Nucleation and growth of tantalum nitride atomic layer deposition on Al2O3 using TBTDET and hydrogen radicals

Abstract

The nucleation and growth of tantalum nitride atomic layer deposition (ALD) was investigated on Al2O3 ALD surfaces on silicon substrates using tertbutylimino trisdiethylamino tantalum (TBTDET) and hydrogen radicals as the reactants. The hydrogen radicals were generated using a hot tungsten filament. Auger electron spectroscopy (AES) was utilized to monitor the atomic composition of the surface versus the TBTDET/hydrogen radical reaction cycles. These studies were conducted in a vacuum apparatus with a sample introduction port, two ALD reactors, and a connecting surface analysis chamber. Initial results with the silicon substrates at 250°C revealed tantalum nitride ALD growth and the oscillation of the N AES signal during the TBTDET/hydrogen radical reaction cycles. However, TBTDET pyrolysis was a problem on the BN heater. The TBTDET pyrolysis threshold of ∼250°C on the BN heater limited the maximum substrate temperature to 170°C. The AES results revealed that the composition of the tantalum nitride ALD films grown at 170°C was TaNx where x∼1. In addition, there were carbon and oxygen impurities in the TaNx film. Aluminum and tantalum AES signals were employed to determine the tantalum nitride ALD thickness on the underlying Al2O3 ALD surface during TBTDET/hydrogen radical reaction cycles at 170°C. The Cumpson method of using the ratio of the Al and Ta AES signals to determine the TaNx ALD film thickness avoided the problem of normalization between different AES spectra. The TaNx ALD nucleated readily on the Al2O3 ALD surface. The Al AES signal approached zero after 20 reaction cycles. The corresponding tantalum nitride film thickness was determined to be 11.6Å after 20 reaction cycles. The film thickness at 5, 10, 15, and 20 reaction cycles yielded an initial ALD growth rate of 0.5Å∕cycle. The ALD growth rate increased to 0.7Å∕cycle for >10 reaction cycles. The efficient initial nucleation and reasonable growth rates for tantalum nitride ALD are desirable for the formation of copper diffusion barriers on interconnection vias.