Bulk Crystal Growth, Epitaxy, and Defect Reduction in Silicon Carbide Materials for Microwave and Power Devices
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Bulk Crystal Growth,
Epitaxy, and Defect Reduction in Silicon Carbide Materials for Microwave and Power Devices
J.J. Sumakeris, J.R. Jenny, and A.R. Powell Abstract We discuss continuing materials technology improvements that have transformed silicon carbide from an intriguing laboratory material into a premier manufacturable semiconductor technology. This advancement is demonstrated by reduced micropipe densities as low as 0.22 cm2 on 3-in.-diameter conductive wafers and 16 cm2 on 100-mm-diameter conductive wafers. For high-purity semi-insulating materials, we confirm that the carbon vacancy is the dominant deep-level trapping state, and we report very consistent cross-wafer activation energies derived from temperature-dependent resistivity. Warm-wall and hot-wall SiC epitaxy platforms are discussed in terms of capability and applications. Specific procedures that essentially eliminate forward-voltage drift in bipolar SiC devices are presented in detail.
the chip) and semi-insulating substrates for microwave devices. We will also discuss the epitaxy platforms and techniques that we have developed to exploit these highquality substrates to produce world-class SiC-based electronic devices.
SiC Bulk Growth and Substrate Preparation Large-diameter SiC crystals are generally grown by sublimation rather than melt growth, because the stoichiometric melting of SiC occurs only at pressures exceeding 10 5 atm and temperatures of more than 32,000C.6 Sublimation growth of SiC has been developed over the past 30 years 7–11 and typically employs a furnace (see Figure 1) in which graphite components constitute the hot zone. During growth, the SiC source sublimes in a low-pressure inert gas ambient (e.g., Ar, He, N2). The subliming molecular species—Si, SiC2, and Si2C— migrate down a temperature gradient from the source and deposit on a monocrystalline SiC seed of the desired orientation.
Crystal Diameter Enlargement Larger-diameter wafers are required for compatibility with available processing equipment and to reduce the per-centimeter cost of the substrate material. At present, 3-in.-diameter substrates are available from multiple vendors, and work is progressing toward 100-mm-diameter substrates. Increasing wafer diameter, along with yield improvements, has allowed the price of commercially available SiC to drop substantially over the last 10 years, from more than $650 cm2 in 1994 to $16 cm2 in 2004.1
Keywords: carbon vacancy, defect reduction, epitaxy, forward voltage, high-purity semi-insulating materials, HPSI, micropipe closure, Shockley basal plane dislocations, silicon carbide.
Introduction In recent years, intensive development efforts have resulted in a dramatic improvement in the quality of silicon carbide materials, both for bulk and epitaxial growth. As a result of this advancement, many high-performance SiC-based devices are now commercially available, including Schottky rectifiers1,2 and metal semiconductor field-effect transistors (MESFETs).1 A further sign of the maturation of SiC device technology
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