CMOS image sensor including photodiodes having different depth according to wavelength of light
An image sensor capable of preventing the cross-talk phenomenon due to a deep penetration depth and a low absorption coefficient of red light in a photodiode region and a method for fabricating the same, wherein the photodiode for collecting incident light has different depths in accordance with the wavelength of the incident light. The photodiode for receiving red light, which has the longest wavelength, has the deepest depth, the photodiode for receiving blue light has the least depth, and the photodiode for receiving green light, which has a wavelength between the red light and the blue light has an intermediate depth.
1. A method for fabricating an image sensor, the method comprising:
forming a plurality of gate electrodes on a substrate including an epi-layer defining a blue color region, a green color region and a red color region;
forming a first ion implantation blocking layer covering the blue color region;
forming a second ion implantation blocking layer covering the blue color region and the green color region;
forming a third ion implantation blocking layer covering the blue color region, the green color region and the red color region;
forming a mask on the third ion implantation blocking layer, the mask exposing upper portions of the epi layer in which a plurality of photodiodes are to be formed;
forming the photodiodes, each having different depths for each color region by applying an ion implantation process to the epi layer; and
forming color filters corresponding to each color region.
2. The method as recited in claim 1 , further comprising the steps of:
forming an n-type ion implantation region through two the ion implantation processes at the step of applying the ion implantation process;
removing the mask;
forming an insulating layer for a spacer on an entire surface including the gate electrode;
forming a spacer contacting to lateral sides of the gate electrode by applying an etch-back process to the insulating layer and the ion implantation blocking layers; and
forming a p-type ion implantation region on the n-type ion implantation region by using the spacer and the gate electrode as a mask.
3. The method as recited in claim 2 , wherein the step of forming the n-type ion implantation region includes the steps of:
performing a first ion implantation; and
performing a second ion implantation with energy lower than the energy applied for the first ion implantation.
4. The method as recited in claim 1 , wherein the step of forming the first ion implantation blocking layer includes further the steps of:
forming a first oxide layer on the epi layer including the gate electrode;
forming a mask covering the blue color region on the first oxide layer; and
forming the first ion implantation blocking layer by etching the first oxide layer with the use of the mask as an etch mask.
5. The method as recited in claim 4 , wherein the mask is formed with a reticle for forming a blue color filter.
6. The method as recited in claim 1 , wherein the step of forming the second ion implantation blocking layer further includes the steps of:
forming a second oxide layer on the first ion implantation blocking layer;
forming a mask covering the blue color region and the green color region on the second oxide layer; and
forming the second ion implantation blocking layer by etching the second oxide layer with the use of the mask as an etch mask.
7. The method as recited in claim 6 , wherein the mask is formed with a reticle for forming a green color filter.
8. The method as recited in claim 1 , wherein the first, the second and the third ion implantation blocking layers are oxide layers.
9. A method for forming a photodiode of an image sensor, comprising the steps of:
forming a field oxide layer in a substrate to define a plurality of color region classified with a blue color region, a green color region and a red color region;
forming a first ion implantation blocking layer covering the blue color region on the subrate;
forming a second ion implantation blocking layer covering the blue color region and the green color region;
forming a third ion implantation blocking layer covering the blue color region, the green color region and the red color region;
forming an n-type ion implantation region in the substrate of each color region through an ion implantation, wherein the n-type ion implantation region in each color region has different depth according to wavelength of light corresponding to each color region;
performing ion implantation of an n-type dopant into the substrate by using the mask as an ion implantation mask;
removing the ion implantation blocking layers; and
forming a p-type ion implantation layer on the n-type ion implantation region.
10. The method as recited in claim 9 , wherein the n-type ion implantation region has a depth being deeper as the wavelength of light corresponding to each color region is longer.
11. The method as recited in claim 9 , wherein the step of forming the n-type ion implantation region includes the steps of:
performing a first ion implantation; and
performing a second ion implantation with energy lower than the energy applied for the first ion implantation.
12. The method as recited in claim 9 ,
wherein the step of forming the n-type ion implantation region includes the steps of:
forming a mask on the third ion implantation blocking layer, the mask exposing upper portions of the substrate in which the photodiodes are formed; and
performing ion implantation of an n-type dopant into the substrate by using the mask as an ion implantation mask.
13. The method as recited in claim 12 , wherein the first, the second and the third ion implantation blocking layer are oxide layers.
14. The method as recited in claim 9 , wherein the step of removing the ion implantation blocking layers is performed by an etch-back process.