Barium, strontium and bismuth contamination in CMOS processes

Contamination aspects of ferroelectric (SrBi2Ta2O9) and high dielectric constant (Ba,Sr)TiO3 materials in CMOS processes were investigated in this paper. TXRF, VPD-TXRF, and ToF-SIMS were used to study the desorption and diffusion properties of Sr, Bi, and Ba contamination on Si at 800 degreesC anneals. Sr and Ba dissolve in native or thermal oxide, and only very small quantities diffuse into silicon, whereas Bi - if annealed in N-2 - evaporates and its diffusion into silicon cannot be detected; in case of O-2 annealing, all Bi is incorporated in the thermal oxide grown. The diffusion constants for Ba and Sr in Si an in the order of 10(-16) cm(2)/s at 800 degreesC. Measurements of minority carrier recombination lifetime of contaminated n and p-type wafers showed no drastic decrease in lifetime for the three elements up to contamination levels of 10(14) at/cm(2). The leakage currents of diodes contaminated after device processing by Ba, Sr, and Bi up with concentrations between 10(12) and 10(14) at/cm(2) have nearly the same value as for non-contaminated diodes. This leads to the conclusion that Sr, Bi, and Ba do not present a drastic risk on minority carrier lifetime and diode leakage current in future Gbit-scale non-volatile Ferroelectric Random Access Memories (NVFeRAMs) or high dielectric constant Dynamic Random Access Memories (high k-DRAMs) generations.