JP4067175B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a solid-state imaging device, and more particularly to a method for manufacturing a solid-state imaging device including a microlens for improving sensitivity.
[0002]
[Prior 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 unit is decreasing due to a demand for miniaturization and high resolution. A so-called on-chip microlens has been developed to compensate for a decrease in photoelectric conversion characteristics accompanying a decrease in the area of the light receiving portion. The microlens is disposed above the light receiving unit formed for each pixel, and improves the effective aperture ratio of the solid-state imaging device by refracting light to be incident on the transfer region and collecting it on the light receiving unit. Is.
[0003]
A conventional method for forming an on-chip microlens will be described with reference to FIG. In FIG. 5, only the periphery of the microlens is shown for simplification. First, a synthetic resin layer 121 is formed on a planarizing layer 102 formed above a semiconductor substrate (not shown) including a light receiving portion and the like (FIG. 5A). The synthetic resin layer 121 is made of a heat-melt curable resin containing a positive photosensitive agent. The synthetic resin layer 121 is irradiated with ultraviolet light 123 such as g-line or i-line (FIG. 5B) and is divided so as to correspond to the respective light receiving portions below (FIG. 5C). Each of the divided synthetic resin portions 122 is deformed into a dome-shaped lens shape by being heated to form a microlens (FIG. 5D).
[0004]
Various solid-state imaging devices that use the microlenses thus formed to further improve sensitivity have been proposed. For example, Japanese Patent Application Laid-Open No. 4-348565 discloses a solid-state imaging device in which microlenses are arranged in a layer below a planarization layer. In such a solid-state imaging device, the sensitivity is further improved by the microlens arranged in the layer. Japanese Patent Application Laid-Open No. 5-134111 discloses a solid-state imaging device in which the refractive index of the planarizing layer forming the microlens is larger than the refractive index of the microlens material. Such a solid-state imaging device has improved light collection efficiency with respect to obliquely incident light.
[0005]
[Problems to be solved by the invention]
In order to further improve the sensitivity of the solid-state imaging device, not only the arrangement of the microlenses and the refractive index of the flattening layer are improved as described in each of the above publications, but also the dead that exists between adjacent microlenses. It is necessary to make the space as small as possible. This is because if the ratio of the condensable area by the microlens is increased, the light condensing efficiency to the light receiving portion is also improved.
[0006]
The distance between the lenses can be reduced by about 0.4 μm by a fine processing technique using an i-line stepper or the like. Due to the deformation of the synthetic resin by heating, the groove width between the synthetic resins divided by i-line or the like is further narrowed. However, if the lens interval is to be reduced to 0.4 μm or less, heating when deforming the synthetic resin and uniformity of the processed shape are strictly required. This is because when the adjacent resins contact each other, the liquefied resin flows from both sides and a desired lens shape cannot be obtained. Therefore, even if the synthetic resin is divided using i-line having a wavelength of 365 nm, it is a reality to stably manufacture a solid-state imaging device including a microlens in which the distance between lenses is reduced to 0.4 μm or less. It was not easy.
[0007]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for stably manufacturing a solid-state imaging device including a microlens with a narrower lens interval.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a method for manufacturing a solid-state imaging device according to the present invention is a method for manufacturing a solid-state imaging device in which a light receiving portion is formed on a surface of a semiconductor substrate and a microlens is disposed above the light receiving portion. A step of forming a synthetic resin layer on the planarizing layer formed above the semiconductor substrate, a step of dividing the synthetic resin layer into synthetic resin portions corresponding to the light receiving portions, and the synthetic resin portion A step of covering at least a part thereof with an overcoat layer, and a step of forming the microlens by deforming the synthetic resin portion into a convex lens shape by heating together with the overcoat layer. And
[0009]
By adopting such a manufacturing method, it is possible to prevent deformation of the microlens due to mutual contact with a lens interval of 0.4 μm or less due to nonuniform heating temperature and processing shape, and a desired lens shape can be uniformly formed. . In other words, it is possible to alleviate the influence of local heating variation, and it is possible to stably manufacture a solid-state imaging device including a microlens with a narrower lens interval.
[0010]
In the present specification, the flattening layer refers to a layer that acts to relax (that is, flatten) unevenness of the lower structure.
[0011]
In the method for manufacturing a solid-state imaging device of the present invention, it is preferable that the overcoat layer is deformable without being solidified at a temperature at which the synthetic resin portion is heated.
[0012]
Moreover, it is preferable that an overcoat layer contains water-soluble resin. This is because there is an advantage that it can be removed only by water development after forming the microlens.
[0013]
However, it is not always necessary to remove the overcoat layer, and it may be left as it is. Moreover, you may leave only a part of overcoat layer or a part of its component. In consideration of such a case, the overcoat layer preferably includes a material having a refractive index lower than that of the material constituting the microlens. This is because an antireflection effect can be expected if the low refractive index layer is left on the microlens.
[0014]
Further, the synthetic resin layer is not particularly limited, but is preferably formed of at least one resin selected from a phenol resin, a styrene resin, and an acrylic resin. These resins serve as materials constituting the microlens.
[0015]
The overcoat layer is preferably formed so that the thickness on the synthetic resin portion is 2 nm to 2 μm.
[0016]
The overcoat layer may be present in a state of covering the synthetic resin portion in the step of heating the synthetic resin portion and deforming it into a convex microlens shape, and in the groove portion that divides the synthetic resin portion by fluidization. May be present in a partially remaining state. In the former case, the overcoat layer is preferably formed in advance such that the thickness on the synthetic resin portion is 200 nm to 2 μm, and in the latter case, the overcoat layer is previously formed on the synthetic resin portion. Is preferably 20 nm to 200 nm.
[0017]
Further, when the overcoat layer is formed by vapor deposition so that the thickness on the synthetic resin portion is 2 to 20 nm, the distance between the lenses can be extremely reduced.
[0018]
Specifically, the present invention is particularly suitable as a method for stably manufacturing a solid-state imaging device in which the interval between adjacent microlenses is 0.4 μm or less.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0020]
FIG. 1 is a cross-sectional view showing an embodiment of a solid-state imaging device manufactured according to the present invention. An example of a method for manufacturing the solid-state imaging device will be described below.
[0021]
First, in the p-type well layer 11 formed on the surface layer of the n-type semiconductor substrate 10, a light-receiving portion (photodiode portion) 12 that is an n-type impurity region is formed together with the vertical transfer register 13 and the like by an ion implantation method. . Next, a silicon oxide film is formed on the p-type well layer 11 by a thermal oxidation method, and a silicon nitride film is further formed thereon by a CVD method (chemical vapor deposition method). However, in FIG. 1, both the silicon oxide film and the silicon nitride film are shown as the insulating film 7. Subsequently, a polycrystalline silicon film is formed on the silicon nitride film by a CVD method. The polycrystalline silicon film is thermally oxidized by removing the upper part of the light receiving portion 12 by etching. As a result, a patterned polycrystalline silicon electrode 8 (gate electrode) and a silicon oxide film covering the electrode 8 are formed.
[0022]
Next, the light shielding film 6 is formed so as to cover the polycrystalline silicon electrode 8 and avoid the upper portion of the light receiving portion 12. As the light shielding film 6, for example, an aluminum film formed by a sputtering method is used. As the light shielding film 6, a metal such as tungsten or a metal compound such as tungsten silicide may be used. An insulating film 5 is formed on the light shielding film 6. As this insulating film 5, a BPSG (boron-phosphorus-silicate glass) film or the like is used. The BPSG film can be formed by a CVD method. The surface of this film has a waveform reflecting the irregularities of the lower structures 6, 7 and 8. However, as shown in FIG. 1, protrusions due to the formation of the polycrystalline silicon electrode 8 and the light shielding film 7 by the BPSG film are relaxed. On the insulating film 5, a protective film made of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or the like is formed by, for example, a CVD method. This protective film plays a role of preventing permeation of moisture, impurities, dust, etc., and does not need to be formed thick (not shown in FIG. 1).
[0023]
Further, a first planarization layer 4 is formed on the protective film. The first planarization layer 4 is preferably made of a material having a refractive index higher than that of the insulating film 5. When the insulating film 5 is made of BPSG as described above, examples of such materials include phenolic resins, styrene resins, acrylic resins, and the like. These resins can be formed by spin coating or the like. As described above, when the planarization layer 4 having a higher refractive index than that of the insulating film 5 is employed and the interface between these films has a waveform as shown in FIG. It will function as a microlens. The BPSG is also a preferable material from the viewpoint of constructing a waveform curve preferable for lens formation. This in-layer microlens, together with an on-chip microlens described later, has an effect of improving the light collection efficiency to the light receiving unit 12.
[0024]
A color filter layer 3 is formed on the first planarizing layer 4. The color filter layer 3 is formed, for example, by a spin coating method using a negative photosensitive acrylic resin as a layer to be dyed, exposed and developed, and patterned so that a predetermined dyed portion remains, and the remaining material portion is formed. It is formed by repeating the process of dyeing for each of the primary colors RGB. An isolation layer is provided between the materials that have been subjected to predetermined dyeing in order to prevent color mixing. However, the color filter may be configured by using complementary colors of yellow, cyan, magenta, and green, and may be configured by dispersing pigments or dyes in the color filter resin instead of dyeing with dyes.
[0025]
A second planarizing layer 2 is formed on the color filter layer 3. The planarizing layer 2 eliminates minute irregularities on the color filter layer 3. The second planarizing layer 2 is also preferably formed by applying acrylic resin or the like by, for example, a spin coating method.
[0026]
After the series of steps described above, on-chip microlenses are formed on the planarization layer 2. The series of steps exemplify the method of manufacturing the solid-state imaging device until the planarization layer 2 is formed, and the present invention is not limited to the structure manufactured by the above steps.
[0027]
A method for forming the on-chip microlens will be described with reference to FIG. In FIG. 2, only the periphery of the microlens is shown for the sake of simplification, as in FIG. 4.
[0028]
First, a synthetic resin layer 21 to be a microlens material is formed on the planarizing layer 2 by spin coating (FIG. 2A). The thickness of the synthetic resin layer may be appropriately selected in consideration of the size of the microlens to be formed and the like, but is usually about 0.8 to 3.0 μm.
[0029]
As the microlens material used for the layer 21, for example, a phenol resin, a styrene resin, and an acrylic resin can be used, but other conventionally used materials can also be used without particular limitation. Specifically, the microlens material is preferably a photosensitive resin obtained by adding naphthoquinonediazide to a polyparavinylphenol resin. This resin can be used as a positive resist, and when heat-treated, it liquefies due to thermoplasticity and deforms into a hemispherical shape, followed by shape fixing and solidification by thermosetting, thereby realizing a cured lens shape. The Further, the photosensitive resin can improve the visible light transmittance to 90% or more by ultraviolet irradiation in the process immediately after development, and can be transformed into a lens shape in this transparent state.
[0030]
Next, the applied and formed synthetic resin layer 21 is selectively exposed. For selective exposure, g-line (wavelength 436 nm) or i-line (wavelength 365 nm) is used depending on the photosensitive agent used. When a positive resist such as the polyparavinylphenol resin is used, the ultraviolet light 23 is irradiated and developed only on a portion to be removed. As the developer, for example, a non-metallic organic ammonium developer is used. By patterning using such an ultraviolet stepper or the like, the synthetic resin layer 21 is divided so as to correspond to each light receiving portion on a one-to-one basis (FIG. 2B).
[0031]
Furthermore, each divided synthetic resin portion 22 is bleached. That is, the opaque material of each synthetic resin portion is made transparent by a decolorization reaction that proceeds by irradiation with ultraviolet light. After bleaching, the synthetic resin portion 22 having a rectangular cross section is covered with the overcoat layer 25 by a method such as spin coating (FIG. 2C).
[0032]
Each synthetic resin portion 22 covered with the overcoat layer 25 is softened by heating, and changes from an initial shape having a rectangular cross section to a dome-shaped lens shape in which the cross section is formed by an upwardly convex curve. It is deformed (FIG. 2D). At the time of this deformation, since the overcoat layer is formed, the adjacent synthetic resin portions are difficult to contact each other. In other words, the overcoat layer 25 exhibits a buffering action so that the synthetic resin portion does not approach rapidly. It is not easy to uniformly heat a single silicon wafer on which a large number of light-receiving portions are formed, and it is difficult to remove variations in lens spacing within a single silicon wafer. However, if the buffer action of the overcoat layer 25 is used, a shape that is constant and has very little variation can be realized even when the distance between adjacent lenses is 0.4 nm or less.
[0033]
The overcoat layer 25 can be used without any particular limitation as long as it is a material capable of exhibiting the above buffering action. On the other hand, the overcoat layer 25 is required not to completely limit the deformation of the synthetic resin portion 22 at the temperature at which the synthetic resin portion 22 is heated (hereinafter simply referred to as “heating temperature”). Therefore, the overcoat layer 25 is preferably softened or liquefied so that at least the synthetic resin portion 22 can be deformed into a lens shape at the heating temperature.
[0034]
As shown in FIG. 2, when the synthetic resin portion is deformed while being covered with the overcoat layer, the preferable thickness (thickness on the synthetic resin portion) when forming the overcoat layer is 200 nm to 2 μm. is there.
[0035]
The overcoat layer 25 may be made of a material that is fluidized when the synthetic resin is deformed. When a material having high fluidity is used, the overcoat layer 25 can be left only in the groove portion formed between the synthetic resin portions during heating. Thus, even if it does not exist in the surface layer portion of the synthetic resin portion, the overcoat layer 25 can exhibit the buffering effect. In this case, as shown in FIG. 3D, it is preferable that the overcoat layer 25 partially remains in the groove portion instead of the entire groove portion. This is because a preferable lens shape is easily obtained. When the overcoat layer 25 is left only in a part of the groove portion between the synthetic resins, as shown in FIG. 3 (e), the formed lens-shaped cross section is left with the overcoat layer remaining. There is a tendency to be linear in the portion that has been.
[0036]
As described above, in the embodiment described with reference to FIG. 3, a preferable thickness (thickness on the synthetic resin portion) when forming the overcoat layer is 20 nm to 200 nm.
[0037]
In addition, a method of heating the overcoat material in a range of, for example, room temperature to 80 ° C., depositing the vapor on the surface of the synthetic resin portion so as to have a thickness of 2 to 20 nm, and then performing heat deformation in the same manner as described above. You may apply. In this case, the remaining layer 25 of the overcoat layer in FIG. 3D is extremely small, and there is almost no portion where the lens-shaped cross section is linear. According to such a method, it is possible to obtain a solid-state imaging device in which the distance between the lenses is 0.2 μm or less and the lens shape is highly uniform.
[0038]
The overcoat layer 25 preferably contains a water-soluble resin. As the water-soluble resin, an acrylic resin, a polyvinyl alcohol resin, or the like can be used. Such a water-soluble resin is preferably used together with a polar solvent such as water or a lower alcohol. A silyl-based solution such as HMDS (hexamethyldisilazane) can also be used. Further, as described above, the overcoat layer may contain a low refractive index substance, and as such a low refractive index substance, a fluorine-based surfactant or the like can be used.
[0039]
There is no restriction | limiting in particular in the formation method of the overcoat layer 25. FIG. When the overcoat layer 25 is formed from a solution containing a water-soluble resin as described above, it can be formed by, for example, a spin coating method or a vapor deposition method.
[0040]
In addition, the said heating temperature is suitably determined according to the synthetic resin which forms a synthetic resin layer. In the case of the photosensitive resin in which naphthoquinone diazide is added to a polyparavinylphenol resin, for example, the heating temperature is preferably 145 to 160 ° C. In addition, when this photosensitive resin is used, it is preferable to heat at 180-200 degreeC further on the characteristic of resin. This is to improve heat resistance and solvent resistance. This reheating step is usually carried out after removing the overcoat layer when the overcoat layer is finally removed.
[0041]
After the microlens 1 is formed, the overcoat layer 25 may be removed by, for example, an aqueous solvent (FIG. 2E), but for the purpose of protecting the microlens, preventing reflection, or the like. You may leave some. In this case, the overcoat material is preferably a water-insoluble material and cured by the reheating step.
[0042]
In the above-described embodiment, the CCD solid-state imaging device including the in-layer lens and the color filter has been described. However, the present invention is not limited to this, and can be used for various solid-state imaging devices. The present invention can also be applied to a solid-state imaging device.
[0043]
By the method described above, it is possible to make the lens interval narrow from the interval S ′ to the interval S as shown in FIG. For example, an aqueous solution containing a water-soluble acrylic resin and a fluorosurfactant is applied to the surface of a synthetic resin portion made of the above polyparavinylphenol-based photosensitive resin by a spin coating method, and the film thickness is 30 to 80 nm. When an overcoat layer of a range is formed and this is heated to 150 ° C. to transform the photosensitive resin into a lens shape, the interval S ′ of about 0.4 μm formed using the i-line stepper is 0.15. It was narrowed uniformly to the interval S in the range of ˜0.30 μm. On the other hand, when the photosensitive resin was similarly heated and deformed in the air without forming an overcoat layer, the microlenses contacted each other in a part on the silicon wafer and could not be uniformly narrowed. .
[0044]
【The invention's effect】
As described above, according to the present invention, a method for manufacturing a solid-state imaging device in which a light receiving portion is formed on the surface of a semiconductor substrate and a microlens is disposed above the light receiving portion is formed above the semiconductor substrate. A step of forming a synthetic resin layer on the planarized layer, a step of dividing the synthetic resin layer into a synthetic resin portion corresponding to the light receiving portion, a step of covering the synthetic resin portion with an overcoat layer, The method includes a step of forming the microlens by deforming the synthetic resin portion into a convex lens shape by heating together with the overcoat layer, thereby reducing variation in deformation of the microlens material due to heating. Since it can be relaxed, it is possible to stably manufacture a solid-state imaging device including a microlens having a narrower lens interval. This manufacturing method improves the sensitivity by narrowing the distance between the lenses and increasing the amount of light collected in the light receiving part, and also realizes a uniform lens shape to prevent unevenness of sensitivity, and allows a large number of silicon wafers on a single silicon wafer. It is also effective in improving the manufacturing yield when forming microlenses.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a solid-state imaging device manufactured according to the present invention.
FIG. 2 is a diagram showing an example of the steps of the production method of the present invention.
FIG. 3 is a diagram showing another example of the process of the production method of the present invention.
FIG. 4 is a cross-sectional view showing a distance between microlenses of a solid-state imaging device manufactured according to the present invention.
FIG. 5 is a diagram illustrating a conventional method for manufacturing a solid-state imaging device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Micro lens 2 1st planarization layer 3 Color filter 4 2nd planarization layer 21 Synthetic resin layer 22 Synthetic resin part 25 Overcoat layer

Claims (12)

A method of manufacturing a solid-state imaging device in which a light receiving portion is formed on a surface of a semiconductor substrate, and a microlens is disposed above the light receiving portion,
Forming a synthetic resin layer on a planarization layer formed above the semiconductor substrate; dividing the synthetic resin layer into synthetic resin portions corresponding to the light receiving portions; and at least one of the synthetic resin portions. A step of covering a part with an overcoat layer, and a step of forming the microlens by deforming the synthetic resin portion into a convex lens shape by heating together with the overcoat layer. Manufacturing method of solid-state imaging device. The method for manufacturing a solid-state imaging device according to claim 1, wherein the overcoat layer is deformable at a temperature at which the synthetic resin portion is heated. The method for manufacturing a solid-state imaging device according to claim 1, wherein the overcoat layer includes a water-soluble resin. The method for manufacturing a solid-state imaging device according to claim 1, wherein the overcoat layer includes a material having a refractive index lower than that of the microlens. The method for manufacturing a solid-state imaging device according to claim 1, wherein the synthetic resin layer is formed of at least one resin selected from a phenol resin, a styrene resin, and an acrylic resin. The method for manufacturing a solid-state imaging device according to claim 1, wherein the overcoat layer is formed so that a thickness on the synthetic resin portion is 2 nm to 2 μm. The solid-state imaging according to claim 1, wherein in the step of heating the synthetic resin portion, the synthetic resin portion is deformed into a convex lens shape in a state where the overcoat layer covers the entire synthetic resin portion. Device manufacturing method. The method for manufacturing a solid-state imaging device according to claim 7, wherein the overcoat layer is formed so that a thickness on the synthetic resin portion is 200 nm to 2 μm. 2. The step of heating the synthetic resin portion, wherein the synthetic resin portion is deformed into a convex lens shape with the overcoat layer partially remaining in a groove portion that divides the synthetic resin portion. The manufacturing method of the solid-state imaging device of description. The method for manufacturing a solid-state imaging device according to claim 9, wherein the overcoat layer is formed to have a thickness of 20 nm to 200 nm on the synthetic resin portion. The method for manufacturing a solid-state imaging device according to claim 1, wherein the overcoat layer is formed by a vapor deposition method so that a thickness on the synthetic resin portion is 2 nm to 20 nm. The method for manufacturing a solid-state imaging device according to claim 1, wherein the synthetic resin portion is heated so that an interval between adjacent microlenses is 0.4 μm or less.

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