Self-Aligned Short-Channel Vertical Power DMOSFETs in 4H-SiC

We describe the first short-channel (0.5 μm) high-voltage (900 and 2,000 V) DMOSFETs in SiC, fabricated by a novel self-aligned process. By reducing the channel length, we reduce the on-resistance of the MOSFET channel so that it is now negligible compared to other resistances in the device. Introduction This paper reports the design, fabrication and performance of the first high-voltage selfaligned short channel DMOSFETs in 4H-SiC. The specific on-resistance of most 4H-SiC MOSFETs fabricated to date is dominated by the MOS channel resistance, due to low inversion layer mobility in 4H-SiC. In this paper we describe a self-aligned DMOS process in which the channel length is reduced to ≤ 0.5 μm, thereby reducing the channel resistance by a factor of four to six. Figure 1 summarizes the performance of a number of SiC DMOSFETs reported to date, along with calculations for DMOSFETs having 3 μm and 0.5 μm channel lengths [1]. The specific on-resistance is the sum of resistances due to the source, channel, accumulation layer, JFET region, and drift region. These calculations assume an inversion mobility of 20 cm/Vsec, a maximum oxide field of 4 MV/cm, and a cell pitch of 11 μm (JFET region width = 6 μm). A significant reduction in on-resistance is predicted for short-channel (0.5 μm) MOSFETs for blocking voltages below 4-5 kV. Figure 1. Overview of MOSFET performance. Curved lines are calculations for DMOSFETs with channel lengths of 3.0 μm and 0.5 μm. LCH = 0.5 μm LCH = 3 μm S pe ci fic O nR es is ta nc e (m Ω c m 2 ) Blocking Voltage (V) Design and Fabrication Figure 2 shows a schematic cross-section of the basic cell. The JFET width LJ is varied on the layout from 4 to 6 μm. Depending on the minimum feature size employed, the cell pitch ranges from 10 μm to 16 μm. Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 1393-1396 doi:10.4028/www.scientific.net/MSF.457-460.1393 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,15:23:31)