Physical models for predicting plasma nitrided Si-O-N gate dielectric properties from physical metrology

Using simple physical models, specific relationships between parameters measured by X-ray photoelectron spectroscopy (XPS) and those measured on MOS transistors are described for silicon oxynitride gate dielectrics prepared by plasma nitridation. Correlations are established between the equivalent oxide thickness (EOT) and gate leakage current and the nitrogen anneal dose and physical thickness as measured by XPS. These correlations, from devices in the 10 to 13 /spl Aring/ EOT range, allow accurate estimates of electrical thickness and leakage without device fabrication, enabling both development and process monitoring for sub-130-nm node gate dielectrics.

I. Introduction

Silicon oxynitride with a few atomic percent nitrogen is currently used for gate dielectrics in state-of-the-art CMOS. Extending oxynitrides to future logic generations requires meeting the International Technology Roadmap for Semiconductors (ITRS) specifications for and gate leakage [1], and plasma nitridation of gate oxides is being actively pursued [2]– [4]. Typically, short-loop capacitor or transistor lots are used to screen gate dielectric processes. Production and measurement of these lots may take weeks, hindering rapid process evaluation. Earlier work by Kapila et al. used Fig. 1. (a) nMOS gate leakage current density plotted against and (b)XPS measured thickness plotted against XPS measured total nitrogen dose for the same for plasma-nitrided oxynitride gate dielectrics. was determined by capacitance-voltage measurements on devices of appropriately small length to avoid parasitic effects [6]– [8]. Total measurement uncertainty in MOS capacitance measurements at results in uncertainty in . Gate leakage current was measured at constant gate drive with ; the uncertainty in leakage current is not greater than 1% of the measured current in the range shown here. XPS measurements were made using a measurement and analysis technique previously discussed [9], resulting and measurements with repeatability better than 2 and 3%, respectively. Circles indicate data used in the analysis as discussed in the text; triangles indicate data from a recent experiment and are not used in calculating fit parameters. time-of-flight secondary ion (ToF-SIMS) nitrogen profiles to predict of plasma-nitrided oxides in a thicker range, but did not address gate tunneling current [5] which is now a limiting factor in CMOS technology [1]. In this letter, we propose simple physical models for estimating both and gate leakage from X-ray photoelectron spectroscopy (XPS) measurements of the nitrogen concentration and physical thickness. The models are successfully applied to data from plasma-nitrided oxides with between 10 and 13 .