Atomic Layer Deposition of AlO[sub x] for Thin Film Head Gap Applications

A 150-200°C atomic layer deposition (ALD) process has been developed for advanced gap and tunnel junction applications for thin films heads. The primary advantage of the ALD process is the near 100% step coverage with properties that are uniform along the sidewall. This process provides smooth ( R a ≃ 2 Å ) , pure (impurities < 2 atom %), AlO x films with excellent breakdown strength (9-10 MV/cm). The process uses trimethylaluminum (TMA) as the aluminum source and water as the oxidant. The optimal precursor/oxidant delivery methods for high breakdown strengths were found to be vapor draw for the TMA and a bubbler for the water. For both reagents, a sweep gas is used to reduce the transit time to the wafer. The ALD AlO x films are continuous and exhibit excellent insulating characteristics even down to 5-10 Å making them a potential candidate for tunnel barriers for magnetic tunnel junctions. By plasma annealing the films in situ every 25-50 Å, the as-deposited tensile stress becomes slightly compressive and the breakdown field exceeds 10 MV/cm. ALD provides a relatively low deposition rate of 0.8 Å/cycle. A small chamber volume that allows the cycle time of 5 s is the key to meeting production throughput requirements of 4-6 w h − 1 for a 100 Å film.