A graphite wafer boat (also called a wafer carrier) is the fixture that holds multiple silicon wafers in precise, evenly spaced slots while they pass through a diffusion furnace, oxidation furnace, or LPCVD reactor. Expo Advanced Materials machines graphite wafer boats to customer drawing from IG-110 and IG-430U ultra-high-purity isostatic graphite, factory-direct from its Noida, India facility, with no distributor mark-up.
This page covers boat design, grade selection, and custom machining capability specifically for wafer boats. For the fuller picture of where graphite is used across CZ crystal growth, CVD/MOCVD reactors, and diffusion furnaces, see Expo’s complete guide to graphite in semiconductor manufacturing.
What Is a Graphite Wafer Boat?
In batch thermal processes — dopant diffusion, thermal oxidation, and low-pressure CVD (LPCVD) — wafers are not processed one at a time. A boat holds a batch of wafers in a rack of precision-machined slots and moves them together into and out of the furnace tube. Graphite is used for this fixture (rather than, for example, quartz) because it withstands the repeated 800–1,200 °C thermal cycling of diffusion and LPCVD processes without warping, and because ultra-high-purity graphite grades do not outgas metallic contaminants that would compromise the wafer surface. (Background: semiconductor device fabrication and chemical vapor deposition.)
Two dimensions define whether a boat fits a given process and wafer set:
- Slot pitch — the spacing between adjacent slots, which must match the process recipe’s wafer-to-wafer gap for uniform gas flow and temperature distribution.
- Wafer-diameter compatibility — the slot width and boat length are cut to the wafer diameter in use. Silicon wafers in production fabs are most commonly 150mm, 200mm, or 300mm in diameter (background: semiconductor wafer standards), and a boat cut for one diameter is not interchangeable with another without remachining.
Horizontal vs Vertical Boat Design
Wafer boats come in two general configurations, and the right one depends on the furnace architecture, not the material:
- Horizontal boats sit inside a horizontal diffusion or oxidation tube, with wafers held vertically in slots along the boat’s length — the traditional configuration for older and mid-generation diffusion furnaces.
- Vertical boats are used in vertical furnace stacks, where wafers are held horizontally, stacked along the boat’s height. Vertical furnace architecture is more common in modern high-throughput fabs because it uses less cleanroom floor space per wafer processed and can offer more uniform gas and temperature distribution across a full batch.
Expo machines both configurations to customer drawing; boat geometry, slot count, and pitch are specified by the customer’s furnace and process, not standardised across the industry.
Grade Selection for Wafer Boats
Grade choice for a wafer boat depends on how directly the wafer contacts the fixture and how strict the process’s contamination budget is.
| Grade | Ash Purity | Typical Boat Use | Notes |
|---|---|---|---|
| IG-110 | <10 ppm ash | Standard LPCVD and diffusion-furnace boats; direct wafer contact | Nuclear-qualified purity; the default grade for most fab boat orders |
| IG-430U | <5 ppm ash | CVD/MOCVD boats, III-V compound semiconductor (GaN, GaAs, InP) processes, advanced-node contact zones | Highest commercially available purity |
Both grades are supplied uncoated for direct-contact boat applications; silicon-carbide (SiC) coating is available through Expo’s coating partner where a process specifies a coated boat surface. For the wider grade table covering susceptors, heaters, and other semiconductor components alongside boats, see Expo’s graphite grades page and isostatic graphite supplier page.
What this page will not do: state a fixed slot count or slot-to-slot repeatability figure as a universal Expo specification. Batch size (commonly in the range of 25–50 wafers per boat, depending on wafer diameter and pitch) and dimensional tolerance are set by the customer’s process and drawing, not by a single catalogue number — Expo machines to the tolerance the drawing calls for, verified by CMM inspection on every order.
Custom Machining Capability for Wafer Boats
Wafer boats are precision multi-slot parts, and Expo’s in-house CNC capability is built for exactly this kind of geometry:
- 5-axis milling for complex slot and profile geometry, to ±0.01 mm.
- Turning for boat rails and cylindrical features, diameter 10–400 mm.
- Thread cutting M2–M80 where boats mount to furnace paddles or push-rod fixtures.
- CMM inspection and a dimensional report issued as standard with every order — critical for a part where slot-to-slot consistency directly affects process uniformity.
- Lead time: 10–15 working days standard on made-to-drawing boats; 5–7 days on urgent orders using stocked billet grades.
- MOQ: 1 piece — Expo machines single prototype boats as well as production-volume batches, with no minimum order.
Supply STEP, IGES, DXF, or a 2D drawing with the required grade, slot pitch, wafer diameter, and quantity, and Expo will quote against the drawing.
Replacement Boats for Existing Furnace and CVD Tools
Beyond new-build boats, Expo also machines OEM-equivalent replacement wafer boats to match an existing furnace or reactor’s boat geometry — useful where a fab’s boats have worn, cracked, or need replacing outside the original tool vendor’s lead time. Supply the boat’s dimensions or a sample for reverse-dimensioning, and Expo machines a like-for-like replacement in the correct grade with full CMM verification, at Expo’s standard factory-direct pricing — 30–45% below European equivalent pricing, quote-based.
India-Manufactured, ISO 9001:2015 Certified
Expo Advanced Materials is the authorised machining partner of TOYO TANSO CO., LTD., Japan — one of the world’s leading isostatic graphite manufacturers — and machines IG-110 and IG-430U billets with full raw-material traceability: original mill certification plus Expo’s own CMM-verified dimensional inspection report on every shipment. Production runs under ISO 9001:2015 certification from Expo’s dedicated graphite-machining facility in Noida (NCR), India.
Expo sells factory-direct with no distributor, wholesaler, or reseller layer between its shop floor and the customer. Export documentation (commercial invoice, packing list, MTC, RoHS on request) is issued as standard for international orders, with air freight the standard mode to semiconductor equipment markets in Taiwan, South Korea, Japan, Germany, and the USA.
For the surrounding semiconductor materials picture — CZ crystal-growth susceptors, CVD reactor components, and grade selection across the full process — see Expo’s Semiconductor industry page and custom graphite machining services.
Frequently Asked Questions
What is a graphite wafer boat used for?
It holds a batch of silicon wafers in precisely spaced slots while they move through a diffusion furnace, oxidation furnace, or LPCVD reactor for high-temperature thermal processing. Graphite is used because it withstands repeated thermal cycling without warping and, in ultra-high-purity grades, does not contaminate the wafer surface.
What graphite grade is used for wafer boats?
IG-110 (<10 ppm ash) is the standard grade for most LPCVD and diffusion-furnace boats. IG-430U (<5 ppm ash) is used where the process demands the highest available purity, such as CVD/MOCVD and III-V compound semiconductor processing.
What’s the difference between horizontal and vertical wafer boats?
Horizontal boats hold wafers vertically in slots along a horizontal furnace tube — the traditional diffusion-furnace configuration. Vertical boats hold wafers horizontally, stacked along a vertical furnace stack, which is more common in modern high-throughput fabs for space and gas-flow-uniformity reasons.
Can Expo machine wafer boats to a custom slot pitch and wafer diameter?
Yes. Slot pitch, wafer-diameter compatibility, and overall boat geometry are machined to customer drawing (STEP, IGES, DXF, or 2D drawing) rather than sold as a fixed catalogue item, with 5-axis milling to ±0.01 mm and CMM-verified dimensional inspection on every order.
Does Expo supply replacement boats for existing furnace or CVD tools?
Yes. Expo machines OEM-equivalent replacement wafer boats to match an existing furnace or reactor’s boat geometry, working from customer dimensions or a sample, in the correct grade with full CMM verification.
What’s the lead time for a custom graphite wafer boat?
10–15 working days standard for made-to-drawing boats; 5–7 days on urgent orders using stocked billet grades. MOQ is 1 piece — Expo machines both single prototypes and production volumes.
Request a Quote
Expo Advanced Materials machines graphite wafer boats in IG-110 and IG-430U ultra-high-purity grades, factory-direct from India with full ISO 9001:2015 traceability and CMM inspection on every order. Contact Expo or call +91 98919 24639 (WhatsApp available) with your boat drawing, grade, and quantity for a quotation within 24 hours.