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How to make a CPU – a simple picture-based explanation

blog.robertelder.org

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Re: How to make a CPU – a simple picture-based explanation

#51

Post by kayson »

ic_dummy wrote: post #37
kayson wrote: post #24

Circuit designer here - feel free to ask any questions about the manufacturing process, design etc. Having a thorough understanding of the process, I thought this was hilarious. But if you really want to understand the process, it's pretty terrible. It spends 10 steps on making a wafer, and then the bulk of the actual process is condensed to 16.

How are the pn junctions created? The article says I can "optionally" dope the wafers. Why is that optional? Are they doped to create both p and n areas, or just one type? Or are multiple wafers used? Or are areas somehow doped after etching? Thank you for entertaining my dumb software person questions.

This is one area the article did a very poor job of explaining. In some processes, you treat the entire wafer before you get started with the rest of the procedure. One example that does this is SOI (silicon on insulator) processes. Others may not need this "global" doping, and from what I know most bulk silicon cmos processes do not do this.

Then you do the lithography (photoresist developing, etching, etc) to expose specific regions on the silicon that you want to dope to create devices like transistors, for example. So first you might expose all of the p-type transistor (PMOS) diffusion areas and dope them. Then you'd remove all the photoresist, repeat the procedure to expose n-type diffusions and dope that. And so on for the various needs of that particular wafer.

PN junctions are created simply by having p-type doped silicon adjacent to n-type doped silicon. The boundary between the two is the PN junction. In practice what I usually see is a square of one type with a ring around it of the other, but these devices are not frequently used.

Re: How to make a CPU – a simple picture-based explanation

#52

Post by kayson »

freedomben wrote: post #26
kayson wrote: post #24

Circuit designer here - feel free to ask any questions about the manufacturing process, design etc. Having a thorough understanding of the process, I thought this was hilarious. But if you really want to understand the process, it's pretty terrible. It spends 10 steps on making a wafer, and then the bulk of the actual process is condensed to 16.

Not what you were offering so feel free to ignore this, but I'm super curious about RISC-V. Do you know if any serious attempts are happening to make RISC-V based systems? And if not, do you know why? Is it too raw/un-polished?

Not my area sorry!

Re: How to make a CPU – a simple picture-based explanation

#54

Post by nynx »

It'd be really awesome if microprocessors, even at a low-end process node like 130 nm, could be made with room-sized machines or smaller. There's a lot of space for companies wanted to manufacture their own MCUs, for instance, without relying on massive supply chains.

I think this'll happen at some point, as silicon manufacturing hits final roadblocks and becomes increasingly commoditized, but it'd be nice if it were sooner rather than later.

(This would be nice for self-sufficient decentralized communities being able to produce their own microelectronics as well.)

Re: How to make a CPU – a simple picture-based explanation

#55

Post by wrycoder »

GhettoComputers wrote: post #43

The article doesn't correspond to reality. >3) Now you have 98% concentrated silicon dioxide. Purify it to 99.9% pure silicon dioxide. >4) Purify it further to 99.9999999% polysilicon metal. >While cutting-edge nanometer scale features are not likely to be accessible for a hobbyist, micron-scale amateur chip fabrication does appear to be quite feasible. I have not tried this myself, but Sam Zeloof has, and you should…

He’s explaining, as crudely as possible, what’s going on in the semiconductor industry as a whole. Even Shenzen and TSMC are only small parts of it.

High purity polysilicon is still produced by zone refining.

Re: How to make a CPU – a simple picture-based explanation

#56

Post by sgarland »

rubylark wrote: post #34
lsiunsuex wrote: post #8

I've always been curious how someone gets into this line of work. Is it all via college / post education and your directly recruited by these companies? Obviously, this is a very hard (impossible?) thing to teach yourself. I can't imagine more than a few universities offer this type of education? Where would you start / what path would you go down to be a chip designer / work for an Intel / AMD ???

My brother and several of his friends do this for a living at Intel. Most of them have Electrical Engineering PhDs, though I believe one is a Chemical Engineer. My brother's thesis specifically was in 2d transistor design and worked under a Material Science professor. I believe most universities have professors who teach Semiconductors classes, whether it is under the name Computer Engineering, Electrical Engineering…

There are other fabs in the US - Samsung, Global Foundries, NXP, and other smaller places.

Re: How to make a CPU – a simple picture-based explanation

#57

Post by timthorn »

pitspotter2 wrote: post #30

The hilarity illustrates an important point. We never just make a thing. A recipe or blueprint is a convenient fiction. Rather we participate in a dynamic evolving process which itself evolved through many cycles of copying, repetition and debugging. Even the first version wasn't strictly original because the idea was borrowed from elsewhere. 'Oh you work at the olive press. How would you like a job with this new-fan…

Take a look at the Toaster Project if you want to see building an item from scratch carried through all the way: http://thetoasterproject.org/

Re: How to make a CPU – a simple picture-based explanation

#58

Post by [deleted] »

sgarland wrote: post #56
rubylark wrote: post #34

Earlier quoted context omitted.

My brother and several of his friends do this for a living at Intel. Most of them have Electrical Engineering PhDs, though I believe one is a Chemical Engineer. My brother's thesis specifically was in 2d transistor design and worked under a Material Science professor. I believe most universities have professors who teach Semiconductors classes, whether it is under the name Computer Engineering, Electrical Engineering…

There are other fabs in the US - Samsung, Global Foundries, NXP, and other smaller places.

[deleted]

Re: How to make a CPU – a simple picture-based explanation

#59

Post by nereye »

GhettoComputers wrote: post #43

The article doesn't correspond to reality. >3) Now you have 98% concentrated silicon dioxide. Purify it to 99.9% pure silicon dioxide. >4) Purify it further to 99.9999999% polysilicon metal. >While cutting-edge nanometer scale features are not likely to be accessible for a hobbyist, micron-scale amateur chip fabrication does appear to be quite feasible. I have not tried this myself, but Sam Zeloof has, and you should…

Somewhat related, it does not seem too expensive (~$100 per chip, minimum *50) to get an ASIC done (purely from a fab perspective and ignoring the large elephant in the room of coming up with a design in the first place), e.g. see https://www.zerotoasiccourse.com/ (no affiliation).

As for the design, one way is to re-use existing IP and join it together, e.g. see https://efabless.com/ etc.

Re: How to make a CPU – a simple picture-based explanation

#60

Post by GhettoComputers »

wrycoder wrote: post #55
GhettoComputers wrote: post #43

The article doesn't correspond to reality. >3) Now you have 98% concentrated silicon dioxide. Purify it to 99.9% pure silicon dioxide. >4) Purify it further to 99.9999999% polysilicon metal. >While cutting-edge nanometer scale features are not likely to be accessible for a hobbyist, micron-scale amateur chip fabrication does appear to be quite feasible. I have not tried this myself, but Sam Zeloof has, and you should…

He’s explaining, as crudely as possible, what’s going on in the semiconductor industry as a whole. Even Shenzen and TSMC are only small parts of it. High purity polysilicon is still produced by zone refining.

Yes it is refined and doped, my point is that he leaves out the sourcing of essential materials that you don't refine but must get that is already pure, it has to be purer than any random silicon its like saying just get any sand that people will assume comes from beaches for construction when its essential that they are not worn or have rounded edges, except this is so specialized that it must come from one mine in the world. The limit was well understood in Soviet Russia with their inability to source the raw materials of comparable purity to produce microchips, even if the design was the same, the USSR was not able to produce them without what is considered essential to chips of good quality. https://www.sciencedirect.com/science/article/abs/pii/S00652...

Even today China cannot match the quality of American chips and relies on US raw materials from Spruce Pine for manufacturing chips. It isn't optional, its like saying you can make a 1:1 steak with nothing but beef bones or chicken. https://ashvegas.com/bbc-report-spruce-pines-high-quality-qu...

>This ultra-pure mineral is essential for building most of the world’s silicon chips – without which you wouldn’t be reading this article.

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