Secondary effects of single crystalline silicon deep- trench etching in a chlorine-containing plasma for 3- dimensional capacitor cells

The main problems occurring during the trench etching in a chlorine containing RIE process are considered: (1) deposition of contaminating films on the trench sidewalls, (2) micro masking effects of those contaminations leading to the so called “black silicom”, and (3) “trenching effects” on the bottom of the trench cell. By means of SIMS and Auger measurements it is shown that the contaminating films on the trench walls are formed by unsaturated B x Cl y species from the BCl 3 plasma. By the same analytical methods it is obtained that the so called black silicon occurring in a pure Cl 2 plasma is caused by micro masking by Al-, Si- oxide clusters which stem from surface adsorbed oxygen and the alumina covered cathode. Furthermore it is observed that the trenching effect occurring with Cl 2 plasma can be significantly reduced by adding BCl 3 . BCl 3 reduces the number of Cl + 2 ions and therefore favours the formation of passivating species on the surface to be etched. This passivating layer in return reduces the trench formation at the bottom.