Ferruccio Frisina

Innovative localized lifetime control in high-speed IGBTs

An innovative method to control carrier lifetime locally and efficiently in Insulated Gate Bipolar Transistors (IGBTs) is presented. It is based on the formation of void layers by low-energy and high-dose He implants and annealing. Voids introduce two well-defined midgap trap levels in silicon. HFIELDS simulations demonstrate the increase of surface hole concentration when a well localized recombination region is introduced in the buffer layer. High-speed IGBTs were fabricated both with voids in the buffer layer or with unlocalized recombination centres. Devices with localized bandgap centres show a lower on-resistance with a fast turn-off behavior.

Optimization of the tradeoff between switching speed of the internal diode and on-resistance in gold- and platinum-implanted power metal-oxide-semiconductor devices

Diffusion of platinum and gold has been used to reduce minority-carrier lifetime in power metal-oxide-semiconductor devices in order to improve the switching characteristics of the internal diode. Gold thin-film deposition and gold- or platinum-ion implantation techniques have been adopted to realize the prediffusion source. For a given reduction in lifetime, the concomitant increase in the on-resistance of the device, as determined by the forward characteristics, is smaller in gold-implanted than in gold-deposited devices; an even smaller increase in on-resistance is obtained by using platinum implantation. Therefore, ion implantation of platinum in power MOS devices fabrication provides a better tradeoff between static characteristics of the devices and switching speed of their internal diodes. >

Diffusion and lifetime engineering in silicon

Diffusion mechanisms in crystalline silicon are reviewed emphasizing the role played by the structural defects like vacancies and self-interstitials. These defects control the diffusion process of some transition metals, such as Au and Pt, which undergo fast long-range diffusion as interstitials and become substitutional by replacing a Si atom in a kick-out reaction. The influence of boundary conditions and sample surfaces on the concentration profiles of these metals are analysed in detail. These profiles can be precisely tailored using ion-implantation to achieve a low fluence diffusion source. Fine tuning of the metal profiles is shown to improve greatly the trade-off between dynamic and static characteristics of some silicon power devices like metal-oxide-semiconductor field effect transistors. Moreover, the possibility to obtain a preferential reduction of lifetime by metal doping in a selected area of a semiconductor device is demonstrated.

Power bipolar transistors with a fast recovery integrated diode

We have integrated a fast recovery diode in the structure of a power bipolar transistor. This integral diode is physically connected between the emitter and the collector of the transistor and can be used as a free-wheeling diode in power switches. Selective reduction of the minority carrier lifetime in the region of the diode was realized by Pt implantation in the diode area followed by an optimized thermal process that limits the lateral diffusion of the metal atoms. Using this metal doping a reduction by a factor of 10 of the reverse recovery charges of the integrated diode is obtained without affecting significantly the current carrying capability of the transistor.

Transient behavior of IGBTs submitted to fault under load conditions

The paper deals with the short circuit behavior during fault under load (FUL) conditions occurring on IGBT devices. The experimental switching transients in FUL with inductive load have been widely investigated. The devices have been tested in several working conditions accounting for the spread of the device characteristics, the parasitic due to the board layout, and the gate driving characteristics aiming to evaluate the switching performances and the influence of the parameters involved into the transient. The effect of the device temperature has been taken into account too. The experimental tests have been carried out using as a workbench a chopper circuit equipped with IGBT devices. As in medium and large power range converters the use of multiple string of IGBT devices is worth to be considered, the parallel and series connections experiencing FUL conditions have been also investigated.

Design of IGBT with integral freewheeling diode

A new power structure integrating a freewheeling diode in the termination region of a punch-through (PT) insulated gate bipolar transistor (IGBT) is presented. The proposed solution requires virtually no silicon area penalty with respect to a standard IGBT. Static and dynamic experimental results show the correct behavior of both IGBT and freewheeling diode. Further, it is shown that the lateral diode surrounding the multicellular IGBT can support IGBT direct current with low on-state voltage drop. The operation mechanisms of the composite structure and design techniques to improve structure dynamic behavior are investigated through two-dimensional numerical device simulations.

Radiation damage–He interaction in He implanted Si during bubble formation and their evolution in voids

Abstract He atoms were implanted in crystalline and pre-amorphized silicon wafers at doses in the 2×10 16 1×10 17 cm −2 range. Using transmission electron microscopy (TEM) we monitored the evolution of He bubbles into voids upon thermal annealing. Bubbles are formed in both crystalline and amorphous silicon. However, in amorphous material bubble interaction with the moving crystalline–amorphous interface during the epitaxial regrowth prevents their evolution into voids. By implanting He at different target temperatures in crystalline Si, thus by changing the structure of radiation damage, we found that the interaction between point defects and He atoms is essential for the generation of He bubbles and for their subsequent evolution into voids.

Characterization of oxide layers grown on implanted silicon

Abstract Boron ions were implanted at 80 keV for a dose of 2 × 1015 cm−2 in crystalline silicon. The silicon crystal was recovered using different annealing processes to produce layers with different secondary defect densities. The quality and the characteristics of the silicon oxide grown on the different surfaces were found to depend on the defects present in the layer immediately under it. The oxide quality was improved by using implanted and annealed silicon with a defect free surface. Iron contaminations, introduced in the wafers at different concentrations (up to 1 × 1015 cm−2), do not affect the oxide layer grown on unimplanted silicon wafers, while it degrades the oxide characteristics of layers grown on implanted and annealed samples. This degradation decreases if the residual damage is reduced by annealing processes.

Modeling and characterization of a merged PiN-Schottky diode with doping compensation of the drift region

In this paper standard-cell Schottky rectifiers along with silicon-based merged PiN Schottky (MPS) and PiN diodes, which are realized using a super junction technology, have been analyzed by conducting extensive device and mixed-mode simulations through two-dimensional finite-element grid. The main issues of concern with these devices such as the forward voltage-drop, the leakage characteristic and the reverse recovery are dealt with, by highlighting the superior performances exhibited by the MPS rectifier in respect to the PiN diodes. Basics on the used technology are also reported, by focusing on the high voltage capability obtainable along with the low forward voltage-drop during the on-state conduction. The reverse recovery behavior pertaining to the MPS diode has been analyzed by resorting to several simulations of the internal plasma dynamics.

Performance Analysis of Merged p-i-n–Schottky Diodes With Doping Compensation of the Drift Region

In this paper, standard-cell Schottky rectifiers along with silicon-based merged p-i-n-Schottky (MPS) and p-i-n diodes, which are realized using a super junction technology, have been analyzed and compared by conducting extensive device and mixed-mode simulations through a 2-D finite-element grid. The main issues that concern these devices, such as the forward voltage drop, the leakage characteristic, and the reverse recovery, are treated, and the superior performances exhibited by the MPS rectifier with respect to the p-i-n diodes are experimentally validated. First, the basics on the used technology are reported by focusing on the high voltage capability of the new devices along with the low forward voltage drop during the on -state conduction. The reverse-recovery behavior belonging to the MPS diode has been analyzed by exploring through several simulations the internal plasma dynamics. 2-D simulations of the turn-on behavior relative to the Schottky, p-i-n, and MPS rectifiers have been carried out in order to analyze the effects of the voltage overshoot phenomenon eventually occurring in the three diode structures