Photoresist Coating
Coating with photoresist is a critical initial step in photolithography, where a light-sensitive polymer (photoresist) is applied uniformly onto a substrate surface.
Process Steps
Wafer Preparat
# Progress on Photoresist Coating in Photolithography
We delved into the critical process of applying photoresist in photolithography, outlining essential steps and considerations to ensure optimal results.
## Key Learnings
1. **Process Steps**:
- **Wafer Preparation**:
- Clean substrate surface.
- Perform dehydration bake (~120°C).
- Apply adhesion promoter if needed.
- **Resist Application**:
- Dispense photoresist at the wafer center.
- Spin coat at RPMs between 1500-6000 for 30-60 seconds.
- **Soft Bake (Pre-bake)**:
- Heat at 95-120°C for 60-90 seconds to remove solvents and improve adhesion.
2. **Key Parameters**:
- **Resist Thickness**:
- Controlled by spinning speed, viscosity, and time.
- **Common Issues**:
- Edge beads, air bubbles, uneven coating, and particle contamination.
3. **Types of Photoresist**:
- **Positive Resist**: Soluble areas post-exposure, ideal for fine features.
- **Negative Resist**: Insoluble areas post-exposure, better adhesion, and etching resistance.
4. **Quality Control Criteria**:
- Thickness uniformity within ±5%.
- Absence of visible defects.
- Good edge coverage.
## Optimization Recommendations
- **Edge Bead Prevention**:
- Optimize spin speed ramp-up.
- Use an edge bead removal system.
- **Air Bubble Elimination**:
- Implement resist degassing pre-application.
- Maintain resist at 21-23°C.
## Completed To-Do's Checklist
- [x] Outlined photoresist coating process.
- [x] Identified common issues and solutions.
- [x] Suggested process optimizations.
This summary encapsulates our progress in understanding and refining the photoresist coating process, setting a solid foundation for future work in photolithography.By Eduarda Ferreira