JPH11307754A - Solid state image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance sensitivity by employing an optical black part of such a structure as requiring no metallic light shielding layer covering a light receiving part thereby decreasing the thickness of a chip. SOLUTION: The solid state image sensor comprises a light receiving part 14 and a detecting part 16 formed in a semiconductor substrate 10, a transfer gate electrode 12 formed between the light receiving part 14 and the detecting part 16 on the semiconductor substrate 10 through an insulating film 11, an impurity diffusion region 17 formed in the semiconductor substrate 10 and connected electrically with a power supply voltage VDD, a reset gate electrode 13 formed between the impurity diffusion region 17 and the detecting part 16 on the semiconductor substrate 10 through the insulating film 11, and a plurality of pixels including an amplifier circuit connected electrically with the detecting part 16 wherein the light receiving part 14 is connected electrically with the power supply voltage VDD for a part of the elements and these elements function as optical black parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a MOS type solid-state imaging device using a MOS (Metal Oxide Semiconductor) transistor for signal reading and a method of manufacturing the same.

[0002]

2. Description of the Related Art Solid-state imaging devices are roughly classified into two types, a CCD (charge coupled device) type and a MOS type, according to a signal reading method. In recent years, M
OS type solid-state imaging device, especially CMOS including peripheral circuits
CMOS manufactured by (complementary MOS) process
The solid-state imaging device has the advantages of low voltage and low power consumption and can be integrated with peripheral circuits on one chip.
It has attracted attention as an image input element for portable equipment such as a small camera for C. In the MOS solid-state imaging device, one pixel is configured by a photodiode (light receiving unit) and one or more (normally, three for amplification, reset, and selection) MOS transistors, and a signal photoelectrically converted by the light receiving unit. Are amplified and output for each pixel.

In a solid-state image pickup device, electric charges (so-called dark current) generated thermally independently of light incident on a light receiving section.
Are integrated, the output signal is mixed with dark current in addition to signal charges in response to incident light. Since the dark current depends on the temperature, the output signal mixed with the dark current increases and decreases depending on the temperature. As a result, there is a problem that a signal accurately responding to the incident image cannot be obtained. Therefore, a method of providing a pixel for outputting a signal corresponding to a dark current component and generally performing arithmetic processing on a signal from another pixel based on a signal from the pixel has been adopted. A pixel that outputs the reference signal to an imaging unit that outputs a signal responsive to an incident image is called an optical black unit (hereinafter, “OB unit”).

FIG. 5 is a sectional view showing a pixel structure of an OB section in a conventional MOS type solid-state imaging device. The pixels in the OB section include a light receiving section 54, a reset transistor (a detecting section 56 as a source, and an impurity diffusion area 57 as a drain).
And a reset gate electrode 53. ), An amplifying transistor 58 and a selecting transistor, are the same as the pixels of the image pickup unit.
A metal light-shielding film 59 is formed above the light receiving part of the part. Since the light receiving unit is shielded from light, the OB
The signals output from the pixels of the section include a dark current component, but do not substantially include a signal responsive to incident light. Therefore, a signal obtained by subtracting a dark current component, that is, a signal that is stable against a temperature change can be obtained by performing arithmetic processing on output signals from other pixels based on the signal from the OB section.

[0005]

As described above, the MOS type solid-state imaging device has a complicated circuit for one pixel because each pixel has three transistors in addition to the light receiving section, and the circuit for wiring is difficult. A metal film is formed in multiple layers (usually 3 to 5 layers). In the conventional MOS-type solid-state imaging device, a metal light-shielding film that covers the light-receiving portion of the OB portion is further laminated in addition to these wiring metal films. As a result, since the chip thickness is increased, when an on-chip type lens is used, the distance between the lens and the light receiving unit is increased, which causes a problem that the light collection rate is reduced, that is, the sensitivity of the imaging apparatus is reduced.

An object of the present invention is to solve the above problems and to provide a high-sensitivity solid-state imaging device.

[0007]

In order to achieve the above object, a solid-state imaging device according to the present invention comprises a light receiving section and a detecting section formed in a semiconductor substrate, and a light receiving section and a detecting section provided between the light receiving section and the detecting section. A transfer gate electrode formed on a semiconductor substrate via an insulating film, an impurity diffusion region formed in the semiconductor substrate and electrically connected to a power supply voltage, and a region between the impurity diffusion region and the detection unit. A plurality of pixels including a reset gate electrode formed on the semiconductor substrate via the insulating film and an amplifier circuit electrically connected to the detection unit are arranged, and some of the pixels are A solid-state imaging device that functions as an imaging unit that outputs a signal responsive to the signal, and that functions as an OB unit that outputs a reference signal when some of the other pixels perform arithmetic processing on the signal.
In the pixel functioning as the B section, the light receiving section is electrically connected to the power supply voltage.

In the solid-state imaging device having such a configuration, a function as an OB portion is provided by adopting a structure in which charges generated in a light receiving portion are not accumulated.
There is no need for a metal light-shielding film that covers the light-receiving portion of the portion B. Therefore, by not forming the metal light-shielding film, the sensitivity of the imaging device can be improved by reducing the chip thickness, and the manufacturing process can be simplified. FIG.
In the OB part having the structure shown in FIG. 1, there is a case where a defect such as light transmission occurs in the metal light shielding film covering the light receiving part of the OB part, and the reference signal may fluctuate depending on the amount of transmitted light due to the defect. However, according to the solid-state imaging device of the present invention, such a problem is avoided, and a stable reference signal can be obtained.

In the solid-state imaging device, in the pixel functioning as the OB portion, it is preferable that a region having a higher impurity concentration than other regions of the light receiving portion is formed on a surface of the light receiving portion. . According to this preferred example, the light receiving section and the power supply voltage can be more reliably connected by the metal wiring.

In the solid-state imaging device, in the pixel functioning as the imaging unit, a region in which an impurity of a conductivity type opposite to that of another region of the light receiving unit is introduced into a surface of the light receiving unit. Is preferably formed. According to this preferred example, since the dark current generated in the light receiving section of the pixel of the imaging section is so small that its influence can be ignored, an output image more accurately responding to the incident image can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid-state imaging device according to the present invention has a plurality of pixels arranged two-dimensionally on a semiconductor substrate, and some of the pixels function as an OB section for obtaining a dark current reference signal. Other pixels function as an imaging unit for obtaining signal charges in response to incident light. As shown in FIG.
2 is arranged so as to surround the periphery of the imaging unit 31.

FIG. 2 is a sectional view showing an example of the structure of a pixel serving as an image pickup unit. In a p-type silicon substrate 20, a light receiving portion 24 and a detecting portion 26, which are n-type impurity diffusion regions, are formed. The impurity concentration of the light receiving portion 24 is not particularly limited as long as it can perform photoelectric conversion, preferably 10 ¹⁵ to
About 10 ¹⁶ cm ^-3 and a diffusion depth of 0.5 to 2.0 μm
About m is appropriate. Preferably, p-type impurity diffusion layer 25 is formed on the surface of light receiving section 24. Suitably, the impurity concentration of the p-type impurity diffusion layer 25 is about 10 ¹⁷ to 10 ¹⁹ cm ⁻³ , and the diffusion depth is about 0.2 to 0.6 μm.
On the other hand, the impurity concentration of the detection unit 26 is not particularly limited as long as it can be electrically connected by metal wiring, but is preferably 10 ²⁰ cm ⁻³ or more. The detection unit 26 is connected to a gate electrode of an amplification transistor 28 formed in the same pixel by a metal wiring.
A transfer gate electrode 22 is formed on the substrate between the light receiving unit 24 and the detecting unit 26 via an insulating film 21. By the transfer gate electrode 22, signal charges can be transferred from the light receiving section to the detecting section, and a signal can be input to the amplifier circuit as a voltage of the detecting section.

In the substrate 20, there is another n-type impurity.
The object diffusion region 27 is formed so as to be separated from the detection unit 26.
I have. The impurity concentration of the impurity diffusion region 27 depends on the metal distribution.
As long as they can be electrically connected by wires
Well, preferably 10²⁰cm ^-3That is all. Also this
The impurity diffusion region 27 has a power supply voltage V_DDTo
It is connected. Between the impurity diffusion region 27 and the detection unit 26
The reset gate voltage is interposed on the substrate between
A pole 23 is formed. That is, this impurity diffusion region
One MO having a drain 27 and a detection unit 26 as a source
An S-type transistor is formed and this transistor is detected
Reset to control the discharge of signal charges held in the
Functions as a transistor. Although illustration is omitted,
Each pixel is further provided with a selection transistor and the like.
You.

FIG. 1 is a sectional view showing an example of the structure of a pixel serving as an OB section. The pixels in the OB section include a light receiving section and three transistors for amplification, reset, and selection, similarly to the pixels in the imaging section. However, by making the circuit structure of the section related to the light receiving section different from that of the imaging section, , So that charges are not accumulated in the light receiving section. That is, the structure is such that the power supply voltage V _DD is applied to the light receiving portion 14 which is an n-type impurity diffusion region formed in the p-type silicon substrate 10,
The charge generated in the light receiving section is constantly discharged. Specifically, an opening for making a contact is formed in an insulating film (insulating film 11, an interlayer insulating film (not shown) or the like) existing on the light receiving section 14, and the light receiving section is formed by the opening. It is in contact with the wiring metal film, and is connected to the power supply voltage V _DD by this metal film.

Therefore, the light receiving section 14 is connected by a metal wiring.
Impurity concentration that can be continued, specifically 10²⁰cm^-3
The above impurity concentration is required. However, as shown in FIG.
Impurities that can be connected by metal wiring
Concentration, preferably 10²⁰cm ^-3N-type impurity with above concentration
If the diffusion layer 15 is provided, the impurity concentration of the light receiving section 14 can be freely set.
Can be set to In this case, the light receiving unit 14
The concentration of the substance is not particularly limited, but is substantially the same as that of the imaging unit.
If the density is used, the light receiving unit of the OB unit and the light receiving unit of the imaging unit
And can simplify the manufacturing process
No.

Further, similarly to the pixels of the imaging section, a detection section 16 and another impurity diffusion region 17 are formed in the substrate, and an insulating film 11 is formed on the substrate 10 between the light receiving section 14 and the detection section 16. , A transfer gate electrode 12 is formed, and a reset gate electrode 13 is formed on the substrate 10 between the detection unit 16 and the impurity diffusion region 17 via an insulating film 11. Further, an amplification transistor 18 and a selection transistor and the like (not shown) are formed. Similarly to the imaging unit, the detection unit 16 is connected to the gate electrode of the amplification transistor 18 and the impurity diffusion region 17 is connected to the power supply voltage V _DD .

FIG. 4 is a diagram showing a circuit configuration in a state where the two pixels are arranged two-dimensionally. However, in FIG. 4, for simplicity, it is shown that the OB section exists only in one row, but in actuality, as described above, the OB section is formed in a plurality of rows and columns so as to surround the imaging section. You.
Hereinafter, the operation of the solid-state imaging device of the present invention will be briefly described with reference to FIG. In this solid-state imaging device, pixels are sequentially selected by a column selection transistor (eg, 400) and a selection transistor (eg, 104, 204) in the pixel, and a signal is output for each pixel. The driving of the column selection transistor and the selection transistor is controlled by a horizontal scanning circuit and a vertical scanning circuit, respectively.

In the image pickup section, an optical signal incident on the light receiving section 101 is photoelectrically converted to generate signal charges, and the charges are accumulated in the light receiving section 101. After the accumulation for a predetermined time is completed, a pulse is applied to the transfer gate electrode 102, and the electric charge accumulated in the light receiving unit 101 is transferred to the detecting unit 103. Next, a pulse is applied to the gate electrode of the selection transistor 104 so that the amplification transistor 10
5 is activated, and the voltage of the detection unit 103 is changed to the vertical output line 30.
Read to 0. After the signal voltage is read, a pulse is applied to the gate electrode of the reset transistor 106, and the charge held in the detection unit 103 is discharged to the power supply. The signal read out to the vertical output line 300 is sent to a noise canceling circuit, and a noise component caused by variation in the threshold value of the amplification transistor of each pixel is subtracted and output. Note that the drive timing of each transistor in the pixel is controlled by a timing generation circuit.

On the other hand, in the OB section, since the power supply voltage V _DD is applied to the light receiving section 201, the signal charges generated by the photoelectric conversion in the light receiving section 201 are constantly discharged without being accumulated. . The transfer gate electrode 202 and each of the transistors (the selection transistor 204, the amplification transistor 205, and the reset transistor 206) are driven in the same manner as in the above-described operation of the imaging unit, the signal is read out to the vertical output line 300, and the noise cancellation circuit The noise component is subtracted and output. Therefore, the signal output from the OB unit is a signal corresponding to the electric charge (dark current) generated in a part other than the light receiving unit, in other words, the charge component generated in the light receiving unit is removed from the signal obtained in the imaging unit. It is a signal equivalent to. Therefore, by performing an arithmetic process for subtracting the output signal of the OB unit from the output signal of the imaging unit, a signal corresponding to the electric charge generated in the light receiving unit, that is, almost no dark current component is included, and the image signal is stable against temperature changes. Signal can be extracted.

As described above, the solid-state imaging device according to the present invention realizes the function as the OB section by having a structure capable of discharging the electric charge of the light receiving section. Therefore, the metal light shielding film covering the light receiving section of the OB section is formed. Not required. By not forming the metal light-shielding film, the manufacturing process can be simplified, the chip thickness can be reduced, and the sensitivity of the imaging device can be improved. In a conventional solid-state imaging device having an OB section having a structure as shown in FIG. 5, when a defect that allows light to pass through a metal light-shielding film that covers a light receiving section of the OB section occurs, the reference signal is transmitted to the reference signal. Since the signal corresponding to the light is mixed, the reference signal fluctuates depending on the amount of transmitted light. In the solid-state imaging device of the present invention, such a problem is avoided, and a stable reference signal can be obtained.

In the solid-state imaging device according to the present invention,
The pixel structure of the imaging unit is not limited to the above example. Further, the pixel structure of the OB section is not limited to the above example as long as the light receiving section is connected to the power supply voltage.

Hereinafter, an example of a method for manufacturing a solid-state imaging device according to the present invention will be described. First, a gate insulating film and a field insulating film (both are silicon oxide films) are formed between pixels by thermal oxidation on a p-type silicon substrate. Usually, the thickness of the gate insulating film is 10 to 20 nm.
The thickness of the field insulating film is about 300 to 500 nm. Next, on this silicon substrate, a film thickness of 250
A polycrystalline silicon film of about 400 nm is deposited by a low pressure CVD method, a part of the polycrystalline silicon film is removed by etching, and a transfer gate electrode and a reset gate electrode are formed in each pixel. Next, an n-type impurity such as arsenic or phosphorus is ion-implanted into the silicon substrate to form a light receiving portion in each pixel. This ion implantation
For example, the acceleration voltage 500 keV, a dose of 10 ¹¹ to
It is carried out at about 10 ¹² cm ^-2 . Next, with the light receiving portion of the pixel in the OB portion covered with a resist, p
The p-type impurity ions are implanted, and a p-type impurity diffusion layer is formed on the surface of the light receiving section of the imaging section.

With the light receiving section of the imaging section covered with the resist, ion implantation of an n-type impurity is performed again to form a source region (detection section) and a drain region of the reset transistor. At the same time, a high-concentration n-type impurity diffusion layer is formed on the surface of the light receiving section in the OB section. This ion implantation is performed, for example, at an acceleration voltage of 40 keV and a dose of about 10 ¹⁴ to 10 ¹⁵ cm ⁻² .

After completion of the ion implantation, an interlayer insulating film is formed on the substrate. As the interlayer insulating film, for example,
A phosphorus-doped silicon oxide film formed by the VD method is used. A window is formed in a source region (detection portion) and a drain region of the reset transistor and an interlayer insulating film existing above the light receiving portion of the OB portion to make contact with a wiring metal, and then a metal film such as aluminum is formed. Is formed, and the metal film is patterned by etching. A series of steps of forming the interlayer insulating film, forming the metal film, and patterning is repeated as many times as necessary to form a multilayer wiring. With this multilayer wiring, the source region (detection unit) of the reset transistor is connected to the gate electrode of the amplification transistor formed in the same pixel, and the drain region is connected to the power supply voltage. Connected. Further, a solid state imaging device is obtained through a process of forming a chip by appropriately forming a surface protective film and the like and arranging an on-chip lens for each pixel on the chip surface.

[0025]

As described above, according to the solid-state imaging device of the present invention, the light receiving unit and the detecting unit formed in the semiconductor substrate are insulated on the semiconductor substrate between the light receiving unit and the detecting unit. A transfer gate electrode formed via a film, an impurity diffusion region formed in the semiconductor substrate and electrically connected to a power supply voltage, and a semiconductor substrate between the impurity diffusion region and the detection unit. A plurality of pixels including a reset gate electrode formed through an insulating film and an amplifier circuit electrically connected to the detection unit are arranged, and some of the pixels output signals in response to light. The pixel functions as an OB unit that functions as an OB unit that outputs a signal that serves as a reference when some of the pixels perform arithmetic processing on the signal, and the pixel that functions as the OB unit includes the light receiving unit. Is the power supply voltage Because it is electrically connected, OB
Since no metal light-shielding film is required to cover the light-receiving part, the chip thickness can be reduced by not forming this metal light-shielding film, thereby improving the sensitivity of the solid-state imaging device. Obtainable. Further, since the step of forming the metal light-shielding film is unnecessary, the manufacturing process can be simplified.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of the structure of a pixel in an OB section in a solid-state imaging device according to the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a pixel structure of an imaging unit in the solid-state imaging device of the present invention.

FIG. 3 is a diagram illustrating a region where an imaging unit is formed and a region where an OB unit is formed in the solid-state imaging device of the present invention.

FIG. 4 is a diagram illustrating an example of a circuit structure of the solid-state imaging device of the present invention.

FIG. 5 is a cross-sectional view illustrating an example of a structure of a pixel in an OB section in a conventional solid-state imaging device.

[Explanation of symbols]

10, 20, 50 p-type silicon substrate 11, 21, 51 insulating film 12, 22, 52 transfer gate electrode 13, 23, 53 reset gate electrode 14, 24, 54 light receiving section 15 n-type impurity diffusion layer 25 p-type impurity diffusion Layers 16, 26, 56 Detectors 17, 27, 57 N-type impurity diffusion regions (drain of reset transistors) 18, 28, 58 Amplification transistors 59 Metal light-shielding film 31 Imaging unit 32 Optical black unit 33 Chip 101, 201 Light reception Units 102 and 202 Transfer gates 103 and 203 Detecting units 104 and 204 Transistors for selection 105 and 205 Transistors for amplification 106 and 206 Transistors for reset 300 Vertical output lines 400 Transistors for column selection

Claims (3)

[Claims] A light receiving portion and a detecting portion formed in a semiconductor substrate; a transfer gate electrode formed on the semiconductor substrate between the light receiving portion and the detecting portion via an insulating film;
An impurity diffusion region formed in the semiconductor substrate and electrically connected to a power supply voltage; and a reset gate electrode formed on the semiconductor substrate between the impurity diffusion region and the detection unit via the insulating film. And a plurality of pixels including an amplifier circuit electrically connected to the detection unit, and some of the pixels function as an imaging unit that outputs a signal responsive to light, and another of the pixels functions as an imaging unit. A solid-state imaging device that functions as an optical black unit that outputs a signal serving as a reference when the pixel performs arithmetic processing on the signal, wherein in the pixel that functions as the optical black unit, the light receiving unit includes the power supply. A solid-state imaging device which is electrically connected to a voltage. 2. The solid according to claim 1, wherein in the pixel functioning as the optical black portion, a region having a higher impurity concentration than other regions of the light receiving portion is formed on a surface of the light receiving portion. Imaging device. 3. The pixel functioning as the image pickup unit, wherein a region in which an impurity of a conductivity type opposite to that of another region of the light receiving unit is introduced is formed on a surface of the light receiving unit. 3. The solid-state imaging device according to 1 or 2.