Surface Reaction Mechanisms during Ozone and Oxygen Plasma Assisted Atomic Layer Deposition of Aluminum Oxide

Abstract

We have elucidated the reaction mechanism and the role of the reactive intermediates in the atomic layer deposition (ALD) of aluminum oxide from trimethyl aluminum in conjunction with O(3) and an O(2) plasma. In situ attenuated total reflection Fourier transform infrared spectroscopy data show that both -OH groups and carbonates are formed on the surface during the oxidation cycle. These carbonates, once formed on the surface, are stable to prolonged O(3) exposure in the same cycle. However, in the case of plasma-assisted ALD, the carbonates decompose upon prolonged O(2) plasma exposure via a series reaction kinetics of the type, A (CH(3)) --> B (carbonates) --> C (Al(2)O(3)). The ratio of -OH groups to carbonates on the surface strongly depends on the oxidizing agent, and also the duration of the oxidation cycle in plasma-assisted ALD. However, in both O(3) and O(2) plasma cycles, carbonates are a small fraction of the total number of reactive sites compared to the hydroxyl groups.

Study of the passivation mechanism of c-Si by Al<inf>2</inf>O<inf>3</inf> using in situ infrared spectroscopy

“…As can be seen from the spectrum, Al 2 O 3 deposition on the H-terminated Si surface leads to the consumption of surface Si-H x (x = 1, 2, and 3), which is indicated by the decrease in absorbance in the 2000-2200 cm -1 region [11]. Additionally, we also observe an increase in absorbance in the 2800-3000 and 3200-3700 cm -1 regions, which have been assigned to the CH x (x = 1, 2, and 3) stretching mode and OH stretching mode, respectively [12]. This indicates the presence of impurities in the Al 2 O 3 film in the form of unreacted TMA and hydroxyls.…”

Incomplete elimination of precursor ligands during atomic layer deposition of zinc-oxide, tin-oxide, and zinc-tin-oxide

“…These so-called "difference spectra" show the changes of the surface upon exposure to the precursor or co-reactant. 23,[28][29][30][31] However, information of persisting ligands and other nucleation effects is lost when representing the data in this way, especially when FTIR spectra are only recorded after conditioning the reactor/coating the powder. This will be illustrated with the dataset for SnO 2 ALD shown in Fig.…”

What is limiting low-temperature atomic layer deposition of Al2O3? A vibrational sum-frequency generation study

“…In addition to hydroxyls which form the most important chemisorption site for TMA, it has been reported that TMA can chemisorb on bridged oxygen on a dehydroxilated Al 2 O 3 surface, 9 formates, 10 and carbonates. 11 One of the unresolved issues in understanding the growth of Al 2 O 3 by ALD is the exact cause of the decrease in growth per cycle (GPC) reported at low temperatures.…”

“…1, shows that the decrease in GPC at low temperatures only occurs for the thermal process while the GPC of the plasma process keeps increasing when going to lower temperatures. 3,11 Because both processes only differ in the co-reactant, the likely cause of the lower GPC for the H 2 O-based process is the lack of reactivity of the co-reactant at low temperatures. However, the precise ALD surface chemistry related to this lower reactivity is unclear.…”