Experimental investigation of the respective roles of oxygen atoms and electrons in the deposition of SiO2 in O2/TEOS helicon plasmas

The respective roles of electrons and oxygen atoms in the plasma enhanced chemical vapor deposition of SiO2-like films are investigated in a low-pressure radio-frequency helicon oxygen/tetraethoxysilane (TEOS) plasma. The plasma and film growth are monitored by optical emission spectroscopy and in situ spectroscopic ellipsometry, respectively. The variations of the atomic oxygen density [O] (measured by actinometry) and the deposition rate are studied as a function of the organosilicon fraction in the O2/TEOS plasma. First, on the basis of these measurements and the data available in the literature, it is established that electrons have the key role in TEOS fragmentation while the contribution of O is shown to be very weak. Second, it is shown that organosilicon films deposited in a TEOS rich plasma are etched by O atoms when exposed to a pure oxygen plasma. The etching rate is proportional to [O] and is of the same order of magnitude than the deposition rate, which demonstrates that deposition and etching really compete in O2/TEOS plasma.