A 90 V breakdown high temperature SOI lateral power nMOSFET

Abstract

A high-temperature lateral power MOS field-effect transistor on siliconon-insulator (SOI) material has been demonstrated to operate up to at least 3000C.resistances. This design has only one level of metal (1.5-pm thick AVl%Si), using TiW as a barrier between the silicide and aluminum. The whole FET is passivated This device is targeted initially for hightemperature applications such as engine control and down-hole oil exploration. This power device is easily integrable in our standard digital process flow, enabling high temperature, mixed-signal technology. Prototype solenoid drivers and torque motor drivers have been demonstrated using this technology. TECHNOLOGYThe power device is fabricated using the AUiedSignal 1.25-micron SO1 CMOS process [l]. The starting material (Unibond) is manufactured by SOITEC. The silicon thickness is 0.34 pm atop a 1-pm thick buried oxide. After the island, pwell, n-type extended drain, and field dielectric are defined, a 22.5-nm thick gate oxide is grown in steam, followed by the deposition of POCls-doped LPCVD polysilicon. The nominal gate length is 1.6 pm as defined by the spacing between the n-extended-drain and the n+ source. The effective channel width is over 150 mm.Partially-depleted SO1 transistors are susceptible to snapback [2] or singletransistor latch [3], which tends to worsen with temperature. Our design uses butting n+ and p+ regions on the source side to alleviate these floating body effects.The process also employs 100-nm of cobalt salicide to lower gate and source/drain 0-7803-4540-1/98/$10.00 0 1998 IEEE with 0.8 pm of nitride and 0.3 both deposited using a low-temperature plasma method. of oxide, To achieve a high blocking voltage, we use a lightly-doped n-type extended drain and terminate the polysilicon gate on a thicker field oxide on the drain side. Figure 1 shows a cross-section of the transistor.

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“…An SOI device also exhibits better thermal ruggedness than a comparable bulk device since threshold voltage drift is greatly reduced. For these reasons SOI devices are being widely investigated for power electronics in high-temperature environments [10][11][12]; however, this interest has not yet extended to RF power applications.…”