Influence of plasma pulsing on the deposition kinetics and film structure in low pressure oxygen/hexamethyldisiloxane radiofrequency plasmas

The deposition rate and structure of films deposited in an oxygen/hexamethyldisiloxane 85 : 15 low pressure radiofrequency plasma are investigated as a function of the pulse parameters. The variations of the deposition rate with the plasma-off and plasma-on times are compared to a model involving characteristic rise and decay times for the deposition, which are found to be equal to 2 and 80 ms, respectively. Such a long decay time suggests the presence of long lifetime species, which act as precursors to the film growth. These latter allow to reduce the average applied power without significantly reducing the deposition rate. On the other hand, the structure and the properties of the deposited film can be controlled and varied from SiO2-like to SiOxCyHz organic film by tuning the pulse parameters. Pulsed plasmas are shown to be very attractive in order to deposit graded composition layers without changing the oxygen to organosilicon flow rate ratio.