Control and characterization of structure transformation for tantalum films
Yi-Chien Weng1,2*, C.-T. Liang2, J. G. Lin1
1Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
2Graduate Institute of Applied Phicics, National Taiwan University, Taipei, Taiwan
* presenting author:yichien weng,
Tantalum (Ta) thin film exhibits two different types of crystal structures. One is tetragonal (β-Ta) and the other is body-centered cubic (α-Ta). β-Ta and α-Ta have very different properties, distinguished by high and low value of resistivity (ρ), negative and positive temperature coefficient of resistance (TCR), respectively. 1 However, β-Ta is a meta-stable phase which is hard to obtain. Previously the transformation of structure from tetragonal to body-centered cubic is either controlled by changing the film thickness or by the pressure of nitrogen gas. 2 3 Here, a simple synthesis method is proposed to tune the ratio of α-Ta and β-Ta phase by controlling the pre-sputtering time in Ar gas. From X-ray diffraction results the ratio of β-Ta (1-X) increases from 0.11 to 1 with the increase of pre-sputter time from 0 to 40 minute. However by fitting ρ-T curve with σA,B=(XσA)/(1+αA(T-300))+((1-X)σB)/(1+αB(T-300)), 4 the ratio of β-Ta phase can be more precisely determined.

[1] Mildred H. Read and Carl Altman, Applied Physics Letters 7, 51 (1965)
[2] A. Schauer and W. Peters, Thin Solid Films, 27,95 (1975)
[3] A. Schauer and M. Roschy, Thin Solid Films, 12, 313 (1972)
[4] N. Schwartz, W. A. Reed, P. Polash and M. H. Read, Thin Solid Films, 14,333 (1972)

Keywords: Tantalum , Temperature Coefficient of Resistance, Pre-sputtering time