Sims studies of Sr, Bi, and Ta diffusion from SBT in SiO_2

摘要

The diffusion behavior of strontium bismuth tantalate (SBT) in silicon dioxide was investigated in order to assess the contamination risk due to these unusual elements. 90 nm thick SBT layers were deposited by a spin-on technique onto oxidized silicon wafers. Some samples underwent a ferro-anneal to crystallize the SBT in the ferroelectric perovskite phase. After chemical vapor deposition of 500 nm silicon dioxide all samples were annealed for 15 min at temperatures ranging form 650 to 1000 °C. Secondary ion mass spectroscopy (SIMS) was performed to obtain concentration profiles of Sr, Bi, and Ta in the topmost SiO_2 layer. A considerable diffusion effect is observed for Sr even at low temperatures, Bi and Ta behavior depends on whether they underwent a ferro-anneal. To explain the concentration profiles, different diffusion mechanisms in the amorphous SiO_2 have to be taken into account as well as interactions of the diffusants with each other. The SBT crystal structure has been determined by x-ray diffraction to explain the effects of the ferro-anneal.