Investigations at low temperature of 90 nm pitch BEOL for quantum applications

Superconducting Back-end-of-line (BEOL) might be crucial for quantum applications. In the present work, detailed studies of Ta and TaN behavior are reported. While bulk Ta and TaN are superconducting, the T C is affected by deposition conditions and layer thickness. However, 9 nm of Ta deposited on TaN leads to reach a T C of 2 K. we explain this behavior by the growth of Ta as two different phases depending on the growth stages. The second part of this paper reports a huge intrinsic thermal expansion coefficient (TEC) whatever the ULK porosity. The huge TEC can drive to strong residual stress that could affected the superconductivity of the metal line.