Effect of sputtered TiW deposition conditions on barrier properties for submicron metallization

Reports the results of an orthogonal array study of the step coverage of magnetron sputtered TiW. The authors concentrate on the effect of target power (1-2.5 kW), Ar pressure (4-21 mT), and substrate temperature (100-450°C) on coverage into near vertical wall windows (85° wall angle) with aspect ratio ~1.5 (h/w=1.3/0.85) reactive ion etched in a deposited oxide. Scanning electron microscopy (SEM) indicates that coverage defined as the ratio of TiW~1000 Å thick on top of oxide to that in the bottom of the windows, varies between ~25-35%. Coverage improves with moderate power ~2 kW and temperature ~300°C. Ar pressure has a somewhat smaller effect on coverage than either power or temperature. TiW resistivity and stress magnitude also decrease to 0.65-0.7 μΩ-cm and low 10⁹ dynes/cm² respectively, for the sputtering conditions used to maximize step coverage. Reverse bias diode leakage (~3000 Å deep n ⁺/p with ~1000 Å TiSi₂ and window contacts) does not degrade for Al/TiW or Al/CVD W/TiW metallization of the window contacts are annealed at 450°C, 30 min., the highest anneal cycle used in this study. Low leakage was measured for a nominal 1000 Å thick TiW deposited with the conditions giving the best and worst window coverage, indicating that ~300 Å is an acceptable barrier at ⩽450°C