JPS60163459A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To improve the transfer efficiency of horizontal CCD's in a CCD type element by a method wherein the area of a CCD electrode at the part that receives signal charges from a vertical CCD shift register is made larger than that of another electrode. CONSTITUTION:When two receiving openings are provided, a the electrode dimensions L1'' and L2'' of two CCD electrodes 9''-1 and 9''-3 becomes larger than those of the other electrodes 9''-2, 9''-4-9''-6. If the dimensions L1'' and L3'' of the electrodes 9''-1 and 9''-3 corresponding to the two receiving openings are (P-3XIImin)/2, the dimensions of the L1'' and L3'' become the maximum in six CCD electrodes. The electrode capacitance of the receiving opening can be increased to approx. 1.5-2 times of that in the conventional element: it becomes possible to restrict charges for a potential increase VS in the case of their transfer to this electrode to 1/1.5-1/2, thus enabling those for an increase VY to be reduced; accordingly, inflow of charges to projections 11 is prevented.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a photoelectric conversion element on a semiconductor substrate and a charge transfer element for extracting optical information of each element.
Pled Devices, hereinafter abbreviated as CCD.

) or relates to a solid-state image sensor with an integrated MOS shift register.

[Background of the Invention]' A solid-state image sensor is required to have a resolving power equivalent to that of an imaging electron tube used in television broadcasting. For this we need 500 pieces vertically and 8 pieces horizontally.
A matrix of 00 to 1000 picture elements (photoelectric conversion elements) and a corresponding scanning element are required. Therefore, solid-state image sensors are manufactured using MO8 large-scale circuit technology that allows for high integration, and are equipped with a photoelectric conversion element and a charge transfer element (C) for extracting optical information from each element on a semiconductor substrate.
Harge Coupled Devices, hereafter C
(abbreviated as CD) or by integrating MOS transistor registers.

FIG. 1 is a basic configuration diagram of a conventional CCD type solid-state image pickup device characterized by low noise.

1 is a photoelectric conversion element consisting of a photodiode, etc.; 2 and 3;
outputs the optical signal charge accumulated in the photoelectric conversion element group 4
a vertical CCD shift register and a horizontal CCD shift register for taking out data; 5 and 6 are clock pulse generators that generate clock pulses to drive the vertical and horizontal COD shift registers, respectively. Although a two-phase clock pulse generator is shown here, a three-phase or four-phase clock may also be used. Reference numeral 7 denotes a transfer gate that sends the charges accumulated in the photodiodes to the vertical COD shift register 2. This solid-state image sensor becomes a monochrome image sensor in its current form, but if a color filter is laminated on top, each photodiode is provided with color information, making it a color image sensor.

Solid-state imaging devices have advantages such as being small, lightweight, maintenance-free, and low power consumption, and are expected to be the next generation imaging device.
Since charges are transferred in one direction within the COD shift register, which has more than 1000 stages, it is necessary to ensure sufficient transfer efficiency. However, the transfer efficiency of current CCD type elements has not yet reached a value sufficient for practical use due to configuration and structural problems. Especially compared to vertical COD shift registers, 3
Horizontal COD shift registers, which require an order of magnitude higher transfer speed, have low transfer efficiency, resulting in significant deterioration in image quality such as color mixing and deterioration of horizontal resolution.

Figure 2 shows the vertical CCD, which is a factor that deteriorates the transfer efficiency of horizontal CCD shift registers in current CCD type devices.
A combined portion of the OD shift register and the horizontal COD shift 1-register is shown.

The area inside the dotted line 8 is a region where charges can be transferred, that is, a channel. 9-1.9-2.9-3.9-4
are electrodes forming a horizontal COD shift register, 10-1
．． 10-2.10'-1°10'-2 indicates the final stage electrode forming the vertical COD shift register. The vertical COD shift register and the horizontal COD shift register are coupled by a horizontal COD electrode 9-1 extending upward (through this coupling region, the charge sent by the vertical COD shift register is sent into the horizontal CCD shift register). ), a protruding region 11 is formed above the horizontal COD shift register. Horizontal COD
The charge sent into the shift register is transferred at high speed into the horizontal CCD in the direction of arrow 12 (assuming the number of pixels lined up in the horizontal direction is 11, the transfer rate is n times the transfer speed of the vertical COD shift register). speed is required). Here, there is no problem if the transferred charges flow only through the region 13, but some of the charges also stray into the protruding region 11 as shown by arrows 14. Once the charge has strayed into the region 11, it cannot be extracted within a predetermined time for each region, and a considerable number remains in the protrusion region 11 at each stage. As a result, the transfer efficiency decreases and the horizontal resolution decreases. Color mixing occurs.

The image quality deteriorates significantly.

It is conceivable to increase the potential of the region 11 by implanting impurity atoms into the region 11 to eliminate charges straying into the protrusion region 11, or by extremely narrowing the channel radius 15 of the region 11. (However, this potential increase AV cannot be increased infinitely and has a limit, considering the operation when sending charges from the vertical CCD shift register to the horizontal COD shift register.) However, the transfer If the amount of charge is large, the above-mentioned finite potential increase AV will be added, and the charge will still stray into the region 11. Although this improves the transfer efficiency compared to the conventional case, it is still not sufficient to achieve practical image quality.

[Purpose of the invention]

An object of the present invention is to provide specific means for solving the above problems and improving the horizontal COD transfer efficiency in a CCD type device.

[Summary of the invention]

In order to achieve the above object, the present invention increases the area of the COD electrode of the part that receives signal charges from the vertical COD shift register among the COD electrodes constituting the horizontal COD shift register, compared to other electrodes. (Actually, the size of the COD electrode in the receiving part in the transfer direction is increased) to reduce the rise in potential that occurs when charges are sent under the electrode in that part.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail using examples.

FIG. 3 is a diagram showing the configuration of a horizontal COD shift register area constituting the solid-state imaging device of the present invention.

9'-1, 9'-2, 9'-3, 9'-4 are horizontal CO
These are the COD electrodes constituting the D shift register 3. For example, 9'-1 and 9'-3 are the COD electrodes that constitute the D shift register 3.
9'-2 and 9'-4 are the P of the second layer.
o1y -Si (of course, 9'-1, 9'-
3 is the second layer, 9'-2, 9'-4 is the first layer Po
1y-5i). In the solid-state image sensing device of the present invention, the signal charge has the dimensions of the electrode 9'-1 of the horizontal COD shift register corresponding to the receiving port, and / is the size of the other CCD electrode 9'-2 (L2').

It is larger than 9' 3 (L3', ) and 9' 4 (L' 4). On the other hand, in the case of the conventional element shown in FIG. 2, the dimensions of electrodes 9-1 and 9-3 are LlyL3.
are designed to have the same value (L I = L3) m9-2 and 9-1
The dimension L 2 t L 4 of 4 is also the same value (L
2=L4), and the electrode dimension L1 at the inlet of the receiver is not a large value compared to the others.

(Even in conventional devices, the first layer electrode size LI+L3 used for temporary charge accumulation is usually larger than the second layer electrode size L2tL4 used only for charge shifting, and usually I, 1=L3>L2=
It is designed to have the relationship L4. ) Here, we will examine the most desirable relationship regarding the electrode dimensions L+' + L2' v L3' p L12 of the horizontal CCD of the solid-state imaging device of the present invention. First, the dimension L 2 of the second layer electrode 9-2.9-4 used only for charge shifting.
'HL4' is selected as the minimum dimension II min allowed by manufacturing technology (L2' = L4' = I[m
1n). Next, the dimension of 9-3 of the first layer electrode is selected to be the minimum dimension of 1 min allowed by the manufacturing technology (L3
' = I min, and generally lm1n is 11m
(becomes larger than 1n). The receiver is the first layer electrode 9-1 at the entrance.
The dimension L1 is defined as the repetition pitch P of picture elements 7'.

L12. The value after subtracting L12 is L+'=PL2
'L3'-L4'), dimension, is the largest among the four electrodes (L+'>L3'>L2'
=L4') As described above, the effect of making the size of the electrode at the receiving inlet larger than that of other electrodes will be explained with reference to FIG. FIG. 3(a) is a diagram showing a cross-sectional structure of a horizontal COD shift register, where 16 is a P-type Si substrate, 17 is a
18 is the thinly concentrated n-type layer provided to make the channel a buried type (if the channel is a surface type, there is no need for wood chips), and 18 is the first and second layer Po1y-5il! For example, a P-type impurity layer 19 is implanted to create a potential difference between the electrodes, and the substrate 16 and the Po1y-Si electrode 9'-1~
Insulation for separating 9'-4! I! (Generally Si
(O2 membrane is used). Figure (b) is a diagram showing the potential under each electrode during charge transfer.
A signal charge Qn of magnitude corresponding to the amount of incident light.

Q n ++ is temporarily stored in the potential difference VB formed by 18 until the next transfer. Figure (C) is a diagram showing the configuration of electrode 9'-1 corresponding to the receiving part, Figure (d)
is a diagram showing the potential under electrode 9'-1. When the signal charge is transferred below the electrode 9'-1, the potential below the electrode 9'-1 rises by vs as shown in (d). This increase Vs depends on the capacitance C of the electrode 9'-1 and the signal charge Q, and can be expressed as Vs=Q/C. In a conventional solid-state image sensor, when a large signal charge is transferred, the charge is transferred to the protruding region 1 when the rising amount (8) exceeds the potential wall vA that was previously provided by the ion implantation or the narrow channel effect.
1 as well, leading to a decrease in transfer efficiency. Here, vA is usually designed to be larger than the above-mentioned VB. If ■. If it is designed to be smaller than Va, the amount of charge flowing into the protrusion region 11 increases. On the other hand, in the solid-state imaging device of the present invention, the capacitance C increases by an amount corresponding to the increase in the dimension L, -1 of the electrode 9'-1, and as a result, the potential increase Vs can be suppressed to a small value. That is, it is possible to suppress the increase C5 to be smaller than V^, and it is possible to prevent the charge from flowing to the protrusion 11. In the case of the present invention, it is of course assumed that VA is designed to be larger than v6. By making the electrode dimensions in the receiving part as large as possible as in the present invention and keeping the electrode dimensions outside the receiving part as small as possible, the dimension / can be increased to about three times the dimension in conventional elements. can. Therefore, the electrode capacitance in the element of the present invention can be increased to about three times that of the conventional element, and the increase Vs can be suppressed to about 1/3 of that of the conventional element.

The embodiment shown in FIG. 3 shows a case where the horizontal COD shift register is driven by two-phase clock pulses (for example, the first phase clock is applied to electrodes 9'-4 and 9'-1).
Apply the second phase clock to 2,9'-3). Fifth
The figure shows an embodiment in which a horizontal COD shift register is driven by three-phase clock pulses. 9'-1, 9'-2,
9'-3°9"-4, 9'-5, 9'-6 is horizontal C
These are the CCD electrodes that constitute the OD shift register 3, and for example, 9'-1, 9'-3, and 9'-5 are the first layer Po.
1y-Si, 9'-2,9"-4°9
'-6 is formed of the second layer of Po1y-Si. Since the horizontal CCD in this embodiment is driven by three-phase clock pulses, for example, the first clock is applied to 9''-6 and 9'-1, and the second clock + 9y- is applied to 9'-2 and 9''-3.
A third clock is applied to 4 and 9#-5 (not shown). In addition, in this embodiment, each level of horizontal C0D has 2
Although the case where each charging bone is provided with an inlet has been described, a case where one inlet is provided as in the case of FIG. 3 is also applicable. When installing two reception ports like this,
Electrode dimensions Ll of two CCD electrodes 9'-1 and 9'-3
'yL2# is larger than the other electrodes 9''-2, 9''-4 to 9'-6. Specifically, the dimension L 2 of electrode 9'-2, 9"-4°9#-6 used only for electrode shifting
't'L4' F Ll3' is selected as the faith dimension If win that is allowed by the manufacturing technology (L2"=L4
'=L6'=IImin), 9'-5 dimension L, 71 is also the minimum dimension 1 allowed by manufacturing processing technology
Select win (Ls' = lm1n). Dimension L of electrodes 9'-1 and 9'-3 corresponding to two receiving eyes
Let at1eL3' be (P-3XIImin)/2. As a result, the dimension of Ll"PL3' is the largest among the six CCD electrodes, and L' I = L3 '> Ls
The following relationship holds true: 'no L 2N==L 4#=L 6If.

FIG. 6(a) is a diagram showing the cross-sectional structure of the horizontal COD shift register in FIG. 5, and FIG. 6(b) is a diagram showing the (a)
) Figure showing the potential under the electrode shown in (c)
is the electrode 9'-1 or 9R-3 corresponding to the receiving part.
The figure (d) shows the configuration of the electrode 91-1 or 9.
It is a diagram showing the potential under #-3. Electrode 9'-1
If the dimensions 9'-3 and 9'-3 are made as large as possible, the dimension L1' is obtained.

L12 can be increased to about 1.5 to 2 times the dimension L1 in the conventional element. Therefore, in the case of this example, the electrode capacitance of the receiving port is 1.5 to 1.5 of the conventional element.
It can be increased to about twice the size, and the potential increase Vs when charges are transferred under the electrode can be suppressed to 1/1.5 to 1/2 of that of the conventional element. As a result.

It is possible to keep the increase VY smaller than VA,
It is possible to prevent charges from flowing into the protrusion 11.

〔Effect of the invention〕

As explained above, according to the solid-state image sensor of the present invention,
By making the area of the CCD electrode that receives the signal charge from the vertical CCD shift register larger than that of other electrodes among the CCD electrodes forming the horizontal CCD shift 1 register, the transfer charge of the signal charge within the horizontal CCDCD is increased. It becomes possible to reduce the rise in potential when transferred under the CCD electrode. As a result, when transferring charges in the horizontal COD, charges flowing into the protruding region can be eliminated, and the transfer efficiency of the horizontal COD shift register can be significantly improved. Also, when the future line ls@ increases, the charge is transferred from the vertical COD shift register to the horizontal GC.
It is conceivable that the dimension given to the channel width of the protruding region to be received in the D shift register will be significantly reduced, and a problem may arise in which it becomes virtually impossible to send charge, but in the present invention, the horizontal C of the receiving portion
Since the OD electrode is made large in size, the above problem can be prevented from occurring. Furthermore, the present invention can be realized by changing the layout pattern at the time of device design, and the device can be manufactured using exactly the same manufacturing technology as in the past, so there is no need to worry about lowering the manufacturing yield of the device.

Note that although the explanations in section 2 have been made with reference to C and CD type image sensors, which are considered to be the most promising among solid-state image sensors, CPD image sensors, which are considered to be another promising element (
It is obvious that the present invention can also be applied to Charge Priming Devices. A CPD type element consists of three regions: a picture element section that uses the source of a MOS transistor as a photodiode, a horizontal COD shift register, and a coupling section that sends the signal from the picture element section to the horizontal CCD shift register. COD 11 that constitutes the COD shift register! Among the poles, for the charge receiver, the area of the electric bridge corresponding to the insertion part may be made larger than the other parts. Horizontal COD when the present invention is applied to a CPD type device
The configuration and structure of the shift register are the same as those in the embodiments shown in FIGS. 3 to 6, and illustrations thereof are omitted.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a conventional solid-state image sensor, FIG. 2 is a diagram explaining the configuration of the conventional device and its problems, and FIG. 3 is a diagram showing an example of the configuration of the solid-state image sensor of the present invention. 4 is a diagram illustrating the structure and operation of the device of the present invention shown in FIG. 3, FIG. 5 is a diagram showing an example of a configuration different from that shown in FIG. 3 of the solid-state image sensor of the present invention, and FIG. 5 is a diagram illustrating the structure and operation of the element of the present invention shown in FIG. 5. FIG. 1... Photoelectric conversion element, 3... Horizontal CCD shift register, 9'-1, 9'-2, 9'-3, 9'-4...
・Horizontal CCD shift register electrode, 10-1°10-
2.10'-1, 10'-2... Electrodes of vertical CCD shift register. Figure 1 Figure Z Figure 3 Mouth flat 4 Low\-16 Child 5 Figures 2 to 16

Claims (1)

[Claims] On the same semiconductor substrate, a group of photoelectric conversion elements, a group of CCD shift registers for vertical scanning or a single MOS shift register for reading and scanning optical signals, and a CCD shift register for horizontal scanning.
In a solid-state imaging device that integrates a group of CD shift registers, the vertical COD shift register or the MOS of the COD electrodes constituting the horizontal COD shift register
The electrode dimensions of the part of the COD electrode corresponding to the charge transfer direction, which corresponds to the part that receives the signal charges sent by the shift register, are set by other COD electrodes of the same layer made in the same process.
A solid-state imaging device characterized in that the size is larger than that of an OD electrode.