Epitaxial Growth of AlN on Si Substrates with Intermediate 3C-SiC as Buffer Layers
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carbide and the AIN layer is less than 1%. It therefore seems feasible to deposit hexagonal SiC on Si substrates if single-crystal 2H-A1N can be grown as an interlayer. The focus of this paper is the epitaxial growth and characterization of AIN single crystal films on Si(1 11) substrates. The AIN films were grown on thin 3C-SiC buffer layers previously formed by carbonization of the Si( 111) substrates. EXPERIMENTAL Si (111) wafers oriented 3' off axis toward direction were used as substrates. The surface of each Si wafer was converted to a thin 3C-SiC( 11) layer via gas-source molecular beam epitaxy (MBE) prior to chemical vapor deposition (CVD) of an AIN film. Before conversion, the wafers were dipped in HF, rinsed with deionized H 20, and placed on a SiCcoated graphite susceptor. The MBE reactor, with a base pressure of 10-9 Torr, was equipped with an in-situ reflection high-energy electron diffractometer (RHEED) for surface crystallographic analysis. The substrate was ramped from room temperature to 970'C at 7-8°C /min and kept at 970°C for 60 min. Ethylene (C2H 4) was supplied from room temperature at a flow rate of 1.8 sccm. The SiC coated Si substrates were loaded in a CVD reactor. Trimethylalumimum (TMA) and ammonia (NH 3) were used for AIN deposition. The flow rates for TMA, NH 3, and additional H2 were 26 gtmol/min, 1500 sccm, and 3000 sccm, respectively. The AIN was grown at 1100°C for 90 min at a growth rate of 11I/min. For comparison, an AIN film was also directly deposited on Si(1 11) substrate under the same process conditions. 407 Mat. Res. Soc. Symp. Proc. Vol. 572 ©1999 Materials Research Society
Film thickness was measured by spectroscopic ellipsometry (SE). Crystallinity was examined with RHEED, X-ray diffraction (XRD), and electron diffraction. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to study surface morphology and defect formation. Auger electron spectrometry (AES) was conducted using a 5.0 keV primary beam at 30' angle of incidence to determine chemical compositions and the extent of C and 0 throughout the films. Sputtering during Auger depth profile analysis was accomplished by using a beam of 1.0 keV Xe÷ incident at 45'. RESULTS AND DISCUSSION Figure 1 is a RHEED pattern from the [110] azimuth of the converted SiC on the Si(l 11) substrate. It shows a single-domain (3x2) reconstruction of the cubic SiC. The formation of single crystalline 3C-SiC was confirmed by XRD as shown in Fig. 2. The two peaks at 2-theta =35.5* and 75.5* are SiC (111) and (222), respectively; the other two peaks represent Si (111) and (222). The Si (222) peak is actually Si (444) observed in second order. The d-spacing of the SiC (111) peak is 2.52A corresponding to a cubic SiC lattice constant of 4.36A, therefore the SiC lattice is fully relaxed. 5 4
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2-Theta Figure 1 RHEED pattern from the [110] azimuth of the converted SiC on the Si(1 11) substrate showing a single-domain (3x2) reconstruction of the cubic SiC.
Figure 2 XRD thet
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