JP2917361B2 - Solid-state imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a solid-state imaging device having an effective imaging area and an optical black area.

[Summary of the Invention]

The present invention provides a semiconductor substrate of a first conductivity type, a well region of a second conductivity type on which the semiconductor substrate is formed, and a hole accumulation layer of a second conductivity type provided in the well region and suppressing a current generated on the surface. And provided in the well region below the hole accumulation layer,
First for forming a potential well for storing electric charge
An effective imaging region for extracting a signal charge having a conductivity type impurity region and an optical black region for extracting a dark current reference signal having a second conductivity type hole accumulation layer provided in a well region and suppressing a current generated on the surface; The signal charge in the effective imaging region is accumulated in the potential well, and the charge generated in the optical black region is swept out to the semiconductor substrate to obtain a reliable dark current reference signal. .

[Conventional technology]

Normally, in a CCD solid-state imaging device, an optical black (optical black) region for obtaining a dark current reference signal is formed, and a signal from an effective imaging region is arithmetically processed based on a signal from the optical black region. You.

6 and 7 show a cross section of a main part of a conventional interline transfer type solid-state imaging device. FIG. 6 shows a cross section of an effective imaging area, and FIG. 7 shows a cross section of an optical black area. It is. As shown in FIG. 6, the effective imaging region is an n ⁺ -type impurity diffusion region 10 on the surface of the silicon substrate 100.
1 is formed, and the region where the n ⁺ -type impurity diffusion region 101 is formed functions as a light receiving section. A reading section 102 is formed adjacent to the n ⁺ -type impurity diffusion region 101, and a channel layer 103 is formed adjacent to the reading section 102.
The channel layer 103 is for transferring electric charges, and is driven by a transfer electrode 104 thereon. In this effective imaging region, an opening is formed above the n ⁺ -type impurity diffusion region 101 constituting the light receiving section, and the light-shielding film 105 is formed of n ⁺
It is not formed on the impurity diffusion region 101 of the mold. On the other hand, as shown in FIG. 7, a light-shielding film 105 is formed on the entire surface in the optical black region. That is, n ⁺ -type impurity diffusion regions 10 formed in the same structure, respectively.
1, the reading section 102, the channel layer 103, the transfer electrode 104, and the like are all formed under the light-shielding film 105. In particular, in the optical black region, the light-shielding film 105 also exists on the n ⁺ -type impurity diffusion region 101. At the time of signal output, the light shielding film 1
The electric charge in the area masked by 05 is transferred to the channel layer 103 via the read section 102, and is read as a dark current reference signal serving as a black level reference.

[Problems to be solved by the invention]

However, in the solid-state imaging device having the optical black region as described above, when the light-shielding film 105 in the optical black region has a defect that causes light transmission, the current of the carrier generated by the light transmission is added to the dark current component. Will be. Therefore, the reference such as the black level fluctuates due to the transmitted light, and an accurate dark current reference signal cannot be obtained due to the influence.

In view of the above technical problems, an object of the present invention is to provide a solid-state imaging device that can reliably obtain a dark current reference signal even when light transmission or the like occurs.

[Means for solving the problem]

In order to achieve the above object, a solid-state imaging device of the present invention is provided in a semiconductor substrate of a first conductivity type, a well region of a second conductivity type on which the semiconductor substrate is formed, and a well region,
A second conductivity type hole accumulation layer for suppressing a current generated on the surface; a first conductivity type impurity region provided in a well region below the hole accumulation layer for forming a potential well for accumulating charges; And an optical black region for extracting a dark current reference signal provided in the well region and having a second conductivity type hole accumulation layer for suppressing current generated on the surface. Then, the signal charge in the effective imaging region is accumulated in the potential well, and the charge generated in the optical black region is
It is swept out to the semiconductor substrate.

Here, as a structure for sweeping out the charges generated in the optical black region, a structure in which the potential is inclined in the depth direction of the substrate and there is no peak may be used. For example, a p-type well region is formed in an n-type semiconductor substrate in an effective imaging region, and n-type well region is formed as an effective imaging region.
In a p ⁺ npn vertical overflow drain structure element in which a p ⁺ -type hole accumulation layer is formed on the impurity region, an optical black region is formed of n
It has a p ⁺ pn structure in which a p ⁺ type hole accumulation layer is formed in a p type well region formed in a type semiconductor substrate. That is, unlike the effective imaging region, the impurity region is not formed in the optical black region. The light-shielding film may have a configuration in which only the effective imaging region is opened, or may have a configuration in which both the effective imaging region and the optical black region are opened. That is, since charges are swept out in the optical black region, a reliable dark current reference signal can be obtained regardless of the presence or absence of the light shielding film.

[Action]

In general, the dark current component includes a dark current of the light receiving section, a dark current of the vertical register section, and a dark current of the horizontal register section. However, in the light receiving section of the optical black region of the solid-state imaging device of the present invention, electric charges are accumulated. Therefore, the dark current component of the light receiving section is not added, and the dark current component of the register section is used as a reference signal. Also,
Since a hole accumulation layer is formed in the effective imaging region and the optical black region, a current generated on the surface is suppressed. Therefore, even when light passing through the light-shielding film is generated, the adverse effect that the dark current reference signal fluctuates is prevented.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

The present embodiment is an example of an interline transfer type CCD imager, and has a structure in which charges are constantly discharged to the semiconductor substrate in the optical black region.

FIG. 5 is a plan view showing the relationship between the effective imaging section 51 and the optical black section (OPB section) 52 on the chip 50 of the CCD imager of this embodiment. In the figure, an optical black section 52 indicated by a hatched area is disposed so as to surround the effective imaging section 51, and has about 20 to 50 pixels at both ends in the horizontal (H) direction and both ends in the vertical (V) direction. It is arranged about 10 to 20 pixels according to.

The CCD imager of this embodiment has a structure in which a p-type well region is formed on an n-type silicon substrate.

FIG. 1 shows a cross-sectional structure of the effective imaging section, in which a p-type well region 2 is formed on an n-type silicon substrate 1. In the light receiving portion 3, a hole accumulation layer 4 made of ap ⁺ -type impurity region is formed on the surface of the well region 2. The current generated on the surface of the light receiving section 3 is suppressed by the hole accumulation layer 4. Below the hole accumulation layer 4, an n-type impurity region 5 for functioning as a sensor is formed. As described above, the light receiving section 3 has a p ⁺ npn structure, and charges are accumulated in the potential well corresponding to the n-type impurity region 5. The silicon substrate 1 is supplied with a required substrate voltage Vsub, and by controlling the substrate voltage Vsub, it is possible to sweep out excessive charges and perform an electronic shutter operation. An insulating film 6 is formed on the light receiving portion 3, and a light-shielding film 7 made of an aluminum film on the insulating film 6 is opened. Therefore, the light incident from the opening 8 of the light shielding film 7 is photoelectrically converted by the light receiving unit 3 and read out as signal charges.

An n-type channel layer 9 for transferring charges as a vertical register is formed in the p-type well region 2. At the bottom of the n-type channel layer 9, a p-type second well region 10 for reducing smear is formed, and a channel formed of ap ⁺ -type impurity region is provided between the n-type channel layer 9 and another vertical column. A stopper region 11 is formed. The n-type channel layer 9 is separated from the light receiving section 3, and the separated area is used as the reading section 12. The transfer electrode 13 is formed on the channel layer 9.
And on the read section 12 via the insulating film 6. Although not shown in the figure, the transfer electrode 13 actually has a plurality of layers and is supplied with a multi-phase clock. The transfer electrode 13 is driven by a ternary clock,
Is the highest, the electric charge from the light receiving section 3 is transferred to the channel layer 9 by the potential of the reading section 12.

Similarly, the sectional structure of the optical black portion is
The structure is as shown in the figure. The light receiving portion 23 of the optical black portion has a well region 2 formed on an n-type silicon substrate 1 and a hole accumulation layer 4 formed on the surface of the well region 2. No n-type impurity region is formed. The structure of the light receiving section 23 is a p ⁺ pn structure. The structure other than the light receiving unit 23 is the same in the effective imaging unit and the optical black unit. That is, the reading unit 12 is provided apart from the light receiving unit 23, and is in contact with the reading unit 12 for each vertical column.
A channel layer 9 made of a type impurity region is formed.
A second well region 10 and a channel stopper region 11 are formed so as to surround the channel layer 9 at the bottom of the substrate and at the other vertical column side. The structure on the board is the same,
On the transfer electrode 13, the light shielding film 7 opened in the light receiving section 23 is formed.

FIG. 3 is a potential diagram of the light receiving section 3 of the effective imaging section, and FIG. 4 is a light receiving section 23 of the optical black section.
FIG. As shown in FIG.
Since the potential of the effective imaging section has a potential well corresponding to the n-type impurity region 5, it is possible to accumulate signal charges there. Further, by changing the substrate voltage Vsub, an overflow drain and an electronic shutter operation can be performed. However, as shown in FIG. 4, the potential of the optical black portion gradually becomes deeper from the hole accumulation layer on the surface, and becomes the potential of the n-type silicon substrate 1 without any peak. Therefore, the charges generated by the light incident on the light receiving unit 23 are constantly swept out to a deep portion of the substrate, and the charges are not accumulated in the light receiving unit 23 of the optical black portion.

In the CCD imager of this embodiment having such a structure, the dark current reference signal from the optical black section is only the dark current components in the vertical and horizontal registers. That is, in the CCD imager of the present embodiment, the current component flowing by diffusion from the substrate is reduced due to the combination of the n-type silicon substrate 1 and the p-type well region 2 and the hole accumulation layer 4 is employed. Therefore, the current generated on the surface of the light receiving unit is also suppressed. Therefore, in the CCD imager of the present embodiment, the dark current component itself from the light receiving section is sufficiently small. Since the dark current from the light receiving section is extremely small,
Even if only the effective imaging section contains the dark current component from the light receiving section and the optical black section does not contain the dark current component from the light receiving section, the dark current from the light receiving section is calculated in the calculation processing for the black level reference. The ingredients will not be a problem. Of course, since the signal from the optical black section is not affected by light transmission or the like, a reliable dark current reference signal can be obtained.

Further, in the CCD imager of the present embodiment, the light receiving portion 23 of the optical black portion has a structure in which electric charges are swept out to the substrate. Therefore, the light shielding film 7 of the optical black portion is opened similarly to the effective imaging portion. For this reason, in the conventional device in which only the optical black portion is entirely covered, slight variations in the device due to the covering have occurred, but in the CCD imager of the present embodiment, the structure of the light shielding film 7 is different from that of the optical black portion. It is the same as that of the effective image pickup unit, and there is no slight variation of the elements.

Although the CCD imager of this embodiment has a structure in which the n-type impurity region 5 is not formed in the optical black portion, the n-type impurity region 5 is formed in order to eliminate the potential peak of the optical black portion.
Alternatively, an impurity of the opposite conductivity type may be implanted to compensate. Further, the present invention is not limited to the interline transfer type, and the same applies to the frame interline transfer type.

[Effects of the Invention] In the solid-state imaging device of the present invention, in the light receiving portion in the optical black region, electric charge is swept out to the semiconductor substrate without being accumulated, so that the dark current component of the light receiving portion is not added,
The dark current component of the register section is used as a reference signal.
Further, since a hole accumulation layer is formed in the effective imaging region and the optical black region, a current generated on the surface is suppressed. Therefore, even when light passing through the light-shielding film is generated, the adverse effect that the dark current reference signal fluctuates is prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structure of an effective image pickup unit as an example of the solid-state image pickup device of the present invention, FIG. 2 is a cross-sectional view showing a structure of an optical black unit as an example thereof, and FIG. FIG. 4 is a potential diagram of the optical black portion, and FIG. 5 is a plan view of the chip of the example. FIG. 6 is a cross-sectional view showing the structure of an effective image pickup unit as an example of a conventional solid-state image sensor, and FIG. 7 is a cross-sectional view showing the structure of an optical black unit as an example of a conventional solid-state image sensor. DESCRIPTION OF SYMBOLS 1 ... Silicon substrate 2 ... Well region 3, 23 ... Light receiving part 4 ... Hole accumulation layer 5 ... Impurity region 9 ... Channel layer 13 ... Transfer electrode 51 ... Effective imaging part 52 ... Optical black Department

Claims (1)

(57) [Claims] A first conductivity type semiconductor substrate; a second conductivity type well region in which the semiconductor substrate is formed; and a second conductivity type positive electrode provided in the well region for suppressing a current generated on the surface. An effective imaging region for extracting a signal charge having a hole accumulation layer and a first conductivity type impurity region provided in the well region below the hole accumulation layer and forming a potential well for accumulating electric charge; An optical black region that is provided in the well region and has a second conductivity type hole accumulation layer that suppresses a current generated on the surface, and that extracts a dark current reference signal. A charge generated in the optical black region and discharged to the semiconductor substrate.