µm (micrometer)
A unit length equal to 1-millionth of a meter (1/1,000th of a mm). A human hair is about 80 µm in diameter.
Alignment
Position, or the act of positioning performed
with an aligner. When transferring the mask pattern to the
wafer with a stepper or other system, the alignment mask already
on the wafer is detected optically, and the new pattern is
positioned so that its alignment marks precisely match those
of the previously transferred pattern. Because of the form
they take, these alignment marks are also referred to as alignment
patterns. In general, this term is used instead of position
or positioning.
Argon fluoride
A light source used in the repeated exposure
of a mask pattern in the photolithography process, with the
objective of transferring the pattern to the surface of a
wafer. An argon fluoride excimer laser, or ArF excimer laser,
has a wavelength of 193nm and is expected to serve as a light
source for pattern resolutions of 0.07 to 0.13 microns.
Chamber
A sealed reaction vessel used for a variety
of physical and chemical reactions. In IC manufacture, processes
involving gas injection, increasing temperature, illumination
and electricity generated by magnetic fields are performed
on wafers loaded into a chamber. Chemical Vapor Deposition
(CVD) and sputtering systems employ chambers to form thin
film, and etching systems use chambers in film etching. A
chamber pumped free of air for processing is referred to as
a vacuum chamber.
E-beam (Electron beam)
A focused stream of electrons, an E-beam can
be employed in lithography as a light source for the transfer
of patterns to photoresist-coated wafers. The E-beam, controlled
and shaped by an electromagnetic lens, writes the pattern
onto the wafer. In addition to single-stroke techniques using
a point beam or a variable-rectangular beam, a partial mask
(aperture) can also be used for batch-area writing. High-resolution
patterns can be transferred using an E-beam as a light source,
and direct writing is performed, eliminating the need for
a mask. However, this method of lithography requires a long
period of time between the completion of the design pattern
data and actual exposure. E-beam lithography is currently
used in mark fabrication, production of some ASIC devices
and prototyping. Low throughput has prevented this method
of lithography from being employed in general IC manufacture
on a large scale.
EUV (Extreme Ultraviolet)
Light with a wavelength between 10 and 100nm
is classified as EUV light. This is considerably shorter than
that of visible light. The use of EUV in pattern transfer
provides very high resolution and enhanced focal length. EUV
photolithography enables the integration of more circuit patterns
into the silicon wafer.
FeRAM
Ferroelectric Random Access Memory. Another form of non-volatile memory now under development, FeRAM combines the advantages of existing RAM and ROM devices, including high speed and support for frequent rewrites. Both read and write can be performed at low voltages, making it a good candidate for use in power-sensitive mobile equipment.
Flat Panel Displays
(FPD)
These display devices have flat front surfaces, and a thin, panel-shaped body.
Compared to cathode ray tube (CRT) displays, they offer the same size screen in a much smaller package. The first FPDs were liquid crystal displays, which had problems such as a limited number of colors and slow response time when the image changed, but technological advances have resolved these issues. In addition to LCDs, flat panel displays are also made using technologies such as plasma display panels (PDPs), light emitting diodes (LEDs), electroluminescence (EL) and vacuum fluorescent displays (VFDs).
g-line
A light source used in the repeated exposure
of a mask pattern in the photolithography process, with the
objective of transferring the pattern to the surface of a
wafer. Classified as visible light, g-line light has a wavelength
of 436nm and is used to resolve patterns of 0.5 microns or
larger. Steppers employing this light are called g-line steppers.
i-line
A light source used in the repeated exposure
of a mask pattern in the photolithography process, with the
objective of transferring the pattern to the surface of a
wafer. Classified as ultraviolet light, i-line light has a
wavelength of 365nm and is used to resolve patterns of 0.25
to 0.5 microns. Steppers employing this light are called i-line
steppers.
Immersion lithography
Stepper resolution is normally expressed as
R = k (process coefficient) x lambda (light source
wavelength) / NA (numerical aperture; the brightness of the
projection lens). The shorter the wavelength of the light
source and the higher the NA of the lens, the higher the resulting
resolution. NA itself is expressed as n x sin theta,
where n is the refractive index of the material through
which the light passes, and theta is the angle of incidence
of that light. Normally this light beam passes through air,
meaning that n = 1. In immersion lithography, however,
a liquid with a refractive index of greater than 1 is placed
between the projection lens and the wafer, resulting in a
corresponding increase in the NA of the system. For a given
incident angle theta, minimum feature size can be reduced
(improved) to 1/n. For a given NA theta can be reduced,
allowing the focal depth to be increased n times.
If an ArF laser is used as the light source, distilled water
with a refractive index of 1.44 is placed between the projection
lens and the wafer. This technique has been used for some
time in microscopes.
Integrated Circuit (IC)
An electronic circuit incorporating electronic devices (transistors, diodes, resistors, capacitors, etc.) formed into an integral block on a semiconductor wafer. Since the electronic devices are formed on the same wafer as the internal wiring used to interconnect them all, within a single manufacturing process line, all of the functions of the individual components are available within this single chip.
The IC technology proposed in 1959 enabled mass production of electronic circuits in small, lightweight packages offering high efficiency and cost-performance. These ICs can be found in a great variety of electronic products today, and will serve as the core of even more innovative products tomorrow.
Krypton fluoride
A light source used in the repeated exposure
of a mask pattern in the photolithography process, with the
objective of transferring the pattern to the surface of a
wafer. A krypton fluoride excimer laser, or KrF excimer laser,
has a wavelength of 248nm and is used for pattern resolutions
of 0.13 to 0.25 microns. The KrF excimer laser is the most
advanced stepper light source used in mass production today.
Liquid Crystal Display
(LCD)
Display devices make good use of the characteristics of liquid crystal. The narrow gap between two thin sheets of glass is filled with liquid crystal, and when voltage is applied to the electrodes installed on the inside surface of the glass substrate the polarity of the liquid crystal molecules changes. This, in turn, changes the transparency of the liquid crystal. The display panel is divided into tiny regions called pixels, and the transparency of each pixel in individually controlled to display letters or images. Liquid crystal does not emit light, so the light source for the display is either incoming light reflected by the LCD panel, or a backlight mounted behind the liquid crystal. LCD displays are generally classified as either simple matrix LCD (STN, etc.) or active matrix LCD (TFT, etc.), depending on how current to the display is controlled, and the type of display required depends upon the application.
Microfabrication Technology
Microfabrication technology is essential in
the manufacture of multi-function, high-performance ICs, making
it possible to fabricate the extremely fine patterns and electrical
connections needed to boost integration levels and density.
Microfabrication technology is the key element in boosting
IC operating speed and reducing dissipation, and because the
resulting chips are smaller it is possible to fit more of
them on a single wafer, resulting in lower manufacturing cost.
Microfabrication technology includes technologies such as
lithography (which transfers the patterns) and etching (which
creates them). The level of microfabrication technology is
indicated by the smallest design rule that can be used, expressed
in either µm (micrometers) or nm (nanometers).
Moore's Law
Defined by Gordon Moore, a founder and former
president of American semiconductor manufacturing giant Intel
Corporation in 1965, Moore's Law states that the number of
transistors integrated into an IC doubles roughly every two
years. The global semiconductor industry has grown in accordance
with this law. Recently, there have been claims that the limits
of microfabrication technology are close and that it will
be difficult to maintain the pace of development, but Moore
has commented that an industry-wide effort should allow us
to continue for quite a while to come.
MRAM
Magnetic Random Access Memory, a type of RAM
utilizing the magneto-resistance effect. A type of non-volatile
memory, which retains stored information even when the current
is off. It offers fast access, high integration levels and
an infinite number of rewrites. Development is under way now,
and it is viewed as a strong candidate for memory in computers
and many other types of equipment.
NA (Numerical aperture)
Normally used in its abbreviated form, NA defines
lens brightness as NA = n x sin alpha, where alpha
is the angle of incidence of the most oblique light entering
the lens, and n is the refractive index of the lens.
NA is a key parameter in determining stepper resolution.
nm (nanometer)
A unit of length equal to 1-billionth of a
meter (1/1,000th of a µm).
OUM
Ovonics Unified Memory. This non-volatile memory
stores data using chalcogenide, in the same way as CD-RW or
DVD-RAM media. Advantages include ease in achieving high integration,
unlimited number of reads, low drive voltage and dissipation,
and high 1012 write/erase cycles. Even better, it can be manufactured
using standard process technology, together with logic circuits.
Development is under way now, with an eye on use in mobile
phones and mobile computer memory.
Resolution
Resolution is a measurement indicating the
degree of intricacy of a pattern to be transferred onto a
wafer in the photolithography process. The resolution ( R
) for steppers, key systems in the process, can be expressed
as R = k * lambda/NA, where the wavelength of the light source
is represented by lambda and the lens' numerical aperture
by NA. Plainly stated, the resolution of a pattern increases
when a light source with a shorter wavelength is introduced,
and/or when a lens with a higher numerical aperture is employed.
Scan (step-and-scan) method
One type of lithography used to transfer the
mask pattern to the wafer. The exposure field is larger than
that in the case of a stepper, so light is emitted through
a slit in the lens while the reticle stage scans across the
chip, covering its entire surface. Scanning using a narrower
lens slit results in reduced aberration compared to larger
lens openings, regardless of the shape of the opening. The
exposure field is enlarged as it is determined by the length
of the slit and the scan distance of the reticle stage. The
scan method is being used more frequently for advanced ICs
(ULSI chips) with large footprints and high-resolution patterns.
Scanners, however, are generally more expensive than steppers
due to the scanning mechanism required for the reticle stage.
Step-and-repeat
Many of the front-end processes (diffusion
processes) employed to form multiple chips on a single wafer
progress in single-chip units. When one chip has been processed,
the processing point is shifted by one step — the degree
of which is determined by the size of the chip — and
processing of the next chip begins. This sequence is repeated
until each chip on the wafer is completed, thus the process
is referred to as "step-and-repeat".
System Displays
(from SEMI FPD Expo)
This technology forms crucial circuits needed
by the LCD panel, such as the drivers, controllers and power
supply, directly on the substrate, for low-temperature polysilicon
TFT, CG silicon TFT and other liquid crystal designs. Forming
these circuits directly on the display substrate offers advantages
such as multi-function performance, thinner and lighter products,
lower power consumption, and fewer parts. These are already
in production for use in mobile phones, PDAs, mobile game
systems, digital cameras and automotive equipment.
Throughput
This term is generally used to indicate the
amount of information that a computer can process within a
fixed period of time. In IC manufacture, it indicates the
number of wafers that a stepper can process — usually
expressed in terms of wafers per hour. |
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