A Research Of Multi-function Switched-beam Antenna Array

The strained silicon technology has been widely studied and adopted in the small-sized device, effectively reduce the carrier effective mass and scattering rate, enhance carrier mobility by band modulating. With the rapid development of wireless communication technology, in order to meet the needs of high-speed transmission of high-quality information, the RF power LDMOS widely used in the base station RF silicon and handheld devices has downsized to as small as a few tenths of microns. Some researchers have already applied the silicon technology in the small size LDMOS to overcome the development obstacles and achieved good results.But these devices also suffer from the degradation of the breakdown voltage by applying the mainstream stress technology, not taking into account the special device structure of the LDMOS. Therefore, we creatively propose the method of introducing useful stress to the channel and drift region of the LDMOS by two intrinsic strained silicon nitride film. Based on the small size LDMOS process line of the cooperation agency, we explore the method of applying stress. The main research work are:First, the magnitude of the intrinsic stress in the silicon nitride film plays a major role in the size of the stress in the LDMOS. Therefore, we sum up the ways to deposit high stress silicon nitride film by PECVD. At last, we make a plan for depositing high stress film considering the use of the equipment in the agency.Secondly, by the aid of the finite element simulation software Abaqus, We have simulated the wafer warpage problem caused by the stress. We find out that we can eliminate the warpage problem by reducing the covered area by the strained film.Subsequently, we worked out the method to introduced useful stress to the channel and drift region of the LDMOS under the limit of the process line. First of all, in the front-end process we deposit a thin oxide layer, which is used to barrier metal ion in the back-end process and connects silicon nitride film with the wager, on the surface of the device post silicide of source and drain. Then, depositing tensile strained silicon nitride film on the entire surface of the device by PECVD in back-end process. Followed by high temperature annealing, the tensile strained film will turn into compressive strained. Then etching away the silicon nitride thin film on the drift region. After that, depositing tensile strained silicon nitride film on the entire surface of the device. The stress application process is completed after etching away the tensile strained silicon nitride out of the drift region.Finally, by using Sentaurus process and device simulation tools, we simulate the device based on LDMOS device process provided by the co-operation. When the stress in the two intrinsic silicon nitride film is 1 GPa of the fully strained LDMOS, the driving current device improved by 10.2%, transconductance improved by 14.6%, and frequency increase by 7.5% with unchanged breakdown voltage, compared with no strained device.