JPH051081Y2 - - Google Patents

Description

[Detailed explanation of the idea] (b) Industrial application fields The present invention relates to a solid-state image sensor.

(b) Conventional technology In general, regarding solid-state image sensors, please refer to the Nikkei Electronics article published on December 17, 1984, ``Solid-state image sensors and image pickup tubes that are actively moving in response to the demands of home video cameras.'' As introduced, there are MOS type, frame transfer type CCD type, and interline type.
There is a CCD type, and in both cases, since they have a semiconductor structure made of a silicon substrate, there is a problem that dark current component noise mixes with the photodetection current component.

Therefore, in the conventional device, as schematically shown in FIG. , A... were used as the light receiving section IM for the imaging light, and the cells A' in that particular row were shielded from light and used as the dark current detection section OPB. That is, an attempt has been made to obtain a true image signal free of noise by subtracting the dark current component from the dark current detection section OPB from the image signal containing dark current component noise from the light receiving section IM.

However, the dark current detection unit OPB is usually a photoelectric conversion cell A′ that has the same structure as the light receiving unit IM configured on a semiconductor substrate, and a light shielding film made of aluminum is adhered to the top surface of the photoelectric conversion cell A′. There is a problem in that the dark current value differs between the photoelectric conversion cell A of the light receiving section IM and that A' of the dark current detecting section OPB due to the effect of the metal light shielding film. That is, even if these two dark current values are canceled out, a true image signal cannot be obtained.

Here, the reason why the dark current values in each cell A, A' in the dark current detecting section OPB and the light receiving section IM are different is as follows.

This phenomenon is usually referred to as the Alnneal effect, and due to the presence of an aluminum film on a semiconductor element, H ₂ O molecules near the aluminum film are decomposed during annealing treatment such as during contact bonding, and aluminum reacts with oxygen. do. This is interpreted to be caused by hydrogen atoms filling dangling bonds at the Si--SiO ₂ interface of the semiconductor device, for example.

Therefore, in the cell A' of the dark current detecting section OPB to which the aluminum film is deposited, the interface state density is smaller than that of the cell A of the light receiving section IM. Therefore, e.g.
If the interface state density of A' is 7×10 ⁹ /cm ² ev, then that of cell A is 9×10 ⁹ /cm ² ev, and the dark current in the dark current detection part OPB is the same as that in the light receiving part IM. The dark current will be smaller than the actual dark current.

Such a conventional solid-state image sensor has a polysilicon gate 1 on a semiconductor substrate, as shown in the cross-sectional view of FIG.
are arranged through a gate oxide film 2, and an interlayer insulating film 3 on this polysilicon gate 1
A light shielding pattern 5 made of aluminum is deposited on the dark current detection portion OPB. Then, a wiring pattern 4 formed in the same process as the light shielding pattern 5 is provided.

(c) Problems to be solved by the invention As mentioned above, if an aluminum light-shielding pattern as thick as the wiring pattern 4 is provided in the dark current detection part OPB, the dark current value will be greatly reduced due to the above-mentioned alunil effect. Moreover, the variation in the values becomes extremely large. Therefore, instead of directly providing a light-shielding pattern on the dark current detection unit OPB, it is necessary to place another light-shielding plate made of chromium or the like on a glass substrate over the element, which reduces the size of such an imaging device. It was intended to limit the

(d) Means for solving the problem The solid-state image sensor of the present invention thins the metal coating mainly made of aluminum in the dark current detection part, and adds new metal on the thinned metal coating as necessary wiring. It has a two-layer structure formed by laminating films.

(E) Effects According to the present invention, the dark current detection part only needs to have a film thickness as thin as necessary for light shielding, so the annealing process for film formation can be shortened, the Alanneal effect is small, and the dark current can be detected stably and at an appropriate value.

(F) Embodiment FIG. 1 shows a cross section of the solid-state imaging device of the present invention.
The device shown in the figure differs from the conventional device shown in FIG. 2 in that the aluminum light-shielding film 5' of the dark current detection section OPB is made thinner, and the wiring 4' is made of two-layer aluminum wiring. That is, the underground layer 41 of the wiring 4' made of aluminum is first formed on the interlayer insulating film 3.
The light shielding film 5' In addition to realizing a thinner film,
The wiring 4' has a sufficient film thickness.

In such a solid-state image sensor, the dark current detection section
Since the light shielding film 5' on the OPB is sufficiently thinner than the wiring 4', the above-mentioned Alnyl effect hardly appears and the second
The dark current at the OPB is lower than that of the conventional element shown in the figure.
It becomes equal to that of IM and is stable without variation. Therefore, the detected dark current from this OPB can be used to offset the dark current of the light receiving section IM, and a clear image signal without noise can be obtained.
Moreover, the wiring 4' has a sufficient thickness to obtain sufficient conductivity for electrical conduction.

(g) Effects of the invention According to the solid-state imaging device of the invention, the light-shielding film made mainly of aluminum in the dark current detection section is made much thinner than the film thickness of the wiring, so dark current is reduced due to the Alnyl effect. It is possible to eliminate most of the variation or variation, thereby making it possible to perform appropriate dark current correction. Therefore, without providing a light shielding means separate from this element, it greatly contributes to miniaturization of such a device.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the solid-state image sensing device of the present invention;
The figure is a sectional view of a conventional element, and FIG. 3 is a schematic plan view of a solid-state image sensor. 4, 4'... Wiring, 5, 5'... Light shielding film, 41...
...lower layer, 42...upper layer.

Claims (1)

[Scope of utility model registration request] A solid-state imaging device with a semiconductor structure that includes a plurality of photoelectric conversion cells, uses the majority of the photoelectric conversion cells as a light receiving section, and forms a dark current detection section by coating a metal film on a specific number of other photoelectric conversion cells. The element is provided with wiring made of a two-layer structure of metal mainly made of aluminum, and the metal coating of the dark current detection section is formed thinner than the lower metal layer of the wiring in the same process as the upper metal layer of the wiring. A solid-state image sensor characterized by: