Silicon Nitride (Si3N4) Etch

Category: Etch

Process Overview

Silicon nitride (Si₃N₄) etch is a critical dry etching process used to pattern or remove silicon nitride layers in semiconductor and data center manufacturing. Si₃N₄ serves as a dielectric, etch stop, or stressor in devices like FinFETs, MEMS, and 3D NAND. Precise etching ensures dimensional accuracy and prevents damage to underlying layers. The process uses reactive ion etching (RIE) with fluorocarbon-based chemistries (e.g., CHF₃/O₂) to achieve high selectivity and anisotropic profiles.

In data center applications, Si₃N₄ etch enables high-density interconnects and isolation structures, directly impacting signal integrity and power efficiency. Poor etch uniformity or selectivity can lead to yield loss, making equipment reliability and process control essential.

Key Process Parameters

| Parameter | Typical Range/Value | Standard Reference |
|---------------------|------------------------------------------|--------------------------|
| Chamber Pressure | 20–50 mTorr | SEMI E19 for RIE chambers|
| Gas Flow (CHF₃) | 20–50 sccm | SEMI CF63 gas safety |
| Gas Flow (O₂) | 5–20 sccm | |
| RF Power | 500–1000 W (13.56 MHz) | JEDEC JESD22-B117 |
| Temperature | 20–40°C (ASHRAE Class I chamber control) | ASHRAE TC 9.9 |
| Etch Rate | 50–200 nm/min (CHF₃/O₂ ratio-dependent) | ISO 13966 etch metrics |

Equipment & Parts Required

1. Electrostatic Chucks (ESCs): Secure wafers and provide thermal uniformity. Caladan’s ESCs use advanced dielectric materials for stable 20–40°C wafer temperature control.
2. Edge Rings: Prevent plasma instability at chamber edges. Caladan’s anti-sputter edge rings reduce particle generation during high-power etch.
3. RF Generators: Deliver 500–1000 W at 13.56 MHz for plasma ignition. Caladan’s generators meet SEMI F20 for power stability (±1% deviation).
4. Mass Flow Controllers (MFCs): Regulate CHF₃/O₂ flows (±1% accuracy). Caladan’s MFCs integrate with process feedback loops for real-time correction.
5. Quartz Showerheads: Distribute gas evenly. Caladan’s RF-transparent, low-outgassing designs prevent fluorocarbon deposition blockages.

Common Issues & Troubleshooting

1. Low Etch Rate: Check MFC calibration (CHF₃/O₂ ratio) or increase RF power. Replace quartz showerhead if fluorocarbon residues reduce gas permeability.
2. Particulate Contamination: Worn edge rings or ESC delamination may generate particles. Replace edge rings every 5,000 cycles or when SEMI S23 particle counts exceed 500 particles/cm².
3. Non-Uniform Profiles: ESC temperature gradients or RF field imbalance cause etch non-uniformity. Recalibrate ESC heaters or replace RF matching networks.

Frequently Asked Questions

Q: What is the typical etch rate for Si₃N₄ using CHF₃/O₂ plasma?
A: “The etch rate ranges from 50–200 nm/min, depending on power, gas ratio, and pressure. At 500 W and 30 mTorr, a 150 nm/min rate is common with 80% Si₃N₄/SiO₂ selectivity.”

Q: How to prevent fluorocarbon polymer buildup on the showerhead?
A: “Increase O₂ percentage in the gas mix during descum steps. Replace the showerhead if throughput drops by >15% due to clogging.”

Q: What RF power is recommended for sub-10nm node etch?
A: “High-density plasma sources at 1000–1500 W (with 2 MHz bias) are preferred for sub-10nm critical dimensions, per SEMI E142 guidelines.”

Q: Why is chamber pressure critical in Si₃N₄ etch?
A: “Pressures below 20 mTorr increase ion energy, risking substrate damage, while >50 mTorr reduces anisotropy. Maintain 30–40 mTorr for most applications.”

Q: How often should edge rings be replaced?
A: “Inspect edge rings every 2,500 cycles. Replace when erosion exceeds 50 µm or particle counts rise above ISO 4406 class 14/12.”

---

Parts for This Process

Looking for parts to support this process? Caladan Semi stocks used and refurbished components including: ESCs, edge rings, RF generators, MFCs (CHF3, O2), quartz showerheads.

Browse Parts →