Epitaxy Systems

Si and SiGe epi reactors, design, and in-situ monitoring

Epitaxy Reactor Design

Epitaxy requires the highest cleanliness and temperature control of any deposition process:

Single-wafer reactors: Dominant for advanced logic. The wafer sits on a rotating susceptor in a cold-wall chamber. Lamp heating provides rapid temperature ramping (50°C/s) to process temperatures of 500–1100°C.
Gas system: Ultra-pure precursors (SiH₄, SiH₂Cl₂, GeH₄) with ppb-level purity requirements. Mass flow controllers provide precise gas composition control for SiGe alloy composition.
In-situ monitoring: Real-time measurements during growth:
- Pyrometry for wafer temperature
- Reflectometry for film thickness and growth rate
- Residual gas analyzers for chamber cleanliness
Selective epi: HCl is added to the gas mix to etch deposited material on non-silicon surfaces while allowing growth on exposed silicon only.

Key Concept: Pre-epi Clean

Even a single monolayer of oxide or carbon on the silicon surface will prevent epitaxial growth. Reactors include an in-situ hydrogen bake (800–1100°C) to remove native oxide before growth. This clean step is as critical as the deposition itself.

ALD Reactors

Stepper & Scanner Basics

Knowledge Check

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Why is an in-situ hydrogen bake performed before epitaxial growth?

To remove native oxide from the silicon surface so crystal growth can proceedTo heat the wafer to the correct temperatureTo calibrate the temperature sensorsTo purge the chamber of previous process gases