Franz Josef Niedernostheide

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.

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.

Thyristor with integrated forward recovery protection function

A completely self-protected light-triggered high-power thyristor has been developed and fabricated. The integrated protection functions comprise overvoltage protection, dV/dt protection and forward recovery protection. Turn-on characteristics of 8 kV, 4000 A prototype samples under diverse conditions are presented, demonstrating the reliable operation of all the protection functions.

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.

Automated vertical design optimization of a 1200V IGBT

Many important performance parameters in an IGBT power semiconductor are heavily affected by its field-stop profile, its device thickness and its collector-side p-doping concentration. To find the optimum combination of these design parameters is of high importance for an optimal IGBT design. The optimization criteria include low switching and on-state losses as well as limited maximum overshoot voltage and modest current and voltage rise and fall times. This work focusses on an automated global optimization scheme to solve this issue. The method and definition of a proper target function are briefly explained. Finally, design optimizations found under different constraints are discussed.

Exploring the limits of the safe operation area of power semiconductor devices

TCAD simulations of power devices are an important tool to investigate destruction mechanisms of power diodes and IGBTs. It is found that the dynamics of filamentation is the key for understanding the limits of the safe operation area. For both diodes and IGBTs, destructive and non-destructive filamentation mechanisms are identified and the resulting destruction mechanisms are discussed.

Conversion Efficiency of Radiation Damage Profiles into Hydrogen-Related Donor Profiles

By introducing radiation damage and hydrogen and successively annealing with low thermal budgets, hydrogen-related donors are created in oxygen-lean silicon. Hydrogen-related donor profiles are induced in float-zone silicon by implanting hydrogen and/or helium and successive annealing with or without additional hydrogen introduction by a hydrogen plasma. The efficiency of the conversion of the radiation-induced damage into the hydrogen-related donors differs in dependence of the method of damage and hydrogen introduction. In proton implanted samples, the ultimate introduction rate of the donors is significantly lower than it is in helium and hydrogen co-implanted samples. Furthermore, the depth distribution of the hydrogen-related donors shows a deviance from the simulated distribution of the radiation damage induced by proton implantation not seen in case of helium-induced damage. The change in doping efficiency is discussed in respect to the hydrogen content in the different experiments.