Quick Answer
A quartz gas injector is a high-purity fused silica tube, ring, or multi-port manifold that delivers process gas into a diffusion, LPCVD, or CVD furnace at a defined location and hole pattern. It is not the process tube. The tube is the reaction chamber; the injector owns gas distribution.
Film thickness and dopant uniformity along the wafer load depend on hole diameter, hole pitch, angular orientation, and insertion depth. FGQuartz fabricates quartz injectors and injector rings to customer drawing — single-lance, multi-hole, ring, and side-arm geometries — using oxy-hydrogen flame welding and CNC drilling. No minimum order quantity. Send the drawing or a sample and we reply within 24 business hours.
Key Takeaways
Spec the injector as part of the furnace quartz set, not as a separate afterthought. A mismatched injector will produce a non-uniform film even when the tube and boat are correct.
Three geometries cover most tools: a single-lance injector tube, a multi-hole injector tube, and an injector ring. Side-arm injectors welded onto the process tube are a fourth option when the gas must enter through the chamber wall.
Hole pattern is the drawing. OD/ID and length get the part into the furnace; hole count, diameter, spacing, and clocking decide whether the film is uniform.
Quartz is used because it stays chemically inert in chloride, hydride, and oxide chemistries and survives the same thermal cycle as the process tube.
Common failures are weld cracks at the side arm, hole erosion, and particle generation from an unpolished inner bore — not “the quartz being the wrong grade.”
For RFQ, send furnace platform, wafer size, process chemistry, mating tube ID, and a hole-pattern drawing, or the worn sample.
What a Quartz Gas Injector Actually Is
Inside a horizontal or vertical furnace the process tube defines the hot envelope. The wafer boat holds the load. The paddle inserts and extracts it. None of those parts put gas where the reaction needs it. That is the injector’s job.
A quartz injector is a wetted fused-silica gas path: precursor or dopant gas leaves the metal gas box, enters the quartz, and is released into the tube through one or more orifices. Because the gas contacts only SiO₂ after the final seal, the injector does not add metallic contamination to the film.
It is a different component from the process tube, which is the reaction chamber. A furnace liner is a sacrificial inner wall and does not distribute gas. A quartz showerhead is a large-area multi-hole plate or cap — a different drawing from a lance injector. Metal mass-flow hardware stays with the tool OEM. FGQuartz supplies the quartz: injectors, injector rings, multi-port manifolds, and, when the drawing calls for it, the side-arm welded onto the process tube.
A matched furnace set is covered in our diffusion furnace quartz parts guide. This article is only about the injector.
How Injectors Work in Diffusion, LPCVD and CVD
All three processes deposit or drive a film from a gas-phase species. They do not ask the injector for the same flow field.
Diffusion and oxidation
Dopant sources such as POCl₃ and BBr₃, and oxidants, are introduced at one end or through a side port. The injector sets the entry point and prevents a hard jet from washing the first few wafers. Uniformity along a 100–300 mm load is mostly a tube-and-boat problem; the injector’s job is a stable, centered feed and a hole size that does not choke or blast.
LPCVD
Low pressure lengthens the mean free path. Species travel farther before reacting, which is why LPCVD coats complex geometry well — and why a bad hole pattern shows up as a thickness smile or frown along the boat. Multi-hole lances and injector rings exist for this reason: they spread the partial pressure instead of dumping it at one axial station.
CVD
Atmospheric or sub-atmospheric CVD shortens the mean free path. Local jetting from an oversized orifice creates a thick spot in front of the hole and a starved zone behind it. Hole diameter and standoff from the wafer edge matter more than in LPCVD.
The chemistry changes. The quartz does not. The same fused-silica injector geometry is reused across nitride, oxide, polysilicon, and dopant recipes. What changes is hole pattern, insertion depth, and how the injector is joined to the tube.
Quartz Injector Types FGQuartz Manufactures
We do not sell a catalog SKU. Geometry follows the tool. The forms below cover the drawings we see most often from semiconductor customers.
Single-lance injector tube
A straight fused-silica tube, usually open or flame-sealed at the distal end, with one or a few orifices. Used when the process wants a single axial feed — many diffusion and oxidation recipes. Simple to replace and easy to reverse-engineer from a broken sample. Specify overall length, OD/ID, end treatment, orifice diameter, and distance from the tip.
Multi-hole quartz injector tube
A lance with a drilled or flame-opened hole pattern along its length. This is the default LPCVD and CVD injector when gas must be distributed along the wafer load. Hole diameter is typically in the 0.5–3 mm range. Pitch and clocking — holes at 12 o’clock versus staggered 10/2 o’clock — are process-specific. CNC diamond drilling holds hole position. Flame-opened holes are acceptable when the drawing allows a fire-polished edge and a slightly looser diameter tolerance.
Quartz injector ring
A toroidal or segmented ring that sits at a fixed axial station and releases gas around the tube circumference. Used when the recipe needs azimuthal uniformity more than axial distribution — some CVD and vertical-furnace layouts. Rings are flame-welded from tube stock, then drilled. Mating to the feed tube is the stress concentrator; that weld gets extra annealing.
Side-arm and multi-port injector
A branch welded through the wall of the process tube or onto a flange neck. Tees, Y-joints, and crosses fall in this family. They are custom quartz fabrication work: oxy-hydrogen welding, fire polish, anneal. The side-arm angle, penetration depth, and internal lip all affect the jet. If you send a cracked tube with the arm still attached, we reverse-engineer the arm rather than guessing from a photo.
Showerhead-style quartz distributor
A plate, cap, or large-diameter drilled face that spreads gas over an area. Common on some CVD and PECVD chambers. This is a cold-machining job more than a tube-drawing job: CNC milling, grinding, hole arrays. Only build it when the drawing or sample defines hole count and pattern. Do not copy a metal showerhead pitch onto quartz without checking thermal expansion and hole-edge strength.
Hole Pattern and Gas Uniformity
This is the section that belongs on the drawing, not in a process recipe document.
Hole diameter: too small and the injector becomes a restriction; pressure drop rises and holes erode faster. Too large and the gas jets, producing a local thick film. If you are copying a worn injector, measure the original hole, not the eroded one.
Pitch: axial spacing sets how many injection stations the load sees. LPCVD films are sensitive to this. A pattern that worked on a 150 mm boat will not automatically work on a 300 mm boat in a longer tube.
Clocking: holes aimed at the wafer edge, at the tube wall, or staggered, change recirculation. There is no universal angle. Copy the qualified tool.
Open versus closed distal end: a closed, flame-sealed end forces all gas through the holes. An open end dumps leftover flow out the tip and is only correct if the original part was open.
Insertion depth: the injector that stops 50 mm short of the first wafer and the injector that runs past the last wafer are different tools. Depth belongs on the drawing as a dimension from a flange face or tube end, not as “insert until it looks right.”
If you do not have a drawing, send the furnace model, wafer size, process (diffusion / LPCVD / CVD), and the mating quartz tube inner diameter. We can often reconstruct a starting pattern from the sample plus those four facts. We will not invent a hole pattern for an unproven recipe — that is process engineering, not quartz fabrication.
How the Injector Mates with the Process Tube
Four interfaces show up on almost every RFQ.
Slip-fit into the tube or liner. OD of the injector must clear the tube ID with a defined gap. Give both diameters. A tight fit that rattles at room temperature can bind after thermal expansion.
Ground joint or tapered neck. Repeatable insertion depth, used on laboratory and some production tools. Specify the joint size, not just “tapered.”
Flanged end. Flame-welded flange against a metal or quartz end cap. Flange OD, thickness, bolt circle if any, and seal face finish all need to be on the drawing.
Welded side-arm. The injector is not removable. Replacement means a new tube-and-arm assembly. Plan the spare as a set; see the diffusion furnace quartz parts article.
Whatever the interface, the inner bore that sees gas should be fire-polished. Ground ID sheds particles into the first run.
Why Quartz Is Used for Gas Injectors
Fused silica is the default because it matches the rest of the hot zone. It stays in continuous service in the same temperature band as the process tube, typically up to about 1100–1200 °C depending on chemistry. It is chemically inert toward common hydride, chloride, and oxide precursors, and does not plate out metal ions the way a stainless injector would. Low thermal expansion means a long lance does not walk out of alignment every cycle. Optical clarity allows inspection of hole condition and internal deposits.
Grade follows the process, not a marketing name. Semiconductor furnace injectors are made from high-purity fused silica consistent with the tube they sit in. Optical-grade JGS1 is the wrong specification unless the part also has to transmit deep UV — an injector generally does not. If the tube specification already lists OH content and trace metals, put the same line on the injector drawing so the two parts age together.
Material properties are tabulated on our technical specifications page. Copy the values you need onto the injector print; do not point at a generic “quartz” callout.
Design Constraints That Show Up in Fabrication
The academic list is material compatibility, thermal expansion, and flow control. The shop list is more specific.
Weld stress at the branch. Side-arms and ring feed tubes crack at the weld, not in the straight lance. We anneal after welding. If your previous injector died at the joint, say so — we will change the fillet and anneal cycle before copying the rest of the geometry.
Thermal shock on load and unload. A thin-wall lance equalizes faster than a thick ring. Do not specify heavy wall “for strength” unless the drawing needs it; extra mass increases thermal gradient and does not fix a bad weld.
Hole-edge strength. Drilled holes need a chamfer or fire polish. A sharp diamond-drilled edge is a crack starter and a particle source.
Chemistry attack. Some etch and clean steps enlarge holes over time. That is wear, not a manufacturing defect. When you requalify a replacement, measure holes on a new part, not on the scrap.
Metal-to-quartz transition. If the injector starts in stainless and becomes quartz, the joint is usually on the customer’s gas box, not in our flame shop. Tell us where quartz begins.
Finite-element models of the furnace flow are the process team’s tool. Our job is to hold the hole positions and weld integrity that those models assume. We do not design mass-flow controllers or recipes.
Request a Quartz Gas Injector Quote
A quartz gas injector is a small part with a large effect on film uniformity. Treat hole pattern, insertion depth, and the joint to the process tube as the design, not as details to be guessed on the shop floor.
FGQuartz has built semiconductor-grade fused silica components in Lianyungang since 2005, including injectors, injector rings, and the tubes they run in. Send the furnace model, wafer size, process chemistry, and the drawing — or the failed sample — and the engineering review comes back as a manufacturable injector, not a catalog nearest-size.
Request a manufacturing quote. We respond within 24 business hours.