Characterization and modeling of the charge distribution in silicon/silicon-germanium/silicon P-channel MOSFETS.

摘要

Silicon-based semiconductor devices have dominated the field of microelectronics for the last thirty years. Metal-oxide semiconductor field effect transistors (MOSFETs) are the predominant silicon-based device structure that comprise the majority of today's logic and memory chips. Silicon-based heterojunction devices have only recently been made possible with the introduction of silicon-germanium (SiGe) films grown on silicon substrates. With the advent of advanced processes such as molecular beam epitaxy (MBE), Si-based Si1-x Gex heterostructures are a reality. These Si-based heterostructures offer both increased performance and a greatly enhanced range of possible device configurations, coupled with the maturity of silicon processing.; One of the most interesting applications of SiGe heterostructures is incorporating a Si1-x Gex layer in the channel of a p-channel MOSFET. In order to fully optimize such a structure, the charge distribution in the Si1-x Gex channel, as well as the Si-surface channel, must be well characterized. To achieve this level of understanding, a fully self-consistent coupled solution of the Schrodinger and Poisson equations applied to the Si/ Si1-x Gex/Si p-channel MOSFET was written and validated. This quantum mechanically-based level of understanding is required due to the quantum nature of the Si/ Si1-x Gex/Si system. This work demonstrates the quantum nature of such a structure and reveals the limitation of the Poisson-only classical solution.; The main focus of this work is the simulation of the Si/ Si1-x Gex/Si p-channel MOSFET as a function of Ge mole fraction (x) as well as the critical physical parameters such as the Si1-x Gex channel thickness, Si-surface channel thickness and gate bias. Through extensive simulation, the optimal physical design features of such a device are arrived at. Two-dimensional simulation results demonstrate the performance advantage of such device structures compared to Si-only MOSFETs. In order to validate the simulations, Si/ Si1-x Gex/Si MOS capacitor structures are fabricated via MBE and characterized by means of capacitance-voltage (C-V) measurements and Fourier Transform Infrared (FTIR) spectroscopy measurements. The C-V measurements are made at room temperature and reveal the distribution of charge in both the Si1-x Gex well and the Si-surface well as a function of gate bias and Ge mole fraction (x). The FTIR spectra reveal the transition energies of carriers in the Si1-x Gex quantum well and are also calibrated to lineshape calculations that describe the transition peaks resulting from the wave function solutions of the Schrodinger and Poisson equations.