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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.
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.
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.
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.
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