JP2003273344A - Ccd solid-state image sensing element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate potential gradient of each picture element by coming into contact with each picture element for a photoelectric conversion element of each unit picture element in two-dimensional array. <P>SOLUTION: In a region ranging over a photosensitive region of a photodiode 120 and an upper surface of a light screening film 190, a contact film 200 connecting a p+type region 120A of a photodiode 120 and a light screening film 190 is provided, and the p+type region 120A and the light screening film 190 are held at the same potential. The potential of the p+type region 120A of the photodiode 120 is thereby uniform all over an imaging region regardless of increase and decrease of hole involved in change in the amount of light received, and usual potential gradient can be eliminated. Image output of a uniform level is thereby possible all over an image. A saturation signal level of the photodiode 120 can be set properly to a handling charge amount of a CCD vertical transfer register and the saturation signal level can be improved. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device having a plurality of photoelectric conversion elements and a charge transfer section for transferring signal charges generated by each photoelectric conversion element.

[0002]

2. Description of the Related Art Conventionally, a plurality of photodiodes (photoelectric conversion elements) constituting a unit pixel are formed on a semiconductor chip.
There is provided a CCD solid-state imaging device arranged in a dimensional array and provided with a CCD vertical transfer register and a CCD horizontal transfer register for transferring signal charges generated by each photodiode.

FIG. 3 is a schematic plan view showing the structure of such a CCD solid-state image pickup device. A plurality of photodiodes 2 are provided in the imaging area provided in the central portion of the semiconductor chip 10.
0s are arranged in a vertical / horizontal two-dimensional matrix, and a plurality of CCD vertical transfer registers 30 are provided along each photodiode column. The CCD horizontal transfer register 40 is arranged outside the image pickup area and is connected to the end of each CCD vertical transfer register 30, and the output unit 50 is arranged at the end of the CCD horizontal transfer register 40. There is. The signal charges generated by each photodiode 20 are read out by each CCD vertical transfer register 30, transferred in the vertical direction, and output to the CCD horizontal transfer register 40. Then, it is transferred in the horizontal direction by the CCD horizontal transfer register 40 and output to the FD (floating diffusion) section of the output section 50. The output section 50 detects the potential fluctuation of the FD section due to the signal charge, converts it into a voltage signal, performs necessary amplification, and outputs it as an image pickup signal.

FIG. 4 is an abbreviated plan view and a sectional view taken along the line cc showing the structure of each unit pixel in the solid-state image sensor shown in FIG. This solid-state image pickup device includes an N-type silicon substrate 10
A P-type well region is formed in the photo diode 20 and the CCD vertical transfer register 30 is provided. The photodiode 20 includes a P + type region 20A provided on the surface layer of the semiconductor substrate 10 and an N type region 20B provided below the P + type region 20A. Light incident from the upper surface of the P + type region 20A is referred to as a P + type region 20A. In the N region 20B, holes and electrons are separated, the holes escape to the P + type region 20A side, and the electrons are separated into N regions.
HA accumulated in the depletion layer formed below the mold region 20B
It has a D structure. CCD vertical transfer register 3
0 is provided on one side of the photodiode 20 so as to separate the read gate region 50, and by controlling the gate potential of the read gate region 50, the signal charge accumulated in the lower layer of the photodiode 20 is CCD. It is read to the channel area of the vertical transfer register 30. A pixel separation region 60 is formed on the other side of the photodiode 20 to block the leakage of signal charges to adjacent pixels.

On the N-type silicon substrate 10, C
A transfer electrode 80 made of a polysilicon film is formed corresponding to the upper region of the CD vertical transfer register 30 via an insulating film 70A, and a light shielding film 90 is formed thereabove via an insulating film 70B. The light shielding film 90 is used for the photodiode 20.
Has an opening 90A corresponding to the light receiving region of
The upper portions of the CCD vertical transfer register 30 and the transfer electrode 80 are shielded from light. Although not shown in the drawing, the light shielding film 90
In the upper layer, a plurality of upper wiring layers are formed via various interlayer insulating films, and color filters and microlenses are mounted on the upper wiring layers via the planarizing film.

[0006]

By the way, in the above-mentioned conventional CCD solid-state image pickup device, each photodiode 20 is provided.
The holes generated in 2) flow toward the P + type region 20A side, further flow in the vertical direction along the P type region such as the pixel isolation region 60, and are discharged to the contact provided outside the imaging region. Various methods are used to arrange the contacts for discharging the holes, but in any case, it is necessary to arrange the contacts at a position separated from each pixel by a certain amount or more. In addition, in such a hole discharging path, if the resistance is too small, problems such as shading occur, so that a structure is adopted in which a certain resistance or more is given to discharge the holes.

However, in the structure in which the holes generated in each pixel are discharged to the contact apart from each pixel in this way, the hole current from each pixel flows through the discharge paths of different distances and flows into the contact. A voltage drop due to the hole current occurs in each photodiode, a potential difference occurs in the P + type region 20A of each photodiode, and a potential gradient occurs in the entire imaging region. It should be noted that such a potential gradient becomes remarkable when a light amount of a certain amount or more is received. For this reason, the level of the output image is entirely inclined in the vertical direction, which causes a problem that the image quality is deteriorated. Further, for example, when setting the saturation signal level of each pixel in relation to the amount of charge handled by the vertical transfer register, the saturation signal level cannot be effectively raised due to the potential gradient between each pixel as described above. Occurs. Particularly, in recent years, the number of pixels of the solid-state image pickup device has been increased, and the distance difference between each pixel and the contact has been increased accordingly, which becomes a more serious problem.

Therefore, an object of the present invention is to make a contact for each pixel with respect to the photoelectric conversion elements of each unit pixel arranged two-dimensionally, eliminating the potential gradient of each pixel and outputting an image of a uniform level in the entire image. And to provide a solid-state image sensor capable of improving the saturation signal level.

[0009]

In order to achieve the above object, the present invention comprises a plurality of photoelectric conversion elements each of which constitutes a unit pixel, and a charge transfer section for transferring signal charges generated by the photoelectric conversion elements. In the solid-state imaging device, the transfer electrode of the charge transfer unit is provided on the provided semiconductor substrate, and a light-shielding film having an opening corresponding to the light receiving region of the photoelectric conversion element is further provided on the transfer electrode. A contact film that connects the light-receiving surface of the photoelectric conversion element and the light-shielding film is provided in at least a part of the area from the light-receiving surface of the photoelectric conversion element to the light-shielding film, and the light-receiving surface of the photoelectric conversion element and the light-shielding film are provided in the same area. It is characterized by being held at a potential.

In the solid-state image pickup device of the present invention, a contact film for connecting the light-receiving surface of the photoelectric conversion element and the light-shielding film is provided, and the light-receiving surface of the photoelectric conversion element and the light-shielding film are held at the same potential. It is possible to make contact for each pixel with respect to the photoelectric conversion element of the pixel, eliminate the potential gradient of each pixel, and perform image output at a uniform level in the entire image,
It is possible to improve the saturation signal level.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a solid-state image sensor according to the present invention will be described below. The embodiments described below are preferred specific examples of the present invention, and various technically preferable limitations are given. However, the scope of the present invention is not limited to the present invention in the following description. Unless otherwise stated, the present invention is not limited to these embodiments. FIG. 1 is an abbreviated plan view and an aa line sectional view showing the configuration of each unit pixel in a CCD solid-state imaging device according to a first embodiment of the present invention. Note that the overall structure of the CCD solid-state image sensor is similar to that shown in FIG. 3, for example.

As shown in FIG. 1, the photodiode 12
0 is a P + type region (hole accumulation region) 120A provided in the surface layer of the semiconductor substrate 110 and N provided in the layer below it.
And a P + type region 120A.
The NAD region 120B separates holes into electrons and holes, releases the holes to the P + type region 120A side, and accumulates the electrons in a depletion layer formed below the N type region 120B. The CCD vertical transfer register 130 includes a read gate region 15 on one side of the photodiode 120.
The read gate region 150 is provided to be separated by 0.
The signal charges accumulated in the lower layer of the photodiode 120 are read into the channel region of the CCD vertical transfer register 130 by controlling the gate potential of the CCD 120. A pixel isolation region 160 is formed on the other side of the photodiode 120 to block the leakage of signal charges to adjacent pixels.

On the N-type silicon substrate 110,
An insulating film 170A made of a silicon oxide film is formed, but unlike the conventional example, this insulating film 170A is removed by etching or the like in the light receiving region of the photodiode 120. A transfer electrode 180 made of a polysilicon film is formed on the upper layer of the insulating film 170A corresponding to the upper region of the CCD vertical transfer register 130, and a light shielding film 190 is formed on the upper layer of the transfer electrode 180 via an insulating film 170B. There is. The light shielding film 190 is made of, for example, a metal film such as aluminum, shields the upper portions of the CCD vertical transfer register 130 and the transfer electrode 180, and has an opening 190A corresponding to the light receiving region of the photodiode 20. As shown, the opening 190A of the light shielding film 190
The inner edge portion of is overlapped with the insulating film 170A and is arranged at a position facing the light receiving region of the photodiode 120. The light shielding film 190 is grounded to the silicon substrate 110 outside the image pickup area.

Then, such a photodiode 12
The light receiving region of 0 and the region extending over the upper surface of the light shielding film 190 are
A contact film 200 that connects the P + type region 120A of the photodiode 120 and the light shielding film 190 is provided. The contact film 200 is made of a refractory metal such as tungsten, and is formed so as to cover the entire light receiving portion of the photodiode 120 and partially cover the upper surface of the light shielding film 190. Although not shown in the figure, a plurality of upper wiring layers are formed on the upper layer of the light shielding film 190 via various interlayer insulating films, and color filters and microlenses are mounted on the upper wiring layers via a flattening film. ing.

Next, the function of the contact film 200 will be described. In the CCD solid-state imaging device of this example, the P + type region 120A of the photodiode 120 and the light shielding film 190 are electrically connected by holding the contact film 200 as described above, and are held at the same potential. Here, since the light shielding film 190 is grounded to the silicon substrate 110 and is held at the reference potential, the potential of the P + type region 120A of the photodiode 120 is imaged regardless of the increase / decrease of holes due to the increase / decrease in the amount of received light. It becomes uniform in the entire region, and the conventional potential gradient can be removed. The light shielding film 190 is made of an aluminum film or the like, and is directly formed on the P + type region 120A.
Since the silicon layer is deteriorated when it is brought into contact with the silicon layer, the contact film 200 made of tungsten or the like is used to prevent the silicon film from being deteriorated, and the light shielding film and the P + type region 120A of the photodiode 120 have the same potential. Hold on.

Further, such a contact film 200 is
By forming a sufficiently thin film, the attenuation of the light incident on the photodiode 120 can be made extremely small, the potential gradient of each pixel can be eliminated without causing a decrease in sensitivity, and an image output of a uniform level in the entire image can be obtained. It can be carried out. It is also possible to improve the saturation signal level by making the pixel potential uniform. The material of the contact film 200 is not limited to tungsten, and the thickness of the contact film 200 is optimized so that the required light transmittance can be obtained. Although the contact film 200 shown in FIG. 1 extends to the upper surface of the light shielding film 190, it does not necessarily have to have such a shape, and for example, the opening 190A of the light shielding film 190 may be used.
It may be formed so as to be in contact with the edge portion of.

Further, in the example shown in FIG. 1, the contact film 200 covering the entire light receiving portion of the photodiode 120 is provided, but as shown in FIG. 2, the contact film 210 contacting only the peripheral region of the light receiving portion is provided. May be. That is, the contact film 210 has an opening 210A at the center, and the opening 210A allows light to enter the photodiode 120 without being attenuated by the contact film 210. The other parts are shown in FIG.
The same elements are denoted by the same reference numerals and the description thereof will be omitted.

Further, the contact film as described above is not necessarily provided in all the unit pixels, but it is possible to obtain a sufficient effect even if it is provided only in a part of the unit pixels. Further, in this type of solid-state image pickup device, the color filter (incident light wavelength selection means) is provided as described above, and the contact is adjusted in accordance with the wavelength of light selected for each pixel by this color filter. The film thickness, shape, or material of the film may be selected and optimized. For example, if the contact film used has a strong attenuation at short wavelengths and a small attenuation at long wavelengths, the contact film should not be provided in the unit pixel that selects the short wavelength, and only in the unit pixel that selects the long wavelength. A contact film may be provided.

Recently, there has been proposed a solid-state image pickup device which obtains an image of a wide dynamic range by picking up and combining both a low luminance image pickup signal and a high luminance image pickup signal. Therefore, by providing the above-mentioned contact film corresponding to the pixel for imaging the low-luminance imaging signal,
It is possible to connect the light-shielding film and the photodiode without causing a problem of light attenuation by the contact film. Further, by more positively utilizing the light attenuating action of the contact film, by providing a contact film as a sensitivity lowering means in the pixel of the low brightness image pickup signal as described above, low brightness image pickup in which incident light is attenuated can be performed. It can also be realized.

[0020]

As described above, according to the solid-state image pickup device of the present invention, the contact film for connecting the light receiving surface of the photoelectric conversion element and the light shielding film is provided, and the light receiving surface of the photoelectric conversion element and the light shielding film are made the same. Since the photoelectric conversion element of each unit pixel can be contacted for each pixel because it is held at the potential, it is possible to eliminate the potential gradient of each pixel and perform image output at a uniform level in the entire image, and the saturation signal It is possible to improve the level.

[Brief description of drawings]

FIG. 1 is an abbreviated plan view and an aa line sectional view showing a configuration of each unit pixel in a CCD solid-state imaging device according to a first embodiment of the present invention.

FIG. 2 is an abbreviated plan view and a cross-sectional view taken along the line bb, showing the configuration of each unit pixel in a CCD solid-state imaging device according to a second embodiment of the present invention.

FIG. 3 is a schematic plan view showing a configuration of a CCD solid-state image sensor.

4A and 4B are an abbreviated plan view and a cross-sectional view taken along line cc showing the configuration of each unit pixel in a CCD solid-state image sensor according to a conventional example.

[Explanation of symbols]

110 ... Semiconductor substrate (silicon substrate), 120 ... Photodiode, 120A ... P + type region, 120B ...
... N-type area, 130 ... CCD vertical transfer register, 14
0 ... CCD horizontal transfer register, 150 ... readout gate area, 160 ... pixel separation area, 170A, 170
B ... Insulating film, 180 ... Transfer electrode, 190 ... Shading film, 190A ... Opening part, 200, 210 ... Contact film.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4M118 AA02 AA05 AB01 BA13 CA04                       CA40 DA03 FA06 FA20 FA28                       FA33 GB03 GB11 GC07 GD04                       GD07                 5F049 MA02 MB03 NA04 NA20 NB05                       QA03 QA20 RA02 RA08 RA10                       SE02 SE05 SE11 SE17 SS03

Claims (18)

[Claims] 1. A semiconductor substrate provided with a plurality of photoelectric conversion elements each of which constitutes a unit pixel and a charge transfer section for transferring signal charges generated by the photoelectric conversion elements,
In a solid-state imaging device in which a transfer electrode of the charge transfer unit is provided, and a light-shielding film having an opening corresponding to the light receiving region of the photoelectric conversion element is further provided on the transfer electrode, a light receiving surface of the photoelectric conversion element is provided. A contact film for connecting the light-receiving surface of the photoelectric conversion element and the light-shielding film is provided in at least a part of the light-shielding film, and the light-receiving surface of the photoelectric conversion element and the light-shielding film are held at the same potential. Characteristic solid-state image sensor. 2. The photoelectric conversion element is a photodiode having a hole accumulation region provided on the surface of the semiconductor substrate and a charge generation region provided below the hole accumulation region, and the contact film is the hole The solid-state imaging device according to claim 1, wherein the solid-state imaging device is in contact with the surface of the storage region. 3. The solid-state imaging device according to claim 1, wherein the contact film is formed so as to cover the entire light receiving surface of the photoelectric conversion device. 4. The solid-state imaging device according to claim 1, wherein the contact film is formed in a state of being in contact with a part of a light receiving surface of the photoelectric conversion element. 5. The solid-state imaging device according to claim 1, wherein the contact film is formed in a state of being in contact with an edge portion of the opening of the light shielding film. 6. The contact film is formed of a metal film made of a material different from that of the light shielding film.
The solid-state image sensor according to claim 1. 7. The solid-state image sensor according to claim 1, wherein the contact film is formed of a refractory metal film. 8. The solid-state image sensor according to claim 1, wherein the contact film is formed of a tungsten film. 9. The solid-state image sensor according to claim 1, wherein the contact film is formed to have a film thickness that allows light to pass therethrough. 10. The solid-state imaging device according to claim 1, wherein the contact film is provided for a photoelectric conversion element of a part of the unit pixels of the plurality of unit pixels provided on the semiconductor substrate. 11. The plurality of unit pixels are formed on a semiconductor substrate in two.
A plurality of CCD vertical transfer registers, which are arranged in a dimensional array, in which the charge transfer sections are provided in the column direction of the plurality of unit pixels, and which read out signal charges from each pixel and transfer them in the vertical direction; 2. The solid-state image sensor according to claim 1, further comprising one or a plurality of CCD horizontal transfer registers that receive the signal charges transferred from the CCD and transfer the signal charges in the horizontal direction. 12. The solid-state image sensor according to claim 11, further comprising an output unit that converts the signal charge transferred from the CCD horizontal transfer register into an electric signal and outputs the electric signal. 13. The solid-state image sensor according to claim 1, further comprising a wavelength selection unit that selects a wavelength of light incident on the plurality of unit pixels. 14. The solid-state image pickup device according to claim 13, wherein the contact film is provided only in a unit pixel in which a specific wavelength is selected by the wavelength selection unit. 15. The solid-state imaging device according to claim 13, wherein at least one of the film thickness, shape, and material of the contact film is selected according to the wavelength selected by the wavelength selecting means. 16. A unit pixel of a part of the plurality of unit pixels is a unit pixel which is detected by lowering the sensitivity, and the contact material is provided only on the unit pixel which is detected by lowering the sensitivity. The solid-state image sensor according to claim 1. 17. A part of the plurality of unit pixels is a unit pixel that is detected by lowering the sensitivity, and the contact material is provided as a sensitivity lowering unit of the unit pixel that is detected by lowering the sensitivity. The solid-state image sensor according to claim 1. 18. The solid-state image sensor according to claim 1, wherein the light shielding film is grounded to the semiconductor substrate.