Wafer Etching (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.
Atomic Layer Etching (ALE)
Atomic Layer Etching (ALE) is an advanced dry etching technique designed for ultimate precision at the atomic scale. Instead of continuous plasma bombardment, ALE operates in self-limiting cycles that remove only a few atomic layers at a time. This makes it especially suited for sub-5 nm nodes, 3D NAND, and emerging device architectures requiring extreme control.
- Process Principle: Alternating steps of surface modification (chemical adsorption) and removal (ion bombardment or plasma excitation).
- Advantages: Near-atomic precision, superior uniformity, reduced damage to underlying layers, improved selectivity.
- Constraints: Lower throughput compared to conventional RIE; complex process integration; still maturing for high-volume manufacturing.
- Applications: FinFET and GAA transistor patterning, 3D NAND stair-step etch, advanced DRAM structures, and critical interconnect layers.
Representative ALE Equipment Vendors
- Lam Research (U.S.): Introduced ALE systems integrated into advanced plasma etch platforms.
- Tokyo Electron Limited (TEL, Japan): Developing ALE-capable modules for sub-5 nm applications.
- Applied Materials (U.S.): Offers ALE within integrated etch-deposition systems.