How to Select the Best Plasma Asher for Microfabrication

The micro- and nanofabrication world relies on photoresist stripping and surface preparation to keep device patterns crisp. Every lithography cycle produces a temporary photoresist mask that must be removed cleanly before the next layer can be deposited or etched, and modern processes can involve 10–40 masking steps. Historically wet chemistries were used to dissolve resists, but rising environmental concerns and the drive for higher precision have pushed fabs toward dry plasma ashing.

Dry ashing exposes wafers to oxygen plasma generated by RF or microwave energy and removes organic materials by oxidizing them into volatile by-products. It offers high selectivity to organics, avoids pattern collapse, generates minimal hazardous waste and delivers high throughput. To decide which plasma asher suits your line, you need to understand the technology options and weigh them against throughput, wafer size and budget constraints.

Why Plasma Ashing Matters

• Precision and repeatability – Targets photoresist and organic residues with minimal interaction with underlying films like silicon or silicon dioxide; avoids surface-tension effects that can collapse high-aspect-ratio features.
• Environmental and safety benefits – Oxygen plasma stripping produces mainly CO₂ and H₂O, reducing hazardous solvent use and disposal costs.
• High throughput – Modern single-wafer strip tools can process wafers in under 60 seconds and are often integrated with lithography or etch clusters.

Use Cases Beyond Photoresist Removal

• Sacrificial polymers or polyimide removal – Microwave plasma systems are effective for SU-8 removal and isotropic sacrificial layer etching in MEMS.
• Releasing temporary adhesives – Breaks down bonding adhesives without attacking metal or dielectric layers.
• Pre-bond surface activation and cleaning – Removes contaminants and activates bonding sites for improved adhesion.
• General surface cleaning – Descum after lithography, residue removal before deposition, and surface prep for improved wettability.

Plasma Asher Technologies

Microwave vs. RF Plasma

Plasma is generated when energy ionizes oxygen gas; both RF (13.56 MHz) and microwave (2.45 GHz) sources are used. Microwave plasma produces a high concentration of chemically active species while keeping the substrate bias low, leading to fast ash rates and minimal ion bombardment—ideal for delicate layers and advanced nodes. RF plasma equipment is generally less expensive and widely available but may require slower processing or downstream configurations to minimize damage.

In-situ vs. Downstream (Afterglow)

• In-situ (direct) plasma – Wafer is exposed directly to the discharge; high ash rates but possible ion/UV damage. Remote operation or added cooling can mitigate risk.
• Downstream (afterglow) – Plasma is generated in a separate chamber; reactive radicals flow over the wafer after electrons/ions recombine, avoiding electrical damage. Examples include the Gasonics Aura 1000, March PX-500, and March PX-1000.

Single-Wafer vs. Batch Processing

Single-wafer ashers deliver higher throughput and uniformity, while batch tools load multiple wafers on a quartz boat and can reduce cost per wafer. PVA TePla’s GIGAbatch platforms combine batch advantages with modern sources, and the GIGAfab A200–300 series offers automatic single-wafer ashing up to 300 mm.

Comparing Leading Plasma Asher Brands

How to Select the Right Plasma Asher

1. Match wafer size and production volume – For 200–300 mm high-throughput lines, consider automatic single-wafer tools like TePla’s GIGAfab. For R&D or legacy 3–6 in lines, downstream systems like the Gasonics Aura 1000 or ESI e3511 may suffice.
2. Choose the appropriate plasma source – Microwave provides higher radical density and lower substrate bias for fast, low-damage ashing. RF can be cost-effective; downstream helps protect sensitive substrates.
3. Consider process chemistry and materials – Verify gas lines/MFCs for O₂, and additives such as CF₄ or H₂; polyimide/adhesive removal may require higher temperatures or remote plasma.
4. Evaluate throughput and integration – Look for cassette-to-cassette automation, robotic transfer, and end-point detection; many single-wafer tools can process a wafer in under 60 seconds.
5. Assess process control and reliability – Seek optical emission end-point detection, tight temperature control (e.g., IR lamps), strong uniformity, and high uptime.
6. Plan for lifetime cost and support – Balance price with reliability, spares availability, and service/warranty options—especially for pre-owned tools.

Why Refurbished Plasma Ashers Make Sense

Refurbished semiconductor equipment can dramatically reduce capital expenditures while maintaining performance. Beyond cost and sustainability benefits, refurbished tools offer immediate capacity—used systems are in stock and can be integrated quickly. The quality of refurbishment is critical: systematic reconditioning, calibration, testing, and warranty coverage distinguish refurbished equipment from “as-is” used tools.

Benefits of Refurbished Equipment from ClassOne

• Enhanced reliability – Rebuilt to OEM-level specifications with critical part replacement.
• Proven performance – Rigorous testing, chamber matching, and qualification.
• Warranties and support – Warranty coverage and optional service agreements.
• Cost savings without sacrificing quality – Typical savings of 40–70% compared with new systems.

Cost-Savings and Sustainability Data

Industry analyses commonly report 20–70% savings when purchasing refurbished semiconductor equipment. Upgrades can reduce power and maintenance costs, shortening payback periods while keeping functional machinery out of landfills.

Spotlight: Why Choose a Used TePla Plasma Asher?

• Broad configuration options – Batch and single-wafer tools in manual or fully automated versions; GIGAbatch for batch and GIGAfab A200–300 for automatic single-wafer up to 300 mm.
• High ash rate with low damage – Microwave sources deliver high radical density at low bias for fast, damage-free cleaning—suitable for fragile substrates.
• Versatile applications – Photoresist removal, descum, wafer cleaning, and SU-8 removal.
• Refurb-friendly installed base – Strong availability and proven refurbishment pathways through ClassOne.

Conclusion

Plasma ashing is a cornerstone of microfabrication, enabling precision photoresist removal, sacrificial layer release, and surface preparation. Choosing the right asher means balancing wafer size, throughput, plasma source, process control, and total cost of ownership. Microwave ashers offer high ash rates with minimal damage, while downstream systems protect sensitive substrates. Brands like PVA TePla, Gasonics, and ESI provide options across diameters and automation levels.

For fabs seeking maximum ROI, refurbished plasma ashers offer compelling advantages: substantial cost savings, environmental benefits, and immediate availability—especially when sourced from reputable refurbishers that provide OEM-level reconditioning and warranties.