High Rate Growth of SiO2 by Thermal ALD Using Tris(di-methylamino)silane and Ozone
Atomic layer deposition (ALD) of SiO2 has been explored using a wide variety of precursors ranging from halides to organometalic silanes and silanols. Yet few existing ALD processes for SiO2 are satisfactory. Tris(dimethylamino)silane (TDMAS) is a promising ALD precursor for SiO2, which was previously reported using hydrogen peroxide (H2O2) as the oxidant. However, it required temperatures greater than 450°C to remove Si-H surface species completely.
In this work, ozone (O3) as a strong oxidizer has been used for the thermal ALD deposition of SiO2 from tris(dimethylamino)silane in the temperature range of 80 to 350°C. The exposure (EXPO) mode characteristic of Cambridge NanoTech’s ALD systems has been applied to both TDMAS and O3 half cycles with significantly increased growth rate as compared to either non-exposure (continuous) or partial exposure mode. In contrast, fresh H2O2 resulted in very little growth under full exposure conditions between 250 and 350°C. Electrical properties of the SiO2 films have been characterized by a mercury probe. Dielectric constant and breakdown strength measurements at various stages after depositions revealed changing film properties over time that indicated possible existence of substantial amount of hydroxide, a common problem for CVD and ALD SiO2 films. Secondary ion mass spectrometry (SIMS) analysis confirmed the existence of 15 to 20 at% hydrogen in the films. Annealing of these films at 300°C or higher, especially in ammonia atmosphere, improved electrical properties dramatically.
Paper presented at ALD 2011.