Novel Ashing Process of Heavily Implanted Photoresist

Popping of heavily implanted photoresist during plasma stripping occurs during the conventional ashing process using oxygen radicals at the fixed temperature range of 250 C or higher. We introduce preheating of wafers in air at atmospheric pressure prior to the ashing step. They do not suffer from low ashing rate or substrate damage. It is found that this pre-heating step accelerates outgassing from the bulk of the photoresist without popping. Since heat transfer from hot wafer stage to wafer is better in air than in vacuum, it also increases wafer temperature faster, and thus also the ashing rate. In this paper, we monitor the surface-morphology and chemical-bonding changes before and after heat-treatment by SEM and XPS, respectively, and find that heating in vacuum increases amorphous carbons in the photoresist surface more than heating in air. KCI Citation Count: 1