JP2830016B2 - Charge transfer device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charge transfer device in which charges are transferred by a transfer electrode formed on a transfer region, and particularly to a structure in which a metal wiring layer is connected to a semiconductor layer. A charge transfer device.

[Summary of the Invention]

According to the present invention, in a charge transfer device in which charges are transferred by a transfer electrode formed on a transfer region formed on a substrate surface, a first semiconductor layer serving as a transfer electrode is connected to a second semiconductor layer via a contact hole. By connecting the second semiconductor layer to the metal wiring layer in a region other than the contact hole, the resistance of the wiring is reduced and the potential of the transfer region is prevented from being changed. This is extended over the transfer area and used as a transfer electrode.

[Conventional technology]

In a charge transfer device such as a CCD, a reduction in sheet resistance of a transfer electrode is required for performing high-speed transfer and miniaturizing a wiring layer.

Techniques for reducing the resistance of such transfer electrodes include:
As in JP-A-56-87379, a metal thin film such as an aluminum wiring layer is provided so as to be connected to a part of the transfer electrode,
A technique of applying a transfer clock pulse to a transfer electrode via the metal thin film is known.

Further, in order to reduce the resistance of the transfer electrode, a technique of forming a high melting point metal layer or forming a silicide layer is also known. In the case where an aluminum wiring layer is formed on a transfer electrode, there is a technique of forming a barrier metal layer such as molybdenum or titanium for preventing a reaction with a metal below the aluminum wiring layer.

[Problems to be solved by the invention]

However, in a charge transfer device having a structure in which a silicide layer or a high-melting point metal layer is formed, it is difficult to form an insulating film such as an oxide film satisfactorily. It is difficult to form them by overlapping each other.

In a charge transfer device in which a metal thin film is connected to a transfer electrode and a transfer clock pulse is supplied through the metal thin film, when the metal thin film is formed directly on the transfer electrode, the work function of the lower part of the metal thin film is reduced. Due to the fluctuation, the depth of the potential well changes, and the charge cannot be transferred as designed.

In the case where the barrier metal layer is formed, there arises a problem that a selectivity with respect to the underlying insulating film (oxide film) cannot be obtained.

In view of the above-mentioned technical problems, the present invention realizes a low resistance and solves the problem of the barrier metal layer,
It is still another object of the present invention to provide a charge transfer device that prevents a change in potential of a transfer region.

[Means for solving the problem]

A charge transfer device according to the present invention proposed to achieve the above object includes a first semiconductor layer serving as a transfer electrode formed via an insulating film on a transfer region formed on a surface of a substrate. A first contact hole formed in an insulating film covering the first semiconductor layer, the first contact hole being connected to the first semiconductor layer via the first contact hole; A second semiconductor layer extending from above onto an insulating film formed on the transfer region;
A second contact hole formed in the insulating film covering the first semiconductor layer so as to be displaced from the first contact hole, and connected to the second semiconductor layer via the second contact hole. And a metal wiring layer.

As the first semiconductor layer and the second semiconductor layer constituting the charge transfer device according to the present invention, for example, a polysilicon layer or the like is used. The first semiconductor layer may have a single-layer structure or a structure including a plurality of layers. The second semiconductor layer is a semiconductor layer formed above the uppermost layer of the first semiconductor layer,
An insulating film is interposed between the first semiconductor layer and the first semiconductor layer. The second semiconductor layer may be a single layer or a plurality of layers.

Further, the charge transfer device may be a solid-state imaging device having light receiving units arranged in an area or a line. An example of the metal wiring layer is an aluminum wiring layer, but other high melting point metals, silicide layers and the like are used.

[Action]

In the charge transfer device of the present invention, the position of a contact hole formed between the first semiconductor layer and the second semiconductor layer;
The position where the metal wiring layer formed on the second semiconductor layer connects to the second semiconductor layer is different from the plane layout. Therefore, the first semiconductor layer is not located below the region where the metal wiring layer is connected to the second semiconductor layer in such a manner as to affect the potential, so that the resistance is reduced and the work function varies. Is solved, and the barrier metal becomes unnecessary.

Further, since the second semiconductor layer extends on the insulating film covering the transfer region formed on the surface of the substrate, it is used as a transfer electrode together with the first semiconductor layer.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

First, an example serving as a premise of the charge transfer device according to the present invention will be described with reference to FIG.

The charge transfer device shown in FIG. 1 is an example in which a metal wiring layer is an aluminum wiring layer, and a buffer layer is formed on a contact hole of a first polysilicon layer below the aluminum wiring layer. .

In the structure, as shown in FIG. 1, a transfer region 12 for transferring charges is formed on the surface of a silicon substrate 11.
A necessary impurity is introduced into the transfer region 12 so as to form a transfer portion or a storage portion. On the transfer region 12, a first polysilicon layer 14 serving as a transfer electrode is formed via an insulating film 13. Although not shown, the first polysilicon layer 14 is adjacent to another polysilicon layer via an insulating film in a direction perpendicular to the cross section. The first polysilicon layer 14 is a first or second polysilicon layer. The first polysilicon layer 14 is covered with an interlayer insulating film 15. A contact hole 16 is formed in the interlayer insulating film 15, and the first polysilicon layer 14 faces the bottom of the contact hole 16.

The second polysilicon layer 17, which is the second semiconductor layer, is formed on the first polysilicon layer 14 through the contact hole 16.
Connect to That is, the second polysilicon layer 17 is connected to the first polysilicon layer 14 in the region of the contact hole 16 and is formed around the interlayer insulating film 15 around the region. The end of the layer 17 is provided on the interlayer insulating film 15. The second polysilicon layer 17 is, for example, a third polysilicon layer.

Then, the contact hole of the second polysilicon layer 17 is formed.
The buffer layer 18 is formed on the region 16. This buffer layer 18
Is the next aluminum wiring layer 19 and the second polysilicon layer
It is a layer for preventing mutual diffusion of 17 and is formed using, for example, a silicon oxide layer or a silicon nitride layer. The region where the buffer layer 18 is formed is a region above the contact hole 16, and the second polysilicon layer 17 in the region covering the contact hole 16 is covered with the buffer layer 18.

The second portion covered with the buffer layer 18 in the region of the contact hole 16
The polysilicon layer 17 is connected to the aluminum wiring layer 19 in a region outside the buffer layer 18, that is, in a region other than the region of the contact hole 16. By using the aluminum wiring layer 19 as the wiring layer, the sheet resistance can be reduced as compared with the polysilicon layer. Since the buffer layer 18 is present in the region of the contact hole 16, the adverse effect that the potential of the transfer region 12 fluctuates due to the aluminum wiring layer 19 is suppressed.

As described above, in the charge transfer device of the present embodiment, the aluminum wiring layer 19 is connected to the first polysilicon layer 14 via the second polysilicon layer 17, but the first polysilicon layer 14
A buffer layer 18 is formed on the contact hole 16 between the first polysilicon layer 17 and the second polysilicon layer 17, and the buffer layer 18 can prevent the aluminum wiring layer 19 and the polysilicon layer 14 from mutually diffusing. For this reason, it is possible to prevent the potential of the transfer region 12 below the first polysilicon layer 14 from fluctuating,
There is no problem of barrier metal etching. Of course, the aluminum wiring layer 19 can reduce the resistance of the wiring layer.

In the above embodiment, only the transfer region 12 is formed on the surface of the silicon substrate 11, but a structure having a light receiving portion and other regions may be used. Aluminum wiring layer
19 may also be used for light shielding.

FIG. 2 shows an example in which a second polysilicon layer is extended and an aluminum wiring layer is connected.

In the structure, as shown in FIG. 2, a transfer region 22 for transferring charges is formed on the surface of the silicon substrate 21.
A necessary impurity is introduced into the transfer region 22 so as to form a transfer portion or a storage portion. On the transfer region 22, a first polysilicon layer 24 serving as a transfer electrode is formed via an insulating film 23, and is adjacent to another polysilicon layer via the insulating film in a direction perpendicular to the cross section. The first polysilicon layer 24 is a first or second polysilicon layer, and is covered with an interlayer insulating film 25. In this interlayer insulating film 25, a contact hole 26 is formed so as to expose the first polysilicon layer 24.

The second polysilicon layer 27, which is the second semiconductor layer, is formed on the first polysilicon layer 24 through the contact hole 26.
And is patterned into a shape extending therefrom onto the interlayer insulating film 25. The second polysilicon layer 27 extending in this manner is covered with an interlayer insulating film 28, and the interlayer insulating film 28 is opened to form an aluminum wiring layer 30.
A contact hole 29 is formed to establish a connection. Then, an aluminum wiring layer 30 for reducing the sheet resistance of the wiring is formed in the contact hole 29. Here, the position of the contact hole 29 is not a position on the region of the contact hole 26 on the first polysilicon layer 24 but a position other than the region of the contact hole 26 and extends on the interlayer insulating film 25. Second polysilicon layer
It is formed in 27 parts. Since the positions of the two contact holes 26 and 29 are shifted as described above, the aluminum wiring layer 3
The fluctuation of the work function due to 0 is suppressed, and the fluctuation of the potential of the transfer region 22 can be suppressed.

As described above, in the charge transfer device of this embodiment, since the positions of the two contact holes 26 and 29 are different, the transfer region 2
The fluctuation of the potential of 2 is suppressed, and problems such as aluminum spikes are also prevented.

Although only the transfer region 12 is formed on the surface of the silicon substrate 11 in the present embodiment, a structure having a light receiving portion and other regions may be used.

Next, specific examples of the charge transfer device according to the present invention will be described.

In the charge transfer device according to the present invention, the second polysilicon layer functions as a part of the transfer electrode.

In the structure, as shown in FIG. 3, a transfer region 32 for transferring charges is formed on the surface of the silicon substrate 31.
On the transfer region 32, a first polysilicon layer 34, which is a first semiconductor layer, is formed via an insulating film 33, and functions as a transfer electrode. The first polysilicon layer 34 is a first polysilicon layer. The first polysilicon layer 34 is covered with an insulating film 35, and a contact hole 36 is formed in the insulating film 35. Then, the second polysilicon layer 37 made of the second polysilicon layer is connected through the contact hole 36. The second polysilicon layer 37 is
From the polysilicon layer 34 to the insulating film 33.
Therefore, the first polysilicon layer 34 and the second polysilicon layer 37 function as transfer electrodes, and the regions corresponding to the transfer regions 22 function as storage units and transfer units by, for example, separately implanting impurities.

The second polysilicon layer 37 is covered with an insulating film 38. The insulating film 38 has a contact hole for connecting the second polysilicon layer 37 and the aluminum wiring layer 40.
39 is formed. Then, an aluminum wiring layer 40 is formed in a required pattern on the contact hole 39, and the polysilicon layers 37, 3 are formed through the aluminum wiring layer 40.
4 is supplied with a transfer clock signal. Here, the position of the contact hole 39 is a position other than on the contact hole 36. For this reason, a change in the work function due to the aluminum wiring layer 40 is suppressed, and a change in the potential of the transfer region 32 can be suppressed. Also, alloy spikes can be prevented without the need for barrier metal.

Another example of the charge transfer device according to the present invention will be described with reference to FIG.

The structure shown in FIG. 4 has a structure having three polysilicon layers, and further prevents the aluminum wiring layer from being adversely affected.

In the structure, an insulating film 43 is formed on a silicon substrate 41 as shown in FIG. On the surface of the silicon substrate 41 below the insulating film 43, although not shown, impurities are introduced into required regions to form transfer regions and the like. This insulating film
On the 43, a first polysilicon layer 44 functioning as a transfer electrode is formed by patterning. The first polysilicon layer 44 is a first polysilicon layer. This first
The polysilicon layer 44 is covered with an insulating film 45. The insulating film 45 has a contact hole on the first polysilicon layer 44.
46 is formed.

Next, the second polysilicon layers 47 and 48, which are the second semiconductor layers, are formed using the second polysilicon layer. One second polysilicon layer 47 is connected to the first polysilicon layer 44 via the contact hole 46 and extends from the contact hole 46 along the insulating film 45 on the first polysilicon layer 44. Exist. Further, the other second polysilicon layer 48 is adjacent to the first polysilicon layer 44 via an insulating film 45, one end of which overlaps the first polysilicon layer 44, and the other end of which is the insulating film 43. And the silicon substrate 41. Therefore, the second polysilicon layer 48 is used for controlling the potential of the surface of the silicon substrate 41. Further, a third polysilicon layer 50 is formed on the second polysilicon layer 48 via an insulating film 49. The third polysilicon layer 50 also has the same cross-sectional shape as the second polysilicon layer 48, one end of which overlaps the second polysilicon layer 48, and the other end of which has the insulating film 43 interposed therebetween. Silicon substrate
Formed facing 41. This third polysilicon layer
Similarly to the second polysilicon layer 48, a silicon substrate 41 is also provided.
Is used to control the potential of the surface.

The second polysilicon layers 47 and 48 and the third polysilicon layer 50 are covered with an interlayer insulating film 51, respectively. Each polysilicon layer 47, 48, 50 has an interlayer insulating film 51
Are formed to form contact holes 52, 53, 54. Here, the position of the contact hole 52 is
It is assumed that the position of 46 is shifted on a plane. Further, the second polysilicon layer 48 and the third polysilicon layer 50 below the contact holes 53 and 54 are overlaid on the other polysilicon layers 44 and 48, respectively. Contact holes on the upper end side
53 and 54 are formed. The aluminum wiring layers 55 are connected to the polysilicon layers 47, 48, 50 via these contact holes 52, 53, 54.

In the charge transfer device having such a structure, a polysilicon layer which exists directly on the insulating film 43 in a region below the contact holes 52, 53, 54 is not formed. Therefore, the adverse effect that the work function fluctuates due to the diffusion of aluminum in the aluminum wiring layer 55 is prevented. In addition, since the barrier metal is not required, alloy spikes and the like can be prevented, and the aluminum wiring layer 55 can reduce the sheet resistance of the wiring layer.

Although the first polysilicon layer 44 is a transfer electrode,
The second polysilicon layer 48 or the third polysilicon layer 50
May be transfer electrodes or control electrodes such as a readout gate and an overflow control gate in a solid-state imaging device such as a CCD.

〔The invention's effect〕

As described above, in the charge transfer device of the present invention, the second semiconductor layer is connected to the metal wiring layer in a region other than the contact hole connecting the first semiconductor layer and the second semiconductor layer. For this reason, the first semiconductor layer is not located below the region where the metal wiring layer is connected to the second semiconductor layer in such a manner as to affect the potential, so that the resistance is reduced and the barrier metal is formed. It becomes unnecessary.

Further, since the second semiconductor layer extends over the transfer region formed on the substrate surface, the second semiconductor layer can be used as a transfer electrode together with the first semiconductor layer. It can function as a unit. Further, since the second semiconductor layer extends over the transfer region formed on the substrate surface, it can be directly connected to the metal wiring on the channel, so that a more efficient transfer electrode can be formed. I can do it.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a main part of an example of a charge transfer device on which the present invention is based, and FIG. 2 is a cross-sectional view schematically showing another example of a charge transfer device on which the present invention is based. It is a fragmentary sectional view. FIG. 3 is a cross-sectional view of main parts schematically showing an example of the charge transfer device according to the present invention, and FIG. 4 is a cross-sectional view of main parts schematically showing another example of the charge transfer device of the present invention. . 31,41 silicon substrate 32 transfer region 33,43 insulating film 34,44 first polysilicon layer 135,45 insulating film 36,46 contact hole 37,47 Second polysilicon layer 18 Buffer layer 30, 40, 55 Aluminum wiring layer

Claims (1)

(57) [Claims] A first semiconductor layer serving as a transfer electrode formed on a transfer region formed on a surface of the substrate via an insulating film; and an insulating film covering the first semiconductor layer. First
And a contact hole connected to the first semiconductor layer via the first contact hole and extending from the first semiconductor layer on the insulating film formed on the transfer region. A second semiconductor layer, a second contact hole formed in the insulating film covering the second semiconductor layer so as to be displaced from the first contact hole, and via the second contact hole A charge transfer device having a metal wiring layer connected to the second semiconductor layer;