Molecular beam epitaxy

From ArticleWorld

Molecular beam epitaxy (MBE) is a method of thin film deposition used in semiconductor fabrication technology.

Invented in the late 1960s by J. R. Arthur and A. Y. Cho of the Bell Telephone Laboratories, the method of MBE essentially involves the heating of ultra-pure elements like gallium and arsenic till they begin to evaporate. When these elements are made to condense on a wafer, a single crystal of semiconductor material is formed. In this example it would be gallium arsenide. The beams of evaporated atoms being directed onto the wafer surface have large mean free path lengths. The entire process is carried out in a highly vacuumized environment.

Shutters in front of each furnace are controlled by a computer to bring about precise thicknesses of deposited layers. This technique is a crucial part of many semiconductor fabrications, including that of lasers and light emitting diodes.

The necessary vacuum is maintained with the help of liquid nitrogen in a system of cryopumps. This maintains a temperature at the boiling point of nitrogen, which is at -196 degrees Celsius. The wafers on which crystal-growth is undertaken, however, may possess high temperature of the order of several hundred degrees Celsius. A technique called Reflection High Energy Electron Diffraction (RHEED) is used for monitoring the operations.