| AVS 61st International Symposium & Exhibition | |
| Thin Film | Tuesday Sessions |
| Session TF+PS-TuM |
| Session: | ALD for Emerging Applications |
| Presenter: | Jie Qi, University of Connecticut |
| Authors: | J. Qi, University of Connecticut X. Jiang, University of Connecticut B.G. Willis, University of Connecticut |
| Correspondent: | Click to Email |
Atomic layer deposition (ALD) has become an important technique for the deposition of nanometer thin dielectric and metallic thin films with applications in semiconductors, nanotechnology, catalysis, and energy. In particular, nanoscale metallic structures are gaining importance for fabrication of plasmonic antenna with applications in biochemical sensors, photocatalysis, and solar energy harvesting devices. A key feature of nanoscale plasmonic materials is a strong dependence of the plasmon resonance on size and shape of the nanostructure. ALD offers a unique means to control the size, composition, and particle-particle junctions of nanostructures with high precision. The latter is particularly important for creating hot spots where electric fields are strongly enhanced. A key challenge for ALD is the strict control of film composition and uniformity. Although a number of works have been published on the uniformity and layer by layer growth of amorphous dielectric thin films, the crystalline structures of metals present significantly increased complexity. Moreover, when seed layers, prefabricated nanostructures, or particles are involved, the sensitivity of film growth to surface structure has received relatively little attention so far.
In this work, we study the effects of surface preparation and seed layer properties on ALD Cu thin films relevant to plasmonic devices. Pd and Pt are used as seed layers for both planar thin films and two dimensional nanostructures. ALD growth was studied for different sized nanostructures and surface preparations including: e-beam deposition, high temperature annealing, solvent cleans, and UV/Ozone (UVO) pretreatment, as well as different ALD growth conditions. Samples were analyzed by XPS, SEM, AFM, EDS, and other techniques to compare film uniformity and surface structures. A strong dependence of Cu ALD growth quality was found for different nanostructures and surface preparations. Nucleation of Cu was greatly enhanced when UVO pre-treatment was performed on e-beam evaporated seed layers, but AFM results showed surface roughness increased with UVO cleaning time, which indicates rough, non-uniform growth. Seed layer thickness also played a role and it was observed that smoother and more uniform Cu thin films are obtained with thinner seed layers. Overall, planar thin films are poor models for nanostructure growth. Nanostructures are significantly more sensitive to surface preparations and growth conditions because of the similar length scales of nuclei and nanostructure size.