JP2002124653A - Solid-state image-pickup element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To thin the shading film of a solid image-pickup element. SOLUTION: In the solid-state image-pickup element, a shading film 44 is formed on the region of an effective pixel region 36, wherefrom light receiving portions 1 dare excluded. The shading film 44 is formed of a plurality of films, so that they include at least an aluminum layer 41 and an aluminum oxide layer 42.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a solid-state imaging device.

[0002]

2. Description of the Related Art For example, a frame interline transfer (FIT) type, an interline transfer (I
In a CCD solid-state imaging device of the T) type or the like, as shown in FIG. 4, a plurality of light receiving sections 1 serving as pixels are arranged in a matrix, and a vertical transfer register 2 having a CCD structure is provided on one side of each light receiving section row. A so-called optical black area for defining a black reference level on an area including at least the vertical transfer register 2 except for the light receiving section 1 of the effective pixel area 4 of the effective pixel area 4 of the imaging section 3 5, a light-shielding film, for example, an Al light-shielding film 6 is formed on the entire surface of the light-emitting element 5 as indicated by oblique lines.

FIG. 5 is a diagram showing A in the effective pixel area 4 shown in FIG.
1 shows an example of a cross section on line A. Reference numeral 11 denotes a first conductivity type, for example, an N-type silicon substrate. An N-type impurity diffusion region 13 and a vertical transfer register 2 are formed in a first second conductivity type, that is, a P-type well region 12 on the substrate 11. N-type transfer channel region 14 and P-type channel stop region 1
5, a P-type positive charge accumulation region 16 is formed on the N-type impurity diffusion region 13, and a second P-type well region 17 is formed immediately below the N-type transfer channel region 14. Here, the light receiving unit (photoelectric conversion unit) 1 is constituted by the photodiode PD formed by the PN junction j between the N-type impurity diffusion region 13 and the P-type well region 12.

A transfer electrode 19 made of polycrystalline silicon is formed on the transfer channel region 14, the channel stop region 15, and the readout gate portion 7 constituting the vertical transfer register 2 via a gate insulating film 18. The vertical transfer register 2 is constituted by 14, the gate insulating film 18 and the transfer electrode 19.

[0005] An interlayer insulating film 20 is laminated on the transfer electrode 19 and the entire surface including the positive charge accumulation region 16, and is further formed on the interlayer insulating film 20 corresponding to the transfer electrode 19 to a thickness of, for example, about 800 nm by sputtering or the like. The formed metal light shielding film 6 of aluminum or the like is selectively formed. A surface protection film 22 is formed on the upper layer.

The Al light-shielding film 6 blocks light that is directly incident on the vertical transfer register 2, reduces the occurrence of smear due to the light incident in the effective pixel area 4, and electrically prevents the optical black area 5 from emitting light. A black reference level is defined.

[0007]

In recent years, with the high integration of solid-state imaging devices, it has become necessary to reduce the size not only in the planar direction of the device but also in the thickness direction in consideration of disconnections and the like. Have been. However, when the thickness of the metal light-shielding film 6 is reduced, the grain boundaries of the crystal grains 24 of the metal light-shielding film 6 are easily aligned as shown in FIG. When this occurs, light is transmitted through the pinhole 25 and the light-shielding property is reduced. Therefore, in the effective pixel region 4, the smear due to the transmitted light 26 increases, causing a problem that the solid-state imaging device is defective.

On the other hand, in the optical black area 5, there arises a problem that the reference level of black fluctuates due to light transmission.

SUMMARY OF THE INVENTION In view of the above, the present invention provides a solid-state image pickup device which secures light-shielding properties even when the thickness of a light-shielding film is reduced, and achieves high reliability.

[0010]

According to the present invention, there is provided a solid-state imaging device comprising a light-shielding film formed on an area other than a light-receiving portion in an effective pixel area, wherein the light-shielding film comprises a plurality of films. The plurality of films are formed so as to include at least an aluminum layer and an aluminum oxide layer. Further, according to the present invention, in the solid-state imaging device, the light-shielding film is formed of a three-layer film, an aluminum oxide layer as a second layer is formed on an aluminum layer as a first layer, and an aluminum oxide layer is formed on the aluminum oxide layer. The structure is such that an aluminum layer as a third layer is formed.

In the present invention, since the light-shielding film is formed of a plurality of films including at least an aluminum layer and an aluminum oxide layer, the continuity of the crystal orientation of the light-shielding film is cut off when the light-shielding film is thinned. That is, even if the light-shielding film is thinned with the high integration of the solid-state imaging device, the light-shielding property of the light-shielding film is ensured. Therefore, the smear component is reduced, and the reference level of black in the optical black area does not change. When a light-shielding film having a three-layer film structure in which an aluminum layer is disposed above and below an aluminum oxide layer is formed, light-shielding properties when the light-shielding film is made thinner are further improved, smear components are reduced, and an optical black region is formed. Of the black reference level can be stabilized.

[0012]

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

FIGS. 1 and 2 show an embodiment in which the present invention is applied to a frame interline transfer (FIT) type CCD solid-state imaging device. As shown in FIG. 1, a FIT-type CCD solid-state imaging device 30 according to the present embodiment has a plurality of light-receiving units 1 serving as pixels arranged in a matrix, and has a vertical CCD structure on one side of each light-receiving unit row. The imaging unit 31 provided with the transfer register 2 and the CCs corresponding to the plurality of vertical transfer registers 2 of the imaging unit 31 on a one-to-one basis.
A storage unit 33 provided with a plurality of vertical transfer registers 32 having a D structure; a horizontal transfer register 34 having a CCD structure disposed on one side of the storage unit 33; and an output circuit connected to the output side of the horizontal transfer register 34 35. The other area including the vertical transfer register 2 except the light receiving section 1 of the effective pixel area 36 in the imaging section 31 and the so-called optical black area 37 for defining the black reference level and the entire surface of the horizontal transfer register 34 As shown in the figure, a light-shielding film 44 described later is formed as shown by oblique lines.

In the CCD solid-state imaging device 30, the signal charges photoelectrically converted in each light receiving section 1 in accordance with the amount of light received are read out to the vertical transfer register 2, and the vertical transfer register 2
And is temporarily stored in the vertical transfer register 32 of the storage unit 33. Then, the signal charges are transferred to the horizontal transfer register 34 for each horizontal line, sequentially transferred in the horizontal transfer register 34, and output through the output circuit 35.

In this embodiment, the light shielding film 38 is configured as shown in FIG. FIG. 2 shows a cross-sectional structure of the effective pixel region 36 (a cross-sectional view taken along line BB in FIG. 1). In the effective pixel region 36, the first second conductivity type, that is, the P-type well region 1 on the first conductivity type, for example, the N-type silicon substrate 11 is formed.
2, an N-type impurity diffusion region 13, an N-type transfer channel region 14 constituting the vertical transfer register 2 and a P-type channel stop region 15 are formed, and a P-type impurity diffusion region 13 is formed on the N-type impurity diffusion region 13. The positive charge storage region 16
Second P-type well regions 17 are formed directly below the transfer channel regions 14, respectively.

Here, the photodiode PD by the PN junction j between the N-type impurity diffusion region 13 and the P-type well region 12 constitutes the light receiving section (photoelectric conversion section) 1. On the transfer channel region 14, the channel stop region 15, and the read gate unit 7 that constitute the vertical transfer register 2,
A transfer electrode 19 made of, for example, polycrystalline silicon is formed with a gate insulating film 18 interposed therebetween.
4. The vertical transfer register 2 is constituted by the gate insulating film 18 and the transfer electrode 19. An interlayer insulating film 20 is formed on the entire surface including the transfer electrode 19 and the positive charge accumulation region 16.

In the present embodiment, the transfer electrode 19
A light-shielding film is formed of a plurality of films including at least an aluminum layer and an aluminum oxide layer on the portion of the interlayer insulating film 20 corresponding to. In the example of FIG. 2, a first layer of aluminum (Al) thin film 41, a second layer of aluminum oxide thin film 42, and a third layer of aluminum (Al) thin film 43
A light-shielding film 44 having a three-layer film structure is formed. Second
The aluminum oxide thin film 42 of the first layer has a crystal orientation different from that of the first and third aluminum thin films 41 and 43. Here, the aluminum thin film 4
Reference numerals 1 and 43 include pure Al, Al containing a small amount of Si, and the like, as described later. This light-shielding film 44 is formed by sputtering and oxidation. Reference numeral 22 denotes an uppermost surface protective film.

The light-shielding film 44 is provided by D.S. The film is formed using a C magnetron sputtering apparatus and oxygen plasma processing. D. The C magnetron sputtering apparatus has a vacuum transfer chamber in the center, a pre-evacuation chamber, and an Al-1% Si
It has a processing chamber and the like to which a target is attached. First,
D. The silicon substrate on which the solid-state imaging device is built is transported to the processing chamber of the C magnetron sputtering apparatus, where the Al-1% Si thin film 41 as the first thin film is deposited.
Is formed to a thickness of 200 nm. The conditions at this time were as follows: the pressure of the argon gas was 8 mTorr, 6K C power
W, the sputtering time was 18 sec. Al deposited
The -1% Si thin film 41 becomes a columnar crystal having a (111) crystal orientation.

Next, the silicon substrate is transported to an oxygen plasma processing chamber, and the surface of the first Al-1% Si thin film 41 is subjected to oxygen plasma processing to form a second aluminum oxide thin film 42. I do.

Next, the silicon substrate is again placed in D. C is transferred to the processing chamber of the magnetron sputtering apparatus, and the third layer of Al-1% S is formed on the second layer of the aluminum oxide thin film 42.
An i thin film 43 is formed to a thickness of 200 nm. Al-1%
The Si thin film 43 has a (111) crystal orientation,
The lattice constant is 2.863 °.

FIG. 3 is a schematic view of the light-shielding film 44 formed. The crystal orientation of the Al-1% Si thin film 421 of the first layer is determined by the aluminum oxide thin film 42 of the second layer (intermediate film).
Is cut off. That is, since the third Al-1% Si thin film 43 of the third layer does not inherit the columnar crystal of the lower Al-1% Si thin film 41 of the first layer as it is, the crystal grain boundaries through which the light 45 passes are cut off. It will be. The aluminum oxide thin film 42 of the second layer disturbs the crystal orientation of the Al thin film 43 of the third layer.

By the above steps, the Al-1% Si thin film 4
1. A light-shielding film 44 having a three-layer structure of an aluminum oxide thin film 42 and an Al-1% Si thin film 43 is obtained. In the subsequent steps, the film having the three-layer film structure is etched into a desired pattern by using a method similar to a usual method, and a target solid-state imaging device is formed.

According to the above-described embodiment, the light shielding film 44
Al-1% S so as to break the continuity of crystal orientation
i thin film 41, aluminum oxide thin film 42 and Al-1%
The light shielding property of the light shielding film 44 can be improved by forming the light shielding film 44 with a laminated film including the Si thin film 43. Therefore, as the solid-state imaging device becomes more highly integrated, the light-shielding film can be made thinner, and a highly reliable solid-state imaging device having less smear components and having no fluctuation in the black reference level can be obtained.

In the above example, the same Al-1% Si thin film is used as the first thin film 41 and the third thin film 43, but the two thin films 41 and 43 may be different from each other. For example, the first layer may be an Al-1% Si thin film, the second layer may be an aminium oxide thin film, and the third layer may be a W thin film.
Further, the light-shielding film can be formed with a two-layer film structure. That is, the first layer can be an Al-1% Si thin film, and the second layer can be an aluminum oxide thin film.

The first thin film is preferably made of Al-1 which is suitable for contacting a silicon region in another part.
Instead of using% Si, for example, the lower half in contact with the silicon surface of the first-layer thin film may be made of Al-1% Si, and the upper half may be made of pure Al. The third layer can also be formed of pure Al.

In the above example, the present invention is applied to a FIT type CCD solid-state image pickup device.
The present invention can also be applied to a T) type CCD solid-state imaging device or the like.

[0027]

According to the present invention, the light-shielding properties of the light-shielding film can be improved even when the film thickness is reduced. Therefore, the thickness of the light-shielding film can be reduced, and a highly reliable and highly integrated solid-state imaging device can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a sectional view taken on line BB of FIG. 1;

FIG. 3 is a schematic diagram of a light-shielding film according to the present embodiment.

FIG. 4 is a configuration diagram of an imaging unit of a solid-state imaging device for explaining a conventional example.

FIG. 5 is a sectional view taken along line AA of FIG. 4;

FIG. 6 is a schematic diagram of a conventional Al light-shielding film having a single-layer structure.

[Explanation of symbols]

1 ... light-receiving unit, 2, 32 ... vertical transfer register,
3, 31: imaging unit, 4, 36: effective pixel area,
5, 37: optical black area, 6: light-shielding film, 33: storage unit, 34: horizontal transfer register, 35: output circuit, 41: first-layer thin film, 4
2 ... second layer thin film, 43 ... third layer thin film, 44
... Shading films

Claims (2)

[Claims] 1. A solid-state imaging device having a light-shielding film formed on a region other than a light-receiving portion of an effective pixel region, wherein the light-shielding film is formed of a plurality of films, and the plurality of films are at least aluminum layers. And a solid-state imaging device comprising an aluminum oxide layer. 2. The light-shielding film comprises a three-layer film, a second layer of an aluminum oxide layer is formed on an aluminum layer of a first layer, and a third layer is formed on the aluminum oxide layer. The solid-state imaging device according to claim 1, wherein an aluminum layer is formed.