METHOD OF ION IMPLANTATION FOR ACHIEVING DESIRED DOPANT CONCENTRATION

PROBLEM TO BE SOLVED: To provide a method of forming a plurality of MOSFETs each of which has a uniquely determined threshold voltage. SOLUTION: A doped well or a tub is formed for each MOSFET. Next, a patterned mask is used in order to form a material line near each semiconductor well. In this case, the line width depends on a desired threshold voltage of the MOSFET. Leaning ion implantation is performed with an acute angle against the surface of a substrate so that an ion beam passes through a material line. A thicker line has a smaller transmission coefficient against the ion beam. Accordingly, the intensity of the ion beam is lowered that reaches an adjoining semiconductor well. By properly selecting a line width, the dopant concentration in the tub, therefore, a final MOSFET threshold voltage can be controlled. COPYRIGHT: (C)2010,JPO&INPIT