Various Methods Used to Etch Titanium Dioxide Columnar Thin Films Using a CF 4 Reactive Ion Etch Recipe
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1174-V10-04
Various Methods Used to Etch Titanium Dioxide Columnar Thin Films Using a CF4 Reactive Ion Etch Recipe Martin R. Kupsta1, Michael T. Taschuk1, Michael J. Brett1,2, Jeremy C. Sit1,* 1) Electrical and Computer Engineering, ECERF W2-023, University of Alberta, Edmonton, AB, T6G 2V4 Canada 2) NRC National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, AB, T6G 2M9 Canada * Correspondence: [email protected], +1-780-492 3937 ABSTRACT A dry etch recipe was developed for porous nanostructured TiO2 thin films fabricated using glancing angle deposition (GLAD). Unlike wet chemical etches, the technique reported here preserves the vertical post nanostructure, eliminating clumping. A highly controllable and easily tailored reactive ion etching process with CF4 alone, or combined with O2, was investigated. The anisotropic etch modifies the morphology and density of standard GLAD films, which is of interest for sensing applications. INTRODUCTION Glancing angle deposition (GLAD) is a versatile technique for depositing nanostructured thin films in a single process step [1]. In GLAD, the substrate is held at an oblique angle from the vapour source. After the initial nucleation stage, deposition shadows are produced which promote the formation of columnar microstructures. Through real-time measurement of the vapour flux rate and control of substrate motion, it is possible to produce a wide variety of nanostructures, including the vertical posts used here. Several techniques have been used to modify GLAD nanostructures after deposition, including etching [2-4] and oxidization [5-6] processes. Here we report the development of a flexible anisotropic etch process. The modification of GLAD thin film pore distributions is of interest for sensor applications, where rapid diffusion of analyte throughout the film volume improves response time. The combination of the high surface area of GLAD thin films with high diffusivity channels is expected to improve sensor performance, and motivates the development of the etch recipes presented here. We have developed a post-deposition etch process for GLAD thin films that allows for a reduction in film density through an anisotropic etch, based on work previously reported [7, 8]. By using CF4 in a reactive ion etch (RIE), we achieved a highly controllable and easily tailored etch. Wet chemical etches do not offer the same controllability due to the small structures that exist in our films. When introduced to a liquid, GLAD films exhibit a high capillary force interaction between posts and demonstrate the “nano-carpet” effect [9], as shown in Figure 1. By varying CF4 and O2 concentrations and plasma power in the etch gas recipe we were able to achieve results suitable for pattern transfer, introduction of a bimodal pore distribution, and density reduction.
Figure 1: 880 nm vertical post GLAD thin film after 5 s buffered oxide etch. The etch is difficult to control and results in clumping of the film. EXPERIMENT Initial testing of etch recipes was performed on a batch
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