P. R. J. Barroy

Measurements of characteristic transients of planar electrostatic probes in cold plasmas

This article describes how to extract accurate information about a plasma from a capacitively coupled planar probe that is biased using pulsed radio-frequency excitation. The conditions necessary to observe correct saturation of the probe current are investigated, particularly the use of correct geometry and biasing for the guard ring. With these precautions the probe is an effective diagnostic for electron tail temperature at energies beyond those probed by conventional cylindrical probes. The dynamic response of the probe is investigated using conventional sweep voltages and shows the onset of displacement current and inertial effects associated with ions and electrons. In addition the effect of insulating films on the probe surface is examined, showing how the probe continues to operate even when it is coated. Characteristic changes caused by the presence of an insulating film give information about its electrical properties and its thickness.

The effects of incident electron current density and temperature on the total electron emission yield of polycrystalline CVD diamond

The effects of temperature and incident electron current density on the total electron emission yield (TEEY) of polycrystalline diamond deposited by the chemical vapour deposition technique (CVD) were investigated at low electron beam fluence. It was found that the TEEY reversibly increases with the temperature and reversibly decreases with the current density. This behaviour is explained on the basis of a dynamic competition between the accumulation of holes (positive space charge), which internally reduces the secondary electron emission, and the thermally activated conductivity that tends to reduce the space charge formation.

Importance of fluorine surface diffusion for plasma etching of silicon

Dry etching of silicon is an important process in the manufacturing of integrated circuits and micromachined devices. Traditionally, the etch rate limiting step for an isotropic silicon etching process is considered to be the arrival of fluorine atoms directly from the gas phase onto the silicon surface, and the mechanism to promote anisotropy is the prevention of lateral etching by the formation of an inhibiting layer on the vertical walls. Furthermore, isotropic dry etching is considered to etch features in the same way as isotropic wet etching. Conventional mechanisms cannot explain, however, the perfect anisotropic etching of silicon with pure SF6, when no polymer is formed. Neither can it be understood how a deep (>50 μm), isotropic, dry etching process applied to silicon can result in structures with a pinched neck and sharp ridges, in contrast with a wet etching process, where the corners are rounded and no pinching of the neck is observed. It is proposed that long-range diffusion of fluorine atoms...

Sheath reversal during transient radio-frequency bias

Optical imaging is performed with temporal and spatial resolution in a capacitively coupled plasma. The region imaged is in front of an RF biased planar probe embedded in the center of the ground electrode of a standard Gaseous Electronics Conference (GEC) reference cell. Two main periods of interest stand out. The local sheath induced by the biasing and the main plasma bulk are affected. The first interesting period is at the onset of the RF burst on the planar probe. The voltage applied to the surface can locally reverse the sheath in front of this surface. A second interesting period is after the build up of self bias and before the extinction of the RF burst. During the steady self-bias phase, the local perturbation of optical emission amounts to less than 10%, whereas in the sheath reversal phase it reaches 70%.

Time-resolved perturbations near a self-biased, planar probe

Summary form only given. Modulated discharges are of interest to todays plasma processing technology as a means of manipulating plasma properties. Furthermore, a modulated perturbation of a discharge can be used for diagnostic purposes. Experiments reported here have been performed in a GEC reference reactor. Time resolved experiments were carried out on the plasma disturbance caused by the transient biassing of a surface-mounted, planar probe. This particular probe utilizes the nonlinearity of the plasma sheath to derive a bias potential from the rectification of an imposed RF signal. Following the onset of a burst of RF excitation, a self-bias develops over a period of several tens of microseconds. The time scale of this phase is determined by external capacitance. During the early stages, before the self bias has begun to build up, the surface potential can be swept above that of the local plasma. As a consequence, on a time scale typically of several microseconds, the plasma potential, the electron temperature and the ion and electron densities are perturbed during this early phase. A Langmuir probe, an emissive probe and a retarding field energy analyzer have been used to follow the perturbation in time. Argon, neon and hydrogen plasmas have been studied. The time-resolved measurements show that the bulk plasma is perturbed even though the area of the perturbing surface is small compared to the discharge electrodes it. This observation confirms associated work with time-resolved optical emission, which first identified the extent of plasma disturbance. The electron density and temperature are most affected. Data are presented and the physical mechanisms behind the effects are investigated. This work is relevant both to plasma diagnostics and plasma processing schemes involving pulse-modulated excitation.