JP3452828B2 - Solid-state imaging device and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device, and more particularly, to a solid-state image pickup device having a protective film functioning as a hydrogen supply source for suppressing dark current and a method for manufacturing the same. It is a thing.

[0002]

2. Description of the Related Art In a solid-state image pickup device, a protective film is usually formed in order to protect a pixel portion and a circuit portion. The protective film is also used as a hydrogen supply source for suppressing dark current, which is a problem peculiar to the solid-state imaging device. Hydrogen contained in the protective film diffuses into the silicon substrate in the process involving heating,
Terminates the silicon dangling bond. When the dangling bond is terminated, the interface state in the silicon substrate is lowered and dark current is suppressed.

As the protective film, a silicon nitride film formed by a plasma chemical vapor deposition method (plasma CVD method) is often used. This silicon nitride film contains hydrogen that can be released due to SiH ₄ and NH ₃ contained in the film forming gas. The silicon nitride film has a property of hardly permeating hydrogen, and also acts as a barrier that confines hydrogen once released to the silicon substrate side. As described above, the silicon nitride film has characteristics suitable as a protective film for a solid-state imaging device.

On the other hand, in order to reduce the pixel area due to miniaturization of the solid-state image pickup device, there is an urgent need to develop elemental technology for improving the sensitivity of the solid-state image pickup device. One of the effective measures for improving the sensitivity is to reduce the reflection of the incident light to the solid-state imaging device.

For example, Japanese Patent Application Laid-Open No. 10-256518 discloses a solid-state image pickup device having a protective film made of a silicon nitride film and a low reflection film formed in contact with the light receiving portion side of the protective film. ing. In this solid-state imaging device, the light reflected from the silicon substrate is suppressed by forming the low reflection film. The film specifically disclosed as the low reflection film is a silicon nitride film formed by a low pressure CVD method.

In general, the reflection of a light beam incident on a medium having a different refractive index increases according to the difference in the refractive index of the medium. The low reflection film as described in JP-A-10-256518 has an effect of suppressing reflection from a silicon substrate having a higher refractive index than a film formed above the substrate in a solid-state imaging device.

[0007]

By the way, the refractive index of the film laminated above the substrate is not uniform, and in particular, the silicon nitride film formed as the protective film has the refractive index formed adjacent to the silicon nitride film. It is relatively higher than the refractive index of the film. Therefore, not only the reflection from the silicon substrate but also the reflection from the protective film poses a problem for improving the sensitivity of the solid-state imaging device. However, if the formation of the protective film is omitted because reflection from the protective film is a problem, the dark current cannot be reduced and the reliability of the device cannot be maintained.

Therefore, the present invention provides a solid-state image pickup device in which reflection of incident light from the protective film is suppressed even though it has a structure in which a protective film effective for suppressing dark current is formed, and a manufacturing method thereof. The purpose is to provide.

[0009]

In order to achieve the above object, the first solid-state image pickup device of the present invention comprises a plasma in an atmosphere containing hydrogen-containing gas molecules above a light-receiving portion formed in a semiconductor substrate. deposited by chemical vapor deposition, and the silicon nitride film, comprising a multilayered film in which a silicon nitride oxide film is laminated to a film having a lower refractive index than the silicon nitride film, as the multilayer film, a silicon nitride Made of oxide film
First layer, second layer made of silicon nitride film and silicon
A third layer made of a oxynitride film is laminated in order from the light receiving portion side.
And the first layer and the third layer each have a thickness of 95 nm.
Has a thickness of about 195 nm, and the second layer has a thickness of about 190 nm.
It is characterized by having a thickness of 390 nm .

In the second solid-state image pickup device of the present invention, a silicon nitride film and a silicon nitride film are provided above the light receiving portion formed in the semiconductor substrate as a protective film for supplying hydrogen to the semiconductor substrate. Film with lower refractive index than nitride film
And a silicon oxynitride film that is a laminated film are formed, and the multi-layer film is made of a silicon oxynitride film.
First layer, second layer made of silicon nitride film and silicon
A third layer made of a oxynitride film is laminated in order from the light receiving portion side.
And the first layer and the third layer each have a thickness of 95 nm.
Has a thickness of about 195 nm, and the second layer has a thickness of about 190 nm.
It is characterized by having a thickness of 390 nm .

According to the solid-state imaging device of the present invention, the reflection of incident light from the protective film is suppressed, and the sensitivity of the solid-state imaging device is improved. Further, since the protective film is formed, it is possible to suppress dark current and maintain the reliability of the device.

[0012]

[0013]

In the present invention, the first layer and the third layer each have a thickness of 95 nm to 195 nm, and the second layer has a thickness of 190 nm.
Since having a thickness of Nm～390nm, visible light region (wavelength: 380 nm to 780 nm) can be further reduced reflected light at. The thickness of the first layer and the third layer is more preferably 120 nm to 150 nm. The thickness of the second layer is more preferably 250 nm to 300 nm.

Further, in the solid-state imaging device of the present invention, it is preferable that the content ratio of nitrogen to nitrogen and oxygen in the silicon oxynitride film becomes higher as it approaches the silicon nitride film in the film thickness direction. The silicon oxynitride film is preferably formed to have a composition continuous with the silicon nitride film on the surface in contact with the silicon nitride film.

Further, in the solid-state imaging device of the present invention, the refractive index of the silicon nitride oxide film, in the film thickness direction, it is preferable to be higher closer to the silicon nitride film. The refractive index of this film is preferably formed so as to have a continuous refractive index with that of the silicon nitride film on the surface in contact with the silicon nitride film.

In the solid-state image pickup device of the present invention, the first layer
And the refractive index of the third layer is the same as that of the second layer in the film thickness direction.
It is preferable that it continuously changes so that it becomes higher as it approaches .

Further, in the solid-state image pickup device of the present invention, the multilayer film is an insulating film formed so as to cover the light- shielding film and the light-receiving portion for blocking the incidence of external light on portions other than the light- receiving portion , or the insulating film. It is preferably formed on the flattening film formed on the film.

According to the method of manufacturing a solid-state image pickup device of the present invention, a silicon nitride film and a silicon nitride film are provided above a light receiving portion formed in a semiconductor substrate as a protective film for supplying hydrogen to the semiconductor substrate. Is a film with a low refractive index
A silicon oxynitride film that is laminated,
First layer made of silicon oxynitride film, silicon nitride film
Second layer made of silicon nitride and third layer made of silicon oxynitride film
Are laminated in order from the light receiving portion side, and the first layer and the front
The third layer has a thickness of 95 nm to 195 nm, respectively.
And the second layer has a thickness of 190 nm to 390 nm.
And a multi-layered film according to the first aspect of the present invention including a step of continuously forming a multi-layered film according to a plasma CVD method in the same chamber containing hydrogen-containing gas molecules.

According to the manufacturing method of the present invention, reflection of incident light from the protective film is suppressed, and a solid-state image pickup device having improved sensitivity can be efficiently manufactured.

In the method for manufacturing a solid-state image pickup device of the present invention, it is preferable to introduce a nitrogen-containing gas molecule and an oxygen-containing gas molecule into the chamber to form a silicon oxynitride film.

In the method for manufacturing a solid-state image pickup device according to the present invention, the ratio of the nitrogen-containing gas molecule to the total amount of the nitrogen-containing gas molecule and the oxygen-containing gas molecule in the chamber is continuously changed, whereby the silicon oxynitride film is formed. It is preferable that the ratio of nitrogen to the total amount of nitrogen and oxygen be made higher in the film thickness direction as it approaches the silicon nitride film.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an enlarged cross-sectional view showing the vicinity of a light receiving portion of one embodiment of the solid-state imaging device of the present invention.

In this solid-state imaging device, the light receiving portion 1 is formed on the surface of the p-type well layer 12 formed on the n-type silicon substrate 15.
3 is formed. The light receiving unit 13 is formed for each pixel vertically and horizontally arranged on the surface of the silicon substrate. Also, p
On the surface of the mold well layer 12, a charge transfer unit 14 is formed adjacent to the light receiving unit 13 in order to transfer the charges generated by the photoelectric conversion function of the light receiving unit 13. The surface of the silicon substrate is covered with the gate insulating film 11.

A gate electrode 10 is formed on the gate insulating film 11.
Are formed so as to draw a predetermined pattern. The gate electrode 10 is covered with the first insulating film 9. The light-shielding film 8 is formed on the first insulating film 9 so that the light-receiving portion 13 has an opening above it. The light-shielding film 8 is used as the light receiving portion 1.
A light ray from the outside which is incident on a region other than 3 is blocked. Further, the second insulating film 7 is formed so as to cover all of these films. A protective film 20 is formed on the second insulating film 7.
Is formed. A flattening film 3, a color filter layer 2, and an on-chip microlens 1 are formed in this order on the protective film 20.

Each component other than the protective film 20 can be manufactured by a conventionally used method. The light receiving portion 13 and the charge transfer portion 14 in the silicon substrate are manufactured by the ion implantation method. The gate insulating film 11 is formed by thermal oxidation of the silicon substrate. The gate electrode 10 is formed by etching the formed polysilicon film. The first insulating film 9 is formed, for example, by laminating a silicon oxide film formed by oxidizing a gate electrode and a silicon oxide film formed by thermally decomposing TEOS (tetraethylorthosilicate) by a low pressure CVD method. As the light-shielding film 8, a tungsten silicide film, a tungsten film, or the like can be used. As the second insulating film 7, for example, a silicon oxide film doped with impurities such as boron and phosphorus and formed by a plasma CVD method can be used.

The flattening film 3 can be formed using, for example, an acrylic resin. Color filter layer 2
Is formed using a resin material in which a dye or a pigment is dispersed. The on-chip microlens 1 is formed using, for example, a phenol resin. The on-chip microlens 1 is molded into a dome shape by heating a resin layer divided so as to correspond to the light receiving portion.

The protective layer 20 will be described below. In this embodiment, the protective film 20 is formed on the first insulating film 7. The protective film 20 is formed by laminating three layers of a first protective film 6, a second protective film 5, and a third protective film 4 in this order. First protective film 6 and third protective layer 4
Is a silicon oxynitride film (hereinafter referred to as “p-SiON film”) formed by a plasma CVD method. The second protective film 5 is a silicon nitride film (hereinafter referred to as "p-SiN film") formed by a plasma CVD method.

The p-SiN film preferably has a composition represented by Si _v N _w (where 0.75 ≦ v / w ≦ 1.25). This composition is in an amorphous state in which a dangling bond of Si exists, and as a result, the bond between Si and hydrogen is easily formed, which has an effect of suppressing dark current. The refractive index of this film is about 2.0 in the visible light range, although there is some difference depending on the Si / N ratio.
On the other hand, the p-SiON film is preferably Si _x O _y N _z (0
≦ z / (y + z) ≦ 1, 0.75 ≦ x / (y + z) ≦
It has a composition represented by 1.5). In these films, when the ratio of Si is high, the bond between Si and hydrogen is increased, but the film quality becomes hard, and when the ratio of Si is too low, Si
The bond between hydrogen and hydrogen decreases, but the film quality becomes softer. Although the refractive index of this film varies somewhat depending on the composition,
It is about 1.47 to 2.0 in the visible light region.

As shown in FIG. 1, two layers of p-SiON are used.
If the p-SiN film is sandwiched between the films, the change in the refractive index at the interface of the p-SiN film is relaxed and the reflection from the protective film is suppressed. Further, when the film thickness of each layer is adjusted to the preferable range exemplified above, the reflection from the protective film is further suppressed.

If the composition of the p-SiON film is continuously changed in the film thickness direction, the reflection from the protective film can be suppressed more effectively. FIG. 2 shows a film configuration (cross section AA ′ in FIG. 1) above a light receiving portion in a solid-state imaging device including such a p-SiON film and a change in refractive index in this film configuration. It should be noted that FIG. 2 shows a change in the refractive index when each layer other than the protective layer is made of the typical material exemplified above.

In the embodiment shown in FIG. 2, the p-SiON films 4 and 6 are formed so that the refractive index becomes higher as they get closer to the p-SiN film 5. Specifically, p-SiO
In the N films 4 and 6, as the p-SiN film 5 is approached, the ratio of nitrogen to the total amount of nitrogen and oxygen (z / (y +
z)) is high. The p-SiON films 4 and 6 are p
In the portion in contact with the -SiN film 5, p-SiN is substantially used.
Composition of film (composition containing substantially no oxygen; z / (y +
The film is formed so that z) = 1).

On the other hand, the p-SiON films 4 and 6 are made of p-Si.
It has the lowest refractive index at the end opposite to the N film 5. In the form shown in FIG. 2, the p-SiON film 6 is
The opposite end is in contact with the silicon oxide film which is the second insulating film 7. At this end, the p-SiON film 6 is formed so as to have substantially the composition of the silicon oxide film (composition substantially containing no nitrogen; z / (y + z) = 0).

The p-SiON film 4 is in contact with the acrylic resin film, which is the flattening film 3, at the end opposite to the p-SiN film 5. Even at this end, p-Si
The ON film 4 is formed so as to have a composition of a silicon oxide film (a composition substantially not containing nitrogen; z / (y + z) = 0). Since the refractive index of the acrylic resin is almost equal to the refractive index of the silicon oxide film, as shown in FIG. 2, the refractive index also changes substantially continuously at this end.

As described above, the protective film including the p-SiON films 4 and 6 and the p-SiN film 5 has a refractive index which is substantially continuous not only inside the protective film but also between the protective film and the adjacent film. Configured to have a distribution. Specifically, as shown in FIG. 2, from the silicon substrate side, the refractive index of 1.4
7 silicon oxide layers 11, 9, 7 having a refractive index of 1.4
P-SiON film 6 gradually increasing from 7 to 2.0, p-SiN film 5 having a refractive index of 2.0, refractive index of 2.0 to 1.47
The p-SiON film 4 that gradually decreases to a resin layer having a refractive index of about 1.49 is formed in this order. With such a refractive index distribution, in this solid-state imaging device, reflection from the protective film is effectively suppressed.

Although FIG. 1 shows a mode in which the protective film 20 is formed on the insulating film 7, the formation position of the protective film 20 is not particularly limited and, for example, it is formed on the flattening film 3. Good. When it is formed on the flattening film 3, it may be formed on an aluminum wiring arranged on the flattening film 3.

P-SiON films 4, 6 and p-SiN5
The film is formed by a plasma CVD method in an atmosphere containing hydrogen-containing gas molecules such as SiH ₄ and NH ₃ . Therefore, these films are formed as films containing hydrogen in the films. Hydrogen is released in a process involving heating performed after forming the protective film, and terminates dangling bonds on the surface of the silicon substrate. When the dangling bond is terminated,
The order of interfaces in the silicon substrate is lowered and dark current is suppressed. The p-SiN film also functions as a barrier that traps the released hydrogen on the silicon substrate side. In addition, these films are formed in an atmosphere containing nitrogen-containing gas molecules such as NH ₃ , N ₂ and N ₂ O. Furthermore, the p-SiON film is formed in an atmosphere containing oxygen-containing gas molecules such as N ₂ O.

Next, the protective film 20 formed by the plasma CVD method.
A method of forming the will be described. P-SiO of protective film 20
The N films 4, 6 and the p-SiN5 film can be formed in the same chamber while changing the flow rate ratio of the film forming gas. If the film is formed in this way, it is easy to realize a continuous refractive index distribution.

3 to 6 show examples of controlling the flow rate ratio of the film forming gas (FIGS. 3 to 5) and applied voltage (FIG. 6). In this example, SiH ₄ , N ₂ O, NH ₃ ,
N ₂ and He are used. SiH ₄ is a source of Si and H, N ₂ O is a source of N and O, N ₂ O
H ₃ is a source of N and H. N ₂ and He are diluent gases, but N ₂ also acts as a source of N ₂ .

As shown in FIG. 3, the flow rate of SiH ₄ is substantially constant during the period of forming the protective film. In addition, NH ₃
Although not shown, the He and He flow rates are also supplied at substantially constant flow rates as shown in FIG.

On the other hand, N ₂ O is not supplied when the p-SiN film is formed, but is supplied so as to be continuously increased or decreased at a predetermined rate when the p-SiON film is formed. More specifically, as shown in FIG. 4, the p-SiON film 6 is formed.
During the film formation, N ₂ O is supplied so as to decrease as it approaches the p-SiN film 5, and the supply is stopped at the end portion on the p-SiN film side. Since N ₂ O is the only O supply source, stopping the supply of N ₂ O also stops the supply of oxygen to the p-SiON film. On the other hand, at the time of forming the p-SiON film 4, N ₂ O is supplied so as to increase with distance from the p-SiN film 5.

As shown in FIG. 5, N ₂ is p-SiN.
When forming the film and the p-SiON film, respective predetermined amounts are supplied. By adjusting the supply amount of N ₂ , the nitrogen content in the film is adjusted.

By applying a voltage as shown in FIG. 6 to form each film, the protective film 20 is continuously formed in the same chamber while sandwiching the time for adjusting the film forming gas. Stacked.

7 to 9 are views showing changes in the supply amount of each film forming gas when the thickness of the protective film is adopted instead of the film forming time. FIG. 10 is a diagram showing changes in the refractive index in the film thickness direction of the protective film formed by the above method.

The method of adjusting the composition of the film formed by the plasma CVD method is not limited to the above method. For example SiH ₄
It is also possible to control the ratio of O and N in the film by changing the flow rate of. However, when adjusting the film composition by the flow rate of SiH _{4, if} the flow rate of SiH ₄ is too high, the Si content becomes too high and the film quality becomes hard.

As described above, the protective film is made up of hydrogen-containing gas molecules (SiH ₄ , NH _3, etc.) and oxygen-containing molecules (N
It is preferable to form the film by the plasma CVD method, which is performed while appropriately supplying ₂ O).

When the solid-state image pickup device having the film structure as described in the above embodiment was actually manufactured, the sensitivity of the solid-state image pickup device was about as compared with the conventional structure in which only the silicon nitride film was formed as the protective film. It was possible to improve by 5%.

[0048]

As described above, according to the present invention,
In the solid-state imaging device, by forming a multilayer protective film,
It is possible to suppress reflection from the protective layer while maintaining the function of the protective layer such as suppressing dark current. Further, such a protective layer can be efficiently formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of one form of a solid-state imaging device of the present invention.

FIG. 2 is a film configuration of the solid-state imaging device shown in FIG.
It is a figure which shows the refractive index of each film in this film structure).

FIG. 3 is a diagram illustrating a SiH versus film formation time when a protective film is formed by a plasma CVD method in the solid-state imaging device of the present invention.
FIG. 7 is a diagram showing a control example of ₄ .

FIG. 4 shows N ₂ O versus film formation time when a protective film is formed by a plasma CVD method in the solid-state imaging device of the present invention.
It is a figure which shows the example of control of.

FIG. 5 is a diagram showing an example of controlling N ₂ with respect to a film forming time when a protective film is formed by a plasma CVD method in the solid-state imaging device of the present invention.

FIG. 6 is a diagram showing an example of controlling an applied voltage with respect to a film formation time when a protective film is formed by a plasma CVD method in the solid-state imaging device of the present invention.

FIG. 7 is a graph showing S with respect to the thickness of the protective film when the protective film is formed by the plasma CVD method in the solid-state imaging device of the present invention.
is a diagram illustrating an example of control of iH _4.

FIG. 8 is a diagram showing an N ratio with respect to a film thickness of a protective film when the protective film is formed by a plasma CVD method in the solid-state imaging device of the present invention.
It is a figure which shows the example of control of ₂ O.

FIG. 9 is a diagram showing an N ratio with respect to a film thickness of a protective film when the protective film in the solid-state imaging device of the present invention is formed by a plasma CVD method.
FIG. 6 is a diagram showing a control example of ₂ .

FIG. 10 is a diagram showing changes in the refractive index in the film thickness direction of the protective film formed by the plasma CVD method according to the control example shown in FIGS.

[Explanation of symbols]

1 on-chip micro lens 2 filter layers 3 Flattening film 4 Third protective film (p-SiON film) 5 Second protective film (p-SiN film) 6 First protective film (p-SiON film) 7 Second insulating film 8 Light-shielding film 9 First insulating film 10 Gate electrode 11 Gate insulating film 12 p-type well layer 13 Light receiving part 14 Charge transfer unit 15 n-type silicon substrate 20 Protective film

Claims (9)

(57) [Claims] Above 1. A light receiving portion formed in a semiconductor substrate, which is formed by a plasma chemical vapor deposition in an atmosphere containing a hydrogen-containing gas molecules, and a silicon nitride film is lower than the silicon nitride film Silicon nitride, which is a film with a refractive index
Comprising a multilayer film in which a reduction oxide film are stacked, as the multilayer film, the first consisting of a silicon nitride oxide film
Layer, a second layer made of a silicon nitride film and silicon nitride
A third layer made of an oxide film is stacked in order from the light receiving portion side.
Is, the first layer and the third layer each 95nm~19
The second layer has a thickness of 5 nm, and the second layer has a thickness of 190 nm to 390.
A solid-state imaging device having a thickness of nm . Above wherein the light receiving portion formed in a semiconductor substrate, as a protective film for supplying hydrogen to the semiconductor substrate, a film having a silicon nitride film, a lower refractive index than the silicon nitride film multilayer film and is a silicon nitride oxide film are laminated is formed, as the multilayer film, the first consisting of a silicon nitride oxide film
Layer, a second layer made of a silicon nitride film and silicon nitride
A third layer made of an oxide film is stacked in order from the light receiving portion side.
Is, the first layer and the third layer each 95nm~19
The second layer has a thickness of 5 nm, and the second layer has a thickness of 190 nm to 390.
A solid-state imaging device having a thickness of nm . Ratio of 3. A nitrogen to the total amount of nitrogen and oxygen in the silicon nitride oxide film, in the film thickness direction, claim 1 becomes higher closer to the silicon nitride film
Alternatively, the solid-state imaging device described in 2 . Wherein the refractive index of the silicon nitride oxide film,
In the film thickness direction, the solid-state imaging device according to any one of claims 1 to 3 higher closer to the silicon nitride film. Wherein the refractive index of the first layer and the third layer, in the thickness direction, according to claim 1-4 which is changing communication <br/> continue to so as to be higher toward the second layer The solid-state imaging device according to any one of claims. 6. A multilayer film, light-shielding film and an insulating film formed so as to cover the light receiving portion for shielding the incident external light to regions other than the light-receiving portion or the flattened formed on the insulating film, film, a solid-state imaging device according to any one of claims 1 to 5 formed on the. Above 7. receiving portion formed in a semiconductor substrate, as a protective film for supplying hydrogen to the semiconductor substrate, it is a film having a lower refractive index than the silicon nitride film and a silicon nitride film Laminated with silicon oxynitride film
A multi-layered film, which comprises a silicon oxynitride film
Layer, a second layer made of a silicon nitride film and silicon nitride
A third layer made of an oxide film is stacked in order from the light receiving portion side.
The first layer and the third layer each have a thickness of 95 nm
The second layer has a thickness of 195 nm, and the second layer has a thickness of 190 nm to 3
A method for manufacturing a solid-state imaging device, comprising the step of continuously forming a multi-layer film having a thickness of 90 nm in the same chamber containing hydrogen-containing gas molecules by a plasma chemical vapor deposition method. 8. The method of manufacturing a solid-state imaging device according to claim 7 , wherein a nitrogen-containing gas molecule and an oxygen-containing gas molecule are introduced into the chamber to form a silicon oxynitride film. 9. By continuously changing the ratio of the nitrogen-containing gas molecule to the total amount of the nitrogen-containing gas molecule and the oxygen-containing gas molecule in the chamber, the nitrogen content of the nitrogen and oxygen in the silicon oxynitride film can be adjusted. 9. The method for manufacturing a solid-state imaging device according to claim 8 , wherein the ratio is increased in the film thickness direction as it approaches the silicon nitride film.