Understanding the Major Types of Wafer Cassettes

1. FOUP (Front Opening Unified Pod)

FOUPs are the industry standard in 300mm fabs. They are rigid, sealed containers designed to house 25 wafers in a controlled micro-environment. Each FOUP includes:

● A standardized front interface for robotic load/unload

● Identification features such as RFID tags or barcodes

● Compatibility with SEMI E84, E87, and E88 standards for factory automation

FOUPs are essential in high-volume manufacturing where contamination control and automation are priorities.

2. FOSB (Front Opening Shipping Box)

FOSBs are typically used for the transportation of 300mm wafers between facilities. While they appear similar to FOUPs, they lack certain automation-ready features such as bottom docking and tool interface compatibility. Key differences include:

● Simpler structure optimized for shipping, not automation

● Manual access or modified openers for certain fab environments

● Often incompatible with FOUP load ports

FOSBs are ideal for inter-fab transport but may cause process interruptions if misused in automated lines.

3. Open Wafer Cassettes (100mm–200mm)

For legacy nodes and R&D fabs, open cassettes are still in use, especially for 150mm and 200mm wafers. These cassettes are:

● Typically top-loading

● Made from plastics like PFA or polycarbonate

● Exposed to ambient cleanroom air

Because they lack environmental sealing, they are unsuitable for advanced clean process nodes but remain widely used in certain markets.

Key Compatibility Challenges in Automated Environments

As fabs integrate multiple tools and transport systems, cassette compatibility becomes a non-trivial concern. Below are the most common issues engineers and equipment integrators face:

1. Load Port Mismatch

Many wafer handling systems are designed specifically for FOUPs. Attempting to use a FOSB on a FOUP load portmay lead to mechanical alignment errors, wafer damage, or tool downtime.

2. Automation Protocol Conflicts

FOUPs are designed for SEMI-compliant AMHS (Automated Material Handling Systems), including OHT (Overhead Hoist Transport) and stockers. In contrast, FOSBs and open cassettes often require manual intervention or custom adapters, undermining automation.

3. Contamination Risk

Fabs transitioning from 200mm to 300mm lines often encounter difficulties when using both sealed (FOUP) and open cassette formats in proximity. This hybrid environment raises the risk of airborne particle cross-contamination.

4. Tool Interface Incompatibility

Some process tools are only configured for specific cassette types. Retrofitting a system to support both FOUP and FOSB, or 200mm and 300mm cassettes, typically involves hardware changes, software reconfiguration, and cleanroom requalification.

Designing for Cross-Cassette Compatibility

To reduce downtime and improve fab flexibility, some manufacturers now provide:

● Dual-compatible load ports that accept both FOUPs and FOSBs

● Wafer sorters or transfer systems that can transfer wafers between different cassette types

● RFID and sensor arrays to detect cassette type and alignment before tool engagement

● Custom adapters for legacy equipment during migration phases

While these solutions add cost and complexity, they offer a viable path for fabs undergoing generational transitions or mixed-node production.

Conclusion

Wafer cassettes like FOUPs and FOSBs serve distinct but essential roles in semiconductor manufacturing. Ensuring proper compatibility among cassette types, load ports, and automation protocols is critical for maintaining efficiency and minimizing production risks. As fabs grow increasingly automated, understanding these cassette types—and the engineering decisions behind them—will remain a core aspect of fab design and operations.

For fabs looking to streamline cassette handling across diverse wafer formats, Fortrend offers a range of intelligent wafer transfer systems and sorter solutions designed to bridge the compatibility gap between FOUPs, FOSBs, and legacy cassettes. Our equipment supports seamless integration with AMHS and EFEM modules, enhancing throughput while protecting wafer integrity.

To learn more about how Fortrend can support your fab's automation goals, please contact our team at sales@fortrend.com.