Claude Laure

Enhanced deposition rates in plasma sputter deposition

Langmuir probe and emission spectroscopic measurements are performed in a high frequency (100 MHz) argon plasma used for the sputter deposition process of thin films of palladium (dedicated to catalysis applications). The metal source is a helicoidal palladium wire which is negatively biased with respect to the plasma potential. This induces sputtering by the ions present in the plasma. The probe results show that the presence of the helicoidal wire in the chamber does not affect the total ion flux at the substrate location. However, as the bias voltage on the wire and/or the argon pressure are increased, a secondary direct current (DC) discharge is created inside the helicoidal wire which follows a Paschen-like law; the breakdown voltage is lower than in the case of a conventional Ar discharge, probably as a result of the presence of primary electrons generated by the main high frequency (HF) plasma. This second discharge is characterized by a strong flux peak inside the helicoidal wire, which probably arises from a hollow cathode type discharge. From emission spectroscopy and deposition analysis, it is shown that this secondary plasma causes an increase of the sputtered Pd atom number and, consequently, an enhanced deposition rate.

Plasma assisted evaporation of palladium

We studied the deposition of palladium on silicon using a high-frequency argon plasma. It is shown that the argon ions are focused and sputtered a biased helicoidal palladium wire. An auxiliary continuous discharge enhancing palladium evaporation rate is obtained for a pressure and bias voltage above 50 m Torr and -200 V respectively, as revealed by optical emission spectroscopy. The growth rate is between 0.5 and 20 A as deduced from x-ray photoelectron spectroscopy. Scanning tunnelling microscopy studies reveal that growth proceeds through nucleation.

Ion extraction from a helicon source and PIC simulation

The design of an ion extraction system often requires the help of computer codes. This article describes an experimental setup based on a helicon source equipped with a three-grid extraction system and that is used as an ion source. A numerical approach based on a particles in cells (PIC) method is introduced. The results obtained with the ion source for different gases are compared with the simulation and are used in order to validate the computer code. The numerical code is the first component of an ion source design package that deals with grid erosion and ion beam current distribution on the target.

Plasma assisted deposition of Pd thin films

Abstract In this work we studied the deposition of Pd on a silicon surface by a non-conventional plasma assisted deposition technique. The Pd source is a negatively biased Pd wire located in the deposition chamber and sputtered by the plasma ions. Emission spectroscopy and Langmuir probe measurements are used to characterize the plasma and to determine the experimental parameters influencing the deposit features, especially the Pd deposition rate (1–5 ML min −1 ) (ML = monolayer). It has been evidenced that exact control of the deposited Pd quantity (several ML) can be performed by adjusting the deposition time duration or the Pd wire bias. The Pd films devoted to catalysis applications, exhibit interesting characteristic: they are polycrystalline, flat and composed of small Pd spheres with a diameter of hundreds A.

TIME RESOLVED DIAGNOSTIC OF ION BEAM ENERGY DISTRIBUTION FUNCTION FOR PLASMA THRUSTERS

In order to test time resolved diagnostics, a controlled energy fluctuation source has been designed. This source is able to give beams of fluctuating energy in different time controlled regimes. Two operating modes have been tested. The first one is a square wave modulation of the ion beam energy. The second one is a triangular shaped energy variation in time. This source has been used to qualify a time resolved Retarding Field Energy Analyzer. Measuring the energy distribution functions of the ion beam, the RFEA is able to restitute both energy shapes at a 30-kHz frequency thanks to an appropriate data acquisition and treatment system.