JP2003258234A - Solid-state image sensor and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a solid state image sensor in which read-out voltage is lowered, unnecessary read-out of charges is prevented at the time of charge transfer, and generation of noise due to application of a high read-out voltage to the transfer electrodes is prevented. <P>SOLUTION: Photosensors 104 are arranged in matrix on a semiconductor substrate 106 and a vertical charge transfer register 4 is extended for each array of photosensors. A first transfer electrode 6 of the vertical charge transfer register 4 does not extend to the read-out gate 130 side, and the side 18 of a light shielding film 14 composed of a metallic material is arranged on the read-out gate 130 through an insulation film 126. When charges are read out from the photosensor 104, the light shielding film 14 is used as a read-out gate electrode and a read-out voltage is applied thereto. Since the side 18 functioning as the gate electrode extends over the entire width of the read-out gate 130, the read-out voltage can be lowered as compared with the conventional one. Furthermore, a voltage is not applied to the read-out gate 130 at the time of transfer and a high voltage is not required to be applied to the transfer electrode at the time of reading out charges. <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 and a method for driving the solid-state image pickup device, and more particularly to a technique for reading signal charges from an optical sensor to a charge transfer register.

[0002]

2. Description of the Related Art FIG. 3 is a partial plan view showing a conventional solid-state image pickup device, and FIG. 4 is a partial sectional side view showing the conventional solid-state image pickup device. Note that FIG. 4 shows a cross section taken along line AA ′ in FIG. As shown in FIG. 3, the conventional general solid-state imaging device 102 includes a large number of optical sensors 104 arranged in a matrix on a semiconductor substrate 106.
For each column 04, a vertical charge transfer register 108 is arranged adjacent to the column of the photosensors 104 and extends in the direction of the photosensor column. The vertical charge transfer register 108 includes first and second transfer electrodes 110, 112, which are arranged alternately in the direction of the column of photosensors 104, the boundary between the first and second transfer electrodes 110, 112 being: In the column direction of the photosensors 104, the photosensors 104 are located at the middle position. Further, the first and second transfer electrodes 110 and 112 in the same row are commonly connected by the wiring portions 114 and 116. The wiring portion 114 of the first transfer electrode 110 is formed on the wiring portion 116 of the second transfer electrode 112 via an insulating film,
The wiring portion 116 is formed on the surface of the semiconductor substrate 106 via an insulating film.

Explaining the sectional structure, as shown in FIG. 4, a P-type layer 118 is formed in an N-type semiconductor substrate 106.
Is formed, an N-type buried channel layer 120 constituting the vertical charge transfer register 108 is formed on the upper layer of the P-type layer 118, and an N-type layer 122 and a P-type layer 124.
An optical sensor 104 is provided. A P-type layer 121 is formed below the buried channel layer 120. The insulating film 12 is formed on the surface of the semiconductor substrate 106.
6 is formed, and the first transfer electrode 110 is arranged on the buried channel layer 120 via the insulating film 126 at the position of the vertical charge transfer register 108. On the transfer electrode, a light-shielding film 1 that covers the transfer electrode
28 is formed via an insulating film. The light shielding film 128 is omitted in FIG.

The substrate surface portion between the buried channel layer 120 of the vertical charge transfer register 108 and the photosensor 104 is a read gate portion 130, while the substrate surface opposite to the read gate portion 130 with the photosensor 104 interposed therebetween. The part is the element isolation part 132. In the first transfer electrode 110 (second transfer electrode 112), the corresponding side portion on the photosensor 104 side has the buried channel layer 120.
Has a structure in which the lower surface extends from the side portion to the optical sensor 104 side, the lower surface faces the read gate section 130 via the insulating film 126, and the transfer electrode also serves as the read gate electrode of the read gate section 130.

When the signal charges received by the photosensor 104 are read from the photosensor 104 to the vertical charge transfer register 108, a high voltage read voltage is applied to the first transfer electrode 110 which also serves as a read gate electrode. As a result, the signal charges are applied to the readout gate unit 13 as a result.
0 to the embedded channel layer 120 of the vertical charge transfer register 108.

[0006]

However, such a conventional solid-state image pickup device 102 has the following problems. That is, when the signal charge generated by the photosensor 104 is read to the vertical charge transfer register 108, in order to sufficiently read the signal charge, a read voltage is applied to the read gate unit 130 in a wide range in the column direction of the photosensor 104. Is effective. Therefore, it is possible to apply the read voltage not only to the first transfer electrode 110 but also to the second transfer electrode 112. But the second
Since the wiring portion 116 of the transfer electrode 112 is formed on the surface of the semiconductor substrate 106 via the insulating film, when a read voltage is applied to this portion, the adjacent optical sensor 10
The signal charges also move between four, resulting in color mixing in the vertical direction in the captured image.

Therefore, in the conventional solid-state image sensor 102,
In the case of miniaturizing pixels for the purpose of increasing the number of pixels or downsizing, the width of the read gate unit 130 (the length of the photosensor 104 in the column direction) is narrowed, and the signal charge read efficiency is reduced. As a result, there is no choice but to deal with the problem by increasing the read voltage, resulting in an increase in power consumption.

Further, the first transfer electrode 110 also serves as the read gate electrode as described above, and the read gate portion 1
Vertical charge transfer register 1 because it extends over 30
Even during charge transfer in 08, the read gate unit 130
A certain amount of voltage is applied to. Therefore, during the charge transfer, the vertical charge transfer register 10 from the optical sensor 104 is transferred.
In order to prevent blooming and smear caused by the leakage of the signal charges to 8, the read gate section 130 must be formed long and a sufficient distance between the photosensor 104 and the vertical charge transfer register 108 must be secured. But,
Such a structure is disadvantageous for miniaturization of pixels.

Further, in the conventional solid-state image sensor 102,
When reading the signal charge, a read voltage higher than that at the time of transfer is applied to the first transfer electrode 110, so that the buried channel layer 12 forming the vertical charge transfer register 108 is applied.
The potential of 0 becomes high. As a result, when the pixel is miniaturized, a high electric field is applied to the element isolation section 132 and charges move through the element isolation section 132, causing random noise and degrading image quality. As the pixels are miniaturized, the high electric field becomes stronger and random noise is more likely to occur.

The present invention has been made to solve such a problem, and an object thereof is to lower the read voltage when reading signal charges from the photosensor to the charge transfer register and to reduce the charge during charge transfer. It is an object of the present invention to provide a solid-state image sensor and a method for driving the solid-state image sensor, which can prevent leakage and can avoid the generation of noise due to application of a high voltage for reading charges to the transfer electrodes.

[0011]

In order to achieve the above-mentioned object, the present invention achieves the above objects, photosensors in rows, charge transfer registers extending along the rows of the photosensors, the photosensors and the charge transfer registers. And a light-shielding film that covers the charge transfer register and that reads out the signal charge generated by the photosensor that is received by the photosensor to the charge transfer register and is formed on the semiconductor substrate. In the solid-state imaging device, which transfers the signal charge generated by each sensor by the charge transfer register, the light-shielding film is formed of a conductive material, and a part of the light-shielding film is opposed to the surface of the readout gate unit via an insulating film. It is characterized by being

The present invention also includes a row of optical sensors,
A charge transfer register extending along the row of the photosensors, and a read gate that is interposed between the photosensors and the charge transfer registers and reads out signal charges generated by the photosensors to the charge transfer registers. Department,
A light-shielding film covering the charge transfer register is formed on a semiconductor substrate, and the light-shielding film is formed of a conductive material while the signal charges generated by the photosensors are transferred by the charge transfer register. And a method for driving a solid-state imaging device, a part of which faces the surface of the read gate portion through an insulating film,
The signal charge generated by the photosensor is read to the charge transfer register through the read gate unit by applying a read voltage to the light shielding film.

In the solid-state image pickup device of the present invention, since a part of the light-shielding film made of a conductive material faces the upper surface of the read gate portion via the insulating film, the signal charges received by the photosensor are charged. When reading out to the transfer register, a read-out voltage may be applied to the light-shielding film based on the driving method of the solid-state imaging device of the present invention. The light-shielding film can be formed over the entire width of the read gate portion, and therefore the signal charges can be sufficiently read out even if the voltage applied to the light-shielding film is low. That is, according to the present invention, the read voltage can be lowered, and thus the power consumption of the solid-state imaging device can be reduced.

Further, in the present invention, the transfer electrode of the charge transfer register only has to function as a transfer electrode,
Since it does not need to be formed on the read gate portion, no voltage is applied to the read gate portion during charge transfer, and leakage of charges can be avoided. As a result, blooming and smear can be prevented even when pixels are miniaturized. Further, at the time of charge transfer, for example, a negative voltage can be applied to the light-shielding film to more reliably prevent unnecessary reading of signal charges.

In the present invention, it is not necessary to apply a high voltage for reading out the signal charge to the transfer electrode.
A high electric field is locally generated, and the charge is moved through the element isolation portion adjacent to the vertical charge transfer register to generate random noise. Therefore, good image quality can be obtained.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partial sectional side view showing an example of a solid-state image sensor according to the present invention, and FIG. 2 is a partial plan view of an embodiment. 1 and 2, the same elements as those of FIGS. 3 and 4 are designated by the same reference numerals. In addition,
FIG. 1 shows a cross section taken along the line AA ′ in FIG. Hereinafter, an example of the solid-state imaging device of the present invention will be described with reference to these drawings, and at the same time, an embodiment of a method for driving the solid-state imaging device of the present invention will be described.

As shown in FIG. 2, in the solid-state image pickup device 2 of the embodiment, a large number of optical sensors 104 are provided on the semiconductor substrate 1.
06 are arranged in a matrix, and the vertical charge transfer registers 4 are arranged for each row of the photosensors 104 adjacent to the row of the photosensors 104 in the direction of the photosensor row. The vertical charge transfer register 4 includes first and second transfer electrodes 6, 8 which in turn are photosensors 10.
They are arranged in the direction of four columns. Also, the first and second
The transfer electrodes 6 and 8 of the
0, 12 are connected in common, the wiring portion 10 of the first transfer electrode 6 is formed on the wiring portion 12 of the second transfer electrode 8 via an insulating film, and the wiring portion 12 is an insulating film. It is formed on the surface of the semiconductor substrate 106 via.

Further, as shown in FIG. 4, the P-type layer 11 is formed in the N-type semiconductor substrate 106 which constitutes the solid-state image pickup device 2.
8 is formed, and an N-type buried channel layer 120 that constitutes the vertical charge transfer register 4 and an optical sensor 104 that includes an N-type layer 122 and a P-type layer 124 are provided on the upper layer portion of the P-type layer 118. Has been. A P-type layer 121 is formed below the buried channel layer 120. An insulating film 126 is formed on the surface of the semiconductor substrate 106.
And an insulating film 126 is formed on the buried channel layer 120 at the location of the vertical charge transfer register 4.
The first transfer electrodes 6 are arranged via the. A light shielding film 14 made of a conductive material such as aluminum is formed on the transfer electrode via an insulating film.
As shown in FIG. 2, the light-shielding film 14 covers the first and second transfer electrodes 6 and 8 and the wiring portions 10 and 12, while having an opening 16 at a position on the photosensor 104. ing. The substrate surface portion between the buried channel layer 120 of the vertical charge transfer register 4 and the optical sensor 104 is a read gate portion 130, while the optical sensor 10 is provided.
The surface of the substrate on the opposite side of the readout gate section 130 with the element 4 interposed therebetween serves as an element isolation section 132.

Then, the solid-state image pickup device 2 of the present embodiment example
Then, as shown in FIG. 1, the transfer electrode is
The side of the corresponding optical sensor 104 is the optical sensor 104.
The side portion 18 of the light-shielding film 14 is not extended to the side, and the lower surface of the side portion 18 is arranged so as to face the surface of the read gate portion 130 via the insulating film 126, and also functions as a read gate electrode. .

In the solid-state image pickup device 2 having the above-mentioned structure, when the signal charge received by each photosensor 104 is read out to the vertical charge transfer register 4, the first transfer electrode of the vertical charge transfer register 4 is read. A high level voltage is applied to 6 and a low level voltage is applied to the second transfer electrode 8. Then, a high level voltage is applied to the light shielding film 14 as the read gate electrode. This allows the optical sensor 1
The signal charge generated by 04 is read out to the buried channel layer 120 below the first transfer electrode 6 of the vertical charge transfer register 4 through the read gate unit 130.

Here, as can be seen from FIG. 2, the light shielding film 1
Since the side portion 18 of the No. 4 extends over the entire width W of the read gate portion 130 (FIG. 1), the read voltage applied to the light-shielding film 14 is applied to the entire read gate portion 130, and the voltage is applied. Since the area becomes large, the signal charges can be sufficiently read out even at a voltage lower than that of the conventional one. Therefore, the power consumption can be reduced by lowering the read voltage. Further, in the boundary portion 104A between the optical sensors 104, the light-shielding film 14 has the wiring portions 10 and 12
Since it is formed on the above, by applying a read voltage to the light shielding film 14, the signal charges are not mixed between the photosensors 104 that are vertically adjacent to each other in FIG. .

After the signal charges are read out, four-phase transfer clocks φV1 to φV are applied to the first and second transfer electrodes 6 and 8.
4 is applied to sequentially transfer the signal charges on the buried channel layer 120 in the extending direction of the vertical charge transfer register 4. At this time, since the first and second transfer electrodes 6 and 8 are not formed on the read gate section 130 as in the conventional case, the voltage of the transfer clock is not applied to the read gate section 130 during charge transfer. Therefore, even when pixels are miniaturized, leakage of charges can be avoided, and blooming and smear can be prevented.

Further, it is also effective to set the voltage applied to the light-shielding film 14 at the time of charge transfer to a negative voltage, not just 0V. That is, if a negative voltage is applied to the light-shielding film 14 at the time of charge transfer, when the transfer clock is applied to the first and second transfer electrodes 6 and 8, the read gate unit 130 is affected by the voltage of the transfer clock. Even if an electric field is generated, it can be canceled out, and charge leakage
It can be avoided more reliably.

Further, in the present embodiment, it is not necessary to apply a high voltage for reading the signal charge to the first and second transfer electrodes 6 and 8, so that the buried channel layer 1 is formed.
The potential of 20 does not become particularly high. Therefore, even if the pixels are miniaturized, a high electric field is locally applied to the element isolation section 132 at the time of reading out the signal charge, and the electric charge is moved through the element isolation section 132. As a result, random noise is not generated, which is excellent. Image quality is obtained.

Since the signal charges can be efficiently read out by using the light-shielding film 14 as a read-out electrode, it is easy to miniaturize the pixel. Further, since the transfer voltage is not applied to the read gate section 130 during the charge transfer, it is not necessary to lengthen the read gate section 130, and also in this respect, miniaturization is facilitated. Further, it is not necessary to apply a high voltage for reading to the transfer electrodes, and even if the pixel is miniaturized, a high electric field is not applied to the element isolation portion 132, which is advantageous for the pixel miniaturization.

In the present embodiment, since the light shielding film 14 also serves as the read gate electrode, the read voltage is applied to the read gate section 130 of each photosensor 104 at once, and the all-optical sensor 104 must be used. From the same time, the signal charges are read out to the vertical charge transfer register 4. However, even with such a configuration, it is easy to transfer the signal charges by the interlace method.

That is, at the time of reading the signal charge, of the transfer clocks φV1 to φV4 shown in FIG.
1, φV3 is high level, and φV2 and φV4 are low level. As a result, the signal charges read from the photosensor 104 are accumulated under the first transfer electrodes 6 (A) and (B). Then, for example, for even fields,
Before starting the transfer of signal charges, first transfer clock φV
Switch 4 to high level. As a result, the signal charges accumulated under the first transfer electrodes 6 (A) and (B) are transferred to the first transfer electrode 6 (A), the second transfer electrode 8 (A), and the first transfer electrode 6 (A). Underneath 6 (B) accumulates and mixes. After that, the signal charges mixed as described above are sequentially transferred by the normal four-phase clocks φV1 to φV4.

Also in the case of an odd field, when the signal charges are read with φV1 and φV3 at the high level and φV2 and φV4 at the low level as described above, the signal charges are transferred to the first transfer electrodes 6 (B) and (C). Accumulate below. Next, in the case of this odd field, the transfer clock φV2 is switched to the high level. As a result, the first transfer electrode 6 (B),
(C) The signal charge accumulated below is transferred to the first transfer electrode 6
(B), the second transfer electrode 8 (B), and the whole under the first transfer electrode 6 (C) are accumulated and mixed. afterwards,
The signal charges mixed as described above are sequentially transferred by the normal four-phase clocks φV1 to φV4. That is, the signal charges of the photosensors 104 (A) and (B) are mixed in the even field, and the photosensor 1 is mixed in the odd field.
Since the signal charges of 04 (B) and (C) are mixed, the interlace system can be realized.

[0029]

As described above, in the solid-state image pickup device of the present invention, a part of the light-shielding film made of a conductive material faces the upper surface of the read gate portion via the insulating film, so that the optical sensor receives light. When the signal charge generated by the above is read into the charge transfer register, a read voltage may be applied to the light shielding film based on the driving method of the solid-state image pickup device of the present invention. The light-shielding film can be formed over the entire width of the read gate portion, and therefore the signal charges can be sufficiently read out even if the voltage applied to the light-shielding film is low. That is,
According to the present invention, it is possible to reduce the read voltage, and thus it is possible to realize low power consumption of the solid-state image sensor.

Further, in the present invention, the transfer electrode of the charge transfer register only has to function as a transfer electrode,
Since it does not need to be formed on the read gate portion, no voltage is applied to the read gate portion during charge transfer, and leakage of charges can be avoided. As a result, blooming and smear can be prevented even when pixels are miniaturized. Further, at the time of charge transfer, for example, a negative voltage can be applied to the light-shielding film to more reliably prevent unnecessary reading of signal charges.

Further, in the present invention, it is not necessary to apply a high voltage for reading the signal charge to the transfer electrode.
A high electric field is locally generated, and the charge is moved through the element isolation portion adjacent to the vertical charge transfer register to generate random noise. Therefore, good image quality can be obtained. Further, since the signal charges can be efficiently read out by using the light-shielding film as the read-out electrode, miniaturization of pixels becomes easy. In addition, since the transfer voltage is not applied to the read gate portion during charge transfer, it is not necessary to lengthen the read gate portion, and this also facilitates miniaturization. Further, it is not necessary to apply a high voltage for reading to the transfer electrode, and even if the pixel is miniaturized, a high electric field is not applied to the element isolation portion, which is advantageous for the pixel miniaturization.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional side view showing an example of a solid-state image sensor according to the present invention.

FIG. 2 is a partial plan view of a solid-state image sensor according to an embodiment.

FIG. 3 is a partial plan view showing a conventional solid-state image sensor.

FIG. 4 is a partial cross-sectional side view showing a conventional solid-state imaging device.

[Explanation of symbols]

2, 102 ... Solid-state image sensor, 4, 108 ... Vertical charge transfer register, 6, 110 ... First transfer electrode, 8,
112 ... Second transfer electrode 10, 12, 114, 11
6 ... Wiring part, 14, 128 ... Shading film, 16 ... Opening, 18 ... Side part, 104 ... Optical sensor, 106 ...
Semiconductor substrate, 118, 124 ... P-type layer, 120 ... Buried channel layer, 122 ... N-type layer, 126 ... Insulating film, 130 ... Read gate section, 132 ... Element isolation section.

Claims (7)

[Claims] 1. A light sensor forming a row, a charge transfer register extending along the row of the light sensor, and being interposed between the light sensor and the charge transfer register, the light sensor receives and generates the light. A read gate portion for reading the generated signal charges to the charge transfer register and a light-shielding film covering the charge transfer register are formed on a semiconductor substrate, and the signal charges generated by the photosensors are transferred by the charge transfer register. The solid-state image sensor, wherein the light-shielding film is made of a conductive material, and a part of the light-shielding film faces the surface of the read gate portion with an insulating film interposed therebetween. 2. The solid-state image pickup device according to claim 1, wherein the light-shielding film is made of a metal material. 3. The charge transfer register includes a charge transfer path formed on a surface portion of the semiconductor substrate and a transfer electrode arranged on the charge transfer path via an insulating film, and the light shielding film is The solid-state imaging device according to claim 1, wherein the solid-state imaging device is formed on the transfer electrode via an insulating film so as to cover the transfer electrode. 4. The photosensors are arranged in a matrix on the semiconductor substrate, and the charge transfer registers are provided adjacent to the photosensor columns for each photosensor column. The solid-state image sensor according to claim 1. 5. An array of photosensors, a charge transfer register extending along the array of photosensors, and a photosensor that is interposed between the photosensor and the charge transfer register to receive and generate the photosensors. A read gate portion for reading the generated signal charges to the charge transfer register and a light-shielding film covering the charge transfer register are formed on a semiconductor substrate, and the signal charges generated by the photosensors are transferred by the charge transfer register. A method of driving a solid-state imaging device, wherein the light-shielding film is formed of a conductive material, and a part of which faces the surface of the readout gate portion via an insulating film. A signal voltage generated by the photosensor is applied to the charge transfer register through the read gate unit by applying a read voltage to the charge transfer register. Method for driving the solid-state imaging device, wherein the reading. 6. A voltage for canceling an electric field generated in the read gate section by the voltage applied to the charge transfer register when the signal charge is transferred by the charge transfer register, is applied to the read gate section. The method for driving a solid-state image sensor according to claim 5. 7. The photosensors are arranged in a matrix on the semiconductor substrate, and the charge transfer registers are provided adjacent to the photosensor columns for each photosensor column. The method for driving a solid-state image sensor according to claim 5.