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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.
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, a large number of process steps are necessary to produce the desired semiconductor integrated circuits. In general the steps can be grouped into four areas:
- Front End Processing
- Back End Processing
- Test
- Packaging.
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.
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