Measurement Of Optical Constants Of Thin A-c:h Films

Amorphous hydrogenated carbon films (a-C:H) are very interesting materials for optical applications. They are transparent in the near IR part of the spectrum and its refractive index and absorption coefficient may be changed with the deposition parameters. In this paper we measure the optical constants of a-C:H films, deposited by plasma enhanced chemical vapor deposition as a function of the radio frequency power. The measurements were performed by the method of Abeles in λ = 633 nm and by the approximation of Lambert-Beer in the transmission measurements using a spectrophotometer. Both methods do not require the use of thick films that are difficult to deposit due to the intrinsic stress of these films. The measurements were compared with that obtained by the fringe peaks in transmission measurements of a thick film. Our results showed that it is possible, in our system, to deposit homogeneous and uniform films with any refractive index chosen between 1.8 and 2.2 at λ = 633 nm.314251254Holland, L., Ojha, S.M., The growth of carbon films with random atomic structure from ion impact damage in a hydrocarbon plasma (1976) Thin Solid Films, 58, pp. 107-116Angus, J.C., Koidl, P., Domitz, S., (1986) Plasma Deposited Thin Films, p. 89. , J. Mort, & F. Jansen. Boca Raton: CRC PressKakuchi, M., Hikita, M., Tamamura, T., Amorphous carbon films as resist masks with high reactive ion etching resistance for nanometer lithography (1986) Appl. Phys. Lett., 48, pp. 835-837Kragler, K., Günther, E., Leuschner, R., Falk, G., Hammerschimidt, A., Von Seggern, H., Saemann-Ischenko, G., Scanning-tunneling-microscopy based lithography employing amorphous hydrogenated carbon as a high-resolution resist mask (1995) Appl. Phys. Lett., 67, pp. 1163-1165Martino, R., Ferguson, R., Molless, A., Liebmann, L., Neisser, M., Weed, J., Callegari, S., Lithographic evaluation of the hydrogenated amorphous carbon film (1995) J. Vac. Sci. Technol. B, 13 (6), pp. 2949-2953Lima, C.R.A., Soares, L.L., Cescato, L., Alves, M.A.R., Braga, E.S., Diffractive structures holographically recorded in amorphous hydrogenated carbon (a-C:H) films (1997) Opt. Lett., 2223, pp. 1805-1807Françon, M., (1961) Progress in Microscopy, , New York: Row, Patterson & Elmsford. Chap. 6Born, M., Wolf, E., (1975) Principles of Optics, , Oxford: Pergamon Press. chap. 13Freeman, E., Paul, W., Optical constants of r.f. sputtered hydrogenated amorphous Si (1979) Phys. Rev. B, 20, pp. 716-72