Growth and patterning of strontium-titanate-oxide thin films for optical devices applications
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Growth and patterning of strontium-titanate-oxide thin films for optical devices applications M. Gaidi1, L. Stafford2, M. Chaker1, J. Margot2, & M. Kulishov3 1
INRS-Énergie, Matériaux et Télécommunications, Varennes, Québec, Canada Département de physique, Université de Montréal, Montréal, Québec, Canada 3 Adtek Photomask, Montréal, Québec, Canada 2
ABSTRACT Strontium-titanate-oxide (STO) thin films have been deposited on silicon substrates by means of a reactive pulsed-laser-deposition technique. The influence of the oxygen deposition pressure on the microstructural properties of the films has been investigated by means of various characterization techniques. It was found that the crystalline quality of the film significantly deteriorates as the oxygen pressure increases. This is accompanied by an increase of the film microporosity. The microstructure of the film is found to directly impact the optical quality of the films. In particular, due to the higher density and crystallinity of the films deposited at lower oxygen pressure, films characterized by lower optical losses can be achieved in such conditions. These films have been used in the context of the development of optical waveguides. For this purpose, patterning of the STO films was investigated using sputter-etching with a high-density argon plasma operated in the very low pressure regime. Highly anisotropic features have been produced with high etch rate and good selectivity over resist. Preliminary results indicate the STO films can be successfully incorporated in functional waveguides. INTRODUCTION Strontium-titanate-oxide (SrTiO3 or STO) thin films are of great interest for several applications, including the fabrication of optical devices for telecommunication systems. This is because STO is characterized by a high transparency in the visible and infrared regions. It can also be used as a buffer layer for the growth of electro-optic materials with a perovskite structure such as (Pb,La)ZrTiO3 [1]. The integration of STO layers into optical devices requires understanding of both deposition and patterning processes. This is crucial since the performances of the device are expected to critically depend on film properties and patterning characteristics. For example, STO films can be used as core or cladding layers in optical waveguides : in this case, the attenuation and propagation coefficients of the wave in the waveguide are likely to be strongly influenced by the film microstructural properties and by the etching quality. STO thin films were grown using a reactive pulsed-laser-deposition (RPLD) technique. In a first step, we investigate the influence of the oxygen buffer gas pressure employed during RPLD on the microstructural properties of the films and we examine how they influence the optical quality. In a second step, sputter-etching of patterned STO layers with a high-density argon plasma is investigated. Specifically, we examine the influence of the argon pressure on the STO etch rate, pattern selectivity and etching anisotropy. Finally
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