JPH03212979A - Infrared sensor - Google Patents

Abstract

PURPOSE:To obtain an infrared sensor whose sensitivity is high by a method wherein a diaphragm region is formed on the main face of a substrate, a semiconductor layer is formed and a p-n junction is formed in the semiconductor layer. CONSTITUTION:An SiO2 layer 2 is formed on a (100) plane of an Si substrate 1; an inverted square truncated pyramid is etched under the central part to form a cavity 3. p-type Si layers 5, 6 are formed on the SiO2 layer; n-type Si layers 7, 8 are formed in them. The Si layers 5 to 8 are formed of poly-Si or a single crystal by an SOI technique. They are covered with SiO2 9; openings 10 to 1 3 are formed. Al interconnections 14 to 17 are attached; they are protected by SiO2 18. A slit 1 9 is formed in SiO2's 18, 9, 2; a diagonal of a diaphragm region 4 is formed additionally. An anisotropic etching operation is executed from the slit 19 to form the cavity 3. An infrared-rays absorbing layer is formed on the protective film 18. Regarding the region 4, its thermal conductivity is low, and its time constant of temperature change against a change in an infrared-rays incident amount is small. When the reverse bias characteristic of a diode which is extremely sensitive to a temperature change is utilized, an effective infrared sensor can be obtained.

Description

[Detailed description of the invention] [Industrial application field] This invention relates to an aspiration infrared sensor.

[Conventional technology]

Aspirational infrared sensors include pyroelectric type, thermomobile type,
There is a bolometa type. Each of these types of infrared sensors is
Each uses changes in spontaneous polarization, changes in electromotive force, and changes in resistance due to temperature.

The Aspiration infrared sensor is not only used as a single element, but is also being developed as an image sensor arranged in a -dimensional or two-dimensional array.

[Problem to be solved by the invention]

Aspiration infrared sensors have the advantage of not requiring cooling compared to quantum infrared sensors such as infrared sensors using IgcdTe, but have the disadvantage of low sensitivity. For this reason, efforts have been made to reduce the thermal conductivity of the infrared light receiving section and improve the sensitivity, but this is still insufficient.

Furthermore, in order to improve the sensitivity, it is effective to operate the sensor in an accumulation mode.

For signal storage, it is convenient for the signal to be in the form of a charge. However, the signals of conventional Aspiration infrared sensors are changes in spontaneous polarization in the case of the pyroelectric type, electromotive force in the thermoelectric type, and
The bolometa type has the disadvantage that the resistance changes, and the signal needs to be converted into an electric charge. Furthermore, infrared sensor arrays have the disadvantage that the conversion rate of each pixel varies and fixed pattern noise occurs.

[Means to solve the problem]

There are six infrared sensors of this invention.

One of them is an infrared sensor having a structure characterized by having a diaphragm region provided on the main surface of a substrate, a semiconductor layer provided in this diaphragm region, and a pn junction provided in this semiconductor layer. be.

The second is a structure characterized by a diaphragm region provided on the main surface of the substrate, a semiconductor layer provided in this diaphragm region, and a metal layer forming a Schottky junction with this semiconductor layer. It is an infrared sensor.

Third, a semiconductor substrate of a first conductivity type, a large number of diaphragm regions arranged on the main surface of this semiconductor substrate, and a semiconductor layer provided in each of these diaphragm regions;
A pn junction provided in this semiconductor layer, a CCD provided corresponding to the large number of diaphragm regions, and this CC
D and the diaphragm region, the drain is the channel of the CCD, and the source of a second conductivity type opposite to the first conductivity type is connected to the second conductivity type region of the pn junction. The configuration is characterized by having a transfer gate.

The fourth infrared sensor includes a semiconductor substrate, a large number of diaphragm regions arranged on the main surface of the semiconductor substrate, a semiconductor layer provided in each of these diaphragm regions, and a metal layer forming a Schottky junction with the semiconductor. a CCD provided corresponding to the plurality of diaphragm regions;
provided between the CCD and the diaphragm region,
This structure is characterized in that the drain is the channel of the CCD, and the source is a transfer gate connected to one terminal of the Schottky junction.

Fifth, a semiconductor substrate of a first conductivity type, a large number of diaphragm regions arranged on the main surface of this semiconductor substrate, and a semiconductor layer provided in each of these diaphragm regions;
a pn junction provided in the semiconductor layer, a signal line provided corresponding to the large number of diaphragm regions, a drain provided between the signal line and the diaphragm region, and a drain connected to the signal line; an infrared ray characterized by comprising a transfer gate in which a source of a second conductivity type opposite to the first conductivity type is connected to the second conductivity type region of the pn junction, and a gate is connected to an output of a shift register. It is a sensor.

Sixth, a semiconductor substrate, a large number of diaphragm regions arranged on the main surface of the semiconductor substrate, a semiconductor layer provided in each of these diaphragm regions, and a metal layer forming a Schottky junction with the semiconductor layer; a signal line provided corresponding to the plurality of diaphragm regions; a signal line provided between the signal line and the diaphragm region; a drain connected to the signal line; and a source connected to one terminal of the Schottky junction. and a transfer gate connected to the output of the shift register.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIGS. 1A and 1B are a plan view and a sectional view, respectively, of an aspiration infrared sensor according to a first embodiment of the present invention, showing a silicon substrate 1+ in the 000 direction (100).

An underlayer 2 of a silicon nitride film or an oxide film is formed using the CVD method or plasma CVD method, and a silicon substrate 1 is placed under the center portion of the underlayer 2 in the shape of an upside-down truncated pyramid. It is etched to form a cavity 3. The membrane covering the upper surface of the cavity 3 is called a diaphragm 4. N-type 9937 layers 5 and 6 on underlayer 2 and this n-type 9937 layer
N-type silicon chips 7.8 are formed in the layers 5.6, respectively. For the n-type 9937 layers 5 and 6 and the n-type silicon layers 7 and 8, polysilicon or single crystal silicon using SOI technology is used. n-type 9937 layer 5,
An insulating layer 9 is formed on the n-type 9937 layer 7.8. The insulating layer 9 is formed of an insulating material such as an oxide film or a nitride film. Contact holes 10 to 13 are opened in this insulating layer 9. The p-type silicon scrap 5.6 and the n-type 9937 layer 7.8 are connected to the aluminum interconnections 14-17 through the contact holes 10-13. A protective film 18 such as an oxide film or a nitride film is formed on the aluminum wirings 14 to 17 for the purpose of protecting the device. Protective film 1
8. Insulating layer 9. A slit 19 is formed in the underlayer 2. The slit 19 is located diagonally of the diaphragm region 4. A cavity 3 is formed through this slit 19 using an anisotropic etching solution. The protective film 18, the insulating film 9, and the underlayer 2 are formed by etching an n-type 9937 layer 5.6 using an anisotropic etching solution.
and protects the n-type 9937 layers 7 and 8. Although not shown, an infrared absorbing layer is formed on the protective film 18.

The aspiration infrared sensor according to the present invention absorbs incoming infrared rays. In areas other than the diaphragm area 4, the heat capacity is large and the thermal conductivity up to the package is high, so the temperature increase can be ignored. On the other hand, in the diaphragm region 4, the thermal conductivity up to the package is low, causing a temperature rise. Furthermore, since the heat capacity is small, the time constant of the temperature change in the diaphragm region 4 is small with respect to the change in the amount of incident infrared rays.

The reverse bias current of the pn junction diode formed in the diaphragm region 4 increases as the temperature rises, as shown in FIG. When the reverse bias voltage applied to the pn junction is sufficiently large, the temperature dependence of the saturation current JS is mainly expressed as
1). However, EII is the semiconductor bandgap,
k is Boltzmann's constant and T is the operating temperature. As can be seen from equation (1), the saturation current JS changes greatly depending on temperature. As a result, a reverse bias current is generated according to the amount of incident infrared rays, and even if the pn junction that operates as an infrared sensor is not ideal and leakage from the interface is large, the leakage current will increase as the temperature rises. There is no problem because it increases in the activated form as shown in equation (1).

FIG. 3 is a plan view (FIG. 3(a)) and a cross-sectional view (FIG. 3(b)) of an aspiration infrared sensor according to a second embodiment of the present invention. Components shown with the same symbols as in FIG. 1 indicate the same components. In this embodiment, a truncated pyramid-shaped cavity 20 is formed by performing anisotropic etching from the back surface 1 of a silicon substrate 1. Other than this, this embodiment is the same as the first embodiment except that there is no slit in the diaphragm region. The operation is similar to the first embodiment.

FIGS. 4(a) and 4(b) are a plan view (FIG. 4(a)) and a sectional view (FIG. 4(b)) of an aspiration infrared sensor according to a third embodiment of the present invention. Components shown with the same symbols as in FIG. 1 indicate the same components. The difference from the first embodiment is that in the first embodiment, a pn junction diode is formed on the diaphragm region 4, whereas in the third embodiment, a shot junction diode is formed. That is, a Schottky junction diode is formed, which includes an n-type 9937 layer 21.22 on the underlayer 2 and a platinum silicide layer 23.24 on the n-type silicon 121.22. Materials other than platinum silicide may be used as the metal forming the Schottky junction diode, and p-type may also be used as the semiconductor.

In a Schottky junction diode, the temperature dependence of the saturation current Js when the reverse bias voltage is sufficiently large is mainly J5~exp(-EsB/kT) (2). However, ESB is the height of the Schottky junction barrier. As can be seen from equation (2), the change in saturation current J5 due to temperature is of the activation type and is large. Therefore, like the first embodiment, it can be used as an aspirational infrared sensor.

Next, an example of an infrared image sensor in which a large number of aspiration infrared sensors are arranged will be shown. In the aspiration infrared sensor of this invention, p
Since the n-junction diode or the cross-junction diode is operated in a reverse bias state, it is possible to use a method used in a solid-state imaging device for visible light that uses a pn-junction diode in the light receiving section. These methods perform an accumulation operation in which signal charges are accumulated in a storage capacitor of a pixel portion and then read out, and have high sensitivity.

FIG. 5 is a schematic plan view of a fourth embodiment of the present invention.

The fourth embodiment is an n-channel infrared image sensor in which the aspiration infrared sensors of the first to third embodiments are arranged in one dimension. In the figure, a large number of diaphragms are arranged in one dimension, and pn junction diodes 25 as shown in FIG. 1 are formed on each of the diaphragms.

The p-type side terminal of the pn junction diode 25 is connected to a p-type silicon substrate, and the n-type side terminal is connected to an n-type source of a transfer gate 26 provided in each pixel. An embedded readout CCD 27 is provided corresponding to the transfer gate 26. The buried layer of the readout CCD 27 also serves as the drain of the transfer gate 26 . A floating diffusion layer type output section 28 is provided at the end of the read CCD 21 in the transfer direction.

In this image sensor, the pn junction diode 25 and the source reverse bias capacitance of the transfer gate 26 are
The reverse bias current of junction diode 25 is accumulated. The temperature of the diaphragm rises in accordance with the amount of incident infrared rays, and the reverse bias current changes accordingly, so this accumulated charge becomes a signal charge. When the accumulation period ends, the transfer gate 26 is turned on, the accumulated signal charges are transferred to the readout CCD 27, and at the same time, the reverse bias voltage of the pn junction diode 25 is reset. Transfer gate 26 is turned off and the next accumulation period begins. The signal charges transferred to the readout CCD 27 during the accumulation period are sequentially transferred to the output section 28, and the signals are taken out to the outside.

FIG. 6 is a schematic plan view of a fifth embodiment of the invention.

The fifth embodiment is an n-channel infrared image sensor in which the aspiration infrared sensors of the first to third embodiments are two-dimensionally arranged. In the figure, a large number of diaphragms are arranged two-dimensionally, and pn junction diodes 2a as shown in FIG. 1 are formed on each of the diaphragms.

The p-type side terminal of the pn junction diode 2a is connected to the p-type silicon substrate, and the rl-type side terminal is connected to the n-type source of the transfer gate 30 provided in each pixel.

A buried vertical CCD 31 is provided corresponding to the transfer gate 30. The buried layer of the vertical CCD 31 also serves as the drain of the transfer gate 30. A horizontal CCD 3 is located at the end of the vertical CCD 31 in the transfer direction.
2 is provided. Furthermore, a floating diffusion layer type output section 33 is formed at the end of the horizontal CD 32 in the transfer direction.

In this image sensor, similarly to the fourth embodiment,
During the accumulation period, signal charges are accumulated in the reverse bias capacitance of the pn junction diode 2a and the source of the transfer gate 30. When the accumulation period ends, the transfer gate 30 is turned on and the accumulated signal charges are transferred to the vertical CC
Moved to D31. At the same time, the reverse bias voltages of the two pn junction diodes are reset. When transfer gate 30 is turned off, the next accumulation period begins.

During the accumulation period, the signal charges transferred to the vertical CCD 31 are sequentially transferred to the output section 33 by the functions of the vertical CCD 31 and the horizontal CCD 32, and the signals are taken out to the outside.

In the fourth and fifth embodiments, it is possible to use the transfer gates 26 and 30 in common with the electrodes of the CCD, as is the case with visible CCD image sensors.

FIG. 7 is a schematic plan view of a sixth embodiment of the invention.

The sixth embodiment is an n-channel infrared image sensor in which the aspiration infrared sensors of the first to third embodiments are arranged two-dimensionally, and is a so-called MOS type. 37 is a pn junction diode formed in the diaphragm region, and 38 is a vertical switch (transfer gate) for vertical readout.
It is formed of an OS transistor. vertical switch 38
The gates of each row are commonly connected to taps 41 of a vertical shift register 40 that generates pulses delayed by a horizontal period. Further, the drains of the vertical switches 38 are commonly connected to each other by a vertical signal line 3a for each row. 42 is formed of a MOS transistor which is a horizontal switch. The gate of the horizontal switch 42 is connected to each tap 44 of the horizontal shift transistor 43, the source is connected to three vertical signal lines, and the drain is connected to an output line 45.

In this image sensor, similarly to the fourth embodiment,
During the accumulation period, signal charges are accumulated in the reverse bias capacitance of the pn junction diode 37 and the source of the vertical switch 38. The accumulated signal charge is transferred to any tap 41 of the vertical shift register 40 when it becomes high level.
The vertical switches 38 in the rows connected to the rows become conductive, and signal charges are read out to the three corresponding vertical signal lines. This signal charge is sequentially read out to an output line 45 by each tap output 44 from the horizontal shift register 43 via a horizontal switch. In this way, when all the signals of the pn junction diode 37 corresponding to an arbitrary tap 41 of the vertical shift register 40 are read out, the vertical shift register 40 advances by one stage and the next tap becomes high level.
At the same time, pn junction diode 3 in the row corresponding to that tap
7 signal charges are read out to three corresponding vertical signal lines. By repeating the same operation thereafter, the signal charges stored in the pn junction diode 37 shown in FIG. 7 can be sequentially read out row by row.

〔Effect of the invention〕

The Aspiration infrared sensor according to the invention is very sensitive because it uses the reverse bias characteristics of a diode that is very sensitive to temperature changes. Further, since the signal is in the form of charge, it is easy to operate in the accumulation mode, and it can be realized with a simple configuration. Therefore, a -dimensional or two-dimensional image sensor can be easily realized.

In the fourth to sixth embodiments, only the n-channel type was explained, but a p-channel type can also be realized.

Further, the pn junction diode on the diaphragm may be replaced with a Schottky junction diode.

Regarding the MO3 type image sensor, only the two-dimensional case, which is the sixth embodiment, has been shown, but it can also be used as a -dimensional infrared image sensor.

[Brief explanation of drawings]

FIGS. 1(a) and (b) are a plan view and a cross-sectional view of an infrared sensor according to a first embodiment of the present invention, FIG. 2 is a current-voltage characteristic of a pn junction diode, and FIGS. 3(a) and ( b) is a plan view and a sectional view, respectively, of an infrared sensor according to a second embodiment of this invention, and FIGS. 4(a) and (b) are a plan view and a sectional view, respectively, of an infrared sensor according to a third embodiment of this invention. Figures 5, 6, and 7 are the 4th part of this invention. FIG. 5 is a schematic plan view of an infrared sensor according to a sixth embodiment. 1... Silicon substrate, 4... Diaphragm region, 5
．． 6...p-type silicon layer, 7,8.21...n-type semiconductor layer, 23...platinum silicide layer, 25,29°3
7... pn junction diode, 26.30... transfer gate, 27... readout CCD, 31...
Vertical CCD, 32...Horizontal CCD, 38...Vertical switch (transfer gate), 3...Vertical signal lines.

Claims (1)

[Claims] 1. An infrared sensor characterized by having a diaphragm region provided on the main surface of a substrate, a semiconductor layer provided in this diaphragm region, and a pn junction provided in this semiconductor layer. . 2. An infrared sensor comprising a diaphragm region provided on the main surface of a substrate, a semiconductor layer provided in the diaphragm region, and a metal layer forming a Schottky junction with the semiconductor layer. 3. A semiconductor substrate of a first conductivity type, a large number of diaphragm regions arranged on the main surface of this semiconductor substrate, a semiconductor layer provided in each of these diaphragm regions, and a pn junction provided in this semiconductor layer. a CCD provided corresponding to the plurality of diaphragm regions, a second CCD provided between the CCD and the diaphragm region, the drain of which is the channel of the CCD, and a second conductivity type opposite to the first conductivity type. An infrared sensor characterized in that a conductivity type source has a transfer gate connected to the second conductivity type region of the pn junction. 4. A semiconductor substrate, a large number of diaphragm regions arranged on the main surface of this semiconductor substrate, a semiconductor layer provided in each of these diaphragm regions, a metal layer forming a Schottky junction with this semiconductor, a CCD provided corresponding to the diaphragm region; a CCD provided between the CCD and the diaphragm region; and a drain connected to the CCD.
and a transfer gate whose source is connected to one terminal of the Schottky junction. 5. A semiconductor substrate of a first conductivity type, a large number of diaphragm regions arranged on the main surface of this semiconductor substrate, a semiconductor layer provided in each of these diaphragm regions, and a pn junction provided in this semiconductor layer. a signal line provided corresponding to the plurality of diaphragm regions; and a signal line provided between the signal line and the diaphragm region, having a drain connected to the signal line, and having a conductivity type opposite to the first conductivity type. An infrared sensor comprising a transfer gate whose source of a second conductivity type is connected to the second conductivity type region of the pn junction and whose gate is connected to an output of a shift register. 6. A semiconductor substrate, a large number of diaphragm regions arranged on the main surface of the semiconductor substrate, a semiconductor layer provided in each of these diaphragm regions, a metal layer forming a Schottky junction with the semiconductor layer, a signal line provided corresponding to a diaphragm region, a signal line provided between this signal line and the diaphragm region, a drain connected to the signal line, and a source connected to one terminal of the Schottky junction, and a transfer gate, the gate of which is connected to the output of a shift register.