Lecture 21: Silicon wafer manufacturing

The first step in integrated circuit (IC) fabrication is preparing the high purity single crystal Si wafer. This is the starting input to the fab. Typically, Si wafer refers to a single crystal of Si with a specific orientation, dopant type, and resistivity (determined by dopant concentration). Typically, Si (100) or Si (111) wafers are used. The numbers (100) and (111) refers to the orientation of the plane parallel to the surface. The wafer should have structural defects, like dislocations, below a certain permissible level and impurity (undesired) concentration of the order of ppb (parts per billion). Consider the specs (specifications) of a 300 mm wafer shown in table 1 below. The thickness of the wafer is less than 1 mm, while its diameter is 300 mm. Also, the wafers must have the 100 plane parallel to the surface, to within 2◦ deviation, and typical impurity levels should be of the order of ppm or less with metallic impurities of the order of ppb. For doped wafers, there should be specific amounts of the desired dopants (p or n type) to get the required resistivity.