Semiconductor device including impurity layer having continuous portions formed at different depths and method of manufacturing the same

A semiconductor device, comprising:

• a substrate having a main surface and including a semiconductor material of a predetermined conductivity type which has a predetermined impurity concentration;
• a trench formed extending from said main surface of said substrate towards the inside of said substrate;
• a dielectric substance formed in said trench, serving as a trench isolation;
• a first impurity layer having the same conductivity type as said predetermined conductivity type of said substrate and an impurity concentration higher than said predetermined impurity concentration of said substrate and extending in said substrate, being opposed to said main surface of said substrate;
• and
• a second impurity layer having a conductivity type opposite to said predetermined conductivity type of said substrate, formed in a portion inside said main surface of said substrate,
• wherein said first impurity layer includes
• a first portion;
• and
• a second portion continuous with said first portion, extending deeper than said first portion from said main surface of said substrate, and
• part of said first portion of said first impurity layer is formed in said second impurity layer.