Making the Chips that Run the World

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Making the Chips that Run the World

• Sabit, Ian Dominique O.
• BSCS-4

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IntroductionMany ingredients and dozens of steps
are needed to make a chip or a microprocessor and
recipes vary, depending on the intended use of
the chip.
PreparationThere are various ingredients used to
build microprocessors and one important and
fundamental ingredient Silicon.
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Silicon Wafers cut from an ingot of pure silicon,
are used by Intel to make microprocessors.
Silicon, the primary ingredient of beach sand, is
a semiconductor of electricity. Semiconductors
are materials that can be altered to be either a
conductor or an insulator.
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Chemicals and gases are used throughout the
chip-making process. Some, like
hexamethyldisilazane, are complex and difficult
to pronounce. Others, such as boron, are simple
elements found in the Periodic Table of the
Elements.
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Metals, such as aluminum and copper, are used to
conduct the electricity throughout the
microprocessor. Gold is also used to connect the
actual chip to its package.
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Ultraviolet (UV) Light has very short wavelengths
and is just beyond the violet end of the visible
spectrum. UV light is used to expose patterns on
the layers of the microprocessor in a process
much like photography.
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Masks used in the chip-making process are like
stencils. When used with UV light, masks create
the various circuit patterns on each layer of the
microprocessor.
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FabricationMicroprocessors are built in layers
on a silicon wafer through various processes
using chemicals, gases, and light.
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On the wafer, the first layer of silicon dioxide
is grown by exposing it to extreme heat and gas.
This growth is similar to the way rust grows on
metal when exposed to water. The silicon dioxide
on the wafer, however, grows much faster and is
too thin to be seen by the naked eye. The wafer
is then coated with a substance called
photoresist. Photoresist becomes soluble when
exposed to ultraviolet light.
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LayeringIn a process called photolithography,
ultraviolet light is then passed through a
patterned mask, or stencil, onto the silicon
wafer. The mask protects parts of the wafer from
the light. The light turns the exposed areas into
a gooey layer of photoresist. Each layer on the
microprocessor uses a mask with a different
pattern.
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EtchingThe gooey photoresist is completely
dissolved by a solvent. This reveals a pattern of
photoresist made by the mask on the silicon
dioxide. The revealed silicon dioxide is etched
away with chemicals. The rest of the photoresist
is removed. This process leaves ridges of silicon
dioxide on the silicon wafer base.
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LayersTo begin another layer, a second, thinner
layer of silicon dioxide is grown over the ridges
and etched areas of the wafer base. Then, a
layer of polysilicon and another layer of
photoresist are applied. Ultraviolet light is
then passed through a second mask, exposing a new
pattern on the photoresist. The photoresist is
dissolved with solvent to expose the polysilicon
and silicon dioxide, which are then etched away
with chemicals.
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The remaining photoresist is removed, leaving
ridges of polysilicon and silicon dioxide.
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Ion ImplantationThrough a process called ion
implantation (also called doping), the exposed
areas of the silicon wafer are bombarded with
various chemical impurities called ions. Ions are
implanted in the silicon wafer to alter the way
silicon in these areas conducts electricity.
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Layers upon LayersThe layering and masking
processes are repeated, creating windows that
allow for connections to be made between the
layers. Atoms of metal are deposited on the
wafer, filling the windows. Another masking and
etching stage leaves strips of the metal that
make the electrical connections. Roughly 20
layers are connected to form the microprocessor's
circuitry in a 3-dimensional structure. The exact
number of layers on a wafer depends on the design
of the microprocessor.
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On the wafer, the microscopic circuitry of each
and every microprocessor is tested. Then the
wafer is cut with a diamond saw, separating the
microprocessors.
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PackagingEach microprocessor is then inserted
into a protective package which allows it to
connect to other devices. The type of package
depends on the type of microprocessor and how it
will be used. Each packaged microprocessor is
tested one more time, marking the last step in
the chip-making process. The microprocessors are
now ready to be sent to companies that will use
them to make everyday items.
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GlossaryEtchThe removal of selected portions
of materials to define patterned layers on chips.
IonsAtoms or molecules that have a net
electrical charge. In semiconductor
manufacturing, ions are the source of chemical
impurities that alter the conductivity of
silicon.
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MasksMasks used in the chip making process are
like stencils. When used with the UV light, masks
create the various circuit patterns on each layer
of the microprocessor. MetalsMetals, such as
aluminum and copper are used to conduct the
electricity throughout the microprocessor. Gold
is also used to connect the actual chip to its
package.
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PhotolithographyThe process of reproducing the
chip's circuitry pattern onto the wafer surface
by using ultraviolet light and stencils or masks
to transfer the image photomechanically.
PhotoresistA substance which becomes soluble
when exposed to ultraviolet light used to help
define circuit patterns during chip fabrication.
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PolysiliconConductive material used as an
interconnect layer on a chip. Silicon
DioxideGrown on a wafer during chip fabrication
to serve as an insulating layer. Silicon
IngotA large, cylindrical, single crystal made
from purified silicon. The cylinder is sliced
into thin wafers which are used for making
computer chips.
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Silicon WaferIntel uses wafers of pure silicon
cut from a silicon ingot to make microprocessors.
Silicon, the primary ingredient of beach sand, is
a semiconductor of electricity. Semiconductors
are materials that can be altered to be either a
conductor or an insulator. Ultraviolet
LightUltraviolet light has very short
wavelengths and is just beyond the violet end of
the visible spectrum. UV light is used to expose
patterns on the layers of the microprocessor in a
process much like photography.
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In a black tent at Sumitomo Sitix, in Phoenix,
Arizona, Carrie Sielski uses a light as bright as
an airplane beacon to check silicon wafers for
dust and other impurities. Wafers that pass this
final test are sent to chip makers such as Intel.
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Rosemary Gerald checks the temperature of a
finished crystal while Gary Burgess works the
furnace controls.
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These finished chips, each about a half-inch
across, have not yet been cut apart.