Substrates Used for Optical Coatings

university wafer substrates

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.

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Thermal Oxide on Silicon Wafer Thicknes 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.

Reference #118922 for specs and pricing.

 

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

  1. 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.

  2. High-Reflectivity (HR) Coatings

    • Purpose: Maximize reflection of specific wavelengths.
    • Application: Found in laser optics for semiconductor metrology, laser annealing, and wafer inspection tools.

  3. 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.

  4. Photoresist Coatings

    • Purpose: Photosensitive layers that enable precise patterning of semiconductor features.
    • Application: Essential in photolithography for defining circuit elements before etching or deposition.

  5. Protective Coatings

    • Purpose: Protect wafers from contamination, oxidation, or mechanical damage.
    • Application: Includes materials like SiO₂ and Si₃N₄ for passivation layers.

  6. 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.

Would you like details on specific deposition techniques or materials used for a particular semiconductor application?

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)

PVD methods are widely used for depositing dielectric, metallic, and optical coatings with high precision.

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)

CVD methods enable the deposition of high-quality optical coatings with precise thickness control.

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)

Photonic devices rely on precise optical coatings to guide, reflect, or transmit light efficiently.

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. Extreme Ultraviolet (EUV) Lithography

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:

  1. Wavelength range (EUV, UV, visible, IR).
  2. Required reflectivity/transmission properties.
  3. 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?