Charging and the secondary electron–electron emission on a trench surface: broadening and shift of ion energy spectrum at plasma trench etching

Abstract

Trench surface charging at the plasma etching of dielectrics and semiconductors is a negative phenomenon because it leads to non-uniform etching of the trench bottom, undesirable etching of its wall, etch stop and breakdown of lower level device elements. To investigate the charging of a SiO2 trench surface by argon radio frequency discharge plasma we applied the 3D Monte Carlo method for modelling the electron and ion trajectories inside a trench and used the 2D analytical method to calculate electric fields and potentials produced by the deposited charges. The secondary electron–electron emission was taken into account as a really important mechanism of electrical charge redistribution on the trench surface. The ion energy spectra were calculated for the trench aspect ratios (depth d/width w) of 1–20 and trench widths of 11, 22 and 45 nm for 180 eV ion flux. The transformation of an initial ion energy spectrum from a delta function at 180 eV into bell-shaped curves with peak shifts of 10–60 eV and broadening of 5–30 eV is obtained.