| During coating (evaporation of metals, sputtering, PECVD), the resist film may be heated by the evaporation source radiation, the condensing heat of the growing film, or the kinetic energy of the ions, above its softening point (110-130°C for most positive tone and image reversal AZ® resists). Hereby the resist profile starts rounding allowing the coating material to cover also the resist profile side-walls. As a consequence, subsequent lift-off will work worse or become impossible.Possible workarounds are i) an optimized heat coupling of the substrate to its holder (e.g. some turbo pump oil for proper heat transfer from strained, curved substrates), ii) a sufficiently high heat buffer (massive substrate holder construction) or iii) heat removal (e.g. black anodized aluminium as rear infrared radiator) from the substrate holder, iv) a reduced deposition rate or/and a multistage deposition with cooling interval(s) in between, v) UV-curing, or vi) a thermally stable photo resist (e.g. AZ® 701mir or AZ® 66xx series in positive mode or TI 35ES in image reversal mode), or AZ®nLOF negative resist for highest thermal stability. |
Product request: Positive Resists for Coating/Lift-off
Literature: Image Reversal Resist Processing