Dominique Planson

Angle etch control for silicon carbide power devices

Silicon carbide plasma etching results are reported. Etching experiments are performed in a distributed electron cyclotron resonance reactor, using a SF6/O2 gas mixture, on both 3C‐ and 6H‐SiC. A special interest has been given to the slope of the etched sidewalls. Slopes between 30° and 80° have been achieved by varying selectivities between SiC and the SiO2 masking layer. Two parameters have been investigated to modulate selectivity: bias voltage and O2 additive flow. A wide range of selectivities (from 1 to 6.5) has been obtained for suitable etch rate (100 to 270 nm/min) with very smooth surfaces.

Low-doped 6H-SiC n-type epilayers grown by sublimation epitaxy

Abstract Sublimation epitaxy has not yet been a technique of prime importance to grow epitaxial 6H-SiC layers because grown layers have always shown a residual net doping level higher than 10 16 cm −3 and a high compensation level. We present here results obtained with an optimized technology of sublimation epitaxial growth, which can be used to obtain structurally perfect layers with a concentration of uncompensated donors as low as 10 15 cm −3 . These layers have been both physically and electrically characterized. Deep level transient spectroscopy indicates that the concentration of deep levels is greatly reduced. As a consequence the hole diffusion length is significantly increased up to about 2.5 μm, as confirmed by electron beam induced current measurements. So these optimized layers are envisaged for the fabrication of high voltage diodes or bipolar transistors.

High-Voltage 4H-SiC Thyristors With a Graded Etched Junction Termination Extension

For the first time, a graded etched junction termination extension (JTE) is applied to completed 4H-SiC gate turn-off thyristors. These devices demonstrate the feasibility of nonimplanted high-voltage SiC thyristors. The maximal measured forward breakdown voltage of 7.8 kV corresponds very well to the ideal value of 8.1 kV. This letter explains the conceptual procedure to realize an optimal four-step JTE and compares measurement results with those obtained from finite-element simulations.

Modeling and high temperature characterization of SiC-JFET

Silicon Carbide (SiC) is considered as the wide band gap semiconductor material that can presently compete with silicon (Si) material for power switching devices. Compact circuit simulation models for SiC devices are of extreme importance for designing and analyzing converter circuit, in particular, if comparisons with Si devices should be performed. In this paper, three kinds of Silicon Carbide JFET samples were characterized at temperatures up to 225degC. The characterizations are based on the DC (Current - Voltage) characteristic measurements using a curve tracer and on the AC (Capacitance - Voltage) measurements using an impedance analyzer and on the switching characteristics using un clamped inductive load. The purpose is to establish an analytical model that is based on the physical and behavioural analysis of the SiC [JFET, taking into account the two physical channels and the influence of temperature. As shown, the model is validated with both steady State and transient characteristics. Validation of the model shows excellent agreement with measured data. The physical approach implemented in this model is crucial to describe the transient behaviour over a wide range of application conditions and temperatures. This model will be used later in the design of a power converter.

High temperature characterization of SiC-JFET and modelling

Silicon Carbide (SiC) is considered as the wide band gap semiconductor material that can presently compete with Silicon (Si) material for power switching devices. Compact circuit simulation models for SiC devices are of extreme importance for designing and analyzing converter circuit, in particular, if comparisons with Si devices should be performed. In this paper, three different kinds of Silicon Carbide JFET samples were characterized at temperatures up to 225degC. The characterization is based on the DC (Current - Voltage) characteristic measurements using a curve tracer and on the AC (Capacitance - Voltage) measurements using an impedance analyzer. We keep in mind to establish an analytical model that will be used in the design of a power converter.

The role of nickel and titanium in the formation of ohmic contacts on p-type 4H?SiC

The formation of low resistivity ohmic contacts to p-type 4H–SiC is achieved. Transfer length method (TLM)-based structures were fabricated on 0.8 µm thick epitaxial p-type silicon carbide (4H–SiC) layers. TLM metal patterns were obtained by a lift-off procedure and electron beam deposition of Ni, Ti and Al. The electrical properties of the contacts were examined using current/voltage measurements. Contact resistivity as a function of annealing was investigated over the temperature range from 700 to 1000 °C. The lowest contact resistivity of 1.5 × 10−5 Ω cm2 was obtained for the Ni/Ti/Al/Ni contact after annealing at 800 °C for 90 s. Using secondary ion mass spectrometry, energy-dispersive x-ray spectroscopy and x-ray diffraction measurements, we quantitatively and qualitatively determined the formation and the nature of the ohmic contact to p-type SiC.

Pressureless Silver Sintering Die-Attach for SiC Power Devices

Pressureless silver sintering is an interesting die-attach technique that could overcome the reliability limitations of the power electronic devices caused by their packaging. In this paper, we study the manufacturing parameters that affect the die attach: atmosphere, drying time, heating ramp rate, sintering temperature and duration. It is found that sintering under air gives better results, but causes the substrates to oxidize. Sintering under nitrogen keeps the surfaces oxide-free, at the cost of a weaker attach.

Design of a 600 V silicon carbide vertical power MOSFET

Silicon carbide (SiC) owns very interesting properties to fulfil the requirements of new power electronic applications. This paper reports the design of two vertical power MOSFETs, able to sustain a forward blocking voltage of 600 V. In order to evaluate the performance, 2D-simulations were performed taking into account the current technological constraints and the SiC materials parameters.

Optical beam induced current measurements based on two-photon absorption process in 4H-SiC bipolar diodes

Using a pulsed green laser with a wavelength of 532 nm, a duration pulse of ∼1 ns, and a mean power varying between 1 and 100 mW, induced photocurrents have been measured in 4H-SiC bipolar diodes. Considering the photon energy (2.33 eV) and the bandgap of 4H-SiC (3.2 eV), the generation of electron-hole pair by the conventional single photon absorption process should be negligible. The intensity of the measured photocurrents depends quadratically on the power beam intensity. This clearly shows that they are generated using two-photon absorption process. As in conventional OBIC (Optical Beam Induced Current), the measurements give an image of the electric field distribution in the structure under test, and the minority carrier lifetime can be extracted from the decrease of the photocurrent at the edge of the structure. The extracted minority carrier lifetime of 210 ns is consistent with results obtained in case of single photon absorption.

SiC power semiconductor devices for new applications in power electronics

This paper addresses the benefits of SiC semiconductor, owning excellent physical properties able to fulfill new scope of applications in terms of high temperature, high voltage and for more specific applications. Devices and applications developed at Ampere laboratory are detailed.