High Resistivity / Float Zone (FZ) Wafers
Float Zone (FZ) silicon wafers with ultra-high resistivity (>10 kΩ·cm) and extreme purity — oxygen and carbon content below 5×10¹⁵ atoms/cm³. The preferred substrate for RFICs, silicon photonics, high-voltage power devices, and radiation detectors. No Czochralski-induced oxygen precipitates or bulk micro-defects.
What is Float Zone (FZ) Silicon?
Float Zone (FZ) silicon is produced by a crucible-free crystal growth method in which a radio-frequency (RF) coil traverses a polycrystalline silicon rod, melting a narrow zone that recrystallizes into a single crystal as the coil moves. Because the molten silicon never contacts a crucible — unlike the Czochralski (CZ) process where silicon melts inside a quartz crucible — FZ silicon is essentially free of the oxygen and carbon contamination that is unavoidable in CZ material. This purity translates into extraordinary electrical properties: resistivity exceeding 30 kΩ·cm, minority carrier lifetimes above 1 millisecond, and the complete absence of oxygen precipitates.
While CZ silicon dominates the global wafer market (~95% of all silicon wafers) due to its cost-effectiveness at 300mm and its ability to incorporate beneficial oxygen for internal gettering, FZ silicon is irreplaceable for applications where substrate loss, carrier recombination, and impurity-driven leakage currents are the primary performance limiters. The RF front-end of every 5G smartphone, the optical transceivers in every data center, and the particle detectors at CERN all depend on FZ silicon's unique combination of ultra-high resistivity and ultra-low impurity content.
At GINECHIP, we supply FZ silicon wafers in diameters from 100mm to 200mm with resistivity from 10 kΩ·cm to > 30 kΩ·cm. Both N-type (phosphorus-doped, including NTD) and P-type (boron-doped) are available. We also offer FZ wafers as handle substrates for custom SOI fabrication and as starting material for GaN-on-Si epitaxy where the substrate's mechanical integrity at MOCVD temperatures is critical.
FZ vs CZ Silicon: A Detailed Comparison
The choice between FZ and CZ silicon is not a matter of "better" or "worse" — it is application-driven. The table below provides a head-to-head technical comparison to help you determine which substrate technology is optimal for your process requirements.
| Parameter | Float Zone (FZ) | Czochralski (CZ) |
|---|---|---|
| Crystal Growth Method | RF-heated traveling molten zone through polysilicon rod. No crucible needed — zero contact with foreign materials. | Polysilicon melted in quartz (SiO₂) crucible. Seed crystal pulled slowly from the melt while rotating. Crucible dissolution inevitable. |
| Oxygen Concentration | < 5×10¹⁵ atoms/cm³ — effectively oxygen-free silicon | 5–20×10¹⁷ atoms/cm³ — dissolved from quartz crucible walls during growth |
| Carbon Concentration | < 5×10¹⁵ atoms/cm³ — no contact with hot graphite furnace components | 1×10¹⁶ – 5×10¹⁷ atoms/cm³ — from graphite susceptor and heater elements |
| Maximum Resistivity | > 30 kΩ·cm — near-intrinsic silicon achievable (undoped FZ) | ~1–3 kΩ·cm — limited by background doping from crucible dissolution and ambient contamination |
| Minority Carrier Lifetime | > 1 ms — no recombination centers from oxygen precipitates or heavy-metal-decorated defects | 10–100 μs — oxygen precipitates and associated dislocation loops act as recombination-generation centers |
| Oxygen Precipitates | None — no dissolved oxygen means no precipitation is possible. No internal gettering capability. | Abundant — intentionally engineered through thermal cycling to create internal gettering zones for metal contaminants |
| Mechanical Strength at High Temperature | Superior — oxygen-free silicon exhibits higher yield strength above 800°C. Preferred for GaN MOCVD epitaxy. | Lower — dissolved oxygen pins dislocations at low temperature but provides less strengthening above 800°C |
| Maximum Wafer Diameter | 200mm (8″) — limited by melt-zone stability. 300mm FZ in R&D stage only. | 300mm (12″) — standard high-volume production. 450mm pilot line demonstrated. |
| Relative Cost | $$ – $$$$ — premium substrate, lower throughput, smaller ingot diameters | $ — commodity material, extremely high volume, fully automated 300mm fabs |
| Primary Applications | RF/mmWave ICs, silicon photonics, high-voltage power (> 3.3 kV), radiation detectors, THz components, GaN-on-Si epitaxy | CMOS logic, DRAM, NAND flash, image sensors, general-purpose analog/mixed-signal ICs |
Neutron Transmutation Doping (NTD)
For applications requiring the most precise doping uniformity achievable, GINECHIP offers Neutron Transmutation Doped (NTD) FZ silicon. In this process, an undoped FZ silicon ingot is irradiated with thermal neutrons in a nuclear reactor. A fraction of the ³⁰Si isotopes (3.1% natural abundance) capture a neutron and transmute into ³¹P (phosphorus) — a donor atom — via the reaction:
³⁰Si (n,γ) → ³¹Si → ³¹P + β⁻ (t₁/₂ = 2.62 hours)
Because the neutron flux is uniform throughout the ingot volume, the resulting phosphorus doping concentration is uniform to within ±3% across the entire crystal — dramatically better than the ±15–25% typical of conventional melt-doping methods. This uniformity is critical for high-voltage power devices where the breakdown voltage depends sensitively on the doping concentration in the drift region.
Technical Specifications
| Parameter | Available Range / Values |
|---|---|
| Crystal Growth Method | Float Zone (FZ) — crucible-free, RF-heated molten zone |
| Wafer Diameter | 100mm (4″), 150mm (6″), 200mm (8″) |
| Resistivity Range | > 10 kΩ·cm (standard), up to > 30 kΩ·cm (premium) — P-type / N-type |
| Dopant Type | P-type (Boron), N-type (Phosphorus); NTD-Phosphorus for ultra-uniform doping |
| Oxygen Concentration | < 5×10¹⁵ atoms/cm³ (FTIR) — essentially oxygen-free vs CZ (5–20×10¹⁷) |
| Carbon Concentration | < 5×10¹⁵ atoms/cm³ (FTIR) — no graphite crucible contact |
| Orientation | 〈100〉, 〈111〉, 〈110〉 (off-cut on request) |
| Thickness | Standard SEMI spec per diameter (e.g. 725μm for 200mm); custom on request |
| TTV / Bow / Warp | < 5μm TTV, < 20μm Bow, < 30μm Warp (200mm); tighter on request |
| Surface Finish | Single-side polished (SSP) or double-side polished (DSP), Epi-Ready |
| Lifetime (Minority Carrier) | > 1 ms (μ-PCD) — orders of magnitude above CZ material |
| NTD Doping Option | Neutron Transmutation Doping for resistivity uniformity ±3% (vs ±15% conventional) |
Applications & Market Segments
RFICs & 5G/mmWave Front-Ends
FZ high-resistivity silicon (> 10 kΩ·cm) minimizes substrate-induced insertion loss in RF switches, LNAs, and phase shifters operating above 6 GHz. At mmWave frequencies (28–60 GHz), CZ substrates become prohibitively lossy due to finite substrate resistivity and parasitic surface conduction; FZ-Si with a trap-rich interface is the substrate of choice for 5G beamformer ICs.
Silicon Photonics
SOI waveguides on FZ handle wafers eliminate free-carrier absorption at 1310nm and 1550nm telecom wavelengths. The absence of oxygen precipitates removes scattering centers. Required for high-Q ring resonators, Mach-Zehnder modulators, and photonic integrated circuits (PICs) in datacom transceivers and LIDAR.
High-Voltage Power Devices
IGBTs, PiN diodes, and thyristors rated above 3.3 kV rely on FZ silicon for its wide depletion region capability. The near-intrinsic resistivity (> 30 kΩ·cm) of undoped FZ-Si enables blocking voltages exceeding 10 kV in a single device. NTD doping delivers the precise, uniform phosphorus concentration required for symmetric blocking characteristics.
Radiation Detectors
FZ silicon is the detector-grade material for particle physics experiments (CERN, Fermilab, KEK), medical PET/CT scanners, and X-ray synchrotron sensors. The ultra-low oxygen content eliminates trapping centers that would otherwise degrade charge collection efficiency. NTD-FZ provides the doping uniformity essential for large-area strip and pixel detectors.
Terahertz & Sub-mmWave Components
Frequencies above 100 GHz demand substrates with effective resistivity exceeding 10 kΩ·cm to suppress dielectric loss and mode conversion. FZ-Si substrates are used for THz waveguide components, metamaterial arrays, and on-chip antennas for 6G research and security imaging.
Substrate for GaN-on-Si Epitaxy
GaN HEMT epitaxy on silicon requires a substrate that survives the high-temperature MOCVD process (> 1000°C) without slip-line generation. FZ-Si with its superior mechanical strength at elevated temperature and absence of oxygen-precipitate-induced warpage is the preferred 200mm platform for RF GaN-on-Si power amplifiers and power-switching HEMTs.
Metrology & Quality Assurance
FZ silicon's defining characteristic — extreme purity — demands metrology capable of detecting contaminants at concentrations orders of magnitude below the detection limits of standard semiconductor characterization tools. Our FZ wafer qualification protocol combines electrical, optical, and chemical techniques to certify every parameter.
Need Ultra-High Purity FZ Silicon?
Specify your diameter, resistivity, doping type (N/P/NTD), orientation, and quantity — our FZ substrate specialists will provide a detailed quotation with full material certification within 24 hours.