JP3326798B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates are those which relate to the solid-state imaging equipment.

[0002]

2. Description of the Related Art In recent years, solid-state imaging devices using a charge transfer device represented by a charge-coupled device (hereinafter, referred to as a CCD) have been widely used because of their low noise characteristics and the like. I have.

Hereinafter, a structure used in a conventional solid-state imaging device will be described with reference to the drawings.

FIG. 24 is a plan view of a so-called CCD type solid-state imaging device. The solid-state imaging device includes a photoelectric conversion element unit 1, a vertical CCD transfer electrode unit 2, a horizontal CCD transfer electrode unit 3, and an output unit 4.

When light emitted from a subject enters the photoelectric conversion element 1, electron-hole pairs are generated in the photoelectric conversion element 1 by the light. The electrons generated in this manner are sent from the photoelectric conversion element unit 1 to the vertical CCD transfer electrode unit 2. The electrons of the photoelectric conversion element units 1 arranged in the longitudinal direction of the vertical CCD transfer electrode unit 2 are simultaneously sent to the vertical CCD transfer electrode unit 2. Further, the electrons taken out by the vertical CCD transfer electrode unit 2 are sent to the horizontal CCD transfer electrode unit 3. The electrons of the vertical CCD transfer electrodes 2 arranged perpendicular to the longitudinal direction of the horizontal CCD transfer electrode unit 3 are simultaneously sent to the horizontal CCD transfer electrode unit 3.

The electrons taken out by the horizontal CCD transfer electrode unit 3 in this manner are output through the output unit 4. This output signal is output as an image of a subject from an output medium such as a display through an image reproducing circuit.

FIG. 25 shows a photoelectric conversion element section 1 and a vertical CCD.
FIG. 3 is a cross-sectional view of the solid-state imaging device taken along line AA ′ passing through the transfer electrode unit 2.

There is a p-layer 6 formed on an n-type substrate 5 and having a predetermined range of depth and concentration. An n-layer photoelectric conversion element is formed in a predetermined region inside the p-layer 6. A high concentration p layer 8 is formed in the p layer 6 at a position separated from the n layer 7. An n-layer 9 serving as a transfer channel which is a vertical CCD is provided in the p-layer 8.

The signal charges stored in the n-layer 7 are read out to the n-layer 9, and the signal charges are transferred in the n-layer 9 in a direction perpendicular to the plane of the drawing.

The high concentration p layer 10 formed on the n layer 7
It is formed in order to prevent the generation of dark current due to the Si-SiO ₂ interface state.

Between the p layer 6 and the substrate 5, a positive potential is applied to the substrate,
A reverse bias voltage Vsub, which becomes a negative potential, is
Is applied. That is, a reverse bias voltage Vsub is applied between the p layer 8 and the substrate 5. Therefore, the p layer 6 below the photoelectric conversion element formed by the n layer 7 is depleted. When the p-layer 6 is depleted, the charge that has become excessive in the amount of charge that can be accumulated in the n-layer 7 is discharged to the substrate 5 side. Thus, the blooming phenomenon is prevented.

Further, by applying a pulse voltage to the n-type substrate 5, it is possible to perform a so-called electronic shutter operation of discharging all signal charges in the n-layer 7 to the substrate 5 side.

An insulating film 12 such as SiO ₂ is formed on the surface of the substrate 5. On the insulating film 12, the vertical CCD transfer electrodes 13 are formed on the p layer 8 and the n layer 9 constituting the vertical CCD section 2 and on the region including the gap region between the n layer 7 and the p layer 8. . Further, an insulating film 12 is formed on the side wall and the upper surface of the transfer electrode 13 to protect the solid-state imaging device from physical impact.

The vertical CCD transfer electrode 13 functions as an electrode for reading electrons accumulated in the n-layer 7 to the p-layer 8 or the p-layer 9 serving as a vertical CCD transfer channel.

As described above, in order to prevent the blooming phenomenon and perform the electronic shutter operation, it is necessary that the p layer 6 has a concentration and a depth in a predetermined range.

FIG. 26 shows an impurity concentration distribution along the line BB 'passing through the photoelectric conversion element portion 1 of FIG. FIG. 27 shows the net value of the impurity concentration in FIG. In both figures, the vertical axis indicates the impurity concentration. The horizontal axis indicates the distance from the substrate surface. The upper side of the vertical axis indicates the concentration of p-type impurity atoms, and the lower side of the vertical axis indicates the concentration of n-type impurity atoms.

The broken lines 14, 15, 16, 17 in FIG. 26 p layer 10, p layer 6, respectively, of FIG 25 shows the impurity concentration of the substrate 5, n layer 7.

The solid line 18 in FIG. 27 shows the net value of each impurity concentration in FIG. The hatched area 19 is the net impurity distribution of the n-layer 7 of the photoelectric conversion element, and indicates the total amount of effective donors accumulated in the n-layer.

The impurity concentration 1 of the n-layer 7 as a photoelectric conversion element
7 has the highest concentration on the surface of the substrate 5, and the concentration decreases toward the inside of the substrate 5. Above the n-layer 7, a p-layer 10 is formed to reduce dark current. The impurity concentration 14 of the p layer 10 is higher than that of the n
Little spread inside. Therefore, the n layer 7 becomes the net impurity 19.

Although the p-layer 6 has a low impurity concentration, its distribution is widely distributed. That is, the concentration gradually decreases as the surface of the substrate 5 reaches the inside of the substrate 5 with the maximum concentration point.

In order to prevent the blooming phenomenon in the solid-state image pickup device, it is necessary to read out the electrons accumulated in the photoelectric conversion device to the vertical CCD transfer electrode portion and then to completely deplete the n-layer 7 of the photoelectric conversion device. There is. For this reason, it is necessary that the total amount of effective donors indicated by the net impurity concentration 19 is set to the upper limit of the amount of charges that can be accumulated in the n-layer 7. That is, the total amount of effective donors determines the upper limit of the saturation characteristics of the photoelectric conversion element.

The net impurity concentration 19 is obtained by subtracting the impurity concentration 14 of the p layer 10 and the impurity concentration 15 of the p layer 6 from the value obtained by adding the impurity concentration 16 of the substrate 5 to the impurity concentration 17. The net impurity concentration 19 is determined by the impurity concentration 14 and the impurity concentration 17 from each process restriction. The impurity concentration 17 has the highest concentration on the surface of the substrate 5. The portion having the highest concentration is compensated by the impurity concentration 14 of the p-type layer 10 of the opposite conductivity type.

FIGS. 28 to 31 are sectional process views of a conventional CCD solid-state imaging device. Boron, which is a p-type impurity, is ion-implanted on the main surface of the n-type substrate 5. Thereafter, a p-layer 6 is formed by a high-temperature heat treatment. After that, a resist pattern is formed by using normal photolithography in a region other than a region serving as a vertical CCD transfer channel. Using the resist pattern as a mask, boron is ion-implanted to form a p-layer 8. Thereafter, the vertical C is again formed using photolithography.
A resist pattern is formed in a region other than the region where the n-layer 9 is formed in the p-layer 8 serving as a CD transfer channel. Using the resist pattern as a mask, phosphorus is ion-implanted to form an n-layer 9. Thereafter, an insulating film 12 is deposited on the main surface of the substrate 5 by thermal oxidation. Further, the vertical CCD transfer electrode 1 is formed on the insulating film 12.
An electrode material to be No. 3 is formed (FIG. 28).

[0024] Further, a registry <br/> bets pattern 20 wider realm than the area to be the transfer electrodes 13 by using a photolithography on the electrode material. The electrode material is dry-etched using the resist pattern 20 as a mask to form the insulating film 12.
Etch until is exposed. Next, phosphorus ions are implanted using the resist pattern 20 as a mask and using the insulating film 20 as a protective film. By this ion implantation, an n-layer 7 serving as a photoelectric conversion element is formed (FIG. 29).

After that, the resist pattern 20 is removed. On the surface of the substrate 5, an electrode material in a region wider than the insulating film 12 and the transfer electrode 13 is formed. Next, the transfer electrode 13
A resist pattern is formed in a region other than the region to be formed, and the electrode material is dry-etched using the resist pattern as a mask. The transfer electrode 13 is formed by the above steps. At this time,
A transfer electrode 13 must be provided in the gap between the n-layer 7 and the p-layer 8 from which electrons are read out from the photoelectric conversion element to the vertical CCD transfer channel. For this reason, in the dry etching at the time of manufacturing the transfer electrode 13, since the side wall end of the n-layer 7 originally serving as the photoelectric conversion element and the side wall end of the transfer electrode 13 match, one side wall end of the transfer electrode 13 is shortened. It is formed to a predetermined length (FIG. 30).

Next, boron is ion-implanted using one end of the transfer electrode 13 and a resist as a mask. Thus, a p-layer 10 for preventing dark current is formed on n-layer 7 (FIG. 31).

[0027]

However, such a conventional charge transfer device has the following drawbacks.

The impurity concentration 17 has the highest concentration on the surface of the substrate 5, and the portion having the highest concentration is compensated by the impurity concentration 14 of the p-type layer 10 of the opposite conductivity type. Therefore, of the impurity concentration 17 of the n-layer 7 introduced as a photoelectric conversion element, a region having a relatively low concentration is used as the photoelectric conversion element. That is, in a photoelectric conversion element having a low concentration, the total amount of effective donors that can be accumulated therein is small, and the saturated charge amount cannot be sufficiently increased.

For this reason, the amount of impurities introduced to the impurity concentration 17 is increased. Furthermore, the introduced impurities to diffuse into the deep portion of the substrate by a high-temperature heat treatment, increasing the body volume of the photoelectric conversion element is performed.

However, when the high-temperature heat treatment is performed, the impurity concentration 17 spreads in a direction perpendicular to the surface of the substrate 5. For this reason, it also diffuses into the gap between the p layer 8 and the n layer 7 and the n layer 9 which is a vertical CCD transfer channel.

The positional relationship between the end of the n-layer 7 and the vertical CCD transfer electrode 12 is determined by the mask alignment accuracy in the exposure step performed when the transfer electrode 12 is formed and the diffusion of the n-layer 7 formed by diffusion. It depends on the area. For this reason, it is extremely difficult to control the position formed by the thermal diffusion at a high temperature. If the controllability of the position between the end of the n-layer 7 and the vertical CCD transfer electrode 12 is poor, electrons that become signals are left in the photoelectric conversion element when reading out from the photoelectric conversion element to the vertical CCD transfer channel.

The electrons left behind in this manner cause an afterimage phenomenon, and significantly degrade the image quality.

On the other hand, when the introduction amount is increased, defects during ion implantation increase, and so-called white flaws increase. For this reason, the yield decreases .

[0034]

According to the present invention, there is provided a solid-state image pickup device comprising: a semiconductor substrate;
The main impurity of one conductivity type in the photoelectric conversion element part that accumulates
The first region and the substrate surface side of the first region are opposite in conductivity type.
A second region in which pure substances are distributed, and one conductivity type of the first region.
The concentration maximum of the impurity in the substrate depth direction is the substrate in the second region.
It is deeper than the inner end.

Further , signal charges are stored in the semiconductor substrate.
The first one where the main one conductivity type impurity of the photoelectric conversion element portion is distributed
Reverse conductivity type impurities are distributed in the region and the substrate surface side of the first region
End portion of the first region on the substrate surface side
Is the concentration electrode of the impurity of the opposite conductivity type in the second region in the depth direction of the substrate.
It is deeper than most of the substrate.

[0036]

[0037]

As described above, in the solid-state imaging device according to the present invention, the n-layer serving as the photoelectric conversion element is realized by ion implantation with high acceleration energy. You can have.

For this reason, it is possible to increase the total amount of effective donors that can be stored in the photoelectric conversion element and to sufficiently increase the saturation charge.
I can .

[0039]

[0040]

On the n-layer of the photoelectric conversion element, a p-layer for preventing dark current is formed. A maximum value of the concentration of the n-layer serving as a photoelectric conversion element is formed inside the substrate by ion implantation. Therefore, the net value of the impurity concentration of the p-layer on the substrate surface can be made higher than the concentration of the p-layer of the conventional solid-state imaging device. Therefore, a solid-state imaging device having a photoelectric conversion element having low dark current characteristics can be obtained.

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

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

FIG. 1 is a sectional view of a solid-state imaging device according to a first embodiment of the present invention. This embodiment has the same structure as the conventional solid-state imaging device shown in FIG. 25.

There is a p-layer 6 formed on an n-type substrate 5 and having a predetermined range of depth and concentration. An n-layer photoelectric conversion element is formed in a predetermined region inside the p-layer 6. A high concentration p layer 8 is formed in the p layer 6 at a position separated from the n layer 7. An n-layer 9 serving as a transfer channel which is a vertical CCD is provided in the p-layer 8. The signal charges stored in the n-layer 7 are read out to the n-layer 9, and the signal charges are transferred in the n-layer 9 in a direction perpendicular to the plane of the drawing. A high concentration p layer 10 is formed on n layer 7 and on the surface of substrate 5. The p layer 10 is formed to prevent generation of dark current due to the interface state of Si—SiO ₂ .

An insulating film 12 such as SiO ₂ is formed on the surface of the substrate 5. On the insulating film 12, the vertical CCD transfer electrodes 13 are formed on the p layer 8 and the n layer 9 constituting the vertical CCD section 2 and on the region including the gap region between the n layer 7 and the p layer 8. . Further, an insulating film 12 is formed on the side wall and the upper surface of the transfer electrode 13 to protect the solid-state imaging device from physical impact.

The vertical CCD transfer electrode 13 transfers electrons accumulated in the n-layer 7 via the p-layer 8 to the vertical CCD transfer channel.
It also functions as an electrode for causing the n-layer 9 to be read out.

FIG. 2 shows the impurity concentration distribution in the substrate along the line AA ′ passing through the p-layer 10 and the n-layer 7 and the p-layer 6 of the photoelectric conversion element and the substrate 5 shown in FIG. Also, in FIG.
3 shows a net impurity distribution of the impurity concentration distribution of FIG.

In the present invention, as shown in FIG. 1, the sectional shape of the solid-state imaging device is exactly the same as that of the conventional one, but the impurity concentration distribution of the formed impurity layer is different. This will be described in more detail.

In both figures, the vertical axis indicates the impurity concentration. The horizontal axis indicates the distance from the substrate 5 surface. Above the horizontal axis, that is, above the vertical axis, the concentration of the p-type impurity is shown, and below the horizontal axis, that is, below the vertical axis, the concentration of the n-type impurity is shown.

Dashed lines 21, 22, 23, and 24 in FIG. 2 indicate the impurity concentrations of the p layer 6, the substrate 5, the n layer 7, and the p layer 10 of FIG.

A solid line 25 in FIG. 3 indicates a value obtained by combining the respective impurity concentrations in FIG. 2 (hereinafter referred to as a net value). The shaded area 26 indicates the net impurity concentration of the n-layer 7 of the photoelectric conversion element. The total amount of effective donors stored in the n-layer 7 is shown.

The impurity concentration 2 of the n-layer 7 as the photoelectric conversion element
No. 3 has a point where the highest concentration, that is, the highest concentration, exists inside the substrate 5. On the surface of the substrate 5, the impurity concentration of the n-layer 7 is low, and the concentration increases toward the inside of the substrate 5.
As described above, the maximum value of the impurity concentration of the n-layer 7 exists inside the substrate 5, and the impurity concentration of the n-layer 7 decreases further toward the inside of the substrate than the depth at which the maximum value is obtained. In the conventional solid-state imaging device, the impurity concentration of the n-layer 7 is formed so as to have a maximum region in a region as shallow as the impurity concentration of the surface of the substrate 5 or the p-layer 10 for reducing dark current is distributed. Have been.

A p-layer 10 is formed on the n-layer 7 to reduce dark current. impurity concentration 24 of p layer 10
Are formed so as to have a higher concentration than the concentration of the n-layer 7 and to be less spread into the substrate 5.

Further, the p-layer 6 is formed inside the substrate 5 so as to at least overlap the end of the n-layer 7 of the photoelectric conversion element which is deep inside the substrate 5. The impurity concentration 21 starts to increase from a portion overlapping with the n-layer 7 and is distributed so as to have a maximum value in a deep portion of the substrate 5. In the conventional solid-state imaging device, the impurity concentration of the p layer 6 is
It is formed so as to have a maximum region in a region as shallow as the depth where the impurity concentration of the p-layer 10 for reducing the dark current is distributed on the surface of the substrate 5. The distribution of the impurity concentration is low and extends to a considerably deep portion of the substrate 5.

[0060] The difference in the distribution of impurity concentration as that of the solid-state imaging device of the conventional invention, a large difference in the amount of effective donors accumulated in the photoelectric conversion element is caused.

That is, the total amount of effective donors represented by the net impurity concentration 26 is obtained as follows. From the value obtained by adding the impurity concentration 22 of the substrate 5 to the impurity concentration 23, the impurity concentration 24 of the p layer 10 and the impurity concentration 2 of the p layer 6 are obtained.
It is obtained from a value obtained by subtracting one.

In the conventional solid-state imaging device, the impurity concentration of the n-layer 7 of the photoelectric conversion element is about the depth at which the impurity concentration of the surface of the substrate 5 or the p-layer 10 for reducing dark current is distributed. It is formed so as to have a maximum region in a shallow region. Therefore, the region having the highest impurity concentration in the n-layer 7 serving as the photoelectric conversion element is canceled by the high-concentration, shallow p-layer 10 formed on the surface of the substrate 5. Therefore, the absolute amount of effective donors stored in the photoelectric conversion element decreases. Further, although the impurity concentration of the p-layer 6 is low, it is distributed deeply to the deep portion of the substrate 5, so that the concentration of the n-layer 7 of the photoelectric conversion element is reduced as a whole. Therefore, the absolute amount of effective donors stored in the photoelectric conversion element decreases.

On the other hand, in the solid-state imaging device of the present invention, the n-layer 7 serving as a photoelectric conversion element is in a region as shallow as the surface of the substrate 5 or a depth where the impurity concentration of the p-layer 10 for reducing dark current is distributed. The impurity concentration is formed to be extremely low. For this reason, the n-layer 7 serving as a photoelectric conversion element has almost no problem with the high impurity concentration 24 formed on the surface of the substrate 5, that is, the concentration that is canceled out by the shallow p-layer 10 in the distribution state. For this reason, the absolute amount of the effective donor accumulated in the photoelectric conversion element is reduced to a level that does not cause a problem as compared with the conventional case.

Further, the impurity concentration 21 of the p layer 6 is formed deep in the substrate 5. The end of the impurity concentration 21 is distributed so as to overlap the end of the n-layer 7 of the photoelectric conversion element. Also here, in the region of the impurity concentration 23 overlapping with the impurity concentration 21, the n-type impurity concentration is formed to be extremely low. For this reason, the concentration at which the n-layer 7 serving as the photoelectric conversion element is canceled by the impurity concentration 21 is such that there is almost no problem. For this reason, the absolute amount of the effective donor accumulated in the photoelectric conversion element is reduced to a level that does not cause a problem as compared with the conventional case. As described above, when the p layer 6 and the n layer 7 are overlapped, the impurity concentration 21 is restricted as follows. First, when there is no overlap, the solid line 25 of the net impurity concentration shown in FIG. 3 has a shape as shown in FIG. A region where effective donors are accumulated is formed as a protruding region in a deep portion of the substrate 5. In the photoelectric conversion element having such a shape, since the net impurity concentration 26 is not canceled by the impurity concentration 21, the net net impurity concentration 26 is substantially increased. As the net impurity concentration 26 increases, the total effective donor amount increases.

When the overlapping region is shallow, the concentration of the maximum value a of the impurity concentration 21 in the overlapping region must be higher than the impurity concentration b of the substrate 5. That is, the concentration of “a” indicates the concentration of the impurity concentration 6 at the end of the impurity concentration distribution of the n-layer 7. If the value of a is smaller than the value of b, the impurity concentration has a protruding shape at the deep portion of the substrate 5 as shown by the solid line 25 of the net impurity concentration shown in FIG.

Conversely, when the value of a is extremely larger than the value of b, the wall of the solid line 25 on the p-side rises. That is, the potential barrier formed between n layer 7 and substrate 5 is increased. If the potential barrier is high, the blooming phenomenon can be prevented by increasing the voltage to be applied to the substrate 5.

However, when the distribution of the impurity concentration 21 is steep, the region where the n layer 7 and the p layer 6 overlap is shallow, the value of a is extremely larger than the value of b, and the thickness of the p layer 6 is thin. The net impurity concentration 26 is reduced by the amount by which the net impurity concentration 26 is canceled by the impurity concentration 25.
Will be higher. Therefore, the total amount of effective donors becomes large. Further, a sufficient effect can be obtained even if the voltage to be applied to the substrate 5 is low.

The maximum point of the impurity concentration 23 of the n-layer 7 is located in a region which does not overlap with the impurity concentrations 21 and 24 of the p-layer 10 and the p-layer 6 at all. By forming the impurity concentration 23 in this manner, the total amount of effective donors can be increased.

As described above, the impurity concentration 23 of the n-layer 7 is
It overlaps with the impurity concentrations 21 and 24 of the layer 10 and the p-layer 6 only at the respective ends. That is, the impurity concentration 24 of the p layer 10 and the impurity concentration 21 of the p layer 6 do not overlap with each other, and both are continuous by the impurity concentration 23 of the n layer 7. By forming such an impurity concentration distribution, the total amount of effective donors accumulated in the n-layer 7 of the photoelectric conversion element can be significantly increased.

On the other hand, at the net impurity concentration 25, the area of the diagonal line 26 indicating the total effective donor amount accumulated in the n-layer 7 of the photoelectric conversion element is larger than the area of the diagonal line 19 indicating the conventional total amount.

For this reason, the upper limit of the saturation characteristic of the photoelectric conversion element becomes larger than that of the conventional one, and the saturation charge amount of the solid-state imaging device, that is, the dynamic range can be greatly improved.

Here, the concentration of the substrate 5 is about 10 ¹⁵ cm ^−3.
It is. The concentration of the p layer 10 is 10 ¹⁸ to 10 ¹⁹ cm ⁻³ ,
Its diffusion length is 0.5 microns. The concentration of the p layer 6 is about 10 ¹⁵ cm ⁻³ , and the region has a diffusion length of 1.5 μm to 3.0 μm from the surface of the substrate 5. n-layer 7
Has a concentration of 10 ¹⁶ to 10 ¹⁷ cm ^-3 and a diffusion length of 1.
8 microns. Therefore, the area where the n-layer 7 and the p-layer 6 overlap is 0.3 μm.

FIG. 5 shows the impurity concentration in the solid-state imaging device according to the second embodiment. Specifically, the p shown in FIG.
The impurity concentration in the substrate along the line AA ′ passing through the layer 10, the n-layer 7, the p-layer 6, and the substrate 5 of the photoelectric conversion element is shown.

FIG. 6 shows the net value of the impurity concentration in FIG. In the present invention, as shown in FIG. 1, the cross-sectional shape of the solid-state imaging device is exactly the same as that of the conventional one, but the impurity concentration distribution of the formed impurity layer is different. This will be described in more detail.

In both figures, the ordinate and abscissa show exactly the same as in FIGS. Dashed lines 27, 28, 29, 3 in FIG.
0 denotes the p layer 6, the substrate 5, the n layer 7, and the p layer 10 of FIG.
Is shown.

The solid line 31 in FIG. 6 shows the net value of each impurity concentration in FIG. The shaded region 32 indicates the net impurity concentration of the n-layer 7 of the photoelectric conversion element. The total amount of effective donors stored in the n-layer 7 is shown.

The impurity concentration 2 of the n-layer 7 as the photoelectric conversion element
No. 9 has the highest concentration inside the substrate 5, that is, the point where the concentration is maximum. On the surface of the substrate 5, the impurity concentration of the n-layer 7 is low, and the concentration increases toward the inside of the substrate 5.
As described above, the maximum value of the impurity concentration of the n-layer 7 exists inside the substrate 5, and the impurity concentration of the n-layer 7 decreases further toward the inside of the substrate than the depth at which the maximum value is obtained. As described above, n
The distribution of the impurity concentration of the layer 7 is the same as in the first embodiment.

Further, a p-layer 10 is formed on the n-layer 7 to reduce dark current. As in the first embodiment, the impurity concentration 30 of the p-layer 10 is higher than that of the n-layer 7 and is formed so as to be less spread inside the substrate 5.

The difference from the first embodiment is that the p-layer 6 is formed at a low concentration from the surface of the substrate 5 to the deep portion of the substrate 5 like the impurity concentration 15 of the conventional solid-state imaging device. .

That is, the impurity concentration 6 has a local maximum value on the surface of the substrate 5. Further, the distribution state extends to the deep part of the substrate 5. The diffusion depth of the p layer 6 is formed deeper than the diffusion depth of the n layer 7.

The difference in the distribution of the impurity concentration between the solid-state image pickup device of the present invention and the conventional solid-state image pickup device causes a large difference in the total amount of effective donors accumulated in the photoelectric conversion element.

That is, the total amount of effective donors represented by the net impurity concentration 32 is obtained as follows. From the value obtained by adding the impurity concentration 28 of the substrate 5 to the impurity concentration 29, the impurity concentration 30 of the p layer 10 and the impurity concentration 2 of the p layer 6 are obtained.
It is obtained from the value obtained by subtracting 7.

In the conventional solid-state imaging device, the impurity concentration of the n-layer 7 of the photoelectric conversion element is about the depth at which the impurity concentration of the surface of the substrate 5 or the p-layer 10 for reducing dark current is distributed. It is formed so as to have a maximum region in a shallow region. Therefore, the region having the highest impurity concentration in the n-layer 7 serving as the photoelectric conversion element is canceled by the high-concentration, shallow p-layer 10 formed on the surface of the substrate 5. Therefore, the absolute amount of effective donors stored in the photoelectric conversion element decreases. Further, although the impurity concentration of the p-layer 6 is low, it is distributed deeply to the deep portion of the substrate 5, so that the concentration of the n-layer 7 of the photoelectric conversion element is reduced as a whole. Therefore, the absolute amount of effective donors stored in the photoelectric conversion element decreases.

On the other hand, in the solid-state imaging device according to the present invention, the n-layer 7 serving as a photoelectric conversion element is formed on the surface of the substrate 5 or in a region as shallow as the depth where the impurity concentration of the p-layer 10 for reducing dark current is distributed. The impurity concentration is formed to be extremely low. For this reason, the n-layer 7 serving as the photoelectric conversion element has a concentration that is negligible by the high impurity concentration 30 formed on the surface of the substrate 5, that is, the concentration that is canceled out by the shallow p-layer 10 in the distribution state. For this reason, the absolute amount of the effective donor accumulated in the photoelectric conversion element is reduced to a level that does not cause a problem as compared with the conventional case. But the first
In the embodiment, the impurity concentration 27 of the p layer 6 is
Is formed in the deep part of. The end of the impurity concentration 27 is distributed so as to overlap the end of the n-layer 7 of the photoelectric conversion element.
Therefore, the n-layer 7 serving as a photoelectric conversion element has an impurity concentration of 2
The density canceled by 7 was of little concern. In comparison with this, in the second embodiment, the p-layer 6
Is formed by diffusing from the surface of the substrate 5 in the same manner as the conventional solid-state imaging device. For this reason, the absolute amount of effective donors stored in the photoelectric conversion element is smaller than in the first embodiment. Compared with the conventional case, the total amount of effective donors is reduced to the extent that no problem occurs in the second embodiment.

In the second embodiment, only the n-layer 7 is different from the conventional solid-state imaging device. In the first embodiment, the region where the n-layer 7 and the p-layer 6 overlap is a problem, but in the second embodiment, it can be easily formed by a conventional process.

At net impurity concentration 31, hatched line 3 indicating the total effective donor amount accumulated in n layer 7 of the photoelectric conversion element.
The area of 2 is larger than the area of the oblique line 15 indicating the conventional total amount.

For this reason, the upper limit value of the saturation characteristic of the photoelectric conversion element is larger than that of the conventional one, and the saturation charge of the solid-state imaging device can be increased.

Here, the concentration of the substrate 5 is 10 ¹⁵ cm ⁻³ . The concentration of the p layer 10 is 10 ¹⁸ to 10 ¹⁹ cm ⁻³ , and the diffusion length is 0.5 μm. The concentration of the p layer 6 is about 2 × 10 ¹⁴ cm ^-3, the region surface of the substrate 5 or al
It is an expansion Chicho 5.5 micron. The concentration of the n-layer 7 is 10 ¹⁶
At 〜１０10 ¹⁷ cm ^-3 , its diffusion length is 1.8 microns. Therefore, the area where the n layer 7 and the p layer 6 overlap is 1.8 microns.

When the solid-state imaging device is formed under the above conditions, the saturation charge amount of the conventional solid-state imaging device is 4 × 1.
0 ⁴ / of was about pixel is obtained a value of about 1.2 × 10 ⁵ / pixel.

[0090] illustrates a cross-sectional structure of a solid-state imaging device according to a first embodiment of another invention in FIG. This figure is a cross-sectional view of a region corresponding to the solid-state imaging device shown in FIG. 25 of the prior art.

A p-layer 33 having a predetermined range of depth and concentration is formed on an n-type substrate 5. A partial region of the n-layer photoelectric conversion element 7 is formed in the p-layer 33.
A high concentration p layer 8 is formed on the p layer 33, and the p layer 8
An n layer 9 serving as a vertical CCD transfer channel is provided therein. Further, a p-layer 34 having a high concentration and a small thickness is formed in contact with the bottom of the photoelectric conversion element 7. p layer 34
It is formed on an n-type substrate 5 sandwiched between a layer 33 and a p-layer 33 adjacent thereto. A high concentration p layer 10 is formed on the photoelectric conversion element 7. Further, the p layer 8 is formed by the n layer 7 and the p layer
It is formed separately from the layer 10.

On the n-type substrate 5, a vertical CCD transfer electrode 13 is formed at least in a region other than a predetermined region of the photoelectric conversion element 7 via an insulating film 12 such as SiO ₂ .

The n-layer 7 of the photoelectric conversion element is formed on two regions of a low-concentration thick p-layer 33 and a high-concentration thin p-layer 34.

The signal charges stored in the n-layer 7 of the photoelectric conversion element are read out to the n-layer 9, and the signal charges are transferred in the n-layer 9 in a direction perpendicular to the plane of the drawing.

The high-concentration p-layer 10 formed on the n-layer 7 of the photoelectric conversion element is formed to prevent the generation of dark current due to the interface state of Si—SiO ₂ .

As described above, in the solid-state imaging device of the present invention,
Forming the structure is different from the conventional solid-state imaging device, n layer 7 of the photoelectric conversion element, a thick p layer 23 at low concentrations, even without least a high concentration in a thickness thin two regions of the p layer 34 That is the point.

Here, a substrate 5 having a concentration of 10 ¹⁵ cm ^-3 was used. The concentration of the p layer 33 is 10 ¹⁵ cm ⁻³ ,
Its diffusion length is 3 microns. The concentration of the n-layer 7 is 10 ¹⁶
At 〜１０10 ¹⁷ cm ^-3 , its diffusion length is 1.8 microns. The concentration of the p layer 10 is 10 ¹⁸ to 10 ¹⁹ cm ⁻³ ,
Its diffusion length is 0.5 microns. The concentration of the p layer 8 is 3
At × 10 ¹⁷ cm ^-3 , its diffusion length is 1.2 microns. The concentration of the n-layer 9 is 5 × 10 ¹⁶ cm ⁻³ and its diffusion length is 0.8 μm. The concentration of the p layer 34 is 4 × 10 ¹⁵ c
At m ^-3 , its diffusion length is 1.5 microns.

The p-layer 34 is formed at a position separated from the n-layer 9 which is a vertical CCD transfer section of the n-layer 7 which is a photoelectric conversion element. The p layer 34 is formed along the long side of the n layer 7 of the photoelectric conversion element. The length in the long side direction of the p layer 34 is 3
Micron. If this length is longer and formed along the long side of the n-layer 7 of the photoelectric conversion element, the applied voltage for operating the electronic shutter can be reduced.
That is, the pulse voltage to be applied to the substrate 5 to discharge all the signal charges accumulated in the n-layer 7 to the substrate 5 can be reduced.

The n-layer 7 and the p-layer 34 of the photoelectric conversion element
The end farthest from the n-layer 9, which is the vertical CCD transfer section, coincides in this embodiment. The same effect can be obtained even when the end of the p layer 34 extends from the end of the n layer 7 to the adjacent p layer 33. As described above, since there is a margin in the positional relationship for forming the end portion, a margin in manufacturing is increased.

On the other hand, when the end of the p layer 34 is shorter than the end of the n layer 7, the n layer 7 comes into direct contact with the substrate 5 and no signal charges can be stored in the n layer 7.

Further, the thickness of the p layer 34 in the depth direction of the substrate 5 is 1.5 μm. This thickness affects the value of the pulse voltage to be applied to the n-layer 7 when operating the electronic shutter of the solid-state imaging device. That is, when the thickness is smaller than this thickness, the potential barrier generated between n layer 7 and substrate 5 becomes low. Therefore, the voltage to be applied to the substrate 5 can be reduced.

When the thickness is larger than this thickness, the potential barrier generated between n layer 7 and substrate 5 becomes higher. Therefore, it is necessary to increase the voltage to be applied to the substrate 5.

The n-type substrate 5 is provided between the p-layer 33 and the n-type substrate 5.
Reverse voltage Vs which becomes a positive potential and the p-layer 33 becomes a negative potential.
ub is applied.

When a positive voltage Vsub is applied to the n-type substrate 5 in order to prevent the blooming phenomenon, the potential distribution along the lines CC ′ and DD ′ shown in FIG. 7 is shown in FIG. , 9.

FIG. 8 is a diagram for explaining in detail that the solid-state imaging device of the present invention is effective in reducing the blooming phenomenon.

A broken line 36 in FIG. 8 indicates the C- line shown in FIG.
The C ′ line and the solid line 37 show the potential distribution along the DD ′ line. The regions 10, 7, 33 and 5 are each a high concentration p layer 1
0, n layer 7 of photoelectric conversion element, p layer 33 with low concentration and thick, n
3 shows the thickness of the mold substrate 5 in the depth direction.

When the potential Vsub is applied, the value of the minimum potential 38 in the low-concentration thick p-layer 33 is higher than the value of the minimum potential 39 in the high-concentration thin p-layer 34. .

In the n-layer 7 of the photoelectric conversion element, a potential well is formed. Therefore, the charges generated in the n-layer 7 and the periphery thereof move along the potential forming the well of this potential. As a result, charges are accumulated in the potential well. Further, the accumulated electric charge increases, and the minimum potential 38
When an electric charge having a potential exceeding the above occurs, it becomes an excess electric charge and moves along the electric potential distribution of the p layer 33. As a result, excess charges are discharged to the n-type substrate 5.

The blooming phenomenon is a phenomenon that occurs when high-brightness light enters the n-layer 7 of the photoelectric conversion element. That is, a large amount of electrons are instantaneously generated in the photoelectric conversion element by the incident light. Only a certain amount of electrons can be stored in the photoelectric conversion element. Therefore, when the amount of electrons generated instantaneously is large and is larger than the capacity stored in the photoelectric conversion element, excessive electrons flow into the transfer channel of the adjacent vertical CCD. Such a phenomenon is called a blooming phenomenon.

FIG. 8 shows that the potential distribution in the photoelectric conversion element is
FIG. 9 shows two types of distributions shown by a broken line 36 and a solid line 37 shown in FIG. 8. The electrons formed in the n-layer 7 of the photoelectric conversion element are
The potential is accumulated in the well. When the accumulation amount increases, electrons flow to the p-layer 33 from the lower potential portion of the two distribution shapes of the n-layer 7 of the photoelectric conversion element. The minimum potential 38 in the distribution state indicated by the solid line 37
Is lower than the minimum potential 39 of the dashed line 36, so that electrons flow from the region having the potential distribution of the solid line 37 to the p-layer 33 first.

FIG. 9 is a diagram for explaining in detail that the solid-state imaging device according to the present invention has a configuration effective for performing the operation of the electronic shutter.

The electronic shutter is to discharge all the signal charges accumulated in the n-layer 7 of the photoelectric conversion element to the n-type substrate 5. FIG. 9 shows the substrate 5 when the operation of the electronic shutter is performed.
It is a potential distribution in the inside. That is, the operation of the electronic shutter is to discharge all the electrons accumulated in the n-layer 7 of the photoelectric conversion element to the substrate 5. If the stored electrons are not completely discharged, when the electronic shutter is operated, a different amount of electric charge is accumulated (remaining) inside each photoelectric conversion element. Therefore, a fixed pattern is generated by the remaining charges.

A positive voltage Vsub higher than that in FIG. 8 is applied to the n-type substrate 5 in order to operate the electronic shutter.

FIG. 9 shows a line CC ′ and a line DD ′ in FIG.
The potential distribution along the line is shown by a broken line 40 and a solid line 41, respectively.

The regions 10, 7, 33 and 5 in FIG. 9 respectively show the high-concentration p-layer 10, the n-layer 7 of the photoelectric conversion element, the low-concentration thick p-layer 33, and the Is shown.

When the potential Vsub is applied, the minimum potential 42 of the p-layer 34 having a high concentration and a small thickness is higher than the minimum potential 43 of the p-layer 33 having a low concentration and a large thickness, and the minimum potential 42 is It is lower than the potential 44 of the n-layer 7. Therefore, the signal charges stored in the n-layer 7 of the photoelectric conversion element are:
It moves along the dashed line 42 with a lower potential. At this time, since the potential indicated by the broken line 42 is lower than the minimum potential 44 in the n-layer 7 of the photoelectric conversion element, all signal charges accumulated in the photoelectric conversion element are discharged to the n-type substrate 5.

FIG. 10 is a diagram illustrating the relationship between Vsub and the potential for explaining the reason for this.

The solid line 45 and the broken line 46 in FIG. 10 show the Vsub voltage dependency of the minimum potential in the low-concentration thick p-layer 33 and the high-concentration thin p-layer 34, respectively.

The solid line 45 shows that the minimum potential in the p-layer 33 gradually increases as the Vsub potential increases.

On the other hand, the broken line 46 indicates that the minimum potential in the p layer 34 sharply increases as the Vsub potential increases.

This difference is due to the fact that, when comparing the p-layer 33 and the p-layer 34, the impurity concentration of the p-layer 33 is lower than the impurity concentration of the p-layer 34 and the thickness thereof is larger. That is, the p-layer 34 has a high impurity concentration and a small thickness.

Therefore, the dependence of the amount of charge stored in the n-layer 7 of the photoelectric conversion element on the Vsub potential is represented by the solid line 45 below the intersection 47 and the broken line 46 above the intersection 47 in FIG.
Is determined. That is, the amount of charge stored in the photoelectric conversion element has Vsub potential dependence as shown in FIG. The state shown in FIG. 8 during accumulation in the photoelectric conversion element, that is, the state shown in FIG. 8 corresponds to the region 48 in FIG.

When discharging the signal charges by operating the electronic shutter, the electronic shutter is operated in a state shown in FIG. 9, that is, in a state where the voltage is higher than the solid line shown in FIG. By doing so, the operation of the electronic shutter can be performed with the pulse voltage that causes the photoelectric conversion element having a high saturated charge amount to have a low Vsub.

Thus, in order to prevent the occurrence of blooming, the change in the maximum accumulated charge amount is V
It is preferable to perform the process in a Vsub potential dependent region that is gentle with respect to the sub potential.

The use in such a region facilitates the adjustment of the Vsub potential of the camera-integrated VTR. Further, by using such a Vsub potential region, a decrease in the maximum accumulated charge amount of the photoelectric conversion element can be reduced.

On the other hand, when the electronic shutter is operated, the change in the maximum accumulated charge amount is Vsub as in the region 49.
Is preferably used in a region having a sharp Vsub dependency with respect to

The potential for operating the electronic shutter is realized by adding a clock voltage to the potential applied when preventing blooming.

In the solid-state imaging device of the present invention, when operating the electronic shutter in the conventional solid-state imaging device, the electronic shutter can be operated at a voltage lower than the applied clock voltage.

That is, when operating the electronic shutter in the conventional solid-state imaging device, the clock voltage applied is 3
0 In the solid-state imaging device of this embodiment whereas the bolt may be operating the electronic shutter at a low voltage of 18 volts.

By forming the low-concentration thick p-layer 33 and the high-concentration thin p-layer 34 in contact with the n-layer 7 of the photoelectric conversion element, the Vsub of the video camera for preventing blooming is formed. The potential can be easily adjusted, and the maximum accumulated charge amount (saturated charge amount) of the photoelectric conversion element can be increased. Further, it can be realized with a low clock voltage for operating the electronic shutter.

Further, a high-concentration shallow p-layer 34 is formed so as to partially overlap the n-layer 7 of the photoelectric conversion element, as shown by a broken line 35 in FIG. That is, by forming the n-layer 7 at the position shown by the broken line 35, the thickness of the n-layer 7 in contact with the high-concentration and thin p-layer 34 is substantially reduced. Therefore, when the signal charges of the photoelectric conversion element are read, the n-layer 7 of the photoelectric conversion element is in a depleted state. Therefore, the potential distribution generated there becomes deeper on the reading side, and it becomes easier to prevent the occurrence of an afterimage.

[0132] Next, the solid-state imaging device of the second embodiment of another invention with reference to FIG 2.

FIG. 12 is a cross-sectional view of the prior art (FIG. 24 ).
It is sectional drawing which followed the -A 'line. A p-layer 33 having a predetermined range of depth and concentration is formed on the n-type substrate 5. A partial region of the photoelectric conversion element of the n-layer 7 is formed in the p-layer 33. The p-layer 33 has a high concentration of the p-layer 8.
Are formed, and an n-layer 9 serving as a transfer channel which is a vertical CCD is provided in the p-layer 8. Further, a high concentration and thin p layer is in contact with a part of the bottom of the n layer 7 of the photoelectric conversion element.
A layer 34 is formed. The p layer 34 is formed on the n-type substrate 5 sandwiched between the p layer 33 and the adjacent p layer 33. On the n-layer 7 of the photoelectric conversion element, a high-concentration p-layer 10 is formed. The p layer 8 is composed of the p layer 7 and the p layer 10.
And are formed apart from each other.

On the n-type substrate 5, a transfer electrode 13 of a vertical CCD is formed at least in a region other than a predetermined region of the n-layer 7 of the photoelectric conversion element via an insulating film 12 such as SiO ₂ .

Here, the difference from the first embodiment of the present invention is that the p-layer 34 having a high concentration and a small thickness is formed on the reading side of the p-layer 8 serving as a vertical CCD transfer channel.

That is, the portion of the n-layer 7 of the photoelectric conversion element that is in contact with the high-concentration and thin p-layer 34 is formed slightly deeper than the portion that is in contact with the low-concentration and thick p-layer 33. The shape of the n-layer 7 of the photoelectric conversion element is a key shape, and a p-layer 34 is formed at the tip of the short side. Thus, when the n-layer 7 of the photoelectric conversion element is depleted, the potential on the read side of the photoelectric conversion element increases. For this reason, the charge of the photoelectric conversion element can easily move at the time of reading. Therefore, it is easier to prevent the occurrence of an afterimage.

Here, a driving method of the solid-state imaging device of FIG. 7 will be described with reference to FIGS.

In FIG. 7, p layer 8 is electrically grounded. A positive voltage is applied to the substrate 5. Therefore, a reverse bias state is provided between the p-layers 8, 33, and 34 and the substrate 5. FIG. 8 shows the potential distribution in the signal charge accumulation period at this time as a potential distribution along the line CC ′ and line DD ′ in FIG. 7 as described above.

In this period, the minimum potential 38 of the p-layer 33 is
Is deeper than the minimum potential 39 of the p layer 34. Therefore, the electrons that have become excessively charged in the n-layer 7 of the photoelectric conversion element must move along the minimum potential 38 and be discharged to the substrate 5. For this purpose, a predetermined voltage may be applied to the substrate 5.

On the other hand, FIG. 9 shows the potential distribution along the line CC ′ and line DD ′ in FIG. 7 during the period in which the operation of the electronic shutter is performed, as described above. .

In this period, it is necessary to apply a higher voltage to the substrate 5 than in the signal charge accumulation period. By applying a higher voltage to the substrate 5, all the signal charges accumulated in the n-layer 7 can be discharged to the n-type substrate 5. For this purpose, the minimum potential 42 of the p layer 34 needs to be higher than the maximum potential 44 of the n layer 7.

By forming the p-layer 33 at a low concentration and increasing the thickness of its distribution and forming the p-layer 34 at a high concentration and deep, the electronic shutter can be operated at a lower voltage than in the conventional case. At this time, the potential of the minimum potential 43 of the p layer 33 is lower than the minimum potential 42 of the p layer 34. That is, as the Vsub potential applied to the substrate 5 is increased, the minimum potential 43 of the p-layer 33 becomes
Can overtake.

Thus, the potential shutter can be operated even if the potential applied to the substrate 5 is low.

[0144] A third embodiment of the following other invention will be described with reference to FIG. FIG. 13 is a cross-sectional view of the prior art (FIG. 24 ).
It is sectional drawing which followed the -B 'line. A p-layer 33 having a predetermined range of depth and concentration is formed on the n-type substrate 5. The region sandwiched between the p layer 33 and the adjacent p layer 33 is the n-type substrate 5. The p-layer 34 is formed on the n-type substrate 5 sandwiched between the p-layer 33 adjacent to the p-layer 33. p layer 3
The n-layer 7 of the photoelectric conversion element is formed continuously in a part of each of the p-layer 3 and the p-layer 34. A p-layer 52 for isolation is formed between adjacent photoelectric conversion elements.

[0145] The present invention, first and second when compared to the embodiment of, the p-layer 8 and the p layer 33, n layer 9 serving as a transmission channel in the p layer 8 is not provided structure of the present invention It is.

Further, a p-layer 34 having a high concentration and a small thickness is formed in contact with a part of the bottom of the n-layer 7 of the photoelectric conversion element. On the n-layer 7 of the photoelectric conversion element, a high-concentration p-layer 10 is formed.

A transfer electrode 50 of a vertical CCD is formed on the n-type substrate 5 at least in a region other than a predetermined region of the n-layer 7 of the photoelectric conversion element via an insulating film 12 such as SiO ₂ . Further, a transfer electrode 51 of the vertical CCD is formed via the insulating film 12.

One high-concentration and thin p-layer 34 is formed at a separation portion between a photoelectric conversion element and an adjacent photoelectric conversion element. That is, the p layer 34 is formed in common for the two photoelectric conversion elements.

In this manner, the number of the p-layers 34 having a high concentration and a small thickness can be reduced to half the number of the photoelectric conversion elements. Further, since the area of the high-concentration and thin p-layer 34 in contact with the photoelectric conversion element can be reduced, blooming can be easily prevented.

FIG. 14 is a sectional view taken along the line CC ′ of FIG.
7 is an impurity atom concentration distribution in a depth direction along a line. 5
3, 54, 55, 56 and 57 are high-concentration p layers 1 respectively.
0, n layer 7 of photoelectric conversion element, p layer 3 with high concentration and small thickness
4, the impurity concentration of the low-concentration thick p-layer 33 and the n-type substrate 5.

In order to form the p layer 34 as an impurity concentration 55 which is a high-concentration and thin layer, the impurity concentration 54 of the n-layer 7 of the photoelectric conversion element is set to be higher in the substrate than in the surface of the substrate 5. Is formed so as to have the maximum value. With such a structure, a decrease in the net impurity concentration in the n-layer 7 of the photoelectric conversion element can be reduced. Therefore, the characteristics of the photoelectric conversion element do not deteriorate. At this time, the impurity concentration 56 of the low-concentration and thick p-layer 33 is also high-concentration and the thickness of the p-layer 33 is small.
By forming a structure having the maximum value of the impurity atom concentration distribution inside the substrate rather than the substrate surface like the layer 34,
The independence of the impurity concentration 55 of the low-concentration thick p-layer 33 and the high-concentration thin p-layer 34 is easily maintained, and the control of the impurity concentration becomes easier.

The above-described structure can be realized by implanting an impurity such as boron at an acceleration energy of 200 KeV or more when forming the p-layer 34 having a high concentration and a small thickness.

The net impurity concentration distribution around the photoelectric conversion element thus formed is as shown in FIG. 58,5
Reference numerals 9, 60 and 61 denote a high-concentration p layer 10, an n-layer 7 of a photoelectric conversion element, a high-concentration and thin p-layer 34, and an n-type substrate 5, respectively.
Shows the net impurity concentration. Reference numerals 62 and 63 denote the low impurity concentration of the p layer 33 and the net impurity concentration of the n-type substrate 5, respectively. At this time, the impurity concentration distribution can be more easily controlled by implanting the low-concentration thick p-layer 33 at an acceleration energy of 200 KeV or more, similarly to the high-concentration and thin p-layer 34.

FIGS. 16 to 19 are sectional process views of the solid-state imaging device according to the first embodiment of the present invention . Boron, which is a p-type impurity, is ion-implanted into substantially the entire main surface of the n-type substrate 5 having a specific resistance of 20 ohm.cm. Here, boron ion implantation is performed at an implantation amount of about 5 × 10 ¹¹ / cm ² . This ion implantation introduces boron into the surface of the substrate 5.

Thereafter, the substrate 5 is heat-treated to form the p-layer 6. In the solid-state imaging device according to the second embodiment of the present invention , ions are introduced into the surface of the substrate 5 and thermally diffused so that the impurity concentration is distributed over a wide range. That is, by heat-treating the substrate 5 at a high temperature, the ion-implanted boron is diffused to form the p-layer 6.

The p-layer 6 is formed such that the ions are introduced into the substrate surface, but the ions are diffused over a wide range by a high-temperature heat treatment.

After that, a resist pattern is formed by using ordinary photolithography in a region other than a region serving as a vertical CCD transfer channel. Using the resist pattern as a mask, boron is ion-implanted to form a p-layer 8.

Thereafter, the previous resist pattern is removed by dry etching using an oxygen-based gas. Further, a resist pattern is formed again by photolithography in a region other than the region where the n-layer 9 is formed in the p-layer 8 serving as a vertical CCD transfer channel.

Using the resist pattern as a mask, phosphorus is ion-implanted to form n layer 9. Thereafter, the resist pattern is removed by using oxygen-based dry etching.

Next, an insulating film 12 is formed on the main surface of the substrate 5 by thermal oxidation. Here, an oxide film is used as the insulating film 12.

Further, an electrode material for forming the vertical CCD transfer electrode 13 is formed on the insulating film 12. Further, a resist is applied on the electrode material (FIG. 16).

Next, the resist in the region other than the region wider than the region to be the transfer electrode 13, that is, the region where the n-layer 7 to be the photoelectric conversion element is to be formed is removed by ordinary photolithography using photolithography. Then, a resist pattern 20 is formed. Dry etching is performed on the electrode material using the resist pattern 20 as a mask to form the insulating film 12.
Etch until is exposed.

Next, using the resist pattern 20 and the electrode material as a mask, phosphorus ions are implanted using the insulating film 12 as a protective film. By this ion implantation, an n-layer 7 serving as a photoelectric conversion element is formed (FIG. 17).

Here, phosphorus ion implantation is performed at an acceleration energy of 360 to 800 keV and an implantation amount of 1.2 × 10 ^{12 to} 3.4 ×
Perform at 10 ¹² / cm ² .

From the above, it is not necessary to increase the amount of impurities introduced into the photoelectric conversion element as in the conventional case. In order to increase the introduction amount, a considerable time loss is caused. Therefore, the throughput when forming the solid-state imaging device does not decrease.

In addition, it is not necessary to diffuse the introduced impurities into the deep part of the substrate by high-temperature heat treatment, thereby increasing the volume of the photoelectric conversion element. Therefore, defects in the substrate caused by the high-temperature heat treatment do not occur. Further, the impurity is diffused from the other diffusion layers, and there is no need to control to have a desired impurity concentration. In addition, by performing the high-temperature heat treatment, the photoelectric conversion elements are diffused and spread, and are not diffused into the vertical CCD transfer channel or the gap between the transfer channel and the photoelectric conversion element.

Further, regarding the positional relationship between the end of the photoelectric conversion element and the end of the vertical CCD transfer electrode, it is not difficult to control the position of the diffusion layer by performing a high-temperature heat treatment. Therefore, the positional relationship between the two can be easily obtained. This can prevent the blooming phenomenon of the solid-state imaging device from occurring, and can suppress the deterioration of the image quality due to the deterioration of the saturation characteristics.

After that, the resist pattern 20 is removed. On the surface of the substrate 5, an electrode material in a region wider than the insulating film 12 and the transfer electrode 13 is formed. Next, the transfer electrode 13
The resist pattern is formed realm to be, dry etching the electrode material using the resist pattern as a mask.
Through the above steps, the transfer electrode 13 is formed (FIG. 18).

At this time, the electrons are vertically transferred from the photoelectric conversion element.
The transfer electrode 13 must be provided on the gap between the n-layer 7 and the p-layer 8 read out to the D transfer channel. For this reason, in the dry etching when the transfer electrode 13 is formed, the side wall end of the n-layer 7 originally serving as a photoelectric conversion element and the transfer electrode 1
Since the side wall ends of the transfer electrodes 13 coincide with each other, one side wall end of the transfer electrode 13 is formed to have a predetermined length.

Next, an insulating film 12 is deposited on the main surface of the substrate 5. Using the transfer electrode 13 and the resist pattern as a mask, boron ions are implanted. As a result, a p-layer 10 for preventing dark current is formed on the n-layer 7 (FIG. 19).

Although the description here has been made with reference to the example of the n-type photoelectric conversion element, it is needless to say that the same effect can be obtained in the case of the p-type photoelectric conversion element.

It is needless to say that the same effect can be obtained even if the polarity of the applied voltage is reversed by reversing the polarity of the conductivity type.

It is needless to say that the ion species to be implanted need not be limited to those listed here. 20 to 23 are sectional process views of the solid-state imaging device according to the first embodiment of the present invention .

On the main surface of n-type substrate 5, a resist pattern is formed in a region other than the region serving as p layer 33. That is, a resist pattern is formed on the substrate 5 in the region of the high-concentration and thin p-layer 34 formed below the photoelectric conversion element. Next, boron as a p-type impurity is ion-implanted into the entire surface of the substrate 5 using the resist pattern as a mask.

Thereafter, the resist pattern is removed by using oxygen-based dry etching. Next, a new resist pattern 64 is formed in a region to be the p layer 33. That is, the resist pattern 64 is formed on the substrate 5 other than the region of the high concentration and thin p layer 34 formed under the photoelectric conversion element. Next, boron, which is a p-type impurity, is ion-implanted into n-type substrate 5 using resist pattern 64 as a mask (FIG. 2).
0).

Thereafter, the resist pattern 64 is removed by using oxygen-based dry etching.

In the above two boron ion implantation steps,
The order of the injections may be changed.

At this time, when the end portions of the diffusion layers of the p layer 33 and the p layer 34 overlap, the impurity concentration in the overlapped portion increases, and the thickness also increases. For this reason, the overlapped portion does not contribute to discharging signal charges to the substrate.

If the end portions of the diffusion layers of the p layer 33 and the p layer 34 are formed so as not to overlap with each other, the p-type impurity concentration in the non-overlapping gap becomes low. For this reason, the saturated charge amount decreases or Vsub to be applied
The voltage will drop.

After that, a resist pattern is formed by using photolithography in a region other than a region serving as a vertical CCD transfer channel. Using the resist pattern as a mask, boron is ion-implanted to form a p-layer 8.

Thereafter, the resist pattern is removed by dry etching using an oxygen-based gas. Further, a resist pattern is formed again by photolithography in a region other than the region where the n-layer 9 is formed in the p-layer 8 serving as a vertical CCD transfer channel.

Using the resist pattern as a mask, phosphorus is ion-implanted to form n-layer 9. Thereafter, the resist pattern is removed by using oxygen-based dry etching.

Next, an insulating film 12 is formed on the main surface of the substrate 5 by thermal oxidation. Here, an oxide film is used as the insulating film 12.

Since the thickness of this oxide film is used as a mask for ion implantation of a photoelectric conversion element formed in a later step, the thickness must be controlled with high precision.

Further, an electrode material for forming the vertical CCD transfer electrode 13 is formed on the insulating film 12. Further, a resist pattern 65 is formed on the electrode material using photolithography in a region other than a region wider than a region to be the transfer electrode 13. The electrode material is dry-etched using the resist pattern 65 as a mask until the insulating film 12 is exposed (FIG. 21).

Next, phosphorus ions are implanted using the resist pattern 65 and the electrode material as a mask and using the insulating film 12 as a protective film. By this ion implantation, an n-layer 7 serving as a photoelectric conversion element is formed.

The distribution of the impurity concentration of p layer 7 is high in the region formed on substrate 5 and low in the region formed on p layer 33. That is, the n-layer 7 of the photoelectric conversion element formed on the substrate 5 is determined by the sum of the n-type impurity concentration of the substrate 5 and the ion-implanted n-type impurity concentration. On the other hand, the n-layer 7 of the photoelectric conversion element formed on the p-layer 33
Is determined by the sum of the p-type impurity concentration of the p-layer 33 and the ion-implanted n-type impurity concentration.

As described above, the n-layer 7 of one photoelectric conversion element
Within the region, regions having different impurity concentrations are formed.

Further, the high-concentration thin p-layer 34 is controlled so as to be formed at the bottom of the diffusion layer of the n-layer 7 serving as a photoelectric conversion element.

In the second embodiment of the invention of the above-described solid-state imaging device, the high-concentration and thin p-layer 34 is formed on the transfer electrode 13 side.

Also in this case, in the region where p layer 34 and n layer 7 overlap, the impurity concentration is the sum of the impurity concentrations of n layer 7 and p layer 34 .

Here, the portion of the n-layer 7 of the photoelectric conversion element which is in contact with the p-layer 34 having a high concentration and a small thickness is replaced with a p-layer 3 having a low concentration and a large thickness.
It is formed slightly deeper than the part in contact with 3. The shape of the n layer 7 of the photoelectric conversion element is a key shape, and the p layer 3
4 are formed. Thereby, n of the photoelectric conversion element
When the layer 7 is depleted, the potential on the read side of the photoelectric conversion element increases. For this reason, the charge of the photoelectric conversion element can be easily moved at the time of reading.

As described above, the key type n layer is formed such that the junction surface between the p layer 34 and the n layer 7 is deeper than the junction surface between the p layer 33 and the n layer 7. That is, when the p-layer 34 is formed, the acceleration energy of boron to be ion-implanted is
The ion implantation is performed at a higher acceleration energy than the ion implantation for forming the p-layer 33. Therefore, by increasing the thickness of the n-layer 7 in the depth direction of the substrate 5, the potential at that portion is increased.

From the above, it is not necessary to increase the amount of impurities introduced into the photoelectric conversion element as in the conventional case. In order to increase the introduction amount, a considerable time loss is caused. Therefore, the throughput does not decrease when the solid-state imaging device is formed.

Further, it is not necessary to diffuse the introduced impurities into the deep part of the substrate by the high-temperature heat treatment to increase the volume of the photoelectric conversion element. Therefore, defects in the substrate caused by the high-temperature heat treatment do not occur. Further, the impurity is diffused from the other diffusion layers, and there is no need to control to have a desired impurity concentration. In addition, by performing the high-temperature heat treatment, the photoelectric conversion elements are diffused and spread, and are not diffused into the vertical CCD transfer channel or the gap between the transfer channel and the photoelectric conversion element.

The positional relationship between the end of the photoelectric conversion element and the end of the vertical CCD transfer electrode is not difficult to control by controlling the position of the diffusion layer by performing a high-temperature heat treatment. Therefore, the positional relationship between the two can be easily obtained. This can prevent the blooming phenomenon of the solid-state imaging device from occurring, and can suppress deterioration in image quality.

Thereafter, the resist pattern 65 is removed. On the surface of the substrate 5, an electrode material in a region wider than the insulating film 12 and the transfer electrode 13 is formed. Next, the transfer electrode 13
The resist pattern is formed realm to be, dry etching the electrode material using the resist pattern as a mask.
Through the above steps, the transfer electrode 13 is formed (FIG. 22).

At this time, electrons are emitted from the photoelectric conversion element in a vertical CC direction.
The transfer electrode 13 must be provided on the gap between the n-layer 7 and the p-layer 8 read out to the D transfer channel. For this reason, in the dry etching when the transfer electrode 13 is formed, the side wall end of the n-layer 7 originally serving as a photoelectric conversion element and the transfer electrode 1
Since the side wall ends of the transfer electrodes 13 coincide with each other, one side wall end of the transfer electrode 13 is formed to have a predetermined length.

Next, an insulating film 12 is deposited on the main surface of the substrate 5. Using the transfer electrode 13 and the resist pattern as a mask, boron ions are implanted. Thus, a p-layer 10 for preventing dark current is formed on n-layer 7 (FIG. 23).

As described above, in the method of manufacturing a solid-state imaging device according to the present invention, since the n-layer serving as the photoelectric conversion element is realized by ion implantation with high acceleration energy, the impurity concentration distribution is the highest in the substrate. High area can be provided.

As a result, the total amount of effective donors that can be stored in the photoelectric conversion element increases, and the saturation charge can be sufficiently increased.

Since the photoelectric conversion element is formed by ion implantation, the positional relationship between the end of the photoelectric conversion element and the vertical CCD transfer electrode depends on the accuracy of the mask alignment in the exposure step performed when forming the transfer electrode 12. Is determined. Therefore, there is no need to control the position formed by thermal diffusion at a high temperature, and the controllability of the position between the end of the photoelectric conversion element and the vertical CCD transfer electrode is high. This makes it difficult for the solid-state imaging device to cause an afterimage phenomenon, and can prevent image quality from deteriorating.

Further, in the impurity concentration distribution of the n-layer forming the photoelectric conversion element by ion implantation, the maximum value of the concentration can be set inside the substrate. Therefore, the total amount of effective donors accumulated in the photoelectric conversion element increases. Therefore, it is possible to obtain a solid-state imaging device including a photoelectric conversion element having high saturation characteristics.

A p-layer for preventing dark current is formed on the n-layer of the photoelectric conversion element. A maximum value of the concentration of the n-layer serving as a photoelectric conversion element is formed inside the substrate by ion implantation. Therefore, the net value of the impurity concentration of the p-layer on the substrate surface can be made higher than the concentration of the p-layer of the conventional solid-state imaging device. Therefore, a solid-state imaging device having a photoelectric conversion element having low dark current characteristics can be obtained.

In the method of manufacturing a solid-state imaging device according to the present invention, the impurity concentration of the photoelectric conversion element is highest at the deep portion of the substrate. Therefore, it is not necessary to increase the amount of impurities introduced into the photoelectric conversion element, which has been conventionally performed. In order to increase the introduction amount, a considerable time loss is caused. Therefore, the throughput when forming the solid-state imaging device does not decrease. Further, a decrease in yield due to white spots can be prevented.

Further, it is not necessary to diffuse the introduced impurities into the deep part of the substrate by the high-temperature heat treatment to increase the area of the photoelectric conversion element. Therefore, defects in the substrate caused by the high-temperature heat treatment do not occur. Further, the impurity is diffused from the other diffusion layers, and there is no need to control to have a desired impurity concentration. In addition, by performing the high-temperature heat treatment, the photoelectric conversion elements are diffused and spread, and are not diffused into the vertical CCD transfer channel or the gap between the transfer channel and the photoelectric conversion element.

Although the description here has been made with reference to the example of the n-type photoelectric conversion element, it is needless to say that the same effect can be obtained in the case of the p-type photoelectric conversion element.

[0208]

According to the present invention, a photoelectric conversion element is formed.
(The first region) formed by the main impurities and the dark current
Formed by the main impurities that constitute the layer that reduces
The overlap with the (second region) is reduced, and the photoelectric conversion element
The absolute amount of the effective donor that determines the amount of signal charge stored is
Dramatically larger than before, sufficient saturation charge
Become larger. Further, the first region and the second region are
The amount of ion implantation to form each is reduced
You. If the amount of these ions implanted is large, so-called white scratches may occur.
As the probability of ion implantation increases, the reduction
Very high technical value.

[Brief description of the drawings]

FIG. 1 is a sectional view for explaining a solid-state imaging device according to a first embodiment of the present invention;

FIG. 2 is a diagram for explaining an impurity concentration of the solid-state imaging device according to the first embodiment of the present invention;

FIG. 3 is a diagram for explaining a net impurity concentration of the solid-state imaging device according to the first embodiment of the present invention;

FIG. 4 is a diagram for explaining a net impurity concentration of the solid-state imaging device according to the first embodiment of the present invention;

FIG. 5 is a diagram for explaining an impurity concentration of a solid-state imaging device according to a second embodiment of the present invention;

FIG. 6 is a diagram for explaining a net impurity concentration of a solid-state imaging device according to a second embodiment of the present invention;

FIG. 7 is a cross-sectional view for explaining a solid-state imaging device of the first embodiment of another invention

[8] the potential distribution diagram for explaining a blooming phenomenon of the first embodiment of another invention

[9] the potential distribution diagram for explaining the operation of the electronic shutter of the first embodiment of another invention

Figure 10 is a diagram for explaining a substrate potential of the first embodiment of another invention

11 is a diagram for explaining a maximum accumulated charge amount of the first embodiment of another invention

FIG. 12 is a cross-sectional view for explaining a solid-state imaging device of the second embodiment of another invention

[13] The third alternative cross-sectional view for a solid-state imaging device of Example illustrating the other invention

Figure 14 is a diagram for explaining an impurity concentration of the solid-state imaging device according to the first embodiment of another invention

Diagram for explaining the net impurity concentration of the solid-state imaging device according to the first embodiment of FIG. 15 another invention

Diagram for explaining the actual施例method for manufacturing the solid-state imaging device in FIG. 16 the present invention

Diagram for explaining the actual施例method for manufacturing the solid-state imaging device in FIG. 17 the present invention

Figure 18 is a diagram illustrating the actual施例method for manufacturing the solid-state imaging device of the present invention

Diagram for explaining the actual施例method for manufacturing the solid-state imaging device in FIG. 19 the present invention

Figure 20 is a diagram illustrating the actual施例method for manufacturing the solid-state imaging device of another invention

Figure 21 is a diagram illustrating the actual施例method for manufacturing the solid-state imaging device of another invention

Figure 22 is a diagram for explaining the actual施例method for manufacturing the solid-state imaging device of another invention

Figure 23 is a diagram for explaining the actual施例method for manufacturing the solid-state imaging device of another invention

FIG. 24 is a plan view illustrating a conventional solid-state imaging device.

FIG. 25 is a cross-sectional view illustrating a conventional solid-state imaging device.

FIG. 26 is a diagram for explaining the impurity concentration of a conventional solid-state imaging device.

FIG. 27 is a diagram for explaining the net impurity concentration of the conventional solid-state imaging device.

FIG. 28 is a cross-sectional view for explaining a conventional method of manufacturing a solid-state imaging device.

FIG. 29 is a cross-sectional view for explaining a method for manufacturing a conventional solid-state imaging device.

FIG. 30 is a cross-sectional view for explaining a conventional method of manufacturing a solid-state imaging device.

FIG. 31 is a cross-sectional view for explaining a method of manufacturing a conventional solid-state imaging device.

[Explanation of symbols]

 Reference Signs List 5 substrate 6 p layer 7 n layer 8 p layer 9 p layer 12 insulating layer

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Sumio Terakawa 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electronics Corporation (56) References JP-A-60-170968 (JP, A) JP-A-62- 131566 (JP, A) JP-A-62-217656 (JP, A) JP-A-3-171668 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/148 H01L 21 / 339 H01L 29/762 H04N 5/335

Claims (10)

(57) [Claims] To 1. A semiconductor board, a first region mainly one conductivity type impurity of the photoelectric conversion element unit for accumulating the signal charges are distributed, the opposite conductivity type impurity into the substrate surface side of the first region
A distributed second region, wherein the concentration maximum of one conductivity type impurity of the first region in the substrate depth direction is deeper in the substrate than an end of the second region on the substrate inner side. A solid-state imaging device characterized by the above-mentioned. To 2. A semiconductor board, a first region mainly one conductivity type impurity of the photoelectric conversion element unit for accumulating the signal charges are distributed, the opposite conductivity type impurity into the substrate surface side of the first region
A distributed second region, wherein the end of the first region on the substrate surface side is deeper in the substrate than the concentration maximum of the opposite conductivity type impurity in the second region in the substrate depth direction. A solid-state imaging device characterized by the above-mentioned. 3. A photoelectric storage device for storing signal charges in a semiconductor substrate.
The first region where the main one conductivity type impurity of the conversion element portion is distributed
And a reverse conductivity type impurity is present on the substrate surface side of the first region.
A second region distributed therein, wherein one conductivity type of the first region is different.
The concentration maximum of the pure substance in the substrate depth direction is the second region.
Deeper than the end of the inside of the substrate,
The end of the first region on the substrate surface side is the same as the end of the second region.
Than the concentration maximum of the opposite conductivity type impurity in the substrate depth direction.
A solid-state imaging device, which is located deep in the substrate. Wherein said the concentration of the concentration maximum of the substrate depth direction of the opposite conductivity type impurity in the second region is 1 × 10 ¹⁸ ~1 × 10
Claims 1 to ³ characterized in that it is ¹⁹ cm- ^3.
3. The solid-state imaging device according to any one of 3 . 5. The method according to claim 1, wherein the first region includes an acceleration energy in the substrate.
Ion implantation of the one-conductivity-type impurity at an energy of 200 keV or more.
3. The method according to claim 1, wherein
The solid-state imaging device according to claim 4. 6. The substrate further comprises a reverse conductivity type diffusion layer.
Of the impurity of the opposite conductivity type in the diffusion layer in the depth direction of the substrate.
The concentration maximum part is the base of the one conductivity type impurity of the first region.
Being deeper in the substrate than the concentration maximum in the plate depth direction
The method according to any one of claims 1 to 5, wherein
Solid-state imaging device. 7. The device according to claim 1, further comprising a diffusion layer of a reverse conductivity type on the substrate.
For example, in the diffusion layer, The first area and the second area are provided.
6. The method according to claim 1, wherein
The solid-state imaging device according to any one of the above. 8. A transfer channel of one conductivity type is provided on the substrate.
A transfer channel that is separated from the first area.
9. The method according to claim 1, wherein
The solid-state imaging device according to any one of the above. 9. The method according to claim 9, wherein the second region is a dark current prevention layer.
The method according to any one of claims 1 to 8, wherein
Solid-state imaging device. 10. The first area and the second area are each
The main impurity introduction conditions for forming each of the concentration maxima
Therefore, the one conductivity type impurity or the opposite conductivity type impurity is separated.
Claim 1 or Claim 2, characterized in that the area is a cloth.
Item 10. The solid-state imaging device according to any one of Items 9.