Making Tokens, Pt. 1: Sand into Silicon

This is the first piece in a five-part series tracing the actual supply chain behind a single AI token. You can see all five steps on the home page. This one is about the first step: turning rocks into a tightly controlled semiconductor feedstock.

The starting material isn't sand. It's quartz.

People use the word "sand" loosely when they talk about silicon. The furnace feed is selected quartz or quartzite, not the beach sand you're picturing. Beach sand is contaminated with shell fragments, organic matter, iron oxides, and a parade of other minerals. You can't make a chip out of it.

The furnace feed is selected quartz or quartzite. High-purity quartz used to make crucibles is a related supply chain, but it is not interchangeable with the feedstock reduced to silicon. Spruce Pine is famous for that crucible supply chain. Treating all of these materials as one grade of "sand" hides the distinction.

Grade, impurities, and application determine the price. A mine-gate price for ordinary quartz cannot stand in for the cost of semiconductor crucible material.

Stage 1a: Metallurgical-grade silicon

The first chemical transformation is a carbothermic reduction, run in a submerged-arc electric furnace at around 1900 °C:

SiO₂ + 2C → Si + 2CO

You feed quartzite and a carbon source (typically a mix of metallurgical coal, charcoal, and woodchips) into the top of the furnace. Large electrodes supply the heat needed for the reduction. The carbon reduces the silica, the molten silicon collects at the bottom, and the carbon leaves as carbon monoxide off the top. What pours out at the bottom is called metallurgical-grade silicon (MGS), which is roughly 98-99% pure.

The energy demand is substantial: the furnace needs high-temperature electrical heating throughout the run. The CO that leaves the furnace is enough that there's a whole secondary discussion about how to handle the CO₂ footprint of silicon, which is one reason the industry is increasingly siting these furnaces near hydropower (Iceland, Norway, Quebec, the Pacific Northwest).

MGS is fine for things like making silicones, aluminum-silicon alloys, and steel. It is many, many orders of magnitude too dirty to make chips out of. You wouldn't get a working transistor out of MGS if you tried for a thousand years.

Stage 1b: From MGS to trichlorosilane

To get to electronic-grade purity (we'll come back to what "electronic-grade" actually means in a moment), the silicon has to be put through a chemical purification loop. The trick is that silicon itself is hard to purify directly, because it has a very high boiling point and tends to drag impurities along with it through any straightforward refining. Instead, the industry converts the silicon into a compound that is easy to purify, then converts it back.

The standard route is via trichlorosilane (SiHCl₃, "TCS"):

Si (MGS) + 3 HCl → SiHCl₃ + H₂

This reaction is run in a fluidized bed at around 300 °C. TCS is a liquid at room temperature with a boiling point of just 32 °C, which means it can be distilled. And distilled. And distilled. Modern TCS plants run multi-stage fractional distillation columns that achieve breathtaking purity, removing boron, phosphorus, iron, aluminum, and the rest of the periodic table down to single-digit parts per billion.

The output of this stage is ultra-pure trichlorosilane, which is then ready for the next conversion.

Stage 1c: The Siemens reactor

Here's where the magic finally happens. Inside a Siemens reactor (named after the German company that developed the process in the late 1950s), you have a bell jar with thin polysilicon "seed rods" hanging vertically and heated electrically to about 1100 °C. You introduce a flow of TCS and hydrogen into the chamber. The reverse reaction takes place on the hot rod surfaces:

SiHCl₃ + H₂ → Si + 3 HCl

Silicon deposits on the rods as polycrystalline material, growing them outward during the reactor run. The HCl byproduct is recycled back to the first conversion step, which is one reason TCS chemistry has dominated polysilicon production for so long: the chlorine cycle is closed.

At the end of a Siemens run, you open the reactor and remove the grown polycrystalline silicon rods. These rods are smashed into "polysilicon chunks" the size of fist-sized rocks, which is how electronic-grade poly is shipped to wafer makers.

What does "9N" actually mean

The semiconductor industry talks about purity in "nines." 6N means 99.9999% pure (one part per million of impurity). Each additional "N" is a factor of ten cleaner. 9N and 11N are shorthand for 99.9999999% to 99.999999999% pure: one part per billion to one part per hundred billion of impurity.

If 11N is interpreted as a total impurity mass fraction of 10⁻¹¹, a kilogram contains 10 nanograms, not micrograms, of impurity. Real product specifications also distinguish individual metallic contaminants, dopants, and the way purity is measured. A count of nines is a useful shorthand, not a complete wafer specification.

The practical point is the purification burden. Small traces of the wrong element can change electrical behavior. The buyer needs control of the impurity profile, not just a large number of nines.

Purification and deposition consume substantial energy. The exact intensity depends on the plant, feedstock, recovery loops, and product grade. Wacker describes how its polysilicon production reuses manufacturing byproducts in integrated material loops. A single industry-wide kWh/kg figure would need a dated source and a defined process boundary.

Polysilicon serves both photovoltaics and semiconductors. Those customers have different specifications and purchasing economics. Solar-market price headlines do not automatically describe the material a leading-edge wafer producer buys.

Wacker and Hemlock are examples of semiconductor-grade suppliers. The useful question is whether the supplier can repeatedly meet the required impurity limits. An undated global tonnage or market-share estimate is a poor substitute for that qualification.

What the buyer pays for

The value added here is purification. You start with silicon-bearing rock and end with a feedstock whose unwanted atoms have been tightly controlled. Raw-material, energy, and processing costs all enter the result. I would not infer a current price multiple from a handful of spot prices for different grades.

This is the first thing a token costs. The next stage, pulling a single crystal out of this polysilicon, is where the chemistry gets boring and the physics gets weird.

Sources and calculation notes

Wacker: polysilicon, for applications and integrated material loops.
SUMCO: production processes, for polysilicon feedstock and deliberate dopant addition during crystal growth.
The 11N example above is a mass-fraction calculation: 1 kg × 10⁻¹¹ = 10 ng. It is not a vendor purity certificate.