Heat-resistant photoresist composition, photosensitive substrate, and process for forming heat-resistant positive or negative pattern

A process for forming a negative pattern which comprises

• coating a photosensitive liquid on a substrate, said photosensitive liquid being prepared by dissolving a heat-resistant photoresist composition in an organic solvent, the photoresist composition comprising a polyimide precursor having a structural unit represented by formula (I):
• ##STR20## wherein the arrows each indicate a bond which can be substituted by isomerization, R.sup.1 represents a skeleton of benzene, naphthalene, perylene, diphenyl, diphenyl ether, diphenyl sulfone, diphenylpropane, diphenylhexafluoropropane, benzophenone, butane or cyclobutane, and R.sup.2 represents a skeleton of diphenyl ether, diphenyl thioether, benzophenone, diphenylmethane, diphenylpropane, diphenylhexafluoropropane, diphenyl sulfoxide, diphenyl sulfone, biphenyl, pyridine or benzene, and a compound represented by formula (IIa):
• ##STR21## wherein R.sub.5 and R.sub.6 each represent an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms, and wherein said compound represented by formula (IIa) is present in an amount of from 5 to 50 parts by weight per 100 parts by weight of the polyimide precursor,
• drying the resulting coating to form a film on the substrate,
• irradiating the resulting film with actinic rays through a photomask,
• heat-treating the irradiated film at a temperature of about 170.degree. C. or more, and
• removing unexposed areas of the film by development with an alkaline developing solution, wherein the step of heat treating the irradiated film at a temperature of about 170.degree. C. or more is conducted after the film is irradiated and before the film is developed.