Successive reactions of gaseous trimethylaluminium and ammonia on porous alumina

Abstract

Successive reactions of gaseous trimethylaluminium (TMA) and ammonia on porous alumina were studied with the goal of Ðnding suitable process conditions for preparing aluminium nitride (AlN) by atomic layer deposition (ALD), a technique based on separate saturating gasÈsolid reactions. The reaction of TMA was studied at 353È623 K on alumina dehydroxylated at 473È1073 K, and the following reaction of ammonia at 423È823 K. Reference samples were prepared by reacting ammonia at 623 and 823 K with alumina dehydroxylated at 833 K. The samples were characterised by elemental analysis of carbon and nitrogen and by IR and 1H NMR. TMA reacted with alumina in a saturating manner at 353È573 K. Reaction took place through ligand exchange with surface OH groups, with release of methane, and through dissociation of TMA on pairs of coordinatively unsaturated Al and O ions. Aluminium-bonded methyl groups remained on the surface. Decomposition of TMA occurred at 600 K and above. Ammonia had reacted with most of the methyl groups by 573 K, but 723 K was required to remove them all. Primary, secondary and tertiary amino groups were formed in the reaction, and ammonia molecules were adsorbed on the surface. The average H/N ratio in the amino groups decreased with increasing reaction temperature. Good temperatures for AlN deposition by ALD seem to be any temperature up to 573 K for the TMA reaction and 723 K or above for the ammonia reaction.

Atomic Layer Deposition of Gadolinium Aluminate using Gd(iPrCp)3, TMA, and O3 or H2O

“…This may be attributed to enhanced H 2 O desorption and purge, as discussed below, or to an onset of Gd( i PrCp) 3 or TMA precursor desorption. [31][32][33] Furthermore, this indicates that Gd( i PrCp) 3 is thermally stable at least up to 300 8C. In addition, the WiW non-uniformity of the H 2 O process did slightly improve with temperature.…”

“…Again, the observations seem to suggest that Gd x Al 2-x O 3 deposition is carried out in a CVD rather than in an ALD mode. Since TMA is known to be stable at temperatures of 300 À 325 8C, [31][32][33] and Gd( pulses. The surface chemistry leading to the deposition characteristics of the O 3 -based process is currently not yet understood, and further research is necessary to clearly identify the underlying processes that explain the above observations.…”

Self-limiting low-temperature growth of crystalline AlN thin films by plasma-enhanced atomic layer deposition

“…Temperature dependency of the deposition rate, observed within the range of 200-400°C, may be due to the effect of temperature on the number and type of reactive sites present on the surface before and after the chemisorption, or the effect of temperature on the preferred reaction mechanisms [22]. Self-decomposition of TMA molecules may also be responsible from the increasing growth rate with temperature, however this is unlikely since the lowest temperature reported for the decomposition of TMA is~300°C [30]. In order to investigate this further, TMA and NH 3 saturation characteristics were studied at higher deposition temperatures.…”

Formation of Metal Oxide Particles in Atomic Layer Deposition During the Chemisorption of Metal Chlorides: A Review

“…[48±50,68] A decrease in the amount of bonded metal with increasing reaction temperature is somewhat unusual for reactants used in ALD. For organometallic reactants, the amount bonded typically stays constant (e.g., AlMe 3 [69] ) and for metal b-diketonates, it typically increases (e.g., La(thd) 3 [70] ).…”