Mark J. Loboda

Growth of crystalline 3C-SiC on Si at reduced temperatures by chemical vapor deposition from silacyclobutane

Low‐pressure chemical vapor deposition of SiC on carbonized Si from the single‐source organosilane precursor silacyclobutane (c‐C3H6SiH2,SCB) has been investigated from 800 to 1200 °C. On atmospheric pressure‐carbonized (100)Si, SiC films grown at 900 °C and above exhibit a transmission electron diffraction pattern consisting only of sharp spots with cubic symmetry. X‐ray diffraction (XRD) of these films exhibit primarily the (200) and (400) SiC lines. XRD of films grown at 900 °C on Si(111) exhibits only an extremely large SiC(111) peak with a full width at half‐maximum of 450 arcsec. Using a SCB flow rate of 1 sccm, a SiC growth rate of 4–5 μm/h was obtained on Si at 900 °C. Crystalline SiC films have also been grown by SCB at a temperature of 800 °C.

Effect of carbonization on the growth of 3C‐SiC on Si (111) by silacyclobutane

Chemical vapor deposition of SiC on Si (111) from silacyclobutane (c‐C3H6SiH2, SCB) has been carried out on propane carbonized and on virgin Si substrates. The carbonization was performed at 760 Torr and the SiC growth at 5 Torr. Transmission electron diffraction (TED) and x‐ray diffraction were used to determine the crystallinity of the resulting films. The minimum temperature for obtaining crystalline films, as indicated by a TED pattern consisting of sharp spots with (111) SiC crystal hexagonal symmetry, was lower with carbonization (∼800–900 °C) than without (∼1000 °C). However, the carbonization process creates voids in the Si just below the SiC/Si interface, while SCB growth without carbonization produces a very smooth and void‐free interface. Fourier‐transform infrared measurements of SiC films grown at 1200 °C without carbonization exhibit a sharp (full width at half‐maximum=30 cm−1) Si‐C absorption peak at 794 cm−1.

Evidence of negative bias temperature instability in 4H-SiC metal oxide semiconductor capacitors

Generation lifetimes and interface state densities of n-type 4H-SiC metal oxide semiconductor (MOS) capacitors are characterized by using the pulsed MOS capacitor technique. A decrease in lifetime and increase in interface state density occurs when the devices are negatively biased at 400°C. This behavior is consistent with an effect seen in Si∕SiO2 devices known as negative bias temperature instability. A portion of the lifetime degradation caused by this effect can be recovered by removing the negative bias as well as by positively biasing the device.

Stacking faults created by the combined deflection of threading dislocations of Burgers vector c and c+a during the physical vapor transport growth of 4H–SiC

Observations have been made, using synchrotron white beam x-ray topography, of stacking faults in 4H–SiC with fault vectors of kind 1/6⟨202¯3⟩. A mechanism has been postulated for their formation which involves overgrowth by a macrostep of the surface outcrop of a c-axis threading screw dislocation, with two c/2-height surface spiral steps, which has several threading dislocations of Burgers vector c+a, with c-height spiral steps, which protrude onto the terrace in between the c/2-risers. Such overgrowth processes deflect the threading dislocations onto the basal plane, enabling them to exit the crystal and thereby providing a mechanism to lower their densities.

Reduced temperature growth of crystalline 3C‐SiC films on 6H‐SiC by chemical vapor deposition from silacyclobutane

3C‐ on 6H‐SiC (0001) epitaxial growth from the single‐source organosilane precursor silacylobutane (c‐C3H6SiH2) has been investigated over the temperature range of 800–1100 °C. Spectrophotometry was used to determine an optical absorption edge of ∼2.27 eV for the films grown at 900 °C, corresponding approximately to the energy band gap of 3C‐SiC. The crystallinity, structure, strain, and dislocation density in the 3C‐SiC thin films were determined using double crystal x‐ray diffractometry (DCXRD). The films grown at 800–1000 °C were found to be exclusively 3C‐SiC. The films grown at 1100 °C were a mixture of 3C, 4H, and 6H polytypes of SiC. All films shown an excellent surface morphology. The optimum films are obtained at 900 °C, exhibiting structural properties nearly equal to those of the substrate: narrow DCXRD peak width (∼17 arcsec) and low dislocation density (∼3×106 cm2).

Homoepitaxial Growth of 4H-SiC Using a Chlorosilane Silicon Precursor

Epitaxial growth of SiC films was performed on 4H SiC n+ substrates utilizing a chlorosilane/propane chemistry in both single wafer and batch CVD systems. Variations of the chlorosilane flow under fixed conditions of gas composition, temperature and pressure resulted in growth rates between 4 to 20 μm/hr. Fixing the chlorosilane flow rate to achieve a growth rate of approximately 4 μm/hr, the effects of temperature, pressure and gas composition on background dopant incorporation, epitaxial layer uniformity and epitaxial defect generation were investigated. Intentional n and p-type doping has been demonstrated over the carrier range 1×1018-1×1020/cm3. This paper presents the first reported of use of chlorosilane precursors to grow high quality undoped, n and p doped SiC epilayers.

Nonuniformities of electrical resistivity in undoped 6H-SiC wafers

Chemical elemental analysis, temperature-dependent Hall measurements, deep-level transient spectroscopy, and contactless resistivity mapping were performed on undoped semi-insulating (SI) and lightly nitrogen-doped conducting 6H-SiC crystals grown by physical vapor transport (PVT). Resistivity maps of commercial semi-insulating SiC wafers revealed resistivity variations across the wafers between one and two orders of magnitude. Two major types of variations were identified. First is the U-shape distribution with low resistivity in the center and high in the periphery of the wafer. The second type had an inverted U-shape distribution. Secondary-ion-mass spectrometry measurements of the distribution of nitrogen concentration along the growth axis and across the wafers sliced from different locations of lightly nitrogen-doped 6H–SiC boules were conducted. The measured nitrogen concentration gradually decreased along the growth direction and from the center to the periphery of the wafers. This change gives ri...

Carrier Generation Lifetimes in 4H-SiC MOS Capacitors

The field of SiC electronics has progressed rapidly in recent years, but certain electronic properties remain poorly understood. For example, a consensus has not been reached as to the specific point defects which limit minority carrier recombination, and little is known about defects which limit generation lifetimes. This paper investigates generation lifetimes using the pulsed MOS capacitor technique and compares the results with defect densities, recombination lifetimes, and Schottky diode characteristics in the same material for the first time. Carrier generation lifetimes in 4H-SiC epilayers range from less than 1 ns to approximately 1 μs and depend strongly on measurement conditions and data interpretation. They are limited by dislocations only at densities higher than 106 cm-2.The only point defect that is theoretically capable of limiting generation lifetime to the levels currently observed in 4H-SiC is EH 6/7. However, this defect cannot account for the case where generation lifetimes are lower than recombination lifetimes in the same area. This is not seen in silicon and seems to be inconsistent with theory. Possible reasons for these perplexing results are discussed, and it is attempted to form a framework with which further understanding of the significance of carrier generation lifetime measurements in SiC can be achieved.

Scaling of Chlorosilane SiC CVD to Multi-Wafer Epitaxy System

A SiC epitaxy process based on chlorosilane/propane chemistry has been successfully transferred from a single-wafer R&D system to a multi-wafer CVD reactor. The optimized process results in very smooth epi surface (RMS~0.24nm) and minimum surface pits (less than 0.5/cm2). Both n-type and p-type doping in a wide range are demonstrated using nitrogen and aluminum, respectively. The high performance benchmarks for thickness uniformity (intra-wafer variation <1% and inter-wafer variation <1%) and doping uniformity (intra-wafer variation <6% and inter-wafer variation <3%) are achieved on 5 x 3-inch wafers. The carrier lifetime in these epilayers measured by μ-PCD is over 5 μs, the longest value reported so far for SiC epitaxial wafers.

Characterization of 100 mm Diameter 4H-Silicon Carbide Crystals with Extremely Low Basal Plane Dislocation Density

Synchrotron White Beam X-ray Topography (SWBXT) studies are presented of basal plane dislocation (BPD) configurations and behavior in a new generation of 100mm diameter, 4H-SiC wafers with extremely low BPD densities (3-4 x 102 cm-2). The conversion of non-screw oriented, glissile BPDs into sessile threading edge dislocations (TEDs) is observed to provide pinning points for the operation of single ended Frank-Read sources. In some regions, once converted TEDs are observed to re-convert back into BPDs in a repetitive process which provides multiple BPD pinning points.