JP4333615B2 - Solid-state image sensor - Google Patents

Description

  The present invention relates to a solid-state imaging device in which a light receiving portion having an opening such as a CCD solid-state imaging device is formed.

  In a solid-state imaging device, the optical system tends to be as small as 1/3 inch or 1/4 inch, and the aperture of the light receiving portion is reduced in response to downsizing of the solid-state imaging device and increase in the number of pixels. .

Here, if the opening of the light receiving portion is enlarged for the purpose of improving the sensitivity, smear due to the incidence of light on the charge transfer portion is likely to occur, so there is a limit to increasing the opening of the light receiving portion.

  Further, if the sensitivity is improved by electrically amplifying the signal charge obtained by photoelectric conversion of the light receiving unit from the incident light, the influence of noise on the signal value is increased and the S / N characteristic is deteriorated.

  In addition, the white spots generated due to crystal defects in the semiconductor substrate and contamination in the manufacturing process in the manufacture of the elements have not been defective until now. There is a problem that the yield is reduced by being greatly affected by the white spot of the level.

  In order to solve the above-described problems, the present invention provides a solid-state imaging device that can improve S / N characteristics and sensitivity and can be manufactured with high yield.

The solid-state imaging device according to the present invention includes a light-receiving portion having an opening formed as a pixel. A low-reflection film is provided on the opening of the light-receiving portion, and a film for supplying hydrogen is formed above the low-reflection film. And a low reflection film is formed with a width narrower than the width of the opening of the light receiving portion, and the film for supplying hydrogen and the light receiving portion are in contact with each other.

According to the configuration of the present invention described above, by providing the low reflection film on the light receiving portion, the ratio of the incident light to the light receiving portion being reflected is reduced and reflected and escapes from the light receiving portion. The ratio of light can be reduced and the amount of received light can be increased. Therefore, the sensitivity of the solid-state image sensor can be improved.
Furthermore, by providing a film for supplying hydrogen on the low-reflection film, hydrogen can be supplied to the substrate surface to reduce the interface state .

  According to the above-described solid-state imaging device according to the present invention, the sensitivity can be improved by forming the low reflection film on the opening.

  Further, according to the present invention, since the film for supplying hydrogen is provided in the upper layer of the low reflection film, the supply of hydrogen to the semiconductor substrate is performed to reduce the interface state of the substrate surface, and the dark current resulting therefrom Can be reduced.

Then, when a part of the low reflection film is removed to make the width narrower than the width of the opening on the light receiving part, the effect of improving the sensitivity is maintained, while the hydrogen from the upper layer to the light receiving part of the semiconductor substrate is maintained. Since supply is possible, an increase in dark current due to interface states and the like can be more effectively suppressed.
At this time, since the low reflection film is not provided under the projecting portion of the light shielding film, smear can be reduced.

The present invention comprises a light receiving portion having an opening portion is formed as a pixel, a low reflection film is provided on the opening of the light receiving portion has a film supplying hydrogen to the upper layer than the low reflection film, a low In the solid-state imaging device, the reflective film is formed to be narrower than the width of the opening of the light receiving unit, and the film supplying hydrogen and the light receiving unit are in contact with each other.

  Hereinafter, embodiments of the solid-state imaging device of the present invention will be described with reference to the drawings. A CCD solid-state imaging device 1 shown in FIG. 1 outputs an image pickup area 4 composed of a photosensor 2 that performs photoelectric conversion and a vertical transfer CCD register 3 constituting a light receiving section, and a signal charge transferred from the vertical transfer CCD register 3 as an output section. 6 is composed of a horizontal transfer CCD register 5 for transfer.

FIG. 2 is an enlarged view of the imaging region 4 of the CCD solid-state imaging device 1 of FIG.
An opening 7 formed by an opening of a light-shielding film made of, for example, Al, and a transfer electrode 8 (8a, 8b) made of polycrystalline silicon for reading and transferring, which are formed in a light receiving portion 2 made of a photosensor that receives incident light. In the CCD solid-state imaging device 1 having the above, a low reflection film 9 (9a, 9b, 9c, 9d) for suppressing reflection is provided on the opening 7.
By providing this low reflection film 9, the sensitivity can be improved.

In the embodiment of FIG. 2, a low reflection film 9 is provided extending in the vertical direction in parallel with the vertical transfer register 3. For example, complementary colors of magenta, cyan, yellow, and green on each photosensor 2 are provided. Corresponding to the colors of four color filters (not shown), there are provided four types of low reflection films 9a, 9b, 9c, 9d with different film thicknesses and refractive indexes as described later. The conditions such as the film thickness and refractive index of the low reflection film between the photosensors 2 adjacent in the vertical direction are arbitrary, but in FIG. 2, it is the same as one of the four types of low reflection films (9c). As a condition.
Although not shown, a color filter, an on-chip lens, and the like are formed on the photosensor 2 of the light receiving unit 7 of each element.

3A shows a cross-sectional view in the horizontal direction (so-called H direction) in FIG. 2, and FIG. 3B shows a cross-sectional view in the vertical direction (so-called V direction) in FIG.
Although not shown, the semiconductor substrate 10 includes a semiconductor region that forms the charge storage unit 11, a transfer channel region that forms the vertical transfer register 3, a read gate unit 12, a channel stop region, and the like.

An insulating film 13, part of which is a gate insulating film, is formed on the surface of the semiconductor substrate 10, and a transfer electrode 8 is formed on the transfer channel region and the read gate portion 12 via the insulating film 13. An interlayer insulating layer 14 is entirely formed covering the transfer electrode 8. The transfer electrode 8, the insulating film 13, and the transfer channel region form a vertical transfer register 3 having a CCD structure. On the interlayer insulating layer 14, a light shielding film 15 and a protective film 16 for blocking light to other parts except the light receiving part 2 are sequentially formed, and a planarizing film 17 is formed thereon. The light shielding film 15 is made of, for example, metal, and an opening is formed in a portion corresponding to the light receiving portion 2 of the light shielding film 15, and this opening corresponds to the opening portion 7 of the light receiving portion 2.
On the planarizing film 17, a color filter 20 that transmits light of a specific color and an on-chip lens 21 that is processed into a spherical shape and collects light are formed.

  In the present embodiment, as described above, the low reflection film 9 is formed on the opening 7 of the light receiving unit 2, and the low reflection film 9 is formed between the insulating film 13 and the protective film 16. It is formed so as to cover the opening 7 in the horizontal direction and on the interlayer insulating layer 14 on the transfer electrode 8 in the vertical direction.

Further, SiN (including hydrogen due to plasma) formed by plasma CVD is used for the protective film 16, particularly an upper protective film 19 (see FIG. 4) described later, Al containing hydrogen in the light shielding film 15 or the like. May be used to form a film for supplying hydrogen to the upper layer of the low reflection film 9.
Thereby, hydrogen can be supplied to the semiconductor substrate 10 to reduce the interface state existing at the interface between the semiconductor substrate 10 and the insulating film 13 thereon.

Conventionally, an enlarged view of the vicinity of the opening as shown in FIG. 8, CCD in the solid-state imaging opening 7 of the photosensor 2 of the element, the incident light L _F is a color filter 20, the planarizing film 17, the upper protective layer 19, About 25% of the incident light L _F is reflected in the semiconductor substrate 10 through the lower protective film 18 made of a PSG (phosphosilicate glass) transparent protective film and the insulating film 13 made of SiO ₂ or the like, and the reflected light L _R. It has become.

In the present embodiment, particularly, as shown in FIG. 4A, which is an enlarged view of the vicinity of the opening, low reflection is provided between the insulating film 13 and the protective film 16 composed of the lower protective film 18 and the upper protective film 19. By providing the film 9 , the sensitivity can be improved.

Energetically, if no decay energy in the membrane permeation or reflection or the like, holds the relationship that the energy of the energy + reflected light L _R energy = transmitted light L _T of the incident light L _F.

Thickness as a low reflection changes depending on the wavelength of the incident light L _F.
This is similar to the optical interference in thin films, changes the color (wavelength) of the refractive index and incident light L _F of the film.
Representative elements, the optical path difference between the reflected light L _R of the incident light L _F and the semiconductor substrate 10 can be a phase delay. The phase difference α that amplifies the transmitted light L _F is an even multiple of π in the low reflection film 9 and the insulating film 13 made of SiO ₂ .
This is due to the phase difference between the incident light LF and the light incident on the semiconductor substrate 10 by the reflected light from the upper surface of the low reflective film 9 (the surface in contact with the protective film 16).

  That is, the following relationship 1 holds.

[Equation 1]
Phase difference = {π (2nd) / (λ · cosψb)} × 2m
n: refractive index of the film
d: Film thickness
λ: wavelength
ψb: refractive index
m: natural number

  Actually, changes in film thickness and wavelength are complicated due to multiple reflections by a multilayer film structure such as the insulating film 13 and the upper protective film 19 on the semiconductor substrate 10 and a light-collecting state by an on-chip lens.

In the above-described embodiment, the single-layer low reflection film 9 having the same refractive index is provided from the viewpoint of work efficiency.
In the case of the low reflective film 9 having the same refractive index of a single layer, only a specific color is amplified, and there is a possibility that the other colors may have a decreasing effect depending on the color.

Therefore, for example, as shown in FIG. 2, changing the film thickness corresponding to the color If membrane having the same refractive index in other words each sensor 2 each color of the incident light L _F. FIG. 2 shows a case where the film thickness is changed with respect to the complementary color checkered arrangement.

In addition, films having different refractive indexes can be combined in two layers, and the sensitivity can be improved for each color. An enlarged view of the vicinity of the opening in this case is shown in FIG. 4B.
In this case, the low reflection film 9 is constituted by a stack of the first low reflection film 9X and the second low reflection film 9Y.

For example, the first low-reflection film 9X refractive index n _A, when the second low-reflection film 9Y is a refractive index n _B, if n _A> n _B, as shown in FIG. 4B, for example, the refractive index is large even when one of the low reflective film is laminated by placing underneath, each of the low reflective film 9X the color, it is possible to improve the sensitivity by changing the thickness of 9Y. The stacking order of the low reflective film 9X having a high refractive index and the low reflective film 9Y having a low refractive index is not particularly limited, and may be, for example, the reverse stacking order of FIG. Preferably, the stacking order is such that a better signal is obtained.

  As described above, according to the present invention, the sensitivity can be improved by using the low reflection film 9 corresponding to the color regardless of the film thickness and arrangement.

Next, as a specific example, a case where a SiN film formed by low pressure CVD is used as the low reflection film 9 will be described.
At this time, as a film structure, in FIG. 4A, the film thickness of the low reflection film 9 is about 40 nm, and the film thickness of the insulating film 13 is about 350 nm.
For the low reflection film 9, Oite the semiconductor substrate 10 and the insulating film 13, if the film thickness of the low reflection film 9 in this structure and 40 nm, reflectance becomes minimum at an incident light wavelength 600nm~620nm is 1-2 % it became.

Further, the film thickness of the low reflection film 9 in the case of 30 nm, the wavelength of minimum was around 500 nm.
Therefore, when the low-reflection film 9 is formed of, for example, a SiN film formed by low-pressure CVD and, for example, a primary color filter 20 is provided, the low-reflection film is about 45 nm for red and low-reflection for green. If the film is formed with a film thickness of about 35 nm and the blue low reflection film is formed with a film thickness of about 25 nm, the maximum sensitivity can be obtained for each color.

Similarly, in the CCD solid-state imaging device of the three- plate type (the type in which the incident light from the lens is separated for each color such as R, G, B by a prism or the like and a separate CCD is provided for each color) On the other hand, the sensitivity can be improved by manufacturing three CCD solid-state imaging devices each with the above-mentioned film thickness.

  In the case of the combination of the low-reflectance films 9X and 9Y having different refractive indexes shown in FIG. 4B, the combination of the refractive index and the film thickness that gives the minimum reflectance with respect to the wavelength can be selected.

Further, when a complementary color filter 20 is used as the color filter 20, it is possible to adjust by changing the film thickness by spectroscopy.
In particular, since the effect of improving the sensitivity is large in green, the film thickness is adjusted to about 35 nm for green, and the film thickness is adjusted to the spectrum for other colors. This makes it possible to respectively improve the sensitivity for each color to obtain a sensitivity improvement.

In the above-described embodiment, the present invention is applied to a solid-state imaging device having a matrix arrangement. However, like a so-called line sensor, a color filter of the same color is formed on a photosensor in the same row, and different colors are obtained. The present invention can be similarly applied to a solid-state imaging device in which a plurality of rows of photosensors each having a color filter are formed to correspond to a plurality of colors.
In this case as well, by forming a low-reflective film with a different refractive index and thickness for each row corresponding to each color, the sensitivity is improved and the transmittance to the light receiving unit is controlled to facilitate signal processing. Can do.

Next, still another embodiment of the present invention will be described.
In the solid-state imaging device 30 of the above-described embodiment, the low reflection film is formed by changing the film thickness in accordance with the color of the pixel. However, in this embodiment, the low reflection film having the same film thickness for each pixel. A membrane is provided.
In addition, the upper protective film 19 and the light-shielding film 15, etc., on the upper layer of the low reflection film 9 are made to contain hydrogen and have a film for supplying hydrogen.

As shown in the plan view of the imaging region of the solid-state imaging device in FIG. 5, in the present embodiment, the low reflection film 9 is formed in a strip shape corresponding to the row of the light receiving portions 2, and the light receiving portion. than the width W _p of the opening 7 on the two forming a narrow width W _L.

When the low reflection film is formed on the entire imaging region by SiN (refractive index 2.0) formed by low pressure CVD, and the film thickness is 20 to 40 nm, the sensitivity is improved by about 20% compared to the conventional case. As a result, the dark current increased, which was about 5 times that when the low reflection film was not provided.
This is because the low reflection film is formed over the entire surface, and the low reflection film suppresses the supply of hydrogen to the substrate from the upper protective film, the light shielding film, etc. This increases the dark current.

According to this embodiment, the gap and the low reflection more to form a low reflection film 9 in a narrow width W _L from the opening 7 the width W _p of the light receiving portion 2, the opening 7 and the low reflection film 9 Hydrogen is supplied from the upper protective film 19 and the light shielding film 15 to the semiconductor substrate 10 through the vicinity of the transfer electrode 8 where the film 9 is not formed. In particular, hydrogen is also supplied to the light receiving unit 2 through the gap between the opening 7 and the low reflection film 9. Therefore, the interface state can be eliminated.
For these reasons, it is possible to reduce the dark current to the same extent as that of a normal solid-state imaging device while suppressing the reflection of incident light to the opening 7 on the light receiving unit 2 and maintaining the above-described sensitivity improvement effect.

  The low reflection film 9 having the above-described structure is formed by forming a photoresist layer on the entire surface after forming the low reflection film 9 and patterning the photoresist layer for removing the low reflection film. 5 can be formed into a pattern shown in FIG. 5 by providing a step of removing the low reflection film 9 by etching.

Further, by the low reflective film 9 as described above having a width W smaller than _p the width W _L of the opening 7 can be formed by self-alignment of the low reflection film 9 with respect to the opening.
Accordingly, it is possible to reduce the output difference due to the position of the pixel due to the mask formed by the photoresist layer being shifted and the low reflective film 9 being formed shifted.

Next, still another embodiment of the solid-state imaging device of the present invention will be shown.
In the embodiment shown in FIG. 5 described above, the low reflection film 9 is formed at the center of the opening on the light receiving portion. In the solid-state imaging device 40 of this embodiment, FIG. 6 is a plan view of the imaging region. In particular, the low reflection film 9 of the pixel in the central portion 41 is formed at the center of the opening 7 on the light receiving portion 2, whereas the low reflection film 9 of the pixels in the peripheral portions 42 and 43 is formed in the light receiving portion. 2 is formed by shifting from the center of the opening 7 on the outside to the outside.
That is, the pixel 42 on the right side from the center part 41 is provided with the low reflection film 9 shifted from the center of the opening 7 to the right side, and the pixel 43 on the left side from the center part is shifted from the center of the opening part 7 to the left side for low reflection. A membrane 9 is provided.

  With this configuration, for example, when the light incident on the solid-state imaging device from the light source is not a parallel light but a point light source, the difference in the incident angle between the central pixel 41 and the peripheral pixels 42 and 43 is different. It can correspond to.

FIG. 7 shows the state of incident light on the central pixel 41 and the peripheral pixels 42 and 43 in the case of a point light source.
Light 52 from a point-like light source 51 such as a pinhole formed by the diaphragm is incident straight on the central pixel 41 and incident on the center of the opening 7 on the light receiving unit 2, but the peripheral pixel 42. , 43 are incident obliquely. For this reason, in the peripheral pixels 42 and 43, the microlens 21 is placed in the opening 7 so that the light 53 that is transmitted through the microlens 21 and is focused into the opening 7 on the light receiving unit 2. Formed by shifting from directly above to the inside At this time, since the position of the microlens 21 is set so that the light 53 incident from the microlens 21 to the light receiving unit 2 is not kicked by the light shielding film 15, the light 53 is incident outside the center of the opening 7.

  In the solid-state imaging device 40 of the present embodiment, the low reflection film 9 is shifted from the center of the opening 7 to the outside in the peripheral pixels 42 and 43 corresponding to the incident light 53 shown in FIG. The reflection can be effectively suppressed even for the light 53 that is formed and incident obliquely, and the sensitivity can be improved.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

1 is a schematic configuration diagram (plan view) of a CCD solid-state imaging device according to the present invention. FIG. 2 is an enlarged view of an imaging area of the CCD solid-state imaging device in FIG. 1. It is sectional drawing of the light-receiving part vicinity of FIG. A It is sectional drawing of a horizontal direction. B is a cross-sectional view in the vertical direction. FIG. 4 is an enlarged view of the vicinity of the opening in FIG. 3 showing an example of forming a low reflection film. A This is an example in which the low reflective film is a single layer. B This is an example in which the low reflective film is a two-layer laminate. It is a top view of the imaging area | region of the other CCD solid-state image sensor by this invention. It is a top view of the imaging area | region of the further another CCD solid-state image sensor by this invention. It is a figure explaining the state of the incident light to the pixel of the center part in the case of a point light source and the pixel of a peripheral part. It is an enlarged view near the opening part of the conventional CCD solid-state image sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,30,40 ... CCD solid-state image sensor, 2 ... Photosensor (light-receiving part), 3 ... Vertical transfer register, 4 ... Imaging area, 5 ... Horizontal transfer register, 6 ... Output part, 7 ... Opening part, 8, 8a , 8b ... transfer electrode, 9, 9a, 9b, 9c, 9d ... low reflection film, 9X ... first low reflection film, 9Y ... second low reflection film, 10 ... semiconductor substrate, 11 ... charge storage section, 12 ... readout Gate part, 13 ... insulating film, 14 ... interlayer insulating layer, 15 ... light shielding film, 16 ... protective film, 17 ... flattening film, 18 ... lower protective film, 19 ... upper protective film, 20 ... color filter, 21 ... ON Chip lens 41... Center pixel, 42 and 43. Peripheral pixel 51. Light source 52 and 53 incident light, L _F incident light, L _R reflected light, L _T transmitted light

Claims (1)

In a solid-state imaging device in which a light receiving portion having an opening is formed as a pixel,
A low reflection film is provided on the opening of the light receiving unit,
A film for supplying hydrogen is provided above the low reflection film,
The solid-state imaging device, wherein the low-reflection film is formed with a width narrower than a width of the opening of the light receiving unit, and the film supplying hydrogen and the light receiving unit are in contact with each other.

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