Dielectric properties of SiOx like films deposited from TMS/O2 mixture in low pressure microwave plasma

• Thin layers were deposited by microwave plasma using tetramethylsilane (TMS) and oxygen mixtures as precursors.
• The thin layers composition was dependent of the oxygen concentration in the TMS/O2 precursor.
• A more inorganic character was observed with the increase of the oxygen concentration in the precursor.
• Dipolar groups in the deposited layers are the mainly cause of the permittivity values increase.

In this study, dielectric and physicochemical properties of thin films prepared in low pressure microwave plasma reactor have been investigated. The films have been deposited from tetramethylsilane or a mixture of tetramethylsilane and oxygen (TMS/O2). The plasma discharge power and the working pressure in the reactor were kept constant and equal to 400 W and 1 mTorr, respectively. The deposition rate and refractive index have been found to decrease with increasing oxygen proportion in the mixture. For films deposited from TMS, the deposition rate and refractive index were about 800 Å/min and 1.55 respectively. Whereas, for films deposited from 90% of O2 and 10% of TMS, their values were in the order of 50 Å/min and 1.47, respectively. When the oxygen rate in the mixture increases, FTIR analysis shows more formation of Si–O–Si groups with a significant decrease of organics groups (such as Si–CH3 and –CHx). At high oxygen flow rate (90%) in the precursor mixture, the deposited films are SiOx-like structure. The dielectric constant value was close to 3.6 when the films are deposited using low oxygen proportion and close to 4.5 for films deposited with high O2 rate in the precursor.