JP2005175072A - Solid state imaging apparatus and its fabricating process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid state imaging apparatus exhibiting high condensation efficiency to a photoelectric converting section even if condensation of incident light through a lens is insufficient. <P>SOLUTION: The solid state imaging apparatus comprises a photoelectric converting section 1 for converting incident light into charges, a first dielectric film 82 formed above the photoelectric converting section 1, a second dielectric film 83 formed into funnel shape which touches only a part of the first dielectric film 82 facing the opening at the photoelectric converting section 1 and increases the opening area as receding from the photoelectric converting section 1, and a third dielectric film 21 formed in contact with the side face of the second dielectric film 83 and having an inner hollow layer 9. Refractive index of the third dielectric film 21 is higher than that of the second dielectric film 83 and atmospheric pressure of the hollow layer 9 is 0.5 atm or below. Total reflection is caused by refractive index difference on the boundary surface of the hollow layer 9 and the dielectric film 21 and incident light deviating from condensation through a lens is guided to the photoelectric converting section 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device mounted on a digital still camera, an integrated video camera, or the like and a manufacturing method thereof.

In recent years, solid-state imaging devices have been widely put into practical use for imaging units of integrated video cameras and digital still cameras. Among them, an interline transfer type CCD solid-state imaging device (hereinafter referred to as IT-CCD) is particularly focused on because of its low noise characteristics.
FIG. 3 is a schematic diagram showing a configuration of a general IT-CCD.
As shown in FIG. 3, the solid-state imaging device 100 includes a photodiode 1 having a photoelectric conversion function, a vertical transfer unit 2 having a buried channel configuration that transfers signal charges in the vertical direction, a vertical transfer gate 3 that controls vertical transfer, A horizontal transfer unit 4 for transferring signal charges in the horizontal direction and an output unit 5 are provided.

FIG. 4 is a diagram illustrating a unit pixel 200 including the photodiode 1, the vertical transfer unit 2, and the vertical transfer gate 3 in FIG. 3.
FIG. 5 is a schematic cross-sectional view taken along the line AA ′ of the unit pixel 200 shown in FIG.
As shown in FIG. 5, a unit pixel 200 includes a photodiode 1 having a photoelectric conversion function formed in a silicon substrate 11, a vertical transfer unit 2 having a buried channel configuration for transferring signal charges in the vertical direction, and a vertical transfer. The vertical transfer gate 3 to be controlled, the dielectric film 81 mainly composed of SiO ₂ formed on the vertical transfer gate 3, the incident light formed on the dielectric film 81 on the vertical transfer unit 2, the vertical transfer gate 3, etc. The light shielding film 6 for preventing the light from entering the region, the light shielding film 6, the dielectric film 82 mainly composed of SiO ₂ formed on the photodiode 1, the protective film 10 formed on the dielectric film 82, and the protective film 10 And an organic dielectric film 12 formed on the upper portion of the dielectric film 12 and a lens 7 formed of an organic film for condensing incident light on the photodiode 1 on the dielectric film 12.

Note that the dielectric film 12 has both the role of flattening and the role of a color filter.
Various methods for manufacturing a solid-state imaging device have been proposed (see, for example, Patent Documents 1 and 2).
FIG. 6 is a diagram showing a part of a conventional method for manufacturing a solid-state imaging device. In FIG. 6A, up to the light shielding film 6 is formed, and then the dielectric film 82 is formed on the light shielding film 6, and then the protective film 10 is formed on the dielectric film 82. Thereafter, as shown in FIG. 6B, after forming the organic dielectric film 12 on the protective film 10, the lens 7 is formed on the dielectric film 12.
Japanese Patent No. 2869280 JP 7-45805 A

However, the solid-state imaging device having the conventional configuration has a problem that the incident light cannot be effectively used because the incident light is not condensed on the photodiode when the lens is not sufficiently condensed. .
That is, the light incident on the solid-state imaging device is effectively collected by the lens 7 and incident on the photodiode 1 when entering the solid-state imaging device perpendicularly, but the incident angle deviates from the vertical. The light is not condensed on the photodiode 1 but is irregularly reflected on the surface of the light shielding film 6 as shown in FIG. 5, so that the incident light cannot be used effectively.

In particular, with the recent miniaturization of cameras, solid-state imaging devices are required to have smaller unit pixels and shorter exit pupil distances for lenses used in cameras.
The downsizing of the unit pixel leads to a reduction in the opening width of the photodiode 1, which is the opening of the light shielding film 6, and the film thickness of the vertical transfer gate 3 cannot be reduced at a rate of the reduction ratio of the opening width. It has a vertical shaft structure, and it is difficult to collect incident light.

Further, the shortening of the exit pupil distance of the camera lens means that the proportion of light whose angle of incident light to the solid-state imaging device is away from the vertical increases, and these are also effective for the incident light to the photodiode 1. Makes it difficult to collect light.
In addition, according to the technique disclosed in Patent Document 1, a gas layer is formed by applying a water-soluble resin, covering the upper part with another resin, and then dissolving the water-soluble resin later. With this technology, it is difficult to apply a water-soluble resin thinly and evenly on the surface of a solid imaging device with severe irregularities, resulting in a liquid pool in the recess, or the entire recess is filled with resin, or a part of the recess is foamed Since a region where the resin cannot be applied is formed, it is not a manufacturing method for obtaining uniform characteristics.

  Further, according to the technique disclosed in Patent Document 2, light is collected using total reflection at the boundary by using a material having a high refractive index of about 2.0 such as a titanium oxide film on the photodiode. Although improved, a material having a high refractive index also has an adverse effect that the light absorptance increases at the same time and attenuates before the light is incident on the photodiode. This effect is particularly noticeable on the short wavelength side in the visible region, and the color balance of incident light tends to be biased toward the red direction.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solid-state imaging device with high efficiency of condensing incident light onto a photodiode even when the condensing by the lens is insufficient, and a manufacturing method thereof.

  In order to achieve the above object, a solid-state imaging device according to the present invention includes a photoelectric conversion unit that converts incident light into electric charge, a first dielectric film formed on the photoelectric conversion unit, and the first dielectric film. A second dielectric film formed on the top of the film in contact with only the portion facing the opening of the photoelectric conversion unit, and a side surface of the second dielectric film, and has a hollow layer inside. And a third dielectric film.

The second dielectric film has a funnel shape in which an opening area increases as the distance from the photoelectric conversion unit increases.
The refractive index of the third dielectric film is higher than the refractive index of the second dielectric film.
The refractive index of the second dielectric film is 1.4 or more and less than 1.6, and the refractive index of the third dielectric film is 1.6 or more and less than 3.4.

The air pressure of the hollow layer is 0.5 atm or less.
According to the configuration of the present invention, the total reflection of incident light is caused by the difference in refractive index formed at the boundary between the hollow layer and the dielectric film, whereby the incident light can be effectively condensed on the photoelectric conversion unit. . In particular, even in a solid-state imaging device having a narrow vertical shaft-like structure, incident light can be effectively collected even if the incident angle to the solid-state imaging device is away from the vertical. In addition, most of the upper portion of the photoelectric conversion portion can be formed of a low refractive material, and attenuation before light enters the photoelectric conversion portion can be minimized while maximizing the total reflection effect.

Moreover, since the hollow layer has a low atmospheric pressure and its refractive index approaches that of a vacuum, the refractive index difference between the hollow layer and the dielectric film can be further increased, and the effect of condensing incident light on the photoelectric conversion unit can be obtained. Can be raised.
Thereby, the sensitivity characteristic of a solid-state imaging device can be improved.
Furthermore, it is further characterized by further comprising a charge transfer means that is formed in contact with the photoelectric conversion unit and transfers charges accumulated in the photoelectric conversion unit in a predetermined direction.

Furthermore, it is further characterized by further comprising charge detection means that is formed in contact with the photoelectric conversion unit and converts charges accumulated in the photoelectric conversion unit into a voltage.
Further, in the method for manufacturing a solid-state imaging device according to the present invention, a step of forming the first dielectric film on the photoelectric conversion unit, and a fourth dielectric film on the first dielectric film. Forming a step, etching a portion of the fourth dielectric film opposite to the opening of the photoelectric conversion portion, forming a second dielectric film on the first and fourth dielectric films, and A step of selectively etching the second dielectric film up to the fourth dielectric film above the light-shielding film at the outer periphery of the boundary of the photoelectric conversion unit, and the first and second A step of selectively etching the fourth dielectric film surrounded by the dielectric film using the first and second dielectric films as a mask to form a recess; and enclosing the hollow layer in the recess Forming the third dielectric film.

Furthermore, in the step of forming the third dielectric film, the encapsulated hollow layer is formed by using a CVD method and increasing the film formation speed during the formation.
Further, the step of forming the third dielectric film is performed under reduced pressure.
As a result, the dielectric film at the boundary of the hollow layer can be formed simultaneously with the encapsulating process of the hollow structure, so that the manufacturing cost of the solid-state imaging device can be reduced. Moreover, the uniformity of the formed film can be achieved. Moreover, since a photoresist is not used at the time of hollow layer etching, good selectivity can be obtained.

Furthermore, in the step of forming the third dielectric film, the protective film is formed by continuing to form the film as it is immediately after enclosing the hollow layer.
Thereby, the manufacturing process of a solid-state imaging device can be reduced.
Further, the fourth dielectric film is a dielectric film or a conductive film having a refractory metal having a melting point of 700 ° C. or higher as a component.

  As a result, since this film easily reacts with active species of F and Cl, it can be easily removed by etching.

According to the present invention, by providing a hollow layer having a low atmospheric pressure in the inorganic dielectric film layer, total reflection that maximizes the refractive index difference of the dielectric film can be used, and incident light is effectively converted into a photoelectric conversion unit. Therefore, the sensitivity characteristic can be greatly improved. Further, the hollow layer has a boundary with a film having a high refractive index, so that it is effective even for incident light with a steep angle.
In addition, the layer having a high refractive index is only a thin film region that forms a boundary with the hollow layer, and the film above the photoelectric conversion unit can suppress the refractive index to a low level and can suppress the absorption of incident light to the minimum. .

In addition, a method for manufacturing a solid-state imaging device is a method in which a hollow layer can be formed uniformly, thereby realizing the effect of the present invention that makes the maximum use of the refractive index difference.
In addition, the step of forming a high refractive index film on the inner surface of the hollow layer can be used to enclose the hollow layer, thereby suppressing an increase in man-hours and contributing to cost reduction.
The same effect can be obtained even if a protective film is formed as an extension of the encapsulating process. This can further contribute to man-hour reduction.

  These technologies are good because they can cope with changes in the incident light angle due to the deep vertical tunneling of the photoelectric conversion unit accompanying the reduction of the unit pixel of the solid-state imaging device and the short exit pupil distance of the camera lens. Imaging characteristics can be obtained. Therefore, the practical effect is great.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram illustrating a cross-sectional structure of the solid-state imaging device according to the first embodiment of the present invention.
As shown in FIG. 1, a unit pixel 201 includes a photodiode 1 having a photoelectric conversion function formed in a silicon substrate 11, a vertical transfer unit 2 having a buried channel configuration for transferring signal charges in a vertical direction, and a vertical transfer. The vertical transfer gate 3 to be controlled, the dielectric film 81 mainly composed of SiO ₂ formed on the vertical transfer gate 3, the incident light formed on the dielectric film 81 on the vertical transfer unit 2, the vertical transfer gate 3, etc. The light shielding film 6 for preventing the light from entering the region, the light shielding film 6 and the dielectric film 82 mainly formed of SiO ₂ formed on the photodiode 1, and only the portion of the dielectric film 82 facing the opening of the photodiode 1. contact, the dielectric film 83 composed mainly of SiO ₂ formed on the funnel-shaped opening area widens with increasing distance from the photodiode 1, the upper portion of the dielectric layer 83, also dielectric film The dielectric film 21 mainly composed of SiN formed with the hollow layer 9 inside between 2 and 83, the protective film 10 formed on the dielectric film 21, and formed on the protective film 10 An organic dielectric film 12 and a lens 7 formed of an organic film for condensing incident light on the photodiode 1 are provided on the dielectric film 12.

The dielectric film 12 uses both the role of flattening and the role of a color filter.
In the solid-state imaging device according to the first embodiment of the present invention configured as described above, the refractive index of the hollow layer 9 and the SiN film 21 is larger in the SiN film 21. Further, the dielectric constant of the hollow layer 9 is a vacuum dielectric constant of 1. Accordingly, total reflection occurs at the interface of the hollow layer 9 from the SiN film 21 side according to the refractive index difference.

When the refractive index of the SiN film 21 is n, the total reflection angle θ is
cos θ = 1 / n (1)
An angle that satisfies this relationship. For example, when n = 2.0, θ = 60.0 ° according to equation (1). This means that total reflection occurs in a range from the surface in contact with the light incident point at the boundary between the SiN film 21 and the hollow layer 9 to an angle of 60.0 °.

  Thereby, even if the incident light is not sufficiently collected by the lens 7 and the incident light is not collected directly at the opening of the photodiode 1, the photodiode 1 is guided by the incident light by total reflection at the interface of the hollow layer 9. Incident light can be collected effectively.

FIG. 2 is a diagram illustrating the method for manufacturing the solid-state imaging device according to the first embodiment of the present invention.
In FIG. 2A, up to the light shielding film 6 is formed, and after the dielectric film 82 is formed on the light shielding film 6, heat flow is performed, and the dielectric film 13 mainly composed of SiN is formed on the dielectric film 82. Is shown. In this step, for example, a SiN film formation method such as CVD in which the film formation temperature is lowered using plasma or UV is used. The process up to the formation of the dielectric film 82 is the same as the conventional method for manufacturing a solid-state imaging device.

  Next, as shown in FIG. 2B, the photoresist 14 is patterned so as to open at the top of the photodiode 1, thereby etching the dielectric film 13 on the top of the photodiode 1.

  Next, FIG. 2C shows a state in which after the photoresist 14 is removed, a dielectric film 82 on the photodiode 1 and a dielectric film 83 on the dielectric film 13 are formed and planarized.

Next, FIG. 2D shows a state where the dielectric film 83 is etched by the photoresist 24 at the boundary portion between the adjacent pixels (upper part of the light shielding film 6).
Next, in FIG. 2E, the photoresist 24 is removed, and the dielectric film 13 containing SiN as a main component is etched after etching at the boundary portion of adjacent pixels in the previous process, so that a hollow layer (concave portion) is obtained. 19 is formed.

For example, only the dielectric film 13 mainly containing SiN is selectively etched by dry etching using a gas containing F (fluorine) or Cl (chlorine) as a main component of etching, such as CF ₄ or CCl _4. Can be removed.

  Next, in FIG. 2F, the SiN layer 21 is formed on the inner surface of the hollow layer 19 so as to contain the hollow layer 9, and the SiN film 21 is formed up to the surface of the dielectric film 83. Thereafter, the whole is covered with a protective film 10, and thereafter, an organic film 12 and an organic film lens 7 are sequentially formed thereon. Note that the organic film 12 has a role of flattening and a role of a color filter as in the conventional example.

By the way, since the SiN film 13 is formed by a film forming method such as a CVD method, the uniformity of the formed film which is a problem in the method of applying a water-soluble resin as disclosed in Patent Document 1 is completely different. The problem disappears.
In addition, when a dielectric film or a conductive film having a refractory metal having a melting point of 700 ° C. or higher, such as a Ti film or a TiN film, is used instead of the SiN film 13, the film reacts with F or Cl active species. Easy to remove by etching.

  Further, when the hollow layer 19 is formed by etching, an organic photoresist is not used, and the patterned dielectric films 82 and 83 are substituted for the photoresist. When a photoresist is used during dry etching, a product generated from the photoresist during etching becomes an etching active species, and the selectivity is lowered. Selectivity can be obtained.

  In addition, the SiN film 21 is formed by using a formation method such as plasma CVD or UV-CVD that can obtain a film having a low temperature and good uniformity. At this time, in order to form a film uniformly on the inner surface of the hollow layer 19 at the initial stage of formation, the hollow layer 19 is formed, for example, under the condition that the gas flow rate is reduced than usual, and is returned to the normal formation condition in the middle. At the opening in the pixel boundary region, the formation of a film proceeds rapidly and the hollow layer 9 can be enclosed. In addition, since the film is formed in a reduced pressure state in the CVD process, the hollow layer 9 can be enclosed in a state where the atmospheric pressure is low by using this film.

Moreover, the protective film 10 can be simultaneously formed by continuing formation of a film | membrane as it is immediately after an encapsulation at the process of encapsulating the hollow layer 9.
In the embodiment of the present invention, the film that encloses the hollow structure is formed of a SiN film. However, other films such as a SiON film having a refractive index of 1.6 or more have the same effect. Not too long.

In the embodiment of the present invention, a CCD solid-state imaging device is taken as an example, but it goes without saying that the same applies to a MOS solid-state imaging device.
It goes without saying that the present invention is effective for any other solid-state imaging device provided with a photodiode having a photoelectric conversion function.
Further, when the unit pixel is further miniaturized in the surface direction and the photodiode surface is located in the deep part, the hollow layer is substantially perpendicular to the origin of the upper part of the photodiode in the deep part or partially approaches the center of the photodiode and narrows its opening. It may be shaped such that it rises while taking its shape and its opening widens at the top. Even in this case, it goes without saying that the light collected at the upper part is efficiently guided to the photodiode in the deep part by the guide by total reflection, and the present invention is effective.

  In addition, the hollow layer rises almost vertically from the starting point of the upper part of the photodiode, or partially closes to the center of the photodiode and takes a shape that narrows the opening. The light condensed at the opening of the hollow layer is efficiently guided to the photodiode in the deep part by the guide by the total reflection, and the guide effect of the incident light by the total reflection using the hollow layer of the present invention can be sufficiently obtained. It is clear that the effect of can be obtained.

  The present invention can be applied to a CCD solid-state imaging device, a MOS solid-state imaging device and a manufacturing method thereof mounted in a digital still camera or an integrated video camera.

It is a figure which shows the cross-section of the solid-state imaging device which concerns on Example 1 of this invention. (A)-(f) is a figure which shows the manufacturing method of the solid-state imaging device which concerns on Example 1 of this invention. It is a schematic plan view of the conventional solid-state imaging device. It is a schematic plan view of a unit pixel of a conventional solid-state imaging device. It is a figure which shows the cross-section of the conventional solid-state imaging device. (A) And (b) is a figure which shows the manufacturing method of the conventional solid-state imaging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photodiode 2 Vertical transfer part 3 Vertical transfer gate 4 Horizontal transfer part 5 Output part 6 Light shielding film 7 Lens 9 Hollow layer 10 Protective film 11 Silicon substrate 12 Organic dielectric film 13 SiN dielectric film 14, 24 Photoresist 19 Hollow layer (recessed part) )
21 SiN dielectric film 81, 82, 83 SiO ₂ dielectric film 100 Solid-state imaging device 200, 201 Unit pixel

Claims (12)

A photoelectric conversion unit that converts incident light into electric charge;
A first dielectric film formed on the photoelectric conversion unit;
A second dielectric film formed in contact with only the portion of the first dielectric film that faces the opening of the photoelectric conversion unit;
A solid-state imaging device comprising: a third dielectric film formed in contact with a side surface of the second dielectric film and having a hollow layer therein. The solid-state imaging device according to claim 1, wherein the second dielectric film has a funnel shape in which an opening area increases as the distance from the photoelectric conversion unit increases. The solid-state imaging device according to claim 1 or 2, wherein the refractive index of the third dielectric film is higher than the refractive index of the second dielectric film. The refractive index of the second dielectric film is 1.4 or more and less than 1.6, and the refractive index of the third dielectric film is 1.6 or more and less than 3.4. The solid-state imaging device described. 5. The solid-state imaging device according to claim 1, wherein the air pressure of the hollow layer is 0.5 atm or less. 6. The apparatus according to claim 1, further comprising charge transfer means that is formed in contact with the photoelectric conversion unit and transfers charges accumulated in the photoelectric conversion unit in a predetermined direction. Solid-state imaging device. The solid-state imaging according to any one of claims 1 to 5, further comprising charge detection means that is formed in contact with the photoelectric conversion unit and converts the charge accumulated in the photoelectric conversion unit into a voltage. apparatus. It is a manufacturing method of the solid-state imaging device according to claim 1,
Forming the first dielectric film on the photoelectric conversion unit;
Forming a fourth dielectric film on top of the first dielectric film;
Etching a portion of the fourth dielectric film facing the photoelectric conversion portion opening;
Forming and planarizing a second dielectric film on top of the first and fourth dielectric films;
Selectively etching the second dielectric film onto the fourth dielectric film on the light shielding film at the outer periphery of the boundary of the photoelectric conversion unit;
Selectively etching the fourth dielectric film surrounded by the first and second dielectric films using the first and second dielectric films as a mask to form a recess;
Forming the third dielectric film that encloses the hollow layer in the recess. A method for manufacturing a solid-state imaging device, comprising: 9. The encapsulated hollow layer is formed by using a CVD method in the step of forming the third dielectric film, and increasing the film formation rate during the formation. Manufacturing method of solid-state imaging device. The method for manufacturing a solid-state imaging device according to claim 8 or 9, wherein the step of forming the third dielectric film is performed in a reduced pressure state. 11. The method according to claim 8, wherein in the step of forming the third dielectric film, the protective film is formed by continuing the film formation as it is immediately after the hollow layer is enclosed. The manufacturing method of the solid-state imaging device of description. The solid-state imaging device according to any one of claims 8 to 11, wherein the fourth dielectric film is a dielectric film or a conductive film having a refractory metal having a melting point of 700 ° C or higher as a component. Production method.

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