JP3394878B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a CCD type solid-state image pickup device (hereinafter referred to as an area sensor) in which pixels are arranged two-dimensionally.

[0002]

2. Description of the Related Art Area sensors are widely used as image pickup devices for electronic still cameras and video cameras. The structure of the area sensor will be described with reference to the drawings.

FIG. 7 is a plan view showing the structure of a conventional area sensor. This area sensor is arranged two-dimensionally on a semiconductor substrate 11 and includes pixels 12 each including a photoelectric conversion portion for performing photoelectric conversion. A vertical CCD register 13 which is provided between the pixel columns and which vertically transfers the signal charges transferred from the pixels 12, and a horizontal CCD register 14 which is horizontally arranged adjacent to the bottom of the vertical register 13. The output circuit 15 is provided adjacent to the downstream end of the horizontal transfer direction.

To explain the general operation of such an area sensor, the signal charge generated by photoelectric conversion in each pixel 12 by incident light is transferred to a corresponding transfer stage of an adjacent vertical CCD register 13 at a predetermined timing (see FIG. (Not shown), sequentially transferred in the vertical CCD register 13 in the direction of the horizontal CCD register (downward in FIG. 7), transferred from the final stage of the vertical CCD register to the horizontal CCD register 14, and transferred to the horizontal CCD register. The signal charges of one pixel row (line) transferred to 14 are sequentially transferred and output from the output circuit 15 to the outside. In this case, the transfer pulse has two phases or four phases, and the signal charges for each row are read out.

The structure of the vertical CCD register in the area sensor of FIG. 7 will be described with reference to FIGS. 8 and 9. The vertical CCD register 13 has an insulating film 1 on the semiconductor substrate 11.
6, a first transfer electrode 17 made of, for example, polycrystalline silicon and a second transfer electrode 18 similarly made of polycrystalline silicon, with transfer electrode structures overlapping at their ends. It has become. FIG. 9 is a cross-sectional view showing a cross-sectional structure taken along the line AA ′ of FIG. 8. According to this, in the pixel portion, the second transfer electrode 18 is insulated on the first transfer electrode 17. Structures are shown overlapping through the membrane 16.

As is apparent from FIG. 8, the first transfer electrode 17 and the second transfer electrode 18 are provided with notch-shaped recesses 17a and 18a corresponding to the pixels, and have openings formed therein. There is. A light shielding film 19 is formed on the vertical CCD register via an insulating film 16, and an opening 19a is provided corresponding to the pixel portion.
9a is located inside the recesses 17a and 18a of the transfer electrode. Then, a signal charge is generated in the photoelectric conversion portion by the incident light from the opening portion 19a of the light shielding film 19, and the vertical C
It is transferred to the CD register and transferred vertically.

[0007]

In the area sensor of the conventional structure shown in FIGS. 8 and 9, in order to form the opening 19a of the light shielding film 19, a film such as aluminum, which is a light shielding film material, is formed over the entire surface. After the formation, the photoresist is applied, the mask pattern is transferred, and the light-shielding film is patterned by a photo-etching method (hereinafter abbreviated as PEP: Photo Engraving Process) in which etching is performed. Problems occur.

First, the transfer electrode 1 of the vertical CCD register
When the light-shielding film 9 is formed on 7 and 18 by the PEP process as described above, the gap between the inner end of the opening 19a of the light-shielding film 19 and the transfer electrode end ( There is a problem that L1 and L2 in FIG. 8 vary. If the distances L1 and L2 are small, the light blocking becomes insufficient, and the incident light leaks into the vertical CCD register to cause smear, which deteriorates the image quality. This smear characteristic is an important optical characteristic of the area sensor, and in order to stabilize the smear characteristic, it is necessary to suppress the misalignment of the mask pattern to a variation of about ± 0.1 to 0.3 μm. . In order to realize this, it is necessary to design the distances L1 and L2 between the end of the light-shielding film and the end of the transfer electrode to be a few commas to 1 μm more than usual. This not only lowers the degree of integration, but also reduces the aperture width of the light-shielding film by about 0.2 to 0.4 μm, which is 10 to 20% smaller than the aperture width Lo of the light-shielding film (usually about 2 μm). Is reduced.

Second, since the overlapping portion of the transfer electrodes 17 and 18 usually has a step of about 1 μm, the P of the light shielding film 19 is increased.
During the EP process, the register film becomes thicker in the vicinity of this step portion, and as a result, for example, when a positive resist is used, the resist removal pattern becomes smaller than that in the flat portion, and the width of the light-shielding film opening varies. This causes non-uniformity of sensitivity (unevenness of the substrate). To avoid this,
Normally, the distance between the end of the light-shielding film and the end of the transfer electrode needs to be separated by about 1 μm, which also reduces the aperture of the light-shielding film, resulting in a decrease in sensitivity.

In FIGS. 8 and 9 used in the above description, the pixel information of half the total number of pixels is read by one reading.
The so-called interlaced reading type area sensor is shown, but recently, an all-pixel independent reading type area sensor suitable for multimedia use has been developed.

FIG. 10 and FIG. 11 show the structure of such an area sensor of the all-pixel independent reading system.

As shown in FIG. 11 which is a sectional view taken along the line FF 'in FIG. 10, the vertical CCD register has transfer electrodes 23, 2 laminated on a substrate 21 with an insulating film 22 interposed therebetween.
4 and 25 are provided. Each of these transfer electrodes is made of polycrystalline silicon. Further, the entire vertical CCD register is covered with the light shielding film 26, and the opening 26a provided corresponding to the pixel is located inside the end of each transfer electrode.

Three-phase clock pulses are applied to the transfer electrodes of the three layers, and the signal charges of all the pixels can be read out independently of each other.

In the transfer electrode structure having such a structure, it is necessary to pass three transfer electrode wirings between pixels.
As is apparent from the above, the structure has a larger step than the case of FIG. Therefore, it becomes more difficult to form the opening of the light shielding film with PEP, and the vertical CCD
L3 from the edge of the transfer electrode to the edge of the light-shielding film in the direction parallel to
Must be separated by about 1 μm or more. As a result, the light-shielding film 7
However, there is a problem that the aperture size of the device becomes small and the sensitivity is deteriorated.

The present invention has been made in view of the above-mentioned problems of the conventional area sensor, and it is possible to provide a large opening portion with a small step difference between the stacked transfer electrodes, a small alignment margin, and a large opening portion. An object of the present invention is to provide a method for manufacturing an image pickup device.

[0016]

According to the method of manufacturing a solid-state image pickup device of the present invention, the distance between the first transfer electrode and the adjacent transfer electrode in the pixel portion is provided on the one conductivity type semiconductor substrate via the insulating film. Are formed so as to be separated from each other by a distance sufficient to include the pixel portion and are sufficiently closer to each other in the transfer portion, and a portion corresponding to the pixel is formed from an upper surface and a side surface of the first transfer electrode. And a step of forming a light-shielding film so as to fill the space between the adjacent transfer electrodes of the transfer section, and forming an opening in a self-aligned manner in a portion corresponding to the pixel section, and And a step of etching back the light-shielding film so that the filling between the transfer electrodes is maintained.

It is preferable to further include a step of separating the light shielding film of the adjacent transfer stage on the transfer electrode, and a step of further forming a light shielding film in the separated light shielding film portion.

According to the method of manufacturing the solid-state image pickup device of the present invention, the opening for the pixel is formed in a self-aligned manner by using the film thickness difference of the light shielding film caused by the step of the transfer electrode. Since it is not necessary to consider the alignment margin and the variation during PEP, it is possible to improve the accuracy and the integration degree.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing an example of a solid-state image pickup device manufactured by the method for manufacturing a solid-state image pickup device according to the present invention. An insulating film (not shown) is formed on a semiconductor substrate 1.
The transfer electrodes 3 are arranged in the vertical direction with a predetermined pitch therebetween. Similar to the case of FIG. 8, this transfer electrode has a sufficiently large concave portion 3a so that the pixel is included in the pixel portion, and the convex portion 3b forms the transfer portion.

A light-shielding film 4 made of a metal material such as aluminum or a refractory metal silicide such as molybdenum silicide or titanium silicide is provided on the entire surface including the transfer portion, and an opening portion is formed corresponding to the pixel portion. Four
a is formed.

FIG. 2 is a sectional view showing the AA 'section of FIG.

According to the figure, since the light shielding film is formed on the transfer electrode 3 of one layer via the insulating film 2, the step difference is smaller than that of the conventional structure. In this way, it is possible to reduce the step of the transfer electrode and improve the reliability.

In this figure, two light-shielding films 4-1 and 4-2 on the transfer electrode 3 face each other with a gap 5 therebetween. This is because, as will be described later, because the light-shielding film 4 is used as a transfer electrode, an independent voltage can be applied at the transfer stage.

3A and 3B are cross-sectional views showing a cross section taken along the line BB ′ in FIG. 1, where FIG. 3A shows a state after the light-shielding film is deposited, and FIG. 3B shows a state after the etching. In addition, the deposition of the light shielding film is
In the case of a metal film, vapor deposition is performed, and in the case of a refractory metal silicide film, it is performed by a CVD method or the like.

This BB 'cross-section position is a place where the pixel portion exists, and the gap L1 between the adjacent transfer electrodes 3 is large. At such a position, due to the influence of the step, FIG.
As shown in, the thicker portion 4b is formed on the upper surface and the upper side surface of the transfer electrode, and the thinner portion 4c is formed on the lower side surface and the pixel position.

FIG. 3B shows a state in which the state of FIG. 3A is etched back by anisotropic etching such as RIE. By this etching back, the light-shielding film in the pixel portion is completely removed and the opening having the width L1 is formed in a self-aligned manner, but the light-shielding film remains in the transfer electrode portion although the film thickness is reduced.

Since it is possible to form the openings in a self-aligning manner in this manner, it is not necessary to take a large margin for mask misalignment, and the light-shielding film opening size is set to the conventional one.
It can be expanded by 20% to improve the sensitivity.

4A and 4B are cross-sectional views showing the CC ′ cross section of FIG. 1, where FIG. 4A shows the state after the light-shielding film has been deposited, and FIG. 4B shows the state after the etching. At this position, the distance L2 between adjacent transfer electrodes is short, so that the gap between the transfer electrodes is completely filled with the light-shielding film after the light-shielding film is deposited, as shown in FIG. On the contrary, the gap L2 is required so that the filling is performed, and the film thickness needs to be sufficient so that the filling is surely performed. When etching back is performed in this state, as shown in FIG. 4B, the film thickness is simply reduced, the state in which the gap is filled remains unchanged, and the entire vertical CCD register section is covered. It becomes a state.

In order to use the light-shielding film 4 as a transfer electrode, patterning is required so that the light-shielding film and the transfer electrode 3 are alternately arranged. Therefore, as shown in FIG. 1, the light-shielding film is striped so that the light-shielding film 4 is separated on the transfer electrode 3. At the time of etching the stripe-shaped light-shielding film, PEP is appropriately performed to cover a necessary portion, so that the element can be protected.

Light-shielding becomes incomplete due to the removal of the stripes. Therefore, after the state shown in FIG. 2, it is necessary to form a light-shielding film again on the removed portion via an insulating film. In this case, since the periphery of the transfer electrode pattern around the pixel portion is covered with the light shielding films 7-1 and 7-2, it is sufficient that the second light shielding film to be added has a width capable of covering only the gap. Is. Further, the gap on the transfer electrode 5 between the pixels may be covered if necessary.

Next, an example in which the present invention is applied to an all-pixel reading type area sensor will be described with reference to FIG. 5 and FIG. 6 which is a sectional view taken along the line D-D '.

This is obtained by replacing the transfer electrode of the third layer with a light shielding film in the conventional type described with reference to FIGS. That is, as shown in FIG. 6, a first-layer electrode 3 made of polycrystalline silicon, a second-layer electrode 6 made of polycrystalline silicon, and a metal layer serving also as a third-layer electrode on the semiconductor substrate 1 with an insulating film 2 interposed therebetween. Alternatively, the light shielding layer 7 which is a refractory metal silicide layer is formed in a laminated state.
As is apparent from FIG. 5, the portions of the vertical CCD register not covered with the transfer electrodes 3 and 6 are covered with the light shielding film 7, and the cross-sectional shape of the state covered with the light shielding film is as shown in FIGS. Is the same as.

In the three-phase drive all-pixel readout type area sensor, the same phase is applied to the third-layer transfer electrode formed of the light-shielding film 7, so that it is necessary to separate the electrodes differently from the case of FIG. There is no.

Various modifications of the present invention are possible other than the above-described embodiment. For example, not only the light-shielding film can be used as the transfer electrode, but also the transfer gate from the pixel to the vertical CCD register can be additionally used.

[0036]

According to the solid-state imaging device manufacturing method of the present invention, the opening for the pixel is formed in a self-aligned manner by using the film thickness difference of the light shielding film caused by the step of the transfer electrode. As a result, it is possible to improve the accuracy and the degree of integration without having to consider the mask alignment margin and the variation during PEP.

[Brief description of drawings]

FIG. 1 is a plan view illustrating a cell structure of an area sensor manufactured by a method of the present invention.

FIG. 2 is a cross-sectional view showing a cross-sectional structure taken along the line AA ′ in FIG.

FIG. 3 is a BB ′ of FIG. 1 before and after a photo-etching process.
Sectional drawing according to process which shows the cross-section along the line.

FIG. 4 is the CC ′ of FIG. 1 before and after the photo-etching process.
Sectional drawing according to process which shows the cross-section along the line.

FIG. 5 is a plan view illustrating a cell structure of an all-pixel readout type area sensor manufactured according to the present invention.

FIG. 6 is a cross-sectional view illustrating a cell structure of an all-pixel readout type area sensor manufactured according to the present invention.

FIG. 7 is a diagram illustrating a configuration of a conventional area sensor.

FIG. 8 is a plan view illustrating a cell structure of a conventional area sensor.

FIG. 9 is a sectional view illustrating a cell structure of a conventional area sensor.

FIG. 10 is a plan view illustrating a cell structure of a conventional all-pixel reading type area sensor.

FIG. 11 is a cross-sectional view illustrating a cell structure of a conventional all-pixel readout type area sensor.

[Explanation of symbols]

1,11,21 Semiconductor substrate 2,16,22 Insulation film 3, 17, 18, 23, 24, 25 Transfer electrodes 4,19,26 Light-shielding film 12 pixels 13 Vertical CCD register 14 Horizontal CCD register 15 Output circuit

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Claims (3)

(57) [Claims] 1. A first transfer electrode is separated from an adjacent transfer electrode in a pixel section by a distance sufficient to include the pixel section on an electrically conductive semiconductor substrate with an insulating film interposed therebetween. And a step of forming them so as to be sufficiently closer to each other, and a portion corresponding to the pixel is thinner than the upper surface and the side surface of the first transfer electrode so that the space between the adjacent transfer electrodes of the transfer section is embedded. Forming a light-shielding film, and forming an opening in a portion corresponding to the pixel portion in a self-aligning manner, and etching back the light-shielding film so that the filling between the transfer electrodes of the transfer portion is maintained. A method of manufacturing a solid-state imaging device, comprising: 2. The method of manufacturing a solid-state imaging device according to claim 1, further comprising a step of separating a light shielding film of an adjacent transfer stage on the transfer electrode. 3. The method for manufacturing a solid-state imaging device according to claim 2, further comprising the step of forming a light-shielding film on the separated light-shielding film portion.