Thus, most
of the heat is lost due to air convection. During spin coating
of pure paraffin, a heat gun was used to heat the COC surface
above the paraffin melting point of 55–56 ◦C. This generated
even more air convection, resulting in even shorter spin coating
times (2 s spread and 3 s spin). Although the process worked, an
important trade off of the reduced spin time is a reduction in film
thickness uniformity—we measured pure paraffin film thickness
to vary by more than 2 m over the wafer surface. However,
when using OpticlearTM to spin coat paraffin under a conventional
lamp to preheat COC substrates, the spin coating time was
increased to 20 s and the film thickness uniformity was improved
dramatically (see Fig. 4). Observed thickness variations were
0.3–0.5m, depending on the film thickness. The thickness of
paraffin films deposited using the OpticlearTM approach varied
from 3 to 7m when changing deposition speed from 2000 to
6000 rpm.