JP3270254B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a charge transfer device (CC).
The present invention relates to a solid-state imaging device using D), and more particularly to a solid-state imaging device in which a CCD transfer electrode structure is improved.

[0002]

2. Description of the Related Art A solid-state image pickup device is a device used as an image pickup device in a video camera, an electronic still camera or the like. This device converts input light into a signal charge, stores the signal charge in a photoelectric conversion storage unit, and transfers and outputs the signal charge using a CCD or the like.

In recent years, in order to reduce the size and cost of cameras, it has been required to reduce the power consumption and the chip size of solid-state imaging devices. To reduce power consumption, CC
It is necessary to reduce the capacitance between the D transfer electrodes, that is, increase the gap between the electrodes.

In the prior art, a vertical transfer CCD is used.
Both the electrode and the horizontal transfer CCD electrode have an overlapping structure of, for example, two-layer polysilicon, and are formed in the same process. Therefore, the gap between the transfer electrodes of the vertical transfer CCD and the gap between the transfer electrodes of the horizontal transfer CCD are equal.

FIG. 8 is a plan view showing an example of the arrangement of transfer electrodes in a conventional solid-state image pickup device. Reference numeral 81 denotes a first-layer polysilicon electrode, and reference numeral 82 denotes a second-layer polysilicon electrode. φV
The transfer electrodes of the vertical transfer CCD to which .phi. Is applied and the horizontal transfer CCD to which .phi.H is applied are both constituted by two-layer overlapping polysilicon electrodes. Conventionally, the reason why the double-layer overlapped polysilicon electrode structure is used for both the vertical and horizontal transfer electrodes is to increase the transfer efficiency of the CCD. The gap between the transfer electrodes is determined by the interlayer insulating film between the first polysilicon layer and the second polysilicon layer, and is usually smaller than the minimum dimension determined by the limit of lithography. In the conventional structure, the vertical transfer CC
The gap S between the transfer electrodes of D becomes equal to the gap R between the transfer electrodes of the horizontal transfer CCD.

In general, the power consumption of a CCD type solid-state imaging device is occupied by a large percentage of the power consumption of a horizontal CCD having a high driving frequency. When the inter-capacity is reduced, there is a problem that the transfer capability of the vertical CCD deteriorates and it becomes difficult to transfer a large amount of signal charges without being left behind.

FIG. 9 explains that when the gap between the transfer electrodes is increased, the transfer efficiency when a large amount of electric charges is transferred is deteriorated.
This will be described with reference to FIG. FIG. 9 illustrates the case of the four-phase drive, but all of the three or more-phase CCDs are valid. In this case, by changing φV2 from the high level to the low level, the channel potential below the transfer electrode is lowered, and the charge is transferred below φV3 and φV4. At this time, when there is a charge under φV2, φV1
If a potential pocket is generated under the gap between .phi.V2 and .phi.V2, signal charges cannot be completely transferred.

Generally, the generation of a channel potential pocket under the gap between transfer electrodes depends on the difference in channel potential under the electrodes on both sides of the gap if the gap is constant. If this difference is small, pockets occur, but if they are large, pockets do not. When transferring a large amount of signal charge, a pocket is generated before the signal charge is completely transferred, and as shown in FIG. 9, the signal charge is trapped in the pocket, and the transfer efficiency is degraded. On the other hand, when the signal charge is small, the transfer of the signal charge ends before the pocket occurs, so that the transfer efficiency does not deteriorate. When the gap becomes small, the pocket can be suppressed with a small potential difference.

For the above reasons, the transfer efficiency of a CCD generally depends on the amount of transfer charge and the gap length between transfer electrodes as shown in FIG. As can be easily understood from FIG. 10, it is necessary to reduce the gap between the transfer electrodes in order to increase the transfer charge amount. As another method for increasing the transfer charge amount, a method of increasing the area of the vertical CCD is conventionally known. However, in this case, there is a problem that the chip area increases.

[0010]

As described above, conventionally, the vertical transfer CCD electrode and the horizontal transfer CCD electrode have a double-layer polysilicon overlapped structure,
The structure was such that the electrode gap was equal to the horizontal transfer CCD electrode gap. In general, the power consumption of a CCD solid-state imaging device is dominated by the power consumption of a horizontal CCD having a high driving frequency.However, in order to reduce the power consumption of the horizontal CCD, the gap between transfer electrodes is increased to increase the capacitance between electrodes. If the size is reduced, there is a problem that the transfer capability of the vertical CCD deteriorates and it becomes difficult to transfer a large amount of signal charges without being left behind.

The present invention has been made in view of the above circumstances, and has as its object to realize low power consumption of a horizontal CCD and to transfer a large amount of signal charges without deteriorating transfer efficiency. To provide a solid-state imaging device.

[0012]

In order to solve the above problems, the present invention employs the following configuration. That is, the present invention provides a plurality of photoelectric conversion storage units two-dimensionally arranged on a semiconductor substrate, and a plurality of vertical transfer CCDs for vertically transferring signal charges read from these photoelectric conversion storage units.
And a horizontal transfer CCD that receives signals from these vertical transfer CCDs and transfers signal charges in the horizontal direction. In the solid-state imaging device, the gap between the transfer electrodes of the vertical transfer CCD is set to be smaller than the gap between the transfer electrodes of the horizontal transfer CCD. Is also set to be narrow.

Here, preferred embodiments of the present invention include the following. (1) Both the transfer electrode of the vertical transfer CCD and the transfer electrode of the horizontal transfer CCD have a single-layer gate structure. (2) Both the transfer electrode of the vertical transfer CCD and the transfer electrode of the horizontal transfer CCD have a two-layer overlap gate structure. (3) The transfer electrode of the vertical transfer CCD has a two-layer overlap gate structure, and the transfer electrode of the horizontal CCD has a single-layer gate structure. (4) Both transfer electrodes of the vertical transfer CCD and the horizontal transfer CCD have a two-layer overlap gate structure,
D is made of first and second layer polysilicon, and the horizontal transfer CCD is made of second and third layer polysilicon. (5) The material forming the transfer electrode includes W, Mo, Ti, and at least one of silicide, polycrystalline silicon, and amorphous silicon thereof.

According to the present invention, in the method for manufacturing a solid-state imaging device having the above-described structure, a first conductive layer is formed on a semiconductor substrate and patterned, and the first conductive layer is formed on a surface of the patterned first conductive layer. Is formed, and then a second conductive layer is deposited and patterned to form a vertical transfer CCD from the first conductive layer and the second conductive layer, and the patterned second conductive layer is further formed. Forming a second oxide film thicker than the first oxide film on the surface of the first layer, and then depositing and patterning a third layer conductive layer, and forming the second layer and the third conductive layer.
The horizontal transfer CCD is formed from the conductive layer.

[0015]

According to the present invention, the gap between the transfer electrodes of the horizontal transfer CCD is made large (wide) to realize low power consumption, and the gap between the transfer electrodes of the vertical transfer CCD is made small (narrow) to generate a large amount of signals. Charges can be efficiently transferred.

Here, in the CCD, when the gap between the transfer electrodes is large, the capacity between the transfer electrodes is small, and when the gap between the transfer electrodes is small, the capacity between the transfer electrodes is large.
When the capacitance between the transfer electrodes is large, the power consumption also increases. Further, the transfer charge amount increases when the gap between the transfer electrodes is small, but the transfer charge amount decreases when the gap between the transfer electrodes is large. That is, in the CCD, when the gap between the transfer electrodes is large, the power consumption is small, and the transfer charge amount is small. Conversely, when the gap between the transfer electrodes is small, the power consumption increases and the transfer charge amount increases.

According to the present invention, since the horizontal transfer CCD has a large gap between transfer electrodes, power consumption can be reduced. The horizontal transfer CCD has multiple vertical transfer CCs.
Since only one chip is required for D, even if the area is increased, the chip area hardly increases. Therefore, even if the gap between the electrodes is increased, the transfer charge amount can be sufficiently secured by increasing the area. On the other hand, since the vertical transfer CCD has a small gap between the transfer electrodes, the transfer charge amount can be sufficiently increased. Since the power consumption of the vertical transfer CCD is extremely smaller than that of the horizontal transfer CCD driven at high speed, an increase in power consumption hardly causes a problem.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a plan view showing a transfer electrode arrangement in a solid-state imaging device according to a first embodiment of the present invention.
The transfer electrodes of both the vertical transfer CCD 1 and the horizontal transfer CCD 2 have a single-layer gate structure made of polysilicon 11. Although not shown in the figure, photoelectric conversion storage units composed of photodiodes are arranged in a matrix, a plurality of vertical transfer CCDs are vertically arranged adjacent to the photoelectric conversion storage units, and a horizontal transfer CCD is a vertical transfer CCD. One is arranged at the end of the CCD.

The gap S between the transfer electrodes of the vertical transfer CCD is smaller than the gap R between the transfer electrodes of the horizontal transfer CCD. Since the horizontal transfer CCD has a large gap between the transfer electrodes, the capacitance between the electrodes is small and power consumption can be saved. In addition, since the gap S is small in the vertical transfer CCD, it is possible to prevent signal charges from being left behind when transferring a large amount of charges, which is a problem in the related art.

FIGS. 2A and 2B are diagrams showing a cross-sectional structure of a CCD transfer electrode in the present embodiment. FIG. 2A shows an example of a vertical transfer CCD, and FIG. 2B shows an example of a horizontal transfer CCD. In the figure, 21 is a p-type silicon substrate, 22 is a buried n-type impurity layer (CCD channel), 23 is a silicon oxide film as a transfer gate insulating film, 24 is a first layer polysilicon as a transfer electrode, and 25 is a p-type. It is an impurity layer. In this example,
The transfer electrodes of both the vertical transfer CCD and the horizontal transfer CCD are made of single-layer polysilicon.

As described above, according to the present embodiment, the vertical transfer C
Each transfer electrode of the CD and the horizontal transfer CCD is formed of single-layer polysilicon, and the gap between the transfer electrodes of the horizontal transfer CCD is made larger than the gap S between the transfer electrodes of the vertical transfer CCD. Can increase the transfer charge amount, and can reduce the power consumption of the horizontal transfer CCD.

In this case, the vertical transfer CCD has a horizontal C
Since the driving frequency is much lower than that of the CD and the power consumption is extremely small, an increase in the power consumption due to the small gap between the transfer electrodes hardly causes a problem. Further, as for the horizontal transfer CCD, it is necessary to increase the area of the horizontal transfer CCD in order to suppress the reduction of the transfer charge amount due to the increase in the gap. However, since the number of horizontal transfer CCDs is one, even if the area is increased, the increase in the area as a whole is slight and causes almost no problem. That is, in the present embodiment, the effects of reducing power consumption and increasing the amount of transfer charges can be achieved at the same time. Second Embodiment In the first embodiment, the transfer electrodes of both the vertical transfer CCD and the horizontal transfer CCD are formed of a single-layer polysilicon electrode, but it is not always necessary that both transfer electrodes have a single-layer gate structure.

FIG. 3 is a plan view showing a transfer electrode arrangement in a solid-state imaging device according to a second embodiment of the present invention.
The vertical transfer CCD 1 has a two-layer gate overlap gate structure composed of a first layer polysilicon 31 and a second layer polysilicon 32, and the horizontal transfer CCD 2 has a two layer gate composed of a second layer polysilicon 32 and a third layer polysilicon 33. It has a gate overlap gate structure.

Also in this embodiment, the gap S between the transfer electrodes of the vertical transfer CCD is smaller than the gap R between the transfer electrodes of the horizontal transfer CCD. Therefore, similarly to the first embodiment,
In a horizontal transfer CCD, the gap between transfer electrodes is large,
The inter-electrode capacitance is small, and power consumption can be reduced. In addition, since the gap S is small in the vertical transfer CCD, it is possible to prevent signal charges from being left behind when transferring a large amount of charges, which is a problem in the related art.

FIGS. 4A and 4B are diagrams showing a cross-sectional structure of a CCD transfer electrode in the present embodiment. FIG. 4A shows an example of a vertical transfer CCD, and FIG. 4B shows an example of a horizontal transfer CCD. In the figure, 41 is a p-type silicon substrate, 42 is a buried n-type impurity layer (CCD channel), 43 is a silicon oxide film as a transfer gate insulating film, and 45 is a p-type impurity layer. In this embodiment, unlike the first embodiment, the transfer electrodes of both the vertical transfer CCD and the horizontal transfer CCD are formed of two-layer overlapping polysilicon.

FIGS. 5A to 5C are sectional views showing the steps of a method for manufacturing a CCD transfer electrode according to this embodiment. First, as shown in FIG. 5A, an n-type buried impurity layer (CCD channel) 42 is formed on a p-type silicon substrate 41, and the first-layer polysilicon 31 is patterned via a silicon oxide film 43. . Further, after oxidizing the first layer polysilicon 31, a second layer polysilicon 32 is deposited.

Next, as shown in FIG. 5B, the second-layer polysilicon 32 is patterned and then oxidized. Here, in order to obtain the difference between the gaps R and S, the oxidation of the second-layer polysilicon 32 is performed more than the oxidation of the first-layer polysilicon 31, so that the oxide film thickness is increased. Further, a two-layer CCD barrier p-type impurity diffusion layer 45 is formed, and a third-layer polysilicon 33 is deposited. Finally, FIG.
As shown in (c), the third-layer polysilicon 33 is patterned.

As described above, according to the present embodiment, the vertical transfer C
The second polysilicon 32 is commonly used by the CD and the horizontal transfer CCD, and the vertical transfer CCD and the horizontal transfer CCD having different gaps between the transfer electrodes as a whole have three layers of polysilicon while both have a two-layer overlap gate structure. 31,3
2, 33. In this case, since the gap between the transfer electrodes can be changed only by changing the oxide film thickness of the polysilicon, the manufacturing process is easy. (Embodiment 3) FIG. 6 is a plan view showing a transfer electrode arrangement in a solid-state imaging device according to a third embodiment of the present invention.
The vertical transfer CCD 1 has a two-layer gate overlap gate structure composed of a first layer polysilicon 61 and a second layer polysilicon 62, and the horizontal transfer CCD 2 has a single layer gate structure composed of the first layer polysilicon 61.

Also in this embodiment, the gap S between the transfer electrodes of the vertical transfer CCD is smaller than the gap R between the transfer electrodes of the horizontal transfer CCD. Therefore, similarly to the first embodiment,
In a horizontal transfer CCD, the gap between transfer electrodes is large,
The inter-electrode capacitance is small, and power consumption can be reduced. Further, since the gap between the electrodes is small in the vertical transfer CCD, it is possible to prevent signal charges from being left behind when transferring a large amount of charges, which has been a problem in the prior art.

FIG. 7 is a cross-sectional view showing the transfer electrode structure of the horizontal transfer CCD in this embodiment, in which 71 is a p-type silicon substrate, 72 is a buried n-type impurity layer (CCD channel),
73 is a silicon oxide film, 74 is a first layer polysilicon as a transfer electrode, and 75 is a p-type impurity layer.

In this embodiment, different from the first embodiment, the transfer electrodes of the vertical transfer CCD are formed of two-layer overlapping polysilicon, and the transfer electrodes of the horizontal transfer CCD are formed of single-layer polysilicon. In this case, it is easy to manufacture the gap between the transfer electrodes of the vertical transfer CCD smaller than in the first embodiment, so that more charges can be transferred than in the first embodiment.

The present invention is not limited to the above embodiments. In the embodiment, polysilicon is used as the transfer electrode material. However, the present invention is not limited to this. Amorphous silicon can be used, and refractory metals such as W, Mo, and Ti, or silicides thereof can be used. The solid-state imaging device is not limited to a flat-type solid-state imaging device in which a photoelectric conversion storage unit and a CCD unit are formed on the same substrate surface. It can also be applied to Further, the horizontal transfer CCD is not necessarily limited to one, and a plurality of horizontal transfer CCDs may be arranged. In addition, various modifications can be made without departing from the scope of the present invention.

[0033]

As described above in detail, according to the present invention, the gap between the transfer electrodes of the vertical transfer CCD is made smaller than the gap between the transfer electrodes of the horizontal transfer CCD, so that even if the power consumption is reduced, a large amount It is possible to realize a solid-state imaging device capable of transferring the electric charges without deteriorating the transfer efficiency.

[Brief description of the drawings]

FIG. 1 is a plan view showing an arrangement of transfer electrodes in a solid-state imaging device according to a first embodiment.

FIG. 2 is a sectional view showing a transfer electrode structure according to the first embodiment.

FIG. 3 is a plan view showing an arrangement of transfer electrodes in a solid-state imaging device according to a second embodiment.

FIG. 4 is a sectional view showing a transfer electrode structure according to a second embodiment.

FIG. 5 is a sectional view showing a manufacturing process of a transfer electrode in the second embodiment.

FIG. 6 is a plan view showing an arrangement of transfer electrodes in a solid-state imaging device according to a third embodiment.

FIG. 7 is a sectional view showing a transfer electrode structure according to a third embodiment.

FIG. 8 is a plan view showing an arrangement of transfer electrodes in a conventional solid-state imaging device.

FIG. 9 is a diagram for explaining deterioration of transfer efficiency when transferring a large amount of charges.

FIG. 10 is a diagram showing the transfer charge dependence of transfer efficiency.

[Explanation of symbols]

Reference Signs List 1 vertical transfer CCD 2 horizontal transfer CCD 11 single-layer polysilicon 21, 41, 71 p-type silicon substrate 22, 42, 72 embedded buried n-type impurity layer (CCD channel) 23, 43.73 silicon oxide film 24, 74 ... first layer polysilicon 25, 45, 75 ... p-type impurity layer 31, 61 ... first layer polysilicon 32, 62 ... second layer polysilicon 33 ... third layer polysilicon

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-241863 (JP, A) JP-A-4-207076 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/14-27/148

Claims (5)

(57) [Claims] A plurality of photoelectric conversion storage units arranged two-dimensionally on a semiconductor substrate; a plurality of vertical transfer CCDs for vertically transferring signal charges read from these photoelectric conversion storage units; In a solid-state imaging device including a horizontal transfer CCD that receives signals from the vertical transfer CCD and transfers signal charges in a horizontal direction, a gap between the transfer electrodes of the vertical transfer CCD is narrower than a gap between the transfer electrodes of the horizontal transfer CCD. A solid-state imaging device characterized by being set. 2. The solid-state imaging device according to claim 1, wherein the transfer electrodes of the vertical transfer CCD and the transfer electrodes of the horizontal transfer CCD both have a single-layer gate structure. 3. The solid-state imaging device according to claim 1, wherein the transfer electrodes of the vertical transfer CCD have a two-layer overlap gate structure, and the transfer electrodes of the horizontal CCD have a single-layer gate structure. 4. The transfer electrodes of the vertical transfer CCD and the horizontal transfer CCD both have a two-layer overlap gate structure.
2. The solid-state imaging device according to claim 1, wherein said vertical transfer CCD is made of a first layer and a second layer polycrystalline silicon, and said horizontal transfer CCD is made of a second layer and a third layer polycrystalline silicon. 5. The transfer electrode is made of W, M
o, Ti and their silicides, polycrystalline silicon,
2. The solid-state imaging device according to claim 1, comprising at least one of amorphous silicon.