No abstract

The characteristics and performance of SPM and XPA were investigated for the sub-110 nm and below memory lithography. Various alignment strategies using SPM and XPA were compared on the production wafer for improved overlay performance. It is evident that SPM out-performs XPA for most of layers as CMP can easily over polish XPA due to the low pattern density. Based on these results, it is believed that SPM will be a promising candidate for sub-Il Onm memory process with better overlay performance.

This paper employs a novel electro-thermal modeling methodology to assist eFuse test-key design. The temperature distribution for eFuse is simulated based on electrical Joule-heating and thermal heat conduction in eFuse and surrounding materials. The electrical Joule-heating strongly depends on the contact pads and wiring shapes. The thermal heat conduction is important for the hot-spot to reach the burn-out temperature range. The final temperature distribution and hot-spot for each type of test-key under preset electrical operation condition depend on material electrical and thermal properties. Thermal boundary conditions are applied to establish thermal equivalent surrounding effects. Test structure design splits include anode/cathode shapes, wiring sizes, and via configurations. Simulated test-key designs with hot-spots in the desired position and failing in the melting temperature range are then selected to build actual test vehicles. This electro-thermal modeling assisted test-key design methodology effectively speeds up the turnaround time and reduces the development cost.

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.