Why are Processors Square (and Wafers Circular)?

in all these product launches whenever a company shows up a processor it's always square and a lot of you have been asking me why a process is square and why are the uh things that we make processors from wafers round in this video i'll tell you why what's your minimum specification [Music] r [Music] now before you make processors you must bless the wafers uh as i'm sure most of you know the way we make processors is that we actually build the transistors and the wires on these circular things called wafers now these wafers in the past used to be two inch three inch four inch uh modern day chips are actually made using six six and eight inch wafers that's actually the most common but the leading edge processors are made on a 12-inch wafers so processors are square or well technically rectangular but let's just say square for now and wafers are round you sounds like you're going to get a lot of wastage when you actually make squares out of a circular base now i'm going to go through why that base is circular first so we can get on to why processes are square so when you manufacture a wafer you have a pot of molten pure silicon from quartz and the way you get an ultra pure silicon out of that is you put in a seed crystal of pure silicon and you gradually draw it out rotating slowly as it goes this produces essentially what is a single crystal of silicon and due just because you're making the molten silicon become solid the way that it grows out is in a circular cylindrical fashion you end up with a cylindrical silicon what we call an ingot now the rate at which you pull and the exact features the exact environment that you're pulling that ingot into is how you get the size of your ingot and the idea is that you get a full long silicon uh cylindrical ingot you know and modern day ingots weigh three four hundred kilos these are big massive long things and the best way to think about it is if you think of salami so if we just take the ingot as it is or if we take the salami and we cut the salami up here i'm using a french salami i'd much rather use a romanian salami from sibiu it's really nice if you can find it at your local romanian shop but the point is when you cut your salami when you cut your ingot you're going to get what is essentially circles now typically before the cutting you the ingots go through an amount of polishing to make sure that the ingot is you know fully 300 millimeters in diameter and then you cut into wafers if you're going to turn that circle into a square you're already cutting bits off uh the bits off the wafer already now as i mentioned before in a previous video these wafers cost about 400 in their unused state especially for 12-inch leading-edge process nodes like tsmc samsung and intel and another reason why they are circular the wafers is because you have to then go through polishing them now polishing them is easiest when you can rotate it at a high speed and the best way to get an even rotation at high speed is with a circle another reason why these wafers are circular is actually in manufacturing the chips themselves now chips consist of transistors at the smallest dimensions and then on top of that you build metal layers and metal layers which are essentially the wires going everywhere and to do that takes hundreds and hundreds of steps and it's through this magical process called photolithography that this actually happens one step of this photolithography is actually depositing what we call a photoresist you're essentially pouring a liquid onto the wafer making it an even layer across you shine light onto the wafer now with this liquid through a mask so that any bits of that liquid that is exposed to the light solidify in anything that's not stay liquid you can then pour the liquid off deposit your metal etch the metal and then move on to subsequent steps but the point is actually getting that liquid onto the wafer with a uniform thickness with a circular wafer you can spin the wafer at high speed and that forms your uniform layer if you did that with a square wafer then it would be quite hard to spin because you'd have the liquid flowing off everywhere and you wouldn't end up with a uniform layer not only that some of these processes are actually done at high temperature so with a square wafer you would actually get a concentration of the heat density when you heat the wafer up at the edges and particularly at the corners creating a weak point in the silicon don't forget this silicon is it's kind of like glass essentially so with a circular wafer you still do get an extra bit of heating on the edges but there are no points for that heat to actually affect the mechanical properties of the wafer so that's circular wafers why do we cut square processors from them now the point is it comes back to similar things as to when we were cutting the salami cutting the silicon ingot you want a cut that goes straight through from edge to edge and with a circular wafer the easiest cut from edge to edge is actually just doing straight lines so you end up with squares or rectangles now you could say well that produces a lot of wastage especially if your chips are big that means a lot of silicon goes to waste well in this case the silicone wafer is cheap part is the cheap part of the process it's the manufacturing that it's most difficult so you want to make sure that each chip you make is absolutely 100 on there now if you were say to cut hexagons this is a an idea that's been postulated to me in the comments why don't we get hexagons out of the way folks that means that there is less wastage of the silicon wafer itself well if i show a diagram of how we tessellate hexagons you can see that there is no straightforward edge to edge cut you're going to end up hitting hitting the next processor along and you will end up having to cut around it now the tools to cut around it are a lot more expensive than the tools to actually just do straight up through we could move to a hexagon way of making processes this requires actually putting the tools to cut in a non-uniform non-edge-to-edge way these are a lot more expensive and just creates a lot more complexity and a lot more variation in the cutting process when these processes are laid out as squares or as rectangles on the wafer they're kept a very small distance apart and we usually call that the scribe line this means that if there is a cut there is a little leeway each way now organizing scribe lines saying hexagons might be a straightforward enough process but actually trying to cut them is where it gets difficult so this is why we stay with square chips rather than going through anything fancy like i don't imagine circular chips becoming uh truthful anytime soon unless you know somebody does a wafer scale circular chip and that's why square processors and round wafers are here to stay now an update for the channel uh many thanks to the new 10 000 subscribers we've had in the last week you're amazing i love you all and we just hit a million views as well and it couldn't be possible with all of you watching and many more videos on how we make processes and all the little fun things in history coming up soon [Music] you

Channel: TechTechPotato

Views: 119,472

Keywords: semiconductor, wafer, round wafer, square wafer, silicon, silicon wafer, silicon ingot, tsmc 7nm, tsmc 5nm, tsmc 3nm, tsmc 2nm, intel 10nm, intel 14nm, intel 7nm, intel 5nm, samsung 7nm, ingot, wafer cut, wafer dice, processor, why is a processor square, why is a wafer round, hwo to make wafers, how to make processors, why is cpu square, square cpu, why are wafers round, ian, cutress, techtechpotato, eat wafers, amd, intel, samsung, qualcomm, best wafer, best cpu, how to eat cpu

Id: Rhs_NjaFxeo

Length: 8min 23sec (503 seconds)

Published: Tue May 11 2021