Investigation of the Expansion of an Oxygen Microwave Remote Plasma for the Growth of Functional Oxide Thin Films
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The expansion of an oxygen low-pressure microwave plasma was investigated in order to determine the optimal plasma parameters for the growth of functional oxide semiconductors. Langmuir probe measurements show that the electron density (n e ) increases with the injected power up to a saturation value of 3.0 × 109 cm−3 determined at 10 mTorr while electron temperature (T e ) remains constant at a value of 1.5 eV. When pressure is varied, n e shows a maximum value at a range from 12 to 20 mTorr while T e decreases monotonously with increasing pressure. In addition, both n e and T e decrease with the axial distance from the plasma source. These effects were discussed through the loss mechanisms in the remote plasma. For a pressure of 13 mTorr and at a substrate temperature of 500 °C, plasma enhanced oxidation of pure metallic Ti thin films lead to the formation of a pure TiO2 anatase phase compared to a mixed phase of TiO2 and TiO in the absence of plasma activation. For Mn thin films, the exposure to oxygen remote plasma led to the formation of MnO2 as opposed to obtaining Mn3O4 when oxidation is performed in the oxygen gas ambient. Remote plasma processing was thus found to provide selective pathways to control oxidation states, stoichiometry and phase composition of technologically attractive oxide thin films.
KeywordsLangmuir probe Plasma expansion Remote plasma oxidation Titanium oxide Manganese oxide
This work was supported by the University Research Board (URB) of AUB and the Lebanese National Scientific Research Council (LNSRC). Central facilities were used within the Central Research Science Laboratory (CRSL) of AUB. The authors would like to thank Prof. Michel Moisan for valuable discussions and Mr. Youssef Gabriel for technical support.
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