Ultra-thin Film Metrology Technique: Grazing Incident X-Ray Fluorescence

Thickness measurements for a couple of atomic layer ultra-thin nitride and high-K dielectric materials (TaN, TiN, HfOx) were performed using our self-developed instrument, the ÅX- T100,via grazing incident x-ray fluorescence (GIXRF). Single-site repeatability results demonstrate that our instrument exhibits excellent precision with CV%=0.09%. An analysis of the wafer mapping results including 49 data points indicates a wafer thickness uniformity (uniformity %) of less than 3%. Considering the features of the x-ray fluorescence technique, which include non-invasiveness, immunity to surface oxidation, applicability to both metals and dielectrics, and suitability for transparent and opaque materials, GIXRF stands out as a perfect non-invasive metrology tool for measuring ultra-thin film thickness and composition at the angstrom level.

I. Introduction

For decades, semiconductor processing technology and device integration have relied on SiO₂ as the gate dielectric and doped polysilicon as the gate electrode. Scaling down the device gate length enables the fabrication of more devices per wafer, thereby increasing device density and reducing the cost per chip. However, as the gate dielectric becomes thinner in pursuit of higher device density, gate leakage current due to tunneling effects increases, and the power required to operate transistors rises. Since tunneling current density follows an exponential decay behavior in relation to the dielectric constant , increasing the dielectric constant has become the dominant approach to reduce leakage current. Consequently, there is an urgent need for new high-K dielectric materials, such as certain metal oxides. For instance, the dielectric constants for , and , are 3.9, 7.8, and 25, respectively [1].