Wafer Fabrication Equipment - Page 2 of 2: PVD; CVD, Lithography/Etch Equipment

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Semiconductor Wafer Fabrication Equipment (Page 2 of 2)

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Physical Vapor Deposition Systems

Physical vapor deposition, or PVD, is the process of depositing a material over a substrate by first converting the material to gaseous state, transporting it across the substrate through pressure control, and allowing the vapor to condense over the target area. This is widely used in the deposition of thin-film aluminum layers on wafers. The source material may be converted into vapor either by evaporation or sputtering.

A typical sputter-type PVD system consists of a sputter chamber, a pre-processing chamber, vacuum pumps, power supplies, sputtering targets, sputtering gas supply, flow control systems, monitors, wafer handling mechanisms and a computerized controller. Varian, Novellus, and KDF are examples of manufacturers of PVD equipment. See also: PVD by Sputtering; PVD by Evaporation.

Chemical Vapor Deposition Systems

Chemical Vapor Deposition, or CVD, is the process of transforming gas molecules known as the precursor into solid thin-film or powder material on the surface of a substrate. CVD comes in various methods. In the fabrication of semiconductor devices, however, the most popular method is known as Plasma-Enhanced CVD, or PECVD. PECVD uses plasma to decompose a reactant gas, such as silane (SiH4), to produce reaction products that precipitate on the surface of the substrate as a new layer.

Inside a PECVD reactor, a strong electric field ignites a plasma between two electrodes, one of which holds the substrate. This plasma ignition cracks the molecular bonds of the process gas, which in turn are able to crack more process gas molecules before reaching the surface of the substrate. Eventually a new layer is deposited on the substrate. For example, when silane is used as precursor, plasma ignition frees up Si and SiH radicals, which also crack more silane molecules on their way to the surface of the substrate, where silicon is deposited. Novellus and Applied Materials are examples of suppliers of CVD systems. See also: Chemical Vapor Deposition.

Photolithography Equipment

Photolithography is an optical process used to create circuit patterns on the silicon wafer. This consists of using photoresist materials and masks to selectively expose or cover areas on the die to which new materials may be added or from which existing materials may be removed. Photolithography consists of a series of steps and, consequently, requires several individual equipment to accomplish these steps.

The equipment used in photolithography include: 1) resist coating equipment to deposit the photoresist on the wafer; 2) ovens for soft-baking the photoresist; 3) exposure systems to subject the resist to some form of radiation; 4) development systems to remove or retain (depending on photoresist type) the exposed areas of the resist, leaving behind a mask pattern that may be used for other wafer fabrication processes. Nikon, Canon, and Karl Suss are examples of manufacturers of photolithography equipment. See also: Optical Lithography.

Etching Equipment

Etching is the process of removing materials or layers from the wafer, of which there are two types: wet and dry etching. As these names imply, wet etching involves the use of liquid chemicals while dry etching involves the use of reactant gases to remove materials.

Wet etching equipment consists of systems that: 1) allow diffusion of reactants to the surface of the wafer; 2) provide the proper conditions for chemical reaction of these reactants with the material being removed; and 3) extract the reaction products from the surface.

Plasma etching is one type of dry etching, using plasma to produce chemically reactive species from inert gases. The reactive gases are then made to react with the material to be etched. Plasma etchers come in many configurations, but a typical plasma etching system consists of: 1) an etching chamber; 2) a pumping and pressure control system; 3) an RF power supply; 4) gas handling systems; and 5) electrodes. Technics and Tegal are examples of manufacturers of etching systems.

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