JPS6341071A - Solid state image sensing element - Google Patents

Abstract

PURPOSE:To obtain a video image having less after-image by inclining the potential distribution of a photodetector to a vertical transfer unit. CONSTITUTION:An impurity concentration of the reading side of a photodetector 9 is increased to reduce a potential of the gate region 10 side of the photodetector 9 from its opposite side, thereby inclining the potential of the photodetector 9 to a vertical transfer unit 11. That is, a voltage sufficient to read out a signal charge from the photodetector 9 to the unit 11 is applied to the region 10, the potential of the region 10 is reduced to the vicinity of the potential of the photodetector 9, and the signal charge stored in the photodetector 9 is read out to the unit 11, but since the potential of the photodetector 9 is inclined to the direction of the unit 11, a signal charge flows along the inclination of the potential of the photodetector 9 to the unit 11, and most of the charge stored in the photodetector 9 can be read out.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a solid-state imaging device useful for use in video cameras and the like.

2. Description of the Related Art In evaluating the performance of solid-state image sensors, one of the most important parameters is the afterimage characteristic, and devices with good afterimage characteristics are being actively developed.

The solid-state image sensor will be described below with reference to the drawings.

First, the structure and operation of the interline transfer type solid-state image sensor will be explained with reference to FIGS. 3 and 4.

In FIG. 3, 12 is a photodiode as a photoelectric conversion element, 13 is a vertical transfer section, and this vertical transfer section 1
3 is constituted by vertical transfer gates 14, 15°16.17. Reference numeral 18 denotes a signal readout gate, which is isometrically common to the vertical transfer gates 14 and 16. 1
One is a vertical transfer pulse supply terminal. 2o is a horizontal transfer unit, and this horizontal transfer unit 2o is a horizontal transfer game) 21.2
2. 23 is a horizontal transfer pulse supply terminal. Reference numeral 25 denotes a charge detection section, which converts the transferred signal charge into a signal voltage. The charge detection section 25 is normally a floating defage g7 amplifier (Flo
Ating Diffu, 5ion Amplifio
r). 26 is a signal output terminal.

The operation of the interline transfer type solid-state image sensing device having the above configuration will be explained next.

The photodiode 12 photoelectrically converts incident light from an object to obtain a signal charge. After the signal charges obtained by photoelectric conversion are read into the vertical transfer gates forming the vertical transfer section 13 via the signal readout gate 18, the signal charges are read by the vertical transfer pulses supplied from the vertical transfer pulse supply terminal 19.
The data are sequentially transferred in the vertical direction, that is, in the direction of the horizontal transfer unit 20, and read into the horizontal transfer unit 20 one horizontal line at a time. The signal charge read into the horizontal transfer section 20 is sequentially transferred to the charge detection section 24 by the horizontal transfer pulse supplied from the horizontal transfer pulse supply terminal 23, converted into a voltage by the charge detection section 24, and then output from the signal output terminal 26. Obtained as a point sequential signal. A television signal is obtained by inputting the point sequential signal obtained as described above to a signal processing section and processing it.

FIG. 4 shows a timing chart of vertical transfer pulses supplied to the vertical transfer pulse supply terminal of the interline transfer type solid-state image sensing device, and the explanation will be given below.

, , 27 and 28 are charge read pulses for reading one signal charge from the photoelectric conversion element to the vertical transfer section 13, and 29 is a charge read pulse for reading the signal charge read out to the vertical transfer section 13 to the horizontal transfer section 2.
This is a vertical transfer pulse that is sequentially transferred in the o direction. Based on the operation of the interline transfer solid-state image sensor, the signal charge accumulated in the photoelectric conversion element between the charge readout pulse 27 of the first field and the charge readout pulse 28 of the second field is transmitted to the television of the second field. The signal charge accumulated in the photoelectric conversion element between the charge read pulse 28 of the second field and the charge read pulse 27 of the first field is converted to the signal charge of the first field based on the operation of the interline transfer solid-state image sensor. It becomes a television signal.

FIG. 5 is a sectional view of a photoelectric conversion section and a vertical transfer section of a conventional interline transfer solid-state imaging device.

A first N-type impurity layer 31 serving as a photoelectric conversion section is diffused into the P-type semiconductor substrate 30 . Also, the P-type semiconductor substrate 3
If the second N-type impurity layer 32 for reading out the photoelectrically converted signal charge is a gate area interconnection/COD, it becomes a vertical transfer section. Further, the P-type semiconductor substrate 3Q has a first
and the second N-type impurity layers 31 and 32 as one unit, and a stopper layer 34 made of a P+-type impurity layer is provided to isolate these units. This gate area 33
A polycrystalline silicon gate 36 is provided on the P-type semiconductor substrate 3o on which the second N-type impurity layer 32 and the stopper layer 34 are located, with a gate insulating film 36 interposed therebetween.

FIG. 6 is a diagram showing the potential distribution of the photoelectric conversion section and the vertical transfer section of the interline/transfer solid-state imaging device.

FIG. 6a shows the potential distribution immediately before the signal charges accumulated in the photoelectric conversion section 37 are read out to the vertical transfer section 38. At this time, since sufficient voltage is not applied to the gate region 39 to transfer the signal charge from the photoelectric conversion section 37 to the vertical transfer section 38, the potential of the gate region 39 is lower than the potential of the photoelectric conversion section 37.
It is located in a place higher than the potential of FIG. 6 shows the potential distribution during the period when signal charges accumulated in the photoelectric conversion section 37 are read out from the photoelectric conversion section 37 to the vertical transfer section 38. During this period, a voltage sufficient to read signal charges from the photoelectric conversion section 3 to the vertical transfer section 38 is applied to the gate region 39, and the potential of the gate region 39 is lower than that of the photoelectric conversion section 37.
can be lowered to near its potential. When the potential of the gate region 39 decreases, the signal charge accumulated in the photoelectric conversion section 37 is transferred to the vertical transfer section 38, and as shown in FIG. After that, it is taken out to the outside.

Problems to be Solved by the Invention Although signal charges are extracted through such a process, not all of the charges accumulated in the photoelectric conversion section 37 can be read out during the signal charge readout period, and some of the charges remain as residual charges. It remains in the photoelectric conversion section 37 as. FIG. 6C shows the potential distribution after charges are read out from the photoelectric conversion section 37 to the vertical transfer section 38. Some charges that could not be read out remain in the photoelectric conversion unit 37. This residual charge 40 is read out together with the signal charge in the next read period: C1, and thus appears on the screen as an afterimage.

The only way to solve the problem is to focus on the potential distribution of the photoelectric conversion part of a solid-state image sensor, and when performing impurity diffusion during the manufacture of a solid-state image sensor,
Diffusion is performed so that the potential distribution of the photoelectric conversion section is inclined toward the vertical transfer section.

Effect: With this configuration, charges that were conventionally left behind as afterimage charges can also be read out, making it possible to realize clear video images.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a cross-sectional view of a solid-state image sensor according to the present invention. The P-type semiconductor substrate 1 has a first layer which becomes a photoelectric conversion section.
N-type impurity layer 2. The second N-type impurity layer 3 is diffused, and the second impurity layer 3 has a higher impurity concentration than the first impurity layer 2. Hereinafter, they will be referred to as photoelectric conversion units 2 and 3, respectively. In addition, the P-type semiconductor substrate 1 has a third N, which serves as a vertical transfer section that reads and vertically transfers photoelectrically converted signal charges.
The type impurity layer 4 is connected to the photoelectric conversion section 2°3 via the gate region 5.
It is located adjacent to. Hereinafter, the third N-type impurity layer will be referred to as the vertical transfer section 4. Further, the P type semiconductor substrate 1 is provided with a strip layer 6 made of a P+ type impurity layer for separating the photoelectric conversion sections 2, 3 and the vertical transfer section 4 as one unit.

This vertical transfer section 4. A polycrystalline silicon gate 8 is provided on the P-type semiconductor substrate 1 where the gate region 5 and the stopper layer 6 are located, with a gate insulating film 7 interposed therebetween.

Conventionally, the structure of the photoelectric conversion section was formed by diffusing N-type impurities at a single concentration, but in this embodiment, the impurity concentration is not made uniform, and the readout side of the photoelectric conversion section 2,
That is, the concentration on the side near the gate region 5 of the photoelectric conversion section 2 is made higher than that on the opposite side. In FIG. 1, there is a photoelectric conversion section in which impurities with a higher concentration than the photoelectric conversion section 2 are diffused. By configuring as above, conventionally,
Charges remaining as afterimage charges are also easily read out to the vertical transfer section, and as a result, clear video images can be realized. The principle will be explained with reference to FIG.

FIG. 2 is a diagram showing the potential distribution of the photoelectric conversion section and the vertical transfer section of the solid-state imaging device according to the present invention.

FIG. 2a shows the potential distribution immediately before the signal charges accumulated in the photoelectric conversion section are read out to the vertical transfer section. Since the impurity concentration on the readout side of the photoelectric conversion section 9, that is, on the gate region 1o side, is increased, the potential on the gate region 10 side of the photoelectric conversion section 9 is lower than that on the opposite side. In other words, the photoelectric conversion section 9
It is possible to tilt the potential toward the vertical transfer section 11 side.

FIG. 2 shows the potential distribution during the period when signal charges accumulated in the photoelectric conversion section 9 are read from the photoelectric conversion section 9 to the vertical transfer section 11. From the photoelectric conversion section 9 to the vertical transfer section 1 in the gate region 10
1 is applied with a voltage sufficient to read out signal charges, the potential of the gate region 10 is lowered to near the potential of the photoelectric conversion section 9, and the signal charges accumulated in the photoelectric conversion section 9 are read out to the vertical transfer section 11. However, since the potential of the photoelectric conversion section 9 is inclined in the direction of the vertical transfer section 11, the signal charge flows into the vertical transfer section 11 along the inclination of the potential of the photoelectric conversion section 9. Most of the charges accumulated in 9 can be read out. That is, the afterimage charges that conventionally remained in the photoelectric conversion section are also read out, making it possible to realize a video image with less afterimages.

Effects of the Invention The solid-state imaging device of the present invention makes it possible to realize video images with little afterimage, and the effects are very significant.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main parts of the solid-state image sensor according to the present invention, and FIG. 2 is a potential diagram for explaining the operation of FIG. 1.
Fig. 3 is a circuit diagram for explaining signal readout from a solid-state image sensor, Fig. 4 is a waveform diagram of each part in Fig. 3, Fig. 6 is a sectional view of main parts of a conventional solid-state image sensor, The figure is a regular waveform diagram illustrating the operation of FIG. 6. 1... P-type semiconductor substrate, 2, 3... Photoelectric conversion section, 4... Vertical transfer section, 6... Gate region, 6... Door stopper layer 7...
Gate insulating film, 8... Polycrystalline silicon gate,
9...Photoelectric conversion section, 1Q...Gate region, 11...Vertical transfer section. Name of agent: Patent attorney Toshio Nakao and one other person condolence
2 Figure 8
″″″″″″− Figure 16

Claims (1)

[Claims] An interline transfer solid state in which a photoelectric conversion section, a signal charge vertical transfer section, and a signal charge horizontal transfer section are independent, and a charge readout gate reads out signal charges accumulated in the photoelectric conversion section to the signal charge vertical transfer section. In the image sensor,
A solid-state imaging device, characterized in that the potential distribution of the photoelectric conversion section is tilted toward the signal charge vertical transfer section.