Rapid Thermal Processor

Role in QLT Fabrication

The Rapid Thermal Processor (RTP) provides precise, short-duration thermal anneals that are essential for optimizing metal-to-semiconductor contacts and relieving film stress without exceeding the thermal budget of previously deposited layers. Unlike conventional tube furnaces that ramp at 5–10°C/min, the RTP uses high-intensity tungsten-halogen lamp arrays to heat a single wafer at rates up to 50–150°C/s, reaching the target temperature in seconds rather than minutes.

In QLT's fabrication flow, the RTP performs quick spike anneals (typically 10–30 seconds at peak temperature) that achieve the desired metallurgical transformation while limiting total heat exposure. This is critical because extended high-temperature processing can degrade PECVD SiO₂ film quality, alter TiN heater resistivity beyond the 135–165 Ω target window, and cause interdiffusion at metal interfaces.

The RTP serves several key functions in QLT's process:

• Contact sintering ● forms low-resistance ohmic contacts between Ti adhesion layer and Au pads by promoting Ti-Au interdiffusion at 350–400°C for 30 s
• TiN heater stabilization ● brief anneal at 450°C crystallizes sputtered TiN, stabilizing resistivity and reducing drift over device lifetime
• Stress relief ● rapid thermal cycling relaxes compressive stress in PECVD SiO₂ without H₂ desorption from passivated interfaces
• Dopant activation ● activates ion-implanted dopants in GeSi SPAD structures (if integrated) with minimal diffusion
• Silicide formation ● enables TiSi₂ or NiSi contact formation for integrated detector structures

RTP vs Conventional Furnace Anneal

Process Requirements for QLT

Technical Specifications

Mattson Technology (AG Associates) RTP

Applied Materials Vantage RTP

Process Integration

QLT PROCESS FLOW ● Rapid Thermal Processor (Step B7b — Contact Sintering):

PRE-REQUISITES:
├── TiN heaters deposited and patterned (Step B6-B7)
├── Ti/Au contact pad metallization complete (e-beam evap)
├── Lift-off resist stripped; wafer clean
└── Pre-anneal resistance measurement on TiN test structures

RECIPE A: Ti/Au Contact Sintering (350°C, 30s)
├── Load wafer onto RTP susceptor
├── Purge chamber with N₂ (5 SLM, 30 s)
├── Ramp: 50°C/s to 350°C
├── Soak: 30 seconds at 350°C
│   └── Ti-Au interdiffusion forms adherent contact
├── Cool: lamp off; gas-assisted cool at ~30°C/s
├── Unload when T < 100°C
└── Measure contact resistance (target: < 10⁻⁶ Ω·cm²)

RECIPE B: TiN Heater Stabilization (450°C, 10s spike)
├── Load wafer; purge N₂
├── Ramp: 75°C/s to 450°C
├── Spike: 10 seconds at 450°C
│   ├── Partially crystallizes amorphous sputtered TiN
│   ├── Stabilizes resistivity (reduces drift from 15% to < 2%)
│   └── Brief exposure prevents excessive grain growth
├── Cool: 50°C/s to < 200°C
├── Unload; measure sheet resistance
└── Target: 20–30 Ω/sq for 100 nm TiN

RECIPE C: PECVD SiO₂ Stress Relief (400°C, 60s)
├── After PECVD SiO₂ top cladding deposition
├── Ramp: 50°C/s to 400°C in N₂
├── Soak: 60 seconds
│   ├── Relieves compressive stress in PECVD SiO₂
│   ├── Reduces wafer bow from ~50 μm to < 20 μm
│   └── Does NOT desorb H from Si-H bonds (requires > 500°C)
├── Cool: natural + gas assist
└── Measure wafer bow (profilometry or Fizeau interferometer)

THERMAL BUDGET TRACKING:
├── RTP spike (450°C × 10s):   thermal budget = 4,500°C·s
├── FGA furnace (425°C × 90 min): thermal budget = 2,295,000°C·s
├── RTP is 500× lower thermal budget than FGA
├── This preserves PECVD film properties and metal interfaces
└── RTP and FGA are complementary, not competing processes

PROCESS SEQUENCE:
Step B6:  Sputter TiN heaters
Step B7:  Pattern TiN (lift-off or etch)
Step B7b: RTP spike anneal (TiN stabilization) ← THIS STEP
Step B8:  PECVD SiO₂ top cladding
Step B8b: RTP stress relief (optional)
Step B9:  Forming gas anneal (furnace, 425°C, 90 min)
Step B10: Via etch through SiO₂ to Au pads

Vendor Options & Pricing

New System Pricing

Refurbished Market

Facility Requirements

Space and Utilities

Safety & Handling

Hazard Summary

Lamp Maintenance

RTP LAMP MAINTENANCE:

LAMP LIFETIME:
├── Typical rated life: 500–2000 hours of operation
├── At low duty cycle (R&D): may last 2–5 years
├── Monitor lamp intensity: replace when output drops > 10%
├── Track hours in process log
└── Keep 1–2 spare lamp modules on hand

REPLACEMENT INDICATORS:
├── Discoloration of quartz envelope (brownish tint = tungsten evaporation)
├── Decreased ramp rate (controller compensating for weak lamps)
├── Temperature non-uniformity increase
├── Lamp failure (open circuit — system will alarm)
└── Visual inspection during scheduled PM (quarterly)

REPLACEMENT COST:
├── Individual lamp (standard T3 halogen): $20–$50 each
├── Full lamp module (10–20 lamps): $200–$600
├── AMAT proprietary lamp arrays: $500–$2,000 per module
├── Annual lamp budget (R&D use): $200–$1,000
└── Labor: 30–60 minutes for module swap (trained operator)