An etching process is generally divided into two types these
are chemical and physical etching, sand blasting corresponds
to the latter, and is shown in Fig. 4. This technology has
recently been introduced as a bulk micro-machining technique
for brittle material, such as glass, or silicon, and so on. It is
based on mechanical material removal from a substrate by a
jet of particles. Abrasives of a micro-scale are accelerated by
high-pressure airflow through a micro nozzle, and then when
the particles collide with a brittle substrate at high velocity
(80~200m/s) and density, high compressive stresses arise
around the impact site, giving rise to a plastically deformed
zone. The removal rate by sand blasting depends on the
substrate materials properties, kinetic energy of abrasives on
the air compressor, jet velocity, the number of coming and
going of nozzle, and so on. Another important factor to
consider is degree of DFR film coating