Comprehensive Study of the Chemical, Physical, and Structural Evolution of Molecular Layer Deposited Alucone Films during Thermal Processing

Thermal processing of molecular layer deposited (MLD) hybrid inorganic–organic alucone thin films produced porous and low-k materials. Alucone films were deposited by MLD using trimethyl aluminum and ethylene glycol at 120 °C. Changes in the film density and thickness during annealing were monitored using in-situ X-ray reflectivity and were compared to atomic layer deposited (ALD) alumina films. The chemical evolution of the as-deposited and annealed alucone films during post-deposition heating with and without UV was probed using infrared spectroscopy, Rutherford backscattering, nuclear reaction analysis, and 15N spectroscopy, providing a detailed understanding of the induced changes. The concentration of OH groups decreased after depositing 1 nm of alumina capping layer as a barrier to moisture uptake, which also decreased the etch rate in CF4/O2 plasma. The lowest dielectric constant of the processed alucone films (k min = 4.75) was 25% lower than the lowest values measured in ALD alumina counterparts (k min = 6.7). Large thickness decreases for alucone films were observed at ∼200 °C of anneal temperatures. Removal of retained organic components by thermal processing of MLD films is demonstrated to be a promising and versatile route to porous thin films for a wide range of applications including low dielectric constant materials.