and does not etch further. This etch may be
used in a number of steps. BOE
can be used at the beginning of the process to define holes in the
thermally grown oxide to
fabricate contacts with the Silicon substrate. BOE can also be used
to define contact (via) by
etching the Spin on glass layer.
The BOE etch process is based on the following reaction:
SiO2 + 6HF → H2SiF6 + 2H2O
where H2SiF6 is soluble in water.
A buffering agent, ammonium fluoride (NH4F) is also added to the
solution to maintain HF
concentration and to control pH (to minimize photoresist
attack):
Buffering reaction: NH4F ↔ NH3 + HF
b) Developer Solution is used in the darkroom for developing (i.e. converting latent image to visible image) x-ray films used in conventional (screen film) radiography.