Research On The Influence Of Hot Carrier Stress On The Low-frequency Noise Of MOSFET

Since the deep submicron manufacturing process is widely used inMOS devices,the reliability problems of devices caused by hot carrier effects gain importance.With the widespread application of MOSFET in RF circuits,the hot carrier effect and the degradation mechanism under RF stress have become been widely concerned.The damage caused by the hot carrier effect under high lateral electric field and high RF drive in the MOSFETs could lead to the increase of the low-frequency noise（LF）.And the phase noise in RF circuits would increase due to the upconversion of the LF noise of MOSFET.Therefore,studying the effect on the LF noise of devices by the hot carrier stress（DC stress and RF stress）has a practical application value for improving the reliability of the device.Many researches on the degradation of the LF noise after various kinds of hot-carrier（HC）stress have been made.It is found that an increase in the trap density due to hot-carrier stress also leads to an increase in the LF noise.Hence,the LF noise can be a useful tool to estimate device reliability and diagnose defects and failures inMOSFETs.Therefore,the LF noise has been a key indicator utilized in the estimation of semiconductor device reliability.In this thesis,the accelerated degradation lifetime tests onMOS devices with various hot carrier stress methods including DC stress and RF stress have been explored.Experimental results on the electrical parameters and the LF noise have been got before and after the stress.And the degradation mechanism of the device is studied by characterizing the degradation of the LF noise.The main research work and innovations are as follows:Three kinds of DC stress have been applied to n-MOSFETs.The experimental results show that the same DC stress has different effects on the low-frequency band（f≤1000 Hz）and the high-frequency band（f>1000 Hz）of noise at different gate voltages which is related to the trap density distributions.In order to explain this phenomenon,a method to distinguish the types of defects caused by different stresses has been proposed,which is to divide the degradation of the LF noise into two parts to analyze:the low-frequency band for a small V_gs value(V_gs≤0.7 V)and the high-frequency band for a large V_gs value(V_gs>0.7 V).As a consequence,the degradation of the LF noise at the low-frequency band for small V_gs values is attributed to the gate oxide traps,and the interface traps results in the degradation of the LF noise at the high-frequency band for large V_gs values.Nine different kinds of RF stress have been applied to the gate of n-MOSFETs to explore the effects of the input frequency and the power on the LF noise,and the change of the LF noise frequency indexγis used to analyze the degradation mechanism of RF stress.Besides,the impacts of RF stress on the devices have been compared with the DC stress condition.It is found that the degradation of electrical parameters after RF stress is relatively small,while the LF noise is more sensitive to the damage caused by RF stress.Compared with the noise results after DC stress,the noise degradation after RF mainly occurs in the saturation region.And the LF noise after RF stress rises more rapidly at a large V_gs value,while the DC stress causes more degradation at a small V_gsvalue.The increment of the LF noise raises as the growth of V_gs,while the?S_id reduces under DC stress for the opposite case.The value ofγdecreases after RF stress,and the value ofγis below 1 after the worst-case RF stress which indicates the generation of traps close to the interface is the main reason for the increment of noise.In this thesis,the degradation mechanisms of devices under various hot carrier stress conditions have been analyzed intuitively and accurately by characterizing the degradation of the LF noise,especially when the degradation of electrical parameters is not obvious enough.Based on the measured noise data,the Mc Whorter model is used to estimate the trap density of the device after hot carrier stress,and the feasibility of the?N-?μnoise model after hot carrier stress has also been discussed.