Local structure analyses of contamination metals on the silicon wafer after LSI processes using XAFS technique

It is well known that metallic contamination on the silicon wafer, suffered during VLSI fabrication processes such as thin film depositions and etching, brings about lowering device performance. Determination of the chemical or structural properties of contamination metals is necessary in order to specify and remove the cause of contamination. However, the measurements are extremely difficult, because the contamination metals have very low concentrations. Grazing incidence XAFS by the x-ray fluorescence yield method is useful for the purpose. We applied the technique for the investigation of iron and copper contaminations on silicon wafers after fabrication processes.

The silicon wafers contaminated intentionally in the process chamber were used as samples. The contamination level of iron and copper was of the order of 10¹¹–10¹³ atoms/cm². The measurements were performed at the beamline 12C of the Photon Factory in KEK. The incident angles from the silicon surfaces were about 1 degree. A Lytle type ionization chamber was used in order to detect x-ray fluorescence photons in large solid angles. Good quality spectra were obtained. It was found from the analysis of the spectra that iron is mainly binding to fluorine and copper is binding to chlorine. The results were very useful for process improvements.