Protective coatings are in most cases composed of novolacs or PMMA polymers. Both polymers ensure a sufficiently high protective effect against mechanical damages as well as sufficiently high resistance against acidic solutions. PMMA resists (e.g. AR-PC 503 or 504) in addition provide a safe protection against strong alkaline solutions (up to 40 %), which is not the case for novolacs. The stability in the presence of most organic solvents is relatively low for both, and only tempering at > 180 °C makes these resists sufficiently stable. Associated with this however are difficulties when tempered resist films are to be removed. Another drawback is the formation of PMMA strings during coating, which means that “cotton candy” structures develop during the spin-off.
Resist SX AR-PC 5000/31 is a hybrid of both polymers. Through a selected tempering in a range between 120 – 170 °C, the resistance against alkaline solutions and organic solvents can be adjusted. After a bake at these temperatures, removal is still possible and no string formation is observed.