Effect of the ion bombardment energy on silicon dioxide films deposited from oxygen/tetraethoxysilane plasmas in a helicon reactor

Silicon dioxide films are deposited on silicon substrates from oxygen/tetraethoxysilane (TEOS) plasmas in a helicon reactor operated at low pressure (5 mtorr). The effect of the negative dc self-bias voltage Vb (0 to −200 V) on structural and electrical bulk properties of SiO2 films is investigated. The structural characterization has been performed using Fourier-transform infrared (FTIR) spectroscopy, spectroscopic ellipsometry and wet etching. Electrical measurements including capacitance-voltage (C-V), current-voltage (I-V) and constant current stressing (CCS) have been carried out on metal-oxide-semiconductor (MOS) capacitors. As soon as a dc self-bias is applied (∣Vb∣≥50 V), a significant enhancement of the oxide quality is observed in terms of macroscopic densification and reduction in the porosity. These modifications in the structural properties of the deposited SiO2 films are correlated with an improvement in the I-V characteristics but C-V and CCS measurements revealed that limiting the substrate bias at −50 V leads to best quality silicon dioxide films.