Accuracy and repeatability of X-ray metrology

All metrology tools must make a trade-off between data quality and wafer throughput. Moreover, most X-ray metrology may be performed on regions inside the scribe lines. This paper discusses the appropriate choices of trade-offs for throughput, repeatability and spot size, choosing examples from silicon-germanium composition and thickness metrology. The repeatability varies from 0.7% to 0.1% la with data collection cycles between 20 s and 1000 s. We show that for most of the parameters deten-nined by X-rays the metrology is absolute, and that both accuracy and tool matching is achieved by traceable calibration of the X-ray wavelength and the angle encoders on the tools. Tool matching achieved by this absolute approach to metrology is typically 0.2% in thickness and 0.05% in composition for Si-20%Ge layers similar to 50 nm thick. For 30 nm metal or dielectric layers measured within a 100 mm scribe line, 0.65% 1 sigma repeatability is achieved at 150 measurement points/hr and 0.33% at 75 sites/hr.