Write the explained by Czochralski(CZ) technique and Bridgeman technique.

Write the explained by Czochralski (CZ) technique and Bridgeman technique .Czochralski technique :-

This technique was developed by Czochralski and this process is used to grow silicon crystal from which silicon wafers are produced.

                   The process is characterized by a liquid -solid monocomponent growth system.This technique involves the solidification of atoms from a liquid phase at an interface.It is used for Cz crystal growth is known as "puller".The speed of growth is determined by the number of sites on the face of the crystal and the specifies of heat transfer at the interface.

                     Working:- Polycrystalline silicon is placed in the crucible and the furnace is heated to melt silicon.A suitably oriented seed crystal is placed over the crucible in the seed holder. The seed is dipped into the melt.The seed is then slowly pulled up.So freezing at the solid -liquid interface occurrs and single crystal is formed.The seed crystal in this form is known as ingot.

         In the growth process,a known amount of dopant is added to the melt to obtain desired doping concentration in the growth crystal. Boron is usually added for p-type material and phosphorus for n-type . 

          After grinding the ingot wafers by diamond saws. The surface orientation thickness,taper and bow are determined from slicing.Wafer polishing can be done on a single wafer in a batch processing manner.The polishing pad is made up of artificial fabric.The wafers are mounted on a fixture,pressed against this pad under high pressure and are rotated.A mixture of polishing slurry and water, dipped on to the pad does the polishing.The wafers are now ready for the fabrication of integrated circuit.

Bridgeman technique :-

                  A Bridgeman system uses a two zone furnace for growing single crystal Gallium arsenide. 

The first zone is held at a low temperature (610°C)to maintain the required overpressure of arsenic.The second zone is held above the melting point of gallium (1240°C).The tube is made up of quartz and the boat carrying the seed crystal and melt is made up of a graphite.The seed crystal and the melt are of Polycrystalline gallium arsenide and arsenic is kept at another end of the tube.

                 The seed is at the left end of the boat to have proper crystal orientation.The gradual freezing of the melt allows a single crystal to propagate at the liquid -solid interface.A single crystal of gallium arsenide can be grown in this way.

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