Thin films with nanometer-scale pillar microstructure
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Thin films with nanometer-scale pillar microstructure K. Robbie Department of Physics, Queen’s University, Kingston, Ontario, Canada K7L 3N6
C. Shafaia) and M.J. Brett Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, T6G 2G7 (Received 16 March 1998; accepted 14 April 1999)
Thin films possessing microstructure composed of isolated vertical pillars were deposited by glancing angle deposition (GLAD) without the need for subsequent etch processing. The GLAD technique uses substrate rotation and oblique angle flux incidence to deposit a porous columnar thin film with engineered microstructures. Thin films with a pillar microstructure were fabricated from a variety of metals, metal oxides and fluorides, and semiconductors. The rate and incident angle of vapor flux, as well as the substrate rotation speed during deposition, were found to critically affect pillar microstructure. Thin films with pillar diameters and densities as low as 30 nm and 3 pillars per m2, respectively, were deposited. The low stress, high surface area, and porous nature of these films suggests use of pillar microstructure films in optical, chemical, biological, mechanical, magnetic, and electrical applications. I. INTRODUCTION
The fabrication of nanometer-scale pillars is of interest in many fields. Some examples are quantum effect devices, magnetic memory media, optical coatings, nanoscale sensors, field emitters, and large surface area chemical and biological reaction surfaces. Recent studies have used electron beam lithography and etching to fabricate pillars of silicon1,2 and nickel3 on silicon substrates and gold–platinum4 on silicon and GaAs substrates. The use of electron beam lithography and etching in fabrication of nanometer-scale pillars is both time consuming and expensive. The requirements of lithography limits pillar fabrication on very flat substrates such as silicon wafers. The need to etch lithographic patterned films limits material choice to those with suitable etchants. In this paper we describe a one-step fabrication method for nanometer-scale pillars. Thin film microstructures can be engineered on a nanometer scale in three dimensions through active control of the substrate orientation relative to the vapor flux during deposition. Extreme incident flux angles during deposition (greater than 70° from the substrate normal) result in significant atomic shadowing during film growth;5–8 this strongly influences the columnar microstructure of a thin film. Oblique angle flux incidence, together with limited adatom diffusion (or mobility), gives deposited films a porous columnar microstructure, a)
Present address: Department of Electrical and Computer Engineering, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2.
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http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 7, Jul 1999 Downloaded: 06 Feb 2015
with the columns inclined toward the evaporant source.5–9 Through manipulation of the angle of flux incidence du
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