Complete Quartz Component Guide for Diffusion Furnace Systems

A horizontal diffusion furnace contains six to twelve individual quartz components. Each has a specific function, material requirement, and replacement schedule. This guide covers every major quartz component in a standard horizontal furnace system — what it does, what it’s made of, and how to specify it.

The Diffusion Furnace System Overview

A horizontal diffusion furnace consists of a resistively heated tube furnace with a quartz process tube (or pair of tubes) through which wafers are loaded in boats. Process gases flow through the tube over the wafer stack. The full quartz component set includes:

Outer (liner) tube
Inner (process) tube
Wafer boat
Source tube or gas injector
Gas distribution baffle
Push rod
Boat stand / pedestal
End cap flanges (sometimes quartz)

Component 1: Outer Tube (Liner Tube)

Function: Isolates the inner process tube from the furnace heating elements. Prevents contamination from the refractory furnace liner. Can be sacrificially replaced rather than the expensive inner tube.

Material: Grade 1 natural fused quartz or Grade 3 opaque quartz

Key specifications:

OD: Matched to furnace tube ID with 2–5 mm radial clearance
Wall: 2–4 mm
Length: Process zone length + 100–200 mm
Bow: < 2 mm per 1000 mm length

Replacement interval: 12–24 months (or when devitrification or deposition buildup is visible)

Component 2: Inner (Process) Tube

Function: Primary reaction chamber — the wafers process inside this tube. The tube material directly affects wafer contamination levels.

Material: Grade 1 (standard diffusion) or Grade 2 synthetic silica (CVD, gate oxide, advanced processes)

Key specifications:

OD/ID tolerance: ±0.5 mm / ±0.3 mm
Wall uniformity: ±0.3 mm
Bow: < 1 mm per 1000 mm
Inner surface finish: Ra ≤ 1.6 μm
He leak rate (flanged): < 1×10⁻⁹ mbar·L/s

Replacement interval: 6–18 months depending on process chemistry and temperature

Component 3: Wafer Boat

Function: Holds wafers at the correct pitch during thermal processing. The boat geometry controls wafer-to-wafer spacing and therefore process uniformity.

Material: Grade 1 (standard) or Grade 2 synthetic silica (ultra-high-purity processes)

Key specifications:

Slot pitch: Specified by process (4.76 mm / 6.35 mm / 7.62 mm / 9.52 mm for 4”/6”/8”/12” wafers)
Slot pitch tolerance: ±0.1 mm (tight) or ±0.2 mm (standard)
Slot width: Wafer thickness + 0.15–0.3 mm clearance
Seating angle: 88° ± 0.5° (near-vertical for gas uniformity)

Replacement interval: 3–12 months (boats are consumable — slots wear and widen with each loading cycle)

Component 4: Gas Injector / Source Tube

Function: Distributes process gas (O₂, N₂, Cl₂, POCl₃, etc.) along the length of the wafer stack for uniform gas exposure.

Material: Grade 1 (standard) or Grade 2 synthetic silica (where gas purity is critical)

Key specifications:

Hole diameter: 0.3–2 mm (matched to flow rate and process)
Hole positional accuracy: ±0.02 mm
Tube OD: 6–25 mm (matched to furnace tube ID clearance)
He leak rate (end fittings): < 1×10⁻⁹ mbar·L/s

Replacement interval: 6–24 months (or when hole enlargement affects gas uniformity)

Component 5: Gas Distribution Baffle

Function: Conditions gas entering the process zone — prevents direct impingement of cold gas on wafers near the furnace entrance.

Material: Grade 1 (transparent) or Grade 3 (opaque — for combined gas conditioning + thermal shielding)

Key specifications:

OD: Tube ID − 1–3 mm (close-fit to direct gas flow through central opening)
Central opening: 20–40% of tube cross-section area
Flatness: < 0.2 mm
Perpendicularity: < 0.2 mm

Replacement interval: 12–36 months (long service life — not in direct contact with aggressive chemistry)

Component 6: Push Rod

Function: Mechanical tool for loading and unloading the wafer boat into and out of the process tube.

Material: Grade 1 natural fused quartz

Key specifications:

OD: 10–25 mm (sufficient stiffness for boat weight + process tube length)
Straightness: < 2 mm bow per 1000 mm
Length: Furnace tube length + 200–400 mm handle extension

Replacement interval: 12–36 months (replace when bent or contaminated)

Ordering Replacement Components

When ordering replacement components, provide:

Furnace OEM and model — we maintain a database of standard tube dimensions by furnace model
Wafer size — determines boat slot pitch and tube OD
Process chemistry — determines Grade 1 vs. Grade 2 requirement
Current component dimensions — OD, ID, wall, length (measure worn component if drawing is unavailable)

We typically respond with a quotation within 24 hours and can ship standard components in 5–10 working days.

Complete Quartz Component Guide for Diffusion Furnace Systems