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Through the utilization of a mixture of appropriate materials, a method of masking several photolayers of a semiconductor, a printed circuit board or a packaging substrate with one photo mask is achieved.
English (United States)
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Reversible Photosensitive Masking Media for Semiconductor
Through the utilization of a mixture of appropriate materials, a method of
masking several photolayers of a semiconductor, a printed circuit board or a
packaging substrate with one photo mask is achieved.
By incorporating photochromic properties into a semiconductor photo mask,
one mask is useful for deep ultraviolet (UV), middle UV, far UV, infrared (IR) and
X-ray transmittance exposure. Photochromic glass is an optical quality
borosilicate composition containing a dispersion of light-sensitive silver halide
crystals. These crystals are responsible for the unique property of variable light
transmission, darkening in the 220 to 405 nanometer (UV) range and clearing in
the 700 to 1200 nanometer (infrared) range, depending upon the composition of
the glass. Some compositions have a cleared transmittance of up to 90%, while
others exhibit a darkened transmittance of as low as 5%. Most importantly, the
cycle is reversible and will not fatigue with time.
To fabricate a mask with photochromic properties, a quartz mask blank is
coated with resist and etched to form holes 1.5 to 3.0 millimeters in depth, as
shown in Fig. 1. The etched holes are then filled with a powdered glass/silver
halide mixture and heated to cause the mixture to flow. Note that the mixture melt
temperature is well below that of quartz. When used as a photomask in the deep
UV exposure range, as shown in Fig. 2, the area of the...