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A schematic diagram of the plasma beam/QCM apparatus. An inductively coupled plasma is in the main chamber and the plasma is extracted to the mass spectrometer side chamber and QCM side chamber, both of which are differentially pumped using turbomolecular pumps. QCM sample is coated with silicon oxide to investigate the etching behavior of silicon oxide.
A model for angular dependence of oxide etching yield curve. Ion-induced chemical etching and isotropic etching are assumed. Below 72° where the etching component is greater than the isotropic deposition component the yield curve falls in the net etching regime, while below 72° where the isotropic deposition is greater net deposition is expected.
A comparison between projected etching yield curves based on the model shown in Fig. 2 and an actual measured curves. (a) Silicon oxide etching yield curves according to the simple model with ion-induced chemical etching and isotropic deposition. As the isotropic deposition component increases, the entire etching yield curve moves downward parallel to the original curve. (b) Oxide etching yield curves measured.19 As oxygen content is decreased in plasma, the plasma becomes more polymer forming. The figure shows as the deposition becomes more significant as a result of decrease in oxygen, the yield curve does not only shift down parallel to the original curve but also changes the shape. This indicates that the deposition component is not isotropic.
Silicon oxide etching yield curves measured at two different temperatures. , , ion energy, and source power. To identify the deposition component in the process, the measured yield curves are subtracted from the etching components showing “negative” deposition curves. These deposition curves show typical characteristics of sputtering curve, indicating that the deposition is an ion-induced process. (a) Yieid curve at (b) Yield curve at .
Comparison of model fit with measured angular dependent etching yield curve. For modeling, sputtering-shaped deposition curves were subtracted from ion-induced chemical etching curves. Measured etching yield and plasma etching yield curve23 are used for sputtering-shaped deposition component and ion-induced chemical etching component, respectively. The model fits (dotted lines) agree well with measured data (squares and triangles). (a) Model fit and measured data with temperature variation. ( and ). The ratios of normalized deposition curve to normalized etching curve are 0.8 and 0.4 for low temperature and high temperature, respectively. (b) Model fit and measured data with chemistry variation. The ratios of normalized deposition curve to normalized etching curve are 1.05 and 0.6 for and , respectively.
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