How to Make a CPU from Scratch (Fun Warning!)

Step 1: Grab yourself a rock

Okay, not just any rock - what you really need is something like quartz that contains silicon dioxide, and now, smash it! What you’re left with is 98% concentrated silicon dioxide (also found in purified sand, but let’s stick with 'rock' :)).

Step 2: Purify, purify, purify

Take your smashed rock, and purify it until you reach 99.9% pure silicon. Keep purifying it even more, to 99.9999999% electronic-grade silicon. This ultra-pure silicon is what makes CPUs work so well.

Step 3: Grow a crystal

Place the purified silicon into a crucible and heat it to 1698 K (over 1400 °C or 2500 °F). Take a 'seed' crystal—a tiny single crystal of silicon—and dip it into the molten silicon. Slowly pull it out as it cools (in a process called the Czochralski method), and you’ll grow a large, beautiful monocrystal of pure silicon, ready to become your CPU!

Step 4: Slice it up, but not with a knife

Slice that crystal into thin slices called wafers. This takes precision sawing to cut the silicon into ultra-thin, polished wafers that will eventually hold millions (or billions) of transistors.

Step 5: 'Add some flavor', aka doping

Now dope your silicon wafer by adding boron or phosphorus atoms. This gives the silicon electrical properties, allowing it to conduct positive or negative charges (essential for making transistors).

Step 6: Etch - photolithography time!

Cover the wafer with a layer of photoresist. Then, take a specially etched quartz mask and shine a laser beam through it onto the wafer. The shadows created by the mask will expose specific areas of the photoresist. (This light exposure doesn’t directly control chemical reactions but reveals where etching or doping will happen after development.)

Step 7: Develop and Etch

Next, develop the photoresist and etch away the exposed parts of the wafer with acid. This process sculpts tiny paths for electricity to flow, shaping each transistor. Wash off any leftover photoresist, and voilà—your wafer is etched!

Step 8: What is epitaxy?

Now, it’s time to stack layers with a process called epitaxy. This adds more silicon or other materials to the ultra-thin layers. With each layer, use chemical-mechanical polishing to make it smooth again, keeping everything neat and flat for all those future connections.

Step 9: Interconnections and Polishing

Add tiny copper interconnections to link up all the transistor paths. This is like adding the wiring that will help different parts of the CPU 'talk' to each other. More chemical-mechanical polishing ensures each layer is perfectly flat, keeping those connections clean and functional.

Step 10: Slice it up again

Cut your finished silicon wafer into individual chips, called dies. Each die is a tiny, complete circuit with millions of transistors ready to power a computer.

Step 11: Package it

Now, connect each die to the CPU pins using bond wires or the flip-chip method. Bond wires are tiny, delicate connections, while flip-chip involves flipping the die to connect directly to contacts on the package (both provide electrical paths from the silicon to the outside world).

And that's how you made a CPU!

From smashing a 'rock' to connecting microscopic wires, you’ve built yourself a CPU! Each tiny piece, from the doped silicon to the interwoven copper connections, plays a crucial role in creating the powerhouse that drives everything from your smartphone to supercomputers.

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