Page 195 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

INTRODUCTION 175

P M M M P*M
M M M M hv M
M p M P M M p M P* M
M M P M M Actinic photons M M P*M M
M M from UV source M M
P = Photoinitiator Photoinitiator excitation
M = monomer

P-M» M M P-M MM
M P<S M M P* M M
M M»M
M p M P M M p M P M
M M P-M M
M M M M
Chain initiation Free-radical generation

P-M--M'
p
^M X yi P > M
M P M M P
P- > M
Chain propagation Chain termination (—)

Figure 7.3 Example of a simplified free-radical photopolymerisation sequence used in MSL

Intensity j/ \
Light 1 / \
-
source / \ Gaussian beam
fS V.
— •-
1

Cured spot
Resist

Figure 7.4 Theoretical intensity profile of the UV beam (Gaussian) and the resultant spot cured
within the photoresist

The fraction of light transmitted through an absorbing system is given by the
Beer-Lambert law (see for example, Wayne (1998)):

= exp(—aCd)
7 t// 0 (7.1)