Silicon Carbide (SiC) is an important compound with many benefits to man kind, ranging from early usage as an abrasive to its recent use as an intrinsic semiconductor. SiC is typically man made, since it rarely exists in nature in the form of the natural moissanite. The production of crystalline SiC with increasing size and high quality has been accomplished using Physical Vapor Transport (PVT) for the high power and low frequency applications. Although high quality crystals could be produced using this method, growth defects like micropipes, dislocations, etc., could not be completely inhibited. Thus, the preparation of the SiC powder used in this process requires additional energy, which makes the High Temperature Chemical Vapor Deposition (HTCVD) technique more attractive and could be considered as an efficient alternative to the PVT method, which requires lower throughput capacity than PVT due to saving the exergy destroyed in the powder formation process (used in the PVT method) and due to its low precursor’s cost and their disposition for continuous feeding. Therefore, in this work, a vertical hot-wall reactor with an upward flow direction, was built and suited for the investigation of the epitaxial growth of low defect SiC single crystalline using the HTCVD technique. The gases are injected into the reactor through a water cooled flange and a nozzle including an optical access for the temperature measurement. The exhaust gases were removed by four openings at the top of the reactor. The substrates were fastened on a graphite seed-holder and hanged in the reactor using a graphite cord. The precursors used were silane (SiH₄), propane (C₃H₈) and hydrogen (H₂) while helium was used as a carrier gas. The temperature profile was measured by means of two color pyrometer. A maximum temperature of 2180°C was measured on the reactor walls, while a temperature of 2025°C was measured on the seed-holder, which was hanged 18 cm below the outlet flange.
Non-seeded growth of polycrystalline SiC was carried out and used for indicating the growth parameters that were later used as a reference for the setup of the epitaxial growth experiments. In the epitaxial growth experiments the deposition was firstly performed on on-axis 6H-SiC seeds. At a temperature of 1995°C, a growth rate of 32 µm/h was achieved. This temperature was achieved at a substrate position of 30 cm below the outlet flange (5 cm above the middle plane of the inductive coil). Layers that grew on on-axis substrates were shown to have a plain surface morphology. The growth rate has shown a significant dependency on the C₃H₈ within low range of its concentrations. The step flow mechanism is activated when off-axis seed-crystals with a tilt angle of 3.5° and 8° are used. On the film layers that were grown on the off-axis substrate with a tilt angle of 3.5°, flat terraces with sharp edges could be recognized by optical microscopy. Instead, wavy surface morphology resulted on the films grown on the 8° off-axis seed. Increasing the temperature beyond 1955°C resulted in higher growth rates on the off-axis surfaces; meanwhile, no growth rate enhancement was obtained on the on-axis surfaces. A maximum growth rate of 100 µm/h was achieved at a growth emperature of 2060°C. The epitaxial growth of SiC by HTCVD was successfully carried out for long periods up to 3 hours using the hot-wall reactor.
The growth of thick epilayers of SiC can be realized at high growth rates for several hours, which makes it very important to measure the mass change of the substrate during deposition. On the other hand, investigating the growth rate for a wide range of the process parameters, can be accomplished by the application of an in-situ measuring technique, which can save a lot of experimental time and cost. Accordingly, a magnetic suspension balance (MSB) was successfully integrated into the hot-wall reactor and used for the in-situ measurement of the mass change during deposition. In order to minimize the experimental cost, this technique was only applied during non-seeded growth experiments, where polycrystalline SiC was deposited directly on a graphite seed-holder with 50 mm diameter. The mass change could be successfully recorded at a growth temperature of 1950°C, flow velocity of 0.0075 m/s and a pressure of 800 mbar. The dependency of the growth rate on the precursor (SiH₄, C₃H₈ and H₂ concentrations was investigated individually while the mass change was recorded in-situ.