MASS-SPECTRAL INVESTIGATION OF THE RADIOFREQUENCY PLASMA DEPOSITION OF HEXAMETHYLDISILOXANE

Experiments have been performed with the aim of enhancing our understa nding of the reactions that take place within inductively coupled, rad io-frequency (RF) plasmas of hexamethyldisiloxane (HMDSO). These plasm as have been investigated using a combination of mass spectrometry (MS ) and deposition rate measurements. Thin films of HMDSO were deposited onto silicon substrates and analyzed by X-ray photoelectron spectrosc opy (XPS). At low plasma power, the positive-ion MS data reveal that e xtensive molecular oligomerization takes place within the plasma gas p hase. However, no significant formation of neutral oligomeric species was detected. XPS analysis revealed the surface stoichiometry of the d eposit to be closer to that of the oligomers detected by MS than that of the starting compound (M). At higher plasma power, increased fragme ntation of the monomer was observed, with a concomitant loss of the hi gher mass positively charged species. Again, no significant formation of neutral species of mass greater than M was detected. The deposition rate increased from ca. 6.5 to 15 ng s(-1) over the power range inves tigated. We conclude that at low plasma power ion-molecule reactions a re responsible for deposit formation. We propose that at high power th e ionic component of these plasmas is still important, in terms of dep osition.