Letter #12 How we manufacture silicon: computers’ crucial ingredient not found in nature

In her “Letter to Greta Thunberg” series, Katie Singer explains the real ecological impacts of so many modern technologies on which the hope for a bright green (tech) future is based on.

A letter to Greta Thunberg
by Katie Singer

Dear Greta,

Could we discuss silicon, that substance on which our digital world depends? [1] Silicon 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 electricity [2] 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 coke, [3] or metallurgical coke) and a slow-burning wood. These three substances are transported to a facility with a submerged-arc furnace.[4]

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 3000F (1649C) 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 2012F (1100C). 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 acid [13] 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. [16] Now, manufacturers make 1000 times more transistors than farmers grow grains of wheat and rice combined. [17]

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 [18], one smartphone holds more than 1000 substances, each with their own energy-intensive, GHG-emitting, toxic waste-emitting supply chain. [19] 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. [21]

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 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.[22] (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?

Katie Singer

Katie Singer’s writing about nature and technology is available at www.OurWeb.tech/letters/. Her most recent book is An Electronic Silent Spring.


  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?” https://www.researchgate.net/publication/335083312_Why_do_we_burn_coal_and_trees_to_make_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. https://planetofthehumans.com/
  2. Schwarzburger, Heiko, “The trouble with silicon,” https://www.pv-magazine.com/magazine-archive/the-trouble-with-silicon_10001055/ September 15, 2010.
  3. Stockman, Lorne, “Petroleum Coke: The Coal Hiding in the Tar Sands,” Oil Change International, January,2013; www.priceofoil.org
  4. Silicon processing: from quartz to crystalline silicon solar cells; https://www.researchgate.net/publication/265000429_Silicon_processing_from_quartz_to_crystalline_silicon_solar_cells; Daqo new Energy: The Lowest-Cost Producers Will Survive (NYSE:DQ), 2017, https://seekingalpha.com/article/4104631-daqo-new-energy-lowest-cost-producers-will-survive.
  5. “Greenhouse gas emissions from global shipping, 2013-2015; https://theicct.org/sites/default/files/publications/Global-shipping-GHG-emissions-2013-2015_ICCT-Report_17102017_vF.pdf
  6. Chalamala, B., “Manufacturing of Silicon Materials for Microelectronics and PV (No. SAND2018-1390PE), Sandia National Lab, NM, 2018. https://www.osti.gov/servlets/purl/1497235; Polysilicon Production: Siemens Process (Sept. 2020); Kato, Kazuhiko, et. al., “Energy Pay-back Time and Life-cycle CO2 Emission of Residential PV Power System with Silicon PV Module,” Progress in Photovoltaics: Research and Applications, 6(2), 105-115, John Wiley & Sons, 1998; https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1099-159X(199803/04)6:2%3C105::AID-PIP212%3D3.0.CO;2-C
  7. Schwarzburger, 2010; Troszak, “The effect of embodied energy on the energy payback time (EPBT) for solar PV;” https://www.researchgate.net/publication/335612277_The_effect_of_embodied_energy_on_the_energy_payback_time_EPBT_for_solar_PV/figures
  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.; http://www.dec.ny.gov/dardata/boss/afs/permits/929110007800009_r3.pdf
  11. “Polysilicon Market Analysis: Why China is beginning to dominate the polysilicon market,” 2020, https://www.bernreuter.com/polysilicon/market analysis/; 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, www.siteselection.com.
  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. https://marginalrevolution.com/marginalrevolution/2019/01/claims-about-transistors.html
  18. www.DearGreta.com/letter-3/
  19. 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.
  20. www.DearGreta.com/letter-5/
  21. Needhidasan, S., 2014.
  22. Hickey, Colin, et al. “Population Engineering and the Fight against Climate Change.” Social Theory and Practice, vol. 42, no. 4, 2016, pp. 845–870., www.jstor.org/stable/24870306.

10 thoughts on “Letter #12 How we manufacture silicon: computers’ crucial ingredient not found in nature”

  1. “Sobering facts” would be a considerable understatement regarding Katie Singer’s letter.

    It is nothing less than stunning to think that our species is so self-centered, greedy, and indifferent to the life of the planet that created us as to have ever considered such technologies, to say nothing of employing them as fast and as widely as possible — and that all our destruction is done in the name of “progress.”

    It is no understatement to say that our industrial behavior is the equivalent of running a collective whorehouse, where the women for sale are our own mothers — tied down and forcibly raped, 24/7.

    I keep thinking back to 1900, when there were one-fifth the number of us there are today, living without aircraft, electronics, radio, TV, or an internet, and when cars were widely considered a nuisance fad. No one had home electricity until 1882, and more than half of America was still without it in 1925. And yet my grandmother (1884-1962) never spoke of her youth as being anything close to backward or impoverished.

    All the rest of our “progress” notwithstanding, we would have only 20% of our current problems, if we had just kept our population at the 1900 level, as every other species did — with the exception of those we grow to slaughter and eat, and the million or so we have reduced or exterminated, in our pretense of “intelligent life.”

    Dramatically reducing our numbers is essential to Earth’s survival as a life-sustaining planet, and it is the one issue our leaders dare not mention, due to our global presumption of “reproductive rights.” (To my knowledge, Greta Thunberg never mentions it, either.)

    Alan Weisman, author of “The World Without Us,” said we could return to the 1900 world population level in 200 years, by means of a global one-child policy. And while a two-child policy isn’t enough, two states in India have at least achieved that, simply by denying government jobs and loans to families with three or more kids.

    In addition to Greta Thunberg, Katie’s letter should also go to all “green” fantasy junkies, such as AOC and Biden. I suspect some of them know better. But they also know that telling voters to produce, sell, and consume as little as possible isn’t good politics, and the rest of society acts accordingly.

    (The annoying grammar teacher who lives in my head would also compels me to mention that the correct term is “fewer children,” not “less children.”)

  2. I don’t get the point of these “letters.”

    1. Greta Thunberg is a global hero, but she’s a TEENAGER that is compelled to lecture adult politicians and business leaders because they are continuing to destroy the Earth and everything living here. To my knowledge, Thunberg has never advocated for any type of technology, but instead insists that the people with the power and means to do so actually do something to fix the existential problem of global warming/climate change.

    2. I see no point in picking out individual human misbehavior regarding the natural environment. EVERYTHING that modern humans do is unnatural and harmful, including basic necessities like eating food and drinking water (with the lone exception of breathing). The problem is the human attitude toward anything not human; in this, humans are the Nazis of species, looking down on and often destroying anything not human for that reason alone. This attitude problem causes/allows humans to overconsume and overbreed, which are the physical roots of the problems. Sure, computers and cell phones are problems, but they’re mere symptoms and there are countless others.

  3. Having read the article, yes, silicone products are vastly better than burning coal. Since no solution was offered, we can assume the status quo would remain. Burning coal.
    In reality, silicone production can be made green. That is the solution not offered by the author.
    I read articles like this and become sure that they are coal and other burn industry written.

    1. You are clueless. DGR is about as far from fossil fuel industry advocacy as it gets.

      You can’t have your cake and eat it too, and childishly fantasizing that “silicone production can be made green” won’t make it so. Everything comes from something, so all technology is harmful, period. Wake up and grow up: we need to greatly reduce consumption and start living a lot more simply & naturally. Anything less is doing nothing for the environment.

        1. Wow. You must be a Democrat, because just like Republicans, Democrats are a cult, and you seem to be a cultist. You are the only one here saying that fossil fuels are better, but to show how delusional you are you claim that we are saying that. It’s all bad as I already said, and changing from one harmful technology to another won’t fix anything.

  4. All issues are proportional. Some good is better than no good. Slamming a step in the right direction takes us backward. The trick is to get 51% of the voting population onboard with steps in the right direction. Most people are not going to embrace living in tents.
    Reading comprehension is an intelligence revealer. I am for banning all burnables as renewables ramp up.
    I’m an Independent that votes for reps that want to expand renewables.

    1. I think that you mean that it’s all relative, which is true. However, replacing one destructive source of artificial energy needed for your lifestyle with another one — because you have some have-your-cake-and-eat-it-too fantasy that another form of energy is not destructive, when it in fact is quite so — has nothing to do with relativism. Here’s where relativism comes in regarding destructive human activity regarding artificial energy:

      Humans are the only species on Earth that extract things from below the Earth then burn, and/or processes them into synthetic products. This is what we’re talking about, it’s called industrial society. Your fantasy that you can keep your totally unnatural lifestyle by switching to “green” technologies is a total lie.

      1. These so-called green technologies are not at all green. For example, production of solar panels requires mining, a very harmful activity. The silicon used to make solar panels does not come from sand as most people have been led to believe. Furthermore, these “green” energy sources can themselves be very destructive when they are done in a large scale and/or in natural areas. Desert areas in California are being destroyed with large solar farms, natural areas on land & water are being ruined by solar & wind farms, etc. (In case you feel no connection to the natural world, aesthetic harm is also actual harm.)

      2. Fossil fuel and nuclear energy sources are not being replaced by wind and/or solar sources. Instead, humans are just using more energy. So your claim that expanding “renewables” is a “good” falls apart right there.

      3. These “green” energy sources need backup because the sun isn’t always shining nor the wind always blowing. Those backups are from the “burnables” that you allegedly oppose.

      DGR advocates for the replacement of industrial society with far more natural living. (Agriculture is also extremely harmful and unnatural, but that’s another issue.) We advocate for the Earth and everything living here, and realpolitik or any form of electoral politics is not a method of accomplishing this. DGR has one idea of how to remove industrial society from our planet, I have a different one. But our goal is the same, and if you don’t share that goal I don’t know what you’re doing on this site. This is not Sierra Club!

  5. Brief reply to Woody:

    Solar and wind power are only “green” at the end user level. Either type of power also requires a backup plant, powered by fossil fuels or nuclear energy, for the half of the time when the sun is down and the wind isn’t blowing.

    If all vehicles were electric, power demands would more than double, and could not be met with wind and solar.

    Both wind turbines and solar panels are plastic — made from oil, not recyclable, not biodegradable, and with a servive life of only 25 years or so.

    Simply meeting the current energy demands of Europe and North America would require covering a desert half the size of the Sahara with solar panels, which would themselves generate enough heat to raise global temperatures by almost half a degree Celsius.

    Bottom line: Survival basically requires eliminating most 20th century technologies, such as motor vehicles, industrial agriculture, and the power grid, and reducing population by 80-90%. That would require no more than one-child families, and that most people who can’t take care of themselves (including everyone in nursing homes) simply accept the fact that it’s time to go, and die with peace and dignity.

    This is the norm for every species but our own, and we have the knowledge to do it without the suffering that befalls most animals, who either starve to death or are eaten by predators.

    The bottom line is that in the long run, you either live in balance with nature, or you die. It sounds brutal, but only if you insist on having more than your share. People in indigenous communities have always respected nature’s limits, and have done quite well. The Polynesians and most tribes in the Americas had no serious complaints until colonial exploiters arrived, and introduced greed into the equation.

    The slaves who escaped in what is today Suriname simply withdrew into the forest, and took up the lifestyle of their ancestors in Africa. They respect all of nature as if even the air and the ground were living things, and that the right to be alive means taking only what you need and doing so as kindly as possible.

    Not coincidentally, the interior of Suriname appears to be pristine forest, which it is. No one lives there but native tribes and those resettled Africans, known as Maroons. They have the right to live. The rest of us forfeited the right to life when we began farming, mining, and building cities. By natural law, we should be dead. And it looks like the law has finally caught up with us.

    1. I would say that death is not “brutal” if you understand what “life” is. We, meaning all life, are just the universe separating itself in order to become aware of itself and maybe to have some fun. The universe is expanding at a rapid rate now, but it will eventually reverse course and collapse back on itself, though this will be so far into the future in human terms that the amount of time for us is unimaginable. So yeah, death hurts if viewed in a small-minded sense, but it’s not a big deal and is just part of the natural order.

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