JP2003209245A - Solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve light-receiving sensitivity, to increase a quantity of charge handled by a vertical transfer register, and to enhanced and electronic shutter function and an discharging function of excessive charge, by magnifying a sensor fill factor. <P>SOLUTION: Light-receiving regions 120A of a photo sensor part 120 and separation parts 130, by which he light-receiving regions 120A are separated one another, are exclusively formed on a first surface (light-receiving surface) 100 of a CCD solid-state imaging device. Each of vertical transfer registers 210 and each of overflow drain parts 220 are formed in parallel in each region corresponding to each pixel raw of the photo sensor part 120 on a second surface (driving electrode surface) 200 of the CCD solid-state imaging device. The vertical transfer registers 210 and the overflow drain parts 220 are controlled independently. Signal charge of the photo sensor part 120 is read out and output by controlling the vertical transfer registers 210. An electronic shutter function is realized by controlling the overflow drain parts 220. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solid-state image sensor used in various image sensors.

[0002]

2. Description of the Related Art A conventional CCD solid-state image pickup device includes a plurality of photosensor portions which form image pickup pixels on one surface of a semiconductor substrate, and a vertical type which transfers signal charges accumulated in the photosensor portions for each row of the photosensor portions. The transfer register and the horizontal transfer register for transferring the signal charges transferred by the vertical transfer register to the output section are arranged. FIG. 6 is a plan view showing the outline of such a CCD solid-state image sensor. Photosensor sections 20 each having a photoelectric conversion function are arranged in a two-dimensional matrix in the imaging area 10 provided in the center of the imaging element chip. A plurality of vertical transfer lines are arranged along each column of the photosensor sections 20. A register 30 is provided. Then, a horizontal transfer register 40 is arranged outside the imaging region 10 so as to be connected to an end of each vertical transfer register 30, and an output unit 50 having a charge-signal conversion function is provided at an end of the horizontal transfer register 40. Is provided.

FIG. 7 is an enlarged plan view showing the arrangement of elements in the image pickup area 10 of the CCD solid-state image pickup element shown in FIG. As shown in the figure, the light receiving regions 22 of the photo sensor unit 20 described above are arranged in a two-dimensional array, and one side of each light receiving region 22 is a read gate unit for reading out the signal charge of the photo sensor unit 20 to the vertical transfer register 30. 60 is arranged, and the vertical transfer register 30 is arranged via the gate portion 60. Further, a separating section 70 is provided on the other side of the light receiving area 22 of the photo sensor section 20 to prevent leakage of signal charges between adjacent image pickup pixels and prevent color mixture.

However, in the above-mentioned conventional CCD solid-state image pickup device, the light receiving region 22 of the photosensor unit 20, the read gate unit 60, and the vertical transfer register 30 are arranged in parallel on one surface of the image pickup device chip. The arrangement area (sensor aperture ratio) of the light receiving region 22 cannot be increased with respect to the chip size, which is an obstacle to improving the light receiving sensitivity. Further, since the layout area of the vertical transfer register 30 is also restricted, it is difficult to increase the amount of charge handled. Therefore, recently, the light receiving area 22 of the photosensor section 20 is arranged on one side of the semiconductor substrate so that the light receiving amount area 22 of the photosensor section 20 and the arrangement area of the vertical transfer register 30 are increased without increasing the chip size. ,
By arranging the vertical transfer registers 30 on the opposite surface, both surfaces of the semiconductor substrate can be effectively used to expand the light receiving area 22 of the photosensor section 20 and the arrangement area of the vertical transfer registers 30. A so-called back-illuminated solid-state image sensor has been proposed (for example, Japanese Laid-Open Patent Publication No. 2-212058).
No. 001-257337). In this back-illuminated solid-state imaging device, the light-receiving region of the photosensor portion can be formed by using almost the entire area of the imaging region provided on one surface of the semiconductor substrate, and the sensor sensitivity can be improved without increasing the chip size. , The amount of charge handled by the vertical transfer register can be increased.

[0005]

In the backside illumination type solid-state image pickup device disclosed in Japanese Patent Laid-Open No. 2001-257337 mentioned above, a virtual NPN is used by using a laminated structure in a silicon substrate which constitutes an image pickup device chip. A transistor is formed, and the vertical overflow drain functions by the operation of the transistor to discharge the excess charge of the photosensor portion from the transparent electrode on the light receiving surface side. That is, in this backside illumination type solid-state image pickup device, the vertical transfer register is arranged in a state that almost entirely occupies the region of the silicon substrate opposite to the image pickup region where the photosensor portion is provided. The excess charges of the photo sensor section are discharged to the light receiving area side which avoids the vertical transfer register.

In view of such an actual situation, the present invention provides a structure for arranging the light receiving surface of the photo sensor portion and the vertical transfer register on both sides of the semiconductor substrate to efficiently discharge the excess charge of the photo sensor portion. We propose a vertical overflow drain structure, and its purpose is to improve the light receiving sensitivity by increasing the sensor aperture ratio and increase the amount of charge handled in the vertical transfer register, as well as the function of discharging excess charge and the electronic shutter. An object of the present invention is to provide a solid-state image sensor whose function can be easily enhanced.

[0007]

According to the present invention, a semiconductor substrate and two-dimensionally arrayed in an image pickup region of the semiconductor substrate are provided.
A plurality of photosensor units each of which constitutes an image pickup pixel having a photoelectric conversion function, a vertical transfer register for transferring the signal charges accumulated in the photosensor unit for each photosensor unit column, and a vertical transfer register for transferring the signal charges. In a solid-state imaging device having a horizontal transfer register for transferring signal charges to an output part and an overflow drain part for discharging surplus charges of the photosensor part in the depth direction of the semiconductor substrate, a first surface side of the semiconductor substrate is provided. The plurality of photosensor units are provided, and the vertical transfer register and the overflow drain unit are provided in parallel on the second surface side of the semiconductor substrate for each region corresponding to each pixel column of the photosensor unit. And

According to the solid-state imaging device of the present invention, a plurality of photosensor portions are provided on the first surface side of the semiconductor substrate, and vertical transfer is performed on the second surface side for each area corresponding to each pixel column of the photosensor portion. Since the register and the overflow drain portion are provided in parallel, the light receiving area of the photosensor portion can be arranged on the first surface of the semiconductor substrate by using almost the entire image pickup area, and the light receiving area can be made larger than the chip size. Therefore, it can contribute to the improvement of the sensor sensitivity. Further, on the second surface of the semiconductor substrate, a sufficient layout area of the vertical transfer register can be taken, which contributes to securing a sufficient amount of charge to be handled, and the overflow drain portion can be arranged using the remaining region. It is possible to efficiently guide the excess charges of the photo sensor unit caused by the excessive light receiving amount generated on one surface to the second surface side on the opposite side to efficiently discharge the charges. That is, since the overflow drain portion can secure a sufficient discharge path of the excess charge for each photosensor portion and an effective vertical overflow drain structure can be obtained, the excess charge of the photosensor portion overflows to the vertical transfer register side. Such a thing can be easily prevented. Further, an electronic shutter function can be easily realized by using such an overflow drain section.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. 1 is an enlarged plan view showing an arrangement of elements in an image pickup area of a first surface of a CCD solid-state image pickup element according to an embodiment of the present invention, and FIG. 2 is a C diagram shown in FIG.
FIG. 3 is an enlarged plan view showing an element arrangement in a region corresponding to FIG. 1 on the second surface of the CD solid-state imaging element. As shown in FIG.
On the first surface (light-receiving surface) 100 of the CCD solid-state image sensor according to the present embodiment, the light-receiving area 120A of the photosensor section 120 and the separation section for separating the respective light-receiving areas 120A are arranged in a two-dimensional array over the entire imaging area 110. 130 are arranged. Compared to the configuration shown in FIG. 7, the read gate unit 60
The area (sensor aperture ratio) of the light-receiving region 120A is relatively increased due to the elimination of the vertical transfer register 30.

Further, as shown in FIG. 2, the second surface (driving electrode surface) of the CCD solid-state image sensor according to the present embodiment.
In 200, a vertical transfer register 210 and an overflow drain section 220 are arranged. That is, the vertical transfer register 210 and the overflow drain unit 220.
Are formed in strips extending in the vertical direction (indicated by the arrow A), and are provided in parallel in each region corresponding to each pixel column in the vertical direction of the photo sensor unit 120, and in the horizontal direction. The vertical transfer registers 210 and the overflow drains 220 are alternately arranged. Also,
Vertical transfer register 210 and overflow drain unit 2
Separation parts 130A and 230 are linearly arranged between the two and 20 to electrically separate the two. Of these, the separation unit 130A corresponds to the separation unit 130 on the first surface shown in FIG. 1, and is the first separation unit that separates each pixel column of the photosensor unit 120. The separation unit 230 is a second separation unit that separates the vertical transfer register 210 and the overflow drain unit 220 in each pixel column of the photo sensor unit 120.

Although the overflow drain portion 220 is shown exposed on the surface in FIG. 2, in reality, since the transfer electrode of the vertical transfer register 210 is arranged on this second surface, the overflow drain portion 220 is exposed. Part 220
Shall be placed in a state of being covered with an insulating film or the like. Further, a wire (not shown) for discharging electric charge is connected to the overflow drain portion 220. Further, the bias voltage of the vertical transfer register 210 and the bias voltage of the overflow drain section 220 as described above can be individually controlled by a bias voltage control section provided in a drive circuit (not shown). Further, also in the CCD solid-state image sensor according to the present embodiment, the imaging area 110
A horizontal transfer register and an output unit are provided outside of, but the description thereof will be omitted because they have substantially the same configuration as the conventional one.

FIG. 3 is a partial cross-sectional view showing the internal structure of the CCD solid-state image sensor according to the present embodiment.
The cross section at line a is shown. Also, FIG. 4 and FIG.
4A and 4B are explanatory views showing an impurity distribution and a potential structure of the CCD solid-state imaging device in the present embodiment, FIG. 4 shows an impurity distribution and a potential structure in a cross-sectional area of the vertical transfer register 210, and FIG. 3 shows the impurity distribution and potential structure in the cross-sectional area of.

First, as shown in FIG. 3, the semiconductor substrate 300 is provided with the above-mentioned separating portions 130 and 230, and the regions separated by these separating portions 130 and 230 are exposed on the first surface 100 side. The sensor unit 120 is provided,
A vertical transfer register 210 and an overflow drain 220 are provided on the second surface 200 side. The photo sensor unit 120 includes a lower N− type photoelectric conversion layer 122 and an upper P ++ type light receiving layer 1 on the first surface 100 side of the semiconductor substrate 300.
21 is provided to form a photodiode.
Note that a color filter, a microlens, or the like is attached to the top surface of the photosensor portion 120 with an insulating film or a protective film interposed therebetween, but it is omitted here. Photo sensor unit 120
The light incident on the P ++ type light receiving layer 121 passes through the N− type photoelectric conversion layer 122, is converted into a signal charge, and is accumulated in the lower depletion layer.

Further, the vertical transfer register 210 and the overflow drain section 220 are formed in the area partitioned by the separating section 230 described above. The vertical transfer register 210 is formed of an N + type layer 211, a P type layer 212, and an N + type layer 213 that are sequentially formed in the direction from the first surface 100 to the second surface 200. Note that transfer electrodes and the like are arranged on the upper surface of the N + type layer 213 of the vertical transfer register 210 via an insulating film, but they are omitted here. Figure 4
As shown in (B) and (C), in the vertical transfer register 210, a virtual gate is configured by a laminated structure of an N + type layer 211, a P type layer 212, and an N + type layer 213, and the photosensor is controlled by controlling a bias voltage. By controlling the potential at the boundary with the portion 120, the gate potential is controlled and the signal charge is accumulated and read.

On the other hand, the overflow drain section 220
Is an N + type layer 221, a P type layer 222, and an N ++ type layer 223, which are sequentially formed from the first surface 100 to the second surface 200.
Is formed. As shown in FIG. 5B, in the overflow drain part 220, the overflow barrier O is formed at the boundary with the photo sensor part 120 due to the laminated structure of the N + type layer 221, the P type layer 222, and the N ++ type layer 223.
Although FB is formed, the potential thereof is lower than the gate potential of the vertical transfer register 210 during charge accumulation due to the difference in impurity concentration.
The electric charges overflowing over the overflow transfer gate 210 flow into the overflow drain part 220 side, not in the read gate part on the vertical transfer register 210 side, and are discharged to the outside from the overflow drain part 220. Further, as shown in FIG. 5C, by controlling the bias voltage of the overflow drain part 220 to control the potential at the boundary with the photosensor part 120, the potential of the overflow barrier OFB is lowered to lower the photosensor part 120. It also functions as an electronic shutter that forcibly discharges the accumulated charge of.

Although specific embodiments of the present invention have been described above, the present invention is not limited to the examples shown in FIGS. 1 to 5, and various modifications can be made without departing from the spirit of the present invention. It is possible. For example, the layer structure, impurity distribution, potential structure, etc. of each part shown in FIGS. 3 to 5 are merely examples for obtaining the function of the present invention, and other methods can be adopted. Further, the present invention is most suitable for the solid-state image pickup device using the CCD as described above.
It can also be applied to a MOS sensor type image pickup device and the like.

[0017]

As described above, according to the solid-state image pickup device of the present invention, a plurality of photosensor portions are provided on the first surface side of the semiconductor substrate, and the second surface side is provided with each pixel column of the photosensor portion. Since the vertical transfer register and the overflow drain portion are provided in parallel for each corresponding region, the light receiving area of the photosensor can be made larger than the chip size on the first surface of the semiconductor substrate, which can contribute to improvement in sensor sensitivity. On the second surface of the semiconductor substrate, a sufficient layout area of the vertical transfer register can be taken, which contributes to securing a sufficient amount of charge to be handled, and an overflow drain section can be arranged using the remaining area, and a surplus of the photo sensor section can be provided. The charge can be discharged efficiently. Further, an electronic shutter function can be easily realized by using such an overflow drain section. Therefore, it is possible to provide an element structure that is extremely advantageous in downsizing, upsizing, increasing the number of pixels, increasing the speed, and improving the quality of the solid-state imaging element.

[Brief description of drawings]

FIG. 1 is an enlarged plan view showing an element arrangement in an image pickup area of a first surface of a CCD solid-state image pickup element according to an embodiment of the present invention.

FIG. 2 is a view showing a second surface of the CCD solid-state imaging device shown in FIG.
FIG. 6 is an enlarged plan view showing an element arrangement in a region corresponding to.

FIG. 3 is a partial cross-sectional view showing the internal structure of the CCD solid-state imaging device shown in FIG.

FIG. 4 is an explanatory diagram showing an impurity distribution and a potential structure in a cross-sectional area of a vertical transfer register of the CCD solid-state imaging device shown in FIGS.

5 is an explanatory diagram showing an impurity distribution and a potential structure in a cross-sectional region of an overflow drain portion of the CCD solid-state imaging device shown in FIGS.

FIG. 6 is a plan view showing an outline of a conventional CCD solid-state imaging device.

7 is an enlarged plan view showing an element arrangement in an image pickup area of the CCD solid-state image pickup element shown in FIG.

[Explanation of symbols]

100 ... First surface (light receiving surface), 110 ... Imaging area, 1
20 ... Photo sensor part, 120A ... Light receiving area, 1
30, 130A, 230 ... Separation part, 200 ... Second surface (driving electrode surface), 210 ... Vertical transfer register, 220
...... Overflow drain part.

Claims (8)

[Claims] 1. A semiconductor substrate, a plurality of photosensor portions which are two-dimensionally arranged in an image pickup region of the semiconductor substrate and which form image pickup pixels each having a photoelectric conversion function, and signals accumulated in the photosensor portion. A vertical transfer register that transfers charges for each photosensor unit column, a horizontal transfer register that transfers the signal charges transferred by the vertical transfer register to an output unit, and excess charges of the photosensor unit in the depth direction of the semiconductor substrate. In the solid-state imaging device having an overflow drain part that discharges to a plurality of photosensor parts, the plurality of photosensor parts are provided on the first surface side of the semiconductor substrate, and the pixel columns of the photosensor part are provided on the second surface side of the semiconductor substrate. Solid-state imaging device, wherein the vertical transfer register and the overflow drain portion are provided in parallel for each region corresponding to 2. A first separating unit that horizontally separates the first surface and the second surface of the semiconductor substrate for each pixel column of the photosensor unit, and the photosensor on the second surface of the semiconductor substrate. A second separating unit that horizontally divides a region corresponding to each pixel column of the unit into two, and the vertical transfer register and the overflow are provided in the regions divided by the first separating unit and the second separating unit. The solid-state imaging device according to claim 1, wherein the drain portions are arranged alternately in the horizontal direction. 3. The solid-state imaging device according to claim 1, wherein the overflow drain portion is provided in a buried state which is not exposed on the second surface of the semiconductor substrate. 4. The solid-state image pickup device according to claim 1, wherein the transfer electrode of the vertical transfer register is provided on the second surface of the semiconductor substrate. 5. The solid-state imaging device according to claim 1, further comprising a bias voltage control unit that individually controls a bias voltage of the vertical transfer register and a bias voltage of the overflow drain section. 6. A constant difference is provided between the potential of the overflow barrier section between the photosensor section and the overflow drain section and the potential of the read gate section between the photosensor section and the vertical transfer register. ,
6. The solid-state image sensor according to claim 5, wherein the excess charges of the photo sensor unit are discharged to the overflow drain unit side with the read gate unit closed. 7. The read gate section is opened to control the potential of the read gate section between the photosensor section and the vertical transfer register based on the charge read timing to the vertical transfer register. 7. The solid-state image pickup device according to claim 6, wherein the accumulated charges are read out to the vertical transfer register side. 8. An electronic shutter function for forcibly discharging the electric charge of the photo sensor unit by controlling the potential of the overflow barrier unit between the photo sensor unit and the overflow drain unit based on shutter timing. The solid-state image sensor according to claim 6.