Process fabricating semiconductor device having two ion-implantations carried out by using a shared photo-resist mask

A process of fabricating a semiconductor device, comprising the steps of:

• a) preparing a semiconductor substrate including
• a first impurity region of a first conductivity type formed in a first surface portion thereof,
• a second impurity region of a second conductivity type opposite to said first conductivity type formed in a second surface portion of thereof,
• a third impurity region of said second conductivity type formed in a third surface portion thereof and
• an insulating layer covering said first, second and third impurity regions and having first and second contact holes to which said first and second impurity regions are exposed, respectively;
• b) forming an ion-implantation mask on said insulating layer and having first and second openings over said second and third impurity regions, respectively;
• c) implanting a first dopant impurity through said first opening and said second contact hole into said second impurity region under a first acceleration energy too small to cause said first dopant impurity to reach said third impurity region so as to form a fourth impurity region of said second conductivity type nested in said second impurity region;
• d) implanting a second dopant impurity through said second opening and said insulating layer into said third impurity region under a second acceleration energy too large to cause said second dopant impurity to stop in said second impurity region so as to form a fifth impurity region of said first conductivity type nested in said third impurity region;
• e) removing said ion-implantation mask;
• and
• f) implanting a third dopant impurity through said first contact hole into said first impurity region at dose too small to change said fourth impurity region from said second conductivity type to said first conductivity type so as to form a sixth impurity region of said first conductivity type nested in said first impurity region.