Improving an LDMOST by variation of lateral doping on epitaxial-layer drift region

Abstract

Variation of lateral doping (VLD) is applied to the epitaxial-layer drift region in LDMOSTs, resulting in non-uniform doping concentration. In addition to a decrease in on-resistance, it improves electric field distribution on the surface of drift region, and thus increases the breakdown voltage. We studied the condition of using the VLD technique, and compared it with the conventional technique of optimizing the epitaxial-layer uniform concentration. Results from TSPUREM 4 and MEDICI simulations indicate that when the epitaxial-layer doping concentration is 1.5 × 10 15 cm −3, applying VLD to the drift region increases the breakdown voltage by as much as 34% (187–251 V), while the specific on-resistance is lowered by 55% (49–22 mΩ cm 2), which are remarkable improvements. On the other hand, if the doping concentration of epitaxial-layer is already high, the improvement of applying VLD is limited.