Fabrication And Hot Carrier Reliability Of Strained LDMOS

Strained silicon technology improves device performance by adjusting carrier mobility,and has been widely used in advanced CMOS technology.Introducing strain into silicon-based power devices can also optimize the tradeoff between on-resistance and breakdown voltage,breaking through the“Si-limit”.At present,the application of strained silicon technology in power LDMOS is still in its infancy.Most of the existing researches focus on the effect of strain on the electrical characteristics of LDMOS,and lack of research on the process realization and reliability of strained silicon LDMOS.Therefore,in this paper,strained silicon LDMOS is successfully fabricated by introducing a Si N layer with internal stress into the contact etch stop layer(CESL),and then the effect of strain on the hot carrier reliability of LDMOS is further studied.In this paper,the power LDMOS device using strained CESL process is successfully developed.The CESL with internal strain is used to introduce uniaxial tensile strain into 18/20/24/30 V LDMOS device.Higher drain current,transconductance and breakdown voltage can be obtained in n-type LDMOS devices with strained CESL.At the same time,the strain can also reduce the on-resistance by about 9%.The distribution of process induced strain in the device is directly measured by tipenhanced Raman spectroscopy.The strain distribution is introduced into TCAD simulation at the same time,and the effects of strain on carrier transport and electrical characteristics of the device are studied in detail.The results show that the strain increases the electron mobility of the inversion channel and part of the drift region,thus optimizing the tradeoff between the on-resistance and the breakdown voltage.The strained CESL process provides a practical and cost-effective solution for the practical application of strained silicon LDMOS.The effect of mechanical strain on the hot carrier reliability of p-type LDMOS is also studied.In order to eliminate the interference factors caused by process and structure changes,mechanical strain is introduced into the device by bending the silicon wafer.The experimental results show that uniaxial compressive strain can improve transconductance,drain current and hot carrier reliability of p-type LDMOS at the same time.Furthermore,the mechanism of strain affecting the reliability of the device is revealed by charge pumping test and TCAD simulation.Uniaxial tensile strain changes the electric field distribution inside the device,reduces the impact ionization rate at the bird's beak region,and then suppresses the generation of interface states,which improves the hot carrier reliability of the device.