AVS 47th International Symposium
    Surface Engineering Tuesday Sessions
       Session SE-TuM

Paper SE-TuM8
Optimization of In Situ Substrate Surface Treatment in a Cathodic Arc Plasma: A Plasma Diagnostics and STEM-EDX Study

Tuesday, October 3, 2000, 10:40 am, Room 201

Session: Interface Engineering and Graded Films: Structure and Characterization
Presenter: C. Schönjahn, Sheffield Hallam University, UK
Authors: C. Schönjahn, Sheffield Hallam University, UK
A.P. Ehiasarian, Sheffield Hallam University, UK
W.-D. Münz, Sheffield Hallam University, UK
D.B. Lewis, Sheffield Hallam University, UK
R. New, Sheffield Hallam University, UK
R.D. Twesten, University of Illinois, Urbana
I. Petrov, University of Illinois, Urbana
Correspondent: Click to Email
It has been shown previously that the in situ substrate cleaning step prior to PVD deposition affects the interface formation which influences the adhesion of the coating on the substrate. Most promising results were obtained for Cr ion bombardment where the Cr ions are extracted from a cathodic arc source by negatively biasing the substrates with U@sub s@=-1200V. The main objective of the current project is a further optimization of the in situ substrate surface pre-treatment with respect to reduced process costs and lower risk for local substrate overheating. Langmuir probe measurements show that the presence of Ar leads to a two-fold increase of the speed of the cathode spot thus reducing the amount of macro particles emitted by the cathodic arc source. The presence of Ar leads to an increased ion current density of j = ~30 Am@super -2@ for P@sub Ar@ = 8x10@super -2@ Pa compared to j = 6 Am@super -2@ at background pressure of P@sub tot@ = 7x10@super -4@ Pa due to the ionization of Ar in the cathode spot and in charge exchange reactions with Cr ions as observed by Optical Emission Spectroscopy. Although the mean energy of bombarding species decreases the higher ion flux suggests a more effective removal of substrate material. This is indeed observed by measuring an effective etching rate of 4 nm.min@super -1@ at P@sub tot@ = 7x10@super -4@Pa compared to 8 nm.min@super -1@ at P@sub Ar@ = 8x10@super -2@Pa. However, owing to the loss of high energy Cr ions, metal ion implantation, which was shown to be beneficial for adhesion, is reduced. The implantation profiles were studied by STEM-EDX analysis on electron transparent cross sections. Based on these results a two stage ion bombardment procedure is proposed. The first stage is Cr bombardment at an Ar pressure of 8x10@super -2@ Pa for intensive cleaning. This is followed by pure Cr ion bombardment for enhanced ion implantation due to the higher portion of multiply charged Cr ions to achieve enhanced adhesion.