Threshold Voltage Modeling of Recessed Source/Drain Soi Mosfet with Vertical Gaussian Doping Profile

Abstract

Recessed-source/drain silicon-on-insulator (Re-S/D SOI) MOSFETs are being researched in both academia and industry because of its high drain current drive capability. In a Re-S/D SOI MOSFET, source and drain regions are stretched into the buried oxide (BOX) in order to reduce the series resistance. The electrical parameters are most important parts in defining the functionality of the device. First objective of the project work is to meet the electrical parameter specifications like threshold voltage, subthreshold swing, ON current and leakage current specified in ITRS 2011 and some other technical literature by adjusting of physical parameters like, silicon channel thickness, channel length and gate oxide thickness, that means it has to find out the physical parameters of the device for the standard values of electrical parameters. So, it has to maintain these device parameters for given specified values, the channel thickness, oxide thickness and gate length are adjusted accordingly. Fully depleted Re-S/D SOI MOSFETs possess good short channel immunity and close to ideal subthreshold characteristics. A number of attempts have been done to model the subthreshold characteristics of Re-S/D SOI MOSFETs with undoped or uniformly doped channel for getting more physical insight. However, the actual doping profile after the ion implantation step differs from uniform profile and resembles much with the Gaussian profile. In addition, the Gaussian profile in turn gives two more parameters, projected range (RP) and straggle (σp), which can control the device characteristics. In this project work, an effort has been done to develop a novel model for the threshold voltage of Re-S/D SOI MOSFETs with vertical Gaussian doping profile in the channel. The twodimensional Poisson’s and Maxwell equation has been solved in the channel region of the iii device considering the proper boundary conditions. The developed analytical model predicts the threshold voltage of the device for wide variations in the device parameters. MATLAB has been used for calculation of the analytical model results with variations in the device parameters. The model results are compared by the result obtained with ATLASTM device simulator to verify the accuracy of the model.