How is Thermal Oxide Deposited onto Silicon Wafers?
Question: Are the thermal oxides on silicon substrates? Also, what is the difference between wet and dry thermal oxides?
Answser: Wet Thermal Oxide uses steam and Dry Thermal Oxide using Oxygen.
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Dry oxide ≈10–300 nm · Wet oxide ≈0.12–20 µm · One-side growth options · Fast worldwide shipping.
By default Wet and Dry Thermal Oxidation is grown on both sides of the wafer. But if you need to grow oxide on just one side, usually the polished side, then dry oxide is an option. Dry oxididation is also the only option if you need very thin oxide layer. Dry thermal oxide is more expensive because the method uses molecular oxygen instead of pure steam to create the oxide layer.
Wet Thermal Oxide wet oxidation on silicon uses wafer vapor that grows on the silicon surface. Wet oxide layer thickness range from 0.12 to 2.4µm, or even up to 20µm in some cases!
Dry Thermal Oxide, dry oxidation is grown in the absence of wafer vapor, this yields a more dense Oxide layer but only layers from 10 to 300nm are practical. The Oxide layer is a thermally grown SiO2 layer, grown by actually oxidizing the Silicon atoms on the Silicon wafer surface. Chlorinated DRY Thermal Oxide is grown with the exclusion of wafer and any hydrocarbon contaminants. It is the ultimate electrical insulator. 10 to 300nm is possible.
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Video: Wet Vs. Dry Oxidation Process Explained
What is the Refractive Index of Wet and Dry Oxide?
Refractive index of WET and DRY Thermal Oxide are not measurably different.
Leakage current is less and dielectric strength is higher for DRY than for WET Thermal Oxide.
At very low thicknesses, less than 100nm, DRY Oxide thickness can be controlled more precisely because it grows slower than WET Thermal Oxide.
Wet Thermal Oxide vs. Dry Thermal Oxide
Thermal oxidation is one of the most important processes used during semiconductor fabrication. By growing a layer of silicon dioxide (SiO2) directly from the silicon surface, researchers obtain an extremely dense, uniform dielectric that offers superior electrical insulation compared to deposited oxide films.
The two primary oxidation methods are wet thermal oxidation and dry thermal oxidation. Although both produce high-quality silicon dioxide, they differ significantly in growth rate, achievable thickness, electrical performance, and ideal applications.
Wet vs Dry Thermal Oxide Comparison
| Property | Wet Thermal Oxide | Dry Thermal Oxide |
|---|---|---|
| Oxidizing Gas | Steam (H₂O) | Oxygen (O₂) |
| Typical Thickness | 0.12–20 µm | 10–300 nm |
| Growth Rate | Fast | Slow |
| Film Density | Very High | Highest |
| Electrical Quality | Excellent | Superior |
| Leakage Current | Low | Lowest |
| Typical Applications | Isolation, MEMS, SOI, CMP | Gate oxide, MOSFETs, CMOS |
When Should Wet Thermal Oxide Be Used?
Wet thermal oxidation uses water vapor during oxidation, allowing silicon dioxide to grow several times faster than dry oxidation. This makes it the preferred process whenever thick oxide layers are required.
Researchers commonly specify wet oxide for:
- Electrical isolation layers
- SOI wafers
- MEMS fabrication
- Optical waveguides
- Microfluidic devices
- CMP pad conditioning wafers
- Protective dielectric coatings
UniversityWafer supplies wet thermal oxide layers from approximately 0.12 µm up to 20 µm, making them suitable for both standard semiconductor processing and specialty research applications.
Why Choose Dry Thermal Oxide?
Dry thermal oxidation grows silicon dioxide using pure oxygen instead of steam. Because oxidation occurs much more slowly, the resulting oxide is denser, smoother, and exhibits lower interface defect density.
Dry oxide is typically selected when researchers require:
- Ultra-thin gate dielectrics
- High dielectric strength
- Minimal electrical leakage
- Excellent thickness uniformity
- High-performance MOS devices
- CMOS and integrated circuit fabrication
For oxide layers below approximately 100 nm, dry oxidation provides significantly better thickness control than wet oxidation.
Thermal Oxide vs Deposited Oxide
Unlike PECVD, sputtered oxide, or electron beam deposited films, thermal oxide is created by consuming silicon from the wafer itself. This produces an interface with exceptional uniformity, low defect density, and excellent adhesion.
Because of these properties, thermally grown SiO2 remains the industry standard dielectric for:
- MOSFET gate oxides
- CMOS integrated circuits
- Power devices
- MEMS sensors
- Silicon photonics
Single-Side Dry Thermal Oxide
Dry thermal oxidation can also be performed on only one side of the wafer when required. Single-side oxide is frequently specified for microfabrication processes where the backside must remain bare for bonding, backside metallization, or subsequent wafer processing.
Typical Dry Thermal Oxide Specifications
| Parameter | Typical Specification |
|---|---|
| Wafer Diameter | 100 mm (4") |
| Orientation | (100) |
| Dopant | Boron, P-Type |
| Resistivity | 1–10 Ω·cm |
| Oxide Thickness | 200 ±14 nm Dry Thermal Oxide |
| TTV | <10 µm |
| Bow / Warp | <40 µm |
| Surface Finish | Single-Side Polished |
Research Applications
UniversityWafer thermal oxide wafers have been used in research involving phase-shift lithography, MEMS devices, silicon photonics, CMOS development, dielectric isolation, optical waveguides, and advanced microfabrication processes.
If your project requires a specific oxide thickness, wafer diameter, orientation, resistivity, or polishing configuration, simply send us your specifications and quantity for a fast quotation.