Detailed Process for Repairing Atomic Oxygen-Damaged PI Substrates via Low-Temperature Plasma Annealing

Abstract: Polyimide (PI) substrates in spacecraft applications are susceptible to atomic oxygen (AO) erosion, leading to suRFace roughening and electrical degradation. Low-temperature plasma annealing efficiently repairs AO-damaged layers through ion activation and chemical reconstruction, restoring PI functionality.

I. Atomic Oxygen Damage Mechanism

1. Oxidative Etching:
   AO (>5 eV) breaks C-N/C-O bonds, oxidizing aromatic rings into volatile CO/CO₂, forming a honeycomb porous structure (damage depth ≈0.1–1 μm).

2. Performance Degradation:

   • Surface resistivity ↑ 10³×

   • Dielectric loss tangent ↑ 50%

   • Tensile strength ↓ 30–40%

II. Repair Mechanism of Plasma Annealing

Core Principle: Chemical reconstruction of damaged layers by plasma-active species (electrons/ions/radicals)

1. Bond Repair:

   • ·H radicals in N₂/H₂ plasma reduce C=O bonds, promoting imide ring re-closure.

   • Ar⁺ ion bombardment removes loose fragments, exposing intact polymer layers.

2. Surface Repassivation:
   O₂/Ar plasma at 150℃ forms a dense SiOₓ-like layer (thickness ≈50 nm), inhibiting AO penetration.

III. Process Parameter Optimization

IV. Repair Efficacy Characterization

1. Surface Morphology:

   • AFM shows roughness (Ra) reduced from 120 nm to <10 nm.

2. Chemical Structure:

   • FTIR confirms 95% recovery of C=O peak intensity at 1650 cm⁻¹.

3. Electrical Properties:

   • Volume resistivity restored to >10¹⁵ Ω·cm.

4. AO Resistance:
   Post-AO exposure (5×10²⁰ atoms/cm²), mass loss rate decreases by 98%.

V. Advantages vs. Thermal Annealing