Approaching the limit for quantitative SIMS measurement of ultra-thin nitrided SiO2 films

As the demands of device performance force gate oxide thicknesses to 2 nm a nd less, more and more pressure is placed on conventional characterization techniques to measure such thin films. Although SIMS has been utilized to a ccurately measure ultra-thin nitrided oxide layers for years, we are approa ching the limit at which quantitative measurements can be made, simply beca use SIMS is a sputtering process. Measurements at a very low beam energies (300-1000 eV) and incidence angles (60-80 degrees) indicate ion mixing dept hs significantly less than 1 nm can be achieved. with the angle of incidenc e being more important than the beam energy in improving depth resolution. Despite these limitations, we have achieved excellent agreement between SIM S and XPS for measurements of N areal density in 1.7-2.4 nm thick films. Be cause the ion mixing depth is significantly less than the film thickness, S IMS can give both the distribution and amount of N within these thin layers . (C) 2001 Elsevier Science B.V. All rights reserved.