In this work a planar, radio frequency induction plasma source is characterized in terms of ion density, electron temperature, and plasma potential using a single Langmuir probe in oxygen and noble gases. Probe measurements of density were also verified using microwave interferometry. Measured argon ion densities increase nearly linearly with power from 1×1011 cm−3 at 300 W rf power to 6×1011 cm−3 at 1.2 kW at 1×10−3 Torr. Krypton ion densities are also linear with power but saturate above 1 kW at a density of 2×1012 cm−3 at 1×10−3 Torr. Electron temperatures increase with decreasing pressure from 3 eV at 26×10−3 Torr to 7 eV at 0.3×10−3 Torr. Plasma potentials are typically 15–30 V and increase with decreasing pressure. Ion saturation current in oxygen at 5×10−3 Torr is 2.5% uniform over diagonals of 20 cm when a magnetic multipole bucket is used to confine the plasma. Ion generation energy cost in argon is 100–250 W/A.
The electromagnetic fields which drive a radio-frequency induction plasma are both modeled and measured. The plasma source consists of a planar, square coil separated from a low pressure plasma chamber by a 2.54-cm-thick quartz window. A small loop antenna, which is sealed in a pyrex tube, is immersed in the discharge to determine the magnitude and direction of the rf magnetic field. The measured B field is primarily radial and axial. Typical rf field strengths vary from 2 to 7 G for rf powers of 0.1–1 kW. The radial B field decays exponentially in the axial direction. The skin depth of the electromagnetic field is 1.6–3.6 cm which is consistent with Langmuir probe measured ion densities (typically 3×1011 cm−3) in argon. Invoking Maxwell’s equations to deduce the rf electric field from the measured B field, we find the E field to be primarily azimuthal. Peak field strengths increase from 100 V/m at 100 W to 200 V/m at 600 W where they saturate for higher powers. Finally, we present a 3D finite element solution for the fields produced by this plasma source which employs a cold, collisionless plasma model to relate the relative plasma permittivity εr to the electron plasma frequency, ωpe, using εr=1−(ωpe/ω)2. The measured fields support this numerical solution.
The internal tensile stress in polycrystalline diamond films deposited on silicon substrates has been measured from 100 to 700 K by a vibrating-membrane method. The stress increases strongly with temperature, in a manner consistent with the elastic accommodation of the differential thermal strain between diamond and silicon. The results indicate that the films contain a tensile growth stress of about 500 MPa at the deposition temperature of 1123 K. Derived values of the biaxial elastic modulus fall in the range 730–850 GPa.
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