JPH04367237A - Ccd solid-state image sensing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CCD solid-state image pickup device, and more particularly to a structure of a horizontal register and its transfer stage that improves charge transfer efficiency.

0002

2. Description of the Related Art Generally, as shown in FIG. 4, a CCD solid-state imaging device has an imaging area 13 consisting of a photosensor 11 that performs photoelectric conversion and a vertical register 12, and a vertical register 1.
The horizontal register 15 transfers the signal charge transferred from 2 to the output section 14 in accordance with the horizontal scanning line of the television.

In particular, as shown in FIG. 5A, the horizontal register 15 is an
On this horizontal register 15, first and second transfer electrodes 23 made of first and second polycrystalline silicon layers are formed with a gate insulating film 22 interposed therebetween. and 24 are formed, and furthermore, these two transfer electrodes 23 and 24 are formed as a set, and are sequentially arranged and formed in the horizontal direction. First and second transfer electrodes 23 and 2
An interlayer insulating film 25 made of SiO2 or the like is interposed between the two layers. One transfer stage is constructed by combining two adjacent transfer electrodes 23 and 24, and by alternately applying two-phase driving pulses φ1 and φ2 having opposite phases to each transfer stage, a signal is generated. Direction of charge in one direction (direction of arrow)
Transfer sequentially to

However, in this case, since two-phase drive pulses φ1 and φ2 are applied to each transfer stage,
As shown in FIG. 2, a fringing electric field is generated under the interlayer insulating film 25 between the transfer electrodes 23 and 24 of each transfer stage. This fringing electric field causes the interlayer insulating film 2 to
A potential dip (potential pocket) d occurs below 5, causing a phenomenon in which signal charge is not completely transferred.

Therefore, in order to avoid the above phenomenon, conventionally, as shown in FIG. 6A, a P-type impurity (for example, boron (B)) is diffused in the horizontal register 15, for example, under the second transfer electrode 24. In this way, a P-type impurity diffusion region 26 is formed. According to this example, the potential under the second transfer electrode 24 becomes shallower than the potential under the first transfer electrode 23 (this shallower potential is generally called an implant barrier), so as shown in FIG. 6B. , a step-like potential having a downward slope along the charge transfer direction is formed. As a result, a potential dip does not occur under the interlayer insulating film 25 between each set of transfer electrodes 23 and 24, and charge transfer is directed, so that signal charge transfer efficiency is improved.

[0006]

However, in the conventional CCD solid-state image sensing device shown in FIG. The potential difference between φ1 and φ2 changes moment by moment, and when the potential difference becomes small,
As the electric field in each transfer stage becomes weaker, a portion where the slope of the potential in the charge transfer direction becomes almost horizontal occurs, causing a disadvantage that the transfer of signal charges is restricted in the horizontal portion.

[0007] Furthermore, when the potential of the two-phase drive pulses φ1 and φ2 is lowered, if the potential drops below twice the potential difference formed by the implant barrier, the transfer electric field between the transfer stages becomes weaker. Therefore, a dip in potential occurs in the portion indicated by A in FIG. 6B, which again impedes the transfer of signal charges. Furthermore, if the implant barrier is made too small, a potential dip will occur in the portion indicated by B. In this case, the transfer voltage applied to transfer electrodes 4 and 5 must be increased.

For these reasons, in the conventional CCD solid-state image sensor, the transfer voltage, that is, the two-phase drive pulse φ
There is a disadvantage that it becomes difficult to lower the voltages of 1 and φ2.

The present invention has been made in view of the above problems, and its purpose is to make the strength of the transfer electric field uniform in each transfer stage, and to prevent potential dips from occurring within the transfer stage. It is an object of the present invention to provide a CCD solid-state image sensor that can reduce the transfer voltage, increase the speed of charge transfer, and miniaturize the transfer stage.

Further, while following the configuration of the conventional transfer stage, the present invention can strengthen the transfer electric field in each transfer stage, suppress the occurrence of potential dips within the transfer stage, and reduce the transfer voltage. Another object of the present invention is to provide a CCD solid-state image sensor that can speed up charge transfer.

[0011]

[Means for Solving the Problems] The CCD solid-state image sensing device of the present invention provides two-phase driving pulses φ1 alternately to a large number of transfer electrodes 4 and 5 which are sequentially arranged and formed in the horizontal direction on a horizontal register 2. and φ2 to form one transfer electrode 4
Alternatively, one transfer stage may be formed by 5, and the impurity concentration of the horizontal register 2 under each transfer electrode 4 and 5 may be continuously changed in the direction of charge transfer.

Furthermore, the CCD solid-state image sensor of the present invention has a plurality of transfer electrodes 4 and 5 arranged and formed in the horizontal direction in sequence on the horizontal register 2, in which two adjacent transfer electrodes 4 and 5 are assembled. , two-phase drive pulses φ1 and φ2 are alternately supplied to each set of transfer electrodes 4 and 5.
constitute one transfer stage, and the impurity concentration of the horizontal register 2 under one of the transfer electrodes 5 in the set of transfer electrodes 4 and 5 is continuously changed in the direction of charge transfer. do.

[0013]

[Operation] According to the above-described structure of the first aspect of the present invention, since one transfer stage is formed by one transfer electrode 4 or 5, a potential dip occurs due to the presence of the interlayer insulating film 6. In addition, the length of the transfer stage can be reduced. In addition, each transfer electrode 4 and 5
Since the impurity concentration of the lower horizontal registers 2 is changed continuously in the direction of charge transfer, 2
The strength ε of the transfer electric field can be made uniform regardless of the potential difference between the phase drive pulses φ1 and φ2, and the potential shape having a downward slope along the transfer direction can be maintained. This leads to lower transfer voltages, higher speed charge transfer, and miniaturization of transfer stages.

Further, according to the configuration of the second aspect of the present invention described above, since the conventional configuration in which one transfer stage is configured by one set of transfer electrodes 4 and 5 is followed, there is no need to worry about the formation of the transfer stage. Regarding wiring formation, conventional manufacturing processes can be used as they are. In addition, since the impurity concentration of the horizontal resistor 2 under one of the transfer electrodes 5 in the pair of transfer electrodes 4 and 5 is changed continuously in the direction of charge transfer, it is more powerful than the conventional one. A transfer electric field can be created. This leads to lower transfer voltage and faster charge transfer.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1A is a block diagram showing the main parts of the CCD solid-state image pickup device according to the first embodiment, particularly a horizontal register and its transfer stage, and FIG. 1B is a potential diagram thereof.

As shown in the figure, in this CCD solid-state image sensing device, a horizontal register 2 is constructed of, for example, an N-type impurity diffusion region formed in a P-type silicon substrate 1, and a gate is formed on this horizontal register 2. First and second horizontal transfer electrodes 4 and 5 are formed by first and second polycrystalline silicon layers through an insulating film 3, and these two transfer electrodes 4 and 5 are formed into a set, respectively. They are arranged and formed sequentially in the horizontal direction. Note that the first and second transfer electrodes 4
and 5, an interlayer insulating film 6 made of SiO2 or the like is interposed.

In this example, two-phase driving pulses φ1 and φ2 having opposite phases are alternately applied to each transfer electrode 4 and 5, respectively. That is, for example, the first drive pulse φ1 is supplied to the first transfer electrode 4, and the second drive pulse φ2 is supplied to the second transfer electrode 5. Therefore, one transfer electrode 4 or 5 constitutes one transfer stage.

Furthermore, in this example, impurity diffusion regions 7 are formed by ion-implanting P-type impurities, such as boron (B), into the surface of the horizontal register 2 under each transfer electrode 4 and 5 in the horizontal register 2. do. Each impurity diffusion region 7 is
The P-type impurity concentration is formed so as to decrease continuously in the direction of signal charge transfer (direction indicated by the arrow). That is, when viewed from the impurity concentration of the horizontal register 2, the N-type impurity concentration under each transfer electrode 4 and 5 is formed so as to increase continuously in the direction of signal charge transfer.

Therefore, as shown in the figure, in the impurity concentration distribution of the impurity diffusion region 7, the interior angle is smallest at the portion corresponding to one end a of one transfer electrode 4 or 5, and the interior angle is smallest at the portion corresponding to one end a of one transfer electrode 4 or 5. The portion corresponding to a has a substantially right-angled triangular shape with a sawtooth impurity concentration distribution as a whole.

Here, when the first drive pulse φ1 is set to a high level (5V) and the second drive pulse φ2 is set to a low level (0V), as shown in FIG. 1B, one end of the first transfer electrode 4 The potential under a is the highest, and the next
The potential below one end a of the transfer electrode 4 is the lowest, and the potential shape therebetween has a downward slope along the signal charge transfer direction, that is, a downward slope to the left. The transfer electric field strength ε at this time is ε=Δφ/2L. Here, Δφ represents the potential difference, and L represents the length of the transfer stage.

From this, by adjusting the maximum depth h in the impurity concentration distribution of the impurity diffusion region 7, the strength ε of the transfer electric field can be set. Further, since one transfer stage is formed by one transfer electrode 4 or 5, a potential dip due to the presence of interlayer insulating film 6 does not occur. Therefore, the potential shape between the transfer electrodes 4 and 5 has a flattened slope from the vertex p1 to the vertex p2.

Furthermore, even if the respective potentials of the two-phase drive pulses φ1 and φ2 change over time, the inclination angle θ of the potential under each transfer electrode 4 and 5 is always the same, and the strength of the transfer electric field ε becomes uniform. From this, the impurity concentration of the impurity diffusion region 7 can be set freely, and the transfer potential, that is, each potential of the two-phase drive pulses φ1 and φ2 can be lowered. Note that the impurity diffusion region 7 can be formed by appropriately selecting the direction of ion implantation and the shape of the resist.

By the way, in the past, as shown in FIGS. 5 and 6, one transfer stage was constructed by two transfer electrodes 23 and 24, so the minimum gate length of each transfer electrode 23 and 24 was set to L. In this case, the length of one transfer stage is 2L. In this case, the length of 1 bit is 4L. on the other hand,
In the case of the first embodiment, one transfer electrode 4 or 5
Since one transfer stage is constituted by , the length of one transfer stage is L, and the length of 1 bit is 2L. As a result, the length of the transfer stage is reduced to 1/2 compared to the conventional case.
It can be reduced to

As mentioned above, according to the first embodiment,
Since one transfer stage is configured with one transfer electrode 4 or 5, it is possible to suppress the occurrence of a potential dip due to the presence of the interlayer insulating film 6, and to reduce the length of the transfer stage. can do. In addition, since the impurity concentration of the horizontal register 2 under each transfer electrode 4 and 5 is changed continuously in the direction of charge transfer, the transfer electric field is The strength ε can be made uniform, and a potential shape having a downward slope along the transfer direction can be maintained. Therefore, according to the first embodiment, it is possible to lower the transfer voltage, increase the speed of charge transfer, and miniaturize the transfer stage. For this reason, we are currently developing ultra-compact CCD solid-state image sensors and high-speed CCDs compatible with HDTV.
This will be effective for the development of CD solid-state image sensors.

In the first embodiment, the impurity diffusion region 7 is formed by diffusion of P-type impurities.
Alternatively, as shown in a modified example of FIG. 2, the impurity diffusion region 7 may be formed by diffusing an N-type impurity, for example, phosphorus (P). In this case, the impurity concentration distribution in the impurity diffusion region 7 is set to have an approximately right angle in a portion corresponding to one end a of each transfer electrode 4 or 5, and the smallest internal angle in a portion corresponding to one end a of the next transfer electrode 4 or 5. so that it has an approximately right-angled triangular shape.

Therefore, in this case as well, as in the first embodiment, when viewed from the impurity concentration of the horizontal register 2, the N-type impurity concentration increases continuously in the direction of signal charge transfer. distribution, and its potential shape is the same as in the first embodiment.

Next, a second embodiment that follows the conventional transfer stage will be described with reference to FIG. 3. Components corresponding to those in FIG. 1 are designated by the same reference numerals.

The CCD solid-state imaging device according to the second embodiment forms a set of two adjacent transfer electrodes 4 and 5, and supplies two-phase drive pulses φ1 and φ2 alternately to each set. , has the same configuration as the conventional transfer stage (see FIGS. 5 and 6), in which one transfer stage is composed of one set of transfer electrodes 4 and 5.

In this second embodiment, P-type impurities such as boron (B) are ion-implanted into the surface of the horizontal register 2 under the second transfer electrode 5 in the horizontal register 2 to form a trapezoidal shape. An impurity diffusion region 8 having an impurity concentration distribution is formed. Each impurity diffusion region 8 is formed such that its P-type impurity concentration decreases continuously in the direction of signal charge transfer (direction indicated by the arrow).

That is, when looking at the impurity concentration of the horizontal register 2, the N-type impurity concentration under the second transfer electrode 5 is formed to increase continuously in the direction of signal charge transfer. In this case, the strength ε of the transfer electric field can be set by adjusting the depths h1 and h2 below one end a and the other end b of the second transfer electrode 5 in the impurity distribution of the impurity diffusion region 8. , it becomes possible to form a stronger electric field than the conventional transfer electric field. This leads to improved signal charge transfer efficiency.

Therefore, according to the second embodiment, since the conventional structure in which one transfer stage is formed by one set of transfer electrodes 4 and 5 is followed, the steps from the formation of the transfer stage to the formation of the wiring are Conventional manufacturing processes can be used as is. Furthermore, in the pair of transfer electrodes 4 and 5, the impurity concentration of the horizontal register 2 under the second transfer electrode 5 is changed continuously in the charge transfer direction, so that A strong transfer electric field can be created. Therefore, according to the second embodiment, it is possible to lower the transfer voltage and increase the speed of charge transfer while following the configuration of the conventional transfer stage.

[0032]

Effects of the Invention According to the CCD solid-state imaging device of the present invention, the strength of the transfer electric field in each transfer stage can be made uniform, and the occurrence of potential dips in the transfer stage can be suppressed, and the transfer voltage can be reduced. It is possible to reduce the voltage, increase the speed of charge transfer, and miniaturize the transfer stage. Further, according to the CCD solid-state image sensor according to the present invention, while following the configuration of the conventional transfer stage, the transfer electric field in each transfer stage can be made strong, and the occurrence of potential dips within the transfer stage can be suppressed, and the transfer It is possible to reduce the voltage and increase the speed of charge transfer.

[Brief explanation of drawings]

[Fig. 1] Main parts of a CCD solid-state image sensor according to a first embodiment (
1 is a configuration diagram showing a horizontal register and its transfer stage) and its potential diagram.

FIG. 2 is a configuration diagram showing the main parts (horizontal register and its transfer stage) of a CCD solid-state image sensor according to a modification of the first embodiment, and a potential diagram thereof.

[Fig. 3] Main parts of a CCD solid-state image sensor according to a second embodiment (
1 is a configuration diagram showing a horizontal register and its transfer stage) and its potential diagram.

FIG. 4 is a schematic plan view showing the general configuration of a CCD solid-state image sensor.

FIG. 5 is a configuration diagram showing the main parts (horizontal register and its transfer stage) of a conventional CCD solid-state image sensor and its potential diagram.

[Fig. 6] Main parts of a CCD solid-state image sensor according to another conventional example (
1 is a configuration diagram showing a horizontal register and its transfer stage) and its potential diagram.

[Explanation of symbols]

1 Silicon substrate 2 Horizontal register 3 Gate insulating film 4 First transfer electrode 5 Second transfer electrode 6 Interlayer insulation film 7 Impurity diffusion region

Claims (2)

[Claims] Claim 1: Sequentially arranged horizontally on a horizontal register,
Two-phase driving pulses are alternately supplied to each of the formed large number of transfer electrodes, one transfer stage is configured with one transfer electrode, and the impurity concentration of the horizontal register under each transfer electrode is reduced. A CCD solid-state image pickup device characterized in that charges change continuously in the direction of charge transfer. 2. Sequentially arranged horizontally on a horizontal register,
Among the many transfer electrodes formed, two adjacent transfer electrodes are set as a set, and two-phase drive pulses are alternately supplied to each set, so that one transfer stage is formed by one set of transfer electrodes. What is claimed is: 1. A CCD solid-state image pickup device characterized in that the impurity concentration of each horizontal register under one of the transfer electrodes in the set of transfer electrodes changes continuously in the charge transfer direction.