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Mon 18 Jan 2010 04:00 AM

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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.

From sand to silicon
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From sand to silicon
The Photolithography and ion implanting.
From sand to silicon
The Photolithography and ion implanting.
From sand to silicon
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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.

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.

Masks are created during the design phase and are used to define the circuit pattern on each layer of a chip. The exposure to light chemically changes the uncovered portions of the photoresist and exposed photoresist will become soluble.

The exposed areas of photoresist are removed, revealing a portion of the material underneath. This material is removed through a process called "etching". The remaining photoresist is then removed, leaving a pattern on the silicon wafer, and additional materials, such as polysilicon, which conducts electricity, are deposited on the wafer through additional lithography and etching steps. Each layer of material has a unique pattern, and together, they will form the chip's circuitry in a three-dimensional structure.

In an operation called "doping," the exposed areas of the silicon wafer are bombarded with various chemical impurities called "ions." Implanting ions provides positive and negative charges and the electrical charges help the transistor to turn on and off, thereby passing electrical current through the transistor's gate.

To provide a link to the additional layers put on the wafer, "windows" are formed by repeating the masking and etching steps. Metal is applied to fill in the "windows," thereby forming electrical connections between the chip's layers, while copper is used as an excellent conductor to form those metal layers that act as interconnects of transistors.

Testing

Once the layering is complete, the wafers are prepared for testing. In order to withstand the processes and equipment used in the layering process, wafers must be relatively thick. This thickness must be reduced by 33 percent before the wafers can be cut into individual microprocessors. Thus, the wafer goes through a series of steps to reduce its thickness and to remove impurities from its backside.

Once the wafer's thickness is reduced, a layer of another material is deposited on the backside of the wafer to provide a good surface for die to be attached at assembly. This also provides an electrical contact from the back of the integrated circuit to the external package during the assembly process.

The wafers are then tested to determine the quality of each processing step. Separate components, such as transistors, resistors and capacitors are tested to determine whether or not the chips function properly. If a processing problem exists, this data can be analyzed to determine what processing step caused the problem.

Finally, following all of this, the processors are completed, class-tested, and retail packaged. The transformation from being grains of sand to being the brains behind our computers is completed.

Silicon Speak

Silicon Valley

Silicon Valley is the southern part of the San Francisco Bay Area in Northern California, United States. The term originally referred to the region's large number of silicon chip innovators and manufacturers, but eventually came to refer to all the high-tech businesses in the area; it is now generally used as a metonym for the high-tech sector .

Dubai Silicon Oasis

Dubai Silicon Oasis is a technology park under development in Dubai, United Arab Emirates which was launched in October 2002 by Sheikh Mohammed bin Rashid Al Maktoum, UAE Vice President & Prime Minister and ruler of Dubai, aiming to become a world centre for electronic innovation, research, and development.

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