Enhanced annealing of implantation-induced defects in 4H-SiC by thermal oxidation

Abstract

Electrically active, unintentionally introduced defects in a semiconductor crystal may lead to undesirable device properties, and it is therefore important to gain control and understanding of such defects in order to achieve control at device level. Intrinsic defects are usually harder to remove and control than impurities, and in SiC these defects are not only numerous, but also extremely thermally stable, making them somewhat difficult to remove or deactivate. Bulk defects, specifically those corresponding to the Z 1/2 and EH 6/7 levels measured using deep level transient spectroscopy (DLTS), appear in concentrations around 10 12-10 13 cm −3 in as-grown material, while the density of interface states (D it) numbers around 10 14 eV −1 cm −2 in typical thermally oxidized 4H-SiC material. These two factors severely limit the minority carrier lifetime and the channel mobility in MOS-devices, respectively, and are therefore highly relevant problems to study and-if possible-solve.

Oxidation-enhanced annealing of implantation-induced Z1/2centers in 4H-SiC: Reaction kinetics and modeling

“…5 and similar to that found in Ref. 12, where only one temperature was studied (1150 • C), they suggest a rapid diffusivity on the order of 10 −8 cm 2 /s. The variation with T is weak and in fact, opposite to that anticipated for a thermally activated process, i.e., D CI decreases with increasing T .…”

“…In the ultimate limit of annihilation efficiency, every injected C I contributes to the loss of Z 1/2 , as assumed by the present authors in Ref. 12, and then the flux of C I being emitted from the SiO 2 /SiC interface can be extracted from the total loss of [Z 1/2 ] versus t, Fig. 3.…”

“…The decreasing annihilation rate of Z 1/2 with increasing depth (see findings in the literature. 11,12 Hereafter, this species will be referred to as C I and it is generated during the oxidation process. However, an injection into the SiC bulk is not the only alternative for C I ; competing reactions exist and their relative importance increases with decreasing temperature (see Fig.…”

“…6 Z 1/2 is typically present with concentrations on the order of 10 12 -10 13 cm −3 in as-grown material but can be reduced by high-temperature annealing, although a complete removal is challenging since Z 1/2 remains or even reforms at temperatures approaching 2000 • C. 7,8 Recently, however, several reports have shown that [Z 1/2 ] (brackets denote concentration values) can be reduced below the detection limit ( 10 10 cm −3 ) in a surface layer by either a shallow carbon implantation followed by annealing at 1600 • C, 9 or, perhaps more conveniently, thermal oxidation performed on the Si-face at comparatively low temperatures (∼1100 • C). [10][11][12] Effectively, a "defect-free" layer with an extension of several tens of micrometers in thickness can be formed. In both cases, the removal of Z 1/2 was attributed to in-diffusion of a defect species, presumably the carbon interstitial (C I ), which reacts with and annihilates Z 1/2 .…”

Radiation hardness of n-type SiC Schottky barrier diodes irradiated with MeV He ion microbeam

“…It is an acceptor like defect with an extreme thermal stability up to 2000°C [30]. It has been shown that Z 1/2 defect limits the minority carrier lifetime and therefore strongly affects device properties [34]. Very recently the microstructure of Z 1/2 was revealed to be a single carbon-vacancy [35,36].…”