A new method to estimate the negative ion density in reactive gas plasmas with a Langmuir probe is proposed. This method has the advantage that the negative ion density is evaluated only by taking the ratio of the ion saturation–electron saturation current ratio obtained from the I–V curve of the Langmuir probe measured in an electronegative-gas mixture plasma to that measured in a reference noble gas plasma. The negative ion density in a SF6/Ar double plasma is estimated utilizing this method. Furthermore, the negative ion density measured with this method is confirmed to agree with that calculated from the measured phase velocity of the ion acoustic wave (fast mode) in the SF6/Ar double plasma, where positive and negative ion masses are obtained from the spectrum analysis with a quadrupole mass spectrometer.
A covering of an alumina insulating layer was deposited on the top of a C60 thin-film field-effect transistor (FET) by rf magnetron sputtering with Ar gas, in order to passivate the FET action from the degradation due to oxygen adsorption. The deposited alumina was amorphous and slightly oxygen deficient from the stoichiometry. The stability of FET action in air was considerably improved and no degradation has been detected even for more than one month.
A very-high-frequency (VHF) -excited SiH4 plasma was generated using a ladder-shaped electrode where the discharge frequency ranged up to 100 MHz and the plasma parameters were measured using a heated Langmuir probe. In the SiH4 plasma as well as in the H2 plasma, it was confirmed that when the discharge frequency is increased, the electron density increases while the electron temperature decreases. The electron density obtained at 100 MHz was 1.7×1010 cm-3, which is sevenfold that at 13.56 MHz. It was also found that the electron temperature tends to increase with increasing gas pressure in the SiH4 plasma at a very high frequency of 100 MHz.
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