Research On Influence Of Discharge Parameters On Capacitive Discharge With Different Frequency

Low pressure capacitively coupled discharges (CCPs) are widely used in semiconductor and microelectronic industries for thin film etching, deposition and surface treatment. There is an increasing interest for very high frequency (VHF) CCP discharges, aimed at higher electron density and lower ion bombardment energy on the powered electrode. Various benefits of VHF capacitive plasmas in materials processing have been reported, for example, higher growth and etching rate, better uniformity of deposition film and less micro-loading effect. In low pressure radio frequency (RF) discharges, the energetic electrons interact with parent gas to support processes of excitation, dissociation and ionization while self-bias voltage of the powered electrode affects the distribution of plasma sheath electric field and the ion energy and thus determines the etching rate and etch profiles. Therefore, the study on influence of discharge parameters upon electron density as well as electron temperature and bias voltage is of great importance for the understanding of plasma process and improvement of high quality etching process.There are mainly two research contents in this paper. In the first part, a study is conducted on influence of discharge parameters (power, pressure and driving frequency) upon a conventional CCP. The evolutions of electron density ne and electron temperature Te over a wide range of gas pressures have been investigated by a dual probe while the variation of bias voltage is measured by an oscilloscope. It is shown that, regardless of frequency, electron temperature gives a significant decrease until it comes to a stable value and as driving frequency and pressure go up,electron temperature also exhibits a decrease due to the continuous collisions between electrons and around particles. Electron density presents an analogous parabolic increase at low discharge power while it increases linearly at high discharge power. From low pressure to high pressure, electron density increases at first and then it doesn't change a lot or even start to go down. Besides, a second order dependence of electron density on driving frequency is observed over the frequency range from 13.56MHz to 60MHz. Bias voltage goes up with discharge power while it decreases with pressures as well as frequencies.In the second part, the coupling and modulations between high frequency and low frequency in dual frequency CCP have been studied. It is found that, electron density is mainly determined by the input-power of high frequency and independent control of electron density by driving frequency can be improved by higher ratio of two frequencies. Self-bias voltage of electrode increases as its input-power goes up and the voltage induced by low frequency is higher than that of high frequency.