Glass Wafers for Semiconductor & Optical Use: A Buying Guide
Glass wafers are thin, precisely polished discs used as substrates in MEMS, microfluidics, photolithography, and optical devices — anywhere a process needs the optical clarity, electrical insulation, or chemical stability that silicon alone can't provide.
Key Specifications at a Glance
| Parameter | Typical Value |
|---|---|
| Common materials | Fused silica/quartz, borosilicate, aluminosilicate, soda-lime |
| Diameter | 50 mm–300 mm (2-inch to 12-inch equivalents) |
| Thickness | 0.1 mm–3 mm |
| Polish | Single-side polished (SSP) or double-side polished (DSP) |
| Surface roughness | Ra < 1 nm (optical/bonding grade) |
| Coating options | AR, ITO, metallic mirror, custom |
Choosing a Material
- Fused silica / quartz — the widest optical transmission range (UV through IR) and lowest thermal expansion; the best choice for photolithography, spectroscopy, and high-temperature MEMS processing
- Borosilicate (e.g., Borofloat, Pyrex-type) — good visible-range transmission and moderate thermal resistance at a lower cost than fused silica; common in general MEMS and microfluidics
- Aluminosilicate — higher strength and chemical durability, often used where mechanical robustness matters as much as optical performance
- Soda-lime — the lowest-cost option, suitable when neither UV transmission nor extreme thermal stability is required
Why Glass Instead of Silicon
Glass is transparent where silicon isn't, which matters directly for optical devices and indirectly for many MEMS and microfluidic designs that need to observe a process visually. Glass is also an excellent electrical insulator, with resistivity many orders of magnitude higher than silicon, making it useful as an isolation layer or dielectric carrier. The trade-off is thermal conductivity — glass conducts heat far more slowly than silicon, so thermal design needs extra attention in any wafer assembly that includes heaters or high-power components.
Applications
- Photolithography and semiconductor process substrates
- MEMS and microfluidic device fabrication
- Anodic bonding to silicon wafers
- Optical windows, test flats, and coating substrates
Buying Tips
Match the CTE (coefficient of thermal expansion) of the glass to whatever it will be bonded to — a mismatch between glass and silicon during anodic bonding or thermal cycling is a common source of delamination or cracking. For optical or lithography use, also confirm the transmission range and OH content of the specific fused silica grade (JGS1/JGS2/JGS3 or equivalent), since that determines UV and IR performance.
