Study on the Effects of Copper Oxide Growth on the Peel Strength of Copper/Polyimide

In this study, various copper oxides [CuO, Cu₂O, and Cu₂O + polybenzimidazole (PBI)] were studied as alternative adhesion layers. Specimens were aged under harsh conditions (300°C, 5% O₂ or humid condition), and then peel tests were conducted to investigate the reliability of Cu oxides/polyimide (PI). The peel strength of the bare Cu, CuO, and Cu₂O specimens dropped substantially, close to nil, due to void formation after 2 h of aging at 300°C. The degree of void formation near the Cu₂O/Cu interface showed a clear inverse relationship with the peel strength, suggesting that the formation of voids beneath the Cu₂O layer was directly responsible for the peel strength degradation. Void growth was controlled by Cu₂O layer growth, while voids originated from the difference between the diffusion rate of Cu atoms through the Cu₂O layer and Cu layers. Humidity tests did not lower the peel strength significantly in any of the specimens, none of which showed voids that were detrimental to the peel strength, in contrast to the results of the aging treatments at 300°C.