JPH065721B2 - Solid-state image sensor - Google Patents

Description

The present invention relates to a solid-state image pickup device.

(B) Conventional technology For details on solid-state image sensors, refer to Nikkei Electronics' article "Solid-state image sensors and camera tubes that show active movement in response to demands for home video cameras" published on December 17, 1984. As has been introduced, there are MOS type, frame transfer type CCD type, and interline type CCD type. In either case, since the semiconductor structure is made of a silicon substrate, the photodetection current component On the other hand, there is a disadvantage that dark current component noise is mixed.

Therefore, in such a conventional device, as schematically shown in FIG. 5, for example, photoelectric conversion cells A, A, A, ...
, Except for one specific row, are used as the light receiving section IM of the imaging light, and the specific row of cells A, ... Are shielded and used as the dark current detecting section OPB. That is, the true current image signal without noise is obtained by subtracting the dark current component from the dark current detection unit OPB from the image signal including the dark current component noise from the light receiving unit IM.

(C) Problems to be Solved by the Invention However, the dark current detection part OPB is normally provided with a light shielding film made of aluminum on the upper surface of the photoelectric conversion cell A having the same structure as the light receiving part IM formed on the semiconductor substrate. Since it has been deposited, the light-shielding portion I is affected by the metal light-shielding film.
There is a disadvantage that the value of the dark current is different between the photoelectric conversion cell A of M and the photoelectric conversion cell A of the dark current detector OPB. That is, a true image signal cannot be obtained even if these dark current values are canceled out.

(D) Means for Solving the Problems The solid-state imaging device of the present invention is to make the cell structure of the dark current detecting section different from the cell structure of the light receiving section so that the dark current values generated in both of them coincide with each other. .

(E) Action According to the solid-state imaging device of the present invention, by changing the cell structure, the interface level of the dark current detection part, the bulk level, etc. can be set to be the same as that of the light receiving part. Can be matched.

(F) Embodiment FIG. 1 is a schematic view of an embodiment of the solid-state image pickup device of the present invention. 5 is different from the conventional device shown in FIG. 5 in that the structure of the cells A ′ ... Of the dark current detecting portion OPB is different from the structure of the cells A, A, A. Contrasts are shown in FIGS. 2, 3, and 4, respectively.

In the case of FIG. 2, an interline CCD type, MOS
1A and 1B, the cell A of the light receiving section IM and the cell A'of the dark current detecting section OPB are shown in FIG. The area of the cell A'of the same photodiode PD shown in FIG. 9B is larger than that of the cell A of the photodiode PD surrounded by the channel stop CS and the transfer gate TG. ing. Lateral cells A and A'of both of these
Since the pitch is the same, the width of the CCD channel CH is smaller in FIG. 6B, but since the dark current is about 1/40 of the photodetection current, there is no problem.

In the case of FIG. 3, it corresponds to the frame transfer type CCD type, and FIG. 3A shows the cell A of the light receiving part IM,
(b) shows the cells A'of the dark current detector OPB, respectively. The figure is composed of a first layer gate FG, a second layer gate SG, and an opening window S and is divided by a channel stop CS.
The cell A'of the same cell (A) in FIG. 9B, that is, the area of the second layer gate SG is larger than that of the cell A in FIG.

The case of FIG. 4 also corresponds to the frame transfer type CCD type, and FIG.
The cell A of the light receiving part IM including F, and FIG. 6B shows the cell A ′ of the dark current detecting part OPB which does not need to include the overflow gate OG and the overflow drain OF, and the cell A of FIG. Compared with the above, the area of the cell A ′ in FIG. 9B is increased by the amount that the overflow gate OG and the overflow drain OF are not provided.

Here, the reason why the dark current values in the cells A and A'in the dark current detecting portion OPB and the light receiving portion IM are different is considered as follows.

This phenomenon is usually called the Alnneal effect, and due to the presence of the aluminum film on the semiconductor element, H in the vicinity of the aluminum film during annealing such as contact bonding occurs.
₂ O molecules are decomposed and aluminum reacts with oxygen.
This means that when hydrogen atoms are present in a semiconductor device such as Si-SiO.
_It is considered that the cause is filling the dangling bond at the _two interfaces.

Therefore, the dark current detector OP with the aluminum film deposited thereon
The cell A ′ of B has a smaller interface state density than the cell A of the light receiving section IM. Therefore, for example, the interface state density of the cell A ′ is 7 × 10 ⁹ / cm ² eV and that of the cell A is 9 × 10 ⁹
/ Cm ² eV, the ratio of the cell A to the cell A ′ is 7: 9 in the area of the photodiode PD in FIG. 2 and the area of the gate SG related to charge storage in FIGS. 3 and 4 described above. Is set to the ratio of. As a result, the dark current values generated in the cell A and the cell A ′ are equal, and of course, the temperature characteristics of the dark current are also the same, and the correction of the dark current component in the image signal of the solid-state image pickup device can be performed accurately. Done.

(G) Effect of the Invention As is clear from the above description, the solid-state imaging device of the present invention is configured to make the dark current detection section and the light receiving section have different cell structures so that the dark current values of both cells match. Therefore, by subtracting the dark current value from the dark current detecting unit from the image signal including the dark current component noise from the light receiving unit, it is possible to obtain a true image signal in which the dark current component noise is completely removed. Therefore, by using the element of the present invention, it is possible to obtain a reproduced image of good quality.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the solid-state image sensor of the present invention, FIGS. 2 (a) (b), 3 (a) (b), and 4 (a).
(b) is a schematic diagram of comparison of essential parts of the elements of the present invention, which are different from each other.
The figure is a schematic view showing a conventional element. A, A '... cell, IM ... light receiving part, OPB ... dark current detecting part, CS ... channel stop, PD ... photodiode, CH ... CCD channel, TG ... transfer gate, OG ... overflow gate, OF ... overflow drain, S ... Opening window, FG ... First layer gate, SG
… Second layer gate.

Claims (1)

[Claims] 1. A plurality of photoelectric conversion cells are used, and a majority of photoelectric conversion cells are used as a light receiving section, and a metal film is deposited on other specific number of photoelectric conversion cells to form a dark current detecting section. In a solid-state image sensor having a semiconductor structure, the area of the photoelectric conversion cell of the dark current detecting section where charge accumulation is performed is made wider than the area of the photoelectric conversion cell of the light receiving section where charge accumulation is performed to detect dark current. A solid-state imaging device characterized in that the dark current value generated in the light receiving section and the dark current value generated in the light receiving section are matched.