JP2002184966A - Solid state image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid state image sensor comprising a light receiving section 20 arranged, on the surface part of a semiconductor substrate 1, with a plurality of photosensors 19 for converting incident light photoelectrically, an optical black section 23 arranged with a photosensor 22 for detecting the black signal level by intercepting the incident light, and a hydrogen shielding insulation film 4 formed on the light receiving section 20 and the optical black section 23 in which the relation between the output level when the light of the light receiving section 20 does not enter and the output level of the optical black section 23 can be adjusted arbitrarily. SOLUTION: The ratio of the area at each part of the hydrogen shielding insulation film 4 covering a photosensor 19, 22 to the area of each photosensor 19, 22 (the ratio of area between the hydrogen shielding insulation film and the photosensor) is differentiated between the photosensor 19 at the light receiving section 20 and the photosensor 22 at the optical black section 23. For example, the ratio of area between the hydrogen shielding insulation film and the photosensor is set higher at the optical black section 23 than at the light receiving section 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensing device, and more particularly, to a light receiving portion having a plurality of photosensors for photoelectrically converting incident light on a surface of a semiconductor substrate, and a black signal level which is shielded from incident light. The present invention relates to a solid-state image pickup device in which an optical black portion provided with a photosensor for detecting a light is formed, and a hydrogen shielding insulating film made of silicon nitride is formed on the light receiving portion and the optical black portion.

[0002]

2. Description of the Related Art A solid-state imaging device such as a CCD (Charge Co.)
As shown in FIG. 2, an upled device type solid-state imaging device includes, as shown in FIG. 2, a light receiving unit 20 in which a large number of photosensors 16 for photoelectrically converting incident light are arranged, for example, vertically and horizontally (in a matrix). In general, an optical black portion 23 provided with a plurality of photosensors 22 used for detecting a black signal level while blocking the light is provided adjacent to the optical black portion 23. In the example shown in FIG. 2, one optical black section 23 is provided on each side of the light receiving section 20 (both sides in the horizontal transfer direction). In the drawings,
The satin pattern indicates that light is shielded.

Reference numeral 21 denotes each photo sensor (1) in the light receiving section 20.
9) Vertical transfer registers provided corresponding to the vertical columns, 2
Reference numeral 4 denotes each photo sensor (2
2) A vertical transfer register provided corresponding to a vertical column,
In both cases, the signal charges from the photo sensors 19 and 22 are transferred in the vertical direction. Reference numeral 25 denotes a horizontal transfer register provided on the vertical transfer destination side of the light receiving section 23 and the optical black sections 23 on both sides thereof, and horizontally transfers the signal charges vertically transferred by the vertical transfer registers 21 and 24. Reference numeral 26 denotes a charge detection unit provided on the horizontal transfer destination side of the horizontal transfer register 25, which converts signal charges horizontally transferred by the horizontal transfer register 25 into a voltage and outputs the voltage.

In a signal processing circuit (not shown) at the subsequent stage of the charge detecting section 26, an optical black section 2 is provided.
The output from the photosensor 19 of the light receiving unit 20 is subjected to signal processing based on the black signal level which is the output from the photosensor 22 of No. 3 as a video signal. As an example of the signal processing, a black signal level output from the photo sensor 22 of the optical black unit 23 is used as a reference for determining black.

As shown in FIGS. 3A and 3B, the photosensors 19 in the light receiving section 20 and the photosensors 22 in the optical black section 23 are light-shielded. The structure is different only in that the photosensor 22 is not covered with the film and the photosensor 22 is covered with the light-shielding film. In other respects, the structure and the size do not differ. This is based on the recognition that accurate detection of the black signal level requires no difference in structure and size other than whether or not light is incident.

Here, the photosensor 19 and the photosensor 22 in the conventional example will be compared with reference to FIG.
FIG. 3A shows the photo sensor 19 of the light receiving unit 20,
(B) shows the photo sensor 22 of the optical black section 23
In each of (A) and (B), the upper figure is a cross-sectional view and the lower figure is a plan view. In the drawings, 1 is a silicon semiconductor substrate, 2 is a gate insulating film made of SiO ₂ ,
Reference numerals 3 and 3 denote vertical transfer electrodes made of polysilicon, which are made of two different layers of polysilicon.

Reference numeral 4a denotes a low reflection film formed on the photosensor 19 of the light receiving section 20 via the gate insulating film 2;
Is a low-reflection film formed on the photosensor 23 of the optical black portion 23 with the gate insulating film 2 interposed therebetween.
For example, it is made of silicon nitride, and is formed in order to lower the reflectance on the photosensor surface (reduce the reflection) and improve the sensitivity. W1 is the width of the low reflection film 4a, and W2 is the width of the low reflection film 4b.
2 were substantially the same as each other. That is, the photo sensor 4
Both a and b are formed in strips extending in the vertical transfer direction and have widths W1 and W2, but the widths are set to be the same.

Reference numeral 5 denotes a light-shielding film made of, for example, aluminum.
As shown in FIG. 3A, the openings 6 are formed, whereas the photosensors 22 of the optical black portion 23 are not formed with openings as shown in FIG. It is shaded.

Reference numeral 7 denotes a passivation film, 8 denotes a color filter, and 9 denotes an on-chip micro lens. FIG.
As shown in (A) and (B), in the related art, the photosensor 19 in the light receiving unit 20 and the photosensor 22 in the optical black unit 23 are not covered with the light-shielding film 5, but only differ. Otherwise, the structure and size were the same.

[0010]

However, in the conventional solid-state imaging device, the photo sensor 19 of the light receiving unit 20 when the amount of light incident on the light receiving unit 20 is set to 0 (when the light receiving unit 20 is not irradiated with light). And the output from the photosensor 22 of the optical black unit 23 are not actually coincident with each other, though they should originally coincide with each other. This problem is due to precise signal processing by black signal level,
For example, a black signal level is subtracted from the signal component from the photo sensor 19, and the process of obtaining an accurate video signal corresponding to the light intensity is prevented.

More specifically, the output of the optical black section 20 when the optical black section 20 is not irradiated with light tends to be larger than the output of the optical black section 23, in other words, the output of the optical black section 23. Tend to be lower than the actual black signal level.

The inventors of the present invention have investigated the cause of such an output difference, and the degree of hydrogenation of dangling bonds differs depending on whether the dangling bond is covered with the light-shielding film 5. The degree of hydrogenation of the photosensor 22 is higher than that of the uncovered one, and as a result, the level of the black signal component of the photosensor 22 of the optical black unit 23 is lower, which is the output difference. There was found. However, since the photo sensor 22 in the optical black portion 23 is covered with the light shielding film 5 and the photo sensor 19 in the light receiving portion 20 must not be covered with the light shielding film 5, the light shielding film 5 is modified to solve this problem. It cannot be solved.

[0013] Then, when a method for fundamentally solving the problem was sought, the silicon nitride forming the light shielding film 4 has a property of shielding hydrogen atoms, that is, a hydrogen shielding property. The idea of changing the degree of hydrogenation by changing the area between the light-shielding film 4 and the opening 6 by changing the area of the light-shielding film 4 was obtained. The present invention has been made as a result of further searching after obtaining such an idea.

That is, the present invention is to make it possible to arbitrarily adjust the relationship between the output level of the light receiving section when no light is incident and the output level of the optical black section, for example, to make the level difference zero. With the goal.

[0015]

According to a first aspect of the present invention, there is provided a solid-state imaging device, wherein the ratio of the area of each portion of the hydrogen shielding insulating film covering each photosensor to the area of each photosensor, that is, the ratio of the hydrogen shielding insulating film to the photosensor is reduced. The sensor area ratio may be different between the photosensor constituting the light receiving section and the photosensor constituting the optical black section.

Therefore, according to the solid-state imaging device of the first aspect, the area ratio of the hydrogen shielding insulating film to the photosensor is set independently for the photosensor constituting the light receiving portion and the photosensor constituting the optical black portion. Therefore, the degree of hydrogenation of the dangling bond can be independently adjusted by the photosensor constituting the light receiving portion and the photosensor constituting the optical black portion, and thus the light of the light receiving portion is not incident. The relationship between the output level at that time and the output level of the optical black unit can be arbitrarily adjusted, for example, by setting the level difference to zero.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention basically relates to
The sensor hydrogen shielding insulating film area ratio is
And the optical black section.
Although it is different from the photo sensor, the hydrogen shielding insulation
The film is preferably made of silicon nitride SiN. To
This is due to the supply of hydrogen atoms that hydrogenate dangling bonds.
Effectively shuts off the supply path, so the hydrogen shielding insulating film
Hydrogen of dangling bond due to difference in sensor area ratio
The degree of conversion can be changed,
_TwoEffective reflection due to the refractive index relationship with the gate insulating film made of
It also functions as a low-reflection film that lowers the efficiency
is there.

In general, it is preferable that the area ratio of the hydrogen shielding insulating film to the photosensor is larger in the photosensor constituting the optical black portion than in the photosensor constituting the light receiving portion. This is because, as described above, the output of the light receiving unit when the light is not emitted tends to be larger than the output of the optical black unit, in other words,
The output of the optical black part tends to be lower than the actual black signal level, but this tendency is corrected by increasing the hydrogen shielding insulating film-to-photosensor area ratio and reducing the degree of hydrogenation of the optical black part. Then,
This is because the output level difference between the light receiving unit and the optical black unit when the light from the light receiving unit does not enter can be reduced to zero or zero.

However, due to various factors, the output of the light receiving section when the light is not irradiated may be smaller than the output of the optical black section. In that case, conversely, it can be said that the hydrogen shielding insulating film-to-photosensor area ratio of the photosensor in the optical black portion needs to be smaller than that of the photosensor in the light receiving portion. Therefore, it is not always essential to make the photosensor constituting the optical black portion larger than the hydrogen shielding insulating film-to-photosensor area ratio of the photosensor constituting the light receiving portion. In addition, the hydrogen shielding insulating film is formed in a belt shape,
By changing the relationship between the widths W1 and W2, the hydrogen shielding insulating film-to-photosensor area ratio may be different between the light-receiving portion and the optical black portion, or may be independently formed in an island shape for each photosensor. By forming and changing the area, the area ratio of the hydrogen shielding insulating film to the photosensor may be different between the light receiving portion and the optical black portion.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated embodiments. 1A and 1B show a main part of one embodiment of the solid-state imaging device according to the present invention. FIG. 1A shows a photosensor 19 of a light receiving section 20, and FIG. 1B shows an optical black section 23. (A) and (B), the upper figure is a sectional view, and the lower figure is a plan view.

In the drawings, 1 is a silicon semiconductor substrate,
Reference numeral 2 denotes a gate insulating film made of SiO ₂ , and reference numerals 3 and 3 denote vertical transfer electrodes made of polysilicon, which are made of two different layers of polysilicon. 4a is the photo sensor 19 of the light receiving section 20
A low-reflection film made of silicon nitride and having a hydrogen-shielding property formed thereon with the gate insulating film 2 interposed therebetween. It is a low-reflection film made of silicon nitride formed through the film, and therefore has a hydrogen-shielding property. Originally, it is formed to lower the reflectance on the photosensor surface (reduce the reflection) and improve the sensitivity. Is done. Therefore, in the description of the present embodiment and the conventional example, the insulating films 4a and 4b are referred to as low reflection films.

However, in the present invention, the low reflection films 4a and 4b further change the width of the supply path of hydrogen necessary for hydrogenation of the dangling bond according to the difference in the width, so that the dangling bond is not changed. It also plays a role in changing the degree of hydrogenation. W1 is the width of the low-reflection film 4a, and W2 is the width of the low-reflection film 4b. In the related art, the widths W1 and W2 are substantially the same as each other. Is set to W1 <W2.

That is, the low-reflection films 4a and 4b are both formed in a belt shape extending in the vertical transfer direction and have widths W1 and W2, which are set to W1 <W2. Specifically, W1 is 2.8 μm and W2 is 3.2 μm, and a difference of 0.4 μm is set between W1 and W2 [note that the width of each pixel 19 and 22 (horizontal transfer) The length (length in the vertical transfer direction) is 5.3 μm, the length (length in the vertical transfer direction) is 9.8 μm, the width of the opening (length in the horizontal transfer direction) is 3.4 μm, and the length (vertical transfer direction). Is 6.8 μm].

The reason for providing the difference between W1 and W2 is as follows.
Portion between the inner surface of opening 6 and light-shielding film 5 (that is, portion of photosensors 19 and 22 not covered by low-reflection film 5)
(In other words, the area ratio of the hydrogen-shielding insulating film to the photosensor is changed), and the width of the path through which hydrogen atoms for hydrogenating dangling bonds on the surface of the semiconductor substrate are different. In order to change the degree of hydrogenation.

The degree of hydrogenation naturally increases with an increase in the width of the path through which the hydrogen atom passes.
As a result, the black signal component decreases and the degree of hydrogenation decreases and the black signal component increases as the width of the path through which the hydrogen atoms pass is narrower. As a result, the output when the light from the light receiving unit 20 is not irradiated tends to be higher in level than the output from the optical black unit 23, in other words, the output from the optical black unit 23 is higher than the actual black signal level. It can correct the tendency to become lower.

Reference numeral 5 denotes a light-shielding film made of, for example, aluminum.
As shown in FIG. 1A, the openings 6 are formed, whereas the photo sensors 22 of the optical black section 23 are not formed with openings as shown in FIG. It is shaded. 7 is a passivation film, 8
Denotes a color filter, and 9 denotes an on-chip micro lens.

As described above, in the present solid-state imaging device, the width W1 of the low-reflection film 4a and the width W2 of the low-reflection film 4b are made different (W1 <W2). The patterning mask film of the low reflection film 4 made of silicon nitride SiN can be easily realized by using a film having a pattern whose widths W1 and W2 have the above-described values.

[0028]

According to the solid-state imaging device of the present invention, the area ratio of the hydrogen shielding insulating film to the photosensor is set independently for the photosensor constituting the light receiving portion and the photosensor constituting the optical black portion. Therefore, the degree of hydrogenation of the dangling bond can be independently adjusted by the photosensor constituting the light receiving portion and the photosensor constituting the optical black portion, and thus the light of the light receiving portion is not incident. The relationship between the output level at that time and the output level of the optical black unit can be arbitrarily adjusted, for example, by setting the level difference to zero.

According to the solid-state image pickup device of the second aspect, the output of the light receiving section when the light is not irradiated tends to be larger than the output of the optical black section, in other words, the output of the optical black section is the actual output. The tendency to be lower than the black signal level can be corrected by increasing the area ratio of the hydrogen shielding insulating film to the photosensor to reduce the degree of hydrogenation of the optical black portion, and consequently the light of the light receiving portion. When the light is not incident, the output level difference between the light receiving section and the optical black section can be made small or zero.

According to the third aspect of the present invention, the silicon nitride SiN used as the hydrogen shielding insulating film is provided.
Does not only function to effectively lower the reflectance in relation to the refractive index with the gate insulating film made of SiO ₂ , but also effectively shuts off the supply path of hydrogen atoms for hydrogenating dangling bonds. The degree of hydrogenation of dangling bonds can be effectively changed in accordance with the difference in the area ratio of the shielding insulating film to the photosensor, and thus the black signal level can be adjusted.

[Brief description of the drawings]

FIGS. 1A and 1B show a main part of an embodiment of a solid-state imaging device according to the present invention, in which FIG. 1A shows a photosensor 19 of a light receiving section 20, and FIG. Part 2
3A and 3B, wherein the upper figure is a cross-sectional view and the lower figure is a plan view in both FIGS.

FIG. 2 is a plan view showing a CCD solid-state imaging device.

FIGS. 3A and 3B show a main part of a conventional example of a solid-state imaging device, and FIG. 3A shows a photosensor of a light receiving unit;
(B) shows a photo sensor of an optical black portion,
In both (A) and (B), the upper figure is a sectional view, and the lower figure is a plan view.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon semiconductor substrate, 2 ... Gate insulating film,
4 ... Hydrogen shielding insulating film (low reflection film made of silicon nitride), 5 ... Light shielding film, 19 ... Photosensor of light receiving section, 20 ... Light receiving section, 22 ... Optical black Photosensor of section, 23... Optical black section.

Claims (3)

[Claims] 1. A light-receiving section having a plurality of photosensors for photoelectrically converting incident light disposed on a surface of a semiconductor substrate, and an optical black section having a photosensor for detecting a black signal level by blocking incident light. And a solid-state imaging device in which a hydrogen-shielding insulating film having a hydrogen-shielding property is formed on the light-receiving portion and the optical black portion, wherein an area of an area of each portion of the hydrogen-shielding insulating film covering each of the photosensors is formed. A solid-state imaging device, wherein the ratio to the area of each photosensor is different between the photosensor constituting the light receiving section and the photosensor constituting the optical black section. 2. A ratio of an area of each portion of the hydrogen shielding insulating film covering each of the photosensors to an area of each of the photosensors, wherein a ratio of an area of the photosensor constituting the optical black section to that of the photosensor constituting the light receiving section is smaller. 2. The solid-state imaging device according to claim 1, wherein the sensor is made larger. 3. The solid-state imaging device according to claim 1, wherein said hydrogen shielding insulating film is made of silicon nitride.