JPS6084868A - Charge transfer device - Google Patents

Abstract

PURPOSE:To enable the great improvement of the charge transfer efficiency during an accumulation period by a method wherein a buried channel is provided under a double step gate adjacent to the photo charge accumulation part. CONSTITUTION:The photo charge accumulation part 1 and an accumulation gate 10 are connected inside, which are further connected to a substrate 2. A shift gate 5 serves to transfer charges accumulated under the gate 10 to the CCD part 6 and determines the time of accumulation. In the case of photo irradiation to the part 1, the charges photoelectrically converted in this region move down to the gate 10 as the result of making a difference in potential by the difference in the concentration between the region 11 under a barrier gate 9 and the region 12 under the gate 10. This transfer of charges are performed during the period of accumulation, and the rate of leaving charges becomes 0.5% or less. The transfer from the gate 10 to the CCD part 6 is by the buried channel CCD mode, and the rate of remaining charges due to this transfer becomes 0.02% or less.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a charge transfer device.

(Conventional structure and its problems) Recently, CCD (charge coupled device) with charge transfer function
The development of COD image sensors is progressing, and COD image sensors are being actively developed as an application thereof.

FIG. 1 shows a cross section of a conventional CCD solid-state imaging device near a photoelectric conversion section. Reference numeral 1 denotes a photoelectric charge accumulating portion which has a conductivity type opposite to that of the substrate 2 and performs photoelectric conversion and accumulation functions. 3 is a channel stopper which has the same conductivity type as the substrate 2 and has a higher concentration than the substrate 2, and 4 is a photocharge storage section 1.
5 is a photo-charge storage section 1 which determines the potential of
This is a shift gate that serves to transfer the charge of 1 to the CC0 section 6 and also determines the accumulation time, and 7 is a gate oxide film.

FIG. 2 shows the potential of the structure of FIG.

Now, the charge 8 under the photocharge storage section 1 and the photogate 4 is
To transfer to the C0 section 6, a pulse voltage is applied to the shift gate 5 to shift from the state shown in FIG. 2(a) to the state shown in FIG. 2(b). Transfer at this time is BBD transfer, shift gate 5
Even if the width of the pulse applied to is made sufficiently long, more than 2% of the charges accumulated under the photocharge storage section 1 and the photogate 4 will remain. As a result, it mixes with the signal of the next accumulation period, resulting in an afterimage in the case of an image sensor.

FIG. 3 shows a conventional example improved in the above points.

The photogate 4 shown in FIG. 1 is divided into a barrier gate 9 and an accumulation gate 10. Barrier gate 9 is a gate that determines the potential of photocharge storage section 1 .

(accumulation gate) 10 is a gate for accumulating the charges photoelectrically converted in the photocharge accumulating section 1 within the accumulating time;
It is necessary to apply a potential that makes the texture deep.

FIG. 4 shows the potential of the structure of FIG.

In the structure shown in Fig. 3, the charges photoelectrically converted in the photocharge accumulation section 1 immediately move to the bottom of the accumulation gate, and the charges are moved during the accumulation time, so that less than 0.5 inches of charges are left behind. .

Further, in order to transfer the charge 8 below the storage gate 10 to the CCD section 6, a pulse voltage is applied to the shift gate 5 and the fourth charge 8 is transferred to the CCD section 6.
Move from the state shown in (&) to the state shown in (b). This transfer is
In CcD transfer, the amount of charge left behind is 0.1% or less, and as a result, the amount of charge left behind during transfer from the photocharge storage section 1 to the 600 section 6 is 0.6% or less. However, in the structure shown in FIG. 3, separate voltages must be applied to the barrier gate 9 and the storage gate 10, and there are various problems in the voltage setting and supply method.

In view of the above drawbacks, the present invention provides a charge transfer device that can increase transfer efficiency and reduce unused charges.

(Structure of the Invention) In order to achieve this object, the charge transfer device of the present invention includes:
It includes a photocharge accumulation section having a conductivity type opposite to that of the substrate, and a two-stage gate consisting of a barrier gate and an accumulation gate that determine the potential of the photocharge accumulation section, and a buried channel is formed directly under the two-stage gate. The structure is as follows.

(Explanation of Examples) Examples will be described below with reference to the drawings.

FIG. 5 shows a cross section of the vicinity of a photoelectric conversion section of a CCD solid-state imaging device according to an embodiment of the present invention. Reference numeral 1 denotes a photocharge storage region, which is a region having a conductivity type opposite to that of the substrate 2. 3 is a channel stopper region which is of the same conductivity type as the substrate 2 and has a higher concentration than the substrate 2; 9 is a barrier gate that determines the potential of the photocharge storage section 1; S,! +, 1i is abundant in the well region having the opposite conductivity type to the substrate. 1o is a storage gate that stores charges generated in the photocharge storage section l, and 12 is a well region having a conductivity type opposite to that of the substrate and having a concentration υ higher than that of the well region 11.

The photocharge storage section 1 and the storage gate 10 are connected internally, and furthermore, they are connected to the substrate 2. Reference numeral 5 denotes an accumulation gate) A shift gate serves to transfer the charges accumulated under 10 to the 600 section 6 and determines the accumulation time, and 7 is a gate oxide film. FIG. 6 shows the potential of the structure of FIG.

In FIG. 5, when the photoelectric charge storage section 1 is irradiated with light, the charges photoelectrically converted in this region are transferred to the barrier gate 9 when no pulse voltage is applied to the digital camera 5 (FIG. 6(a)). As a result of the difference in density between the area 11 under the storage gate 10 and the area 12 under the storage gate 10, the area moves under the storage gate 10. This movement of charge takes an accumulation period. Further, the transfer from the storage gate 10 to the 600 unit 6 is in the embedded channel ClCD mode,
The amount of charge left behind due to this transfer is less than 0002%9
As a result, a solid-state imaging device with good afterimage characteristics can be obtained.

(Effects of the Invention) As described above, the present invention provides -
Charge transfer efficiency within the storage period can be significantly improved.

[Brief explanation of drawings]

1 and 3 are cross-sectional views of the vicinity of the photoelectric conversion section of a conventional CCD solid-state imaging device, respectively, and FIGS. 2 and 4 are diagrams showing the potential in each structure of FIGS. 1 and 3, respectively. (a) shows the state of the storage period, and (b) shows the state of the transfer period. FIG. 5 shows the CC in one embodiment of the present invention.
FIG. 6 is a cross-sectional view of the vicinity of the photoelectric conversion section of the solid-state imaging device D.
A diagram showing the potential in the structure of Figure 5, (a)
indicates the storage period, and (b) indicates the state of the transfer period. 5... River Shift Gate 6 River... Song C
CD section, 9...Barrier gate, 1o...
...Track accumulation gate, 11.12...well area. Patent applicant Matsushita Electronics Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] A photocharge accumulation section having a conductivity type opposite to the -conductivity type is formed on the surface of a semiconductor substrate having one conductivity type, and a two-stage gate consisting of a barrier gate and an accumulation gate that determines the potential of the photocharge accumulation section. A charge transfer device comprising: a buried channel having the opposite conductivity type formed directly under the two-stage gate.