JP2008258203A - Solid-state image sensor and its fabrication process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state image sensor which can restrain inflow of an overcoat layer to a microlens, and to provide its fabrication process. <P>SOLUTION: The solid-state image sensor 1 comprises a semiconductor substrate 2, a light-receiving portion 4 formed in the P-well 3 of the semiconductor substrate 2, a charge transfer portion 5 formed in the P-well 3 of the semiconductor substrate 2, a microlens 14 formed of resin above the light-receiving portion 4, and an overcoat layer 15 formed of resin on the microlens 14 wherein the microlens 14 and the overcoat layer 15 are formed of the same kind of resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device and a manufacturing method thereof, and more particularly to a solid-state imaging device in which an overcoat layer is formed on a microlens and a manufacturing method thereof.

  Currently, solid-state imaging devices are used in optical devices such as digital still cameras and video cameras. In general, a solid-state imaging device includes a semiconductor substrate, a light receiving unit formed on the semiconductor substrate, and a charge transfer unit that is formed on the semiconductor substrate and transfers charges generated in the light receiving unit. Further, a color filter and a microlens are formed in the opening above the light receiving unit. Incident light to the solid-state imaging device is irradiated to the light receiving unit through the macro lens and the color filter, and is photoelectrically converted by the light receiving unit. Charges generated in the light receiving unit by photoelectric conversion are transferred to the outside via the charge transfer unit.

  In particular, a microlens formed above the light receiving portion is effective in preventing a decrease in the area of the light receiving portion and a decrease in sensitivity due to the downsizing of the solid-state imaging device and the increase in the number of pixels. This is because the microlens can more efficiently guide incident light to the light receiving unit.

  However, there is a problem that a part of the incident light is reflected by the surface of the microlens and a part of the incident light is not guided to the light receiving unit.

Therefore, in order to solve this problem, in Patent Document 1, an overcoat layer having an antireflection function is formed on the surface of the microlens.
JP 2004-31532 A

  The overcoat layer and the microlens are generally formed of a resin. Depending on the difference in the resin used for the overcoat layer and the microlens, the overcoat layer flows into the gap between the microlenses. For this reason, the thickness of the overcoat layer on the microlens becomes thin, and there is a possibility that the function expected of the overcoat layer cannot be achieved.

  In order to solve the above-described problems, an object of the present invention is to provide a solid-state imaging device capable of suppressing the flow of an overcoat layer into a gap between microlenses and a manufacturing method thereof.

  In order to achieve the above object, the solid-state imaging device of the present invention transfers a semiconductor substrate, a light receiving portion formed on the semiconductor substrate, and charges generated on the light receiving portion formed on the semiconductor substrate. A charge transfer unit; a resin microlens formed above the light receiving unit; and a resin overcoat layer formed on the microlens, wherein the microlens and the overcoat layer are of the same type of resin. It is characterized by being.

  In the present invention, by using the same type of resin for the microlens and the overcoat layer, the overcoat layer can be prevented from flowing into gaps or grooves between the microlenses. As a result, an overcoat layer having a predetermined function can be formed on the microlens. The same kind of resin means that the main components are common. Accordingly, the same kind of resin includes those in which the main component is completely coincident with other additives, and those having the same main component but different additives.

  In the solid-state imaging device of the present invention, it is preferable that the refractive indexes of the microlens and the overcoat layer are different. This is because an optical function is imparted to the overcoat layer by utilizing the refractive index difference between the microlens and the overcoat layer.

  In the solid-state imaging device of the present invention, it is preferable that the refractive index of the overcoat layer is smaller than the refractive index of the microlens. This is because when the refractive index of the overcoat layer is small, an antireflection function can be imparted to the overcoat layer as an optical function.

  In the solid-state imaging device of the present invention, the resin of the microlens and the overcoat layer is selected from the group consisting of acrylic resin, phenol resin, epoxy resin, polyester resin, urethane resin, melamine resin, urea resin, styrene resin, and silicone resin. It is preferable that the single material is included.

  This is because these resins are particularly suitable for forming microlenses and overcoat layers of solid-state imaging devices.

  In the solid-state imaging device of the present invention, a plurality of microlenses are formed, and there is a gap between the microlenses. Also, a plurality of microlenses are formed, and a groove is provided between the microlenses. The shape of the microlens in the solid-state imaging device is specified.

  The gap is a gap that is formed because the microlenses are separated from each other. The groove refers to a gap for separating each microlens in a state where the microlenses are in contact with each other.

In the solid-state imaging device of the present invention, it is preferable that the overcoat layer has a region having a film thickness satisfying the following formula, and the region covers 30% or more of the projected area of the microlens.
Film thickness = (λ) / (4 · (n ₀ · n ₁ ) 1/2) ± 25%
[Λ: wavelength of incident light, n ₀ : refractive index of air, n ₁ : refractive index of overcoat layer]
In the present invention, the overcoat layer and the microlens are made of the same resin, thereby improving the followability of the overcoat layer to the shape of the microlens. As a result, when the overcoat layer is actually used, the film thickness of the overcoat layer and the area covering the microlens can be set to appropriate values, and the transmittance can be made substantially equal to the ideal value.

  In the solid-state imaging device of the present invention, it is preferable that an in-layer lens is further provided between the light receiving unit and the microlens. This is because by providing the in-layer lens, incident light can be efficiently irradiated onto the light receiving portion.

  In the solid-state imaging device of the present invention, it is preferable that a color filter is further provided between the inner lens and the microlens.

  In order to achieve the above object, the present invention provides a method of manufacturing a solid-state imaging device according to the present invention, comprising: forming a light receiving portion on a semiconductor substrate and a charge transfer portion for transferring charges generated in the light receiving portion; A step of forming a resin microlens on at least the light receiving portion, and a step of forming a resin overcoat layer on the microlens, wherein the microlens and the overcoat layer are the same type of resin. It is characterized by being.

  In the present invention, the microlens and the overcoat layer are made of the same kind of resin, so that the overcoat layer can be prevented from flowing into gaps or grooves between the microlenses.

  In the method for manufacturing a solid-state imaging device according to the present invention, the step of forming the microlens includes the step of applying a lens resin layer above the light receiving portion, and leaving the lens resin layer in a predetermined shape in a portion corresponding to the light receiving portion. It is preferable to include a step of patterning and a step of deforming the lens resin layer patterned into a predetermined shape into a convex lens by heating.

  In the method for manufacturing a solid-state imaging device according to the present invention, the step of forming the microlens includes a step of applying a lens resin layer above the light receiving portion, a resist layer formed on the lens resin layer, and receiving the resist layer. Forming a hemispherical resist by patterning corresponding to the portion and heating the patterned resist, and transforming the lens resin layer into a convex lens by etching back using the hemispherical resist as a mask It is preferable that it contains.

  A method for forming a microlens is specified. The present invention can be applied to both the reflow method and the etch back method.

  In the method for manufacturing a solid-state imaging device of the present invention, the step of forming the resin overcoat layer preferably includes a step of applying the overcoat material to the microlens and a step of curing the overcoat material.

In the method for manufacturing a solid-state imaging device according to the present invention, the step of forming the resin overcoat layer forms the overcoat layer having a thickness satisfying the following formula to form 30% or more of the projected area of the microlens. It is preferable that the process to include is included.
Film thickness = (λ) / (4 · (n0 · n1) 1/2) ± 25%
[Λ: wavelength of incident light, n0: refractive index of air, n1: refractive index of overcoat layer]
In the present invention, the overcoat layer and the microlens are made of the same resin, thereby improving the followability of the overcoat layer to the shape of the microlens. As a result, when the overcoat layer is actually used, the film thickness of the overcoat layer and the area covering the microlens can be set to appropriate values, and the transmittance can be made substantially equal to the ideal value.

  According to the present invention, since the overcoat layer can be prevented from flowing into the gap between the microlenses, the overcoat layer can exhibit a predetermined optical function.

  Preferred embodiments of a solid-state imaging device and a method for manufacturing the same according to the present invention will be described below with reference to the accompanying drawings. However, the present invention is not limited to these examples.

  FIG. 1 shows a cross-sectional structure of a solid-state imaging device 1 to which the present invention is applied. First, the P-well 3 is formed on the surface layer of the n-type semiconductor substrate 2. By light-implanting n-type impurities into the P-well 3, the light receiving portion 4 and the charge transfer portion 5 are formed in the P-well 3. Next, an insulating film 6 made of, for example, an oxide film is formed on the P-well 3. The insulating film 6 is composed of two layers of oxide film-nitride film or three layers of oxide film-nitride film-oxide film as required.

  Next, a polysilicon layer is deposited on the insulating film 6 by CVD or the like. The polysilicon layer is etched, and parts other than the polysilicon layer on the charge transfer portion 5 are removed. The remaining polysilicon layer becomes the transfer electrode 7. Next, an insulating film 8 is formed so as to cover the transfer electrode 7 by thermal oxidation. Although not shown, a light shielding film is formed except for the upper part of the light receiving unit 4.

  An interlayer insulating film 9 is formed of BPSG so as to cover the light receiving unit 4 and the transfer electrode 7. Since the interlayer insulating film 9 reflects the shape of the base, a recess is formed on the light receiving portion 4. Next, a nitride film is deposited on the interlayer insulating film 9 by a plasma CVD method and etched back to form the in-layer lens 10 on the light receiving portion 4. Although not shown, an antireflection film is formed between the inner lens 10 and the interlayer insulating film 9 as necessary in order to reduce the refractive index difference between the inner lens 10 and the interlayer insulating film 9.

  A planarizing layer 11 is formed on the in-layer lens 10, and then an acrylic resin color filter 12 having spectral characteristics of red, green, and blue is formed. In order to alleviate the step between the red, green and blue filters, a planarization layer 13 is formed on the color filter 12.

  A resin microlens 14 is formed on the planarization layer 13. The microlens 14 is formed of one material selected from the group consisting of acrylic resin, phenol resin, epoxy resin, polyester resin, urethane resin, melamine resin, urea resin, styrene resin, and silicone resin.

  An overcoat layer 15 is formed on the microlens 14. The overcoat layer 15 is formed of a material including one material selected from the group consisting of acrylic resin, phenol resin, epoxy resin, polyester resin, urethane resin, melamine resin, urea resin, styrene resin, and silicone resin. In the present invention, the same type of resin as the microlens 14 is selected as the overcoat layer 15.

  By forming the overcoat layer 15 and the microlens 14 with the same kind of resin, the overcoat layer 15 can be prevented from flowing into the gap between the microlenses 14.

  The inventor has intensively studied to prevent the overcoat layer 15 from flowing into the gap between the microlenses 14, and has focused on the resin material used.

  Conventionally, the microlens above the light receiving portion is made of photosensitive phenol resin, and the overcoat layer on the microlens is made of acrylic resin. When the overcoat layer 31 and the microlens 30 are formed of different materials, many overcoat layers 31 flow into the gaps 32 between the microlenses 30 as shown in FIG. As a result, the overcoat layer 31 did not have the required film thickness, and the function as the overcoat layer 31 was not exhibited.

  On the other hand, in order to obtain the film thickness required for the overcoat layer 31, it is conceivable to increase the amount of the overcoat material to be applied. However, it is difficult to form the overcoat layer 31 having a necessary film thickness on the microlens 30 only by increasing the film thickness of the overcoat layer 31 in FIG.

  Therefore, the microlens and the overcoat layer were made of the same type of fluorine-based acrylic resin material, and the overcoat layer was formed on the microlens. As a result, it was found that although the overcoat layer flows into the gap between the microlenses, more overcoat layer remains on the microlens than in the conventional case. Although the reason is not clear, it is considered that the followability of the overcoat layer to the shape of the microphone lens is improved by using the same resin for the overcoat layer and the microphone lens.

  The inventor studied the optimization of the film thickness of the overcoat layer in consideration of the followability of the overcoat layer to the shape of the microphone lens. The film thickness of the overcoat layer is ideally uniform on the microlens. Actually, even if the microlens and the overcoat layer are made of the same material, it is not possible to completely prevent the overcoat layer from flowing into the gap between the microlenses. However, since the overcoat layer has a follow-up property as compared with the conventional one, it has been found that a predetermined function is exhibited by optimizing the film thickness of the overcoat layer.

  The inventors focused on the antireflection function, which is one of the optical functions of the overcoat layer, and studied the optimization of the film thickness. There are several conditions for the overcoat layer to exhibit its antireflection function. First, the refractive index of the overcoat layer must be lower than the refractive index of the microlens. Secondly, the film thickness d of the overcoat layer needs to satisfy the following relational expression for a predetermined wavelength.

d = (λ) / (4 · (n ₀ · n ₁ ) 1/2)
[Λ: wavelength of incident light, n ₀ : refractive index of air, n ₁ : refractive index of overcoat layer]
Ideally, the overcoat layer is formed with a film thickness d so as to uniformly cover the surface of the microlens. As described above, it is practically difficult to form an overcoat layer with a uniform film thickness d.

Therefore, as shown in FIG. 3A, the overcoat layer 15 is formed on the microlens 14, and the maximum film thickness d _MAX and the minimum film thickness d _MIN with respect to the ideal film thickness d functioning as an antireflection film are set. The area of the filled area was measured. That is, the area of the region satisfying the actual thickness of the overcoat layer = (λ) / (4 · (n ₀ · n ₁ ) 1/2) ± 25% was measured.

  As shown in FIG. 3B, it has been found that if the region 20 covers 30% or more of the projected area of the microlens 14, a predetermined antireflection function is exhibited.

  When λ = 550 nm, the transmittance when the overcoat layer is not formed on the microlens is about 95%. The transmittance when an overcoat layer having a thickness of 100 nm is uniformly formed on the microlens is about 98.6%. However, since it is difficult to form an overcoat layer uniformly in reality, the transmittance of about 98.6% is an ideal value.

  In the present invention, when the region of the overcoat layer having a thickness of 100 nm ± 25 nm covers 44% of the projected area of the microlens, the transmittance was about 98.3%. The ratio to the ideal value is 99.7%, which can be said to be substantially equivalent to the ideal value.

  By improving the followability of the overcoat layer to the microlens, it is possible to obtain a transmittance equivalent to the ideal value.

The inventor who should confirm the above-mentioned contents performed simulation. Table 1 shows the results when the lens height is 600 nm, and Table 2 shows the results when the lens height is 700 nm. As shown in FIG. 6, the thickness of the overcoat layer at the apex of the microlens was fixed to 50 nm, and the thickness of the overcoat layer (bottom thickness) accumulated in the gap between the microlenses was changed. When the lens height was 600 nm, the bottom thickness was changed from 50 nm to 250 nm, and when the lens height was 700 nm, the bottom thickness was changed from 50 nm to 400 nm. The relationship between the area ratio and the prevention effect was investigated. The area ratio represents a coverage ratio in which an overcoat layer having a film thickness of 100 nm ± 25% covers the projected area of the microlens. In addition, the prevention effect is obtained by dividing the difference between the experimental transmittance and the non-overcoated transmittance (95%) by the difference between the ideal transmittance (98.6%) and the non-overcoated transmittance (95%). It is a numerical value. It shows that the transmittance | permeability is so high that a numerical value is large. [Prevention effect = (T1-T0) / (Ti-T0) * 100 [%] (T1: experimental result, T0: no overcoat (95% in the example) Ti: ideal value (98.6% in the example) )]
As is clear from Tables 1 and 2, when the area ratio exceeds 30%, the prevention effect exceeds 80% and approaches the ideal value.

  By improving the followability of the overcoat layer to the microlens, the present invention prevents reflection by simply forming a region having a film thickness in the range of ± 25% from the ideal film thickness by 30% of the projected area of the microlens. We found that the effect is close to the ideal value. In the actual manufacturing process, its significance is very large.

  A method for manufacturing the microlens and the overcoat layer will be described. As shown in FIG. 4A, a lens resin layer 14a mainly composed of a photosensitive acrylic resin is applied on the surface of the planarizing layer 13 on the color filter 12 by a spin coating method. Next, as shown in FIG. 4B, a lens resin layer 14b patterned at a position corresponding to the light receiving portion is formed on the planarizing layer 13 by exposing and developing the lens resin layer 14a. . In order to make the lens resin layer 14b transparent, the lens resin layer 14b is irradiated with UV light.

  Next, as shown in FIG. 4C, heat flow is generated by heat-treating the lens resin layer 14b. The lens resin layer 14b has an arc-shaped pattern on the upper surface without a change in the width of the bottom surface, and the lens resin layer 14b changes its shape to a microlens 14 having a convex lens shape. There is a gap 17 between the microlenses 14.

  Next, as shown in FIG. 4D, an overcoat material mainly composed of an acrylic resin is applied on the microlens 14 by a spin coat method or the like. By evaporating the organic component of the overcoat material, the overcoat material is cured and the overcoat layer 15 is formed.

  Although the overcoat layer 15 is also formed in the gap 17 between the microlenses, the overcoat layer 15 having a desired film thickness is formed so as to cover 40% of the projected area of the microlens 14.

  Further, another microlens and overcoat layer manufacturing method will be described. As shown in FIG. 5A, a lens resin layer 14a mainly composed of photosensitive acrylic resin is applied on the surface of the planarizing layer 13 on the color filter 12 by a spin coating method. A resist layer mainly composed of a photosensitive phenol resin is applied on the lens resin layer 14a, and the resist layer is subjected to exposure and development. As a result, a patterned resist 16 is formed at a position corresponding to the light receiving portion.

  Next, as shown in FIG. 5B, heat flow is generated by heat treatment, and a hemispherical resist 16 is formed on the lens resin layer 14a. Next, as shown in FIG. 5C, the entire surface is etched back using the hemispherical resist 16 as a mask. When the etch back is performed, the resist 16 is removed and a part of the lens resin layer 14a is removed. As a result, the lens resin layer 14 a becomes a convex microlens 14 having substantially the same shape as the hemispherical shape of the resist 16. A groove 18 exists between the microlenses 14.

  Next, as shown in FIG. 5D, an overcoat material mainly composed of an acrylic resin is applied onto the microlens 14 by a spin coat method or the like. By evaporating the organic component of the overcoat material, the overcoat material is cured and the overcoat layer 15 is formed. Although the overcoat layer 15 is also formed in the groove 18 between the microlenses, the overcoat layer 15 having a desired film thickness is formed so as to cover 40% of the projected area of the microlens 14.

  In the above-described embodiment, the microlens and the overcoat layer have been described using the acrylic resin as an example. However, other resins can be used besides the acrylic resin. Various modifications can be made within the technical scope of the present invention.

Schematic sectional view of a solid-state imaging device according to the present invention Diagram showing conventional problems Schematic sectional view for explaining a second embodiment of the solid-state imaging device of the present invention Schematic showing the manufacturing process of the microlens and overcoat layer of the present invention Schematic showing another manufacturing process of the microlens and overcoat layer of the present invention Explanatory drawing showing a simulation model

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Solid-state image sensor, 2 ... N-type semiconductor substrate, 3 ... P-well, 4 ... Light-receiving part 5 ... Charge transfer part, 6 ... Insulating film, 7 ... Transfer electrode, 8 ... insulating film, 9 ... interlayer insulating film, 10 ... inner lens, 11 ... flattened layer, 12 ... color filter 13 ... flattened layer, 14 ... ..Micro lens, 15 ... overcoat layer, 16 ... resist

Claims (14)

In solid-state image sensor,
A semiconductor substrate; a light receiving portion formed on the semiconductor substrate; a charge transfer portion formed on the semiconductor substrate for transferring charges generated at the light receiving portion; and a resin microlens formed above the light receiving portion. And a resin overcoat layer formed on the microlens, wherein the microlens and the overcoat layer are the same type of resin.   The solid-state imaging device according to claim 1, wherein the microlens and the overcoat layer have different refractive indexes.   The solid-state imaging device according to claim 2, wherein a refractive index of the overcoat layer is smaller than a refractive index of the microlens.   The resin of the microlens and the overcoat layer includes one material selected from the group consisting of acrylic resin, phenol resin, epoxy resin, polyester resin, urethane resin, melamine resin, urea resin, styrene resin, and silicone resin. The solid-state image sensor of any one of Claims 1-3.   The solid-state imaging device according to claim 1, wherein a plurality of the microlenses are formed, and a gap is provided between the microlenses.   The solid-state imaging device according to claim 1, wherein a plurality of the microlenses are formed and a groove is provided between the microlenses. The solid-state imaging device according to claim 1, wherein the overcoat layer has a region having a film thickness satisfying the following formula, and the region covers 30% or more of the projected area of the microlens.
Film thickness = (λ) / (4 · (n ₀ · n ₁ ) 1/2) ± 25%
[Λ: wavelength of incident light, n ₀ : refractive index of air, n ₁ : refractive index of overcoat layer]   The solid-state image sensor according to claim 1, further comprising an in-layer lens between the light receiving unit and the microlens.   9. The solid-state imaging device according to 8, wherein a color filter is further provided between the inner lens and the microlens. In the method for manufacturing a solid-state imaging device,
Forming a light receiving portion on the semiconductor substrate and a charge transfer portion for transferring charges generated in the light receiving portion, forming a resin microlens on at least the light receiving portion of the semiconductor substrate, and on the microlens And a step of forming a resin overcoat layer,
The method for producing a solid-state imaging device, wherein the microlens and the overcoat layer are the same type of resin.   The step of forming the microlens includes a step of applying a lens resin layer above the light receiving portion, a step of patterning the lens resin layer in a predetermined shape on a portion corresponding to the light receiving portion, and the predetermined shape The method of manufacturing a solid-state imaging device according to claim 10, comprising a step of deforming the lens resin layer patterned into a convex lens by heating.   The step of forming the microlens includes a step of applying a lens resin layer above the light receiving portion, a resist layer is formed on the lens resin layer, and the resist layer is patterned corresponding to the light receiving portion, and patterned. 11. The method includes: forming a hemispherical resist by heating a subsequent resist; and transforming the lens resin layer into a convex lens by etching back the hemispherical resist using a mask. Manufacturing method of the solid-state image sensor.   The method for producing a solid-state imaging device according to claim 11, wherein the step of forming the resin overcoat layer includes a step of applying an overcoat material to the microlens and a step of curing the overcoat material. 14. The solid according to claim 11, wherein the step of forming the resin overcoat layer includes a step of forming the overcoat layer having a film thickness satisfying the following formula to form 30% or more of the projected area of the microlens. Manufacturing method of imaging device.
Film thickness = (λ) / (4 · (n ₀ · n ₁ ) 1/2) ± 25%
[Λ: wavelength of incident light, n ₀ : refractive index of air, n ₁ : refractive index of overcoat layer]

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