|
Glossary of Terms
A B
C D E
F G H
I J K L
M N O
P Q R
S T U V
W X Y Z
A
Aluminum oxide: The oxide of aluminum is
popularly used for a variety of atomic layer deposition applications.
Its advantages in use include low leakage, excellent thermal stability,
moderate dielectric constant and high breakdown voltage.
back to top
Alloy: See mixture.
back to top
Angstroms: A unit of measurement often used
in measuring very thin films. A typical atom, or the distance between
atoms, is said to be approximately from 3 to 5 angstroms.
back to top
B
Back-end manufacturing: the testing and assembly of chip manufacturing,
which occurs after the wafer has left the clean room.
back to top
C
Capacitors: A circuit element formed by
placing an insulating layer between two conducting layers; its function
is to store a measure of electrical charge until needed. It is a
very important component of memory chips.
back to top
Capacity buys: Buying of equipment by manufacturers in order to increase manufacturing capacity (total output). This is as opposed to technology buys, which are equipment purchases of advanced, cutting-edge equipment for the purposes of developing next-generation technology and other R&D.
back to top
Chemical mechanical polishing (CMP): Polishing
the top surface of a wafer aided by a slurry containing an abrasive
grit suspended in reactive chemical agents. As the name implies,
the polishing action is partly mechanical and partly chemical. Both
metals and oxides can be polished with CMP.
back to top
Chemical vapor deposition (CVD): Deposition
of thin films (usually dielectrics/insulators) on silicon wafers
by placing the wafers in a mixture of gases which react at the surface
of the wafers. CVD can be done at medium to high temperature in
a furnace, or in a CVD reactor in which the wafers are heated but
the walls of the reactor are not. Plasma enhanced CVD avoids the
need for a high temperature by exciting the reactant gases into
a plasma.
back to top
Clean room: The place where semiconductor
manufacturers do all their wafer processing. Dust and particles
which might fall on the wafers during processing and result in the
circuits not working are kept out of the clean room by filtering
the air and managing the air flow. Humans are required to wear specially
designed clean room bunny suits (overalls) and booties over their
street clothes, and must put on gloves and face masks (humans tend
to shed skin and hair). Normal paper is not allowed in clean rooms
-- only clean room low particulate paper may be taken in.
back to top
Cluster tool: A machine which contains more
than one process module. This is particularly useful if there are
a number of processes which have to happen in sequence. An example
of this is the deposition of a multi-layer metal film with each
layer being deposited in a different module (chamber). Cluster tools
nevertheless represent savings in cost and space even if all the
process modules are identical.
back to top
CMP: See chemical mechanical polishing.
back to top
Conductor: A material that allows electrical
current to pass through it.
back to top
Conformality: A term used to describe a
desired quality in thin film technology -- the ability of a deposition
process to deposit films in equal thickness without gaps over all
parts of a complex topology, including high-aspect ratio features.
back to top
CVD: See chemical vapor deposition.
back to top
D
Damascene process: A way of making metal
lines which involves depositing an insulator (oxide), etching a
trench in the oxide, depositing metal everywhere and then polishing
back with CMP so there is just metal left in the trench. This is
the opposite of the traditional sequence which has metal being deposited
first, the metal being patterned through etching, and the oxide
being deposited to try to fill the gaps between the metal. Damascene
processing removes the gap fill problem (getting oxide between the
metal lines). It also results in a different distribution of processes
used in the fab in that it uses an oxide etch instead of a metal
etch, and a metal CMP step instead of an oxide CMP step.
back to top
Dicing: Cutting up the wafer into individual
chips. This is usually done with a circular saw called a dicing
saw.
back to top
Die: The term for a single semiconductor
chip. Strictly speaking, the plural of die is dice, though engineers
have a tendency to use the term die both in the singular and the
plural. back to top
Dielectric: See insulator.
back to top
Digital: A type of circuit in which the signals
can have only one of two possible states (a "1" or a "0").
This is in contrast to analog circuits in which the signals are
continuous and can take on any value within a range.
back to top
Diodes: A two-terminal electronic device
which permits significant current flow in only one direction. Diodes
typically function as a rectifier, i.e., converting alternating
current into direct current.
back to top
Dopant: Tiny amounts of impurities can change
the electronic properties of the silicon, affecting greatly how
it conducts electric current. Selected impurities called dopants
are deliberately introduced into the silicon to create devices such
as transistors. Typical dopant concentrations in silicon range from
one part in a thousand to one part in ten million. Phosphorus, arsenic
and boron are the most common dopants used for silicon. Phosphorus
and arsenic make the silicon n-type, which means that the current
carriers are negatively charged electrons. Boron makes the silicon
p-type because the current carriers are positively charged holes.
Dopants are normally introduced into the silicon by ion implantation.
back to top
Dope: (to dope) To add certain types of
impurities to the silicon to change its crystalline structure and
enhance its ability to conduct electricity.
back to top
Drain: The terminal of an n-type transistor
where electrons exit the transistor when it is "on."
back to top
DRAM: A type of semiconductor memory, dynamic
random access memory. DRAMs account for a significant percent of
the total semiconductor market (between 15 and 30%) and so DRAM
manufacturers are big equipment buyers. DRAM manufacturing is concentrated
in Japan and Korea.
back to top
Dry etching: Another name for plasma etching.
See plasma etching.
back to top
E
Electrical current: The flow of electrons
through a material.
back to top
Electron: A negatively charged particle.
back to top
Electronic circuit: Any complete pathway
through which electrical current can flow.
back to top
F
Fab: Short for wafer fabrication facility
-- a semiconductor factory. Often used to refer to a semiconductor
clean room.
back to top
Footprint: The area a machine takes up in
the clean room. This is important because clean room space is expensive,
and so minimizing the footprint of a machine is a good thing to
do. There are two numbers that semiconductor manufacturers are interested
in -- the footprint and the linear frontage number (length of the
front of the machine). The linear frontage number affects how many
machines will fit into a bay since the machines are all lined up
side-by-side.
back to top
Front-end manufacturing: This refers to
wafer processing that takes place in the clean room, as opposed
to processing that happens after the wafer has been essentially
finished. Note also that front-end manufacturing is also divided
into two further categories, called front-end processing and back-end
processing. Front-end processing is the device formation part, and
the back-end processing (in the wafer fab) is the part in which
all the interconnect (wires) of the integrated circuit are laid
down and defined.
back to top
G
Gate: An element of a transistor to which
voltage may be applied in order to turn a circuit on or off.
back to top
H
High-aspect ratios: The comparative ratio
of the width and length of a structure. In semiconductors, a "trench"
structure exists in various components of integrated circuits, such
as the capacitor. The higher the aspect ratio, the more difficult
it is to deposit conformal and uniform thin films.
back to top
High k dielectric: An insulator which will
not conduct electricity but which, when sandwiched between metal
plates, will easily allow these plates to talk to each other via
electric fields (this is called a capacitor structure). These can
be used as memories, and one structure that is being considered
for very high density DRAMs (dynamic random access memories) is
a layer of barium strontium titanate (BST -- a high k dielectric)
between platinum electrodes. While high k dielectrics are good for
capacitors, the opposite is true of the insulators used to separate
metal lines, for which low k dielectrics are desirable (see low
k dielectric).
back to top
I
Insulator: A material which will not allow
an electric current to flow through it. In semiconductor chips,
commonly used insulators are silicon dioxide (glass) and silicon
nitride (silicon + nitrogen). Also commonly referred to as a dielectric
in the semiconductor industry.
back to top
Integrated circuit: A complete electronic
circuit with transistors and wires connecting these transistors
(metal interconnects) on a semiconductor chip.
back to top
Interconnect: The "wiring" that
connects all of the various functional circuit components.
back to top
Ion implantation: The process by which dopants
are introduced in exact quantities into silicon. A stream of charged
particles (called ions) of phosphorus, arsenic, or boron is created
and then directed at a silicon wafer at a precisely controlled velocity
(energy). In this way both the concentration and depth of the dopant
can be controlled.
back to top
K
k: See low k dielectric and high k dielectric.
back to top
L
Leakage current: Residual current flow through
an insulating layer due either to quantum mechanical tunneling in
ultrathin films and/or residual imperfections in the film such as
impurities, pinholes, or grain boundaries.
back to top
Logic chip: A chip which does computations,
makes decisions, or makes things happen. For example, the main chip
in a computer is a microprocessor and does mathematical computations,
amongst other things.
back to top
Low k dielectric: A type of insulator which
helps isolate metal connections, preventing these from interfering
with each other. Metals which are close together can affect each
other's signals through the electric fields which run between them.
The ease with which the metal lines couple with each other in this
way is affected by the properties of the insulator separating them.
The physical parameter which has direct bearing on this is the dielectric
constant or k. Low k dielectrics are better than high k dielectrics
at suppressing the coupling. Adding fluorine to standard CVD deposited
oxide helps, but it is thought that to go further than this in reducing
k it might be necessary to go to a completely different material
than oxide. While low k dielectrics are desirable for isolating
metal lines in integrated circuits, device engineers seek the opposite
(i.e. high k dielectrics) for memory storage elements called capacitors
(see high k dielectric).
back to top
M
Memory chip: A chip which retains information
for logic chips to use. For example, in a computer, the memory chips
will store the word processing program while it is being used, and
the letters of the word processing documents which are being worked
on. DRAM is the type of memory used most in computers, and is by
far the most important type of memory from a total worldwide revenue
standpoint.
back to top
Micron: One thousand microns make one millimeter.
A human hair is about 100 microns thick. A transistor in an advanced
semiconductor process might have an area of about 4 microns by 1.5
microns (though of course transistors vary greatly in size depending
on their purpose). In general, the micron number assigned to a technology
(e.g. 0.25 micron technology) refers to the width of the smallest
patterned feature of a transistor which is the polysilicon transistor
gate.
back to top
Microprocessors: The central processing
unit of a computer.
back to top
Mixture: A substance composed of two or
more materials such as Al2O3 and HfO2. If the materials are present
in elemental form rather than as part of a compound, then it is
a true alloy. If there is residual order, the more proper term may
be ultrathin layers of nanolaminates.
back to top
N
Nanolaminate: A thin film composed of a
series of alternating sub-layers with different compositions, e.g.,
Al2O3 and Ta2O5.
back to top
Non-volatile memory: Semiconductor memory
which will not forget its data once the power is switched off. This
is in contrast to volatile memory (e.g. DRAMs), which lose their
information when there is no power supplied to the chip.
back to top
P
PECVD: See plasma enhanced chemical vapor
deposition.
back to top
Photolithography: The photographic process used to transfer circuit patterns onto a semiconductor wafer. This is done by projecting light through a patterned reticle, onto a silicon wafer covered with a photosensitive material (photoresist). A reticle is a glass plate with a layer of chrome on one side.
back to top
Physical vapor deposition (PVD): Deposition
of thin films by physical means as opposed to chemical (like chemical
vapor deposition). This is most often used for deposition of metals.
The most common form of PVD is sputtering, in which a metal target
is exposed to a plasma made from a gas like argon which is not chemically
reactive. The excited gas atoms hit the target and knock off metal
atoms which deposit onto a wafer placed below, building up the desired
metal film.
back to top
Plasma enhanced chemical vapor deposition (PECVD):
Chemical vapor deposition in which a plasma is created from the
reactant gases. The ions in the plasma are in an excited state and
so will easily react with the silicon wafer, without the need for
elevated temperatures as in conventional (thermal) CVD.
back to top
Plasma etching: Also called dry etching.
This involves using a plasma to etch a semiconductor layer. The
plasma contains highly excited molecules (reactive ions) which easily
react chemically. There is also a physical bombardment mechanism
in that the ions are accelerated towards the wafer with an electric
field. Plasma etching is usually anisotropic, which means that the
etching takes place in only one direction (line of sight). This
is a key advantage over wet etching with chemicals.
back to top
Plasma: A highly excited gas. Plasmas are
created by exposing gases at low pressure to an electric or electromagnetic
field. In semiconductor processing, plasmas are used for etching
and thin film deposition (the excited state of the gas makes it
very reactive). In everyday life, plasmas are used to give light
in fluorescent light bulbs, neon lamps and blue insect traps.
back to top
Platform: The frame of the machine, including
robotic handling apparatus, needed to feed wafers from their loading
station into the individual process modules in which the processing
will occur. Cluster tools are machines in which more than one process
chamber is mounted on the platform, so that several wafers can be
processed at a time (with identical or different processes).
back to top
Plug: Similar to interconnects, but vertically
(rather than horizontally) aid in connecting various levels in the
intergrated circuits. Consist of a metal filling (often tungsten)
in a hole etched through a layer of insulator.
back to top
Poly lines: See polysilicon.
back to top
Polysilicon: A contraction of "polycrystalline
silicon." Silicon which is deposited on wafers in a form that
is crystalline, but is not one continuous crystal like the silicon
wafers are. Polysilicon is used as a critical part of a transistor
called the transistor gate. It is also sometimes used as a resistor,
and as a wire for connecting things together (although it does not
conduct electricity as well as the metal wires used in integrated
circuits).
back to top
PVD: See physical vapor deposition.
back to top
R
Resistor: an electronic circuit component/device
that has electrical resistance and that is used in an electric circuit
for protection, voltage division, or current control.
back to top
S
Semiconductor: A material such as silicon
whose conductivity is between that of a conductor and an insulator.
Its conductivity can be modulated by adding impurities such as boron
or phosphorus.
Shunts: (or, to shunt) Means to divert electrical current with conducting
lines, usually made of polysilicon.
back to top
Silicon dioxide: Sometimes just called oxide
in the semiconductor industry. Sand on the beach and the glass from
which we make bottles is silicon dioxide. Silicon dioxide is an
insulator, and is used in semiconductor circuits to isolate different
conducting regions. Silicon dioxide can be grown from silicon by
exposing it to oxygen at high temperatures, or it can be deposited
using chemical vapor deposition.
back to top
Silicon nitride: An insulating material
used in semiconductor processing which is a mixture of silicon and
nitrogen. It can be used to protect silicon from being oxidized.
It is also often used right at the end of the process as a protective
capping film on the chip (called a passivation layer). Silicon nitride
is usually deposited by chemical vapor deposition (CVD).
back to top
Silicon: An element on the periodic table
with the symbol Si. Silicon is a semiconductor used to fabricate
most transistors and integrated circuits. Pure silicon is used to
make almost all the semiconductor chips currently sold on the market.
Silicon is not the only semiconductor which can be used to make
integrated circuits, but it does have many properties that make
it quite a bit better for this purpose than the other known semiconductors.
When silicon is combined with oxygen it becomes silicon dioxide.
back to top
Sputtering: A form of physical vapor deposition
(PVD) often used for deposition of metal films.Sputtering involves
knocking metal atoms off a disc of pure metal with charged, energetic,
chemically inactive atoms called ions (from a plasma). The metal
atoms will re-deposit onto the wafer to build up the desired metal
film.
back to top
Stepper: A photolithography machine used
to expose a pattern on a wafer by shining light through a reticle
(a glass plate containing a pattern etched in chrome). Since it
cannot accurately expose the entire wafer at once, a stepper exposes
an area of a smaller size and keeps repeating this until the whole
wafer is covered. This process is called step and repeat. An eight
inch wafer might need about 80 fields for full exposure.
back to top
Stoichometric films: Films which have a
composition which matches the expected composition from the chemical
formula of the material. For example, stoichiometric Al2O3 has 2
atoms of Al for every 3 atoms of O.
back to top
Substrate: In manufacturing of semiconductors,
the surface on which a film is deposited, often the silicon wafer.
back to top
T
Technology buys: Purchases of advanced equipment
by the semiconductor industry for developing next generation technologies
and other R&D, as opposed to buying equipment in order to increase
manufacturing capacity (capacity buys).
back to top
Transistors: Transistors are miniature electronic
switches. They are the building blocks of the microprocessor which
is the brain of the computer. Transisitors have no moving parts
and are turned on and off by electrical signals. The on/off (binary)
switching of transistors facilitates the work performed by microprocessors.
back to top
Tungsten: A metal commonly used to make
the plugs used for connecting metal wires to one another or to the
devices in integrated circuits. Tungsten is usually deposited by
CVD, unlike almost all the other commonly used metals in semiconductor
manufacturing which are generally deposited by sputtering. This
makes it excellent for filling deep narrow holes such as the contact
holes connecting the metal wires to each other and to the semiconductor
devices in an integrated circuit.
back to top
U
ULSI: Ultra large scale integration, refers
to integrated circuites (ICs) containing greater than 100,000 transistors.
back to top
Uniformity: It is important that any given
process affects all areas of the wafer equally. The measure of this
is called the uniformity of the process. A common (though undesirable)
occurrence is that center to edge non-uniformities occur. For example,
the center of the wafer might get etched more rapidly than the edge,
or the edge of a wafer might polish down more quickly than the center.
back to top
V
Voltage: The force or strength of the electrical
pressure in a circuit.
back to top
W
Wafer: Semiconductor processing is done
on round disks of silicon called wafers. A current generation wafer
is 8 inches in diameter, the thickness of a credit card, weighs
about a third of a pound, and is polished to a mirror finish on
one side. It is silvery gray in color.
back to top
|
