Full Epitaxial Trench Type Buried Grid SiC JBS Diodes

The modern SiC Schottky barrier diodes utilize JBS concept that gives surge current capability. However, in planar structures the protection of the Schottky areas from high electric field is not sufficient thus resulting in high leakage currents.

It has been demonstrated that buried grid technology (implanted or epitaxial) gives extremely low leakage currents even at high temperature operation due to superior shielding [1-2]. But the manufacturing complexity limits this technology to niche markets.

Less complicated trench concept of implanted JBS diodes was utilized in [3]. It also enables to improve both the forward voltage drop and the leakage current.

In this paper we present the new concept of fully epitaxial trench JBS diodes. Simulations [3] revealed better trade off of forward and blocking behavior of epitaxial buried grid technology. Epitaxially grown p-n junctions result in increased bipolar injection at high current densities and thus lead to improved surge current capabilities.

The concept of fully epitaxial trench JBS diodes enables cost-efficient manufacturing. Implantation and high temperature annealing steps are replaced with one epi re-growth step that can be performed in multi wafer epi reactors. The re-growth step utilizes Ascatron’s 3D-SiC core technology based on embedded epitaxial growth techniques like presented in [4]. Ring type edge termination is formed simultaneously with the active area grid. The cross section of the epitaxial trench type buried grid JBS device is shown in Fig.1. To optimize the JBS performance the grid spacing is set below 2µm and the n channel has higher doping than the n- drift region.

Fig. 2 shows cross section of the device after p+ epi re-growth in the trenches.

Cross section of the active area of fabricated JBS device is shown in Fig. 3.

Fabricated devices are rated for 20A / 1200V and have leakage currents below 0.1µA at 1000V blocking voltage.

References

1. M. Bakowski, J-K. Lim, W. Kaplan, and A. Schöner, ECS Trans., 41 (8), p. 155 (2011).

2. M. Bakowski, J-K. Lim, W. Kaplan, ECS Trans., 50 (3), p. 415 (2013).

3. M. Aketa, Y. Yokotsuji, M. Miura, and T. Nakamura, Materials Science Forum, 717-720, p. 933 (2012).

4. A. Schöner, N. Sugiyama, Y. Takeuchi, and R.K. Malhan, Materials Science Forum, 600-603, p. 175 (2009).