Nitrogen analysis in high- k stack layers: a challenge

Abstract

In order to increase performance in advanced MOS devices, alternative gate insulators with high electrical permittivity are investigated to replace SiO 2. Recent developments include the presence of nitrogen in or around the HfO 2 stack. It is thus important to be able to acquire knowledge of the depth distribution of the nitrogen in the layers with enough accuracy. This remains a real challenge for SIMS due to varying matrices in which the nitrogen is distributed. We first present results obtained with Xe and Cs profiling. We determined the “best to use” clusters in order to retrieve the maximum information of the data. In the second part, we investigate some less standard operational mode of SIMS profiling. For instance, it has also long been considered that the detection of MCs + clusters suffers from less matrix effect and could thus be advantageous for this kind of analysis, where the Cs surface concentration is reduced by the use of Xe–Cs co-sputtering. We also introduce a new method in order to increase the sensitivity to nitrogen by using a “carbon-based” flooding and using the CN − cluster detection.