Biomedical Engineering Reference
In-Depth Information
(d) RCA clean: RCA clean is the industry standard for removing
contaminants from silicon wafers. The RCA is called because
Werner Kern developed the procedure in 1965 while working
for RCA (Radio Corporation of America). The purpose of the
RCA clean is to remove organic contaminants (such as dust
particles, grease, or silica gel) from the wafer surface with a
5:1:1 H
2
O:H
2
O
2
:NH
4
OH solution; then remove any oxide layer
that may have built up by using a diluted 20:1 H
2
O:HF solution;
and inally remove any ionic or heavy metal contaminants by
using a solution of 6:1:1 H
2
O:H
2
O
2
:HCl.
Regarding the glass substrate cleaning, hydroluoride contained
solution should not be used to avoid surface etching therefore
roughen the substrate surface. Usually glass wafers (or slides)
cleaning could be treated with soap solution irst, and then cleaned
by a solvent, and further processed by a mild acid clean. Water rinse
and nitrogen blow dry are followed for each treatment. More detailed
are described below.
(a) Soap clean: using soapy water to clean the glass substrate is
simple and safe way. When the glass substrate is immersed in
the soapy water, gently rubbing the surface to clean dirt and
residues with lint-free wipe and cotton swab could be more
effective. After inished, rinse the glass substrate with water
and blow dry with nitrogen for further process if necessary.
(b) Solvent clean: similar to silicon cleaning, the main purpose
of using solvent is to clean oils and organic residues on glass
surfaces. Acetone is the most common solvent to be used.
Note that, after the substrate cleaning with acetone, acetone
leaves its own residues. Hence, a two-solvent method is often
used — methanol rinse is followed to remove these residues.
Then rinse the glass substrate in water and blow dry with
nitrogen.
(c) Acid clean: If the glass substrate has metal residues or ionic
contaminations, mild acid could be considered for cleaning.
By using 30% HCl or 30% nitric acid solution, the metal ionic
residues would be easily removed from the glass surface. The
reaction time is usually several minutes, followed by water
rinse and nitrogen blow dry.
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