JPH0424873B2 - - 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 small, lightweight,
It is characterized by low power consumption and high reliability, and there is no worry about burn-in like in image pickup tubes, so it has 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. A group of photoelectric conversion elements 11 arranged, a horizontal shift register 12 electrically coupled to one end of each vertical shift register, and a horizontal shift register 1
It is composed of a charge detection section 13 provided at one end of 2.

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 of the bonding region shown in FIG. 2 taken along the - line. 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 1 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 charge accumulated in the photoelectric conversion element group 11 according to the amount of incident light is read out to the corresponding vertical shift register group 10 for each frame period or field period of the video signal, and then is read out in the horizontal scanning period of the video signal. The signals are sequentially transferred downward in parallel within the vertical shift register group 10 every (1H). The signal charges transferred to the end of the vertical shift register group 10 are injected in parallel into the horizontal shift register 12 every horizontal scanning period (1H) when the vertical transfer gate electrode 23 is turned on.
The signal charge sent to the horizontal shift register 12 is
While the signal charges are transferred from the vertical shift register group 10 in the next cycle, they are sequentially transferred in the horizontal direction and are taken out from the charge detection section 13 as a video signal.

In such a conventional charge transfer imaging device, when a high-brightness subject is imaged, the image may flow in the horizontal direction, or a horizontal line-shaped false signal may appear in front of the image. Unfavorable development was observed in terms of imaging operation. 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 FIGS. 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, Figure 2, Figure 3, Figure 4
The development will be explained using the drawings and 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 becomes 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
− If a level signal charge smaller than _V is transferred, the signal charge does not enter the region 36;
Efficient transfer is performed. However, as shown in figure b, the level of the signal charge is lower than the above potential difference _H −
When the signal charge becomes large enough to exceed _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. Further, when the horizontal charge transfer electrode 27 is turned off as shown in FIG.
A part of the signal charges that have entered the vertical transfer gate 23 are injected into the well 41 under the vertical charge transfer electrode 22 by overcoming the barrier 40 under the vertical transfer gate 23 . The false 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 turns on, and behave as if they were real signal charges. 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 plurality of columns of vertical shift register groups each consisting of a charge transfer device formed on a semiconductor having one conductivity type, a photoelectric conversion element group arranged corresponding to the vertical shift register group, and the vertical A charge transfer horizontal shift register provided adjacent to one end of the shift register group, and a charge transfer 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 charge transfer imaging device comprising a coupling portion between a group of vertical shift registers and the horizontal shift register, and a charge detection portion provided at one end of the horizontal shift register, the charge transfer imaging device comprising: The horizontal shift register is configured such that the impurity concentration of the semiconductor that constitutes the vertical shift register group and the coupling portion is such that the difference in channel potential of the coupling portion is larger than the maximum signal level of the charge transfer imaging device. There is obtained a charge transfer imaging device characterized in that the impurity concentration of the semiconductor is higher than that of the semiconductor.

Next, the present invention will be explained using the drawings.

FIG. 6 shows an embodiment of a charge transfer imaging device according to the present invention, and the basic configuration of the present invention is almost the same as that of the conventional example shown in FIG. 2 is a sectional view of a coupling region 14 between the vertical shift register group 10 and the horizontal shift register 12 shown in FIG. 1, and corresponds to FIG. 3 of the conventional example. In addition, in the figure, the same numbers as in FIG. 3 indicate the same components. In the figure, the channel area and area 36 of the vertical shift register
is formed on a semiconductor layer 38 which has the same conductivity type as the substrate 31 and has a higher concentration than the substrate 31. Generally, the channel potential of a buried channel formed on a highly doped semiconductor substrate is smaller than the channel potential when it is formed on a lightly doped semiconductor substrate. Therefore, for the same gate voltage, the channel potential of the buried channel formed on the semiconductor layer 38 in FIG. 6 is generally shallower than the channel potential of the channel region 37 of the horizontal register. Therefore, as shown in FIG. 4 a, b, and c in the conventional example,
The potential distribution corresponding to is as shown in FIG. 7a, b, and c. Channel area 37 of the horizontal register in FIG.
The channel potential _H of is the same as the conventional example, but
The channel potential _V of the region 36 is lower than that of the conventional example for the reason mentioned above. Therefore, the channel potential difference _H − _V can be obtained with a larger value than in the conventional case. As a result, even if a large amount of signal charges are accumulated as shown in FIG. 7b, the accumulation of signal charges in the region 36 as seen in the conventional example can be avoided. Therefore, as shown in FIG. 7c, even if the horizontal charge transfer electrode 27 is turned off, part of the signal charge is not injected into the vertical register side as in the conventional case. As a result, the previously observed drawbacks are eliminated.

FIG. 8 shows another embodiment according to the present invention,
A semiconductor layer 41 having a conductivity type opposite to that of the substrate is formed on a semiconductor substrate 42 having one conductivity type, and the present imaging device is constructed on this semiconductor layer. In this embodiment, the substrate 3 of the embodiment shown in FIG.
1 corresponds to the semiconductor layer 41, and the semiconductor layer 37 corresponds to the semiconductor layer 40. In this embodiment as well, the semiconductor layer 40 is set to have a higher concentration than the semiconductor layer 41. As a result, in the device according to this embodiment, the semiconductor layer 41 can be regarded as the substrate 31 in FIG. 6, and can be considered in the same way as the embodiment shown in FIG.

As described above, according to the present invention, when a high-brightness subject is imaged using a conventional charge transfer imaging device, development in which the image flows in the horizontal direction or a horizontal line-like false signal appears in front of the image can be avoided. removed.

In the above description, an N-channel device has been described for convenience, but it is clear that the gist of the present invention can also be applied to a P-channel device.

[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 a cross-sectional view along the - line in Figure 2, Figures 4 a, b, and c are schematic potential distribution diagrams in Figure 3, Figure 5 is a diagram showing the channel width dependence of channel potential, and Figure 6. 1 is a sectional view of the coupling area of the vertical shift register and the horizontal shift register in FIG. 1, illustrating the structure according to the invention.
7a, b, and c are schematic potential distribution diagrams in FIG. 6, and FIG. 8 shows another embodiment according to the present invention. In the figure, 10 is a vertical shift register group, 1
1 is a photoelectric conversion element group, 12 is a horizontal shift register, 13 is a charge detection section, 14 is a coupling region of the vertical shift register and horizontal shift register, 20 is a channel region of the vertical shift register, 21 and 22 are vertical charge transfer electrodes, 23 is a vertical transfer gate electrode, 24 and 37 are channel regions of a horizontal shift register, 25 to 29 are horizontal charge transfer electrodes, 30,
36 is an end region of the vertical shift register covered with a part of the horizontal charge transfer electrode, 31 and 42 are semiconductor substrates, 32 is an insulating layer, 33 is a buried channel layer, 3
4 is a channel stop region, 35 is a metal layer, 41
is a semiconductor layer having a conductivity type opposite to that of the semiconductor substrate 42, and 38 and 40 are semiconductor layers having a higher concentration and having the same conductivity type as 31 and 41, respectively.

Claims (1)

[Claims] 1 a plurality of vertical shift register groups consisting of charge transfer devices formed on a semiconductor having one conductivity type; a photoelectric conversion element group arranged corresponding to the vertical shift register group; a charge transfer horizontal shift register provided adjacent to one end; and the vertical 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 charge transfer device comprising a coupling portion between the group and the horizontal shift register, and a charge detection portion provided at one end of the horizontal shift register, the charge transfer device comprising: a channel potential under the horizontal charge transfer electrode and a channel of the coupling portion; The impurity concentration of the semiconductor forming the vertical shift register group and the coupling portion is such that the potential difference is larger than the maximum signal level of the charge transfer imaging device. A charge transfer imaging device characterized in that the impurity concentration is greater than the impurity concentration.