Following the creation of a silicon dioxide layer, the wafer is
coated with a photosensitive material called a "photoresist."
There are
two types of photoresists: positive and negative. Positive photoresists
undergo weakening when exposed to irradiation, whereas negative
photoresists are strengthened. Most semiconductor processes use a
positive resist.
The photoresist is applied by delivering a small amount
of the liquid to the center of the wafer, then spinning the wafer at
high speed to spread the material over the entire surface in a thin,
uniform coating. Sometimes wafers are primed with an adhesive,
hexamethyldisilazane (HMDS). Glycol ethers have been a popular solvent
for carrying HMDS, although some manufacturers have switched to
alternative solvents like xylene, n-butyl acetate, acetone, and
1,1,1-trichloroethane. Table
1 identifies the component makeup of various photoresist
systems.
Use respiratory protection [29 CFR 1910.134] when necessary to further reduce exposure and protect employees.
Design and use specialized processing,
material handling, and storage equipment to properly contain chemicals. Consider both normal use and emergency scenarios.
Install emergency facilities to provide immediate treatment in the event of an
accidental exposure to corrosive materials. According to 29 CFR 1910.151, provide suitable facilities for quick drenching or flushing of the
eyes and body for immediate emergency use
whenever the eyes or body may be exposed to corrosive
materials.
Possible
employee exposure to solvents
used for adhesive application.
Glycol ethers have been a popular solvent.
However, due to reproductive effects associated with
exposures, they have been replaced with other
chemicals.
Replacement solvents for glycol ethers have included
chemicals such as xylene, n-butyl acetate, acetone,
and 1,1,1-trichloroethane.
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