Bias deposition of nanoporous Cu thin films

• NPC films are deposited using bias RF-balanced magnetron sputtering technique.
• The structures of NPC films depend greatly on the substrate surface.
• The effects of substrate bias and substrate temperature are elaborated.
• A new surface selective charging effect is proposed to reveal the growth mechanisms.

Nanoporous Cu (NPC) thin films are deposited at room temperature using the bias RF-balanced magnetron sputtering technique. The morphologies of as-deposited NPC films are characterized by a field-emission scanning electron microscope. It is observed that a bicontinuous triangle-ligament/channel structure or a porous triangle-prism structure can be achieved depending on the substrate surface. Cu thin films are also deposited either without substrate bias or at an elevated substrate temperature, however, in which no nanoporosity is observed. Furthermore, a new surface selective charging effect rather than the traditional ion-bombardment and resputtering effects is proposed for a full explanation and thus the underlying growth mechanisms of as-deposited NPC films are revealed.