Methods for fabricating solid state image sensor devices having non-planar transistors
Methods for fabricating CMOS image sensor devices are provided, wherein active pixel sensors are constructed with non-planar transistors having vertical gate electrodes and channels, which minimize the effects of image lag and dark current.
1. A method for fabricating an image sensor device, comprising:
forming an active region of a unit pixel on a semiconductor substrate, the active region comprising a light receiving region and a transistor region surrounded by an isolation layer; and
forming a transfer gate in proximity to the light receiving and transistor regions, wherein the transfer gate comprises a vertical gate electrode formed in the semiconductor substrate, vertically extended to a predetermined depth below a surface of the semiconductor substrate, and disposed adjacent to a sidewall of the active region.
2. The method of claim 1 , wherein forming the transfer gate further comprises forming a horizontal gate electrode.
3. The method of claim 2 , wherein the horizontal gate electrode is formed on the semiconductor substrate over a portion of the transistor region and the isolation layer.
4. The method of claim 2 , wherein the horizontal gate electrode is formed on the semiconductor substrate over a portion of the light receiving region and a portion of the isolation layer.
5. The method of claim 2 , wherein the horizontal gate electrode is formed on the semiconductor substrate over a portion of the transistor region, a portion of the light receiving region and a portion of the isolation layer.
6. The method of claim 2 , wherein the horizontal and vertical gate electrodes are integrally formed.
7. The method of claim 1 , wherein forming the transfer gate comprises:
forming a recess in the isolation layer to expose a portion of the sidewall of the active region;
forming an insulation layer on the exposed portion of the sidewall of the active region; and
filling the recess with a conductive material to form the vertical gate electrode.
8. The method of claim 7 , wherein the recess is formed only in the isolation layer.
9. The method of claim 7 , wherein forming the recess in the isolation layer comprises etching the isolation layer to form a recess that exposes a portion of the sidewall of the active transistor region, a portion of the sidewall of the light receiving region, or portions of the sidewalls of both the active transistor and light receiving regions.
10. The method of claim 7 , wherein forming the insulation layer comprises forming a conformal insulating layer over the semiconductor substrate to line surfaces within the recess.
11. The method of claim 2 , further comprising forming a buried channel layer in the active region, wherein the buried channel is formed to align to the horizontal gate electrode, wherein the buried channel layer is doped with an impurity of a first conductivity type, and wherein the active region is doped with an impurity of a second conductivity type.
12. The method of claim 11 , further comprising forming a pinning layer in a surface of the active region above the buried channel layer, wherein the pinning layer is doped with an impurity of the second conductivity type.
13. The method of claim 2 , wherein forming the transfer gate comprises:
etching a portion of the active region to form a recessed surface at a depth Dl below the surface of the semiconductor substrate; and
forming the horizontal gate electrode such that at least a portion of the horizontal gate electrode is formed on the recessed surface.
14. The method of claim 1 , wherein forming the transfer gate comprises forming a plurality of vertical gate electrodes in different regions of the semiconductor substrate adjacent to the sidewall of the active region.
15. The method of claim 14 , wherein the vertical gate electrodes are formed separate from each other.
16. The method of claim 14 , wherein at least two of the plurality of vertical gate electrodes are integrally connected to a horizontal gate electrode that is formed over a surface of the semiconductor substrate.
17. The method of claim 1 , wherein forming the transfer gate comprises forming an L-shaped gate electrode on surface regions of the light receiving and active transistor regions, which is connected to the vertical gate electrode.
18. The method of claim 1 , wherein forming the transfer gate comprises forming a rectangular-shaped gate electrode on surface regions of the light receiving and transistor regions, which is connected to the vertical gate electrode.
19. The method of claim 1 , further comprising forming a light receiving element in the light receiving region.
20. The method of claim 19 , wherein the light receiving element is a photodiode.
21. The method of claim 20 , wherein the photodiode is a pinning photodiode.
22. The method of claim 19 , wherein forming the light receiving element comprises forming a hole accumulation diode (HAD) in a surface of the light receiving region and forming a n-well region below the HAD.
23. The method of claim 22 , wherein the vertical gate electrode is formed in the semiconductor substrate at a depth to be adjacent to at least a portion of the n-well region.