Angle resolved mass spectrometry of positive ions transmitted through high aspect ratio channels in a radio frequency discharge

The behavior of positive ions in high aspect ratio structures, relevant to the reactive ion etching of deep trenches, has been studied by means of energy resolved mass spectrometry. High aspect ratio trenches are simulated by capillary plates with various aspect ratios. Angle resolved measurements of the ion current passing through the channels in the capillary plates have been performed in low pressure argon and helium radio frequency plasmas. The angular distribution of the ion counts becomes strongly anisotropic after the ions have passed through the channels. The narrowing of the ion distribution with increasing aspect ratio is explained by the loss of ions at the side walls of the channel. This loss is mainly a consequence of geometrical shadowing; ion loss due to deflection by surface charge on the capillary plates has only little effect at moderate power inputs. At high power inputs ion losses become extremely high, so the transmission through the channel plate decreases almost to zero.