Abstract
We report on a new route to grow epitaxial copper (Cu) ultra-thin films (up to 150 nm thick) at ambient temperature on Si(001) wafers covered with native oxide without any prior chemical etching or plasma cleaning of the substrate. It consists of a single-step deposition process using high power impulse magnetron sputtering (HiPIMS) and substrate biasing. For a direct current (DC) substrate bias voltage of −130 V, Cu/Si heteroepitaxial growth is achieved by HiPIMS following the Cu(001) [100]//Si(001) [110] orientation, while under the same average deposition conditions, but using conventional DC magnetron sputtering, polycrystalline Cu films with [111] preferred orientation are deposited. In addition, the intrinsic stress has been measured in situ during growth by real-time monitoring of the wafer curvature. For this particular HiPIMS case, the stress is slightly compressive (−0.1 GPa), but almost fully relaxes after growth is terminated. As a result of epitaxy, the Cu surface morphology exhibits a regular pattern consisting of square-shaped mounds with a lateral size of typically 150 nm. For all samples, X-ray diffraction pole figures and scanning/transmission electron microscopy reveal the formation of extensive twinning of the Cu {111} planes.
Highlights
The crystallographic orientation of thin films is of great importance in the performance of advanced electronic, optoelectronic, magnetic and superconducting heterostructures and devices, especially when the thickness of the films is reduced to the nanometer scale[1]
Highly ionized metal fluxes were alternatively employed as a pre-treatment using high power impulse magnetron sputtering (HiPIMS)[23, 24] and cathodic arc[25] processes combined with a high negative direct current (DC) bias voltage applied to the substrate
We report on a novel single-step, HiPIMS-based deposition process, controlled by DC biasing the substrate, to grow epitaxial Cu thin films up to 150 nm thick on Si (001) oriented wafers covered with native oxide, without any pretreatment process
Summary
The crystallographic orientation of thin films is of great importance in the performance of advanced electronic, optoelectronic, magnetic and superconducting heterostructures and devices, especially when the thickness of the films is reduced to the nanometer scale[1]. Highly ionized metal fluxes were alternatively employed as a pre-treatment using high power impulse magnetron sputtering (HiPIMS)[23, 24] and cathodic arc[25] processes combined with a high negative direct current (DC) bias voltage applied to the substrate. This new approach is capable of producing interfaces with a well-defined chemistry, which improves the film/substrate adhesion (compared to the results obtained using conventional Ar glow discharges) and promotes local epitaxial growth of subsequent deposited ceramic layers over large areas[23,24,25]. The HiPIMS Cu films are compared to reference films deposited at the same experimental conditions by conventional direct current magnetron sputtering (DCMS)
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