Probe diagnostics of argon-oxygen-tetramethyltin capacitively coupled plasmas for the deposition of tin oxide thin films

Abstract

Langmuir probe measurements in nondepositing and depositing rf capacitively coupled (CCP) plasmas are briefly reviewed and compared to the results obtained in our rf system used for the deposition of tin oxide (SnO2) thin films from argon-oxygen-tetamethyltin [Sn(CH3)4] plasmas. Typically in our experimental conditions for tin oxide deposition, values of kTeff= 1.2−1.5 eV and ne=3−5×109 cm−3 were measured. These values are consistent with those generally reported in other depositing discharges. The shape of the electron energy probability function (EEPF), obtained from the Druyvesteyn procedure, was discussed too. As a consequence of the two electron heating mechanisms in capacitively coupled discharges, that is, ohmic and stochastic heating, the electrons have a bi-Maxwellian EEPF at low pressure (in the range of 10−100 mTorr). Moreover, a deep “hole” appears in the EEPF at the energy which could correspond to the resonant peak of the vibrational excitation cross section of some molecules which can be present in the discharge, such as N2, CH4, or CO.