Characterization of extremely thin epitaxial layers and films by new interference fringes
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Li Lian Department of Physics, Gakushuin University, Mejiro, Tokyo, 171 Japan
Nobuhito Nango Ratoc System Engineering Co., Ltd., Shinmei Building, Nishishijuku 7-7-33, Shinjuku-ku, Tokyo, 160 Japan
Tomoya Ogawa Department of Physics, Gakushuin University, Mejiro, Tokyo, 171 Japan (Received 5 February 1992; accepted 22 March 1992)
The existence and imperfection of several types of epitaxial layers and films on the substrate crystals were successfully detected and characterized nondestructively using a new interference fringes method. It was found that the interference fringes generated by amorphous thin films showed many very tiny bright spots that became discontinuous, which was quite different from the case of fringes generated by a crystalline epitaxially grown layer (smooth fringes). Multiple layers on a substrate were also observed by the fringes that were not concentric, but interlacing.
I. INTRODUCTION Completely nondestructive detection, measurements, and characterization of extremely thin epitaxially grown layers/films and their interfaces between substrate and the thin layers become more and more important and necessary for improvement of device quality, where "extremely thin" means that the film thickness is much less than the wavelength of light. Light scattering tomography (LST) is very effective for quantitative characterization of the microdefects in semiconductor crystals from the viewpoint of nondestructive three-dimensional studies. 12 The microdefects in bulk crystals will be effectively detected by 90° illumination of the LST,1 and the defects near the surface of the crystal will be effectively detected by Brewster angle illumination using an optical fiber system for LST.2'3 Since the thickness of the extremely thin layers is such that the characterization of the existence and the quality of the interface inside the specimens are very difficult, even using Brewster angle illumination and LST with an optical co-focusing system are inadequate, due to strong background scattering light from the interface and some technical problems. Recently, a type of interference fringes due to extremely thin layers was discovered by the present authors. Based on the principles of light scattering and interference, by which the existence of extremely thin films can be nondestructively performed, the quality of the films and the interface properties were characterized. 2182 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 8, Aug 1992 Downloaded: 14 Mar 2015
In this paper, the detection and characterization of imperfections in several different kinds of thin epitaxial layers/films, and the quality of their interfaces by the new interference fringes method are reported. II. PRINCIPLE AND EXPERIMENTAL METHOD A. General features of the new interference fringes The new interference fringes show the following features: (1) The fringes are nearly localized on an extremely thin film and are concentric rings which can be deformed into ovals by oblique illumination of the laser beam. (2) An interval between ne
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