JP2713991B2 - Solid-state imaging device - Google Patents

Description

Description: Object of the Invention (Industrial application field) The present invention relates to a solid-state imaging device having a plurality of horizontal CCDs, and in particular, to a solid-state imaging device in which charge transfer between horizontal CCDs is improved. Related to the device.

(Prior Art) In recent years, CCD image pickup apparatuses have been widely used for home video cameras and the like, and conversion from image pickup tubes has also been advanced in broadcast cameras. Super VHS format (S-VHS format) for home video cameras and HD for TV broadcasting
With the emergence of new systems such as the TV system, the need for multi-pixel solid-state imaging devices is increasing. In these systems, the number of pixels in the vertical direction is about 500 pixels in the S-VHS format, and HDTV
The method is determined to be about 1000 pixels, and the need for multi-pixels is being directed to higher integration of horizontal pixels.

As the number of pixels in the horizontal direction increases, the readout frequency of the signal output and the driving frequency of the horizontal CCD increase. Therefore, the structure of a single horizontal CCD that has been conventionally used increases the power required to drive the CCD. However, problems such as a decrease in transfer efficiency in a horizontal CCD have come to occur. In order to solve these problems, a structure having a plurality of horizontal CCDs has been disclosed. For example, a document (“1/2 inch 768 × 49
Two-element CCD image sensor ”TV Technical Report, February 1986, TEBS
109 ED942).

Hereinafter, an example of a conventional CCD imaging device having the two-line horizontal CCD will be described with reference to FIG. In FIG. 5, reference numeral 10 denotes a semiconductor substrate, reference numeral 20 denotes a photodiode as a photosensitive portion, and reference numerals 30 ₁ ,
~, 30 _M , 30 _{M + 1} , ~, 30 _N are vertical CCDs, and the vertical CCD is φV ₁
Consists of 4 pairs of electrodes ～FaiV ₄ is applied operates in four layers driven. Further, horizontal CCDs 41 and 42 forming one stage are arranged in parallel corresponding to two adjacent columns of vertical CCDs such as 30 _M and 30 _{M + 1} . Output amplifiers 51 and 52 are provided for the two horizontal CCDs 41 and 42, respectively. Also, vertical CCD and horizontal CCD
Between the horizontal CCD and the horizontal CCD are electrodes 53 and 54 for timing the transfer between the vertical CCD and the horizontal CCD.
An electrode 55 for transferring charges between D is provided.

In such a structure, the signal charges accumulated in the photodiode 20 for a certain period are read out to the corresponding vertical CCDs and then transferred in the vertical direction. For example 30 _M, 30 looking at the movement of the signal charges transferred by the vertical CCD two adjacent columns, such as _{M + 1, φ VL} via the electrodes 53 and 54 is given the signal charges transferred to the horizontal CCD41 Of which, vertical CCD30 _{M + 1}
Further horizontal through an electrode 55 to which φ _T is applied.
Transferred to CCD42. The signal charges from the adjacent vertical CCDs distributed to the two horizontal CCDs are transferred in the horizontal direction while being separated into the respective horizontal CCDs, and output from the output amplifiers 51 and 52.

Next, an operation of distributing signal charges to two horizontal CCDs will be described with reference to FIGS. 6 and 7. FIG. FIG. 6 shows the final stage of the vertical CCD (the electrode 56 to which φ _V2 is given),
FIG. 7 is a diagram showing an example of a specific structure of the electrodes 53 and 54, the two horizontal CCDs 41 and 42, and the electrode 55. FIG. 7 is a diagram showing driving pulses applied to each electrode in FIG.

In FIG. 6, the solid line is the first layer electrode, and the broken line is the second electrode.
The electrode of the first layer and the chain line indicate the electrode of the third layer.
The hatched area is an element isolation region. Horizontal
Since the CCDs 41 and 42 operate by the two-layer drive, the electrodes 6 on the channels for temporarily storing the charges during the transfer of the charges in the horizontal direction.
2,63 (here the second layer electrode is used) and the electrode on the channel that serves as a barrier in the horizontal charge transfer
There are four types of electrodes, 64 and 65 (here, the third layer electrode is used). Two sets of φ _H1 and φ _H2 are formed by electrically connecting the electrodes 62 and 64 and the electrodes 63 and 65, respectively. Of the transfer electrode.
In the transfer of charges between the horizontal CCDs 41 and 42, a channel below the horizontal CCD 41 serves as a path for the charges.

6 shows the movement of the signal charges 71 and 72 during transfer, and corresponds to the timing of FIG. At the timing, the signal charges 71 and 72 are transferred from the electrode 56 to the electrodes 53 and 54 and from the electrodes 53 and 54 to the horizontal CCD 41 at the timing. At the timing, the signal electrode 71 stops at the horizontal CCD 41 by the element isolation region. On the other hand, the signal charge 72 is applied to the electrode 55 at the timing, and further to the horizontal CCD 42 at the timing.
Is forwarded to As described above, the signal charges from the adjacent vertical CCDs are distributed to the two horizontal CCDs 41 and 42.

However, this type of apparatus has the following problems. That is, the electrode 62 on the channel through which the charges pass when the charges are transferred between the two horizontal CCDs 41 and 42 has a rectangular shape, and is formed of polycrystalline silicon which is currently used as an electrode material. Jagged around 2000mm around the area. For this reason, the width (length in the horizontal direction) of the electrode 62 varies up to about 4000 ° within one electrode. This variation changes the channel potential through which the signal electrode passes, and changes the potential to a higher value when the width is wider and a lower value when the width is narrower.

This will be further described with reference to FIG. FIG. 8 is a diagram showing, in FIG. 6, an electrode portion relating to the transfer operation of the signal charge 72 and the potential of the channel under each electrode in the transfer operation along the charge transfer direction. Assuming that the designed width of the electrode 62 is L, and that a protrusion of 2000 ° is generated on both sides near the center of the electrode 62 for easy understanding, the electrode width at this portion is L + 4000 °. Electrode width is L + 4000mm
In the portion indicated by, the channel potential is higher by ΔV than the channel potential in the other portions. Where L
Is 4 μm, ΔV is about 50 mV, which is larger than the thermal excitation voltage of electrons (the potential difference of the potential barrier over which electrons can be crossed by thermal excitation) of about 25 mV. That is,
A portion with a high potential (hereinafter referred to as a potential pocket) is locally generated in a channel below one of the electrodes 62, and the charge transfer is not completely performed. And in this case,
Irregular vertical lines are generated on the reproduced screen, and the image quality is significantly deteriorated.

(Problems to be Solved by the Invention) As described above, conventionally, in a solid-state imaging device having a plurality of horizontal CCDs, there is a problem that an opaque vertical line is generated on a reproduction screen due to a poor charge transfer between the horizontal CCDs. Was.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to eliminate a charge transfer failure between horizontal CCDs and to obtain a good image without deterioration in image quality due to generation of vertical lines. An object of the present invention is to provide a solid-state imaging device.

[Constitution of the Invention] The gist of the present invention is that the channel potential on the exit side with respect to the entrance of the signal charge is high in the same channel for the transfer of the signal charge between the horizontal CCDs. The purpose is to select a channel width or a channel width and an impurity doping amount so as to be as follows.

That is, the present invention provides a photosensitive unit arranged in a matrix on a semiconductor substrate, and a plurality of columns formed on the substrate along these photosensitive unit arrangements and reading signal charges stored in the photosensitive unit. A solid body comprising a vertical CCD and a plurality of horizontal CCDs which are arranged in parallel on the substrate in a direction orthogonal to these vertical CCDs and distribute the signal charges of each row transferred from the vertical CCD and transfer the signal charges in the horizontal direction. In the imaging apparatus, the plurality of horizontal CCDs are used as horizontal CCDs among channels of the horizontal CCDs.
The channel to which the signal charges are transferred is formed so that the outlet side is wider than the inlet side of the signal charges in the same channel.

Further, according to the present invention, in the solid-state imaging device, the plurality of horizontal CCDs are configured such that, among the channels of the horizontal CCD, a channel provided with transfer of signal charges by electrons between the horizontal CCDs is in the same channel, and The outlet side is formed wider than the inlet side, and the channel potential is higher on the outlet side than on the inlet side of the signal charge in the same channel,
The channel is formed with different impurity doping amounts.

(Operation) According to the present invention, the electrodes are formed such that the channel through which the signal charges pass during the transfer of charges between the horizontal CCDs is wider on the exit side than on the entrance side of the signal charges in the same channel. This spread of the channel causes a potential gradient such that the potential of the channel increases along the transfer direction of the signal charge between the horizontal CCDs. Therefore, the potential pocket due to the jaggedness of the electrodes can be canceled by this potential gradient, and the complete transfer of the signal charge becomes possible in the transfer between the horizontal CCDs. That is, a transfer failure does not occur when transferring the signal charges between the horizontal CCDs, and it is possible to reproduce a good image without deterioration in image quality due to generation of vertical lines.

Further, by controlling both the channel width and the impurity doping amount as described above, it is possible to more completely transfer signal charges between horizontal CCDs.

(Examples) Hereinafter, details of the present invention will be described with reference to the illustrated examples.

FIG. 1 is a schematic configuration diagram showing a CCD image pickup apparatus using a two-line horizontal CCD according to one embodiment of the present invention, and shows the arrangement of electrode units in the last stage of a vertical CCD. The same parts as those in FIG. 6 are denoted by the same reference numerals. In this embodiment, the channel 80 through which signal charges pass during transfer between the horizontal CCDs 41 and 42 is wider on the exit side (electrode 55) than on the entrance side (electrodes 53 and 54) of signal charge. Is formed. Here, the electrode 61 on the channel 80 is formed by the electrode of the second layer, and the shape of the electrode 61 on the horizontal CCD 41 becomes the shape of the channel 80. Therefore, the channel shape is realized by forming the electrode 61 such that the width thereof is wider on the exit side with respect to the entrance side of the signal charge. The basic structure other than the channel 80 and the electrode 61,
The operation of the charge transfer is the same as that of the conventional device shown in FIGS. 6 and 7, and the description thereof is omitted here.

In FIG. 1, a channel 80 is a horizontal CCD 4 of a signal charge 72.
Since the channel 80 is formed so as to become wider along the transfer direction, the potential gradient in the channel 80 is higher on the electrode 55 side than on the electrodes 53 and 54, and the charge Transfer can be done quickly.

FIG. 2 shows a case where the center value of the width of the channel 80 is 4 μm and 3
The change of the channel potential when the channel width is changed from μm to 5.5 μm is shown. In FIG. 2, the potential difference between the channel widths of 3 μm and 5.5 μm is about 420 mV. here,
Assuming that the vertical length of the channel 80 is 15 μm, the potential gradient is 28 mV / μm. The potential pocket due to the jaggedness of the electrode 61 occurs in the channel having this potential gradient, but when viewed from the channel potential, the potential pocket exists in the inclined portion, so the size of the potential pocket is substantially smaller by the potential gradient. Become. Therefore, the potential pocket of 5 mV, which has been a problem in the conventional structure, is effectively reduced to 22 mV, which is lower than the thermal excitation voltage of electrons, so that signal charges can be completely transferred.

Thus, according to the present embodiment, the width of the electrode 61 is formed wider on the exit side with respect to the entrance side of the signal charge, and the horizontal CCDs 41 and 42 are formed.
The potential of the channel 80 used for the transfer of the signal charge between the two is set higher on the outlet side than on the inlet side. For this reason, horizontal
The transfer of signal charges between the CCDs 41 and 42 can be performed promptly, and the potential pocket caused by the jaggedness of the electrode 61 can be canceled by the potential gradient of the channel 80. Therefore, it is possible to completely transfer signal charges in the transfer between horizontal CCDs, and to prevent the deterioration of image quality due to the generation of vertical lines,
A good image can be reproduced. In addition, there is an advantage that it can be easily realized only by changing the width of the electrode 61 along the signal charge transfer direction without changing the basic configuration.

FIG. 3 is a plan view showing a main part of another embodiment of the present invention, in which the electrodes 64 and 65 are the second layer, and the electrode 61 on the channel is the third layer. In this case, as shown in FIG. 3, the shape of the channel 80 is the portion of the horizontal CCD 41 that is not covered by the second layer electrodes 64 and 65, and the third layer electrode 61 completely fills the channel 80. There is no restriction on its shape as long as it is formed so as to cover the surface. Even with such a configuration,
Since the shape of the channel 80 is wider on the outlet side than on the inlet side in the signal charge transfer direction between the horizontal CCDs 41 and 42, the same effect as in the first embodiment can be obtained.

Note that the present invention is not limited to the above-described embodiments. In the embodiment, as shown in FIG.
Although the shape of the trapezoid has a constant increase in width with respect to the vertical direction, a fringe electric field is generated by the electrodes 43, 44, the electrodes 45, and the like in portions near the entrance and exit of the signal charge of the channel 80. I have. Therefore, the width of the channel 80 (the width of the electrode) may be changed only in the vicinity of the center as shown in FIG. Further, the width ratio is not constant, and the width of the channel may be changed only near the center.

In addition to the variable channel width, a potential difference may be provided depending on the type and amount of impurities doped in the channel region. For example, as shown in FIG. 4 (c), boron (B) is applied to the signal charge inlet side 81 of the channel 80 at 5 × 10 ¹⁵ -1 × 10 ¹⁶ / c.
Doping about m ³ , phosphorous (P) or arsenic (As) on exit side 82
To increase the channel potential on the exit side of the signal charge. Further, by selecting the impurity species and the doping amount, it is possible to give a gradient to the channel potential in the signal charge transfer direction without changing the channel width.

Further, in the embodiment, the structure of the two-electrode horizontal CCD has been described as an example. However, a plurality of horizontal CCDs having three or more wires may be used for a channel through which charges are transferred when transferring charges between the horizontal CCDs. Thus, the present invention can be applied. In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above in detail, according to the present invention, in the channel between the horizontal CCDs for distributing the signal charges of the vertical CCDs, the exit side of the signal charges is closer to the exit side in the same channel. Can be formed. Therefore, it is possible to eliminate the influence of the potential pocket caused by the jaggedness or the like in the peripheral portion of the electrode, to completely transfer the charges, and to obtain a reproduced image without deterioration of image quality due to irregular vertical lines. Becomes

[Brief description of the drawings]

FIG. 1 is a plan view showing a schematic configuration of a CCD image pickup apparatus according to an embodiment of the present invention, and is a plan view showing a configuration of a vertical CCD after the last stage, and FIG. FIG. 3 is a characteristic diagram showing a change in channel potential with respect to a channel width, FIG. 3 is a plan view showing a main part configuration of another embodiment of the present invention, FIG. 4 is a plan view illustrating a modification, 5 to 8 are views for explaining a conventional CCD image pickup apparatus. FIG. 5 is a plan view showing the entire structure, and FIG.
FIG. 7 is a plan view showing the configuration after the last stage of the vertical CCD, FIG. 7 is a signal waveform diagram showing signals applied to respective electrodes, and FIG. 8 is a schematic diagram showing a change in channel potential along the signal charge transfer direction. It is. 10 ... semiconductor substrate, 20 ... photodiode (photosensitive part), 30 ₁ , ..., 30 _N ... vertical CCD, 41, 42 ... horizontal CCD, 51,
52 …… Output amplifier, 53, ～, 55 …… Vertical transfer electrode, 61, ～,
65 horizontal transfer electrodes, 71, 72 signal charges, 80 channels.

Claims (3)

(57) [Claims] 1. A photosensitive unit arranged in a matrix on a semiconductor substrate, and a plurality of columns formed on the substrate along the arrangement of the photosensitive units and reading signal charges stored in the photosensitive unit. A solid body comprising a vertical CCD and a plurality of horizontal CCDs which are arranged in parallel on the substrate in a direction orthogonal to these vertical CCDs and distribute the signal charges of each row transferred from the vertical CCD and transfer the signal charges in the horizontal direction. In the image pickup apparatus, among the plurality of horizontal CCDs, of the channels of the horizontal CCD, a channel provided for transfer of signal charges between the horizontal CCDs has an outlet side wider than an inlet side of signal charges in the same channel. A solid-state imaging device characterized by being formed as described above. 2. In the plurality of horizontal CCDs, of the channels of the horizontal CCD, a channel provided for transferring signal charges between the horizontal CCDs has a continuous output port side with respect to an input side of signal charges in the same channel. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is formed so as to be wider as desired. 3. A plurality of photosensitive units arranged in a matrix on a semiconductor substrate, and a plurality of columns arranged on the substrate along the arrangement of the photosensitive units and reading signal charges stored in the photosensitive units. A solid body comprising a vertical CCD and a plurality of horizontal CCDs which are arranged in parallel on the substrate in a direction orthogonal to these vertical CCDs and distribute the signal charges of each row transferred from the vertical CCD and transfer the signal charges in the horizontal direction. In the image pickup apparatus, the plurality of horizontal CCDs include, among the channels of the horizontal CCD, a channel provided for transfer of signal charges due to electrons between the horizontal CCDs, and an exit side with respect to an entrance side of the signal charges in the same channel. It is formed so as to be wider and the channel potential is higher on the outlet side than on the inlet side of the signal charge in the same channel,
A solid-state imaging device formed by changing the impurity doping amount of a channel.