Solid-state image sensor having a substrate with an impurity concentration gradient

A solid-state image sensor comprising:

• a semiconductor substrate;
• a photoelectric conversion portion formed in a surface region of said semiconductor substrate;
• a third region formed above said photoelectric conversion portion, having a same conductivity type as that of a first region and having almost a same impurity concentration as that of said first region;
• and
• noise cancelers each formed adjacent to said photoelectric conversion portion, configured to remove noise of a signal read from said photoelectric conversion portion, wherein
• said semiconductor substrate has a conductivity type such that carriers of said signal are minority charge carriers, and has said first region where a concentration of impurities determining said conductivity type is high and a second region where a concentration of said impurities in said first region is low,
• said impurity concentration in said second region is gradually lower toward a surface of said semiconductor substrate, and
• said impurity concentration in said first region is 1×1018 cm−3 or higher.

A solid-state image sensor comprising:

• a semiconductor substrate;
• a photoelectric conversion portion formed in a surface region of said semiconductor substrate;
• and
• noise cancelers each formed, adjacent to said photoelectric conversion portion for removing noise of a signal read from said photoelectric conversion portion, wherein
• said semiconductor substrate has an impurity concentration which gradually lowers from a first region of said semiconductor substrate toward a second region, which is shallower than the first region, and gradually increases from the second region toward a surface of said photoelectric conversion portion and the impurity concentration of said surface of said photoelectric conversion portion is lower than that of the first region of said semiconductor substrate,
• wherein said impurity concentration within said first region is substantially constant as depth increases away from said photoelectric conversion portion.

A solid-state image sensor comprising:

• a semiconductor substrate;
• a photoelectric conversion portion formed in a surface region of said semiconductor substrate;
• and
• noise cancelers each formed, adjacent to said photoelectric conversion portion for removing noise of a signal read from said photoelectric conversion portion, wherein
• said semiconductor substrate has an impurity concentration which gradually lowers from a first region of said semiconductor substrate toward a second region, which is shallower than the first region, and gradually increases from the second region toward a surface of said photoelectric conversion portion and the impurity concentration of said surface of said photoelectric conversion portion is lower than that of the first region of said semiconductor substrate,
• wherein said impurity concentration within said first region does not decrease as depth increases away from said photoelectric conversion portion.