Vapor phase treatment-total reflection X-ray fluorescence for trace elemental analysis of silicon wafer surface

Vapor phase treatment (VPT) was under investigation by the International Organization for Standardization/Technical Committee 201/Working Group 2 (ISO/TC201/WG2) to improve the detection limit of total reflection X-ray fluorescence spectroscopy (TXRF) for trace metal analysis of silicon wafers. Round robin test results have confirmed that TXRF intensity increased by VPT for intentional contamination with 5 × 109 and 5 × 1010 atoms/cm2 Fe and Ni. The magnification of intensity enhancement varied greatly (1.2-4.7 in VPT factor) among the participating laboratories, though reproducible results could be obtained for average of mapping measurement. SEM observation results showed that various features, sizes, and surface densities of particles formed on the wafer after VPT. The particle morphology seems to have some impact on the VPT efficiency. High resolution SEM observation revealed that a certain number of dots with SiO2, silicate and/or carbon gathered to form a particle and heavy metals, Ni and Fe in this study were segregated on it. The amount and shape of the residue should be important to control VPT factor.