INDENTATION OF NEGATIVE PHOTORESIST FILMS FOR LIFT-OFF LITHOGRAPHY

Films of the AZ nLOF 2020, AZ nLOF 2070 and AZ nLOF 5510 negative photoresists (PR) with a thickness of 0,95 – 6,1 μm, deposited on the surface of silicon wafers by the centrifugation method, were studied by the indentation method. It was experimentally established that the behavior of AZ nLOF 5510 and AZ nLOF 20XX series photoresists during indentation differs dramatically. AZ nLOF 5510 films have high adhesion to silicon; not even single cases of cracking or peeling of films from the silicon substrate were observed. Additional stabilizing treatment and ion etching of AZ nLOF5510 films leads to their embrittlement and an increase in microhardness by 50 % – from 0,14 to 0,21 GPa. The strength and adhesive properties of the AZ nLOF 20XX series films are significantly worse than those of AZ nLOF 5510. The fracture toughness coefficient K1C (crack resistance) of the AZ nLOF 20XX films varied within 3,1–3,8 MPam1/2 and increased slightly after stabilizing treatment and ion etching. The specific peel energy G was 0,185 J/m2 for AZ nLOF 2020 and 0,63 J/m2 for AZ nLOF 2070. Ion etching resulted in a sharp (~ 30-fold) decrease in the G values. The true microhardness of the AZ nLOF 20XX series films was within 0,1– 0,2 GPa and increased after stabilizing treatment and ion etching, which is due to the cross-linking of photoresist molecules. The obtained experimental data are explained taking into account the ordering of the photoresist film structure near the PR/silicon interface due to the orientation of molecules and conformational changes in the structure of the main component of the photoresist - phenol-formaldehyde resin. The differences in the strength and adhesive properties of the AZ nLOF 20XX series photoresists are associated with the presence of residual solvent in the films.