Just as in building a house, you need a construction plan to construct a chip. The construction plans for the chip are made and tested with a computer.
From the construction plans, masks with the circuit patterns are made.
Under precisely monitored conditions, a pure silicon crystal is grown. Circuit manufacturing demands the use of crystals with an extremely high grade of perfection.
The silicon is sawed into thin wafers with a diamond saw. The wafers are then polished in a number of steps until their surface has a perfect mirror-like finish.
The silicon wafer is covered with a layer of insulating silicon oxide.
A covering film of protective material is put on top of the insulating silicon oxide. This material, a bit like the film in any ordinary camera, is sensitive to light.
UV-light is shone through a mask and onto the chip. On the parts of the chip that are hit by light, the protective material breaks apart.
The wafer is developed, rinsed and baked. The development process removes the parts of the protective material exposed to light.
The wafer is treated with chemicals in a process called "etching." This removes the unprotected insulating material, creating a pattern of non-protected silicon wafer parts surrounded by areas protected by silicon oxide.
The wafer is run through a process that alters the electrical properties of the unprotected areas of the wafer. This process is called "doping." Steps 5-10 are repeated to build the integrated circuit, layer by layer. Other layers of conducting or isolating layers may also be added to make the components.
Back End – Adding the Connecting Wires
Finally, when all the components of the chip are ready, metal is added to connect the components to each other in a process called metalization. This is done in a way similar to the making of the components. First a conducting metal like copper is deposited over the chip.
On top of the metal a layer of UV-sensitive photo resist is added.
Next, a mask that describes the desired layout of the metal wires connecting the components of the chip is used. UV-light is shone through this mask. The light hits the photo resist that isn't protected by the mask.
In the next step, chemicals are used to remove the photo resist hit by UV-light.
Another step of etching removes the metal not protected by photo resist.
This leaves a pattern of metal that is the same as the one described by the mask. Now, the chip has a layer of wires that connect its different components.
Today, most integrated circuits need more than one layer of wires. Advanced circuits may need up to five different layers of metal to form all the necessary connections. In the last picture we have added another layer of metal to our example. As you can see, a layer of insulating material is put between the two metal layers to prevent the wires from connecting in the wrong places. Of course, to add the second layer we had to go through the same steps as when adding the first layer of metal.
When the final layer of connecting metal wires have been added, the chips on the silicon wafer are tested to see if they perform as intended.
The chips on the wafer are separated with a diamond saw to form individual integrated circuits.
Finally, each chip is packed into the protective casing and subjected to another series of tests. The chip is now finished and ready to be shipped to manufacturers of digital devices around the world.
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