JPS617662A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To obtain a solid-state image pickup element having a large numerical aperture by utilizing a Schottky junction electrode formed onto a region, in which charges are stored and transferred, as an electrode for a CCD and enabling optical detection and the transfer of charges. CONSTITUTION:When electrodes 181-184 having Schottky junctions and gate electrodes 171-174 are biassed at the same voltage, potential to holes in a P type region 162 in the lower sections of the electrodes 171-174 is made lower than that in the lower sections of the electrodes 181-184. When infrared rays are projected under the state in which potential in the region 162 under the electrodes 182, 184 is biassed so as to be made lower than potential in the region 162 under the electrodes 171, 173, electron-hole pairs are generated in the electrodes 181-184. Holes having energy exceeding the barriers of Schottky junctions among the electron-hole pairs are injected to the region 162. When driving pulses deflected to negative number from 0V, phase thereof is displaced at 180 deg., are each transmitted over conductors phiA1, phiA2, optical signal charges collected to sections except the electrodes 172, 174 are transferred in the right direction. According to the constitution, an image pickup element having a large numerical aperture is obtained.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a Schottky bonded gold J that is sensitive to light.
The present invention relates to a solid-state imaging device using an I4III electrode as a transfer electrode of a charge-coupled device (hereinafter referred to as a CCD).

[Prior art]

When a solid-state imaging device in which a photodetection system 7 ray and a charge transfer device are formed on the same semiconductor substrate is used in an imaging device, it can be made compact,
A lightweight, low power consumption, and highly reliable imaging device can be realized.

In the field of imaging in the visible region, solid-state imaging devices having the resolving power of an imaging electron tube have recently been developed with the development of silicon integrated circuit technology.

On the other hand, infrared imaging devices can capture thermal images of objects, so they are useful for environmental monitoring, night vision monitoring, and resource exploration.

It is used in many fields such as temperature distribution observation.

However, most infrared imaging devices currently in practical use use a single infrared detector to capture thermal images through mechanical scanning. Therefore, in recent years, the development of solid-state image sensors in the infrared region has been vigorously promoted. Things are still being developed.

A conventional infrared solid-state imaging device is shown in FIG.

In FIG. 1, 1 is an infrared light detection section using a Schottky junction, 2 and 3 are a vertical shift register and a horizontal shift register made of COD, respectively, and 4 is from the infrared light detection section 1 to the shift register 2. 5 is a charge detection section.

FIG. 2 is a cross-sectional view taken along the line A--A in FIG.

The metal side electrode of the Schottky junction of the infrared light detecting section 1 is formed by vapor-depositing metal or metal silicide such as platinum silicide, palladium silicide, iridium silicide, etc. 8 is the n- side electrode around this metal side electrode 7. A guard ring 9 is a gate electrode of the transfer gate 4, an n-type region 10 overlaps a part of the metal side electrode 7, and 11.12 is a gate electrode of the CCD of the vertical shift register 2 and an n-type buried region. Channel, 13 is a silicon oxide film for element isolation and insulation, 14
14 is a silicon oxide film for protecting the device, and 14 is a silicon nitride film for protecting the device.

Next, the operation will be explained.

The infrared light incident on the infrared light detection section 1 generates electron-hole pairs in the metal side electrode T of the Schottky junction. Among these holes, those with energy exceeding the height of the Schottky barrier are injected into the p-type silicon substrate 6, and optical signal charges are accumulated in the Schottky junction. Infrared light detection section 1
The maximum detectable wavelength of is determined by the height of the Schottky barrier.

For example, if PtSi is used for the metal side electrode 7, the height of the Schottky barrier between PtSi and p-type St is 0.25ev, so 0. Light with an energy of −25 ev or more (photon with a wavelength of 5 μm or less can be detected). The optical signal charge is transferred to the n-type buried channel 12 of the CCD of the shift register 2. After the optical signal charge is transferred to the vertical shift register 2, the transfer gate 4 is closed, and the infrared light detector 1 receives the optical signal of the next period. On the other hand, the optical signal charge transferred to the vertical shift register 2 is transferred vertically in the n-type buried channel 12 of the CCD, and is transferred to the horizontal shift register for every horizontal line of each vertical shift register 2. 3, the signal is transferred in the horizontal direction and taken out from the charge detection section 5 as a video signal.

In this way, a video signal corresponding to the amount of infrared light incident on each pixel of the infrared light detection section 1 is obtained.

Since the conventional infrared solid-state image sensor is configured as described above, in the horizontal direction, a transfer gate 4 and a vertical shift register 2 are provided between each pixel of the infrared light detection section 1.
Because of this, the aperture ratio (the ratio of the area of the effective photosensitive area to the area of the imaging region) was small. The area ratio between the infrared light detection section 1 and the vertical shift register 20 is determined by the amount of optical signal charge that can be accumulated by the Schottky junction of the infrared light detection section 1 and the maximum charge transfer amount that can be transferred by the CCD of the vertical shift register 2. There was a drawback that the area of the infrared light detection section 10 could not be increased. Therefore, in the conventional infrared solid-state imaging device, there is a limit to increasing the aperture ratio by increasing the size of the infrared light detection section 1.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and a part of the electrode of the COD of the vertical shift register is used as the metal side electrode of the Schottky junction.
The present invention provides an infrared solid-state image pickup device with a large aperture ratio by providing an infrared light detection function and enabling light detection using a vertical shift register. An embodiment of the present invention will be described below with reference to the drawings.

[Embodiments of the invention]

FIGS. 3 and 4 are a plan view and a sectional view of essential parts showing an embodiment of the present invention.

In Fig. 3, 15 is an n-type silicon substrate, 161°1
62, 163 and 164 are p-type regions formed in the surface region of the n-type silicon substrate 15, which become p-type buried channels of the CCD. 171, 172° 173, 174 are electrically connected in the horizontal direction, and the p-type regions 161 to 164
Gate electrodes 181, 182, 183, and 184 of the CCD formed on the 0 surface with an insulating film sandwiched therebetween are electrically connected in the horizontal direction, and are electrically connected to the gate electrodes 171 to 174 in the vertical direction.
Schottky junction electrodes are arranged alternately and insulated from each other to form a Schottky junction with the surfaces of the p-type regions 161 to 164. φ48. φA2 is the gate electrode 111 to 174 and the Schottky junction electrode 181.
.about.184 (assuming that it represents the conductor to which it is applied at the same time).

FIG. 4 is a cross-sectional view taken along line X-X in FIG. 3, and shows 191.
192, 193, and 194 are the gate electrodes 17, respectively.
1 to 174 and the Schottky junction electrodes 181 to 184
This is an insulating film that provides insulation between the two.

Next, the operation will be explained.

In FIG. 4, the potential distribution for holes in the p sub-region 162 is shown by a broken line when the conducting wire φAl is biased to 0vVC and the conducting wire φ,2 is negatively biased.

Schottky junction electrodes 181 to 184 and gate electrode 17
1 to 174 are biased to the same voltage, the potential for holes in the p sub-region 162 under these two electrodes is higher than that of the Schottky junction electrode 1 under the gate electrodes 111 to 174.
It is lower than 81-184. Therefore, the potential of the p sub-region 162 under the Schottky junction electrode 182°184 is changed to the conductive wire φ4. Gate electrode 1 biased to Ov by
11° 173 so that the potential is lower than the potential of the p sub-region 162 under the conductor φ, 2 is biased negatively, the p sub-region 162
The potential distribution for holes is as shown by the broken line in FIG.

When infrared rays are incident in this state, busy electron/hole pairs are generated within the Schottky junction electrodes 181 to 184. Of these holes, those with energy exceeding the Schottky junction barrier φms are injected into the p sub-region 162. For example, if platinum silicide PtSi is used as the material for the Schottky junction electrodes 181 to 184, φmm = 0.25
eV, and a hole signal charge corresponding to the amount of incident light is injected into infrared rays having a wavelength of up to 5 μm. p subregion 1
The holes injected into the gate electrode 17 have the lowest potential.
2°174 and accumulated as optical signal charges. At temperature, φms = Q, and at a Schottky barrier as low as 25 eV, there are many thermally generated carriers, so optical signal charges cannot be accumulated.However, infrared solid-state imaging devices are generally operated at a low temperature below the liquid nitrogen temperature of 77, Since the generation of generated carriers can be sufficiently reduced, it becomes possible to accumulate original signal charges.

After accumulating the optical signal charge for a certain period of time, the conductor φ, 1゜φAt
When driving pulses φAI+φ, which swing negatively from Ov, which are 180° out of phase with each other, are applied to the gate electrode I
The optical signal charges collected under T2.174 are transferred to the right in the diagram of FIG. The maximum charge transfer amount that can be transferred is
Depends on the amount of charge stored in.

Next, an embodiment of a method for manufacturing the main part of the present invention will be described with reference to FIG.

In FIG. 5, p sub-regions 162<161, 163, 164) are formed on an n-type silicon substrate 15 by epitaxial growth or ion implantation, and
The surface of the mold region 16''2 is thinly oxidized to form a gate silicon oxide film 20, and the gate electrodes 111 to 111 are made of polysilicon.
174 is formed. Thereafter, a silicon oxide film 20 is laminated by the CVD method, resulting in the shape shown in FIG. 5(a). Next, the silicon oxide film 20 is anisotropically etched to form a silicon oxide film 201 on both sides of the polysilicon gate electrodes 171 to 1140.
If the etching is performed while leaving the portions 202, 203, and 204, the result will be as shown in FIG. 5(b).

When a metal such as platinum, iridium, or palladium is vapor-deposited thereon and metal silicide* is formed by heat treatment, Schottky junction electrodes 181 to 184 are formed in a self-aligned manner as shown in FIG. 5(C). Further, since metal silicide is also formed on the polysilicon, the wiring resistance of the polysilicon decreases.

Next, an embodiment of the overall configuration of the solid-state image sensing device of the present invention will be described with reference to FIG.

In FIG. 6, 21 is the COD of the photosensitive section having the structure shown in FIGS. 3 and 4, and 22 is the CCD of the storage section.

φ11. φ43. , φcI and φc2 are the CCD 22 of the storage section and the horizontal shift register 3 of the horizontal readout section, respectively.
Two-phase drive circuit of CCD (also represents the conductor)
It is. Since the CCD 21 in the photosensitive section must detect infrared rays, the CCD has the structure shown in FIGS. It can also be constructed using COD, which is commonly used and which forms electrodes by sandwiching them.

Next, the operation will be explained.@ The optical image of the object to be imaged is formed on the CCD 21 of the photosensitive section. In the CCD 21 of the photosensitive section, connect the conductor φ,1 to QVK.
, conductive wire φA2 is negatively biased, and after accumulating optical signal charges for a certain period of time according to the principle described in FIG. 4, conductive wires φ, 8. φ,,
and conductor wire φ38. A two-phase drive pulse is applied to φ□, the CCD 21 of the photosensitive section and the CCD 22 of the storage section are operated, and the optical signal charge for one screen that has been accumulated in the C0D21K of the photosensitive section is transferred to the CCD 22 of the storage section. Since light is incident even while the optical signal charges are being transferred, it is desirable that this transfer is sufficiently fast compared to the optical signal charge accumulation time. In addition, since the CCD 22 of the storage section temporarily stores the optical signal for one screen that was stored in the photosensitive section (') CCD 21, the CCD 22 of the storage section
D22 must have the same number of electrodes as or more than the number of electrodes of CCD21 in the photosensitive section. CCD2 in storage section
When the transfer to 2 is completed, the conductor φ, 7. φ, 2 and φ
A two-phase driving pulse is applied to C1l and φc2, respectively, and the CCD 22 of the storage section and the horizontal shift register 3 of the horizontal readout section are
is operated to read out one screen's worth of optical signal charges stored in the CCD 22 of the storage section for each horizontal line. During this time, the CCD 21K of the photosensitive section accumulates the optical signal of the next cycle.

In this way, image signals corresponding to the light images formed on the CCD 21 of the photosensitive section are successively output.

Also, during the optical signal accumulation period, the conducting wire φ, 0. The bias applied to φA2 is set such that φA1 is set to Ov, φ, , is biased negatively, and in the next cycle, φ,1 is set to negative, and φA2 is biased to OvK, and the area where the optical signal is accumulated is shifted every cycle. Vertical resolution can be increased by performing an operation that configures one screen in two cycles.

In the above embodiment, the CCD 22 in the storage section and the horizontal shift register 3 are driven in two phases, but other types of driving methods may be used as long as the accumulation and transfer of signal charges is possible.
A CD may also be used.

Although the CCD 21 of the photosensitive section is driven in two phases as shown in FIG. 4, other types of driving methods are also possible.

FIG. 7 shows an embodiment of another method for driving the CCD 21 of the photosensitive section.

In FIG. 7, if the voltages applied to the gate electrodes 111-174 and the Schottky junction electrodes 181-184 are the same, the potential of the p-type region 162 under the gate electrodes 111-174 and Schottky junction electrodes 181-184 is
The lower part of 71-174 is lower. . Therefore, the Schottky junction electrodes 181 to 184 and the gate electrodes 171 to 11
Driving pulses with different voltages are applied to Schottky junction electrodes 181 to 184 and gate electrodes 111 to 174 at high and low levels of the respective driving pulses.
The potentials of the p-type region 162 under the p-type region 162 are made to be the same.

That is, the conducting wire φjl+φ, 7. φ, 3. Four-phase drive pulses with phases shifted by 90 degrees from each other are applied to φA4. However, φ, φ, 8 and φ, 2. In order to equalize the potentials of the p-type region 162 under each electrode, the high-level and low-level voltages of the driving pulses are different for φ and 4, respectively. 7th
The broken lines in the figure indicate that the conductors φAll φ, , are at high level, and the conductors φ, 3. It shows the potential distribution for holes in the p-group region 162 when φ,4 is at a low level. After accumulating optical signal charges in this state, the conductors φ, 1. φAz+ φA3
1 By applying a four-phase drive pulse to No. φ1, the optical signal charge can be transferred to the right in FIG. 4. The overall operation is the same as in FIG. 6.

In the case of the driving method shown in FIG. 7, compared to the driving method shown in FIG. 162, the maximum amount of charge transfer is increased, and the gate electrode 1 does not have infrared sensitivity.
Since the widths of 71 to 174 can be narrowed, the aperture ratio can be further increased. However, the driving method shown in FIG. 7 requires more complicated driving pulses than the driving method shown in FIG.

When the solid-state image sensor of the present invention is used to observe a stationary object, the signal charge readout time can be sufficiently shortened compared to the optical signal charge accumulation time in the photosensitive section, so that the CCD 22 in the storage section is not required. Also, use a shutter etc. to control the CC of the photosensitive area.
Even if measures are taken to prevent infrared light from entering during the optical signal charge transfer of D21, the CCD 22 in the storage section is no longer necessary.

In the above embodiments, the electrode of the Schottky junction of C0D21 in the photosensitive area is made of platinum silicide (PtSi) and the substrate is made of Si, but the material of the electrode may be other metal silicide or metal, and the substrate may be made of other metals. It may be a semiconductor. however,
The maximum wavelength of light that can be detected is determined by the combination of the electrode material and the conductor material of the substrate, so depending on the combination, the maximum detectable wavelength may be in the visible range.

In addition, although we mainly explained imaging in the infrared region,
Since a Schottky junction is used in the photosensitive section, it is clear that imaging in the visible region and the wavelength region below the visible region is also possible.

Furthermore, although the mutual separation of the p-type regions 161 to 164 of the CCD is explained as that of the n-type silicon substrate 15,
They may be electrically isolated by an insulating film.

Further, the buried channel of the COD is not limited to a p-type region, but may be an n-type region. However, in this case, a p-type substrate is used, the signal charges are electrons, and the voltage applied to each electrode is reversed.

〔Effect of the invention〕

As explained in detail above, the present invention utilizes the Schottky junction electrode formed on the second conductivity type region that accumulates and transfers charge as a COD electrode, thereby increasing photosensitivity and charge transfer. Therefore, there is an advantage that a solid-state imaging device with a large aperture ratio can be obtained.

Furthermore, since the Schottky junction electrodes and gate electrodes can be arranged alternately, it is easy to sufficiently reduce the gap between the electrodes, which has the effect of minimizing deterioration in transfer efficiency.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional infrared solid-state image sensor, Fig. 2 is a cross-sectional view taken along line A-A in Fig. #I1, and Fig. 3 is a block diagram of an embodiment of the main part of the solid-state image sensor according to the present invention. , 4th
The figure is a cross-sectional view taken along X-XfijK in Figure 3, and Figure 5 Ca.
), (b), and (c) are schematic diagrams illustrating an embodiment of the method for manufacturing the main parts of the present invention, and FIG. 6 is a schematic diagram of an embodiment of the overall configuration of the solid-state image sensor according to the present invention. FIG. 7 is a schematic diagram illustrating another method of driving the main parts of the solid-state image sensing device according to the present invention. In the figure, 1 is an infrared light detection section, 2 is a vertical shift register, and 3 is a vertical shift register.
is a horizontal shift register, 4 is a transfer gate, and 5 is a horizontal shift register.
1 is a charge detection section, 6 is a p-type silicon substrate, 7 is a metal side electrode, 8 is a guard ring, 9 is a gate electrode, 10 is an n region, 11 is a gate electrode of CCD, 12 is an n-type buried channel of CCD, 13 is a silicon oxide film, 14 is a silicon nitride film, 1
5 is an n-type silicon substrate, 20 is a silicon oxide film, 21 is a photosensitive portion COD, 22 is a storage portion COD, 161-164 are p-type regions, 171-174 are gate electrodes, 181-18
4 is a Schottky junction electrode, 191 to 194 are insulating films,
201 to 204 are silicon oxide films, 211 to 214 are silicon oxide films, φ, 1. φ, 2. φ1. ．． φml+φcin φ
c2 is a conducting wire. In addition, the same reference numerals in the figures indicate the same or equivalent parts. (Spontaneous) Showa 6% Indication of January 23rd case Patent application No. 59-129483 Name of the invention Relationship to the solid-state image pickup device correction case Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Jinhachibe Katayama

Claims (2)

[Claims] (1) A semiconductor substrate of a first conductivity type, and one or more semiconductor substrates formed on a surface region of the semiconductor substrate having a conductivity type opposite to the first conductivity type, which accumulates and transfers charges. a Schottky junction electrode that forms a Schottky junction on the second conductivity type region and performs photoelectric conversion; and at least one of the second conductivity type regions. A solid-state imaging device comprising a plurality of electrode rows arranged alternately, and a gate electrode disposed on the second conductivity type region with an insulating film interposed therebetween. (2) The solid-state imaging device according to claim (1), wherein the regions of the second conductivity type are electrically isolated from each other by an insulating film.