Low-Temperature Atomic Layer Deposition of Tungsten using Tungsten Hexafluoride and Highly-diluted Silane in Argon

Inherent chemical hazards in atomic layer deposition (ALD) processes can be mitigated significantly by careful selection of precursor materials. This work describes the effect of silane (SiH4) exposure on tungsten ALD growth when the silane is heavily diluted (2 at.-%) in argon. A wide ALD temperature window from 200 to approximate to 300 degrees C is identified, exhibiting a growth rate of between 5 and 6 angstrom per ALD cycle using SiH4 and tungsten hexafluoride (WF6) exposures of approximate to 6x105 and approximate to 5x105 Langmuirs (L), respectively. For deposition at lower temperature (150 degrees C), growth rates of approximate to 4.5 angstrom per cycle are obtained using a silane exposure of 30s per cycle, where the partial pressure of silane at the inlet is controlled at 40 mTorr (corresponding to 1.2x106 L of silane). Compositional analysis by secondary ion mass spectroscopy (SIMS) and Auger electron spectroscopy (AES) show less than approximate to 5 at.-% Si in the W films, with the smallest Si content in films deposited at 300 degrees C. We also describe effects of hot-wall reactor preconditioning on film growth. We conclude that the dilute silane co-reactant offers an alternative to the common disilane, borosilane, or undiluted silane precursors, allowing well-controlled W deposition at 150 degrees C.