Trace metal contamination quantification on Silicon wafers using ToF-SIMS: RSF determination from deposited droplet standards

ToF-SIMS is now widely used in the microelectronic industry for contamination monitoring of silicon wafers, particularly for metallic elements. However, the accuracy of the technique is still questioned considering the discrepancies, sometimes up to a factor of 10, observable in existing Relative Sensitivity Factors (RSF) databases. A new standard preparation method using intentionally contaminated dried droplets is studied here. It is applied for Na, Fe, Zn and Mo on native oxide silicon wafers. Large-area analysis (macroraster) is used to image the entire droplet residue of typically several mm in diameter overcoming heterogeneity or droplet movement difficulties. General agreement is obtained with existing data in the literature, however, with disparities still ranging around a factor of two are likely due to top surface ionization unsteadiness. Copyright (C) 2010 John Wiley & Sons, Ltd.