Corning 7980 UV-Grade Fused Silica Substrate with Low-Stress LPCVD Silicon Nitride (Si₃N₄) Thin Film

Overview

This product is a precision-engineered optical substrate consisting of Corning 7980 high-purity UV-grade fused silica, coated with a stoichiometric silicon nitride (Si₃N₄) thin film deposited via low-pressure chemical vapor deposition (LPCVD). Designed for demanding photonic, MEMS, and microfabrication applications, the substrate leverages the exceptional UV transmission (down to 185 nm), low thermal expansion coefficient (≈0.53 × 10⁻⁶ /°C), and high homogeneity of Corning 7980 HPFS. The Si₃N₄ film—grown using a proprietary low-stress LPCVD process—minimizes intrinsic compressive/tensile stress to mitigate thermally induced micro-cracking at the Si₃N₄/SiO₂ interface, a known failure mode arising from the significant mismatch in coefficients of thermal expansion (CTE) between Si₃N₄ (~2.5–3.2 × 10⁻⁶ /°C) and fused silica.

Key Features

• UV-Grade fused silica substrate (Corning 7980 HPFS) certified to ASTM F795 and MIL-O-13830B specifications for optical homogeneity and bubble/inclusion limits
• Double-sided, stoichiometric Si₃N₄ film deposited by LPCVD under controlled temperature (750–850 °C) and pressure (<1 Torr), ensuring high refractive index uniformity (n ≈ 2.00 ±0.02 @ 633 nm) and low extinction coefficient (k < 1×10⁻⁴)
• Tight thickness control: 1.3 µm ±5% across full aperture, verified by spectroscopic ellipsometry and cross-sectional TEM
• Surface flatness maintained at TTV <20 µm, enabling compatibility with lithographic alignment systems requiring sub-micron overlay registration
• CNC-ground edges and double-sided 60/40 polish compliant with ISO 10110-7 surface quality standards
• Clear aperture defined by a 2.0 mm exclusion zone from physical edge, minimizing edge-related stress concentrations and coating non-uniformity

Sample Compatibility & Compliance

The substrate is compatible with standard semiconductor processing tools—including plasma etchers (ICP/RIE), wet chemical stations (HF-based etchants, SC1/SC2 cleans), and vacuum metallization chambers. Its thermal stability supports rapid thermal processing (RTP) up to 900 °C without delamination or blistering. All batches undergo rigorous metrology verification per ISO/IEC 17025-accredited protocols, including spectral transmittance (200–2500 nm), stress mapping via wafer curvature analysis (Stoney equation), and FTIR verification of Si–N bond stoichiometry. Documentation includes material traceability certificates, CTE matching reports, and outgassing data compliant with NASA ASTM E595 for space-qualified optics.

Software & Data Management

While this is a passive optical component (not an instrument with embedded firmware), full metrological documentation is provided in standardized digital formats: CSV files for spectral transmission curves, PDF reports for surface inspection (with annotated interferograms), and XML metadata bundles containing lot-specific deposition parameters (temperature ramp profiles, gas flow ratios, chamber pressure logs). These datasets are structured to integrate into enterprise LIMS or MES platforms supporting ASTM E1382-compliant data exchange. Audit trails for calibration records and cleanroom environmental logs (temperature, humidity, particle counts) are retained for ≥10 years in accordance with GLP and ISO 9001:2015 requirements.

Applications

• Mask blanks and reticles for deep-UV (DUV) lithography systems operating at 193 nm and 248 nm wavelengths
• MEMS pressure sensor diaphragms requiring hermetic encapsulation and high Young’s modulus (Si₃N₄ ≈ 280 GPa)
• Passivation layers for GaN-based optoelectronic devices and high-electron-mobility transistors (HEMTs)
• Substrates for atomic layer deposition (ALD) seed layers and hard mask development in advanced node CMOS fabrication
• Reference standards in optical thin-film metrology labs for calibrating ellipsometers and spectrophotometers

FAQ

Is the Si₃N₄ film stoichiometric and what is its typical refractive index?
Yes—the LPCVD process targets near-stoichiometric Si₃N₄ (Si:N ≈ 3:4), confirmed by XPS and FTIR. Refractive index at 633 nm is typically 2.00 ±0.02, with variation <±0.005 across the clear aperture.

Can these wafers be used in high-vacuum or UHV environments?
Yes—outgassing tests per ASTM E595 show total mass loss (TML) <0.5% and collected volatile condensable materials (CVCM) <0.05%, meeting ESA ECSS-Q-ST-70-02C requirements for space hardware.

What is the maximum recommended thermal ramp rate during annealing?
To avoid interfacial cracking, thermal ramp rates exceeding 5 °C/min above 400 °C are not advised; isothermal holds at 700 °C for ≤30 min are validated for stress relaxation without film degradation.

Do you provide custom dimensions or alternative thicknesses?
Yes—custom diameters (up to Ø150 mm), thicknesses (0.3–2.0 mm), and Si₃N₄ thicknesses (0.5–5.0 µm) are available under NRE-supported engineering agreements, with lead times aligned to Corning’s substrate availability and LPCVD chamber scheduling.