JP4556475B2 - Solid-state imaging device and manufacturing method thereof - Google Patents

Description

The present invention relates to a solid-state imaging device and a method for manufacturing the same .

  Conventionally, various proposals have been made for the purpose of improving sensitivity in a solid-state imaging device.

  As one of them, a configuration is proposed in which a hole is formed at a position immediately above the light receiving portion, and a high refractive index material is filled in the hole to form a waveguide structure (for example, Patent Document 1 and Patent Document). 2).

FIG. 4 shows a schematic cross-sectional view of a solid-state imaging device provided with this waveguide structure.
A light receiving portion (photodiode) 52 is formed in a region separated by the element isolation layer 53 of the semiconductor substrate 51 such as a silicon substrate.
A transfer gate electrode 55 is formed on the semiconductor substrate 51 on the left side of the light receiving portion (photodiode) 52 via a gate insulating film 54.
A two-layer wiring layer 58 connected to the semiconductor substrate 51 through a contact layer (conductive plug) 57 is provided.
These two wiring layers 58 are covered with an insulating layer 59.
On this insulating layer 59, a passivation film (protective film) 61, a planarizing film 62, a color filter 63, and an on-chip lens 64 are formed.

Then, above the light receiving portion (photodiode) 52, a hole formed in the insulating layer 59 is filled with a high refractive index material layer 60 to constitute a waveguide as will be described in detail later.
In the figure, reference numeral 56 denotes an etching stopper film, which serves as an etching stopper at the time of etching for forming a hole in the insulating layer 59.

The waveguide optically connects the on-chip lens 64 and the light receiving unit (photodiode) 52.
By utilizing the fact that the refractive index of the high refractive index material layer 60 serving as the core material inside the waveguide is higher than that of the insulating layer 59 serving as the cladding portion, at the interface between the high refractive index material layer 60 and the insulating layer 59. The incident light having an incident angle larger than the critical angle θ can be totally reflected.
Due to the reflection at the interface, incident light can be directed to the light receiving portion (photodiode) 52, so that the light collection efficiency to the light receiving portion (photodiode) 52 can be increased.
Japanese Patent Laid-Open No. 11-121725 Japanese Patent Laid-Open No. 10-326885

However, as the solid-state imaging device is miniaturized, the area of each pixel is reduced, and accordingly, the opening area of the hole is reduced and the aspect ratio (width / depth ratio) of the hole is increased.
Further, for example, in the configuration having the multilayer wiring layer 58 as shown in FIG. 4, the height of the insulating layer 59 covering the wiring layer 58 is increased, so that the waveguide is formed deeply. This also increases the aspect ratio of the hole.
By increasing the aspect ratio of the hole as described above, the embedding property is deteriorated when the hole is filled with a high refractive index material. For this reason, there is a concern about deterioration of the light condensing property and variation in pixel characteristics.

  Further, when etching is performed to open the hole portion of the waveguide, the semiconductor substrate 51 and the like in the vicinity of the light receiving portion 52 may be damaged, which causes white spots.

Therefore, in order to avoid damage due to this etching, the hole portion of the waveguide is not formed up to the vicinity of the semiconductor substrate 51, and the etching is stopped halfway to raise the bottom surface of the waveguide and away from the light receiving portion (photodiode) 52. It is possible.
However, in this case, the oblique light emitted from the waveguide may not be collected on the light receiving unit (photodiode) 52.

It is also conceivable to increase the diameter of the waveguide in order to increase the light collection rate to the waveguide.
Also in this case, there is a possibility that the oblique light emitted from the waveguide is not collected on the light receiving unit (photodiode) 52 by expanding the diameter of the waveguide.

  As in these cases, when the oblique light emitted from the waveguide is not collected on the light receiving portion (photodiode) 52, it is diffused to the adjacent gate electrode 55 as indicated by an arrow 71 in FIG. Since it diffuses into the element isolation region 53, the effect of improving the sensitivity cannot be obtained sufficiently.

In order to solve the above-described problems, the present invention provides a solid-state imaging device having a configuration that can be easily manufactured with a high yield and has good characteristics such as sensitivity, and a manufacturing method thereof .

The solid-state imaging device of the present invention is formed by a semiconductor substrate , a light receiving portion in which a photoelectric conversion element is formed on the semiconductor substrate , and a silicon nitride film provided above the light receiving portion and formed by a plasma CVD method. a layer lens that the lens surface is formed on the light receiving side, the polyimide resin is composed by being filled in the hole portion formed by connecting on this layer lens, waveguide and, layer lens And a silicon oxide layer around the hole .

According to the configuration of the above-described solid-state imaging device of the present invention, an intralayer lens having a lens surface formed on the light receiving portion side is provided above the light receiving portion, and the intralayer lens is formed by surrounding silicon oxide layers. By using a silicon nitride film having a higher refractive index, incident light can be condensed on the lens surface on the light receiving portion side of the in-layer lens and can be incident on the light receiving portion.
Furthermore, the waveguide is configured by filling a polyimide resin having a refractive index higher than that of the silicon oxide layer around the hole in the hole formed by connecting on the in-layer lens. The waveguide can act as a core part, and the surrounding layers can act as a cladding part, and incident light can be reflected by the outer wall of the waveguide and guided to the light receiving part.
Therefore, the degree of condensing incident light on the light receiving portion can be increased, and more incident light can be incident on the light receiving portion.

And since there is an in-layer lens connected under the waveguide, the vertical distance between the waveguide and the light receiving portion can be increased, and the etching end point when the hole of the waveguide is formed by etching Is on the inner lens. Thereby, damage to the semiconductor substrate near the light receiving portion can be suppressed.
At the same time, since the depth of the waveguide can be reduced and the aspect ratio can be reduced, the embedding property of the filling material of the waveguide can be improved.

In addition, by in-layer lens are formed of a silicon nitride film, a silicon nitride film is a high refractive index material (silicon nitride film, the refractive index n = 2.0) since, condensing the above An effect is obtained.

Further, by the silicon nitride film layer lens is a silicon nitride film formed by a plasma CVD method, the silicon nitride film formed by plasma CVD method contains a large amount of hydrogen, in the preparation of silicon Hydrogen can be supplied from the nitride film to the semiconductor substrate of the light receiving unit. As a result, the dangling bonds are terminated, the generation of interface states can be suppressed, and the generation of white spots can be suppressed.

In the solid-state imaging device according to the present invention, the filling material of the waveguide is a polyimide resin having a low refractive index with respect to the silicon nitride film of the in-layer lens , so that at the interface between the waveguide and the in-layer lens. Since it is possible to prevent the incident light from being reflected, the sensitivity can be improved by increasing the amount of incident light directed toward the light receiving portion.

According to the above-described present invention, the degree of condensing incident light can be increased by the action of the inner lens and the waveguide, and more incident light can be incident on the light receiving unit, so that the sensitivity can be improved. .
In addition, since damage to the semiconductor substrate near the light receiving portion can be suppressed, generation of white spots due to damage to the semiconductor substrate can be suppressed.
Therefore, a solid-state image sensor having good characteristics can be realized.

In addition, according to the present invention, since the embedding property of the filling material of the waveguide can be improved, a solid-state imaging device having good characteristics can be easily manufactured, and the manufacturing yield can be improved. Become.
Therefore, a highly reliable solid-state imaging device can be realized.

As an embodiment of the present invention, FIG. 1 shows a schematic configuration diagram (cross-sectional view) of a solid-state imaging device. FIG. 1 shows a cross-sectional view of one pixel of a solid-state image sensor.
In this embodiment, the present invention is applied to a CMOS solid-state imaging device.

In this solid-state imaging device, a light receiving portion (photodiode) 2 is formed in a region separated by an element isolation layer 3 of a semiconductor substrate 1 such as a silicon substrate to constitute a pixel.
A transfer gate electrode 5 is formed on the semiconductor substrate 1 on the left side of the light receiving portion (photodiode) 2 through a gate insulating film 4.
A two-layer wiring layer 8 connected to the semiconductor substrate 1 via a contact layer (conductive plug) 7 is provided.
These two wiring layers 8 are covered with an insulating layer 9.
A passivation film (protective film) 11, a planarizing film 12, a color filter 13, and an on-chip lens 14 are formed on the insulating layer 9.

In the present embodiment, an in-layer lens 6 is provided above the light receiving unit 2.
This in-layer lens 6 is formed of a material having a refractive index higher than that of the surrounding insulating layer 9 and having a lens surface 6A having a convex curved surface on the light receiving portion 2 side.
As a material of the in-layer lens 6, for example, a nitride film such as a silicon nitride film (refractive index n = 2.0) can be used.
In particular, by using a nitride film formed by a plasma CVD method as the nitride film, an effect of suppressing the generation of white spots by supplying hydrogen can be obtained as will be described later.

In the present embodiment, in particular, the waveguide 10 is connected to the inner lens 6.
The waveguide 10 is formed by filling a hole formed in the insulating layer 9 above the inner lens 6 with a material having a higher refractive index than the surrounding insulating layer 9.
As a filling material of the waveguide 10, for example, a resin having a relatively high refractive index such as a polyimide resin (refractive index n = 1.7) can be used.

  By providing this waveguide 10, the inside has a higher refractive index than the surrounding insulating layer 9, so that the core part that transmits light inside the waveguide 10 and the surrounding insulating layer 9 act as a cladding part, As indicated by arrows in FIG. 1, incident light can be reflected on the outer wall surface 10 </ b> A of the waveguide 10. Thereby, incident light can be guided toward the light receiving unit 2.

The filling material (light transmission core material) of the waveguide 10 is desirably a material having a refractive index lower than that of the material constituting the intralayer lens 6, for example, a plasma silicon nitride film (n = 2.0).
This makes it possible to prevent incident light from being reflected and returning upward at the boundary surface between the waveguide 10 and the intralayer lens 6.

In the configuration shown in FIG. 4, light is emitted at the bottom of the waveguide 60 toward the insulating layer 59 having a lower refractive index than the material filled in the hole of the waveguide 60. For this reason, as shown by an arrow 72 in FIG. 4, oblique light having a critical angle or more is totally reflected at the interface at the bottom of the waveguide 60 and returns toward the top of the waveguide 60.
On the other hand, in the configuration of the present embodiment, the intralayer lens 6 is connected under the waveguide 10, and the intralayer lens 6 is silicon having a refractive index higher than that of the polyimide resin as a filling material of the waveguide 10. Since it is made of a nitride film, reflection at the interface between the waveguide 10 and the inner lens 6 can be prevented.

In the configuration shown in FIG. 4, when a polyimide resin is used as a filling material of the waveguide, the metal content of the polyimide resin is higher than that of other resins such as a resist (for example, the sodium content is 0.1%). 4 ppm), metal diffusion occurs on the surface of the photodiode 52, and as a result, there is a concern that white spots increase.
On the other hand, in the configuration of the present embodiment, since the intralayer lens 6 is provided between the photodiode 2 and the waveguide 10, even if a polyimide resin is used as the filling material of the waveguide 10, It is possible to suppress metal diffusion by the silicon nitride film of the lens 6. Thereby, generation | occurrence | production of the white spot resulting from metal diffusion can be suppressed.

The material of the inner lens 6 and the filling material of the waveguide 10 may be the same material.
However, in that case, it is desirable to suppress the diffusion of the metal described above and to have a good embedding property, so that the material is further limited or the manufacturing process needs to be devised.

The solid-state imaging device of the present embodiment can be manufactured, for example, as follows.
First, in the same manner as in the conventional manufacturing method, a photodiode 2 is formed in a semiconductor substrate 1 made of, for example, a silicon layer, and a transfer gate electrode 5 is formed on the semiconductor substrate 1 via a gate insulating film 4.
Thereafter, an insulating layer 21 such as silicon oxide is formed to cover the transfer gate electrode 5 (see FIG. 2A above).

Next, as shown in FIG. 2B, a concave groove (concave surface) 21A for forming an in-layer lens is formed in the insulating layer 21 by isotropic etching. For this etching, for example, a gas such as C4F ₈ , O ₂ , Ar is used by using a down flow plasma.

Next, a plasma silicon nitride film is formed on the entire surface by plasma CVD. At this time, for example, silane gas (SiH ₄ ) and nitrogen gas are used.
Thereafter, the plasma silicon nitride film is cut down to the surface of the insulating layer 21 by an etch back method, and the inner lens 6 is formed on the concave groove (concave surface) 21A of the insulating layer 21 as shown in FIG. 2C. At this time, for example, a gas such as CH ₂ F ₂ , O ₂ , Ar is used as an etching gas.
Furthermore, annealing (for example, 400 ° C.) is performed to supply hydrogen 22 from the plasma silicon nitride film constituting the inner lens 6 to the semiconductor substrate 1 of the light receiving unit 2.

  Next, after an interlayer insulating film, a contact layer 7 and a multilayer wiring layer 8 are formed, the whole is covered with an insulating layer. As a result, as shown in FIG. 2D, the inner lens 6, the contact layer 7, and the multilayer wiring layer 8 are covered with the insulating layer 9.

Next, as shown in FIG. 3E, a hole 23 serving as a waveguide is opened in the insulating layer 9 by anisotropic etching. This anisotropic etching is performed by, for example, RIE (reactive ion etching) using C ₄ F ₈ , O ₂ , and Ar.
At this time, the plasma silicon nitride film of the inner lens 6 acts as an etching stopper. An etching selectivity of about 10 can be secured between the insulating layer (for example, silicon oxide) 9 and the inner lens (plasma silicon nitride film) 6.

Next, the hole is filled to form a transparent film of the waveguide filling material. For example, a polyimide resin is embedded in the hole by a coating method.
Subsequently, the transparent film is entirely removed to the surface of the insulating layer 9 by an etch back method or a CMP (Chemical Mechanical Polishing) method, and a global planarization process is performed. As a result, the transparent film remains only in the hole and the waveguide 10 is formed (see FIG. 3F above).

Thereafter, a passivation film (protective film) 11, a planarizing film 12, a color filter 13, and an on-chip lens 14 are sequentially formed in the same manner as in the conventional manufacturing method.
In this way, the solid-state imaging device shown in FIG. 1 can be manufactured.

  According to the above-described embodiment, the in-layer lens 6 having the lens surface 6A formed on the light receiving unit 2 side is provided above the light receiving unit (photodiode) 2, and the intra-layer lens 6 is surrounded by the surrounding lens 6A. By being made of a material having a refractive index higher than that of the insulating layer 6 (for example, a silicon nitride film), incident light can be condensed on the lens surface 6A and incident on the light receiving unit 2.

  Further, by providing a waveguide 10 connected to the inner lens 6 and filled with a material having a refractive index higher than that of the surrounding insulating layer 9, the waveguide 10 is provided as a core portion and the surrounding insulating layer. 9 is allowed to act as a cladding part, and incident light can be reflected by the outer wall 10A of the waveguide 10 and guided to the light receiving part 2.

Accordingly, the degree of condensing incident light onto the light receiving unit 2 can be increased, and more incident light can be incident on the light receiving unit 2.
This makes it possible to improve sensitivity.

In addition, since the waveguide 10 is provided on the intralayer lens 6, there is the intralayer lens 6 connected directly below the waveguide 10, and the waveguide 10 and the light receiving unit 2 are connected by the intralayer lens 6. The vertical distance H can be increased. The end point of etching when the hole of the waveguide 10 is formed by etching is on the inner lens 6.
Thereby, damage to the semiconductor substrate 1 in the vicinity of the light receiving unit 2 can be suppressed.
At the same time, the depth of the waveguide 10 can be reduced by the amount of the inner lens 6, and the aspect ratio of the hole can be reduced, so that the filling property of the filling material of the waveguide 10 can be improved. .

Furthermore, the material of the inner lens 6 is a nitride film formed by plasma CVD, so that the nitride film has a higher refractive index than the oxide film used for the insulating layer 9 (for example, the refractive index n is a silicon nitride film). = 2.0), the above-described light collecting effect is obtained. Further, since the nitride film formed by the plasma CVD method has a high hydrogen content, it is possible to supply hydrogen to the semiconductor substrate 1 in the vicinity of the light receiving portion 2 at the time of manufacture.
Thereby, dangling bonds can be terminated and the occurrence of white spots can be suppressed.

  Furthermore, the filling material of the waveguide 10 is made of a material having the same refractive index or a lower refractive index than the material of the in-layer lens 6, thereby reflecting at the interface between the waveguide 10 and the in-layer lens 6. The light condensing rate to the light receiving unit 2 can be improved by condensing the light incident obliquely toward the light receiving unit 2.

That is, according to the solid-state imaging device of the present embodiment, it is possible to realize a solid-state imaging device having high sensitivity, few white spots, and good characteristics.
In addition, a solid-state imaging device having good characteristics can be easily manufactured, and the manufacturing yield can be improved.
Therefore, a highly reliable solid-state imaging device can be realized.

The method for forming the inner lens is not limited to the method for forming the concave surface by isotropic etching shown in FIGS. 2B to 2C, and the inner lens can be formed by other methods. is there.
For example, by using PSG (phosphosilicate glass), BPSG (boron / phosphosilicate glass), etc., a recess is formed using steps such as a wiring layer, and then reflowing is performed to adjust the shape of the curved surface of the recess to form a lens surface. Then, there is a method of filling the recess with a material having a high refractive index such as a nitride film to form an in-layer lens.

  Further, the upper surface of the inner lens (the surface opposite to the light receiving portion) is not limited to the plane shown in FIG. 1, and may be a curved surface convex upward, for example, in order to improve the light collecting property.

In the above-described embodiment, the present invention is applied to the CMOS type solid-state imaging device. However, the present invention can also be applied to solid-state imaging devices having other configurations.
For example, the present invention can be applied to a CCD solid-state imaging device.
In any configuration of the solid-state imaging device, the effect of the present invention can be obtained by applying the present invention and providing an intralayer lens above the light receiving portion and providing a waveguide connected to the intralayer lens. It is done.

  The present invention is not limited to the above-described embodiments, and various other configurations can be taken without departing from the gist of the present invention.

1 is a schematic configuration diagram (cross-sectional view) of a solid-state imaging device according to an embodiment of the present invention. FIGS. 2A to 2D are process diagrams showing a method for manufacturing the solid-state imaging device of FIG. E and F are process diagrams showing a method of manufacturing the solid-state imaging device of FIG. It is a schematic sectional drawing of the solid-state image sensor which provided the waveguide structure on the light-receiving part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 2 photodiode (light-receiving part), 3 element isolation layer, 4 gate insulating film, 5 transfer gate electrode, 6 inner lens, 7 contact layer, 8 wiring layer, 9 insulating layer, 10 waveguide, 13 color Filter, 14 on-chip lens

Claims (4)

A semiconductor substrate ;
A light receiving portion formed by forming a photoelectric conversion element on the semiconductor substrate ;
An in-layer lens provided above the light receiving portion, formed of a silicon nitride film formed by a plasma CVD method, and having a lens surface on the light receiving portion side ;
A waveguide configured by filling a polyimide resin into a hole formed on the intra-layer lens , and
A solid-state imaging device including a silicon oxide layer around the inner lens and around the hole . The solid-state imaging device according to claim 1, wherein a surface of the intralayer lens on the waveguide side is a horizontal plane. A step of forming a silicon oxide layer on the semiconductor substrate after forming the photoelectric conversion element of the light receiving portion on the semiconductor substrate;
Forming a concave groove for forming an in-layer lens in the silicon oxide layer by isotropic etching;
A step of forming a silicon nitride film on the entire surface by plasma CVD;
Etching back the silicon nitride film to the surface of the silicon oxide layer to form an in-layer lens on the concave groove;
Covering the whole with a silicon oxide layer;
Forming a hole serving as a waveguide in the silicon oxide layer by anisotropic etching;
And filling the hole with polyimide resin by a coating method.
Manufacturing method of solid-state image sensor. The method for manufacturing a solid-state imaging device according to claim 3, wherein the isotropic etching is performed using downflow plasma.

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