Ion implantation in 4H–SiC

https://doi.org/10.1016/j.nimb.2007.12.049Get rights and content

Abstract

Silicon carbide offers unique applications as a wide bandgap semiconductor. This paper reviews various aspects of ion implantation in 4H–SiC studied with a view to optimise ion implantation in silicon carbide. Al, P and Si ions with keV energies were used. Channelling effects were studied in both a-axis and c-axis crystals as a function of tilts along major orthogonal planes and off the major orthogonal planes. Major axes such as [0 0 0 1] and the [112¯0] and minor axis like the [112¯3] showed long channelling tails and optimum tilts for minimising channelling are recommended. TEM analyses of the samples showed the formation of (0 0 0 1) prismatic loops and the (112¯0) loops as well,in both a and c-cut crystals. We also note the presence of voids only in P implanted samples implanted with amorphising doses. The competing process between damage accumulation and dynamic annealing was studied by determining the critical temperature for the transition between crystalline and amorphous SiC and an activation energy of 1.3 eV is extracted.

Introduction

Silicon carbide is a promising wide bandgap semiconductor and has unique properties for specific device applications as already observed by Shockley in the 1950’s. It has a wide range of applications for high temperature, high power and high frequency devices. For instance, silicon carbide devices can operate at 600 °C while current silicon devices will not operate at temperatures higher than 350 °C. Another unique property of SiC is its ability to exist in several crystal forms known as polytypes [1] which have different bandgaps. Ion implantation is the most viable process to achieve both lateral and in depth control over dopant incorporation. Defects are an important by-product of ion implantation and it is crucial to understand defect formation and the nature of the defects in order to cater for the needs of the devices. A major hurdle for the SiC devices was the propagation of stacking faults to the surface under forward bias leading to device failure [2], [3], [4]. Several groups showed a polytypic transformation resulting from two Shockley partials gliding on neighbouring basal planes [3], [5], [6] creating a 3C SiC lamellae in between. These 3C–SiC lamellae behave like quantum wells in 4H–SiC crystals because of the different bandgaps associated with the different polytypes. In this paper, we review selected results from our work. In the first part of the paper, we will show the effect of channelling on Al distribution in both a-cut and c-cut 4H–SiC and we will recommend optimum tilt orientation for these crystal to minimise channelling. The second part of the paper concentrates on the transmission electron microscopy (TEM) studies of P implanted 4H–SiC. The third part of the paper addresses the issue of dynamic annealing in silicon carbide during ion implantation with a view to understand which defects are responsible for defect annihilation during ion implantation.

Section snippets

Channelling in a-cut and c-cut 4H–SiC

For doping, the junction depth is determined by the implant depth which is predominantly varied with the implant energy. However, because of the difference in the channelled and random stopping power of ions in a crystal, the depth of the junction will also depend on the extent of channelling of the implant ions. In the Si microelectronics industry, a 7° tilt of the substrate is commonly used to avoid channelling of the implanted ions in (1 0 0)Si. There is very little literature to recommend the

TEM study of P implanted samples

There are two main structural defects widely reported in SiC, namely the interstitial loops on the (0 0 0 1) habit plane, the prismatic (0 0 0 1) loops [8] and the Shockley partials gliding on the basal plane of type 1/3〈11¯00〉[9]. Our studies on 4H–SiC implanted with 400 keV P+ showed that at a low dose of 4×1014cm-2 at room temperature, there is no amorphisation and little swelling resulting from the implant (≈6% volume increase) whereas the higher dose of 1×1015cm-2 showed a buried amorphous region

Dose rate effects in Si implanted 4H–SiC

One of the implantation parameters, that is least mentioned in the majority of papers, is the dose rate or ion flux. This is primarily because dose is often the parameter most taken into consideration because of the concentration. However, it is well known that dynamic annealing is a crucial factor in determining the level of damage in ion implanted material. Schultz et al. [12] demonstrated in silicon that by varying the implant temperature and the ion flux, one can determine the activation

Conclusion

In summary we have shown that channelling was significant not only along the major axes such as the a-axis and the c-axis but also along the [112¯3] axis. Optimum tilts to minimise channelling for c-cut crystals were 9° tilt along the (110¯0) or 8° tilt in a plane between the {112¯0} and the {101¯0} planes. For a-cut crystals, either a 10° tilt in the (11¯00) plane or a 10° tilt in the plane halfway between the (11¯00) and the (0 0 0 1) planes (orthogonal to the a-axis) was a suitable orientation

Acknowledgements

The australian authors thank the Australian Research Council for support under the Discovery grant and fellowship program. The authors acknowledge the STINT (Swedish Foundation for international cooperation in research and higher education) program.

References (15)

  • P. Pirouz et al.

    Ultramicroscopy

    (1993)
  • A.R. Verma et al.

    Polymorphism and Polytypism in Crystals, Wiley Monographs in Crystallography

    (1966)
  • H. Lendenmann et al.

    Mater. Sci. Forum

    (2001)
  • J.Q. Liu et al.

    Appl. Phys. Lett.

    (2002)
  • A. Galeckas et al.

    Appl. Phys. Lett.

    (2002)
  • T.A. Kuhr et al.

    J. Appl. Phys.

    (2002)
  • H.J. Chung et al.

    Appl. Phys. Lett.

    (2002)
There are more references available in the full text version of this article.

Cited by (0)

View full text
Copyright © 2007 Elsevier B.V. All rights reserved.