▶ Materials Needed to Create a WaferA 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 IngotSilicon 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 WafersIngots, 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 SurfaceSliced 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?