JP4710693B2 - Color image sensor and color image sensor manufacturing method - Google Patents

Description

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

  In a conventional color imaging device, color filters of a plurality of colors are formed on a plurality of photoelectric conversion elements provided on a semiconductor substrate, adjacent to each other using a photolithography technique, without a gap. The color filter has a thickness of approximately 1 μm. Color filters include those that are colorless.

  In recent years, the number of pixels of an image sensor has been increased, and in recent years, the number of pixels has reached several million. In addition, as the number of pixels increases, the ratio of the area occupied by various wirings and electronic circuits for operating each pixel in each pixel increases, and the photoelectric conversion element actually receives light in each pixel at present. Therefore, the ratio of the area that can be used (opening ratio) is about 20 to 40%.

  This means that the photosensitivity of the image sensor is lowered.

  In order to improve the photosensitivity of the image pickup element, a microlens is disposed on the color filter in correspondence with the photoelectric conversion element (Japanese Patent Laid-Open Nos. 59-122193 and 60-38989). This is disclosed in Japanese Patent Publication (Patent Document 2), Japanese Patent Application Laid-Open No. 60-53073 (Patent Document 3), and Japanese Patent Application Laid-Open No. 2005-294467 (Patent Document 4).

  Further, Japanese Patent Application Laid-Open No. 59-198754 (Patent Document 5) discloses the use of a hemispherical colored microlens as a color filter.

In addition, the amount of light that can be received by the photoelectric conversion element is increased by disposing the photoelectric conversion element as close as possible to the surface of the semiconductor substrate in the semiconductor substrate that constitutes the image pickup element, thereby improving the sensitivity of the image pickup element. This is disclosed in Japanese Patent Application Laid-Open No. 2005-217439 (Patent Document 6) and Japanese Patent Application Laid-Open No. 2005-223084 (Patent Document 7).
JP 59-122193 A JP 60-38989 A JP 60-53073 A JP 2005-294467 A JP 59-198754 A JP 2005-217439 A Japanese Patent Laying-Open No. 2005-223084

  In the conventional example in which the microlens is arranged on the color filter so as to correspond to the photoelectric conversion element in order to improve the light sensitivity of the image pickup element, the side surfaces of the color filters of a plurality of colors that are adjacent to each other and in contact with each other without a gap. Part of the light incident on the portion close to the microlens enters the adjacent color filter from a similar portion on the side surface of the adjacent color filter, and causes color mixing in the light near the side surface of the adjacent color filter.

  In a photoelectric conversion element in which color mixing occurs, color reproducibility and brightness decrease, and color unevenness occurs in the entire color imaging element.

  Moreover, the entry of part of the light from the adjacent color filter is more likely to occur as the incident angle of the incident light to the photoelectric conversion element becomes shallower.

  In order to improve the sensitivity of the image sensor, the amount of light that can be received by the photoelectric converter is increased by arranging the photoelectric converter in the semiconductor substrate constituting the image sensor as close as possible to the surface of the semiconductor substrate. Even in this case, it is necessary to form color filters of a plurality of colors corresponding to the plurality of photoelectric conversion elements. Therefore, even in this case where the microlens is not used, in the same manner as the case where the microlens is used, a part of light from the adjacent color filter is incident on the light near the side surface of the adjacent color filter. Causing color mixing to produce the same result as described above.

  In order to prevent such color mixing, Japanese Patent Laying-Open No. 2005-294467 (Patent Document 4) discloses a technique for forming a microlens with an upper portion of a color filter and a transparent resin placed on the upper surface of the color filter. Are listed. That is, the central part of the convex curved surface is formed on the microlens by the surface of the transparent resin placed on the upper surface of the color filter, and the upper surface area of the color filter around the transparent resin is on the microlens. An annular peripheral portion of the convex curved surface is formed.

  Such a microlens is formed by transferring the shape of the lens matrix to the transparent resin by dry etching using the lens matrix formed on the surface of the transparent resin as a mask. However, such a processing process by dry etching complicates the manufacture of the color image sensor and increases the manufacturing cost. In addition, since the color filters of different colors have different etching rates when dry-etched under the same etching conditions, the upper surfaces of the color filters adjacent to each other having different colors are formed by the surface of the transparent resin. A difference occurs in the curvature of the annular peripheral portion of the convex curved surface formed on the microlens, which is formed following the convex curved surface on the central portion of the lens, and is further dry-etched to form the microlens. Since the degree of roughness of the surface areas of the color filters of different colors forming the annular peripheral part of the convex curved surface on top of each other is different, a plurality of colors corresponding to multi-color filters The color balance of the light incident on the photoelectric conversion element becomes poor, and color unevenness occurs in the entire color imaging element.

  In the conventional example using a hemispherical colored microlens as a color filter in order to improve the optical sensitivity of the image sensor, the length of the optical path of light after entering the microlens at the center and the periphery of the microlens There is a difference. If the length of the optical path passing through the color filter is different, a difference occurs in the coloring of the light passing through each optical path. As a result, there is a large difference in spectral characteristics between the light passing through the central portion and the peripheral portion of the microlens. In the microlens, the amount of light passing through the peripheral portion is larger than the amount of light passing through the central portion, so that the light dispersed by the microlens colored so as to serve also as a color filter becomes light as a whole. This means that a microlens colored to double as a color filter has a low color separation ability. On the other hand, when the color of the microlens is darkened, the brightness of the light dispersed by the microlens colored as a color filter is lowered, and when the amount of the colorant contained in the microlens is increased, the surface of the microlens is increased. The smoothness of the lens is impaired, and the function as a microlens is degraded.

  Furthermore, the conventional multi-color filter is a color filter of a predetermined color without gaps adjacent to each other using a photolithographic technique from a negative photosensitive color resin layer on a plurality of photoelectric conversion elements provided on a semiconductor substrate. Although formed sequentially from the filter, in the color filter of the second and subsequent colors, the surface of the color filter is lower at the center than at the periphery of the color filter. Further, it is very difficult to uniformly flatten or make the surface of the color filters of a plurality of colors flat.

  In addition, in the negative photosensitive color resin layer, if the content of the coloring material increases, the pattern light does not reach the bottom of the negative photosensitive color resin layer at the time of pattern exposure, and the degree of cure at the bottom of the resin layer is insufficient. Become. For this reason, the adhesion between the pattern exposure part and the substrate becomes insufficient, and the pattern exposure part, that is, the part that should be left on the semiconductor substrate as a color filter during development after pattern exposure is easily peeled off from the semiconductor substrate.

  The present invention has been made under the above circumstances, and an object of the present invention is to improve the photosensitivity of an image sensor, and to prevent color mixture in a plurality of photoelectric conversion elements, and to further provide a color separation capability. Color imaging that is high in color and does not cause color unevenness in the entire color image sensor without deteriorating the color balance of light incident on the plurality of photoelectric conversion elements corresponding to the color filters of multiple colors It is to provide an element.

  Another object of the present invention is to provide a method for manufacturing a color image pickup device that easily and reliably manufactures the color filter for the color image pickup device described above.

  In order to achieve the above-described object of the present invention, a color imaging device according to the present invention is formed with a plurality of photoelectric conversion elements provided on a semiconductor substrate and on a plurality of photoelectric conversion elements adjacent to each other without a gap. And a plurality of color filters. In each of the multiple color filters, the surface opposite to the corresponding photoelectric conversion element is formed into a spherical convex shape to constitute a microlens, and each of the multiple color filters is adjacent to each other. It has a feature that it has side surfaces that contact each other without a gap.

  A color imaging device manufacturing method according to the present invention is a color imaging device manufacturing method in which a color filter is formed on a photoelectric conversion element provided on a semiconductor substrate: an ultraviolet absorbing layer on the photoelectric conversion element of the semiconductor substrate Forming a positive color resist layer of a desired color on the ultraviolet absorption layer; forming a hemispherical shape after development on the surface of the positive color resist layer; A pattern exposure step of exposing the pattern so that a convex shape remains; a development step of developing the positive color resist layer and leaving a hemispherical convex shape on the surface of the positive color resist layer; and a positive color after completion of the development step A hard film processing step of performing a hard film processing on the resist layer.

  The color imaging device according to the present invention, characterized in that it is configured as described above, has a hemispherical convex surface on the side opposite to the corresponding photoelectric conversion device in each of the color filters of a plurality of colors. Therefore, the amount of light incident on the photoelectric conversion element can be increased, and the light sensitivity of the color image sensor can be improved, and part of the light from the adjacent color filter can be obtained. The color filters of the plurality of photoelectric conversion elements are not mixed with each other, and each of the color filters of the plurality of colors has side surfaces that are adjacent to each other and are in contact with each other without gaps, so that the surface functions as a microlens. As a color filter that can sufficiently color-separate light that has entered different optical path lengths from the center and the periphery of It has only a high color separation capability. In addition, it is not necessary to form a part of the convex curved surface on the microlens by dry etching on each surface of the multi-color filter, and as a result, dry etching is not performed on each surface of the multi-color filter. Roughness caused by the difference in the degree does not occur, and the color balance between the color filters of the plurality of colors does not deteriorate, and as a result, no color unevenness occurs in the entire color image sensor.

  In addition, in the color imaging device manufacturing method according to the present invention configured as described above, a positive color resist of a desired color is formed on the ultraviolet absorbing layer formed on the photoelectric conversion device of the semiconductor substrate. After forming the layer and exposing the pattern so that a hemispherical convex shape remains on the surface of the positive color resist layer after development, the positive color resist layer is developed to develop the hemispherical convexity on the surface of the positive color resist layer. Unlike the conventional color filter manufactured by using the photolithographic technique from the negative photosensitive color resin layer, the film is processed on the positive color resist layer after completion of development. Regardless of the order of filter formation, even for all color filters, the surface of the color filter should be centered rather than the height of the periphery of the color filter. More easily it can be high convex shape to a desired height. Moreover, even if the amount of the color material in the positive color resist layer is increased to some extent, unlike the case where the amount of the color material is increased in the conventional negative photosensitive color resin layer described above, the color at the time of development after pattern exposure is increased. The filter is not peeled off from the semiconductor substrate.

  Next, a color filter is formed on the image pickup device by the color filter manufacturing method for the color image pickup device according to the embodiment of the present invention, and the color image pickup device according to the embodiment of the present invention is manufactured. Will be described in detail with reference to the accompanying drawings.

  FIG. 1A shows a schematic longitudinal section of an image sensor 14 in which a plurality of CMOS photoelectric conversion elements 12 are provided on a semiconductor substrate 10. In this embodiment, the photoelectric conversion element is a CMOS photoelectric conversion element 12. However, according to the concept of the present invention, the photoelectric conversion element may be a CCD photoelectric conversion element. Such a configuration of the image sensor 14 is well known and will not be described in further detail here.

  The pixel size in plan view to which the present invention can be applied is in the range of about 10 μm to about 1 μm, and in this embodiment, it is in the range of about 2.5 μm to about 2.2 μm.

  Next, as shown in FIG. 1B, an ultraviolet absorbing layer 16 is formed on the surface of the plurality of photoelectric conversion elements 12 in the imaging element 14, and a positive type of a desired color is further formed thereon. A color resist layer 18 is formed. In this embodiment, the UV absorption layer 16 has a thickness UVH of approximately 0.1 μm, and the positive color resist layer 18 has a thickness PCRH of approximately 1.2 μm.

  The positive color resist layer 18 is formed, for example, by adding a color material of a desired color to a positive photosensitive resin, and further adding an organic solvent such as cyclohexane or PGMEA, an acid-decomposable resin, a photoacid generator, and a dispersant. It is created by adding.

  The positive color resist layer 18 is usually prepared in three colors of green, blue, and red.

  The green positive color resist layer 18 is formed of, for example, C.I. I. Pigment yellow 150, C.I. I. Pigment green 36, and C.I. I. Pigment Green 7 is added.

  Further, the blue positive color resist layer 18 is made of, for example, C.I. I. Pigment blue 15: 6, and C.I. I. Pigment Violet 23 is added.

  Further, the red positive color resist layer 18 is made of, for example, C.I. I. Pigment red 177, C.I. I. Pigment red 48: 1, and C.I. I. Pigment Yellow 139 is added.

  The positive photosensitive resin is, for example, a combination of a novolak resin and a quinonediazide compound, and an alkali-soluble vinyl polymer can be further added to this combination.

  In addition, the positive photosensitive resin may be a polyvinylphenol derivative or an acrylic resin.

  The color material may be an organic pigment or dye of a color other than those described above.

  Furthermore, a lactic acid ester may be added to the organic solvent.

  The acid-decomposable resin is a resin having a group that can be converted into an alkali-soluble group (for example, a carboxyl group or a phenolic hydroxyl group) by contacting with an acid.

The photoacid generator is a compound that generates an acid when irradiated with light, and one or more of such compounds can be used. Examples of the photoacid generator include salts with onium halogen ions, BF ₄ ions, PF ₆ ions, AsF ₆ ions, SbF ₆ ions, CF ₃ SO ₃ ions, organic halogen compounds, and naphthoquinone diazide sulfonic acid compounds. A photosulfonic acid-generating compound can be used.

  Next, a portion corresponding to the photoelectric conversion element 12 on which the color filter of a desired color (for example, green) is correspondingly formed on the surface of the positive color resist layer 18 is centered on the center of the corresponding photoelectric conversion element 12 after development. Then, pattern exposure 22 is performed using a halftone mask 20 having a gradation of a pattern that leaves a hemispherical convex shape.

FIG. 2 shows a schematic plan view of the halftone mask 20 to be used. Normally, the halftone mask has a size five times as large as the pattern to be actually formed, and pattern exposure is performed by reducing the pattern to 1/5 at the time of pattern exposure. The halftone mask has gradations (gray scales) concentrically. The concentric gradation is formed by adjusting the number of fine black dots (or white dots) per unit area on the halftone mask, for example, when the size is reduced by 1/5, for example, the size of the exposure light wavelength or less. . Thus, the halftone mask can have concentric gradations with different light transmittances concentrically.
In the halftone mask 20 used in this embodiment, the number of black dots is increased on the concentric circle centered on the center of the photoelectric conversion element 12, and as a result, the light concentrically increases toward the center. The transmittance of is reduced.

  The halftone mask 20 of this embodiment is a 5-fold reticle, and has a pattern with a size five times larger than the size of the pattern exposed on the surface of the positive color resist layer 18. Then, using a stepper exposure apparatus (not shown), the pattern of the halftone mask 20 is reduced to 1/5, and the surface of the positive color resist layer 18 is exposed.

  Thereafter, when the positive color resist layer 18 is developed, only the portion that is not exposed in the positive color resist layer 18, that is, the portion corresponding to the photoelectric conversion element 12 for which a color filter of a desired color is desired to be formed. However, it remains as the first color filter 24 of a desired color having a hemispherical convex surface centered on the center of the photoelectric conversion element 12.

  At this time, the projecting height PH at the center from the periphery of the hemispherical convex surface 24a of the first color filter 24 is approximately 0.5 μm in this embodiment, and from the periphery to the ultraviolet absorbing layer 16. Is left with a substantially vertical side surface 24 b having a height of about 0.7 μm with respect to the surface of the semiconductor substrate 10.

  Finally, the hardening process is performed on the color filter 24 thus formed.

  Next, a positive color resist layer of another desired color (for example, blue) is formed on the ultraviolet absorbing layer 16, and the positive color of the desired color described above with reference to FIGS. The pattern exposure process, the development process, and the film hardening process similar to those when forming the color filter 24 of the desired color from the mold color resist layer 18 are repeated to form another color filter of the desired color. The portion corresponding to the photoelectric conversion element 12 that is desired has another desired color having a hemispherical convex surface centered on the center of the photoelectric conversion element 12 as shown in FIG. The second color filter 26 is obtained.

  Further, a positive color resist layer of another desired color (for example, red) is formed on the ultraviolet absorbing layer 16, and the positive type of the desired color described above with reference to FIGS. 1B and 1C. The pattern exposure process, the development process, and the film hardening process similar to those performed when the color filter 24 of the desired color is formed from the color resist layer 18 are repeated to form another color filter corresponding to the desired color. The portion corresponding to the photoelectric conversion element to be selected is the same as the first color filter 24 of the desired color and the second color filter 26 of the other desired color shown in FIG. A third color filter of another desired color having a hemispherical convex surface centered on the center of the photoelectric conversion element is obtained.

  In this way, the plurality of first color filters 24, the second color filters 26, and the third color formed in a desired arrangement on the plurality of photoelectric conversion elements 12 of the imaging element 10 via the ultraviolet absorption layer 16. The filters are adjacent to each other and contact the side surfaces 24b and 26b without any gap.

  When the first to third color filters 24 and 26 having different colors are formed, the positive color resist layer 18 for forming each of the first to third color filters 24 and 26 is used. The pigments contained in each are different from each other. As a result, the photosensitivity at the time of exposure and the development at the time of development are different from each other, so that they are used for the positive color resist layer 18 of each color. The gradation level of the halftone mask to be adjusted is adjusted to be optimal for manufacturing a color filter of a desired size from the positive color resist layer 18 of each color.

  That is, when a color filter is manufactured from the positive color resist layer 18 of each color in this way, by using a dedicated halftone mask, the color filter of each color becomes the optical filter of each color. It is possible to manufacture to the dimension which can perform performance best.

  The coloring material added to the positive color resist layer 18 may be a dye, but an organic pigment is preferable in consideration of heat resistance and light resistance.

  In addition, when an organic pigment is added as a coloring material to the positive color resist layer 18, the positive color resist layer is considered in view of quality in various manufacturing processes when a color filter is manufactured from the positive color resist layer 18. The solid ratio of the organic pigment in 18 is preferably 30% to 50%, particularly preferably around 40%. If the solid ratio is lower than 30%, it is impossible to obtain a desired sufficient coloring effect on the positive color resist layer 18, and if the solid ratio exceeds 50%, a hemispherical convex shape, that is, a hemispherical convex lens shape, In the color filter made from the positive color resist layer 18 after development increases the residue mainly composed of pigment, and causes color mixing in the light passing through such a color filter. The light passing through such a color filter is not preferable because it causes noise in the image signal output from the photoelectric conversion element 12.

  When the solid ratio of the organic pigment in the positive color resist layer 18 is such, the minimum thickness of the color filter necessary for obtaining desired spectral characteristics is approximately 0.4 μm.

  And since the thickness of the flat color filter for the conventional color image sensor was about 1 μm, the thickness of the side surface of the functionally same portion as the conventional flat color filter in the color filter of the color image sensor of the present invention. When the solid ratio of the pigment is 30% to 50%, the range of 0.4 μm to 0.9 μm is preferable, and the range of 0.5 μm to 0.7 μm is most preferable.

  Furthermore, in the color filter of the color image sensor of the present invention, a hemispherical convex surface that produces an effect as a microlens is formed on the top of the color filter in order to improve the degree of condensing on the photoelectric conversion element corresponding to the color filter. The height of the included portion is 5 μm to 6 μm at which the photoelectric conversion element is provided in the semiconductor substrate of the conventional imaging device, and photoelectric conversion is performed in the semiconductor substrate as described in Patent Documents 6 and 7. The above-mentioned depth in which the element is arranged as close as possible to the surface of the semiconductor substrate is 2 μm to 3 μm, and the thickness and desired color of the ultraviolet absorbing layer formed on the photoelectric conversion element in the semiconductor substrate In consideration of the thickness of the positive color resist layer, the light condensing degree to the photoelectric conversion element corresponding to the color filter is preferably made as much as possible. In the range of 1.8μm~0.1μm it is preferred.

(A) is a schematic longitudinal cross-sectional view of the image pick-up element before a color filter is formed by the color image pick-up element manufacturing method according to one embodiment of this invention; (B) is one of this invention. In the color imaging device manufacturing method according to the embodiment, a halftone is formed after an ultraviolet absorbing layer is formed on a plurality of photoelectric conversion elements provided on a semiconductor substrate of the imaging device and a positive color resist layer is further formed. It is a longitudinal cross-sectional view which shows a mode that pattern exposure is carried out so that a hemispherical convex shape may remain after development on the surface of a positive type color resist layer using a mask; (C) is exposed in (B) FIG. 2 is a longitudinal sectional view schematically showing a state in which a positive color resist layer is developed later and a hemispherical convex shape is left on the surface of the positive color resist layer; and (D) is an embodiment of the present invention. of The present invention after a color filter of a color different from the previously manufactured color filter is manufactured by the same manufacturing method adjacent to the previously manufactured color filter by the color imaging device manufacturing method according to the embodiment It is a longitudinal cross-sectional view which shows schematically the color image pick-up element according to one embodiment. In the color imaging device manufacturing method according to the embodiment of the present invention, pattern exposure is performed so that a hemispherical convex shape remains on the surface of the positive color resist layer after development after the positive color resist layer is formed. It is a schematic top view of the halftone mask used.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate, 12 ... Photoelectric conversion element, 14 ... Image pick-up element, 16 ... Ultraviolet absorption layer, 18 ... Positive color resist layer, 20 ... Halftone mask, 22 ... Exposure, 24 ... Color filter, 24a ... Convex shape Surface, 24b ... Side, 26 ... Color filter

Claims (5)

A plurality of photoelectric conversion elements provided on a semiconductor substrate, and a plurality of color filters formed on the plurality of photoelectric conversion elements adjacent to each other without a gap;
In each of the color filters of a plurality of colors, the surface opposite to the corresponding photoelectric conversion element is formed in a hemispherical convex shape to constitute a microlens,
Each of the color filters of a plurality of colors has side surfaces that are adjacent to each other and in contact with each other with no gap therebetween.   The height of the side surface is in the range of 0.4 μm to 0.9 μm, and the height from the boundary between the surface and the side surface to the convex vertex of the surface is in the range of 1.8 μm to 0.1 μm. The color imaging element according to claim 1, wherein A color imaging element manufacturing method for forming a color filter on a photoelectric conversion element provided on a semiconductor substrate,
An ultraviolet absorbing layer forming step of forming an ultraviolet absorbing layer on the photoelectric conversion element of the semiconductor substrate;
A positive color resist layer forming step of forming a positive color resist layer of a desired color on the ultraviolet absorbing layer;
A pattern exposure step of exposing the pattern so that a hemispherical convex shape remains on the surface of the positive color resist layer after development;
Developing the positive color resist layer, leaving a hemispherical convex shape on the surface of the positive color resist layer; and
A hard film processing step for performing a hard film processing on the positive color resist layer after the development step;
A method of manufacturing a color imaging device, comprising:   The pattern exposure step uses a halftone mask having a gradation of a pattern that leaves a hemispherical convex shape after development on the surface of the positive color resist layer. The color image sensor manufacturing method.     The height of the hemispherical convex shape left on the surface of the positive color resist layer after the development process is in the range of 1.8 μm to 0.1 μm, and intersects the surface of the hemispherical convex shape in the positive color resist layer. The color image sensor manufacturing method according to claim 3, wherein a height of the side surface to be in the range of 0.4 μm to 0.9 μm.

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