JP5016527B2 - Thermal infrared image sensor - Google Patents

Description

  The present invention relates to a thermal infrared imaging device.

A thermal infrared imaging element is an element that converts infrared rays absorbed by an infrared absorbing structure into heat and converts a temperature change caused by the heat into an electrical signal by some method. In a conventional thermal infrared imaging device, a structure has been proposed in which only the thin film wiring of the signal readout wiring is used as the wiring on the temperature detection unit to reduce the heat capacity of the temperature detection unit (for example, Patent Document 1).
Furthermore, as a structure for improving the infrared absorption efficiency without increasing the heat capacity of the temperature detection unit, a method of providing a reflective film thermally grounded on the substrate between the temperature detection unit and the infrared absorption structure is proposed. (For example, Patent Document 2).

In a thermal infrared imaging device, it is required to increase the number of pixels by reducing the pixel size and to improve the performance of the temperature detection unit. When the normal pixel size is reduced, the performance deteriorates because the infrared absorption area per pixel is reduced. Measures to prevent this include an optical method by improving the ratio (aperture ratio) of the infrared absorption structure within one pixel, an improvement in infrared absorption efficiency, a method for increasing the thermoelectric conversion efficiency of the temperature detection unit, and a void structure. There is a thermal method by improving the structure of a support leg that thermally separates a temperature detection unit and a support substrate.
For the thermal method, it is effective to reduce the thermal conductance of the support legs. As the pixel size is reduced, the area in which the support legs can be arranged decreases, and in order to maintain the conventional thermal conductance, it is essential to make the support legs thinner and finer.
JP 2002-340685 A JP 2005-233671 A

  However, if the wiring of the supporting leg portion is thinned to reduce the thickness of the supporting leg, there is a problem that it is difficult to directly connect to the low resistance wiring used as the readout wiring in the upper layer.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal infrared imaging device that can be thinned and miniaturized in support legs, can be reduced in size while maintaining infrared absorption efficiency, and can be stably manufactured.

In order to achieve the above object, a thermal infrared imaging device according to the present invention includes a substrate and a temperature detection unit held away from the substrate by a support leg, and the temperature detection unit is provided on the support leg. A thermal infrared imaging device connected to the second wiring on the substrate by the first wiring, wherein the second wiring is provided in a lower layer wiring formed on the substrate and in an upper layer away from the lower layer wiring from the substrate And an upper-layer wiring connected to the lower-layer wiring, and the first wiring and the lower-layer wiring partially overlap with each other through an insulating layer, and the lower-layer wiring and the The first wiring is connected via a via hole provided in the insulator layer .
Another thermal infrared imaging device according to the present invention includes a substrate and a temperature detection unit held away from the substrate by a support leg, and the temperature detection unit is mounted on the substrate by a first wiring provided on the support leg. A thermal infrared imaging device connected to the second wiring, wherein the second wiring is provided on a lower layer wiring formed on the substrate and on an upper layer farther from the substrate than the lower layer wiring and connected to the lower layer wiring And further comprising an intermediate wiring provided on the lower layer closer to the substrate than the upper layer wiring and the lower layer closer to the substrate than the lower layer wiring and the first wiring, The lower layer wiring and the intermediate wiring are connected.

In the thermal infrared imaging device according to the present invention configured as described above, the second wiring formed on the substrate is formed so as to include a lower layer wiring and an upper layer wiring provided above the lower layer wiring. Since the first wiring is connected to the lower layer wiring, the level difference caused by the wiring on the substrate when the supporting leg is processed is reduced, and the supporting leg can be formed with fineness and high dimensional accuracy.
Thereby, a thermal infrared imaging device having a small size, high sensitivity, and high sensitivity uniformity can be obtained.

Embodiment 1. FIG.
Hereinafter, the thermal infrared imaging device according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a thermal infrared imaging device according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AB in FIG. In the plan view of FIG. 1, the reflection film pattern on the support leg 2 and the infrared absorption structure 12 are not shown.

  As shown in FIG. 2, in the thermal infrared imaging device of the first embodiment, the portion surrounded by the trench 4 below the temperature detection unit 1 is removed from the substrate 3 to form a recess, which is irradiated. The infrared ray absorbing structure 12 that absorbs the infrared rays and the temperature detection unit 1 that transfers heat generated by the infrared ray absorbing structure 12 and converts the heat into an electric signal are supported by the support legs 2 and are separated from the substrate 3 and are hollow. Is held in. As a result, the temperature detector 1 is thermally separated from the substrate 3.

  On the other hand, the electrical signal supplied from the horizontal drive wiring 5 changes according to the temperature change of the temperature detection unit 1, and the changed signal is sent from the vertical signal readout wiring 6 to a signal readout circuit (not shown). Is read out.

Hereinafter, the configuration of each part will be described in detail.
In the following description, regarding the lower layer wiring 8 and the upper layer wiring 11 which will be described mainly with reference to the cross-sectional view of FIG. 2, a layer close to the substrate 3 is referred to as a lower layer, and That's it. In this specification, the same layer means that a plurality of layers are formed away from the substrate 3 by the same distance. Further, the horizontal drive wiring 5 and the vertical signal readout wiring 6 shown mainly in the plan view of FIG. 1 are names as viewed from the circuit configuration side in which the lower layer wiring 8 and the upper layer wiring 11 are connected. That is, a part of the horizontal drive wiring 5 is composed of the lower layer wiring 8, the remaining part is composed of the upper layer wiring 11, a part of the vertical signal readout wiring 6 is composed of the lower layer wiring 8, and the rest is composed of the upper layer wiring 11. Is done.

  The temperature detection unit 1 includes a plurality of PN junction diodes 7 formed in a single crystal silicon layer (SOI layer). The thin film wiring 9 connects between the PN junction diodes 7, between the PN junction diodes and the support legs 2, and is connected to the lower layer wiring 8 which is a part of the horizontal drive wiring 5 and the vertical signal readout wiring 6.

  The lower layer wiring 8 is shared with the gate wiring of the transistor in the peripheral circuit section. The support leg 2 is formed by covering the thin film wiring 9 with an insulator, and the thin film wiring 9 embedded in the insulator between the temperature detection unit 1 and the horizontal drive wiring 5 and between the temperature detection unit 1 and the vertical signal readout wiring 6. While being electrically connected, the temperature detection unit 1 to which the infrared absorbing structure 12 is attached is held in a state separated from the substrate. Further, the support leg 2 is preferably formed to be narrow and thin so that the thermal conductance is small in order to thermally separate the substrate 3 and the temperature detector 1. For example, the thin film wiring 9 is made of a titanium compound. The thickness is about 50 nm, and the width of the support leg 2 is set to about 0.5 μm.

The reflective film 10 is formed so as to mainly cover the upper portion of the support leg 2.
The upper layer wiring 11 is disposed at substantially the same height as the reflective film 10 (also referred to as the same layer), and fulfills a wiring function connected to the lower layer wiring 8 connected to the horizontal drive wiring 5 and the vertical signal readout wiring 6. At the same time, it functions as a reflective film. As the reflective film 10, it is preferable to use a metal having a low resistance and a high infrared reflectivity, such as aluminum, titanium, and chrome. By using such a metal, the upper wiring 11 and the reflective film 10 are made of the same material. It can be formed in a process.

  Although not specifically shown in the drawing, the infrared absorption structure 12 is composed of a metal film that absorbs infrared rays and an insulating layer that sandwiches the metal film. The infrared detection structure 12 is in thermal contact with the temperature detection unit 1, and the horizontal drive wiring 5. And the entire detection structure including a part of the vertical signal readout wiring 6 is formed. Here, the insulator layer is made of a dielectric such as silicon oxide, for example.

  In the thermal infrared imaging device according to the first embodiment configured as described above, as shown in the following description of the manufacturing process, the wiring before the support leg 2 is formed is the lower layer wiring 8 and the thin film wiring connected thereto. 9, and the thin film wiring 9 can be formed to a thickness of, for example, about 50 nm. Therefore, a layer for forming the support leg 2 is formed on the surface of the low step. As a result, it is possible to form a support leg that is fine and has high dimensional accuracy. Accordingly, a thermal infrared imaging device having a low thermal conductance, high sensitivity, and high sensitivity uniformity can be obtained.

  Further, since the horizontal drive wiring 5 and the vertical signal readout wiring 6 are connected by the upper wiring 11 in the same layer as the reflective film 10, the level difference under the upper wiring 11 is reduced and a flat reflective film structure is formed. Thus, a thermal infrared imaging device with improved manufacturing yield and stable performance can be obtained.

Hereinafter, the manufacturing method of the thermal infrared imaging device according to Embodiment 1 of the present invention will be described with reference to FIGS.
In this manufacturing method, first, as shown in FIG. 3, a trench 4 is formed in the substrate 3 by embedding a film having resistance to Si etching.
Next, the detection film 13 is formed on the substrate 3, the lower layer wiring 8 is formed above the detection film 13 via an insulator, and an insulator is further formed. In this way, the detection film 13 and the lower layer wiring 8 embedded in the insulator 21a are formed.

  In order to reduce the contact resistance between the thin film wiring 9 and the PN junction diode 7, the lower layer wiring 8 needs to be heat-treated at 800 ° C. or more. Therefore, it is preferable to use a low resistance metal wiring material that can withstand this. Preferred materials include titanium, tungsten, polysilicon and the like. The lower layer wiring 8 is formed as a part of the horizontal drive wiring 5 and the vertical signal readout wiring 6, and the adjacent pixels are not connected at this time.

  Next, using a known photolithography process and etching process, a through-hole leading to the lower layer wiring 8 and the detection film 13 is formed at a predetermined position of the insulator 21a, and the thin film wiring 9 is formed as shown in FIG. Then, the lower layer wiring 8 and the detection film 13 are connected. As shown in FIG. 4, in the region surrounded by the trench 4 including the temperature detection film 13 and the thin film wiring 9, the insulating film 21a is made thinner than the other wiring parts. This part is a part that will later become the temperature detection unit 1 and the support leg 2, and is thinned to reduce the heat capacity of the detection unit 1 and the thermal conductance of the support leg 2.

  The thin film wiring 9 is made of, for example, a titanium alloy having a thickness of about 50 nm. Thus, since the thin film wiring 9 is formed by a very thin film, if the thin film wiring 9 itself is a lower layer wiring, the thin film wiring 9 is removed by processing when forming a contact hole with the upper layer wiring, which is good. Contact performance cannot be obtained. Therefore, in the first embodiment, in order to solve this problem, the lower layer wiring 8 connected to the upper layer wiring 11 is provided separately from the thin film wiring, and the lower layer wiring 8 and the thin film wiring 9 below the thin film wiring 9 are connected. By doing so, the horizontal drive wiring 5, the vertical signal readout wiring 6 and the temperature detection unit 1 are connected.

After forming the thin film wiring 9, an insulator layer of about 100 nm is deposited.
In a normal semiconductor process, a planarization process is performed after the wiring process by a known technique such as CMP (Chemical Mechanical Polishing) or an etch back method using dry etching. However, in the thermal infrared imaging device of the present invention, it is preferable that the insulator layer on the thin film wiring 9 in FIG. 2 is thin, and higher film thickness uniformity is required. Therefore, it is preferable to deposit only a thin insulator layer on the thin film wiring 8.

  Next, as shown in FIG. 5, a portion that becomes the support leg 2 is separated from the temperature detection unit 1 by, for example, etching to form the support leg 2. After the support legs 2 are formed, a sacrificial layer 14 is formed as shown in FIG. The sacrificial layer 14 is formed of a heat resistant organic film. Next, as shown in FIG. 6, an insulating film is deposited, and the sacrificial layer 14 is opened by photolithography, and only a part of the insulating layer on the lower wiring 8 is removed and opened to reflect. The film 10 and the upper layer wiring 11 are formed simultaneously. The upper layer wiring 11 is connected to the lower layer wiring 8 through the opening. Here, since an organic film is deposited as the sacrificial layer 14 using means such as spin coating, it is not necessary to perform a special planarization process when forming the reflective film structure. Here, in the first embodiment, the reflective film structure includes the reflective film 10 and the upper layer wiring 11.

Next, an insulating layer is deposited on the reflective film 10 and the upper wiring 11, and an opening reaching the sacrificial layer 14 is formed in the insulating layer. Next, a sacrificial layer 15 is formed on the insulator layer. Thereby, the sacrificial layer 15 connected to the sacrificial layer 14 through the opening hole formed in the insulator layer is formed.
Next, an infrared ray absorbing through the sacrificial layer 15 and the sacrificial layer 14 at the center of the temperature detection unit 1 and reaching the temperature detection unit 1 is formed, and the infrared ray is connected to the temperature detection unit 1 through the through hole. Structure 12 is formed. The infrared absorption structure 12 has a structure in which a metal layer is sandwiched between insulator layers, and is formed of, for example, a chromium film having a thickness of 5 nm and silicon oxide having a thickness of 100 nm, for example.

Next, a region surrounded by the trench 4 in FIG. 1 in the substrate 3 is removed by isotropic etching with xenon difluoride to form a concave shape, and finally the sacrificial layers 14 and 15 are removed. . In this manner, the infrared absorption structure 12 and the temperature detection unit 1 connected to the infrared absorption structure 12 are held on the substrate while being separated from the substrate. Here, as shown in FIG. 2, the infrared absorption structure 12 is formed so as to cover the entire pixel above the temperature detection unit 1, the support leg 2, and the reflective film 10, and is thermally connected only to the temperature detection unit 1. The
As described above, the thermal infrared detector of FIG. 2 is completed.

Embodiment 2. FIG.
A thermal infrared imaging device according to the second embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a plan view of the thermal infrared imaging device of the second embodiment, and FIG. 9 is a cross-sectional view taken along line CD in FIG. In the plan view of FIG. 8, the temperature detector 1, the reflective film 1 pattern on the support leg 2, and the infrared absorbing structure 12 are not shown. Although the basic structure of the thermal infrared imaging device of the second embodiment is the same as that of the first embodiment, the thermal wiring of the first embodiment is different in that the intermediate wiring 16 is provided between the lower layer wiring 8 and the upper layer wiring 11. This is different from the type infrared imaging device.

  The lower layer wiring 8 is formed only at a connection portion where the thin film wiring 9 is connected to the horizontal drive wiring 5 and the vertical signal readout wiring 6, the vertical signal readout wiring 6 is constituted by only the intermediate wiring 16, and the horizontal driving wiring 5 is the thin film wiring 9. The upper layer wiring 11 is constituted only by the upper part of the wiring. The reason why the upper layer wiring 11 is not formed above the thin film wiring 9 is to reduce the step around the pixel before forming the layer constituting the support leg 2.

  That is, in the first embodiment, the wiring before the support leg processing is two layers of the lower layer wiring 8 and the thin film wiring 9, but in this embodiment, the intermediate wiring 16 is added to the upper layer of the lower layer wiring 8 and the thin film wiring 9. In this configuration, since the intermediate wiring 16 is above the thin film wiring 9, aluminum having a relatively low melting point can be used as the semiconductor material. Aluminum has a very low resistance, and is a metal that is often used in semiconductor processes and has an established processing technique. Further, it goes without saying that the vertical signal readout wiring 6 may be the intermediate wiring 16 and the horizontal driving wiring 5 may be the upper layer wiring 11 in this embodiment.

  In the second embodiment configured as described above, the thin film wiring 9 is connected to the upper layer vertical signal readout wiring 6 or the horizontal driving wiring 5 through the lower layer wiring 8, so that the pixel before the support leg 2 is formed. The inner step can be reduced as compared with the conventional example, and the same effect as in the first embodiment can be obtained. Further, by adding the intermediate wiring 16, the wiring length of the lower wiring 8 having a relatively high resistance can be made shorter than that of the first embodiment, so that a low resistance wiring can be realized. Thereby, the reliability of wiring can be improved, and a thermal infrared imaging device with less output voltage distribution can be realized.

Embodiment 3. FIG.
Hereinafter, the thermal infrared imaging device according to the third embodiment of the present invention will be described with reference to FIGS. 10 and 11. FIG. 10 is a plan view of the thermal infrared imaging device, and FIG. 11 is a cross-sectional view taken along the line EF of FIG. In the plan view of FIG. 10, the temperature detection unit 1, the reflection film pattern on the support leg 2, and the infrared absorption structure 12 are not shown. The thermal infrared imaging element of the third embodiment has the same basic structure as that of the first embodiment, but in the third embodiment, a contact hole for connecting the lower layer wiring 8 and the upper layer wiring 11 and a lower layer The second embodiment is different from the first embodiment in that the contact holes for connecting the wiring 8 and the thin film wiring 9 are formed to overlap each other at substantially the same position.

  In the above configuration, since the thin film wiring 9 is a thin film compared to the lower layer wiring and the upper layer wiring, when the contact hole of the upper layer wiring 11 is formed, the thin film wiring 9 in the contact hole portion is removed. There is no problem because the lower layer wiring 8 and the upper layer wiring 11 are connected. In addition, the two contact holes are not the same size, for example, by changing the aspect ratio, etc., and by securing the contact area of only the lower layer wiring 8 and the thin film wiring 9 and only the lower layer wiring 8 and the upper layer wiring 11, Thus, a good connection between the thin film wiring 9 and the upper layer wiring 11 can be secured.

  In the third embodiment configured as described above, the connection between the lower layer wiring 8, the thin film wiring 9, and the upper layer wiring 11 is set at a substantially common position, so that the thin film wiring 9, the vertical signal readout wiring 6, and the horizontal driving wiring in the pixel. The area required for connection with 5 can be reduced. Thereby, the pixel area can be reduced. In addition, the lower layer wiring 8 often has higher resistance than the upper layer wiring 11, and in this embodiment, the area (wiring length) required for the lower layer wiring 8 can be reduced. Therefore, the vertical signal readout wiring 6 and the horizontal driving wiring 5 are reduced. It becomes possible to reduce the resistance.

Embodiment 4 FIG.
The fourth embodiment is a thermal infrared imaging device in which a plurality of thermal infrared imaging devices of Example 1 are arranged in an array. FIG. 12 is a plan view of the thermal infrared imaging device, and FIG. 13 is a cross-sectional view taken along the line GH. In the thermal infrared imaging device configured as described above, the signals driven by the horizontal drive wiring 5 are converted into electrical signals in response to temperature changes in the respective temperature detection units 1 and sequentially sent to the vertical signal readout wiring 6. Read through. In the fourth embodiment, an array of X = 2 and Y = 2 pixels is used, but any combination of X and Y is possible.

  The thermal infrared imaging device according to the fourth embodiment can reduce the manufacturing variation of the support legs in each element portion, and can form the reflection film flat, so that the performance variation between the pixels can be reduced and manufactured with a high yield. be able to.

It is a top view which shows the thermal type infrared imaging element of Embodiment 1 which concerns on this invention. It is sectional drawing which shows the thermal type infrared imaging element of Embodiment 1 which concerns on this invention. It is sectional drawing which shows the 1st step of the manufacturing method of the thermal type infrared imaging element of Embodiment 1 which concerns on this invention. It is sectional drawing which shows the 2nd step of the manufacturing method of the thermal type infrared imaging element of Embodiment 1 which concerns on this invention. It is sectional drawing which shows the 3rd step of the manufacturing method of the thermal type infrared imaging element of Embodiment 1 which concerns on this invention. It is sectional drawing which shows the 4th step of the manufacturing method of the thermal type infrared imaging element of Embodiment 1 which concerns on this invention. It is sectional drawing which shows the 5th step of the manufacturing method of the thermal type infrared imaging element of Embodiment 1 which concerns on this invention. It is a top view which shows the thermal type infrared imaging element of Embodiment 2 which concerns on this invention. It is sectional drawing which shows the thermal type infrared imaging element of Embodiment 2 which concerns on this invention. It is a top view which shows the thermal type infrared imaging element of Embodiment 3 which concerns on this invention. It is sectional drawing which shows the thermal type infrared imaging element of Embodiment 3 which concerns on this invention. It is a top view which shows the thermal type infrared imaging element of Embodiment 4 which concerns on this invention. It is sectional drawing which shows the thermal type infrared imaging element of Embodiment 4 which concerns on this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Temperature detection part, 2 Support leg, 3 Substrate, 4 Trench, 5 Horizontal drive wiring, 6 Vertical signal readout wiring, 7 PN junction diode, 8 Lower layer wiring, 9 Thin film wiring, 10 Reflective film, 11 Upper layer wiring, 12 Infrared absorption Structure, 13 Temperature sensing film, 14 Sacrificial layer (first layer), 15 Sacrificial layer (second layer), 16 Intermediate wiring, 21a, 21b Insulator layer.

Claims (7)

A thermal infrared imaging device comprising a substrate and a temperature detection unit held away from the substrate by a support leg, wherein the temperature detection unit is connected to a second wiring on the substrate by a first wiring provided on the support leg The second wiring has a lower layer wiring formed on the substrate and an upper layer wiring provided in an upper layer far from the substrate than the lower layer wiring and connected to the lower layer wiring,
The first wiring and the lower layer wiring partially overlap with each other through an insulating layer, and the lower layer wiring and the first wiring overlap with each other through a via hole provided in the insulating layer. Connected thermal infrared imaging device.   The lower layer wiring and the upper layer wiring partially overlap with each other through an insulating layer, and the lower layer wiring and the upper layer wiring overlap with each other through a second via hole provided in the insulating layer. The thermal infrared imaging device according to claim 1, wherein the thermal infrared imaging device is connected. The via hole and the second via hole thermal infrared imaging device according to claim 2, wherein is provided at least partially overlap each other. A thermal infrared imaging device comprising a substrate and a temperature detection unit held away from the substrate by a support leg, wherein the temperature detection unit is connected to a second wiring on the substrate by a first wiring provided on the support leg The second wiring has a lower layer wiring formed on the substrate and an upper layer wiring provided in an upper layer far from the substrate than the lower layer wiring and connected to the lower layer wiring,
The lower wiring and the first wiring further include an intermediate wiring provided on the lower substrate closer to the substrate than the upper wiring, and the lower wiring and the intermediate wiring are connected to each other. thermal infrared imaging device being. The first wiring and the lower layer wiring partially overlap with each other through an insulating layer, and the lower layer wiring and the first wiring overlap with each other through a via hole provided in the insulating layer. The thermal infrared imaging device according to claim 4, which is connected to each other . The lower layer wiring and the upper layer wiring partially overlap with each other through an insulating layer, and the lower layer wiring and the upper layer wiring overlap with each other through a second via hole provided in the insulating layer. The thermal infrared imaging device according to claim 5, which is connected to each other . Thermal type infrared sensing device thermal infrared detecting elements are arranged in an array according to any one of claims 1-6.

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