Anisotropic trench etching of silicon with high aspect ratio and aperture of 30–50 nm in a two-stage plasma-chemical cyclic process

Abstract

The plasma-chemical cyclic process with alternation of etching and passivation stages (steps) is used to form trenches several tens of nanometers in width in silicon. The developed technology is characterized by a small duration of the stages (about 1 s); at each step, the etching time amounts to fractions of a second with a considerable amount of time being spent on the removal of a passivation layer from the bottom of the trench. The time of a pause between the steps is shown by the experiments to be a crucial parameter affecting the profile shape. To improve the selectivity of the etching process with respect to the mask, we use low values of the RF bias at the etching step (10–20 W) and rather high working pressures (more than 7 Pa). The experiments show that trenches can be formed with a mask underetch of about 2–3 nm, which is comparable to the wall roughness, for a high selectivity of the etching process with respect to the mask. For the trenches formed, the width is 30–50 nm, the aspect ratio is above 30, and the wall slope is 89°–90°.