Patent Publication Number: US-2021190601-A1

Title: Thermal sensor and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 108147398, filed on Dec. 24, 2019. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a thermal sensor and a manufacturing method thereof. 
     Description of Related Art 
     Generally, a common thermal sensor is formed by a transistor and a thermal sensing device electrically connected to the transistor. The thermal sensing device generally includes a thermal absorbing layer and a thermal reflective layer disposed underneath. After the thermal absorbing layer absorbs heat, a signal may be transmitted to the transistor electrically connected thereto. For the heat that passes through the thermal absorbing layer without being absorbed, the thermal reflective layer may reflect the heat back to the thermal absorbing layer to achieve the object of maximum thermal absorbing efficiency. 
     In the current manufacturing process, usually after a structure such as a transistor or an interconnect is formed, the thermal sensing device is formed above the structure. In this way, the overall structure has a considerable thickness, which is not conducive to the thinning trend in the industry. In addition, for the material selection of the thermal absorbing layer, it is preferable to select a doped semiconductor material having a higher seebeck coefficient. However, when implanting a dopant into a semiconductor material, a high-temperature heat treatment may be required to diffuse the dopant, thereby causing damage to a previously formed metal member (such as a wire, a connecting element, a metal heat-reflective layer, etc.) In addition, in the case in which a doped region is used as the thermal reflective layer of the thermal sensing device, the issue of poor reflection efficiency due to excessive diffusion of a dopant in the doped region from the high-temperature heat treatment also occurs. 
     SUMMARY OF THE INVENTION 
     The invention provides a thermal sensor having a metal silicide reflective layer. 
     The invention provides a manufacturing method of a thermal sensor used for manufacturing the thermal sensor. 
     The thermal sensor of the invention includes a transistor and a thermal sensing device. The thermal sensing device is disposed in a recess in a substrate and electrically connected to the transistor. The thermal sensing device includes a first dielectric layer, a metal silicide reflective layer, a second dielectric layer, and a thermal absorbing layer. The first dielectric layer is disposed on sidewalls and a bottom of the recess. The metal silicide reflective layer is disposed on the first dielectric layer located on the bottom of the recess. The second dielectric layer is disposed at a top of the recess. The thermal absorbing layer is disposed on the second dielectric layer. 
     In an embodiment of the thermal sensor of the invention, the transistor is horizontally adjacent to the thermal sensing device. 
     In an embodiment of the thermal sensor of the invention, a material of the metal silicide reflective layer is, for example, tungsten silicide, titanium silicide, aluminum silicide, nickel silicide, or a combination thereof. 
     In an embodiment of the thermal sensor of the invention, the metal silicide reflective layer is further disposed on the first dielectric layer located on the sidewalls of the recess. 
     In an embodiment of the thermal sensor of the invention, the thermal absorbing layer is, for example, a P-type silicon-doped layer, an N-type silicon-doped layer, or a combination thereof. 
     In an embodiment of the thermal sensor of the invention, the P-type silicon-doped layer and the N-type silicon-doped layer are, for example, disposed on the second dielectric layer and adjacent to each other. 
     The manufacturing method of a thermal sensor of the invention includes the following steps. A recess is formed in a substrate. A first dielectric layer is formed on sidewalls and a bottom of the recess. A metal silicide reflective layer is formed on the first dielectric layer located on the bottom of the recess. A second dielectric layer is formed at a top of the recess. A thermal absorbing layer is formed on the second dielectric layer. A transistor is formed on the substrate, wherein the transistor is electrically connected to the thermal absorbing layer. 
     In an embodiment of the manufacturing method of the thermal sensor of the invention, a material of the metal silicide reflective layer is, for example, tungsten silicide, titanium silicide, aluminum silicide, nickel silicide, or a combination thereof. 
     In an embodiment of the manufacturing method of the thermal sensor of the invention, the metal silicide reflective layer is further formed on the first dielectric layer located on the sidewalls of the recess. 
     In an embodiment of the manufacturing method of the thermal sensor of the invention, the thermal absorbing layer is, for example, a P-type silicon-doped layer, an N-type silicon-doped layer, or a combination thereof. 
     In an embodiment of the manufacturing method of the thermal sensor of the invention, the P-type silicon-doped layer and the N-type silicon-doped layer are, for example, disposed on the second dielectric layer and adjacent to each other. 
     In an embodiment of the manufacturing method of the thermal sensor of the invention, a method of forming the second dielectric layer at the top of the recess includes the following steps. A sacrificial layer is filled in the recess after the metal silicide reflective layer is formed. The second dielectric layer is formed on the sacrificial layer. The sacrificial layer is removed. 
     Based on the above, in the invention, before the transistor and other metal members are formed, the thermal sensing device is formed in the recess in the substrate, so that the transistor and other metal members may be prevented from being subjected to the influence from the high-temperature heat treatment during the manufacture of the thermal sensing device. In addition, in the thermal sensing device, a metal silicide reflective layer is used as the thermal reflective layer having a thermal reflectivity similar to that of a metal reflective layer, and is not readily damaged in the subsequent high-temperature heat treatment. 
     In order to make the aforementioned features and advantages of the disclosure more comprehensible, embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1A  to  FIG. 1C  are cross-sectional views of a manufacturing process of a thermal sensor shown according to an embodiment of the invention. 
         FIG. 2  is a cross-sectional view of a thermal sensor shown according to another embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1A  to  FIG. 1C  are cross-sectional views of a manufacturing process of a thermal sensor shown according to an embodiment of the invention. First, referring to  FIG. 1A , a substrate  100  is provided. The substrate  100  is a semiconductor substrate such as a silicon substrate. Next, a recess  102  is formed in the substrate  100 . A forming method of the recess  102  includes, for example, performing a patterning process. In the present embodiment, the size of the recess  102  is not limited as long as the recess  102  does not penetrate the substrate  100 . The width and depth of the recess  102  depend on the functional requirements of the thermal sensing device to be formed. Then, a first dielectric layer  104  is formed on the sidewalls and the bottom of the recess  102 . In the present embodiment, the first dielectric layer  104  is, for example, an oxide layer. A forming method of the first dielectric layer  104  includes, for example, performing a chemical vapor deposition process or a thermal oxidation process. 
     Then, referring to  FIG. 1B , a metal silicide reflective layer  106  is formed on the first dielectric layer  104  located on the bottom of the recess  102 . The material of the metal silicide reflective layer  106  is, for example, tungsten silicide, titanium silicide, aluminum silicide, nickel silicide, or a combination thereof. The forming method of the metal silicide reflective layer  106  includes, for example, performing a chemical vapor deposition process to form a metal silicide material layer on the first dielectric layer  104 , and then performing a patterning process to remove the metal silicide material layer on the sidewalls of the recess  102  and outside the recess  102 . The thickness of the metal silicide reflective layer  106  may be designed according to requirements, and the invention is not limited in this regard. In the present embodiment, the metal silicide reflective layer  106  is located on the entire bottom of the recess  102 , but the invention is not limited thereto. In other embodiments, depending on the functional requirements of the thermal sensing device to be formed, the metal silicide reflective layer  106  may be located only on a portion of the bottom of the recess  102 . In addition, in the present embodiment, the metal silicide reflective layer  106  is a single-layer structure, but the invention is not limited thereto. In other embodiments, depending on the functional requirements of the thermal sensing device to be formed, the metal silicide reflective layer  106  may be a multilayer structure. 
     Then, a sacrificial layer  108  is filled in the recess  102 . The material of the sacrificial layer  108  is, for example, titanium silicide, aluminum silicide, nickel silicide, or a combination thereof, but the invention is not limited thereto. In the present embodiment, the sacrificial layer  108  completely fills the recess  102 , but the invention is not limited thereto. In other embodiments, the sacrificial layer  108  may not completely fill the recess  102 , or the top surface of the sacrificial layer  108  may be slightly higher than the top of the recess  102  (i.e., slightly higher than the top surface of the first dielectric layer  104  on the surface of the substrate  100  outside the recess  102 ). 
     Then, referring to  FIG. 1C , a second dielectric layer  110  is formed on the sacrificial layer  108  (refer to  FIG. 1B ). In the present embodiment, the second dielectric layer  110  is, for example, an oxide layer. The forming method of the second dielectric layer  110  includes, for example, performing a chemical vapor deposition process to form a dielectric material layer on the sacrificial layer  108  and on the first dielectric layer  104  outside the recess  102 , and then performing a patterning process to remove at least a portion of the dielectric material layer on the first dielectric layer  104  outside the recess  102 . In this way, the second dielectric layer  110  is located at least above the entire recess  102  and may be extended onto the first dielectric layer  104  outside the recess  102  according to actual requirements. 
     Next, a thermal absorbing layer  114  is formed on the second dielectric layer  110 . In the present embodiment, the thermal absorbing layer  114  includes a P-type silicon-doped layer  114   a  and an N-type silicon-doped layer  114   b  respectively located on the second dielectric layer  110  and adjacent to each other, but the invention is not limited thereto. In other embodiments, the thermal absorbing layer  114  may be the P-type silicon-doped layer  114   a , the N-type silicon-doped layer  114   b , or other suitable thermal absorbing material layers. In particular, when the thermal absorbing layer  114  is the P-type silicon-doped layer  114   a , the N-type silicon-doped layer  114   b , or a combination thereof, during the process of forming the thermal absorbing layer  114 , a high-temperature heat treatment is needed to diffuse a dopant after the dopant is implanted. Since the metal silicide reflective layer  106  may withstand a higher temperature, the metal silicide reflective layer  106  is not damaged. In other words, since the metal silicide reflective layer  106  is not readily damaged by the high-temperature heat treatment, the P-type silicon-doped layer  114   a  and/or the N-type silicon-doped layer  114   b  having a higher seebeck coefficient may be used as the thermal absorbing layer  114 , so that the thermal sensor of the present embodiment has better performance. 
     Then, the sacrificial layer  108  is removed. The method of removing the sacrificial layer  108  is known to those skilled in the art, and is not repeated herein. After the sacrificial layer  108  is removed, the first dielectric layer  104  located on the sidewalls and the bottom of the recess  102  and at the second dielectric layer  110  located at the top of the recess  102  form a cavity  112 . The object of the cavity  112  is to prevent the heat penetrating the thermal absorbing layer  114  from being dissipated due to contact thermal conduction, and the cavity  112  may be designed to match the wavelength to be reflected to achieve the effect of increasing reflection efficiency. In this way, a thermal sensing device  115  of the present embodiment is formed. 
     Next, the first dielectric layer  104  outside the recess  102  is removed to expose the surface of the substrate  100 . Then, a transistor  116  electrically connected to the thermal sensing device  115  is formed on the substrate  100  to form a thermal sensor  10  of the present embodiment. In the present embodiment, the transistor  116  includes a gate dielectric layer  116   a  and a gate  116   b  sequentially disposed on the substrate  100  and a source/drain region  116   c  located in the substrate  100  on two sides of the gate  116   b . The forming method of the transistor  116  is known to those skilled in the art and is not repeated herein. In the present embodiment, the transistor  116  may be horizontally adjacent to the thermal sensing device  115 , but the invention is not limited thereto. 
     In the present embodiment, since the transistor  116  is formed only after the thermal sensing device  115  is formed, the transistor  116  and other metal members formed subsequently are not damaged by the influence from the high-temperature heat treatment when the thermal absorbing layer  114  is formed. In other words, since the transistor  116  and other metal members formed subsequently are not damaged by the influence from the high-temperature heat treatment, the P-type silicon-doped layer  114   a  and/or the N-type silicon-doped layer  114   b  having a higher seebeck coefficient may be used as the thermal absorbing layer  114 , so that the thermal sensor of the present embodiment has better performance. 
     In addition, in the present embodiment, the material of the metal silicide reflective layer  106  may be matched with the transistor  116  subsequently formed and other members subsequently formed, so the issue of mutual contamination between a front-end process and a rear-end process does not occur. For example, if a metal reflective layer is used, when the metal silicide layer in the transistor is subsequently formed, the metal silicide may be formed at the metal reflective layer. Alternatively, the metal forming the metal reflective layer may be formed in other regions and affect the subsequently formed elements. 
     The thermal sensor  10  in  FIG. 1C  is taken as an example to describe the thermal sensor of the invention. 
     Referring to  FIG. 1C , the thermal sensor  10  includes a thermal sensing device  115  and a transistor  116 . The thermal sensing device  115  is disposed in the recess  102  in the substrate  100  and is electrically connected to the transistor  116 . The thermal sensing device  115  includes the first dielectric layer  104 , the metal silicide reflective layer  106 , the second dielectric layer  110 , and the thermal absorbing layer  114 . The first dielectric layer  104  is disposed on the sidewalls and the bottom of the recess  102 . The metal silicide reflective layer  106  is disposed on the first dielectric layer  104  located on the bottom of the recess  102 . The second dielectric layer  110  is disposed at the top of the recess  102  and forms the cavity  112  with the first dielectric layer  104 . The thermal absorbing layer  114  is disposed on the second dielectric layer  110  and includes the P-type silicon-doped layer  114   a  and the N-type silicon-doped layer  114   b  adjacent to each other. 
     When heat from the outside reaches the thermal absorbing layer  114 , the thermal absorbing layer  114  absorbs the heat and may transmit a signal to the transistor  116  electrically connected thereto. Unabsorbed heat passes through the thermal absorbing layer  114  and enters the cavity  112 . At this time, the metal silicide reflective layer  106  may reflect the heat entering the cavity  112  to the thermal absorbing layer  114  to be absorbed. In this way, the effect of maximum thermal absorption may be achieved. In the present embodiment, since the thermal reflective layer is the metal silicide reflective layer  106  having a reflectivity similar to that of a metal, maximum thermal absorption may be facilitated. 
     In the above embodiments, the metal silicide reflective layer  106  is located at the bottom of the recess  102 , but the invention is not limited thereto. In other embodiments, the metal silicide reflective layer  106  may further be located on the sidewalls of the recess  102 , which will be described below. 
       FIG. 2  is a cross-sectional view of a thermal sensor shown according to another embodiment of the invention. Please refer to  FIG. 2 . In the present embodiment, the difference between a thermal sensor  20  and the thermal sensor  10  is that the metal silicide reflective layer  106  is not only located at the bottom of the recess  102  but also extended upward to be disposed on the sidewalls of the recess  102 . In this way, the heat passing through the thermal absorbing layer  114  may be more effectively reflected to the thermal absorbing layer  114  to achieve the effect of maximum thermal absorption. 
     Although the invention has been described with reference to the above embodiments, it will be apparent to one of ordinary skill in the art that modifications to the described embodiments may be made without departing from the spirit of the invention. Accordingly, the scope of the invention is defined by the attached claims not by the above detailed descriptions.