Conversion of silicon ingots into polished wafer is carried out by shaping, slicing, lapping and edge grind, etching, polishing and cleaning operations. For many applications, the quality of a polished wafer is not sufficient mainly due to defects generated during crystal growth in the bulk of the wafer. The best solution to this problem is to deposit an additional layer of high purity Silicon on the top of a polished wafer substrate. This process is known as epitaxy. This has the additional advantage in that the electrical resistivity of the surface layer can be different than that of the substrate.

Silicon Epitaxial Growth Process

Silicon epitaxial deposition (epitaxy) refers to the process of growing a thin layer of single-crystal silicon over a single-crystal silicon substrate. Epitaxy is different from the Czochralski process in that the crystal can be grown below the melting point. In semiconductors, the deposited film is often the same material as the substrate, and the process is known as homo-epitaxy. An example of this is silicon deposition over a silicon substrate. If the layer and substrate are of different materials such as Al_xGa_1-x As on GaAs, the process is termed as hetero-epitaxy. Epitaxy can be achieved by molecular beam epitaxy (MBE) method where the physical transport of material is carried out to a heated substrate. In Vapor Phase Epitaxy, materials such as Si, Ga, As, dopants etc. are transported in the form of volatile compounds to the substrate, where they react to form the epitaxial layer.