|The main solvent of almost all AZ® and TI photoresists is PGMEA (2-methoxy-1-methylethylacetate), which is also supplied as thinner (AZ® EBR solvent, the former AZ® 1500 thinner). Dependant on the adjusted viscosity, typical photoresists contain between 55-85% PGMEA.
The high (154°C) boiling point of PGMEA, and the low vapour pressure (approx. 2 mbar at room temperature) prevent fast evaporation out of open containments and during dispense. Thereby, PGMEA allows reproducible and safe (flashpoint 42°C) resist processing. PGMEA is one of very few solvents which do only cause minor particle formation even at high resist dilution ratios.
After softbake, remaining PGMEA impacts on subsequent processed in two ways: During development, PGMEA converts into acetic acid hereby increasing the dark erosion (and also the development rate) in the developer. During subsequent baking or coating steps (e.g. hardbake, metallization), remaining solvent lowers the softening temperature (causing resist roundening) and may additionally cause bubbling at elevated temperature due to the promoted evaporation.|