ANGLE-RESOLVED MASS-SPECTROMETRY OF POSITIVE-IONS TRANSMITTED THROUGHHIGH-ASPECT-RATIO CHANNELS IN A RADIO-FREQUENCY DISCHARGE

The behavior of positive ions in high aspect ratio structures, relevan t to the reactive ion etching of deep trenches, has been studied by me ans of energy resolved mass spectrometry. High aspect ratio trenches a re simulated by capillary plates with various aspect ratios. Angle res olved measurements of the ion current passing through the channels in the capillary plates have been performed in low pressure argon and hel ium radio frequency plasmas. The angular distribution of the ion count s 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 chann el. This loss is mainly a consequence of geometrical shadowing; ion lo ss due to deflection by surface charge on the capillary plates has onl y little effect at moderate power inputs. At high power inputs ion los ses become extremely high, so the transmission through the channel pla te decreases almost to zero.