First Stage: From Sand to Silicon

Silicon is one of the most abundant elements on earth but it never exists in its basic form, but all sand are composed mainly of silica.
But to extract silicon form silica we needed some chemical processes to follow first one is reduction which is used to remove oxygen from compound and this can be done by heating silica together with carbon in high temperature in absence of oxygen.

From this formula we can deduce that we will get by this process pure silicon accompanied by a very toxic element called carbon mono-oxide which we deal with it very carefully.

There is a problem with is equation because it doesn’t tell you something which is very critical to us we call it impurities because we made this silicon from sand so it accompanied easily with dirty materials, in order to remove these impurities we first crush this silicon into powder in order to go several physical and chemical purification methods till it becomes pure enough where we call that silicon of “semiconductor grade silicon” that means that it is ready to be used in IC industry.

But to make it easy for us for second process we add another step before we finish, we need to have a monocrystalline bulk because photolithography stage which we will discuss next depend on having a mono crystalline bulk, semiconductor grade silicon is of type amorphous so we need to turn it into monocrystalline silicon, and the simplest way to do this is by Czochralsky process.

where the semiconductor grade silicon(powdered amorphous silicon) is inserted into a quartz(a form of silicon dioxide) metal container surrounded by graphite encasing. We use quartz because it is of heat resistance than silicon and also inert so it willnot interact with the silicon inside and add impurities. Then we heat this container to a temperature slightly above the melting point of silicon, in order to make sure that silicon will be in liquid form, but we need to solidify it in a regularly crystallized form. But before solidification we add dopant to molten silicon to guarantee  uniform distribution through out the resulting silicon ingot(a cylinder of molten silicon)
after that we add very small pieces  of high-grade monocrystalline silicon on the cylinder(we call it seed) and while it is revolving around its self
then we pull the cylinder up and wait till it cools then the melt solidifies in a crystalline pattern because cooling is very gradual.
The silicon ingot now is monocrystalline not cylindrical and has point edges at top and bottom because of the holder that used to hold the molten when it moves out it formed these edges so we start polishing sides and remove ends in order to make it have smooth surface.

Then the ingot Is then sliced to form disc-like units called wafers which will built on it in next stage.

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Hisham Elreedy is Digital Electronics Engineer, Graphics Designer, Blogger, Youtuber. Inspired to teach all he knows from his experience in studying undergraduate engineering by creating useful posts