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<p>Electronic interconnects benefit from copper due to its superior conductivity and low cost. Direct-write processes are desired for flexibility, ease and agility in mesoscale, hybrid and packaging electronics manufacturing. Vacuum cold spray (VCS) is an attractive process, but depends on optimization of many parameters to obtain efficient deposition and maximum fidelity. This study uses VCS with different powder feedstocks, nozzle diameters, nozzle standoffs and scan numbers to produce copper lines and pads on glass and silicon substrates. Electron microscopy reveals plasticity-based deposition, building films to thicknesses of several microns. Profilometry and image analysis portray the line profiles, with data fit to Gaussian curves to obtain accurate heights, widths and integrated cross-sectional areas. A figure of merit (FOM), combining height, rectangularity ratio and number of scans, is used to judge the deposition and geometric form of the lines. The FOM in this study has a wide range from 3 to 61&#xa0;nm/scan. Both the line FOM and rectangularity are correlated with a drop in relative electrical resistivity. A 20-scan, 50-mm-long line is found to have a low electrical resistivity = 4.34 × 10<sup>−8</sup>&#xa0;Ωm, just 2.5 times that of pure bulk copper. The results suggest that VCS copper holds promise for direct writing of interconnects, and the FOM approach is proposed for comparative studies in process development.</p>

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Direct-Write Copper via Vacuum Cold Spray: Comparing Process Parameters, Line Profiles and Electrical Resistivity

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月29日

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  • Thomas Hands,
  • Alex Valdez,
  • Paul Fuierer

摘要

Electronic interconnects benefit from copper due to its superior conductivity and low cost. Direct-write processes are desired for flexibility, ease and agility in mesoscale, hybrid and packaging electronics manufacturing. Vacuum cold spray (VCS) is an attractive process, but depends on optimization of many parameters to obtain efficient deposition and maximum fidelity. This study uses VCS with different powder feedstocks, nozzle diameters, nozzle standoffs and scan numbers to produce copper lines and pads on glass and silicon substrates. Electron microscopy reveals plasticity-based deposition, building films to thicknesses of several microns. Profilometry and image analysis portray the line profiles, with data fit to Gaussian curves to obtain accurate heights, widths and integrated cross-sectional areas. A figure of merit (FOM), combining height, rectangularity ratio and number of scans, is used to judge the deposition and geometric form of the lines. The FOM in this study has a wide range from 3 to 61 nm/scan. Both the line FOM and rectangularity are correlated with a drop in relative electrical resistivity. A 20-scan, 50-mm-long line is found to have a low electrical resistivity = 4.34 × 10−8 Ωm, just 2.5 times that of pure bulk copper. The results suggest that VCS copper holds promise for direct writing of interconnects, and the FOM approach is proposed for comparative studies in process development.