KTI-820, a positive photoresist, was hardened using a formaldehyde and hydrochloric acid solution consisting of five parts hydrochloric acid (HC1)and one part formaldehyde. The experiment involved varying the duration of the bath from three to ten minutes and varying the temperature of the bath from 70 to 100 degrees centigrade. The results of this process showed resist flow and thickness loss. The thickness loss was a result of the EC1 attacking the resist during the soak in the HC1 and formaldehyde solution.
Stricker, Brian E.
"Positive Photoresist Hardening Using Formaldehyde Soak Methods,"
Journal of the Microelectronic Engineering Conference: Vol. 4:
1, Article 36.
Available at: https://scholarworks.rit.edu/ritamec/vol4/iss1/36