Photoresist
Photoresist
Photoresist
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Light, water are the main drivers of this process<br />
Starting material will not dissolve in the developer; carboxylic acid,<br />
however, readily reacts with and dissolves in basic solutions (pH ><br />
7); novolac resin dissolves easily in developer<br />
Typical developer solutions are KOH or NAOH diluted with water<br />
Dark areas of the photomask will protect the resist from light and<br />
will “stay” after developing → positive image<br />
Negative resists are suited to features > 2 µm due to swelling during<br />
development; they are based on a resin of cyclized polyisoprene p and<br />
bis-aryl diazide (PAC); these compounds lose N 2 on light exposure<br />
and form free radicals that react with a site in the resin; this cross-<br />
linking produces a highly insoluble film in the developer and<br />
pattern is formed by washing away the unpolymerized resist →<br />
negative image
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