Backside illuminated imaging device, semiconductor substrate, imaging apparatus and method for manufacturing backside illuminated imaging device
A backside illuminated imaging device performs imaging by illuminating light from a back side of a p substrate to generate electric charges in the substrate based on the light and reading out the electric charges from a front side of the substrate. The device includes n layers located in the substrate and on an identical plane near a front side surface of the substrate and accumulating the electric charges; n+ layers between the respective n layers and the front side of the substrate, the n+ layers having an exposed surface exposed on the front side surface of the substrate and functioning as overflow drains for discharging unnecessary electric charges accumulated in the n layers; p+ layers between the respective n+ layers and the n layers and functioning as overflow barriers of the overflow drains; and an electrode connected to the exposed surface of each of the n+ layers.
1. A method for manufacturing a backside illuminated imaging device that performs imaging by receiving light at a back side of a semiconductor substrate to generate electric charges in the semiconductor substrate based on the light and reading out the electric charges from a front side of the semiconductor substrate, the method comprising:
forming a first impurity diffusion layer and a fourth impurity diffusion layer in the semiconductor substrate such that the fourth impurity diffusion layer is formed in a direction from a front side surface of the semiconductor substrate to an inner side of the semiconductor substrate and the first impurity diffusion layer having a first conductivity is formed below the fourth impurity diffusion layer, the fourth impurity diffusion layer having a second conductivity and preventing a dark current;
forming an insulating layer on the semiconductor substrate in which the first impurity diffusion layer and the fourth impurity diffusion layer are formed;
forming an opening in a portion of the insulating layer to expose a portion of a surface of the fourth impurity diffusion layer;
forming a second impurity diffusion layer at the exposed portion in the fourth impurity diffusion layer by self-alignment in which the insulating layer serves as a mask; and
embedding a conductive material in the opening to form an electrode,
wherein a portion except the second impurity diffusion layer of the fourth impurity diffusion layer constitutes a third impurity diffusion layer.
2. The method according to claim 1 , wherein the second impurity diffusion layer is formed by vertical ion implantation to a surface of the fourth impurity diffusion layer exposed from the opening.
3. The method according to claim 1 , wherein the second impurity diffusion layer is formed by oblique ion implantation in at least four directions to a surface of the fourth impurity diffusion layer exposed from the opening.
4. The method according to claim 1 , further comprising:
forming a fifth impurity diffusion layer having the second conductivity below the second impurity diffusion layer by self-alignment in which the insulating layer serves as the mask, between the forming of the second impurity diffusion layer and the forming of the electrode,
wherein a portion except the second impurity diffusion layer of the fourth impurity diffusion layer and the fifth impurity diffusion layer constitute the third impurity diffusion layer.
5. The method according to claim 4 , wherein the fifth impurity diffusion layer includes impurities having a diffusion coefficient larger than that of impurities in the second impurity diffusion layer.
6. The method according to claim 4 , wherein the fifth impurity diffusion layer is formed by vertical ion implantation to a surface of the fourth impurity diffusion layer exposed from the opening.
7. The method according to claim 4 , wherein the fifth impurity diffusion layer is formed by oblique ion implantation in at least four directions to a surface of the fourth impurity diffusion layer exposed from the opening.
8. The method according to claim 1 , wherein the conductivity material is tungsten.