CVD Growth of SiC on Ultrathin SOi 2 : A Step Towards Development of a Compliant Substrate for SiC and III-V Compounds
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INTRODUCTION Fabrication of silicon carbide (SiC) structures on Si wafers is desirable for a number of reasons including their use as low-cost, large-area substrates for high-power, high-temperature electronics, and their use as lattice-matched substrates for group III-nitrides. Epitaxial SiC has been grown on Si either by direct deposition, or by carbonization of the Si surface. The carbonization process has to date, provided the lowest defect SiC on Si [1-5].. However a lower defect density is needed before SiC on Si is suitable for device applications. In the past few years, there has been rapid progress with separation by implantation of oxygen (SIMOX) technology, in which a relatively defect-free Si top layer is produced on an oxide layer on a Si substrate [6]. These structures have been used as substrates to grow epitaxial layers such as GeSi [7,8] or silicides [9]. Recently, we developed a Low-Energy SIMOX [10-13]_process (LES) which can produce SIMOX structures with ultrathin (< 500A) Si layers. These layers are thinner than the usual highly strained transition layer produced during growth of SiC on Si. When the ultrathin Si layer of a SIMOX wafer (rather than the surface of a Si wafer) is converted to SiC by carbonization, or used as a substrate for SiC epitaxy, it is expected to have fewer crystal defects, for two reasons: (1) the buried SiO 2 layer will soften at the carbonization or growth temperature and will relieve stresses associated with lattice constant changes, and (2) there will be minimum stress in the SiC epitaxial layer, or in the converted layer during carbonization, since the thin Si layer is expected to yield first [8]. It has been observed that during the carbonization process the lattice constant of the transition layer changes from that of Si to that of SiC in a distance up to 300A [20]. Thus, ultrathin SIMOX structures (300A or less) appear to be an excellent substrate for carbonization. In this paper we report preliminary results on the epitaxial growth of SiC on a Si film with a thickness less than 300A and compared it with bulk or thick SIMOX substrates. Our present data shows that better crystalline SiC can be obtained on thin Si even when the process does not carbonize the thin Si layer. Work is in progress to carbonize the entire Si top layer of SIMOX and present results are the first step toward development of a compliant substrate for SiC and GaN. 357 Mat. Res. Soc. Symp. Proc. Vol. 410 01996 Materials Research Society
EXPERIMENTAL PROCEDURE This work employed a SPI-MOCVD 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 HCI to remove the surface oxide and impurities. However, for a LES wafer (with a thickn
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