Research Of Reliability Based On Hot Carrier Effect For LDMOSFET

LDMOSFET(Latcrally Diffused Metal-Oxide-Semiconductor Field-Effect Tran-sistor) is a kind of High-voltage power device, which is of a strong competitive advantage in the field of communications, radar and other field of high-tech. LDMOS can perform well in the higher drain-source voltage and high frequency, high temperature conditions. In these areas, surrounded by a poor environment, the design of high voltage power device is an integral part of an integrated circuit, or even the key and difficult points of the entire design.The typical structure of the ordinary MOS is only an inversion layer channel between two active regions, thus forming a simple current loop, but in the field of high-power devices, requirements (high gain, high current) makes this simple structure of the MOS unusable. The drift region structure of the LDMOS solved this problem and even make the effect of short-term channel significantly weakened. LDMOS devices has been toward the direction of the high-gain, high efficiency. With the gate oxide thickness, junction depth, the channel length decreasing, the MOSFET channel electric field intensity increases, the carriers will get higher energy in the strong electric field because of the hope of high-gain and high efficiency of the device, which called hot carriers. A big part of high energy electrons directly become a part of drain current, while a small part of high energy electrons will go across the Si/SiO2barrier to become a part of the gate current, which may become the formation of electro traps which seriously threat the reliability of devices by making the device threshold voltage, transconductance degradation.According to LDMOS impact ionization mechanism, the substrate current and part of the gate current is generated because of the collision ionization. The substrate current is higher than the gate current by several orders of magnitude, whose characterization reflects the degree of impact ionization of the device, so the substrate current to a certain extent can reflect the extent of the device hot-carrier effects. In this paper, firstly it is discussed the basic electrical properties of the LDMOS, such as Ⅳ characteristics, subthreshold characteristics, breakdown characteristics, etc.; then, combining with MEDICI simulation software, according to the structural characteristics and electrical properties of the LDMOS, on the basis of the substrate current model of ordinary MOS, this paper establishes a substrate current model for long-channel LDMOS. to predict the LDMOS device degradation characteristics as accurately as possible caused by hot-carrier effects, we should apply the worst stress conditions to LDMOS device. Due to the difference between LDMOS and ordinary MOS structure, this paper analyzes the LDMOS worst hot carrier stress conditions, and detailed discusses the hot carrier effects in different structures.As device dimensions shrink, the strong electric field-effect of LDMOS directly affect the device reliability, high-energy carriers may not only lead to hot carrier effects, but also from other ways to threat to the normal work of the device, such as parasitic BJT effect and Kirk effect, etc. In the end, on the view of safety of area, we made Analysis of four kinds of negative effects which may threat the reliability of LDMOS device.