Amanda Goyette

Synthesis and characterization of highly-conducting nitrogen-doped ultrananocrystalline diamond films

Ultrananocrystalline diamond (UNCD) films with up to 0.2% total nitrogen content were synthesized by a microwave plasma-enhanced chemical-vapor-deposition method using a CH4(1%)/Ar gas mixture and 1%–20% nitrogen gas added. The electrical conductivity of the nitrogen-doped UNCD films increases by five orders of magnitude (up to 143 Ω−1 cm−1) with increasing nitrogen content. Conductivity and Hall measurements made as a function of film temperature down to 4.2 K indicate that these films have the highest n-type conductivity and carrier concentration demonstrated for phase-pure diamond thin films. Grain-boundary conduction is proposed to explain the remarkable transport properties of these films.

Measurements and modeling of ion energy distributions in high-density, radio-frequency biased CF4 discharges

Models of ion dynamics in radio-frequency (rf) biased, high-density plasma sheaths are needed to predict ion bombardment energies in plasma simulations. To test these models, we have measured ion energy distributions (IEDs) in pure CF4 discharges at 1.33 Pa (10 mTorr) in a high-density, inductively coupled plasma reactor, using a mass spectrometer equipped with an ion energy analyzer. IEDs of CF3+, CF2+, CF+, and F+ ions were measured as a function of bias frequency, bias amplitude, and inductive source power. Simultaneous measurements by a capacitive probe and a Faraday cup provide enough information to determine the input parameters of sheath models and allow direct comparison of calculated and measured IEDs. A rigorous and comprehensive test of one numerical sheath model was performed. The model, which includes a complete treatment of time-dependent ion dynamics in the sheath, was found to predict the behavior of measured IEDs to good accuracy over the entire range of bias frequency, including complica...

Ion fluxes and energies in inductively coupled radio-frequency discharges containing CHF3

Measurements of ion energy distributions, relative ion intensities, and absolute total ion current densities were made at the grounded electrode of an inductively coupled Gaseous Electronics Conference (GEC) radio-frequency reference cell for discharges generated in CHF3 and its mixtures with argon. In general, the dominant ion species detected were not due to direct ionization of the CHF3 feed gas. Results are presented for plasmas generated with and without a confining quartz annulus that has recently been used to extend the operating parameter range of inductively coupled GEC cells for certain etching gases. Compared to similar plasmas generated without the annulus, the presence of the ring increases the ion flux density by approximately a factor of 2, and increases the mean ion energies. The presence of the ring does not significantly affect the measured relative ion intensities.

Ion energy distribution and optical measurements in high-density, inductively coupled C4F6 discharges

Hexafluoro-1,3 butadiene (C4F6) is a potential etching gas with a very low global warming potential for the manufacturing of semiconductors, unlike commonly used fluorocarbon gases such as CF4 and c−C4F8. We report ion energy distributions, relative ion intensities and absolute total ion current densities measured at the edge of an inductively coupled gaseous electronics conference radio-frequency reference cell for discharges generated in pure C4F6 and C4F6:Ar mixtures. In addition, the ratio of radical densities relative to CF measured using submillimeter absorption spectroscopy and optical emission spectroscopy measurements are presented. These measurements of the C4F6 plasmas were made for several different gas pressures (0.67, 1.33, and 2.66 Pa) and gas mixture ratios (25%, 50%, 75%, and 100% C4F6 volume fractions).

Ion velocities in the presheath of electronegative, radio-frequency plasmas measured by low-energy cutoff

Simple kinematic considerations indicate that, under certain conditions in radio-frequency (rf) plasmas, the amplitude of the low-energy peak in ion energy distributions (IEDs) measured at an electrode depends sensitively on ion velocities upstream, at the presheath/sheath boundary. By measuring this amplitude, the velocities at which ions exit the presheath can be determined and long-standing controversies regarding presheath transport can be resolved. Here, IEDs measured in rf-biased, inductively coupled plasmas in CF4 gas determined the presheath exit velocities of all significant positive ions: CF3+, CF2+, CF+, and F+. At higher bias voltages, we detected essentially the same velocity for all four ions. For all ions, measured velocities were significantly lower than the Bohm velocity and the electropositive ion sound speed. Neither is an accurate boundary condition for rf sheaths in electronegative gases: under certain low-frequency, high-voltage criteria defined here, either yields large errors in pr...

Electron drift in C4F6 and C4F6/Ar mixtures

We report measurements of electron drift velocities as a function of density-reduced electric field, w(E/N), for hexafluorobutadiene (C4F6) and mixtures of C4F6 with Ar. The w(E/N) for the mixtures of C4F6 with Ar can aid Boltzmann transport equation analyses aimed at calculating cross-section sets for C4F6.

Velocity boundary conditions for positive ions entering radio-frequency sheaths in electronegative plasmas

Under certain conditions in radio-frequency (rf) plasmas, the amplitude of the low-energy peak in ion energy distributions (IEDs) measured at an electrode depends sensitively on the velocity at which ions approach the sheath. By measuring IEDs, incident ion velocities can be determined. Here, IEDs were measured in inductively coupled plasmas in 1.3 Pa of CF4, at rf sheath voltages up to 100 V at 1 MHz, obtained by biasing a counterelectrode. From measured IEDs and sheath voltages, we determined the incident velocities of all significant positive ions: CF3+, CF2+, CF+, and F+. At higher bias voltages, we detected essentially the same velocity for all four ions, suggesting that some collisional process keeps different ions at the same velocity as they emerge from the presheath. For all four ions, measured velocities were significantly lower than the Bohm velocity uB and the electropositive ion sound speed cs, because of negative ion effects. From the measured velocities, an upper bound for negative ion temp...