Universal Test Structure and Characterization Method for Bias-Dependent Drift Series Resistance of HV MOSFETs C. Anghel N. Hefyene A. Ionescu costin.anghel@epfl.ch EPFL-STI-IMM-LEG CH-1015 Lausanne Switzerland S.F. Frère R. Gillon J. Rhayem Alcatel Microelectronics, Westerring 15, Oudenaarde, Belgium Abstract A simple, fast and accurate characterisation method dedicated to the evaluation of bias-dependent drift resistance of the HV MOS transistors is presented. The procedure relies on a novel test design structure that gives direct information about the impact of the drift zone on the overall HV MOSFET characteristics. Intrinsic (MOS channel) and extrinsic (including drift region) characteristics, obtained by adapted measurements, are used for parameter extraction and physical effects identification. For the first time the variation of the drift resistance from room temperature up to 150°C is extracted. Very good performance when combining a BSIM3V3 low voltage model with a drift resistance quasi- empirical model is reported. 1. Introduction High-Voltage MOSFETs are key components for smart power, RF and automotive integrated circuits. The most versatile HV architecture is the Extended Drain MOSFET (XDMOS) and one of its most critical issues is the on-resistance, R on . Major advances in the design and modelling of these devices are related to the accurate evaluation of their bias-dependent drift series resistance, R drift , critically dependent on the design of the extended drain region, which impacts the HV performance. Especially, the quantitative comparison of R on with the drift resistance, R drift , is valuable insight for HV design. Moreover, R drift bias-dependence on drain, V D , and gate voltage, V G , appears to be the origin of the so-called quasi-saturation phenomena that were subject of many reports, physical analysis and controversy last years [1-3]. 2. Novel Test Structure We report a new, universal test structure, called MESDRIFT, and the associated characterisation that are able to accurately provide the bias-dependent drift series resistance without any prior information about the detailed technological architecture of the drain extension. The proposed MESDRIFT structure (designed by Alcatel Microelectronics) is depicted in Fig. 1: it simply reproduces the 100V n-channel extended drain X-DMOS device architecture in a dedicated test structure, with the key difference that a small contact is smartly engineered in the drift region, near the end of the MOS channel. This contact is dedicated to probe the intrinsic drain voltage, V k , without any significant impact on the electrical characteristics. S G D K-contact B + - - + VMU Bias-dependent drift resistance Intrinsic MOSFET R drif V D V G N + Fig. 1 MESDRIFT structure: cross section and measurement setup. 3. Experiment 3.1 Validation of the test structure In order to validate the MESDRIFT structure, its transfer and output characteristics were measured and compared with identical measurements performed on the original device (fig.2). Although, the breakdown of the MESDRIFT structure shifts down in comparison with the original one (due to the n + implant in the proximity of the metallurgical pn junction) the measured characteristics present no significant change for low and medium drain voltage values. Consequently, the drift region with drain and source biased can be observed for the whole analogue voltage domain. V K