Liu Xingfang

Fast Homoepitaxial Growth of 4H-SiC Films on 4° off-Axis Substrates in a SiH4-C2H4-H2 System

Homoepitaxial growth of 4H-SiC epilayers is conducted in a SiH4-C2H4-H2 system by low pressure hot-wall vertical chemical vapor deposition (CVD). Thick epilayers of 45 μm are achieved at a high growth rate up to 26 μm/h under an optimized growth condition, and are characterized by using a Normaski optical microscope, a scanning electronic microscope (SEM), an atomic force microscope (AFM) and an x-ray diffractometer (XRD), indicating good crystalline quality with mirror-like smooth surfaces and an rms roughness of 0.9 nm in a 5 μm × 5μm area. The dependence of the 4H-SiC growth rate on growth conditions on 4° off-axis 4H-SiC substrates and its mechanism are investigated. It is found that the H2 flow rate could influence the surface roughness, while good surface morphologies without Si droplets and epitaxial defects such as triangular defects could be obtained by increasing temperature.

Effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition

The effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence (PL) with the excitation wavelength as short as ~ 177 nm. Annealing experiments were carried out in either N2 or vacuum atmosphere with the annealing temperature ranging from 1200 °C to 1600 °C. It is found that surface roughness reduced and compressive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties, a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N2 or vacuum atmosphere. We attribute these deep-level emission peaks to the VAL—ON complex in the AlN material.

Multi-wafer 3C SiC heteroepitaxial growth on Si(100) substrates

Epitaxial growth of semiconductor films in multiple-wafer mode is under vigorous development in order to improve yield output to meet the industry increasing demands. Here we report on results of the heteroepitaxial growth of multi-wafer 3C-SiC films on Si(100) substrates by employing a home-made horizontal hot wall low pressure chemical vapour deposition (HWLPCVD) system which was designed to be have a high-throughput, multi-wafer (3x2-inch) capacity. 3C-SiC film properties of the intra-wafer and the wafer-to-wafer including crystalline morphologies, structures and electronics are characterized systematically. The undoped and the moderate NH3 doped n-type 3C-SiC films with specular surface are grown in the HWLPCVD, thereafter uniformities of intra-wafer thickness and sheet resistance of the 3C-SiC films are obtained to be 6%similar to 7% and 6.7%similar to 8%, respectively, and within a run, the deviations of wafer-to-wafer thickness and sheet resistance are less than 1% and 0.8%, respectively.

Characterization of Obtuse Triangular Defects on 4H-SiC 4° off-Axis Epitaxial Wafers

We investigate the triangular defects with different structural features on 4H-SiC epilayers by a Nomarski microscope, a Candela optical surface analyzer and ultraviolet photoluminescence (UV-PL) imaging. Both the foreign particles and the substrate scratches can cause the formation of the obtuse triangular defects. The central area of some obtuse triangular defects can have the spatially confined core, in which the in-grown stacking faults can be observed under the UV-PL imaging. In contrast, the obtuse triangular defects induced by the scratches appear in the form of band-like defects, of which the width depends on the scratch direction and reaches the maximum when the scratch direction is parallel to the step flow direction. The formation mechanisms of these obtuse triangular defects are discussed.

High-quality homoepitaxial layers grown on 4H-SiC at a high growth rate by vertical LPCVD

High quality, homoepitaxial layers of 4H-SiC were grown on off-oriented 4H-SiC (0001) Si planes in a vertical low-pressure hot-wall CVD system (LPCVD) by using trichlorosilane (TCS) as a silicon precursor source together with ethylene (C2H4) as a carbon precursor source. The growth rate of 25–30 μm/h has been achieved at lower temperatures between 1500 and 1530 °C. The surface roughness and crystalline quality of 50 μm thick epitaxial layers (grown for 2 h) did not deteriorate compared with the corresponding results of thinner layers (grown for 30 min). The background doping concentration was reduced to 2.13 × 1015 cm−3. The effect of the C/Si ratio in the gas phase on growth rate and quality of the epi-layers was investigated.

Doped Polycrystalline 3C-SiC Films Deposited by LPCVD for Radio-Frequency MEMS Applications

Polycrystalline 3C-SiC films are deposited on SiO2 coated Si substrates by low pressure chemical vapour deposition (LPCVD) with C3H8 and SiH4 as precursors. Controlled nitrogen doping is performed by adding NH3 during SiC growth to obtain the low resistivity 3C-SiC films. X-ray diffraction (XRD) patterns indicate that the deposited films are highly textured (111) orientation. The surface morphology and roughness are determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface features are spherulitic texture with average grain size of 100 nm, and the rms roughness is 20nm (AFM 5 x 5 mu m images). Polycrystalline 3C-SiC films with highly orientational texture and good surface morphology deposited on SiO2 coated Si substrates could be used to fabricate rf microelectromechanical systems (MEMS) devices such as SiC based filters.

Surface saturation control on the formation of wurtzite polytypes in zinc blende SiC nanofilms grown on Si(100) substrates

We investigate the formations of wurtzite (WZ) SiC nano polytypes in zinc blende (ZB) SiC nanofilms hetero-grown on Si-(100) substrates via low pressure chemical vapor deposition (LPCVD) by adjusting the Si/C ratio of the introduced precursors. Through SEM, TEM, and Raman characterizations, we find that the nanofilms consist of discrete WZ SiC nano polytypes and ZB SiC polytypes composed of WZ polytypes (WZ + ZB) and disordered ZB SiC polytypes, respectively, according to Si/C ratios of 0.5, 1.5, and 3. We attribute the WZ polytype formation to being due to a kinetic mechanism based on the Si/C surface saturation control.

Epitaxial growth on 4H-SiC by TCS as a silicon precursor

Epitaxial growth on n-type 4H-SiC 8° off-oriented substrates with a size of 10 × 10 mm2 at different temperatures with various gas flow rates has been performed in a horizontal hot wall CVD reactor, using trichlorosilane (TCS) as a silicon precursor source together with ethylene as a carbon precursor source. The growth rate reached 23 μm/h and the optimal epilayer was obtained at 1600 °C with a TCS flow rate of 12 sccm in C/Si of 0.42, which has a good surface morphology with a low RMS of 0.64 nm in an area of 10 × 10 μm2. The homoepitaxial layer was obtained at 1500 °C with low growth rate (< 5 μm/h) and the 3C-SiC epilayers were obtained at 1650 °C with a growth rate of 60–70 μm/h. It is estimated that the structural properties of the epilayers have a relationship with the growth temperature and growth rate. Silicon droplets with different sizes are observed on the surface of the homoepitaxial layer in a low C/Si ratio of 0.32.

Growth of a Novel Periodic Structure of SiC/AlN Multilayers by Low Pressure Chemical Vapour Deposition

A novel 10-period SiC/AlN multilayered structure with a SiC cap layer is prepared by low pressure chemical vapour deposition (LPCVD). The structure with total film thickness of about 1.45 mu m is deposited on a Si (111) substrate and shows good surface morphology with a smaller rms surface roughness of 5.3 nm. According to the secondary ion mass spectroscopy results, good interface of the 10 period SiC/AlN structure and periodic changes of depth profiles of C, Si, Al, N components are obtained by controlling the growth procedure. The structure exhibits the peak reflectivity close to 30% near the wavelength of 322 nm. To the best of our knowledge, this is the first report of growth of the SiC/AlN periodic structure using the home-made LPCVD system.

Raman scattering detection of stacking faults in free-standing cubic-SiC epilayer

We report on stacking fault (SF) detection in free-standing cubic-SiC epilayer by the Raman measurements. The epilayer with enhanced SFs is heteroepitaxially grown by low pressure chemical vapour deposition on a Si(100) substrate and is released in KOH solution by micromechanical manufacture, on which the Raman measurements are performed in a back scattering geometry. The TO line of the Raman spectra is considerably broadened and distorted. We discuss the influence of SFs on the intensity profiles of TO mode by comparing our experimental data with the simulated results based on the Raman bond polarizability (BP) model in the framework of linear-chain concept. Good agreement with respect to the linewidth and disorder-induced peak shift is found by assuming the mean distance of the SFs to be 11 angstrom in the BP model.