What Is Involved in Integrated Circuit Fabrication?
Integrated circuit fabrication involves a process of creating very thin surface layers of semiconducting material atop a substrate layer, usually made out of silicon, that can be chemically altered at the atomic level to create the functionality of various types of circuit components, including transistors, capacitors, resistors, and diodes. It is an advance over previous circuitry designs where individual components of resistors, transistors, and more were hand-attached to a connecting breadboard to form complex circuitry. An integrated circuit fabrication process works with components that are so small that billions of them can be created in an area of a few square centimeters as of 2011, through various photo lithography and etching processes in a microchip fabrication facility.
An integrated circuit, or IC, chip is literally a layer of semiconducting material where all the circuit components are interconnected in one series of manufacturing processes so that all of the components no longer need to be manufactured individually and assembled later. The earliest form of microchip integrated circuit was produced in 1959 and was a crude assembly of several dozen electronic components. The sophistication of integrated circuit fabrication increased exponentially, however, with hundreds of components on IC chips by the 1960s, and thousands of components by 1969 when the first true microprocessor was created. Electronic circuits as of 2011 have IC chips a few centimeters in length or width that can hold millions of transistors, capacitors, and other electronic components. Microprocessors for computer systems and memory modules that contain mostly transistors are the most sophisticated form of IC chips as of 2011, and can have billions of components per square centimeter.
Since the components in integrated circuit fabrication are so small, the only effective way to create them is to use a chemical etching processes that involve reactions on the wafer surface from exposure to light. A mask or sort of pattern is created for the circuit, and light is shone through it onto the wafer's surface which is coated with a thin layer of photoresist material. This mask allows patterns to be etched into the wafer photoresist that is then baked at a high temperature to solidify the pattern. The photoresist material is then exposed to a dissolving solution that removes either the irradiated region or the masked region of the surface depending on if the photoresist material is a positive or negative chemical reactant. What's left behind is a fine layer of interconnected components at a width of the wavelength of light used, which can be either ultraviolet light or x-rays.
After masking, integrated circuit fabrication involves the doping of the silicon or implantation of individual atoms of usually phosphorus or boron atoms into the surface of the material, which gives local regions on the crystal either a positive or negative electrical charge. These charged regions are known as P and N regions, and, where they meet, they form a transmission junction to create a universal electrical component known as a PN junction. Such junctions are about 1,000 to 100 nanometers wide as of 2011 for most integrated circuits, which makes each PN junction about the size of a human red blood cell, which is roughly 100 nanometers in width. The process of creating PN junctions is tailored chemically to exhibit various types of electrical properties, making it possible for the junction to act as a transistor, resistor, capacitor, or diode.
Due to the very fine level of components and connections between components on integrated circuits, when the process breaks down and there are faulty components, the entire wafer has to be thrown away as it cannot be repaired. This level of quality control is ramped up to an even higher level by the fact that most modern IC chips as of 2011 consist of many layers of integrated circuitry stacked atop one another and connected to one another to create the final chip itself and give it more processing power. Insulating and metallic interconnect layers must also be placed between each circuit layer, as well as to make the circuit functional and reliable.
Though many reject chips are produced in the integrated circuit fabrication process, the ones that do work as final products that pass electrical testing and microscope inspections are so valuable that it makes the process highly profitable. Integrated circuits now control almost every modern electronic device in use of as of 2011, from computers and cell phones to consumer electronics such as televisions, music players, and game systems. They are also essential components of automobile and aircraft control systems and other digital devices that offer a level of programming ability to the user, ranging from digital alarm clocks to environmental thermostats.
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