Optical / Insulating Coatings · Defect fix

Reactive Al₂O₃ — Stop the Arcing

Aluminium oxide by reactive sputtering of an Al target in O₂ — the classic arc-prone process — run clean and stable to full thickness.

DEMO — generic parameters

The problem: The run arcs constantly. The Al target poisons over into an oxide skin, charge builds on the insulating layer, and it discharges — arcs blow micro-droplets into the film and scrap the coating.

🔍 Root Cause (why it arcs)

MechanismInsulating oxide forms on the target race-track; charge accumulates until dielectric breakdown → arc

TriggerRunning too far into the "poisoned" reactive regime in straight DC

🛠️ The Fix — approach

Power ModePulsed-DC — periodically reverses to discharge the target skin before it can arc

Reactive ControlHold the transition (metallic ↔ poisoned) point with an O₂ feedback ramp, not a fixed flow

ConditioningPre-burn the target in pure Ar, shutter closed, to strip the oxide skin first

🔒 Locked

🎯 Dialed-in Anti-Arc Parameters

Pulse Frequency100 kHz

Reverse Time2.5 µs

O₂ Feedback Setpoint88% of metallic discharge voltage

O₂ Ramp+0.4 sccm / 20 s to setpoint, then PID hold

Arc-HandlingSupply arc-suppression at < 10 µs response

⚠️ Failure Mode Warnings

Arcs return → O₂ setpoint too high, target re-poisoning — back off the ramp
Deposition rate collapses → over-pulsed or O₂ too low (metallic film, not oxide)
Absorbing/grey film → sub-stoichiometric Al₂O₃, raise O₂ toward setpoint

Your supply, your target, your gas lines.

Pulse and ramp values depend on your exact power supply and chamber. LabForge dials them to your hardware.

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