Study On Growth Behaviors Of Metal Nanomaterials By Atomic Layer Deposition Technique

Atomic Layer Deposition (ALD) is now being widely studied for its unique reaction mechanism and some advantages, such as large area uniformity, excellent three-dimensional conformality, and sub-mono layer thickness control. Although some progress has been made on metal materials prepared by thermal ALD or plasma-enhanced ALD (PEALD), compared to extensive and intensive researches on oxide materials, it is still lacking and scarce. At present, only some metals can be deposited by ALD, among which several reactions and growth mechanisms are unclear yet. ALD noble metals in high-aspect-ratio structures or porous powders are urgent and necessary due to great demands from new energy and catalysis fields. In addition, ALD of metal alloys is rare now and extensive work is needed.This thesis focuses on developing the ALD/PEALD processing for metals or alloys. The impact of various processing parameters on Ir and Co metal thin films has been deeply investigated. The growth behavior of ALD Ir in AAO templates with nano-channel has been characterized systematically. Finally, the CoPtx alloys have been explored by combination of PEALD and ALD.Main achievements are summarized as follows:1. The effect of different substrates and processing conditions on thermal-ALD Ir metal thin films has been studied. XPS and SEM results reveal that the amount of-OH on the substrate is very important for the nucleation of Ir. The optimal processing has been achieved for ALD Ir films on Si substrates with in-situ 3 nm ALD Al2O3 layer. The maximum GPC is 0.78 A/cycle. The influence of Ir source pulse time and O2 pulse flux on the growth rate and nucleation of Ir has also been evaluated. It is found that Ir(acac)3 pulse time of 2 s and O2 pulse flux of 50 sccm are enough to attain chemical saturation adsorption on ALD growth surfaces with stable ALD window.2. The growth behavior of ALD Ir has been investiagted in AAO templates with various pore sizes and aspect-ratios systematically. Under the same growth parameters, the Ir infiltration depth into the AAO templates is in proportion to the pore size. For the same AAO, the infiltration depth is in proportion to the square root of Ir pulse time, i.e. I= kd√t. It follows diffusion-limited ALD model, indicating the pore size of AAO and the Ir pulse time are key factors for infiltration depth. The Ir pulse time to obtain conformal Ir coating throughout the whole AAO channels is in proportion to the square of the aspect-ratio of AAO templates. Moreover, other ALD processing parameters can also impact the result. For instance, insufficient purge time would cause CVD-like reaction, and larger oxygen flux would accelerate the lose of Ir(acac)3 at the entrence then decrease the infiltration depth in AAO templates.3. Co metal films have been deposited successfully by PEALD. Different metal precursors, substrates, and reductive reactants have been compared. The results indicate that ex-situ ALD Al2O3 surface, CoCp(CO)2 and H2 plasma is beneficial to growth of PEALD Co metal because of their higher reaction activity. The optimal PEALD Co processing has been achieved on ex-situ ALD Al2O3 surface with 2 s CoCp(CO)2 pulse time and 100 sccm H2 plasma flux. The GPC value is 0.41 A/cycle. Finally, the CoPtx alloys have been attempted using various Co/Pt deposition cycle ratios by combination of PEALD and ALD.