Here we answer questions frequently asked about silicon wafers.
What are silicon wafers used for?
All kinds of familiar things around us, like personal computers, mobile phones including smartphones, as well as TVs, air conditioners, and other home appliances, are made using silicon wafers. A silicon wafer is the all-important substrate material of the semiconductor devices that are the “brains” of such electronic products.
Semiconductor devices are of many different types, from the individual semiconductor elements such as diodes and transistors created to perform a specific function to complex integrated circuits, combining millions or tens of millions of these elements on square chips a few centimeters across. Most of these semiconductors are made using silicon wafers.
Just what is silicon, anyway?
Silicon (Si) is the second most common element on earth, after oxygen.
It may be the second most common element, but I don’t recall ever seeing it. Where is it found?
In fact, silicon is the main component making up the earth, sand, and stones under our feet. Silicon bonds very readily with oxygen, so most of it is oxidized and exists in the form of a whitish mineral called silica.
Is the silicon in silicon wafers different from the silicone used in shampoo, rubber, and so on?
Both silicon and silicone come from the same raw material, silica, but it would be best to think of them as completely different. To make the silicon used in silicon wafers, the silica that is its raw material is processed to a purity of 99.999999999% (11 nines), until it is a nearly pure silicon crystal.
Silicone, on the other hand, is a synthetic resin made using silica as a raw material, forming what is called a high molecular organosilicon compound. Silicones are used in shampoo, rubber, tissue paper, and various cosmetics, for example.
What are the qualities of semiconductors?
Different substances tend to have different resistivity, the ease with which electricity flows in them. Substances like metals, in which electricity flows readily, are called conductors. Glass and rubber are examples of insulators, which are highly resistant to electrical flow. Then there are substances with resistivity in between these two extremes. These are called semiconductors.
Besides silicon, examples of semiconductors include germanium (Ge) and gallium arsenide (GaAs).
Are there different kinds of semiconductors?
Semiconductors have resistivity in between that of conductors and insulators, but the substances themselves have nearly the same qualities as insulators. To enable them to conduct electricity, very minute amounts of metal atoms (impurities) have to be introduced by “doping” in the silicon wafer production processes. Depending on the doping atoms used, semiconductors are classified as either N-type or P-type semiconductors.
An N-type semiconductor has an excess of electrons in the silicon wafer, and these so-called free electrons have the role of enabling the flow of current. In a P-type semiconductor, on the other hand, doping results in a shortage of electrons, causing gaps or “holes.” Electrons move to fill these holes, causing current to flow.
How did silicon come to be used so commonly for semiconductors in the first place?
Four main reasons can be given to explain this.
- 1.As the second most common element on earth, silicon is a plentiful resource.
- 2.Impurities are readily removed, making it easy to purify.
- 3.It is easy to control resistivity by adjusting the crystal structure and the amount of impurities.
- 4.A stable oxide layer can be formed, for ease of circuit integration and other processing.