JPH04116976A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To accurately compensate variation in an output at the time of darkness in a photoelectric conversion region and to prevent reduction in dynamic range of a charge reader by preventing leakage of a light in an OB region. CONSTITUTION:A light 22 incident on an OB region is condensed to part of a metal light screening film 18 on a vertical CCD register by a microlens 21. Thus, the light condensed to the film 18 on a photodetector 12 is reduced to 1/10 or less as compared with a conventional structure having no microlens 21. Accordingly, even if the film 18 on the photodetector 12 leaks a light, it is reduced to 1/10 or less as compared with prior art. Further, since the light incident on the OB region is condensed to most flat and uniformly thick regions B, C of the film 18, the light is scarcely incident on a region A which in which the light is easily leaked due to irregular thickness of the film 18 having large uneven steps. Thus, in a solid-state image sensing device of this invention, the light leakage of the OB region can be greatly reduced as compared with prior art.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a solid-state imaging device, and particularly to a structure that increases the light shielding effect in an optical black area.

<Prior art> Fig. 4 shows a charge coupled device (hereinafter referred to as 1'-CCDJ).
The figure shows a schematic diagram of a CCD solid-state image sensor using an interline transfer method, in which 1 is a light receiving section consisting of a pn junction photodiode, 2 is a vertical CCD register section, 3 is a horizontal CCD register section, and 4 is a photoelectric conversion section. Area 5 is an optical black area (hereinafter referred to as "OB area") mainly for forming a black level, and this area is covered with a metal light-shielding film to rapidly block light incidence.

FIGS. 2 and 3 show the cross-sectional structures of a part of the photoelectric conversion region 4 and a part of the OB region 5, respectively, of the CCD solid-state imaging device. That is, 11 is, for example, a p-type silicon substrate, 12 is an n-layer provided on a part of the surface of the substrate 11 and has a conductivity type opposite to that of the substrate 11;
corresponds to

Reference numeral 13 denotes an n-layer provided close to the n-layer 12 on the surface of the substrate 11, and corresponds to 1 and the vertical CCD register section 2. 14 is a channel stopper part, 15 and 16 are polysilicon electrodes of the first layer and second layer, respectively, and 17
1 is a silicon oxide insulating layer, 18 is a metal light-shielding film, and 19 is a protective film.

In the above CCD solid-state image sensor, when light enters the photoelectric conversion region 4, signal charges generated are accumulated in one layer 12 of the light receiving section 1. The accumulated charge above is the vertical CC
After being transferred to the n-layer 13 of the D register section 2, the transfer lock pulse causes the water droplet C to move inside the vertical CCD register section 2.
The data is transferred in three directions to the CD register section. Then horizontal CC
The charges transferred to the D register section 3 are transferred in the horizontal direction, converted into voltage by the output section 6, and read out.

In a CCD solid-state image sensor, an output component (dark current) is detected at room temperature even if light incidence is completely interrupted, and this output component increases as the temperature rises.

On the other hand, when light is incident, signal processing is performed to subtract the output component (dark current) detected in the OB region from the output component detected in the photoelectric conversion region 4. As a result, even if the dark current fluctuates due to temperature changes,
By detecting the amount of change in this dark current in the OB region and compensating for it, a decrease in the dynamic range of the charge readout section (vertical CCD register section 2) is suppressed. Therefore, the second
As shown in the figure and FIG. 3, the OBB region 5 has the same structure as the photoelectric conversion region 4, except that the light receiving portion 1 thereof is also covered with a metal light shielding film 18.

<Problems to be Solved by the Invention> By the way, the metal light shielding film 18 is made of, for example, AI! Alternatively, it is made of AA'Si or the like, but it is formed with a film thickness of about 1 μm due to problems such as generation of pinholes and processing restrictions. However, after forming the metal light-shielding film 18, heat treatment such as H2 annealing is performed for the purpose of recovering damage to the substrate, but as a result, grains due to crystal precipitation grow within the metal light-shielding film 18. Due to this, a slight amount of light enters the substrate 11 in the OBB area 5,
This may cause light leakage. Furthermore, there is a gap of 1 μm between the light receiving section 12 and the vertical CCD register section 13, as shown in FIG.
Since there is a certain degree of level difference, the coverage of the metal light shielding film 18 may be deteriorated in the OBB region 5 due to the level difference, and light leakage may occur particularly in the area A. When light leakage occurs in the OBB region 5 due to the above reasons, it becomes impossible to accurately compensate for the fluctuations in the dark output component by the signal processing described above, which may cause serious defects in the solid-state imaging device. become.

Therefore, an object of the present invention is to prevent light leakage in the OB region, thereby making it possible to accurately compensate for fluctuations in the dark output component in the photoelectric conversion region, and preventing a decrease in the dynamic range of the charge readout section. An object of the present invention is to provide a solid-state imaging device.

Means for Solving the Problems> In order to achieve the above object, the solid-state imaging device of the present invention has a plurality of light receiving sections on a semiconductor substrate of one conductivity type and a function of sequentially reading out signals photoelectrically converted by the light receiving sections. It consists of a photoelectric conversion region and an OB region having the same structure but whose entire surface is shielded from light by a light shielding film, and is characterized in that a microlens is formed on the OB region to enhance the light shielding effect.

<Example> Hereinafter, the present invention 3 will be explained in detail with reference to Examples.

The OB area of the CCD solid-state image sensor shown in FIG. 1 is different from the OB area of the conventional COD solid-state image sensor shown in FIG. 3 in the following points. That is, in FIG. 1, the protective film 19
A flattening film 20 is formed on top of the flattening film 20, and a mitalo lens 21 is further formed on top of the flattening film 20 to prevent light from entering the first layer 12, which is a photodiode. The rest of the structure is the same as the conventional structure shown in FIG. 3, so the same parts in FIG. 1 as in FIG. 3 are given the same reference numerals. The method for forming the microlens 21 is, for example, disclosed in Japanese Patent Publication No. 60
-59752. There is a method described in JP-A-64-10666 and the like.

As shown in FIG. 1, light 22 incident on the OB region is focused by a microlens 21 onto a part of the metal light shielding film 18 on the vertical CCD register section.

As a result, the light focused on the metal light shielding film 18 on the light receiving section 12 is reduced to one-tenth or less of that of a conventional structure without the microlens 21. Therefore, even if the metal light-shielding film 18 on the light-receiving section 12 causes light leakage, it will be reduced to one-tenth or less compared to the conventional case. In addition, the light incident on the OB area is transmitted through the metal light shielding film 1.
Since the light is focused on areas B and C where the metal light-shielding film 18 is flatest and has a uniform thickness, most of the light is focused on area A, which has severe unevenness and unevenness in thickness and is likely to cause light leakage. Light no longer enters.

As described above, in the solid-state imaging device of the present invention, light leakage in the OB region can be significantly reduced compared to conventional devices. In addition, when the structure of the present invention is used in a solid-state imaging device with a microlens, a microlens for increasing the amount of light incident on the light receiving section formed in the photoelectric conversion region and increasing the sensitivity, and a microlens for increasing the sensitivity formed in the OB region of the present invention are provided. Microlenses for improving the light shielding effect can be formed at the same time.

Note that the present invention is not limited to the above-mentioned embodiments, and may be applied to color solid-state imaging devices provided with color filters, and is not limited to interline transfer type CCD image sensors.
Frame transfer type CCD image sensor,
It can be applied to all types of solid-state imaging devices such as MOS image sensors.

In short, it is applicable to all solid-state imaging devices that have a light receiving section and a function of sequentially reading out signals photoelectrically converted by the light receiving section on a semiconductor substrate of one conductivity type, and a part of which is an OB region.

<Effects of the Invention> As is clear from the above description, according to the solid-state imaging device of the present invention, it is possible to prevent light leakage in the OB region and accurately compensate for fluctuations in the dark output component in the photoelectric conversion region. This makes it possible to prevent the dynamic range of the charge readout section from decreasing.

[Brief explanation of drawings]

FIG. 1 shows an OB of an embodiment of a solid-state imaging device according to the present invention.
2 and 3 are cross-sectional views showing the photoelectric conversion region and OB region of a conventional solid-state imaging device, respectively. FIG. 4 schematically shows the configuration of a conventional solid-state imaging device. FIG. Explanation of symbols 1.12... Light receiving section, 2, 13... Vertical CCD register section, 3... Horizontal CCD register section, 4... Photoelectric conversion area, 5... OB area 15.16 ... Polysilicon electrode, 18 ... Metal light shielding film, 19 ... Protective film, 2° ... Flattening film, 21 ... Microlens.

Claims (1)

[Claims] 1. On a semiconductor substrate of one conductivity type, there is a photoelectric conversion area consisting of a plurality of light receiving parts and a function of sequentially reading out the signals photoelectrically converted by the light receiving parts, and an optical black area having the same structure but whose entire surface is shielded from light by a light shielding film. What is claimed is: 1. A solid-state imaging device in which a microlens is formed on the optical black region to improve a light shielding effect.