Thermal Evaporator

Role in QLT Fabrication

The thermal evaporator is responsible for depositing a 500 nm stoichiometric As₂S₃ (arsenic trisulfide) thin film onto LIGENTEC Si₃N₄ waveguide chips. This hybrid nonlinear overlay enables optical parametric conversion (OPC) modules ● the core of QLT's GAP03 product line.

Chalcogenide glasses like As₂S₃ offer exceptional third-order nonlinearity (n₂ ≈ 2–5 × 10⁻¹⁸ m²/W, 100–200× fused silica) and broad mid-IR transparency (visible to >10 μm). Recent Nature Communications work (Xia et al., 2025) confirmed that low-temperature thermal deposition of chalcogenide films onto silicon nitride circuits enables reconfigurable nonlinear photonics without wafer bonding ● directly validating QLT's hybrid integration approach.

This is the MOST UNUSUAL deposition step in our process ● very few labs evaporate chalcogenide glasses onto photonic chips. The MIT group (Hu Lab) and ANU group (Luther-Davies, Madden) have published extensively on single-source thermal evaporation of As₂S₃ from resistively heated tantalum/tungsten boats under high vacuum (10⁻⁶–10⁻⁷ Torr), achieving films up to 5 μm thick with losses < 0.2 dB/cm at 1550 nm.

Process Requirements

Why Thermal Evaporation

Recommended Configuration

The Nexdep is rated as a "workhorse" by 300-user clean room labs (NNCI member facilities). It supports reactive evaporation (optional O₂/N₂ injection) and can be retrofitted with sputtering cathodes or e-beam sources.

Process Integration

QLT PROCESS FLOW ● Thermal Evaporator (Step G3):

PRE-REQUISITES:
├── LIGENTEC SiN chip returned with waveguides + SiO₂ cladding (Step B1-B8)
├── OPC module windows opened by lithography + etch (Step G1-G2)
└── Glovebox (#35) operational with N₂ atmosphere

STEP 1: Source Preparation (Glovebox)
├── Weigh 2–3 g As₂S₃ bulk glass (6N, from AMI or IRradiance)
├── Crush to ~1 mm pieces with agate mortar under amber light
└── Load into tungsten boat; place boat in sealed transfer container

STEP 2: Chamber Preparation
├── Vent evaporator chamber with dry N₂
├── Install loaded boat on source terminals (heavy copper lugs)
├── Mount chip on substrate holder (heated chuck, center position)
├── Install clean QCM crystal (Au-coated, 6 MHz)
└── Close chamber; start pump-down sequence

STEP 3: Pump-Down & Conditioning
├── Rough pump to < 100 mTorr (5 min)
├── Open gate valve to turbo pump
├── Pump to < 5×10⁻⁷ Torr (45–90 min)
└── Start substrate heater ramp to 150°C

STEP 4: Deposition
├── Ramp source current (1 A/s) until QCM reads 5 nm/min
├── Open substrate shutter
├── Monitor rate and thickness in real-time (Aeres® or QCM controller)
├── Total deposition time: ~100 minutes for 500 nm
└── Close shutter when target thickness reached

STEP 5: Cool-Down & Unload
├── Turn off source power; maintain substrate heater at 100°C for 10 min
├── Cool substrate to < 80°C
├── Vent with dry N₂
└── Transfer chip to glovebox immediately (minimize ambient exposure)

STEP 6: Post-Deposition Anneal
├── Anneal at 130°C for 24 hours in N₂ (inside glovebox)
└── This relieves film stress and stabilizes refractive index

STEP 7: Qualification
├── Ellipsometry: verify n = 2.40 ± 0.02, thickness 500 ± 10 nm
├── Raman spectroscopy: verify As₂S₃ stoichiometry peaks
└── Visual inspection under amber light: no cracks, delamination, or haze

Vendor Options & Pricing

New System Pricing

Used/Refurbished Market

Vendor Directory

Price History and Market Dynamics

THERMAL EVAPORATOR PRICE TREND (used Denton/Edwards class):

2018-2019:  $5-12k (abundant academic surplus)
2020-2021:  $6-15k (stable; some COVID lab closures reduced supply)
2022-2023:  $8-18k (modest increase; photonics/MEMS demand growing)
2024-2025:  $8-15k (stable; supply exceeds demand)
2025-2026:  $8-15k (stable; FAVORABLE BUYER'S MARKET)

TREND: Thermal evaporators are COMMODITY ITEMS in the used market.
Every time a lab upgrades to e-beam or sputtering, they sell their
thermal system. Prices are STABLE and LOW.

KEY BUYERS:
├── Academic startup labs
├── MEMS packaging (Au/Cr adhesion layers)
├── Organic electronics / OPV research
└── Chalcogenide photonics (our niche ● very small market)

Facility Requirements

Floor Space and Layout

Electrical Requirements

NOTE: Thermal evaporators use LOW VOLTAGE, HIGH CURRENT source power supplies. The NANO 36 standard supply is 12V @ 400A. Heavy copper lugs are required between power supply and source feedthrough.

Environmental and Special Requirements

Safety & Handling

Hazard Summary

Required Safety Infrastructure

Required Training

• Arsenic handling and awareness (EH&S certified)
• Vacuum system operation
• QCM operation and calibration
• Emergency procedures (arsenic spill response)
• LOTO for electrical maintenance