Influence of electron shading on highly selective SiO2 to Si etching

The dependence of the poly-Si etch rates at the bottoms of SiO2 holes on the patterns of the poly-Si films is investigated using fluorocarbon gas plasma. The etch rate of poly-Si film which is separated from large open areas exposed to plasma is higher than that of film which is connected to large open areas. This tendency is exaggerated as the aspect ratio of the hole increases. From Auger electron spectroscopy of the inside of the hole, a carbon peak is detected on the sidewall just above the poly-Si film which is separated from large open areas. This result indicates that low-energy ions, which are a deposition species, are deflected at the bottom of the hole by the positive charge resulting from the electron shading effect. This causes a decrease in the deposition of fluorocarbon polymer on the poly-Si film, resulting in an increase in poly-Si etch rates.