GaN / Compound Semiconductor Etch (ICP-RIE)

Category: Etch

Process Overview

GaN (Gallium Nitride) and compound semiconductor etching via Inductively Coupled Plasma-Reactive Ion Etching (ICP-RIE) is a critical process for fabricating high-performance power devices, RF components, and optoelectronics. Unlike silicon, GaN’s wide bandgap and chemical inertness require precise plasma conditions to achieve anisotropic etching with minimal damage. ICP-RIE combines high-density plasma (via ICP source) with reactive chemistries (e.g., Cl₂/BCl₃) to enable sub-micron feature definition, critical for advanced nodes in data center power management and 5G infrastructure.

The process operates in a vacuum chamber where ions bombard the wafer, selectively removing material. Uniformity, etch rate, and selectivity are tightly controlled by adjusting gas mixtures, pressure, and RF power. This process is essential in compound semiconductor manufacturing due to GaN’s role in improving energy efficiency and reducing heat generation in high-power applications.

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Key Process Parameters

| Parameter | Typical Range | Units |
|-------------------------|------------------------------|-----------|
| Chamber Pressure | 10–100 | mTorr |
| ICP Source Power | 500–1500 | W |
| RF Bias Power | 100–500 | W |
| Gas Flow (Cl₂/BCl₃/Ar) | 10–100 / 5–50 / 5–50 | sccm |
| Chamber Temperature | 50–100 | °C |
| Etch Rate (GaN) | 50–200 | nm/min |

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Equipment & Parts Required

1. ICP Plasma Sources
   Generate high-density plasma (≥10¹¹ ions/cm³) for precise ion energy control. Critical for balancing etch rate and material selectivity. Caladan’s ICP sources enable stable plasma at low pressures (≤20 mTorr), aligning with SEMI S23 standards for plasma processing safety.

2. ESCs (Electrostatic Chucks)
   Secure wafers and maintain uniform temperature (±2°C across the wafer) during etch. Essential for preventing thermal gradients that cause non-uniform etching. Caladan ESCs integrate with active cooling systems to meet ISO 14644-1 cleanroom thermal stability requirements.

3. MFCs (Mass Flow Controllers)
   Regulate Cl₂, BCl₃, and Ar gas flows with ±1% accuracy. Caladan’s MFCs ensure repeatable Cl₂/BCl₃ ratios (e.g., 2:1) for optimal radical density and etch profile control.

4. Turbo Pumps
   Achieve and maintain base pressures (<1×10⁻⁶ Torr) for consistent plasma ignition. Caladan turbo pumps support rapid cycling between process steps, reducing idle time in high-throughput data center fab environments.

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Common Issues & Troubleshooting

1. Plasma Instability
   Cause: Faulty ICP coil matching or degraded MFC calibration.
   Fix: Recalibrate MFCs or replace ICP source capacitors. Verify gas flows match SEMI E142 process gas handling standards.

2. Non-Uniform Etch Profiles
   Cause: ESC temperature gradients (>3°C variation).
   Fix: Inspect ESC heater elements and replace if necessary. Ensure cooling water flow meets ASHRAE TC 9.9 thermal management guidelines.

3. Particle Contamination
   Cause: Turbo pump seal leakage introducing contaminants.
   Fix: Replace turbo pump seals and perform chamber baking at 100°C to outgas residues.

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Frequently Asked Questions

Q: What is the typical etch rate for GaN in ICP-RIE?
A: "The etch rate for GaN ranges from 50–200 nm/min, depending on Cl₂/BCl₃ ratios and ICP power settings."

Q: Why is chamber pressure critical in this process?
A: "Pressures between 10–100 mTorr balance ion energy and radical density; lower pressures (e.g., 20 mTorr) improve anisotropy for sub-µm features."

Q: How do you prevent ESC delamination during high-power etch?
A: "Maintain ESC temperature below 80°C using closed-loop water cooling and verify adhesive bond integrity per JEDEC JESD22-B108."

Q: What gas mixture is most common for GaN etching?
A: "A 2:1 Cl₂/BCl₃ mixture with 10% Ar is standard for GaN, providing sufficient Cl radicals and ion bombardment energy."

Q: How often should turbo pumps be serviced for this application?
A: "Turbo pumps should undergo seal inspection and lubricant replacement every 2,000 operational hours to maintain vacuum stability."

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Parts for This Process

Looking for parts to support this process? Caladan Semi stocks used and refurbished components including: ICP plasma sources, ESCs, MFCs (Cl2, BCl3, Ar), turbo pumps.

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