Wafer Development (Step )
Development is the process step that follows photolithography exposure. It selectively dissolves either the exposed or unexposed regions of the photoresist, leaving behind a patterned resist layer that defines where material will be etched, implanted, or deposited. Development is a critical step for transferring circuit features with precision and repeatability.
Process Overview
- Purpose: Reveal the latent image in the photoresist after exposure to form precise patterns.
- Sequence: Wafer is coated with photoresist, exposed through a mask, baked, and then immersed or sprayed with developer solution.
- Positive Resist: Exposed regions become soluble in the developer and are removed.
- Negative Resist: Exposed regions crosslink and remain after development; unexposed areas are removed.
- Iteration: Performed multiple times throughout wafer processing — once for each lithography layer.
Wet vs Dry Development
| Method | Process | Advantages | Constraints |
|---|---|---|---|
| Wet Development | Immersion or spray with aqueous developer (commonly TMAH in UPW) | Uniform, high-resolution, scalable to EUV | High UPW use, chemical waste, resist collapse at very small features |
| Dry Development | Plasma or supercritical CO2 removal of soluble regions | Less chemical waste, potential for sub-10 nm scaling | Experimental, limited throughput, not widely adopted |
Major Equipment Vendors
- TEL (Tokyo Electron Limited): Lithography track systems that integrate coat, bake, and develop modules.
- SCREEN Semiconductor Solutions (Japan): Developer tracks and coat/develop clusters.
- Applied Materials (U.S.): Lithography track systems and process integration with scanners.
Process Consumables
- Developers: Aqueous TMAH (2.38% typical), MIF (metal-ion-free) alternatives for EUV resists.
- Ultrapure Water (UPW): Used for pre-develop rinsing and post-develop cleaning.
- Solvents: NMP and others for negative resist or specialty materials.
Cleanroom & Environment
- Conducted in Class 1 cleanroom environments to avoid particle defects.
- Integrated with coat/bake tracks and scanners for full automation.
- Strict temperature and humidity control critical for CD uniformity.
Advantages & Constraints
- Advantages: High selectivity, repeatability, and precision for nanoscale patterns.
- Constraints: TMAH toxicity and wastewater handling, resist collapse at sub-20 nm features, cost of integrated track systems.
Market Outlook
Development remains inseparable from photolithography, and market demand scales directly with the adoption of new lithography nodes. EUV resists and alternative developers are under intensive research, but wet TMAH-based development remains the global standard for advanced fabs.