Silicon Nitride (SiNₓ) Coated Wafers
Silicon nitride (SiNₓ) is one of the most reliable and versatile dielectric coatings used in semiconductor, MEMS, photovoltaic, and photonic fabrication. It provides outstanding electrical isolation, chemical resistance, and mechanical stability, making it an essential material for modern microdevices.
Popularity of SiNₓ Wafers
In semiconductor manufacturing, SiNₓ serves as a dielectric, passivation, and masking layer with applications that extend from transistor fabrication to integrated optical circuits. Its ability to be deposited by LPCVD and PECVD allows engineers to balance density, stress, and temperature limits according to the process requirements. LPCVD provides high-purity, stoichiometric films for high-temperature flows, while PECVD enables low-temperature deposition compatible with backend metallization and delicate substrates.
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LPCVD Silicon Nitride — Characteristics & Benefits
The Low-Pressure Chemical Vapor Deposition (LPCVD) process yields the most conformal and dense SiNₓ films. Using dichlorosilane (SiH₂Cl₂) and ammonia at 700–850 °C, LPCVD nitride forms a nearly stoichiometric Si₃N₄ layer with exceptional breakdown voltage, chemical resistance, and thermal stability. These films exhibit high tensile strength, making them suitable for use as membranes, masks, and mechanical support layers.
- Excellent conformity over complex wafer topography and deep trenches.
- High film density with low hydrogen content.
- Breakdown field above 8 MV/cm; dielectric constant ~7.5.
- Ideal for oxidation barriers, DRIE masks, and structural MEMS elements.
- Available as single- or double-side coatings with low TTV and high uniformity.
Because LPCVD requires high deposition temperatures, it is best suited for front-end processes and bare silicon substrates rather than post-metallization layers. It remains the preferred choice wherever mechanical robustness and purity are critical.
PECVD Silicon Nitride — Flexible and Low-Temperature
The Plasma-Enhanced Chemical Vapor Deposition (PECVD) technique operates below 350 °C and uses silane (SiH₄) with ammonia or nitrogen plasma to form a hydrogen-rich SiNₓ film. PECVD nitride offers tunable stress (compressive or tensile), adjustable refractive index, and excellent film reproducibility. It is the coating of choice for photonic, optical, and back-end semiconductor processes.
- Compatible with temperature-sensitive wafers and post-CMOS steps.
- Stress control between −300 MPa (compressive) and +300 MPa (tensile).
- Typical refractive index 1.9–2.1 @ 633 nm, tunable via gas ratios.
- Excellent step coverage and optical transparency for 400–1600 nm.
- High throughput and lower process cost compared to LPCVD.
PECVD SiNₓ is widely used in LEDs, solar ARC coatings, and integrated waveguides, where precise optical constants and controlled film stress are essential. The process also enables dual-side coatings for sensors and optical cavities.
Comparing LPCVD vs PECVD Silicon Nitride
Both deposition types produce high-quality SiNₓ, but their differences allow each to serve unique roles:
| Property | LPCVD SiNₓ | PECVD SiNₓ |
|---|---|---|
| Deposition Temp. | 700–850 °C | ≤ 350 °C |
| Film Density | High, low-H | Medium, H-rich |
| Stress Range | Tensile (400–900 MPa) | −300 to +300 MPa tunable |
| Uniformity | ± 3 % | ± 5 % |
| Main Uses | MEMS, masks, oxidation barrier | Passivation, photonics, solar |
Key Applications of SiNₓ Films
- Microelectronics: Passivation, interlevel dielectric, and diffusion masking.
- MEMS: Mechanical membranes, etch stops, and high-strength windows.
- Photonics: SiNₓ waveguides and resonators with n≈2.0 for visible–IR light.
- Solar Energy: Anti-reflective and surface-passivating layers for high-efficiency cells.
- Biotech: Biocompatible dielectric coatings for implantable and analytical microsystems.
Why Choose UniversityWafer?
We deliver ready-to-ship and custom-coated SiNₓ wafers with precise control of film thickness, refractive index, and stress. Clients may request data sheets with ellipsometry, thickness mapping, and defect inspection. Our coatings are compatible with Si, SOI, GaAs, Quartz, and Sapphire substrates.
Silicon Nitride (SiNₓ) Films on Silicon
Silicon nitride is one of the most widely used dielectric materials in semiconductor, MEMS, and photonics manufacturing. Deposited using LPCVD or PECVD methods, SiNₓ provides exceptional chemical durability, mechanical strength, and dielectric reliability. UniversityWafer supplies wafers with single- or double-sided SiNₓ coatings, with custom options for thickness, refractive index, and film stress.
Deposition Methods
The properties of silicon nitride depend heavily on the chosen deposition process and gas chemistry.
- LPCVD Silicon Nitride: Deposited at 700–850 °C from dichlorosilane (SiH₂Cl₂) and ammonia. Produces dense, stoichiometric Si₃N₄ films with low hydrogen content and excellent uniformity. Ideal for hard masks, MEMS structures, and oxidation barriers.
- PECVD Silicon Nitride: Deposited below 350 °C using silane (SiH₄) and ammonia or nitrogen plasma. Enables stress-tuned and index-adjustable films for photonic and back-end device applications. Useful for coatings over metals or temperature-sensitive layers.
Material Characteristics
- Mechanical Strength: High hardness and Young’s modulus (>250 GPa); excellent for membranes and windows.
- Thermal Stability: LPCVD films withstand repeated 1000 °C oxidations; PECVD versions suitable up to 400 °C.
- Electrical Properties: Dielectric constant ~7.5; breakdown field 8–10 MV/cm; leakage current <10⁻⁹ A/cm².
- Chemical Resistance: Stable against most acids and oxidizers; etchable in hot phosphoric acid or CF₄/O₂ plasma.
- Optical Transparency: Transmits from visible to near-IR; absorption edge ≈ 300 nm.
Controlling Stress and Refractive Index
Silicon nitride stress can be tuned from compressive to tensile by adjusting precursor ratios and plasma power. Typical low-stress PECVD films are near ±100 MPa, while tensile LPCVD nitride can exceed 900 MPa for mechanical stability in MEMS membranes. Refractive index (n) values between 1.9 – 2.1 correspond to stoichiometry control:
- Si-rich: Higher n (~2.1), lower stress, slightly higher absorption.
- N-rich: Lower n (~1.9), transparent, excellent barrier properties.
These parameters determine film suitability for waveguides, AR coatings, or passivation layers. UniversityWafer can reproduce process conditions from prior foundry data or academic publications for matching performance.
Applications
- Microelectronics: Isolation, gate spacers, and dielectric masks for ion implantation or etching.
- MEMS Devices: Structural layers, suspended membranes, and mechanical bridges for sensors and actuators.
- Photonics: SiN-on-SiO₂ waveguides, low-loss optical resonators, and integrated optical filters.
- Solar & Photovoltaics: Anti-reflective (ARC) and surface-passivating layers to boost conversion efficiency.
- Packaging & Reliability: Moisture and alkali barrier over die surfaces and interconnects.
- Biomedical & Sensor Systems: Chemically stable, biocompatible coating for implantable MEMS and biochips.
Etching and Patterning
SiNₓ can be selectively etched using hot H₃PO₄ (wet) or CF₄/O₂ plasma (dry). Etch rate, anisotropy, and selectivity depend on stoichiometry and film density. LPCVD nitride offers high selectivity vs. SiO₂, while PECVD nitride’s hydrogen content allows smoother removal for patterning. Photolithography and lift-off processes can define openings for MEMS windows, through-wafer membranes, or optical couplers.
Integration & Multilayer Stacks
UniversityWafer provides SiNₓ/SiO₂ multilayers for waveguides, SiNₓ over metals for dielectric isolation, and SiNₓ/SiNₓ:SiO₂ composites for refractive-index engineering. We can match oxide/nitride pairs for quarter-wave thickness, or provide graded index profiles for photonic mode control. Double-sided deposition and wafer bonding are also supported for specialty MEMS designs.
Example Use Cases
- Optical Resonators: 400 nm PECVD SiNₓ on SiO₂ for low-loss photonics.
- MEMS Pressure Sensor: 1 µm LPCVD nitride membrane, tensile >700 MPa, uniform within ±3%.
- Passivation Stack: 100 nm PECVD SiNₓ + 300 nm SiO₂ for CMOS-compatible overcoats.
- Solar ARC Layer: 75 nm SiNₓ (n≈2.05) deposited on p-Si ⟨100⟩ to maximize light trapping.
Typical Specifications
- Thickness Range: 50 nm – 5 µm (± tolerance <5 %)
- Uniformity: ≤ ±3 % (LPCVD), ≤ ±5 % (PECVD)
- Stress Range: −300 MPa (compressive) to +900 MPa (tensile)
- Index: 1.90 – 2.10 (at 632 nm / 1550 nm)
- Substrates: Si ⟨100⟩ / ⟨111⟩, 2″–12″, SSP/DSP, low TTV/warp
- Etch Rate: ~10 nm/min in 85% H₃PO₄ @ 180 °C (for LPCVD films)
Ordering & Quotes
To request a quote, include the following: wafer diameter, orientation, nitride thickness, refractive index target, film stress, and deposition type (LPCVD or PECVD). Custom multi-layer, double-side, or low-particle options are available for cleanroom and R&D use.