H.-J. Schulze

600 V Reverse Conducting (RC-)IGBT for Drives Applications in Ultra-Thin Wafer Technology

Reverse conducting IGBTs are fabricated in a large productive volume for soft switching applications, such as inductive heaters, microwave ovens or lamp ballast, since several years. To satisfy the requirements of hard switching applications, such as inverters in refrigerators, air conditioners or general purpose drives, the reverse recovery behavior of the integrated diode has to be optimized. Two promising concepts for such an optimization are based on a reduction of the charge- carrier lifetime or the anti-latch p+ implantation dose. It is shown that a combination of both concepts will lead to a device with a good reverse recovery behavior, low forward and reverse voltage drop and excellent over current turn- off capability of a trench field-stop IGBT.

Anode Design Variation in 1200-V Trench Field-stop Reverse-conducting IGBTs

Reverse-conducting (RC) IGBTs with a monolithically integrated reverse diode are meanwhile available for soft-switching applications such as lamp ballast or inductive cooking as well as for hard-switching applications such as inverters in refrigerators, air conditioners or general purpose drives. In this paper, we present results on the electrical behavior of 1200-V RC-IGBTs designed predominantly for soft switching applications. Miscellaneous parameters of the RC- IGBT, namely its thickness, the field-stop profile and the p-emitter dose were varied under the additional constraint to improve the behavior also for more severe switching conditions.

Influence of buffer structures on static and dynamic ruggedness of high voltage FWDs

It is required to design free wheeling diodes (FWDs) to be robust against static and dynamic avalanche. Therefore we investigate the effect of different buffer structures and the influence of various bulk parameters. By numerical device simulation the effect of the buffer doping, base doping and base width on the static and dynamic behaviour of FWDs is analysed. We show the promising features of well designed buffers for ruggedness and their coherences to the static reverse characteristics.

The CIBH Diode - Great Improvement for Ruggedness and Softness of High Voltage Diodes

The concept of controlled injection of backside holes (CIBH) is a novel and path breaking method for the optimization of the electrical characteristics of diodes. Buried p-doped layers at the cathode side of the diode inject holes in the base region during reverse recovery. Due to this injection the snap-off of the diode can be suppressed effectively. The main intention of this paper is to take advantage of the CIBH concept for designing a fast switching 3.3 kV diode with low Vf, low switching losses, high ruggedness and strongly improved softness. A new promising effect of the CIBH design, which we call DSDM (dynamic self damping mode), further increases the soft reverse recovery behavior and results in a nearly snap-off free diode characteristic.

Reduction of the temperature dependence of leakage current of IGBTs by field-stop design

In this paper we propose a new method to reduce the temperature dependence of the leakage current of IGBTs by reducing the temperature dependence of the anode-side current gain αpnp. The temperature dependence of αpnp can be reduced by using field-stop zones that contain doping atoms with deep levels in the band gap of silicon. We demonstrate how the temperature dependence of the leakage current is influenced when using deep-level donors instead of shallow-level donors in the field-stop zone.

Tailoring of field-stop layers in power devices by hydrogen-related donor formation

Hydrogen-related donors can be formed by using only a moderate thermal budget, so that this process can be used to create field-stop layers in thin power devices. The electrical characteristics of 1200 V IGBTs and diodes provided with such field-stop layers are presented and compared with the characteristics of conventionally processed devices. Moreover, tailoring the field-stop distribution by multi-energy proton implantations offers new opportunities for optimizing the performance of power devices.

Filament-induced thermomigration of an aluminum drop at the cathode-side of high-voltage power diodes

This paper shows how a buried aluminum eutectic drop at the cathode-side of a high-voltage power diode can affect the device behavior. The aluminum drop driven by thermo-migration, moves from the contact metallization some micrometers into the chip and forms a buried eutectic. Thermomigration [1] becomes stronger as the temperature gradient increases. High temperature gradients can be achieved at the cathode side if a single filament is triggered. Simulation results show that an early surface-punch-through at a spike may reduce the reverse-recovery ruggedness of the power diode. Such a detrimental filamentation can be avoided by a well-defined fabrication process of the device.

Use of 300 mm magnetic Czochralski wafers for the fabrication of IGBTs

As in other semiconductor industries, there is a strong trend to use larger wafer diameters for the fabrication of power devices. However, for wafer diameters above 200 mm float-zone (FZ) silicon which is traditionally used for IGBTs is not available. Therefore, there is a need to use silicon material which has been fabricated by the magnetic Czochralski (Cz) method to make use of 300 mm wafers for IGBT-production. As this material contains a relatively high concentration of oxygen, the influence of carbon/oxygen-complexes has to be taken into account. CIOI-complexes can be decorated with hydrogen atoms resulting in donor-like complexes. Particularly, the application of proton-irradiation for the doping of the field-stop zone results in a relatively high concentration of interstitial carbon which is continuatively associated with the generation of undesired donors.

IGBT field-stop design for good short circuit ruggedness and a better trade-off with respect to static and dynamic switching characteristics

The doping profile of the field-stop zone influences the static characteristics (Vce, sat, Vbr) and the dynamic switching characteristics (dic/dt, dVCE/dt, softness) of IGBTs. Furthermore, the short-circuit ruggedness is strongly influenced by the rear side structure of the IGET. In this work, box-like field-stop profiles in combination with a constant p-emitter were analyzed by TCAD simulations. The findings were used to optimize and realize field-stop profiles by proton implantation with the focus to achieve an improved short-circuit ruggedness at the same softness.

Critical overcurrent turn-off close to IGBT current saturation

A failure mechanism in the edge termination of a 1200V IGBT during overcurrent turn-off is studied with simulations and verified by experiments. The position of the destruction in the experiment can be correlated to the formation of a critical filament in the simulation. The destruction mechanism is investigated in detail. It is only observed if the IGBT enters its current saturation regime. I.e., the IGBT survives a turn-off from the same current level for an increased gate voltage. It is shown that an IGBT provided with a properly-designed High Dynamic Ruggedness (HDR) edge termination structure [1] is no longer susceptible to the destruction mechanism.