Light scattering from fused polycrystalline aluminum oxide surfaces.

The results of a study of the topography of fused polycrystalline aluminum oxide surfaces using reflected coherent light of 6328-A wavelength are reported. It is shown that the wavelength and angular dependences of the specular intensity can be understood in terms of optical scattering theory in the Kirchhoff approximation for a surface with a Gaussian roughness distribution. The values of the rms roughness obtained optically by fitting the experimental observations to the theory agree well with those obtained from Talysurf measurements. Estimates of the rms slope and correlation distance of the surface structure are obtained from a treatment of the specular and diffuse components of the reflected light intensity using the Beckmann model. An empirical relationship is shown to exist between the mean surface grain size as determined by microscopic observation using the line intercept method and the rms surface roughness. These results have formed the basis of an optical technique for rapidly estimating the mean surface grain size on high alumina substrates used in the microelectronics industry.

Optical propagation in sheet and pattern generated films of ta(2)o(5).

Attention is drawn to the properties of Ta(2)O(5) film which make it attractive as a new dielectric medium for use in integrated optical circuitry. The Ta(2)O(5) film discussed was formed by thermally oxidizing sputtered , beta-tantalum films in an oxygen atmosphere. Measurements showed that these films will support propagation of coherent red (6328-A.) light with a loss of 0.9 dB cm(-1) and coherent blue (4880-A) light with a somewhat higher loss of 4.1 dB cm(-1). From measurements of the coupling angle at which propagation of the various modes takes place, refractive indices for the TE and TM modes at 6328 A, 5145 A, and 4880 A were obtained. The loss mechanisms are discussed, and it is shown that most of the loss is due to scattering during the internal reflections at the air-oxide and oxide-substrate film surfaces. A small fraction of the loss appears to occur in the interior of the film. With Ta(2)O(5) it is demonstrated for the first time that optical circuit components can be formed for use in integrated optics by employing existing thin-film technology. The basic process steps include the pattern generation of the beta-Ta followed by thermal oxidation of the pattern. Experimental studies of propagation in straight and curved waveguides are described. It was found that the losses in pattern generated waveguides are of the order of 5 dB cm(-1) to 7 dB cm(-1), with the excess loss due to scattering from the waveguide edges. It is concluded that improvements in the smoothness of the boundaries of circuit elements are desirable to reduce transmission losses in pattern generated film.