In the updated iteration of many digital products such as smartphones, technological changes have quietly occurred. Cutting-edge chips such as Apple's A15 bionic chip are enabling more innovative technologies. How are these chips made, and what are the key steps?
The powerful performance of modern digital products such as smartphones, personal computers, and game consoles goes without saying, and most of these powerful performances come from those very small but complex enough technological products - chips. The world is surrounded by chips: in 2020, more than a trillion chips were produced worldwide, which is equivalent to 130 chips per person on the planet. However, even so, the recent shortage of chips is still manifested, and this number has not yet reached the upper limit.
Although chips can already be produced on such a large scale, producing chips is not an easy task. The process of manufacturing chips is complex, and today we will cover six of the most critical steps: deposition, photoresist coating, lithography, etching, ion implantation, and encapsulation.
sedimentation
The deposition step begins with a wafer, which is cut from a 99.99% pure silicon cylinder (also called a "silicon ingot") and polished to an extremely smooth finish, and then a thin film of conductor, insulator or semiconductor material is deposited onto the wafer according to structural needs so that the first layer can be printed on it. This important step is often referred to as "deposition".
As chips become smaller, printing patterns on wafers becomes more complex. Advances in deposition, etching, and lithography technologies are key to keeping chips smaller and thus driving the continuation of Moore's Law. This includes innovative technologies that use new materials to make the deposition process more precise.
Photoresist coating
The wafer is then coated with a photosensitive material called "photoresist" (also called "photoresist"). Photoresist is also divided into two types - "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 structure and become easier to dissolve in preparation for etching and deposition. Negative photoresists, on the other hand, aggregate areas exposed to light, which makes them more difficult to dissolve. Positive photoresists are most used in semiconductor manufacturing because they can achieve higher resolutions, making them a better choice for the lithography stage. There are many companies in the world that now produce photoresists for semiconductor manufacturing.
photoetching
Lithography is crucial in the chip manufacturing process because it determines how small the transistors on the chip can be. At this stage, the wafer is placed in a lithography machine (yes, a product produced by ASML) and exposed to deep ultraviolet light (DUV). Many times they are thousands of times smaller than grains of sand.
Light is projected onto the wafer through the "mask plate", and the optical system of the lithography machine (the lens of the DUV system) reduces the designed circuit pattern on the mask plate and focuses on the photoresist on the wafer. As previously introduced, when light hits the photoresist, a chemical change occurs, and the pattern on the mask plate is printed onto the photoresist coating.
Getting the exposure pattern exactly right is a tricky task, and particle interference, refraction, and other physical or chemical defects can all occur in the process. That's why sometimes we need to optimize the final exposure pattern by specifically correcting the pattern on the mask so that the printed pattern becomes what we need it to look like. Our system combines the algorithmic model with the data from the lithography machine and the test wafer through computational lithography to produce a mask plate design that is completely different from the final exposure pattern, but this is exactly what we want to achieve, because only then can we get the desired exposure pattern.
Etching
The next step is to remove the degenerate photoresist to show the desired pattern. During the "etching" process, the wafers are baked and developed, and some photoresist is washed off, revealing a 3D pattern of open channels. The etching process must accurately and consistently form conductive features without affecting the overall integrity and stability of the chip structure. Advanced etching technology enables chipmakers to use double, quadruple, and spacer-based patterns to create tiny sizes for modern chip designs.
Like photoresists, etching is also divided into "dry" and "wet". Dry etching uses gas to determine the pattern of exposure on the wafer. Wet etching chemically cleans the wafer.
A chip has dozens of layers, so the etching must be carefully controlled so as not to damage the bottom layer of the multilayer chip structure. If the purpose of etching is to create a cavity in the structure, it is necessary to ensure that the depth of the cavity is exactly correct. In some chip designs up to 175 layers, such as 3D NAND, the etching step is particularly important and difficult.
Ion implantation
Once the pattern is etched on the wafer, the wafer is bombarded with positive or negative ions to adjust the conductive properties of some of the patterns. As the material of the wafer, the raw material silicon is not a perfect insulator, nor is it a perfect conductor. The electrical conductivity of silicon is somewhere in between.
The flow of electricity can be controlled by directing charged ions into silicon crystals, creating electronic switches, transistors, the basic components of the chip, which is "ionization," also known as "ion implantation." After the layer is ionized, the remaining photoresist to protect the area from etching will be removed.
encapsulation
Manufacturing a chip on a single wafer requires thousands of processes, from design to production, which takes more than three months. To remove the chip from the wafer, it is cut into a single chip with a diamond saw. These chips, known as "bare crystals," are split from 12-inch wafers, the most commonly used sizes in semiconductor manufacturing, and because chips vary in size, some can contain thousands of chips, while others contain only a few dozen.
These bare crystals are then placed on a "substrate" that uses metal foil to direct the input and output signals of the bare crystals to the rest of the system. We then put a lid on it with a "heat shield", a small flat metal protective container filled with coolant to ensure that the chip can stay cool while running.
It's just getting started
Now, chips are part of your smartphones, TVs, tablets, and other electronics. It may only be the size of a thumb, but a chip can contain billions of transistors. Apple's A15 bionic chip, for example, contains 15 billion transistors that can perform 15.8 trillion operations per second.
Of course, semiconductor manufacturing involves far more steps than that, and the chip also has to go through more than measurement inspection, plating, testing, etc., and each chip has to go through hundreds of times before becoming part of the electronic device.
---- the full text ends here, if you like, please click "Watching" or share to the circle of friends.