Effect of heat and moisture on thick positive photoresist

A Novolac resin AZ 4903 for lithographic evaluation is discussed from the standpoint of moisture and heat effects. Differential gravimetric and thermogravimetric analyses (DTG and TGA) were used for investigating the chemical changes of the photoresist associated with heat. The variations of moisture (humidity levels) were used to evaluate the hydrolyzation of the photoresist. The hydrolyzation was followed by UV light exposure and development of photoresist. Scanning electron and optical microscopy was used to determine the efficiency of photoresist development. The DTG and TGA revealed five chemical changes in photoresist (AZ 4903) materials due to the effect of heat from 25 to 700°C. The changes are related to the lithographic process. The first process is due to evaporation of high volatile solvent; the second process is due to removal of low volatile solvent and nitrogen (partly); the third process is due to removal of photosensitizer and monomer; the fourth process is due to removal of low molecular resin; and the fifth process is due to decomposition of organics. The increase of humidity for hydrolyzation reduced the resist developing time. A 40% time saving is possible for hydrolyzation at 70% humidity compared to the time required for hydrolyzation at 40% humidity. However, the quantity of water required for hydrolyzation remained constant