Optimizing IC Interconnection: A Functional Approach to Innovation (Stay updated on the project's progress)

SYSTEM FUNCTIONAL MODEL

The first result from the System Functional Modeling of the structure is to replace the Ta barrier for the fine air gap:

Indeed, Fine Air Gap (FAG) can successfully replace the Ta-barrier layer. We do not need a thick gap; even a very fine gap is good enough to prevent Cu diffusion into ILD. The FAG purpose is to destroy an interphase boundary.

Fine air gap structure advantages:

1. No Cu diffusion that can contaminate the ILD
2. Air gaps can trap the voids that may be formed due to Cu-electromigration; generally, the electromigration in such configuration should be investigated and solved.
3. Additional volume for metal lines
4. Generally - possibility to reduce RC-delay
5. Cost reduction - Ta is a very expensive material

PROCESS FUNCTIONAL MODEL - traditional process:

Summary of the process functional modeling:

1. At least 16 operations, including 3 metrology operations, are needed to build one interconnection layer.
2. The process's average effectiveness is close to 70%, which is excellent. However, only about 30% of operations contribute value to the product. Therefore, the rest of the operations should be eliminated or simplified.

Some directions for the process development:

1. Etch Stop is needed only above Cu to prevent Cu diffusion from the bottom Cu metal line to the top ILD. Instead of depositing the Etch Stop material with CVD, it is proposed that a process of selective deposition of PMMA with dissolved SiC or SiN be developed. The liquid can be spun on the wafer and removed from the ILD (SiO2) areas.
2. Photolithography - Perform development of the exposed resist in wet etch equipment. More than that, why do we need to develop exposed PR at all? Exposed PR is removed by an aqueous solution, meaning it can be removed by plasma. So, the idea is to apply plasma etch directly after exposure.
3. Wet cleaning after dry etch - Why do we need to develop exposed PR at all? Exposed PR is removed by an aqueous solution, meaning it can be removed by plasma. So, the idea is to apply plasma etch directly after exposure. The aim is to eliminate expensive wet etch operations.
4. Polish (CMP) - To simplify the Polish (CMP) operation, it is proposed that the bulk of the Cu be removed at the electroplater just after the completion of the electrodeposition. It is a straightforward process to reverse the polarity to make the wafer an anode and give (-) to the anode. This will dissolve the main affected part of the Cu and simplify the following operation - polish.