Deep U.V. Hardening of Positive Photoresist Patterns

Thermal deformation of positive photoresist patterns during high temperature treatments is significantly reduced by flood exposure of the photoresist with a low pressure mercury lamp containing deep UV at λ = 254 nm . Patterns formed in the positive photoresists AZ‐1470, AZ‐1350J, AZ‐2400, Hunt 204, KTI II and Kodak 809, after exposure with a low pressure Hg lamp, withstood a 180° C bake for 30 minutes while retaining their linewidth and standing wave pattern on the sidewall of the resist lines. Flood exposure of the photoresist patterns with near UV ( λ > 300 nm ) had the opposite effect. The stability of the patterns towards thermal deformation after deep UV exposure was found to be due to the formation of an outer skin of higher polymerization. If the skin is removed using an oxygen plasma the underlying photoresist behaves similarly to samples which received only near UV exposure. Positive resist solubility properties in acetone and AZ thinner were also studied.