JP2006049825A - Solid state imaging device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise the condensing efficiency of obliquely incident lights, reduce the smear components and suppress the crosstalk. <P>SOLUTION: The solid state imaging device 12 comprises an optical guide 21 tapered to increase its cross section upward on a photoelectric converter element 12 through an insulation film 16 and an etching stopper film 17 laid on the element 12, and a condensing lens 22 having a structure integrated with the optical guide 21 having a higher refractive index than a layer insulation film 20. The lens 22 is made of the same material as that of the optical wave guide 21. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device with high light collection efficiency to a photoelectric conversion device, less smear and color mixing (crosstalk), and high reliability, and a method for manufacturing the same.

  In recent years, solid-state imaging devices have been widely used in digital cameras, mobile phones with photo functions, and the like. Along with the downsizing and higher functionality of these devices, the solid-state imaging device used for them is also required to have more pixels and improve sensitivity. In order to realize this, a solid-state imaging device has been proposed in which an on-chip microlens or a condensing lens is provided above the photoelectric conversion element to improve condensing efficiency.

  A specific structure of a conventional solid-state imaging device having two lenses such as an on-chip microlens and a condenser lens will be described with reference to FIGS. 9 and 10. FIG. 9 and 10 are cross-sectional views showing the structure of a conventional solid-state imaging device.

  In FIG. 9, a photoelectric conversion element 107 and a charge transfer unit 106 which are light receiving units are provided on the surface layer of the semiconductor substrate 105. A transfer electrode 104 and a light shielding film 103 covering the transfer electrode 104 are provided on the charge transfer unit 106, and a condensing lens 108, which is a first condensing unit, is provided on the photoelectric conversion element 107. Is provided. The light shielding film 103 and the condensing lens 108 are covered with the flattening layer 102, and the second condensing unit is disposed on the flattening layer 102 above the condensing lens 108. An on-chip microlens 101 is provided. In this structure, assuming that the refractive index of the on-chip microlens 101 is n1, the refractive index of the planarizing layer 102 is n2, and the refractive index of the condenser lens is n3, n1≈n2 <n3.

  In FIG. 10, a photoelectric conversion element 107 and a charge transfer unit 106 which are light receiving units are provided on the surface layer of the semiconductor substrate 105. A transfer electrode 104 and a light shielding film 103 covering the transfer electrode 104 are provided on the charge transfer unit 106. The photoelectric conversion element 107 and the light-shielding film 103 are covered with the first planarization layer 109, and the first light condensing portion is located above the photoelectric conversion element 107 on the first planarization layer 109. A condensing lens 108 is provided. A second flattening layer 102 is provided on the first flattening layer 109 and the condensing lens 108, and the second condensing portion is turned on on the second flattening layer 102. A chip microlens 101 is provided. In this structure, the refractive index of the on-chip microlens 101 is n1, the refractive index of the second planarizing layer 102 is n2, the refractive index of the condenser lens 108 is n3, and the refractive index of the first planarizing layer 109 is n4. Then, n1≈n2 <n3≈n4.

  In addition, as a solid-state image pickup device that improves the light collection efficiency, a solid-state image pickup device having a condensing function instead of a condensing lens has been proposed. A specific structure of such a solid-state imaging device will be described with reference to FIG. FIG. 11 is a cross-sectional view showing the structure of a conventional solid-state imaging device.

  In FIG. 11, the surface layer portion of the silicon substrate 202 includes a photoelectric conversion element 203 which is a light receiving portion, a read gate 204 adjacent to one end of the photoelectric conversion element 203, a charge transfer portion 205 adjacent to the read gate 204, A channel stop 206 adjacent to the other end of the conversion element 203 is provided. The silicon substrate 202 is covered with an insulating film 207, and a transfer electrode 208 is provided on the charge transfer unit 205 with the insulating film 207 interposed therebetween. The insulating film 207 and the transfer electrode 208 are covered with an interlayer insulating film 209, and a portion of the interlayer insulating film 209 located above the transfer electrode 208 is covered with a light shielding film 210. A planarization layer 212 is provided on the light shielding film 210.

An opening 211 formed by removing the planarization layer 212 and the light shielding film 210 is provided on the photoelectric conversion element 203. Inside the opening 211, there are a first transparent film 214 that covers the bottom and side surfaces, a second transparent film 215 that covers the inside of the first transparent film 214, and a second film that covers the inside of the second transparent film 215. 3 transparent films 216 are provided. A passivation film 217 and a color filter layer 218 are sequentially provided on the planarization layer 212 and the first transparent film 214 to the third transparent film 216, and an on-chip microlens 219 is provided on the color filter layer 218. Is provided. In this structure, the refractive index of the first transparent film 214 is n1, the refractive index of the second transparent film 215 is n2, the refractive index of the third transparent film 216 is n3, and the refractive index of the planarizing layer 212 is n4. Then, n1>n2>n3> n4.
Japanese Patent No. 2956132 JP-A-11-121725

  Among the conventional solid-state imaging devices obtained in this way, in the solid-state imaging device shown in FIG. 9, since the condenser lens 108 is directly above the photoelectric conversion element 107, the condenser lens 108 to the on-chip microlens 101. As the distance increases, obliquely incident light may not be collected on the photoelectric conversion element 107 as indicated by a dotted line in FIG. For this reason, the light collection efficiency is lowered, and not only the obtained image becomes dark, but also the oblique incident light enters the light shielding film 103 and is photoelectrically converted by the transfer electrode 104 to become a smear component and the image quality is deteriorated. End up.

  In the solid-state imaging device shown in FIG. 10, the oblique incident light refracted by the condenser lens 101 may not be condensed on the photoelectric conversion element 107 as indicated by a dotted line in FIG. 10. When such incident light is reflected on the light-shielding film 103 and a part thereof enters the adjacent photoelectric conversion element 107, color mixing (crosstalk) is caused and image quality is deteriorated.

  In the solid-state imaging device shown in FIG. 11, when the first transparent film 214, the second transparent film 215, and the third transparent film 216 are sequentially formed in the hole 211, the upper part of the hole 211 Since the cross-sectional area of the gas inlet gradually decreases, the raw material gas does not easily enter the inside of the hole 211 and a void (gap) is generated. Since the inside of the void is vacuum or air, scattered light is generated due to the void and the sensitivity is lowered. Furthermore, since the first transparent film 214 to the third transparent film 216 are made of laminated films formed of different materials for the optical waveguide, solid-state imaging is caused by differences in linear expansion coefficient, internal stress generated during film formation, and the like. A large stress is generated in the device, and there are problems such as increase of a leak current and cracks, and an increase in the number of steps for forming a laminated film results in a decrease in manufacturing yield.

  The present invention solves the above-described conventional problems, and has high light collection efficiency to a photoelectric conversion element, less smear components and less color mixture (crosstalk) between adjacent photoelectric conversion elements, and highly reliable solid-state imaging. An object is to provide an element and a manufacturing method thereof.

  The solid-state imaging device of the present invention includes a plurality of photoelectric conversion elements provided in a semiconductor substrate, an insulating film provided on the semiconductor substrate, and at least above the photoelectric conversion element via the insulating film. An optical waveguide provided; an interlayer insulating film covering a side of the optical waveguide; a transfer electrode and a light shielding film provided in the interlayer insulating film and insulated from each other by the interlayer insulating film; A refractive index of the optical waveguide and the condenser lens is higher than that of the interlayer insulating film, and the optical waveguide is in a direction from the photoelectric conversion element toward the condenser lens. It has a taper shape in which a cross-sectional area (area of a plane parallel to the semiconductor substrate) is increased.

  As a result, the light incident on the substrate with the incident light perpendicular to the substrate is refracted by the condenser lens and condensed on the photoelectric conversion element, and the light incident on the substrate at an angle (oblique incident light) is also obtained. Then, the light is totally reflected on the side surface of the optical waveguide and condensed on the photoelectric conversion element. As described above, since it is possible to collect even oblique incident light that could not be collected in the configuration without the conventional optical waveguide, the light collection efficiency is improved and the oblique incident light is not easily incident on the transfer electrode or the like. Therefore, it is possible to reduce smear components, and it is difficult for incident light to propagate to adjacent pixels, so that color mixing (crosstalk) can be prevented.

  The condensing lens is preferably made of the same material as that of the optical waveguide and is preferably integrated with the optical waveguide. In this case, the number of manufacturing steps can be reduced, the yield can be improved, and the concentration can be improved. Since there is no interface between the optical lens and the optical waveguide, there is no refraction or reflection of light between them, and light incident on the condenser lens can be propagated to the optical waveguide without leakage.

  The side surface of the optical waveguide preferably has an angle of 60 ° or more and less than 90 ° with respect to the semiconductor substrate. In this case, when the hole is formed in the interlayer insulating film during manufacturing and the material of the optical waveguide is embedded In addition, since the source gas easily enters the hole, generation of voids is prevented. Therefore, it is possible to prevent the incident light from being scattered by the void.

  The height of the optical waveguide is preferably larger than the diameter of the condenser lens. This is because when the height of the optical waveguide is lower than the diameter of the condenser lens, the effect of the optical waveguide is reduced with respect to obliquely incident light. When the diameter is larger than the diameter, obliquely incident light can be effectively condensed on the photoelectric conversion element by the optical waveguide, and the effect of the optical waveguide is further increased.

  More preferably, the side surface of the optical waveguide has an angle of 70 ° to 80 ° with respect to the semiconductor substrate. In this case, when the hole is formed in the interlayer insulating film at the time of manufacturing and the material of the optical waveguide is embedded, the source gas is more likely to enter the hole when the angle with respect to the semiconductor substrate is 80 ° rather than 90 °. Therefore, the generation of voids can be prevented more reliably. Further, when the angle with respect to the semiconductor substrate is 70 ° rather than 60 °, the total reflection of the obliquely incident light at the interface between the optical waveguide and the interlayer insulating film can be performed efficiently.

The optical waveguide and the condensing lens have a refractive index of 2.0 or more, titanium oxide (refractive index 2.2 to 2.5), tantalum oxide (refractive index 2.0 to 2.3), oxidized Niobium (refractive index 2.0-2.3), tungsten oxide (refractive index 2.2), zirconium oxide (refractive index 2.05), zinc oxide (refractive index 2.0), indium oxide (refractive index 2. 0), hafnium oxide (refractive index 2.0 to 2.1), and the interlayer insulating film has a refractive index of 1.5 or less and is composed mainly of silicon oxide. Preferably it consists of. In this way, by using a material with a high refractive index for the optical waveguide and the condensing lens, and using a material with a low refractive index for the interlayer insulating film, the difference in refractive index between the optical waveguide and the interlayer insulating film can be greatly increased. The amount of light totally reflected can be increased and light can be efficiently collected on the photoelectric conversion element.
In addition, as a material of a transparent insulating film having a refractive index of 2.0 or more, silicon nitride (refractive index of 2.0) is conventionally used as a material for an optical waveguide. When this is used for an optical waveguide, Since a large internal stress is generated during film formation, it often causes white scratches in the output image due to crystal defects. By using titanium oxide, tantalum oxide, niobium oxide, tungsten oxide, zirconium oxide, zinc oxide, indium oxide, and hafnium oxide, the internal stress can be reduced compared to silicon nitride. Generation can be prevented.
Furthermore, any material used for the optical waveguide and the condensing lens is an oxide, and these materials are excellent in hydrogen permeability. Therefore, the heat treatment in a hydrogen atmosphere, which is performed in the manufacturing process of the solid-state imaging device as the dark current reduction process, can be effectively advanced.

  An etching stopper film provided on the insulating film may be further provided, and the optical waveguide may be provided above the photoelectric conversion element via the insulating film and the etching stopper film.

The etching stopper film is preferably made of aluminum oxide or aluminum nitride. In this case, when dry etching for forming a hole in the interlayer insulating film to form an optical waveguide is performed, a fluorine-based gas is used, so that the silicon oxide that is the interlayer insulating film as a main component is used. The selection ratio can be increased, and etching can be stopped efficiently. Thereby, the space | interval of an optical waveguide and a photoelectric conversion element can be controlled to a desired value, and variation can be decreased. Further, an optical waveguide made of titanium oxide, tantalum oxide, niobium oxide, tungsten oxide, zirconium oxide, zinc oxide, indium oxide, hafnium oxide having a refractive index of 2.0 or more, and silicon oxide having a refractive index of 1.5 as main components. By sandwiching an intermediate aluminum oxide having a refractive index of 1.7 or an aluminum nitride having a refractive index of 1.9, the refractive index can be changed stepwise to insulate from the optical waveguide. It is possible to suppress the light entering the film from being reflected at the interface and finally reducing the amount of light entering the photoelectric conversion element, and to have the effect of increasing the light collection efficiency.
The etching stopper film can also have a function as an insulating film. In this case, the insulating film / etching stopper film is preferably made of highly insulating aluminum oxide or aluminum nitride. With this configuration, when dry etching is performed to form a hole in an interlayer insulating film to form an optical waveguide, a fluorine-based gas is used, so that a material mainly composed of silicon oxide that is an interlayer insulating film is selected. The ratio can be increased and etching can be stopped efficiently. Further, instead of an insulating film mainly composed of silicon oxide having a refractive index of 1.5, an aluminum oxide or aluminum nitride having a higher refractive index is insulated between the optical waveguide having a refractive index of 2.0 or more and the photoelectric conversion element. Since the difference in refractive index from the optical waveguide can be reduced by sandwiching it as a film and etching stopper film, reflection of light entering the photoelectric conversion element from the optical waveguide on the substrate is mainly composed of silicon oxide. This can be suppressed as compared with the case where an insulating film is used, and the light collection efficiency can be increased.

  A method for manufacturing a solid-state imaging device according to the present invention includes a plurality of photoelectric conversion elements provided in a semiconductor substrate, an insulating film provided on the semiconductor substrate, and an interlayer insulation provided above the insulating film. In a method of manufacturing a solid-state imaging device including a film, a transfer electrode and a light shielding film provided in the interlayer insulating film and insulated from each other by the interlayer insulating film, the interlayer insulating film is disposed above the photoelectric conversion element. A step (a) of forming a hole having a tapered shape whose diameter increases toward the upper part in the located portion, and after the step (a), the refraction is performed from the inside of the hole to the top of the hole. And (b) forming an optical waveguide and a condensing lens made of a material having a higher rate than the interlayer insulating film.

  In the solid-state imaging device manufactured by this method, light incident as incident light perpendicular to the substrate is refracted by the condenser lens and condensed on the photoelectric conversion element, and at an angle inclined with respect to the substrate. The incident light (obliquely incident light) is also totally reflected by the side surface of the optical waveguide and collected on the photoelectric conversion element. As described above, since it is possible to collect even oblique incident light that could not be collected in the configuration without the conventional optical waveguide, the light collection efficiency is improved and the oblique incident light is not easily incident on the transfer electrode or the like. Therefore, it is possible to reduce smear components, and it is difficult for incident light to propagate to adjacent pixels, so that color mixing (crosstalk) can be prevented.

  According to the solid-state imaging device of the present invention, by providing the optical waveguide, the light that has reached the condenser lens can be efficiently condensed on the photoelectric conversion element, and the smear component can be reduced. Can also be prevented.

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

(Embodiment 1)
Example 1
Hereinafter, a CCD (Charged Coupled Device) solid-state imaging device of Example 1 will be described with reference to FIG. FIG. 1 is a cross-sectional view illustrating the structure of the solid-state imaging device according to the first embodiment of the present invention.

  In the solid-state imaging device illustrated in FIG. 1, the photoelectric conversion element 12, the charge transfer unit 13 disposed on both sides of the photoelectric conversion element 12, the photoelectric conversion element 12, and the two charge transfer units 13 are formed on the surface of the silicon substrate 11. A read gate 14 interposed between one of them and a channel stop 15 interposed between the photoelectric conversion element 12 and the other charge transfer unit 13 are provided. An insulating film 16 made of silicon oxide is provided on the silicon substrate 11.

  A transfer electrode 18 made of polysilicon is provided on the charge transfer portion 13 with an insulating film 16 interposed therebetween, and the transfer electrode 18 is covered with a light shielding film 19 made of tungsten. An interlayer insulating film 20 made of silicon oxide having a refractive index of 1.45 is provided on the transfer electrode 18, and this interlayer insulating film 20 is transferred between the transfer electrode 18 and the light shielding film 19. The electrodes 18 and the light shielding film 19 are insulated from each other, and the transfer electrodes 18 are insulated from each other by being interposed between the adjacent transfer electrodes 18.

  On the other hand, an optical waveguide 21 made of titanium oxide having a refractive index of 2.50 having a forward taper shape with a sectional area increasing upward is provided on the photoelectric conversion element 12 with the insulating film 16 interposed therebetween. It has been. The side surface of the optical waveguide 21 is in contact with the interlayer insulating film 20. On the optical waveguide 21, a condenser lens 22 made of the same titanium oxide as the optical waveguide 21 is provided integrally with the optical waveguide 21. On the condenser lens 22 and the interlayer insulating film 20, a planarizing layer 23 made of a transparent polymer resin having a refractive index of 1.50 and a color filter 24 made of a transparent polymer resin having a refractive index of 1.55 are provided. On-chip microlenses 25 made of a transparent polymer resin having a refractive index of 1.60 are sequentially stacked.

  In the solid-state imaging device of the present embodiment, the light incident on the on-chip microlens 25 at an incident angle perpendicular to the substrate is further refracted by the condenser lens 22 as indicated by the solid line arrow in FIG. It is condensed on the photoelectric conversion element. On the other hand, light (obliquely incident light) incident at an angle greatly inclined from the vertical direction with respect to the substrate is also totally reflected at the boundary between the optical waveguide 21 and the interlayer insulating film 20 and collected on the photoelectric conversion element 12. In this way, it is possible to condense even the oblique incident light that could not be collected in the configuration having no conventional optical waveguide as shown in FIGS. This improves the light collection efficiency and makes it difficult for obliquely incident light to enter the transfer electrode 18 and the like, thereby reducing smear components and preventing the incident light from propagating to the adjacent pixels. ) Can be prevented.

(Comparative Example 1)
FIG. 2 is a cross-sectional view showing the structure of the solid-state imaging device according to Comparative Example 1 of the present invention. The solid-state imaging device shown in FIG. 2 has the same structure as that of the solid-state imaging device shown in FIG. 1 except that no optical waveguide is provided, and is made of the same material. The solid-state imaging device of Comparative Example 1 was created to compare the light collection efficiency with the solid-state imaging device of Example 1, and is not a conventional device. In addition, the comparison of the light collection efficiency was performed by irradiating both solid-state image sensors with light from the perpendicular direction and the oblique direction with respect to the substrate, and measuring the efficiency of light incident on the photoelectric conversion elements.

  As a result, in the solid-state imaging device having the optical waveguide shown in FIG. 1, as shown in Table 1, assuming that the efficiency of the light incident perpendicularly to the substrate is 100, the incident light is inclined at an angle of 10 ° from the vertical direction. The efficiency was 78 for incident light at an angle of 88 ° and 20 °, and 65 for incident light at an angle of 30 °. On the other hand, in the solid-state imaging device having no optical waveguide shown in FIG. 2, assuming that the efficiency of vertically incident light is 100, the efficiency of incident light inclined by 10 ° from the vertical direction is inclined by 76 ° and 20 °. Incident light from an angle of 35 is 35, and incident light from an angle of 30 ° is 12. Increasing the incident angle greatly reduces the light collection efficiency. From this result, it can be seen that the efficiency of obliquely incident light varies greatly depending on the presence or absence of the optical waveguide 21, and the solid-state imaging device of the present embodiment can obtain high light collection efficiency.

(Example 2)
FIG. 3 is a cross-sectional view illustrating the structure of the solid-state imaging device according to the second embodiment of the present invention. In the structure shown in FIG. 3, the planarizing layer 23, the color filter 24, and the on-chip microlens 25 (shown in FIG. 1) are not provided on the condenser lens 22. By doing so, the size in the height direction of the solid-state imaging device can be further reduced, so that light incident on the condenser lens 22 can be efficiently guided to the photoelectric conversion device 12 through the optical waveguide 21. . Therefore, the condensing efficiency of obliquely incident light can be further increased. When the light collection efficiency in the solid-state imaging device of Example 2 was measured, as shown in Table 1, assuming that the efficiency of light incident perpendicularly to the substrate is 100, incident light inclined at an angle of 10 ° from the vertical direction The efficiency of the incident light was 84 for incident light inclined at an angle of 92, 20 °, and 77 for incident light inclined at an angle of 30 °. As described above, in the solid-state imaging device of the second embodiment, as compared with the solid-state imaging device of the first embodiment in which the planarizing layer 23, the color filter 24, and the on-chip microlens 25 are formed on the condenser lens 22, The collection efficiency of obliquely incident light could be increased.

  Note that the image sensor of Example 2 can be used as a solid-state image sensor for monochrome imaging. In addition, in order to use the image pickup device of Embodiment 2 for color images, a color filter for color separation may be separately formed on the light incident side above the image pickup device, for example, in a region where a cover glass is provided. Then, if a method such as color separation is performed for each area of the image sensor and combined by image processing, a color image can be extracted.

(Embodiment 2)
(Example 3)
Hereinafter, a CCD (Charged Coupled Device) solid-state imaging device of Example 3 will be described with reference to FIG. FIG. 4 is a cross-sectional view illustrating the structure of the solid-state imaging device according to the third embodiment of the present invention.

  In the solid-state imaging device illustrated in FIG. 4, the photoelectric conversion element 12, the charge transfer unit 13 disposed on both sides of the photoelectric conversion element 12, the photoelectric conversion element 12, and the two charge transfer units 13 are formed on the surface of the silicon substrate 11. A read gate 14 interposed between one of them and a channel stop 15 interposed between the photoelectric conversion element 12 and the other charge transfer unit 13 are provided. An insulating film 16 made of silicon oxide is provided on the silicon substrate 11. Further, an etching stopper film 17 made of aluminum oxide is provided on the insulating film 16.

  A transfer electrode 18 made of polysilicon is provided on the charge transfer portion 13 with the insulating film 16 and the etching stopper film 17 interposed therebetween, and the transfer electrode 18 is covered with a light shielding film 19 made of tungsten. . An interlayer insulating film 20 made of silicon oxide having a refractive index of 1.45 is provided on the etching stopper film 17 and the transfer electrode 18, and the interlayer insulating film 20 is interposed between the transfer electrode 18 and the light shielding film 19. By interposing, the transfer electrode 18 and the light shielding film 19 are insulated from each other, and by interposing between the adjacent transfer electrodes 18, the transfer electrodes 18 are insulated from each other.

  On the other hand, on the photoelectric conversion element 12, a titanium oxide having a refractive index of 2.50 having a forward taper shape in which the cross-sectional area increases upward with the insulating film 16 and the etching stopper film 17 interposed therebetween. An optical waveguide 21 is provided. The side surface of the optical waveguide 21 is in contact with the interlayer insulating film 20. On the optical waveguide 21, a condenser lens 22 made of the same titanium oxide as the optical waveguide 21 is provided integrally with the optical waveguide 21. On the condenser lens 22 and the interlayer insulating film 20, a planarizing layer 23 made of a transparent polymer resin having a refractive index of 1.50 and a color filter 24 made of a transparent polymer resin having a refractive index of 1.55 are provided. On-chip microlenses 25 made of a transparent polymer resin having a refractive index of 1.60 are sequentially stacked.

  In the solid-state imaging device of the present embodiment, the light incident on the on-chip microlens 25 at an incident angle perpendicular to the substrate is further refracted by the condenser lens 22 as indicated by the solid line arrow in FIG. It is condensed on the photoelectric conversion element. On the other hand, light (obliquely incident light) incident at an angle greatly inclined from the vertical direction with respect to the substrate is also totally reflected at the boundary between the optical waveguide 21 and the interlayer insulating film 20 and collected on the photoelectric conversion element 12. In this way, it is possible to condense even the oblique incident light that could not be collected in the configuration having no conventional optical waveguide as shown in FIGS. This improves the light collection efficiency and makes it difficult for obliquely incident light to enter the transfer electrode 18 and the like, thereby reducing smear components and preventing the incident light from propagating to the adjacent pixels. ) Can be prevented.

(Comparative Example 2)
FIG. 5 is a cross-sectional view showing the structure of a solid-state imaging device according to Comparative Example 2 of the present invention. The solid-state imaging device shown in FIG. 5 has the same structure as that of the solid-state imaging device shown in FIG. 4 except that no optical waveguide is provided, and is formed of the same material. The solid-state image sensor of Comparative Example 2 was created to compare the light collection efficiency with the solid-state image sensor of Example 3, and is not a conventional element. This comparison was performed by irradiating both solid-state image sensors with light from a direction perpendicular to the substrate and an oblique direction, and measuring the efficiency of light incident on the photoelectric conversion elements.

  As a result, in the solid-state imaging device having the optical waveguide shown in FIG. 4, as shown in Table 2, assuming that the efficiency of light perpendicularly incident on the substrate is 100, the incident light is inclined at an angle of 10 ° from the vertical direction. The efficiency was 93 for incident light at an angle of 93, 20 °, and 70 for incident light at an angle of 30 °. On the other hand, in the solid-state imaging device having no optical waveguide shown in FIG. 5, assuming that the efficiency of vertically incident light is 100, the efficiency of incident light inclined at 10 ° from the vertical direction is inclined by 85 ° and 20 °. The incident light from a certain angle is 41, and the incident light from an angle inclined by 30 ° is 16. The light collection efficiency is greatly reduced when the incident angle is increased. From this result, it can be seen that the efficiency of obliquely incident light varies greatly depending on the presence or absence of the optical waveguide 21, and the solid-state imaging device of the present embodiment can obtain high light collection efficiency.

Example 4
FIG. 6 is a cross-sectional view illustrating the structure of a solid-state imaging device according to Embodiment 4 of the present invention. In the structure shown in FIG. 6, the flattening layer 23, the color filter 24, and the on-chip microlens 25 (shown above in FIG. 1) are not provided on the condenser lens 22. By doing so, similarly to the second embodiment, the size of the solid-state imaging device can be further reduced in size, so that the light incident on the condenser lens 22 passes through the optical waveguide 21 to the photoelectric conversion device 12. , Can guide efficiently. Thereby, the condensing efficiency of obliquely incident light can be made higher. As shown in Table 2, when the light collection efficiency in the solid-state imaging device of Example 4 was measured, assuming that the efficiency of the light incident perpendicularly to the substrate is 100, the incident light inclined at an angle of 10 ° from the vertical direction The efficiency was 97 for incident light at an angle of 97 and 20 °, and 83 for incident light at an angle of 30 °. Thus, in the solid-state imaging device of the fourth embodiment, compared with the solid-state imaging device of the third embodiment in which the planarizing layer 23, the color filter 24, and the on-chip microlens 25 are formed on the condenser lens 22, The collection efficiency of obliquely incident light could be increased.

  Further, in the solid-state imaging device of Example 4, compared with the solid-state imaging device having no etching stopper of Example 1, the light collection efficiency of oblique incident light could be increased. This is because, in the solid-state imaging device of Example 4, between the optical waveguide 21 having a refractive index of 2.0 or more and the insulating film 16 having a refractive index of 1.5, aluminum oxide having a refractive index of 1.7 between them, Alternatively, the refractive index can be changed stepwise by sandwiching the etching stopper layer 17 made of aluminum nitride having a refractive index of 1.9. Thereby, it can suppress that the light which enters into the insulating film 16 from the optical waveguide 21 reflects in the interface, and reduces the quantity of the light which finally enters into a photoelectric conversion element. Therefore, the light collection efficiency can be further increased.

(Embodiment 3)
Hereinafter, a method for manufacturing the solid-state imaging device described in the third embodiment will be described with reference to FIG. 7A to 7F are cross-sectional views illustrating manufacturing steps of the solid-state imaging device of the third embodiment. Here, the process after the photoelectric conversion element 12, the charge transfer unit 13, the readout gate 14 and the channel stop 15 are formed in the surface layer portion of the silicon substrate 11 will be described.

  In the manufacturing method of the solid-state imaging device of the present embodiment, first, in the step shown in FIG. 7A, the insulating film 16 made of silicon oxide having a thickness of 20 nm is formed on the silicon substrate 11 by thermal oxidation treatment. An etching stopper film 17 made of aluminum oxide having a thickness of 40 nm is formed on the insulating film 16 by CVD or sputtering. Next, by the CVD method and patterning, the transfer electrode 18 made of polysilicon, the upper part of the transfer electrode 18 are covered on the etching stopper film 17, the light-shielding film 19 made of tungsten, and the light-shielding film 19 are covered. In addition, an interlayer insulating film 20 made of a material mainly composed of silicon oxide such as BPSG (boron phosphorus silicate glass), which is also interposed between the transfer electrode 18 and the light shielding film 19, is sequentially formed.

  Next, in the step shown in FIG. 7B, a resist (not shown) that opens above the photoelectric conversion element 12 is formed on the interlayer insulating film 20, and isotropic dry etching or wet etching is performed. By performing, the part located above the photoelectric conversion element 12 among the interlayer insulation films 20 is removed, and the hole part 26 is formed. Thereafter, the resist (not shown) is removed. The hole portion 26 has a bottom surface portion having a diameter of 1.0 μm located above the photoelectric conversion element, an upper portion having a diameter of 2.0 μm that is an opening of the interlayer insulating film 20, and a height of 2.0 μm. It has a forward taper shape. Moreover, in the hole part 26, there is no level | step difference in a side surface, and the taper angle with respect to the board | substrate of a side surface is 76 degrees.

  Next, in the step shown in FIG. 7C, a titanium oxide film 21a is formed by filling the hole 26 and covering the interlayer insulating film 20 by the CVD method.

  Next, in the step shown in FIG. 7D, a resist (not shown) is applied on the entire surface of the titanium oxide film 21a so that the upper surface is flat, and the etching rate between the titanium oxide film 21a and the resist is increased. By performing dry etching under the same conditions (resist entire surface etch back method) or by performing CMP method, the upper surface of the titanium oxide film 21a is globally planarized, and then the photoelectric conversion element 12 on the titanium oxide film 21a. A resist 27 having the same shape as the condensing lens 22 (shown in FIG. 7E) is formed by patterning and reflowing in a region located above the region.

  Thereafter, in the step shown in FIG. 7E, etching back is performed again using the resist 27 as a mask to remove the exposed portion of the titanium oxide film 21a, whereby the resist shape is formed on the upper surface of the titanium oxide film 21a. Is transferred to form the condenser lens 22. Thereafter, in the process shown in FIG. 7F, the planarization layer 23, the color filter 24, and the on-chip microlens 25 are formed in accordance with a normal imaging element manufacturing process, and the series of manufacturing processes is completed.

  According to the series of manufacturing methods described above, as described in the first embodiment, the optical waveguide has a forward taper shape in which the cross-sectional area increases in the direction from the photoelectric conversion element toward the condenser lens, and has no voids. It is possible to easily produce a solid-state imaging device having

In particular, when forming the hole 26 in the step shown in FIG. 7B, an isotropic dry etching process using, for example, CF ₄ as an etching gas is performed, so that the hole 26 can be more easily formed. The shape can be a forward tapered shape with a large cross-sectional area at the top. The taper angle can be controlled by controlling the type, flow rate, gas pressure, and bias voltage of the etching gas for forming the hole 26. Further, by providing the etching stopper film 17 made of aluminum oxide, the etching can be stopped more reliably when the hole 26 is etched, and the distance between the optical waveguide 21 and the photoelectric conversion element 12 is required at equal intervals. Can be kept at intervals. Thereby, the variation in the characteristic of an element can be reduced.

  As a method of forming the optical waveguide 21 in the hole 26, the CVD method, particularly the thermal CVD method in which the reaction proceeds on the substrate surface, is used, and the coverage of the hole 26 is remarkably improved. Further, the angle of the side surface of the hole portion 26 with respect to the substrate is 60 ° or more and less than 90 °, and more preferably 70 ° or more and 80 ° or less, thereby facilitating the entry of the source gas into the hole portion 26 and the optical waveguide. It is possible to prevent the generation of voids (gap) in the interior of the 21. Here, when the taper angle is 60 ° or less, the incident light is not totally reflected at the interface between the optical waveguide and the interlayer insulating film, and part of the light is transmitted to the interlayer insulating film. Decreases. Further, when the taper angle is 90 °, when the aspect ratio of the hole forming the optical waveguide is increased, the raw material gas is less likely to enter the depth of the hole, and the possibility of generating voids increases. . Actually, by adjusting the etching conditions, the portion located above the photoelectric conversion element as the bottom surface portion has a diameter of 1.0 μm, and the opening portion of the interlayer insulating film 20 as the upper portion also has a diameter of 1.0 μm and a height of 2 μm. When a hole portion having a taper angle of 90 ° is formed with a thickness of 0.0 μm and an optical waveguide is formed in the hole portion, a slit-like void having a maximum width of 100 nm and a height of 700 nm is formed inside the optical waveguide. Occurred. In such an optical waveguide, incident light is scattered at the position of the void, and the efficiency of condensing on the photoelectric conversion element is reduced to 40% as compared with the case where no void is generated.

  In the above description, the etching stopper film 17 is formed of aluminum oxide, but the same effect can be obtained even if aluminum nitride is used.

  In the above description, the etching stopper film 17 made of aluminum oxide is formed on the insulating film 16 made of silicon oxide. However, since the etching stopper film 17 has sufficient insulation, the insulating film 16 made of silicon oxide is not formed, and the aluminum oxide or nitride is formed on the photoelectric conversion element 12 as shown in FIG. An etching stopper film 17 made of aluminum may be directly formed. In this case, since the etching stopper film 17 also has the effect of the insulating film 16, the same effect can be obtained.

  In the above description, titanium oxide having a refractive index of 2.5 is used as the material of the optical waveguide 21 and the condensing lens 22. However, the optical waveguide 21 and the condensing lens 22 of the present invention are limited to this material. The optical waveguide 21 and the condensing lens 22 may be made of a material having a refractive index of 2.0 or more and a material having a refractive index larger than that of the interlayer insulating film 20. Similar effects can be obtained by using tantalum oxide, niobium oxide, tungsten oxide, zirconium oxide, zinc oxide, indium oxide, hafnium oxide, or the like. However, in order to prevent reduction in light collection efficiency due to light reflection between the light collecting lens and the light guide, or to reduce the number of manufacturing steps and improve yield, both are made of the same material. Desirably configured.

  It was obtained by forming an optical waveguide by plasma CVD using silicon nitride (refractive index of 2.0), which is a material of a transparent insulating film having a refractive index of 2.0 or more and used as a semiconductor material. In the output image from the image sensor, white scratches occurred and the image quality deteriorated. This is because a large internal compressive stress was generated during the film formation of silicon nitride, which caused crystal defects in the photodiode. On the other hand, when the above-mentioned titanium oxide, tantalum oxide, niobium oxide, tungsten oxide, zirconium oxide, zinc oxide, indium oxide, and hafnium oxide are used as an optical waveguide, the internal stress can be reduced compared to silicon nitride. Therefore, the occurrence of white scratches can be prevented.

  Further, in the above description, materials made of a transparent polymer resin are used as the planarizing layer 23, the color filter 24, and the on-chip microlens 25 located above the condenser lens 22, but in the present invention, these are used. Is not limited to this material, but a material having the same effect, for example, a material mainly composed of silicon oxide such as BPSG (boron phosphorus silicate glass) for the planarizing layer 23, and a similar material for the color filter 24. An effective oxide thin film, on-chip microlens 25 is made of a material having the same high refractive index as that of the condenser lens. For example, niobium oxide, tungsten oxide, zirconium oxide, zinc oxide, and indium oxide other than titanium oxide and tantalum oxide. Even if hafnium oxide or the like is used, the same effect can be obtained.

  The solid-state imaging device of the present invention is useful as a high-resolution imaging device used for a digital video camera, a digital still camera, a mobile phone with a photographic function, and the like. It can also be applied to elements used in image acquisition devices such as digital scanners and medical / industrial image sensors.

It is sectional drawing which shows the structure of the solid-state image sensor which concerns on Example 1 of this invention. It is sectional drawing which shows the structure of the solid-state image sensor which concerns on the comparative example 1 of this invention. It is sectional drawing which shows the structure of the solid-state image sensor which concerns on Example 2 of this invention. It is sectional drawing which shows the structure of the solid-state image sensor which concerns on Example 3 of this invention. It is sectional drawing which shows the structure of the solid-state image sensor which concerns on the comparative example 2 of this invention. It is sectional drawing which shows the structure of the solid-state image sensor which concerns on Example 4 of this invention. (A)-(f) is sectional drawing which shows the manufacturing process of the solid-state image sensor of this invention. It is sectional drawing which shows the structure of the solid-state image sensor which concerns on Embodiment 3 of this invention. It is sectional drawing which shows the structure of the conventional solid-state image sensor. It is sectional drawing which shows the structure of the conventional solid-state image sensor. It is sectional drawing which shows the structure of the conventional solid-state image sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Silicon substrate 12 Photoelectric conversion element 13 Charge transfer part 14 Read gate 15 Channel stop 16 Insulating film 17 Etching stopper film 18 Transfer electrode 19 Light shielding film 20 Interlayer insulating film 21 Optical waveguide 21a Titanium oxide film 22 Condensing lens 23 Flattening layer 24 Color filter 25 On-chip microlens 26 Hole 27 Resist 101 On-chip microlens 102 Second planarizing layer 103 Light-shielding film 104 Transfer electrode 105 Semiconductor substrate 106 Charge transfer unit 107 Photoelectric conversion element 108 Condensing lens 109 First flattening Formation layer 202 Silicon substrate 203 Photoelectric conversion element 204 Read gate 205 Charge transfer unit 206 Channel stop 207 Insulating film 208 Transfer electrode 209 Interlayer insulating film 210 Light shielding film 211 Opening 212 Flattening layer 214 First transparent film 215 Second transparent film 216 Third transparent film 217 Passivation film 218 Color filter layer 219 On-chip microlens

Claims (9)

A plurality of photoelectric conversion elements provided in a semiconductor substrate;
An insulating film provided on the semiconductor substrate;
An optical waveguide provided above the photoelectric conversion element via at least the insulating film;
An interlayer insulating film covering the side of the optical waveguide;
A transfer electrode and a light shielding film provided in the interlayer insulating film and insulated from each other by the interlayer insulating film;
A condenser lens provided on the optical waveguide;
The refractive index of the optical waveguide and the condensing lens is higher than that of the interlayer insulating film, and the optical waveguide has a tapered shape whose cross-sectional area increases in the direction from the photoelectric conversion element to the condensing lens,
The condensing lens is made of the same material as the optical waveguide and is integral with the optical waveguide. The solid-state imaging device according to claim 1,
A solid-state imaging device, wherein a height of the optical waveguide is larger than a diameter of the condenser lens. The solid-state imaging device according to claim 1,
The solid-state imaging device, wherein a side surface of the optical waveguide has an angle of 60 ° or more and less than 90 ° with respect to the semiconductor substrate. The solid-state imaging device according to claim 3,
The solid-state imaging device, wherein a side surface of the optical waveguide has an angle of 70 ° to 80 ° with respect to the semiconductor substrate. The solid-state imaging device according to claim 1,
The optical waveguide and the condenser lens have a refractive index of 2.0 or more, and at least one of titanium oxide, tantalum oxide, niobium oxide, tungsten oxide, zirconium oxide, zinc oxide, indium oxide, and hafnium oxide. Consists of
The solid-state imaging device, wherein the interlayer insulating film is made of a material having a refractive index of 1.5 or less and having silicon oxide as a main component. The solid-state imaging device according to claim 1,
An etching stopper film provided on the insulating film;
The solid-state imaging device, wherein the optical waveguide is provided above the photoelectric conversion element via the insulating film and the etching stopper film. The solid-state imaging device according to claim 1,
The solid-state imaging device, wherein the insulating film on the semiconductor substrate also has a function as an etching stopper film. The solid-state imaging device according to claim 6 or 7,
The solid-state imaging device, wherein the etching stopper film is made of aluminum oxide or aluminum nitride. A plurality of photoelectric conversion elements provided in a semiconductor substrate, an insulating film provided on the semiconductor substrate, an interlayer insulating film provided above the insulating film, and provided in the interlayer insulating film In a method for manufacturing a solid-state imaging device comprising a transfer electrode and a light shielding film insulated from each other by the interlayer insulating film,
A step (a) of forming a hole having a tapered shape whose diameter increases upward in a portion of the interlayer insulating film located above the photoelectric conversion element;
After the step (a), a step (b) of forming an optical waveguide and a condensing lens made of a material having a refractive index higher than that of the interlayer insulating film from the inside of the hole to the top of the hole. A method for manufacturing a solid-state imaging device.

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