Cross-Sectional TEM Investigation of Low-Temperature Epitaxial Silicon Films Grown by Ultra-Low Pressure CVD
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CROSS-SECTIONAL TEM INVESTIGATION OF LOW-TEMPERATURE EPITAXIAL SILICON FILMS GROWN BY ULTRA-LOW PRESSURE CVD T.R. YEW*, J.H. COMFORT', L.M. GARVERICK*, W.R. BURGER+, and R. REIF+ *: Department of Materials Science and Engineering Department of Chemical Engineering Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology, Cambridge, MA 02139
ABSTRACT In this paper, cross-sectional TEM is used to investigate the quality of silicon epitaxial films grown by ultra-low pressure The dislocation density and epi.chemical vapor deposition at 750*C. substrate interface width were investigated for different Epitaxial films with predeposition Argon sputter cleaning condltions. and interfacial width of dislocation densities of less than 10 cm about 13 A were obtained.
I.
INTRODUCTION
The structure and chemistry of thin solid films can be studied by cross-sectional transmission electron microscopy (XTEM) (i.e., surface In this normal of the film perpendicular to the electron beam). orientation, the substrate, the thin film layers, and the interfaces between them can be directly observed either simultaneously or In this paper, XTEM is used to investigate lowindividually. temperature epitaxial silicon films grown by ultra-low pressure It is shown here how XTEM was used to chemical vapor deposition. improve the quality of epitaxial films by studying the effects of deposition parameters. Donahue and Reif [11 developed a system and a procedure using torr) chemical vapor deposition process for a very low pressure (10 depositing silicon epitaxial films at temperatures as low as 650*C To improve the control of both with and without plasma enhancement. the deposition parameters, an improved reactor has been designed and The epitaxial films investigated here were all grown assembled [2]. in this improved reactor. The contribution of XTEM is in the observation and comparison of the quality of epitaxial films and morphology of interfaces for various bias, power, and time of Argon sputter, the predeposition cleaning High resolution XTEM is also used to get the technique used here [1]. The optimum predeposition lattice images of discrete interfaces. This XTEM characterization cleaning conditions are then identified. made it possible to grow dislocation-free epitaxial films and discrete epi-substrate interfaces at a temperature of 750*C. II.
EXPERIMENTAL PROCEDURES
The experiments include epitaxial growth, XTEM sample preparation, TEM observation, and high resolution TEM investigation. The wafers used are CZ n-type Si with 100-cm resistivity. Before the wafers are loaded to the reactor (which is maintained at 200°C), they are RCA-cleaned, oxidized thermally at 950°C, dipped in
Mat. Res. Soc. Symp. Proc. Vol. 75. 1987 Materials Research Society
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DI water, and cleaned on UVOCS. The reactor is then sealed and pumped down to 2 - 5 x 10 torr and the susceptor and wafer are radiantheated (using lamps) to the deposition temperature for 1½ hours in a 10 mtorr Argon ambient. After that, the in-situ pre
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