From sand to silicon

WINDOWS takes a look at what goes into making the modern day processor. Find out how the microprocessor undergoes transformation from being grains of sand to becoming the ‘brains’ behind your PC.

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From sand to silicon
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By  Gareth Van Zyl Published  January 18, 2010
Gathering Dust

Our computers, metro trains, places of work, media, everything that relies on computers, is ultimately driven by microprocessors and these processors, in turn, come from one earthly source – beach sand, the key ingredient used to make silicon.

Our processors are integrated circuits built on tiny pieces of silicon material. Silicon is used is because it is a semiconductor, a class of materials that can be both an electrical conductor and an electrical insulator.

These microprocessors today contain hundreds of millions of transistors that are interconnected via copper wires, and these transistors then work together to store and manipulate data so that the microprocessors can perform a wide variety of functions.

Wafer Thin

Chipmaker Intel says that from start to finish, it takes a total of 300 steps for a microprocessor to be completed. The process involves layering various materials on top of thin rounds of silicon using chemicals, gases and light.

For this to be achieved, silicon is purified, liquefied and grown into long, cylindrical tubes called "ingots". The ingots are sliced into thin wafers, which are polished until they have flawless, mirror-smooth surfaces.

Very thin layers of material, in carefully designed patterns, are put on the blank silicon wafers. The patterns are computerised designs that are miniaturised so that up to several hundred microprocessors can be put on a single wafer.

Because the patterns are so small, it is usually not possible to deposit material exactly where it needs to be on the wafer, and instead, a layer of material is deposited or grown across the entire wafer surface. The material that is not needed is removed and only the desired pattern remains.

While there are more than 300 steps required to make a working microprocessor, the chip fabrication process can be summarised in a few steps that involve creating conductive properties and testing.

Going Electric

The microprocessor manufacturing process begins with "growing" an insulating layer of silicon dioxide on top of a polished wafer in a furnace at very high temperature. This layer acts as an electrical "gate" that either enables or prevents the flow of electrical current within the microchip.

Photolithography, the process in which circuit patterns are printed on the wafer surface, is what follows. A temporary layer of a light-sensitive material called a "photoresist" is applied to the wafer whilst ultraviolet light shines through the clear spaces of a stencil called a "photomask" or "mask" to expose selected areas of the photoresist.

Moore’s Law

Moore’s Law (hypothesised by Gordon E. Moore, Intel’s co-founder) relates to the long-term trend in computing hardware history in which the number of transistors that can be placed on a circuit has doubled approximately every two years.

The result is that processing speed and memory capacity (for instance) have roughly improved at exponential rates as well. This trend has continued for more than 50 years.

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