Resist-related damage on ultrathin gate oxide during plasma ashing

This paper presents an important observation of plasma-induced damage on ultrathin oxides during O₂ plasma ashing by metal "antenna" structures with photoresist on top of the electrodes. It is found that for MOS capacitors without overlying photoresist during plasma ashing, only minor damage occurs on thin oxides, even for oxide thickness down to 4.2 nm and an area ratio as large as 10⁴. In contrast, oxides thinner than 6 nm with resist overlayer suffer significant degradation from plasma charging. This phenomenon is contrary to most previous reports. It suggests that the presence of photoresist will substantially affect the plasma charging during ashing process, especially for devices with ultrathin gate oxides.