Low temperature chemical vapour synthesis of Cu3Ge thin films for interconnect applications

• Cu3Ge films prepared on 300 mm Si wafers at BEOL compatible temperatures.
• ε1-Cu3Ge phase, independent of film thickness investigated, is stable up to 600 °C.
• Uniform trench filling on narrow lines show promise for interconnect applications.

With the downscaling of the interconnect technology, the resistance of industry standard Cu increases for the sub-20 lines due to the increased grain boundary and surface scattering. With the reduction of the geometry sizes and increase of aspect ratios, the ability to achieve a uniform Cu metallization becomes challenging. Hence, interests on low resistive alternative metals or alloy thin films deposited with good trench filling capability technologies becomes increasingly important. In this context, in the present study, an unconventional route is explored to synthesize Cu3Ge films via CVD of GeH4 gas with thin solid Cu films at BEOL compatible temperatures (250 °C). Results show that ε1-Cu3Ge films could be successfully grown on 300 mm blanket and on patterned wafers by exposing GeH4 precursors over Cu films at 250 °C. The GeH4 CVD conditions were optimized, on different thicknesses of Cu, to grow phase pure and stoichiometric low resistive Cu3Ge layers on blanket wafers. In-situ XRD analyses combined with anneal studies show that the Cu3Ge films are thermally stable up to 600 °C with no signs of decomposition. Our investigation was further extended to the growth of Cu3Ge in trenches and showed that the GeH4 decomposition-cum-reaction with Cu is uniform along the trench depth, completely transforming the Cu to Cu3Ge films with a limited volume expansion, as evidenced by the GIXRD, SEM and TEM analysis.

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