Both the general public
and businesses worldwide have an insatiable appetite for faster,
more complex and cheaper electronic equipment, such as computers,
home entertainment systems, communication products etc. The integrated
circuit (chip) is at the heart of all modern electronic equipment.
In additon, many kinds of consumer and business equipment also incorporate
nano-machine devices. The cost, performance and functionality of
both of these types of devices are driven by the size of the individual
component elements that comprise these devices, with smaller geometries
resulting in increased performance and lower cost per function. Current
circuits can have as many as a billion integrated transistors each
with a minimum size smaller than 0.15 mm!
A human hair is about 100 mm in diameter,
meaning that over 50,000 transistors could be placed on the diameter
of a single hair!
The tiny circuit elements (transistors) are produced on large wafers
(8-12 inches in diameter) of ultra high purity silicon using a photographic-like
technique known as photolithography or microlithography. This technique
was "borrowed" from the printing industry where it is used
to produce copper printing plates. The lithographic process involves
transferring a circuit pattern into a polymer film that has been
coated onto the semiconductor substrate. The polymer is known as
a photoresist. There are two "tones" of resist viz. negative
and positive. After exposure the resist is developed and the resulting
three-dimensional image is used as an etch mask to transfer the pattern
to an underlying thin film of a conductor, semiconductor or insulator
using a chemical process known as plasma or reactive ion etching.
These etching steps chemically remove the exposed thin films. These
processing steps are repeated many times to "build" the
three-dimensional circuit.
In a very similar fashion, the process is used to build devices
into other types of materials, for example to make micro devices
used for computer storage equipment or to make specialized sensing
devices.
The photolithographic "stepper" (similar to a camera)
is at the heart of this technology. Many of us at Ultratech have
spent our entire careers designing, building and maintaining this
complex equipment. There is simply no other opto-mechanical equipment
in the world that is as complex, precise and reliable as these steppers,
not to mention exciting. They must be able to print circuit elements
smaller that 0.15 mm and place them
with a precision of a few nanometers (1.0 mm
= 1000 nm) while the substrate is moving at up to several meters
per second! An entire 12-inch wafer is "printed" in less
than 60 seconds and contain as many as a trillion individual
elements. The smallest and most precise optical mechanical
equipment used in microsurgery and the most precise mechanical systems
are not close to the precision achieved in photolithography equipment. |