SEMICONDUCTOR DEVICE HAVING ELEMENT ISOLATION REGION AND ITS MANUFACTURING METHOD

PROBLEM TO BE SOLVED: To provide semiconductor device having an element isolation region and its manufacturing method in which improvements such as an expansion of an element formation region interval by an expansion of an element isolation region are made.SOLUTION: On a semiconductor substrate 11, an element isolation region 16 comprises: a first selective impurity introduction region 17 to introduce a first conductivity type impurity of a prescribed concentration; and a second selective impurity introduction region 18 to which a second conductivity type impurity of a prescribed impurity concentration lower than the first selective impurity introduction region 17 is introduced selectively. By selecting an impurity concentration of the second selective impurity introduction region 18, the first conductivity type in the region expanded by a lateral impurity diffusion from the first selective impurity introduction region 17 is cancelled to suppress a practical expansion of the element isolation region 16 in a lateral direction.