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
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.”