Lightshield architecture for interline transfer image sensors
View Patent ↗An interline transfer type image sensing device that can be operated at high speed and with low image smear is described. The device incorporates a refractory metal layer which is used for both a light shield over the vertical charge transfer region and as a wiring layer for low resistance strapping of poly crystalline silicon (polysilicon) gate electrodes for the vertical charge transfer region. Plugs provided by a separate metallization layer connect the refractory light shield to the polysilicon gate electrode. These plugs allow high temperature processing after refractory light shield patterning for improved sensor performance without degradation of the polysilicon gate electrode or the refractory lightshield layer.
1. A method for manufacturing an image sensor, the method comprising the steps of:
(a) providing a substrate;
(b) providing a photo-sensitive area disposed in the substrate;
(c) providing a transfer mechanism disposed in the substrate for receiving charge from the photo-sensitive area;
(d) providing a vertical charge-coupled device for receiving charge from the transfer mechanism;
(e) providing a gate dielectric spanning at least a portion of the vertical charge-coupled device;
(f) providing a gate electrode spanning at least a portion of the vertical charge-coupled device;
(g) providing an insulator spanning at least a portion of the vertical charge-coupled device having an opening therethrough;
(h) providing a lightshield spanning at least a portion of the vertical charge-coupled device having an opening therethrough; and
(i) inserting a plug through both the opening in the insulator and the opening in the lightshield; wherein the plug contacts the gate electrode so that the gate electrode is electrically connected to the lightshield.
2. The method in claim 1 wherein step (i) includes providing the plug as two metals.
3. The method image sensor as in claim 2 , wherein step (i) includes providing the two metals as aluminum and titanium/tungsten.
4. The method as in claim 1 , wherein step (i) includes providing the plug as one metal.
5. The method as in claim 4 , wherein step (i) includes providing the one metal as titanium/tungsten.
6. The method as in claim 1 , wherein step (h) includes having the opening in the lightshield occur in a subset of a plurality of the gate electrodes.