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Semiconductor manufacturing processes
Semiconductor manufacturing processes
Semiconductor devices are built up in a series of nanofabrication processes performed on the surface of substrates made from highly pure single crystal silicon. These substrates are usually known as wafers.
Commonly used wafers include the 300 mm type, which offers the advanced miniaturization required for cutting-edge devices, and 200 mm type, which is better suited to the mixed, small lot production needed for devices for the Internet of Things (IoT).
The silicon wafers forming the base of the semiconductor are cleaned. Even slight contamination of a wafer will cause defects in the circuit. Therefore, chemical agents are used to remove all contamination, from ultra-fine particles to minute amounts of organic or metallic residues generated in the production process, or unwanted natural oxide layers generated due to exposure to air.
2. Film Deposition
Thin film layers of silicon oxide, aluminum and other metals that will become the circuit materials are formed on the wafer.
There are a variety of ways to form these thin films, including "sputtering", in which a target material, such as aluminum or other metal, is bombarded with ions, which knocks off atoms and molecules that are then deposited on the wafer surface, "electrodeposition", which is used to form copper wire layers (copper interconnect), chemical vapor deposition (CVD), in which special gases are mixed to cause a chemical reaction that forms a vapor containing the desired material, and then the mole-cules generated in the reaction are deposited onto the wafer surface to form a film, and thermal oxidation, in which the wafer is heated to form a silicon oxide film on the wafer surface.
3. Post-deposition Cleaning
Minute particles adhering to the wafer after the film deposition are removed using brushes or Nanospray with deionized water, or other physical cleaning methods.
4. Resist Coating
The wafer surface is coated with resist (photosensitive chemical). Then the wafer is spun, causing a uniform layer of resist to be formed on the wafer surface by centrifugal force.
The wafer is exposed using short wavelength deep ultraviolet radiation projected through a mask on which the circuit pattern has been formed. Only the areas of the resist layer that are exposed to the light undergo a structural change, thereby transferring the pattern to the wafer. There are a variety of exposure units, including steppers, which expose several chips at a time, and scanners, which expose the wafer using a slit through which light is projected onto the wafer.
Developer is sprayed onto the wafer, dissolving the areas exposed to the light and revealing the thin film on the wafer surface. The remain-ing resist areas that are not exposed at this point become the mask for the next etching process, and that resist pattern becomes the pattern on the layer below.
In wet etching, the exposed thin film on the surface layer is dissolved using chemicals, such as hydrofluoric acid or phosphoric acid, and removed. This forms the pattern. There is also a dry etching method in which the wafer surface is bombarded with ionized atoms to remove the film layer.
8. Implantation of Impurities
In order to give the silicon substrate semiconducting properties, impurities, such as phosphor or boron ions, are implanted in the wafers.
Heat processing is performed using flash lamps or laser radiation to activate the doped ions implanted in the wafer. Instantaneous activation is required to create the micro transistors on the substrate.
10. Resist Stripping
WResist can be stripped off at a wet station, which uses chemicals that remove the resist, or by ashing, which removes the resist by inducing a chemical reaction using gases. The wafer is cleaned after the ashing.
The wafer is separated into individual chips (dicing), the chips are connected to a metal frame called a lead frame using metal wire (wire bonding) and then enclosed in epoxy resin material(packaging).