In recent years, photomask resist strip and cleaning technology development was substantially driven by the industry's
need to prevent surface haze formation through the elimination of sulfuric acid from these processes. As a result, ozone
water was introduced to the resist strip and cleaning processes as a promising alternative to a Sulfuric - Peroxide
Mixture (SPM). However, with the introduction of 193i double patterning, EUVL (Extreme Ultraviolet Lithography) and
NanoImprint Lithography (NIL) the demand on CD-linewidth control and surface layer integrity is significantly
expanded and the use of ozone water is questionable. Ozone water has been found to cause significant damage to metal
based mask surface layers, leading to significant changes in optical properties and CD-linewidth shift.
In this paper HamaTech APE demonstrates the use of an alternative acid-free resist strip and cleaning process, which not
only overcomes the named drawbacks of conventional ozone water use, but reduces resist strip time by 50% to 75%. The
surface materials investigated during this study are; chrome absorber layers on binary masks, MoSi based shifters,
chrome hard mask layers on EPSM, and ruthenium capping layers on EUV masks. Surface material integrity and CD-stability
results using this new, acid-free approach are presented in the following pages.