JPH11108760A - Thermal type infrared detecting delement and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal type infrared element having a diaphragm which has a large thermoelectric converting part of 300 μm or more. SOLUTION: This element has a diaphragm structure (thermoelectric converting part 1) consisting of a thermoelectric material, support films nipping the thermoelectric material and a protecting film, in which a plurality of through holes 2 are formed. When a sacrifice layer situated in the lower part is etched through the through-holes 2, the etchant can be penetrated not only from the clearance in the sides of the thermoelectric converting part 1 but also from above it. Thus, even in a relatively large thermoelectric converting part 1, the sacrifice layer of its lower layer can be etched, and a large diaphragm structure can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal infrared detecting element which does not require cooling and a method for manufacturing the same.

[0002]

2. Description of the Related Art Infrared detectors can be broadly classified into a quantum type utilizing a band structure of a semiconductor or the like and a thermal type utilizing a change in material properties (resistance, dielectric constant, etc.) due to heat. The former is highly sensitive, but requires cooling due to its operating principle. On the other hand, the latter type is called an uncooled type because it does not particularly require cooling, and has many advantages over the quantum type in terms of manufacturing cost and maintenance cost, and has been attracting attention in recent years.

[0003] The thermal infrared detecting element includes a bolometer type,
There are a pyroelectric type and a thermocouple type, both of which generally have a heat separation structure, that is, a so-called diaphragm structure, in order to increase the sensitivity of the detection element. Among them, a bolometer type infrared detecting element having relatively excellent characteristics will be described as an example.

As shown in FIG. 6, the diaphragm structure of this device has a cavity 10, a bolometer thin film 7 as a thermoelectric material, a support film 6, a protective film 8, and a thermoelectric conversion portion 1 and supports them. It consists of a beam 3. The diaphragm structure is such that a sacrificial layer is deposited on a substrate, a support film 6, a bolometer thin film 7, a protective film 8, and an infrared absorption film 9 are further deposited, and each layer is patterned into a desired shape by dry etching or the like. 1 is formed by exposing the sacrificial layer around the thermoelectric conversion part 1 and finally removing the sacrificial layer from the periphery of the thermoelectric conversion part 1 by etching. The portion of the cavity 10 from which the sacrificial layer has been removed is completely void,
It has a structure in which the thermoelectric converter 1 is suspended by beams 3. Opposite sides of the bolometer thin film 7 are in contact with the electrodes 4, and these electrodes are connected to a signal processing circuit via the beam 3, and a change in resistance of the bolometer caused by absorbing infrared rays is converted into an electric signal. I'm taking it out.

[0005]

SUMMARY OF THE INVENTION Thermal infrared detectors have been developed mainly for the purpose of infrared imaging in the vicinity of the 10 .mu.m band. Met. Therefore, in the diaphragm structure, the width of the cavity 10 is 1 to 1.5 μm, and the thermoelectric conversion unit is 30 to 50 μm.
It was appropriate to be about μm □. The characteristics of these infrared detectors include the material and thickness of each layer, the size of the thermoelectric conversion section, the heat capacity due to the length and thickness of the beam, and the properties of thermal conductance and thermoelectric material (resistance temperature coefficient for bolometer)
Considering a wide range of applications, the size of the thermoelectric conversion section is not only about 30 to 50 μm square but also 300 μm
A device having a size of □ or more will be sufficiently required in the future.
However, in the current structure, the region where the sacrificial layer can be etched from around the thermoelectric conversion unit 1, that is, the size of the thermoelectric conversion unit is determined by considering the region where the etchant is sufficiently immersed.
The limit is about 50 μm square, and it has been difficult to manufacture a diaphragm structure having a thermoelectric conversion part larger than that by a conventional method due to structural problems. Therefore, its application range is extremely limited, and it has been applied only to applications where the thermoelectric conversion section is small.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal infrared detecting element having a structure capable of manufacturing even a large thermoelectric converter of 300 μm square or more, and a method of manufacturing the same.

[0007]

According to the thermal infrared detecting element of the present invention, a plurality of through holes are formed in a diaphragm structure comprising a thermoelectric material and a support film and a protective film sandwiching the thermoelectric material. It is a feature. A bolometer thin film is most preferably used as the thermoelectric material.

The shape of the through hole is slit, square, circular or the like. The slit is formed by setting the length direction of the slit through hole 2 to the same direction as the current flowing in the bolometer thin film. The change in the resistance value due to the deformation can be suppressed, and the distortion in the diaphragm can be evenly distributed by forming the shape into a square or a circle.

In such a thermal infrared detecting element, a support film, a thermoelectric material, and a protective film are formed on a sacrificial layer, and then a slit pattern around a diaphragm for forming a beam is formed at the same time as the diaphragm. It can be easily manufactured by forming a pattern for forming a through hole in the inside, and removing the sacrificial layer by etching through a slit pattern around the diaphragm and a pattern for forming a through hole in the diaphragm.

In other words, according to the present invention, by providing a through hole in a portion having a diaphragm structure, when etching the sacrificial layer, not only the slit around the thermoelectric conversion portion but also the etchant from the upper portion thereof is impregnated. I can do it. Therefore, even a relatively large thermoelectric conversion part can etch the sacrificial layer below it, and a large diaphragm structure can be formed. As a result, the degree of freedom in device design including heat capacity and the like is increased, and it is also possible to improve characteristics and expand the device application range. Furthermore, if the method for manufacturing a thermal infrared detecting element of the present invention is used, simultaneously with forming a slit pattern around a diaphragm for forming a beam, a pattern of forming a through hole in the diaphragm is formed, and a pattern around the diaphragm is formed. In order to remove the sacrificial layer by etching through a slit pattern and a pattern for forming a through hole in the diaphragm, an element can be manufactured by a process substantially similar to the conventional one. At this time, by setting the pitch of the through holes to 50 to 100 μm, an effect is obtained that the sacrificial layer below the thermoelectric converter can be uniformly removed in a relatively short time.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure, manufacturing method and operation of a thermal infrared detecting element according to the present invention will be specifically described with reference to FIGS. This embodiment shows a case where a bolometer thin film is used as a thermoelectric material. FIG. 1 is a top view of a thermal infrared detecting element of the present invention. This is a shape in which the thermoelectric converter 1 is suspended by four beams 3. FIG.
A cross-sectional view of A ′ shows a state in which the thermoelectric conversion unit floats in the air and is thermally separated. In the present embodiment, the size of the thermoelectric converter 1 was 300 μm □, and the size of the through hole 2 was 4 μm in width and 50 μm in length. The horizontal pitch of the slits was 50 μm, and they were arranged as shown in FIG. The beam 3 has a width of 30 μm and a length of 50 μm. The electrode 4 is in contact at the upper side and the lower side of the bolometer material constituting the thermoelectric conversion section and is in electrical contact, so that a change in resistance due to heat can be taken out. The current flows vertically, and the slit-shaped through-hole 2 faces in the same direction.

Next, the manufacturing method of this embodiment will be described with reference to FIGS. FIG. 2 is a sectional view of the device before the sacrifice layer 5 is etched, and FIG. 3 is a sectional view of the device after the sacrifice layer 5 is etched. 1. A sacrificial layer 5 is formed on a silicon substrate or the like.
3 μm is formed. Next, the support film 6 is deposited at 3000 ° and the bolometer thin film 7 is deposited at 1000 °.
Pattern processing to 00 μm square. Further, the electrode 4 is patterned by lift-off or the like so as to be in contact with the bolometer thin film 7, and a protective film 8 is deposited on the entire surface. Next, an infrared absorption film 9 is formed in alignment with the 300 μm square bolometer thin film 7. Here, polysilicon as the sacrificial layer 5, a support film 6,
A silicon nitride film was used as the protective film 8, vanadium oxide was used as the bolometer thin film 7, and titanium nitride was used as the infrared absorbing film 9. Next, the outside of the thermoelectric converter 1 is removed by dry etching (ion milling) up to the sacrifice layer 5 except for the beam 3. At the same time, a through hole 2 is also formed (FIG. 2). Finally, it is immersed in an etchant for etching the sacrificial layer. Here, hydrazine was used as an etchant. The etchant penetrates not only from the side of the thermoelectric conversion unit 1 but also from the upper part through the through-hole 2, and the sacrifice layer 5 can be completely removed by etching. Thus, the device is completed. Here, the size of the slit-shaped through hole 2 is 4 μm in width and 50 μm in length. However, this is an example, and any size may be used as long as it does not significantly affect the characteristics and the process is relatively easy to perform. ~ 15μm, length 10 ~ 50μ
The range of m is appropriate.

Next, the operation will be briefly described. When infrared rays enter from the upper surface of the diaphragm structure, the temperature of the thermoelectric conversion section 1 rises due to the effects of the infrared absorbing film 9 and the cavity 10. This temperature rise is stored at a heat capacity determined by the material and thickness of each layer constituting the thermoelectric conversion unit 1, the size of the thermoelectric conversion unit 1, and the like, and the shape such as the length and thickness of the beam and the like are formed. Is released by the thermal conductance determined by the material used. The temperature change obtained by these balances can be converted into an electric signal by the thermoelectric converter 1 and extracted from the electrode 4. In the case of the bolometer, the above-mentioned electric signal is obtained as a change in resistance. However, since the direction of the slit-shaped through hole 2 is made the same as the direction of current flow as in this embodiment, the resistance is significantly reduced due to the slit formation. There is almost no effect. As described above, the main characteristics such as the response speed and the sensitivity of the infrared detecting element are almost determined by the heat capacity and the heat conductance, and the degree of freedom is expanded by using the present invention. An element having a very large thermoelectric conversion part of 300 μm square can be manufactured sufficiently and the characteristics as designed can be obtained. Also, 1 / f which is a problem in noise characteristics, particularly in the case of an uncooled infrared device
Regarding the noise, the larger the element size, the smaller the noise tends to be. Therefore, the infrared detection element having a large thermoelectric conversion unit as in the present invention can achieve a sufficiently low noise.

FIGS. 4 and 5 show a case where the shape of the through hole 2 is square and a case where the shape is circular. The size of the diaphragm was 300 μm square as described above, one side of the square was 10 μm, and the diameter of the circle was 10 μm.
4 and 5, the pitch of the through holes 2 is 100 μm. These have a smaller area where the etchant penetrates than the slit-shaped through-holes described above, but have a feature that the influence of strain in the diaphragm due to the formation of the through-hole is small and the strength is superior.

In the embodiment of the present invention, the support film 6 and the protective film 8
Is a silicon nitride film, the bolometer thin film 7 is vanadium oxide, the sacrificial layer 5 is polysilicon, and the etchant is hydrazine. However, the present invention is not limited to this.

In this embodiment, the bolometer type infrared detecting element has been described. However, from the viewpoint of forming a large diaphragm structure, it is needless to say that the present invention can be applied to a pyroelectric type or a thermocouple type.

[0017]

As described above, when the present invention is used, the degree of freedom in designing a thermal infrared detecting element is expanded, and a thermoelectric conversion unit having a large diaphragm structure of 300 μm square or more can be obtained in the same manner as in the prior art. This makes it possible to produce the infrared sensor of the thermal type sufficiently, so that the application of the thermal infrared detector can be broadened. In addition, the basic characteristics can be improved by increasing the degree of freedom of design, and a sufficiently low noise can be expected by using a large diaphragm.

[Brief description of the drawings]

FIG. 1 is a view of a thermal infrared detecting element of the present invention as viewed from above, showing an embodiment in which the shape of a through-hole is a slit shape.

FIG. 2 is a sectional view of an element before a sacrificial layer is etched.

FIG. 3 is a cross-sectional view of the device after a sacrifice layer is etched.

FIG. 4 is an embodiment in the case where the shape of the through hole is a square.

FIG. 5 is an embodiment in the case where the shape of the through hole is circular.

FIG. 6 is a diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermoelectric conversion part 2 Through-hole 3 Beam 4 Electrode 5 Sacrificial layer 6 Support film 7 Bolometer thin film 8 Protective film 9 Infrared absorption film 10 Cavity

Claims (8)

[Claims] 1. A thermal infrared detecting element having a diaphragm structure comprising at least a support film, a thermoelectric material provided on the support film, and a protection film provided on the thermoelectric material. A thermal infrared detecting element, wherein a plurality of through holes are formed. 2. The thermal infrared detecting element according to claim 1, wherein said thermoelectric material is a bolometer thin film. 3. The thermal type infrared detecting element according to claim 2, wherein said through-hole has a slit shape. 4. The thermal infrared detecting element according to claim 3, wherein the length direction of the slit-shaped through hole is the same as the direction of the current flowing in the bolometer thin film. 5. The thermal infrared detecting element according to claim 1, wherein said through hole is square or circular. 6. The thermal infrared detecting element according to claim 1, wherein the pitch of the through holes is 50 to 100 μm. 7. The thermal infrared detecting element according to claim 1, further comprising an infrared absorbing film on said protective film. 8. After forming at least a support film, a thermoelectric material, and a protective film on the sacrificial layer sequentially, a slit pattern around the diaphragm for forming a beam is formed, and at the same time, a through hole in the diaphragm is formed. And a second step of etching and removing the sacrificial layer through a slit pattern around the diaphragm and a pattern for forming a through hole in the diaphragm. Manufacturing method of infrared detecting element.