AVS 46th International Symposium
    Thin Films Division Monday Sessions
       Session TF+VM-MoA

Paper TF+VM-MoA4
Optical Characteristics of Carbon Nitride: Relationship with Mechanical Behavior and Possible Fullerene-like Microstructure

Monday, October 25, 1999, 3:00 pm, Room 620

Session: Advances in Hard and Superhard Coatings II
Presenter: V. Hajek, Ecole Polytechnique, Canada
Authors: V. Hajek, Ecole Polytechnique, Canada
D. Poitras, Ecole Polytechnique, Canada
D. Dalacu, Ecole Polytechnique, Canada
A. Bergeron, Optical Coating Laboratory Inc.
L. Martinu, Ecole Polytechnique, Canada
K. Rusnak, University of West Bohemia, Czech Republic
J. Vlcek, University of West Bohemia, Czech Republic
Correspondent: Click to Email
Crystalline @beta@-C@sub 3@N@sub 4@ was predicted to exhibit extreme properties, such as hardness, comparable to that of diamond. Although the synthesis of the crystalline metastable phase has not been fully confirmed yet, already prepared "amorphous" CNx films possess very attractive characteristics. In our earlier studies we have shown that these films possess high hardness (up to 30 GPa), high elastic recovery (up to 85 %), and interesting tribological behavior. Such films prepared at temperatures above 200 °C, using magnetron sputtering, are predicted in recent literature to possess a fullerene-like microstructure. In our recent work we suggested to extend this model to account for hydrogen incorporation: Excessive amount (> 1 at. %) of hydrogen in the films is believed to inhibit crosslinking between graphite-like planes containing carbon and nitrogen, and thus to hamper formation of the fullerene-like microstructure. In the present work we focus on the optical properties of CN@sub x@ films studied by spectroscopic ellipsometry and spectrophotometry. Different dispersion relations such as Sellmeier, Cauchy and Drude-Lorenz oscillator were used to determine optical constants n and k. The optical behavior is related to the film microstructure and the film fabrication conditions. CN@sub x@ layers were deposited on Si substrates by reactive DC magnetron sputtering of graphite target in nitrogen plasma at a substrate temperature of 600 °C and at a substrate bias ranging from -300 to -700 V. Films were found substoichiometric in nitrogen (from 12 to 24 at. %), and a concentration of hydrogen between 1 and 5 at. % was revealed by elastic recoil detection (ERD) analysis. Increased hydrogen content was accompanied by lower hardness, elastic recovery and adhesion, by higher electrical resistivity (from 20 to 970 @ohm@cm), by formation of C-H and N-H bonds (FTIR), and by higher optical transparency in the VIS and IR regions. The latter characteristics are related to the variation of optical bandgap which increases with hydrogen incorporation.