Thermal Changes of Photoresist Characteristics

Abstract

We have studied the chemical changes that result in photoresist due to various stresses that the photoresist is subjected to during the recovery and reclamation process.(1) When the roll coater recovery photoresist is kept open at room temperature for 50 days, needle-shaped crystals formed in recovery photoresist. Examination by X-ray diffraction revealed that those crystals are ammonium zinc sulfate hexahydrate that was dissolved from the roll material of coater. It is possible to avoid this problem by appropriate selection of the material that comes in contact with recovered photoresist.(2) When new, tightly sealed photoresist was subjected to thermal stress at 40°C for 100 days, a bead-shaped coagulated material appeared. NMR analysis showed that the coagulated material was mainly a photosensitive ester tetramer formed by a thermal change. In the case of the spin coating, although there is virtually no damage from physical stress, water content of about 1% is absorbed from the air during the spin-coating process, and the photo-active compound is decomposed by the thermal stress on the photoresist, lowering the photosensitivity. This change in the photosensitivity of the photoresist can be virtually eliminated if the photoresist contains no water so that the photo-active compound chemical change does not occur during the distillation process.(3) In the reclamation of photoresist, (a) the photoresist is coated in a dry nitrogen atmosphere with no water content, and next (b) the photoresist in a coater cup is dissolved by a photoresist-solvent and recovered, and then (c) the viscosity of the recovered photoresist is adjusted by distillation is filtered at the end. Fresh photoresist is replenished to it. We offer the resist reprocessor herein.