Manufacturing semiconductors requires a number of processes. There are eight major steps. Let's briefly examine these eight processes as outlined by Samsung Electronics.
The eight major semiconductor processes – pre-process
Wafer manufacturing
A wafer is a substrate used to mount circuits, and is made primarily from silicon (Si) extracted from sand.
By applying high heat to silicon, concentrating and growing it, you can create a silicon pillar called an ingot. This pillar, when sliced thinly horizontally, becomes a wafer. The larger the wafer, the more chips can be produced per wafer. In our lab, we use 8-inch wafers.
Oxidation
Silicon (Si), the raw material of wafers, oxidizes when exposed to air, forming a SiO2layer. This naturally occurring native oxide is difficult to precisely control and can adversely affect the process. Furthermore, before processing, a thick insulating oxide layer is applied to protect the wafer from impurities such as dust and prevent leakage current. Oxidation methods include wet and dry oxidation.
In our lab, we used wafers with SiO2thicknesses of 300 nm.
Photolithography
If you need to make a chip, it would be useless to deposit it all over the wafer, right? So you need to distinguish between the areas on the wafer where you will deposit it and the areas where you won't, and that process is called the photo process.
Photo Resist is coated on the wafer and exposed to ultraviolet light. At this time, a mask is used to create the desired pattern on the wafer.
I will explain the detailed principles in another article, but for now, you just need to know why the photo process is necessary.
Etching
During the process, there are times when it's necessary to remove a film deposited in an unnecessary location. In these cases, etching can be used to remove the film. Because the uniformity of the film affects yield, uniformity is crucial. To maximize process efficiency, the etching method must be selected with the etch rate in mind.
The etching process, like the oxidation process, is divided into wet etching and dry etching.
Deposition & ion implantation
Once the desired pattern is created on the substrate through photolithography and etching, a thin film is deposited through deposition, patterned again, and the deposition process is repeated. This allows the following structure to be formed.
There are two main methods of deposition: PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition).
- PVD: A method of creating a thin film by physically dividing particles into vapor and sputtering and adsorbing them onto a wafer. There are two main methods: evaporation and sputtering.
- CVD: A method of deposition through chemical reaction. A gaseous substance is moved to a substrate and energy is applied through heat or plasma to induce a reaction and form a thin film.
Ion implantation is a process that imparts electrical properties to semiconductors. As will be explained later in the device stage, impurities can be added to silicon to create N-type and P-type semiconductors, and these can be appropriately arranged to create devices such as diodes and transistors.
In other words, you can think of ion implantation as a process of adding impurities to create a conductive semiconductor.
Metal process
To complete a circuit, metal lines are needed. In semiconductors, a process is used to lay metal lines along patterned paths, using materials such as aluminum, tungsten, and titanium.
This is the entire semiconductor manufacturing process, or pre-processing. The post-processing stage, which involves inspecting and packaging the semiconductors to turn them into actual products, is called post-processing.
The eight major semiconductor processes – post-process
EDS process
In wafer manufacturing, the first step of the eight-step process, I mentioned that larger wafers allow for multiple chips to be manufactured at once. The image above shows multiple chips formed on a wafer. The process of testing chip performance and verifying yield is known as Electrical Die Sorting (EDS).
The purpose of EDS is:
- Distinguishing between functioning and abnormal chips
- If an abnormal chip can be made into a normal chip, it becomes a quality product.
- Increase yield by identifying the cause of problems in the process.
- Detect defective chips early to improve the efficiency of subsequent packaging steps.
I also remember, during my master's course, when making semiconductors, I had to do electrical tests such as DC sweep and pulse test at the probe station, measure and analyze the device characteristics, and optimize the process recipe over and over again...
Packaging process
Finally, the final step. Packaging is where we package the tested semiconductors into chips we can use in our everyday lives. First, since multiple chips are made on a wafer, they need to be cut into individual pieces. This process is called "wafer sawing" or "dicing."
These individual chips are very sensitive to shock, so to prevent damage to the chips, they are placed on top of a PCB (Printed Circuit Board) or lead frame, which we are all familiar with.
Lead frames and PCBs not only protect the chips, but also allow them to transmit and receive electrical signals with the outside world through proper wiring. There are two main methods: wire bonding and flip chip.
After that, the chip is completed by the molding process, which seals the chip to safely protect it from the outside, and the final test, the package test.
We've briefly covered the eight major semiconductor manufacturing processes. Now, let's delve into each process in more detail.
References: Samsung Electronics
