How we manufacture silicon

14 01 2021

A letter to Greta Thunberg: computers’ crucial ingredient not found in nature


Originally posted on

Dear Greta,

Could we discuss silicon, that substance on which our digital world depends?1Silicon is a semiconductor, and tiny electronic switches called transistors are made from it. Like brain cells, transistors control the flow of information in a computer’s integrated circuits. Transistors store memory, amplify sound, transmit and receive data, run apps and much, much more.

One smartphone (call it a luxury, hand-held computer with portals to the Internet) can hold more than four billion transistors on a few tiny silicon chips, each about the size of a fingernail.

Computer chips are made from electronic-grade silicon, which can have no more than one impure atom per billion. But pure silicon is not found in nature. Producing it requires a series of steps that guzzle electricity2 and generate greenhouse gases (GHGs) and toxic waste.

Silicon’s story is not easy to swallow. Still, if we truly aim to decrease our degradation of the Earth and GHG emissions, we cannot ignore it.

Step one

Silicon production starts with collecting and washing quartz rock (not sand), a pure carbon (usually coal, charcoal, petroleum coke3, or metallurgical coke) and a slow-burning wood. These three substances are transported to a facility with a submerged-arc furnace4.

Note that transporting the raw materials necessary for silicon production—between multiple countries, via cargo ships, trucks, trains and airplanes—uses oil and generates greenhouse gases.5

Step two

Kept at 3000 °F (1649 °C) for years at a time, a submerged-arc furnace or smelter “reduces” the silicon from the quartz. During this white-hot chemical reaction, gases escape upward from the furnace. Metallurgical-grade silicon settles to the bottom, 97-99% pure—not nearly pure enough for electronics.6

If power to a silicon smelter is interrupted for too long, the smelter’s pot could be damaged.7 Since solar and wind power is intermittent, they cannot power a smelter.

Typically, step two takes up to six metric tons of raw materials to make one metric ton (t) of silicon. A typical furnace consumes about 15 megawatt-hours of electricity per metric ton (MWh/t)8 of silicon produced, plus four MWh/t for ventilation and dust collection; and it generates tremendous amounts of CO2.9

Manufacturing silicon also generates toxic emissions. In 2016, New York State’s Department of Environmental Conservation issued a permit to Globe Metallurgical Inc. to release, per year: up to 250 tons of carbon monoxide, 10 tons of formaldehyde, 10 tons of hydrogen chloride, 10 tons of lead, 75,000 tons of oxides of nitrogen, 75,000 tons of particulates, 10 tons of polycyclic aromatic hydrocarbons, 40 tons of sulfur dioxide and up to 7 tons of sulfuric acid mist.10 To clarify, this is the permittable amount of toxic waste allowed annually for one New York State metallurgical-grade silicon smelter. Hazardous waste generated by manufacturing silicon in China likely has significantly less (if any) regulatory limits.

Step three

Step two’s metallurgical-grade silicon is crushed and mixed with hydrogen chloride (HCL) to synthesize trichlorosilane (TCS) gas. Once purified, the TCS is sent with pure hydrogen to a bell jar reactor, where slender filaments of pure silicon have been pre-heated to about 2012 °F (1100 °C). In a vapor deposition process that takes several days, silicon gas atoms collect on glowing strands to form large polysilicon rods—kind of like growing rock candy. If power is lost during this process, fires and explosions can occur. A polysilicon plant, therefore, depends on more than one source of electricity—i.e. two coal-fired power plants, or a combination of coal, nuclear and hydro power.11

A large, modern polysilicon plant can require up to 400 megawatts of continuous power to produce up to 20,000 tons of polysilicon per year (~175 MW/hours per ton of polysilicon).12 Per ton, this is more than ten times the energy used in step two—and older plants are usually less efficient. A single plant can draw as much power as an entire city of 300,000 homes.

Once cooled, the polysilicon rods are removed from the reactor, then sawed into sections or fractured into chunks. The polysilicon is etched with nitric acid and hydrofluoric acid13 to remove surface contamination. Then, it’s bagged in a chemically clean room and shipped to a crystal grower.

Step four

Step three’s polysilicon chunks are re-melted to a liquid, then pulled into a single crystal of silicon to create a cylindrical ingot. Cooled, the ingot’s (contaminated) crown and tail are cut off. Making ingots often requires more electricity than smelting.14 The silicon ingot’s remaining portion is sent to a slicer.

Step five

Like a loaf of bread, the silicon ingot is sliced into wafers. More than 50 percent of the ingot is lost in this process. It becomes sawdust, which cannot be recycled.15

Step six

Layer by layer, the silicon will be “doped” with tiny amounts of boron, gallium, phosphorus or arsenic to control its electrical properties. Dozens of layers are produced during hundreds of steps to turn each electronic-grade wafer into microprocessors, again using a great deal of energy and toxic chemicals.

Questions for a world out of balance

In 2013, manufacturers began producing more transistors than farmers grow grains of wheat or rice.16Now, manufacturers make 1000 times more transistors than farmers grow grains of wheat and rice combined.

After I learned what it takes to produce silicon, I could hardly talk for a month. Because I depend on a computer and Internet access, I depend on silicon—and the energy-intensive, toxic waste-emitting, greenhouse gas-emitting steps required to manufacture it.

Of course, silicon is just one substance necessary for every computer. As I report in letter #3, one smartphone holds more than 1000 substances, each with their own energy-intensive, GHG-emitting, toxic waste-emitting supply chain.17 One electric vehicle can have 50-100 computers. [20] When a computer’s microprocessors are no longer useful, they cannot be recycled; they become electronic waste.18

Solar panels also depend on pure silicon. At the end of their lifecycle, solar panels are also hazardous waste. (In another letter, I will outline other ecological impacts of manufacturing, operating and disposing of solar PV systems.)

I’d certainly welcome solutions to silicon’s ecological impacts. Given the magnitude of the issues, I’d mistrust quick fixes. Our first step, I figure, is to ask questions. What’s it like to live near a silicon smelter? How many silicon smelters operate on our planet, and where are they? If we recognize that silicon production generates greenhouse gases and toxic emissions, can we rightly call any product that uses it “renewable,” “zero-emitting,” “green” or “carbon-neutral?”

Where do petroleum coke, other pure carbons and the wood used to smelt quartz and produce silicon come from? How/could we limit the production of silicon?

How does our species’ population affect silicon’s production and consumption? I’ve just learned that if we reduced fertility rates to an average of one child per woman (voluntarily, not through coercion of any kind), the human population would start to approach two billion within four generations.19 (At this point, we’re nearing eight billion people.) To reduce our digital footprint, should we have less children? Would we have less children?

What would our world look like if farmers grew more wheat and rice than manufacturers make transistors? Instead of a laptop, could we issue every student a raised bed with nutrient-dense soil, insulating covers and a manual for growing vegetables?

What questions do you have about silicon?




1 Without industrial process designer Tom Troszak’s 2019 photo-essay, which explains how silicon is manufactured for solar panels (and electronic-grade silicon), I could not have written this letter. Troszak, Thomas A., Why Do We Burn Coal and Trees for Solar Panels?Planet of the Humans, Jeff Gibbs and Michael Moore’s documentary, released on YouTube in 2020, also shows how silicon is manufactured for solar panels.
2 Schwarzburger, Heiko, The trouble with silicon, September 15, 2010.
3 Stockman, Lorne, Petroleum Coke: The Coal Hiding in the Tar Sands, Oil Change International, January,2013.
4 Silicon processing: from quartz to crystalline silicon solar cellsDaqo new Energy: The Lowest-Cost Producers Will Survive (NYSE:DQ), 2017.
5 Greenhouse gas emissions from global shipping, 2013-2015.
6 Chalamala, B., Manufacturing of Silicon Materials for Microelectronics and PV (No. SAND2018-1390PE), Sandia National Lab, NM, 2018; Polysilicon Production: Siemens Process (Sept. 2020); Kato, Kazuhiko, et. al., Energy Pay-back Time and Life-cycle CO2Emission of Residential PV Power System with Silicon PV Module, Progress in Photovoltaics: Research and Applications, 6(2), 105-115, John Wiley & Sons, 1998.
7 Schwarzburger, 2010; Troszak, The effect of embodied energy on the energy payback time (EPBT) for solar PV.
8 Kramer, Becky, “Northeast Washington silicon smelter plans raise concerns,” The Spokesman-Review, 11.1.17.
9 Thorsil Metallurgical Grade Silicon Plan; Helguvik, Reykjanes municipality (Reykjanesbaer), Reykjanes peninsula, Iceland, Environmental Impact Assessment, February, 2015.
10 New York State Dept. of Environmental Conservation – Facility DEC ID: 9291100078 PERMIT Issued to: Global Metallurgical Inc.
11 Polysilicon Market Analysis: Why China is beginning to dominate the polysilicon market, 2020; also, Bruns, Adam, 2009.
12 Bruns, Adam, Wacker Completes Dynamic Trio of Billion-Dollar Projects in Tennessee: ‘Project Bond’ cements the state’s clean energy leadership, 2009.
13 Schwartzburger, 2010.
14 Dale, M. and S.M. Benson, “Energy balance of the global photovoltaic (PV) industry-is the PV industry a net electricity producer?” Environmental Science and Technology, 47(7), 3482-3489, 2013.
15 The Society of Chemical Engineers of Japan (ed.), “Production of silicon wafers and environmental problems,” Introduction to VLSI Process Engineering, Chapman & Hall, 1993.
16 Hayes, Brian, “The Memristor,” American Scientist, 2011.
17 Needhidasan, S., M. Samuel and R. Chidambaram, Electronic waste: an emerging threat to the environment of urban India, J. of env. health science and engineering, 2014, 12(1), 36.
18 Needhidasan, S., 2014.
19 Hickey, Colin, et al. Population Engineering and the Fight against Climate Change. Social Theory and Practice, vol. 42, no. 4, 2016, pp. 845–870.



15 responses

14 01 2021

The dirty secret laid bare. Thanks for posting this.

14 01 2021

Good article, but I have no idea why it is directed at Thunberg. What is her relevance. Has she gone into manufacturing computers? or started work for a computer manufacturer? Does she own sand mines? Or is it just a cheap gotcha of some sort? this is a genuine query, because the article is otherwise so good I feel I must be missing something..

14 01 2021

I agree. It’s like Greta is the enemy ?

14 01 2021

No, someone has started a blog called Letter to Greta Thunberg, and it’s aimed at all her hopium filled supporters…

14 01 2021

She is smart and may know already that it is too late re climate change.
But yes, she is probably completely unaware regarding collapse due to resource depletion and energy descent.

15 01 2021

Why blame Thunberg for people ignoring the problems?

Thunberg’s thing is that people should inform themselves and act.

Personally I think that should mean organisation and action rather than going off on your own, because the latter is way too optimistic.

14 01 2021
SoundEagle 🦅ೋღஜஇ

Thank you for alerting us to the issues.

14 01 2021

The “In 2013, manufacturers began producing more transistors than farmers grow grains of wheat or rice. Now, manufacturers make 1000 times more transistors than farmers grow grains of wheat and rice combined.”
boggles my mind and disturbs me greatly.
I immediately thought of the wheat and chessboard problem, which ends up with 18,446,744,073,709,551,615 grains on the board ‘1.4 trillion metric tons.)—about 2,000 times annual world production’.
Still hard for me to comprehend? … is that transistor number certain?
PS I sent your article to Greta – Zarquon bless ‘er.

15 01 2021

depends on whether they are counting the ‘transistors’ on integrated circuit boards, which are part of the electrical layout. I doubt people are making that many individual transistors any more. They used to be pretty big (ie you could pick them up in your fingers….

29 01 2021
Erik Turner

My first thought was that they have to be counting transistors in VLSI chips (CPUs, RAM, Flash). After a quick trip to Wikipedia, I found this:

“In terms of the total number of transistors in existence, it has been estimated that a total of 13 sextillion (1.3×10^22) MOSFETs have been manufactured worldwide between 1960 and 2018. MOSFETs account for at least 99.9% of all transistors, the majority of which have been used for NAND flash memory manufactured during the early 21st century”

For comparison, the number of grains of wheat on the chessboard is 1.8*10^19


15 01 2021
Bruce Teakle

This is an interesting and useful essay, very relevant to our global concerns. However, for me, its direction at Greta gives the whole text a cynical attitude, as if it’s blaming a girl for these problems we all spend our money to create. The essay could more realistically be titled “Dear Elon”, or “Dear renewable energy lobby”.
Everything we spend our money on has a similar story. Consumption, growth: the whole economy is driving these problems.

15 01 2021

Not all gloom and doom, but ..

In 1965, Intel co-founder Gordon Moore made the observation that would become his eponymous “law”: The number of transistors on chips was doubling every 2 years, a time frame later cut to every 18 months. But the gains from miniaturizing the chips are dwindling. Today, chip speeds are stuck in place, and each new generation of chips brings only a 30% improvement in energy efficiency while demand far outstrips any gain. Fabricators are approaching physical limits of silicon because electrons are confined to patches of silicon just 100 atoms wide, forcing complex designs that prevent electrons from leaking out and causing errors.
Companies already make 3D chips with silicon as a way to pack logic and memory functions closer together to speed up processing. But the chips are slowed down by bulky and sparse wiring that carries information between the chip layers. And because 2D silicon chip layers must be fabricated separately at more than 1000°C, there is no way to build up 3D chips in an integrated fabrication plan without melting the lower layers. However 3D chips are being fashioned with transistors made from carbon nanotubes, they are much larger than their silicon equivalents but have much higher energy efficiency. Something that will very probably boost demand… and nanotubes are tricky to produce as well.


15 01 2021

Ignorant me. Seems the number of transistors produced is plausible, but since about the year 2000 they have been around the size of the coronavirus – around 65 nanometers.

Click to access timeline-intel-moores-law.pdf

{ Wonder if ‘shedding transistors’ is dangerous; )

16 01 2021

you lost me when you publish “.. since wind and solar are intermittent they can not be used at all” or words to that effect.
Infantile fearmongering this is.

The world needs about 20x the energy it can get from the sun and so we use fossil fuels. It’s unsustainable and that’s that.

But cut that crap about ” wind and solar can’t be used.” Of course it can.
And when it stops, change over to the grid’s supply until more sun or wind appears.

Can we get a view from someone who runs a silicon furnace? A few facts might enlighten the lot of us.

16 01 2021

They can’t be used at all without fossil fuels backup or words to that effect. Power factor takes no prisoners.

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