The epitaxy fabrication process was invented in 1960 by J.J.
Kleimack, H.H. Loar, I.M. Ross, and H.C. Theuerer. It was a new method for
growing, on a silicon wafer, layer after layer of silicon films identical in
structure with the wafer itself. Epitaxy made possible a tenfold increase in
the operating speed of transistors.
Research into epitaxy continued as demand grew for multilayer semiconductors and semi-insulators. Increasingly precise film thicknesses were required for ever-faster processors, and to meet the need A.Y. Cho perfected Molecular Beam Epitaxy (MBE), an ultra-high vacuum technique that could produce single-crystal growth one atomic layer at a time.
MBE freed molecules of an element by heating it in an effusion oven. Some of these molecules would then escape into a chamber with a vacuum so intense that the freed molecules were drawn into a linear "beam." A substrate wafer was mounted in the center of this beam and the freed molecules could then be deposited, directly atop each other, one layer at a time.