Aluminum oxide films were deposited on silicon substrates by plasmaenhanced chemical vapor deposition (PECVD) using trimethyl-aluminum (TMA), $N_2O$ and He gases. The etch characteristics of aluminum oxide film was studied to use the film as etch barrier material.
The film composition and bonding type of as-deposited films were analyzed using Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy(XPS). The aluminum oxide films were found to contain hydrogen and small amount of carbon.
The aluminum oxide films were etched in a DI water:48% HF solution (100:1. in volume percent), and wet etch rates ratio of aluminum oxide films by PECVD to thermal $SiO_2$ films were 125-375:1. On the other hand the aluminum oxide films were hardly etched in a $CF_4/O_2$ plasma, and dry etch rates ratio of aluminum oxide film to thermal $SiO_2$ films were 1:50-100. Also, the wet and dry etch rates of the aluminum oxide films increased as the deposition temperature lowered or $N_2O$/TMA ratio increased.
Finally, these films were used as etch mask material on thermal $SiO_2$ film in a lift-off mask scheme and their performance was evaluated. The aluminum oxide films by PECVD provided a high selectivity with $SiO_2$ and given a highly anisotropic etch in $SiO_2$.
From the above results, it is believed that the aluminum oxide film by PECVD using TMA source is very promising for the further use in VLSI and microelectronics as a etch barrier mask material.
