THERMAL-STABILITY AND INTERFACE BOWING OF SUBMICRON TISI2/POLYCRYSTALLINE SILICON

The electrical integrity of submicron TiSi2/polycrystalline silicon (poly-Si) lines is investigated when they are subjected to furnace heat treatments at elevated temperatures. The poly-Si basis layer remained undoped or was implanted with boron or arsenic. The TiSi2 layer was formed via a solid-solid reaction between titanium and silicon in a rapid thermal processing system. The linewidth modules, used for electrical characterization, consisted of a Van der Pauw structure together with six bridge resistors. The nominal width of the resistors varied from 0.5-mu-m to 1.0-mu-m. The sheet resistance of large areas was not affected by heat treatments up to 900-degrees-C for 30 min. The narrowest lines were, however, found to disintegrate after annealing at 850-degrees-C. The effect was most pronounced on wafers silicided at a lower temperature. Doped polycrystalline silicide (polycide) structures exhibited an improved thermal stability compared with undoped structures. Cross-sectional scanning and transmission electron microscopy of narrow polycide lines revealed the TiSi2-poly-Si interface to be bowed. The bowing, which was most pronounced on the smallest lines, was also observed on monocrystalline silicon lines, which were included in the experiment. A model is proposed which assumes that the interface bowing is caused by a mechanical pinning of the TiSi2-poly-Si interface by the side-wall spacers. The model was verified by selecting a thinner silicide or reducing the height of the spacers, since both methods suppressed the tendency for bowing.