Study On The Strained NLDMOS With A Single-Trench Based Structure

As a research hotspot in RF field,LDMOS has the advantages of high voltage,good thermal stability,and easy process to integrate with MOS.In the trend of device miniaturization,strain technology can be used to improve the performance of LDMOS,and CESL strain technology is often used because of its simple process.In order to introduce the tensile stress to enhance the electron mobility in the channel,a layer of tensile strain CESL will be deposited on the surface of nLDMOS,but this will introduce the compressive stress to restrain the electron mobility in the drift region.To solve this problem,it has been studied that selectively depositing the tensile strain and the compressive strain CESL in the gate region and the drift region respectively,but this will complicate the related process.Therefore,we propose a new nLDMOS device based on the trench structure,and adopt the compressive strain CESL as the stressor.The trench structure can modulate the stress distribution and realize tensile strain in the channel and drift region at the same time,thus the device performance is improved.Firstly,we use Sentaurus simulation software to study the influence of trench structure on the stress distribution of nLDMOS's channel and drift region.As the results shown,in conventional device,the drift region is introduced by tensile stress,but the channel region is introduced by compressive stress.In the single-trench device,the channel stress changes from compressive stress to tensile stress,and the tensile stress in the drift region is also enhanced,due to the stress modulation of the trench structure.We also study the modulation mechanism of trench structure,and optimize the structure based on it.It is found that there is no special requirement for the aspect ratio of the trench structure,which ensures the process realizability of the trench fabrication.Secondly,we study the electrical characteristics of nLDMOS based on the trench structure,and compare the conventional compressive-strain nLDMOS and stress-free nLDMOS.The results show that the conventional compressive-strain nLDMOS has the lowest output current and the largest transconductance.This means that,although its electron mobility is enhanced in the tensile strained drift region,the mobility's reduction in its compressive strained channel degrades its electrical performance.The output current of trench-based strain nLDMOS is more than 20% higher than that of conventional compressive-strain nLDMOS,and its maximum transconductance is more than 15% higher than that of conventional compressive-strain nLDMOS.At the same time,the output current of trench-based strain nLDMOS is more than 11% larger than that of stress-free device,and its maximum transconductance is 10% larger than that of stress-free device.The simulation results prove that the trench structure can improve the LDMOS device performance.