Method for fabricating image sensor

1. A method for fabricating an image sensor comprising:

forming a first seed layer on a semiconductor substrate;

forming a second seed layer on the first seed layer, wherein the second seed layer is a first polysilicon layer;

forming a blocking layer on the second seed layer;

partially exposing a region for a transistor corresponding to an active region of the semiconductor substrate by patterning the first seed layer, the second seed layer, and the blocking layer;

growing a gate insulating material layer in a portion of the exposed region by selective thermal oxidation of the first seed layer, the second seed layer, and the semiconductor substrate;

filling a gate electrode material layer in the exposed region over the gate insulating material layer;

forming a gate insulating layer pattern and a gate electrode pattern by selectively removing the blocking layer, the gate insulating material layer, the gate electrode material layer, and the first seed layer; the second seed layer and

forming source and drain diffusion layers and a photodiode on both sides of the gate insulating layer pattern and the gate electrode pattern by selectively doping impurity ions into the semiconductor substrate a plurality of times.

2. The method of claim 1 , further comprising doping impurity ions into the gate insulating material layer before forming the source and drain diffusion layers.

3. The method of claim 2 , wherein doping impurity ions into the gate insulating material layer includes heavily doping impurity ions.

4. The method of claim 1 , wherein forming the first seed layer includes depositing an oxide layer.

5. The method of claim 1 , wherein forming the blocking layer includes forming an oxide silicon based layer.

6. The method of claim 1 , wherein the gate insulating material layer is formed to have a thickness between 25 Å and 30 Å.

7. The method of claim 1 , wherein forming the gate electrode material layer includes forming a second polysilicon layer.