Atomic layer deposition of multicomponent oxide materials

Marko Vehkamäki
Abstract & Cover

Atomic layer deposition (ALD) is a method for thin film deposition which has been  extensively studied for binary oxide thin film growth. Studies on multicomponent oxide  growth by ALD remain relatively few owing to the increased number of factors that  come into play when more than one metal is employed. More metal precursors are  required, and the surface may change significantly during successive stages of the  growth. Multicomponent oxide thin films can be prepared in a well-controlled way as  long as the same principle that makes binary oxide ALD work so well is followed for  each constituent element: in short, the film growth has to be self-limiting.  ALD of various multicomponent oxides was studied. SrTiO3, BaTiO3, Ba(1-  x)SrxTiO3 (BST), SrTa2O6, Bi4Ti3O12, BiTaO4 and SrBi2Ta2O9 (SBT) thin films were  prepared, many of them for the first time by ALD. Chemistries of the binary oxides are  shown to influence the processing of their multicomponent counterparts. The  compatibility of precursor volatilities, thermal stabilities and reactivities is essential for  multicomponent oxide ALD, but it should be noted that the main reactive species, the  growing film itself, must also be compatible with self-limiting growth chemistry. In the  cases of BaO and Bi2O3 the growth of the binary oxide was very difficult, but the  presence of Ti or Ta in the growing film made self-limiting growth possible.  The application of the deposited films as dielectric and ferroelectric materials  was studied. Post-deposition annealing treatments in different atmospheres were used to  achieve the desired crystalline phase or, more generally, to improve electrical  properties. Electrode materials strongly influenced the leakage current densities in the  prepared metal–insulator–metal (MIM) capacitors. Film permittivities above 100 and  leakage current densities below 1􀂘10-7 A/cm2 were achieved with several of the  materials.  

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