PITA Fiscal Year 2008 Projects - Product and Process Design and Optimization

Atomistic Characterization and Modeling of Deep Sub-Micron Gate Oxide Breakdown

Principal Investigators: Alan McGaughey, Robert Davis

An integrated modeling/experimental program will be initiated to elucidate the mechanisms of dielectric breakdown in the field effect transistors (FETs) used by Novocell Semiconductor Inc. to produce non-volatile computer memory (NVM). When Novocell recently moved their technology to smaller dimensions, they found that the circuit models that could predict the breakdown of amorphous silica (a-SiO2) layers at larger dimensions were no longer suitable. Novocell needs new models that capture the physics of the breakdown event at these small scales.

Using experimental characterization of FET samples provided by Novocell and atomistic simulation, we will determine: (i) How the microstructure of the a-SiO2 region affects where, when, and how dielectric breakdown occurs, and (ii) How much energy and time are required to reach the complete breakdown condition. The results will be used to develop a model that Novocell can apply to their current NVM technology and extend to future decreases in feature size.

The experimental work will be performed using atomic resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and secondary ion mass spectrometry (SIMS) at Carnegie Mellon University and at Lehigh University. We will determine the microstructure and roughness of the poly-Si/a-SiO2/Si layered structure in the FETs and the arrangement of atoms in and near the oxide layer. We will then correlate these results with the position of the onset of dielectric breakdown. The results will also be used to build realistic atomistic models of the oxide layer and surrounding regions for use in molecular dynamics simulations and lattice dynamics calculations. These atomic-level analysis tools will allow us to quantify the energetics associated with the breakdown event.