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Wet Process Bench
Modutek Corporation, San Jose, CA, USA
HIGH ● Every wafer passes through wet chemistry multiple timesRole in QLT Fabrication
The wet process bench provides controlled chemical baths and DI rinse for all cleaning, developing, and stripping steps:
| Step | Chemistry | Temperature | Time | Purpose |
|---|---|---|---|---|
| Pre-litho clean | Acetone → IPA → DI rinse | Room Temp | 2+2+2 min | Remove organics before resist coat |
| Post-develop rinse | DI water cascade | Room Temp | 2 min | Stop MF-26A development |
| Post-etch clean | O₂ ash residue removal → IPA | Room Temp | 5 min | Clean chip after RIE |
| Resist strip | NMP (N-methylpyrrolidone) or acetone | 70°C | 10–30 min | Lift-off resist removal |
| Piranha clean | H₂SO₄:H₂O₂ (3:1) | 120°C | 10 min | Heavy organic removal (if needed) |
| BHF dip | Buffered HF (BOE 6:1) | Room Temp | Timed (nm/min rate) | SiO₂ etch / native oxide removal |
| Post-As₂S₃ etch clean | IPA → DI rinse | Room Temp | 5 min | Remove etch residue [GAP03 only] |
Process Criticality
- Surface cleanliness directly determines resist adhesion, film quality, and optical performance
- BHF etch precision controls SiO₂ removal rate ● critical for Poovey trench depth
- Resist strip completeness prevents contamination of subsequent process steps
- Cross-contamination between acid and solvent baths must be prevented by strict protocol
Chemical Compatibility Requirements
| Bath Type | Construction Material | Incompatible Materials |
|---|---|---|
| HF / BOE | PTFE (Teflon), HDPE, polypropylene | Glass, stainless steel, ceramics |
| Piranha (H₂SO₄/H₂O₂) | Borosilicate glass (Pyrex), quartz, PTFE | Polypropylene (at 120°C), metals |
| Solvents (acetone, IPA, NMP) | Stainless steel, glass, polypropylene | Some plastics (acetone melts many) |
| Developer (MF-26A, TMAH) | Polypropylene, PTFE | Metals (TMAH etches Al) |
Technical Specifications
| Step | Chemistry | Temperature | Time | Purpose |
|---|---|---|---|---|
| Pre-litho clean | Acetone → IPA → DI rinse | Room Temp | 2+2+2 min | Remove organics before resist coat |
| Post-develop rinse | DI water cascade | Room Temp | 2 min | Stop MF-26A development |
| Post-etch clean | O₂ ash residue removal → IPA | Room Temp | 5 min | Clean chip after RIE |
| Resist strip | NMP (N-methylpyrrolidone) or acetone | 70°C | 10–30 min | Lift-off resist removal |
| Piranha clean | H₂SO₄:H₂O₂ (3:1) | 120°C | 10 min | Heavy organic removal (if needed) |
| BHF dip | Buffered HF (BOE 6:1) | Room Temp | Timed (nm/min rate) | SiO₂ etch / native oxide removal |
| Post-As₂S₃ etch clean | IPA → DI rinse | Room Temp | 5 min | Remove etch residue [GAP03 only] |
| Bath Type | Construction Material | Incompatible Materials |
|---|---|---|
| HF / BOE | PTFE (Teflon), HDPE, polypropylene | Glass, stainless steel, ceramics |
| Piranha (H₂SO₄/H₂O₂) | Borosilicate glass (Pyrex), quartz, PTFE | Polypropylene (at 120°C), metals |
| Solvents (acetone, IPA, NMP) | Stainless steel, glass, polypropylene | Some plastics (acetone melts many) |
| Developer (MF-26A, TMAH) | Polypropylene, PTFE | Metals (TMAH etches Al) |
| Parameter | Specification |
|---|---|
| Manufacturer | Modutek Corporation, San Jose, CA |
| Type | Manual wet process station (operator-loaded) |
| Construction | White polypropylene (acid side); stainless steel optional (solvent side) |
| Material compliance | FM4910 compliant (fire-rated) materials standard; PVDF and Teflon options |
| Positions | 4–6 process baths + 1 QDR (Quick Dump Rinser) + 1 DI overflow rinse |
| Bath capacity | 5–10 L per position |
| Wafer handling | 100 mm Teflon cassette (25 wafers) or single-die holders |
| Exhaust | Integrated 1" lip exhaust on all process tanks + rear exhaust manifold |
| Safety | All stations wired per NFPA 70 & 79; EPO with mushroom button; PVC safety shields |
| DI water | 18.2 MΩ·cm ultrapure supply required; continuous flow DI manifold |
| Drain | Chemical-resistant CPVC to acid neutralization |
| Accessories | Teflon N₂ gun + DI water hand spray (standard); photohelic with interlock to EPO |
| Sizing | Available in any size and length to meet requirements |
| Warranty | 1-year on all parts; 2 copies paper manual + digital |
| Option | Description | Relevance for QLT |
|---|---|---|
| Silicon Nitride Etching Baths | Dedicated bath design for SiN processing | Directly applicable to our SiN waveguide clean |
| Sub-Ambient Baths for BOE | Temperature-controlled BHF baths for precise etch rate | Critical for SiO₂ etch rate control |
| Quartz Tanks | For Piranha and high-temperature processing | Needed if doing regular Piranha cleans |
| Teflon Tanks | For HF/BOE processing | Required for our BHF etch step |
| Acid Fume Scrubber | Standalone acid fume neutralization | Pair with bench if building exhaust is insufficient |
| Acid Neutralization System | Inline neutralization before drain | Required by most jurisdictions for acid waste |
| Fan Filter Units (HEPA) | Overhead HEPA filtration | ISO Class 5 cleanliness over wafer handling |
| Seismic Zone 4 certification | Structural certification for earthquake zones | Applicable for California installations |
Process Integration
Pre-Lithography Clean (Every Wafer, Before Resist Coat)
- Don PPE: safety glasses, nitrile gloves, lab coat
- Place wafer in acetone bath (Bath 1): 2 min soak with gentle agitation
- Transfer to IPA bath (Bath 2): 2 min rinse (removes acetone residue)
- Transfer to DI cascade rinse (Bath 7): 2 min overflow rinse
- N₂ blow-dry using Teflon gun
- Transfer to spin coater (#05) for resist coat
Post-Develop Rinse (After Mask Aligner Exposure + Develop)
- After MF-26A develop (puddle or immersion, 60 s)
- Transfer to DI cascade rinse: 2 min overflow
- N₂ blow-dry
- Inspect under microscope
Resist Strip (After Etch, to Remove Masking Layer)
- Heat NMP bath (Bath 5) to 70°C; verify temperature with thermometer
- Immerse wafer in NMP: 10–30 min (until resist fully dissolved)
- Rinse in IPA bath: 2 min
- DI cascade rinse: 2 min
- N₂ blow-dry
- Optional: O₂ plasma ash (if resist residue remains) ● use ICP-RIE (#01) at 0 W bias
BHF / BOE Dip (Oxide Etch)
- CRITICAL: Full PPE for HF handling ● face shield, acid apron, long-cuff nitrile gloves
- Buddy system required ● never handle HF alone
- Verify calcium gluconate gel is accessible
- Immerse wafer in BOE 6:1 (Bath 4): timed etch (SiO₂ rate ~100 nm/min at RT)
- Quick transfer to QDR: dump-rinse 3 cycles
- DI cascade rinse: 3 min
- N₂ blow-dry immediately (native oxide regrows within minutes in air)
Piranha Clean (Heavy Organic Removal ● When Required)
- CRITICAL: Never add H₂O₂ to warm H₂SO₄ ● always add H₂O₂ to cold H₂SO₄ and let reaction heat naturally
- Mix 3:1 H₂SO₄:H₂O₂ in Pyrex or quartz beaker (NEVER in polypropylene)
- Allow to self-heat to ~120°C
- Immerse wafer: 10 min
- Transfer to QDR: dump-rinse 5 cycles
- DI cascade rinse: 5 min
- N₂ blow-dry
Vendor Options & Pricing
New System Cost
| Configuration | Estimated New Price |
|---|---|
| Basic 4-position manual acid bench (polypropylene) | $10,000–$20,000 |
| 6-position manual bench w/ QDR + DI rinse | $18,000–$30,000 |
| Dual-sided (acid + solvent) complete station | $25,000–$45,000 |
| Semi-automated with PLC + touchscreen + servo motors | $40,000–$80,000 |
| Terra Universal catalog fume hood (standalone) | $5,000–$10,000 |
Where to Buy
| Vendor | Contact | Quote Process |
|---|---|---|
| Modutek | [email protected] / (866) 803-1533 | Consultative: provide process requirements → design review → quote |
| JST Manufacturing | jstmfg.com/contact | Similar consultative process |
| Terra Universal | terrauniversal.com | Catalog items for direct purchase; custom also available |
| Cole-Parmer | coleparmer.com | Individual PP baths, tanks, accessories for self-assembled bench |
| Sistem Technology | sistemtechnology.com | Modutek authorized distributor (international) |
Our Budget Recommendation
Buy NEW: $15,000–$20,000 (Modutek or JST custom 4-position acid bench)
- Configuration: 4 bath positions (acetone, IPA, developer, BOE) + 1 QDR + DI cascade
- Material: White polypropylene body; PTFE-lined baths for HF compatibility
- Exhaust: Integrated 1" lip exhaust connected to building HVAC
- Standards: FM4910 materials; NFPA 70 & 79 wiring; EPO; all safety interlocks
- Lead time: 8–12 weeks from design signoff
Facility Requirements
Floor Space
| Dimension | Requirement |
|---|---|
| 4-position bench footprint | 1.8 m × 0.7 m (72" × 28") |
| 6-position with rinse | 2.4 m × 0.7 m (96" × 28") |
| Service access (front + rear) | 0.8 m clearance |
| Total floor requirement | 3.0 m × 2.3 m (7 m²) |
| Weight (empty) | 100–200 kg |
| Weight (filled with chemicals) | 200–400 kg |
Electrical
| Parameter | Requirement |
|---|---|
| Supply | Single-phase, 120 V, 20 A |
| GFCI | MANDATORY ● all outlets near wet bench |
| Separate circuit | Recommended for heated baths |
Power Consumption
| Component | Power Draw |
|---|---|
| Hot plate / immersion heater | 0.5–2.0 kW per heated bath |
| QDR controller | 0.05 kW |
| DI water system (if standalone) | 0.3–0.5 kW |
| Overhead lighting | 0.1 kW |
| TOTAL | 1.0–3.0 kW typical |
Plumbing
| Utility | Specification |
|---|---|
| DI water supply | 18.2 MΩ·cm, 2–5 GPM |
| DI water connection | ½" PFA or PVDF tubing |
| Acid drain | CANNOT go to regular sewer ● requires acid neutralization tank |
| Solvent drain | Separate collection for waste solvents (HazMat) |
| N₂ gun | Blow-dry station; ¼" Swagelok from house N₂ |
Exhaust
| Parameter | Specification |
|---|---|
| Type | Integrated 1" lip exhaust + rear slot exhaust |
| Flow rate | 200–400 CFM total |
| Duct | 8" (200 mm) PVC or polypropylene to building HVAC |
| Face velocity | 80–120 fpm at operator breathing zone |
| Scrubber | May be required for HF (check local regs) |
Vibration / Sound / Lighting
| Parameter | Specification |
|---|---|
| Vibration sensitivity | NONE |
| Sound | QDR dump can be loud (70 dB burst); otherwise quiet |
| Special lighting | YELLOW SAFELIGHT in developer area (same zone as aligner + spin coater) |
Safety & Handling
Safety Equipment Requirements (CRITICAL)
| Requirement | Specification | Cost |
|---|---|---|
| Emergency eyewash | ANSI Z358.1 compliant; within 10 seconds travel | $200–$500 |
| Emergency shower | ANSI Z358.1 compliant; within 10 seconds travel | $500–$1,500 |
| Chemical splash goggles | For all operators during acid/base handling | $20 each |
| Face shield | For Piranha or HF handling | $30 each |
| Acid apron | Chemical-resistant PVC or rubber | $30 each |
| Nitrile gloves (long-cuff) | 12" cuff for acid handling | $15/box |
| Spill kit | Acid neutralization + absorbent pads | $200 |
| SDS binder | For all chemicals used at bench | Required |
| HF antidote (calcium gluconate gel) | MANDATORY if using BOE/HF | $50 |
| Total safety equipment | $1,000–$2,500 |
HF Safety Protocol
HF (hydrofluoric acid, including buffered BOE) is uniquely dangerous:
- Penetrates skin painlessly and causes deep tissue / bone destruction
- Symptoms may be delayed 1–24 hours after exposure
- Small-area burns can be fatal due to systemic fluoride poisoning
Mandatory controls:
- Buddy system ● never handle HF alone
- Calcium gluconate gel within arm's reach of BOE bath
- Training ● all operators must complete institution-specific HF safety training
- First aid protocol posted ● wash immediately with water (15 min); apply calcium gluconate; call 911 for any HF exposure
- Dedicated PTFE bath with splash guards for BOE
- PPE: face shield + acid apron + 12" nitrile gloves + closed-toe shoes
Hazard Summary
| Hazard | Risk Level | Control |
|---|---|---|
| Chemical splash / acid burn | Medium | PPE mandatory; eyewash within 10 s; training |
| HF exposure | Low | Calcium gluconate; HF training; buddy system; dedicated bath |
| Cross-contamination | Medium | Separate acid/solvent sides; never share DI rinse |
| Solvent fire (acetone, MEK) | Low | No open flames; fire extinguisher; solvent storage cabinet |
| Exhaust failure → fume exposure | Low | Monthly face velocity check; alarm on exhaust blower |