Measuring CET of High-k Dielectrics with Novel Kinetic Approach Using Micro-Site Corona – Kelvin Method

Abstract

Freshly deposited surfaces of high-k dielectrics revealed a new set of challenges for monitoring capacitance equivalent thickness, CET, using micro-site corona – Kelvin metrology. Specifically, ions deposited by corona discharge may have a queue-time dependent high surface diffusivity, which causes charge spreading away from charging spot under the Kelvin voltage probe. This could result in underestimation of dielectric thickness and unrepeatable results. To overcome this problem, we have developed a kinetic approach based on the analysis of the surface voltage transient after point source corona charging. The mathematical solution of the two-dimensional diffusion equation enables fitting of the voltage transient and reliable determination of two parameters: the surface diffusion coefficient and the dielectric capacitance. The latter one gives CET. The kinetic approach was applied to HfO2 layers deposited by atomic layer deposition. Repeatable CET measurements for a range of high-k surface conditions and thicknesses are presented. Elimination of queue-time dependence achieved with the novel kinetic approach is a significant advantage for fab-line monitoring.