Effects of Annealing on the Mechanical and Electrical Properties of DC Sputtered Tantalum Pentoxide (Ta 2 O 5 ) Thin Fil
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Effects of Annealing on the Mechanical and Electrical Properties of DC Sputtered Tantalum Pentoxide (Ta2O5) Thin Films J. M. Purswani1, A. P. Pons1, J. T. Glass2,1, R. D. Evans3,1, J. D. Cogdell3 1 Chemical Engineering, Case Western Reserve University, Cleveland, Ohio 44106 USA 2 Electrical and Computer Engineering, Duke University, Durham, North Carolina 27708 USA 3 The Timken Company, Canton, Ohio 44706 USA ABSTRACT Tantalum oxide (Ta2O5) films were deposited onto p-type silicon substrates using reactive DC magnetron sputtering, and then annealed for one hour in a dry air ambient at temperatures of 730ºC, 780ºC, and 830ºC. Annealing was shown to reduce stress from the as-deposited sample, and resulted in a compressive stress state for samples annealed at 730ºC and a tensile stress state for the other samples. Hardness values were approximately 8 GPa, with the exception of the sample annealed at 780ºC that demonstrated a hardness of 13 GPa. Leakage current generally decreased with annealing, especially at the lower temperatures. Electrical breakdown was observed for as-deposited and the 830ºC annealed films. Resistivities of the films ranged from 6.5 x 109 to 6.1 x 1012 Ω-cm, with the film annealed at 830ºC being the most conductive. Annealing also led to an increase in dielectric constant. Dielectric constants varied from 9.3 for the as-deposited to greater than 30 for the 780ºC and 830ºC annealed sample. Annealing resulted in crystalline films that were close to stoichiometric. INTRODUCTION Tantalum oxide (Ta2O5) is of interest as a replacement material for silicon dioxide in microelectronic circuits. Ta2O5 has a high dielectric constant, good corrosion properties, and a relatively high refractive index. It has good step coverage, is easily dry etched and is compatible with other processes in VLSI processing. Ta2O5 is also used in optics as an antireflective coating and has been proposed for use in solid-state optoelectronic devices. Tantalum oxide films are also of interest for use as high temperature resistors and oxygen sensors [1]. Tantalum oxide films have been deposited by both physical and chemical deposition methods. Films produced by chemical vapor deposition and metal organic solution deposition must be produced at high temperatures and often contain carbon contamination from the metal organic precursor[2-5]. CVD films have better step coverage than sputtered films, but produce films that have less desirable mechanical and electrical properties such as high leakage current [2]. Reactive sputtering has many advantages. For example, it is compatible with the other steps of microelectronic processing. Most importantly, DC sputtering is performed at relatively low temperatures. This allows for the deposition of amorphous films. The major drawback in sputtering, however, is the determination of process conditions to obtain stoichiometric films [6]. In addition, the properties of the film are highly dependent on these conditions [7]. Regardless of method used, it is often necessary to anneal the as-de
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