Method for fabricating an image sensor capable of increasing photosensitivity
An image sensor capable of overcoming a decrease in photo sensitivity resulted from using a single crystal silicon substrate, and a method for fabricating the same are provided. An image sensor includes a single crystal silicon substrate, an amorphous silicon layer formed inside the substrate, a photodiode formed in the amorphous silicon layer, and a transfer gate formed over the substrate adjacent to the photodiode and transferring photoelectrons received from the photodiode.
1. A method for fabricating an image sensor including a photodiode, the method comprising:
etching, with an etch mask, an opening in an epitaxial layer;
depositing an amorphous silicon layer into the opening; and
implanting ions in the amorphous silicon layer to form a P-region of amorphous silicon and an N-region of amorphous silicon;
wherein the etch mask includes a photoresist pattern; and
wherein the photodiode includes the P-region of amorphous silicon and the N-region of amorphous silicon.
2. The method of claim 1 , further comprising:
etching a trench in the epitaxial layer; and
depositing an oxide layer into the trench.
3. The method of claim 2 , further comprising:
planarizing the oxide layer to form a shallow trench isolation structure; and
aligning the amorphous silicon layer with the shallow trench isolation structure.
4. The method of claim 3 , wherein said planarizing the oxide layer comprises using a slurry including a polishing selectivity rate of silicon to silicon oxide between approximately 5:1 to approximately 30:1.
5. The method of claim 2 , wherein said planarizing the oxide layer is performed before said implanting ions in the amorphous silicon layer.
6. The method of claim 1 , further comprising forming a transfer gate adjacent to the photodiode.
7. The method of claim 6 , wherein said forming a transfer gate is performed before said implanting ions in the amorphous silicon layer.
8. The method of claim 1 , wherein the amorphous silicon layer comprises germanium.
9. The method of claim 1 , further comprising performing a heat diffusion process to form the photodiode.
10. The method of claim 1 , wherein the opening comprises a depth greater than the thickness of the photodiode.
11. The method of claim 1 , wherein the amorphous silicon layer is partially buried within the opening.
12. A method for fabricating an image sensor including a photodiode, the method comprising:
forming a trench in an epitaxial layer;
forming an insulation layer in the trench;
aligning the insulation layer with a surface of the epitaxial layer;
etching, with a first photoresist pattern, a portion of the epitaxial layer adjacent to the trench to form an opening;
depositing an amorphous silicon layer in the opening;
aligning the amorphous silicon layer with the top surface of the epitaxial layer; and
forming a P-region of amorphous silicon and an N-region of amorphous silicon in the amorphous silicon layer;
wherein the photodiode includes the P-region of amorphous silicon and the N-region of amorphous silicon.
13. The method of claim 12 , wherein the amorphous silicon layer comprises germanium.
14. The method of claim 12 , wherein said forming a P-region of amorphous silicon and an N-region of amorphous silicon comprises implanting ions in the amorphous silicon layer.
15. The method of claim 14 , wherein said forming a P-region of amorphous silicon and an N-region of amorphous silicon comprises performing a heat diffusion process.
16. The method of claim 12 , wherein said forming a trench in an epitaxial layer comprises using a second photoresist pattern.
17. The method of claim 12 , further comprising forming a transfer transistor before said forming a photodiode.
18. The method of claim 12 , wherein the amorphous silicon layer is partially buried within the opening.