At-line X-ray fluorescence metrology of metals and ultra-thin barrier layers for ULSI applications

X-ray based metrology and inspection can be used for various applications: composition analysis, thin-film thickness measurement, and the determination of crystallographic structure and surface roughness. High resolution imaging is also theoretically possible for defects detection and analysis. In this work we focus on X-ray Fluorescence (XRF). We discuss its principles, the system requirements, and its applications for X-ray metrology. Such systems can be installed in an in-line or at-line configuration for the monitoring of interconnects systems, both aluminum and copper based. The measurement can be done over special test sites on the chip itself or on the scribe-lanes. Measurement over active devices is also possible but electron-hole creation in the gate and field oxide limits the maximum allowed irradiation per unit area. In this work we discuss the guidelines for critical dose and minimum measured area that allow proper and fast metrology. It is concluded that both high-speed and damage free XRF metrology is possible.