JP2005123225A - Color solid-state imaging device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color solid-state imaging device which is equipped with color filters that have a few agglomerate growing black marks and are excellent in shape even when pixels are each 5 μm or below in size, affords to allow a sufficient exposure margin, is equipped with color pixels which are hardly separated off, and high in productivity; and to provide a method of manufacturing the same. <P>SOLUTION: The color solid-state imaging device has a flattening layer 3 flattening the rugged surfaces of a plurality of light receiving elements 2 on the surface of a semiconductor substrate 1 equipped with the light receiving elements 2, a color filter layer composed of color pixels 5 to 7 which are of two or more different colors and each paired up with the light receiving element, and micro-lenses 9 which condense light on the light receiving elements and are each paired up with the light receiving element formed on the flattening layer 3. The flattening layer 3 has recesses which are each paired up with the light receiving element so as to correspond with each other, and the color filter layer is provided so as to fill up the recesses. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color solid-state imaging device and a method for manufacturing the same.

  Solid-state imaging devices such as CCDs and CMOS devices mounted on digital still cameras and portable cameras have been increasing in pixel count and definition, and in particular for digital still cameras, obtain the same resolution as silver salt cameras. Therefore, the number of pixels is 3 million pixels or more, and the size of the pixels is 5 μm or less, and particularly fine one is about 3 μm.

  Also for camera-equipped mobile phones, the number of pixels is increasing while miniaturization is progressing, and the pixel size is 5 μm or less as in the case of digital cameras.

  On the other hand, the solid-state imaging device is provided with a color filter layer (also referred to as a dye pixel) as a pair with the light receiving device for colorization.

  There are a pigment dispersion method, a dyeing method, a dye dispersion method, etc. to form a color filter, but mainly a primary color (red, blue, green) or complementary color (cyan, magenta, yellow) pigment or dye. In this method, a color resist in which a pigment is dispersed in a transparent resin is applied and then a pattern is formed by lithography.

Furthermore, a microlens for taking in light incident on each pixel as much as possible is formed for each pixel in order to improve sensitivity.
JP-A-3-230101

  By the way, when the pixel size is 5 μm or less, the sensitivity is remarkably lowered. In particular, the aperture ratio and the film thickness of the dye pixel have a great influence on the sensitivity. For example, the edge shape of the dye pixel is likely to cause wrinkles (the edge becomes jagged) and noise, and the thicker the film thickness, the more oblique Since the light is blocked with respect to the incident light, the sensitivity may decrease or the colors may be mixed.

  In addition, the color filter is generally formed by lithography as described above, and exposure often uses a stepper with excellent positional accuracy. However, if the color filter is thick, pigment pixels may be peeled off. In some cases, the focus margin is narrowed and the surface is defocused against macroscopic undulations. Therefore, the film thickness of the color filter should be as thin as possible in terms of both imaging characteristics and manufacturing characteristics.

  The color filter is divided into a pigment type and a dye type as described above. The dye type is very fine dye, so that there are few black scratches (black defects due to aggregates etc.) that cause noise, but there is a disadvantage that the film thickness becomes thick due to low coloring power. Moreover, it is inferior to heat resistance and light resistance.

  On the other hand, the pigment type is excellent in reliability such as color characteristics, heat resistance, and light resistance, and has a feature that it is easy to reduce the thickness by adjusting the pigment concentration. On the other hand, there is a defect that the pigment particles tend to aggregate and easily cause defects called black scratches.

  For this reason, in pigment color resists, filtration is performed on the order of submicrons so that aggregated pigment particles do not mix. However, when the color filter film thickness is thin, the pigment concentration becomes high, so that productive filtration is performed. There was a bug that could not be done.

  The present invention has been made in view of such a problem, and even with a pixel size of 5 μm or less, there are few aggregates that become black scratches, a color solid-state imaging device having a color filter with a good shape, and an excellent exposure margin. The present invention provides a color solid-state imaging device with high productivity that does not peel off pigment pixels and a method for manufacturing the same.

The present invention has been studied in detail in order to solve such problems, and the color solid-state imaging device according to claim 1 is a flat surface in which irregularities of a light receiving element are buried in the surface of a semiconductor substrate having a plurality of light receiving elements. In a color solid-state imaging device in which a light-receiving element and a color filter layer composed of a plurality of color pigment pixels and a microlens for focusing on the light-receiving element are formed on the planarization layer
The flattening layer has a concave shape corresponding to a pair with the light receiving element, and a color solid-state imaging device is provided in which a color filter layer is disposed so as to fill the concave shape.

  According to a second aspect of the present invention, in the color solid-state image pickup device according to the first aspect, the cross-sectional shape of the dye pixel is reverse convex, and the film thickness of the central part of the dye pixel is thicker than the edge part.

  Therefore, according to the color solid-state imaging device of claims 1 and 2, the central portion of the pixel where the color filters of the plurality of colors of the planarizing layer are formed in a concave shape, and the original color filter spectral characteristics can be obtained in the concave portion. By setting the thickness and setting the edge part thinner than the original color filter spectral characteristics, a cross-sectional shape with a sharp shape can be formed as a reverse convex color filter. Noise can be significantly suppressed, and an exposure focus margin can be secured.

  In addition, since the film thickness of the color filter can be set with a pigment concentration capable of precision filtration, a color solid-state imaging device having a good color filter with few black scratches can be provided.

  A third aspect of the present invention provides a method for manufacturing a color solid-state imaging device according to the first or second aspect, wherein after the surface of the planarizing layer is smoothed, the plurality of light receiving elements of the planarizing layer are formed before the color filter layer is formed. It has the process of etching so that the part corresponding to may become concave.

  Therefore, according to the method for manufacturing a color solid-state imaging device of claim 3, the portions corresponding to the plurality of light receiving elements of the flattening layer are etched so as to be concave before forming the color filter. Two color solid-state imaging devices can be obtained.

  In the color solid-state imaging device of the present invention, the surface of a semiconductor substrate having a plurality of light receiving elements is composed of a planarizing layer that fills the unevenness of the light receiving elements, and a plurality of dye pixels paired with the light receiving elements on the planarizing layer. In a color solid-state imaging device having a color filter layer and a microlens that collects light on the light receiving element, the flattening layer has a concave shape corresponding to a pair with the light receiving element, and the color filter layer is arranged so as to fill the concave shape. Set up.

  Therefore, the color filter can be set to a certain film thickness, that is, the dye concentration of the color resist can be reduced, so that mass filtration with high productivity is possible. Thereby, a color filter with less aggregated foreign matter can be obtained, and imaging characteristics with less noise and roughness can be provided.

  In addition, since the center of the pixel of the flattening layer is concave and the color filter is embedded in the concave flattening layer, the distance under the lens can be set shorter than the conventional color filter formed on the flattening layer. . Thereby, it is possible to improve imaging characteristics such as sensitivity, smear characteristics, and shading.

  Further, in the color solid-state imaging device of the present invention, the pigment pixel can be prevented from peeling by increasing the thickness of the pigment pixel from the edge portion, and the resolution of the color filter is improved. Even with this pixel, it is possible to obtain a sharp color filter without flickering. Further, since the edge film thickness of the color filter to be resolved is thin, the exposure focus margin is widened, the yield is improved, and a method for manufacturing a color solid-state imaging device with high production efficiency can be provided.

  Embodiments of a color solid-state imaging device according to the present invention will be described below.

  FIG. 1 is an explanatory view showing a cross section of a solid-state imaging device provided with a color filter according to the present embodiment. FIG. 2 is an enlarged view of the color filter shown in FIG. FIG. 3 is a plan view of the color filter shown in FIG.

  First, a color solid-state imaging device according to the present embodiment includes a light-receiving element array in which a plurality of light-receiving elements 2 formed of photodiodes or the like are two-dimensionally arranged in a semiconductor substrate 1 in the cross-sectional view of FIG. Although omitted in FIG. 1, a transfer register portion, a transfer electrode portion, and the like are formed by a CCD.

  An insulating film and a passivation layer are formed on the upper surface of the semiconductor substrate. As shown in FIG. 1, the portion of the light receiving element on the surface of the semiconductor substrate falls into a mortar shape, and the step is about 1 to 2 μm. Then, a first planarizing layer 3 made of a transparent resin such as an acrylic resin is formed on the passivation layer by hollowing out the light receiving element portion, and has a certain thickness so as to be embedded in the concave shape. , Green 5, red 6 and blue 7 color filter layers are provided.

  At this time, the film thickness of the color filter layer depends on the pixel size and the spectral characteristics of the color filter, but when the pixel size is 2 to 5 μm, the film thickness B1 of the pixel edge portion shown in FIG. A range of 0.7 μm is desirable for forming a color filter.

  The film thickness A1 in the central portion of the pixel is approximately the sum of the thickness hollowed out in a concave shape and the pixel edge portion, and a color filter layer having a certain thickness can be obtained.

  A second planarizing layer made of a transparent resin layer and a microlens 9 are formed on the color filter layer.

  In the prior art, when the color filter has a certain thickness, as shown in FIGS. 7 and 8, the distance X from the lens to the light receiving element (hereinafter referred to as the lens lower distance) becomes longer, and the sensitivity decreases and color mixing (color shading) occurs. ), Etc. may occur, but the center of the pixel of the first flattening layer, which is the base of the color filter, is etched by dry etching or the like, and the cross-sectional shape is made concave to make the color filter concave. By embedding in the flattening layer, the distance below the lens can be made thinner by the thickness of C in FIG. 2 than when the color filter is formed on the flattening layer of the prior art.

  Further, as shown in FIG. 3, the thickness B2 of the edge portion of the dye pixel is determined by combining the edge portion of the dye pixel and the side wall upper portion of the lattice-like side wall pattern formed by etching the flattening layer in a concave shape. Stepper exposure wavelength transmission due to the deterioration of the shape of the color pixel due to the defocusing of the stepper and the color characteristics, which was a problem when forming a color filter with a fine size of 5 μm pixels or less. The pigment pixel peeling caused by almost no rate can be solved, and the manufacturing margin can be greatly improved, so that the production efficiency can be increased. In addition, since the color filter can have a certain thickness, it is not necessary to increase the dye concentration of the color resist, and it is possible to perform productive microfiltration, so it is possible to remove aggregates and foreign substances contained in the color resist. it can.

  Accordingly, since the color filter is free from defects caused by pigments such as aggregates, noise can be greatly reduced.

  In the case of the standard spectral characteristics shown in FIG. 4, the film thickness of the color filter capable of microfiltration with productivity needs to be 0.8 μm or more as the film thickness after curing.

  The focus margin during exposure depends on the pixel size, color filter film thickness, and color resist resolution, but when the color resist film thickness is 1 μm, the 3 μm pixel size is approximately ± 0.5 μm and the 2 μm pixel size. When the film thickness of the color resist is about 0.6 μm, it is about ± 1 μm for the 3 μm pixel size and about ± 0.5 μm for the 2 μm pixel size. The above-mentioned furcus margin refers to a range until the focus becomes such that the pixel shape becomes round or the pixel size becomes abnormally large, and the larger this value (margin) is better.

  Since the focus of the stepper is to swell the macro swell of the device, ± 0.5 μm is necessary as the focus margin.

  Accordingly, the film thickness of the color filter is preferably 0.6 μm or less at the pixel edge portion and 0.9 μm or more at the pixel center portion.

  The most problematical problem when the cross-sectional shape of the color filter according to the present invention is changed from the normal □ shape to the reverse convex shape is the color reproducibility, but the color filter film thickness that is not the original color filter spectral characteristic is reduced. If the edge part is devised, no problem occurs. That is, the pixel edge portion may be set to a dimension that removes the light collecting path of the microlens.

  Hereafter, the manufacturing method of the color solid-state image sensor of this invention is demonstrated in detail. 5 and 6 are cross-sectional views in each step showing the method for manufacturing a color image sensor of the present invention.

  FIG. 5A shows a semiconductor substrate 1 having a plurality of light receiving elements 2 having a passivation layer formed on the outermost surface. In the semiconductor substrate used in this embodiment, the pixel pitch in the horizontal and vertical directions is 3.1 μm, the maximum step in the effective pixel region is about 1 μm, and the opening width of the light receiving element is about 0.8 μm.

  FIG. 5B shows a step of forming the first planarization layer 3 made of a transparent resin on the surface layer of the semiconductor substrate. As a method for forming the first planarizing layer, a transparent resin liquid such as an acrylic resin to which a thermosetting agent or a photocuring agent is added is formed by a spin coating method at a rotational speed of 700 to 3000 rpm, and then a hot plate or Heat cure in the range of 160-240 ° C. in a clean oven. When the transparent resin is photocured, it may be photocured before or instead of the heat treatment.

  With this first planarization layer, the step in the effective pixel area where the light receiving elements on the semiconductor substrate are arranged is planarized. That is, the film thickness of the first planarization layer is about 1.5 μm from the bottom of the pixel and 0.5 μm from the top.

  FIG. 5C shows a process of forming a pattern on the first flattening layer by photolithography so as to surround each light receiving element. As a method for forming a frame-like pattern on the first planarization layer, a commercially available positive resist (for example, AZ1350 manufactured by Tokyo Ohka Kogyo Co., Ltd.) is formed at a rotational speed of 2300 rpm by spin coating, After temporary drying on a hot plate at 70 ° C. for 1 minute, exposure is performed with a stepper at an exposure amount of 100 mj, paddle development with an organic developer for about 30 seconds, and then rinse with pure water for about 1 minute. Form a pattern. Subsequently, it heat-sets in the range of 160-240 degreeC with a hotplate.

  The resist pattern 4 has a thickness of 0.5 μm and a line width of 0.6 μm with respect to a pixel pitch of 3.1 μm. Therefore, the opening width of the frame pattern is 2.5 μm.

  FIG. 5D shows a process of etching by dry etching or the like (arrow in the figure) using the pattern as a mask. Etching is performed by dry etching using the frame-like pattern formed in FIG. 5C as a mask.

The dry etching apparatus is a parallel plate type, and as conditions, a mixed gas of CF ₄ and C ₃ F ₃ is used, the substrate temperature is normal temperature, the pressure is 1 Pa, the RF output is 500 W, and the bias is 50 W. Under this condition, the etching rate of the underlying flat layer is about 0.3 μm / min. Therefore, by performing dry etching for about 2 minutes, the thickness of the first planarization layer formed in FIG. 5B is dry-etched by about 0.6 μm, and the planarization layer is etched into a concave shape. A grid-like sidewall pattern is obtained. The obtained concave cross-sectional shape is about 0.6 μm at the center of the pixel, and is a shape obtained by transferring the frame-like pattern formed in FIG.

  FIG. 6E shows the first color filter on the surface layer of the semiconductor substrate having a concave cross-sectional shape formed by etching. A process of forming a green pixel by patterning the green dye pixel 5 by a photolithography method or the like is shown. As the green resist, one filtered in advance with a filter having a filtration accuracy of 0.5 μm is used.

  As a method for forming a green pixel, a green resist film is formed at a rotational speed of 1500 rpm by a spin coating method, temporarily dried on a hot plate at 70 ° C. for 1 minute, and then exposed to 200 mj by a stepper. Then, after performing spray development with an organic developer for about 30 seconds, a pattern is formed by rinsing with pure water for about 1 minute.

  Subsequently, it heat-sets in the range of 160-240 degreeC with a hotplate. The film thickness of the green pixel is about 1 μm at the center of the pixel and about 0.4 μm at the edge. The focus at this time was 0 μm, but a focus margin of ± 1.0 μm was obtained.

  FIG. 6F shows a process of forming red pixels by patterning the red dye pixels 6 by the photolithography method or the like as in the case of green. As the red resist, one filtered in advance with a filter having a filtration accuracy of 0.5 μm is used.

  The central film thickness of the red pixel is 1 μm, which is the same as that of green. The focus margin at the time of exposure was ± 0.9 μm.

  FIG. 6G shows a process of forming blue dye pixels 7 by patterning blue by the photolithographic method or the like like green and red.

  A blue resist that has been filtered in advance with a filter having a filtration accuracy of 0.5 μm is used. The central film thickness of the blue pixel is 1 μm, the same as that of green.

  FIG. 6H shows a process of forming the second planarization layer 8 on the surface layer of the color filter.

  The method for forming the second planarizing layer is a process including coating and curing processes, similar to the method for forming the first planarizing layer in FIG. The planarization layer has a thickness of 0.3 μm.

  FIG. 6I shows a process of forming a microlens for each light receiving element on the planarizing layer. As a method for forming the microlens, a positive resist (for example, TMR-P3 manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied on the planarizing layer of FIG. After temporary drying under the above conditions, exposure is performed with an exposure amount of 300 mj by a stepper, paddle development is performed with an organic developer for about 40 seconds, and then pattern formation is performed by rinsing with pure water for about 1 minute.

  Next, heat curing is performed in a range of 100 to 240 ° C. with a hot plate, and a lens shape is obtained by utilizing surface tension at that time.

  As described above, according to the color solid-state imaging device and the manufacturing method thereof of the present invention, it is possible to set a wide focus margin at the time of exposure, and to obtain a color filter that has high resolution, no flickering, and no pixel peeling. . Furthermore, since the film thickness of the color filter can be set to, for example, 0.9 μm or more, the filterability in color filter microfiltration is greatly improved and the productivity is excellent. Furthermore, it leads to an improvement in the characteristics of the image pickup device by reducing the distance below the lens.

It is sectional drawing of the solid-state image sensor concerning this invention. It is a fragmentary sectional view of the solid-state image sensing device concerning the present invention. It is a top view of the solid-state image sensing device concerning the present invention. It is a graph which shows a standard spectral characteristic. It is explanatory drawing which shows the manufacturing process of the solid-state image sensor concerning this invention. It is explanatory drawing which shows the manufacturing process of the solid-state image sensor concerning this invention. It is sectional drawing of the conventional solid-state image sensor. It is a fragmentary sectional view of the conventional solid-state image sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Light receiving element 3 First planarization layer 4 Resist pattern 5 Green pigment pixel 6 Red pigment pixel 7 Blue pigment pixel 8 Second planarization layer 9 Microlens

Claims (3)

A flattening layer that fills the unevenness of the light receiving element on the surface of the semiconductor substrate having a plurality of light receiving elements, and a color filter layer composed of a plurality of dye pixels paired with the light receiving element on the flattening layer and the light receiving element are condensed. In a color solid-state imaging device formed with a microlens,
A color solid-state imaging device, wherein the planarizing layer has a concave shape corresponding to a pair with the light receiving device, and a color filter layer is disposed so as to fill the concave shape.   2. The color solid-state imaging device according to claim 1, wherein a cross-sectional shape of the dye pixel is reverse convex, and a film thickness of a central portion of the dye pixel is thicker than an edge portion. A flattening layer that fills the unevenness of the light receiving element on the surface of the semiconductor substrate having a plurality of light receiving elements, and a color filter layer composed of a plurality of dye pixels paired with the light receiving element on the flattening layer and the light receiving element are condensed. In the manufacturing method of the color solid-state imaging device in which the microlens is formed,
A method of manufacturing a color solid-state imaging device, comprising: etching the flattening layer so that portions corresponding to the plurality of light receiving elements become concave.