3C-SiC Buffer Layers Converted from Si at a Low Temperature
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"**Departmentof Materials
Science and Engineering, North Carolina State University,
Raleigh, NC 27695 ABSTRACT We have obtained single-crystal 3C-SiC films via conversion of the surface region of Si (I11) and (100) wafers at 970 TC by reaction with C2H 4 in an MBE reactor. The major defects in the films were clusters, voids, and misfit dislocations. Investigation by high resolution TEM images showed low lattice strains in the epitaxial layer due to the formation of 1 misfit dislocation for every 4 to 5 regular SiC planes that are bonded to Si at the interface. The clusters and voids often occurred in pairs. A model for forming the void-cluster pairs is suggested. INTRODUCTION Heteroepitaxial growth of 3C-SiC on Si has been difficult due to the large mismatch in lattice parameters. The difficulty has been partially overcome by use of a two-step growth process. The process involves the growth of a buffer layer followed by the growth of second epitaxial layer. The buffer layer growth is considered to be a critical step for the successful single-crystal growth of 3C-SiC on Si. The first and most common method for growing a buffer layer has been via the reaction of the Si substrate with propane as initially described by Nishino et al. [1, 2]. Propane was introduced into an epitaxial reactor, and the Si substrate was heated rapidly from room temperature to approximately 1360 'C and held at that temperature for a short time (< 5 minutes). Carbon was deposited on the Si substrate from the decomposition of propane. The Si top surface was converted to SiC by the reaction with the deposited C at elevated temperatures. The thin SiC films achieved by this process were approximately 20 nm thick and were reported as polycrystalline 3C-SiC. A single-crystal SiC buffer layer is preferable for achieving higher crystal perfection in the second epitaxial layer. The growth of a single-crystal buffer layer has been pursued by Cheng et al. [3] using a lower temperature (in range of 1000 'C to 1170 'C) and a shorter carbonization time (in the range of 5 to 30 seconds). They observed that the films started to grow as thin circular islands. Lateral growth of the islands led them to coalesce and finally became a continuous film if the proper process parameters were applied. A continuous SiC film (approximately 18 nm thick) could only be obtained under a narrow process window that was at 1070 TC for 15 seconds. The converted films were single crystals but highly defective. High concentrations of defects were observed at the islands centers where nucleation initiated. The defect density decreased away from the island centers. However, defects such as stacking faults were still present. In addition, the films were embedded with high densities of etched pits which were created during the Si-to-SiC conversion process. The SiC films in the vicinity of the pits were misoriented and contained numerous stacking faults. 219
Mat. Res. Soc. Symp. Proc. Vol. 572 © 1999 Materials Research Society
Further decreases in carbonization temperatures were c
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