Low-doped semi-insulating SIC crystals and method

Abstract

The invention relates to substrates of semi-insulating silicon carbide used for semiconductor devices and a method for making the same. The substrates have a resistivity above 106 Ohm-cm, and preferably above 108 Ohm-cm, and most preferably above 109 Ohm-cm, and a capacitance below 5 pF / mm2 and preferably below 1 pF / mm2. The electrical properties of the substrates are controlled by a small amount of added deep level impurity, large enough in concentration to dominate the electrical behavior, but small enough to avoid structural defects. The substrates have concentrations of unintentional background impurities, including shallow donors and acceptors, purposely reduced to below 5 DEG 1016 cm-3, and preferably to below 1 DEG 1016 cm-3, and the concentration of deep level impurity is higher, and preferably at least two times higher, than the difference between the concentrations of shallow acceptors and shallow donors. The deep level impurity comprises one of selected metals from the periodic groups IB, IIB, IIIB, IVB, VB, VIB, VIIB and VIIIB. Vanadium is a preferred deep level element. In addition to controlling the resistivity and capacitance, a further advantage of the invention is an increase in electrical uniformity over the entire crystal and reduction in the densityof crystal defects.

Description

technical field [0001] The present invention relates to the production of semi-insulating SiC material, and the growth of high quality wafers of this material to fabricate substrates useful for RF, microwave and other device applications. Background technique [0002] Silicon carbide (SiC) is a wide bandgap semiconductor material with a unique combination of electrical and thermophysical properties that make it extremely attractive for use in new generations of electronic devices. These properties include high breakdown field strength, high practical operating temperature, high electron saturation velocity, high thermal conductivity, and radiation hardness. These properties enable devices to operate at considerably higher powers, at higher temperatures, and with greater radiation resistance than comparable devices made from more conventional semiconductors such as Si and GaAs (D.L. Barrett et al., J. Crystal Growth, pp. 109, 1991, pp. 17-23). Transistors fabricated from hi...

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Problems solved by technology

These defects include: (1) the nature of intrinsic point defects in SiC crystals and their effect on producing semi-insulating properties is unclear; (2) the nature of SiC high-temperature thermochemistry makes active control of intrinsic point defects practically difficult ; and lead to complex and high production costs; (3) including growth-induced and radiation-induced intrinsic defects, which are generally unstable and anneal over time; in addition, some radiation-induced defects are detrimental to substrate properties (4) Unintentional background impurities that require extremely low concentrations, with 15 cm -3 or lower boron and nitrogen, so that the local point defects with deep energy levels dominate and cause a high degree of compensation; this need is difficult to achieve in practice; and (5) the second approach to achieving extremely high crystal purity ( Specific measures taught by U.S. Patent Nos. 6,218,680 and 6,396,080), such as large source-seed temperature differences (300-350 °C), and higher than usual growth temperatures, can jeopardize the compositional homogeneity of the crystal and promote crystal defect formation ( carbon inclusions, micropipes, secondary grains, etc.)

This is extremely difficult to implement practically and results in process complexity, low substrate yield and high cost

In addition, it needs to use HTCVD crystal growth process, which is industrially more complex and expensive than conventional PVT

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