JP2009152315A - Image sensor and manufacturing method thereof - Google Patents

Abstract

Provided is a highly sensitive image sensor having a color filter having high adhesion to a substrate and excellent shape even with a fine pixel size and having a short distance from a microlens to a photodiode. .
In an image sensor having a semiconductor substrate on which a plurality of photodiodes are formed and green, blue and red color filters formed corresponding to the respective photodiodes, a green region is formed on the semiconductor substrate. An image sensor comprising: a first green color filter formed directly on the substrate; and a second green color filter laminated thereon.
[Selection] Figure 5

Description

  The present invention relates to an image sensor and a manufacturing method thereof.

  Video cameras and digital cameras are increasing in pixel count. For this reason, an image sensor incorporated in a video camera or a digital camera also has high pixels, and the pixel size is expected to be reduced from 2 μm or less to around 1 μm. As the pixel size is further miniaturized, the amount of light incident on the pixel is reduced as the pixel area is reduced, and the sensitivity of the photodiode is lowered. In addition, when the line width of the wiring is reduced and the dielectric layer is thinned, the pixel is easily affected by noise. In order to solve these problems, a microlens is placed above the color filter formed corresponding to the photodiode formed on the semiconductor substrate that serves as the image sensor, and the light sensitivity is increased by collecting the incident light. It is increasing.

  However, even if a microlens is disposed, incident light cannot be efficiently collected if the distance between the microlens and a photodiode made of CMOS or CCD as a light receiving element is large. For example, if the pixel size is 1.5 μm and the distance from the microlens to the photodiode is 5 μm, even if the light incident from the camera lens has an angle of 20 °, the angle from the microlens to the photodiode is 10 °. Only light within a certain angle range can be taken in, resulting in poor light collection efficiency and reduced sensitivity of the image sensor.

  1 (a) and 1 (b), a conventional image having an on-chip color filter (a color filter formed on a semiconductor substrate on which a photodiode is formed and for allowing light of a predetermined wavelength to enter the corresponding photodiode). Sectional drawing of a sensor is shown. 1A shows a cross section of the green (G), blue (B), and green (G) columns, and FIG. 1 (b) shows the green (G), red (R), and green (G) columns. A cross section is shown. A plurality of photodiodes 12 are formed on the semiconductor substrate 11, and a silicon oxide film or a silicon nitrogen oxide film (not shown) is formed on the surface of the semiconductor substrate 11. A planarizing layer (PL) 13 made of a transparent resin is formed on the semiconductor substrate 11. Corresponding to the photodiode, a green color filter 14, a red color filter 15 and a blue color filter 16 are formed on the planarizing layer (PL) 13 and made of a transparent resin in which pigments such as pigments and dyes are dispersed. ing. A smoothing layer (FL) 17 made of a transparent resin is formed on these color filters, and a plurality of microlenses 18 are formed thereon corresponding to the photodiodes.

  The planarization layer (PL) 13 functions as an adhesive layer between the color filter and the semiconductor substrate while planarizing unevenness on the surface of the semiconductor substrate. The smoothing layer (FL) 17 eliminates the steps between the pixels of the three color filters and makes it easier to form the microlens 18 with a good shape. In order to improve the light condensing property, the microlens 18 preferably has a gap between individual lenses as narrow as possible and a lens shape close to an ideal curve. If the level difference between the pixels is large and the flatness of the smoothing layer (FL) 17 is poor, the lens shape may not be a desired shape, and the lens characteristics may vary among the pixels.

  The color filter is formed as follows, for example. That is, first, a color resist including a photosensitive resin, a pigment such as a pigment or a dye, a solvent, and an additive is formed on the planarizing layer (PL) 13 by a coating apparatus such as a spinner. Next, a color resist in a predetermined region is selectively exposed (pattern exposure) through a photomask for pattern exposure using an exposure apparatus such as a stepper. Subsequently, the resist pattern is cured at a temperature of 200 ° C. or more after leaving a color resist pattern at a predetermined portion by developing with an organic alkaline aqueous solution and rinsing with pure water or the like. By repeating such a process three times with a red resist, a green resist, and a blue resist, a green color filter, a red color filter, and a blue color filter are obtained.

  The arrangement and formation order of the color filters will be described with reference to FIGS. This color filter has a so-called Bayer array. First, as shown in FIG. 2A, a green color resist is applied on the planarizing layer 13, and pattern exposure, development, and heat curing are performed to arrange the green color filters 14 in a checkered pattern in the green region. . Next, as shown in FIG. 2B, a blue color resist is applied to the entire surface, and pattern exposure, development and thermal curing are performed to arrange the blue color filters 15 vertically and horizontally in the blue region. Further, as shown in FIG. 2C, a red color resist is applied to the entire surface, pattern exposure, development, and heat curing are performed, and red color filters 16 are arranged vertically and horizontally in the red region.

  In order to improve the color separation of green, blue, and red, it has been proposed that the green region has a two-layer configuration of a first green color filter and a second green color filter (Patent Document 1). reference). Also in this case, the color filter is formed on the planarizing layer. In Patent Document 1, the color filters are formed in the order of one and the other of the first green color filter, the second green color filter, and the red and blue color filters.

  However, when the pixel size is reduced, the shape of the pattern on the photomask is not accurately transferred to the color resist during exposure. As a result, after the development, as shown in FIG. 3A, the corner portion of the green color filter 14 may be chipped, resulting in a gap 14a. Light leaks through the gap 14a, which causes noise in the obtained image.

  In order to form the microlens with a good shape, it is necessary to increase the thickness of the planarization layer (PL) 13 and the smoothing layer (FL) 17 in order to ensure the flatness of the surface serving as the base of the microlens. However, in this case, as described above, the distance from the microlens to the photodiode is increased, so the sensitivity is lowered.

  In order to prevent the occurrence of the gap 14a shown in FIG. 3A, it is conceivable to additionally form a bridge 14b at the corner of the green color filter 14 as shown in FIG. 3B. However, when the bridge 14b is formed, the blue and red regions are reduced, the light condensing property to the blue and red regions is lowered, and the color balance of the image is deteriorated. Further, after forming the green color filter 14, an unnecessary residue of the green resist is likely to be generated, and the opening shape of the pattern is likely to be rounded.

  On the other hand, in order to reduce the distance from the microlens to the photodiode with an emphasis on sensitivity, an image sensor having a structure in which the planarization layer (PL) is omitted as shown in FIGS. Proposed. 4A shows a cross section of the green (G), blue (B), and green (G) columns, and FIG. 4 (b) shows the green (G), red (R), and green (G) columns. A cross section is shown. The image sensor shown in FIGS. 4A and 4B has a laminated structure of semiconductor substrate 11/3 color filters 14, 15, 16 / smoothing layer 17 / microlens 18.

  However, in the image sensors shown in FIGS. 4A and 4B, sufficient exposure light does not easily reach the bottom of the thick color resist during pattern exposure of the resist. The problem of getting worse arises. In particular, when the pixel size is reduced, the contact area between the substrate and the color filter is reduced, so that the problem of pattern peeling due to deterioration of the adhesion of the color filter becomes significant. Note that i-line (365 nm) light is mainly used as the wavelength of exposure light to the resist. Since the blue resist has a low i-line transmittance, the adhesion of the blue resist to the base is particularly small, and the blue resist peeling problem is large. In order to ensure the adhesion of the color filter, it is conceivable to increase the exposure amount to the color resist. However, in that case, it is necessary to increase the correction of the exposure pattern formed on the pattern exposure mask, which deteriorates the shape of the color filter or lowers the resolution. In addition, in a color filter including a pigment as a pigment, the pigment concentration is close to the limit in order to provide the necessary spectral characteristics, so it is difficult to provide the necessary spectral characteristics and improve adhesion. .

1 and FIG. 4, when the blue color filter 15 is formed after the thick green color filter 14 is formed, the green color filter 14 and the blue color filter 15 A horn step is likely to occur at the edge of the blue color filter 15 at the boundary. When a horn step (protrusion) occurs in the blue color filter 15, it is necessary to increase the thickness of the smoothing layer (FL) 17 in order to reduce the influence of the step between pixels. However, in this case, the sensitivity decreases because the distance from the microlens to the photodiode increases.
JP 2006-196532 A

  The object of the present invention is to provide a highly sensitive image sensor having a color filter having high adhesion to a substrate, excellent shape, and a short distance from a microlens to a photodiode even with a fine pixel size. Is to provide.

  According to a first aspect of the present invention, in an image sensor having a semiconductor substrate on which a plurality of photodiodes are formed and green, blue and red color filters formed corresponding to the respective photodiodes, An image sensor comprising: a first green color filter formed directly on the semiconductor substrate; and a second green color filter laminated thereon.

  In the invention according to claim 2, corner portions of the first green color filter are connected by a bridge between two adjacent green pixels arranged in a diagonal direction, and the first green color filter is connected to each other within each green pixel. The image sensor according to claim 1, wherein the second green color filter has a smaller area than the first green color filter.

  The invention according to claim 3 is the image sensor according to claim 1 or 2, wherein the thickness of the first green color filter is 0.05 to 0.5 μm.

  The invention according to claim 4 is characterized in that a smoothing layer and a microlens are further provided on the second green color filter, blue color filter, and red color filter. The image sensor described in the item.

  According to a fifth aspect of the present invention, in manufacturing an image sensor having a semiconductor substrate on which a plurality of photodiodes are formed and green, red and blue color filters formed corresponding to the respective photodiodes, Applying the first green color resist directly on the semiconductor substrate, performing pattern exposure, development and thermosetting to form the first green color filter pattern in the green area, and applying the blue color resist on the entire surface Apply, pattern exposure, development and heat curing to form a blue color filter pattern on the blue area, apply red color resist on the entire surface, pattern exposure, development and heat curing to red area After forming a red color filter pattern on the surface, apply a second green color resist on the entire surface, Exposure, development and thermal curing to form a second green color filter laminated on the first green color filter in the green area, or in a reverse order to the second green color filter and And a step of forming a red color filter.

  According to the present invention, even when the pixel size is around 1 μm, the image has a high sensitivity to the substrate, has a color filter excellent in shape, and has a short distance from the microlens to the photodiode, and has a high sensitivity. A sensor can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  5A and 5B are sectional views of an image sensor according to an embodiment of the present invention. FIG. 5A shows a cross section of the image sensor in the color filter portions of green (G), blue (B), and green (G), and FIG. 5B shows green (G), red (R), green ( The cross section of the image sensor in the color filter part of G) is shown. A plurality of photodiodes 12 made of CMOS or CCD are formed as light receiving elements on the semiconductor substrate 11, and a silicon oxide film or a silicon nitrogen oxide film (not shown) is formed on the surface of the semiconductor substrate 11. In the green region, the first green color filter 21 is formed directly on the semiconductor substrate 11, and the second green color filter 22 is laminated thereon. The two layers of the color filter 21 and the color filter 22 exhibit predetermined spectral characteristics that the green color filter should have. A blue color filter 15 is formed directly on the semiconductor substrate 11 in the blue region. A red color filter 16 is formed directly on the semiconductor substrate 11 in the red region. A smoothing layer (FL) 17 made of a transparent resin is formed on these color filters, and a microlens 18 is formed thereon.

  The arrangement and formation order of the color filters will be described with reference to FIGS. This color filter has a so-called Bayer array. As shown in FIG. 6A, the first green color resist is applied directly on the semiconductor substrate 11, and pattern exposure, development, and heat curing are performed to pattern the first green color filter 21 in the green region. Place. Next, as shown in FIG. 6B, a blue color resist is applied to the entire surface, and pattern exposure, development, and heat curing are performed to arrange blue color filters 15 vertically and horizontally in the blue region. Next, as shown in FIG. 6C, a red color resist is applied to the entire surface, pattern exposure, development, and heat curing are performed, and red color filters 16 are arranged vertically and horizontally in the red region. Next, as shown in FIG. 6 (d), a second green resist is applied to the entire surface, and exposure, development, and thermal curing are performed to form a green region, and the second green resist is formed on the first green color filter 21. A green color filter 22 is arranged. Either the red color filter 16 or the second green color filter 22 may be formed first.

  According to the present invention, since the planarization layer is omitted, the distance from the microlens 18 to the photodiode 12 can be reduced, and high sensitivity can be maintained. Further, the first green color resist formed directly on the semiconductor substrate 11 is thin, and the exposure light sufficiently reaches the bottom during pattern exposure, so that the first green color filter 21 is firmly attached to the semiconductor substrate 11. Can be glued. Further, a horn step (protrusion) is unlikely to occur at the edge of the blue color filter 15 formed in contact with the thin first green color filter 21 and having a thickness greater than that of the first green color filter. No need to thicken. For this reason, the distance between the photodiode and the microlens can be shortened, so that the sensitivity is not lowered. If the thickness of the first green color filter 21 is 0.05 to 0.5 μm, it is effective to obtain these effects. In addition, the second green color filter 22 can be held by the first green color filter 21 that is firmly adhered to the substrate, and peeling can be prevented. Further, since the blue color filter 15 and the red color filter 16 whose side surfaces are in contact with the green color filter 21 are held by the green color filter 21 and the green color filter 22, peeling from the substrate can be prevented. Therefore, it is possible to provide a highly sensitive image sensor having a color filter with excellent adhesion and resolution even with a fine pixel size of about 1 μm.

  7A and 7B are sectional views of an image sensor according to another embodiment of the present invention. In this image sensor, the corner portions of the first green color filter 21 are connected to each other by two bridges 90 between two adjacent green pixels arranged in a diagonal direction, and the second green pixel is connected within each green pixel. The area of the green color filter 22 is smaller than that of the first green color filter 21 in the lower layer. As shown in FIGS. 8A to 8D, this image sensor is also the same as FIGS. 6A to 6D except that the corner portions of the first green color filter 21 are connected to each other by a bridge 90. It can be manufactured by the method.

  In this image sensor, the corner portions of the first green color filter 21 are connected to each other by a bridge 90, but unlike the conventional image sensor shown in FIG. 3, there is no problem that the blue and red regions are reduced. . Of course, no noise is generated in the image due to light leakage through the gap (gap) between the pattern corners. In addition, the area where the first green color filter and the substrate are in contact with each other increases, and the adhesion between the first green color filter and the substrate increases. In addition, a blue color filter and a red color filter are formed so as to overlap with a first green color filter portion protruding in plan view from the second green color filter. Thereby, the contact area between the first green color filter, the blue color filter, and the red color filter is increased, and the holding power of the blue and red color filters by the first green color filter is improved.

  Hereinafter, the material used in the present invention will be described.

  The main sensitivities of the color filters in the image sensor having the three primary color color filters are around 450 nm for blue, 530 nm for green, and 620 nm for red.

  Examples of the green pigment or dye used in the green color filter include the following. Examples of the green pigment include C.I. I. Pigment Green 7, 36, and 37 and Pigment Yellow 139 as a yellow pigment can be mixed and used. Examples of the green dye include C.I. I. Acid green 25, 41 can be used.

  Examples of the blue pigment or dye used in the blue color filter include the following. Examples of blue pigments include C.I. I. Any of CI Pigment Blue 15, 15: 3, 15: 4, 15: 6, 6, 22, and 60 can be used. Examples of blue dyes include C.I. I. Any of Acid Blue 41, 83, 90, 113, and 129 can be used.

  The following are mentioned as a red pigment or dye used for a red color filter. Examples of red pigments include C.I. I. Any one of CI Pigment Red 123, 155, 168, 177, 180, 217, and 220 and Pigment Yellow 139 as a yellow pigment can be mixed and used. Examples of the red dye include C.I. I. Any of Acid Red 37, 50, 111, 114, 257, and 266 can be used.

  In the present invention, in order to form a color filter, it is particularly preferable to use an acrylic pigment-dispersed color resist from the viewpoint of heat resistance.

  For example, a so-called dyeing method can be used in which a transparent resin such as PVA or casein is patterned and a dye is fixed to the transparent pattern to form a color filter.

  In addition, a dye having at least one polymerizable functional group in the molecule is used as a monomer as it is or as a dyed polymer by polymerization, and a photosensitive agent (photoinitiator, etc.) is mixed to form a color resist. It is also possible to use a so-called dye dispersion method in which a resist is patterned by lithography to form a color filter.

  Examples of the dye having at least one polymerizable functional group in the molecule include anthraquinone dyes, nitroso dyes, nitro dyes, azo dyes (that is, monoazo dyes, diazo dyes, triazo dyes, polyazo dyes). Azoic dyes, stilbene dyes, carotenoid dyes, diphenylmethane dyes, triallylmethane dyes, xanthene dyes, acridine dyes, quinoline dyes, methine dyes, polymethine dyes, thiazole dyes , Indamine dyes, indophenol dyes, azine dyes, oxazine dyes, thiazine dyes, sulfur dyes, lactone dyes, amino ketone dyes, hydroxy ketone dyes, indigoid dyes, phthalocyanine dyes, natural organic dyes Products, oxides, inorganic pigments, etc. Et appropriately selected and can be used. A dye having no polymerizable functional group may be used after introducing a functional group.

  These pigments and dyes such as dyes may be used alone or in admixture. In the case of using a mixture of dyes, the two or more kinds of dyes contained in the first green color filter and the second green color filter may be in the same ratio, but the ratios may be changed respectively, It can also be included only in the layer. At this time, depending on the proportion of the pigment, there may be a color that cannot be said to be green (such as yellow), but in the present invention, it is handled as the first or second green color filter.

  As a material of the smoothing layer 17, for example, a thermosetting acrylic resin can be used.

  In the present invention, the first green color filter 21 has the spectral characteristics obtained by a single green filter having the pigment contained in the first green color filter 21 and the pigment contained in the second green color filter 22 together. And the second green color filter 22 are laminated.

A material used for the microlens and a manufacturing method thereof will be described. First, a transparent resin layer is formed on the smoothing layer 17 using, for example, an acrylic resin coating solution. Next, a lens matrix material made of, for example, phenol resin having alkali solubility, photosensitivity, and heat flow is applied on the transparent resin layer. Next, using a known photolithography process, the lens matrix material is patterned so as to leave a region that becomes the lens matrix. The remaining lens matrix material is heat-treated and thermally reflowed, and deformed into a hemisphere to form a lens matrix. By setting the reflow amount to an appropriate amount of about 0.1 μm on one side, a smooth hemispherical shape with a gap between the unit lens molds of, for example, about 0.24 μm can be obtained. Next, using a dry etching apparatus, a mixed gas of CF ₄ and C ₄ F ₈ is used to transfer the shape of the lens matrix to the transparent resin layer using the lens matrix as a mask to form a microlens. If the lens matrix and the transparent resin layer are uniformly etched from above, the etching proceeds downward while maintaining the shape of the lens matrix. Therefore, the shape of the transparent resin layer may be etched to the same shape as the lens matrix. it can. The micro lens has a height of, for example, 1 μm and a gap between unit lenses of, for example, 0.04 μm.

Sectional drawing of the conventional image sensor. The top view explaining arrangement | positioning and formation order of the color filter of the conventional image sensor. The top view explaining the problem of the conventional image sensor. Sectional drawing of the other conventional image sensor. 1 is a cross-sectional view of an image sensor according to an embodiment of the present invention. FIG. 3 is a plan view for explaining the arrangement and formation order of the color filters of the image sensor according to the embodiment of the invention. Sectional drawing of the image sensor which concerns on other embodiment of this invention. The top view explaining arrangement and formation order of the color filter of the image sensor concerning other embodiments of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Semiconductor substrate, 12 ... Photodiode, 13 ... Planarization layer (PL), 14 ... Green color filter, 15 ... Blue color filter, 15 ... Red color filter, 17 ... Smoothing layer (FL), 18 ... Micro lens 21 ... first green color filter, 22 ... second green color filter.

Claims (5)

  In an image sensor having a semiconductor substrate on which a plurality of photodiodes are formed and green, blue and red color filters formed corresponding to the respective photodiodes, a green region is directly formed on the semiconductor substrate. An image sensor comprising: a first green color filter and a second green color filter laminated thereon.   The corners of the first green color filter are connected by a bridge between two adjacent green pixels arranged in a diagonal direction, and the second green color filter is connected to each other in each green pixel. The image sensor according to claim 1, wherein the area is smaller than that of the first green color filter.   3. The image sensor according to claim 1, wherein a thickness of the first green color filter is 0.05 to 0.5 μm.   The image sensor according to any one of claims 1 to 3, further comprising a smoothing layer and a microlens on the second green color filter, the blue color filter, and the red color filter. In manufacturing an image sensor having a semiconductor substrate on which a plurality of photodiodes are formed and green, red, and blue color filters formed corresponding to the respective photodiodes,
Applying a first green color resist directly on the semiconductor substrate, performing pattern exposure, development and thermosetting to form a first green color filter pattern in a green region;
Applying a blue color resist on the entire surface, pattern exposure, development and thermosetting to form a blue color filter pattern in the blue region;
A red color resist is applied to the entire surface, pattern exposure, development and thermosetting are performed to form a red color filter pattern in the red region, and then a second green color resist is applied to the entire surface to perform pattern exposure, development and Heat cure to form a second green color filter laminated on the first green color filter in the green area, or form a second green color filter and a red color filter in the reverse order A process for manufacturing an image sensor.

Images