To “print” something as small as a transistor, we can’t use physical tools—they are too bulky. Instead, we use light as a stencil in a process called Photolithography.
Think of it like a high-tech version of developing a photograph or using a spray-paint stencil, but at the scale of atoms.
1. The “Ink” (Photoresist)
First, a silicon wafer is coated with a light-sensitive liquid called photoresist. This material is engineered to change its chemical structure whenever it is hit by ultraviolet (UV) light.
2. The “Stencil” (The Mask)
Engineers create a Photomask, which is a glass plate with the master blueprint of the chip’s circuitry.
* Deep UV: Uses a “transparent” stencil where light shines through.
* Extreme UV (EUV): Because EUV light is so delicate that it is absorbed by almost everything (even air), the “stencil” is actually a complex mirror that reflects the pattern onto the wafer.
3. The “Flash” (Exposure)
The machine shines a powerful UV light through the mask. The light passes through the clear parts of the stencil and hits the wafer, “drawing” the pattern into the photoresist.
* In modern EUV machines, this light is created by hitting tiny droplets of molten tin with a high-powered laser, creating a plasma that burns at 200,000°C—nearly 40 times hotter than the surface of the sun!
4. The “Sculpting” (Etching)
After exposure, the wafer is washed in a developer solution. The areas hit by light (or not hit, depending on the resist type) dissolve away, leaving the pattern behind. Then, a gas or chemical “eats away” the exposed silicon, carving the permanent 3D structures of the chip.
The Precision Challenge
Because we are working with features only a few nanometers wide, the machines must be incredibly stable. The “wafer stage” that holds the silicon moves with a precision of 0.25 nanometers. To put that in perspective, if the machine were the size of the entire Earth, it would be able to move and hit a target the size of a golf ball.
This process is repeated over 50 times, layer by layer, to build the “skyscraper” structure you saw earlier. Would you like to see how they stack these layers so perfectly on top of each other?
Fabrication Processes of a Chip: Photolithography
This video provides a real-world look inside a cleanroom to show how the chemical developing and UV exposure steps actually look during the manufacturing process.