Estimation of ion incident angle from Si etching profiles

The distribution of angles of incident etching ions was measured using a test sample having an overhanging mask structure. The standard deviation of ion incident angles decreased with decreasing pressure of the etching atmosphere. With conventional reactive ion etchers, standard deviations of 3 to 8° were measured at pressures from 2.6 to 101 Pa. With a microwave plasma etcher, the measured deviation at 1.3 Pa was 2°. The aspect-ratio dependence of etching with SF 6 may be caused by the insufficient radical supply, which becomes the rate-determining step for etching a high-aspect-ratio trench.