JPH10135442A - Solid state imaging element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid state imaging element which suppresses small the step caused due to overlapping of charge transfer electrodes, and does not cause the potential pocket, and does not reduce the effective are of the photoelectric conversion element. SOLUTION: A vertical charge transfer part has a first through fourth charge transfer electrodes 5-8 arranged at the side of each of photoelectric conversion elements 1. Both ends of each of the first and third transfer electrodes 5, 7 cover both ends of each of the second and fourth charge transfer electrodes 6, 8. The first and fourth transfer electrodes 5, 8 extend between the conversion elements 1 orthogonally to the array of the change transfer electrodes to form wirings 5L, 8L. On the first an third charge transfer electrodes 5, 7, a first and second metal wirings 17, 19 are formed to cover each transfer electrode therewith.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solid-state imaging device in which electric charges of each photoelectric conversion element are transferred and taken out by a charge transfer device.

[0002]

2. Description of the Related Art In recent years, with the rapid spread of personal computers, demand for image input cameras and digital still cameras has been increasing. In the early days of these cameras, those for video cameras were diverted as solid-state imaging devices.

However, since the solid-state image pickup device for a video camera employs an interlaced system corresponding to TV display, it has not been possible recently to satisfy the high resolution required for a personal computer. For this reason, an all-pixel reading method (non-interlacing method) having a higher resolution than the interlacing method is adopted.

This all-pixel readout method is a method of reading out all the data of each pixel at once, and extracts the information of one image as it is. Therefore, compared with the interlace method of mixing upper and lower information in one image, This all-pixel readout method is superior in resolution.

[0005] In the case of the solid-state image pickup device of the all-pixel readout method, in order to transfer and extract the electric charge of the photoelectric conversion element, 1
It is necessary to allocate three or more charge transfer electrodes to one photoelectric conversion element. For example, a three-phase driving solid-state imaging device in which three charge transfer electrodes are allocated to one photoelectric conversion element, or one photoelectric transfer element A four-phase drive type solid-state imaging device in which four charge transfer electrodes are provided for a conversion device has been developed.

Comparing the three-phase driving method and the four-phase driving method, the effective area of the charge transfer electrode is larger in the four-phase driving method and about 1.5 times that in the three-phase driving method. Therefore, the four-phase driving method is very advantageous.

[0007]

However, the above 3)
The phase drive method has a portion having a structure in which three charge transfer electrodes 101, 102, and 103 are stacked as shown in FIG. 14, for example. Similarly, the four-phase drive method has a structure in which four charge transfer electrodes 101, 102 and 103 are stacked as shown in FIG. Charge transfer electrodes 111, 112, 113, 114
Since there is a portion having a structure in which the charge transfer electrodes are stacked, a large step is generated at a portion where the charge transfer electrodes overlap, and there is a problem that the charge transfer electrodes are easily cut at these portions and the yield of the solid-state imaging device is reduced.

In order to solve such a problem, the applicant of the present invention has previously filed Japanese Patent Application No. 5-26555 (Japanese Unexamined Patent Application Publication No.
244402). Here, a three-phase drive type device is proposed, in which each gate electrode (charge transfer electrode) is formed from a single polysilicon film, and these gate electrodes are separated. Therefore, the respective gate electrodes do not overlap each other, so that a large step is not generated, and disconnection of the gate electrode can be prevented.

However, when each gate electrode is formed in such a manner as described above, a potential pocket is generated in a gap between the gate electrodes, so that there is a problem that the transfer charge is deteriorated by the potential pocket. Investigation of Four-Phase CCD with Layered Electrodes ", 1996 Annual Conference of the Institute of Television Engineers of Japan, pp5-6, 1996).

Alternatively, a structure as shown in FIGS. 16 and 17 can be considered. Here, each photoelectric conversion unit 121
(Each consisting of two photodiodes)
The first, second, third, and fourth sides of the photoelectric conversion unit 121
The charge transfer electrodes 122, 123, 124, 125 are arranged,
The ends of these charge transfer electrodes 122 to 125 are overlapped with each other, and the first and fourth charge transfer electrodes 122 and 125 are extended between the photoelectric conversion units 121 in a direction orthogonal to the arrangement of the charge transfer electrodes. Forming each wiring 122L, 125L,
Each clock pulse φ2, φ5 is applied, and the second and third charge transfer electrodes 123, 124 are extended in the same direction so as to cross the photoelectric conversion unit 121 to form wirings 123L, 124L. φ4 is applied.

In this case, since the ends of the two charge transfer electrodes only overlap, the step of each charge transfer electrode is different from that in FIG.
4 and FIG. 15, and the potential pocket is not generated between the charge transfer electrodes.

However, since the second and third charge transfer electrodes 123 and 124 cross the photoelectric conversion unit 121, the effective area of the photoelectric conversion unit 121 is reduced, and the amount of incident light is reduced.

Incidentally, as shown in FIG.
Is not composed of two photodiodes, and FIG.
The same can be said for the case where the photoelectric conversion unit 121 is formed of a single photodiode as shown in FIG.

Accordingly, the present invention is to solve such a problem of the prior art, and suppresses the step caused by the overlapping of the charge transfer electrodes to be small, without generating a potential pocket, and effectively using the photoelectric conversion element. It is an object of the present invention to provide a solid-state imaging device that does not reduce the area.

[0015]

In order to solve the above-mentioned problems, the present invention provides a method of arranging a plurality of photoelectric conversion elements and arranging a plurality of charge transfer electrodes beside these photoelectric conversion elements. The first, second, third, and fourth charge transfer electrodes are sequentially arranged in a range from one end of the photoelectric conversion element to the other end for each photoelectric conversion element, and four charge transfer electrodes are provided for one photoelectric conversion element. In a solid-state imaging device to which electrodes are assigned, first and second wirings having a light-shielding property are arranged above each charge transfer electrode to cover these charge transfer electrodes, and a first wiring is provided for each photoelectric conversion element. Is connected to one of the second and third charge transfer electrodes, the second wiring is connected to the other through the contact hole of the first wiring, and the first and fourth charge transfer electrodes are connected to each photoelectric conversion element. Each light in a direction orthogonal to the arrangement of each charge transfer electrode It is extended between the transducer, the first
And the wiring of the fourth charge transfer electrode.

According to such a configuration, the second and third charge transfer electrodes are connected to the first and second wirings covering the respective charge transfer electrodes, so that these charge transfer electrodes are clocked through the respective wirings. A pulse can be applied. Further, since the first and fourth charge transfer electrodes extend between the photoelectric conversion elements and serve as wirings for the respective charge transfer electrodes, it is possible to apply a clock pulse to these charge transfer electrodes through the respective wirings. it can.

Since the wiring of these charge transfer electrodes does not cross the photoelectric conversion element, the effective area of the photoelectric conversion element is not reduced.

Further, since such a configuration is adopted,
The first, second, third and fourth charge transfer electrodes are formed from two conductive layers, the first and third charge transfer electrodes are formed from one conductive layer, and the second and fourth charge transfer electrodes are formed. The end portions of the charge transfer electrodes formed of the other conductive layer and adjacent to each other can overlap each other.

In this case, since only the ends of two adjacent charge transfer electrodes overlap, the step can be suppressed to a small level. Further, since the ends of the charge transfer electrodes overlap each other, a potential pocket is generated. Can be prevented.

Further, the contact hole of the first wiring formed to connect the second wiring to the other of the second and third charge transfer electrodes may be covered with the second wiring and shielded from light. good.

Further, the first wiring may be formed from a high melting point metal material.

[0022]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a plan view showing an embodiment of the solid-state imaging device of the present invention. FIG. 2 shows A in FIG.
1; FIG. 3 is a sectional view taken along line BB 'in FIG. 1; FIG. 4 is a sectional view taken along line CC' in FIG. FIG. 5 is a sectional view taken along the line DD ′ in FIG.

As is apparent from these figures, in this solid-state imaging device, a plurality of photoelectric conversion elements (photodiodes) 1 are arranged in a matrix, and each photoelectric conversion element 1
Each vertical charge transfer section 2 is provided on the side of each column composed of.

Each photoelectric conversion element 1 and each vertical charge transfer section 2
Is formed in the vicinity of the surface of the semiconductor substrate 3,
The surface of the semiconductor substrate 3 is covered with a first insulating film 4.

The vertical charge transfer section 2 includes, for each photoelectric conversion element 1, first, second, third and fourth charge transfer electrodes 5, 6, 7, 8 arranged on the side of the photoelectric conversion element 1. have.

The second and fourth charge transfer electrodes 6 and 8 correspond to FIG.
As shown in (a), a first polysilicon film 9 (for example, doped with a high concentration of P (phosphorus) for use as an electrode) is formed on the first insulating film 4 and then the first polysilicon film 9 is formed. The polysilicon film 9 is patterned as shown in FIG. 7, and is covered with a gate insulating film 11 as shown in FIG. 6B. In this state, the second charge transfer electrode 6 has an island shape and is isolated.

The first and third charge transfer electrodes 5, 7
As shown in FIG. 8A, the second polysilicon film 12 (for example, high-concentration P (phosphorus) is doped for use as an electrode, like the first polysilicon film 9), After being formed on the second and fourth charge transfer electrodes 6 and 8, the second polysilicon film 12 is patterned as shown in FIG. 9, and the gate insulating film 13 is formed thereon as shown in FIG.
Coated with In this state, the third charge transfer electrodes 7 are island-shaped and isolated.

As is apparent from FIG. 3, both ends of the first and third charge transfer electrodes 5, 7 are connected to the second and fourth charge transfer electrodes 6, 7, respectively.
8 covers both ends. For this reason, no gap exists between the charge transfer electrodes 5 to 8, and no potential pocket occurs.

On the first and third charge transfer electrodes 5, 7,
The second insulating film 14 is formed. Then, each of the first contact holes 15 and each of the second contact holes 15 are formed with a mask pattern as shown in FIG.
After the contact holes 16 are formed in the second insulating film 14 and the gate insulating films 11 and 13, a high-melting metal film (for example, W
−Si) is patterned as shown in FIG. 11 to form first metal wirings 17 and second contact holes 16 in the first metal film 17. This first metal wiring 1
7 is shunted to the second charge transfer electrode 6 of each photoelectric conversion element 1 through each first contact hole 15. The clock signal φ 6 is applied to each second charge transfer electrode 6 via the first metal wiring 17.

The third insulating film 1 is formed on the first metal wiring 17.
8 is formed. Then, after forming each second contact hole 16 in the third insulating film 18 with a mask pattern as shown in FIG. 12, a metal film (eg, Al) is patterned as shown in FIG. The wiring 19 is formed. This second metal wiring 19 is shunted to the third charge transfer electrode 7 of each photoelectric conversion element 1 through each second contact hole 16. A clock signal φ7 is applied to each third charge transfer electrode 7 via the second metal wiring 19.

On the other hand, as is apparent from FIG. 1, the first and fourth charge transfer electrodes 5 and 8 extend between the photoelectric conversion elements 1 in a direction orthogonal to the arrangement of the charge transfer electrodes, and 5L,
8L. The clock signals φ5 and φ8 are applied to the first and fourth charge transfer electrodes 5 and 8 of each photoelectric conversion element 1 via these wirings 5L and 8L.

In such a configuration, the first, second and third
When the clock signals φ5, φ6, φ7, φ8 of the respective phases are added to the fourth charge transfer electrodes 5, 6, 7, 8 respectively, the charges of the photoelectric conversion elements 1 in one row are transferred through the vertical charge transfer unit 2. Will be done.

Here, each of the first contact holes 15
And the second contact holes 16 are formed in the second insulating film 14 and the gate insulating films 11 and 13, and thereafter, the second contact holes 16 are formed in the third insulating film 18. Only the first contact holes 15 are formed in the second insulating film 14.
After that, the second contact holes 16 may be formed in the third insulating film 18, the second insulating film 14, and the gate insulating film 13.

In the solid-state imaging device of this embodiment,
Unlike the conventional device shown in FIGS. 14 and 15, each charge transfer electrode does not cross the photoelectric conversion element, and the amount of incident light does not decrease.

Further, as described above, since both ends of the first and third charge transfer electrodes 5 and 7 are covered over both ends of the second and fourth charge transfer electrodes 6 and 8, respectively. There is no gap and no potential pocket between # 8.

Further, each of the charge transfer electrodes 5 to 8 is formed by a two-layer first
And the second polysilicon films 9 and 12, the steps of these charge transfer electrodes 5 to 8 can be smaller than those of the prior art shown in FIGS. That is, it is possible to prevent the other layer covering the step from being cut.

The first and second metal wirings 16, 19
Has a light-shielding property and blocks light to each charge transfer electrode. Further, since each first contact hole 15 formed in the first metal wiring 16 is covered by the second metal wiring 19, light does not enter each charge transfer electrode through these first contact holes 15. . The occurrence of smear is prevented by such light shielding.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible. For example, deforming the shape of each charge transfer electrode or each metal wiring,
The material of each charge transfer electrode, each metal wiring, each insulating film, and the like may be appropriately selected and changed.

[0040]

As described above, according to the solid-state imaging device of the present invention, each charge transfer electrode is covered by the first and second wirings having light shielding properties, and the first and second wirings are provided for each photoelectric conversion element. Two wires are connected to the second and third charge transfer electrodes, and for each photoelectric conversion element, the first and fourth charge transfer electrodes are extended between the photoelectric conversion elements in a direction orthogonal to the arrangement of the charge transfer electrodes. Thus, wirings for the first and fourth charge transfer electrodes are formed.

None of these wirings of the charge transfer electrodes cross the photoelectric conversion element, and the effective area of the photoelectric conversion element is not reduced.

Also, since such a configuration is adopted,
First, second, third, and fourth
The ends of the charge transfer electrodes can be overlapped, and accordingly, the step caused by the overlap of the charge transfer electrodes can be suppressed to a small level, and the generation of potential pockets can be prevented.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a sectional view taken along line AA ′ in FIG.

FIG. 3 is a sectional view taken along line BB ′ in FIG. 1;

FIG. 4 is a sectional view taken along the line CC ′ in FIG. 1;

FIG. 5 is a sectional view taken along line DD ′ in FIG. 1;

6A is a cross-sectional view showing a stacked state of a first polysilicon film for forming second and fourth charge transfer electrodes in FIG. 1, and FIG. 6B is a sectional view showing the second and fourth charge transfer electrodes. Cross section shown

FIG. 7 is a plan view showing patterns of second and fourth charge transfer electrodes in the solid-state imaging device of FIG. 1;

8A is a cross-sectional view showing a stacked state of a second polysilicon film for forming first and third charge transfer electrodes in the solid-state imaging device of FIG. 1, and FIG. Sectional view showing charge transfer electrodes

FIG. 9 is a plan view showing patterns of first and third charge transfer electrodes in the solid-state imaging device of FIG. 1;

FIG. 10 is a plan view showing a mask pattern for forming first and second contact holes in the solid-state imaging device of FIG. 1;

FIG. 11 is a plan view showing a first metal wiring in the solid-state imaging device in FIG. 1;

FIG. 12 is a plan view showing a mask pattern for forming a second contact hole in the solid-state imaging device of FIG. 1;

FIG. 13 is a plan view showing a second metal wiring in the solid-state imaging device of FIG. 1;

FIG. 14 is a cross-sectional view of a conventional solid-state imaging device of a three-phase driving method, which is cut away.

FIG. 15 is a cross-sectional view of a conventional solid-state imaging device of a four-phase drive system, which is cut away.

FIG. 16 is a plan view showing another example of a conventional solid-state imaging device of a four-phase drive system.

FIG. 17 is a cross-sectional view showing the solid-state imaging device of FIG. 16 in a cutaway manner;

FIG. 18 is a diagram illustrating another cross-sectional structure of the solid-state imaging device in FIG. 16;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoelectric conversion element 2 Vertical charge transfer part 3 Semiconductor substrate 4 First insulating film 5 First charge transfer electrode 6 Second charge transfer electrode 7 Third charge transfer electrode 8 Fourth charge transfer electrode 9 First polysilicon film 11,13 Gate insulating film 12 Second polysilicon film 14 Second insulating film 15 First contact hole 16 Second contact hole 17 First metal wiring 18 Third insulating film 19 Second metal wiring

Claims (4)

[Claims] 1. A method of arranging a plurality of photoelectric conversion elements,
A plurality of charge transfer electrodes are arranged beside these photoelectric conversion elements, and the first, second, third, and fourth charges are arranged for each photoelectric conversion element in a range from one end to the other end of the photoelectric conversion element. In a solid-state imaging device in which transfer electrodes are sequentially arranged and four charge transfer electrodes are assigned to one photoelectric conversion element, first and second wirings having light shielding properties are arranged above each charge transfer electrode. Covering the charge transfer electrodes, connecting the first wiring to one of the second and third charge transfer electrodes for each photoelectric conversion element, and connecting the second wiring to the other through the contact hole of the first wiring. Connecting, for each photoelectric conversion element, extending the first and fourth charge transfer electrodes between the photoelectric conversion elements in a direction orthogonal to the arrangement of the charge transfer electrodes, and wiring the first and fourth charge transfer electrodes. Forming a solid-state imaging device. 2. The solid-state imaging device according to claim 1, wherein the first, second, third, and fourth charge transfer electrodes are formed from two conductive layers, and the first and third charge transfer electrodes are formed on one side. The second and fourth charge transfer electrodes are formed from the other conductive layer, and the first, second, third, and fourth charge transfer electrodes are adjacent to each other and have respective ends. Solid-state imaging devices that overlap each other. 3. The solid-state imaging device according to claim 1, wherein the contact hole of the first wiring formed to connect the second wiring to the other of the second and third charge transfer electrodes is formed of the second wiring. A solid-state imaging device that is covered by wiring and shielded from light. 4. The solid-state imaging device according to claim 1, wherein the first wiring is formed from a high melting point metal material.