Method for manufacturing infrared thermopile sensor and sensor thereof

Abstract

This invention provides a method for fabricating an infrared thermopile sensor and the sensor thereof. The method involves forming a cavity within a substrate; forming a sacrificial layer within the cavity; forming an infrared absorption layer on the sacrificial layer and on the substrate surrounding the cavity; forming a thermocouple on the infrared absorption layer within the cavity; forming a release hole penetrating the infrared absorption layer in the area outside the thermocouple on the sacrificial layer, exposing the sacrificial layer; and removing the sacrificial layer within the cavity through the release hole. This invention reduces the difficulty of forming the cavity, improves the etching precision of the cavity formation, and avoids damage to other parts of the sensor during the cavity formation process by first forming the cavity on the substrate and then forming the infrared absorption layer and the thermocouple.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for fabricating an infrared thermopile sensor and the sensor thereof. Background Technology

[0002] Infrared thermopile sensors utilize the principle of potential difference generated by temperature difference to convert the thermal energy of infrared radiation into a detectable electrical signal. A typical infrared thermopile sensor uses multiple pairs of thermocouples connected in series with alternating hot and cold ends as its core. The hot ends are covered with an infrared absorption layer to absorb radiation and generate heat, while the cold ends are isolated from the external environment by a thermally insulating substrate to reduce heat loss and ensure stable signal output. Infrared thermopile sensors are commonly used in non-contact temperature measurement and environmental gas concentration monitoring.

[0003] In infrared thermopile sensors, the cavity serves to isolate the hot-end absorption region from the cold-end substrate, reduce heat conduction between the thermopile and the surrounding environment, and improve the thermopile's response sensitivity to infrared radiation. Therefore, the cavity fabrication process of an infrared thermopile sensor is closely related to the sensor's performance.

[0004] There are two main existing processes for forming cavities. The first process involves etching the substrate from the front side by introducing an etchant through release holes after forming a sacrificial layer. The second process involves forming an infrared sacrificial layer on the front side of the substrate and then etching the cavity from the back side. However, the first process is prone to damaging other parts during cavity formation and it is difficult to precisely control the depth of the cavity. The second method involves more steps, higher costs, and slower etching speeds. Summary of the Invention

[0005] This invention provides a method for fabricating an infrared thermopile sensor and the sensor thereof, which reduces the difficulty of forming the cavity, improves the etching accuracy of forming the cavity, and avoids damage to other parts of the sensor during the cavity formation process.

[0006] According to a first aspect of the present invention, the present invention provides a method for fabricating an infrared thermopile sensor, comprising: Provide substrate; A cavity is formed on the front side of the substrate; The cavity is filled with a sacrificial layer; An infrared absorption layer is formed on the sacrificial layer and on the substrate surrounding the cavity; A thermocouple is formed on the infrared absorption layer in the cavity; In the area outside the thermocouple on the sacrificial layer, a release hole is formed that penetrates the infrared absorption layer, and the release hole exposes the sacrificial layer; The sacrificial layer within the cavity is removed through the release hole.

[0007] Optionally, it may also include forming a metal reflective layer on the bottom surface and sidewalls of the cavity after the cavity is formed and before the sacrificial layer is formed.

[0008] Optionally, the substrate is made of silicon, the sacrificial layer is made of silicon dioxide, and the metal reflective layer is made of either molybdenum or tungsten.

[0009] Optionally, after forming the metal reflective layer and before forming the sacrificial layer, the method further includes forming a first protective film on the surface of the metal reflective layer.

[0010] Optionally, the material of the first protective film is aluminum oxide.

[0011] Optionally, a method for forming a thermocouple includes forming a polycrystalline silicon layer on the infrared absorbing layer in the cavity; The polycrystalline silicon layer is doped with N-type or P-type ions to form a thermocouple.

[0012] Optionally, after forming the thermocouple and before forming the release hole, the method further includes: forming an initial protective layer on the surface of the thermocouple, the sidewall surface of the thermocouple, and the surface of the infrared absorption layer; etching the initial protective layer on the thermocouple until the surface of the thermocouple is exposed, and forming a protective layer, wherein the release hole also penetrates the protective layer; and forming a lead on the surface of the thermocouple.

[0013] Optionally, the protective layer is made of silicon dioxide.

[0014] Optionally, the infrared absorbing layer material includes at least one of vanadium oxide, amorphous silicon, or silicon dioxide-silicon nitride composite materials.

[0015] According to a second aspect of the present invention, an infrared thermopile sensor is provided, which is prepared by the above-described method for preparing an infrared thermopile sensor, comprising: Substrate; A cavity is located on the front side of the substrate; An infrared absorption layer is located on the cavity and on the substrate surrounding the cavity; Thermocouple, located on the infrared absorbing layer in the cavity; A release hole is located on the cavity and in the area outside the thermocouple. The release hole penetrates the infrared absorption layer and communicates with the cavity.

[0016] Compared with the prior art, the technical solution of the embodiments of the present invention has the following beneficial effects: In the fabrication method and sensor of the infrared thermopile sensor of this invention, a cavity is formed on a substrate; a sacrificial layer is formed within the cavity; an infrared absorption layer is formed on the sacrificial layer and on the substrate surrounding the cavity; a thermocouple is formed on the infrared absorption layer on the cavity; a release hole is formed in the area outside the thermocouple on the sacrificial layer, penetrating the infrared absorption layer, exposing the sacrificial layer; and the sacrificial layer within the cavity is removed through the release hole. Therefore, this invention reduces the process difficulty of forming the cavity, improves the etching accuracy of forming the cavity, and avoids damage to other parts during the cavity formation process by first forming the cavity on the substrate and then forming the infrared absorption layer and the thermocouple.

[0017] Furthermore, since a metal reflective layer is formed on the bottom surface and sidewalls of the cavity after the cavity is formed and before the sacrificial layer is formed, the metal reflective layer can reflect the infrared light transmitted into the cavity back to the infrared absorption layer, reducing heat loss and thus improving the sensor's accuracy in detecting temperature. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figures 1-17 This is a schematic diagram of the structure corresponding to each step in the fabrication method of the infrared thermopile sensor according to an embodiment of the present invention. Detailed Implementation

[0020] As described in the background art, the present invention aims to solve the technical problems in the prior art of how to reduce the process difficulty of forming cavities, improve the etching accuracy of forming cavities, and avoid damage to other parts of the sensor during the process of forming cavities.

[0021] In view of this, the present invention proposes a method for fabricating an infrared thermopile sensor, which involves providing a substrate; forming a cavity within the substrate; forming a sacrificial layer within the cavity; forming an infrared absorption layer on the sacrificial layer and on the substrate surrounding the cavity; forming a thermocouple on the infrared absorption layer in the cavity; forming a release hole penetrating the infrared absorption layer in the area outside the thermocouple on the sacrificial layer, exposing the sacrificial layer; and removing the sacrificial layer within the cavity through the release hole. This reduces the difficulty of forming the cavity, improves the etching precision of the cavity formation, and avoids damage to other parts during the cavity formation process.

[0022] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0023] The technical solution of the present invention will be described in detail below with reference to specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0024] Figures 1-17 This is a schematic diagram of the structure corresponding to each step in the fabrication method of the infrared thermopile sensor according to an embodiment of the present invention.

[0025] Please refer to Figure 1 Substrate 100 is provided.

[0026] In this embodiment, the substrate 100 can be made of silicon. Of course, the present invention is not limited thereto, and the substrate 100 can also be made of germanium.

[0027] Please refer to Figures 2-4 A cavity 101 is formed on the front side of the substrate 100.

[0028] Please refer to Figure 2 A mask layer 210 is formed on the substrate 100.

[0029] In this embodiment, the mask layer 210 includes a silicon dioxide (SiO2) layer and a silicon nitride (Si3N4) layer, with the silicon nitride (Si3N4) layer located on the surface of the silicon dioxide (SiO2) layer.

[0030] Please refer to Figure 3 The mask layer 210 is etched to form a patterned first mask layer 200, which has an opening region.

[0031] Please refer to Figure 4 Using the patterned first mask layer 200 as a mask, the substrate 100 is etched to form the cavity 101.

[0032] Next, please refer to Figure 5 Remove the first mask layer 200 of the graphical representation.

[0033] In this embodiment, the process for removing the patterned first mask layer 200 can be as follows: first, the upper Si3N4 (silicon nitride) layer is removed using hot phosphoric acid, wherein the selectivity ratio of hot phosphoric acid to Si3N4 is >100:1; then, the lower SiO2 (silicon dioxide) layer is removed using buffered hydrofluoric acid (BOE), wherein the selectivity ratio of buffered hydrofluoric acid (BOE) to SiO2 is >100:1.

[0034] Please refer to Figure 6 A metal reflective layer 300 is formed on the bottom surface and sidewall surface of the cavity 101.

[0035] Specifically, a metal reflective layer 300 is deposited on the bottom surface, sidewalls, and top surface of the substrate 100 of the cavity 101. The metal reflective layer 300 on the top surface of the substrate 100 is removed by chemical mechanical polishing (CMP), leaving the metal reflective layer 300 on the bottom surface and sidewalls of the cavity 101 to form... Figure 6 The structure shown.

[0036] In this embodiment, the metal reflective layer 300 can reflect the infrared light projected onto the cavity 101 back to the subsequently formed infrared absorption layer, thereby depositing the metal reflective layer 300 on the bottom surface and sidewall surface of the cavity 101, which can improve the utilization rate of infrared light by the sensor.

[0037] As one embodiment, the material of the metal reflective layer 300 can be either molybdenum (Mo) or tungsten (W). Of course, it should be understood that the present invention is not limited thereto, and the material of the metal reflective layer 300 can also be other metal materials with good reflective properties.

[0038] In this embodiment, either Mo or W is used as the metal reflective layer 300, which can better reflect infrared light back to the subsequently formed infrared absorption layer.

[0039] In this embodiment, the thickness of the metal reflective layer 300 can be in the range of 3µm to 5µm. Setting the thickness of the metal reflective layer 300 in the range of 3µm to 5µm can effectively reflect infrared light that passes through the subsequently formed infrared absorption layer and reaches the cavity 101 back to the infrared absorption layer, thereby improving the utilization rate of infrared light by the sensor.

[0040] Please refer to Figure 7 A first protective film 400 is formed on the surface of the metal reflective layer 300.

[0041] The principles for forming the first protective film 400 and the metal reflective layer 300 are the same, so they will not be elaborated on here.

[0042] In this embodiment, the first protective film 400 can serve as a stop layer for removing the sacrificial layer to protect the metal reflective layer 300.

[0043] In this embodiment, the material of the first protective film 400 is aluminum oxide (Al2O3).

[0044] Because Al2O3 is chemically more stable than silicon dioxide, the material of the subsequently formed sacrificial layer, the first protective film 400 formed using Al2O3 can serve as a stop layer for removing the sacrificial layer. Furthermore, since the Al2O3 film is transparent, using Al2O3 as the material for the first protective film 400 ensures that infrared light can be transmitted to the metal reflective layer 300.

[0045] In this embodiment, an excessively thick first protective film 400 would obstruct infrared light from reaching the metal reflective layer 300, while an excessively thin first protective film 400 would be easily damaged during the subsequent release of the sacrificial layer. As an example, the thickness of the first protective film 400 can be set in the range of 500 nm to 1 μm. A first protective film 400 of this thickness is nearly transparent, thus allowing infrared light to be transmitted to the metal reflective layer 300. A first protective film 400 within this thickness range will not be corroded during the subsequent release of the sacrificial layer.

[0046] As an example, the method for forming the metal reflective layer 300 and the first protective film 400 may be as follows: forming an initial metal reflective layer on the bottom surface of the cavity 101, the side wall surface of the cavity 101 and the surface of the substrate 100; forming an initial first protective film on the surface of the initial metal reflective layer; removing the initial metal reflective layer and the initial first protective film outside the cavity 101 to form the metal reflective layer 300 and the first protective film 400.

[0047] In this embodiment, the process for removing the initial metal reflective layer and the initial first protective film outside the cavity 101 can be as follows: forming a second mask layer on the surface of the initial first protective film inside the cavity 101; using the second mask layer as a mask and using BOE to remove the initial first protective film outside the cavity 101; using the second mask layer as a mask and using tungsten etchant and molybdenum etchant to remove the initial metal reflective layer outside the cavity 101.

[0048] Next, please refer to Figure 8 The cavity 101 is filled with a sacrificial layer 500.

[0049] The principles for forming the sacrificial layer 500 and the metal reflective layer 300 are the same, so I won't go into details here.

[0050] In this embodiment, the material of the sacrificial layer 500 is silicon dioxide (SiO2).

[0051] In one embodiment, the method of forming the sacrificial layer 500 may include: depositing an initial sacrificial layer on the surface of a substrate 100 inside and outside the cavity, the initial sacrificial layer completely filling the cavity 101; and removing the initial sacrificial layer from the surface of the substrate 100 outside the cavity 101 to form the sacrificial layer 500.

[0052] In this application, the method for fabricating an infrared thermopile sensor may further include planarizing the surface of the sacrificial layer 500 by chemical mechanical polishing (CMP).

[0053] In this embodiment, planarizing the surface of the sacrificial layer 500 helps to make the structure subsequently deposited on the surface of the sacrificial layer 500 more uniform, thereby making the formed sensor more precise.

[0054] Please refer to Figure 9 An infrared absorption layer 600 is formed on the sacrificial layer 500 and on the substrate surrounding the cavity.

[0055] In one embodiment, the infrared absorption layer 600 material may include at least one of vanadium oxide, amorphous silicon, or silicon dioxide-silicon nitride composite material.

[0056] Specifically, the infrared absorption layer 600 material can be vanadium oxide, or it can be amorphous silicon or silicon dioxide-silicon nitride composite material.

[0057] Next, a thermocouple 700 is formed on the infrared absorption layer 600 on the cavity 101. For specific steps on forming the thermocouple 700, please refer to [link to documentation]. Figures 10-12 .

[0058] Please refer to Figure 10 An initial polycrystalline silicon layer 710 is formed on the surface of the infrared absorption layer 600.

[0059] Please refer to Figure 11 The initial polysilicon layer 710 is etched to form the polysilicon layer 720.

[0060] Please continue to refer to this. Figure 12 N-type and P-type ions are doped in the polycrystalline silicon layer 720 to form thermocouple 700.

[0061] As an example, there can be several thermocouples, and several thermocouples can form a thermopile, which can be arranged around the infrared absorption layer above the cavity 101.

[0062] Please refer to Figure 13An initial protective layer 810 is formed on the surface of the thermocouple 700, the sidewall of the thermocouple 700, and the surface of the exposed infrared absorption layer 600.

[0063] Please refer to Figure 14 The initial protective layer 810 of a portion of the surface of the thermocouple 700 is etched until a portion of the surface of the thermocouple 700 is exposed to form the protective layer 800.

[0064] As an example, the material of the protective layer 800 is silicon dioxide.

[0065] In this embodiment, the protective layer 800 is used to protect the thermocouple 700.

[0066] Please refer to Figure 15 Leads 900 are formed on the surface of thermocouple 700.

[0067] In this embodiment, the material of the lead 900 can be aluminum (Al). Of course, the present invention is not limited to this, and the material of the lead can also be other metals or metal mixtures.

[0068] Please refer to Figure 16 In the area outside the thermocouple on the sacrificial layer 500, a release hole 610 is formed that penetrates the infrared absorption layer 600, and the release hole 610 exposes the sacrificial layer 500.

[0069] In this embodiment, the release air 610 also penetrates the protective layer 800.

[0070] In this embodiment, the process of forming the release hole 610 can be as follows: a patterned third mask layer is formed on the surface of the substrate 100 outside the cavity 101 and on the surface of the lead 900; the protective layer 800 and the infrared absorption layer 600 are etched on the cavity 101 using the third mask layer as a mask.

[0071] Please refer to Figure 17 The sacrificial layer 500 inside the cavity 101 is removed through the release hole 610.

[0072] In this embodiment, the method for removing the sacrificial layer 500 of the cavity 101 can be either dry etching or wet etching.

[0073] In the above-described method for fabricating an infrared thermopile sensor and the sensor thereof, a cavity 101 is formed on a substrate 100; a sacrificial layer 500 is formed within the cavity 101; an infrared absorption layer 600 is formed on the sacrificial layer 500 and on the substrate 101 surrounding the cavity 101; a thermocouple 700 is formed on the infrared absorption layer 600 on the cavity 101; a release hole 610 is formed in the area outside the thermocouple 700 on the sacrificial layer 500, penetrating the infrared absorption layer 600, and the release hole 610 exposes the sacrificial layer 500; the sacrificial layer 500 within the cavity 101 is removed through the release hole 610. Therefore, by first forming the cavity 101 on the substrate 100 and then forming the infrared absorption layer 600 and the thermocouple 700, the present invention reduces the process difficulty of forming the cavity 101 and improves the etching precision of forming the cavity 101.

[0074] Accordingly, please refer to Figure 17 The present invention also provides an infrared thermopile sensor formed by the above-described method for preparing an infrared thermopile sensor, which may include: a substrate 100, a cavity 101, an infrared absorption layer 600, a thermocouple 700, and a release hole 610.

[0075] Cavity 101 is located within substrate 100.

[0076] The infrared absorption layer 600 is located on the cavity 101 and on the substrate 100 surrounding the cavity 101.

[0077] Thermocouple 700 is located on infrared absorption layer 600 on cavity 101.

[0078] The release hole 610 is located on the cavity 101 and in the area outside the thermocouple 700. The release hole 610 penetrates the infrared absorption layer 600 and communicates with the cavity 101.

[0079] Since the infrared thermopile sensor in this embodiment corresponds to the fabrication method of the infrared thermopile sensor described above, please refer to the detailed explanation of the corresponding part in the fabrication method of the infrared thermopile sensor described above for the explanation of each feature structure in the infrared thermopile sensor in this embodiment, and it will not be repeated here.

[0080] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for fabricating an infrared thermopile sensor, characterized in that, include: Provide substrate; A cavity is formed on the front side of the substrate; The cavity is filled with a sacrificial layer; An infrared absorption layer is formed on the sacrificial layer and on the substrate surrounding the cavity; A thermocouple is formed on the infrared absorption layer in the cavity; In the area outside the thermocouple on the sacrificial layer, a release hole is formed that penetrates the infrared absorption layer, and the release hole exposes the sacrificial layer; The sacrificial layer within the cavity is removed through the release hole.

2. The preparation method according to claim 1, characterized in that, Also includes: After the cavity is formed and before the sacrificial layer is formed, a metal reflective layer is formed on the bottom surface and sidewalls of the cavity.

3. The preparation method according to claim 2, characterized in that, The substrate is made of silicon, the sacrificial layer is made of silicon dioxide, and the metal reflective layer is made of either molybdenum or tungsten.

4. The preparation method according to claim 3, characterized in that, After forming the metal reflective layer and before forming the sacrificial layer, the method further includes forming a first protective film on the surface of the metal reflective layer.

5. The preparation method according to claim 4, characterized in that, The material of the first protective film is aluminum oxide.

6. The preparation method according to claim 5, characterized in that, A method for forming a thermocouple includes: forming a polycrystalline silicon layer on the infrared absorbing layer in the cavity; The polycrystalline silicon layer is doped with N-type or P-type ions to form a thermocouple.

7. The preparation method according to claim 6, characterized in that, After the thermocouple is formed, and before the release hole is formed, the method further includes: forming an initial protective layer on the surface of the thermocouple, the sidewall surface of the thermocouple, and the surface of the infrared absorption layer; etching the initial protective layer on the thermocouple until the surface of the thermocouple is exposed, and forming a protective layer, wherein the release hole also penetrates the protective layer; and forming a lead wire on the surface of the thermocouple.

8. The preparation method according to claim 7, characterized in that, The protective layer is made of silicon dioxide.

9. The preparation method according to claim 1, characterized in that, The infrared absorption layer material includes at least one of vanadium oxide, amorphous silicon, or silicon dioxide-silicon nitride composite materials.

10. An infrared thermopile sensor, characterized in that, include: Substrate; A cavity is located on the front side of the substrate; An infrared absorption layer is located on the cavity and on the substrate surrounding the cavity; Thermocouple, located on the infrared absorbing layer in the cavity; A release hole is located on the cavity and in the area outside the thermocouple. The release hole penetrates the infrared absorption layer and communicates with the cavity.

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