Semiconductor manufacturing

Semiconductor device fabrication is the process used to create chips, the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconductor material. Silicon is the most commonly used semiconductor material today, although gallium arsenide, germanium, and many other materials are used in special applications.

The single point of contact between the electronic and physical worlds is the factory where semiconductors are produced -- known as a wafer fabrication facility or "wafer fab." In essence, a wafer fab takes very pure silicon (the basic element in sand, provided in thin discs or "wafers"), modifies it with phenomenal dexterity, precision, and knowledge, and produces integrated circuits-- the physical devices that power the cyber-world.

A wafer is made out of extremely purified silicon that is grown into mono-crystalline cylindrical ingots, using the Czochralski process. These ingots are then sliced into 0.75 mm thick wafers and polished to obtain a very regular and flat surface.

Once the wafers are prepared, many process steps are necessary to produce the desired semiconductor integrated circuits. In general the steps can be grouped into four areas:

Doing this requires leading-edge capabilities in optics, chemistry, mechanics, measurement, and many other fields. It demands huge amounts of capital, both financial (new fabs cost over $1 billion) and intellectual. The complex process constantly redefines its own limitations, and somehow manages to move ahead at a blinding rate, setting the pace for businesses that chips in their products. Consumers in industrialized nations have learned, for example, that a personal computer purchased in January is obsolete by October. The credit (or blame) for this phenomenon lies with the wafer fab, where engineers and scientists continually work towards a single goal: more components on each chip.

Front End Processing refers to the most crucial steps in the fabrication. In this stage the actual semiconductor devices or transistors are created. A typical front end process includes the following: preparation of the wafer surface, patterning and subsequent implantation of dopants to obtain the desired electrical properties, growth or deposition of a gate dielectric, and growth or deposition of insulating materials to isolate neighboring devices.

Once the various semiconductor devices have been created they must be interconnected to form the desired electrical circuits. This "Back End Processing" involves depositing various layers of metal and insulating material in the desired pattern. Typically the metal layers consist of aluminium or more recently copper. The insulating material was traditionally a form of SiO2 or a silicate glass, but recently new low-K materials are being used. The various metal layers are interconnected by etching holes, called "vias" in the insulating material and depositing tungsten in them.

Once the Back End Processing has been completed, the semiconductor devices are subjected to a variety of electrical tests to determine if they function properly.

Finally, the wafer is cut into individual die, which are then packaged in ceramic or plastic packages with pins or other connectors to the outside world.

The packaged chips are then retested to ensure that they were not damaged during packaging and that the die-to-pin interconnect operation was performed correctly.