Charge Damage Caused by Electron Shading Effect

An antenna covered with photoresist patterns having high-aspect-ratio openings caused charge damage to the gate oxide in various processing plasmas. This damage increased with the pattern's aspect ratio, and occurred even when the test wafer was cut into chips about 5 mm square and mounted on a wafer with insulation. These results prove the electron shading model: the photoresist patterns shade the antenna from electrons of oblique incidence, resulting in local charging occurring without a wafer-scale voltage difference, which is essential for conventional charging. The damaging current from this mechanism increased by a factor of more than ten with a decrease in the gate oxide thickness only from 8 nm to 6 nm, implying that the degree of shading depends on the gate charging voltage. An improved model is proposed to accommodate this strong dependence.