What project owners need to know.
A quartz crucible for Czochralski silicon growth is made by arc fusion: high-purity quartz sand is packed against the inside of a rotating mould, held there by centrifugal force, and melted from the inside by an electric arc into a single glass vessel. A vacuum drawn through the mould wall, or controlled inner-layer deposition, removes gas so the inner layer that touches molten silicon is dense and nearly bubble-free, while the outer wall stays bubble-rich and opaque for strength and heat diffusion. The crucible is then cut, cleaned, inspected and in some cases coated. This guide is general industry information drawn from published sources. It is not a process specification, and any figure should be validated against the specific equipment, materials and supplier documentation for a project.
Why the crucible matters
Every Czochralski ingot is grown from silicon melted in a fused-quartz crucible. The crucible must hold molten silicon above about 1,414 °C for many hours without softening, cracking or releasing particles. Its inner surface dissolves slowly into the melt, so it is also the main source of oxygen in Cz silicon. How the crucible is built decides how cleanly it behaves in the puller.
Starting material: high-purity quartz sand
Crucibles are made from high-purity quartz sand, not ordinary silica sand. Impurities such as aluminium, alkalis, iron and titanium in the sand end up in the glass, and from there can enter the melt or encourage bubbles and uneven devitrification. Makers commonly use their purest sand for the inner layer and a slightly lower grade for the outer body. India's Minerals (Evidence of Mineral Contents) Amendment Rules, 2026 define high-purity quartz as SiO2 above 99.99% with total impurities below 50 ppm.
Moulding in a rotating mould
The sand is fed into a hollow mould that spins about its vertical axis. Centrifugal force holds a layer of sand against the inner wall and base in the shape of the crucible. US Patent 4,416,680, granted to Heraeus in 1983, describes a mould with gas-pervious walls, either metal with fine bores or sintered porous metal, and later patents use carbon moulds. Layer thickness and grain size are controlled because they set the final wall thickness and bubble structure.
Arc fusion
An electric arc between carbon electrodes is lowered into the spinning mould and melts the sand from the inside out. The sand nearest the arc fuses into glass, while a thin layer next to the mould stays unmelted and insulates the mould from the heat. When a thick enough fused wall has formed, heating stops and the crucible is removed, in the Heraeus patent by compressed air.
Inner layer vs outer layer
A crucible is deliberately two-layered. The outer body contains many small bubbles, which make it opaque and help it diffuse heat evenly from the heaters. The inner layer, which touches molten silicon, should be as dense and bubble-free as possible, because bubbles near the surface can open during the run and release particles that end dislocation-free growth.
Patents describe several ways to achieve that. The 1983 Heraeus patent draws a vacuum through the mould wall so gas leaves the sand before it seals into glass. US Patent 8,789,391 describes spreading sand grains into the arc so they melt and are flung onto the wall, building the inner layer in place, after flushing the porous wall with helium. US Patent 8,286,447 starts melting at the rim so the vacuum can be held. US Patent 9,593,432 claims a bubble-free inner layer of 80 µm to 4 mm on an opaque, bubble-containing outer body.
- Outer layer: bubble-rich, opaque, gives strength and even heat
- Inner layer: dense, near bubble-free, highest-purity sand
- Vacuum or gas exchange removes trapped gas during fusion
Cutting, cleaning, coating and inspection
After fusion the rim is cut to height, edges are ground, and the crucible is cleaned to remove surface contamination. Some crucibles receive an inner or outer coating, for example a barium compound that makes the surface devitrify into an even cristobalite shell during the pull. Inspection covers dimensions, wall thickness, visual and bubble checks of the inner layer, and purity records for the sand lots used.
What buyers should check
Buyers cannot see inside a crucible maker's furnace, but they can ask for evidence.
- Sand source and certificate of analysis for inner and outer layers
- Inner-layer thickness and bubble specification, and how it is measured
- Coating type, if any, and how it is applied
- Dimensional tolerances for the specific puller and hot zone
- Lot traceability from sand batch to crucible serial number
Where this fits in the quartz-to-wafer chain
The crucible is the link between mined quartz and silicon. Quartz stone is processed into high-purity sand, the sand is fused into a crucible, the crucible holds the polysilicon melt, and the ingot grown from it is sliced into wafers. A weakness at the sand or fusion stage shows up later as lower ingot yield, so crucible quality is an upstream decision with downstream cost.
How JRST supports this requirement
JRST works on the quartz-to-crucible link of the silicon chain: high-purity quartz sand from Pondicherry, crucible sourcing and qualification for Indian Czochralski projects, and the inspection checks that tie crucible quality to ingot yield. Scope is confirmed project by project.
Discuss your requirement
Mohammed Saif Zaveri connects JRST's industrial content to execution conversations.
As Co-Founder and designated partner of JRST Technology LLP, Mohammed Saif Zaveri works across industrial growth, strategic partnerships, client conversations, equipment strategy, and project pathways for silicon, solar, semiconductor, and advanced-manufacturing opportunities.
This knowledge page is part of JRST's public industrial knowledge base, designed to help buyers move from search terms and early research toward a structured technical-commercial discussion.
View Mohammed Saif Zaveri's profileConnect on LinkedInFrequently asked questions
How is a quartz crucible made?
By arc fusion. High-purity quartz sand is held against the inside of a rotating mould by centrifugal force and melted from the inside by an electric arc, with vacuum or gas exchange used to make the inner layer nearly bubble-free.
What is a quartz crucible made of?
Fused silica glass made from high-purity quartz sand. The inner layer uses the purest sand, and the outer body may use a slightly lower grade.
Why does a quartz crucible have a bubble layer?
The bubble-rich outer layer is opaque and diffuses heat evenly. Only the inner layer, which touches molten silicon, needs to be nearly bubble-free.
Why does the purity of the sand matter?
Impurities in the sand go into the crucible glass and can enter the silicon melt, promote bubbles or cause uneven devitrification, all of which can reduce ingot yield.
Is a quartz crucible reusable?
In standard Czochralski growth, no. The crucible devitrifies and usually cracks on cooling, so it is used for one run, though continuous and recharge methods grow several ingots in one crucible before it is discarded.
Does JRST make quartz crucibles?
JRST works upstream on high-purity quartz sand from Pondicherry and on crucible sourcing for Indian ingot projects. Crucible scope is confirmed project by project.
Primary sources and further reading
Last reviewed 2026-10-29. Technical scope, policy eligibility, availability, and commercial terms should be independently confirmed for each project.