| 摘要 |
PURPOSE:To obtain a proper threshold voltage having less scattering in a vertical shield base MOSFET, by a method wherein after each of semiconductor regions is formed, impurity ions for threshold voltage control are implanted through a gate oxide film. CONSTITUTION:Windows are opened on an N type substrate 1' by means of a photographic technique. After a boron ion implantation with a concentration of 3-7X10<13>cm<-2> and annealing, low-concentration impurity regions 2 are formed. Similarly, regions 3, 4 are formed, and a gate oxide film 5 is formed. Through this film, boron ions for threshold voltage control are implanted with a concentration of 1-9X10<11>cm<-2> to form a P region with a surface concentration of 0.9-8X10<16>cm<-2>. Thereby, since the surface concentration in the threshold voltage controlling born ion implantation is almost on the same level with that in the high-dielectric strength low-concentration P type region forming boron ion implantation, a threshold voltage can be controlled, so that it is possible to obtain a proper voltage having less scattering. |
