JP6945665B2 - Solid-state image sensor, electronic equipment and manufacturing method - Google Patents

Description

The present invention relates to a solid-state image sensor, an electronic device, and a method for manufacturing a solid-state image sensor.

In recent years, pixel miniaturization has been progressing in solid-state image sensors such as CMOS (Complementary Metal Oxide Semiconductor) type image sensors and CCD (Charge Coupled Device) type image sensors. With the miniaturization, the signal level output from each pixel tends to decrease, and it is desired to improve the sensitivity of the solid-state image sensor and further reduce noise.

One of the causes of performance deterioration in the solid-state image sensor is a dark current generated even though light is not incident on the solid-state image sensor. For example, when a defect occurs in the semiconductor substrate of the solid-state image sensor, the charge caused by the defect flows into the signal charge storage portion of the solid-state image sensor in addition to the charge obtained by photoelectrically converting the incident light, so that a dark current is generated. appear. Due to the dark current, in the output image of the solid-state image sensor, white scratches occur when there is no incident light, and noise occurs due to the variation of the dark current generated for each pixel even when there is incident light. As described above, there is a problem that the quality of the output image of the solid-state image sensor is significantly deteriorated due to the dark current.

Examples of the defect include a surface dark current generated by the interface imperfections between the surface of the semiconductor substrate and the uppermost surface of the oxide. Patent Document 1 discloses a technique of lowering the interface state to reduce the surface dark current by supplying hydrogen from the passivation film.

Further, as a countermeasure against dark current caused by the stress of the semiconductor substrate, Patent Document 2 describes solid-state imaging using a material having the same coefficient of thermal expansion as the semiconductor substrate in the element separation region for separating the photoelectric conversion units from each other. Elements have been proposed.

Japanese Unexamined Patent Publication No. 60-6856 Japanese Patent No. 4719149

In order to improve the sensitivity of a solid-state image sensor, a method of suppressing reflection of incident light by forming an antireflection film on a semiconductor substrate is known. As the material of the antireflection film, a silicon nitride film having a refractive index of about 2.0 is often used, and in order to further improve the sensitivity, a silicon nitride film having a higher Si content is also used. However, as the Si content of the silicon nitride film increases, the stress in the tensile direction (tensile direction) of the antireflection film also increases, and there is a concern that crystal defects in the semiconductor substrate, which cause dark current in the solid-state image sensor, will increase. there were.

An object of the present invention is to provide a solid-state image sensor or the like capable of reducing the generation of dark current.

(1) One embodiment of the present invention includes a laminated structure in which a substrate including a photoelectric conversion unit, an insulating film, an antireflection film, an interlayer insulating film, and a passivation film are formed in this order, and the passivation is provided. The film has a stress in the compression direction, and the stress is −50 kN / cm ² or less .
( 2 ) Further, in an embodiment of the present invention, in addition to the configuration of (1), the laminated structure is recessed into the interlayer insulating film and the passivation film, and the side wall of the recessed portion is the passivation. A solid-state image sensor in which an optical waveguide covered with a film is further formed.
( 3 ) Further, in an embodiment of the present invention, in addition to the configuration of (1) or (2) , the substrate further includes a charge storage unit for accumulating charges generated in the photoelectric conversion unit. A solid-state imaging device in which a light-shielding film is further formed between the charge storage portion and the interlayer insulating film in the laminated structure.
( 4 ) Further, an embodiment of the present invention is an electronic device including the solid-state image sensor according to the above (1), (2) or (3).
( 5 ) Further, in an embodiment of the present invention, a substrate including a photoelectric conversion unit, an insulating film, an antireflection film, an interlayer insulating film, and a passivation film made of a silicon nitride film are formed in this order. A method for manufacturing a solid-state imaging device having a laminated structure, wherein the passivation film is formed by a chemical vapor deposition method, and in the chemical vapor deposition method, a step of increasing high-frequency power applied to the passivation film and the above-mentioned step. A step of reducing the pressure applied to the passivation film, a step of increasing the temperature at the time of forming the passivation film, a step of reducing the addition amount of _{SiH 4 , and a step of increasing the addition amount of N 2} . A manufacturing method in which any one or more steps are carried out to reduce the stress in the passivation film in the compression direction to −50 kN / cm ^{2 or less.}

According to one aspect of the present invention, it is possible to provide a solid-state image sensor or the like capable of reducing the generation of dark current.

It is a figure which shows typically the laminated structure of the solid-state image sensor which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship between the stress which the passivation film of the solid-state image sensor which concerns on Embodiment 1 of this invention has, and a dark current. It is a figure which shows typically the laminated structure of the solid-state image sensor which concerns on Embodiment 2 of this invention. It is a figure which shows typically the laminated structure of the solid-state image sensor which concerns on Embodiment 3 of this invention. It is a figure which shows typically the laminated structure of the solid-state image sensor which concerns on Embodiment 4 of this invention.

[Embodiment 1]
<Structure of solid-state image sensor>
An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. As shown in FIG. 1, the solid-state image sensor 100 according to the present embodiment includes a semiconductor substrate (base) 1, a first insulating film (insulating film) 4, an antireflection film 5, an interlayer insulating film 6, and a passivation. It has a laminated structure in which a film 8, a flattening film 9, a color filter 10, and a microlens 11 are formed in this order.

The solid-state image sensor 100 is, for example, a CMOS image sensor. A plurality of pixels are formed in the solid-state image sensor 100, and each pixel is provided with a photoelectric conversion unit 2 and the like, which will be described later.

The semiconductor substrate 1 is made of a semiconductor material such as silicon. Further, the semiconductor substrate 1 includes a photoelectric conversion unit 2. The photoelectric conversion unit 2 is a member that converts incident light incident on the solid-state image sensor 100 into an electric signal, and may be, for example, a photodiode or the like. A gate electrode 3 is arranged between the semiconductor substrate 1 and the first insulating film 4. The gate electrode 3 is formed so as to be covered with the first insulating film 4. The gate electrode 3 is preferably arranged at a position that does not interfere with the incident of light on the photoelectric conversion unit 2. The first insulating film 4 is a member that electrically insulates the gate electrode 3, the semiconductor substrate 1, and the antireflection film 5.

A multi-layer wiring structure is formed in the interlayer insulating film 6 by a wiring layer 7 including a plurality of wirings. The interlayer insulating film 6 is a member that electrically insulates each wiring included in the wiring layer 7. The first insulating film 4 and the interlayer insulating film 6 may be, for example, an oxide film or the like. Further, examples of the wiring included in the wiring layer 7 include Al (aluminum) wiring and Cu (copper) wiring.

Although FIG. 1 shows an example in which the wiring layer 7 is formed by three layers, the number of layers of the wiring layer 7 is not limited to this, and may be one layer or two layers, and may be four or more layers. You may. Further, the number of layers of the wiring layer 7 may be different between the pixel region in which the pixels are arranged in the semiconductor substrate 1 and the region other than the pixel region. The area other than the pixel area is, for example, an area for processing an electric signal output from the pixel area.

(Anti-reflective coating)
The antireflection film 5 is a member that suppresses the reflection of light generated when light is incident on the photoelectric conversion unit, and a material having a high refractive index is used. Examples of the material having a high refractive index include a silicon nitride film. Further, in order to increase the refractive index of the antireflection film 5, the flow rate (addition amount) _{of SiH 4} gas when the antireflection film 5 is formed by a chemical vapor deposition method (CVD method: Chemical Vapor Deposition) is increased. , A silicon nitride film having a relatively high Si content may be used.

However, the silicon nitride film has a characteristic that the stress generated in the tensile direction (tensile direction) increases as the Si content increases. Therefore, after high-temperature annealing in the CVD method, the semiconductor substrate 1 is greatly warped in the tensile direction due to the stress in the tensail direction of the antireflection film 5.

Here, when a thin film is formed on a flat substrate, mechanical stress is generated in the film due to the difference between the coefficient of thermal expansion (coefficient of thermal expansion) of the film and the coefficient of thermal expansion of the substrate. Then, in order to relieve the stress, the substrate will be warped. Here, the direction in which the periphery of the substrate is pulled is defined as tension (Tensile), and the direction in which the periphery of the substrate is suppressed is defined as compressive. Therefore, the direction of stress possessed by the film is the tensile direction when acting in the direction of pulling the periphery of the substrate with reference to the substrate, and the compressive direction when acting in the direction of suppressing the periphery of the substrate. ..

The generation of the warp in the antireflection film 5 due to the stress in the tensile direction induces crystal defects in the semiconductor substrate 1. The dark current caused by the crystal defect causes white scratches on the output image of the solid-state image sensor 100. Further, the stress in the tensail direction causes dark currents such as a generated current and a surface leak current due to bandgap reduction to be generated even if the stress is large enough not to cause the crystal defects. Therefore, the dark current in the solid-state image sensor 100 can be reduced by canceling the stress in the tensile direction of the antireflection film 5.

(Passivation membrane)
The passivation film 8 is a protective film made of a silicon nitride film and having an effect of preventing corrosion. Further, the passivation film 8 has an effect of filling the dangling bond by supplying hydrogen electrons, lowering the interface state, and reducing the surface dark current. In one embodiment of the present invention, the passivation film 8 is formed so as to have a stress in the compressive direction (compression direction). The stress in the compressive direction of the passivation film 8 cancels the stress in the tensile direction of the antireflection film 5, and the stress in the compressive direction can be further applied to the semiconductor substrate 1. Therefore, the generated current due to the bandgap expansion, the surface leakage current, and the like are reduced, so that the dark current generated in the solid-state image sensor 100 can be reduced.

Here, a model of dark current reduction due to stress in the compressive direction will be described. The dark current generated in the solid-state image sensor 100 is represented by the following equation (1).

In the formula _(1), the _{I dark} dark _{current, I gen} is the generator current _component, the _{I leak} is surface leakage current component, q is the electron charge, w is the width of the depletion layer, A is a pn junction area , Τ _g is the lifetime, N _c is the effective state density of electrons in the conduction band, N _ν is the effective state density of holes in the valence band, E _g is the band gap, and k is the Boltzmann constant. T is the temperature, the σ is the capture cross section, [nu _th is the thermal velocity, N _st is the interface state density in the depletion layer, a _s is the surface bonding area, respectively.

When the dark current component affected by the stress of the passivation film 8 or the like is taken into consideration, the main dark current components are the generated current component I _gen and the surface leak current component I _leak . Therefore, the diffusion current component and the tunnel current component are not mentioned here.

When the stress in the compressive direction of the passivation film 8 propagates to the silicon on the surface of the semiconductor substrate 1 including the photoelectric conversion unit 2, the lattice constant of silicon on the surface of the semiconductor substrate 1 including the photoelectric conversion unit 2 becomes small. At this time, since the silicon band structure takes an sp3 hybrid orbital, the silicon band gap on the surface of the semiconductor substrate 1 including the photoelectric conversion unit 2 becomes large.

As shown in the above equation (1), when the bandgap _Eg becomes large, the dark current I _dark is exponentially reduced. Therefore, the passive film 8 has a stress in the compressive direction, so that the solid-state image sensor 100 The dark current generated in is effectively reduced.

The graph of FIG. 2 shows the relationship between the stress of the passivation film 8 and the dark current generated in the solid-state image sensor 100, and the horizontal axis shows the stress and the vertical axis shows the dark current. The dark current indicates a relative electric amount when the electric amount of the dark current under the condition where the stress of the passivation film 8 is the lowest is 100.

As shown in FIG. 2, the dark current decreases as the stress of the passivation film 8 increases in the compressive direction, in other words, as the value of the stress increases in the negative direction. In particular, when the stress of the passivation film 8 is −50 kN / cm ² or less (-5E9dyne / cm ² or less), the effect of reducing dark current is large. Therefore, the stress of the passivation film 8 ^{is preferably −50 kN / cm 2} or less.

In addition, on the semiconductor substrate 1, following the passivation film 8, a flattening film 9 for flattening surface irregularities, a color filter 10 for incidenting only light having a wavelength corresponding to a pixel, and light are collected. The microlenses 11 for shining are laminated in this order.

<Manufacturing method of solid-state image sensor>
In the laminated structure of the solid-state imaging device 100 according to the present embodiment, each member other than the passivation film 8 can be manufactured by using a conventional general manufacturing method. The passivation film 8 is formed by a chemical vapor deposition method. The type of chemical vapor deposition method is not particularly limited, but for example, a plasma CVD method is preferable.

In order to control the stress of the passivation film 8 in the compressive direction, the chemical vapor phase growth method includes a step of increasing the high frequency power applied to the passivation film 8 and a step of reducing the pressure applied to the passivation film 8. One or more of a step of increasing the temperature at the time of forming the passivation film 8, a step of reducing the addition amount of _{SiH 4 , and a step of increasing the addition amount of N 2 are carried out.} The stress in the passivation film 8 in the compressive direction is increased.

According to the configuration in which each parameter is adjusted in the chemical vapor deposition method as described above, the composition of the obtained passivation film 8 becomes N-rich. As a result, the effective lattice constant of silicon nitride in the passivation film 8 becomes small, so that the lattice constant difference between the N-rich passivation film 8 and the Si-rich semiconductor substrate 1 becomes large. The larger the lattice constant difference, the greater the stress in the passivation film 8 in the compressive direction.

Therefore, by combining any of the above steps or two or more steps, the passivation film 8 having stress in the compressive direction can be formed. As described above, since the passivation film 8 has stress in the compressive direction, the dark current generated in the solid-state image sensor 100 can be reduced. Therefore, according to the manufacturing method according to the present embodiment, it is possible to obtain the solid-state image sensor 100 in which the generated dark current is small.

<Electronic equipment equipped with a solid-state image sensor>
The solid-state image sensor 100 may be provided in various electronic devices having an image pickup unit. Examples of such electronic devices include digital cameras such as digital video cameras and digital still cameras, image input cameras such as surveillance cameras, scanner devices, facsimile devices, television telephone devices, and mobile phone devices equipped with cameras. However, it is not limited to this.

[Embodiment 2]
Other embodiments of the present invention will be described below with reference to FIG. For convenience of explanation, the members having the same functions as the members described in the above-described embodiment are designated by the same reference numerals, and the description thereof will not be repeated.

The solid-state image sensor 200 according to the present embodiment is different from the solid-state image sensor 100 according to the first embodiment in that it includes an optical waveguide 12. As shown in FIG. 3, the optical waveguide 12 is formed by being recessed into the interlayer insulating film 6 and the passivation film 8 in the laminated structure included in the solid-state imaging device 200. The side wall of the recessed portion is covered with the passivation film 8.

The optical waveguide 12 is obtained by laminating the interlayer insulating film 6 on the semiconductor substrate 1, forming an opening in the interlayer insulating film 6, and forming the passivation film 8 and the translucent material in this order in this order. .. The translucent material may be a member whose refractive index is larger than that of the interlayer insulating film 6. Examples of such a translucent material include, but are not limited to, silicon nitride, resin, and an organic high-refractive index film.

The refractive index of the interlayer insulating film is preferably about 1.4, and in this case, the refractive index of the translucent material is preferably set in the range of 1.6 or more and 2.2 or less. Since the optical waveguide 12 is formed of a translucent material having such a refractive index, incident light can be efficiently guided to the photoelectric conversion unit 2 by refraction.

Although FIG. 3 shows an example in which the bottom of the optical waveguide 12 is in contact with the antireflection film 5 via the passivation film 8, the optical waveguide 12 and the antireflection film 5 are separated from each other. , The interlayer insulating film 6 may be arranged between them.

By providing the optical waveguide 12 in the solid-state image sensor 200, the incident light can be efficiently guided to the photoelectric conversion unit 2. However, due to the adoption of the optical waveguide structure, microcrystal defects are generated in the semiconductor substrate 1 due to process damage caused in the etching process for forming the optical waveguide 12 and the process of embedding the translucent material in the opening. It is inevitable that it will be stored.

Here, the solid-state imaging device 200 has a structure in which the passivation film 8 is formed on the side wall of the optical waveguide 12. Since this is a structure in which stress in the compressive direction is more likely to be applied to the semiconductor substrate 1 side, the dark voltage generated in the solid-state image sensor 200 can be more effectively reduced. That is, since the generation of dark current due to the generation of the microcrystal defects can be effectively suppressed by the passive film 8 having stress in the compressive direction, the optical waveguide 12 efficiently controls the incident light and the generated dark current. It is possible to realize a solid-state image sensor 200 that achieves both reduction and reduction.

[Embodiment 3]
Other embodiments of the present invention will be described below with reference to FIG. As shown in FIG. 4, the solid-state image sensor 300 according to the present embodiment further includes a light-shielding film 13 and a memory unit (charge storage unit) 14 in the solid-state image sensor 200 according to the second embodiment. It is different from the solid-state image sensor 100 according to 1.

The solid-state image sensor 300 includes a light-shielding film 13 and a memory unit 14, so that a global shutter structure for preventing the occurrence of focal plane distortion can be adopted. The light-shielding film 13 and the memory unit 14 may be further provided in the solid-state image sensor 100 instead of the solid-state image sensor 200.

The memory unit 14 is a member that stores and transfers the electric charge generated by the photoelectric conversion unit 2. The memory unit 14 preferably has a low surface hole concentration. This is because when the surface hole concentration of the memory unit 14 is high, the depletion layer extending from the transfer gate is terminated by the holes on the surface, and it becomes difficult for the electric field to be applied to the N region of the memory unit 14. As a result, charge transfer becomes difficult. Further, since the surface hole concentration of the memory unit 14 is low, it is easily affected by the stress of the passivation film 8 and the like, so that the effect of reducing the dark current by the passivation film 8 having stress in the compressive direction becomes larger. Because.

The light-shielding film 13 is a film formed of a material having low translucency. As such a material having low translucency, a metal such as tungsten is used. The light-shielding film 13 is formed between the memory unit 14 and the interlayer insulating film 6 so that the incident light does not directly enter the memory unit 14 and become a noise component. In the present embodiment, since the light-shielding film 13 is formed only at a position substantially opposite to the memory unit 14, the influence of the stress of the metal film such as tungsten on the semiconductor substrate 1 can be reduced.

[Embodiment 4]
Other embodiments of the present invention will be described below with reference to FIG. As shown in FIG. 5, the solid-state image sensor 400 according to the present embodiment does not have a wiring layer 7, and the semiconductor substrate 1 includes a light-shielding film 13, a charge transfer unit 15, and a channel stop 16. In that respect, it differs from the solid-state image sensor 100 according to the first embodiment. The solid-state image sensor 400 may be formed with any one or more of the optical waveguide 12, the light-shielding film 13, and the memory unit 14.

The charge transfer unit 15 is a member that transfers the electric charge generated by the photoelectric conversion by the photoelectric conversion unit 2. Further, the channel stop 16 is a layer having a high doping concentration of impurities. As described above, the solid-state image sensor 400 may be a CCD-type image sensor including a charge transfer unit 15 and a channel stop 16 instead of a CMOS-type image sensor like the solid-state image sensor 100. According to such a configuration, the wiring layer 7 provided in the interlayer insulating film 6 can be simplified or omitted, and light can be efficiently incident on the photoelectric conversion unit 2, so that the light receiving sensitivity can be easily improved.

〔summary〕
The solid-state imaging device (100) according to the first aspect of the present invention includes a substrate (1) including a photoelectric conversion unit (2), an insulating film (first insulating film 4), an antireflection film (5), and interlayer insulation. The film (6) and the passivation film (8) have a laminated structure formed in this order, and the passivation film has a stress in the compression direction.

In the solid-state imaging device according to the second aspect of the present invention, the stress is ^{preferably −50 kN / cm 2} or less in the first aspect.

In the solid-state imaging device according to the third aspect of the present invention, in the first or second aspect, the laminated structure is embedded in the interlayer insulating film and the passivation film, and the side wall of the recessed portion is covered with the passivation film. The broken optical waveguide (12) may be further formed.

In the solid-state imaging device according to the fourth aspect of the present invention, in the first to third aspects, the substrate further includes a charge storage unit (14) for accumulating the charges generated in the photoelectric conversion unit, and the laminated structure includes the charge storage unit (14). A light-shielding film (13) may be further formed between the charge storage portion and the interlayer insulating film.

The electronic device according to the fifth aspect of the present invention includes the solid-state image pickup device according to any one of the first to fourth aspects.

The manufacturing method according to aspect 6 of the present invention has a laminated structure in which a substrate including a photoelectric conversion unit, an insulating film, an antireflection film, an interlayer insulating film, and a passivation film made of a silicon nitride film are formed in this order. The passivation film is formed by a chemical vapor deposition method, and the chemical vapor deposition method includes a step of increasing the high frequency power applied to the passivation film and the passivation film. Either a step of reducing the pressure applied to the passivation film, a step of increasing the temperature at the time of forming the passivation film, a step of reducing the amount of _{SiH 4} added, or a step of increasing the amount of _{N 2 added.} One or more steps are carried out to increase the compressive stress in the passivation film.

[Additional notes]
The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

1 Semiconductor substrate (board)
2 Photoelectric converter 4 First insulating film (insulating film)
5 Anti-reflection film 6 Interlayer insulating film 8 Passivation film 12 Optical wave guide 13 Light-shielding film 14 Memory section (charge storage section)
100, 200, 300, 400 solid-state image sensor

Claims (5)

It has a laminated structure in which a substrate including a photoelectric conversion unit, an insulating film, an antireflection film, an interlayer insulating film, and a passivation film are formed in this order.
The passivation film has a stress in the compression direction and has a stress in the compression direction.
A solid-state image sensor, characterized in that the stress is −50 kN / cm ^{2 or less.} The laminated structure has
The solid-state imaging device according to claim 1, further comprising an optical waveguide that is recessed into the interlayer insulating film and the passivation film, and the side wall of the recessed portion is further covered with the passivation film. .. The substrate further includes a charge storage unit that stores the charges generated in the photoelectric conversion unit.
The laminated structure has
The solid-state imaging device according to claim 1 or 2 , wherein a light-shielding film is further formed between the charge storage portion and the interlayer insulating film. An electronic device comprising the solid-state image pickup device according to any one of claims 1 to 3. A method for manufacturing a solid-state image sensor having a laminated structure in which a substrate including a photoelectric conversion unit, an insulating film, an antireflection film, an interlayer insulating film, and a passivation film made of a silicon nitride film are formed in this order. ,
The passivation film is formed by the chemical vapor deposition method, and the passivation film is formed.
In the chemical vapor deposition method,
The step of increasing the high frequency power applied to the passivation film and
A step of reducing the pressure applied to the passivation membrane and
The step of increasing the temperature at the time of forming the passivation film and
The process of reducing the amount of _{SiH 4 added and}
A solid-state image sensor, characterized in that the stress in the compression direction in the passivation film is reduced to −50 kN / cm ² _{or less by carrying out any one or more steps of increasing the amount of N 2 added.} Manufacturing method.

Images