Resist process issues related to the glass transition changes in chemically amplified resist films
Optical interferometry is applied for in situ measurement of the glass transition temperature in thin resist films (Tgfilm) spin-coated on flat reflective substrates, using a novel, low-cost, rapid methodology. Process issues, such as film thickness and thermal processing effect on Tgfilm were explored using this methodology. In the case of relatively thick films the calculated Tgfilm from the optical interferometry method is in good agreement with the corresponding differential scanning calorimetry (DSC) values. The film thickness effect on Tgfilm in the case of two positive chemically amplified resists (one commercial for DUV and one experimental for 157 nm lithography) is studied and discussed. In both cases, as film thickness decreases the Tgfilm increases indicating strong surface phenomena that should be taken into account in lithographic processing. The presented methodology enabled studies on Tg changes during resist processing in characteristic positive and negative tone chemically amplified resist materials allowing deeper insight in resist optimization issues.
resists optical interferometry glass transition temperature lithography polymers thin films