A "reference cell" for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.

Ion energy distributions were measured at a grounded surface in an inductively coupled, high-density plasma reactor for pure argon, argon–helium, and argon–xenon discharges at 1.33 Pa (10 mTorr), as a function of radio-frequency (rf) bias amplitude, rf bias frequency, radial position, inductive source power, and ion mass. The ground sheath voltage which accelerates the ions was also determined using capacitive probe measurements and Langmuir probe data. Together, the measurements provide a complete characterization of ion dynamics in the sheath, allowing ion transit time effects to be distinguished from sheath impedance effects. Models are presented which describe both effects and explain why they are observed in the same range of rf bias frequency.

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 complicated effects that are observed when the ion transit time is comparable to the rf bias period.

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The effect of radio-frequency bias on electron density in an inductively coupled plasma reactor was measured using a wave cutoff probe, over a wide range of conditions in pure Ar, pure CF4, and 50%–50% mixtures of Ar∕CF4, at pressures of 0.7–4.0Pa (5–30mTorr), bias frequencies of 10–30MHz, bias voltages up to 750V, and inductive source powers of 50–300W. Also, at selected experimental conditions, comparisons with Langmuir probe measurements were made. Two types of bias-induced changes in electron density were detected. First, at high source powers, we observed a bias-induced decrease in electron density, which had a slow time response (several minutes), a linear dependence on bias voltage, and little or no dependence on bias frequency or pressure. This decrease is a gas composition effect caused by etch or sputter products liberated from the wafer surface. Second, at low source powers, we observed a faster, bias-induced increase in electron density, which was proportional to the bias frequency and the square root of the bias voltage. This second effect was caused by absorption of bias power by electrons via stochastic heating. Simple models of each effect were derived and were shown to yield quantitative predictions in agreement with the observations. To obtain correct predictions, the effect of bias-induced electron heating cannot be considered by itself; rather, its effect on the efficiency of the inductive source must also be considered.