Hardening of photoresist

A method of hardening a positive photoresist which comprises exposing a film of positive photoresist material to UV radiation containing sufficient dosage of wavelengths of about 320 nm or below to cause said photoresist to harden while subjecting the film to elevated temperature upon increase in the degree of polymerization due to exposure to said UV radiation wherein said elevated temperature, at any instant during the said exposing, is below the flow temperature of the film at the particular instant, and wherein the resist is subjected to elevated temperature during the exposure to the UV radiation which is greater than the initial flow temperature of the resist at the start of the exposure to the UV radiation, and to thereby harden said positive photoresist.