Barrier properties of electroless deposit of Co-W-P alloy

It is known that the Co alloy deposit has high electromigration resistance and thermal diffusion resistance to Cu. We could prepare electroless deposit of Co-W-P with different W contents on Cu substrate by changing the Co-W-P bath parameter. After heat treatment under 200-400°C with Air or N
₂
conditions, Cu diffusion to the surface was measured. Co-W-P layer has excellent barrier property for Cu in N
₂
heat treatment. However, Cu diffused to the surface when whole of Co-W-P (W=0 and 11wt.%) layer was oxidized in high temperature with air condition. The results indicate that oxidized layer of Co-W-P deposit has no barrier effect for Cu. In Co-W-P deposit in the condition of high W content (W=23wt.%), an unoxidized layer still remained and only a small amount of Cu was detected on the surface. We confirmed that Co-W-P (W=23wt.%) was difficult to oxidize and Cu diffusion was suppressed by preventing oxidization of the Co-W-P deposit.