The microstructure and metal-silicon work function was evaluated for polycrystalline Si (poly-Si) films (∼3500 Å) implanted with BF 2, with and without a CoSi2 superlayer. The poly-Si implant doses were 2, 4, and 6×1015 cm-2, activated at 800-950°C, for various times. The work function is observed to be dependent upon the BF2 dose, the anneal time, the anneal temperature, and independent of the presence of a thin CoSi2 superlayer subsequently sintered on the poly-Si. The work function is not affected by additional implants into a CoSi2 superlayer. The measured work function for this material is shifted to more positive values by penetration of boron from the gate, into the oxide and possibly into the substrate during a ≳900°C activation cycle. The major correlation of CoSi2/poly-Si interface roughness is with poly-Si grain size. The interface becomes smoother as the poly-Si grain size becomes smaller. Similarly, the maximum extent of CoSi2 asperities is less for Co sintered on BF2 implanted poly-Si when the poly-Si is activated at 900°C (smaller grain size) rather than at 950°C. Within statistical limitations of cross-section transmission electron microscopy and sensitivity limitations of Rutherford backscatterings, CoSi2 asperities do not extend close enough to the (4000-Å-thick) poly-Si/SiO2 interface to affect complimentary metal-oxide-semiconductor device characteristics.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)