Limitations of LET in Predicting the Radiation Response of Advanced Devices

The impact of high-Z metals on energy deposition in thin volumes due to direct ionization by ions in space environments is examined. The importance of energy loss straggling in small volumes typical of those found in advanced devices is also evaluated. It is found that direct ionization by protons over a large energy range may contribute significantly to error rates in advanced silicon on insulator devices due to energy loss straggling. This improves on conventional event rate analysis based on linear energy transfer, which does not describe the contributions of direct ionization by protons to the error rate.

I. Introduction

In Order to continue scaling integrated circuits to deep sub-micrometer dimensions, device manufacturers have replaced polysilicon gates with metal gate stacks and typically use metal clad or metal silicide source/drain regions. The metals used in modern processes tend to be considerably heavier than silicon, leading to a high-Z/low-Z interface in many modern devices. The secondary electron environment near a high-Z/low-Z interface has been shown to be significantly perturbed from equilibrium under x-ray and gamma-ray irradiation [1], [2]. However, the secondary electron environment at a high-Z/low-Z interface under ion irradiation has not previously been reported.