Patent Publication Number: US-2015076651-A1

Title: Thermocouple, thermopile, infrared ray sensor and method of manufacturing infrared ray sensor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a thermocouple, a thermopile, an infrared ray sensor and a method of manufacturing an infrared ray sensor. 
     2. Description of the Related Art 
     Recently, development of bolometers, thermopiles, non-cooling thermal infrared ray array sensors using diodes and/or the like, thermal infrared ray line sensors and so forth is being carried out actively. These sensors have sensitivities for wavelength bands from mid infrared bands to far infrared bands and therefore are widely used for night vision cameras for automobiles, human body sensors for security equipment, human body sensors for energy saving of electric/electronic equipment and so forth. 
     In particular, thermopile type sensors do not require driving power sources and are capable of easily realizing low power consumption. Also, it is possible to produce them by materials such as polysilicon or aluminum used in a usual Complementary Metal Oxide Semiconductor (CMOS) process. Therefore, it is easy to realize a monolithic configuration including peripheral circuits. From these viewpoints, development of relatively small-scale infrared ray array sensors using thermopiles is being carried out actively. 
     Further, as materials of thermopiles, it is known to use a pair of n-type polysilicon and p-type polysilicon having mutually different polarities of Seebeck coefficients (for example, see Japanese Laid-Open Patent Application No. 2000-307159 (Patent Reference No. 1)). In a thermopile using n-type polysilicon and p-type polysilicon, n-type polysilicon and p-type polysilicon are placed alternately across hot junctions and cold junctions, and all of the n-type polysilicon and the p-type polysilicon are connected in series using conductive material. 
     Further, in these infrared ray sensors, in order to obtain sufficient sensitivities for weak infrared rays, hot junctions in a thermopile are usually formed on a heat insulating structure such as a bridge structure or a diaphragm structure formed by a MEMS process. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, n infrared ray sensor includes a thermopile. The thermopile includes a first semiconductor material part and a second semiconductor material part, the first semiconductor material part and the second semiconductor material part are laminated, and a dielectric film is provided between the first semiconductor material part and the second semiconductor material part. 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are schematic views illustrating an embodiment,  FIG. 1A  being a plan view and  FIG. 1B  being a sectional view taken along a A-A′ line of  FIG. 1A ; 
         FIG. 2  is a schematic sectional view illustrating another embodiment; 
         FIGS. 3A and 3B  are schematic views illustrating further another embodiment,  FIG. 3A  being a plan view and  FIG. 3B  being a sectional view taken along a B-B′ line of  FIG. 3A ; 
         FIGS. 4A and 4B  are schematic views illustrating yet another embodiment,  FIG. 4A  being a plan view and  FIG. 4B  being a sectional view taken along a C-C′ line of  FIG. 4A ; 
         FIG. 5  is a schematic sectional view showing a connection part between semiconductor material parts in the embodiment of  FIGS. 4A and 4B  in a magnified manner; 
         FIGS. 6A and 6B  are schematic views illustrating yet another embodiment,  FIG. 6A  being a plan view and  FIG. 6B  being a sectional view taken along a D-D′ line of  FIG. 6A  in a magnified manner; 
         FIG. 7  is a schematic sectional view showing a connection part between semiconductor material parts in the embodiment of  FIGS. 6A and 6B ;  FIGS. 8A ,  8 B,  8 C,  8 D and BE are sectional views illustrating an example of processes of manufacturing a thermopile according to the embodiment of  FIGS. 6A and 6B ; 
         FIG. 9  is a schematic sectional view illustrating yet another embodiment; 
         FIG. 10  is a schematic plan view illustrating yet another embodiment; 
         FIGS. 11A and 11B  are schematic views illustrating the related art,  FIG. 11A  being a plan view and  FIG. 11B  being a sectional view taken along a X-X′ line of  FIG. 11A ; 
         FIGS. 12A and 12B  are schematic views illustrating connection parts between thermopile material parts and a conductive material part in an infrared ray sensor in the related art,  FIG. 12A  being a plan view and  FIG. 12B  being a sectional view taken along a Y-Y′ line of  FIG. 12A ; 
         FIGS. 13A ,  13 B and  13 C are schematic views illustrating yet another embodiment,  FIG. 13A  being a plan view,  FIG. 13B  being a sectional view taken along a E-E′ line of  FIG. 13A  and  FIG. 13C  being a sectional view taken along a F-F′ line of  FIG. 13A ; 
         FIG. 14  is a schematic view showing a part enclosed by an alternating long and short dashed line in  FIG. 13B  in a magnified manner; 
         FIG. 15  is a schematic view showing a part enclosed by an alternating long and short dashed line in  FIG. 13C  in a magnified manner; 
         FIGS. 16A ,  16 B,  16 C,  16 D,  16 E,  16 F and  16 G are schematic sectional views illustrating one example of processes of manufacturing a thermopile according to the embodiment of  FIGS. 13A ,  13 B and  13 C; 
         FIG. 17A  is a schematic plan view corresponding to the schematic sectional view of  FIG. 16B ; 
         FIG. 17B  is a schematic plan view corresponding to the schematic sectional view of  FIG. 16D ; 
         FIG. 17C  is a schematic plan view corresponding to the schematic sectional view of  FIG. 16E ; 
         FIG. 17D  is a schematic plan view corresponding to the schematic sectional view of  FIG. 16G ; and 
         FIG. 18  is a schematic sectional view illustrating yet another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Below, using the drawings, the embodiments of the present invention will be described in detail. 
     Generally speaking, in an infrared ray sensor of a thermopile type, the sensitivity of the sensor is in proportion to the number of pairs (the number of thermocouples) in a thermopile. Therefore, the sensitivity increases as the number of pairs in the thermopile is increased. However, as the number of pairs in the thermopile is creased, the size of the sensor increases, the heat capacity increase accordingly and as a result, the response characteristics may be degraded. 
     The embodiments of the present invention have been devised for the purpose of increasing the number of pairs in the thermopile per unit area. 
     In the above-mentioned infrared ray sensor according to the aspect of the present invention, the dielectric film can be, for example, a thermal oxide film of the first semiconductor material part. In yet example, another dielectric film can be laminated on the thermal oxide film between the first semiconductor material part and the second semiconductor material part. A specific material of the other dielectric film is not particularly limited. 
     In the above-mentioned infrared ray sensor according to the aspect of the present invention, in yet another example, the first semiconductor material part and the second semiconductor material part can have impurities introduced thereinto with concentrations that are different between the first semiconductor material part and the second semiconductor material part, the impurities generating carriers with polarities that are the same between the first semiconductor material part and the second semiconductor material part, and the first semiconductor material part and the second semiconductor material part have Seebeck coefficients with polarities that are reversed between the first semiconductor material part and the second semiconductor material part. However, the first semiconductor material part and the second semiconductor material part are not limited thereto in an embodiment of the present invention. 
     In the above-mentioned infrared ray sensor according to the aspect of the present invention, in yet another example, the concentrations of the impurities introduced into the first semiconductor material part and the second semiconductor material part can be selected or adjusted in such a manner that the polarities of the Seebeck coefficients are reversed between the first semiconductor material part and the second semiconductor material part. However, the first semiconductor material part and the second semiconductor material part are not limited thereto in an embodiment of the present invention. 
     In the above-mentioned infrared ray sensor according to the aspect of the present invention, in yet another example, the first semiconductor material part and the second semiconductor material part can be made of semiconductor materials that chiefly include silicon. However, the first semiconductor material part and the second semiconductor material part can be made of semiconductor materials that chiefly include a semiconductor other than silicon. 
     In the above-mentioned infrared ray sensor according to the aspect of the present invention, in yet another example, the impurities introduced into the first semiconductor material part and the second semiconductor material part can be n-type impurities. However, the impurities can be p-type impurities. 
     In the above-mentioned infrared ray sensor according to the aspect of the present invention, in yet another example, in either the first semiconductor material part or the second semiconductor material part, the concentration of the impurity reaches a solid-solubility limit. However, in the first semiconductor material part and the second semiconductor material part, the concentrations of the impurities can be those that do not reach solid-solubility limits. 
     In the above-mentioned infrared ray sensor according to the aspect of the present invention, in yet another example, side faces of the first semiconductor material part and the second semiconductor material part lying along longitudinal directions of the first semiconductor material part and the second semiconductor material part can lie on a same plane. However, the side faces of the first semiconductor material part and the second semiconductor material part lying along longitudinal directions of the first semiconductor material part and the second semiconductor material part can also lie on different planes. 
     A method of manufacturing the infrared ray sensor according to the aspect of the present invention includes etching the first semiconductor material part and the second semiconductor material part simultaneously. However, the infrared ray sensor according to the aspect of the present invention can be manufactured also in a method that does not include etching the first semiconductor material part and the second semiconductor material part simultaneously. 
     Next, an infrared ray sensor in the related art will be described. 
       FIGS. 11A and 11B  are schematic views illustrating the related art,  FIG. 11A  is a plan view and  FIG. 11B  is a sectional view taken along an X-X′ line of  FIG. 11A . 
     On a substrate  101 , thermocouples are formed by first thermocouple material parts  103  and second thermocouple material parts  104  included in a thermopile  102  connected by conductive material parts  105 . A plurality of the thermocouples are connected in series by the conductive material parts  105  to form the thermopile  102 . 
     As materials of the first thermocouple material parts  103  and the second thermocouple material parts  104 , generally speaking, n-type polysilicon and p-type polysilicon having Seebeck coefficients with different polarities are usually used. The first thermocouple material parts  103  and the second thermocouple material parts  104  are connected by the conductive material parts  105  made of aluminum or the like via contact holes  106 . 
     Further, in order to detect weak infrared rays with good sensitivity, a cavity part  107  is formed below the thermopile  102  and a heat insulating structure is provided. The junctions in the thermopile  102  on a thin film part thermally insulated from the substrate  101  by the cavity part  107  act as hot junctions while junctions in the thermopile  102  above the substrate  1  without the cavity part  107  act as cold junctions. Further, an infrared ray absorbing film  108  is formed to cover the hot junctions of the thermopile  102 . 
     The first thermocouple material parts  103  and the second thermocouple material parts  104  are formed on a dielectric film  109  formed on the substrate  101 . On the dielectric film  109 , an interlayer dielectric film  110  is formed to cover the first thermocouple material parts  103  and the second thermocouple material parts  104 . On the interlayer dielectric film  110 , the conductive material parts  105  are formed. The contact holes  106  are formed in the interlayer dielectric film  110  between the first and second thermocouple material parts  103  and  104  and the conductive material parts  105 . On the interlayer dielectric film  110 , another interlayer dielectric film  110  is formed to cover the conductive material parts  105 . These interlayer dielectric films  110  (not shown in  FIG. 11A ) are shown in a manner of being integrated. On the interlayer dielectric films  110 , the infrared ray absorbing film  108  is formed. 
     As the substrate  101 , a silicon substrate is generally used since a Micro Electro Mechanical System (MEMS) process of silicon is used for forming the heat insulating structure. As the dielectric film  109 , a silicon thermal oxide film is usually used. As the interlayer dielectric films  110 , plasma oxide films or Chemical Vapor Deposition (CVD) films of silicon are usually used. As the infrared ray absorbing film  108 , a silicon oxide film, a silicon nitride film, a gold black film or the like is used. 
       FIGS. 12A and 12B  are schematic views illustrating connection parts between thermopile material parts and a conductive material part in an infrared ray sensor in the related art.  FIG. 12A  is a plan view and  FIG. 12B  is a sectional view taken along a X-X′ line of  FIG. 12A . In  FIGS. 12A and 12B , the same reference numerals are given to parts providing the same functions as those shown in  FIGS. 11A and 11B . 
     The first thermocouple material part  103  and the conductive material part  105  are electrically connected through the contact hole  106  formed on a contact part  103   a  of the first thermocouple material part  103 . The second thermocouple material part  104  and the conductive material part  105  are electrically connected through the contact hole  106  formed on a contact part  104   a  of the second thermocouple material part  104 . 
     At the time, in order to ensure positive electric conduction, the size of the contact holes  106  and overlapping amounts between the contact holes  106  and the respective material parts  103 ,  104  and  105  are prescribed in a design rule. Therefore, the sizes of the contact parts  103   a  and  104   a  are increased with respect to the widths of the thermocouple material parts  103  and  104 . Thus, freedom in the layout is restricted. 
     For example, when the thermopile  102  (see  FIGS. 11A and 11B ) is laid out within a predetermined area, since the areas of the contact parts  103   a  and  104   a  are needed, it may be impossible to arrange the thermopile  102  with a highest density. Therefore, the number of thermocouples in the thermopile  102  may be reduced and the sensitivity may be degraded accordingly. 
     Further, when laying out the thermopile  102  having a predetermined number of thermocouples, it is necessary to increase the size of the cavity part  107  since the areas of the contact parts  103   a  and  104   a  are needed. As a result, the heat capacity of the thin film part may increase and the response speed of the sensor may be degraded. 
     According to Patent Reference No. 1, layout is devised to minimize the areas of the contact parts  103   a  and  104   a . However, since it may be impossible to completely avoid providing the contact parts  103   a  and  104   a , it may be impossible to solve the problem completely. 
     Further, electric conduction is achieved by the contact holes  106  at the junctions between the contact part  103   a  of the first thermocouple material part  103  and the conductive material part  105  and the junctions between the contact part  104   a  of the second thermocouple material part  104  and the conductive material part  105 . Therefore, the thickness of the interlayer dielectric films  110  is increased by the thickness of the contact holes  106  and the conductive material part  105 . As the thickness of the interlayer dielectric films  110  is thus increased, the heat capacity of the sensor may increase and the response speed of the sensor may be degraded. 
     Thus, in such an infrared ray sensor using a thermopile formed by p-type polysilicon and n-type polysilicon in the related art, it is necessary to connect polysilicon material parts by conductive material parts. This is because if p-type polysilicon and n-type polysilicon are directly connected, a depletion layer is formed near the connection surface. Therefore, in an infrared ray sensor in the related art, contact parts are absolutely needed for electric conduction between polysilicon and conductive material. 
     Therefore, in an infrared ray sensor in the related art, by an influence of such contact parts, the number of thermocouples Sc be formed on a heat insulating structure having a certain area is restricted, or the size of the heat insulating structure is increased for forming a certain number of thermocouples. Therefore, it may be impossible to obtain sufficient sensitivity of a sensor or sufficient response speed in an infrared ray sensor in the related art. 
     A second objective of the embodiments of the present invention is to avoid providing contact parts using other conductive material parts for electric connection between thermocouple material parts. 
     A thermocouple according to an embodiment of the present invention includes a first semiconductor material part and a second semiconductor material part that are electrically connected. The first semiconductor material part and the second semiconductor material part are such that impurities that generate carriers having the same polarity are introduced with mutually different concentrations and the polarities of Seebeck coefficients are the reverse of one another. 
     In the thermocouple, the concentrations of the impurities introduced into the first it semiconductor material part and the second semiconductor material part can be selected or adjusted in such a manner that the polarities of the Seebeck coefficients are reversed between the first semiconductor material part and the second semiconductor material part, as one example. However, the first semiconductor material part and the second semiconductor material part are not limited thereto in an embodiment of the present invention. 
     In the thermocouple, the first semiconductor material part and the second semiconductor material part can be made of semiconductor materials that chiefly include silicon, as one example. However, the first semiconductor material part and the second semiconductor material part can be made of semiconductor materials that chiefly include a semiconductor other than silicon. 
     In the thermocouple, the impurities introduced into the first semiconductor material part and the second semiconductor material part can be n-type impurities, as one example. However, the impurities can be p-type impurities. 
     In the thermocouple, in either one of the first semiconductor material part and the second semiconductor material part, the concentration of the impurity reaches a solid-solubility limit, as one example. However, in the first semiconductor material part and the second semiconductor material part, the concentrations of the impurities can be those that do not reach solid-solubility limits. 
     In the thermocouple, the first semiconductor material part and the second semiconductor material part can be formed from different layers of semiconductor materials, for example. However, the first semiconductor material part and the second semiconductor material part can be formed by using the same layer of a semiconductor material. 
     A thermopile according to an embodiment of the present invention includes a plurality of the above-mentioned thermocouples connected in series or parallel with each other. 
     An infrared ray sensor in a second mode of the present invention includes the thermopile according to the embodiment of the present invention. The thermopile includes the plurality of thermocouples connected in series with each other. 
     In an infrared ray sensor according to one embodiment of the present invention, the thermopile and a peripheral circuit are formed on the same substrate. However, it is also possible that the thermopile and the peripheral circuit are not formed on the same substrate. 
     In an infrared ray sensor according to one embodiment of the present invention, a plurality of the thermopiles are arranged to form an array. However, it is also possible that the plurality of the thermopiles are arranged to have an arrangement other than an array. For example, the plurality of thermopiles can be arranged linearly or form a staggered arrangement. Further, in an infrared ray sensor according to one embodiment of the present invention, the number of the thermopiles can be one. 
     A thermocouple in an embodiment of the present invention includes a first semiconductor material part and a second semiconductor material part. The first semiconductor material part and the second semiconductor material part have impurities introduced thereinto with concentrations that are different between the first semiconductor material part and the second semiconductor material part. The impurities generate carriers with polarities that are the same between the first semiconductor material part and the second semiconductor material part. The first semiconductor material part and the second semiconductor material part have Seebeck coefficients with polarities that are reversed between the first semiconductor material part and the second semiconductor material part. In this configuration, although the first semiconductor material part and the second semiconductor material part are directly connected, no depletion layer is formed between the first semiconductor material part and the second semiconductor material part. Therefore, by the thermocouple according to the embodiment, it is possible to avoid providing contact parts using other conductive material parts for electric connection between the thermocouple material parts. 
     The thermopile includes the thermocouple according to the embodiment of the present invention. Therefore, since it is possible to avoid providing contact parts using other conductive material parts for electric condition between the thermocouple material parts as mentioned above, in the thermopile, it is possible to reduce the arranging intervals between the thermocouple material parts. Thereby, in the thermopile according to the embodiment, it is possible to reduce the area required for providing the thermopile or increase the number of thermocouples for the same area. 
     Since the infrared ray sensor in the second mode of the present invention includes the thermopile according to the embodiment of the present invention, it is possible to reduce the area required for providing the thermopile or increase the number of thermocouples for the same area as mentioned above. Accordingly, in the infrared ray sensor in the second mode of the present invention, it is possible to reduce the area of the infrared ray sensor itself or increase the sensitivity of the sensor. 
       FIGS. 1A and 1B  are schematic views illustrating an embodiment.  FIG. 1A  is a plan view and  FIG. 1B  is a sectional view taken along an A-A′ line of  FIG. 1A . 
     On a dielectric film  2  formed on a substrate  1 , a plurality of first semiconductor material parts  3  and a plurality of second semiconductor material parts  4  are formed to form a plurality of thermocouples. A thermopile  5  is formed as a result of the plurality of semiconductor material parts  3  and  4  are alternately connected in series. The semiconductor material parts  3  and  4  are electrically connected in a manner of being connected directly. 
     The semiconductor material parts  3  and  4  have impurities introduced thereinto with concentrations that are different between the semiconductor material parts  3  and  4 . The impurities generate carriers with polarities that are the same between the semiconductor material parts  3  and  4 . Further, the semiconductor material parts  3  and  4  have Seebeck coefficients with polarities that are reversed between the semiconductor material parts  3  and  4 . The impurity concentration of the first semiconductor material parts  3  can be higher or lower than the impurity concentration of the second semiconductor material parts  4 . 
     The semiconductor material parts  3  and  4  are formed as a result of the same semiconductor layer being machined. Introduction of the impurities into the semiconductor material parts  3  and  4  can be carried out before or after the machining of the semiconductor layer. Further, impurity can be introduced into areas for forming either of the semiconductor material parts  3  and  4  before machining the semiconductor layer, and then, impurity can be introduced into positions for forming the other of the semiconductor material parts  3  and  4  after machining the semiconductor layer. In this case, in the process of introducing the impurity after machining the semiconductor layer, the impurity can be introduced in addition to the areas where the impurity was introduced before the machining the semiconductor layer. Further, it is also possible to introduce the impurities at a time of forming the semiconductor layer. 
     In order to detect weak infrared rays with good sensitivity, a cavity part  6  is formed in the substrate  1  below the thermopile  5  and a heat insulating structure is formed. Junctions (where the first semiconductor material parts  3  and the second semiconductor material parts  4  are connected) in the thermopile  5  placed above the dielectric film  2  thermally separated from the substrate  1  by the cavity part  6  function as hot junctions. Junctions in the thermopile  5  above the substrate  1  where the cavity part  6  is absent function as cold junctions. 
     On the dielectric film  2 , interlayer dielectric films  7  (not shown in  FIG. 1A ) are formed to cover the thermopile  5 . On the interlayer dielectric films  7 , an infrared absorbing film  8  is formed at a position to cover the hot junctions of the thermopile  5  when viewed from the top. 
     As shown in  FIG. 1B , the infrared ray sensor has a configuration such that the substrate  1 , the dielectric film  2 , the semiconductor material parts  3  and  4 , the interlayer dielectric films  7  and the infrared absorbing film  8  are laminated. As the substrate  1 , a silicon substrate is usually used since a MEMS process of silicon is generally used for forming the heat insulating structure. 
     The dielectric film  2  is a silicon thermal oxide film, for example. The interlayer dielectric films  7  are, for example, plasma oxide films or CVD films of silicon. The infrared ray absorbing film  8  is formed of, for example, a silicon oxide film, a silicon nitride film, a gold black film or the like. However, the materials of these layers are not limited thereto in an embodiment of the present invention. 
     What is different from the infrared ray sensor shown in  FIGS. 11A and 11B  in the present embodiment is that connection between the first semiconductor material parts  3  and the second semiconductor material parts  4  are not carried out using conductive material parts other than the semiconductor material parts  3  and  4  but the semiconductor material parts  3  and  4  are directly connected. According to the present embodiment, the semiconductor material parts  3  and  4  have impurities that generate carriers having the same polarity (positive holes or electrons) introduced thereinto, and also, the impurity concentrations are adjusted so that the polarities of Seebeck coefficients of the semiconductor material parts  3  and  4  are the reverse of each other. Therefore, the semiconductor material parts  3  and  4  are made of semiconductor materials that have the same conductivity type. 
     For example, IEICE Technical Report, ED2009-197, SDM2009-194 (2010-2), pp. 5-9 (Non-patent Reference No. 1) and IEICE Technical Report, ED2010-194, SDM2010-229 (2011-2), pp. 13-17 (Non-patent Reference No. 2) disclose the relation between impurity concentration of phosphorus and Seebeck coefficient of silicon in a thin-film single crystal silicon layer (active layer) in a Silicon on Insulator (SOI) substrate. According to Non-patent References Nos. 1 and 2, the polarity of the Seebeck coefficient of silicon is inverted depending on the impurity concentration of phosphorus. 
     Returning to  FIGS. 1A and 10 , description of the infrared ray sensor will be continued. 
     One example of a base material of the semiconductor material parts  3  and  4  is polysilicon. Into the first semiconductor material parts  3 , phosphorus is introduced in such a manner that the impurity concentration on the order of 1×10 18  to 1×10 19  cm −3  is obtained. Into the second semiconductor material parts  4 , phosphorus having the impurity concentration on the order of 5×10 20  cm −3  which is the solid-solubility limit of phosphorus to silicon is introduced. 
     As another example, into the first semiconductor material parts  3 , boron is introduced in such a manner that the impurity concentration on the order of 1×10 18  to 1×10 19  cm −3  is obtained. Into the second semiconductor material parts  4 , boron having the impurity concentration on the order of 1×10 20  cm −3  which is the solid-solubility limit of boron to silicon is introduced. A basic material of the semiconductor material parts  3  and is polysilicon. 
     Note that a semiconductor material into which n-type impurity is introduced, for example, n-type polysilicon, has a resistance value lower than a semiconductor material into which p-type impurity is introduced, for example, p-type polysilicon. Therefore, by using, as the thermopile  5 , semiconductor material parts  3  and  4  into which n-type impurity is introduced, it is possible to improve the S/N ratio of the sensor. 
     As a specific method of introducing impurity, impurity is to be introduced into the semiconductor material parts  3  and  4  with appropriate concentrations by using a method such as ion implantation, surface diffusion or the like. For the semiconductor material parts  3  or the semiconductor material parts  4 , which have the higher impurity concentration, it is not necessary to introduce the impurity to the solid-solubility limit. Note that when using the semiconductor material parts  3  and  4  of n-type, both phosphorus and arsenic that are n-type impurities can be introduced. 
     Note that the materials, the types of impurities and the impurity concentrations of the semiconductor material parts  3  and  4  mentioned above are examples. What is necessary is that the semiconductor material parts  3  and  4  have impurities that generate carriers having the same conductivity type, and also, the impurity connections are adjusted so that the polarities of Seebeck coefficients of the semiconductor material parts  3  and  4  are the reverse of one another. The materials, the types of impurities and the impurity concentrations of the semiconductor material parts  3  and  4  are not limited to the embodiment in an embodiment of the present invention. Basic semiconductor materials of the semiconductor material parts  3  and  4  can be different from one another. 
     Note that in the infrared ray sensor in the related art in which the thermocouples using p-type polysilicon and n-type polysilicon are used as the thermopile, it is assumed that p-type polysilicon and n-type polysilicon are directly connected. In this case, a depletion layer is formed at a connection part between p-type polysilicon and n-type polysilicon. Therefore, in the infrared ray sensor in the related art, other conductive material parts are necessarily used to connect p-type polysilicon and n-type polysilicon so as to obtain ohmic contact therebetween (see  FIGS. 11A and 11B ). 
     In contrast thereto, according to the embodiment shown in  FIGS. 1A and 1B , the semiconductor material parts  3  and  4  included in the thermopile  5  are made of semiconductor materials having the same conductivity type. Therefore, when the semiconductor material parts  3  and  4  are directly connected, no depletion layer is generated, and therefore, it is not necessary to use other conductive material parts for connection between the semiconductor material parts  3  and  4 . 
     Thus, according to the present embodiment, other conductive material parts and contact parts required together for connecting the semiconductor material parts  3  and  4  are not needed. As a result, the layout restriction is eased. Accordingly, according to the present embodiment, in comparison to the infrared ray sensor in the related art of  FIGS. 11A and 11B , it is possible to increase the number of semiconductor material parts  3  and  4  (thermocouples) connected in series included in the thermopile  5 . As a result, it is possible to improve the sensitivity of the sensor. Further, according to the present embodiment, it is possible to form the thermopile having the same number of the series of stages in a reduced area. As a result, it is possible to reduce the area of the thin film part in the heat insulating structure, reduce the heat capacity and improve the response speed of the sensor. 
     Further, according to the present embodiment, the semiconductor material parts  3  and  4  are directly connected. Therefore, in comparison to the infrared ray sensor in the related art (see  FIGS. 11A and 11B ) in which the thermocouple material parts are connected by the other conductive material parts and the contact parts provided above the thermocouple material parts, it is possible to reduce the thickness of the interlayer dielectric films provided above the cavity part  6 . Thus, according to the present embodiment, it is possible to reduce the heat capacity of the sensor in comparison to the infrared ray sensor in the related art and improve the response speed of the sensor. 
       FIG. 2  is a schematic sectional view illustrating another embodiment. The plan view thereof is the same as that of  FIG. 1A . In  FIG. 2 , the same reference numerals are given to parts having the same functions as those shown in  FIGS. 1A and 1B . 
     In the embodiment shown in  FIGS. 1A and 1B , the cavity part  6  has a tapered shape (see  FIG. 1B ). However, according to the present embodiment of  FIG. 2 , the cavity part  6  is formed vertically with respect to the bottom surface of the substrate  1  without having a tapered shape. The shape of cavity part  6  shown in  FIG. 2  can be formed by anisotropic dry etching. The shape of the cavity part  6  shown in  FIG. 1B  can be formed by wet etching carried out to a single crystal silicon using an alkaline solution. Note that the shape of the cavity part  6  can be any shape. 
       FIGS. 3A and 3B  are schematic views illustrating yet another embodiment.  FIG. 3A  is a plan view and  FIG. 35  is a sectional view taken along a B-B′ line of  FIG. 3A . In  FIGS. 3A and 3B , the same reference numerals are given to parts having the same functions as those shown in  FIGS. 1A and 1B . 
     The present embodiment of  FIGS. 3A and 3B  is different in the heat insulating structure in comparison to the embodiment shown in  FIGS. 1A and 1B . The heat insulating structure in the present embodiment has four beam parts  17  sandwiched by four opening parts  16  formed to pass through the interlayer dielectric films  7  and the dielectric film  2 . The four beam parts  17  support the thin film part in which the hot junctions in the thermopile  5  are formed. The other parts are the same as those of  FIGS. 1A and 1B  and duplicate description will be omitted. 
     By providing such a beam shape, the heat insulation is improved and the sensitivity in the sensor can be improved. The shape shown in  FIGS. 3A and 3B  is one example. Other than the shape of  FIGS. 3A and 3B , it is possible to change the shapes and the number of the beam parts  17  by changing the shapes and the number of the opening parts  16 . Thus, an embodiment of the present invention is not limited to the above-mentioned shape. 
     In the structure shown in  FIGS. 3A and 3B , the cavity part  6  can be formed through the opening parts  16  using a wet etching process with an alkali etchant such as KOH, TMAH or the like. Note that also in the structures shown in  FIGS. 1A and 1B  and  FIG. 2 , it is possible to form beam parts by providing opening parts that pass through the interlayer dielectric films  7  and the dielectric film  2 . 
     Note that in the above-mentioned embodiment of  FIGS. 3A and 3B , the first semiconductor material parts  3  and the second semiconductor material parts  4  are formed in the same semiconductor layer. Further, in order to realize the high impurity concentration of the semiconductor material parts on the order of 10 20  cm −3 , mentioned above as an example, a long period of time is required when using ion implantation and throughput may be degraded. However, it is also possible to form the first semiconductor material parts  3  and the second semiconductor material parts  4  in the same semiconductor layer using photoengraving and ion implantation. 
     In order to realize high impurity concentrations in the semiconductor material parts, there is a case where using a surface diffusion method to introduce impurity is rather advantageous. In this case, impurity diffuses also laterally. Therefore, in order to separately form the first semiconductor material parts  3  and the second semiconductor material parts  4  in the same semiconductor layer using a surface diffusion method, it is necessary to provide some distances between the first semiconductor material parts  3  and the second semiconductor material parts  4 . Thereby, the required area for the thermopile  5  increases. 
     In contrast thereto, by forming the first semiconductor material parts  3  and the second semiconductor material parts  4  using mutually different layers of semiconductor materials, it is possible to reduce the required spaces between the first semiconductor material parts  3  and the second semiconductor material parts  4  even using a surface diffusion method for forming the first semiconductor material parts  3  or the second semiconductor material parts  4 . Using  FIGS. 4A and 4B , an embodiment will be described in which the first semiconductor material parts  3  and the second semiconductor material parts  4  are formed by using mutually different layers of semiconductor materials. 
       FIGS. 4A and 4B  are schematic views illustrating yet another embodiment.  FIG. 4A  is a plan view and  FIG. 4B  is a sectional view taken along a C-C′ line of  FIG. 4A .  FIG. 5  is a schematic sectional view showing a connection part between semiconductor material parts in the embodiment of  FIGS. 4A and 4B  in a magnified manner. In  FIGS. 4A and 4B  and  FIG. 5 , the same reference numerals are given to parts having the same functions as those shown in  FIGS. 1A and 1B . 
     First semiconductor material parts  3  and second semiconductor material parts  4  are formed by using mutually different layers of semiconductor materials. In hot junctions and cold junctions in a thermopile  5 , the second semiconductor material parts  4  in an upper layer are placed over the first semiconductor material parts  3  in a lower layer. According to the present embodiment, only the connection parts of the semiconductor material parts  3  and  4  overlap each other. However, positions at which the semiconductor material parts  3  and  4  overlap each other are not limited thereto in an embodiment of the present invention. 
     As shown in  FIG. 5 , the surface of the first semiconductor material part  3  is covered by the dielectric film  18  except for the connection part connected with the second semiconductor material part  4 . The first semiconductor material part  3  and the second semiconductor material part  4  are electrically connected with one another via an opening formed in the dielectric film  18 . 
     A specific method of forming the configuration is such that, first, a semiconductor layer for forming the first semiconductor material part  3  in a lower layer is formed. Then, the thus formed semiconductor layer is patterned and the first semiconductor material part  3  is formed. Further, thereon, the second semiconductor material part  4  in an upper layer is formed. The dielectric film  18  is, for example, a silicon oxide film such as BPSG, NSG, TEOS or the like formed by plasma CVD or the like. An actual thickness of the dielectric film  18  is not limited in an embodiment of the present invention. Further, the dielectric film  18  can be a laminated film made from a plurality of layers being laminated. 
     Further, when the first semiconductor material parts  3  in the lower layer is made of polysilicon, amorphous silicon or single crystal silicon, the dielectric film  18  can be formed by thermally oxidizing the surface of the first semiconductor material parts  3 . 
     Further, when the second semiconductor material parts  4  in the upper layer are formed, first, the dielectric film  18  is removed at the positions of the connection parts between the first semiconductor material parts  3  and the second semiconductor material parts  4 . Then, a semiconductor layer for forming the second semiconductor material parts  4  is formed, the thus formed semiconductor layer is patterned and thus the second semiconductor material parts  4  are formed. As a result, it is possible to obtain electrical connection between the first semiconductor material parts  3  and the second semiconductor material parts  4 . 
     Into the first semiconductor material parts  3  or the second semiconductor material parts  4 , impurity is introduced through a surface diffusion method. The process of thus introducing impurity in the surface diffusion method can be carried cut before the process of patterning the semiconductor layer or after the process of patterning the semiconductor layer. Further, when the process of introducing impurity is carried out by an ion implantation method, the process can be carried out before the process of patterning the semiconductor layer or after the process of patterning the semiconductor layer. Further, it is also possible to carry out the process of introducing impurity at the same time of forming the semiconductor layer. 
       FIGS. 6A and 6B  are schematic views illustrating yet another embodiment.  FIG. 6A  is a plan view and  FIG. 6B  is a sectional view taken along a D-D′ line of  FIG. 6A .  FIG. 7  is a schematic sectional view showing a connection part between semiconductor material parts in the embodiment of  FIGS. 6A and 6B . In  FIGS. 6A and 6B  and  FIG. 7 , the same reference numerals are given to parts having the same functions as those shown in  FIGS. 4A and 4B  and  FIG. 5 . 
     According to the present embodiment of  FIGS. 6A ,  6 B and  7 , the number of the series of stages of semiconductor material parts  3  and  4  of thermocouples in a thermopile  5  is further increased. According to the present embodiment, in almost all of the area, the first semiconductor material parts  3  and the second semiconductor material parts  4  are laminated together. Thereby, it is possible to obtain the number of the series of stages approximately double in comparison to the embodiment of  FIGS. 4A ,  4 B and  5 . Thus, it is possible to improve the sensitivity of the sensor. 
     The first semiconductor material parts  3  are covered by the dielectric films  18 . At the connection parts between the first semiconductor material parts  3  and the second semiconductor material parts  4 , the dielectric films  18  are removed. 
       FIGS. 8A ,  8 B,  8 C,  8 D and  8 E are schematic sectional views illustrating an example of processes of manufacturing the thermopile  5  according to the embodiment of  FIGS. 6A ,  6 B and  7 . 
     First, a semiconductor layer for forming a semiconductor material part  3  is formed on a dielectric film  2  formed on a substrate  1 . The semiconductor layer is, for example, made of polysilicon. The semiconductor layer is patterned and the first semiconductor material part  3  is formed as shown in  FIG. 8A . A process of introducing impurity into the first semiconductor material part  3  can be carried out before the semiconductor layer is patterned or after the semiconductor layer is patterned. 
     Then, as shown in  FIG. 8B , a dielectric film  18  is formed on the surface of the first semiconductor material part  3 . The dielectric film  18  is, for example, a silicon oxide film obtained from thermally oxidizing the surface of the first semiconductor material part  3 . However, in an embodiment of the present invention, the dielectric film  18  is not limited thereto and can be a silicon oxide film made of BPSG, NSG, TEOS or the like formed by plasma CVD or the like. In this case, the dielectric film  18  is formed also on the dielectric film  2 . Further, the dielectric film  18  can be another type of a dielectric film or can be a laminated film obtained from laminating a plurality of films. 
     Then, as shown in  FIG. 8C , the dielectric film  18  is removed at positions where the semiconductor material parts  3  and  4  are mutually connected (to be connection parts therebetween). 
     Then, as shown in  FIG. 8D , a semiconductor layer  4   a  for forming the second semiconductor material part  4  is formed. The semiconductor layer  4   a  is, for example, made of polysilicon. 
     Then, as shown in  FIG. 6E , the semiconductor layer  4   a  is patterned and the second semiconductor material part  4  is formed. Thereby, a thermopile  5  is formed. A process of introducing impurity into the second semiconductor material part  4  can be carried out before the semiconductor layer  4   a  is patterned or after the semiconductor layer  4   a  is patterned. Thereafter, interlayer dielectric films  7  and an infrared absorbing film  8  are formed. Then, finally, a cavity part  6  is formed (see  FIGS. 6A ,  6 B and  7 ). Note that a timing of forming the cavity part  6  is not limited to a timing after the infrared absorbing film  8  is formed and can be any timing in an embodiment of the present invention. 
       FIG. 9  is a schematic sectional view illustrating yet another embodiment. In  FIG. 9 , the same reference numerals are given to parts having the same functions as those shown in  FIGS. 4A and 4B  and  FIG. 5 . 
     In the present embodiment of  FIG. 9 , as shown, a sensor part  19  including thermopiles  5  and a peripheral circuit part  20  are formed in a monolithic manner. Further, the thermopiles  5  including semiconductor material parts  3  and  4  made of polysilicon and a Polysilicon Insulator Polysilicon (PIP) capacitor  22  in the peripheral circuit part  20  are formed simultaneously by a common process. 
     In the periphery of the sensor part  19 , the peripheral circuit part  20  is formed. The peripheral circuit part  20  generally includes a MOSFET part  21  and the PIP capacitor  22 , as shown in  FIG. 9 . The PIP capacitor  22  has a structure of two layers made of polysilicon and is a device usually used in a CMOS process. 
     Further, the gate electrode in the MOSFET part  21  and the second semiconductor material part  4  are formed by the same semiconductor layer. However, the gate electrode in the MOSFET part  21  can be formed by the same semiconductor layer by which the first semiconductor material part  3  is formed. 
     According to the embodiment described above using  FIGS. 4A ,  4 B and  5  and the embodiment described above using  FIGS. 6A ,  6 B and  7 , in each thermopile  5 , the semiconductor material parts  3  and  4  are formed by mutually different layers of polysilicon, and thus, the structure is similar to the PIP capacitor  22 . Therefore, when the sensor part  19  and the peripheral circuit part  20  are formed in a monolithic manner, it is possible to form the PIP capacitor  22  and the thermopiles  5  using a common process of polysilicon. As to a detailed process, since the process is the same or similar to the process described above using  FIGS. 8A-8E , duplicate explanation will be omitted. 
     Further, in the peripheral circuit part  20 , a plurality of interconnection layers are usually used. Therefore, the thickness of the interlayer dielectric films  7  increases. Therefore, in the sensor part  19 , in order to improve the response speed of the sensor, it is preferable to remove unnecessary parts of the interlayer dielectric films  7  by etching so as to reduce the thickness of the thin film part positioned above the cavity part  6 . 
     Further, although an infrared absorbing film  8  can be separately formed, it is also possible to use an interlayer dielectric film(s)  7 , a passivation film or the like for substitution. Thereby, it is not necessary to use a special material such as gold black, and thus, it is possible to improve affinity with a usual CMOS process. 
       FIG. 10  is a schematic plan view illustrating yet another embodiment. In  FIG. 10 , the same reference numerals are given to parts having the same functions as those shown in  FIG. 9 . 
     According to the present embodiment of  FIG. 10 , sensor parts  19  of thermopile-type infrared ray sensors described above are used as an array sensor. Each sensor part  19  is used as one pixel in an array sensor. 
     In the present embodiment of  FIG. 10 , a thin film part surrounded by an opening part  16  is supported by a beam part  17 . On the thin film part, a thermopile  5  is formed. A shape and/or an arrangement of the beam part  17  and a shape, an area and/or the like of the thin film part depend on the use of the sensor and/or the specification, and therefore, are not limited to those shown in  FIG. 10  in an embodiment of the present invention. 
     As one example, each thermopile  5  has such a structure that semiconductor material parts  3  and  4  are laminated (see  FIG. 7 ). The outputs of the respective pixels are selected by row selection lines  23  and column selection lines  24 , are transmitted to a signal processing circuit (not shown) and are processed. 
     By using the thermopiles in each of which the semiconductor material parts  3  and  4  are laminated according to the present embodiment, it is possible to form more thermocouples on each beam part  17  having a limited width. Thus, it is possible to Improve the pixel sensitivity of the array sensor. 
       FIGS. 13A ,  13 B and  13 C are schematic views illustrating yet another embodiment.  FIG. 13A  is a plan view,  FIG. 13B  is a sectional view taken along an E-E′ line of  FIG. 13A  and  FIG. 13C  is a sectional view taken along an F-F′ line of  FIG. 13A . In  FIGS. 13A-13C , the same reference numerals are given to parts having the same functions as those shown in  FIGS. 1A and 1B . 
     In the embodiment of  FIGS. 13A-13C , on a substrate  1 , a thermopile  5  is formed that includes first semiconductor material parts  31  and second semiconductor material parts  32  that are laminated. At ends of each pair of the semiconductor material parts  31  and  32 , contact holes  33  are formed for obtaining electric connection. Via the contact holes  33  and conductive material parts  34 , the first semiconductor material part  31  and the second semiconductor material part  32  included in the thermopile  5  are electrically connected. 
     The first semiconductor material parts  31  are, for example, made of n-type polysilicon. The second semiconductor material parts  32  are, for example, made of p-type polysilicon. A pair of the first semiconductor material part  31  and the second semiconductor material part  32  are connected and a thermocouple is obtained. A plurality of the thermocouples are connected in series via the contact holes  33  and the conductive material parts  34 , and the thermopile  5  is formed. 
     In the thermopile  5 , each pair of the first semiconductor material part  31  and the second semiconductor material part  32  can be made by using materials of different types having Seebeck coefficients with different polarities. For example, it is usual to use a pair of n-type polysilicon and p-type polysilicon that are usually used in a CMOS process. A material usually used in a CMOS process, for example, can be used as a conductive material embedded in the contact holes  33  and the conductive material parts  34  used for interconnections. Specifically, aluminum can be used, for example. 
     Further, in order to detect weak infrared rays with good sensitivity, a cavity part  6  is formed below the thermopile  5  and a heat insulating structure is formed. Junctions in the thermopile  5  provided on a thin film part thermally insulted by the cavity part  6  function as hot junctions, while junctions in the thermopile  5  provided on a substrate  1  where the cavity part  6  is absent function as cold junctions. 
     An infrared absorbing film  8  is formed to cover the hot junctions of the thermopile  5 . When infrared rays are absorbed by the infrared absorbing film  8  and the thin film part is heated, temperature difference occurs between the hot junctions and the cold junctions, and thus, a thermoelectromotive force is generated in the thermopile  5 . 
     The layer structure in the embodiment of  FIGS. 13A-13C  is such that, on the dielectric film  2  formed on the substrate  1 , the first semiconductor material parts  31 , the second semiconductor material parts  32 , the contact holes  33 , the conductive material parts  34 , respective layers of interlayer dielectric films  7  and the infrared absorbing film  8  are arranged. 
     Specific examples of materials of the respective layers will now be described. As the substrate  1 , since a MEMS process of silicon is used for forming the heat insulating structure, a silicon substrate is usually used. The dielectric film  2  is usually made of a thermal oxide film of silicon. The interlayer dielectric films  7  are made of, usually, plasma oxide films or CVD films of silicon. The infrared absorbing film  8  is made of a silicon oxide film, a silicon nitride film, a gold black film or the like. 
     Below the thermopile  5 , the cavity part  6  is formed, and thereby, heat insulation for the hot junctions in the thermopile  5  is improved. In  FIGS. 13A-13C , the cavity part  6  having a tapered shape is formed. However, the cavity part  6  can be formed vertically with respect to the substrate  1  without having a tapered shape. Further, although the cavity part  6  passes through the substrate  1  in  FIGS. 13B and 13C , an embodiment is not limited thereto as long as a space is formed so that heat insulation is obtained between the hot junctions in the thermopile  5  and the substrate  1  in an embodiment of the present invention. 
     As shown in  FIGS. 13B and 13C , in the thermopile  5  according to the present embodiment, the first semiconductor material part  31  and the second semiconductor material part  32  are laminated. 
       FIG. 14  is a schematic view showing a part enclosed by an alternating long and short dashed line in  FIG. 13B  in a magnified manner.  FIG. 15  is a schematic view showing a part enclosed by an alternating long and short dashed line in  FIG. 13C  in a magnified manner. 
     The first semiconductor material part  31  and the second semiconductor material part  32  are formed to have a laminated shape. The first semiconductor material part  31  and the second semiconductor material part  32  are formed in such a manner that, for example, side faces of these parts  31  and  32  along the longitudinal directions of these parts  31  and  32  are patterned simultaneously. Between the first semiconductor material part  31  and the second semiconductor material part  32 , an interlayer dielectric film  35  is formed. The interlayer dielectric films  35  is formed to be very thin. 
     A specific method of forming the interlayer dielectric films  35  is such that, for example, a thermal oxide film of the first semiconductor material part  31  or the like can be used. Alternatively, it is also possible to deposit, on the surface of the first semiconductor material part  31 , a plasma oxide film or a CVD oxide film of silicon to form a thin film. Especially, when polysilicon is used as a material of the first semiconductor material part  31 , it is advantageous from a viewpoint of forming a thin film and also advantageous from a viewpoint of improving the film quality to use a thermal oxide film of the first semiconductor material part  31  as the interlayer dielectric films  35 . 
     Further, the first semiconductor material part  31  as a lower layer is formed to be longer than the second semiconductor material part  32  as an upper layer. This is for the purpose of forming contact holes  33  for obtaining electric connections at the both ends of the first semiconductor material part  31  and the second semiconductor material part  32 , respectively. 
     Although details of the forming process will be described later, one feature of the infrared ray sensor according to the present embodiment is that side surfaces of the first semiconductor material part  31  and the second semiconductor material part  32  along their longitudinal directions are simultaneously formed by patterning. As a result of these parts  31  and  32  being formed by this process, as shown in  FIG. 15 , the side surfaces of the first semiconductor material parts  31  and the side surfaces of the second semiconductor material parts  32  along their longitudinal directions are formed on the same planes, respectively. 
     The infrared ray sensor according to the present embodiment uses the thermocouples in which the first semiconductor material parts  31  and the second semiconductor material parts  32  are laminated. Thereby, it is possible to increase the number of pairs (thermocouples) per unit area in the thermopile  5 . 
     Further, in the infrared ray sensor according to the present embodiment, the thermal oxide film of the first semiconductor material part  31  is provided as the interlayer dielectric film  35  between the first semiconductor material part  31  and the second semiconductor material part  32 . Therefore, in comparison to a case of using an interlayer dielectric film other than a thermal oxide film, it is possible to reduce the thickness of the interlayer dielectric film  35 . Thereby, it is possible to reduce the heat capacity of the infrared ray sensor according to the present embodiment and it is possible to improve the response characteristics of the sensor. 
     Further, in the infrared ray sensor according to the present embodiment, the side faces of the first semiconductor material parts  31  and the second semiconductor material parts  32  along their longitudinal directions are formed on the same planes, respectively. Therefore, for example, in comparison to a case where a width of a first semiconductor material part is formed larger than a width of a second semiconductor material part, it is possible to reduce the width of the thermocouple including the first semiconductor material part  31  and the second semiconductor material part  32  according to the present embodiment. As a result, in the infrared ray sensor according to the present embodiment, it is possible to increase the number of pairs (the number of thermocouples) per unit area in the thermopile  5 . 
       FIGS. 16A ,  16 B,  16 C,  16 D,  16 E,  16 F and  16 G are schematic sectional views illustrating one example of processes of manufacturing the thermopile  5  according to the embodiment of  FIGS. 13A ,  13 B and  13 C. The sections shown in  FIGS. 16A-16G  are taken along the line E-E′ in  FIG. 13A .  FIG. 17A  is a schematic plan view corresponding to the schematic sectional view of  FIG. 16B .  FIG. 17B  is a schematic plan view corresponding to the schematic sectional view of  FIG. 16D .  FIG. 17C  is a schematic plan view corresponding to the schematic sectional view of  FIG. 16E .  FIG. 17D  is a schematic plan view corresponding to the schematic sectional view of  FIG. 16G . 
     As shown in  FIG. 16A , a first semiconductor material is deposited on a dielectric film  2  formed on a substrate  1 . A process of appropriately introducing impurity to the first semiconductor material part  31  is carried out. A specific method of the process of introducing impurity is a method of using, for example, ion implantation, surface diffusion or the like. 
     As shown in  FIGS. 16B and 17A , the first semiconductor material part  31  is patterned in such a manner that approximately an area for finally forming a thermopile  5  is left. This process of patterning includes a series of processes including a process of forming an etching mask made of resist through photolithography using resist; a process of carrying out etching using the thus formed etching mask; and a process of removing the etching mask. Note that the etching mask can be one formed by a method other than photolithography, such as a mask pattern formed by electron beam lithography or an imprint method. 
     Next, an interlayer dielectric film  35  (omitted in  FIGS. 17A-17D ) is formed. The interlayer dielectric film  35  is formed by, for example, a thermal oxide film of the first semiconductor material part  31 . However, a material of the interlayer dielectric film  35  is not limited thereto in an embodiment of the present invention. For example, an interlayer dielectric film  35  can be formed by depositing a thin plasma oxide film or CVD oxide film of silicon on the first semiconductor material part  31  or on the thermal oxide film of the first semiconductor material part  31 . A material of the interlayer dielectric film  35  is not particularly limited as long as the material is such a material and has such a thickness as to be able to electrically insulate the first semiconductor material part  31  and a second semiconductor material part  32  that is formed in a subsequent process. Since a high voltage is not applied to a thermopile  5 , it is preferable that a thickness of the interlayer dielectric film  35  is a minimum thickness only for preventing the first semiconductor material part  31  as a lower layer and the second semiconductor material part  32  as an upper layer from being short circuited. 
     Then, as shown in  FIG. 16C , the second semiconductor material part  32  is deposited. A process of appropriately introducing impurity to the second semiconductor material part  32  is carried out. A specific method of the process of introducing impurity is a method of using, for example, ion implantation, surface diffusion or the like. 
     As shown in  FIGS. 16D and 17B , the second semiconductor material part  32  is patterned in such a manner that the approximate areas for finally forming the second semiconductor material parts  32  are left. Note that the sizes of the respective second semiconductor material parts  32  and the positions of the end faces along the longitudinal directions of the respective second semiconductor material parts  32  shown in  FIGS. 13A-13C  are defined in this patterning process. 
     Etching is carried out simultaneously on the laminated structure of the first semiconductor material part  31 , the interlayer dielectric film  35  and the second semiconductor material parts  32 . Thereby, the final shapes of the first semiconductor material parts  31 , the interlayer dielectric films  35  and the second semiconductor material parts  32  are formed as shown in  FIGS. 16E and 17C . 
     An interlayer dielectric film  7   a  is formed to be provided between thermocouples including the first semiconductor material parts  31 , the interlayer dielectric films  35  and the second semiconductor material parts  32 , and the an interconnection layer that is formed subsequently. Then, contact holes  33  are formed in the thus formed interlayer dielectric film  7   a  as shown in  FIG. 16F . Note that the interlayer dielectric film  7   a  corresponds to a partial layer of the interlayer dielectric films  7  shown in  FIGS. 13B and 13C . 
     A conductive material is deposited and is patterned to have a desired pattern shape of the conductive material parts  34  as shown in  FIGS. 16G and 17D . Thus, a thermopile  5  is formed. 
     Using  FIGS. 13A-13C , processes to be carried out thereafter will now be described. A passivation film for surface protection is formed, forming of the interlayer dielectric films  7  is completed, and thereafter, an infrared absorbing film  8 , a cavity part  6  and so forth are formed. Thus, an infrared ray sensor of a thermocouple type is completed. 
     According to this manufacturing method as one embodiment, a thermopile  5  of a laminated type is formed by using a process of etching first semiconductor material parts  31  and second semiconductor material parts  32  formed in different layers in batch. Assuming a process of patterning first semiconductor material parts and second semiconductor material parts separately, there is a case where a process of planarizing interlayer dielectric films between the first and second semiconductor material parts is required. In contrast thereto, in the above-mentioned manufacturing method according to the embodiment described above using  FIGS. 13A-13C ,  16 A- 16 G and  17 A- 17 D, such a planarizing process is not needed, and a thermopile  5  of a laminated type is formed that has very thin interlayer dielectric films  35  between the first semiconductor material parts  31  and the second semiconductor material parts  32 . Therefore, it is possible to improve the response speed of the sensor according to the manufacturing method of the embodiment. 
     The above-mentioned manufacturing method according to the embodiment includes the process shown in  FIG. 16B  of patterning the first semiconductor material part  31  before the process shown in  FIG. 16C  of forming the second semiconductor material part  32 . However, an embodiment of a method of manufacturing an infrared ray sensor according to the present invention is not limited thereto. It is also possible that a process of patterning a first semiconductor material part is not included before forming a second semiconductor material part. 
       FIG. 18  is a schematic sectional view illustrating yet another embodiment. In  FIG. 18 , the same reference numerals are given to parts having the same functions as those shown in FIGS.  9  and  13 A- 13 C. 
     According to the present embodiment of  FIG. 18 , a sensor part  19  including thermopiles  5  and a peripheral circuit part  20  are formed in a monolithic manner. The peripheral circuit part  20  is formed by, for example, a CMOS process. The peripheral circuit part  20  includes, for example, a MOSFET part  21  and a PIP capacitor  22 . The PIP capacitor  22  is a capacitative element in which a lower electrode and an upper electrode are formed by polysilicon. 
     When the sensor part  19  and the peripheral circuit part  20  are formed in a monolithic manner, it is necessary to simplify the process. That is, it is preferable that the first semiconductor material parts  31  in the thermopile  5  and the lower electrode of the PIP capacitor  22  are formed by common polysilicon. Further, it is preferable that the second semiconductor material parts  32  in the thermopile  5  and the upper electrode of the PIP capacitor  22  are formed by common polysilicon. Further, it is preferable that the first semiconductor material parts  31  or the second semiconductor material parts  32  and a polysilicon gate electrode of the MOSFET part  21  are formed by common polysilicon. 
     Thus, both of the first semiconductor material parts  31  and the second semiconductor material parts  32  in the infrared ray sensor can be formed by a process that is common with a CMOS process. Therefore, the infrared ray sensor has very high affinity with a CMOS process and it is possible to simplify the process. 
     Further, the peripheral circuit part  20  is usually formed of a plurality of layers. Thus, the interlayer dielectric films  7  become thicker. Therefore, it is preferable that in the sensor part  19 , in order to improve the response speed of the sensor, unnecessary parts of the interlayer dielectric films  7  are removed by etching so that the thickness of the thin film part placed above the cavity part  6  is reduced. 
     Further, although an infrared absorbing film  8  can be separately formed, it is also possible to substitute an interlayer dielectric film  7 , a passivation film or the like for the infrared absorbing film  8 . Thereby, it is not possible to use a special material such as gold black or the like, and thus, affinity with a usual CMOS process can be further improved. 
     According to the embodiment of the infrared ray sensor and the embodiment of the manufacturing method described above using  FIGS. 13A-17D , the first semiconductor material parts  31  are made of n-type polysilicon and the second semiconductor material parts  32  are made of p-type polysilicon. However, specific materials of the first semiconductor material parts  31  and the second semiconductor material parts  32  are not limited thereto in an embodiment of the present invention. It is also possible that first semiconductor material parts  31  are made of p-type polysilicon and second semiconductor material parts  32  made of n-type polysilicon. 
     Further, the first semiconductor material parts  31  and the second semiconductor material parts  32  can be ones into which impurities that generate carriers of the same polarity are introduced with mutually different concentrations, and also, the polarities of Seebeck coefficients thereof can be the reverse of one another. The first semiconductor material parts  31  and the second semiconductor material parts  32  can be formed by the same materials as those of the semiconductor material parts  3  and  4  in the embodiment described above using  FIGS. 1A and 1B . 
     Further, the infrared ray sensor according to the embodiment described above using  FIGS. 13A-13C  and so forth can be applied to a configuration in which a plurality of thermopiles  5  are placed to form an array the same as or similar to the embodiment described above using  FIG. 10 , for example. 
     Thus, the embodiments of the present invention have been described. However, the specific numerical values, materials arrangements, numbers and so forth are examples, embodiments of the present invention are not limited thereto, and variations and modifications may be made without departing from the scope of the present invention. 
     For example, in thermocouples and infrared ray sensors according to embodiments of the present invention, base materials of first semiconductor material parts and second semiconductor material parts are not limited to polysilicon. It is preferable that first semiconductor material parts and second semiconductor material parts are ones into which impurities that generate carriers of the same polarity are introduced with mutually different concentrations, and also, polarities of Seebeck coefficients thereof are the reverse of one another. For example, basic materials of the first semiconductor material part and the second semiconductor material parts can be semiconductor materials other than silicon-based semiconductor materials such as single crystal silicon, amorphous silicon and so forth. 
     Further, in the above-mentioned embodiments, the thermocouples are applied to the thermopiles. However, thermocouples according to embodiments of the present invention are not limited thereto, and can be used for purposes other than thermopiles. 
     Further, in the above-mentioned embodiments, the thermocouples are connected in series in the thermopiles. However, thermopiles according to embodiments of the present invention are not limited thereto, and can be those in which a plurality of thermocouples are connected in parallel. 
     Further, in the above-mentioned embodiments, the infrared ray sensors have the cavity parts. However, infrared ray sensors according to embodiments of the present invention are not limited thereto, and an infrared ray sensor according to an embodiment of the present invention can be one in which a thermopile is provided in which a plurality of thermocouples are connected in series. 
     Thus, the thermocouples, thermopiles and inferred ray sensors have been described in the embodiment. However, the present invention is not limited to the specifically disclosed embodiment and variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on and claims the benefit of priority of Japanese Priority Application No. 2013-192685, dated Sep. 18, 2013, the entire contents of which are hereby incorporated herein by reference.