JP2005033110A - Solid-state imaging device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively supply hydrogen to a substrate necessary for reducing dark current without substantially impairing the antireflection effect of an antireflection film, and to achieve a high output image quality and high sensitivity. A solid-state imaging device is provided.
SOLUTION: A semiconductor substrate 1, a plurality of light receiving portions 2 formed in the semiconductor substrate, and an antireflection film 6 formed above the light receiving portions, wherein the antireflection film is provided above each light receiving portion. Some have openings 6a.
[Selection] Figure 1

Description

  The present invention relates to a solid-state imaging device, and more particularly to a solid-state imaging device with improved image quality and sensitivity of an output image and a manufacturing method thereof.

  At present, a solid-state imaging device mainly uses a CCD (charge coupled device) for reading signal charges. In order to increase the resolution and reduce the size of the optical system, improvement in sensitivity has become an issue as the solid-state imaging device is increased in size and size.

  In general, a solid-state imaging device used for a color camera or the like has a transfer electrode formed on a silicon substrate on which a light receiving portion for obtaining signal charges by photoelectric conversion is formed via an insulating film. It has a structure in which a light shielding film having an opening above the part, a surface protective film, a planarizing film, a color filter, and a microlens are sequentially laminated. The light receiving portions are two-dimensionally arranged so as to be alternately arranged with the CCD portions, and the pair of light receiving portions and the CCD portions constitute one pixel. The incident visible light collected by the microlens is separated into three primary colors of red light (R), green light (G), and blue light (B) for each pixel by a color filter. The separated red light is incident on the R light receiving portion, the green light is incident on the G light receiving portion, and the blue light is incident on the B light receiving portion.

  In such a solid-state imaging device, due to the difference in refractive index between the silicon oxide film used as an interlayer insulating film and the silicon substrate, incident light is reflected on the silicon substrate surface, so that light reaching the photodiode is lost, There was a problem that the sensitivity was lowered.

  In order to solve this problem, by providing an antireflection film made of a silicon nitride film between the silicon substrate and the interlayer insulating film, the reflection of incident light is reduced by utilizing the multiple interference effect and the sensitivity is improved. Has been proposed (see Patent Document 1 and Patent Document 2).

However, the silicon nitride film used as an antireflection film in the conventional solid-state imaging device has poor crystallinity because of its dense crystal structure, and supplies hydrogen to the substrate necessary to reduce dark current. Is hindered, and it is difficult to sufficiently improve the image quality. In order to solve this problem, it has been proposed to form an insulating film on a silicon substrate with a silicon oxide film by LPCVD (Low Pressure Chemical Vapor Deposition) and remove a part of the antireflection film on the transfer electrode ( (See Patent Document 3).
Japanese Patent Laid-Open No. 4-152673 JP-A-4-206571 JP 2000-12817 A

  However, when a part of the antireflection film on the transfer electrode is removed as in the solid-state imaging device in Patent Document 3, the film used as the insulating film on the silicon substrate is not a film with good hydrogen permeability, so that the image quality is improved. There was a problem that it was difficult to achieve sufficient.

  Further, in the conventional solid-state imaging device, all of the R light receiving portion, the G light receiving portion, and the B light receiving portion have the same film thickness. Therefore, the film thickness of the antireflection film is the most reflective for a specific wavelength. The rate is set to be reduced. For this reason, it is impossible to sufficiently reduce the reflection of incident light with respect to visible light in all wavelength regions, and it has been difficult to sufficiently increase the sensitivity of a solid-state imaging device used in a color camera or the like.

  The present invention has been made in view of such circumstances, and it is possible to effectively supply hydrogen to a substrate necessary for reducing dark current without substantially impairing the antireflection effect of the antireflection film. An object of the present invention is to provide a high-sensitivity solid-state imaging device that has a high output image quality and a manufacturing method thereof.

  In order to solve the above problems, a solid-state imaging device of the present invention includes a semiconductor substrate, a plurality of light receiving portions formed in the semiconductor substrate, and an antireflection film formed above the light receiving portion, The antireflection film has an opening in a part above each light receiving portion.

  A solid-state imaging device having another configuration of the present invention includes a semiconductor substrate, a plurality of light receiving portions formed in the semiconductor substrate, an antireflection film formed above the light receiving portion, and a plurality of light contained in incident light. And an optical member that is incident on each of the light receiving portions for each color component. The antireflection film has the opening in part or all of the upper part of the light receiving unit that receives at least one color.

  The method for manufacturing a solid-state imaging device of the present invention includes a step of forming a light receiving portion in a semiconductor substrate and a step of forming an antireflection film above the light receiving portion, and the step of forming the antireflection film includes the steps of: A step of removing a part of the antireflection film located above the light receiving portion by an etching method, or a step of forming an antireflection film in a region excluding a portion above the light receiving portion.

  According to another aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device, the step of forming a light receiving portion in a semiconductor substrate, the step of forming an antireflection film above the light receiving portion, and a plurality of colors included in incident light. Forming an optical member that is incident on each of the light receiving portions for each of the components. The step of forming the antireflection film includes a step of removing a part or all of the antireflection film located above the light receiving portion that receives at least one color by an etching method, or receives at least one color. Forming the antireflection film in a region excluding a part or all of the light receiving portion above.

  According to the solid-state imaging device of the present invention, the antireflection film has an opening in a part above the light receiving portion, thereby effectively supplying hydrogen to the substrate necessary for reducing dark current. Therefore, it is possible to obtain an image pickup signal with higher image quality than in the past. In addition, since only the antireflection effect of a part of the antireflection film is lost, it is possible to obtain an image signal with higher image quality than before without substantially impairing the antireflection effect on the light incident on the light receiving portion. Can do.

  According to another aspect of the solid-state imaging device of the present invention, the antireflection film has the opening at a part or all of the upper part of the light receiving unit that receives at least one color, thereby preventing the antireflection effect. Even when the formation of the opening in the antireflection film is restricted in order to avoid the sensitivity decrease due to the decrease in image quality, the image quality can be sufficiently improved without causing a substantial decrease in sensitivity. For example, the thickness of the antireflection film is uniform for all of the red light receiving portion, the green light receiving portion, and the blue light receiving portion, and has the highest reflectivity in the wavelength region from red light to green light. When the film thickness of the antireflection film is set to be reduced, even if there is an opening in the antireflection film above the blue light receiving portion, no substantial decrease in sensitivity occurs.

  According to the method for manufacturing a solid-state imaging device of the present invention, the solid-state imaging device having the above-described configuration can be easily manufactured.

  Preferably, in the solid-state imaging device of the present invention, the antireflection film above the light receiving unit that receives the light of the first wavelength has an opening in a part or all thereof, and is longer than the first wavelength. The antireflection film above the light receiving portion that receives light having the wavelength of 2 is configured not to have an opening. According to this configuration, for example, when the film thickness of the antireflection film that reduces the reflectance most for the wavelength range of red light and green light is set, the reflectance for blue light is the case without the antireflection film. Since there is almost no change, the problem of sensitivity reduction due to the presence of openings in the antireflection film can be minimized.

  In the solid-state imaging device having any one of the configurations described above, preferably, the opening of the antireflection film is disposed on the upper outer peripheral portion of the light receiving portion. When the portion where the antireflection film is not formed is the peripheral portion of the light receiving portion, there is almost no problem of sensitivity reduction due to a reduction in the antireflection effect. As a result, the image quality can be improved without reducing the sensitivity of the solid-state imaging device used in a color camera or the like.

  The material of the antireflection film can be a silicon nitride film. From the viewpoint of antireflection, it is preferable that the opening portion of the antireflection film is small. Furthermore, when the shape of the light receiving part is a polygon, the opening part of the antireflection film is preferably arranged at the corner part. On the other hand, from the viewpoint of image quality such as so-called white flaw defect and dark current, an antireflection film is not formed on the entire surface of the light receiving portion that receives light of a specific color, preferably blue light. According to this configuration, since the supply of hydrogen to the substrate necessary for reducing the dark current is not hindered, the image quality can be sufficiently improved.

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

(Embodiment 1)
FIG. 1 shows the configuration of the solid-state imaging device in the first embodiment. FIG. 1A is a cross-sectional view, and FIG. 1B is a plan view showing the main part thereof. However, this figure shows only one light receiving portion constituting the solid-state image sensor, and normally, a plurality of light-receiving elements shown in FIG. 1 are arranged in an array to constitute the solid-state image sensor. .

  In FIG. 1A, reference numeral 1 denotes a p-type silicon substrate, and a light receiving portion 2 that is a photodiode is formed in the upper substrate. An insulating film 3 made of a silicon oxide film is formed in a region other than the light receiving portion 2 on the upper surface of the p-type silicon substrate 1. A transfer electrode 4 is formed on the insulating film 3, and the transfer electrode 4 is covered with an interlayer insulating film 5 made of a silicon oxide film. An antireflection film 6 made of a silicon nitride film is formed so as to cover the upper surfaces of the light receiving portion 2 and the interlayer insulating film 5. However, as can be seen from the planar shape shown in FIG. 1B, the antireflection film 6 is provided with an opening 6 a in the peripheral portion of the light receiving portion 2. FIG. 1B only shows the planar shape of the antireflection film 6, and other elements are not shown.

  On the upper surface of the antireflection film 6, a light shielding film 7 made of aluminum having an opening region above the light receiving portion 2 is formed. A surface protective film 8 made of a silicon oxide film, a planarizing film 9, a color filter 10, and a microlens 11 are formed on the upper surface of the light shielding film 7.

  This solid-state imaging device has a structure in which an antireflection film 6 is formed on the light receiving portion 2 and the upper layer of the transfer electrode 4, and an opening 6a is provided in the antireflection film 6 above the light receiving portion 2, so that the antireflection film is provided. Except for the point where 6 does not exist, the structure is the same as that of a conventional solid-state imaging device. As a result of measuring the reflectance of light incident from the opening region of the light-shielding film 7 on this solid-state imaging device, it was the same as the measurement result of the reflectance in the conventional solid-state imaging device.

  According to this structure, it is possible to effectively supply hydrogen to the substrate 1 necessary for reducing the dark current, and it is possible to obtain an image pickup signal with higher image quality than in the past. In addition, since the portion where the antireflection film 6 is not formed is the peripheral portion of the light receiving unit 2, the image quality can be sufficiently improved with almost no problem of sensitivity reduction due to the reduction of the antireflection effect.

  When the dark current generated in the solid-state imaging device of the present embodiment was measured, it was 0.5 mV under a temperature condition of 60 ° C. The dark current generated in the case of the conventional solid-state imaging device was measured with the other conditions being the same, and it was 1.0 mV. The generated dark current was reduced to about half by the structure of the solid-state imaging device of the present embodiment. It was confirmed that it could be reduced.

  Next, the manufacturing method of the solid-state image sensor in this Embodiment is demonstrated based on one Example.

  First, an n-type impurity was ion-implanted into a p-type silicon substrate 1 to form a light receiving portion 2 as a photodiode, and an insulating film 3 made of a silicon oxide film having a thickness of 50 nm was grown by thermal oxidation.

  Next, a polysilicon film having a thickness of 200 nm was grown by CVD (vapor phase epitaxy), and the transfer electrode 4 was formed by dry etching. Thereafter, the transfer electrode 4 was covered with a silicon oxide film by thermal oxidation to form an interlayer insulating film 5. Next, after removing the silicon oxide film on the light receiving portion 2 by wet etching, an antireflection film 6 made of a silicon nitride film having a thickness of 60 nm was grown on the entire surface of the substrate by sputtering. Thereafter, the silicon nitride film above the periphery of the light receiving portion 2 was removed by dry etching to form an opening 6a. Subsequently, a light-shielding film 7 having a thickness of 400 nm made of aluminum was formed by sputtering, and an opening region was formed above the light-receiving portion 2 by dry etching.

  Further, the entire surface of the substrate 1 was covered with a surface protective film 8 made of a silicon oxide film having a thickness of 200 nm by low pressure CVD. Thereafter, the planarization film 9, the color filter 10, and the microlens 11 were formed by using a known technique to obtain a solid-state imaging device.

  Note that the opening 6a is formed in the antireflection film 6 only after forming a silicon nitride film on the entire surface as in the above-described process and then removing a part thereof by dry etching, not only in a part above the light receiving unit 2. An antireflection film 6 may be formed.

  Further, in the above-described manufacturing method, the antireflection film 6 is formed after the silicon oxide film on the light receiving portion 2 is completely removed by wet etching. However, by adjusting the wet etching time, The remaining thickness may be about 5 nm to 25 nm.

  Further, the antireflection film 6 is formed on the light receiving portion 2 and the upper layer of the transfer electrode 4. However, the present invention is not limited to this, and the antireflection film 6 extends to the lower layer of the transfer electrode 4 or the upper layer of the light shielding film 7. It may be a structure to be formed.

  As described above, according to the configuration of the present embodiment, it is possible to effectively supply hydrogen to the substrate necessary for reducing dark current without impairing the antireflection effect, and with high sensitivity, High image quality can be obtained.

(Embodiment 2)
The configuration of the solid-state imaging device in the second embodiment is the same as that in the first embodiment shown in FIG. 1 except for the following points. That is, in the present embodiment, the thickness of the antireflection film 6 made of a silicon nitride film is set to such a thickness that the reflectance is reduced most in the wavelength range of red light and green light. Then, the silicon nitride film formed above the periphery of the light receiving portion 2 by dry etching is removed only for the B (blue) light receiving portion, and the R (red) light receiving portion, G (green). The silicon nitride film above the light receiving portion is not removed.

  In this solid-state imaging device, the reflectance of the light incident from the opening region of the light shielding film 7 is measured. As a result, the incident light is more reliably reflected with respect to the light incident on the R light receiving unit and the G light receiving unit. It was confirmed that reduction could be achieved. For the light receiving part for B, the same result as in the first embodiment was obtained. Further, when the dark current was measured, the result was the same as in the case of the first embodiment.

  The meaning of this configuration is as follows. That is, when the film thickness of the antireflection film is set so that the reflectance is reduced most with respect to the wavelength region of red light and green light, the reflectance for blue light is almost the same as that without the antireflection film. Therefore, in the B light receiving section, it is possible to minimize the problem of sensitivity reduction due to the absence of the antireflection film.

  As described above, according to the configuration of the present embodiment, it is possible to effectively supply hydrogen to the substrate necessary for reducing dark current without impairing the antireflection effect, and with high sensitivity. High image quality can be obtained.

(Embodiment 3)
The configuration of the solid-state imaging device in the third embodiment is the same as that in the first embodiment shown in FIG. 1 except for the following points. That is, in the present embodiment, the thickness of the antireflection film 6 made of a silicon nitride film is set to such a thickness that the reflectance is reduced most with respect to the wavelength range of red light and green light. Then, the silicon nitride film above the light receiving portion 2 is removed by dry etching on the entire surface above the B (blue) light receiving portion, and the R (red) light receiving portion and the G (green) light receiving portion are removed. The upper silicon nitride film is not removed.

  Also for this solid-state imaging device, the dark current was measured and found to be 0.3 mV under a temperature condition of 60 ° C. The dark current generated in the case of the solid-state imaging device of Embodiments 1 and 2 is 0.5 mV, and it has been confirmed that the generated dark current can be further reduced according to the solid-state imaging device of this example.

  Further, as a result of measuring the reflectance, the same results as in the first and second embodiments were obtained for the light incident on the R light receiving unit and the G light receiving unit. Also for the light receiving part for B, the average reflectivity in the wavelength region transmitting through the blue color filter was not different from the first and second embodiments.

  The meaning of this configuration is as follows. That is, when the film thickness of the antireflection film is set so that the reflectance is reduced most with respect to the wavelength region of red light and green light, the reflectance for blue light is almost the same as that without the antireflection film. Therefore, it is possible to minimize the problem of sensitivity reduction due to the absence of the antireflection film.

  As described above, according to the configuration of the present embodiment, it is possible to effectively supply hydrogen to the substrate necessary for reducing dark current without impairing the antireflection effect, and with high sensitivity. It is possible to obtain high image quality.

  In the second and third embodiments, the thickness of the nitride film is set such that the reflectance is reduced most with respect to the wavelength range of red light and green light. The thickness is set such that the reflectance is reduced most with respect to the wavelength region of light and blue light, and the removal of the silicon nitride film above the periphery of the light receiving portion 2 is performed with respect to the R (red) light receiving portion. It is possible to design according to the characteristics of the antireflection film.

  From the viewpoint of antireflection, it is preferable that the area of the opening of the antireflection film is small, and it is more preferable that the area of the light receiving portion is disposed in the periphery.

  Moreover, when the shape of the light receiving part is a polygon, it is preferable that the opening of the antireflection film is arranged at a corner part.

  In the solid-state imaging device according to the present embodiment, an antireflection film is formed on the entire surface of the light receiving portion that receives light of a specific color, preferably blue light, from the viewpoint of image quality such as a so-called white defect or dark current. Preferably not. Accordingly, the supply of hydrogen to the substrate necessary for reducing the dark current is not hindered, so that the image quality can be sufficiently improved.

  The solid-state imaging device of the present invention effectively supplies hydrogen to the substrate necessary to reduce the dark current without substantially impairing the antireflection effect of the antireflection film, and the output image quality is improved. Good and highly sensitive, useful for application to color cameras and the like.

The structure of the solid-state image sensor in embodiment of this invention is shown, (a) is sectional drawing, (b) is a top view which shows the principal part

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Light-receiving part 3 Insulating film 4 Transfer electrode 5 Interlayer insulating film 6 Antireflection film 6a Opening 7 Light-shielding film 8 Surface protective film 9 Flattening film 10 Color filter 11 Micro lens

Claims (7)

In a solid-state imaging device comprising a semiconductor substrate, a plurality of light receiving portions formed in the semiconductor substrate, and an antireflection film formed above the light receiving portion, the antireflection film is formed on each light receiving portion. A solid-state imaging device having an opening in a part on the upper side. A semiconductor substrate, a plurality of light receiving portions formed in the semiconductor substrate, an antireflection film formed above the light receiving portion, and a plurality of color components included in incident light, A solid-state image pickup device comprising an optical member to be incident, wherein the antireflection film has the opening in a part or all of the upper part of the light-receiving portion that receives at least one color. The antireflection film above the light receiving unit that receives light of the first wavelength has the opening in part or all of it, and receives light of the second wavelength that is longer than the first wavelength. The solid-state image pickup device according to claim 2, wherein the antireflection film above the light receiving portion does not have the opening. The solid-state imaging device according to claim 1, wherein the opening of the antireflection film is disposed on an upper outer peripheral portion of the light receiving portion. The solid-state imaging device according to claim 1, wherein a material of the antireflection film is a silicon nitride film. In the method of manufacturing a solid-state imaging device including a step of forming a light receiving portion in a semiconductor substrate and a step of forming an antireflection film above the light receiving portion, the step of forming the antireflection film is performed above the light receiving portion. A method for manufacturing a solid-state imaging device, comprising: removing a part of the antireflection film located on the substrate by an etching method; or forming an antireflection film in a region excluding a part above the light receiving portion. . A step of forming a light receiving portion in the semiconductor substrate, a step of forming an antireflection film above the light receiving portion, and an optical member that is incident on each of the light receiving portions for each of a plurality of color components included in incident light. A step of forming the antireflection film includes etching a part or all of the antireflection film located above the light receiving portion that receives at least one color. A solid-state image pickup device comprising: a step of removing by a method; or a step of forming the antireflection film in a region excluding a part or all of the light receiving portion that receives at least one color Method.

Images