JP2000357786A - Solid state imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid state imaging device having a high condensing efficiency even in a structure using a seal resin. SOLUTION: The device comprises photo diodes 14 for receiving lights, resin- made microlenses 4 having a refractive index n3 formed on the photo diodes 14, thin film lenses 3 having a refractive index n2 formed on the microlenses 4, a seal resin 2 having a refractive index n1 formed on the thin film lenses 3, and a cover glass 1 for covering the seal resin 2 formed on the seal resin 2. The refractive index n2 of the lens 3 is less than n1 and n3 wherein the value of n1 is substantially equal to n3, and the thin film lenses 3 are made of a fluoride and/or oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device including a microlens and a sealing resin on the microlens.

[0002]

2. Description of the Related Art In a solid-state imaging device using a CCD (Charge Coupled Device) or the like, the area of a photodiode serving as a light receiving section has been reduced due to a demand for miniaturization and high resolution. In order to compensate for such a decrease in light-collecting efficiency due to such a decrease in the area of the light receiving section, a so-called micro lens has been developed and used.

[0003] The microlens is usually made of a resin, and is disposed above a light receiving portion formed for each pixel, refracts light that does not directly enter the light receiving portion, and condenses the light on the light receiving portion. This improves the light collection efficiency and the sensitivity.

However, since this microlens is sensitive to moisture, it must be protected by some means when used in a severe environment of high temperature and high humidity.
As disclosed in JP-A-41506, a structure is disclosed in which a microlens is covered and protected by a resin, and a cover glass for sealing the resin is further provided.

[0005]

However, when a microlens is covered with a sealing resin, heat resistance, transparency, spectral performance,
If the resin material is selected in consideration of changes in the refractive index, the same resin as the microlens material must be selected, and the refractive index of the sealing resin becomes almost the same as that of the microlens. Would. As a result, there is a problem that the light condensing effect of the microlens is reduced and the light reaching the microlens cannot be sufficiently condensed on the photodiode.

[0006] Increasing the refractive index of the micro lens,
Efforts have also been made to reduce the refractive index of the sealing resin to increase the light-collecting effect. However, it is still necessary to solve the above-mentioned problems such as heat resistance, transparency, spectral performance, and change in refractive index. Can not.

An object of the present invention is to provide a solid-state imaging device having high light-collecting efficiency even in a structure using a sealing resin in consideration of such a conventional problem.

[0008]

Means for Solving the Problems The first invention (claim 1)
A) a light receiving unit for receiving light, a micro lens having a predetermined first refractive index formed on the light receiving unit, a thin film lens formed on the micro lens, and the thin film A resin portion having a predetermined second refractive index formed on the lens, wherein the refractive index of the thin film lens is smaller than the first refractive index and the second refractive index, The solid-state imaging device is characterized in that the material of the thin film lens is an inorganic material. A second aspect of the present invention (corresponding to claim 2) includes a light receiving unit for receiving light, a micro lens having a predetermined first refractive index formed on the light receiving unit, and A thin-film lens formed thereon; and a resin portion having a predetermined second refractive index formed on the thin-film lens. The thin-film lens has a refractive index of the first refractive index and the second refractive index. The solid-state imaging device is characterized in that the thin-film lens has a refractive index smaller than that of the microlens and is a plate-shaped member that is curved according to a curved surface of the microlens.

In a third aspect of the present invention (corresponding to claim 3), the solid-state image pickup device according to claim 1 or 2, wherein the first refractive index and the second refractive index are substantially the same. It is.

According to a fourth aspect of the present invention (corresponding to claim 4), in the solid-state imaging device according to claim 1, the thin film lens is a lens formed from a fluoride and / or an oxide. is there.

A fifth aspect of the present invention (corresponding to claim 5) is the solid-state imaging device according to any one of claims 1 to 3, wherein the microlens is a lens formed of a resin. is there.

According to a sixth aspect of the present invention (corresponding to claim 6), the first refractive index and the second refractive index are near 1.56, and the refractive index of the thin film lens is 1.36 or more. The solid-state imaging device according to claim 5, wherein the number is 50 or less.

According to a seventh aspect of the present invention (corresponding to claim 7), the thin film lens is formed of a resin material, the diameter of the micro lens is about 4000 nm, and the thickness of the thin film lens is 80 nm or more and 1000 nm. The solid-state imaging device according to claim 2, wherein:

[0014]

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

FIG. 1 is a cross-sectional view of a solid-state imaging device according to an embodiment of the present invention. FIG. 2 shows that light enters a microlens and is condensed on a photodiode of the solid-state imaging device shown in FIG. FIG.

As shown in FIG. 1, a p-type well layer 13 is formed in a surface layer of an n-type semiconductor substrate 12, and a light receiving portion for detecting the intensity of light at predetermined intervals in the p-type well layer 13. Are formed.

A vertical transfer register 15 is formed near the surface of the p-type well layer 13, and an insulating film 10 is disposed on the surface of the p-type well layer 13. A polysilicon electrode 11 is provided thereon, and an insulating film 10 covering the polysilicon electrode 11 is further provided.

The light shielding film 9 covers the polycrystalline silicon electrode 11 and avoids the upper part of the photodiode 14.
Is arranged. The insulating film 8 covers the light shielding film 9.
Is formed, and a first flattening layer 7 for flattening a surface layer is provided thereon.

Further, a color filter layer 6
And a second planarizing layer 5. The microlenses 4 are formed on the second flattening layer 5 so as to correspond to the respective photodiodes 14. A thin film lens 3 is formed on the micro lens 4, a cover glass 1 is provided above the thin film lens 3, and a sealing resin 2 is filled between the thin film lens 3 and the cover glass 1.

FIG. 2 is a diagram showing a part of the solid-state imaging device of FIG. 1 including the main components, as described above.
Hereinafter, the solid-state imaging device according to the embodiment of the present invention will be described with reference to FIG.

[0021] In FIG. 2, and transmits the incident light beam 28 is a cover glass 1 from the vicinity of the center of the microlens 4, through the sealing resin 2, at an incident angle theta ₁₁ in a thin film lens 3. The incident angle θ ₁₁ is relatively small because it is near the center of the thin film lens 3. Therefore, the light ray 28 incident on the thin film lens 3 is slightly refracted.

The refractive index of the sealing resin 2 is n1, and the thin film lens 3 is
Is n2, the incident angle θ ₁₁ and the outgoing angle θ ′ ₁₁ are related by the following Snell's equation (Equation 1).

[0023]

[Number 1] _{n1 · Sin (θ 11) =} n2 · Sin (θ '11) For example, the refractive index n1 of 1.56 of the sealing resin 2, the refractive index n2 of the thin-film lens 3 1.38, θ ₁₁ = Once,
θ ′ ₁₁ = 1.1 degrees, and is only slightly refracted.

The light ray 28 refracted by the thin film lens 3
Since entering the vicinity of the central portion of the microlens 4, the incident angle theta ₁₂ of the microlens 4 is also relatively small. Therefore, the light beam 28 that has reached the microlens 4 travels straight without being refracted, and reaches the photodiode 14.

On the other hand, the light beam 29 incident on the periphery of the microlens 4 passes through the cover glass 1 and then enters the thin film lens 3 via the sealing resin 2. To enter the outer peripheral side of the thin-film lens 3, the incident angle theta ₂₁ becomes larger than theta _11.

As described above, the refractive index of the sealing resin 2 is n
1. When the refractive index of the thin film lens 3 is n2, the following (Equation 2) holds between the incident angle θ ₂₁ and the output angle θ ′ ₂₁ .

[0027]

N1 · Sin (θ ₂₁ ) = n2 · Sin (θ ′ ₂₁ ) When the refractive index n1 of the sealing resin 2 is 1.56 and the refractive index n2 of the thin film lens 3 is 1.38. , θ _'21 is θ
_Greater than ₂₁ .

For example, when θ ₂₁ = 43 degrees, θ ′ ₂₁ = 5
The angle is 0.4 degrees, and a larger change in the outgoing angle occurs than when the light enters from the center. That is, the light is refracted more in the outer peripheral direction than in the case of the central portion.

The refracted light 29 enters the microlens 4 at an incident angle θ ₂₂ .

The position light 29 is incident on the microlens 4 is a considerably outer peripheral side of the microlens 4, the incident angle theta ₂₂ is very large. This incident angle θ ₂₂
It can be seen that the incident angle is larger than the incident angle when it is assumed that the light beam 29 goes straight without being refracted by the thin film lens 3 and enters the microlens 4.

The light beam 29 incident on the micro lens 4
Of the incident angle and theta _22, the emission angle from the microlens 4 and theta _'22, the refractive index of the thin film lens 3 as n2, when the refractive index of the microlens 4 and n3, the following equation (3) is Holds.

[0032]

N2 · Sin (θ ₂₂ ) = n3 · Sin (θ ′ ₂₂ ) When the refractive index n3 of the micro lens 4 is the same as 1.56 of the refractive index n1 of the sealing resin 2, θ ₂₂ = when 75 degrees, θ 'becomes ₂₂ = 58.7 degrees.

When this angle is compared with the angle at the time when the light beam 29 passes through the sealing resin 2, the angle is inclined about 9 degrees inward. That is, the light beam 29 incident on the microlens 4
Is largely refracted, proceeds toward the photodiode 14, passes through the insulating film 8 and the like, and reaches the photodiode 14.

By providing the thin-film lens 3 on the micro-lens 4 in this manner, light incident on the outer peripheral portion of the thin-film lens 3 is also focused on the photodiode 14 by a large refraction effect, so that more light is emitted. Photodiode 14
It is incident on.

Such an effect does not appear in the conventional structure in which the thin film lens does not exist on the micro lens 34 and the sealing resin 32 is in direct contact with the micro lens 34 as shown in FIG.

That is, the light ray 50 incident near the center of the microlens 34 enters the photodiode 44, but the light ray 51 incident near the outer periphery of the microlens 34 does not enter the photodiode 44. This is because the difference between the refractive index n1 of the sealing resin 32 and the refractive index n3 of the microlens 34 must be reduced because heat resistance, transparency, spectral performance, change in refractive index, and the like are taken into consideration.
θ ₂ is because not slightly smaller only than θ _1.

Further, under the same conditions as described with reference to FIG. 2, the refractive index n1 of the sealing resin 32 and the microlens 34
An extreme example in which there is no refraction effect that the refractive index n3 is equal will be described.

According to Snell's relation, in FIG.
The following (Equation 4) holds for the refractive index n1 of the sealing resin 32, the refractive index n3 of the microlens 34, the incident angle θ ₁ , and the output angle θ ₂ .

[0039]

N1 · Sin (θ ₁ ) = n3 · Sin (θ ₂ ) Here, since n1 = n3, θ ₁ = θ ₂ , which means that light incident on the microlens 34 is not refracted at all. It represents that. In other words, it means that all the light rays incident on the microlens 34 go straight and have no light-collecting effect. Therefore, the light beam 51 incident near the outer periphery of the microlens 34 is not focused on the photodiode 44.

On the other hand, in the case of the embodiment of the present invention described with reference to FIG. 2, even if the sealing resin 2 and the microlens 4 have the same refractive index, the thin film lens 3
The light that has entered the outer peripheral portion of the light source is condensed on the photodiode 14 by exhibiting an extremely large refraction effect. This is exactly the effect of the thin film lens 3.

Therefore, the provision of the thin film lens 3 is extremely useful, and compared with the case of FIG.
The light incident on the outer peripheral portion of the thin film lens 3 is largely refracted,
Since more light can be incident on the photodiode 14, the sensitivity is substantially improved, which is useful.

As the material of the insulating film 8 shown in FIG. 2, for example, silicon oxide is used. As the material of the microlens 4, a phenol-based, acrylic-based, or styrene-based resin is used. For example, an acrylic resin is used as the sealing resin 2.

Examples of the material of the thin film lens 3 include fluorides such as magnesium fluoride and aluminum fluoride;
An oxide such as silicon oxide can be preferably used. These materials have a low refractive index, and are preferable as the material of the thin film lens 3 in consideration of the refractive index of a synthetic resin (a phenol resin, a styrene resin, an acrylic resin, etc.) frequently used as a material of the microlens 4.

Further, when an inorganic material is used for the thin film lens 3, the film becomes excellent in heat resistance and the like.

The refractive index n2 of the thin film lens 3 may be smaller than the refractive index n3 of the microlens 4 and the refractive index n1 of the sealing resin 2. For example, the refractive index n of the micro lens 4
If both the refractive index n1 of the thin film lens 3 and the refractive index n1 of the sealing resin 2 are near 1.56, it is preferable that the refractive index n2 of the thin film lens 3 be 1.36 or more and 1.50 or less.

The above-mentioned vicinity of 1.56 is 1.50.
Over 1.60 or less. Further, in order to increase the refraction effect described above, it is preferable to use, as the thin film lens 3, one having a refractive index n 3 of the micro lens 4 and a refractive index n 1 of the sealing resin 2 as small as possible.

On the other hand, when an inorganic substance such as a fluoride or an oxide as described above is used, it is possible to form the thin film lens 3 of 1.36 or more and 1.50 or less even if impurities or the like are contained. As long as such a thin film lens 3 is used, the above-described refraction effect can be generated.

The thin-film lens 3 is not limited to a single-layer film. For example, a two-layer film of a fluoride and an oxide may be used. A middle and high refractive index layer made of titanium oxide, tantalum oxide, niobium oxide, zirconium oxide, indium oxide, aluminum oxide, or the like may be laminated on the low refractive index layer made of the fluoride exemplified above.

The film thickness of the thin film lens 3 is 80 nm or more and 10
It is preferable that the thickness be 00 nm or less. The lower limit is set to 80 nm, because if it is thinner than that, the refraction effect is reduced and the effect is practically negligible. On the other hand, the upper limit is 1.
The reason why the diameter is set to 000 nm is that the diameter of a conventionally used microlens is about 4 to 5 μm (4000 to 5000 nm), and that the microlens is used in the solid-state imaging device of the present invention. .

It has been confirmed that when the film thickness of the thin film lens 3 is set to about 500 nm, a refraction effect appears largely. In addition, the diameter of the microlens according to claim 6 is in the vicinity of 4000 nm when it is 3000 to 5000 nm.
Means the range.

When the thin film lens 3 is made of resin,
In order to be able to withstand a bad environment such as high temperature and high humidity, the film thickness is preferably set to 80 nm or more and 1000 nm or less.

The specific method of forming the thin film lens 3 is not particularly limited as long as it is a method which has been conventionally applied and which can stably form the material constituting the layer on the microlens 4. Can be used without. For example, sputtering methods, such as magnetron sputtering method, high frequency sputtering method, ECR sputtering method, ion beam sputtering method, resistance heating evaporation method,
Deposition methods such as high-frequency heating evaporation method and electron beam evaporation method,
A CVD method such as a plasma CVD method or a light CVD method or a spin coating method can be suitably used.

The refractive index n3 of the micro lens 4 and the sealing resin 2 are set between the sealing resin 2 and the micro lens 4.
Even if the thin film lens 3 of fluoride and / or oxide, which is smaller than the refractive index n1, is provided, heat resistance, transparency, spectral performance, change in refractive index, and the like are not deteriorated. This is because the thin film lens 3 is formed from an inorganic material.

Finally, in this embodiment, the refractive index n1 of the sealing resin 2 and the refractive index n3 of the microlens 4 have been described as being the same. The refractive index n3 may be slightly larger than the refractive index n1 of the sealing resin 2. That is, they may be substantially the same.

Alternatively, when the refractive index n1 of the sealing resin 2 is substantially larger than the refractive index n3 of the microlens 4 beyond the same range, or when the refractive index n3 of the microlens 4 is Even when the refractive index n2 of the thin film lens 3 is larger than n1 by substantially exceeding the same range, n1
If it is smaller than n3, the light-collecting effect described above appears.

[0056]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited by the following examples.

First, as shown in FIG. 1, in a p-type well layer 13 formed in a surface layer of an n-type semiconductor substrate 12, a photodiode 14 as a light receiving portion, which is an n-type impurity region, is provided.
Was formed by an ion implantation method together with the vertical transfer register 15 and the like.

Next, a silicon oxide film is formed by a thermal oxidation method, and a chemical vapor deposition method (CVD method) is further formed thereon.
As a result, a silicon nitride film was formed to form an insulating film 10. Subsequently, C is deposited on the silicon nitride film (insulating film 10).
A polycrystalline silicon film was formed by the VD method.

The polycrystalline silicon film was removed above the photodiode 14 by etching, and was thermally oxidized. As a result, the patterned polysilicon electrode 11 (gate electrode) and the insulating film 10 covering this electrode 11 are formed.
As a result, a silicon oxide film was obtained.

Next, the light shielding film 9 is formed so as to cover the polycrystalline silicon electrode 11 and avoid the area above the photodiode 14.
Was formed. As the light shielding film 9, an aluminum film formed by a sputtering method was used.

The insulating film 8 was formed on the light shielding film 9. As the insulating film 8, BPSG formed by a CVD method is used.
(Boron-phosphorus-silicate glass) film was employed.

Further, a first flattening layer 7 was formed. As the first flattening layer 7, it is preferable to use a material having a higher refractive index than the insulating film 8 (for example, a phenol resin, a styrene resin, or an acrylic resin). The film was formed by the method. This first
The flattening layer 7 functions as an intra-layer microlens. The in-layer microlens, together with the on-chip microlens described later, has an effect of improving the light collection efficiency to the photodiode 14.

The color filter layer 6 was formed on the first flattening layer 7. The color filter layer 6 is formed by spin-coating a negative photosensitive acrylic resin as a layer to be dyed, and is then exposed and developed to be patterned so that a predetermined portion to be dyed remains. This process was repeated for each of the primary colors RGB.

However, the color filter layer 6 may be formed by using a complementary color, or may be formed by dispersing a pigment or a dye in a color filter resin.

The second flattening layer 5 was formed on the color filter layer 6. This flattening layer 5 eliminates minute irregularities on the color filter layer 6. This second planarization layer 5
Was formed by applying an acrylic resin by a spin coating method.

(On-chip) As a material of the microlens 4, a photosensitive resin obtained by adding naphthoquinonediazide to a polyparavinylphenol-based resin was employed. This resin can be used as a positive resist.

Further, when heat treatment is performed, the material is liquefied by thermoplasticity and deformed into a hemispherical shape, and thereafter, the shape is fixed and solidified by thermosetting, and a hardened lens shape is realized.

Further, in the step immediately after the development, the visible light transmittance can be increased to 90% or more by irradiating ultraviolet rays, and the transparent state can be transformed into a lens shape.

The resin layer made of the photosensitive resin is divided by using an i-line stepper, and the divided parts are decolorized by irradiation with ultraviolet light, and further softened by heating to form a dome-shaped lens shape. did.

Further, the thin film lens 3 was formed on the micro lens 4. Magnesium fluoride was used as the material of the thin film lens 3. Further, as a film forming method, an electron beam evaporation method was employed.

The thickness of the thin film lens 3 on the surface of the micro lens 4 thus formed was 0.4 μm.

The sealing resin 2 is filled on the thin film lens 3,
The cover glass 1 was mounted thereon. An acrylic resin was used as the sealing resin 2.

When the difference in the sensitivity of the solid-state imaging device depending on the presence or absence of the thin-film lens was measured, it was confirmed that the sensitivity of the solid-state imaging device was improved by 30% by forming the thin-film lens 3.

The optical calculation based on the refractive index, the film thickness, the microlens shape, and the like also showed that the sensitivity improvement by forming the magnesium fluoride film was increased by about 30%.

The solid-state imaging device prepared as described above was subjected to various performance tests under a special environment.
Performance comparable to conventional was confirmed.

In the above-described embodiment, the CCD solid-state imaging device having the in-layer lens and the color filter has been described. However, the provision of the thin-film lens, which is a feature of the present invention, is not limited to the above. The thin film lens can be provided in various solid-state imaging devices.
It can also be provided in an OS-type solid-state imaging device.

When the shape of the micro lens 4 is a hemispherical type, the thin film lens 3 is a dome-shaped plate member. When the shape of the micro lens 4 is a semi-cylindrical shape as shown in FIG. A semi-cylindrical plate-shaped member corresponding to the curved shape is obtained. In short, the shape of the thin film lens 3 of the present invention is desirably a plate-like member that is curved according to the curved surface of the microlens.

[0078]

As is apparent from the above description, the present invention can provide a solid-state imaging device having high light-collecting efficiency even with a structure using a sealing resin.

[Brief description of the drawings]

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

FIG. 2 is a partial cross-sectional view for describing improvement in light collection efficiency of the solid-state imaging device according to the embodiment of the present invention.

FIG. 3 is a partial cross-sectional view of a conventional solid-state imaging device for explaining a microlens and the like.

FIG. 4 is a perspective view showing a kamaboko type micro lens.

[Explanation of symbols]

 1, 31 cover glass 2, 32 sealing resin 3 thin film lens 4, 34 micro lens 5, 35 second flattening layer 6, 36 color filter layer 7, 37 first flattening layer 8, 38 insulating film 9 light shielding Film 10 insulating film 11 polycrystalline silicon electrode 12, 42 n-type semiconductor substrate 13, 43 p-type well layer 14, 44 photodiode 15 vertical transfer register

Claims (7)

[Claims] A light receiving unit for receiving light; a micro lens having a predetermined first refractive index formed on the light receiving unit; a thin film lens formed on the micro lens; A resin portion formed on a lens and having a predetermined second refractive index, wherein the refractive index of the thin film lens is smaller than the first refractive index and the second refractive index; A solid-state imaging device, wherein a material of the thin film lens is an inorganic material. 2. A light receiving unit for receiving light, a micro lens having a predetermined first refractive index formed on the light receiving unit, a thin film lens formed on the micro lens, and the thin film A resin portion formed on a lens and having a predetermined second refractive index, wherein the refractive index of the thin film lens is smaller than the first refractive index and the second refractive index; The solid-state imaging device, wherein the thin-film lens is a plate-shaped member made of a resin material and curved according to a curved surface of the microlens. 3. The solid-state imaging device according to claim 1, wherein the first refractive index and the second refractive index are substantially the same. 4. The solid-state imaging device according to claim 1, wherein said thin-film lens is a lens formed of a fluoride and / or an oxide. 5. The solid-state imaging device according to claim 1, wherein the microlens is a lens formed of a resin. 6. The method according to claim 1, wherein the first refractive index and the second refractive index are around 1.56, and the refractive index of the thin film lens is 1.
6. The thickness is not less than 36 and not more than 1.50.
The solid-state imaging device according to any one of the preceding claims. 7. The thin-film lens is made of a resin material, the diameter of the micro-lens is near 4000 nm, and the thickness of the thin-film lens is 80 nm or more and 1000 nm or less.
The solid-state imaging device according to any one of claims 2 to 6, wherein the thickness is equal to or less than nm.