JPH0673374B2 - Solid-state imaging device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device used in a video camera or the like.

2. Description of the Related Art FIG. 2 shows an interline transfer type solid-state imaging device using a conventional CCD. Photosensitive pixel section 2, vertical CCD
The layout of the shift register 3, the horizontal CCD shift register 4, and the output unit 5 is shown. Most of the area of the image pickup apparatus 1 is a light receiving area 6, and part of the area is an optical black area 7 (hereinafter referred to as an OB area) for generating dark output components. FIG. 3 is a schematic diagram showing a sectional structure of a part of the light receiving region 6 and a part of the OB region 7 along the line AA ′ in FIG. Here, 8 is an N-type silicon substrate, 9 is a P-well, 10 is an N-type region serving as a photosensitive pixel portion, 11 is an N-type region serving as a CCD transfer channel, 12 is a channel stop portion for pixel separation, and 13 is a dioxide. Silicon film, 14 is polycrystalline silicon that serves as a CCD transfer gate, 15 is a light-shielding aluminum film that is formed excluding the upper portion of the N-type region 8 that serves as the photosensitive pixel portion, and 16 is for surface protection and insulation. Phosphosilicate glass (PS
G) Membrane. The P well 9 is an N type region 10 of the photosensitive pixel.
In this structure, the impurity concentration in the lower part of the N-type substrate 8 is lowered to cause excess charges to overflow into the N-type substrate 8.

In the solid-state imaging device 1, the signal charges generated by the light incident on the light receiving unit 6 are accumulated in the N-type region 10 of the photosensitive pixel unit, and then the vertical CCD register 3 and the horizontal C
The data is transferred from the CD register 4, converted from the voltage by the output unit 5, and read.

Here, even if the light input is completely cut off, an output component (a dark current output component or a kind of leakage current that is thermally generated and called dark current) is observed. Increase. When such a dark current becomes large, there arises a problem that the reference black level necessary for signal processing changes. Therefore, signal processing is performed to subtract the increase in dark current component due to temperature rise, and the OB area 7 is provided to detect the increase in dark current alone. Therefore, the OB region 7 has the same structure as the light receiving unit 6 except that the aluminum film 15 is also formed on the N-type region 10 of the photosensitive pixel portion.

The aluminum film 15 described above is formed by etching after vapor deposition, but the surface of the N-type region 10 that becomes the photosensitive pixel portion is damaged by ions or the like in each step, and the dark current remarkably increases. This is because the interface state density existing at the interface between the SiO ₂ film 13 and the N-type region 10 increases. In order to reduce this, for example, it is usual to perform annealing treatment for about 30 minutes in an atmosphere of 450 ° C., nitrogen of 90%, and hydrogen of 10%.

Problems to be Solved by the Invention However, since the high temperature treatment such as the growth of the protective insulating film including the above annealing is performed after the aluminum film 15 is formed, the light receiving region 6 where the aluminum film 15 does not exist on the surface of the photosensitive pixel and the aluminum on the surface. In the OB area 7 where the film 15 exists
There is a difference in the interface state density including the H ₂ permeation effect. Therefore, a difference occurs between the dark current of the light receiving area 6 and the dark current of the OB area 7. For this reason, the detection of only the dark output component of the light-receiving region has become a serious problem because the action in the OB region is extremely incomplete.

The present invention solves such a problem and provides a solid-state imaging device capable of accurately compensating for the temperature fluctuation of the dark current in the light receiving region without causing a difference in dark current between the light receiving region and the OB region. It is intended to be realized.

Means for Solving the Problems In order to solve this problem, the solid-state imaging device of the present invention is
It is characterized in that the junction depth and the impurity concentration of the well region forming the photosensitive pixel portion in the OB region are shallower or lower than those in the well region forming the photosensitive pixel portion in the light receiving region. .

Action With this configuration, the photosensitive pixel structure in the light receiving area and the OB area are completely the same structure, there is no difference in the state of the interface state between Si and SiO _{2 which is} the source of dark current, and the dark current in both areas is At the same time as the difference does not occur, the electric charge generated by the incident light is not read out at all in the OB region, so the OB characteristic is perfect.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1A is a schematic view showing a sectional structure of a part of the light receiving region and the OB region in the solid-state imaging device according to the present embodiment.
Compared with the conventional structure shown in FIG. 3, the P well in the OB region: P (O
B) 17 has a shape in which the junction depth is made extremely shallow under the N-type region 10 which is a photosensitive pixel portion as compared with the case of the P well 9 in FIG. 3, and the aluminum film 16 has a light receiving region and an OB region. Since it is the same as FIG. 3 except that it has exactly the same shape, the same reference numerals are used and the detailed description thereof is omitted.

As shown in FIG. 1A, the photosensitive pixel structures of the light receiving region and the OB region have exactly the same shape except for the P well shape below the N type region 10. That is, since the aluminum film formation, etching, and hydrogen treatment are performed under the same conditions, there is no difference in the interface state density between Si and SiO ₂ . Therefore, the generation of dark current also shows exactly the same amount and temperature dependency in the light receiving region and the OB region.

At the time of light incidence, all the charges generated in the OB region are swept out to the N-type substrate 8 and do not become signal charges. FIG. 2b shows the mechanism. 6 shows an electron potential distribution of a photosensitive pixel portion in a state where a positive potential (Vsub) is applied to the N-type substrate 8. (The circles in the figure indicate electrons.) In the light-receiving region, the electrons generated on the surface side of the maximum potential value become signal charges, but in the OB region, the maximum potential value is almost equal to the N-type region 10, so
It is swept up on the N-type substrate 8. For this reason, the OB region is not affected by the incidence of light at all, and produces exactly the same dark current as the dark state of the light receiving region.

As described above, the dark current variation in the light receiving region due to the temperature variation can be accurately compensated by the dark current in the OB region.

Note that the present invention is not limited to the above-described embodiment, and when a method other than the CCD method is used as a method for reading out signal charges, the same is true even when a MOS pixel, an amorphous semiconductor, or a compound semiconductor is used as a photosensitive pixel. The effect of is obtained.

As described above, according to the present invention, since there is no difference between the dark current in the light receiving region and the dark current in the OB region, it is possible to accurately compensate for the dark current change due to the temperature change. It is possible to realize a high-quality solid-state imaging device over a wide temperature range.

[Brief description of drawings]

FIG. 1a is a schematic view showing a sectional structure of a part of a light receiving region and an OB region of a solid-state imaging device according to an embodiment of the present invention.
FIG. B is a diagram showing the electron potential distribution along BB ′ and CC ′ in FIG. 1a, FIG. 2 is a schematic diagram showing the configuration and arrangement of a conventional solid-state imaging device, and FIG. 3 is a conventional diagram. FIG. 3 is a schematic diagram showing a cross-sectional structure of a part of a light receiving area and an OB area of the solid-state imaging device of FIG. 1 ... Solid-state imaging device, 2 ... Photosensitive pixel part, 3 ... Vertical CC
D soft register, 4 ... Horizontal CCD shift register, 5 ...
… Output section, 6 …… Light receiving area, 7 …… OB area, 8 …… N type silicon substrate, 9,17 …… P well, 10 …… N for photosensitive pixels
Shaped area, 11 …… N-shaped area for vertical CCD register, 12 …… P ⁺ area for channel stopper, 13 …… Silicon dioxide,
14 …… Polycrystalline silicon, 15 …… Aluminum film, 16 ……
Phosphosilicate glass film.

Claims (1)

[Claims] 1. A semiconductor substrate, a well provided on a main surface of the semiconductor substrate and having a conductivity type different from that of the semiconductor substrate, a plurality of photosensitive pixel portions provided in the well, and the photosensitive pixel portion. And a light-shielding film formed on the semiconductor substrate except a portion directly above the photosensitive pixel portion, and a part of the photosensitive pixel portion among the plurality of photosensitive pixel portions. Is provided in the optical black region for generating the dark output component, the remaining photosensitive pixel portion is provided in the sensor region for receiving light, and the well region forming the photosensitive pixel portion to be the optical black region is the photosensitive pixel portion for receiving light. A solid-state image pickup device having a lower impurity concentration or a shallower junction depth than a well region in which a trench is formed.