Summary: FOSB vs. FOUP
The difference between FOSB and FOUP is "where they're used": the FOUP stays inside the fab, docking with tool load ports via the automated material handling system (AMHS / OHT) so tool robots pick and place wafers directly; the FOSB handles transport between sites and, per SEMI M31, is used by silicon wafer suppliers shipping to IC makers, with wafers transferred to FOUPs on receipt before processing. So the FOUP is designed for cleanliness, repeated opening, and nitrogen purging, while the FOSB is designed for shock and vibration resistance and is bagged and sealed before shipment.
FOSB vs. FOUP comparison table
| Item | FOUP | FOSB |
|---|---|---|
| Full name | Front Opening Unified Pod | Front Opening Shipping Box |
| Also called | Transport pod | Wafer shipping box |
| Used for | In the fab, between tools | Transport between sites |
| In processing? | Yes; robots pick from it | No; moved to FOUP |
| Paired equipment | AMHS / OHT, stockers, tool load ports | Incoming QC, transfer; some open on load ports |
| Design focus | Clean, reopenable, purgeable | Shock-proof transit |
| Typical capacity | 25 | 25 |
| Main SEMI standards | SEMI E47.1 | SEMI M31 (M80 for 450 mm) |
| Before shipping | Stays in the fab | Bagged, labeled, boxed |
Compiled by DEYly from SEMI M31, Wikipedia: FOUP, The Elec.
What is a FOUP? The in-fab "transport pod"
The FOUP arrived with the first 300 mm process tools in the mid-1990s. 300 mm wafers are large and heavy, and a full pod of 25 weighs about 7–9 kg, too much for manual handling, so the FOUP was designed for automation from the start: kinematic coupling plates and holes on the bottom let it sit precisely on a tool's load port and be picked up by overhead hoist transport (OHT) and other automated handling systems (Wikipedia: FOUP).
Inside the fab, FOUPs are opened repeatedly to pick and place wafers, so the interior must stay extremely clean to avoid outside contamination (The Elec). Newer FOUPs can also be purged with protective gas at stockers or tools, reducing exposure to oxygen and moisture while wafers wait.
What is a FOSB? The between-site "shipping box"
Per SEMI M31, the FOSB is used to ship 300 mm wafers from wafer suppliers to customers (usually IC makers) while maintaining wafer quality in transit. It's used at the last step of wafer manufacturing, at incoming inspection, and for transferring wafers into FOUPs at the IC fab; FOSBs are not used in IC manufacturing processes, and the standard recommends automated transfer from FOSB to FOUP (SEMI M31).
Because it travels by truck, air freight, and through customs, the FOSB is designed for shock and vibration resistance (The Elec). Taking the Entegris SB300 as an example: 25 wafers at 10 mm pitch, an ultra-pure polycarbonate shell, 4.6 kg empty and 7.8 kg full (Entegris SB300 datasheet). On some FOSBs, the door can open and close automatically on a load port or be opened by hand (Miraial 300mm FOSB).
One more: FOBIT
Besides FOUPs, SEMI M31 lists FOBITs (front-opening box for interfactory transport) and open cassettes as transfer targets. The reduced-pitch shipping box specified in SEMI E119 fits 25 wafers in roughly the volume of a 13-wafer FOUP, lowering transport costs between IC fabs (SEMI E119).
How do wafers get from FOSB to FOUP?
Loaded at source
After final processing and inspection at the shipper, wafers are loaded into a FOSB.
Bagged, labeled, boxed
The FOSB is bagged and sealed, labeled with lot number and quantity, then boxed for shipment.
Transport
It travels by land or air to the customer, with the FOSB and packaging guarding against shock, vibration, and moisture.
Incoming QC
The customer unboxes, unbags, checks lot numbers, and performs incoming inspection.
Transfer to FOUP
Wafers are transferred from FOSB to FOUP in a clean environment, and only then enter processing and the automated handling system.
How FOSBs are packed
Taking automatic bagging equipment from Germany's cts as an example, the FOSB is first placed in an inner bag, then in an outer bag containing desiccant, sealed, and each one is checked for seal integrity with a test gas. Reports note that doing this by hand is repetitive and monotonous, making errors hard to avoid; that equipment handles 3,000–8,000 FOSBs a month, about 75,000 to 200,000 wafers (Control Design).
Packing materials and specs vary by plant: some use vacuum-sealed aluminum foil barrier bags, others multi-layer bags with desiccant. What they share: bagging, sealing, folding, labeling, and checking lot numbers are highly repetitive tasks where mistakes aren't allowed. For how this stage can be automated, see the wafer box (FOSB) model of the "automatic semiconductor inner-box packing machine."
FAQ
What's the difference between a FOSB and a FOUP?
Their uses differ. The FOUP (front opening unified pod) is used inside the fab with AMHS / OHT and tool load ports to move wafers between process tools; the FOSB (front opening shipping box) ships wafers between sites, for example from silicon wafer suppliers to IC makers, is designed for shock and vibration resistance, and doesn't enter IC processing.
What do FOSB and FOUP stand for?
FOSB stands for front opening shipping box, also called a wafer shipping box; FOUP stands for front opening unified pod (some say universal pod), also called a wafer transport pod.
Can a FOSB go straight into a tool for processing?
No. SEMI M31 clearly states that FOSBs are not used in IC manufacturing processes; after receipt, wafers should be transferred to FOUPs in the fab, and the standard recommends automated transfer.
How many wafers does a FOSB hold?
Standard 300 mm FOSBs typically hold 25; the Entegris SB300, for example, holds 25 at 10 mm pitch. There are also reduced-pitch shipping boxes (SEMI E119) that fit 25 wafers in about the volume of a 13-wafer FOUP, lowering transport costs between sites.
Why are FOUPs purged with nitrogen?
To reduce the effect of oxygen and moisture on wafers while they wait. FOUPs can be purged with protective gas at stockers or tools to improve yield.
How FOSBs are packed
The common approach is to place the FOSB in an inner bag, then in an outer bag with desiccant, seal it, check each seal, and label and box it. Manual packing is repetitive and error-prone, and automated equipment can already handle bagging, sealing, and inspection.