Recent advances in XPS characterization of ultra-thin oxides

As ion energies have steadily decreased over the past several years, an ever increasing fraction of the implanted species lies in the outer 10 nm of the sample. Consequently, there is an increased need for characterization tools capable of providing chemical information in this depth range. The unique ability of X-ray photoelectron spectroscopy (XPS, also known as ESCA) to determine quantitatively the local bonding (i.e., oxidation state) in the outer 10 nm of materials makes it a valuable tool for characterizing low energy ion implanted wafers. It has long been known that by measuring the relative amounts of Si° and SiO₂, the oxide thickness can be measured on films up to 10 nm thick. Examples will be presented showing oxide thickness measurements precise to ±0.1 nm for ultra-thin (<2 nm) oxides. A similar approach can be used to estimate the concentration of implanted species that are present in the SiO₂. Examples will also be given demonstrating the use of XPS in identifying and quantifying organic and inorganic surface carbon species on implanted wafers.