Growth of Crystalline Quality SiC on Thin and Thick Silicon-on-Insulator Structures
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Mat. Res. Soc. Symp. Proc. Vol. 423 0 1996 Materials Research Society
In this paper, we report preliminary results on the epitaxial growth of SiC on a Si thin film with a thickness about 300A, on Si 2000A thick, and on bulk Si. Our recent TEM results (for growth at about 1 100°C) indicate that good crystalline quality SiC can be obtained on thin Si, even when the thin Si layer is not fully carbonized. Ongoing work (growth above 1300'C) identified the process steps to carbonize the entire Si top layer of SIMOX and produce good quality crystalline SiC. The high temperatures samples are presently being analyzed by TEM. EXPERIMENTAL PROCEDURE This work employed a SPI-MOCVDTm reactor typically used for growth of III-V compounds. The growth chamber features a vertical, water-cooled quartz belljar with a three-inch diameter silicon-carbide-coated graphite susceptor. A solid quartz rod supports the susceptor and serves as a light pipe for temperature measurement with a two-color optical pyrometer. In the standard approach for SiC or Si epi sample preparation, a Si substrate is typically etched by HCl to remove the surface oxide and impurities. However, for a LES wafer (with a thickness under 500A) special care is needed to avoid etching the Si thin film or reducing the Si0 2 buried layer. We developed a special process to clean the surface layer ofLES wafers without damaging or etching the Si thin film or buried oxide [12]. Thin SiC on LES, bulk Si, and standard SIMOX were grown at the same time to study the effect of the thickness of the Si top layer on the initial stage of SiC epitaxial growth. The growth procedure was similar to Powell, et.al.[5] except for the differences discussed. Growths were conducted at 1100°C. Research and ULSI-grade gas mixtures were used. Note, that the low Si:C ratio should result in a reduction in the residual nitrogen-doping background by site-competition epitaxy [15,16]. Rutherford backscattering spectroscopy (RBS) was also performed to determine the solid phase Si:C ratio, as well as the thickness of SiC and SIMOX layers. Commonly RBS is performed using an MeV He' beam with the sample oriented such that the incident beam is 10' from the normal of the sample. However, measurements were performed with the beam incident 100, 60' and 750 to the normal of the sample, which increased the effective thickness of the layer up to a factor of four. A Phillips CM20 transmission electron microscope at Case Western Reserve University was utilized to observe cross-sectional specimens. Cross-sectional transmission electron microscopy (XTEM) samples were prepared by sandwiching two films face to face with M-bond epoxy and curing it. Subsequently, the sandwiched sample was sliced by a diamond wheel and each slice was polished down to a thickness of 20 gim, and mounted on a Cu grid. Mounted specimens were further ion-milled to electron transparency. EXPERIMENTAL RESULTS 2 7 Figure 1 is an XTEM of a typical sample implanted at 30 keV with a dose of 2.5 x 101 O/cm and annealed for six hours at 1300°C in N 2.
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