Fundamentals of SiC-Based Device Processing
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Fundamentals of SiC-Based Device Processing M.R. Melloch and J.A. Cooper, Jr.
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Oxidation A beneficial feature of SiC processing technology is that SiC can be thermally oxidized to form SiC>2. When a thermal oxide of thickness x is grown, 0.5x of the SiC surface is consumed, and the excess carbon leaves the sample as CO. Shown in Figure 1 are the oxide thicknesses as a function of time for the Si-face and the C-face of 6H-SiC, and for Si. The oxidation rates are considerably lower for SiC than for Si. The oxidation rate of the Cface of 6H-SiC is considerably greater than that of the Si-face. Hornetz et al.9 have shown that the reason for the slower oxidation rate of the Si-face is due to a 1-nm Si4C4_.vO2 (x < 2) layer that forms between the SiC and the SiO2 during oxidation of the Si-face. When oxidizing the Si-face, the Si atoms oxidize first, which inhibits the oxidation of the underlying C atoms that are 0.063 nm below the Si atoms. When oxidizing the C-face, the C atoms readily oxidize first to form CO, with no formation of the Si4C4-rO2 layer for temperatures above 1000°C. Assessing the quality of thermally grown oxides and the SiO2/SiC interface are challenging tasks. Because of the wide bandgap of SiC, surface states over a large portion of the bandgap cannot emit to the bands at room temperature.
This fact has been overlooked in several investigations of the SiO2/SiC interface with resulting claims of near ideal interfaces. Investigating the SiO2/SiC interface at room temperature is similar to investigating the SiO2/Si interface at a temperature of 77 K. Shown in Figure 2 is the capacitance-voltage (C-V) characteristic for a metal-oxide-SiC (MOS) capacitor.10 Scanning the voltage positive from accumulation, the characteristic goes into deep depletion. Thermal generation at room temperature is negligible in SiC so the capacitor would remain in deep depletion indefinitely. To populate the inversion layer and the surface states,
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Introduction Since the commercial availability of SiC substrates in 1990, SiC processing technology has advanced rapidly. There have been demonstrations of monolithic digital1'2 and analogue3'4 integrated circuits, complementary metal-oxide-semiconductor (CMOS) analog integrated circuits,5 nonvolatile random-access memories,6 self-aligned polysilicon-gate metaloxide-semiconductor field-effect transistors (MOSFETs),7 and buried-channel polysilicon-gate charge-coupled devices (CCDs).8 In this article, we review processing technologies for SiC.
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Time (min) Figure 1. Oxide thickness as a function of oxidation time for the Si-face and C-face of 6H-SiC and for Si.
MRS BULLETIN/MARCH 1997
Fundamentals of SiC-Based Device Processing
methods such as the Terman, AC conductance, and quasistatic C-V techniques have to be applied at elevated temperatur
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