The powerful performance of modern digital products such as smartphones, personal computers, and game consoles is no longer necessary, and most of these powerful performances originate from those very small but sufficiently complex technological products - chips. The world is surrounded by chips: In 2020, more than one trillion chips were produced worldwide, which is equivalent to 130 chips owned and used by every person on the planet. Even so, the recent chip shortages show that this number has not yet reached the upper limit.
Although chips can already be produced on such a large scale, producing chips is no easy task. The process of making a chip is very complex, and today we will introduce the six most critical steps: deposition, photoresist coating, photolithography, etching, ion implantation and packaging.
Deposition
The deposition step begins with wafers, which are cut from 99.99% pure silicon cylinders (also called "silicon ingots") and ground to an extremely smooth surface, which are then converted into conductors, insulators or semiconducting materials as required by the structure A thin film is deposited onto the wafer so that the first layer can be printed on it. This important step is often referred to as "deposition".
As chips get smaller, printing patterns on wafers becomes more complex. Advances in deposition, etching, and lithography are the keys to making chips smaller and thus pushing Moore's Law to continue. This includes innovative technologies that use new materials to make the deposition process more precise.
Photoresist Coating
The wafer is then coated with a light-sensitive material called "photoresist". There are also two types of photoresist - "positive photoresist" and "negative photoresist".
The main difference between positive and negative photoresists is the chemical structure of the material and the way the photoresist reacts to light. For positive photoresists, areas exposed to UV light change the structure and become more soluble in preparation for etching and deposition. Negative photoresists do the opposite, where the light-hit areas polymerize, which makes them more difficult to dissolve. Positive photoresists are the most used in semiconductor manufacturing because they can achieve higher resolutions, making them a better choice for the lithography stage. There are now many companies in the world producing photoresists for semiconductor manufacturing.
Photolithography
Lithography is critical in the chip manufacturing process because it determines how small the transistors on a chip can be. At this stage, the wafer is put into a lithography machine (yes, that's what ASML makes) and exposed to deep ultraviolet (DUV). In many cases they are thousands of times finer than a grain of sand.
Light is projected onto the wafer through the "reticle", and the optical system of the lithography machine (the lens of the DUV system) shrinks the circuit pattern designed on the reticle and focuses it on the photoresist on the wafer. As previously introduced, when light hits the photoresist, a chemical change occurs that imprints the pattern on the reticle onto the photoresist coating.
Getting the exposure pattern exactly right is a tricky task, with particle interference, refraction, and other physical or chemical defects all likely to happen in the process. This is why sometimes we need to optimize the final exposure pattern by specifically modifying the pattern on the reticle to make the printed pattern look what we want. Our system combines algorithmic models with data from the lithography machine and test wafers through "computational lithography" to generate a reticle design that is completely different from the final exposure pattern, but that's exactly what we want to achieve because Only in this way can the desired exposure pattern be obtained.
Etching
The next step is to remove the degraded photoresist to reveal the desired pattern. During the "etch" process, the wafer is baked and developed, and some of the photoresist is washed away, revealing a 3D pattern of open channels. The etch process must precisely and consistently form conductive features without affecting the overall integrity and stability of the chip structure. Advanced etching techniques enable chipmakers to use double, quadruple and spacer-based patterns to create the tiny dimensions of modern chip designs.
Like photoresist, etching is also divided into "dry" and "wet". Dry etching uses gases to define the exposed pattern on the wafer. Wet etching uses chemical methods to clean wafers.
A chip has dozens of layers, so etching must be carefully controlled so as not to damage the bottom layers of the multilayer chip structure. If the purpose of the etching is to create a cavity in the structure, then you need to make sure that the depth of the cavity is exactly right. For some chip designs with up to 175 layers, such as 3D NAND, the etching step is particularly important and difficult.
Ion Implantation
Once the pattern is etched onto the wafer, the wafer is bombarded with positive or negative ions to adjust the conductive properties of parts of the pattern. As a material for wafers, raw silicon is not a perfect insulator, nor is it a perfect conductor. Silicon's electrical conductivity falls somewhere in between.
Directing charged ions into a silicon crystal so that the flow of electricity can be controlled to create the electronic switches—the transistors—the basic building blocks of chips, is called "ionization," also known as "ion implantation." After the layer is ionized, the remaining photoresist protecting the unetched areas is removed.
Package
It takes thousands of steps to make a chip on a single wafer, and it takes more than three months from design to production. To remove the chips from the wafer, they are cut into individual chips with a diamond saw. These chips, called "bare die," are singulated from 12-inch wafers, the most commonly used size in semiconductor manufacturing. Because chips vary in size, some wafers can contain several Thousands of chips, while some contain only a few dozen.
These dies are then placed on "substrates" -- which use metal foils to direct the die's input and output signals to the rest of the system. We then cover it with a lid that has a "vapor chamber," which is a small, flat, metal protective container that holds coolant to keep the chip cool during operation.
Chips are now part of your smartphone, TV, tablet, and other electronics. It may be the size of a thumb, but a chip can contain billions of transistors. For example, Apple's A15 Bionic chip contains 15 billion transistors and can perform 15.8 trillion operations per second.
Of course, there are far more steps involved in semiconductor manufacturing. Chips go through measurement inspections, electroplating, testing, and more. Each chip goes through hundreds of these processes before it becomes part of an electronic device.
