INFRARED SENSOR AND METHOD OF MANUFACTURING INFRARED SENSOR

An infrared sensor includes a first semiconductor substrate, a second semiconductor substrate, a sealing frame, and a first connection. The first semiconductor substrate includes a first main surface and an infrared detection element. The second semiconductor substrate includes a second main surface and a signal processing circuit. The sealing frame surrounds an internal space with the first main surface, the infrared detection element, and the second main surface. The first connection electrically connects the infrared detection element and the signal processing circuit. The internal space is hermetically sealed by the first main surface, the infrared detection element, the second main surface, and the sealing frame. Each of the sealing frame and the first connection is sandwiched between the first main surface and the second main surface.

TECHNICAL FIELD

The present disclosure relates to an infrared sensor and a method of manufacturing an infrared sensor.

BACKGROUND ART

Infrared sensors are classified into the quantum type (cooling type) and the thermal type (non-cooling type). A thermal infrared sensor converts infrared radiation absorbed by an infrared absorber into heat, The thermal infrared sensor converts temperature change caused by the converted heat into an electrical signal. The temperature change by infrared radiation occurs in an infrared detector of the thermal infrared sensor. An insulation structure with which the infrared detector is thermally isolated from the substrate of the thermal infrared sensor increases the temperature change of the infrared detector caused by the infrared detector absorbing the incident infrared radiation. The infrared detector may be held in an internal space in a vacuum in the insulation structure. This suppresses reduction in thermal resistance of the insulation structure due to heat transfer through gas and gas convection in the internal space, thereby further enhancing thermal insulation.

An infrared sensor having an infrared sensor substrate and a signal processing circuit substrate facing each other is also known. An insulation structure is provided between the infrared sensor substrate and the signal processing circuit substrate. The internal space of the insulation structure is hermetically sealed to be thermally insulated, The infrared sensor substrate has a pixel array formed with a plurality of pixels including infrared detection elements. The signal processing circuit substrate has a signal processing circuit for processing an output signal from each infrared detection element. The signal processing circuit is, for example, an analog/digital conversion circuit.

An example of the infrared sensor having the structure as described above is an optical device (infrared sensor) described in WO20061095834 (PTL 1). In the optical device described in the publication above, a photoelectric conversion portion (infrared detection element) faces an aperture (internal space) hermetically sealed. The aperture is hermetically sealed by a first main surface of a substrate (first semiconductor substrate) having the photoelectric conversion portion, the photoelectric conversion portion, a second main surface of a signal processing circuit portion (second semiconductor substrate), a sealing material, and interconnection wiring (first connection).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the optical device described in the publication above, after the substrate and the signal processing circuit portion are electrically connected by the interconnection wiring, the substrate, the signal processing circuit portion, and the connection wiring are hermetically sealed by the sealing material. The aperture is formed by removing the sealing material. Thus, in the optical device described in the publication above, the scaling of the aperture and the electrical connection between the substrate and the signal processing circuit portion are performed separately. This increases the manufacturing cost of the infrared sensor.

The present disclosure is made in view of the problem above and an object of the present disclosure is to provide an infrared sensor and a method of manufacturing an infrared sensor that can suppress increase of the manufacturing cost,

Solution to Problem

An infrared sensor according to the present disclosure includes a first semiconductor substrate, a second semiconductor substrate, a sealing frame, and a first connection, The first semiconductor substrate includes a first main surface and an infrared detection element. The infrared detection element is arranged at the first main surface. The second semiconductor substrate includes a second main surface and a signal processing circuit. The second main surface faces the first main surface. The signal processing circuit processes a signal of the infrared detection element. The sealing frame is connected to the first semiconductor substrate and the second semiconductor substrate. The sealing frame surrounds an internal space with the first main surface, the infrared detection element, and the second main surface. The first connection electrically connects the infrared detection element and the signal processing circuit. The internal space is hermetically sealed by the first main surface, the infrared detection element, the second main surface, and the sealing frame. Each of the sealing frame and the first connection is sandwiched between the first main surface and the second main surface.

Advantageous Effects of Invention

In the infrared sensor according to the present disclosure, increase of the manufacturing cost of the infrared sensor can be suppressed.

DESCRIPTION OF EMBODIMENTS

Embodiments will be described below based on the drawings. In the following, like or corresponding parts are denoted by like reference signs and an overlapping description is not repeated.

First Embodiment

Referring toFIG.1andFIG.2, a configuration of an infrared sensor100according to a first embodiment will be describedFIG.1is a cross-sectional view along line1-I inFIG.2.

Infrared sensor100is an infrared sensor for detecting infrared radiation IR incident on an infrared sensor100. Infrared sensor100according to the present embodiment is a thermal infrared sensor.

As illustrated inFIG.1, infrared sensor100includes a first semiconductor substrate1, a second semiconductor substrate2, a sealing frame3, and a first connection4. First semiconductor substrate1and second semiconductor substrate2are put on each other at a distance from each other. Each of sealing frame3and first connection4is sandwiched between first semiconductor substrate1and second semiconductor substrate2.

In the present embodiment, the Z axis direction is a direction along the direction in which first semiconductor substrate1and second semiconductor substrate2are put on each other. The Z axis positive direction is a direction from first semiconductor substrate1toward second semiconductor substrate2along the Z axis direction. The Z axis negative direction is a direction from second semiconductor substrate2toward first semiconductor substrate1along the Z axis direction. The X axis direction is a direction orthogonal to the Z axis direction and along the direction in which first semiconductor substrate1extends, The Y axis direction is a direction orthogonal to each of the X axis direction and the Z axis direction. The in-plane direction of first semiconductor substrate1is a direction along the X axis direction and the Y axis direction.

In the present embodiment, infrared radiation1R is incident on infrared sensor100along the Z axis negative direction. Infrared sensor100is configured to detect infrared radiation IR incident on infrared sensor100along the Z axis negative direction, In the present embodiment, “infrared radiation IR is incident on infrared sensor100along a certain direction” means that infrared radiation IR having a main component along the certain direction is incident on infrared sensor100, Infrared radiation IR therefore may have a component along a direction different from the certain direction,

First semiconductor substrate1includes a first main surface1a, a first back surface1b,an infrared detection element11, and a control circuit12. First semiconductor substrate1may include a plurality of infrared detection elements11. In the present embodiment, first semiconductor substrate1includes a plurality of infrared detection elements11.

First main surface1aprotrudes outside of sealing frame3along the in-plane direction (the X axis direction and the Y axis direction) of first semiconductor substrate1. First main surface1ahas a flat surface. First back surface1bis opposed to first main surface1a.First back surface1btherefore extends along the in-plane direction (the X axis direction and the Y axis direction) of first main surface1aon the side opposite to second semiconductor substrate2with respect to first main surface1a.

Infrared detection element11is arranged on first main surface1a.Infrared detection element11is configured to generate a detection signal when infrared radiation IR. is incident on infrared detection element11. Thus, first semiconductor substrate1is formed as an infrared sensor substrate. Infrared detection element11is, for example, an element employing MEMS (Micro Electro Mechanical Systems) technology, such as a diode, a resistive bolometer, a ferroelectric thin film, and a thermoelectric element.

In the present embodiment, infrared radiation IR is incident on infrared detection element11through second semiconductor substrate2along the Z axis negative direction. Infrared detection element11is therefore arranged to face second semiconductor substrate2. Infrared sensor100is configured to detect infrared radiation IR incident on infrared detection element11through second semiconductor substrate2. As described later, infrared sensor100may be configured to detect infrared radiation IR incident on infrared detection element11through first back surface1bof first semiconductor substrate1.

In the present embodiment, a pixel PX is formed of two infrared detection elements11as a unit, A plurality of pixels PX form a pixel array PXA. Control circuit12is configured to control a plurality of infrared detection elements11. Control circuit12is configured to control a plurality of pixels PX. The detailed configuration and operation of pixel PX and control circuit12will be described later.

First semiconductor substrate1may further include a not-illustrated support leg. The support leg is arranged on first main surface1a.Infrared detection element11may be held in the air above first main surface1aby the support leg. That is, infrared detection element11may be arranged at a distance from first main surface1aby the support leg,

Second semiconductor substrate2extends along the in-plane direction (the X axis direction and the Y axis direction) of first main surface1a.Second semiconductor substrate2is arranged at a distance from first semiconductor substrate1. Second semiconductor substrate2faces first semiconductor substrate1. Second semiconductor substrate2faces in parallel to first semiconductor substrate1. The distance between first semiconductor substrate1and second semiconductor substrate2along the Z axis direction is the same as the dimension of sealing frame3and first connection4along the Z axis direction.

Second semiconductor substrate2includes a second main surface2a,a second hack surface2b,and a signal processing circuit21. Second main surface2afaces first main surface1a.Second main surface2afaces first main surface1aat a distance from first main surface1a.Second main surface2aprotrudes outside of sealing frame3along the in-plane direction (the X axis direction and the Y axis direction) of first main surface1a.Second back surface2bis opposed to second main surface2a. Second back surface2btherefore extends along the in-plane direction (the X axis direction and the Y axis direction) of second main surface2aon the side opposite to first semiconductor substrate1with respect to second main surface2a.

S1gnal processing circuit21is configured to process a signal of infrared detection element11. Specifically, signal processing circuit21is configured to process a detection signal transmitted from infrared detection element11. In the present embodiment, signal processing circuit21is configured to process a detection signal transmitted from each of a plurality of infrared detection elements11. Thus, second semiconductor substrate2is fanned as a signal processing circuit substrate.

S1gnal processing circuit21includes, for example, a read circuit, an amplifier, a sample hold circuit, an analog/digital converter, and a digital signal processing circuit. The read circuit is configured to read an output signal transmitted from each of infrared detection elements11. The amplifier is configured to amplify a signal transmitted from each of infrared detection elements11. The detailed configuration and operation of signal processing circuit21will be described later.

In the present embodiment, second semiconductor substrate2includes a second substrate portion22and a second infrared transmitting portion IT2. Second substrate portion22and second infrared transmitting portion IT2are configured to transmit infrared radiation IR. Second infrared transmitting portion IT2is configured to transmit infrared radiation IR more than second substrate portion22. Second infrared transmitting portion IT2faces infrared detection element11.

Second infrared transmitting portion IT2contains, for example, an impurity such as phosphorous (F) or boron (B). Thus, second infrared transmitting portion IT2has a resistivity of, for example, 1 Ω·cm or more. The absorption of infrared radiation IR by second infrared transmitting portion IT2has a correlation with the resistivity of second infrared transmitting portion1T2. Therefore, the larger the resistivity of second infrared transmitting portion IT2is, the less infrared radiation IR is absorbed in second infrared transmitting portion IT2. Accordingly, when the resistivity of second infrared transmitting portion IT2is, for example, 1 Ω·cm or more, absorption of the infrared radiation IR wavelength by second semiconductor substrate2is suppressed.

As illustrated inFIG.1andFIG.2, sealing frame3is connected to first semiconductor substrate1and to second semiconductor substrate2. Sealing frame3surrounds an internal space IS with first main surface1a,infrared detection element11, and second main surface2a.Internal space IS is hermetically sealed by first main surface1a,infrared detection element11, second main surface2a,and sealing frame3. As illustrated inFIG.1, internal space IS is sandwiched between first main surface1aand infrared detection element11, and second main surface2aalong the Z axis direction. Each of infrared detection element11and second infrared transmitting portion IT2faces internal space IS. First connection4, control circuit12, and signal processing circuit21are arranged in a region outside internal space IS. As illustrated inFIG.2, internal space IS is surrounded by sealing frame3around the Z axis.

Gas is unable to move between internal space IS and the region outside internal space IS. Accordingly, internal space IS is thermally insulated. In the present embodiment, internal space IS is sealed in a vacuum state. In the present embodiment, internal space IS is not necessarily sealed in a complete vacuum state.

As illustrated inFIG.1, sealing frame3is sandwiched between first semiconductor substrate1and second semiconductor substrate2along the direction (Z axis direction) in which first semiconductor substrate1and second semiconductor substrate2are put on each other. A first end in the Z axis direction of sealing frame3is in contact with first main surface1a.A second end in the Z axis direction of sealing frame3is in contact with second main surface2a.Sealing frame3supports first semiconductor substrate1and second semiconductor substrate2along the Z axis direction. Sealing frame3therefore mechanically connects first semiconductor substrate1and second semiconductor substrate2. Sealing frame3does not electrically connect first semiconductor substrate1and second semiconductor substrate2.

The material of sealing frame3has electrical conductivity. The material of sealing frame3is, for example, metal. The shape of sealing frame3is annular. Sealing frame3has, for example, a hollow prism shape. The shape and dimensions of sealing frame3may be determined as appropriate as long as infrared detection element11is surrounded. Sealing frame3may further surround, for example, control circuit12.

First connection4electrically connects first semiconductor substrate1and second semiconductor substrate2. Specifically, first connection4electrically connects infrared detection element11and signal processing circuit21. The material of first connection4has electrical conductivity. First connection4is formed as, for example, a bump.

First connection4is sandwiched between first semiconductor substrate1and second semiconductor substrate2along the direction (Z axis direction) in which first semiconductor substrate1and second semiconductor substrate2are put on each other. A first end in the Z axis direction of first connection4is in contact with first main surface1a.A second end in the Z axis direction of first connection4is in contact with second main surface2a.First connection4therefore supports first semiconductor substrate1and second semiconductor substrate2along the Z axis direction. First connection4mechanically connects first semiconductor substrate1and second semiconductor substrate2.

Each of sealing frame3and first connection4is sandwiched between first main surface1aand second main surface2a.Each of sealing frame3and first connection4has the same dimension along the direction (Z axis direction) in which first semiconductor substrate1and second semiconductor substrate2are put on each other.

In the present embodiment, the material of first connection4is the same as the material of sealing frame3. The melting point of first connection4is therefore the same as the melting point of sealing frame3.

Infrared sensor100further includes a second connection5. Second connection5is sandwiched between first main surface1aand second main surface2a.A first end in the Z axis direction of second connection5is in contact with first main surface1a.A second end in the Z axis direction of second connection5is in contact with second. main surface2a.Second connection5therefore supports first semiconductor substrate1and second semiconductor substrate2along the Z axis direction. Second connection5mechanically connects first semiconductor substrate1and second semiconductor substrate2. Second connection5does not electrically connect first semiconductor substrate1and second semiconductor substrate2. Second connection5is formed as a dummy bump.

In the present embodiment, second connection5has a higher melting point than first connection4and sealing frame3. For example, when the material of first connection4and sealing frame3is indium (In) or indium alloy, the material of second connection5is nickel (Ni) or copper (Cu).

Infrared sensor100further includes an antireflective film6. In the present embodiment, antireflective film6is arranged on the side opposite to first semiconductor substrate1with respect to second main surface2a.Antireflective film6covers second back surface2b.Antireflective film6overlaps infrared detection element1.1along the Z axis direction. Infrared radiation IR is therefore incident on infrared detection element11through antireflective film6.

Antireflective film6is formed to prevent reflection of infrared radiation IR. In the present embodiment, antireflective film6does not need to completely prevent reflection of infrared radiation IR. Antireflective film6may be formed to suppress reflection of infrared radiation IR incident on antireflective film6.

Antireflective film6is, for example, an antireflection coat (AR coat) such as diamond like carbon (DLC) or zinc sulfide (ZnS).

As illustrated inFIG.2, first connection4includes a plurality of first connection portions41. Each of first connection portions41electrically connects first semiconductor substrate1and second semiconductor substrate2. Each of first connection portions41has, for example, a cylindrical shape. Each of first connection portions41may have the same diameter.

Second connection5includes a plurality of second connection portions51. Each of second connection portions51does not electrically connect first semiconductor substrate1and second semiconductor substrate2. Each of second connection portions51has, for example, a cylindrical shape. Each of second connection portions51may have the same diameter.

Second infrared transmitting portion IT2overlaps infrared detection element11along the direction (Z axis direction) in which first semiconductor substrate1and second semiconductor substrate2are put on each other. Control circuit12and signal processing circuit21do not overlap infrared detection element11along the direction (Z axis direction) in which first semiconductor substrate1and second semiconductor substrate2are put on each other. S1gnal processing circuit21is sandwiched between first connection4and second connection5along the Y axis direction.

As illustrated inFIG.2andFIG.3, the dimensions in the in-plane direction (the X axis direction and the Y axis direction) of first semiconductor substrate1may be larger than the dimensions in the in-plane direction (the X axis direction and the Y axis direction) of second semiconductor substrate2. In the present embodiment, control circuit12is arranged to overlap second semiconductor substrate2in the Z axis direction. Control circuit12may be arranged so as not to overlap second semiconductor substrate2in the Z axis direction. inFIG.3, for convenience of explanation, infrared sensor100is illustrated in a simplified form as appropriate.

Referring now toFIG.4toFIG.6, a configuration of infrared sensor100according to a modification to the first embodiment will be described.FIG.4is a cross-sectional view along line1V-IV inFIG.5.

As illustrated inFIG.4, control circuit12according to the modification to the first embodiment faces second main surface2a.Specifically, control circuit12faces signal processing circuit21. Control circuit12overlaps signal processing circuit21along the Z axis direction.

As illustrated inFIG.5, control circuit12includes a first control circuit portion12aand a second control circuit portion12b. First control circuit portion12aand second control circuit portion12bare electrically connected by not-illustrated wiring. First control circuit portion12aand signal processing circuit21are sandwiched between first connection4and second connection5along the Y axis direction. As illustrated inFIG.5andFIG.4, first control circuit portion12afaces signal processing circuit21.

As illustrated inFIG.5andFIG.6, the dimension along each of the X axis direction and the Y axis direction of first semiconductor substrate1may be the same as the dimension along each of the X axis direction and the Y axis direction of second semiconductor substrate2. InFIG.6, for convenience of explanation, infrared sensor100is illustrated in a simplified form as appropriate.

Referring now toFIG.1andFIG.7, a method of manufacturing infrared sensor100according to the first embodiment will be described.

The method of manufacturing infrared sensor100includes step S101of preparing and step S102of electrically connecting.

As illustrated inFIG.1, first semiconductor substrate1, second semiconductor substrate2, sealing frame3, and first connection4are prepared. In the present embodiment, second connection5is further prepared,

Specifically, first semiconductor substrate1and second semiconductor substrate2are prepared specifically in accordance with the following process. First, a wafer process is used for a silicon (S1) substrate serving as first semiconductor substrate1to form pixel array PXA (seeFIG.1) and control circuit12.

Subsequently, a metallized pattern is formed in each of a region in which sealing frame3is arranged in the silicon substrate serving as first semiconductor substrate1and a region in which sealing frame3is arranged in the silicon substrate serving as second semiconductor substrate2. The region in which sealing frame3is arranged is located outside the pixel array.

Specifically, for example, titanium (Ti) or chromium (Cr) and copper (Cu) are successively deposited by sputtering on the entire first main surface1aof first semiconductor substrate1. Subsequently, a resist pattern is formed by photolithography (lithography technology). Then, nickel (Ni) and gold (Au) are successively formed by electroplating on first main surface1a.Subsequently, the resist pattern is removed. The underlying film is removed. The metallized pattern is thus formed on first semiconductor substrate1.

In second semiconductor substrate2, the metallized pattern is formed in the same manner as in first semiconductor substrate1. Second semiconductor substrate2may be produced separately from first semiconductor substrate1. Second semiconductor substrate2thus may be produced by a conventional common silicon wafer process.

Then, silicon etching or the like is performed by micromachining technology on each of the silicon substrate serving as first semiconductor substrate1and the silicon substrate serving as second semiconductor substrate2, First semiconductor substrate1and second semiconductor substrate2are thus produced.

Then, each of sealing frame3and first connection4is sandwiched between first main surface1a,infrared detection element11, and second main surface2a,whereby internal space IS is surrounded by first main surface1a,infrared detection element11, second main surface2a,and sealing frame3, and internal space IS is hermetically sealed. Second connection5is sandwiched together with sealing frame3and first connection4between first main surface1aand second main surface2a.

Specifically, the first end of sealing frame3is bonded to first main surface1a.The first end of first connection4is bonded to first main surface1a.The second end of sealing frame3is bonded to second main surface2a.The second end of first connection4is bonded to second main surface2a.Thus, internal space IS is sealed. First semiconductor substrate1and second semiconductor substrate2are connected to each other with sealing frame3, first connection4, and second connection5interposed. First semiconductor substrate1and second semiconductor substrate2are arranged at a distance from each other by the dimension along the Z axis direction of sealing frame3, first connection4, and second connection5,

In the present embodiment, internal space IS is hermetically sealed by first main surface1a,infrared detection element11, second main surface2a,and sealing frame3in a vacuum atmosphere, Specifically, first main surface1aand second main surface2aare bonded to sealing frame3in a vacuum atmosphere with the temperature of first semiconductor substrate1and second semiconductor substrate2kept at a temperature equal to or higher than the melting point of the material of sealing frame3.

Each of sealing frame3and first connection4is sandwiched between first main surface1a,infrared detection element11, and second main surface2a,whereby infrared detection element11and signal processing circuit21are electrically connected by first connection4, Specifically, the first end of first connection4is electrically connected to infrared detection element11or not-illustrated wiring connected to infrared detection element11. The second end of first connection4is electrically connected to signal processing circuit21or not-illustrated wiring connected to signal processing circuit21.

As illustrated inFIG.7, in manufacturing, a first wafer10serving as first semiconductor substrate1(seeFIG.1) and a second wafer20serving as second semiconductor substrate2(seeFIG.1) may be used. The process may be performed in a wafer state to produce first semiconductor substrate1. (seeFIG.1.) and second semiconductor substrate2(seeFIG.1). InFIG.7, one scaling frame3, one first connection4, and one second connection5are illustrated, but a plurality of sealing frames3, first connections4, and second connections5are prepared.

As described above, the sealing of internal space IS and the electrical connection between infrared detection element11and signal processing circuit21are performed simultaneously.

Referring toFIG.1, the operation principle and sensitivity of infrared sensor100according to the first embodiment will now be described.

Infrared sensor100is configured to convert infrared radiation IR absorbed by infrared sensor100into heat. Specifically, infrared detection element11is configured to convert infrared radiation IR absorbed by infrared detection element11into heat. Infrared sensor100is configured to convert temperature change caused by the converted heat into an electrical signal. Infrared sensor100is therefore configured to detect infrared radiation IR based on the temperature change of infrared detection element11.

Thus, the temperature change of infrared detection element11due to temperature change of internal space IS is suppressed, thereby improving the sensitivity of infrared sensor100.

Specifically, as illustrated inFIG.1, since infrared detection element11faces internal space IS, the temperature of infrared detection element11changes when the temperature of internal space IS changes, The temperature of internal space IS changes, for example, with the convection of gas filled in internal space IS and heat transfer.

When internal space IS is sealed in a vacuum state, the gas convection and heat transfer is suppressed. Thus, the temperature change of infrared detection element11due to the temperature change of internal space IS is suppressed. Infrared sensor100according to the present embodiment therefore has high sensitivity.

Referring now toFIG.8toFIG.10, a circuit configuration of infrared sensor100according to the first embodiment will be described.

As illustrated inFIG.8andFIG.9, first semiconductor substrate1includes a plurality of column signal lines1C, a plurality of row signal lines1L, and a plurality of pixels PX. Each of column signal lines1C extends along the Y axis direction (seeFIG.1). One end of each of column signal lines1C is connected to a corresponding one of a plurality of output terminals4a.Each of output terminals4a is connected to second semiconductor substrate2by a corresponding one of first connection portions41.

Each of row signal lines1L extends along the X axis direction (seeFIG.1).

A plurality of pixels PX are arranged in a two-dimensional array along the Y axis direction (seeFIG.1) and the X axis direction (seeFIG.2). Pixel array PXA is thus formed. Each of pixels PX includes two infrared detection elements11connected to each other. One of two infrared detection elements11is connected to one column signal line1C among a plurality of column signal lines1C. The other of two infrared detection elements11is connected to one row signal line1L among a plurality of row signal lines1L.

Control circuit12includes a plurality of first switching elements S1, a plurality of first current sources P1, a first column select circuit106, a row select circuit107, and a voltage regulation circuit108. Each of first switching elements S1is connected to a corresponding one of column signal lines1C.

Each of first current sources P1is connected to a corresponding one of column signal lines1C. Each of first current sources P1is connected to column signal line1C through first switching element S1. Each of first current sources P1is connected to a plurality of pixels PX through column signal line1C.

First column select circuit106is configured to selectively connect each of first current sources P1to infrared detection element11through the corresponding column signal line1C. First column select circuit106is configured to selectively connect each of first current sources P1to the corresponding infrared detection element1through first switching element S1.

Row select circuit107is configured to selectively apply a voltage to a plurality of infrared detection elements11through a plurality of row signal lines1L, Voltage regulation circuit108is configured to apply a variable voltage to two infrared detection elements11of each of pixels PX through a plurality of row signal lines1L. Row select circuit107and voltage regulation circuit108are configured as a first voltage source.

FIG.10is a circuit diagram illustrating the configuration of voltage regulation circuit108in detail. InFIG.8andFIG.9, voltage regulation circuit108is on the right side of row select circuit107in the drawing sheet, whereas inFIG.10, voltage regulation circuit108is on the left side of row select circuit107in the drawing sheet.

As illustrated inFIG.10, voltage regulation circuit108includes a plurality of second switching elements S2, a plurality of first amplifiers A1, and a plurality of second amplifiers A2. Each of second switching elements S2, each of first amplifiers A1, and each of second amplifiers A2are connected to a corresponding one of row signal lines1L. A plurality of second switching elements S2, first amplifiers A1, and a plurality of second amplifiers A2are configured as a buffer circuit. An output voltage of the buffer circuit changes with a voltage value input from the power supply of the pixels.

As described above, first semiconductor substrate1has at least a means for enabling voltage to be applied to pixel array PXA and current to flow through pixel array PXA. That is, as illustrated inFIG.8, first semiconductor substrate1has first current sources P1, first column select circuit106, row select circuit107, and voltage regulation circuit108as the means for applying voltage and feeding current to pixel array PXA. A plurality of pixels PX arranged in a two-dimensional array can be selected one by one by first column select circuit106and row select circuit107. A variable voltage can be applied to two infrared detection elements11of each of pixels PX by row select circuit107and voltage regulation circuit108.

As illustrated inFIG.8, second semiconductor substrate2includes a plurality of input terminals4b,a plurality of third switching elements S3, a plurality of fourth switching elements S4, a plurality of second current sources P2, a plurality of operation amplifiers OA, a second column select circuit206, and a third amplifier A3.

Each of input terminals4bof signal processing circuit21is connected to a corresponding one of output terminals4a of first semiconductor substrate1by first connection portion41. Each of third switching elements S3, each of fourth switching elements S4, each of second current sources P2, and each of operation amplifiers OA are connected to a corresponding one of input terminals4b.Each of input terminals4bis connected to the inverting input terminal of operation amplifier OA. Each of input terminals4bis connected to the non-inverting input terminal of operation amplifier OA by third switching element S3and second current source P2. A plurality of second current sources P2are connected to two infrared detection elements11of each of pixels PX by a plurality of input terminals4b,a plurality of first connection portions41, a plurality of output terminals4a, and a plurality of column signal lines1C.

A bias voltage is applied to the non-inverting input terminal of operation amplifier OA through a first external terminal213. Third switching elements S3connect or disconnect a plurality of input terminals4band a plurality of second power supplies in accordance with a control voltage input through a second external terminal212. Third switching elements S3are connected (turned on) when infrared sensor100operates and captures an image. Third external terminal214is connected to the outside.

A plurality of operation amplifiers OA are configured to operate as integral circuits, Second column select circuit206is configured to selectively send output signals from a plurality of operation amplifiers OA to third amplifier A3by a plurality of fourth switching elements S4. Third amplifier A3is configured to amplify a signal. Third amplifier A3is configured to output the amplified signal finally from infrared sensor100.

When infrared sensor100operates and captures an image, a plurality of pixels PX arranged in a two-dimensional array can be selected one by one by second column select circuit206of second semiconductor substrate2and row select circuit107of first semiconductor substrate1. When infrared sensor100operates and captures an image, second current source P2of second semiconductor substrate2is connected to infrared detection element11. When infrared sensor100operates and captures an image, first current source P1of first semiconductor substrate1is not connected to infrared detection element11. A variable voltage is applied to infrared detection element11by row select circuit107and voltage regulation circuit108.

The terminal-to-terminal voltage of second current source P2connected to infrared detection element11and the terminal-to-terminal voltage of second current source P2connected to input terminal4bare input to operation amplifier OA. As a result, third amplifier A3finally outputs a signal in which a voltage drop distribution due to wiring resistance in the horizontal direction is subtracted.

Second semiconductor substrate2is configured such that the output signals of a plurality of infrared detection elements11that are input from first semiconductor substrate1through a plurality of first connection portions41are differentially amplified and output by the integral circuits of operation amplifiers OA. S1nce output signals of a plurality of infrared detection elements11are amplified and the output signals are converted into digital data by a not-illustrated analog/digital converter, a satisfactory output signal can be finally output without being influenced by a circuit at a subsequent stage.

Second semiconductor substrate2may perform signal processing by a not-illustrated digital signal processing circuit after converting the output signals of a plurality of infrared detection elements11into digital data by the not-illustrated analog/digital converter. The digital data has high noise immunity and therefore is suitable for operation processing, The not-illustrated digital signal processing circuit is mounted on second semiconductor substrate2.

Feedback may be performed with an output signal of the not-illustrated digital signal processing circuit so that even more optimum control can be performed on second semiconductor substrate2of infrared sensor100. An output signal of the not-illustrated digital signal processing circuit may be converted into an analog voltage signal by a not-illustrated digital/analog converter and thereafter sent to first semiconductor substrate1through first connection portion41. The not-illustrated digital/analog converter may be mounted on first semiconductor substrate1. The not-illustrated digital/analog converter mounted on first semiconductor substrate1can transfer a signal kept in the form of a digital signal.

Although the configuration in which each of output terminals4a connected to a corresponding one of column signal lines1C of first semiconductor substrate1is connected to input terminal4bof second semiconductor substrate2by first connection portion41has been described, the circuit configuration of each of first semiconductor substrate1and second semiconductor substrate2is not limited thereto and can be selected as appropriate depending on the applications. For example, each of output terminals4a connected to a corresponding one of row signal lines1L of first semiconductor substrate1may be connected to input terminal4bof second semiconductor substrate2by first connection portion41.

The operation effect of the present embodiment will now be described.

In infrared sensor100according to the present embodiment, as illustrated inFIG.1, each of sealing frame3and first connection4is sandwiched between first main surface1aand second main surface2a.Each of sealing frame3and first connection4therefore can be sandwiched by first main surface1aand second main surface2a.Accordingly, sealing frame3and first connection4can be sandwiched together by first main surface1aand second main surface2a.Therefore, the sealing of internal space IS and the electrical connection between first semiconductor substrate1and second semiconductor substrate2can be performed simultaneously. Accordingly, increase of the manufacturing cost of infrared sensor100can be suppressed.

As illustrated inFIG.1, infrared sensor100further includes antireflective film6. Antireflective film6is formed to prevent reflection of infrared radiation IR. Therefore, occurrence of a stray light component due to reflected light of the incident infrared radiation IR can be suppressed compared with when antireflective film6is not provided. The stray light component is a component resulting from unnecessary infrared scattering. Accordingly, reduction of sensitivity of infrared sensor100due to the stray light component can be suppressed.

As illustrated inFIG.1, second semiconductor substrate2includes second substrate portion22and second infrared transmitting portion1T2, Second infrared transmitting portion1T2is configured to transmit infrared radiation IR more than second substrate portion22. The strength of infrared radiation IR incident on infrared detection element11therefore can be enhanced compared with when infrared radiation IR is incident on infrared detection element11through second substrate portion22. Accordingly, the sensitivity of infrared sensor100can be enhanced.

As illustrated inFIG.1, infrared sensor100further includes second connection5. The load applied to sealing frame3and first connection4therefore can be distributed compared with when only sealing frame3and first connection4are sandwiched between first main surface1aand second main surface2a.Accordingly, first semiconductor substrate1and second semiconductor substrate2can he arranged such that first semiconductor substrate1and second semiconductor substrate2face in parallel to each other even when a load is applied to sealing frame3and first connection4.

As illustrated inFIG.1, infrared sensor100further includes second connection5. First main surface1aand second main surface2atherefore can be connected firmly compared with when only sealing frame3and first connection4are sandwiched between first main surface1aand second main surface2a.

Second connection5has a higher melting point than first connection4. Therefore, the mechanical strength of bonding between first semiconductor substrate1and second semiconductor substrate2can be enhanced.

More specifically, first semiconductor substrate1and second semiconductor substrate2are bonded by sealing frame3, first connection4, and second connection5in accordance with the following steps. First, sealing frame3, first connection4, and second connection5are arranged between first semiconductor substrate1and second semiconductor substrate2. Sealing frame3and first connection4are melted by heating at a temperature higher than the melting point of sealing frame3and first connection4and lower than the melting point of second connection5. In a state in which first semiconductor substrate1and second semiconductor substrate2are at a distance from each other by the dimension of second connection5, first semiconductor substrate1and second semiconductor substrate2are mechanically and electrically connected by sealing frame3and first connection4. On the other hand, when first connection4is melted, second connection5is not melted. Therefore, reduction of the strength of second connection5due to the melting of second connection5can be suppressed. Reduction of the parallelism (the evenness of the distance) between first semiconductor substrate1and second semiconductor substrate2due to the melting of second connection5can be suppressed. The mechanical strength of first semiconductor substrate1and second semiconductor substrate2therefore can be enhanced. Displacement of second connection5due to the melting of second connection5can be suppressed. First semiconductor substrate1and second semiconductor substrate2therefore can be bonded to each other at high accuracy.

The material of sealing frame3has electrical conductivity. Sealing frame3therefore can be melted at a temperature at which the material of first connection4having electrical conductivity can be melted. Accordingly, sealing frame3and first connection4can be melted at the same temperature. The manufacturing steps therefore can be simplified compared with when sealing frame3and first connection4are melted at different temperatures.

The material of first connection4is the same as the material of sealing frame3. The melting point of first connection4is therefore the same as the melting point of sealing frame3. Thus, sealing frame3and first connection4can be melted at the same temperature. Accordingly, the manufacturing steps can be simplified compared with when sealing frame3and first connection4are melted at different temperatures.

As illustrated inFIG.1, internal space IS is sealed in a vacuum state. Therefore, occurrence of heat transfer and convection of gas in internal space IS can be suppressed compared with when the pressure of internal space IS is the atmospheric pressure. Accordingly, reduction of thermal resistance of internal space IS can be suppressed. Thus, escape of heat from infrared detection element11to internal space IS by heat transfer can be suppressed. The sensitivity of infrared sensor100therefore can be enhanced.

As illustrated inFIG.1, second connection5does not electrically connect first semiconductor substrate1and second semiconductor substrate2. Second connection5therefore is not in contact with the electrode material of each of first semiconductor substrate1and second semiconductor substrate2. Accordingly, diffusion of second connection5to the electrode materials of first semiconductor substrate1and second semiconductor substrate2can be suppressed.

In infrared sensor100according to the modification to the present embodiment, as illustrated inFIG.4, control circuit12faces signal processing circuit21. Therefore, the dimensions along the in-plane direction (the X axis direction and the Y axis direction) of first semiconductor substrate1can be reduced compared with when control circuit12does not face signal processing circuit21. Accordingly, the dimensions along the X axis direction and the Y axis direction of infrared sensor100can be reduced.

In the method of manufacturing infrared sensor100according to the present embodiment, as illustrated inFIG.1, each of sealing frame3and first connection4is sandwiched between first main surface1a,infrared detection element11, and second main surface2a,whereby internal space IS is surrounded by first main surface1a,infrared detection element11, second main surface2a,and sealing frame3, and internal space IS is hermetically sealed. Each of sealing frame3and first connection4is sandwiched between first main surface1a,infrared detection element11, and second main surface2a,whereby infrared detection element11and signal processing circuit21are electrically connected by first connection4. Therefore, the sealing of internal space IS and the electrical connection between first semiconductor substrate1and second semiconductor substrate2can be performed at the same time. Thus, the manufacturing steps of infrared sensor100can be simplified. Accordingly, increase of the manufacturing cost of infrared sensor100can be suppressed.

As illustrated inFIG.1, internal space IS is hermetically sealed by first main surface1a,infrared detection element11, second main surface2a,and sealing frame3in a vacuum atmosphere. Internal space IS therefore can be sealed in a vacuum state. Accordingly, the sensitivity of infrared sensor100can be enhanced.

As illustrated inFIG.1, second connection5is further prepared. Second connection5is sandwiched together with sealing frame3and first connection4between first main surface1aand second main surface2a.The load applied to sealing frame3and first connection4therefore can be distributed compared with when only sealing frame3and first connection4are sandwiched between first main surface1aand second main surface2a.Accordingly, first semiconductor substrate1and second semiconductor substrate2can be arranged such that first semiconductor substrate1and second semiconductor substrate2face in parallel to each other.

Second Embodiment

Referring now toFIG.11, a configuration of infrared sensor100according to a second embodiment will be described. The second embodiment has the same configuration, manufacturing method, and operation effects as the modification to the first embodiment described above, unless otherwise specified. The same configuration as the modification to the first embodiment described above is denoted by the same reference sign and will not be further elaborated.

As illustrated inFIG.11, second main surface2aaccording to the present embodiment includes a second main surface portion P and a depressed portion G. Second main surface portion P and depressed portion G face internal space IS. Second main surface portion P is a flat surface. Depressed portion G is provided at a position facing infrared detection element11to be depressed from second main surface portion P. Specifically, depressed portion G is provided at a position facing infrared detection element11to be depressed from second main surface portion P along the direction (Z axis direction) in which first semiconductor substrate1and second semiconductor substrate2are put on each other. Depressed portion G overlaps infrared detection element11along the Z axis direction. In the present embodiment, depressed portion G is provided in second infrared transmitting portion IT2.

The operation effect of the present embodiment will now be described.

In infrared sensor100according to the present embodiment, as illustrated inFIG.11, depressed portion G is provided at a position facing infrared detection element11to be depressed from second main surface portion P. The volume of internal space IS is therefore large compared with when second main surface2ais entirely flat. Temperature change of internal space IS can be suppressed with a larger volume of internal space IS. Therefore, the sensitivity of infrared sensor100can be enhanced.

Fluctuations of the degree of vacuum due to temperature change of gas escaping from first semiconductor substrate1, second semiconductor substrate2, and the like are smaller with a larger volume of internal space IS. Accordingly, even when the escaping gas intrudes into internal space IS, fluctuations of the degree of vacuum due to the escaping gas can be suppressed. The escaping gas is gas released from the members.

As illustrated inFIG.11, depressed portion G is provided at a position facing infrared detection element11to be depressed from second main surface portion P. Therefore, the thickness of second semiconductor substrate2at depressed portion U is smaller than the thickness of second semiconductor substrate2in a region in which depressed portion G is not provided. That is, second semiconductor substrate2is thinned at depressed portion G. Accordingly, second semiconductor substrate2has a high transmittivity at depressed portion G. Thus, the strength of infrared radiation IR incident on infrared detection element11can be enhanced. Therefore, the sensitivity of infrared sensor100can be enhanced.

Third Embodiment

Referring now toFIG.12, a configuration of infrared sensor100according to a third embodiment will be described. The third embodiment has the same configuration, manufacturing method, and operation effects as the modification to the first embodiment described above, unless otherwise specified. The same configuration as the modification to the first embodiment described above is denoted by the same reference sign and will not be further elaborated.

In the present embodiment, infrared radiation IR is incident on infrared detection element11through first back surface1balong the Z axis positive direction. Infrared detection element11is configured to detect infrared radiation IR incident on infrared detection element11through first back surface1balong the Z axis direction.

As illustrated inFIG.12, first semiconductor substrate1according to the present embodiment includes a first substrate portion13and a first infrared transmitting portion IT1. First substrate portion13and the infrared transmitting portion are configured to transmit infrared radiation IR. First infrared transmitting portion ITI is configured to transmit infrared radiation IR more than first substrate portion13. First infrared transmitting portion IT1faces infrared detection element11. First infrared transmitting portion IT1is arranged to overlap infrared detection element11in the Z axis direction.

First infrared transmitting portion IT1contains, for example, an impurity such as phosphorous (P) or boron (B). Thus, first infrared transmitting portion IT1has a resistivity of, for example, 1 Ω·cm or more.

The absorption of infrared radiation IR by first infrared transmitting portion IT1has a correlation with the resistivity of first infrared transmitting portion IT1. Therefore, the larger the resistivity of first infrared transmitting portion IT1is, the less infrared radiation IR is absorbed in first infrared transmitting portion IT1. Accordingly, when the resistivity of first infrared transmitting portion ITI is, for example, 1 Ω·cm or more, absorption of the infrared radiation IR wavelength by first semiconductor substrate1is suppressed. The configuration of first infrared transmitting portion IT1may be the same as the configuration of second infrared transmitting portion IT2except for the position where first infrared transmitting portion IT1is arranged.

The operation effect of the present embodiment will now be described.

In infrared sensor100according to the present embodiment, as illustrated anFIG.12, first semiconductor substrate1includes first substrate portion13and first infrared transmitting portion IT1. First infrared transmitting portion IT1is configured to transmit infrared radiation IR more than first substrate portion13. The strength of infrared radiation IR incident on infrared detection element11therefore can be enhanced compared with when infrared radiation IR is incident on infrared detection element11through first substrate portion13. Accordingly, the sensitivity of infrared sensor100can be enhanced.

As illustrated inFIG.12, first infrared transmitting portion IT1is arranged to overlap infrared detection element11in the Z axis direction. Infrared radiation IR is therefore incident on infrared detection element11through first infrared transmitting portion IT1even when infrared radiation IR is incident on first semiconductor substrate1from the first back surface1b side of first semiconductor substrate1. Therefore, infrared detection element11can be detected even when infrared radiation IR is incident on first semiconductor substrate1from the first back surface1bside.

Fourth Embodiment

Referring now toFIG.13, a configuration of infrared sensor100according to a fourth embodiment will be described. The fourth embodiment has the same configuration, manufacturing method, and operation effects as the third embodiment described above, unless otherwise specified. The same configuration as the third embodiment described above is denoted by the same reference sign and will not be further elaborated.

As illustrated inFIG.13, second main surface2aaccording to the present embodiment includes a second main surface portion P and a depressed portion G. Second main surface portion P and depressed portion G face internal space IS. Second main surface portion P is a flat surface. Depressed portion G is provided at a position facing infrared detection element11to be depressed from second main surface portion P. Specifically, depressed portion G is provided at a position facing infrared detection element11to be depressed from second main surface portion P along the direction (Z axis direction) in which first semiconductor substrate1and second semiconductor substrate2are put on each other. Depressed portion G overlaps infrared detection element11along the Z axis direction. Depressed portion G may at least partially overlap infrared detection element11along the Z axis direction.

The operation effect of the present embodiment will now be described.

In infrared sensor100according to the present embodiment, as illustrated inFIG.13, depressed portion G is provided at a position facing infrared detection element11to be depressed from second main surface portion P. Therefore, the sensitivity of infrared sensor100can be enhanced.

Thus, the sensitivity of infrared sensor100can be enhanced even when infrared radiation IR is incident on infrared detection element11through first back surface1b.

Fifth Embodiment

Referring now toFIG.14, a configuration of infrared sensor100according to a fifth embodiment will be described. The fifth embodiment has the same configuration, manufacturing method, and operation effects as the third embodiment described above, unless otherwise specified. The same configuration as the third embodiment described above is denoted by the same reference sign and will not be further elaborated.

As illustrated inFIG.14, infrared sensor100according to the present embodiment further includes antireflective film6. Antireflective film6is arranged on the side opposite to second semiconductor substrate2with respect to first main surface1a.Antireflective film6covers first back surface1b.Antireflective film6is formed to prevent reflection of infrared radiation1R. Antireflective film6may have the same configuration as the configuration of antireflective film6described in the first embodiment except for the position where antireflective film6is arranged.

The operation effect of the present embodiment will now be described.

In infrared sensor100according to the present embodiment, infrared sensor100further includes antireflective film6. Antireflective film6is arranged on the side opposite to second main surface2awith respect to first main surface1a.Antireflective film6therefore covers first back surface1b.Accordingly, occurrence of a stray light component due to reflection of infrared radiation IR can be suppressed even when infrared radiation IR is incident on infrared detection element11from the first back surface1bside of first semiconductor substrate1. Thus, the incidence of infrared radiation IR scattered in first semiconductor substrate1on infrared detection element11can be suppressed. The sensitivity of infrared sensor100can be enhanced even when infrared radiation IR is incident on infrared detection element11from the first back surface1bside of first semiconductor substrate1.

Sixth Embodiment

Referring toFIG.15andFIG.16, a configuration of infrared sensor100according to a sixth embodiment will be described.FIG.15is a cross-sectional view along line XV-XV inFIG.16. The sixth embodiment has the same configuration, manufacturing method, and operation effects as the modification to the first embodiment described above, unless otherwise specified. The same configuration as the modification to the first embodiment described above is denoted by the same reference sign and will not be further elaborated.

As illustrated inFIG.15, second connection5according to the present embodiment has an outer diameter different from that of first connection4. In the present embodiment, second connection5has a larger outer diameter than first connection4. As illustrated inFIG.16, each of second connection portions51of second connection5has an outer diameter different from that of each of first connection portions4of first connection4. Second connection portion51has a larger diameter than first connection portion41.

For example, when the number of first connection portions41is as small as10to100, the outer diameter of second connection5may be larger than the outer diameter of first connection4. Thus, the distribution of load applied to first connection4and second connection5is adjusted when first connection4is bonded to first semiconductor substrate1and second semiconductor substrate2. In the present embodiment, the outer diameter of second connection5is larger than the outer diameter of first connection4. However, the outer diameter of second connection5may be smaller than the outer diameter of first connection4.

The number of second connection portions51of second connection5may be different from the number of first connection portions41of first connection4. In the present embodiment, the number of second connection portions51is smaller than the number of first connection portions41.

For example, when the number of first connection portions41is as small as10to100, the number of second connection portions51may be larger than the number of first connection portions41. Thus, the load applied to first connection4is distributed to second connection5. In the present embodiment, the number of second connection portions51is smaller than the number of first connection portions41. However, the number of second connection portions51may be larger than the number of first connection portions41.

The operation effect of the present embodiment will now be described.

In infrared sensor100according to the present embodiment, as illustrated inFIG.15, second connection5has an outer diameter different from that of first connection4. The outer diameter of second connection5therefore can be adjusted in accordance with the volume of internal space IS, the outer diameter of first connection4, and the number of first connection portions41(seeFIG.16). Thus, the distribution of load applied to sealing frame3, first connection4, and second connection5can be adjusted when first semiconductor substrate1and second semiconductor substrate2are bonded, First semiconductor substrate1and second semiconductor substrate2therefore can be bonded at high accuracy.

As illustrated inFIG.16, the number of second connection portions51is different from the number of first connection portions41. The number of second connection portions51therefore can be adjusted in accordance with the volume of internal space IS, the outer diameter of first connection4, the number of first connection portions41, and the like. The distribution of load applied to sealing frame3, first connection4, and second connection5can be adjusted when first semiconductor substrate1(seeFIG.15) and second semiconductor substrate2are bonded. Therefore, first semiconductor substrate1(seeFIG.15) and second semiconductor substrate2can be bonded at high accuracy.

Embodiments disclosed here should be understood as being illustrative rather than being limitative in all respects. The scope of the present disclosure is shown not in the foregoing description but in the claims, and it is intended that all modifications that come within the meaning and range of equivalence to the claims are embraced here.

REFERENCE SIGNS LIST