4. How high is the adhesion strength of e-beam resists to different wafers?
Adhesion between substrate and coating is a sensitive feature of a resists, which is also true for e-beam resists. PMMA- and copolymer resists are however significantly less prone for adhesion problems than e-beam resists of the AR 7000 product line, where smallest changes of the cleaning procedure or other parameters may have a fatal impact on the adhesion strength. Silica, silicon nitride, and base metals (such as aluminium, copper) generally possess good resist adhesion features, while adhesion on SiO2, glass,noble metals such as gold or silver, and on gallium arsenide is often insufficient. In this case, measures have to be taken to improve adhesion (→Question 3 Pre-treatment of substrates). If the air humidity is too high (> 60 %), adhesion is also substantially reduced.