How are Microchips (CPU) made? - Computers - http://maxpages.com/nanotechnology/How

Microchips, or a computer-engineer may say CPU, is one of the most

extraordinary thing that mankind has ever invented. This small little square shaped

circuit board is more powerful than man can imagine. In this report I will tell you how

this masterpiece is created.

To understand how a microchip works you must first understand how it is built.

I will only show you a potion of the steps of building a real microchip. In reality this

small little circuit board demands more than 250 steps. First of all here are the

ingredients:

Silicon: (Die) Most common element on earth. Silicon is the primary ingredient in beach

sand (silicon dioxide which is not yet pure enough to be used in chips). It is a

semiconductor of electricity. To be made into chips, raw silicon is purified, melted

down, then allowed to solidify. When it is hardened it turns into large crystals called

boules. Each boule is about 8 inches in diameter and over 50 inches long and weighs

hundreds of pounds. Then it is grinded into a perfect 200- mm diameter cylinder (Silicon

Wafer). It will be polished to mirror clean.

Chemicals and gases. Many chemicals and gases are used throughout the chip making

process, for example (hexamethyldisilazane). These are complex chemicals and usually

very hard to pronounce. Some are a lot more simpler like boron, which is found in the

Periodic Table of Elements.

Metals: Metals such as copper and aluminum are used within the chip for conducting

electricity throughout the microprocessor. Gold is also used in more expensive chips to

connect the actual chip to its package.

Ultraviolet Light: Ultraviolet light has very short wavelengths. Its beyond the end of the

visible spectrum. UV light is used to expose patterns on the Chip itself.

Masks: Masks are used with UV light. It create various circuit patterns on each layer of

the micro chip.

Microchips are built on a layer of Silicon wafer, through various processes using

Chemicals, gases and light.

Although a lot of microchips are built on one single sheet of wafer, I am only

going to demonstrate how to build a small piece of a Microchip.

The first step in building a microchip is Fabrication. During Fabrication the first

layer of silicon dioxide is grown by exposing it to heat and gas. It will start to grow. This

growth is similar to how metal rust but it grows much faster. So far this growing is too

thin to be seen by the naked eye. Next the wafer is covered with photoresist. Photoresist

becomes very soluble when exposed to ultraviolet light.

The next step is a Process called layering. Layering or photolithography, a high

beam of ultraviolet light is passed through a specific patterned mask, (or stencil). This is

very creative because not only does the mask provides a pattern it also protects the wafer

from the powerful light. The light turns the exposed area into a gooey layer of

photoresist. To ensure you, each level of a microchip is used with a different mask.

The next step is Etching. By now the gooey photoresits is all dissolved by a strong

solvent. This should reveal a pattern of photoresist made by the mask on the silicon

dioxide.

The chemical will then be etched away the already revealed silicon dioxide.

The rest of the photoresist is removed. The result of this will cause the silicon

wafer base be left with ridges of silicon dioxide.

The next step is another layering process. For this to be done another thin layer of

silicon dioxide is grown over the ridges and etched areas of the wafer base. After this is

done, a layer of thin polysillicon will be added. Then to expose a new pattern on the

photoresist , Ultraviolet light is shined. As a result the photoresist is dissolved to expose

polysilicon and silicon dioxide, which are washed down with chemicals. The rest is then

removed leaving a ton of ridges of polysilicon and silicon dioxide.

If you are already confused it’s all right, I probably am too. If you don’t quite

understand the weird words don’t worry, read it over and over again, it actually took me

awhile to understand it too. If you don’t so far read it again and then continue.

The next step is Ion Transplantation. This is also called doping. The exposed

areas of the wafer are bombed with chemical impurities called ions. This is used to altar

away the silicon conducts electricity.

The next step is basically repeating the first few steps. Layering and masking are

repeated. There’s roughly about 20 layers now connected to the microchip. It forms a 3D

picture. Based on the speed of the processor the layers of the microchip is numbered.

Also atoms of metals are deposited on the wafer filling up the windows. This will

make the electrical connections.

So far we have only built a small potion of a microchip. Making the rest of the

chip is more complex, so far we built the part that actually run the computer, the rest is a

bunch of circularly boards that changes the speeds of the CPU.

A completed circular wafer will have as many chips imprinted on it as can

possibly fit. Because the finished chips are normally square or rectangular, there are

sometimes unused potions at the edge of the wafer, but every attempt is made possible to

use as much wafer down to the last millimeter as possible.

A normal or standard wafer size is 200mm in diameter. Which is you figure out

about 31,416 square millimeters. Take for a example, if a finished Pentium® II 300MHZ

chip, it would have about 7.5 million transistors using only 0.35 micron process. The

finished die would be exactly 14.2 mm on each side. Which means about 150 Pentium II

chips will be made on a single 200mm diameter wafer.

After the whole wafer is made it is cut by a diamond saw forming hundreds of

microchips that are not identical.. Not all chips will be good. The ratio of a bad chip is

called a yield. When a new line of chips that just been manufactured, there’s a good

chance of less than 50% are yields. If a yield is higher it is a good chance that the

manufacture will raise the prices of the chips. They are now tested for the first time, using

a special fixture. The bad ones will be sorted later.

Then each chip is sorted connected to its protective package (Bonding) which

allows it to connect to other devices. The type of package depends on how fast it will be

and how it is used. A example of a packaging is a PGA. A PGA is where the chip has a

grid-like array of pins (similar to AMD K-6-2s) on the bottom of the package. A special

machine will then bond gold wires between the die and the pins on the chip. Than it is

tested one more time and sent to retail or wholesalers.

There’s currently over hundreds of microchips out in the market, made my

different companies. They all have distinct architectures. You are probably heard of these

companies Intel® and AMD®. They are number one in the world. They said that speed

double every 2 years, so by year 2001 or 2002 we will be up to around 2200MHZ or 2.2GHZ .

As software grow, their needs are greater which means faster processors, and the

worlds needs are greater also. Microchips are of great importance to the world. Showing

how these work will make you more appreciative of processors. This infact is a

chemical change and partly physical. I can’t believe what we will do without microchips

or computers basically. Nearly everything now in the technology field depend on this

small thin circuit board. Microchips will be the pathway to mans future.

References

Upgrading and Repairing PCs Special 10th Addition
Scott Mueller with Craig Zacker
1998 Que® Corporation

www.intel.com
February 4th 2000
Museum part.

www.sio2.net
February 7th 2000
Diameter of Silicon

Copyrighted Lin1.2 2000

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Page Updated Wed Jun 6, 2001 5:25pm EDT