JPH0424874B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device using a charge transfer device.

Solid-state imaging devices are characterized by their small size, light weight, low power consumption, and high reliability, and because they do not have to worry about burn-in unlike image pickup tubes, they have been researched and developed in a wide range of fields in recent years.

FIG. 1 is a schematic diagram of one of the charge transfer imaging devices described above, which is called an interline transfer method. It consists of a photoelectric conversion element group 11 arranged and a charge detection section 13 provided at one end of a horizontal shift register 12 electrically coupled to one end of each vertical shift register.

FIG. 2 is an enlarged view of the coupling region 14 between the vertical shift register group 10 and the horizontal shift register 12 in the charge transfer imaging device shown in FIG. , 22 and a vertical transfer gate electrode 23 that controls the transfer of signal charges from the vertical shift register 10 to the horizontal shift register 12. Further, the channel region 24 of the horizontal shift register 12 has horizontal charge transfer electrodes 25, 26, 2.
Covered by 7, 28, and 29. Furthermore, in the figure, the vertical shift register 10 and the horizontal shift register 12 are electrically coupled by covering the end region 30 of the channel region 20 with a part of the horizontal charge transfer electrode 27.

FIG. 3 schematically shows a cross section taken along the bonding region-' line shown in FIG. 2. Semiconductor substrate 3
The above-mentioned vertical charge transfer electrodes 21 and 22, vertical transfer gate electrode 23, and horizontal charge transfer electrode 27 are formed on the main surface of 2 with an insulating layer 32 in between. Further, a buried channel layer 33 having a conductivity type opposite to that of the substrate semiconductor is formed under each of the above electrodes, and an impurity having a conductivity type opposite to that of the buried channel layer 33 is doped outside the channel region. A channel stop region 34 is formed. Further, the main surface of the semiconductor is shielded from light by, for example, a metal layer 35. In the same figure, area 3
Reference numeral 6 indicates a region 30 in FIG. 2 that electrically couples the vertical shift register and the horizontal shift register, and region 37 indicates a channel region of the horizontal shift register.

The operation of the charge transfer imaging device having such a structure is as follows.
In the figure, the signal charges accumulated in the photoelectric conversion element group 11 according to the incident amount correspond to the frame period of the video signal.
Alternatively, after being read out to the corresponding vertical shift register group 10 for each field period, the signals are sequentially transferred downward in parallel within the vertical shift register group 10 for each horizontal scanning period (1H) of the video signal. The signal charge transferred to the end of the vertical shift register group 10 is transferred to the vertical transfer gate electrode 2.
3 is injected in parallel into the horizontal shift register 12 every horizontal scanning period (1H) when it is in the on state. The signal charges sent to the horizontal shift register 12 are sequentially transferred in the horizontal direction while signal charges are transferred from the vertical shift register group 10 in the next cycle, and are taken out from the charge detection unit 13 as a video signal. It will be done.

With such conventional charge transfer imaging devices, when imaging a high-brightness object, the image flows horizontally or a horizontal line-shaped false signal appears in front of the image, which is an unfavorable phenomenon in terms of imaging operation. was observed. This development may cause color shift, such as when the charge transfer imaging device is applied to a single-chip color camera.
It may also be the cause of color shading.

The above development is due to the structure of the coupling area of the vertical shift register and horizontal shift register shown in FIG. 2 or 3. 4a, b, and c schematically show the potential distribution in each part of the cross-sectional view of the bonding region shown in FIG. 3 in order to explain the development, and FIG. Transfer electrode 2
1, 22 and the horizontal charge transfer electrode 27 are in the on state,
The potential distribution at the time when the vertical transfer gate electrode 23 is turned off is shown, and FIG. 4c shows the potential distribution at the time when only the horizontal charge transfer electrode 27 is changed from the above state to the off state. Further, FIG. 5 is a diagram showing the relationship between the width of the channel region and the channel potential in this region. From now on, Fig. 2, Fig. 3, Fig. 4
The above phenomenon will be explained using FIG.

First, in FIG. 4a, the channel potential _V of the region 36 shown in FIG. 3 is smaller than the channel potential _H of the region 37 because the channel width W _V of the region 30 shown in FIG. This is because it is smaller than the width W _H of No. 24. That is, in FIG. 5, the channel potential in the region having the channel width W _H is _H , but the channel potential _V in the region having the channel width W _V is smaller than the channel potential _H due to the narrow channel effect. Therefore, in FIG. 4a, the channel area 37 of the horizontal shift register _is
- When a signal charge at a level lower than _V is transferred, the signal charge does not enter the region 36, and efficient transfer is performed. However, the level of the signal charge as shown in figure b is
When the signal charge becomes large enough to exceed _H - _V , a portion of the signal charge enters the region 36, significantly deteriorating the transfer efficiency of the horizontal shift register. This causes the image to flow in the horizontal direction when capturing a high-brightness object as described above. Furthermore, when the horizontal charge transfer electrode 27 is turned off as shown in FIG. It is injected into the well 41. The signal charges injected into the well 41 are again injected into the horizontal shift register at the timing when the vertical transfer gate electrode 23 is turned on.
It behaves as if it were a true signal charge. This is the cause of the generation of false signals on the horizontal line when imaging a high-brightness object as described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high quality charge transfer imaging device that eliminates the above-mentioned drawbacks.

According to the present invention, a vertical shift register group is formed on a semiconductor substrate of a first conductivity type, and includes a plurality of rows of charge transfer devices that can be driven by the same charge transfer electrode group and are electrically isolated from each other. , a photoelectric conversion section that is electrically separated from each other by a channel stop means between the vertical shift registers and is capable of accumulating charges, and a transfer gate that controls signal charges between the vertical shift register and the photoelectric conversion section. an electrode, a horizontal shift register electrically coupled to one end of the vertical shift register, and the vertical shift register provided by covering the end channel region of the vertical shift register group with a part of the horizontal charge transfer electrode of the horizontal shift register. A coupling part between the shift register group and the horizontal shift register, and a device for detecting signal charges are provided at one end of the horizontal shift register, and the difference between the channel potential under the horizontal electrode and the channel potential of the coupling part is provided. The horizontal shift register is configured with an embedded channel made of a second conductivity type having a higher concentration than the vertical shift register and the coupling portion so that the signal level is higher than the maximum signal level of the charge transfer solid-state imaging device. A characteristic charge transfer imaging device is obtained.

Next, embodiments of the present invention will be described using the drawings.

The basic configuration of the present invention is almost the same as that of the conventional example shown in FIG. FIG. 6a schematically shows a cross section of the charge transfer imaging device according to the present invention taken along the line -' in FIG. The above-described vertical charge transfer electrodes 21 and 22, vertical transfer gate electrode 23, and horizontal charge transfer electrode 27 are formed with an insulating layer 32 in between. Immediately below the electrodes of the vertical charge transfer electrode, vertical transfer gate electrode, and horizontal charge transfer electrode regions 60, for example, a buried channel layer 62 having a conductivity type opposite to that of the substrate semiconductor is formed, and the horizontal charge transfer electrode A buried channel layer 63 having a higher concentration than the buried channel layer 62 and having a conductivity type opposite to that of the substrate semiconductor is formed directly below the electrode in the region 61 . Further, the main surface of the semiconductor is shielded from light by, for example, a metal layer 35. In the same figure, area 6
0 is an area that electrically couples the vertical shift register and the horizontal shift register, and area 61
indicates the channel area of the horizontal shift register.

The operation of the charge transfer device having such a structure is shown in FIG.
Since it is almost the same as the conventional example shown in FIGS. 2 and 3, only the charge transfer pattern in the horizontal shift register will be explained here using FIG. 6b. That is, FIG. 6b schematically shows the potential distribution directly under each electrode in the cross-sectional view shown in FIG. 6a, and the vertical charge transfer electrode 2
1 and 22, the potential distribution is shown when the horizontal charge transfer electrodes 23 are in the on state and the vertical transfer gate electrode 23 is in the off state.

A feature of the present invention is that the channel potential _H of the region 61 shown in FIG. 6b is made sufficiently higher than the channel potential _V of the region 60. This means that when a positive voltage is applied to the region 60 of the second conductivity type directly under the same charge transfer electrode and the region 61 with a higher concentration of the second conductivity type, the concentration of the second conductivity type is higher. The channel potential _H of the first region 61 is higher than the channel potential _V ' of the second conductivity type low concentration region 60. Therefore, in FIG. 6b, the doping amount of the second conductivity type of the region 61 is adjusted so that the channel potential difference _H - _V ' between the region 60 and the region 61 becomes sufficiently larger than the maximum signal level of the charge transfer imaging device according to the present invention. If selected, charge transfer in the horizontal shift register is performed only in the channel region 61, and part of the signal charge does not enter the region 60. Therefore, in the charge transfer imaging device according to the present invention, charge transfer in the horizontal shift register is performed efficiently, and the horizontal flow of the image when imaging a high-brightness object, which was the case in the conventional example, is completely eliminated. In addition, a part of the signal charge does not cross over the barrier 71 under the vertical transfer gate electrode 23 and are injected into the well 72 under the vertical charge transfer electrode 22, so that the signal charge is not injected into the well 72 under the vertical charge transfer electrode 22. The generation of false signals can also be completely prevented.

As described above, according to the present invention, a high-quality charge transfer imaging device that does not generate false signals can be realized.

Although the present invention has been described here using a charge transfer imaging device using an interline transfer method, it can be similarly implemented using a frame transfer method.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an imaging device using an interline transfer method, and FIG. 2 is an enlarged view of a coupling area of a vertical shift register and a horizontal shift register in FIG. 1, showing a conventional example. Figure 3 is -' of Figure 2.
4a, b, and c are schematic diagrams of the potential distribution in FIG. 3; FIG. 5 is a diagram showing the channel width dependence of channel potential; and FIG. 6a is a sectional diagram of the structure according to the present invention. , FIG. 6b is a schematic diagram of the potential distribution in FIG. 6a. In the figure, 10...vertical shift register group,
DESCRIPTION OF SYMBOLS 11... Photoelectric conversion element group, 12... Horizontal shift register, 13... Charge detection section, 14... Coupling area of vertical shift register and horizontal shift register, 2
0... Channel area of vertical shift register, 2
1, 22... Vertical charge transfer electrode, 23... Vertical transfer gate electrode, 24... Channel region of horizontal shift register, 25-29... Horizontal charge transfer electrode, 30, 36, 60... Horizontal charge transfer electrode. Terminal region of vertical shift register partially covered, 31...Substrate semiconductor, 32...Insulating layer, 33
. . . Embedded channel layer, 34 . . . Channel stop region, 35 . . . Metal layer, 37, 61 .

Claims (1)

[Claims] 1. A vertical shift register group consisting of a plurality of rows of charge transfer devices that are formed on a semiconductor substrate of a first conductivity type, that can be driven by the same charge transfer electrode group, and that are electrically isolated from each other, and each of the vertical shift registers. A photoelectric conversion section that is electrically separated from each other by a channel stop means between the registers and capable of accumulating charges, a vertical shift register, a transfer gate electrode that controls signal charges between the photoelectric conversion section, and a vertical shift register. a horizontal shift register electrically coupled to one end; the vertical shift register group and the horizontal shift register provided by covering a channel region at the end of the vertical shift register group with a part of the horizontal charge transfer electrode of the horizontal shift register; A device for detecting signal charges is provided at a coupling portion with the register and at one end of the horizontal shift register, and the difference between the channel potential under the horizontal electrode and the channel potential at the coupling portion is the maximum of the charge transfer solid-state imaging device. A charge transfer imaging device characterized in that the horizontal shift register is configured with a buried channel made of a second conductivity type having a higher concentration than the vertical shift register and the coupling portion so that the signal level is higher than the signal level. .