JPH05190818A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To obtain a solid-state image sensing apparatus having the high sensitivity and the excellent smear characteristic without machining irregularities. CONSTITUTION:A first polysilicon layer 2, a second polysilicon layer 3, an SiO2 insulating film 13 and an SiN film 14 are formed. Thereafter, a second aluminum lower film 6A with a thickness of 8,000Angstrom is formed around a device. The aluminum lower film 6A is patterned. Thereafter, a second aluminum upper film 6B is formed on the entire surface to a thickness of 2,000Angstrom . Then, resist 7 is patterned by lightography technology. Wet etching is performed, and only the second aluminum upper film 6B is removed. Thus a picture element part is opened. Therefore, the part between the picture element parts is covered with a light shielding film. Since the second aluminum upper film 6B is thin, the effective incident light from the side of a lens is not rejected, and the sensitivity is improved. Since the machinability is excellent, an undercut is not generated, and the smear characteristic is improved.

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 pickup device, and more particularly, to a structure of a CCD imager which has good workability and has improved optical characteristics.

[0002]

2. Description of the Related Art Conventionally, as a solid-state image pickup device of this type,
With a two-layer aluminum electrode structure, the second aluminum electrode layer is used as light shielding between pixels. FIG. 4 is a plan view of an imager unit of an interline type solid-state imaging device having a pn junction photodiode as a light receiving element and using a CCD as a vertical scanning circuit. In the figure, 1 is a pn junction photodiode which constitutes a pixel, and 2 is a CCD.
A transfer electrode 3 made of a first polysilicon layer for vertical transfer to the CCD, a transfer electrode 3 made of a second polysilicon layer for making vertical transfer to the CCD similarly to the transfer electrode 2,
Is a polysilicon wiring, 5 is a first aluminum layer forming a shunt wiring of a vertical transfer portion, 6 is arranged in a stripe shape in the horizontal transfer direction so as to shield light between pixels, and is formed as a peripheral wiring in the periphery of the device. 2 shows a second aluminum layer to be formed. Since the second aluminum layer 6 also serves as the wiring of the peripheral pass line portion, the thickness thereof is set thick.

FIG. 5 (A) is a sectional view of the imager portion corresponding to the AA section of FIG. 5 when the second aluminum layer 6 is patterned, and FIG. 5 (B) is also the second aluminum layer. Around the device when patterning 6
FIG. 4 is a cross-sectional view of a pass line portion where a first aluminum layer 5 and a second aluminum layer 6 intersect. As shown in FIG. 5A, in the patterning of the second aluminum layer 6 in the imager section, the resist mask 7 is patterned and the second aluminum layer 6 on the pixel section is wet-etched. At the same time, as shown in FIG. 5B, the resist mask 7 is formed on the second aluminum layer 6 also in the pass line portion around the device.
Are formed, and wet etching is performed for patterning.

In FIGS. 5 (A) and 5 (B), 8 is a silicon substrate in which a p well 9 is formed, and n is formed near the surface.
^{A +} diffusion region 10 is formed. Further, 11 is a first polysilicon layer, 12 is a second polysilicon layer, and 13 is Si.
O ₂ insulating film, 14 is S formed by plasma CVD method
The iN film is shown.

[0005]

In such a conventional solid-state image pickup device, since the plasma SiN film 14 having a high insulating property is formed under the second aluminum layer 6, the patterning of the second aluminum layer 6 is performed. In the case of dry etching, the selection ratio cannot be obtained by dry etching, and wet etching is used. However, when wet etching is performed, the cross section of the second aluminum layer 6 is undercut and becomes an overhang shape as shown in FIG. 6, so that the aluminum layer 6 is not covered up to the bottom and is shielded from light. There is a problem that the smear characteristic deteriorates and the smear characteristic deteriorates. Further, since there are many side etches, instability of workability is caused.
Further, as shown in FIG. 6, when the light is incident after the on-chip lens 15 is formed, the second aluminum layer 6 is thick, so the light passing through the lens end is kicked and the sensitivity is lowered. Is invited. In particular, when a lens of an actual camera is attached, the obliquely incident light increases toward the edge of the CCD image area, and the component kicked by the aluminum layer 6 (second layer) increases, resulting in a decrease in sensitivity, that is, sensitivity shading. The structure makes it easy to wake up. In addition, aluminum has a problem in that unevenness in sensitivity is large because the surface of aluminum is uneven due to crystallization, and the amount of light that is struck by each pixel is different.

The present invention was devised by focusing on such conventional problems, and the incident light efficiently reaches the pixel portion to have high sensitivity, and the workability of the light shielding film is high. It is intended to obtain a solid-state imaging device.

[0007]

Therefore, according to the present invention, the aluminum film of the first layer is used for the shunt wiring of the vertical transfer register portion of the transfer electrode and the light shielding film of the vertical transfer register portion, and the aluminum film of the second layer is used. In the solid-state imaging device in which is used as the light-shielding film of the transfer electrode on at least the vertical pixel separation region, the second-layer aluminum film has a thin film thickness in the light-shielding film part of the transfer electrode and a thick film in other regions. The solution is to be thick.

[0008]

Since the second-layer aluminum film is formed so as to have a small thickness in the light-shielding film portion of the transfer electrode, incident light is not blocked and the line width variation due to wet etching is reduced. Since the overhang shape due to undercut does not occur, it is possible to prevent the smear characteristic from being deteriorated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the solid-state image pickup device according to the present invention will be described below with reference to the embodiments shown in the drawings. It should be noted that the same parts as in the prior art will be described with the same reference numerals.

In this embodiment, the present invention is applied to a structure having two aluminum layers, and the second aluminum layer is also used as a light shielding film between pixels, and its plan view is shown in FIG. Is the same as that shown in.

First, FIG. 1A is a sectional view of the imager portion, showing a state in the middle of a processing step of a portion corresponding to the section AA in FIG. In the figure, 8 is a silicon substrate, and a p well 9 and an n ⁺ diffusion region 10 are formed in this substrate 8. In addition, a first polysilicon layer 11 and a second polysilicon layer 12 which are transfer electrodes are formed on the surface of the silicon substrate 8 via a gate insulating film. Reference numeral 13 is a SiO ₂ insulating film which is interposed between the first polysilicon layer 11 and the second polysilicon layer 12 and covers the surfaces of both polysilicon layers 11 and 12 and the surface of the silicon substrate 18. A SiN film 14 formed by a plasma CVD method is formed on the surface of the SiO ₂ insulating film 13. At this time, the cross section of the pass line portion around the device is as shown in FIG. 1B, and the SiO ₂ insulating film 13 formed on the silicon substrate 8 is formed.
The first aluminum layer 5 is formed by patterning on the O ₂ insulating film 13, and the SiN film 14 is formed thereon. A film thickness of 8000 is formed on the SiN film 14.
A relatively thick second aluminum lower layer film 6A having a thickness of about Å is patterned.

Next, referring to FIG.
As shown in (A), a film thickness of 2000 is formed on the SiN film 14.
A relatively thin second aluminum layer film 6B having a thickness of about Å is deposited by the sputtering method.

The second aluminum upper layer film 6B is simultaneously deposited on the pass line portion around the device, and is also deposited on the SiN film 14 and the second aluminum lower layer film 6A as shown in FIG. 2B. ing. Then, in the imager portion, the resist 7 is patterned above the transfer electrode portion as shown in FIG. 2 (A), and in the pass line portion, the resist 7 is patterned as shown in FIG. 2 (B). Then, the second aluminum upper layer film 6B is patterned by wet etching using the resist mask 7 as a mask. At this time, since the second aluminum upper layer film 6B is thin, side etching is small, and the pixel opening is stably processed. Further, in the peripheral portion of the device, as shown in FIG. 3B, a desired film thickness 1 is formed between the second aluminum lower layer film 6A and the second aluminum upper layer film 6B.
It is possible to form an integral aluminum wiring of about μm.

FIG. 3A is a sectional view showing a state in which the on-chip microlens 15 is formed on the imager section, and shows a state of light incident on the pixel. Since the light-shielding film made of the second aluminum upper layer film 6B is thin, the light bent by the lens is effectively incident on the pixel (sensor unit) without being blocked by the second aluminum upper layer film 6B.

As described above, it is preferable that the light-shielding aluminum layer between the pixels has a thin film thickness as long as the light-shielding property is not lost, and the film thickness cannot be thinned when it is formed at the same time as the second aluminum layer which becomes the peripheral wiring.

As described above, the second aluminum layer having a film thickness necessary for the peripheral wiring is divided into the second aluminum lower layer film 6A and the second aluminum upper layer film 6B to form the wiring portion. Since the film thickness of the light shielding part can be set independently, the optimum aluminum film thickness can be set according to the pixel part opening, the lens curvature, and the height.

Although the embodiment has been described above, the present invention is not limited to this, and various design changes associated with the gist of the configuration can be made.

[0018]

As is apparent from the above description, in the solid-state image pickup device according to the present invention, since the second-layer aluminum film serving as the light-shielding film between pixels can be thinly formed, the line width variation due to wet etching can be prevented. It can be suppressed to a small value, and it is effective in preventing uneven sensitivity between pixels. Further, even after forming the on-chip microlens, effective incident light is not blocked by the light-shielding film and effectively enters the pixel portion, so that sensitivity is improved and sensitivity shading is reduced.

Further, since the film thickness of the second aluminum layer used for shading between pixels can be set independently of the aluminum layer forming the peripheral wiring, there is an effect that the optimum film thickness can be set for each element.

Further, since the second aluminum layer used for shading between pixels has a good workability, it does not have an overhang shape and can sufficiently cover the inter-pixel portion, which has the effect of improving smear characteristics.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a sectional view of an embodiment of the present invention.

FIG. 3 is a sectional view of an embodiment of the present invention.

FIG. 4 is a plan view of a solid-state imaging device.

FIG. 5 is a sectional view of a conventional example.

FIG. 6 is a sectional view of a conventional example.

[Explanation of symbols]

1 ... Pixel part, 2 ... 1st polysilicon layer, 3 ... 2nd polysilicon layer, 5 ... 1st aluminum layer, 6A ... 2nd aluminum lower layer film, 6B ... 2nd aluminum upper layer film.

Claims (1)

[Claims] 1. A first-layer aluminum film is used for a shunt wiring of a vertical transfer register portion of a transfer electrode and a light-shielding film of the vertical transfer register portion, and a second-layer aluminum film is at least on a vertical pixel separation region. In the solid-state imaging device used for the light-shielding film of the transfer electrode, the second-layer aluminum film has a thin film thickness in the light-shielding film portion of the transfer electrode and a large film thickness in other regions. apparatus.