The generation mechanism of photoresist residue after the ashing process of aluminum interconnect etching was investigated by changing the cross-sectional profile of resist pattern, resist thickness, and resist pattern width. The generation mechanism of resist residue after ashing is clarified by analyzing the resist residue with Auger electron spectroscopy. It has been revealed that aluminum is attached to the sidewall of resist pattern during aluminum etching and if the cross section of the resist pattern has a negative slope, the attached aluminum on the sidewall of the resist pattern is scarcely removed by etching ions and the thickness of aluminum does not decrease. This attached aluminum is oxidized in an ashing gas and removal becomes harder. When the ashing process proceeds, the Al2O3 sidewall falls down on the center of the resist pattern and covers the pattern. Therefore, the resist ashing is terminated and resist residue is generated.