What project owners need to know.
Granular polysilicon is high-purity silicon made as small, free-flowing beads in a fluidized bed reactor (FBR), rather than as large rods in a Siemens reactor that must be crushed into chunks. Because granules pour like a bulk material, they can be metered through a feeder, which makes them well suited to topping up crucibles, recharge Czochralski (RCz) and continuous Czochralski (CCz) growth. Their known drawbacks are residual hydrogen, which can make granules burst and splash when they meet molten silicon at about 1,420 °C, and fine dust that can float on the melt or block feed valves. Most plants blend granules with chunk rather than choosing one form. For an Indian ingot project, which today imports close to all of its polysilicon, feedstock form is a puller-specification and supply-agreement decision, not only a purchasing one.
Two forms of the same material
Almost all solar and semiconductor silicon starts as polysilicon purified through a gas-phase route. In the Siemens process, which PV-Manufacturing.org describes, electric current heats U-shaped silicon cores inside a reactor and trichlorosilane is reduced with hydrogen so that silicon deposits on the cores. The product is a thick rod that has to be broken into chunks before it can be loaded into a crucible.
In a fluidized bed reactor, small silicon seed particles are suspended in a rising gas stream while a silicon-bearing gas such as silane or a chlorosilane decomposes on their surfaces. The seeds grow into round granules that leave the reactor ready to use. Patents in the field describe this as the core advantage: granules have bulk-material properties and can go straight into single-crystal production, without crushing. Bernreuter Research reports that a monosilane-fed FBR needs about one tenth of the heating electricity of a Siemens rod reactor, but adds that the saving can be largely eaten up when a high share of the output is unusable silicon dust.
- Siemens: rods grown in a bell-jar reactor, crushed into chunks
- FBR: granules grown on seed particles in a gas stream, used as made
- Both are gas-phase purification routes; the difference is the product's shape and handling
- Ask any supplier which route and which grade each lot comes from
Why the shape matters at the puller
Chunks are irregular and pack loosely. A GlobalWafers patent on crucible loading gives a packing density of about 0.55 for chunks and about 0.70 for granules, and describes alternating layers of the two to reach roughly 0.86 to 0.90. A denser initial charge means more silicon per hot cycle. Bernreuter Research reports that a fifty-fifty mix of chunk and granules can shorten crucible filling time by 40% and raise charge weight by 30%.
The bigger reason is feeding. Recharge Czochralski (RCz) refills a hot crucible between ingots, and continuous Czochralski (CCz) adds silicon while the crystal grows. Both need material that flows through a feeder at a controlled rate. Granules do that naturally; chunks need sizing and more mechanical handling. That is why granular feedstock and continuous growth have long been discussed together.
- Blend, don't switch: most charges mix chunk and granules
- Load chunks against the crucible wall and granules between them, as the patent describes
- Match granule size to the feeder the puller supplier specifies
- Treat feedstock form as part of the RCz or CCz decision, not after it
Hydrogen, dust and the melt
Granules carry their own risks into the hot zone. A 1993 Shin-Etsu Handotai patent records that granules from a fluidized bed can contain enough residual hydrogen to make the melt splash when they are dropped into it at about 1,420 °C. The GlobalWafers loading patent warns that hydrogen can expand suddenly on contact with the melt, and that trapped gas can form bubbles that end up in the ingot. Splattered silicon also lands on graphite and coated hot-zone parts.
Producers have worked on this. A Wacker Chemie patent filed in 2013 claims granules with hydrogen of 0.01 to 0.2 ppmw, compared with around 50 ppmw in older material, along with low fine dust and no ultrafine particle inclusions, which it links to dislocations. The two patents do not set the same hydrogen target, which is the practical lesson: hydrogen, chlorine, dust and particle size are numbers to agree with each supplier and test on arrival, not assumptions. Fine dust matters on its own account, because it can float on the melt and block feed valves.
- Put residual hydrogen, chlorine and fines limits into the supply agreement
- Ask for surface-metal results and the method used to measure them
- Track loss of single-crystal structure against feedstock lot
- Inspect hot-zone parts for silicon splatter after granule-rich runs
Where granular silicon stands in 2025–26
For years FBR was a technology of more promise than volume. Writing in PV Tech in 2014, Johannes Bernreuter questioned whether FBR could reach near electronic-grade purity at low cost and noted that reactors cannot simply be scaled from pilot to industrial size because the fluid dynamics change. His later overview lists only a handful of companies that ever ran FBR plants at scale.
That picture has shifted. TaiyangNews reported in April 2025 that the largest granular producer had 480,000 tonnes of granular capacity at the end of 2024, shipped about 281,900 tonnes that year, and estimated granules at more than 40% of feedstock at its leading customers. The same report cites the producer's own purity figures for metals in the parts-per-billion range. These are company claims, but they show that granular silicon is now a mainstream feedstock option rather than a niche one.
- Treat producer purity and energy figures as claims to verify
- Ask for lot-level certificates, not brochure averages
- Qualify more than one granule source before relying on it
- Watch how n-type customers' specifications treat granular content
What an Indian ingot plant should weigh
A NITI Aayog report, as summarised by Down To Earth, puts India's import dependence at close to 100% for polysilicon and above 90% for wafers, with about 2 GW of wafer capacity in March 2025. Government support for domestic polysilicon has been under discussion but, as of the latest public reporting, not notified. For now, an Indian ingot plant buys imported feedstock, and the choice of form travels with it.
With ALMM List-III proposed to bring ingots and wafers into the approved-list framework from June 2028, plants being specified now will be judged on resistivity window, lifetime and consistency. Feedstock form touches all three: it sets how the puller can be fed, how much silicon each cycle yields and which contamination risks enter the melt. It belongs in the puller specification and the supply agreement together. Current ALMM requirements should always be confirmed directly with MNRE.
- Decide the chunk-granule mix alongside batch, RCz or CCz growth
- Write form, size, hydrogen, dust and metals limits into feedstock contracts
- Plan storage and handling that keeps granules clean and dry
- Keep feedstock lot traceability through to the ingot
How JRST supports this requirement
JRST supports ingot and wafer projects in planning feedstock: linking chunk and granular polysilicon choices to batch, recharge or continuous Czochralski growth, and setting feedstock specifications, supplier qualification and acceptance testing. Figures on this page are drawn from public educational sources, patents, industry analysis and trade reporting, some of them historical or company-reported, and should be validated for the specific project; crystal quality depends on equipment, recipe and operating conditions, and compliance requirements must be confirmed with the relevant authorities.
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
What is granular polysilicon?
High-purity polysilicon made as small, free-flowing beads in a fluidized bed reactor, where silicon from a gas such as silane deposits on suspended seed particles. It can be used as made, without crushing.
How is granular polysilicon different from Siemens chunk polysilicon?
Siemens polysilicon grows as rods in a bell-jar reactor and must be broken into irregular chunks. Granules come out of the reactor round and sized, so they pour and pack like a bulk material.
Why is granular silicon used for recharge and continuous Czochralski growth?
Both methods add silicon to a hot crucible through a feeder. Free-flowing granules can be metered at a controlled rate far more easily than chunks.
Why can granules splash in the melt?
Granules can hold residual hydrogen. When they meet molten silicon at about 1,420 °C the gas can expand suddenly, splashing the melt and depositing silicon on hot-zone parts. Hydrogen limits should be agreed with the supplier.
Should a plant use only granular polysilicon?
Usually not. Published loading methods blend chunks and granules, for example with chunks against the crucible wall, to raise charge density and protect the crucible. The right mix depends on the puller and recipe.
Does India make granular polysilicon?
India currently imports close to all of its polysilicon, according to a NITI Aayog report. Support for domestic polysilicon has been discussed but not notified as of the latest public reporting.
How can JRST help?
JRST can help ingot projects choose feedstock form and blend for their growth route, and plan feedstock specifications, qualification and acceptance testing. Outcomes remain project-specific and must be validated.
Primary sources and further reading
Last reviewed 2026-10-07. Technical scope, policy eligibility, availability, and commercial terms should be independently confirmed for each project.