Study Of The Strained RF LDMOSFETS

Strained technology is widely used in MOS devicesdue to compatible with traditional process, lower carriers effective mass and scattering rate, larger carrier mobility and performance enhancement resulting from band modulation.The traditional CESL strained technique cannot enhance both channel and drift carriers’ mobility at the same time.In addition, with the reduction of device critical size, the traditional strained technique or SOI technology can not improve both short channel effect and the performance of RF LDMOSFET effectively. To solve above problems, this paper has developed studies of strained RF LDMOSFET based on theory and simulation analysis as follows:Firstly, stress and electrical characteristics of the fully strained PSOI RF LDMOSFET have been analyzed by Sentaurus, the finite element simulation software.The drift stress with the same property as channel stress can be introduced by adjusting process parameters to achieve the adverse intrinsic stress in the Si N film to the other part of the film on the device, which could effectively enhance channel and drift carriers’ mobility achieve 24% mobility enhancement for drift region electron. The long and thin drift region with the decreased drift carriers’ mobility leads to large drift resistance and the fully strained RF LDMOSFET with the stress in channel and drift having the same property could get the lower drift resistance due to the higher drift carrier mobility. When the high drain-source voltage is biased, the drift region biased low gate-source voltage is depleted, however when biased high gate-source voltage, is accumulated. The strained RF device(fully strained and channel strained) with depleted drift when the device performance is mainly resulting from the channel gets the nearly the same improvement than the unstrained one, achieve 24% and 28% fT enhancements for channel strained and fully strained RF devices respectively. When the drift region is accumulated at which the drift’s carrier mobility becomes important to the device performance, the fully strained and channel strained respectively get 18.9% and 5.5% improvement than the strained one.Secondly, the stress and electrical characterics of the ultra-thin strained PSOI RF LDMOSFET(UTS PSOI RF LDMOSFET) has been analyzed by Sentaurus and then the devices fabrication processes are explored. The result stated by Sentaurus Sdevice shows that the BOX under channel with ultra-thin SOI could effectively restrain short channel effect(DIBL reduced from 47mV/V to 28mV/V)and enhance the carriers’ mobility resulting from the stress concentration. The incorporation of the local BOX and CESL strained technique could achieve the better performance(73% enhancement magnitude) than either of them and even the sum of them( 37.2% for SOI and 24.6% for strained respectively).