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!