A comparative analysis of different measurement techniques to monitor metal and organic contamination in silicon device processing

Abstract

A few key techniques for the analysis of contamination in silicon are compared for their ability to detect different impurities. Both metal and organic contamination is included in this study. In addition, common contaminants and elements recently introduced in the fabrication process are considered. For what concerns metal contamination, it is shown that different approaches are required depending on the in-depth distribution of the contaminant and hence on its diffusivity. Copper, iron, molybdenum, and tellurium are chosen as examples of contaminants with different diffusivity and solubility properties. Total reflection X-ray fluorescence (TXRF), recombination and generation lifetime measurement techniques, deep level transient spectroscopy (DLTS) and capacitance versus voltage measurements are compared. The detection of slow diffusers is found to be very critical, because a very low dose may result in a non-negligible concentration in the device region. As a consequence, the sensitivity per unit area required for these elements is difficult to reach with surface techniques such as TXRF. On the other hand, very fast diffusers such as copper can hardly be revealed in the solid solution in silicon. Copper in silicon can be revealed at the oxide–silicon interface by TOF-SIMS measurements, or by surface generation velocity measurements with the Zerbst method. For what concerns organic contamination, surface recombination velocity and gate oxide integrity tests were compared. The most relevant effects of organic contamination were observed by electrical stress of the oxide. Indeed, the fraction of capacitors with degraded breakdown voltage increased dramatically in wafers with intentional organic contamination.