Using an RF-driven collecting surface, mounted on the front end of a high-resolution energy-resolved mass spectrometer, the ion energy distribution functions (IEDFs) within a 13.56 MHz argon discharge have been measured and controlled. A technique of RF signal feedback has been developed, in which the RF amplitude and phase (fundamental and first two harmonics) in the sheath are varied, so manipulating the mean bombarding ion energies and widths of the IEDFs. For high RF sheath potentials, the IEDFs are broad and bi-modal. However as the sheath potential drop is reduced (with imposed matched RF signal) the IEDFs narrow, eventually becoming single peaked when no RF potential drop is present in the sheath. The observed widths in the IEDFs broadly agree with simple modelling predictions for the `high frequency' RF sheath regime; however we calculate, from the ion spectral data, marginally thinner sheaths than given by the Child-Langmuir law (derived using the mean DC sheath potential).

Standard laser interferometry is used in dry etch fabrication of semiconductor and MEMS devices to measure etch depth, rate and to detect the process end point. However, many wafer materials, such as silicon are absorbing at probing wavelengths in the visible, severely limiting the amount of information that can be obtained using this technique. At infrared (IR) wavelengths around 1500 nm and above, silicon is highly transparent. In this paper we describe an instrument that can be used to monitor etch depth throughout a thru-wafer etch. The provision of this information could eliminate the requirement of an `etch stop' layer and improve the performance of fabricated devices.We have added a further new capability by using tuneable lasers to scan through wavelengths in the near IR to generate an interference pattern. Fitting a theoretical curve to this interference pattern gives in situ measurement of film thickness. Whereas conventional interferometry would only allow etch depth to be monitored in real time, we can use a pre-etch thickness measurement to terminate the etch on a remaining thickness of film material.This paper discusses the capabilities of, and the opportunities offered by, this new technique and gives examples of applications in MEMS and waveguides.

Using an energy-resolved mass spectrometer situated behind a specially designed electrically isolated target boundary, the bombarding ion energy distribution function (IEDF) in an electron beam-plasma discharge at low pressure (< 0.26 Pa) has been determined. The collimated electron beam (mean energies 50-180 eV and beam currents up to 3 mA) incident upon the collisionless sheath of the target boundary was found to sink its floating potential down to approximately the voltage equivalent of the beam energy. The measured IEDFs were found to agree well with predictions of broad distribution functions with long low-energy tails obtained from a modified Tonks-Langmuir model of the collisionless beam-plasma boundary.