Thermal Oxide for Optical Coating Application
A thin film PVD and etch engineer requested a quote for the following.
We need 100mm P(100) SSP Silicon Wafers with 1 micron of thermal oxide. They will be used for optical coatings application.
Reference #111562 for specs and quantity.
Optimize your optical components with advanced thin-film coatings precisely matched to your wavelength and substrate.
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Thermal Oxide on Silicon Wafer Thickness That Works Best for Optical Coating Applications
Optimal Thermal Oxide Thickness for Optical Coatings
1. Anti-Reflective (AR) Coatings
To minimize reflection at a particular wavelength, the oxide thickness should be λ/4n, where λ is the target wavelength, and n is the refractive index of SiO₂ (~1.46).
- For visible light (~550 nm): 90–120 nm
2. Optical Interference Coatings (Photolithography)
For photolithography tools operating in the UV range:
| Wavelength | Optimal SiO₂ Thickness |
|---|---|
| i-line (365 nm) | 63 nm or 126 nm |
| DUV (248 nm) | 42 nm or 84 nm |
| EUV (13.5 nm) | <10 nm |
3. High-Reflectivity Applications
For high reflectivity in IR applications, a thicker oxide (200–300 nm) is recommended.
4. Silicon Wafer Inspection & Metrology
To increase contrast under an optical microscope, the optimal thermal oxide thickness is:
- 270 nm
- 450 nm
- 600 nm
Key Takeaways
- For anti-reflection: 90–120 nm (visible light)
- For photolithography: 42–126 nm (depending on UV wavelength)
- For high contrast: 270–600 nm
- For IR reflectivity: 200–300 nm
Thick Float Zone Silicon Wafers for Optical Coatings
An optical coatings engineer requested a quote for the following.
We need 2" or 3" Float Zone Silicon Wafers for Optical Coatings deposition.
Reference #118922 for specs and pricing.
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Lithium Niobate Wafers for Optical Coating Applications
An optical coating researcher requested a quote for the following.
We are depositing optical coatings on PPLN(MgO-LiNbO3) for a customer and need 1" diameter witnesses for the spectral measurements. Resisitivity, Dopant and type do not matter. The index of refraction of the crystal that we coat is 2.14 and 2.22. In the coating world, the two axes are just about equal, so I can ignore orientation. I can core drill any size wafer into the 1" diameter that I need. For handling purposes, 1mm thick is nice but I can use as thin as 0.5mm. I only need one side polished but can still use it if both sides are polished.
UniversityWafer, Inc. Quoted:
- LiNbO3 Wafer
- 3", 500um thick, SSP, Y-128 cut, SAW Grade
- Quantity: 5-10 Pieces
Reference #180890 for specs and quantity.
Graphene Substrate Used for Optical Coatings
An optical engineer researching space electronics requested a quote for the following.
We are primarily working with optical coatings and graphene, so we are completely satisfied with transparent wafers and Si-wafers with a ~900 Å SiO2 layer which creates and interference enhancement making single layers of graphene easily detectable.
Reference #32097 for specs and quantity.
What are Optical Coatings and How are They Used to Fabricate Seminconductors?
Optical Coatings in Semiconductor Fabrication
Optical coatings are thin layers of material applied to optical components, such as lenses, mirrors, and wafers, to manipulate light in a controlled manner. These coatings serve several key functions in semiconductor fabrication, particularly in photolithography and thin-film deposition processes.
Types of Optical Coatings in Semiconductor Fabrication
Anti-Reflective Coatings (AR Coatings)
Purpose: Reduce reflections from surfaces, improving light transmission and minimizing loss.
Application: Used on photomask substrates and wafers in photolithography to enhance pattern resolution and reduce standing wave effects.
High-Reflectivity (HR) Coatings
Purpose: Maximize reflection of specific wavelengths.
Application: Found in laser optics for semiconductor metrology, laser annealing, and wafer inspection tools.
Dielectric Coatings (Interference Coatings)
Purpose: Enhance specific wavelengths' reflection or transmission by using multiple thin layers with varying refractive indices.
Application: Used in filters for UV, deep-UV, and extreme-UV (EUV) lithography.
Photoresist Coatings
Purpose: Photosensitive layers that enable precise patterning of semiconductor features.
Application: Essential in photolithography for defining circuit elements before etching or deposition.
Protective Coatings
Purpose: Protect wafers from contamination, oxidation, or mechanical damage.
Application: Includes materials like SiO₂ and Si₃N₄ for passivation layers.
Optical Thin-Film Deposition
Purpose: Used for semiconductor doping, reflective coatings, or anti-reflection coatings in advanced microfabrication.
Application: Common techniques include sputtering, atomic layer deposition (ALD), and chemical vapor deposition (CVD).
Applications in Semiconductor Fabrication
- Photolithography: Optical coatings enhance the resolution and fidelity of patterns transferred onto wafers.
- Wafer Metrology and Inspection: High-reflectivity and anti-reflective coatings improve the accuracy of optical inspection tools.
- Laser Processing: Coatings optimize laser-based wafer cutting, drilling, and annealing.
- Thin-Film Transistors (TFTs): Used in the production of display panels, where optical coatings ensure precise light modulation.
Deposition Techniques and Materials for Optical Coatings in Semiconductor Fabrication
Optical coatings in semiconductor fabrication are deposited using advanced thin-film deposition techniques, each with specific advantages based on the required film thickness, uniformity, and optical properties. Below are the key deposition techniques and materials commonly used:
1. Deposition Techniques
A. Physical Vapor Deposition (PVD)
1.1. Thermal and Electron Beam (E-Beam) Evaporation
Process:
- Material is heated in a vacuum chamber until it evaporates.
- Vapor condenses onto the wafer surface.
- E-beam evaporation provides better control for high-refractive-index materials.
Common Materials:
- SiO₂ (Silicon Dioxide) – Anti-reflective coatings, passivation layers.
- TiO₂ (Titanium Dioxide) – High-refractive-index layer in dielectric stacks.
- Al₂O₃ (Aluminum Oxide) – Protective coatings, passivation.
1.2. Sputtering
Process:
- High-energy plasma bombards a target material, ejecting atoms that coat the wafer.
- Provides excellent film density and uniformity.
Common Materials:
- Si₃N₄ (Silicon Nitride) – Passivation, optical waveguides.
- Ta₂O₅ (Tantalum Pentoxide) – High-index optical coatings for photonic applications.
- ZrO₂ (Zirconium Dioxide) – Low-loss dielectric coatings.
B. Chemical Vapor Deposition (CVD)
2.1. Plasma-Enhanced Chemical Vapor Deposition (PECVD)
Process:
- Uses a plasma to enhance reactions, allowing deposition at lower temperatures.
Common Materials:
- SiO₂ – Anti-reflective and protective coatings.
- Si₃N₄ – Waveguides, passivation layers.
- HfO₂ (Hafnium Dioxide) – High-k optical and dielectric coatings.
2.2. Atomic Layer Deposition (ALD)
Process:
- Alternating exposure of precursor gases enables ultra-thin, conformal coatings with atomic-scale precision.
Common Materials:
- Al₂O₃ – Barrier coatings, anti-reflection layers.
- HfO₂ – High-refractive-index dielectric layers.
- ZnO (Zinc Oxide) – Transparent conductive coatings.
C. Sol-Gel Deposition
Process:
- Solution-based deposition followed by thermal treatment.
- Used for producing porous or nanostructured optical coatings.
Common Materials:
- SiO₂ – Anti-reflection coatings with controlled porosity.
- TiO₂ – Optical waveguides, high-index layers.
2. Applications of Optical Coatings in Semiconductor Devices
| Application | Coating Material | Deposition Method |
|---|---|---|
| Photolithography Masks | SiO₂, MoSi (Molybdenum-Silicon) | PECVD, Sputtering |
| Passivation Layers | Si₃N₄, Al₂O₃ | PECVD, ALD |
| Waveguides in Integrated Photonics | Si₃N₄, TiO₂ | PECVD, Sputtering |
| Anti-Reflective Coatings | SiO₂, Ta₂O₅, HfO₂ | PECVD, ALD |
| UV and EUV Optics | ZrO₂, HfO₂, SiO₂ | ALD, Sputtering |
| Reflective Mirrors (Laser Processing) | Al, Ag, Mo/Si Multilayers | E-Beam Evaporation, Sputtering |
Choosing the Right Deposition Technique
- For ultra-thin conformal coatings → Use ALD.
- For high-volume, high-uniformity coatings → Use PECVD or sputtering.
- For highly transparent and low-loss coatings → Use E-Beam Evaporation.
- For specialty optical coatings with nano-structured layers → Use Sol-Gel.
Recommended Optical Coatings for Specific Semiconductor Applications
Optical coatings play a critical role in advanced semiconductor fabrication, particularly for photonic devices, extreme ultraviolet (EUV) lithography, and integrated optics. Below are tailored recommendations for specific applications.
1. Photonic Devices (Integrated Photonics, Optical MEMS)
Key Requirements
- Low optical loss for waveguides.
- High refractive index contrast for light confinement.
- Thermal stability for high-power applications.
Recommended Coatings and Deposition Methods
| Application | Material | Deposition Method | Purpose |
|---|---|---|---|
| Optical Waveguides | Si₃N₄, TiO₂ | PECVD, Sputtering | High-refractive-index contrast |
| Cladding Layers | SiO₂, Al₂O₃ | PECVD, ALD | Optical confinement |
| High-Reflectivity (HR) Mirrors | HfO₂, Ta₂O₅ | ALD, Sputtering | Enhanced reflection |
| Anti-Reflection (AR) Coatings | SiO₂, MgF₂ | E-Beam Evaporation | Reduced reflection losses |
Additional Considerations
- Si₃N₄ is preferred for waveguides due to its high refractive index (~2.0) and low optical loss.
- Al₂O₃ cladding improves thermal stability in high-power photonics.
- TiO₂ coatings provide excellent light confinement with minimal propagation losses.
2. EUV lithography (wavelength ~13.5 nm) requires highly reflective multilayer coatings to maximize light efficiency.
Key Requirements
- High reflectivity (~70%) at 13.5 nm wavelength.
- Stable against oxidation and contamination.
- Precise thickness control (<1 nm precision).
Recommended Coatings and Deposition Methods
| Application | Material | Deposition Method | Purpose |
|---|---|---|---|
| EUV Reflective Mirrors | Mo/Si Multilayers | Sputtering | High-reflectivity stacks |
| Protective Capping Layer | Ru, B₄C | ALD, Sputtering | Prevents oxidation |
| EUV Photomasks | Ta-Based Absorbers | Sputtering | Pattern definition |
| Low-Defect Optical Coatings | SiO₂, ZrO₂ | ALD | Defect-free thin films |
Additional Considerations
- Mo/Si multilayer coatings are tuned to optimize EUV reflectivity at specific incident angles.
- Ruthenium (Ru) coatings protect against oxidation and contamination.
- ALD ensures atomic-scale precision, reducing phase errors in lithography.
3. Laser-Based Semiconductor Processing
Lasers are used in wafer dicing, annealing, and metrology, requiring coatings optimized for different wavelengths.
Key Requirements
- High reflectivity at laser wavelengths (UV, IR).
- Thermal stability under high-power exposure.
- Minimized scattering and absorption losses.
Recommended Coatings and Deposition Methods
| Application | Material | Deposition Method | Purpose |
|---|---|---|---|
| High-Power Laser Mirrors | Ta₂O₅, HfO₂ | ALD, Sputtering | High-reflectivity coatings |
| UV Lithography Optics | SiO₂, MgF₂ | E-Beam Evaporation | Anti-reflection coatings |
| IR Laser Processing Lenses | ZnSe, SiO₂ | PECVD | Infrared transmission coatings |
| Protective Coatings for Lasers | Al₂O₃, Si₃N₄ | ALD | Scratch-resistant layers |
Additional Considerations
- Hafnia (HfO₂) and Tantalum Oxide (Ta₂O₅) multilayers offer high reflectivity for laser mirrors.
- SiO₂ and MgF₂ coatings are used to minimize losses in 193 nm and 248 nm lithography.
- ZnSe coatings are ideal for CO₂ laser optics (10.6 µm wavelength).
4. Metrology and Wafer Inspection
High-precision optical coatings enhance semiconductor inspection tools, such as ellipsometers, interferometers, and wafer alignment systems.
Key Requirements
- High optical clarity and low absorption.
- Uniform coatings for consistent measurements.
- Stable refractive index over time.
Recommended Coatings and Deposition Methods
| Application | Material | Deposition Method | Purpose |
|---|---|---|---|
| Wafer Inspection Optics | SiO₂, ZrO₂ | ALD, Sputtering | High-transmission layers |
| Ellipsometry Reference Coatings | Al₂O₃, Si₃N₄ | PECVD, ALD | Stable refractive index |
| Interferometry Mirrors | HfO₂, Ta₂O₅ | ALD, Sputtering | Precise phase control |
| Optical Filters | SiO₂/TiO₂ Multilayers | E-Beam Evaporation | Wavelength-selective coatings |
Additional Considerations
- Ellipsometry coatings require precise refractive index control to improve measurement accuracy.
- SiO₂/TiO₂ multilayers are used in narrowband optical filters for semiconductor diagnostics.
- ALD ensures smooth, defect-free coatings, reducing noise in optical metrology systems.
Conclusion
- Choosing the right optical coating depends on:
- Wavelength range (EUV, UV, visible, IR).
- Required reflectivity/transmission properties.
- Thermal and chemical stability in the semiconductor process.
For EUV lithography, Mo/Si multilayers with Ru protection are the standard. For integrated photonics, Si₃N₄ and TiO₂ waveguide coatings provide excellent performance. For laser processing and metrology, high-reflectivity multilayers (HfO₂, Ta₂O₅) ensure precision.
Would you like recommendations for a specific material supplier or process parameters for deposition?