Comparative Study of Films Deposited from HMDSO/O2 in Continuous Wave and Pulsed rf Discharges

We have performed a comparative study of the properties of films deposited in the rf CCP discharges from a mixture of 5% of hexamethyldisiloxane in oxygen at two different pressures 2.5 and 40 Pa in continuous and pulsed modes. Changes in optical and especially mechanical properties of the films were observed due to differing pressure. Slight changes in the properties were also achieved by pulsing the discharge. Films deposited at 2.5 Pa exhibited very low compressive stress and hardness from 5.5 to 6.9 GPa. Soft films of 1.6 GPa maximum hardness possessing a tensile stress and containing more CH3-related groups were deposited at a pressure of 40 Pa. Hard SiO2-like films (11-13.5 GPa) were deposited from the same mixture in the ICP mode of a helicon reactor at the pressure of 0.3 Pa at which the CCP discharge could not be sustained. These films possessed relatively high compressive stress. Increasing off-time up to 15 ms caused a slight decrease in the hardness and in the case of 0.3 Pa ICP films a significant decrease in the compressive stress. The film optical properties were obtained using a model parameterizing the density of states. According to this model, the band gap was found in the range of 7.4-8.2 eV. The films deposited in the CCP exhibited a small absorption peak in UV due to an existence of localized defect states at about 5 eV.

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