Semiconductor
Wafer Fabrication Equipment
Epitaxial
Deposition Equipment
The
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
deposition process.
A
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.
Oxidation
Systems
The
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
the wafers.
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.
Note that
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
oxidation furnaces.
Diffusion
Systems
Diffusion
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.
A
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.
Ion
Implantation Equipment
Ion
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
being introduced.
A
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.
The
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
implantation systems.
<Proceed to Page 2 - PVD; CVD, Lithography/Etch
Equipment>
See Also:
Semiconductor
Eqpt;
Assembly
Equipment;
Test
Equipment;
IC
Manufacturing
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