Growth of aluminum oxide thin films with enhanced film density by the integration of in situ flash annealing into low-temperature atomic layer deposition

Abstract

Aluminum oxide (Al2O3) thin films grown by atomic layer deposition (ALD) at low temperatures exhibit low film densities, and therefore, may not meet the requirements for demanding barrier applications. In this work, a novel approach is presented to obtain improved film densities by short-term thermal treatments while keeping the overall low thermal budget of the deposition process. For that purpose, millisecond flash lamp annealing (FLA) was directly integrated into the ALD process, enabling the thermal treatment of the growing films not only subsequent to the deposition process but already right during the stage of film growth. By applying this in situ FLA after every single ALD cycle, the density of Al2O3 films grown at a substrate temperature of 75°C could be increased from 2.8g/cm3 up to 3.1g/cm3. However, this 10% increase in film density was not related to an ordinary film densification. Instead, the studies reveal that in situ FLA promoted an enhanced and denser film growth, most probably by directly affecting the surface chemistry of the ALD process. The enhanced film growth was observed in terms of a 25% increase in the mass gain per cycle, reaching a level comparable to pure ALD at a deposition temperature of 250°C. Furthermore, the application of in situ FLA also resulted in an improved film composition, increased refractive indices, higher dielectric constants and reduced leakage currents. The presence of molecular hydrogen during the FLA treatments led to an even further improved mass gain per cycle, film composition and dielectric constant. Despite the FLA treatments the films remained amorphous. In addition, the film densities obtained by the application of in situ FLA were not achieved by conventional post deposition annealing with temperatures up to 600°C.