Deposition of zirconium boride thin films by direct current triode sputtering

Abstract

Specular, crack-free thin films of the refractory conductor zirconium boride have been deposited for possible applications in combined contact/diffusion barrier metallization schemes. Films were deposited by dc triode sputtering, which allowed the independent study of the effects of sputtering pressure, target voltage, and current on the film properties. The mole ratio of boron in the films increased (composition tending to ZrB2) and the resistivity decreased with increasing deposition rates which at a fixed target voltage and sputtering pressure increased almost linearly with target current. Decrease in sputtering pressure, with only a minor change in deposition rate, dramatically decreased resistivity and caused stress in the films to change from tensile to compressive. X-ray photoelectron spectroscopy correlated reduced oxygen content to reduced resistivity. Triode sputtering permitted deposition of films at 2 mTorr with a resistivity of 162 μΩ cm which is the lowest reported value for as-deposited films.

Direct current magnetron sputtered ZrB2 thin films on 4H-SiC(0001) and Si(100)

“…The measured amounts being typically below 0.2 at.% for H, Ar, and N and 0.4 at.% for C and 1 at.% for O. Such contents, particularly the oxygen content, must be considered to be low in PVD films compared to the literature [10,[15][16][17][18], as the growth was carried out in a HV system and without external heating in some of the processes. The oxygen level is also low compared to thermally activated CVD films deposited at a temperature of 450 °C [11].…”

“…Results on growth of films with composition deviating, sometimes substantially, from the composition of the utilized source, as well as growth of films with a high level of contaminants have been reported [2,4,6,10,[14][15][16][17][18]. The presence of a foreign element such as oxygen during nucleation of ZrB2 is likely to cause unwanted chemical reactions between the film constituents and the contaminant.…”

“…For the related boride TiB2, it has been shown that excess B segregates to the grain boundaries [22] and it is likely that this would happen in ZrB2 as well. With respect to the resulting properties of sputtered ZrB2 films, it has been reported that B-depleted films exhibit higher resistivity values compared to that of films with a composition closer to stoichiometry [10]. The feasibility of overcoming the inherent drawbacks for such growth conditions in film synthesis during high vacuum (HV) conditions by combining substrate bias and heating should thus be explored.…”

“…The presence of a foreign element such as oxygen during nucleation of ZrB2 is likely to cause unwanted chemical reactions between the film constituents and the contaminant. Such conditions will affect the properties, including the electrical resistivity, [10] of the deposited films and can, for instance, hamper potential epitaxial growth to substrates with a close lattice match, such as 4H-SiC(0001). The necessity of a stoichiometric, growth flux during deposition of ZrB2 films is further supported by thermodynamics, predicting ZrB2 to be a line phase with a narrow homogeneity range (<1 %) [19], thus the composition of the films can only deviate very little to avoid unwanted phase separation.…”

“…The literature shows that ZrB2 films have been deposited by physical vapor deposition (PVD) [7][8][9][10], as well as chemical vapor deposition (CVD). [11,12].…”