Back side SIMS analysis of hafnium silicate

High-k dielectrics are under study as part of the effort to continually reduce semiconductor device dimensions and hafnium silicate (HfSixOy) is one of the most promising high-k materials. A requirement of the dielectric is that the constituent elements cannot diffuse into adjacent device regions during thermal processing. Analysis for inter-diffusion using front side SIMS of high-k dielectrics has been complicated by matrix and sputtering effects. Use of a back side analysis sample preparation procedure that was successful for copper diffusion and site specific studies produced a HfSiO specimen that has less than 250 nm silicon remaining and minimal slope over the analysis region. Magnetic Sector (CAMECA IMS-6F) SIMS analysis of this specimen with low energy O2 + bombardment does not show the matrix and sputtering effects noted in the front side data. Sufficient depth resolution was obtained to define the interface between the silicon substrate and the HfSiO layer and indicate what appears to be an interfacial layer. There is no indication of hafnium diffusion into the silicon substrate.