Investigation Of Performance Of Selective Buried Oxide MOSFETs Based On FDSOI Process Dependence On Back-Plane Doping And Position Of BOX Window

As the size of device(core cell of the chip)is further reduced,the short channel effects(SCEs)of conventional planar MOS devices become even worse,and the productivity and performance cannot be improved according to the Moore's Law.Fully depleted silicon on insulator(FDSOI)devices with their improved short channel effects,small parasitic capacitance,good anti-irradiation performance,dynamic multithreshold voltage,completely eliminated latch-up effect,become the core device for the low-voltage and low-power application beyond 28 nanometer node.However,its thermal conductivity(1.4 W/m·K)is much lower than that of bulk silicon(148 W/m·K),only one percent of the bulk silicon,the buried oxide(BOX)impeds heat conduction badly.Moreover,the thermal conductivity of the active device region,i.e.,the thin-film body silicon on insulator(SOI),is much lower,because it is directly proportional to the film thickness.As a consequence,FDSOI MOSFETs suffer self-heating effect(SHE)severely.Moreover,the shrinking of device's characteristic size makes the effect of single event effect becoming more significant.The device is more sensitive to radiation,and the probability of failure of devices in the radiation environment gradually increases.Therefore,the demand to study the single event effect of devices is increasing.In this thesis,a selective buried oxide(SELBOX)device,with process compatible with FDSOI and improved SHE,was investigated.The investigation is mainly composed of SHE,direct current performance and single event transient(SET)effect.The major contents in this thesis are as follows:Firstly,by the approach of Sentaurus TCAD,the self-heating effect performance of SELBOX and FDSOI MOSFETs were simulated,and the relevant results were obtained.The existence of BOX window can significantly reduce the SHE of SELBOX MOSFETs,and the closer the BOX window to the hotspots,the higher the heat dissipation efficiency is,the more significant improvement of SHE is.When the backplane doping is n-type,SELBOX device with BOX window close to the hotspots is equipped with saturation current of 5.91e-4 A and peak temperature of 317.82 K.The saturation current of SELBOX is five percent higher than FDSOI(5.64e-4 A)with back bias voltage of 0.9 V,and 21 percent higher than FDSOI(4.90e-4 A)with back bias voltage of 0 V.However,the peak temperature of SELBOX is 24.5 K lower than FDSOI(342.30 K)with back bias voltage of 0.9 V,and 20 K lower than FDSOI(337.47 K)with back bias voltage of 0 V.When the back-plane doping is p-type,SELBOX device with BOX window close to the hotspots is equipped with saturation current of 1.22e-4 A and peak temperature of 304.13 K.The saturation current of SELBOX is lower than FDSOI(4.18e-4 A)with back bias voltage of 0.9 V and FDSOI(3.39e-4 A)with back bias voltage of 0 V.The peak temperature of SELBOX is 28 K lower than FDSOI(331.93 K)with back bias voltage of 0.9 V,and 22 K lower than FDSOI(326.12 K)with back bias voltage of 0 V.Secondly,the direct current performance of SELBOX and FDSOI MOSFETs were further simulated and analyzed by the approach of Sentaurus TCAD.The results indicate that,the BP doping type and position of BOX window determine whether the voltage of BOX window can adjust the DC performance of SELBOX MOSFETs as the method of back bias voltage.The results of comparison between SELBOX and FDSOI indicate that,when the back-plane doping is n-type,the DC performance of SELBOX with BOX window located under source side is identical with FDSOI with back bias voltage of 0 V,and the DC performance of SELBOX with BOX window located under drain side is identical with FDSOI with back bias voltage of 0.9 V,the saturation current is 6.40e-4 A,25.5 percent higher than the saturation current of SELBOX with BOX window located under source side.However,when the back-plane doping is p-type,SELBOX with BOX window away from channel region has the same DC performance with FDSOI with back bias voltage of 0 V.Thirdly,the single event transient effect performance of SELBOX and FDSOI MOSFETs were simulated and further analyzed.The doping type of BP affects the peak value of drain current pulse and the collected charge of SELBOX MOSFETs,but the end point of incident heavy ion and the position of BOX window play a dominant role.When the BOX window is located under source side,the transient effect of SELBOX MOSFETs is identical to that of the FDSOI MOSFETs with back bias of 0 V regardless of the position of the end point of the heavy ion.But when the BOX window is located under drain side,the transient effect of SELBOX MOSFETs is nearly equivalent to that of the FDSOI MOSFETs with back bias of 0.9 V when the end point of heavy ion hasn't reached the substrate,while the transient effect of SELBOX MOSFETs is much worse when the end point of heavy ion has reached the substrate.When simulate the inverter in transient radiation environment,the influence induced by heavy ion radiation is the same when the pull down transistors are SELBOX and FDSOI,respectively.This result indicates that the SELBOX has excellent single event transient effect reinforcement as well.The work of this thesis involved deep nanometer technology VLSI core device,having important guiding significance on investigating the process,design and reliability.