JPS63254766A - Charge transfer device - Google Patents

Abstract

PURPOSE:To prevent the decrease in transfer efficiency even if many picture elements are provided, by forming a horizontal transfer part with polysilicon in a three-layered structure, and constituting horizontal transfer electrodes with the polysilicon layers of a first layer and a second layer. CONSTITUTION:A third polysilicon layer, which constitutes a gate electrode 11, is arranged so as to cross first and second polysilicon layers at the approximately central parts in the vertical direction. The first and second polysilicon layers are divided into two parts in the upper and lower directions. Holes are provided at the parts of the first and second polysilicon layers, which correspond to every other vertical CCDs of, e.g., vertical transfer parts 2, in the crossing regions. The third polysilicon layer is arranged on a substrate. In the hole regions, differences are provided in depth of the potential wells of the holes. A barrier region 16 is formed in this way. The transfer efficiency of the horizontal CCD is not effected even if dispersion in machining of the third polysilicon layer becomes large.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a charge transfer device, and more particularly to a charge transfer device that is read out in multiple lines.

(Prior Art) One of the directions of technological development of charge transfer devices is increasing the number of pixels in order to obtain high resolution, and recently, charge transfer devices with 40,000 pixels have been developed.

With the increase in the number of pixels in such devices, fine processing performance and high-speed operation characteristics are increasingly required. As a solution to this
Multiple horizontal Cs connected in parallel to each other via gate electrodes
A nine-point readout type element has been proposed whose characteristics are improved using OD.

For example, in Figure 4, two horizontal 〇0Ds forming one stage are arranged in parallel corresponding to two vertical CODs, and the signal charges from adjacent vertical CODs are distributed to the two horizontal CODs. This shows the case where the data is transferred using

However, in such a multi-line readout element, the conventional structure of the horizontal transfer section is a three-layer polysilicon structure, and the first layer of polysilicon is horizontally zero (the gate electrode between the three sections has a two-layer polysilicon structure). The eyes and third layer of polysilicon are horizontally ca.
Each was used as a p-transfer electrode.

(Problems to be Solved by the Invention) However, in general, processing variations in polysilicon tend to be larger in the second layer than in the first layer, and larger in the third layer than in the second layer. Therefore, in the conventional structure described above, processing variations in the third layer of polysilicon become large, resulting in a drawback that the horizontal COD transfer efficiency is reduced.

The object of the present invention has been made in view of the above-mentioned drawbacks, and has five objects.
Even if the processing variations in the polysilicon layer become large,
An object of the present invention is to provide a charge transfer element that does not affect horizontal COD transfer efficiency.

(c) precautionary means and actions to solve problems), i.e.
The above object of the present invention is to provide a charge transfer element that distributes and reads out signals from photoelectric conversion elements arranged in a matrix to a horizontal transfer section consisting of at least two horizontal CODs connected in parallel to each other via gate electrodes. a first layer of polysilicon and a second layer of polysilicon that form transfer electrodes of the horizontal COD, and a third layer of polysilicon that intersects with the two polysilicon layers to form the gate electrode; A portion of the first and second layer polysilicon in the intersecting region is opened so that the third layer polysilicon is placed on the semiconductor substrate, and a portion under the opening region is opened. This is achieved by a charge transfer element characterized in that barrier regions are formed with potential wells having different depths.

By forming the horizontal caD using the first and second layers of polysilicon in this way, transfer electrodes with less processing variation can be provided, and the transfer efficiency will not decrease even when the number of pixels is increased. Furthermore, by forming a barrier region in the buried channel under the gate electrode in the opening region, 1
A signal supplied to one horizontal COD is transferred to another horizontal CCD under the control of the gate electrode, and then horizontally transferred without returning to the one horizontal CCD.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing one embodiment of a charge transfer device according to the present invention. In this embodiment, an interline transfer type 00D ( (L-0CD) will be described.

This process L-0(!D) includes a light receiving section 1 consisting of a plurality of light receiving elements arranged in a matrix, and a vertical transfer section 2 consisting of vertical 00D corresponding to the vertical rows of the light receiving elements. A horizontal transfer section 10 is arranged at the output end of the transfer section 2 through a gate electrode 5 .

The horizontal transfer section 10 is composed of two HOCDs 2.15 that are connected in parallel to each other via the gate electrodes 11, and the HOODs 12.15 include a large number of horizontal transfer electrodes 14.15 arranged in sets of two. 15, it is driven in two phases by the clock signal φAlφB.

The gate electrode 11 and the horizontal transfer electrodes 14 and 15 are made of polysilicon with a three-layer structure, and the first and second layers of polysilicon form the horizontal transfer electrodes 14 and 15, respectively.
15, and the third layer of polysilicon is the gate electrode 1.
1 respectively.

The gate electrode 11ft: The third layer of polysilicon is arranged to intersect with the first and second layers of polysilicon at approximately the center in the vertical direction.
The polysilicon layer is divided into two vertically. Also,
A portion of the first and second layer polysilicon in the intersecting region, in this example column, a portion of the first and second layer polysilicon corresponding to the vertical COD of every 201 vertical transfer sections. A hole is formed in the silicon so that a third layer of polysilicon is placed on a semiconductor substrate (not shown).

Further, in the opening region, a barrier region 16t is formed by providing a difference in depth (potential energy) of the potential well. That is, this difference is
As is clear from FIG. 3, the impurity concentration of the region facing the lower HOCD 13 formed by being divided by the gate electrode 11 is made higher than that of the region facing the upper HOOD 12, so that even under the same gate voltage, the potential well The depth is increased.

Note that the opening areas are separated by a channel stop 17.

Next, the operation of the charge transfer device according to the present invention configured as described above will be explained with reference to FIGS. 2 and 3.

When the image of the subject is formed on the light receiving section 1 and a charge corresponding to the brightness of the subject is obtained, this charge is transferred by the vertical transfer section 2 and transferred to the first 1110 through the first gate electrode 3.
(! is sent to DI 2.The charge is sent to the 10th HOOD1
The gate electrode 11111 (
From the 10th HOC! 1 of the charge supplied to D12
portion is moved below the gate electrode 11. That is, among the tenth HOCDs 12, the horizontal transfer electrodes 151, 15. , ...The charge below is transferred. At this time, the horizontal transfer electrode's,,p's! does not form the opening area. I... The lower charge remains in the 10th TICCD 12 as it is. The timing at this time corresponds to t=tl in FIG. 2, and the situation is shown by the dotted line in FIG. 3. Then, the gate electrode 11 is
a second HCOD on the level and forming the aperture area;
When the transfer electrode 15 becomes R level, the charges transferred under the opening region 2 are sent to the second HOCD 13.

The timing at this time is 1=1 in FIG. The situation is shown by the solid line in FIG. During this time, the first H(I
The charge on CDI 2 remains the same. The charges distributed to the two HCCDIs 2 and 13 as described above are sequentially transferred and read out in the horizontal direction by the respective horizontal transfer electrodes 14 and 15 using the conventional two-phase drive method. At this time, since the gate electrode 11 acts as a channel barrier and a barrier region 16 is formed in the opening region, each HOCDl 2, 15
The charges distributed to each other can be transferred independently without interfering with each other.

The difference in the depth of the wells under the opening region can be achieved, for example, by performing ion diffusion twice. That is, for example, when ion-implanting Mo8 as an n-type impurity, the first implantation is performed over the entire opening region, and the second implantation is performed in the region where the impurity concentration is desired to be high, in this example, into the horizontal CCD 13 on the lower side. Ion implantation is performed only in the lower part of the facing region.

Note that the absolute value of the impurity concentration may be a well-known value and will not be described here.

Further, the depth of the potential well can be determined not only by the difference in impurity concentration described above but also by the thickness of the oxide film on the opening region.

(Effects of the Invention) As described above, according to the charge transfer device of the present invention,
The horizontal transfer section is formed of polysilicon with a five-layer structure, and the horizontal transfer electrodes are formed from the first and second layers of polysilicon.

An electrode with less processing variation is provided. Therefore, it is possible to manufacture an element whose transfer efficiency does not deteriorate even when the number of pixels is increased.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, Fig. 2 is a ninth timing diagram to explain the operation, Fig. 3 is a potential profile also cited to explain the operation, and Fig. 4 is a conventional FIG. 2 is a device configuration diagram illustrating a multi-line readout element. 1... Light receiving section, 2... Vertical transfer section % 6, 11...
・Gate electrode, 10...Horizontal transfer section, 12.13...
・HOCD. 14.15...Horizontal transfer electrode, 16...Barrier region, 17...Channel stop

Claims (1)

[Claims] In a charge transfer element that distributes and reads out signals from photoelectric conversion elements arranged in a matrix to a horizontal transfer section consisting of at least two horizontal CCDs connected in parallel to each other via gate electrodes, the transfer electrodes of the horizontal CCDs are a third layer of polysilicon that intersects with the two polysilicon layers to form the gate electrode; Parts of the first layer and second layer polysilicon are opened to place the third layer polysilicon on the semiconductor substrate, and the depths of the potential wells under the opening regions are different. A charge transfer device characterized in that a barrier region is formed with a barrier region.