Atomic layer deposition of high-k dielectrics from novel cyclopentadienyl-type precursors

Jaakko Niinistö
Abstract & Cover

The atomic layer deposition (ALD) method was applied for fabricating high permittivity  (high-k) dielectrics, viz. HfO2, ZrO2 and rare earth oxides, which can be used to replace  SiO2 as gate and capacitor dielectric. The dielectrics were processed by ALD using novel  cyclopentadienyl (Cp, -C5H5) precursors together with water or ozone as the oxygen  source. ALD, which has been identified as an important thin film growth technique for  microelectronics manufacturing, relies on sequential and saturating surface reactions of  alternately applied precursors, separated by inert gas purging. The surface-controlled  nature of ALD enables the growth of thin films of high conformality and uniformity with  an accurate thickness control.  The ALD technique is introduced and ALD processes for HfO2, ZrO2 and rare earth oxide  films, as well as the applications of the high-k dielectrics in microelectronics are reviewed.  The need for developing new ALD processes for the high-k materials is emphasized.  ALD processes for HfO2 and ZrO2 were developed using Cp-type precursors. The effect of  different oxygen sources, namely water or ozone, on the film growth characteristics and  properties of the ALD-processed films was examined in detail. The oxide films were  stoichiometric, with impurity levels below even 0.1 at-% for C or H. Electrical  measurements showed promising dielectric properties such as high permittivity values and  low leakage current densities. Other properties, such as structure, interfacial layer thickness  and morphology, were also characterized. Compared to films processed by water, the  ozone-processed films on H-terminated Si showed improved dielectric properties, as well  as higher density, lower roughness and better initial growth rate. In addition, in situ gasphase  measurements by quadrupole mass spectrometry (QMS) were performed in order to  study the ZrO2 growth mechanism.  A number of Cp-precursors were tested for the ALD of several rare earth oxide films. The  thermal stability of many of the precursors was limited, but nevertheless, ALD-type  processes were developed for Y2O3 and Er2O3 films. High reactivity of the Cp-precursors  towards water resulting in high growth rates (1.2-1.7 Å/cycle) and purity of the Y2O3 and  Er2O3 films were realized. Despite the detected partial decomposition of the (CpMe)3Gd  precursor, Gd2O3 films with high growth rate and purity as well as effective permittivity of  about 14 were deposited.  Finally, promising processes for ternary scandates, namely YScO3, GdScO3, and ErScO3,  were developed using either Cp- or β-diketonate-based processes. These as-deposited  ternary films were amorphous exhibiting high effective permittivity (14-15), low leakage  current density, and resistance towards crystallization upon annealing even up to 800°C.  

Source of Information
FinALD40 exhibition material,
Helsinki University of Technology, Department of Chemical Technology, Laboratory of Inorganic and Analytical Chemistry
(Espoo, Finland)
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