Wafer Cleaning Protocol for SCIF Cleanroom
Note: The selection of a wafer cleaning method depends on the specific application requirements and the intended downstream process.
1. Purpose
This protocol outlines standardized procedures for cleaning semiconductor wafers to remove organic contaminants, particles, and metallic impurities prior to microfabrication processes. Proper wafer cleaning ensures high yield, reproducibility, and device performance.
2. Scope
Applicable to all cleanroom users handling:
- Silicon wafers
- Glass substrates
- Oxide-coated wafers
This protocol must be followed before:
- Photolithography
- Thin film deposition
- Etching processes
3. Safety Requirements
Perform all chemical cleaning inside a certified chemical fume hood or wet bench
- Wear full cleanroom PPE:
- Cleanroom suit (bunny suit)
- Nitrile gloves (double gloving recommended)
- Safety goggles / face shield
- Handle chemicals such as Acetone, IPA, DI water, and oxidizing solutions with caution
- Never mix chemicals unless specified
- Dispose of waste in designated labeled containers
- Do not pour chemicals into drains (follow facility waste protocol)
4. Required Materials and Equipment
- Acetone (electronic grade)
- Isopropyl Alcohol (IPA)
- Deionized (DI) water
- Nitrogen (N₂) gun for drying
- Clean beakers (glass or Teflon)
- Wafer tweezers (Teflon-coated)
- Hot plate (optional)
- Spin rinser dryer (SRD) (if available)
- Ultrasonic bath (optional)
5. Cleaning Methods Overview
Three commonly used cleaning levels:
- Solvent Cleaning (Basic)
- Piranha Cleaning (Organic Removal)
- RCA Cleaning (Advanced Contaminant Removal)
6. Procedure
6.1 Basic Solvent Cleaning (Standard Pre-Clean)
Steps:
- Place wafer in a clean Teflon or glass holder
- Rinse with Acetone (1–2 min)
- Optional: Ultrasonic agitation for heavily contaminated wafers
- Transfer immediately to IPA rinse (1–2 min)
- Rinse thoroughly with DI water
- Dry using:
- Nitrogen gun or
- Spin Rinse Dryer (if available)
Purpose:
- Removes organic residues (photoresist, grease, oils)
6.2 Piranha Cleaning (Strong Organic Removal)
⚠️ Extreme caution required
Solution Preparation:
- Mix Sulfuric Acid (H₂SO₄) : Hydrogen Peroxide (H₂O₂) = 3:1
- Always add H₂O₂ to H₂SO₄ slowly
Steps:
- Heat solution to ~80–120°C (if required)
- Immerse wafer for 10–15 minutes
- Remove wafer carefully using Teflon tweezers
- Rinse thoroughly with DI water (≥5 minutes)
- Dry with N₂ or SRD
Purpose:
- Removes strong organic contamination
- Leaves surface hydrophilic
6.3 RCA Cleaning (Standard Semiconductor Cleaning)
RCA-1 (SC-1): Organic + Particle Removal
- Solution:
NH₄OH : H₂O₂ : H₂O = 1 : 1 : 5
Steps:
- Heat to 70–80°C
- Immerse wafer for 10 minutes
- Rinse with DI water
RCA-2 (SC-2): Metal Ion Removal
Solution:
- HCl : H₂O₂ : H₂O = 1 : 1 : 6
Steps:
- Heat to 70–80°C
- Immerse wafer for 10 minutes
- Rinse thoroughly with DI water
Optional Step: HF Dip (Oxide Removal)
- Dilute HF (if facility allows)
- Dip for 10–30 seconds
- Rinse immediately with DI water
- ⚠️ Only trained users should perform HF cleaning
7. Drying Methods
- Nitrogen Blow Dry
- Spin Rinse Dryer (Preferred)
- Avoid watermarks by immediate drying
8. Inspection
Inspect wafer under:
- Optical microscope
- Surface should be:
- Particle-free
- No streaks or residues
- Water should form a uniform film (hydrophilic surface)
9. Waste Disposal
- Collect all solvent waste in labeled containers
- Separate:
- Organic solvents
- Acidic waste
- Follow cleanroom hazardous waste protocol
- Never dispose in sink
10. Common Mistakes to Avoid
- Cross-contamination between chemicals
- Letting wafers dry before DI rinse
- Using contaminated tweezers or beakers
- Improper chemical mixing order
- Skipping DI rinse steps
11. Notes for Cleanroom Practice
- Always use dedicated containers for each chemical
- Label all solutions with:
- Name
- Date
- User initials
- Work efficiently to minimize particle exposure
- Maintain Class 100 / ISO 5 discipline
12. Summary Workflow
Basic Clean → (Optional) Piranha → RCA-1 → RCA-2 → Dry → Inspect
