Perfect silicon disks - BASF.com

Science around us
A news service provided by BASF
Perfect silicon disks
Microchip manufacturers rely on high purity BASF chemicals
February 10, 2005
P 104e
contact
Christian Böhme
Corporate Media Relations
phone +49(0)621 60-20130
fax +49(0)621 60-92693
christian.boehme@basf-ag.de
Modern computers have little room to spare, with as many as a billion transistors
per square centimeter jostling for position on their processors and memory chips.
Imagine the entire population of India holidaying in Washington DC and you’ll have
some idea of the density. What makes it possible is that transistors are so small.
And that, in fact, is the biggest problem in their production. Circuits this tiny can be
paralyzed by a particle smaller than a flu virus. A single misplaced atom may render
a chip useless.
Microchip production is complicated. More than 600 working steps are required to
turn the raw material, quartz sand, into a modern processor. Most of these steps
require the use of special chemicals, for example to clean and etch silicon chips.
“BASF is a leading manufacturer of electronic chemicals,” says Claus Poppe,
Director Global Business Management for Electronic Chemicals. “At least one
BASF product was used in the production of any microchip manufactured today.”
The Story
A single particle of dust is one too many:
BASF experts test chemicals for microchip
manufacture in special clean room
labs.
The first step is to get silicon (the building material for most microchips) from simple
quartz sand. To clean the “dirty” silicon produced, technicians convert it to trichlorosilane
using hydrogen chloride. This clear liquid is easily purified by multiple distillations.
The much cleaner silicon emerging from this process is ready for the next
step, in which specialists use the Czochralski method (see info box) to grow
impressive shiny silver crystals up to two meters tall with a perfect interior structure.
Special saws cut these crystals into paper-thin wafers that form the basis of microchip
production, but they need to be smoothed down first and polished to a shine.
Again, a number of high-purity BASF chemicals such as nitric acid, sulfuric acid
and hydrochloric acid are used for the polishing and cleaning process. The finished
wafers are round disks measuring up to 30 centimeters across. Their surface has to
be absolutely perfect with no irregularities larger than a couple of nanometers – if
they were the size of a football pitch, this would mean no bumps larger than onetenth
of a millimeter.
Basis of each microchip: The paper-thin
wafer is smoothed down and polished
to a shine with high-purity chemicals.
Text, photography and illustration are available at:
www.basf.de/science_around_us
BASF Aktiengesellschaft
67056 Ludwigshafen, Germany
Telephone +49(0)621 60-0
Telefax +49(0)621 60-20129
http://www.basf.de
E-Mail: presse.kontakt@basf-ag.de

Science around us
A news service provided by BASF
Perfect silicon disks
Microchip manufacturers rely on high purity BASF chemicals
Christian Böhme
Corporate Media Relations
phone +49(0)621 60-20130
P 104e
When computers were first produced, technicians were able to solder transistors by hand.
Today’s tiny circuits call for a different technique. The modern technology for etching transistors
onto wafers is called photolithography. In this process, specialists first apply a barrier
layer to the silicon which they illuminate using a mask. The layer dissolves at the sites
exposed to light and the underlying silicon layer is etched. Chip manufacturers treat the
etched locations with chemicals and repeat the process a number of times, building up
transistors layer by layer, like building houses from layers of blocks.
Finished transistors will not work if more than one atom out of a million is faulty. But dirt is
everywhere. Metal devices invariably give off unwanted atoms. Humans transmit impurities
by a mere touch or breath. That’s not counting the approximately half a billion particles of
dust floating around a normal room. For this reason every step of chip manufacture takes
place in pristine working areas where all the furnishings are plastic and filters are installed
to remove the last particle of dust from the ambient air. Anyone entering these facilities
must wear a full set of protective gear including gloves and a face mask.
“Finished microchips must be absolutely free of contaminants, so the chemicals that are
used in their manufacture have to be extremely pure,” explains Dr. Karl-Rudolf Kurtz, head
of BASF’s Electronic Materials business unit. “BASF currently supplies around 30 chemicals
of electronic grade purity.” BASF is equipped with cleanroom labs to check the chemicals’
purity before they are delivered to chip manufacturers. “We have the technology to detect
impurities in trace amounts of less than one microgram per tonne of product. That’s like a
needle in 100,000 haystacks. Detecting tiny concentrations of these magnitudes is only
possible with state of the art spectrometry.”

Science around us
A news service provided by BASF
Perfect silicon disks
Microchip manufacturers rely on high purity BASF chemicals
Christian Böhme
Corporate Media Relations
phone +49(0)621 60-20130
P 104e
Gordon Moore, co-founder of Intel, worked out a hypothesis in 1965 based on his observations
of the market. He predicted that the number of transistors per unit of surface area
would double every year as microchip technology progressed. Moore’s law basically still
applies to this day, with transistors getting smaller and smaller all the time. For as long as
the trend still holds, the quality of electronic chemicals must continue to rise.
The Prospects
BASF is a leading supplier of chemicals to the semiconductor industry. The global
electronic chemical business acquired from Merck KGaA at the start of 2005 will significantly
strengthen BASF’s market position. Electronic chemicals distribution is organized in a
global business management system for easier ordering and shorter delivery times. BASF
was conferred the UK gas supplier BOC Edwards’ Supplier Quality Award for the reliability
and quality of its electronic gases hydrogen chloride and ammonia. BASF is also the world’s
only supplier of hydroxylamine free base, a highly active solvent for cleaning microchips.
The Graphics

Science around us
A news service provided by BASF
Perfect silicon disks
Microchip manufacturers rely on high purity BASF chemicals
Christian Böhme
Corporate Media Relations
phone +49(0)621 60-20130
P 104e
From beach sand to computer chip
The Info Box
Silicon (from the Latin silex meaning ‘flint’) is the second most abundant element in
the earth’s crust after oxygen and is contained in most minerals. Elemental silicon is a
semiconductor. Its electronic properties can be modified in a targeted fashion by
introducing foreign atoms, a process called doping. Silicon is widely used in microelectronics
and solar cell technology.
The Czochralski method is the technology used to grow the large crystals required
in the chip industry. A tiny but perfectly formed crystal is immersed in a melted purified
silicon bath that is only slightly warmer than the melting point. If the crystal is removed
from the molten silicon carefully enough, silicon atoms will remain attached. The attached
atoms align themselves precisely to the structure of the little seed crystal. The
process results in the growth of ideal monocrystals up to two meters tall. The method
was named after the Polish scientist Jan Czochralski who discovered it by serendipity
in 1916 after accidentally dipping his quill into a tub of molten metal instead of an inkpot.
Hydroxylamine is a colorless crystalline compound produced from nitrates and
hydrogen. BASF is the world’s only supplier of pure hydroxylamine in the form of a
50 percent aqueous solution. The 7,000 tonne production capacity in Ludwigshafen is
enough to supply the entire global microchip industry, where the compound is used to
clean chips after etching.
Transistors switch an electric current on or off between two connectors, depending
on the voltage applied to a third connector attached to the respective transistor. They
can also increase the flow of current. Silicon-based microchip transistors are very fast
switchers, economical and tiny. Modern computers could not have been developed
without them.
Further information can be found at:
http://www.intel.com/pressroom/kits/manufacturing/making_a_chip_bkgrnd.htm
http://www.siltronic.com/internet/webcache/de_DE/Products/Poster_2004.pdf
http://en.wikipedia.org/wiki/Microprocessor
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www.basf.de/science_around_us
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