JPS61287166A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To discharge excess charges, and to improve the opening area ratio of a photodiode by forming a Schottky diode without shaping an overflow control gate. CONSTITUTION:A bringing to a plus bias of the cathode side of a Schottky diode 33 is prevented, and an anode thereof is attracted to overflow drain voltage Vofd. In this case, Vofd corresponds to the overflow drain voltage of conventional devices, and the forward voltage Vf of the Schottky diode 33 corresponds to potential being set by an overflow control gate. That is, when the set value of (Vofd+Vf) is made previously higher than potential on the OFF of a signal phit, excess charges are not overflow to a CCD channel 12, thus preventing the generation of a blooming phenomenon. Excess charges generated by the incidence of intense beams are discharged to a potential well corresponding to only the Vf section of the Schottky diode by the presence of the Schottky diode 33, and discharged to the outside by an overflow drain electrode wiring 30.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a solid-state imaging device, and particularly to a solid-state imaging device that removes excess charge and has a blooming suppressing function.

(Prior art) Conventionally, technologies in this field include (2) Proceedings of the 1982 International Conference of the Television Society, (1982) Television Society of Japan, Fujiwara et al., "2-2 Solid-state imaging device using epi-wafer" J, (1) Proceedings of the 1882 International Conference of the Television Society, (1982) Television Society, Takeuchi et al. "2-6 Driving method of vertical overcrow structure CCD image sensor - Part 1-" Document (1) discloses a device having a blooming suppression function by providing an overflow gate and an overflow drain in a planar manner, and Document (2) discloses a device having an overflow gate and an overflow drain in a planar manner to have a blooming suppressing function, and document (2) discloses an NPH in the depth direction of the semiconductor substrate.
A multi-layered structure having a blooming suppressing function is disclosed. Among these, the solid-state imaging device shown in Document (1) will be explained below using the drawings.

FIG. 2 is an overall plan view showing an example of the configuration of a conventional solid-state imaging device. In this device, a large number of photodiodes 2
are arranged in a matrix, and a plurality of columns of vertical CCDs 4 are provided between these photodiodes 2. vertical C
A horizontal acos is provided at the lower end of the OD via a transfer gate 6. An output preamplifier 10 is provided on the output side of the horizontal CD 8.

In FIG. 3, the fourth factor shows the structure near the photodiode 2. A CCD clock line 13 and a CCD clock line 14 are provided on the channel 12 of the vertical CCD 4 formed on the semiconductor substrate 20.

A control electrode 15 is provided between the channel 12 and the photodiode 2 . On the opposite side of the channel 12 of the photodiode 2 is an overflow control gate 1.
B and overflow drain electrode wiring 1B are provided. This overflow drain electrode wiring 16 and the overflow drain 21 adjacent to the photodiode 2 are connected by a contact 17. As shown in FIG. 4, the cross-sectional configuration of this solid-state imaging device is as shown in FIG.
An N- impurity layer 23 forming the CCD channel 12, an N- impurity layer 22 forming the photodiode 2, and an N-impurity layer 21 forming the overflow drain are formed. Further, a CCD clock line 13, a control electrode 15, and an overflow control gate 18 are formed via a gate oxide film 24. Furthermore, a passivation layer 28 is formed, and an overflow drain electrode wiring 1B is embedded in this passivation layer 26. On this padding layer 2θ, an aluminum layer 25 as a light shielding film is placed on the photodiode 2θ.
It covers everything except the top.

Next, the operation of this solid-state imaging device will be explained using FIG. 5. A pulse that is turned on at a predetermined interval is inputted to the control electrode 15 as a signal φt to bring the potential of the photodiode 2 to an initial state. When the signal φt is turned off, the photodiode 2 is kept at a constant potential. The light is photodiode 2
When the zero-order signal φt is turned on, a signal charge is generated and accumulated in the potential well of the photodiode 2.
The accumulated signal charge is transferred to the CCD channel 12. The signal φt is turned off and the next signal charge is accumulated. The above operation is repeated to read out the photoelectrically converted signal charges one after another.

Here, when strong light is input, too many signal charges are generated, and a phenomenon in which surplus charges appear in the COD channel, that is, a blooming phenomenon occurs. In order to prevent this blooming phenomenon, the overflow control gate 18
, and overflow drain electrode wiring 18 are provided. The voltage Vofcg applied to the overflow control gate 18 is set to be higher than the potential of the signal φt when it is off. Therefore, the excess charge overflows not into the CCD channel 12 but into the overflow drain 21, so that no blooming phenomenon occurs.

(Problems to be Solved by the Invention) However, in the device having the above configuration, since it is necessary to provide an overflow control gate, an overflow drain, etc., there is a problem that the opening area of the photodiode becomes small.

The present invention provides a solid-state imaging device that solves the problem of the prior art in that the opening area of the photodiode becomes small.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides a photosensitive section that generates signal charges according to the intensity of incident light, and a method for transferring the signal charges generated in the photosensitive section. In a solid-state imaging device equipped with a transfer section, a Schottky barrier diode is composed of a part of an impurity layer of a photosensitive part and a metal layer in contact with a part of this impurity layer; A connected excess charge discharge electrode is provided to discharge excess electrode from the photosensitive section.

(Function) According to the present invention, since the solid-state imaging device is configured as described above, the Schottky diode and the excess charge discharge electrode are
It functions to discharge excess charge that cannot be accumulated in the photodiode, thus eliminating the above-mentioned problem.

(Embodiment) FIG. 1 is a plan view of a solid-state imaging device showing a first embodiment of the present invention, and FIG. 6 is a cross-sectional view taken along the line B-B. CCD channel 1
2 is provided. By controlling the potential of the transfer electrode 15, the signal charge accumulated in the photodiode 2 is transferred to C
Transfer to CD channel 12. CCD clock lines 13 and 14 are provided on the CCD channel 12, and by applying an alternating electric field to these CCD clock lines 13 and 14, signal charges on the CCD channel 12 can be transferred. An overflow drain electrode wiring 30 is provided on the opposite side of the channel 12 of the photodiode 2,
A Schottky diode 33 is configured by bringing the impurity layer of the photodiode 2 into contact with the metal layer of this electrode wiring.

As shown in FIG. 6, the cross-sectional structure of this solid-state imaging device is such that an N- impurity layer 22 forming a CCD channel 12 and an N impurity layer 21 forming a channel stopper are formed on the surface of a P-type semiconductor substrate 20. has been done. A control electrode 15 is formed on the semiconductor substrate 20 between the N- impurity layer 22 and the N- impurity layer 23 with a gate oxide film 24 interposed therebetween. A CCD clock line 13 is formed on the N- impurity layer 23. Further, an overflow drain electrode wiring 30 is formed on the N- impurity layer 22. This is an aluminum layer, and this aluminum layer and the N- impurity layer 22 are in contact to form a Schottky diode 33. The specific resistance of the N- impurity layer 22 is 1 to 2Ω・
Forward voltage of Schottky diode in cm Vf = 0
．． 2-0.3V.

VF=0.4V at about 0.5Ω・C11 can be obtained in about 20 minutes at a heat treatment temperature of 500°C, which is called a sink.

Furthermore, an aluminum film 25 for light shielding is formed via a passivation film 32. Note that a field oxide film 31 is formed on the N° impurity layer 21 for channel stop.

Next, the operation will be explained using FIG. 7. Photodiode 2
The operation of accumulating signal charges, transferring them to the CCD channel 13, and transferring them on the CCD channel 13 is the same as in the conventional case. In this embodiment, the characteristics of the Schottky diode 33 are utilized, which differs from the conventional method in the operation of discharging excess charge that causes the blooming phenomenon. The cathode side of the Schottky diode 33 is prevented from being subjected to a positive bias, and the anode is connected to the overflow drain voltage Vofd.

In this case, Vofd corresponds to the overflow drain voltage of the conventional device, and the forward voltage Vf of the Schottky diode 33 corresponds to the potential set by the overflow control gate. That is, (Vofd+
By setting the set value of Vf) higher than the potential of the signal φt when it is off, surplus charges will not overflow into the CCD channel 12, and the blooming phenomenon can be prevented.

Due to the presence of the Schottky diode 33, surplus charges generated by strong light incidence are discharged into a potential well corresponding to Vf of this Schottky diode, as shown in FIG. This discharged charge is discharged to the outside by the overflow drain electrode wiring 30.

In this way, in this embodiment, excess charge can be discharged without providing an overflow control gate as in the conventional case. Therefore, the opening area ratio of the photodiodes can be increased, and the arrangement pitch of the photodiodes can be made finer.

A solid-state imaging device according to a second embodiment of the present invention is shown in FIGS. 8 and 9. Components that are the same as those in the first embodiment are denoted by the same reference numerals, and their explanations will be omitted. The difference from the first embodiment is that the overflow drain electrode wiring 30 is in contact with the N- impurity layer 22 of the photodiode 2 as well as the N-impurity layer 21 for channel stop, forming a Schottky diode 33. In this embodiment, the 7 nodes of the Schottky diode 33 are connected to the semiconductor substrate 20.
Therefore, the potential of the signal φt when it is off needs to be lower than (Vsub - Vf). For this purpose, the MOS transistor having the control electrode 15 as a gate may be an enhancement type MOS (Run Lister) whose threshold voltage is higher than Vf.

According to this embodiment, since the Schottky diode can be formed across the channel stop region, the photodiode opening 1. It is possible to increase the area and to make the arrangement pitch of the photodiodes finer.

The present invention is not limited to the above embodiments, and various modifications are possible.For example, it may be formed on a P well in an N type semiconductor substrate, or it may be formed on an N type semiconductor substrate with the conductivity type reversed. Further, the Schottky diode may be formed of a metal other than aluminum and a semiconductor.

(Effects of the Invention) As described in detail above, according to the present invention, surplus charges can be discharged by providing a Schottky diode without providing an overflow control gate.
The aperture area ratio of the photodiode can be improved,
A solid-state imaging device with good sensitivity can be realized. Furthermore, since the arrangement pitch of the photodiodes can be reduced, a solid-state imaging device with high resolution and high density integration can be realized. Furthermore, if the number of pixels is the same, the chip area can be reduced, making it possible to realize an inexpensive solid-state imaging device.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a solid-state imaging device showing a first embodiment of the present invention, FIG. 2 is a plan view showing the entire solid-state imaging device, and FIG.
4 is a sectional view taken along the line A-A in FIG. 3, FIG. 5 is a diagram for explaining the operation of FIG. 3, and FIG. 7 is a diagram for explaining the operation of FIG. 6, and FIG. 8 is a cross-sectional view taken along line B-B in the figure.
FIG. 9 is a cross-sectional view of a solid-state imaging device showing an embodiment of the present invention, and is a diagram for explaining the operation of FIG. 8. 2...Photodiode, 4...Vertical C
OD, 6...Transfer gate, 8...Horizontal CCD, 10...Preamplifier, 12...
...CCD channel, 13, 14...CCD clock line, 15...control electrode, te...
...Overflow drain electrode wiring, 18...
・Overflow drain control gate, 20...
... Semiconductor substrate, 24 ... Gate oxide film,
25...Aluminum layer, 2e...Puffsivation layer, 30...Overflow drain electrode wiring, 33...Schottky diode - Applicant's representative Takashi Kakimoto Fig. 1 Fig. 2 Fig. 3 31kOA-A, [m Fig. 4 ofd Fig. 3 operation explanatory diagram Fig. 5 B-β sectional view of the first prisoner Fig. 6 Toshi 6 operation explanatory diagram FIG. 7: A sectional view of another solid-state imaging device according to the present invention FIG. 8: An explanatory diagram of the operation of FIG. 8 FIG. 9

Claims (1)

[Scope of Claims] A solid-state imaging device comprising a photosensitive section that generates signal charges according to the intensity of incident light, and a transfer section that transfers the signal charges generated in the photosensitive section, comprising: an impurity in the photosensitive section; a Schottky barrier diode composed of a part of the layer and a metal layer in contact with a part of the impurity layer; and an excess charge connected to the metal layer of the Schottky barrier diode to discharge excess charge from the photosensitive area. A solid-state imaging device comprising: an ejection electrode.