Patent Publication Number: US-2011073978-A1

Title: Infrared imaging device and method for manufacturing same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of International Application PCT/JP2009/063890, filed on Aug. 5, 2009. This application also claims priority to Japanese Application No. 2008-246850, filed on Sep. 25, 2008. The entire contents of each are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to an infrared imaging device and a method doe manufacturing the same. 
     BACKGROUND 
     In recent years, the research and development of so-called MEMS (Micro Electro Mechanical Systems) including suspended structural bodies formed on semiconductor substrates have been performed actively. 
     Devices in which such MEMS are applied include infrared imaging devices. Of these, uncooled infrared imaging devices do not require a cooling mechanism, are capable of being downsized and provided on a chip, and have great promise for future development in applications in a wide range of fields. 
     Such an infrared imaging device includes an infrared detection unit that includes an infrared absorption unit for converting the incident infrared rays into heat and a thermoelectric conversion unit for converting the heat into an electrical signal. Thermally separating the infrared detection unit from its surroundings and increasing the thermoelectric conversion efficiency are important for increasing the detection sensitivity of infrared rays. 
     Therefore, methods are used to suppress the diffusion of heat to the surroundings by mounting the infrared imaging device in a vacuum package and removing the substrate and the element-separating oxide films around the infrared detection unit by etching and the like to make a cavity around the infrared detection unit. 
     Further, to increase the detection sensitivity, it is important to use a structure in which the surface area ratio of the infrared detection unit to the entirety is as high as possible to efficiently absorb the incident infrared rays. 
     As an infrared imaging device having such a structure, for example, a structure has been discussed in which a temperature sensor, a thermally insulating support leg supporting the temperature sensor, and an infrared absorption layer formed to thermally contact the temperature sensor are provided; and the temperature sensor, the thermally insulating support leg, and the infrared absorption layer are formed in different planes spatially separated from each other (for example, refer to JP-A 2004-317152 (Kokai)). 
     On the other hand, technology also has been proposed to provide an eave-like portion in an infrared light receiving unit to increase the detection sensitivity (for example, refer to JP-A 2005-43381 (Kokai)). 
     In suspended structural bodies of such infrared absorption layers, eave-like portions, and the like, it is desirable to increase the surface area as much as possible to increase the sensitivity, while it is desirable to reduce the volume as much as possible to increase the response rate. Therefore, as a result, the thicknesses are designed to be thin. Therefore, the mechanical strength of the infrared absorption layer and the eave-like portion decrease; and the configurations easily deform. Accordingly, for example, the suspended structural body deforms due to internal stress during the formation of the suspended structural body and fluctuation of the process conditions; a phenomenon called sticking occurs in which the suspended structural body sticks to the substrate and interconnections disposed therearound; and as a result, the detection sensitivity of the infrared imaging device decreases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1C  are schematic views illustrating an infrared imaging device according to a first embodiment; 
         FIGS. 2A and 2B  are schematic cross-sectional views illustrating infrared imaging devices of comparative examples; 
         FIGS. 3A to 3C  are schematic views illustrating infrared imaging devices of variation examples according to the first embodiment; 
         FIG. 4  is a schematic cross-sectional view illustrating an infrared imaging device according to a first example; 
         FIGS. 5A to 5C  are schematic cross-sectional views in order of the processes, illustrating a method for manufacturing the infrared imaging device according to the first example; 
         FIGS. 6A to 6C  are schematic cross-sectional views in order of the processes, continuing from  FIG. 5C ; 
         FIGS. 7A to 7C  are schematic cross-sectional views in order of the processes, continuing from  FIG. 6C ; 
         FIGS. 8A to 8C  are schematic cross-sectional views in order of the processes, continuing from  FIG. 7C ; 
         FIGS. 9A and 9B  are schematic views illustrating an infrared imaging device according to a second example; 
         FIG. 10  is a graph illustrating a characteristic of the infrared imaging device according to the first embodiment; and 
         FIG. 11  is a flowchart illustrating a method for manufacturing an infrared imaging device according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, an infrared imaging device includes a substrate, an infrared absorption unit, a thermoelectric conversion unit, a support body, and an interconnection. The infrared absorption unit is provided on the substrate and apart from the substrate to absorb an infrared ray. The thermoelectric conversion unit is provided apart from the substrate and in contact with the infrared absorption unit between the infrared absorption unit and the substrate. The thermoelectric conversion unit is configured to convert a temperature change due to the infrared ray absorbed by the infrared absorption unit into an electrical signal and to output the electrical signal. The support body supports the thermoelectric conversion unit on the substrate and apart from the substrate and is configured to transmit the electrical signal. The interconnection is connected with the support body and configured to transmit the electrical signal in reading the electrical. The infrared absorption unit includes a protrusion provided on a rim of the infrared absorption unit to protrude toward the substrate. 
     According to another embodiment, an infrared imaging device includes a substrate, an infrared absorption unit, a thermoelectric conversion unit, a support body, and an interconnection. The infrared absorption unit is provided on the substrate and apart from the substrate to absorb an infrared ray. The thermoelectric conversion unit is provided apart from the substrate and in contact with the infrared absorption unit between the infrared absorption unit and the substrate. The thermoelectric conversion unit is configured to convert a temperature change due to the infrared ray absorbed by the infrared absorption unit into an electrical signal and to output the electrical signal. The support body supports the thermoelectric conversion unit on the substrate and apart from the substrate and is configured to transmit the electrical signal. The interconnection is connected with the support body and configured to transmit the electrical signal in reading the electrical signal. The infrared absorption unit includes a thick portion on a rim of the infrared absorption unit. A thickness of the thick portion is thicker than a thickness of a central portion of the infrared absorption unit. 
     According to yet another embodiment, a method is disclosed for manufacturing an infrared imaging device. The device includes a substrate, an infrared absorption unit, a thermoelectric conversion unit, a support body, and an interconnection. The infrared absorption unit is provided on the substrate and apart from the substrate to absorb an infrared ray. The thermoelectric conversion unit is provided apart from the substrate and in contact with the infrared absorption unit between the infrared absorption unit and the substrate to convert a temperature change due to the infrared ray absorbed by the infrared absorption unit into an electrical signal and to output the electrical signal. The support body supports the thermoelectric conversion unit on the substrate and apart from the substrate and is configured to transmit the electrical signal. The interconnection is connected with the support body and configured to transmit the electrical signal in reading the electrical signal. The method can form the thermoelectric conversion unit and the support body on the substrate. The method can deposit a sacrificial layer by chemical vapor deposition to cover the thermoelectric conversion unit and the support body. The method can form an infrared absorption film served as the infrared absorption unit on the sacrificial layer and patterning a configuration of the infrared absorption film. In addition, the method can remove the sacrificial layer. 
     Embodiments will now be described in detail with reference to the drawings. 
     The drawings are schematic or conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values thereof. Further, the dimensions and the proportions may be illustrated differently among the drawings, even for identical portions. 
     In the specification and the drawings of the application, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate. 
     First Embodiment 
       FIGS. 1A to 1C  are schematic views illustrating the configuration of an infrared imaging device according to a first embodiment. 
     Namely,  FIG. 1A  is a schematic perspective view;  FIG. 1B  is a plan view; and  FIG. 1C  is a cross-sectional view along line A-A′ of  FIGS. 1A and 1B . 
     As illustrated in  FIGS. 1A to 1C , the infrared imaging device  10  according to the first embodiment includes a substrate  110 , an infrared absorption unit  150 , a thermoelectric conversion unit  120 , a support body  130 , and an interconnection  140 . 
     The infrared absorption unit  150  is provided on the substrate  110  and apart from the substrate  110  and absorbs infrared rays. 
     The thermoelectric conversion unit  120  is provided apart from the substrate  110  between the infrared absorption unit  150  and the substrate  110  and converts a temperature change due to infrared rays absorbed by the infrared absorption unit  150  into an electrical signal. For better heat conduction from the infrared absorption unit  150  to the thermoelectric conversion unit  120 , the infrared absorption unit  150  and the thermoelectric conversion unit  120  may be provided, for example, in contact with each other. 
     The thermoelectric conversion unit  120  may include a silicon pn junction diode. Thereby, the change of the heat can be converted into an electrical signal with low noise and high sensitivity. The thermoelectric conversion unit  120  also may include resistance elements, transistors, etc. 
     The support body  130  transmits the electrical signal from the thermoelectric conversion unit  120  while supporting the thermoelectric conversion unit  120  on the substrate  110  and apart from the substrate  110 . To reduce the heat conduction as much as possible, it is desirable for the support body  130  to include a material having a low thermal conductivity and for the support body  130  to be as thin and long as possible within the extent of design feasibility. For example, in this specific example as illustrated in  FIG. 3B , the support body  130  is disposed with a thinner and longer configuration by having a spiral configuration. 
     The infrared absorption unit  150 , the thermoelectric conversion unit  120 , and the support body  130  are provided apart from the substrate  110  to reduce the heat conduction to the substrate  110 . The infrared absorption unit  150 , the thermoelectric conversion unit  120 , and the support body  130  are maintained in a cavity. Hereinbelow, the infrared absorption unit  150  in particular is referred to as a suspended structural body. 
     One end of the support body  130  is connected to the thermoelectric conversion unit  120 ; and the other end is connected to the interconnection  140  provided at the periphery of the thermoelectric conversion unit  120 . 
     The interconnection  140  reads the electrical signal from the support body  130 . 
     The infrared absorption unit  150 , the thermoelectric conversion unit  120 , and the support body  130  form one infrared detection element, i.e., a pixel. 
     The pixel is multiply provided, for example, in a matrix configuration to form an infrared imaging region. The interconnection  140  is provided in a lattice configuration between each of the pixels; the output of the thermoelectric conversion unit  120  of each of the pixels is drawn out of the infrared imaging region via the support body  130  and the interconnection  140 ; and the intensity of the infrared rays detected by each of the pixels is output. 
     The region between line A 1  and line A 2  of  FIGS. 1A to 1C  is one pixel region. 
     The infrared absorption unit  150  is provided, for example, to cover the thermoelectric conversion unit  120 , the support body  130 , and a portion of the interconnection  140  and is designed to reduce the insensitive region as much as possible. 
     The structural body illustrated in  FIGS. 1A to 1C  is vacuum-sealed in a not-illustrated package. 
     Herein, the face of the infrared absorption unit  150  opposing the substrate is referred to as a lower face  150   d ; and the face of the infrared absorption unit  150  opposite to the lower face  150   d  is referred to as an upper face  150   u.    
     In the infrared imaging device  10  according to this embodiment, the infrared absorption unit  150  includes a protrusion  150   p  provided on a rim  150   a  of the infrared absorption unit  150  to protrude toward the substrate  110 . The protrusion  150   p  is provided, for example, along the rim  150   a  of the infrared absorption unit  150 . 
     In other words, the lower face  150   d  at the protrusion  150   p  protrudes further toward the substrate  110  side than does the lower face  150   d  around the protrusion  150   p.    
     In this specific example, the lower face  150   d  at the protrusion  150   p  is disposed higher than the lower face  150   d  at the portion of the infrared absorption unit  150  contacting the thermoelectric conversion unit  120  as viewed from the substrate  110  (in the direction away from the substrate as viewed from the substrate). 
     The face of the thermoelectric conversion unit  120  on the side opposite to the substrate  110  is higher than the face of the support body  130  on the side opposite to the substrate  110 . 
     In this specific example, the upper face  150   u  of the portion corresponding to the protrusion  150   p  has a configuration substantially conforming to the lower face  150   d  of the protrusion  150   p . In other words, the infrared absorption unit  150  further has a trench  150   q  provided on the face (the upper face  150   u ) of the infrared absorption unit  150  on the side opposite to the substrate  110  on the backside of the protrusion  150   p , where the trench  150   q  is recessed toward the substrate  110  side. In other words, the cross-sectional configuration of the infrared absorption unit  150  at the protrusion  150   p  is a Y-shaped configuration. In the case where the protrusion  150   p  is provided, for example, along the rim  150   a , the trench  150   q  is provided along the protrusion  150   p . In other words, the trench  150   q  is provided along the rim  150   a.    
     The mechanical strength of the infrared absorption unit  150  is increased by providing the protrusion  150   p  and the trench  150   q  along the rim  150   a  of the infrared absorption unit  150 . 
     Thus, by the infrared imaging device  10  according to this embodiment, sticking can be suppressed by increasing the mechanical strength of the suspended structural body; and a highly sensitive infrared imaging device can be provided. 
     As illustrated in  FIGS. 1A to 1C , the film thickness of the infrared absorption unit  150  at the portion of the protrusion  150   p  and the trench  150   q  is thicker than the film thickness of the infrared absorption unit  150  at a central portion  150   c  of the infrared absorption unit  150 . In other words, the infrared absorption unit  150  includes a thick portion  150   t  provided at the rim  150   a  of the infrared absorption unit  150  and having a thickness thicker than that of the central portion  150   c  of the infrared absorption unit  150 . The thick portion  150   t  is provided, for example, along the rim  150   a  of the infrared absorption unit  150 . Thereby, sticking can be suppressed and a highly sensitive infrared imaging device can be provided by increasing the mechanical strength of the suspended structural body and increasing the infrared absorption efficiency. 
     COMPARATIVE EXAMPLES 
       FIGS. 2A and 2B  are schematic cross-sectional views illustrating the configurations of infrared imaging devices of comparative examples. 
     Namely,  FIG. 2A  illustrates the structure of an infrared imaging device  19   a  of a first comparative example; and  FIG. 2B  illustrates the structure of an infrared imaging device  19   b  of a second comparative example. 
     In the infrared imaging device  19   a  of the first comparative example as illustrated in  FIG. 2A , the configuration of the infrared absorption unit  150  is different from that of the infrared imaging device  10  according to this embodiment. In other words, the infrared absorption unit  150  of the infrared imaging device  19   a  has, for example, the eave-like configuration discussed in JP-A 2005-43381 (Kokai). 
     In other words, although the peripheral region of the infrared absorption unit  150  has an eave-like portion apart from the substrate  110 , the peripheral region has a flat cross-sectional structure; and the protrusion  150   p  and the trench  150   q  are not provided toward the substrate  110 . The film thickness of the infrared absorption unit  150  is substantially uniform from the central portion  150   c  to the rim  150   a ; and the thick portion  150   t  is not provided. Therefore, the mechanical strength of the infrared absorption unit  150  is low; a sticking phenomenon occurs in which, for example, the suspended structural body deforms due to internal stress and fluctuation of the process conditions and the suspended structural body sticks to the substrate and the interconnections disposed therearound; and the sensitivity decreases. 
     In the infrared imaging device  19   b  of the second comparative example as illustrated in  FIG. 2B  as well, the configuration of the infrared absorption unit  150  is different from that of the infrared imaging device  10  according to this embodiment. In other words, the infrared absorption unit  150  of the infrared imaging device  19   a  has a configuration in which the eave-like configuration of the infrared imaging device  19   a  is bent in the substrate  110  direction at the rim  150   a.    
     In other words, in such a case as well, the protrusion  150   p  and the trench  150   q  are not provided toward the substrate  110 . Also, the film thickness of the infrared absorption unit  150  is substantially uniform from the central portion  150   c  to the rim  150   a ; and the thick portion  150   t  is not provided. To this end, in such a case as well, the mechanical strength of the infrared absorption unit  150  is low; the sticking phenomenon occurs in which, for example, the suspended structural body deforms due to internal stress and fluctuation of the process conditions and the suspended structural body sticks to the substrate and the interconnections disposed therearound; and the sensitivity decreases. 
     Conversely, the protrusion  150   p  is provided along the rim  150   a  in the infrared imaging device  10  according to this embodiment. Therefore, the low mechanical strength of the rim  150   a  is increased. Further, the mechanical strength is increased because the film thickness of the infrared absorption unit  150  is thicker and the thick portion  150   t  is provided at the portion of the protrusion  150   p . In such a case, by providing the trench  150   q  in a position corresponding to the protrusion  150   p , an increase of the volume of the infrared absorption unit  150  due to the protrusion  150   p  being provided can be suppressed; and the thermal capacity of the entirety can be maintained in a low state as much as possible. 
       FIGS. 3A to 3C  are schematic views illustrating the configurations of infrared imaging devices of variation examples according to the first embodiment. 
     In an infrared imaging device  10   a  of a variation example according to this embodiment as illustrated in  FIG. 3A , although the protrusion  150   p  and the trench  150   q  are provided in the infrared absorption unit  150 , the configuration of the trench  150   q  is different from that of the infrared imaging device  10 . In other words, the infrared imaging device  10  illustrated in  FIGS. 1A to 1C  is an example in which the trench  150   q  of the infrared absorption unit  150  has a V-shaped configuration and a face substantially parallel to the major surface of the substrate  110  is not provided in the trench  150   q.    
     On the other hand, in the infrared imaging device  10   a  as illustrated in  FIG. 3A , a bottom face substantially parallel to a major surface of the substrate  110  is provided in the trench  150   q  of the infrared absorption unit  150 . 
     The cross-sectional configurations of the trench  150   q  and the protrusion  150   p  change due to the distance between the thermoelectric conversion unit  120  and the interconnection  140  and the structure of the support body  130  provided therebetween. Thus, the cross-sectional configuration of the trench  150   q  (and the protrusion  150   p ) is arbitrary. 
     In the case of the infrared imaging device  10   a  as well, the film thickness of the infrared absorption unit  150  is thick at the portion of the protrusion  150   p  and the trench  150   q . In other words, although there is little difference between the film thicknesses of the central portion  150   c  and the portion at the bottom face of the trench  150   q , the film thickness at the portion of the wall face of the trench  150   q  is thick. In other words, in this specific example, the thick portion  150   t  is the portion of the wall face of the trench  150   q.    
     Thus, in the case where the trench  150   q  has a bottom face parallel to the major surface of the substrate  110 , the protrusion  150   p  and the trench  150   q  are provided along the rim  150   a  where the mechanical strength is low. Therefore, the mechanical strength can be increased; the sticking can be suppressed; and a highly sensitive infrared imaging device can be provided. 
     In an infrared imaging device  10   b  of a variation example according to this embodiment as illustrated in  FIG. 3B , although the protrusion  150   p  is provided in the infrared absorption unit  150 , the depth of the trench  150   q  is shallower than that of the infrared imaging device  10 . In such a case as well, the thick portion  150   t  is provided. In such a case as well, the mechanical strength can be increased; the sticking can be suppressed; and a highly sensitive infrared imaging device can be provided. 
     The depth of the trench  150   q  may be reduced further and the trench  150   q  may be substantially not provided. In such a case as well, the mechanical strength can be increased. However, as described above, in the case where the protrusion  150   p  is provided and the depth of the trench  150   q  is reduced radically or the trench  150   q  is not provided, the volume of the infrared absorption unit  150  increases and the thermal capacity increases. Therefore, it is desirable to provide the trench  150   q  with an appropriate depth. However, according to the relationship between the protrusion amount and width of the protrusion  150   p  and the film thickness and total surface area of the infrared absorption unit  150 , it is not always necessary to provide the trench  150   q , and only the protrusion  150   p  may be provided. 
     In an infrared imaging device  10   c  of a variation example according to this embodiment as illustrated in  FIG. 3C , although the protrusion  150   p  is provided in the infrared absorption unit  150 , the protrusion  150   p  is provided linked to the rim  150   a . In other words, in the infrared imaging devices  10 ,  10   a , and  10   b  recited above, the protruding portion  150   p  is provided proximally to the rim  150   a  along the rim  150   a ; and the lower face  150   d  at the portion of the protrusion  150   p  opposing the substrate  110  is positioned further toward the substrate  110  side than is the lower face  150   d  at the rim  150   a . Conversely, in the infrared imaging device  10   c , the position (the height) with respect to the substrate  110  of the lower face  150   d  at the portion of the protrusion  150   p  opposing the substrate  110  is substantially the same as the position (the height) of the lower face  150   d  at the rim  150   a.    
     Thus, in the case where the protrusion  150   p  is provided linked to the rim  150   a  as well, the rim  150   a  where the mechanical strength of the infrared absorption unit  150  is low can be reinforced by the protrusion  150   p ; the mechanical strength of the infrared absorption unit  150  can be increased; the sticking can be suppressed; and a highly sensitive infrared imaging device can be provided. 
     Although the trench  150   q  may not be provided in such a case as well, as recited above, it is desirable for the trench  150   q  to be provided. In the case of the infrared imaging device  10   c , the thick portion  150   t  corresponds to the portion where the protrusion  150   p  is provided. 
     In the infrared imaging devices  10 ,  10   a ,  10   b , and  10   c  according to this embodiment, it is desirable for the protrusion  150   p  and the trench  150   q  to be provided along the rim  150   a  of the infrared absorption unit  150 . Further, it is desirable for the protrusion  150   p  and the trench  150   q  to be provided continuously to enclose the central portion  150   c  of the infrared absorption unit  150  on the inner side of the rim  150   a . Thereby, the strength of the rim  150   a  of the infrared absorption unit  150  can be increased further. 
     Because the mechanical strength of the rim  150   a  is low, it is desirable for the protrusion  150   p  and the trench  150   q  to be provided in portions as proximal as possible to the rim  150   a  to reinforce the mechanical strength. 
     Similarly, it is desirable to provide the thick portion  150   t  along the rim  150   a  of the infrared absorption unit  150  in the infrared imaging devices  10 ,  10   a ,  10   b , and  10   c  according to this embodiment. Further, it is desirable for the thick portion  150   t  to be provided continuously to enclose the central portion  150   c  of the infrared absorption unit  150 . Thereby, the strength of the rim  150   a  of the infrared absorption unit  150  increases further. 
     However, the embodiments are not limited thereto. It is sufficient for the protrusion  150   p , the trench  150   q , and the thick portion  150   t  to be provided along the rim  150   a  of the infrared absorption unit  150 ; and these may be provided, for example, intermittently in a portion of the sides or a portion of the corners of the rim  150   a  of the infrared absorption unit  150 . 
     First example 
       FIG. 4  is a schematic cross-sectional view illustrating the structure of an infrared imaging device according to a first example. 
     The infrared imaging device  11  according to the first example of this embodiment as illustrated in  FIG. 4  has the structure of the infrared imaging device  10  illustrated in  FIGS. 1A to 1C . 
     The pitch of the pixel in the infrared imaging device  11 , i.e., a width W 1  from line A 1  to line A 2 , is 30 μm. A width W 2  of the thermoelectric conversion unit  120  is 20 μm; a width W 3  of the support body  130  is 1.0 μm; and a width (a distance) W 4  between the support body  130  and the thermoelectric conversion unit  120  is 0.5 μm. The distance between the support body  130  and the interconnection  140  also is 0.5 μm. 
     A height t 1  of the interconnection  140  (the height from the substrate  110 ) is 4.3 μm. A distance t 2  between the face of the thermoelectric conversion unit  120  on the side opposite to the substrate  110  and the face of the support body  130  on the side opposite to the substrate  110  is 2.0 μm. A distance t 3  between the support body  130  and the lower face  150   d  at the protrusion  150   p  of the infrared absorption unit  150  is 3.0 μm. 
     As recited above, the face of the support body  130  on the side opposite to the substrate  110  is more proximal to the substrate  110  side than is the face of the thermoelectric conversion unit  120  on the side opposite to the substrate  110 ; and a difference in levels exists. In other words, the face of the thermoelectric conversion unit  120  on the side opposite to the substrate  110  is higher than the face of the support body  130  on the side opposite to the substrate  110 . Thereby, as described below, in the case where a sacrificial layer is provided on the thermoelectric conversion unit  120  and the support body  130  to cover the thermoelectric conversion unit  120  and the support body  130 , the height of the sacrificial layer changes due to the difference in levels. As a result, the protrusion  150   p  and the trench  150   q  can be provided in the infrared absorption unit  150  formed on the sacrificial layer. 
     In this specific example, the infrared absorption unit  150  has a stacked structure of, for example, a lower absorption layer  151  (a first infrared absorption layer) made of a silicon oxide film, an upper absorption layer  153  (a second infrared absorption layer) made of a silicon oxide film provided to oppose the lower absorption layer  151 , and an intermediate absorption layer  152  (a third infrared absorption layer) made of a Si 3 N 4  film provided between the lower absorption layer  151  and the upper absorption layer  153 . The silicon oxide film has an absorption peak in a wavelength region of about 9 μm. On the other hand, the Si 3 N 4  film has an absorption peak in a wavelength region of about 13 μm. In other words, the light absorption wavelength regions of the two are different. Thereby, by providing the infrared absorption unit  150  with a stacked structure of different materials as in this specific example, the infrared absorption unit  150  can have good absorption characteristics with respect to a wide wavelength range; and the sensitivity to infrared rays increases. 
     In the case where different materials are stacked, it is desirable to employ a structure using the same material as the lower absorption layer  151  and the upper absorption layer  153  and a material different therefrom as the intermediate absorption layer  152  because the internal stress occurring between the different materials can be cancelled. The combination of the material used as the lower absorption layer  151  and the upper absorption layer  153  and the material used as the intermediate absorption layer  152  may be set appropriately based on the absorption characteristics of infrared rays, the mechanical strength, the suitability of the manufacturing processes, etc. 
     Also in the infrared imaging device  11  having such a structure, the low mechanical strength of the rim  150   a  is reinforced by the protrusion  150   p  and the thick portion  150   t ; the increase of the volume of the infrared absorption unit  150  is suppressed by the trench  150   q ; the mechanical strength of the infrared absorption unit  150  can be increased; the sticking can be suppressed; and a highly sensitive infrared imaging device can be provided. 
     A method for manufacturing the infrared imaging device  11  of this example will now be described. 
       FIGS. 5A to 5C  are schematic cross-sectional views in order of the processes, illustrating the method for manufacturing the infrared imaging device according to the first example. The structures inside the interconnection  140 , the support body  130 , and the pn junction diode, i.e., the thermoelectric conversion unit  120 , are not illustrated. 
       FIGS. 6A to 6C  are schematic cross-sectional views in order of the processes, continuing from  FIG. 5C . 
       FIGS. 7A to 7C  are schematic cross-sectional views in order of the processes, continuing from  FIG. 6C . 
       FIGS. 8A to 8C  are schematic cross-sectional views in order of the processes, continuing from  FIG. 7C . 
     As illustrated in  FIG. 5A , first, a buried silicon oxide film layer  102  and a monocrystalline silicon layer  103  are stacked sequentially on a monocrystalline silicon support substrate  101 . In other words, an SOI substrate is formed. The monocrystalline silicon support substrate  101  corresponds to the substrate  110 . 
     Then, element separation is performed by STI (Shallow Trench Isolation). In other words, an element separation region is specified using photolithography; the monocrystalline silicon layer  103  of the element separation region is removed by etching using RIE (Reactive Ion Etching); subsequently, an element-separating silicon oxide film (not illustrated) is filled using CVD (Chemical Vapor Deposition); and planarizing is performed using CMP (Chemical Mechanical Polishing). At this time, the region which is the support structure also is defined as the element separation region and the element-separating silicon oxide film is filled. 
     Continuing, the pn junction diode served as the thermoelectric conversion unit  120  is formed. At this time, for example, an n +  electrode region is specified using photolithography; an n +  diffusion layer region is formed in a region of the monocrystalline silicon layer  103  proximal to the surface using ion implantation; then, a p +  electrode region is formed in a deep region of the monocrystalline silicon layer  103 ; and a diffusion layer interconnection region is formed to link the p +  electrode region to the contact diffusion layer region existing in the surface of the monocrystalline silicon layer  103 . 
     Then, a polysilicon layer is formed; and the support body  130  is formed using photolithography and RIE. During this process, the gate electrodes of the MOS transistors used in the peripheral circuit, etc., may be formed simultaneously. 
     Continuing, a first inter-layer insulating film is formed using CVD. Subsequently, RIE and the like are used to make contact holes on the n + /p +  layer regions of the pn junction diode and in contact portions between the Al interconnection and the polysilicon forming the electrode support structure; and subsequently, plugs are filled by sputtering and CMP. Subsequently, aluminum alloy is deposited by sputtering and patterned to form the first metal interconnection. Subsequently, as described below, a silicon oxide film and a silicon nitride film are formed by stacking as layers served as the infrared absorption unit  150  and passivation of the MOS transistors and the like. 
     Then, as illustrated in  FIG. 5B , etch-back is performed on the thermoelectric conversion unit  120 , the support body  130 , the interconnection  140 , and the buried silicon oxide film layer  102  using a dry process. Subsequently, an amorphous silicon film is deposited with a thickness of 3 μm using CVD (Chemical Vapor Deposition) at 350° C. as a sacrificial layer  104 . 
     Continuing, as illustrated in  FIG. 5C , a resist  105  is formed on the sacrificial layer  104  and patterned into a prescribed configuration using photolithography. At this time, the distance from an end portion  105   a  of the resist  105  to an end portion  120   a  of the thermoelectric conversion unit  120 , i.e., an overlap δ 1  between the resist  105  and the thermoelectric conversion unit  120 , is set to be greater than 0 μm and less than 1 μm. 
     Then, as illustrated in  FIG. 6A , the amorphous silicon film of the sacrificial layer  104  on the upper face of the thermoelectric conversion unit  120  is removed using RIE. 
     Continuing, as illustrated in  FIG. 6B , the resist  105  is peeled. 
     Then, as illustrated in  FIG. 6C , a Si 3 N 4  film  106  served as the lower absorption layer  151  of the infrared absorption unit  150  is formed using CVD. 
     Continuing as illustrated in  FIG. 7A , a SiO 2  film  107  served as the intermediate absorption layer  152  of the infrared absorption unit  150  is formed on the Si 3 N 4  film  106  recited above using CVD. 
     Then, as illustrated in  FIG. 7B , a Si 3 N 4  film  108  served as the upper absorption layer  153  of the infrared absorption unit  150  is formed using CVD. 
     Continuing as illustrated in  FIG. 7C , a resist  109  is formed, and the resist  109  is patterned into a prescribed configuration using photolithography. At this time, to reduce the region insensitive to the infrared rays, it is desirable for the distance from an end portion  109   a  of the resist  109  to an end portion  140   a  of the interconnection  140 , that is, an overlap δ 2  between the resist  109  and the interconnection  140 , to be set to be greater than 0 μm and less than half the width of the interconnection  140 . 
     Then, as illustrated in  FIG. 8A , the Si 3 N 4  film  108 , the SiO 2  film  107 , and the Si 3 N 4  film  106  are removed using RIE. 
     Continuing as illustrated in  FIG. 8B , the resist  109  is peeled; and the lower absorption layer  151 , the intermediate absorption layer  152 , and the upper absorption layer  153  are formed. 
     Then, as illustrated in  FIG. 8C , TMAH (Tetra-Methyl-Ammonium-Hydroxide) is used to perform anisotropic wet etching to remove the sacrificial layer  104  and a portion of the upper face of the monocrystalline silicon support substrate  101 ; a suspended structure is formed on the monocrystalline silicon support substrate  101  (the substrate  110 ); and the infrared imaging device  11  of this specific example is constructed. 
     In such a case, the structures of the protrusion  150   p , the trench  150   q , and the thick portion  150   t  of the infrared absorption unit  150  can be controlled by the design of the thermoelectric conversion unit  120 , the support body  130 , and the interconnection  140  of the infrared imaging device  11 . 
     In this specific example, the distance t 2  between the face of the thermoelectric conversion unit  120  on the side opposite to the substrate  110  and the face of the support body  130  on the side opposite to the substrate  110  is 2.0 μm. Therefore, the protrusion amount of the protrusion  150   p , similarly to the distance t 2 , is about 2.0 μm. On the other hand, the thickness of the amorphous silicon film which is the sacrificial layer  104  is 3.0 μm. Therefore, the distance t 3  between the support body  130  and the lower face  150   d  at the protrusion  150   p  of the infrared absorption unit  150  is 3.0 μm. 
     However, as described below, the distance t 2  and the distance t 3  change due to the design of the thermoelectric conversion unit  120 , the support body  130 , and the interconnection  140  of the infrared imaging device  11  and the coverability during the formation of the sacrificial layer  104 . 
     Second Example 
       FIGS. 9A and 9B  are schematic views illustrating the configuration of an infrared imaging device according to a second example. Namely,  FIG. 9A  is a schematic perspective view; and  FIG. 9B  is a cross-sectional view along line A-A′ of  FIG. 9A . 
     In the infrared imaging device  12  according to the second example as illustrated in  FIGS. 9A and 9B , the support body  130  has a structure having a bent meandering configuration. In such a case as well, the infrared absorption unit  150  includes the protrusion  150   p  and the trench  150   q , which are provided along the rim  150   a , and the thick portion  150   t.    
     Thereby, the low mechanical strength of the rim  150   a  is reinforced by the protrusion  150   p  and the thick portion  150   t ; the increase of the volume of the infrared absorption unit  150  is suppressed by the trench  150   q ; the mechanical strength of the infrared absorption unit  150  can be increased; the sticking can be suppressed; and a highly sensitive infrared imaging device can be provided. 
     In the case where the support body  130  has two bent portions between the thermoelectric conversion unit  120  and one of the interconnections  140  as in the infrared imaging device  12  according to this example, the width of the protrusion  150   p  can be increased and the width of the trench  150   q  can be increased by the design of the support body  130 . In such a case, for example, it is easy for the trench  150   q  to have a structure having a bottom face substantially parallel to the major surface of the substrate  110 . Further, at least one selected from the protrusion  150   p , the trench  150   q , and the thick portion  150   t  may be multiply provided substantially parallel along the rim  150   a  on one side of the infrared absorption unit  150  by the design of the support body  130 . 
     Thus, in the infrared imaging devices according to this embodiment, the numbers of the protrusions  150   p , the trenches  150   q , and the thick portions  150   t  are arbitrary. 
     As described above, in the infrared imaging devices  10 ,  10   a ,  10   b ,  10   c ,  11 , and  12  according to this embodiment and the examples, providing the trench  150   q  has the effect of suppressing the increase of the volume of the infrared absorption unit  150 , suppressing the increase of the thermal capacity, and increasing the sensitivity while increasing the mechanical strength of the rim  150   a  of the infrared absorption unit  150  due to the protrusion  150   p  and the thick portion  150   t . Further, as described below, providing the trench  150   q  can increase the sensitivity by an effect other than the effect of suppressing the increase of the volume. 
       FIG. 10  is a graph illustrating a characteristic of the infrared imaging device according to the first embodiment. 
     Namely,  FIG. 10  illustrates the result of a simulation of a light absorption amount ratio RA of infrared rays when changing the thickness of the sacrificial layer  104 , i.e., the distance t 3  between the support body  130  and the lower face  150   d  at the protrusion  150   p  of the infrared absorption unit  150  in the structure of the infrared imaging device  11  of the first example illustrated in  FIG. 4 . 
     In this case, the width (the wing width) W 5  of the region not in contact with the thermoelectric conversion unit  120  of the infrared absorption unit  150  illustrated in  FIG. 4  was constant at 6 μm; and the light absorption amount ratio of infrared rays was calculated changing the distance t 3  formed reflecting the thickness of the sacrificial layer  104 . In this case, a configuration was used in which the cross-sectional configuration of the peripheral portion of the infrared absorption unit  150  had an arc-like configuration having a single radius and the numbers of the protrusions  150   p  and the trenches  150   q  could change with the change of the distance t 3 . The thickness of the infrared absorption unit  150  was constant at 1.0 μm. In  FIG. 10 , the distance t 3  is plotted on the horizontal axis and the infrared light absorption ratio RA is plotted on the vertical axis. The infrared light absorption ratio RA is the ratio to the case of the infrared absorption unit  150  having a flat cross-sectional configuration at the peripheral region as in the infrared imaging device  19   a  of the first comparative example illustrated in  FIG. 2A , which is taken to be 1. 
     As illustrated in  FIG. 10 , the infrared light absorption ratio RA increases as the distance t 3  increases. 
     In  FIG. 10 , the datum where the distance t 3  is 0.5 μm corresponds to the case where the thickness of the sacrificial layer  104  is 0.5 μm and three combinations of the trench  150   q  and the protrusion  150   p  having the arc-like configuration are formed in the peripheral portion of the infrared absorption unit  150 . 
     The datum where the distance t 3  is 1.0 μm corresponds to the case where the thickness of the sacrificial layer  104  is 1.0 μm, two combinations of the trench  150   q  and the protrusion  150   p  having the arc-like configuration at the peripheral portion of the infrared absorption unit  150  are formed, and the outermost circumference has a configuration bent toward the substrate side. 
     The datum where the distance t 3  is 2.5 μm corresponds to the case where the thickness of the sacrificial layer  104  is 2.5 μm and one combination of the trench  150   q  and the protrusion  150   p  having the arc-like configuration at the peripheral portion of the infrared absorption unit  150  is formed. 
     Thus, the infrared light absorption ratio RA increases as the distance t 3  increases from 0.5 μm to 1.0 μm and to 2.5 μm. The infrared light absorption ratio RA is substantially saturated when the distance t 3  is about 2.5 μm. 
     Thus, increasing the distance t 3  increases the infrared light absorption ratio RA. This increase is caused by the depth of the trench  150   q  increasing due to the increase of the distance t 3 , which leads to an effective increase of the thickness of the infrared absorption unit  150  with respect to the incident infrared rays at the wall face of the trench  150   q , and the light absorption efficiency increases. 
     Thus, the infrared light absorption ratio RA can be increased by increasing the thickness of the sacrificial layer  104 , i.e., the distance t 3  between the support body  130  and the lower face  150   d  at the protrusion  150   p  of the infrared absorption unit  150 . 
     Here, the condition for the trench  150   q  to form when the protrusion  150   p  is formed between the support bodies  130  is as follows. That is, the trench  150   q  forms when Formula (1) recited below is satisfied, where D is the distance between the substrate  110  and the face of the protrusion  150  on the substrate  110  side; L is at least one selected from the distance between the thermoelectric conversion unit  120  and the support body  130 , the distance between the support body  130  and the support body  130  adjacent thereto (the distance between the support bodies  130 ), and the distance between the support body  130  and the interconnection  140 ; and T is the film thickness of the flat region of the infrared absorption unit  150 . 
         L &gt;(2 D+ 2 T )  (1)
 
     In this specific example, this condition is 
         W 4&gt;(2× t 4+2 ×t 1+2 T )  (2)
 
     The condition for the trench  150   q  to form when forming the protrusion  150   p  on the support body  130  is as follows. That is, the trench  150   q  forms when Formula (3) recited below is satisfied, where the face of the thermoelectric conversion unit  120  on the side opposite to the substrate  110  is higher than the face of the support body  130  on the side opposite to the substrate  110 , I is the distance between the thermoelectric conversion unit  120  and the interconnection  140  (referring to  FIG. 4 ), B is the distance between the support body  130  and the face of the protrusion  150   p  on the substrate  110  side, and T is the film thickness of the flat region of the infrared absorption unit  150 . 
         L &gt;(2 B +2 T )  (3)
 
     In this specific example, this condition is 
         W 4&gt;(2 ×t 3+2 T )  (4)
 
     Formula (3) and Formula (4) correspond to the condition for the trench  150   q  to form in the case where the protrusion  150   p  and the trench  150   q  are formed by the method illustrated in  FIG. 5A  to  FIG. 8C  (i.e., the case where a spacing of the distance W 4  is provided between the thermoelectric conversion unit  120  and the support body  130 , a difference in levels (the distance t 2 ) is subsequently provided between the thermoelectric conversion unit  120  and the support body  130 , and then the sacrificial layer  104  is provided thereon). 
     Formula (1) to Formula (4) recited above are conditions for the trench  150   q  to form in the case where the sacrificial layer  104  is deposited substantially isotropically. 
     In the case where Formula (1) to Formula (4) are not satisfied, for example, the sacrificial layer  104  is too thick; the upper face of the sacrificial layer  104  does not reflect the gap between the support body  130  and the thermoelectric conversion unit  120  and the gap between the support body  130  and the interconnection  140  and undesirably is planarized; and the trench  150   q  of the infrared absorption unit  150  is not formed or has a shallow depth. 
     Because the distance t 3  between the support body  130  and the lower face  150   d  at the protrusion  150   p  of the infrared absorption unit  150  substantially matches the thickness d of the sacrificial layer, Formula (3) becomes Formula (5) recited below. 
         I &gt;(2 d +2 T )  (5)
 
     By satisfying at least one selected from Formula (1) to Formula (5) recited above, the trench  150   q  is formed; the infrared light absorption ratio RA is increased; and, as described above, the increase of the volume of the infrared absorption unit  150  is suppressed, the increase of the thermal capacity is suppressed, and the sensitivity can be increased while increasing the mechanical strength of the rim  150   a  of the infrared absorption unit  150  due to the protrusion  150   p  and the thick portion  150   t.    
     On the other hand, the condition for the thick portion  150   t  to form between the support bodies  130  is as follows. That is, the thick portion  150   t  forms when 2D&lt;L&lt;(2D+2T), where D is the distance between the substrate  110  and the face of the thick portion  150   t  on the substrate  110  side; L is at least one selected from the distance between the thermoelectric conversion unit  120  and the support body  130 , the distance between the support body  130  and the support body  130  adjacent thereto (the distance between the support bodies  130 ), and the distance between the support body  130  and the interconnection  140 ; and T is the film thickness of the flat region of the infrared absorption unit  150 . In this specific example, this condition is (2×t 4 + 2 t 1 )&lt;L&lt;(2×t 4 +2×t 1 +2T). 
     The condition for the thick portion  150   t  to form on the support body  130  is as follows. That is, the thick portion  150   t  forms on the support body  130  when 2B&lt;I&lt;(2B+2T), where the face of the thermoelectric conversion unit  120  on the side opposite to the substrate  110  is higher than the face of the support body  130  on the side opposite to the substrate  110 , I is the distance between the thermoelectric conversion unit  120  and the interconnection  140 , and B is the distance between the support body  130  and the face of the protrusion  150   p  on the substrate  110  side. In this specific example, this condition is 2t3&lt;I&lt;(2×t3+2T). 
     Second Embodiment 
       FIG. 11  is a flowchart illustrating a method for manufacturing an infrared imaging device according to a second embodiment. 
     The method for manufacturing the infrared imaging device according to this embodiment is a method for manufacturing an infrared imaging device, the device including: the substrate  110 ; the infrared absorption unit  150  provided on the substrate  110  and apart from the substrate  110  to absorb infrared rays; the thermoelectric conversion unit  120  provided apart from the substrate  110  and in contact with the infrared absorption unit  150  between the infrared absorption unit  150  and the substrate  110  to convert a temperature change due to infrared rays absorbed by the infrared absorption unit  150  into an electrical signal; the support body  130  transmitting the electrical signal from the thermoelectric conversion unit  120  while supporting the thermoelectric conversion unit  120  on the substrate  110  and apart from the substrate  110 ; and the interconnection  140  used to read the electrical signal from the support body  130 . That is the interconnection  140  is configured to transmit the electrical signal in reading the electrical signal. 
     In the method for manufacturing the infrared imaging device according to this embodiment, first, the thermoelectric conversion unit  120  and the support body  130  are formed on the substrate  110  (step S 110 ). 
     Then, the sacrificial layer  104  is deposited using CVD to cover the thermoelectric conversion unit  120  and the support body  130  (step S 120 ). 
     For example, as described in regard to  FIGS. 5A to 5C , the sacrificial layer  104  may include amorphous silicon. Then, the thermoelectric conversion unit  120  and the support body  130  can be covered by using CVD that moderately follows the planar configuration of the thermoelectric conversion unit  120 , the planar configuration of the support body  130 , and the planar configuration between the thermoelectric conversion unit  120  and the support body  130 . Then, the protrusion  150   p  and the trench  150   q  can be formed easily in the infrared absorption unit  150  described below formed on the sacrificial layer  104 . 
     Subsequently, as illustrated in  FIG. 6A , the resist  105  is provided on the sacrificial layer  104 ; and the sacrificial layer  104  is patterned into a prescribed configuration. 
     In other words, it is sufficient to provide the sacrificial layer  104  using CVD to cover the thermoelectric conversion unit  120  and the support body  130 ; and the method of patterning the configuration of the sacrificial layer  104  is arbitrary. 
     Then, after step S 120 , an infrared absorption film served as the infrared absorption unit  150  is formed on the sacrificial layer  104 ; and the configuration of the infrared absorption film is patterned (step S 130 ). The method described in regard to  FIG. 6A  to  FIG. 8C  may be employed. 
     Then, the sacrificial layer  104  is removed (step S 140 ). 
     Thereby, the protrusion  150   p  and the trench  150   q  can be provided along the rim of the infrared absorption unit  150 ; the thick portion  150   t  can be provided; the sticking can be suppressed by increasing the mechanical strength of the infrared absorption unit  150 ; and a highly sensitive infrared imaging device can be provided. 
     In such a case, the trench  150   q  can be formed appropriately by making settings to satisfy Formula (1) to Formula (5) recited above. 
     Hereinabove, exemplary embodiments of the invention are described with reference to specific examples. However, the invention is not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components included in infrared imaging devices and methods for manufacturing infrared imaging devices from known art. Such practice is included in the scope of the invention to the extent that similar effects thereto are obtained. 
     Further, any two or more components of the specific examples may be combined within the extent of technical feasibility and are included in the scope of the invention to the extent that the purport of the invention is included. 
     Moreover, all infrared imaging devices and methods for manufacturing infrared imaging devices practicable by an appropriate design modification by one skilled in the art based on the infrared imaging devices and the methods for manufacturing infrared imaging devices described above as embodiments of the invention also are within the scope of the invention to the extent that the purport of the invention is included. 
     Furthermore, various modifications and alterations within the spirit of the invention will be readily apparent to those skilled in the art. All such modifications and alterations should therefore be seen as within the scope of the invention. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modification as would fall within the scope and spirit of the inventions.