JP6826484B2 - Manufacturing method of infrared detector - Google Patents

Description

The present invention relates to a method for manufacturing an infrared detection device having improved sensor performance.

A conventional infrared sensor is formed on a semiconductor substrate (chip) such as silicon, and is mounted on a mounting substrate such as a wiring board. The infrared sensor receives infrared rays from the outside and detects the temperature distribution and the presence or absence of a heat source.
Patent Document 1 discloses a conventional infrared sensor (infrared detection device). Infrared detection devices composed of infrared detection elements include thermopile type, pyroelectric type and bolometer type. As the thermopile type infrared detection element, there is one shown in FIG. In the thermopile type infrared detection element shown in the figure, a diaphragm 102 is provided on the upper surface of the silicon semiconductor substrate 101, and p-type polysilicon 110 and n-type polysilicon 111 are alternately connected to the upper surface of the diaphragm 102 by aluminum wiring 112. As a result, a pair of thermocouples 113 is formed.

The thermocouples 113 are arranged in parallel with the semiconductor substrate 101 side as a cold contact and the heat absorption region 105 side as a warm contact, and are electrically connected in series to form a thermopile. The heat absorbing film 105 is provided on the diaphragm 102 on which the thermopile is arranged via the interlayer insulating layer 103. At this time, the heat absorption film 105 is arranged in the center of the element. Here, the thermoelectromotive voltage of the infrared detection element is determined by the temperature difference between the heat absorption film 105 and the semiconductor substrate 101. This temperature difference depends on the magnitude of the thermal resistance from the end of the heat absorption film 105 to the end of the cavity 106 of the semiconductor substrate 101.

The cavity 106 formed in the semiconductor substrate 101 is for thermally separating the cold contact side and the hot contact side of the thermocouple 113. The infrared detection element has a quadrangular pyramid-shaped cavity 106 that opens above the semiconductor substrate 101 under the diaphragm 102 by forming etching opening holes 107 at the four corners of the diaphragm 102 and then performing anisotropic etching of silicon. Is forming.

Patent Document 2 discloses a pyroelectric infrared sensor as a conventional infrared detection device (see FIG. 8). The infrared detector shown in this figure is
It has a structure in which a sensor chip mounted on a substrate is arranged in a package and a lens is attached to the upper part of the package. An infrared detection device having such a configuration collects infrared rays radiated from an object such as an object on a sensor chip by a lens, and generates an output signal from the sensor chip according to the incident infrared energy. There is.

In the figure, the infrared detection device includes a sealing can 200 having an opening 100, an infrared incident window 300 attached to the opening 100, and a pyroelectric body 400 which is, for example, a thin film located in the sealing can 200. A lens 500 located in front of the infrared incident window 300 and having an image point distance in the vicinity of the pyroelectric body 400, a drive unit 600 for moving the lens 500 left and right in a direction perpendicular to the optical axis direction, and the above. It is composed of an aperture 700 located in front of the lens 500.
The infrared ray 800 emitted from the object to be detected passes through the aperture 700, passes through the infrared incident window 300 through the pyroelectric body 400 located on the image point by the lens 500, and then forms an image.

JP-A-2002-162291

Japanese Unexamined Patent Publication No. 09-11365

The conventional infrared detection device described in Patent Document 2, for example, having a structure in which a chip mounted on a wiring board is arranged in a package and a lens is attached to the upper part of the package, has a plurality of conventional infrared detection devices on a chip made of a semiconductor substrate. It has an infrared detection unit composed of an infrared detection element of. This infrared detection unit is composed of a plurality of array-shaped infrared detection elements.
Further, in an infrared detection device using an infrared detection unit including a two-dimensional array-shaped infrared detection element for the purpose of spatial recognition shown in FIG. 9, a low-cost condensing lens may be used. When such a low-cost condensing lens is used, the infrared rays emitted from the object are not sufficiently focused by the condensing lens, which causes a problem that the focal area becomes large. Then, when the focal spot diameter on the chip is sufficiently larger than the infrared detection element, the adjacent element is also detected, which causes a problem that the target object to be detected cannot be accurately spatially recognized. ..

This problem will be described in detail with reference to FIG.
Of the infrared detection elements formed on the chip 100, three adjacent infrared detection elements 101, 102, and 103 are shown. For the infrared detection element, for example, a thermopile element is used. The infrared detection elements 101, 102, and 103 formed on the chip 100 are provided on the diaphragm structure. The diaphragm structure is composed of cavities 104, 105, 106 and membranes 110, 111, 112 such as a silicon nitride film formed on the surface of the chip 100 so as to cover the cavities. Although not shown, the thermopile element is formed on the thermopile element, and absorption portions 107, 108, and 109 for absorbing infrared rays are formed on the thermopile element.
An infrared detection device having such a structure is used to detect infrared rays emitted from an object. The infrared rays emitted from the object are focused on a lens (not shown) of the device, and are applied to a predetermined infrared detection element 101 of the detection unit in which the infrared detection elements of the chip 100 are arranged.

In this example, since a low-cost lens that collects infrared rays is used, the focused infrared rays are not sufficiently focused by the lens, and the focal area becomes large. As shown in the figure, the irradiation region 114 of the infrared 113 is widened, and therefore, the focused infrared 113 is not irradiated only to the absorption unit 107 of the infrared detection element 101, but is applied to the adjacent infrared detection elements 102 and 103. Is also irradiated, so it may not be possible to accurately recognize the object to be sensed.
The present invention has been made under such circumstances, and is a low-cost condensing lens in an infrared detection device using an infrared detection unit composed of two-dimensional array-shaped infrared detection elements for the purpose of spatial recognition. Provided is an infrared detection device capable of accurately spatially recognizing an object to be sensed even by using.

One aspect of the method for manufacturing an infrared detection device of the present invention is a method for manufacturing an infrared detection device having an infrared detection unit composed of a plurality of infrared detection elements formed in a two-dimensional array, in which an alkali is formed on a semiconductor substrate from the surface side thereof. A step of forming a cavity corresponding to each of the infrared detection elements by silicon anisotropic etching with a solution, a step of forming an infrared detection unit on the cavity from the surface side, and heat by infrared rays detected by the infrared detection unit. A step of forming a thermopile portion that outputs an electromotive force, and a step of thinning the semiconductor substrate until an opening is exposed from the back surface side of the semiconductor substrate through each region in which the infrared detection element is formed. It is characterized by having a step of installing the semiconductor substrate on the circuit substrate so that infrared rays from the object are incident from the back surface side. A barrier layer that does not allow infrared rays to pass through may be provided on the back surface of the semiconductor substrate except for the opening.

In the infrared detection device of the present invention, since the collected infrared rays are incident on the heat absorbing film of the infrared detecting element through the bottom of the opened cavity, the cavity itself is limited to those in which the infrared rays are incident on the heat absorbing film. Since the infrared rays diffused by others are prevented from reaching the heat absorbing film of other infrared detection elements, it is possible to accurately recognize the object to be sensed even by using a low-cost condensing lens.

FIG. 3 is a partial cross-sectional view of a chip for explaining a light receiving state of an infrared detection element constituting the infrared detection device according to the first embodiment. FIG. 3 is a plan view of the chip on which the infrared detection element shown in FIG. 1 is formed. FIG. 5 is a cross-sectional view illustrating a state in which the chip shown in FIG. 1 is irradiated with infrared rays focused by a lens. The process sectional view explaining the manufacturing method of the cavity constituting the infrared ray detection apparatus which concerns on Example 2. FIG. The process sectional view explaining the manufacturing method of the cavity constituting the infrared ray detection apparatus which concerns on Example 3. FIG. FIG. 3 is a process sectional view illustrating a method of manufacturing a cavity constituting the infrared detection device according to the fourth embodiment. Plan view (a) and cross-sectional view (b) of the conventional infrared detection element Schematic diagram of a conventional pyroelectric infrared sensor. FIG. 3 is a partial cross-sectional view of a chip for explaining a light receiving state of an infrared detection element constituting a conventional infrared detection device.

Hereinafter, embodiments of the invention will be described with reference to Examples.

The first embodiment will be described with reference to FIGS. 1 to 3.
The infrared detection device described in this embodiment is a thermopile type device provided with a lens that collects infrared rays emitted from an object.
FIG. 2 is a plan view of a chip mounted on a circuit board. A plurality of infrared detection elements including infrared detection elements 11-13 are built in the chip 1 made of silicon or the like. The plurality of infrared detection elements constitute the detection area 4. A peripheral area 5 is arranged around the detection area 4, and a signal processing circuit for processing a signal from the detection area is formed therein. This signal processing circuit may be formed on another chip, formed on a circuit board together with the chip 1, and electrically connected to each other by a bonding wire.

As shown in FIG. 3, the chip 1 is adhered to the circuit board 10. The chip 1 on the circuit board 10 is sealed by a package 7 such as a metal case. A lens 8 for collecting light is provided on the ceiling of the package 7 so that infrared rays can be received. The infrared rays 6 emitted from the object 9 are focused by the lens 8 provided on the package 7, and the focused infrared rays 2 are received from the back surface side by a predetermined infrared detection element 11 of the chip 1. Therefore, the chip 1 is connected to the circuit board 10 on the front surface side, and is electrically connected to the circuit of the circuit board 10 by, for example, a flip chip connection.
In this embodiment, since the lens 8 that collects the infrared rays 6 is low in cost, the infrared rays 2 are not sufficiently focused and the focal area becomes large (see FIGS. 1 and 3). Therefore, the area irradiated with the infrared ray 2 is widened and diffused to the adjacent infrared ray detecting elements 12 and 13.
Therefore, in this embodiment, the back surface of the chip is thinned to open the bottom of the cavity, infrared rays are received from the back surface of the chip, and infrared rays diffused into the opening are prevented from entering the inside. By using a barrier, the influence of such diffusion is prevented. Then, as a barrier, the back surface of the chip is coated with a silicon oxide film.

Hereinafter, the structure of the infrared detection element 11 formed on the chip 1 will be described with reference to FIG. 1 (since the infrared detection elements 12 and 13 have the same structure, the description thereof will be omitted). The semiconductor substrate constituting the chip 1 has a front surface and a back surface on the opposite surface thereof, and a plurality of elements including infrared detection elements 11-13 are formed on the front surface. The infrared detection element has a diaphragm structure, and the cavity constituting this structure is opened, and the collected infrared rays are irradiated to the infrared detection element through the opening.
A plurality of thermopile elements (not shown) are formed on the chip 1. Each thermopile element is formed on a dedicated diaphragm structure. For example, the diaphragm structure of the infrared detection element 11 is composed of a concave cavity 14 formed on the surface of the chip 1 in a concave shape and a membrane 20 located on the cavity 14, on which a thermopile element is formed and placed. Will be done. A heat absorbing film or an infrared absorbing film (hereinafter referred to as an absorbing film) is formed on the upper surface of the thermopile element, respectively.

The thermopile element is configured by forming and arranging a plurality of thermocouples in series. The thermopile is a thermal sensor that generates thermoelectromotive force according to the infrared energy radiated from individual objects in a non-contact manner, and its absolute energy amount (temperature) can be detected.
The thermocouple that constitutes the thermopile element is a type of thermometer, and the temperature is measured by joining both ends of thin wires of two different types of conductive materials and measuring the thermoelectromotive force generated by the temperature difference between the two joint points. It is a device to measure.

A thermopile having a structure in which a plurality of thermocouples made of different types of conductive materials are connected in series is provided on the chip 1. The hot contact portion of the thermocouple is arranged near the center of the chip, for example, and the cold contact portion is arranged at the peripheral portion thereof. The thermopile is covered with an insulating film such as SOG (Spin On Glass). On this insulating film, for example, an absorbing film 17 made of gold, silver or the like that absorbs heat is arranged via an amorphous silicon film so as not to cover the hot contact portion and the cold contact portion of the thermopile. ..
As described above, the thermopile element is provided on the diaphragm structure on the chip 1. This diaphragm structure is composed of a cavity 14 and a membrane 20 formed on the surface of the chip 1 so as to cover the cavity 14.

The cavity 14 is formed by silicon anisotropic etching or the like, and the membrane 20 is formed of, for example, a silicon nitride film by, for example, a plasma CVD method. The thickness is about 100 nm. A polysilicon film constituting a thermocouple is formed on the membrane 20. The polysilicon film is coated with an insulating film such as a BPSG (Boron-doped Phospho-Silicate Glass) film, and the surface of the insulating film is flattened. Then, an aluminum film constituting a thermocouple is formed on the flattened insulating film, and the aluminum film and the polysilicon film are joined to form a plurality of thermocouples. The aluminum film is covered with the insulating film on which the absorbing film 17 is mounted via the amorphous silicon film.
Since the cold contact portion is arranged on the chip 1 acting as a heat sink and is not covered with the absorbing film 17, the temperature does not easily change even if it comes into contact with gas, but the hot contact portion floats from the chip 1. Since it is formed on the cavity 14, the heat capacity is small, and since the absorption film 17 is formed on the cavity 14, the temperature changes sensitively and the sensitivity is good.

Next, the light receiving state of the infrared detector of FIG. 1 will be described with reference to FIG.
The infrared rays 6 from the object 9 are focused by a condenser lens 8 made of an organic material such as polyethylene or a material that transmits infrared rays such as silicon, and the condensed infrared rays 2 are inside from the opening on the bottom surface of the cavity 14. Enter and irradiate the absorption film 17 on the cavity 14.
The lens 8 that collects infrared rays 6 is low in cost, and the collected infrared rays 2 are not sufficiently focused, the focal area is expanded, and the infrared rays are diffused to the adjacent infrared detection elements 12 and 13. The region 3 irradiated to the chip 1 of the infrared ray 2 is divided into a region 31 irradiated to the absorption film 17 of the infrared ray detecting element 11 and a diffusion region 32 diffused to the other infrared ray detecting elements 12 and 13.

Since the infrared ray 2 irradiates the absorption film from the opening at the bottom of the cavity, it is preferable and efficient to match the shape of the opening. Further, even if the opening at the bottom of the cavity is used as an infrared ray incident path, since silicon itself, which is a material of the chip, is an infrared ray transmitting material, there is a possibility that infrared rays are diffused to other than the incident path. Therefore, a barrier layer that does not allow infrared rays to pass through may be provided on the back surface of the chip except for the opening. A silicon oxide film (SiO2) can be used as the barrier layer.
As described above, in this embodiment, since the focused infrared rays are incident on the absorption film of the infrared detection element through the bottom of the opened cavity, the cavity itself is limited to the one in which the infrared rays are incident on the absorption film. Since the diffused infrared rays are prevented from reaching the absorption film of other infrared detection elements, it is possible to accurately spatially recognize the object to be sensed even by using a low-cost condensing lens.

The second embodiment will be described with reference to FIG.
In the following examples including this example, an SOI (Silicon on Insulator) substrate is used as the semiconductor substrate used for the chip. As shown in FIG. 4A, the SOI substrate 40 includes a silicon substrate 41, an insulating film 42 formed of a silicon oxide film formed on the silicon substrate 41, and a silicon single crystal layer 43 formed on the insulating film 42. It is composed of. The SOI substrate is a method in which oxygen is ion-implanted into a silicon substrate and heat-treated to form an insulating film, or the surface of the silicon substrate is oxidized and another silicon substrate that has not been surface-treated is bonded onto the surface. It is formed by one of two methods of forming.

First, membranes 44 and 45 made of silicon nitride or the like are formed on the silicon single crystal layer 43 in a region where an infrared detection element is to be formed (FIG. 4A). Next, the back surface of the SOI substrate is ground to expose the insulating film 42 (FIG. 4 (b)).
Next, cavities 46 and 47 are formed under the membrane by anisotropic etching of silicon. Etching is performed until the insulating film 42 is exposed. At this time, the silicon oxide film serves as a stopper (FIG. 4 (c)). Next, the insulating film 42 is wet-etched with phosphoric acid or the like to remove the bottoms of the cavities 46 and 47 to form openings.
Further, an infrared detection unit (not shown) is formed on the membrane, and absorption films 48 and 49 are formed on the infrared detection unit (not shown) (FIG. 4 (d)).

As described above, in this embodiment, since the focused infrared rays are incident on the absorption film of the infrared detection element through the bottom of the opened cavity, the cavity itself is limited to the one in which the infrared rays are incident on the absorption film. Since the diffused infrared rays are prevented from reaching the absorption film of other infrared detection elements, it is possible to accurately spatially recognize the object to be sensed even by using a low-cost condensing lens. Further, by matching the opening at the bottom of the cavity with the shape of the absorbing film, infrared rays can be efficiently irradiated to the infrared detection element.

Next, the third embodiment will be described with reference to FIG.
This embodiment is characterized in that the silicon substrate under the SOI substrate is not removed until the cavity is formed and the absorption film is formed.
As shown in FIG. 5A, the SOI substrate 50 includes a silicon substrate 51, an insulating film 52 made of a silicon oxide film formed on the silicon substrate 51, and a silicon single crystal layer 53 formed on the insulating film 52. It is composed of. Membranes 54 and 55 such as silicon nitride are formed on the silicon single crystal layer 53. Cavities 56 and 57 are formed by etching the insulating film 52 and the silicon single crystal layer 53 under the membrane. Etching is performed until the silicon substrate 51 is exposed. Infrared detectors (not shown) are formed on the membranes 55 and 54, and absorption films 58 and 59 are formed on the infrared detectors (not shown). Next, as shown in FIG. 5B, the back surface of the SOI substrate is ground to polish and remove the silicon substrate 51 to expose the insulating film 52.

As described above, in this embodiment, since the focused infrared rays are incident on the absorption film of the infrared detection element through the bottom of the opened cavity, the cavity itself is limited to the one in which the infrared rays are incident on the absorption film. Since the diffused infrared rays are prevented from reaching the absorption film of other infrared detection elements, it is possible to accurately spatially recognize the object to be sensed even by using a low-cost condensing lens. Since the size of the cavity opening needs to match the size of the absorption film, the size of the opening at the bottom of the cavity can be determined by adjusting the thickness of the silicon single crystal layer on the SOI substrate. The insulating film is used as a mask against infrared rays.

Next, the fourth embodiment will be described with reference to FIG.
This embodiment is characterized by using a backside reflective film.
First, the membranes 64 and 65 are formed on the silicon single crystal layer 63 in the region where the infrared detection element is to be formed (FIG. 6A). Next, the back surface of the SOI substrate is ground to expose the insulating film 62 (FIG. 6 (b)). Next, cavities 66 and 67 are formed under the membrane by anisotropic etching of silicon. Further, a back surface reflective film 68 such as aluminum is formed on the insulating film 62. The back surface reflective film 68 has an opening portion corresponding to the opening on the bottom surface of the cavities 66 and 67 (FIG. 6 (c)).

Next, the insulating film 62 is wet-etched to remove the insulating film between the cavity and the opening of the back surface reflective film so that the cavity is made conductive with the outside. Further, an infrared detection unit (not shown) is formed on the membrane, and absorption films 69 and 70 are formed on the infrared detection unit (not shown) (FIG. 6 (d)).
As described above, in this embodiment, since the focused infrared rays are incident on the absorbing portion of the infrared detecting element through the bottom of the opened cavity, the cavity itself is limited to the one in which the infrared rays are incident on the absorbing film. Since the diffused infrared rays are prevented from reaching the absorption film of other infrared detection elements, it is possible to accurately spatially recognize the object to be sensed even by using a low-cost condensing lens. Since the size of the cavity opening needs to match the size of the absorption film, the size of the opening at the bottom of the cavity can be determined by adjusting the thickness of the silicon single crystal layer on the SOI substrate. The insulating film and the back surface reflective film can also be used as a mask against infrared rays.

1 ... Chip (semiconductor substrate)
2 ... Condensed infrared rays 3 ... Infrared irradiation area 4 ... Chip detection area 5 ... Chip peripheral area 6 ... Infrared rays 7 ... Package 8 ... Lens 9 ...・ ・ Object 10 ・ ・ ・ Circuit board 11, 12, 13 ・ ・ ・ Infrared detection element 14, 15, 16, 46, 47, 56, 57, 66, 67 ・ ・ ・ Cavity 17, 18, 19, 48, 49, 58, 59, 69, 70 ... Absorbent film 20, 21, 22, 44, 45, 54, 55, 64, 65 ... Membrane 31 ... Infrared irradiation area 32 ... Infrared diffusion Regions 40, 50, 60 ... SOI substrate 41, 51, 61 ... Silicon substrate 42, 52, 62 ... Insulation film 43, 53, 63 ... Silicon single crystal layer 68 ... Backside reflective film

Claims (2)

In a method for manufacturing an infrared detection device having an infrared detection unit composed of a plurality of infrared detection elements formed in a two-dimensional array, the infrared detection elements are respectively subjected to silicon anisotropic etching with an alkaline solution from the surface side of the semiconductor substrate. A step of forming a corresponding cavity, a step of forming an infrared detection unit on the cavity from the surface side, a step of forming a thermopile portion that outputs a thermostatic force due to infrared rays detected by the infrared detection unit, and the above. A step of thinning the semiconductor substrate until the opening is exposed from the back surface side of the semiconductor substrate through each region where the infrared detection element is formed, and infrared rays from the object are incident from the back surface side. A method for manufacturing an infrared detection device, which comprises a step of installing the semiconductor substrate on a circuit substrate. The method for manufacturing an infrared detection device according to claim 1, wherein a barrier layer that does not allow infrared rays to pass through is provided on the back surface of the semiconductor substrate except for the opening.

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