Low-k Reliability Improvement with Optimal Dummy Insertion

To improve low-k film reliability in BEOL, a process modeling methodology is employed to analyze stress and surface morphology evolution during BEOL fabrication process. The stress built-up in low-k dielectrics is found to be directly linked to material density increase, which correlates with laboratory measurement of low-k material volume shrinkage. Densification stress redistribution shows strong dependence on metal layout and curing process, but weak dependence on trench depth and etch stop layer. It is also found that volume shrinkage due to low-k material densification can lead to large vertical displacement, which causes surface recess and unevenness. To mitigate densification induced low-k reliability risks, dummy metal insertion becomes necessary to trade off stress concentration and surface recess. Various dummy insertion schemes are studied and their impacts on low-k material stress and surface recess are evaluated. Dummy metal insertion guidelines for low-k reliability optimization in BEOL structures are developed.