Semiconductors : The Silicon C
Silicon is the raw material most often used in integrated circuit (IC)fabrication. It is the second most abundant substance on the earth. It isextracted from rocks and common beach sand and put through an exhaustivepurification process. In this form, silicon is the purist industrialsubstance that man produces, with impurities comprising less than one partin a billion. That is the equivalent of one tennis ball in a string ofgolf balls stretching from the earth to the moon. Semiconductors are usually materials which have energy-band gapssmaller than 2eV. An important property of semiconductors is the abilityto change their resistivity over several orders of magnitude by doping. Semiconductors have electrical resistivities between 10-5 and 107 ohms.Semiconductors can be crystalline or amorphous. Elemental semiconductorsare simple-element semiconductor materials such as silicon or germanium. Silicon is the most common semiconductor material used today. It isused for diodes, transistors, integrated circuits, memories, infrareddetection and lenses, light-emitting diodes (LED), photosensors, straingages, solar cells, charge transfer devices, radiation detectors and a
In the hot furnace,the dopant atoms enter the areas of exposed silicon, forming a pattern ofn-type material. The scientist began to think that if one transistor could bebuilt within one solid piece of semiconductor material, why not multipletransistors or even an entire circuit. If the dopant atoms had more electrons than thesemiconductor atoms, the doped regions were called n-type to signify andexcess of negative charge. Depending on the level of complexity, an IC will require from5 to 18 different glass masks, or "work plates" to create the layers ofcircuit patterns that must be transferred to the surface of a silicon wafer. Silicon is conventionally doped with Phosphorus, Arsenic and Antimony andBoron, Aluminum, and Gallium acceptors. Most of this oxide layer is left on the waferto serve as an electrical insulator, and only small openings are etchedthrough the oxide to expose circuit contact areas. Now I will tell you the method of how the integrated circuits and thesilicon chip is formed. In the early 1900's before integrated circuits and silicon chipswere invented, computers and radios were made with vacuum tubes. The result is a precise rendering, in its exact size,of a single circuit layer, often less than one-quarter inch square. Now I will give you some brief history of the evolution of electronicswhich will help you understand more about semiconductors and the siliconchip. Because these dopant atoms haddifferent amount of electrons than the semiconductor atoms, they formedconductive paths. The wafer is then washedin a solvent that removes the soft photoresist, but leaves the hardenedphotoresist on the wafer. The first layer of thechip is now complete, and the masking process begins again: a new layer ofoxide is grown, the wafer is coated with photoresist, the second maskpattern is exposed to the wafer, and the oxide is etched away to reveal newdiffusion areas.
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