Atomic Layer Deposition of Noble Metal Thin Films

Titta Aaltonen
Abstract & Cover

Noble metal thin films have several potential applications for example in integrated circuits. In this work, new noble metal processes have been developed for atomic layer deposition (ALD), which is a gas phase thin film deposition method based on alternate saturative surface reactions. The self-limiting film growth mechanism of ALD leads to films with excellent conformality and good large area uniformity. In addition, the film thickness can be accurately controlled by the number of the applied growth cycles. ALD processes for ruthenium, platinum, iridium, rhodium, and palladium were studied. All the processes are based on the reaction of the metal precursor with oxygen, the process temperatures being in the range of 200–450 °C. Metallic ruthenium films with low resistivity (< 20 μΩ⋅cm) and low impurity contents (< 0.2 at.% H, < 0.2 at.% C, and < 0.4 at.% O) were grown from a cyclopentadienyl precursor RuCp2. Ruthenium films grown from a β-diketonato precursor Ru(thd)3 had higher resistivities, higher impurity contents, and longer incubation time for onset of the film growth. High quality platinum films were grown from MeCpPtMe3. The films had strong (111) orientation even at the lowest growth temperatures. Iridium films with low resistivities (< 18 μΩ⋅cm), low impurity contents (< 1.0 at.% H, < 0.3 at.% C, and < 0.5 at.% O), and smooth surface morphology were grown from Ir(acac)3 and oxygen. Metallic rhodium films were grown from Rh(acac)3 and oxygen. ALD of palladium was also studied but self-limiting film growth was not obtained. Reaction mechanism studies were performed in order to gain better understanding of the chemistry in the studied noble metal ALD processes. It was found that adsorbed oxygen atoms react with the ligands of the noble metal precursor during the metal precursor pulse. Unreacted ligand species that remain on the surface after the metal precursor pulse react with oxygen during the following oxygen pulse. The main reaction by-products detected during the both reaction steps were water and carbon dioxide. 

Source of Information
FinALD40 exhibition material,
University of Helsinki, Department of Chemistry, Laboratory of Inorganic Chemistry
(Helsinki, Finland)
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