JP2838816B2 - Solid-state imaging device and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a back-illuminated solid-state imaging device which uses light incident from the back surface of a semiconductor substrate (the surface on which a light receiving portion is not formed) and a method of manufacturing the same.

[0002]

2. Description of the Related Art An infrared solid-state imaging device is an example of a back-illuminated solid-state imaging device. First, an outline of the infrared solid-state imaging device will be described with reference to FIG. In FIG. 2, a plurality of light receiving units 101 are arranged in a matrix (4 × 4 in the figure) in an imaging region 111, and charges for transferring charges photoelectrically converted by the light receiving units 101 for each column. Transfer means (vertical CCD 102) is formed. Outside the imaging area 111, a charge transfer means (horizontal CCD 112) connected to each vertical CCD 102 is provided along the row direction, and the charges carried by the vertical CCD 102 are further transferred by the horizontal CCD 112. Output terminal 11
3 to the outside.

Here, the operation of the infrared solid-state imaging device of FIG. 2 is as follows. First, in the first period of T ₀ → T ₁ , incident light is photoelectrically converted by each light receiving unit 101 and accumulated in the light receiving unit. The charges generated during the period of T ₀ → T ₁ are simultaneously transmitted from each light receiving unit 101 to the vertical CCD ₁₀ at time T ₁ .
2 (indicated by arrow i). The charges transferred to the vertical CCD 102 are all transferred to the horizontal CC in the subsequent period of T ₁ → T _2.
D112 (shown by arrow j) and read from output terminal 113. To perform the above operation, the vertical CCDs 102 in each column must be driven at the same timing.

Next, a conventional wiring structure employed for driving each vertical CCD 102 at the same timing will be described with reference to FIG. FIG. 3 (a)
FIG. 3B is a schematic plan view showing the light receiving unit 101 and the vertical CCD 102 in an enlarged manner in detail, and FIG.
BB 'sectional drawing of FIG. In FIG. 3, each light receiving unit 101
Columns have charge transfer means (vertical CCD) 102a, 102
b is provided as described with reference to FIG.
Each light receiving portion 101 is surrounded by element isolation regions 107 and 108, and first electrodes 103a and 103b and second electrodes 104a and 104b are provided alternately on each of the vertical CCDs 102a and 102b (FIG. 3A). In this example, the first electrode is provided with an oblique line rising to the right, and the second electrode is provided with an oblique line rising to the left. The first electrode and the second electrode (103a and 104a, 103b
And 104b) are laminated via an insulating layer 109 as shown in the cross-sectional view of FIG.

Charges are transferred by applying a predetermined clock pulse to the first electrodes 103a, 103b and the second electrodes 104a, 104b. As described above, the vertical CCDs 102a, 102b in each column are at the same timing. Since it is necessary to drive the first electrodes (103
a and 103b), the second electrode (104a and 104b)
Are connected to each other using an element isolation region 108 provided between the light receiving units 101 adjacent in the column direction (the wiring unit is shown by a dotted line in the figure).

As shown in the partial sectional view of FIG. 3 (c), a wiring portion connects a wiring 106a for connecting the first electrodes and a second electrode on the element isolation region (selective oxide film) 108. The wiring 106b has a structure in which the wiring 106b is stacked via an insulating layer.

Next, a conventional method for manufacturing the above-described infrared solid-state imaging device will be described with reference to FIG. First, the surface of the semiconductor substrate 110 is selectively oxidized to provide element isolation regions 107 and 108. Next, the first electrodes 103a, 103a are formed using polysilicon doped with P (phosphorus) or the like.
03b and a wiring 106a connecting the first electrode are formed,
Cover with an insulating layer 109. After that, a wiring 106b for connecting the second electrodes 104a and 104b and the second electrode is formed on the insulating layer 109 using the same polysilicon. Thereafter, a silicide layer is provided on the light receiving unit 101, and the front surface is further covered with an insulating layer 109. Although not shown in the figure, a reflective film made of Al or the like may be further provided on the uppermost insulating layer 109 in order to increase the utilization efficiency of incident light.

[0008]

One problem with a solid-state imaging device such as the above-described infrared solid-state imaging device is to increase the number of pixels to increase the spatial resolution and improve the resolution. Increasing the number of pixels while keeping the imaging area of the solid-state imaging device constant inevitably reduces the pixel size, and accordingly, the size of the light receiving unit also decreases, causing a problem that the photodetection sensitivity decreases. . Therefore, in order to solve this problem, the area ratio occupied by the light receiving portion in one pixel (hereinafter, referred to as an aperture ratio).
It is extremely important to prevent the decrease in the photodetection sensitivity when the number of pixels is increased by increasing the number of pixels.

Here, returning to FIG. 3 again, problems in the prior art will be described. In FIG. 3, the range of one pixel can be considered as a region A surrounded by a thick line,
As is clear from the figure, one pixel A includes the light receiving unit 101, the vertical CCD 102a, and the light receiving unit 101 and the vertical CCD 102a.
And an element isolation region 108 provided between the light receiving units 101 in the same column and provided with wiring for connecting the respective electrodes of the CCD. Of these, it is desirable that both of the element isolation regions 107 and 108 be as narrow as possible. As the element isolation regions 107 and 108 become narrower, the light receiving portion 101 can be made wider by that amount, thereby preventing a decrease in photodetection sensitivity when the aperture ratio is increased and the number of pixels is increased.

However, in the solid-state imaging device according to the prior art, the element isolation region 107 having no wiring can be narrowed within a range permitted by the electrical characteristics of element isolation. However, a wiring for connecting the CCD electrodes to each other is provided. In fact, the element isolation region 108 cannot be narrowed to the same level as the region 107. The reason will be described below.

As described above, the CCD first electrode 103
a, 103b and CCD second electrodes 104a, 104b
After the formation of the element isolation regions 107 and 108 is completed,
Before the light receiving portion 101 is formed, it is formed using polysilicon, and the wirings 106a and 106b connecting the electrodes are also formed using polysilicon simultaneously with the electrodes.
Here, polysilicon has a higher resistance than a metal material such as Al. Therefore, when polysilicon is used as the wiring material, it is necessary to reduce the wiring resistance by increasing the wiring width to some extent. As a specific example, in the region 108, a polysilicon wiring (10) for connecting the CCD first electrodes and the CCD second electrodes to each other is used.
The width of 6a, 106b) needs to be about 1.5 to 2.0 μm. On the other hand, the separation width of the region 107 is 1.0
Sufficient electrical characteristics can be ensured if it is about μm. Accordingly, the element isolation region 107 having no wiring can be narrowed to a width of about 1.0 μm, while the element isolation region 108 in which the polysilicon wiring is formed has a width of 1.5 μm to 2.0 μm.
Is required, and the width of the region 108 cannot be reduced to the same width as the region 107.

That is, in the prior art, the wiring for connecting the electrodes of the charge transfer means is formed on the element isolation region, so that the separation width of the region where the wiring is provided must be large. However, there is a problem that the aperture ratio is reduced by that much, and the light detection sensitivity is lowered.

The present invention has been made in view of the above, and provides a solid-state imaging device capable of improving aperture ratio and obtaining high photodetection sensitivity, and a method of manufacturing the same.

[0014]

According to the present invention, there is provided a solid-state imaging device comprising: a plurality of light receiving units for photoelectrically converting light incident from one surface of a semiconductor substrate on the other surface; Vertical CC for reading out the charge generated in the light receiving section
D and wiring for driving the vertical CCD are formed, and in order to solve the above-described problem, the vertical CCD connected to each of the vertical CCD electrodes is driven on the light receiving section. In order to perform wiring.
In a preferred aspect, the material of the wiring is a different material from the CCD electrode.

In the method of manufacturing a solid-state imaging device according to the present invention, the vertical CCD and the light receiving section are formed on one surface of a semiconductor substrate, and then, on the light receiving section, each CCD electrode of the vertical CCD is provided. Wiring for driving the connected vertical CCD is formed of a different material from the CCD electrode.

[0016]

In the solid-state imaging device according to the present invention, wiring for driving the vertical CCD (wiring connected for each CCD electrode of the vertical CCD) is provided in a layer (insulating layer) different from each CCD electrode of the vertical CCD. Since the wiring is formed in the upper layer through the light-receiving section, the wiring connecting the respective CCD electrodes can be freely routed into the imaging area including the area on the light receiving section. Therefore,
The element isolation region on the light receiving portion forming surface can be a minimum width that can obtain predetermined electric characteristics regardless of wiring,
The aperture ratio of the solid-state imaging device can be increased.

Further, according to the present invention, since the area of the wiring for driving the vertical CCD does not affect the aperture ratio of the solid-state imaging device at all, the wiring width can be made sufficiently large and the electric resistance of the wiring can be increased. It is also advantageous in terms of lowering the value and ease of manufacture.

Furthermore, in the present invention, each of the vertical CCDs
The wiring connecting the electrodes (the wiring connecting the first electrodes and the wiring connecting the second electrodes) can be provided on the same plane without causing a short circuit, so that the wiring is formed by an insulating layer as in the conventional case (FIG. 3C). There is no need to laminate through. Further, in the present invention, the image pickup device (the light receiving portion and various diffusion regions provided as necessary)
Since the wiring is formed after the formation, high-temperature heat is not applied after the wiring is formed. This provides the advantages described below.

Although a metal material such as Al is an excellent wiring material in terms of low electric resistance, it has low heat resistance as compared with polysilicon and the like, and has a thinner wiring and insulating layer compared with polysilicon and the like. It must be very large, and it is very difficult to obtain a laminated structure in manufacturing. For example, in the case of using polysilicon, the thickness of the wiring may be set to about 5000 ° and the thickness of the insulating layer (oxide film) may be set to about 2000 °, whereas in the case of Al, the thickness of the wiring is set to 1 μm. A SiO ₂ film of about 1 μm must be provided as an insulating layer. However, in the conventional solid-state imaging device, it is completely considered that the wiring connecting the electrodes of the charge transfer means is performed using a metal such as Al (which is completely different from using Al for the wiring of the peripheral circuit). Had not been.

On the other hand, in the present invention, it is not necessary to form the wiring connecting the electrodes into a laminated structure, and the wiring is formed after the high-temperature heat treatment step is completed. It can be made of metal. By wiring between the electrodes with a metal material having a low electric resistance, the operation characteristics of the solid-state imaging device can be improved.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is an enlarged plan view showing a part of an imaging region of an infrared solid-state imaging device according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. is there.

In FIG. 1, charge transfer means (vertical CCDs) 2 a and 2 b are provided in a row of each light receiving section 1, and each light receiving section 1 is surrounded by element isolation regions 7 and 8. The width of each of the element isolation regions 7 and 8 in this embodiment is set to a minimum width (about 1.0 μm) at which a predetermined electrical characteristic can be obtained. The first CCD 3a is provided on each of the vertical CCDs 2a and 2b.
a, 3b and the second electrodes 4a, 4b are provided alternately (in FIG. 1 (a), the first electrode is diagonally sloping to the right and the second electrode is diagonally sloping to the left). The ends of the first electrode and the second electrode (3a and 4a, 3b and 4b) are laminated via an insulating layer 9 (the laminated structure of this part is not shown).

Wirings 6a and 6b connecting the electrodes of the vertical CCDs 2a and 2b are provided on the light receiving portion on the light receiving portion forming surface (via the insulating layer 9) so as to pass over substantially the center of the electrodes in the same row. It is provided so as to cross. FIG. 1B shows a wiring structure of the second electrode portions 4a and 4b, and an insulating layer 9 is interposed on a layer on which the light receiving portion 1, the element isolation region 7, and the second electrodes 4a and 4b are formed. Wirings 6b are formed, and each second electrode 4 is formed through a through hole 5 provided in the insulating layer 9.
a, 4b. The part of the wiring of the first electrode is the same as that of FIG. 1B, and the wiring 6a and the first electrodes 3a and 3b are connected via the through holes 5 provided in the insulating layer 9.

Next, a method of manufacturing the infrared solid-state imaging device shown in FIG. 1 will be described. First, a thin oxide film is provided on the surface of the semiconductor substrate 10, and this oxide film is selectively oxidized to form element isolation regions 7 and 8. As described above, the width of each of the element isolation regions 7 and 8 is set to the minimum necessary width for ensuring predetermined electrical characteristics.

After the element isolation regions 7 and 8 are formed, an impurity implantation / diffusion step is performed as necessary, and then the CCD first electrode 3
a and 3b, and then the CCD second electrodes 4a and 4b are formed using an electrode material such as polysilicon. In the present invention, at this stage, all the electrodes (3a, 3b, 4)
a, 4b) are isolated states, and the first electrodes and the second electrodes are not connected to each other.

Next, the thin oxide film on the region serving as the light receiving portion is removed to provide a silicide layer of platinum or the like, thereby forming the light receiving portion 1. Thereafter, an insulating layer 9 is provided on the entire light receiving portion 1, the element isolation regions 7, 8 and the first and second electrodes 3a, 3b, 4a, 4b, and a through hole 5 is formed at a location substantially corresponding to the center of each electrode. Drilling.

Finally, on the insulating layer 9, the first electrodes 3a, 3
1b and a wiring 6b connecting the second electrodes 4a and 4b are provided (in FIG. 1A, the wirings 6a and 6b are provided).
b), and the infrared solid-state imaging device of FIG. 1 is obtained.

In this embodiment, the wirings 6a and 6b are formed by using Al, and Al is deposited on the insulating layer 9 (at this time, the through holes 5 are also filled with Al) by photolithography. Perform patterning. FIG.
In (a), for simplicity, the widths of the wirings 6a and 6b are all assumed to be the same, and are linearly patterned, but the shape of the wiring itself is not particularly limited. Unless the wiring 6a connecting the first electrode and the wiring 6b connecting the second electrode are short-circuited,
For example, a wide portion may be provided partially.

Although not shown in the figure, when an Al reflective film is provided, the upper surface of the insulating layer 9 is covered with an Al film to form a reflective film before forming the wirings 6a and 6b, and further through the insulating layer. Thus, the wirings 6a and 6b are formed on the reflection film.

In the infrared solid-state imaging device obtained as described above, when light enters from below the paper surface of FIG. 1B (the light enters from the side opposite to the surface on which the light receiving unit 1 is formed, The wirings 6a and 6b provided above do not hinder the incidence of light at all), the incident light is photoelectrically converted by the light receiving unit 1, and the electric charge is stored in the light receiving unit 1. Next, when a clock pulse is applied to the first electrode, charges are transferred from the light receiving section 1 to below the first electrodes 3a, 3b, and further, the first electrode 3a, 3b and the second electrode 4
By sequentially applying clock pulses to a and 4b,
As described with reference to FIG.
And read out.

In this embodiment, since the widths of the element isolation regions 7 and 8 are both set to the minimum width at which predetermined electric characteristics can be obtained, the region 8 (108 in FIG.
The aperture ratio is improved as compared with the related art in which the width of (corresponding to) must be large.

Further, in this embodiment, the wirings 6a and 6b for connecting the electrodes of the vertical CCD are formed of Al, so that the electrodes between the electrodes are connected to each other as compared with the related art in which the electrodes are connected by the same polysilicon. Connection resistance is reduced. Thereby, when driving the vertical CCD at a high operating frequency, distortion of the clock pulse can be reduced, and excellent operating characteristics can be obtained.

In the embodiment described above, the wirings 6a, 6a
Although b is formed of Al, in the present invention, it is needless to say that the wiring connecting each electrode of the charge transfer means may be other than Al, and an Al alloy, a metal silicide, or the like may be used. Alternatively, a non-metallic material such as polysilicon may be used. When the wirings 6a and 6b are formed using polysilicon, it is desirable to increase the width of the wiring in order to reduce the connection resistance between the electrodes.

Although the CCD is used as the charge transfer means in the above embodiment, other charge transfer means, for example, a CSD (Charge Sweep Device) may be used.

Further, in the above description, an infrared solid-state imaging device has been described as an example. However, the present invention is not limited to an infrared solid-state imaging device, and a rear incident surface having sensitivity to visible light, ultraviolet light, X-rays, and the like. The present invention can also be applied to a solid-state imaging device of the type.

[0036]

As described above, according to the present invention, the wiring for driving the vertical CCD is formed using the area on the light receiving section, so that the area of the light receiving section is enlarged as compared with the conventional case. Thus, the aperture ratio can be increased, and the sensitivity of the solid-state imaging device can be increased. In the present invention, CC
Since it is easy to form the wiring between the D electrodes with a metal material having a small electric resistance, there is also an effect that the waveform distortion of the driving pulse hardly occurs when the operation is performed at a high speed.

[Brief description of the drawings]

FIG. 1A is a partially enlarged plan view of a solid-state imaging device according to an embodiment of the present invention, and FIG. 1B is a sectional view taken along the line AA ′ of FIG. 1A.

FIG. 2 is an explanatory diagram for describing an outline of a solid-state imaging device.

3 (a) is a partially enlarged plan view of a conventional solid-state imaging device, FIG. 3 (b) is a sectional view taken along the line BB 'of FIG. 3 (a), and FIG. 3 (c) is a view of FIG. 3 (a). FIG. 3 is a partial cross-sectional view of a wiring portion of the solid-state imaging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light-receiving part 2a, 2b Vertical CCD transfer part 3a, 3b 1st electrode 4a, 4b 2nd electrode 5 Through-hole 6a, 6b Al wiring 7, 8 Element isolation area 9 Insulation layer

Claims (3)

(57) [Claims] 1. A plurality of light receiving sections for photoelectrically converting light incident from one side of the semiconductor substrate on one side of the semiconductor substrate, and a vertical section for reading out charges generated in the light receiving section. In a solid-state imaging device in which a CCD and wiring for driving the vertical CCD are formed,
A solid-state imaging device comprising wiring for driving the vertical CCD connected to each CCD electrode of the vertical CCD. 2. The solid-state imaging device according to claim 1, wherein a material of the wiring is different from a material of the CCD electrode. 3. A plurality of light receiving units for photoelectrically converting light incident from the other surface of the semiconductor substrate on one surface of the semiconductor substrate, and a vertical surface for reading out charges generated in the light receiving unit. In the method for manufacturing a solid-state imaging device in which a CCD and a wiring for driving the vertical CCD are formed, after forming the vertical CCD and the light receiving unit, the CCD electrodes of the vertical CCD are provided on the light receiving unit. A wiring for driving the vertical CCD connected to the CCD is formed of a material different from that of the CCD electrode.