Semiconductor device having solid-state image sensor with suppressed variation in impurity concentration distribution within semiconductor substrate, and method of manufacturing the same

A method of manufacturing a semiconductor device comprising the steps of:

• (a) preparing a substrate;
• (b) forming a gate structure on a main surface of said substrate;
• (c) forming a mask member having an opening over an end portion of said gate structure and over a specified region of said main surface adjacent to said end portion;
• (d) implanting impurities from an almost vertical direction with respect to said main surface using said mask member as an implantation mask under conditions that said impurities can penetrate through a film thickness of said gate structure, thereby forming a first impurity-introduced region of a first conductivity type functioning as one electrode of a photodiode in said main surface under said end portion and in said specified region;
• (e) forming a second impurity-introduced region of a second conductivity type functioning as the other electrode of said photodiode in said specified region;
• and
• (f) forming a third impurity-introduced region of said first conductivity type in said main surface to be opposite to said first impurity-introduced region with said gate structure interposed therebetween.