Self-limiting deposition of copper from copper beta-diketonates and plasma electrons

Copper metallic films are essential components in semiconductor devices. We study deposition of copper films by a pulsed electron chemical vapor deposition (e-CVD) process using free electrons from a plasma discharge as reducing agents, with copper beta-diketonates, Cu(hfac)2 and Cu(acac)2 as the copper source. The mass gain per deposition cycle, as monitored by a quartz crystal microbalance (QCM) sensor, suggests that the pulsing allows us to access a process window with a self-limiting deposition process. X-ray photoelectron spectroscopy (XPS) shows that the films are not metallic copper and that they are contaminated by carbon, oxygen, and when Cu(hfac)2 was used, also fluorine. Optical emission spectroscopy (OES) suggests that this is caused by redeposition of precursor fragments from plasma volume decomposition of precursor molecules desorbing during the plasma step. This redeposition limits the control of the surface chemistry during the plasma step of the deposition cycle.