CVD and PVD copper integration for dual damascene metallization in a 0.18 μm process

Abstract

Various methods of copper filling are studied as interconnect metallizations in advanced ultra large scale integration (ULSI) devices. The filling mode comprising organometallic chemical vapor deposition (OMCVD) Cu followed by physical vapor deposition (PVD) Cu reflow for 0.3 μm diameter trench and via filling has been investigated. This paper presents an evaluation of both the long-throw PVD copper, and CVD copper fundamental process steps. The excellent step coverage of CVD Cu as a seed layer is presented. The corresponding initial PVD Cu deposition step requires a low DC power to facilitate Cu reflow before creating the characteristic overhang of the PVD process, which in turn facilitates subsequent void formation. So the PVD DC power was optimised at 1.6 kW. Furthermore, the full sequential integration of the CVD and PVD process was investigated as a function of liner thickness, deposition temperature and DC power. The filling process has been optimised with a relatively thick liner, to avoid dewetting on the TaN barrier, and with a high deposition temperature to obtain sufficient reflow. However, a thin PVD Cu ‘flash’ layer was necessary to resolve interface stability issues between CVD Cu and TaN. Electrical results are compared to those from a standard copper process flow and these first results are 15% higher than with a standard copper metallization.