Summary: VHF H2 and SiH4/H2 plasma was produced using a ladder shaped electrode of 1 200 mm × 141 mm and the plasma parameters were measured with the Langmuir probe. It was found that uniform VHF plasma is achieved over 1 m at a frequency of 60 MHz. VHF plasma was also produced at high pressure. When the pressure was increased from 0.3 Torr to 4 Torr, the plasma density decreased at high pressure, while the electron temperature was around 10 eV at high pressure. Furthermore, Langmuir probe characteristics indicated that there exists a high amount of negative ions at high pressure.
Two very-high-frequency powers between which the phase difference is varying in split of time are supplied to a ladder-shaped electrode through multiple feeding points located at symmetrical positions of the electrode to generate a large-area uniform plasma. Theoretical calculations of the voltage distribution at several phase difference show good agreement with experiments. Plasma emission uniformity within ±15% is demonstrated at 60MHz for the substrate size of 1.4×1.1m, with nitrogen gas of 10Pa.
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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