Determination of trace metallic impurities on 200-mm silicon wafers by time-of-flight secondary-ion-mass spectroscopy

Abstract

Surface contamination on silicon wafers is an important issue in integrated circuit fabrication. The concentration of many surface metallic impurities is below the detection limit of total reflection x-ray fluorescence (TXRF). Vapor phase decomposition—atomic absorption spectroscopy (VPD-AAS) cannot reveal the lateral distribution of these impurities even though the detection limits can be as low as 107 atoms/cm2. The time-of-flight secondary-ion-mass spectroscopy (TOF-SIMS) technique can deliver sensitivity close to that by VPD-AAS for many metallic impurities. For example, the detection limits of Fe, Al, Na, and K are 6×108, 3×108, 7×107, and 3×107 atoms/cm2, respectively. In addition, this technique can disclose the lateral distribution of the impurities as well as information on organic contaminants. This article addresses some of the latest development of TOF-SIMS in the determination of surface impurities of 200-mm silicon wafers. When choosing conditions such that the analysis is integrated throughout the native oxide layer, good quantitative correlation with TXRF and VPD-AAS data can be achieved.