Johannes Georg Laven

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.

RCDC-IGBT study for low-voltage applications

The desaturation and charge recovery behavior for 1200-V RC-IGBTs with diode control is investigated. The low thickness of the drift-region of modern 1200-V IGBTs results in significantly reduced time constants of the diode-control feature. While a low desaturation time constant is well acceptable, the recovery time constant becomes critical when compared to typical locking time requirements of common gate driver units. The impact of different locking times on the overall performance is discussed and a novel device concept for RC-IGBTs is presented which overcomes this issue. The FWD-mode of the novel RC-IGBT is desaturated at a gate-emitter voltage of 0 V allowing for the first time a desaturation pulse pattern which may disregard the locking time requirements of the driving-unit.

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.

A new sub-micron trench cell concept in ultrathin wafer technology for next generation 1200 V IGBTs

The overall growing trend towards electrification and, at the same time, the urgent need to minimize energy consumption strongly requires higher energy efficiency in power electronics. We present a new technology concept for next generation 1200 V IGBTs with vastly reduced overall power losses using an optimized micro-pattern trench (MPT) cell design with sub-micron mesas. Further important parameters relevant for inverters driving electrical machines were optimized, including turn-off softness, dv/dt-controllability, and short circuit capability, providing a right-fit solution to customer requirements.

Hydrogen decoration of radiation damage induced defect structures

The defect complexes that are formed when protons with energies in the MeV-range were implanted into high-purity silicon were investigated. After implantation, the samples were annealed at 400 °C or 450 °C for times ranging between 15 minutes and 30 hours. The resistivity of the samples was then analyzed by Spreading Resistance Profiling (SRP). The resistivity shows minima where there is a high carrier concentration and it is possible to extract the carrier concentration from the resistivity data. Initially, there is a large peak in the carrier concentration at the implantation depth where most of the hydrogen is concentrated. For longer anneals, this peak widens as the hydrogen diffuses away from the implantation depth. Following the changes in resistivity as a function of annealing time allows us to characterize the diffusion of hydrogen through these samples. Differences in the diffusion were observed depending on whether the silicon was grown by the magnetic Czochralski (m:Cz) method or the Float zone...

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.

The Efficiency of Hydrogen-Doping as a Function of Implantation Temperature

– For a conventional proton implantation doping process applied to crystalline silicon comprising proton implantation and subsequent furnace annealing the effect of the substrate temperature set during implantation is examined for temperatures between 50 °C and 200 °C. The formation efficiency of the hydrogen related donors in the maximum of the related doping profiles is shown to linearly increase with the implantation temperature. Regarding the dose rate, a reverted effect is found. The appearing effects are explained by considering the evolution of the initial implantation damage towards a vacancy related precursor species of the hydrogen related donor. Additional information about the implantation temperature dependent defect distribution is gained from Fourier-DLTS results.

Metastable Defects in Proton Implanted and Annealed Silicon

Two metastable defects with energy levels at Ec-0.28eV and Ec-0.37eV, which previously have been reported in proton implanted- and in proton implanted and annealed crystalline silicon are discussed. Recent results on the peculiar behavior of these defects upon periodical application of two different bias conditions during DLTS measurement are reviewed. Two specifically designed DLTS measurement sequences are proposed in order to further reveal the defects transformation rates and respective activation energies.

H + implantation profile formation in m:Cz and Fz silicon

Implanting hydrogen ions (H+) into silicon creates defects that can act as donors. The microscopic structure of these defects is not entirely clear. There is a difference in the resulting doping profiles if the silicon is produced by the float zone (Fz) process or the magnetic Czochralski (m:Cz) process. Silicon produced by the m:Cz process has higher concentrations of oxygen and carbon than silicon produced by the Fz process. The presence of the oxygen and carbon affects the formation of defects and thereby the doping profile. We implanted high resistivity p-type m:Cz and Fz wafers with protons. Due to the n-type doping from the H+ implantation, a pn-junction was generated in the sample. Simulations indicate that the H+ implantation depth is 148 μm. Spreading Resistance Profiling (SRP) measurements of as-implanted and not annealed samples show a donor peak at 148 μm in the Fz samples but the peak is at about 160 μm depth in m:Cz samples. After a low temperature anneal of the m:Cz samples at temperatures between 150 and 250 °C for at least 30 minutes, the expected end of range (EOR) donor peak (at about 148 μm) appears. For higher annealing temperatures, the hydrogen related donor complexes (HTDs) become activated and the EOR peak becomes dominant in the implantation profile. In an SRP study we show the evolution of the doping profile of hydrogen implanted m:Cz and Fz wafers as a function of the annealing temperature. To monitor the depth of the formed pn-junction and the effective local diffusion length in the proton radiation damaged region, Electron Beam Induced Current (EBIC) measurements were performed.

MeV-proton channeling in crystalline silicon

Hydrogen implantation has become an important application in the fabrication of power semiconductor devices. With the product requirement of a well-defined implantation profile, adequate control of the incident beam angle is necessary in order to avoid channeling effects. With respect to the different scan systems of commercial implanters and the crystal alignment of the bulk material the implant tilt and twist angles have to be adapted. We used commercially available <;100>-oriented silicon wafers to examine planar channeling along a {110}-plane for proton energies in the range of 0.5-2.5 MeV. The critical angle as a function of proton energy is determined from photothermal response measurements (TWIN).