Atomic Layer Deposition of Aluminum Phosphate Using AlMe₃, PO(OMe)₃, and O₂ Plasma: Film Growth and Surface Reactions

Abstract

High Resolution Image Download MS PowerPoint Slide High purity, uniform, and conformal aluminum phosphate (AlP x O y ) thin films were deposited by atomic layer deposition (ALD) between 25 and 300 °C using supercycles consisting of (i) PO(OMe) 3 dosing combined with O 2 plasma exposure and (ii) AlMe 3 dosing followed by O 2 plasma exposure. In situ spectroscopic ellipsometry and mass spectrometry were applied to demonstrate the ALD self-limiting behavior and to gain insight into the surface reactions during the precursor and coreactant exposures, respectively. Compared to earlier reported AlP x O y ALD studies using H 2 O and O 3 as coreactants or without using coreactans, the use of an oxygen plasma generally leads to higher growth per cycle values and promotes phosphorus incorporation in the film. Specifically, when using a 1:1 PO x:Al 2 O 3 cycle ratio and a substrate temperature of 150 °C, the growth per supercycle is found to be 1.8 Å. The [P]:[Al] atomic ratio for this process is approximately 0.5 (∼AlP 0.5 O 2.9 ) and can be tailored by changing the ratio between the two cycles or the substrate temperature. In literature reports where the same aluminum precursor was used, the [P]:[Al] atomic ratio was limited to 0.2 or a very high number of phosphorus cycles was needed in order to increase the phosphorus content. Instead, we demonstrate deposition of films with a composition close to AlPO 4 by using a 2:1 PO x:Al 2 O 3 cycle ratio. The limited incorporation of P in the film is suspected to derive from the steric hindrance of the relatively bulky phosphorus precursor. Mass spectrometry suggests that the PO(OMe) 3 precursor chemisorbs on the surface without the release of reaction products into the gas phase, whereas Al(Me) 3 already undergoes methyl ligand abstraction upon chemisorption.