Contents
1. Wafer diameter: inch or mm?
The semiconductor industry uses two names side by side, and both are nominal. The inch naming dates from the earliest sizes, while SEMI standards specify millimetres. So "4 inch" is actually 100 mm (about 3.94 inch), "6 inch" is 150 mm, "8 inch" is 200 mm and "12 inch" is 300 mm.
When ordering, state both (for example "4 inch / 100 mm") to avoid confusing 3 inch (76.2 mm) with 100 mm, or 125 mm with 150 mm — two pairs that often get mixed up.
2. Why larger wafers are thicker
Thickness is not arbitrary. The wider the wafer, the more it must bear its own weight, gripping forces during handling and thermal stress in high-temperature furnaces. Too thin for its diameter, a wafer is prone to warping, crystal slip or breakage.
Standard thickness therefore rises with diameter, from about 275 µm at 2 inch to 725 µm at 8 inch and 775 µm at 12 inch. Standard thickness is also the cheapest choice; unusually thin or custom-thick wafers usually cost more because breakage during processing rises.
3. Standard wafer size table
| Size (inch) | Diameter (mm) | Typical thickness | Commonly used for |
|---|---|---|---|
| 2 | 50.8 | ~275 µm | Research, sapphire / InP / GaAs substrates, teaching |
| 3 | 76.2 | ~380 µm | Older lab tools, compound semiconductors, R&D |
| 4 | 100 | 525 µm | R&D, MEMS, SiC / GaAs, university labs |
| 6 | 150 | 675 µm | MEMS, power electronics, LEDs, mainstream SiC |
| 8 | 200 | 725 µm | Analog, power, sensors, mature-node production |
| 12 | 300 | 775 µm | Advanced logic and memory, high-volume production |
4. Area grows with the square of the diameter
The number of chips per wafer scales with area, that is with the square of the diameter. A 300 mm wafer has 2.25 times the area of a 200 mm wafer, and a 200 mm wafer about 1.78 times that of a 150 mm wafer. The share of area lost at the rim also shrinks as the wafer grows, which is why high-volume manufacturing keeps moving to larger sizes.
For research labs this logic mostly does not apply. You typically need only a few small chips, so a large wafer just costs more and demands larger equipment.
5. Flats and notches
Every wafer carries a mark on its edge showing crystal orientation and, on smaller wafers, the doping type. Wafers up to 150 mm typically use a flat, a straight cut along part of the rim; 200 mm and 300 mm wafers typically use a notch, a small V-shaped groove, because it wastes less area.
If your alignment equipment locates the flat or notch automatically, make sure you choose the right type. Crystal orientation is covered in what a silicon wafer is.
6. Different materials, different common sizes
Silicon comes in every size, but other materials are limited by how hard it is to grow large single crystals:
- SiC — 4 inch and 6 inch are common; 8 inch is ramping up. Cost per area falls noticeably at larger sizes but remains far above silicon.
- GaAs — common at 4 inch and 6 inch.
- InP — mainly 2 inch to 4 inch; larger sizes remain limited and expensive.
- Sapphire — from 2 inch to 8 inch; 4 inch and 6 inch are typical for LEDs.
For compound-semiconductor research, smaller sizes are therefore often the practical choice, on both cost and availability. See also choosing wafers for research.
7. Which size for your lab?
- Start from the equipment. Chucks, cassettes, etch chambers and mask aligners accept only certain sizes. A wafer larger than the tool maximum cannot be used.
- Smaller pieces can run on a carrier. If your tool supports it, small pieces or wafers can sit on a carrier or adapter. The reverse is not possible.
- Need many small chips? Buying one larger wafer and cleaving or dicing it can be cheaper than buying many small wafers, especially for silicon.
- Do not pick a big size "just in case". Price per wafer climbs quickly with diameter, while experimental results do not improve if your tools cannot use the extra area.
8. Specifications to state when ordering
Size is only one line of the requirement. For an accurate quote, provide the full set below:
- Diameter (inch / mm), thickness and tolerance.
- Growth method (CZ or FZ) — see CZ vs FZ silicon wafer.
- Crystal orientation, dopant type and level, resistivity.
- Single-side (SSP) or double-side (DSP) polish, and grade Prime / Test / Dummy.
- Flat or notch, quantity and required delivery time.
How these factors affect price is analysed in silicon wafer pricing.
Frequently asked questions
How many mm is a 4-inch wafer?
A 4-inch wafer has a nominal diameter of 100 mm, slightly smaller than a true 4 inches (101.6 mm). Likewise 6 inch is 150 mm, 8 inch is 200 mm and 12 inch is 300 mm. Only 2 inch (50.8 mm) and 3 inch (76.2 mm) match true inch values closely.
Why is a 300 mm wafer thicker than a 200 mm wafer?
A wider wafer must bear more of its own weight, more handling force and more thermal stress. If it were as thin as a smaller wafer, it would warp, slip or break easily. Standard thickness therefore rises from 725 µm at 200 mm to 775 µm at 300 mm.
Can a 4-inch tool process a 6-inch wafer?
No. A wafer larger than the maximum size will not fit the chuck and cassette. The reverse works if the tool supports it: smaller pieces or wafers can sit on a carrier or adapter. Establish your tool's maximum size before choosing a wafer.
What wafer size should a research lab choose?
Pick the size that matches your equipment, commonly 4 inch or 6 inch for university and R&D labs. Do not choose larger than needed, since price per wafer climbs quickly with diameter. If you need many small chips, you can buy a larger wafer and cut it into pieces.
Need wafers in the right size for your equipment?
Tell us your tool's maximum size and your purpose, and Digifund's technical team will propose the diameter, thickness and specification set with a quote within 24 business hours. Digifund supports small R&D and teaching orders.
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