JPH04111467A - Infrared solid state image pickup device - Google Patents

Abstract

PURPOSE:To increase the reset voltage dependence of optical sensitivity in an infrared detector and facilitate the change of the optical sensibility by said reset voltage by forming an impurity intake passage which introduces a specified amount of impurities into a Schottky barrier diode interface on a semiconductor side. CONSTITUTION:An infrared light which enters from the rear side of a p type silicon semiconductor substrate 1 reaches an optical conversion layer 2 of a Schottky junction for photoelectric conversion where generated optical signal load is once stored by the Schottky junction and then it is transferred to an n type buried channel 5 by applying a read out pulse to a gate electrode 6 from a TG scanner 25. When a region 12 in which a specified amount of n type impurities are introduced, is formed on the interface of a p type substrate side 1 of the Schottky junction, the relation between reset voltage and the amount of output signal is turned in linear mode. If an attempt is made to set the voltage VTG of 'H' level of a read out pulse of a TG scanner 25 under this condition, the reset voltage will depend on the voltage VTG of the 'H' level, which makes it possible to control optical sensitivity by means of luminous energy which enters.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an infrared solid-state imaging device, and more specifically, to an improved structure of an infrared solid-state imaging device using a Schottky barrier diode as an infrared photodetector. It is.

[Conventional technology]

In recent years, an infrared solid-state imaging device has been developed that uses a Schottky barrier diode as an infrared photodetector, that is, an infrared detector, and has a sufficient number of pixels for practical use.

Here, FIG. 4 is a plan view schematically showing an outline of the arrangement of an infrared solid-state image sensor used in this type of Schottky barrier diode infrared detector according to a conventional example, and FIG. 4 is a cross-sectional structural diagram corresponding to the V-V line of one unit of the infrared solid-state imaging device in FIG. 4. FIG.

That is, in the conventional configuration shown in FIG.
22 is an infrared light detection unit arranged in an array in vertical and horizontal two-dimensional directions using Schottky junctions, and 22 is an infrared light detection unit using a charge sweep method (hereinafter referred to as C3D method) that transfers charges in the vertical direction. A vertical shift register 23 is a CCD type horizontal shift register that transfers charges in the horizontal direction, and 24 is an output section that reads out the charges to the outside.

Also, 25 is a transfer gate (hereinafter referred to as TG)
The scanner 26 is a CSD scanner, and a gate electrode (component of the vertical shift register 22) 6 on one horizontal line is electrically connected to each of these scanners 25 and 26 via a scanning line wiring 7. , a read pulse from the TG scanner 25 and a transfer pulse from the C3D scanner 26 can be applied to each.

Next, in the configuration shown in FIG. 5, reference numeral l denotes a p-type silicon semiconductor substrate, and 2 denotes a metal electrode made of a metal such as platinum, palladium, or iridium, or a metal silicide such as platinum silicide, baradium silicide, or iridium silicide. 3 shows a Schottky junction photoelectric conversion layer formed by a substrate 1 and a substrate 1, and 3 is an n-type region formed to reduce electric field concentration in the peripheral part of the photoelectric conversion layer 2 and prevent dark current. It is a guard ring.

Further, 4 is a vertical shift register 2 from the photodetector 21.
n''' of the transfer gate section that transfers the signal charge to 2.
type areas, 5.6 are respectively the vertical shift registers 2
The gate electrode 6 serves as both the electrode of the transfer gate portion and the transfer electrode of the C3D.

Furthermore, 7 is a scanning line wiring made of aluminum wiring, 8 is a field insulating film for element isolation and insulation made of a silicon oxide film, and 9. IO is an insulating film between the eyebrows made of an oxide film, etc.; 11 is formed on the photoelectric conversion layer 2 with the insulating film 10 between the eyebrows sandwiched therebetween; it reflects the infrared light that has passed through the photoelectric conversion layer 2; This is an Aj2 reflective film for making the light incident on the Aj2.

Next, the operation of the conventional device with the above configuration will be described.

In the case of the conventional device configuration, infrared light incident from the back side of the p-type silicon semiconductor substrate 1 reaches the photoelectric conversion layer 2 of the Schottky junction and is photoelectrically converted, and the generated optical signal charge is It is once accumulated at the Schottky junction.

The signal charge once accumulated in this Schottky junction is transferred to the n-type buried channel 5 by applying a read pulse from the TG scanner 25 to the gate electrode 6. Moreover, the photoelectric conversion layer 2 of the Schottky junction is
When this read pulse is applied, the signal charge is read out and at the same time is reset to a voltage corresponding to the read pulse voltage, and after the reset, the newly detected optical signal charge is accumulated until the next readout.

Therefore, in the CSD method, first, the scanning line wiring 7
One of the -
The signal charge on the horizontal line is transferred to the n-type buried channel 5, and the C3D scanner 26 transfers the signal charge to the scanning line wiring 7.
By applying a vertical transfer pulse to the gate electrode 6 , the signal charge is transferred in the vertical direction and enters the horizontal shift register 23 .

In this case, the gate electrode 6 serves both as the transfer gate electrode for reading signal charges and as the C3D transfer gate for transferring signal charges, as described above.

After that, due to the COD of the horizontal shift register 23,
The signal charges are transferred in the horizontal direction and read out from the output section 24 as a video signal of one horizontal line.

Next, the horizontal line selected by the TG scanner 25 is shifted by one step and a read pulse is applied,
By repeating similar operations, the desired one-screen video output can be obtained as a result.

Here, as described above, if the gate electrode 6 serves both as a transfer gate electrode for reading signal charges and as a CSD transfer gate for transferring signal charges, a vertical transfer pulse is applied to the gate electrode 6. In order to prevent the transfer gate from opening when the transfer pulse is being transferred, it is necessary to set the threshold voltage of the transfer gate to be at least higher than the "H" level voltage of the vertical transfer pulse. Note that the A°C reflective film 11 is similar to the photoelectric conversion layer 2.
By reflecting the infrared light that has passed through without being absorbed by the photoelectric conversion layer 2 and making it enter the photoelectric conversion layer 2 again, the light receiving sensitivity can be improved.

In the photoelectric conversion layer 2 made of the Schottky junction, it is possible to detect a light component having an energy higher than the height of the Schottky barrier. For example, a Schottky junction between platinum silicide (PtSi) and p-type silicon can be detected. In some cases, light components with wavelengths of about 5.6 μm or less can be detected.

Further, FIG. 6 is an explanatory diagram showing a schematic configuration of an optical system in an infrared imaging device using the infrared solid-state imaging device.

In the configuration shown in FIG. 6, reference numeral 61 indicates an infrared lens;
2 is an aperture stop of the infrared lens 61; 63 is a cooling cold shield set to limit the angle of incidence of infrared light; 64 is located within the cold shield 63 and serves as a focal point of the infrared lens 61; The infrared solid-state image sensor 65 is a cooler head of the cold shield 63, which is arranged corresponding to the position.

Therefore, in order to reduce thermal noise, the infrared solid-state image sensor 64 is used after being cooled by a cooler head 65, and in this type of infrared optical system,
Since thermal radiation from the lens barrel of the infrared lens 61 is incident as noise light, the cooled cold shield 6
3 limits the angle of incidence of infrared light to suppress the incidence of noise light.

Furthermore, if an aperture matching optical system is used in which the aperture stop 62, which determines the spread of the signal beam, matches the aperture of the cold shield 63, each detection element of the infrared solid-state image sensor 64 sees the lens barrel through the aperture of the cold shield 63. Kotona(
Therefore, unnecessary infrared rays emitted from the lens barrel are not incident on the detection element, noise output is reduced, and the S/N ratio is improved. Therefore, an aperture matching optical system is often used in the optical system of an infrared imaging device.

[Problem to be solved by the invention]

As mentioned above, conventional infrared solid-state imaging devices are often used with aperture matching optical systems, but they are used to image objects that emit a large amount of infrared rays, such as high-temperature objects. In this case, in order to prevent the output of the infrared solid-state imaging device from becoming saturated, it is necessary to make adjustments such as reducing the amount of incident light or reducing the sensitivity of the device.

In the case of a visible light imaging device, this can be adjusted by narrowing down the aperture diaphragm of the infrared lens; When the aperture is narrowed down, the aperture matching with the cold shield becomes poor, which increases noise light and degrades the S/N ratio.

In conventional infrared solid-state imaging devices, it is impossible to adjust the device sensitivity.

Therefore, in the case of conventional infrared solid-state image sensors, in order to image objects with a large amount of infrared radiation, such as high-temperature objects, it is necessary to accept the deterioration of the S/N ratio and use the aperture diaphragm of the infrared lens. The only way to take countermeasures was to narrow down the number of people.

This invention was made to solve these conventional problems, and its purpose is to make it possible to easily change the infrared sensitivity of a Schottky barrier diode by changing the voltage applied to the diode. This allows the infrared detector itself to have a sensitivity adjustment function, so that even when strong infrared light is incident, the light receiving sensitivity can be adjusted without having to narrow down the aperture of the infrared lens, and without saturating the output of the element. I did it like that.

An object of the present invention is to provide this type of infrared solid-state imaging device.

[Means to solve the problem]

In order to achieve the above object, the infrared solid-state imaging device according to the present invention improves the photosensitivity of the infrared detector by forming an impurity-introduced region in which a required amount of impurities is introduced on the semiconductor side of the Schottky barrier diode interface. The dependence on the reset voltage is increased so that the photosensitivity can be easily changed depending on the reset voltage.

That is, the present invention has an infrared detector using a Schottky barrier diode formed by joining a first conductivity type semiconductor and a metal or metal silicide, and a voltage is applied to the infrared detector. In the configuration of an infrared solid-state imaging device, the infrared solid-state imaging device has a mechanism for accumulating a photocharge signal generated by incident infrared rays and reading out the photocharge signal, wherein the first conductivity type at the interface of the Schottky barrier diode is A required amount of impurity of the second conductivity type is introduced into the semiconductor side of the infrared detector to form an impurity-introduced region, and the voltage applied to the infrared detector can be changed depending on the impurity-introduced region. This is an infrared solid-state imaging device.

[Function 1] Therefore, in the infrared solid-state imaging device of the present invention, the impurity-introduced region formed by introducing a required amount of impurity of the second conductivity type into the semiconductor side of the first conductivity type in the Schottky junction is It has the effect of thickening the reset voltage dependence of the photosensitivity of the detector, and for this reason, the photosensitivity can be easily changed by the reset voltage, and the output is not saturated in response to the amount of incident light. The light sensitivity of the infrared detector can be adjusted.

〔Example〕

Hereinafter, one embodiment of the infrared solid-state imaging device according to the present invention will be described in detail with reference to FIGS. 1 to 3.

FIG. 1 is a plan view schematically showing the arrangement of an infrared solid-state image sensor using a Schottky barrier diode according to this embodiment as an infrared photodetector, and FIG. 2 is a plan view of one unit of infrared rays in FIG. ■−■ with solid-state image sensor
This is a cross-sectional structure diagram corresponding to the line portion, and in the embodiment configurations of FIGS. 1 and 2, the same reference numerals as in the conventional configuration of FIGS. 4 and 5 indicate the same or equivalent parts.

That is, in the configuration of this embodiment shown in FIG. 1 as well, the reference numeral 21 denotes a photodetecting section using a Schottky junction arranged in a one-dimensional or two-dimensional array; 22 is a vertical shift register using a C3D method to transfer charges in the vertical direction, 23 is a horizontal shift register using a CCD method to transfer charges in the horizontal direction, and 24 is an output section for reading out charges to the outside.

Further, 25 is a TG scanner, 26 is a CSD scanner, and each of these scanners 25 and 26 has a scanning line wiring 7.
A gate electrode (component of the vertical shift register 22) 6 on one horizontal line is electrically connected through the gate electrode so that a read pulse from the TG scanner 25 and a transfer pulse from the C3D scanner 26 can be applied to each. It has become.

Next, in the configuration shown in FIG. 2, the symbol l is a p-type silicon semiconductor substrate, and the symbol 2 is a metal such as platinum, palladium, or iridium, or a metal silicide such as platinum silicide, baradium silicide, or iridium silicide. A Schottky junction photoelectric conversion layer formed by an electrode and a substrate 1 is shown, and 3 is an n-type region for mitigating electric field concentration in the peripheral area of the photoelectric conversion layer 2 and preventing dark current. It is a guard ring by.

Further, 4 is a vertical shift register 2 from the photodetector 21.
The n+ type regions 5 and 6 of the transfer gate portion that transfer signal charges to the vertical shift registers 22 and 2 are respectively
The gate electrode 6 serves as both the electrode of the transfer gate portion and the transfer electrode of the C3D.

Further, 7 is a scanning line made of aluminum wiring, 8 is a field insulating film made of a silicon oxide film for isolation and insulation, 9.10 is an insulating film between the eyebrows made of an oxide film, etc., and 11 is the photoelectronic film. This is an AJ2 reflective film that is formed on the conversion layer 2 with the glabellar insulating film 10 interposed therebetween, and reflects infrared light that has passed through the photoelectric conversion layer 2 and makes it enter the layer 2 again.

Furthermore, 12 constitutes the gist of this invention.

This is an n-type impurity introduction region introduced into the interface on the substrate 1 side at the Schottky junction in the photoelectric conversion layer 2.

Next, the operation of the embodiment device having the above configuration will be described.

Even in the case of the configuration of the embodiment device, infrared light incident from the back side of the p-type silicon semiconductor substrate l reaches the photoelectric conversion layer 2 of the Schottky junction and is photoelectrically converted, and the generated optical signal Charge is once accumulated by the Schottky junction, and the signal charge once accumulated in this Schottky junction is transferred to the n-type buried channel 5 by applying a read pulse from the TG scanner 25 to the gate electrode 6. .

Furthermore, when the readout pulse is applied to the photoelectric conversion layer 2 of the Schottky junction, the signal charge is read out and at the same time, the photoelectric conversion layer 2 is reset to a voltage corresponding to the readout pulse voltage, and after the reset, until the next readout, Accumulate newly detected optical signal charges.

Now, in the C3D method, as mentioned earlier,
First, one of the scanning line wirings 7 is selected by the TG scanner 25, and a readout pulse is applied to the gate electrode 6 on one horizontal line connected to the scanning line wiring 7, so that the corresponding -horizontal line The upper signal charge is transferred to the n-type buried channel 5, and is also transferred to the C3D scanner 26.
By applying a vertical transfer pulse from the scanning line wiring 7 to the gate electrode 6, the signal charge is transferred in the vertical direction and enters the horizontal shift register 23.

Also in this case, the gate electrode 6 here serves both as a transfer gate electrode for reading signal charges and as a C3D transfer gate for transferring signal charges.

Thereafter, the signal charge is transferred in the horizontal direction by the CCD of the horizontal shift register 23, and read out from the output section 24 as a video signal of one horizontal line.

Next, the horizontal line selected by the TG scanner 25 is shifted by one step and a read pulse is applied,
By repeating the same actions as above, the result is:
The desired one-screen video output can be obtained.

Further, as described above, the gate electrode 6 is connected to the electrode of the transfer gate from which the signal charge is read out, and the C which transfers the signal charge.
When the transfer gate also serves as the SD transfer gate, in order to prevent the transfer gate from opening when a vertical transfer pulse is applied to the gate electrode 6, the threshold voltage of the transfer gate is set to It is necessary to set the voltage to be at least higher than the "H" level voltage of the vertical transfer pulse.

In this case, the first reflective film 11 reflects the infrared light that has passed through the photoelectric conversion layer 2 without being absorbed, and
By making the light enter the light again, it is possible to improve the light receiving sensitivity.

In this case, too, in the photoelectric conversion layer 2 made of the Schottky junction, it is possible to detect a light component having an energy higher than the height of the Schottky barrier. In the case of a Schottky junction with , it is possible to detect light components with wavelengths of about 5.6 μm or less.

Next, FIG. 3 is a graph showing the photosensitivity dependence of an infrared detector using a Schottky junction in the infrared solid-state imaging device.

In FIG. 3, curve a indicates the reset voltage dependence of the photosensitivity of the infrared detector at the Schottky junction in the conventional structure, and the curve a indicates the p-type substrate 1 side at the Schottky junction in this example structure. There is an n-type impurity at the interface of
2 shows the dependence of the photosensitivity of the infrared detector on the reset voltage when the n-type impurity introduced region 12 is formed by introducing phosphorus.

As is clear from the characteristics shown in FIG. 3, in the conventional Schottky junction, the dependence of the photosensitivity of the infrared detector on the reset voltage is small, and therefore it is difficult to adjust the photosensitivity using the reset voltage. On the other hand, in the infrared detector in which the n-type impurity doped region 12 is formed at the interface of the Schottky junction on the p-type substrate 1 side, as in the configuration of this embodiment, the photosensitivity can be easily increased by adjusting the reset voltage. It can be adjusted, and the amount of n-type impurity introduced at this time has a sufficient effect even if it is not introduced until the interface is reversed to the n-side. Even in the conventional Schottky junction where no impurity doped region is formed, the dependence of photosensitivity on the reset voltage is relatively large in the region where the reset voltage is low, and in this example as well, phosphorus (P)
By introducing n-type impurities such as arsenic (As) into the interface, the electric field strength at the interface is reduced even in regions where the reset voltage is high, and the reset voltage is reduced to the same level as in the conventional region where the reset voltage is low. Dependency increases.

In addition, if impurities are introduced so that the pole (thin region (approximately several tens of micrometers or less)) of the interface becomes n-type, the barrier apex of the Schottky barrier will be formed at a position deeper than the interface, and the reset voltage of the photosensitivity will increase. Dependency increases.However,
If too much impurity is introduced, as shown in curve C, the photosensitivity will drop significantly, the barrier height will correspondingly increase, and the cut-off wavelength will become short (which makes it difficult to use). become unable.

Then, as in the example structure described above, by forming a region doped with an appropriate amount of n-type impurity at the p-type silicon semiconductor interface constituting the Schottky junction, the photosensitivity can be reset. The voltage dependence can be made as shown in the curve shown in Fig. 3. In this state, if the "H" level voltage ■1° of the read pulse of the TG scanner 25 shown in Fig. 1 is made variable, The reset voltage is this degree
Since it depends on the voltage (a) at the °H" level, the photosensitivity can be adjusted depending on the amount of incident light.

In the above embodiment, an example was described in which the transfer gate and the transfer gate have a common electrode, but the transfer gate electrode and the transfer gate electrode are formed electrically separated, and hand,
(In this case, the voltage vT0 can be made lower, so the adjustment range of the voltage Vta becomes wider.

In addition, in the above embodiment, a Schottky junction infrared detector constituting one pixel is arranged two-dimensionally, and the signal readout in the vertical direction is performed using the CDS method. may be arbitrary, and the signal readout method may also be a CCD method, etc.
Or MO8 method (MOS-T in the output section of the infrared detector)
In this case, the same operation and effect as in the embodiment can be obtained.

〔Effect of the invention〕

As detailed above, according to the present invention, an infrared detector using a Schottky barrier diode formed by joining a first conductivity type semiconductor and a metal or a metal silicide is provided, and the infrared detection In an infrared solid-state image sensor, which is configured with a mechanism for accumulating a photocharge signal generated by incident infrared rays while a voltage is applied to the device and reading out the photocharge signal, a A required amount of impurity of the second conductivity type is introduced into the semiconductor side of the first conductivity type to form an impurity introduction region, so that the voltage applied to the infrared detector can be changed by the impurity introduction region. For example, when capturing an image of a high-temperature object with a large amount of infrared radiation, it is necessary to destroy the aperture alignment of the optical system and use S/
The photosensitivity of the infrared detector is reduced by simply reducing the voltage of the signal readout pulse, rather than by narrowing down the aperture stop of the infrared lens, which would degrade the N ratio. It is possible to prevent the output from saturating and enable imaging, and as a result, the light sensitivity of the infrared detector can be adjusted extremely easily according to the amount of incident light so that the output does not become saturated. It has several features.

[Brief explanation of the drawing]

FIG. 1 is a plan view schematically showing the arrangement of an infrared solid-state image sensor using a Schottky barrier diode as an infrared detector according to an embodiment of the present invention, and FIG. 2 is a unit in FIG. 1. - with an infrared solid-state image sensor
■A cross-sectional structure diagram corresponding to the lined part, Figure 3 is a graph showing the photosensitivity dependence of an infrared detector using a Schottky junction in the above infrared solid-state imaging device, and Figure 4 is a graph showing the same infrared solid-state imaging according to the conventional example. FIG. 5 is a plan view schematically showing the arrangement of the device; FIG. 5 is a cross-sectional structural diagram corresponding to the ■-V line of one unit of the infrared solid-state imaging device in FIG. 4; and FIG. 6 is the infrared imaging device. FIG. 2 is an explanatory diagram showing a schematic configuration of an optical system of FIG. l... p-type silicon semiconductor substrate, 2... photoelectric conversion layer, 3... guard ring, 4
...N+ type region 5...N type buried channel, 6...Gate electrode, 7...Scanning line wiring, 8...
...Field insulating film, 9.10...Interlayer insulating film, 11...A4 reflective film, 12...N-type impurity doped region, 21...Photodetection section, 22... ...Vertical shift register, 23...Horizontal shift register, 24...Output section, 25...Transfer gate scanner, 26...
・C3D scanner. Agent Masu Oiwa Yutada Riki amounttO゛C5Ds''?Y7

Claims (1)

[Claims] An infrared detector using a Schottky barrier diode formed by bonding a first conductivity type semiconductor and a metal or metal silicide, and a voltage applied to the infrared detector. In the configuration of an infrared solid-state imaging device, the infrared solid-state imaging device is equipped with a mechanism for accumulating a photocharge signal generated by incident infrared rays and reading out the photocharge signal, wherein the first conductivity type at the interface of the Schottky barrier diode is A required amount of impurity of the second conductivity type is introduced into the semiconductor side of the infrared detector to form an impurity-introduced region, and the voltage applied to the infrared detector can be changed depending on the impurity-introduced region. Infrared solid-state image sensor.