Electrochemical polishing (ECP) of copper using hydroxyethylidenediphosphonic acid (HEDP) has been investigated as an alternative to chemical mechanical polishing (CMP) for integration of low-k dialectrics in microelectronic devices. An optimal copper ECP process produces smooth polishing and a fast removal rate. For this investigation copper anodic polarisation curves in HEDP-phosphoric acid solutions were measured and copper ECP effects in various HEDP-phosphoric acid solutions were examined. Copper surface smoothing effects in various HEDP-phosphoric acid solutions were evaluated with atomic force microscopy. It was shown that HEDP and HEDP-phosphoric acid solutions have polarisation curves with a limited current plateau characteristic of ECP. Twenty to forty per cent of HEDP solutions had a maximum limiting current density of approx 80 A cm~(-2). Adding phosphoric acid to HEDP solutions increased the limiting current to a maximum, beyond which further addition caused a decrease. An optimal ECP effect (removal rate = 1.8 mu m min~(-1), 80 percent reduction in mean roughness) was achieved with a solution of 30 HEDP + 30H_3PO_4 + 40H_2O (vol.- percent). A higher removal rate was achieved by decreasing the concentration of phosphoric acid, but his resulted in a reduction of the smoothing effect.
展开▼
