HVAC/HEPA Filtration System

Role in QLT Fabrication

Every nanoscale feature on the QLT photonic chip — 900 nm waveguides, 150 nm taper tips, 250 nm Poovey switch air gaps — is vulnerable to particle contamination. A single 0.5 µm particle landing on a waveguide during lithography or deposition creates a scattering defect that can add 0.1–1.0 dB of excess loss, potentially ruining a die. The HVAC/HEPA system creates and maintains the controlled cleanroom environment that makes sub-micron fabrication possible.

The cleanroom environment controls far more than just particles:

• Particle control ● HEPA/ULPA filtration removes airborne contaminants ≥ 0.12 µm that cause defects in lithography, deposition, and etch processes
• Temperature stability ● ±0.1°C in the lithography bay prevents thermal expansion/contraction of photomasks and wafers that would cause overlay errors exceeding 10 nm
• Humidity control ● ±1% RH prevents photoresist absorption of moisture (causes scumming and CD variation), electrostatic discharge damage to devices, and condensation on chilled optical surfaces
• Chemical vapor removal ● Activated carbon and chemical filters remove airborne molecular contamination (AMC) — volatile organics, acids, bases — that deposit on wafer surfaces and degrade film adhesion
• Positive pressure ● Cleanroom operates at +0.03–0.05" w.g. relative to surrounding spaces, preventing infiltration of unfiltered air through doors and pass-throughs
• Laminar flow ● Unidirectional (vertical) airflow at 0.3–0.5 m/s sweeps particles downward into return plenums, preventing recirculation across wafer surfaces

ISO Cleanliness Classes Required by Process Step

Technical Specifications

Air Handling Unit (AHU) Requirements

Filtration System

Fan Filter Units (FFUs)

Cleanroom Architecture

QLT CLEANROOM AIRFLOW DESIGN:

VERTICAL LAMINAR FLOW (ISO 5 Zones):

    ┌─────────────────────────────────┐
    │  INTERSTITIAL SPACE (ductwork)  │
    │  Supply from AHU → distribution │
    ├─────────────────────────────────┤
    │  ████ FFU ████ FFU ████ FFU ██  │  ← HEPA/ULPA ceiling (80-100%)
    │  ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓  │  ← Laminar flow 0.45 m/s
    │                                 │
    │      [EQUIPMENT + WAFERS]       │  ← Work zone (10 ft clear)
    │                                 │
    │  ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓  │
    ├─────────────────────────────────┤
    │  ▓▓▓▓ RAISED FLOOR (perforated) │  ← 18-24 in. raised floor
    │  Return air plenum → back to AHU│
    └─────────────────────────────────┘

PRESSURE CASCADE:
├── Lithography bay:    +0.05 in. w.g. (cleanest)
├── Process bays:       +0.04 in. w.g.
├── General cleanroom:  +0.03 in. w.g.
├── Gowning room:       +0.02 in. w.g.
└── Corridor/outside:   0.00 in. w.g. (reference)

AIR LOCK SEQUENCE:
├── Personnel entry: Corridor → Air shower → Gowning → Cleanroom
├── Material entry: Loading dock → Pass-through → Wipe-down → Cleanroom
└── Emergency egress: Crash-bar doors (break pressure seal)

Process Integration

QLT CLEANROOM HVAC INTEGRATION:

ZONE 1: LITHOGRAPHY BAY (ISO 5, 1,500 sq ft)
├── Dedicated AHU with reheat coil for ±0.1°C control
├── 100% ULPA ceiling coverage (150 FFUs, 2×4 ft)
├── Humidity: steam humidifier + desiccant dehumidifier
├── Chemical filtration on makeup air (AMC removal)
├── Equipment served: DUV stepper, contact aligner, spin coater
├── Heat load: ~30 kW (stepper dominates)
└── Exhaust: solvent exhaust from resist processing (50–100 CFM)

ZONE 2: DEPOSITION & ETCH BAY (ISO 6, 2,500 sq ft)
├── Shared AHU with Zone 3, zone reheat for ±0.5°C
├── 35% HEPA ceiling coverage (90 FFUs)
├── Equipment served: PECVD, ICP-RIE, sputtering, evaporator
├── Heat load: ~45 kW (vacuum pumps + RF generators)
├── Exhaust: process gas exhaust to scrubber (200–400 CFM)
└── Special: gas cabinet exhaust continuous (SiH₄ area)

ZONE 3: WET BENCH & CLEAN (ISO 5, 1,000 sq ft)
├── Dedicated AHU or split from Zone 1
├── 90% ULPA ceiling coverage (110 FFUs)
├── Equipment: RCA wet bench, solvent bench, spin-rinse-dryer
├── Heat load: ~15 kW
├── Exhaust: acid exhaust (HF, HCl) and solvent exhaust (acetone, IPA)
└── Special: acid-resistant ductwork (polypropylene or PVDF)

ZONE 4: METROLOGY & TEST (ISO 7, 2,000 sq ft)
├── AHU with ±1°C control (adequate for most instruments)
├── 20% HEPA ceiling coverage (50 FFUs)
├── Equipment: SEM, AFM, ellipsometer, optical test stations
├── Heat load: ~20 kW
├── Special: SEM room requires vibration isolation + EMI shielding
└── Temperature excursions affect measurement drift — monitor closely

ZONE 5: PACKAGING & ASSEMBLY (ISO 7, 2,000 sq ft)
├── Standard HVAC with HEPA ceiling terminals
├── 15% HEPA ceiling coverage (35 FFUs)
├── Equipment: die bonder, wire bonder, fiber attach station
├── Heat load: ~10 kW
└── Humidity important for wire bonding adhesion

Vendor Options & Pricing

HVAC System Vendors

Filtration & FFU Vendors

Total System Cost Breakdown

Facility Requirements

Building Infrastructure

Annual Operating Costs

Safety & Handling

Hazard Summary

Emergency Procedures

CLEANROOM HVAC EMERGENCY RESPONSE:

CHEMICAL EXHAUST FAILURE:
├── BAS alarm triggers immediately on loss of exhaust flow
├── Affected wet bench automatically shuts off chemical dispensing
├── Evacuate zone if toxic gas alarm triggers (SiH₄, HF, HCl)
├── Do NOT re-enter until exhaust is verified operational
└── Secondary exhaust fan auto-starts (if N+1 configured)

TEMPERATURE EXCURSION (> ±1°C from setpoint):
├── BAS sends alarm to facilities engineer (SMS + email)
├── Lithography operations PAUSE (thermal drift causes overlay errors)
├── Investigate: chiller status, AHU coil valve, outdoor conditions
├── Resume lithography only after 30 min of stable ±0.1°C readings
└── Log event in cleanroom deviation log

PARTICLE EXCURSION (ISO 5 zone exceeds Class 100):
├── Continuous particle counter triggers alarm
├── Stop all open-wafer processing (resist coat, develop)
├── Check: door seals, FFU status, personnel count, recent maintenance
├── Perform recovery count: 3 consecutive readings at Class 100
└── Resume processing after root-cause documented

POWER FAILURE:
├── Generator starts within 10 seconds (HVAC controls + critical fans)
├── Full HVAC restoration within 5 minutes
├── If extended outage: close all chemical containers, cover wafers
├── Monitor temperature and particle counts during recovery
└── Perform certification particle counts before resuming ISO 5 work