We studied the erosion and feature stability of fused silica patterns under different template cleaning conditions. The conventional sulfuric acid and hydrogen peroxide mixture (SPM) cleaning is compared with an advanced nonacid process. Spectroscopic ellipsometry optical critical dimension measurements were used to characterize the changes in pattern profile with good sensitivity. This study confirmed the erosion of the silica patterns in the traditional acid-based SPM cleaning mixture () at a rate of per cleaning cycle. However, the advanced nonacid cleaning process only showed critical dimension shift of per cleaning. Contamination removal and pattern integrity of sensitive 20-nm features under MegaSonic assisted cleaning was also demonstrated.