Project 8 (EMPA)

Title: Pulsed RF GD analysis of non-conductive thin films

Researchers: Sebastian Schmidt (ESR), Elisa Barisone (ESR)

Coordinator: EMPA, Laboratory for micro-mechancis and nano-structures
Responsible Scientist: Johann Michler
Other partner: CUFR JFC Albi, IFW

State of the Art:

Pulsed glow discharges combined with a Mass Spectrometer or an Optical Emission Spectrometer have been studied in some depth over the last few years. It has been found that employing short pulses of high power can significantly improve the detection limits through increased ionisation and/or excitation yiels and reduced spectral interference. In most cases, however, a direct current discharge has been used and the studies were consequently limited to conductive materials. A different adavantage of using pulsed discharges is the reduces thermal stress imposed on the analyte sample, because the average power dumped in the sample can be controlled independently from the plasma power, by varying the duty cycle. In work recently published by EMPA , the feasibility and interest of pulsed RF discharges are demonstrated. The effect of pulsed discharges on thin layers has not yet been studied in detail.

Objective and Innovation:

The aims of this work are to understand and optimise the pulsed RF-plasma so as to take full benefit of its advantages in Content Depth Profiling (CDP) on non-conductive thin films in both OES and MS. The work is also motivated by the wish of making information on molecular structure of the sample accessible to direct analysis with GD-TOFMS. During the projected research work, which is the subject of a PhD work, Elisa Barisone will determine the specific properties of the three different phases (ignition, plasma-on, afterglow) of a pulsed RF-discharge. Each of the three phase differs in its emission and ionisation yield. It has also been found that the formation of molecular species varies in these phases. It part of the planned work to study the effect of the pulse sequence on the temporal separation in the generation of different plasma species and its effect on depth resolution and sputtering yield. 

Improving the depth profile capabilities of pulse glow discharge spectrometer not only requires a good understanding of the plasma processes but also the surface properties of the analysed samples must be characterised and their influence on the ultimately achievable depth resolution studied.

During the research work, Elisa Barisone will be trained in understanding fundamental plasma processes, their importance to the analysis and instrumental techniques for optimisation of the achieved results. She is currently working on measurements of the secondary electron emission yields. The secondary electron emission yield "gamma" is a material dependent parameter. It influences the impedance of the glow discharge. In her experiments Elisa determines the effective gamma by measuring the break down voltage.

Preliminary results of the measurement of the effective electron emission yield have been presented on poster (2-13)

• E. Barisone, Ph.Belenguer, Ph.Guillot, J. Michler, Th. Nelis, L. Therese; "Experimental Determination of Effective Secondary Electron Emission Yields of Conductive and Non-Conductive" at the 19th ESCAMPIG, poster (2-13) July 2008, conference in Granada and
  
• at the 4th international GD-Day at Horiba Jobin Yvon, France, in September 2008, poster No 10.
• M.Aeberhard, E.Barisone,Th.Nelis; "Different ways to improve the cleanliness of the sputter source in GD-OES systems." at the "Deutsche GD-Anwender Treffen" Berlin April 2008.
  
• and at the 4th international GD-Day at Horiba Jobin Yvon, France, in September 2008, poster No 1.
• E.Barisone, "Experimental Determination of Effective Secondary Electron Emission Yields of Conductive and Non-Conductive", oral presentation at 2nd year meeting of EC STREP EMDPA 24-26.09.2008
  

A 3 month stay at the Leipniz Institute for Material Research in Dresden is planned, because complementary knowledge on radio frequency technology, analysis of solid materials and mass spectrometry is available. The project is carried out in close collaboration with the University of Oviedo, project 9,  as related studies are performed simultaneously at the laboratories.

About the Laboratory for Mechanics of Materials and Nanostructures at EMPA in Thun

In our laboratory run by Johann Michler, we investigate mechanical materials properties from the nano to macro-scale using experimental, analytical, and computational techniques. Current cutting edge research within European projects and the ETH competence center on high temperature materials focuses on micro- and nano- mechanical properties of materials (instrumentation, scale effects related to microstructure and physical dimension. For this purpose, we develop metallic model materials either via electrodeposition in combination with UV- and electron beam lithography, nanoporous membranes and via focused electron or ion beam processing and push resolution frontiers of materials microanalysis instrumentation, for instance of glow discharge based surface depth profiling and tip enhanced micro-Raman spectroscopy.

We focus on solutions for Swiss SMEs to increase mechanical reliability, production efficiency, and lifespan of new materials and systems ranging from thin films, watch parts and solar cells to power plant component