SIMS Analyses Applied to Open an Optical Window in 4H-SiC Devices for Electro-Optical Measurements

Mihai Lazar (1, 2) , François Jomard (3) , Duy Minh M Nguyen (1, 2) , Christophe Raynaud (2, 1) , Gontran Pâques (4) , Sigo Scharnholz (4) , Dominique Tournier (1, 2) , Dominique Planson (1, 2)

1 EE - Ampère, Département Energie Electrique
2 INSA Lyon - Institut National des Sciences Appliquées de Lyon
3 GEMAC - Groupe d'Etude de la Matière Condensée
4 ISL - Institut franco-allemand de recherches de Saint-Louis

4H-SiC vertical bipolar power diodes have been fabricated with bilayer metallic anode contact based on an Al-Ti-Ni ohmic contact and a thick Al over-metallization. An optical window of 100 × 100 µm 2 has been created through the anode contact with a SIMS Cameca IMS 4F equipment using Cs + primary ions at 10 kV and with a beam spot size of 500 nm. The current/voltage characteristics of the diodes show that the SIMS process does not induce an increase of the leakage currents in forward nor in reverse bias. OBIC UV photogeneration occurs under the optical window and not under the contact metal. Introduction Wide bandgap semiconductors and silicon carbide materials in particular are very promising for high temperature, high-power and high-frequency device applications. In order to reduce the fabrication cost by decreasing the on-state resistance and the thickness of the epitaxial layers, the two epitaxial layer parameters, thickness and doping level, must be optimized for a projected blocking voltage, like the n-base in high voltage devices [1]. Device structure design needs an understanding of the avalanche mechanism in reverse biased junctions with a precise determination of the impact ionization coefficient in the required electrical field range. To understand the avalanche mechanism in the reverse biased junction, Optical Beam Induced Current (OBIC) is a suitable method that enables to extract the ionization coefficients [2, 3]. During OBIC measurements, an UV laser beam has to penetrate in the SiC epilayer close to the junction under the metallization contact. Thus, an optical window is needed through the contact metallization on the surface which could be the anode contact in the case of vertical bipolar diodes. We propose and demonstrate in this paper a simple method to open this window on SiC vertical bipolar devices. This method can be extended to other wide band-gap semiconductors like diamond or other hard technological materials. Extraction of impact ionization coefficients using OBIC requires a breakdown in the bulk of the main junction under the avalanche mode. Therefore, the lateral protection such as mesa and/or JTE, but also the optical window, must be accurately designed and fabricated [4]. In general, an optical window in the anode is realized by photolithography patterns. With this method we have realized several runs of SiC diodes and frequently we had difficulty in obtaining bulk breakdown in the avalanche mode. We therefore propose an alternative method that could be useful in specific cases, in particular by enabling us to focus on the geometry of the lateral periphery of the vertical power devices.

Mots clés: 4H-SiC; SIMS; OBIC; optical window; impact ionization coefficients; bipolar diode

Domaines: Energie électrique

Mihai Lazar, François Jomard, Duy Minh M Nguyen, Christophe Raynaud, Gontran Pâques, et al.. SIMS Analyses Applied to Open an Optical Window in 4H-SiC Devices for Electro-Optical Measurements. Materials Science Forum, 2012, 717-720, pp.885-888. ⟨10.4028/www.scientific.net/MSF.717-720.885⟩. ⟨hal-02166414⟩