Semiconductors: The silicon chipSilicon is the raw material most often used in the manufacture of integrated circuits (IC). It is the second most abundant substance on earth. It is extracted from rocks and common beach sand and subjected to an exhaustive purification process. In this form, silicon is the purist industrial substance that man produces, with impurities comprising less than one part in a billion. This is equivalent to a tennis ball in a series of golf balls stretching from the earth to the moon. Semiconductors are generally materials with energy band gaps less than 2eV. An important property of semiconductors is their ability to change their resistivity over several orders of magnitude by doping. Semiconductors have electrical resistivities ranging from 10-5 to 107 ohms. Semiconductors can be crystalline or amorphous. Elementary semiconductors are semiconductor materials with single elements such as silicon or germanium. Silicon is the most commonly used semiconductor material today. It is used for diodes, transistors, integrated circuits, memories, infrared sensing and lenses, light emitting diodes (LEDs), photosensors, strain gauges, solar cells, charge transfer devices, radiation detectors and a variety of other devices. Silicon belongs to group IV of the periodic table. It is a fragile gray material with a cubic diamond structure. Silicon is conventionally doped with acceptors of phosphorus, arsenic and antimony and boron, aluminum and gallium. The energy deficit of silicon is 1.1 eV. This value allows operation of silicon semiconductor devices at higher temperatures than germanium. I will now give you a brief history of the evolution of electronics which will help you better understand semiconductors and the silicon chip. In the early 1900s, before the invention of integrated circuits and silicon chips, computers and radios were made with vacuum tubes. The vacuum tube was invented in 1906 by Dr. Lee DeForest. Throughout the first half of the 20th century, vacuum tubes were used to conduct, modulate and amplify electrical signals. They made possible a variety of new products, including the radio and the computer. However, vacuum tubes had some inherent problems. They were bulky, delicate and expensive, used a lot of energy, took a long time to warm up, got very hot and eventually burned out. The first digital computer is in middle of paper..., the second mask pattern is exposed at the edge and the oxide is etched to reveal new diffusion areas. The process is repeated for each mask (up to 18) needed to create a particular integrated circuit. Precise alignment of each mask to the wafer surface is of critical importance. It is misaligned by more than a fraction of a micrometer (a millionth of a meter), the entire wafer is useless. During the last diffusion, an oxide layer develops again on the water. Most of this oxide layer is left on the edge to serve as an electrical insulator, and only small openings are etched through the oxide to expose the contact areas of the circuit. To connect these areas, a thin layer of metal (usually aluminum) is deposited over the entire surface. The metal dips into the contact areas of the circuit, touching the silicon. Most of the surface metal is then etched away, leaving an interconnection pattern between the circuit elements. There..