The etching contamination remaining in Al-base SiO2 contact holes after hole fabrication followed by a series of cleaning treatments was analyzed by using thermal desorption spectroscopy. The hole aspect ratio dependence was measured for fluorinated aluminum molecules, the major desorption species. The amount of contaminant material in the holes was found to increase with the sidewall area of the holes, suggesting that the contaminant material desorbs from the bottom surface and accumulates on the SiO2 sidewall during contact hole etching.