AVS 50th International Symposium
    Thin Films Wednesday Sessions
       Session TF-WeM

Paper TF-WeM5
Optical Properties and Microstructure of Plasma Deposited Ta@sub 2@O@sub 5@ and Nb@sub 2@O@sub 5@ Optical Thin Films

Wednesday, November 5, 2003, 9:40 am, Room 329

Session: Optical Thin Films and Photovoltaics I
Presenter: O. Zabeida, Ecole Polytechnique of Montreal, Canada
Authors: H. Szymanowski, Ecole Polytechnique of Montreal, Canada
J.-P. Masse, Ecole Polytechnique of Montreal, Canada
O. Zabeida, Ecole Polytechnique of Montreal, Canada
J.E. Klemberg-Sapieha, Ecole Polytechnique of Montreal, Canada
L. Martinu, Ecole Polytechnique of Montreal, Canada
Correspondent: Click to Email
Advanced optical filter applications require not only an appropriate control of the optical constants of the thin films but also a suitable control of other film properties such mechanical performance, thermal and environmental stability, absence of refractive index inhomogeneities and others. In this respect, plasma enhanced chemical vapor deposition (PECVD) allows one to fabricate films with low as well as with high refractive index, and it also offers a possibility for stress compensation, control of refractive index gradients, and high deposition rates at low substrate temperature. In the present work we study the characteristics of two high index optical materials, namely amorphous tantalum pentoxide (Ta@sub 2@O@sub 5@) and niobium pentoxide (Nb@sub 2@O@sub 5@) obtained by PECVD, respectively, from penta-ethoxy tantalum Ta@sub 2@(OC@sub 2@H@sub 5@)@sub 5@ and penta-ethoxy niobium, Nb@sub 2@(OC@sub 2@H@sub 5@)@sub 5@, precursors. We particularly investigated the effect of the energetic conditions on the film growth by using different modes of plasma excitation, namely radio frequency (RF), microwave (MW) and dual-mode microwave/radio frequency (MW/RF) discharges. Under sufficient ion bombardment, controlled by the RF-induced negative substrate bias, the dense Ta@sub 2@O@sub 5@ and Nb@sub 2@O@sub 5@ films exhibited a refractive index of 2.16 and 2.26 (at 500 nm), respectively, while the extinction coefficient was below 10@super -5@, as determined by spectroscopic ellipsometry, spectrophotometry and thermal deflection optical calorimetry. We found that increasing ion bombardment during the film growth leads to an appreciable increase of carbon concentration incorporated in the films, as indicated by a strong double peak at 1400 and 1500 cm-1 in the FTIR spectra. Elastic recoil detection (ERD) measurements reveal an atomic concentration of 2.5% and 5,5% of carbon in the bulk of the Ta@sub 2@O@sub 5@ and Nb@sub 2@O@sub 5@ films. The presence of carbon did not appear to negatively affect the film optical and mechanical performance and stability. We discuss the possible mechanism of carbon bonding in these films in a form of metal chelate and bridging groups.