Wafer Fabrication Equipment
equipment used in depositing epitaxial layers on the wafer is often
referred to as ‘epitaxial reactor’. Epitaxial reactors are high-temperature chemical vapor
deposition systems. There
are two major types of epitaxial deposition equipment, namely, the
‘pancake reactor’ and the ‘barrel reactor’.
These two types got their names from the shapes of their
susceptor, which is the part that holds the wafers during the epitaxial
basic epitaxial reactor should consist of at least the following:
a) a reactor tube or chamber to isolate the epitaxial deposition
environment; b) a system that distributes the various chemical species
for epitaxial deposition in a very controlled manner; c) a system for
heating the wafers; and d) a system for scrubbing the effluent gases. Applied
Materials is an example of a manufacturer of Epi deposition equipment.
formation of silicon dioxide (SiO2) on a silicon substrate is known as
oxidation. Generally this
is accomplished by thermal oxidation, wherein the wafer is exposed to an
oxidizing environment at elevated temperature. Thus, an oxidation
system has to have a heat source to elevate the temperature of the
oxidizing environment and a system for delivering the oxidizing gases to
A basic oxidation system
would consist of the following: a) a cabinet that houses the various parts of the furnace; b) a heating system; c) a temperature
measurement and control system; d) process tubes where the wafers
undergo oxidation; e) a system for moving the oxidizing gases into and
out of the process tubes and f) a
loading station where the wafer boats are loaded into and unloaded from
the process tubes.
thermal oxidation is basically a diffusion process, so it can also be
accomplished by diffusion
systems designed not only for depositing dopants into wafers, but
for oxidation purposes as well. Tempress
Systems, Bruce Technologies, and Tystar are examples of manufacturers of
is the transfer of a species resulting from concentration
gradients. Diffusion can pertain to either oxidation or dopant
deposition, but it is generally used to refer to the latter.
In the early
days of semiconductor manufacturing, diffusion was extensively used in the controlled deposition of
impurity atoms or dopants into the silicon substrate,
which is the foundation of p-n junction formation. Ion
implantation has become the primary means for dopant deposition in
recent years, but diffusion is still necessary in certain applications.
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typical diffusion system, also known as a diffusion furnace, is very
similar to (and in some cases, the same as) an oxidation furnace.
It is an equipment designed to provide an
environment of high temperature and controlled gas flow to wafers. It
consists of a heating element, a diffusion tube, a diffusion boat, and a dopant delivery system. The wafer is exposed to the dopant gases at high
temperature inside the furnace, a mechanism that is very similar to
oxidation for growing SiO2 films. ASM, Tempress
Systems, and Tystar are examples of manufacturers of diffusion furnaces.
implantation is used in wafer fabrication to selectively deposit dopant
ions into the surface of the wafers. This process involves the
direct introduction of highly energetic, charged atomic species onto the
target substrate. Its application to semiconductor manufacturing
requires a great deal of control to ensure that the dopants are
introduced in precise quantities at the correct location and depth
without inducing any damage to the silicon lattice structure of the
substrate. Needless to say, an ion implantation equipment is
very complex, needing to accurately implant and monitor the species
typical ion implantation equipment consists of a feed source, an ion
source, a device for extracting and analyzing ions, an acceleration
tube, a scanning system, a system end station, a high vacuum system, and
a computerized control system.
feed source contains the material where the species for implantation
will come from. The acceleration tube determines the energy content of
the ions while the scanning system ensures uniform distribution of the
ions over the target. The system end station measures the implant dose
and minimizes dose errors. Applied
Materials, Eaton, and Varian are examples of manufacturers of ion
Vapor Deposition Systems
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
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.
Vapor Deposition Systems
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
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
and Applied Materials are examples of suppliers of CVD systems.
Chemical Vapor Deposition.
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.
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:
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.
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.
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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