Thermal Stability Limits of Thin TiSi2: Effect on Submicron Line Resistance and Shallow Junction Leakage

Abstract

, the silicide most commonly used for a low resistivity self‐aligned salicide process, must become thinner as the junction depth and poly‐Si gate height decrease so as not to affect junction leakage and gate work function. The thermal stability of the thinner during the back‐end thermal process cycles, is an important concern. We report on the thermal stability of 300 to 700 Å thin on As, P, or doped poly‐Si to annealing at 750 to 850°C for 10 to 30 min determined by the increase in the resistance of long 0.3 to 1.5 μm wide poly‐Si meander lines. The increase in line resistance is correlated with changes in the microstructure. Poly‐Si lines ≤0.5 μm wide with ≤500 Å increase their resistance after annealing at 750°C, 30 min. 500 Å is stable on >0.5 μm wide poly‐Si lines after annealing at ≥800°C, 15 min. Silicide instability increases the reverse bias diode leakage measured for ∼1500 Å shallow n+ junctions whereas it does not increase diode leakage for ∼2000 Å shallow p+ junctions. Increasing thickness improves thermal stability. Dopant type and concentration affect the thermal stability through their effect on the thickness (thinner on As doped Si) sintered with a particular Ti sintering process. We use Rutherford backscattering spectroscopy, transmission electron microscopy, and scanning electron microscopy to correlate the increase in effective sheet resistance of submicron wide poly‐Si lines and the increase in ultra shallow junction leakage with an increase in roughness for 700 Å thick and agglomeration for ≤500 Å thin .