The continuous miniaturization of semiconductor devices requires highly controlled thin films deposited on 3D structures. Atomic layer deposition (ALD) has been shown to be a powerful technique in producing uniform, conformal films with great control over the thickness down to atomic level. Similar reactions are extended to molecular layer deposition (MLD) where organic fragments are retained in the film growth. ALD and MLD are combined to produce inorganic-organic hybrid materials with tunable composition and properties.
ALD SiO2, which is traditionally difficult to grow due to lack of suitable precursors, was deposited using a new group of volatile aminosilanes, cyclic azasilanes (AZ) and O3 as precursors under a wide range of temperatures. The AZs possess high vapor pressure and reactivity for ring opening reactions upon exposure to -OH groups. Subsequent oxidation with O3 afford silanol groups, which are amenable to further reaction with AZs. The growth rates obtained are 0.6–1.2 Å/cycle for various silanes under different ALD conditions. Cyclic azasilanes offered a novel group of chemicals for the preparation of ALD SiO2, enabled detailed study of the adsorption of silanes and surface oxidation mechanism, and lead to new surface fundtionalities.
Using the functionalities AZs created after ring-opening reactions, hybrid inorganic-organic MLD films were grown based on this class of molecules, maleic anhydrides (MA), metal-organics, and water. In some processes, diffusion within the film was evidenced by large growth rates (~9 nm per cycle). However, use of TMA arrested this diffusion. During annealing, films exhibited densification while maintaining low surface roughness. Porosity was evidenced by small dielectric constants. These chemistries offer a route to tunable thin films and have potential applications in diffusion barriers, low dielectric constant layers, and passivation layers.
To understand the detailed growth behavior of precursor diffusion, quartz crystal microbalance (QCM) data have been acquired during half reactions at 100 °C, revealing the diffusion of precursors AZ and MA. Large mass gains were observed after 50 cycles, when the films were sufficiently thick for significant diffusion in and out of precursors. The diffusion behavior is highly dependent on the substrate temperature and purge time. This non-ideal MLD growth could be potentially useful when long deposition time is undesired.
Besides the in-situ study of diffusion during MLD reactions, we also monitored the half cycles during ALD Al2O 3 by conductance measurement across a silicon channel region. Interfaces between semiconductors and metal oxides are important, where electronic behavior plays an important role on overall device behavior. The resolution of negative fixed charge between silicon surface and metal oxide is demonstrated with the chemistries of ALD film growth. These measurements provide the possibility to engineer interfaces with controlled amounts of positive or negative charge.
|Advisor:||Strandwitz, Nicholas C.|
|Commitee:||Pearson, Raymond A., Snyder, Mark A., Vinci, Richard P.|
|Department:||Materials Science and Engineering|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-B 79/10(E), Dissertation Abstracts International|
|Subjects:||Engineering, Materials science|
|Keywords:||ALD, Cyclic azasilane, MLD, Porous, Precursor diffusion, Transconductance|
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