"Z2" - Upgraded Homemade Silicon Chips

a few years ago i made the world's first homemade silicon chip in my garage fab i just made version 2 which has 100 transistors on it and they're smaller better and faster than the old one i made an array of 12 of these so that's 1 200 transistors on the same piece of silicon intel's first processor had only 2 000 transistors so we're already approaching a decent level of complexity and i should be able to make some really interesting circuits out of this soon i did some cool projects with my first chip like a led flasher and a guitar distortion pedal they worked really well but needed one or two nine volt batteries attached to them because the threshold voltage of the old mosfets were really high this new chip is made on a polysilicon gate process all these details are on the write up on my blog but the effect of that is that they work well at very low voltages they have a threshold voltage of only about 1 volt and that means that i can power them off of 3.3 and 5 volt logic levels they draw less power and i should be able to pack more of them into a smaller die area for simple chips like this the process actually starts in photoshop there's only four layers to design and it's easier to use this than to use some more complicated software i start with a lot of 200 millimeter wafers that have some pretty specific starting parameters they're way too big so i dice them up using a diamond scribe into smaller bits i normally do about half inch squares like this but i can process larger things up to about two inch wafers the first layer to define is the doped layer that makes the source and drains the mosfets i put it on this homemade spin coater and then i deposit photoresist on top of it you only need about 100 microliters or so to cover a small wafer like this and we spin it at 4000 rpm for 30 seconds after all the excess photoresist has been spun off it's dried on a hot plate at about 95 degrees c for one minute this drives off the rest of the solvents and leaves us with a solid film the result is a beautiful looking and uniform covering of the whole wafer then it's off to the homebuilt maskless photolithography stepper for exposure the basic idea is that we load up an image on this laptop that we want to project onto the chip then there's a standard dlp projector and some optics that shoot that down and reduce it onto the wafer i have a whole video on this tool so i recommend checking that out in the center you see a little blue dot that's the entire exposure field it lasts about nine seconds then the blue goes away at the end of the exposure we can step the wafer to another location and expose that part too just like processing filament a dark room the next step is development i put it in a couple percent potassium hydroxide solution for about a minute and this etches away the parts of the photoresist that were exposed because it's a positive photoresist i wash it with water to get rid of the residual developer and then we're ready to do the next step i can put under a microscope to inspect it and make sure everything worked out well if it didn't you can always just strip off the photoresist layer and try again with maybe a different exposure or development time now the image is formed in the photoresist i transfer that into the underlying polysilicon layer using an etchant once it's etched we don't need the photoresist mask layer anymore so that can be stripped off using acetone the wafer is then cleaned and dried and we spin on a dopant this is a phosphorous solution that's suspended in a liquid silicon dioxide this is spun on just like the photoresist and then we bake it at very high temperature over 1000 degrees c for about 45 minutes this drives in the phosphorus atoms into the little wells that we just defined using lithography and that basically forms the source and drains of the mosfets i have to push it into the center of the furnace using this quartz rod and then at the end of the process we pulled out the other side the process of spin coating photoresist baking it exposing it and developing it is then repeated exactly twice once for the gate layer and then again for the contact the gate is etched just like we did before with the polysilicon etchant and the contact layer has to be etched as well because now after the high temperature step there's a layer of silicon dioxide insulating everything so after the contact mask is formed you have to use something like hydrofluoric acid or chf3 reactive ion etching to get rid of that insulator so we can make good electrical contact then we stick the wafer into a vacuum chamber to either sputter or thermally evaporate metal i'm evaporating aluminum a thick layer of about a micron or so and then we do the whole photolithography process again of spin coating and exposing and developing to define that metal layer once that's done stick the wafer into a warm phosphoric acid bath that etches off the residual aluminum and finally the chip is done at this point i'll inspect the chip pretty thoroughly and take a lot of close-up pictures to measure parameters like gate length and width and layer thicknesses if i do a cross-section i can put it on the probe station which has a bunch of really small tungsten needles and allow me to make connections directly to the transistors it's very finicky and these transistors are so small that it's not actually that trivial to make contact to them but anyway i boot up all this test equipment that allows me to characterize them i do a little bit of programming to define the kind of tests i want to do and then hopefully we're greeted with this great curve so this is the id versus vds curve of an n channel mosfet here's an ideal one taken off of the internet and then here's the one that i'm getting from my fets and they look great i hope you found that interesting and enjoyed learning about my second integrated circuit i got a bunch of requests to set up a patreon or something like that i'm not sure if that's the best way to do it but i'll put a link in the description if you want to support more homebrew semiconductor fabrication experiments like this thanks for watching

Channel: Sam Zeloof

Views: 1,610,211

Keywords: electrical, engineering, electronics, diy, arduino, homemade

Id: IS5ycm7VfXg

Length: 5min 46sec (346 seconds)

Published: Fri Aug 13 2021