Conductor Etch — Tungsten (W)

Category: Etch

Process Overview

Conductor Etch — Tungsten (W) is a critical plasma etching process used to pattern tungsten layers in semiconductor and data center interconnect manufacturing. Tungsten, often deposited as a barrier or via-fill material, requires precise anisotropic etching to define conductive pathways without damaging underlying dielectrics. This process typically follows tungsten deposition and precedes copper plating or dielectric etch steps.

The etch relies on reactive ion etching (RIE) using fluorine-based chemistries (e.g., SF₆) and chlorine (Cl₂) to achieve high selectivity and aspect ratio control. Tungsten’s high melting point (3422°C) and chemical inertness demand optimized plasma conditions to balance etch rate, uniformity, and profile control. Poorly executed etching can lead to micro-loading effects, residue, or via necking, which degrade device performance.

In data center ASIC manufacturing, this process is vital for creating high-density via arrays in advanced nodes (e.g., 5nm and below). It ensures electrical connectivity while maintaining signal integrity for high-speed computing workloads.

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Key Process Parameters

| Parameter | Typical Range | Notes |
|---------------------|----------------------------|------------------------------------|
| Chamber Pressure | 8–15 mTorr | Optimized for anisotropic profiles |
| RF Power (13.56MHz) | 800–1200 W | Controls ion energy and density |
| Bias Power (2MHz) | 200–400 W | Enhances directional ion bombardment |
| Gas Mixture | SF₆ (120 sccm) + Cl₂ (30 sccm) | Adjusted for selectivity over SiO₂ |
| Chamber Temperature | 25–35°C | Prevents thermal stress on wafers |
| Etch Rate | 200–400 nm/min | Varies with plasma uniformity |

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Equipment & Parts Required

1. ESCs (Electrode Shadow Covers): Prevent plasma arcing and ensure uniform etch profiles by shielding the electrode perimeter. Caladan’s ESCs are designed for tight tolerance alignment in high-power RF environments.
2. RF Generators (13.56MHz + 2MHz Bias): Drive plasma generation and ion energy. Caladan’s dual-frequency generators enable precise control over etch anisotropy.
3. Mass Flow Controllers (MFCs): Regulate SF₆ and Cl₂ flows to maintain consistent chemistry ratios. Caladan’s MFCs meet SEMI E127 standards for gas delivery accuracy (±1% of setpoint).
4. Endpoint Detection System: Uses optical emission spectroscopy (OES) to detect via clearing events. Caladan’s sensors integrate with real-time process analytics for sub-10nm node compatibility.

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Common Issues & Troubleshooting

1. Non-Uniform Etch Profiles

   • Cause: Misaligned ESCs or RF power imbalances.
   • Fix: Recalibrate ESC positioning and verify RF matching network settings. Replace ESC if arcing is observed.

2. Excessive Tungsten Residue

   • Cause: Insufficient Cl₂ flow reducing chlorine-based passivation.
   • Fix: Audit MFC calibration; replace faulty Cl₂ MFC (e.g., Caladan Model MFC-220-C).

3. Endpoint Detection Failure

   • Cause: Contaminated OES lens or outdated spectral algorithms.
   • Fix: Clean or replace endpoint sensor (Caladan Part No. EPD-45X) and update firmware.

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Frequently Asked Questions

Q: What is the typical etch rate for tungsten in this process?
A: "The etch rate ranges from 200–400 nm/min, depending on plasma uniformity and gas chemistry. A 10% increase in SF₆ flow typically raises the rate by 15–20%."

Q: How do you prevent micro-loading during tungsten etch?
A: "Maintain a Cl₂/SF₆ ratio of 1:4 and ensure chamber pressure stays below 15 mTorr. This minimizes polymer buildup in high-density via regions."

Q: Which industry standard governs gas purity for SF₆ and Cl₂?
A: "SEMI C14 outlines gas purity requirements (≥99.999% for SF₆ and Cl₂) to prevent contamination in advanced node etching."

Q: Why is a 2MHz bias power used alongside 13.56MHz?
A: "The 2MHz bias enhances ion energy modulation for vertical etch profiles, while 13.56MHz ensures high plasma density. This dual-frequency approach is critical for sub-5nm aspect ratios."

Q: How often should endpoint detection sensors be calibrated?
A: "Calibrate OES sensors weekly or after 50 process runs, per ASHRAE 12-2019 guidelines for process monitoring reliability."

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Parts for This Process

Looking for parts to support this process? Caladan Semi stocks used and refurbished components including: ESCs, RF generators (13.56MHz + 2MHz bias), MFCs (SF6, Cl2), endpoint detection.

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