A semiconductor foundry is a factory that makes chips for other companies. A chip company sends its design. The foundry prints that design onto silicon wafers over about three months, in a clean room, and delivers the finished wafers. A factory of this kind is called a fab, short for fabrication plant.
Most chip companies have no fab. They are fabless companies: they design chips and pay a foundry to make them. A leading fab costs tens of billions of dollars, and only a company that sells enormous numbers of chips could keep one busy. A foundry keeps its fab busy with orders from hundreds of customers. The largest foundries are in Taiwan. Others are in South Korea, the United States, China, Singapore and Europe.
Each foundry offers processes. A process is a fixed recipe of steps, materials and design rules for one generation of chip, such as 28 nm or 3 nm. The name is a label for the generation, not a measured length. A nanometre is a billionth of a metre. Newer processes fit more transistors into the same area, but they cost much more. Most chips, such as those in meters, cars and televisions, use older processes, because they are cheaper and well proven.
Here is a typical case. A fabless company in Hyderabad has designed a chip that controls the picture on smart televisions, for a 28 nm process at a foundry in Taiwan. Its final layout files, from physical design and sign-off, go to the foundry. This moment is called tape-out. The foundry makes a set of about 40 masks. A mask is a quartz plate that carries the pattern of one layer. At 28 nm, a full mask set can cost one to two million US dollars. Then 25 wafers start through the line. Each wafer is 300 millimetres across and holds about 1,800 copies of the chip, each about 6 millimetres square. Each copy is called a die. Over 12 weeks, every wafer goes through hundreds of steps on manufacturing equipment, checked by wafer inspection and measurement. At the end, the foundry tests each die with fine probes. On average, about 1,620 dies on each wafer work. That is a yield of about 90%. The wafers are then shipped to an assembly and test plant, where the dies are cut apart and packaged.
Small companies and colleges need only a few chips to test a design. For them, foundries run multi-project wafers, also called shuttles. Many designs share one mask set and one run of wafers, so each one pays only a small part of the cost.
The foundry does not design the chip. But it gives its customers design rules and libraries of ready-made basic circuits, which load into their electronic design automation (EDA) tools. It also buys ultra-pure gases and speciality chemicals for its steps. India's first commercial foundry is being built at Dholera in Gujarat, as the page on semiconductor fabs in India describes.