Oxygen diluted hexamethyldisiloxane plasmas investigated by means ofin situinfrared absorption spectroscopy and mass spectrometry

The gas phase species produced in rf plasmas of hexamethyldisiloxane (HMDSO), Si 2 O(CH 3 ) 6 , diluted with oxygen, have been investigated. The complementarity of Fourier transform infrared absorption spectroscopy and mass spectrometry allows the determination of the most abundant neutral components present in the discharge. The measurements reveal that methyl groups (CH 3 ), abundantly formed by the dissociation of the HMDSO molecule, are the precursor for the most abundant species which stem from two kinds of reaction. The first kind of reaction is combustion of CH 3 by oxygen-producing formaldehyde (COH 2 ), formic acid (CO 2 H 2 ), carbon monoxide (CO), carbon dioxide (CO 2 ) and water. It is shown that high mass carbonated radicals, such as Si x O y C z H t , first diffuse to the surface and then the carbon is removed by oxygen etching to form CO 2 . The second is hydrocarbon chemistry promoted by CH 3 , producing mainly hydrogen (H 2 ), methane (CH 4 ) and acetylene (C 2 H 2 ).