Part 1, What Is a Wafer?

Can we last a day without semiconductors? It may not be as easy as you think with the semiconductors found in many aspects of our daily lives now, including in mobile phones, laptops, cars, TVs, and credit cards. These semiconductors are very closely connected to our lives. How are they made?

You may have heard of eight essential semiconductor processes if you know a thing or two about the semiconductors. Countless tasks that are required to manufacture a semiconductor are categorized into 8 essential processes, as our title suggests, “Eight Essential Semiconductor Processes.” For the renewal of the Samsung Semiconstory blog, we plan to cover eight essential semiconductor processes once again, the most popular content on this channel. Today, we’ll take a look at the first step, “Creating a Wafer.” We’ll discover what this wafer, core material to integrated circuits really is and how the wafer is made.

▶ Materials Needed to Create a Wafer

A quick question before we start! How are semiconductor integrated circuits related to wafers? An integrated circuit is a semiconductor chip that incorporates many electrical components that process various functions. Integrated circuits are manufactured by creating many identical circuits on a substrate called a wafer. Therefore, a wafer is the foundation for the semiconductor. It’s similar to making a pizza—we prepare a dough first so that we can add toppings later. A wafer is a disc thinly sliced from a silicon rod that is made of elements such as Si or GaAs . Most wafers are made of silicon extracted from sand. Silicon Valley in the U.S. started out with the semiconductor industry and eventually became the center of the global software industry. Its name is reportedly a combination of “silicon”, a raw material for semiconductors, and “valley” from Santa Clara Valley. The name “Silicon Valley” may help you remember that silicon is an essential raw material for the semiconductor wafers. Silicon is rich in supply, being the most abundant element in nature. Its environmentally friendly properties are an added bonus. Should we take a closer look at the wafer manufacturing process?

Step 1. Building an Ingot

Silicon extracted from sand needs to go through a purification process before it can be used to make semiconductors. It is heated until it melts into a high purity liquid and then gets solidified by crystallization. The resultant silicon rod is called an ingot. Only ingots with ultra high purity can be used for semiconductor processes, which require extremely high precision down to a few nanometers.

Step 2. Slicing Ingots to Create Thin Wafers

Ingots, shaped like a spinning top, are sliced into thin, disc-shaped wafers of uniform thickness using sharp diamond saw blades. The diameter of an ingot determines the size of a wafer, such as 150 mm (6 inch), 200 mm (8 inch), and 300 mm (12 inch) wafers. The thinner the wafer is, the lower the manufacturing cost, and the larger the diameter is, the greater the number of semiconductor chips that can be produced per wafer. Therefore, wafers are becoming increasingly thinner and larger.

Step 3. Lapping and Polishing Wafer Surface

Sliced wafers need to be processed to achieve a smooth, mirror-like finish. The surface of sliced wafers is rough and contains defects, which could negatively affect the precision of circuits. Abrasive chemicals and polishing machines are used to polish the surface of a wafer. A polished wafer before any further processing is called a bare wafer, suggesting that no chips have been fabricated yet. The wafer would eventually look like the following after integrated circuits are fabricated on the bare wafer using many physical and chemical processes. Shall we review the name of each part of a wafer with IC chips?

① Wafer: A circular plate (disc) that is a core raw material used in semiconductor ICs. ② Die: You can see many small squares on wafers. Each square is called a die and is an IC chip into which electronic circuits are integrated. ③ Scribe Line: These dies look as though they are glued to one another to the naked eye, but, in fact, there are gaps between the dies. This gap is called a scribe line. The purpose of this scribe line between dies is to cut out each die and assembled it into a chip after the wafer processing. The scribe line is a space where a diamond saw can safely cut the wafer. ④ Flat Zone: This zone is introduced to help identify the wafer structure and serves as a reference line during wafer processing. Because the structure of a wafer is too small to see with our eyes, the orientation of the wafer is determined based on this flat zone. ⑤ Notch: Wafers with a notch have recently become available instead of a flat zone. Notched wafers are more efficient than wafers with a flat zone in that a greater number of dies can be produced from notched wafers. The semiconductor industry is largely categorized into the wafer industry, which manufactures wafers, and the fabrication (FAB) industry, which designs and creates circuits on wafers. There is also the assembly industry, where processed wafers are cut into dies and packaged for protection from moisture and physical damage. Today, we have covered what a wafer is, what each part is called, and how wafers are manufactured. We hope that you find this Eight Essential Semiconductor Processes series interesting and helpful. Please don’t forget to check our next posting!