Comparison of germanium and silicon dry etching by using inductively coupled BCl₃ plasma

We have investigated the etch rates and the angle subtended for Ge and Si as a function of the BCl₃ flow rate, the inductively coupled plasma (ICP) power, and the work pressure. The Ge etch rate is always greater than the Si etch rate, and the maxima of the Ge and Si etch rates are observed to be functions of the BCl₃ flow rate. The peak etch rate is at 40 seem BCl₃ flow rate. The etch rate of Ge decreases from 2370 to 1780 Å/min as the BCl₃ flow rate increases from 40 to 80 seem. Also, the etch rate of Si decreases from 640 to 460 Å/min as the BCl ₃ flow rate increases from 20 to 80 seem. The largest Ge/Si etch rate ratio is obtained for BCl₃ flow rate of 60 seem. The etch rate of Ge decreases from 2835 to 2094 Å/min as the ICP power increases from 200 to 500 W whereas the etching rate of Ge increases from 2370 to 2900 A7ring;/min as the work pressure increases from 10 to 50 mTorr. As the BCl₃ flow, ICP power, and work pressure, increase the angle subtended also increases. Optical emission spectroscopy (OES) has been used to examine the gas phase species in the plasma, and emission from excited atomic B and Cl has been identified. The composition of the reaction layer on germanium due to the BCl₃ plasmas has been obtained by using X-ray photoelectron spectroscopy (XPS). The reaction layer on germanium due to inductively coupled BCl₃ plasma etching is found to be typically a very thin layer of the Ge-Cl and Ge-O.