Planarization (Step )
Metallization creates the conducting paths that connect transistors, memory cells, and other devices on a chip. It begins with the formation of local contacts to source, drain, and gate regions, then expands into multilayer interconnect networks that span the entire integrated circuit. Advanced metallization relies on copper, cobalt, and ruthenium interconnects, along with barrier and liner materials to prevent diffusion and ensure reliability.
Process Overview
- Purpose: Form conductive contacts and interconnects between devices and across chip layers.
- Sequence: Contact formation ? barrier/liner deposition ? metal fill ? planarization (CMP) ? repeat across multiple layers.
- Iteration: Dozens of metallization and planarization steps are required for advanced chips, with 10–15+ metal layers at leading-edge nodes.
- Transition: Marks the start of Back-End-of-Line (BEOL) processing, though initial contacts are considered Middle-of-Line (MOL).
Metallization Techniques
| Method | Process | Advantages | Constraints |
|---|---|---|---|
| Aluminum Interconnects (Legacy) | PVD sputtering of aluminum, patterned by etch | Low cost; simple integration; still used in power and analog | High resistance; scaling limits below 250 nm |
| Copper Damascene | Trenches etched in dielectric, filled with copper by electroplating | Low resistance, high reliability; standard for logic and memory | Requires diffusion barriers (TaN, Co, Ru); complex CMP |
| Cobalt & Ruthenium Interconnects | Emerging metals for MOL and BEOL layers | Improved electromigration resistance; thinner barrier requirements | Integration challenges; supply chain scaling still maturing |
Major Equipment Vendors
- Applied Materials (U.S.): Leading supplier of metallization deposition, electroplating, and CMP systems.
- Lam Research (U.S.): Provides plasma etch and deposition solutions for metal patterning and barrier layers.
- Tokyo Electron Limited (TEL, Japan): Metal etch, deposition, and cleaning equipment for BEOL integration.
- Ebara (Japan): CMP tools widely used for copper damascene integration.
Process Consumables
- Metals: Copper sulfate plating solutions, cobalt, ruthenium, aluminum targets.
- Barrier/Liner Materials: Tantalum, TaN, TiN, Ru, Co thin films deposited by PVD or ALD.
- Dielectrics: Low-k and ultra-low-k dielectric materials to minimize capacitance.
- Slurries & Pads: CMP consumables for planarization after metal fill.
Cleanroom & Environment
- Metallization requires Class 1–10 cleanroom bays due to defect sensitivity in interconnect layers.
- Electroplating introduces unique challenges for wastewater treatment and chemical recycling.
- Copper contamination control is critical — even trace amounts can degrade device performance.
Advantages & Constraints
- Advantages: Enables multi-level interconnects and scaling of logic/memory devices.
- Constraints: CMP complexity, diffusion barrier requirements, electromigration reliability at advanced nodes, and scaling limits for copper.
Market Outlook
Metallization is evolving as scaling challenges push copper toward its physical limits. Cobalt and ruthenium are being adopted for local interconnects at 7 nm and below, while copper remains dominant for global wiring. Research continues into alternative metals, barrierless integration, and air-gap dielectrics to reduce resistance-capacitance (RC) delay.