Silicon from beach to smart phones by Professor Peter Ivey 30th July 2018


Peter Ivey is a member of Stumperlowe Probus Club.  He gained degrees in Physics at Bristol University before working in BT Labs for 15 years.  In 1989 he joined the University of Sheffield and left in2003 to run his own company in designing microchips.

His previous talk was an introduction to microchip technology and this talk covers what is special about silica.  Whilst silica is an oxide of silicon and is a major constituent of sand, sand is too impure for microchip use. The silica used is quartzite (silicon dioxide SiO2) and it is mined.  Oxygen is removed from the silicon using high temperature procedures to produce polysilicon.  The electronics industry uses polysilicon with impurity levels of less than one part per billion.  The polysilicon is recrystallized to grow single crystal boules using the Czochralski process.  It is then diamond cut into thin wafers using a “salami slicer”.  These wafers are then buffed using very high powered physical and chemical buffers to produce the base for the chips.

Peter then explained how a good insulator like silicon can become a semiconductor.  It has an atomic number 14.  Four of its fourteen electrons reside in silicon’s outer shell and combine with eight other electrons form other atoms to form a tight bond.  If a phosphorous impurity (one part in 10 billion) is introduced, Phosphorous has one more electron than Silicon and this “spare” electron can flow from negative to positive (N type).  Boron on the other hand creates a “hole” and permits a flow from positive to negative (P type).  Electronic chip manufacture is all about purity.

The circuits used in chip manufacture use extremely fine photolithography.  Copper is the conductor used to fill the depression created connecting the billions of transistors.  There might be twenty layers of connections all separated by insulation layers in a smartphone chip the size of a thumb nail.  There will be several miles of “wires” between transistors in such a chip.  The gaps between circuits is so small that a single dust particle could cause a short circuit.

The need to produce electronic chips in such a pure and clean environment means that the factories are incredibly expensive and are few and far between.  They produce chips to customers’ designs.  Whilst the manufacturing machines are enclosed in a very pure environment, they require frequent maintenance, so the surrounding environment must also be as clean as possible for when the engineers access them.  An ordinary atmosphere could take weeks to clean to the required level for the machines.

Peter’s talk was a brilliant insight into a world at the core of our modern existence.  He guided us through quite complex technology in a way that his audience could grasp.  He was inundated with questions that means that no one was sleeping.  An excellent talk!