Breakdown Voltage Model And New Structures Of The Lateral High Voltage Devices With Thin Drift Region

As a key device in high voltage integrated circuit,lateral high-voltage device has been deeply investigated by many scholars.With the quick development of semiconductor technology,the power devices and conventional low-voltage devices are scaled down.Because of the 2-D nature of electrical field in the drift region the 1-D model could not explain deeply the physical mechanism of the device.Owing the complexity of the boundary conditions,the 2-D model of the high-voltage device with some terminal technology is difficult to be solved. The model of the electrical field and breakdown voltage that can describe the interaction between the lateral and vertical electrical fields must be developed.It is a hotspot for many device designers to improve the trade-off between the breakdown voltage and the specific on-resistance of the high-voltage device.Novel thin drift region high-voltage device compatible with CWOS technology is an important developing trend of power semiconductor technology.In this dissertation,the 2-D breakdown voltage models and the new structures to improve the trade-off between the breakdown voltage and the on-resistance of the thin drift region high-voltage device are investigated.A 2-D surface electrical field model of the thin drift region D-RESURF device and a breakdown voltage model of the thin drift region device with step doping profile are firstly proposed.Three new structure of high-voltage devices are developed, i.e.the thin double drift region high voltage device,the low doped drain SOI high voltage device with P buffed layer and the PSOI high voltage device with double-faced step buffed oxide layer,and the partial experiments are carried out.The 2-D model for the surface electrical field of the D-RESURF device with sturface implanted P_b region is developed based on Poisson equation.The vertical electrical field influences strongly the surface electrical field when the drift region is thin.Besed on the model, the influence of the structure parameters on the coupling effect between the vertical electrical field and the surface electrical field has been examined.The optimal criterion for the maximum breakdown voltage and the minimum on-resistance has also been obtained.The dependence of the breakdown voltage on drift region length and thickness is calculated.The 900V D-RESURF devices have been fabricated with the guide of the analytical model.The 2-D breakdown voltage model of the S-RESURF device for the incompletely depleted drift region is given.The characteristic of the S-RESURF device is investigated when breakdown occurs at the P_bodyN_e junction,N⁺N_e junction and vertical PN junction.A 2-D RESURF criterion including the charge sharing effect is derived when optimum surface dectrical field is realized.A 2-D breakdown voltage model of the thin drift region device with step doping profile is demonstrated.A new electrical field peak appears between two regions with different doping concentration by the interaction of the lateral electrical field.The surface electrical field peaks are reduced by the coupling of the vertical electrical field,which leads to more or less uniform field profile in drift region.Based on the model,the influence of the structure parameters on the charge sharing is investigated;the optimum relationship among the structure parameters of the high-voltage device is obtained.The current of the thin drift region device with surface step doping profile flows mostly on the surface of the drift region which reduces the on-resistance of the device.The thin dirft region device with step doping profile enhances the trade-off between the breakdown voltage and the on-resistance and has a better technology tolerance.A structure of the thin double drift region is proposed.The current can flow mostly along the surface of the drift region because the doping concentration of the surface implanted N^- layer is very high and the on-resistance of the high-voltage device is declined.P buried layer is implanted under the channel region which improves the drift region electrical field distribution. The electrical field modulation of the P buried layer inducts a new electrical field peak in the surface electrical field which leads to more or less uniform field profile.For the same drift region doping dose,with the increase of the surface N^- layer's doping concentration and the decrease of the thickness,the drain current is enhanced greatly.The results show that the breakdown voltage of the thin double drift region device is increased by 16%and the on-resistance is decreased by 24%compared to the conventional device.P buried layer is incorporated inside the N drift region of the SOI device with low doped drain,which is called BLD SOI device.By the influences of the buffed layer's additional electrical field and the buried oxide layer's vertical electrical field,the surface electrical field near the channel is reduced and the optimal drift region doping concentration is increased,so the on-resistance is decreased significantly.A low doped drain region is introduced near the drain which can reduce the drain curvature and enhance the breakdown voltage.The results show that compared to the conventional SOI device the breakdown voltage of the BLD SOI device is increased by 29%and the on-resistance is decreased by 22%.Over 700V SOI high voltage device is manufactured successfully with the guide of the model.A novel structure of PSOI high voltage device with double-faced step buried oxide layer is proposed,which is called DSB PSOI.The surface electric field reaches nearly ideal uniform distribution due to the additive electric field modulation by double step buried oxide layer.A silicon window underneath the source helps to reduce self-heating. Depletion region spreads into the substrate and the vertical electric field in the buried layer is enhanced,which results in a higher breakdown voltage.A 2-D optimal relation between the structure parameters is also obtained.The results indicate that the breakdown voltage of DSB PSOI device is increased by 58%and temperature is declined by 10-30K in comparison to conventional SOI device,maintaining the low on-resistance.