CN116481653A - MEMS thermopile infrared detector and preparation method thereof - Google Patents
MEMS thermopile infrared detector and preparation method thereof Download PDFInfo
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- CN116481653A CN116481653A CN202310310400.1A CN202310310400A CN116481653A CN 116481653 A CN116481653 A CN 116481653A CN 202310310400 A CN202310310400 A CN 202310310400A CN 116481653 A CN116481653 A CN 116481653A
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
- B81B7/0083—Temperature control
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
- B81B7/02—Microstructural systems; Auxiliary parts of microstructural devices or systems containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS]
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
- B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
- B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
- B81C1/00023—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems without movable or flexible elements
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/02—Constructional details
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
- G01J5/12—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using thermoelectric elements, e.g. thermocouples
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
- G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
- G01J5/12—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using thermoelectric elements, e.g. thermocouples
- G01J5/14—Electrical features thereof
- G01J5/16—Arrangements with respect to the cold junction; Compensating influence of ambient temperature or other variables
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/01—Manufacture or treatment
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
- H10N10/10—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects
- H10N10/13—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects operating with only the Peltier or Seebeck effects characterised by the heat-exchanging means at the junction
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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Abstract
The invention discloses an MEMS thermopile infrared detector and a preparation method thereof, wherein the MEMS thermopile infrared detector comprises the following components: a substrate; a first infrared absorbing layer on the substrate; the thermopile is positioned on the first infrared absorption layer and comprises thermocouple strips which are arranged around the central area of the first infrared absorption layer, one end of each thermocouple strip, which is close to the central area of the first infrared absorption layer, is a hot end, and one end, which is far away from the central area of the first infrared absorption layer, is a cold end; the first reflecting layer is positioned on the first infrared absorption layer and surrounds the thermopile at the periphery of the cold end of the thermocouple strip; and a passivation layer covering the thermopile and the first reflection layer. According to the method, the first reflecting layer is arranged on the periphery of the cold end of the thermocouple strip so as to reflect infrared radiation around the cold end of the thermocouple strip, reduce heat absorption of the cold end of the thermocouple strip, improve the temperature difference between the cold end and the hot end of the thermocouple strip and further improve the sensitivity of the MEMS thermopile infrared detector.
Description
Technical Field
The invention relates to the technical field of electronics, in particular to an MEMS thermopile infrared detector and a preparation method thereof.
Background
Infrared detectors are one of the most critical components in infrared systems. The thermopile infrared detector is a non-refrigeration type infrared detector developed earlier, and a plurality of thermocouple strips based on the Seebeck effect are connected in series to amplify response voltage, so that the purpose of measurement is finally achieved. The key thermosensitive device, thermocouple, is one element to convert temperature difference into potential difference by means of thermoelectric effect of conductor or semiconductor material, and has two ends connected together to form one closed loop, one end to absorb radiation energy to raise temperature and the other end to produce temperature difference. The thermopile infrared detector has the advantages of small volume, capability of working at room temperature, wide-spectrum infrared radiation response, capability of detecting constant radiation quantity, low preparation cost and the like, so that the thermopile infrared detector has wide application in the aspects of safety monitoring, medical treatment, life detection and the like.
Early thermopile infrared temperature sensors were obtained by depositing thermocouple materials onto plastic or alumina substrates, and devices obtained by this method were large in size and not easily mass-produced. With the development and application of MEMS (Micro-Electro-Mechanical System) technology, the thermopile infrared temperature sensor has further developed, and the practice shows that the performance of the micromechanical thermopile infrared thermopile manufactured by the MEMS technology is greatly improved compared with that of the traditional thermopile device because the heat conduction of the micromechanical thermopile infrared thermopile can be effectively reduced and the integration level of the micromechanical thermopile infrared temperature sensor is improved. In addition, the MEMS thermopile infrared detector has the advantages of light weight, low power consumption, good durability, low price, stable performance and the like, and is widely applied to various fields of automobiles, aerospace, aviation, electronics industry and the like.
At present, how to continuously optimize the performance of the MEMS thermopile infrared detector, in particular how to further improve the sensitivity of the MEMS thermopile infrared detector is a research and development hot spot. At present, the potential difference is increased by increasing the logarithm of the thermocouple strips, so that the sensitivity is improved. Practice has shown that this approach is not significant in terms of the method of improving the sensitivity of the device.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a MEMS thermopile infrared detector and a method for manufacturing the same, which can improve the sensitivity of the MEMS thermopile infrared detector by improving the temperature difference between the cold end and the hot end of a thermocouple strip.
To achieve the above object, a first aspect of the present invention provides a MEMS thermopile infrared detector, comprising:
a substrate;
a first infrared absorbing layer on the substrate;
the thermopile is positioned on the first infrared absorption layer and comprises thermocouple strips which are arranged around the central area of the first infrared absorption layer, one end of each thermocouple strip, which is close to the central area of the first infrared absorption layer, is a hot end, and one end, which is far away from the central area of the first infrared absorption layer, is a cold end;
the first reflecting layer is positioned on the first infrared absorption layer and surrounds the thermopile at the periphery of the cold end of the thermocouple strip; and
and a passivation layer covering the thermopile and the first reflection layer.
Preferably, the thermopile comprises a plurality of groups of thermocouple strips, and a blank area is arranged between two adjacent groups of thermocouple strips;
the first reflective layer includes a first portion opposite the cold ends of the thermocouple strips and a second portion between adjacent sets of thermocouple strips and protruding toward the blank area.
Preferably, an etching stop layer is arranged between the substrate and the first infrared absorption layer;
the substrate is provided with a back cavity, and the back cavity penetrates through the substrate and exposes the etching stop layer.
Preferably, the substrate further comprises a second reflective layer covering a surface of the substrate remote from the etch stop layer and covering a surface of the etch stop layer exposed via the back cavity.
Preferably, the thermoelectric power generation device further comprises an isolation groove, wherein the isolation groove is positioned in the blank area and surrounds the thermopile; the isolation groove penetrates through the passivation layer and the first infrared absorption layer and is communicated with the back cavity.
Preferably, the isolation groove comprises a plurality of mutually separated strip-shaped grooves, and the strip-shaped grooves are parallel to the extending direction of the adjacent thermocouple strips in the extending direction parallel to the surface of the first infrared absorption layer.
Preferably, the spacing between the strip-shaped groove and the outermost thermocouple strip in each group of thermocouple strips is the width of at least one thermocouple strip.
Preferably, the device further comprises an electrode structure positioned on the first infrared absorption layer, and the electrode structure is electrically connected with the thermopile;
and a through hole is formed in the passivation layer so as to expose the electrode structure.
Preferably, the method further comprises:
a second infrared absorption layer on the passivation layer;
and a metamaterial structure positioned on the second infrared absorption layer.
Preferably, the metamaterial structure comprises:
a metal reflecting layer, wherein the projection of the metal reflecting layer on the first infrared absorption layer covers the central area of the first infrared absorption layer and the hot end of the thermocouple strip;
the intermediate dielectric layer is positioned on the metal reflecting layer; and
and the metal microstructure layer is positioned on the intermediate medium layer and comprises periodically arranged structural units.
Preferably, the metal microstructure layer comprises periodically arranged cross-shaped structures, the cross-shaped structures comprise first strip-shaped structures extending in a first direction and second strip-shaped structures extending in a second direction, and the first direction and the second direction are perpendicular to the thickness direction of the substrate.
Preferably, the distance between adjacent cross-shaped structures is 2000-4000 nanometers; and/or
The first direction is perpendicular to the second direction, and the width of the first strip-shaped structure is 200-2000 nanometers; the length of the first strip-shaped structure is 1500-2000 nanometers; the width of the second strip-shaped structure is 200-2000 nanometers; the length of the second strip-shaped structure is 1500-2000 nanometers.
The second aspect of the invention provides a method for preparing an infrared detector of a MEMS thermopile, comprising the following steps:
forming a first infrared absorption layer on a substrate;
forming a thermopile on the first infrared absorption layer, wherein the thermopile comprises thermocouple strips which are arranged around the central area of the absorption layer, one end of each thermocouple strip, which is close to the central area of the first infrared absorption layer, is a hot end, and one end, which is far away from the central area of the first infrared absorption layer, is a cold end;
forming a first reflecting layer on the first infrared absorption layer, wherein the first reflecting layer surrounds the thermocouple strip at the periphery of the cold end of the thermocouple strip; and
a passivation layer is formed over the thermopile and the first reflective layer.
Preferably, the thermopile comprises a plurality of groups of thermocouple strips, and a blank area is arranged between two adjacent groups of thermocouple strips;
the first reflective layer includes a first portion opposite the cold ends of the thermocouple strips and a second portion between adjacent sets of thermocouple strips and protruding toward the blank area.
Preferably, the method further comprises:
forming an etching stop layer on the substrate, and then forming the first infrared absorption layer on the etching stop layer; and
and forming a back cavity on the substrate, wherein the back cavity penetrates through the substrate and exposes the etching stop layer.
Preferably, the method further comprises: and forming a second reflecting layer on the surface of the substrate away from the etching stop layer and the surface of the etching stop layer exposed through the back cavity.
Preferably, an isolation groove surrounding the thermopile is formed in the blank area, penetrates through the passivation layer and the first infrared absorption layer, and is communicated with the back cavity.
Preferably, the isolation groove comprises a plurality of mutually separated strip-shaped grooves, and the strip-shaped grooves are parallel to the extending direction of the adjacent thermocouple strips in the extending direction parallel to the surface of the first infrared absorption layer.
Preferably, the method further comprises:
forming a second infrared absorption layer on the passivation layer;
and forming a metamaterial structure on the second infrared absorption layer.
Preferably, the step of forming the metamaterial structure comprises:
forming a metal reflecting layer on the second infrared absorption layer, wherein the projection of the metal reflecting layer on the first infrared absorption layer covers the hot end of the thermocouple strip;
forming an intermediate dielectric layer on the metal reflecting layer; and
and forming a metal microstructure layer on the intermediate dielectric layer, wherein the metal microstructure layer comprises periodically arranged structural units.
According to the MEMS thermopile infrared detector provided by the invention, the first reflecting layer is arranged on the periphery of the cold end of the thermocouple strip so as to reflect infrared radiation around the cold end of the thermocouple strip, so that the heat absorption of the cold end of the thermocouple strip is reduced, the temperature difference between the cold end and the hot end of the thermocouple strip is improved, and the sensitivity of the device is improved.
In a preferred embodiment, the first reflective layer comprises a first portion and a second portion, the first portion being opposite the cold end of the thermocouple strip to reflect infrared radiation near the cold end of the thermocouple strip; the second part is positioned in a blank area between the thermocouple strips of the adjacent groups and extends towards the central area of the first infrared absorption layer so as to effectively reflect infrared radiation near the cold ends of the thermocouple strips and further increase the temperature difference between the cold ends and the hot ends of the thermocouple strips, thereby further improving the sensitivity of the device.
In a preferred embodiment, a second reflective layer is disposed on a side of the first infrared absorbing layer remote from the thermopile, such that after infrared radiation is transmitted through the multilayer film structure from the front side of the device, the infrared radiation can be reflected by the second infrared reflective layer to the first infrared absorbing layer and absorbed again by the first infrared absorbing layer, thereby improving the overall heat absorption rate of the device.
In a preferred embodiment, the MEMS thermopile infrared detector further comprises an isolation trench surrounding the thermopile, i.e. the thermopile is located within the area defined by the isolation trench. The thermal pile is isolated from the outside by the isolating groove, so that heat conduction is reduced, heat is accumulated at the hot end of the thermocouple strip, the temperature of the hot end of the thermocouple strip is improved, and the temperature difference between the cold end and the hot end of the thermocouple strip is further improved.
Drawings
The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the present invention with reference to the accompanying drawings, in which:
FIG. 1a shows a top view of a MEMS thermopile infrared detector of an embodiment of the present invention;
FIG. 1b is a cross-sectional view taken along the direction AA of FIG. 1 a;
FIG. 1c is a cross-sectional view along BB of FIG. 1 a;
FIG. 2a is a schematic view of a portion of a metal microstructure layer according to an embodiment of the present invention;
FIG. 2b shows a partial schematic view of a metal microstructured layer in accordance with another embodiment of the present invention;
FIGS. 3a to 9a are schematic top view structures of stages in the fabrication of a MEMS thermopile infrared detector according to an embodiment of the present invention;
fig. 3b to 9b are schematic cross-sectional views along AA direction of fig. 3a to 9 a;
fig. 3c to 9c are schematic cross-sectional views of fig. 3a to 9a along BB direction.
Detailed Description
The invention will be described in more detail below with reference to the accompanying drawings. Like elements are denoted by like reference numerals throughout the various figures. For clarity, the various features of the drawings are not drawn to scale. Furthermore, some well-known portions may not be shown.
The invention may be embodied in various forms, some examples of which are described below.
Fig. 1a shows a schematic top view of a MEMS thermopile infrared detector according to an embodiment of the present invention, fig. 1b is a cross-sectional view along AA direction of fig. 1a, and fig. 1c is a cross-sectional view along BB direction of fig. 1 a.
Referring to fig. 1a, 1b and 1c, the MEMS thermopile infrared detector includes: a substrate 110, a first infrared absorbing layer 130 on the substrate 110, a thermopile 150 on the first infrared absorbing layer 130, and a passivation layer 170 on the first infrared absorbing layer 130 and the thermopile 150.
The substrate 110 may be, in particular, a semiconductor substrate commonly used in MEMS infrared thermopiles, such as a P-doped silicon substrate. The substrate 110 has oppositely disposed first and second surfaces.
The substrate 110 may have a back cavity 111 thereon, the back cavity 111 extending through the substrate 110. By providing the back cavity 111 through the substrate 110, heat loss due to heat conduction of the substrate 110 can be reduced. An etch stop layer 120 may also be provided on the first surface of the substrate 110, with a portion of the etch stop layer 120 exposed through the back cavity 111. The etch stop layer 120 serves on the one hand as a support layer for the first infrared absorbing layer 130 and on the other hand as a stop layer when etching to form the back cavity 111. In one embodiment, the etching stop layer 120 is a silicon oxide layer, and the thickness is, for example, 400 nm to 600 nm, but not limited thereto.
The first infrared absorbing layer 130 is located above the etch stop layer 120, i.e., the first infrared absorbing layer 130 is located on a surface of the etch stop layer 120 remote from the substrate 110 for absorbing incident infrared light. In a specific embodiment, the first infrared absorbing layer 130 is, for example, a low stress silicon nitride layer. The silicon nitride material has higher absorptivity to infrared light, and the silicon nitride material with low stress has higher mechanical property. The thickness of the first infrared absorbing layer 130 is, for example, 600 nm to 1000 nm. In other embodiments, the material of the first infrared absorbing layer 130 is a composite dielectric layer composed of silicon oxide and silicon nitride. The first infrared absorbing layer 130 has a central region and an edge region surrounding the central region. However, the specific dimensional ratio of the center region to the edge region is not limited in this embodiment.
The thermopile 150 is located above the first infrared absorbing layer 130, and the thermopile 150 includes a plurality of thermocouple strips arranged around a central region of the first infrared absorbing layer 130. One end of each thermocouple strip, which is close to the central area of the first infrared absorption layer 130, is a hot end, and the other end is a cold end. The thermopile 150 specifically includes a first thermocouple strip 151 and a second thermocouple strip 152, where the first thermocouple strip 151 and the second thermocouple strip 152 are alternately arranged, paired, and connected end to end. In a specific embodiment, the material of the first thermocouple strip 151 is polysilicon with a thickness of 300 nm to 600 nm, and the material of the second thermocouple strip 152 is aluminum with a thickness of 100 nm to 300 nm. In other embodiments, the material of the first thermocouple strip 151 and the second thermocouple strip 152 may be doped polysilicon and Ti, doped polysilicon and Au, or N-doped polysilicon and P-doped polysilicon, or other materials with appropriate seebeck coefficients.
The specific arrangement of the first thermocouple strip 151 and the second thermocouple strip 152 is not limited in this application. In this embodiment, the first thermocouple strip 151 and the second thermocouple strip 152 are located on the same layer. In other embodiments, the first thermocouple strip 151 and the second thermocouple strip 152 may be arranged in a layered manner, i.e., the first thermocouple strip 151 and the second thermocouple strip 152 are stacked and separated by an insulating layer, and the ends of the two are connected in series through the insulating layer.
A passivation layer 170 is positioned on the thermopile 150 and covers the first infrared absorbing layer 130. In this embodiment, the passivation layer 170 is made of silicon oxide, for example.
Further, the MEMS thermopile infrared detector also includes an electrode structure 140 to enable electrode extraction to the thermopile 150. In this embodiment, the electrode structure 140 is disposed on the first infrared absorption layer 130 and electrically connected to two ends of the thermopile 150. Specifically, the electrode structure 140 includes a first electrode 141 and a second electrode 142 that are separated from each other, and the first electrode 141 and the second electrode 142 are connected to two free ends of a thermocouple strip connected end to end, respectively. The electrode structure 140 is made of a material such as gold, silver, aluminum, or the like, which is commonly used in MEMS infrared thermopiles.
MEMS thermopile infrared detector 10 also includes a via a through passivation layer 170, through which electrode structure 140 is exposed for electrical connection to external circuitry.
According to the Seebeck effect (Seebeck effect), i.e. the first thermoelectric effect, the thermopile infrared detector generates a response voltage:
△U＝NT ab α ab
wherein N is the logarithm of a thermopile thermocouple strip, T ab Alpha is the temperature difference between the cold end and the hot end of the thermocouple strip ab Is the seebeck coefficient difference.
According to the formula, the temperature difference between the cold end and the hot end of the thermocouple strip is in proportional relation with the output voltage DeltaU; and after the material of the thermocouple strip of the thermopile is determined, the voltage output of the device can be improved by increasing the logarithm N of the thermocouple strip, so that the sensitivity is improved. However, practice has shown that an increase in the logarithm N of the thermocouple strip does not necessarily increase the output voltage of the device. Presumably, as the logarithm N of the thermocouple strip increases, the thermal conductivity of the whole device increases, so that the temperature difference and the resistance value of the cold end and the hot end of the thermocouple strip are wholly reduced, and finally the sensitivity improving effect is difficult to be expected. Therefore, the effect of increasing the output voltage and the sensitivity of the device by increasing the logarithm N of the thermocouple strip is far smaller than that of a way of increasing the temperature difference between the cold end and the hot end of the thermocouple strip to a certain extent.
Based on the finding, the first reflecting layer is arranged on the periphery of the cold end of the thermocouple strip so as to reflect infrared radiation around the cold end of the thermocouple strip, reduce the heat absorption of the cold end of the thermocouple strip, and improve the temperature difference (T ab ) Further, the output voltage (DeltaU) and the sensitivity of the thermopile infrared detector are improved. By providing a second reflective layer on the side of the first infrared absorbing layer remote from the thermopile, the overall heat absorption rate of the device is improved. By arranging the isolation groove, the heat of the hot end of the thermocouple strip is limited to be conducted outwards, and the heat is prevented from being conducted from the hot end to the cold end on the suspended multilayer film structure, so that the temperature of the hot end of the thermocouple strip is further kept, and the temperature difference (T) between the cold end and the hot end of the thermocouple strip is further improved ab ) Is effective in (1).
Specifically, in the present embodiment, the thermopile 150 includes a plurality of groups of thermocouple strips, each group of thermocouple strips includes a plurality of first thermocouple strips 151 and second thermocouple strips 152 alternately arranged, and a blank area is provided between adjacent groups of thermocouple strips. In the structures shown in fig. 1a, 1b and 1c, the thermopile 150 includes four groups of thermocouple strips, each group of thermocouple strips includes a plurality of first thermocouple strips 151 and second thermocouple strips 152 which are parallel to each other and are alternately arranged, and a blank area is provided between adjacent groups of thermocouple strips. In this embodiment, the thermocouple strips are arranged in groups, and a blank area is provided between adjacent groups of thermocouple strips, so that enough space is provided for the arrangement of the first reflective layer and the isolation groove.
As shown in fig. 1a, the first reflective layer 161 is located on the first infrared absorbing layer 130, separated from the thermopile 150 and the electrode structure 140. More specifically, the first reflective layer 161 is located at the edge region of the first infrared absorbing layer 130 and is located at the periphery of the thermocouple strip cold end, surrounding the thermopile 150. By arranging the first reflecting layer 161 on the periphery of the cold end of the thermocouple strip, infrared radiation around the cold end of the thermocouple strip can be reflected, so that the thermal absorption of the cold end of the thermocouple strip is reduced, the temperature difference between the cold end and the hot end of the thermocouple strip is improved, and the sensitivity of the MEMS thermopile infrared detector is further improved.
Further, as shown in fig. 1a and 1b, the first reflective layer 161 includes a first portion 161a and a second portion 161b, the first portion 161a being opposite to the cold end of the thermopile 150, i.e., the first portion 161a is located outside the cold end of the thermopile 150 to reflect infrared radiation near the cold end of the thermocouple strip; the second portion 161b is located in the blank area between adjacent groups of thermocouple strips and extends and protrudes toward the central area of the absorber layer 130 to ensure that the infrared radiation near the cold ends of the thermocouple strips is sufficiently reflected, further increasing the temperature difference between the cold and hot ends of the thermocouple strips. In this embodiment, the first portion 161a and the second portion 161b are integrally connected to achieve wrapping of the cold end of the thermocouple strip, and further increase the temperature difference between the cold end and the hot end of the thermocouple strip.
In this embodiment, as shown in fig. 1b and 1c, the second reflective layer 162 covers the second surface of the substrate 110 and the surface of the etching stop layer 120 exposed through the back cavity 111. The materials of the first and second reflective layers 161 and 162 may each be a metal material having high reflectivity, such as gold, silver, aluminum, etc., and the materials of the first and second reflective layers 161 and 162 may be the same or different.
By providing the second reflective layer 162 on the side of the first infrared absorbing layer 130 away from the thermopile 150, after infrared radiation sequentially passes through the passivation layer 170, the first infrared absorbing layer 130 and the etching stop layer 120, the infrared radiation can be reflected to the first infrared absorbing layer 130 by the second reflective layer 162 and absorbed by the first infrared absorbing layer 130 again, thereby improving the overall heat absorption rate of the device.
With further reference to fig. 1 a-1 c, the MEMS thermopile infrared detector provided in this embodiment may further include a second infrared absorbing layer 180 and a metamaterial structure 190. The second infrared absorbing layer 180 covers the passivation layer 170, and the material thereof is, for example, silicon nitride, but not limited thereto. The metamaterial structure 190 is located on the second infrared absorbing layer 180, and a projection of the metamaterial structure 190 on the first infrared absorbing layer 130 covers a central area of the first infrared absorbing layer 130 and a hot end of the thermocouple strip.
Specifically, the metamaterial structure 190 includes a metal reflective layer 191, an intermediate dielectric layer 192, and a metal microstructured layer 193, which are stacked in this order. Wherein metal reflective layer 191 is positioned on second infrared absorbing layer 180, intermediate dielectric layer 192 is positioned on metal reflective layer 191, and metal microstructured layer 193 is positioned on intermediate dielectric layer 192. The absorption rate of the device in the infrared band is improved by arranging the metamaterial structure 190.
In this embodiment, the material of the metal reflective layer 191 is, for example, aluminum, and the thickness is, for example, 10 nm to 200 nm; the material of the intermediate dielectric layer 192 is, for example, silicon oxide, and the thickness is, for example, 100 nm to 300 nm; the material of the metal microstructure layer 193 is, for example, aluminum, and the thickness thereof is, for example, 50 nm to 200 nm. In other embodiments, the materials and thicknesses of the metal reflective layer 191, the intermediate dielectric layer 192, and the metal microstructured layer 193 can be arbitrarily set by those skilled in the art as desired. For example, the material of the metal reflective layer 191 may be any one or any combination of gold, silver, copper, aluminum, titanium, nickel, and chromium. The material of the intermediate dielectric layer 192 may be any one or any combination of silicon dioxide, silicon nitride, and aluminum oxide. The material of the metal microstructure layer 193 is any one or any combination of gold, silver, copper, aluminum, titanium, nickel, and chromium.
The metal microstructured layer 193 comprises a periodic arrangement of structural elements comprising one or more geometric structures having a light absorption enhancing effect in the infrared spectral range.
FIGS. 2a and 2b illustrate partial schematic structural views of a metal microstructured layer, respectively, in one particular embodiment; referring to fig. 2a and 2b, the metal micro-structure layer 193 includes a plurality of 'cross' -shaped structures periodically arranged, wherein the 'cross' -shaped structures include a first stripe-shaped structure 193a extending in a first direction and a second stripe-shaped structure 193b extending in a second direction, wherein the first direction and the second direction form a predetermined angle, an included angle between the two directions is not 0 degree or 180 degrees, and a plane formed by the two directions is parallel to a surface of the first infrared absorption layer 130 and perpendicular to a thickness direction of the substrate 110.
Wherein, the distance u between adjacent cross structures is 2000-4000 nanometers, for example. The first and second stripe structures 193a and 193b have a width of, for example, 200 nm to 2000 nm and a length of, for example, 1500 nm to 2000 nm. For example, reference may be made to the cross-shaped structure shown in fig. 2a and 2b, wherein the first direction is perpendicular to the second direction, i.e. the first stripe 193a is perpendicular to the extension direction of the second stripe 193 b. Taking the second stripe structure 193b as an example, the dimension of the second stripe structure 193b along the first direction, i.e. the width a of the second stripe structure 193b is, for example, 200 nm to 2000 nm, and typically 200 nm to 1800 nm; the dimension of the second stripe structure 193b along the second direction, i.e. the length b of the second stripe structure 193b, is, for example, 1500 nm to 2000 nm. Wherein a is generally less than b. The first stripe structure 193a has a similar size and will not be described again.
The widths of the first and second bar structures 193a and 193b may be equal or unequal, and the lengths of the first and second bar structures 193a and 193b may be equal or unequal.
By adopting the metamaterial structure 190, the light absorption of the infrared band can be improved, so that the infrared absorption rate of the MEMS thermopile infrared detector can be improved.
Further, as shown in fig. 1a and 1c, the isolation trenches S are located in the empty region between adjacent sets of thermocouple strips, surrounding the thermopile 150, i.e., the thermopile 150 is located within the region defined by the isolation trenches S. The isolation groove S isolates the thermopile 150 from the outside, limits heat of the hot end of the thermocouple strip from being conducted outwards, plays a role in keeping the temperature of the hot end of the thermocouple strip to a certain extent, and further improves the temperature difference between the cold end and the hot end of the thermocouple strip.
In this embodiment, the isolation trench S penetrates at least the second infrared absorbing layer 180, the passivation layer 170, and the first infrared absorbing layer 130. For example, in the structure shown in fig. 1b and fig. 1c, the isolation groove S penetrates through the multilayer film structure (including the second infrared absorption layer 180, the passivation layer 170, the first infrared absorption layer 130 and the etching stop layer 120) and the second reflection layer 162 of the MEMS thermopile infrared detector, and is communicated with the back cavity 111, so that the multilayer film structure and the thermopile 150 inside the multilayer film structure are suspended, and therefore, heat conduction of the hot end of the thermocouple strip can be effectively limited, and a certain temperature maintaining effect is achieved on the hot end of the thermocouple strip.
Further, the isolation grooves S are positioned at two sides of each group of thermocouple strips, so that heat is prevented from being conducted from the hot end to the cold end on the suspended multilayer film structure, and the effects of keeping the temperature of the hot end of each thermocouple strip and further improving the temperature difference between the cold end and the hot end of each thermocouple strip are further achieved. Practices show that after the isolation groove is added, the average temperature difference of the cold end and the hot end can be improved by about 0.5-1.0 ℃.
The isolation groove S specifically comprises a plurality of mutually separated strip-shaped grooves, and the plurality of strip-shaped grooves are positioned on the outer side of each group of thermocouple strips. For example, in the structure shown in fig. 1a, the thermopile 150 includes four groups of thermocouple strips, and each group of thermocouple strips is provided with a strip-shaped groove on two sides, that is, two strip-shaped grooves separated from each other are respectively provided in a blank area between two adjacent groups of thermocouple strips. The extending direction of the strip-shaped groove is parallel to the extending direction of the adjacent thermocouple strip. The length of the strip-shaped groove is equal to or equivalent to that of the adjacent thermocouple strip, and the strip-shaped groove and the first reflecting layer 161 are arranged at intervals. In this embodiment, the distance between the strip-shaped groove and the adjacent thermocouple strip (i.e. the outermost thermocouple strip in each group of thermocouple strips) is at least 1-1.5 times the width of one thermocouple strip, so as to give consideration to the mechanical strength of the suspended multilayer film structure under the condition of keeping the temperature of the hot end of the thermocouple strip.
Fig. 3a to 9a are schematic top view structures of the MEMS thermopile infrared detector of the present embodiment at various stages in the fabrication process, and fig. 3b to 9b are schematic cross-sectional views along AA direction of fig. 3a to 9 a; fig. 3c to 9c are schematic cross-sectional views of fig. 3a to 9a along BB direction; the MEMS thermopile infrared detector manufacturing process of the present embodiment will be described below with reference to the drawings.
As shown in fig. 3a, 3b and 3c, an etch stop layer 120 and a first infrared absorbing layer 130 are sequentially formed on a substrate 110.
In this step, for example, an etching stop layer 120 and a first infrared absorption layer 130 are sequentially formed on the first surface of the substrate 110 using a deposition process. The etching stop layer 120 is, for example, a silicon oxide layer, and has a thickness of, for example, 400 nm to 600 nm, but not limited thereto. The first infrared absorbing layer 130 is, for example, a low stress silicon nitride layer, and has a thickness of 600 nm to 1000 nm, for example.
As shown in fig. 4a, 4b and 4c, a first thermocouple strip is formed on the first infrared absorbing layer.
In this step, a polysilicon layer is formed on the first infrared absorbing layer 130, for example, using a deposition process, followed by ion implantation and annealing of the polysilicon layer to form a doped polysilicon layer. Then, the polysilicon layer is patterned by photolithography and etching processes to form a plurality of first thermocouple strips 151.
As shown in fig. 5a, 5b and 5c, a second thermocouple strip, an electrode structure and a first reflective layer are formed on the first infrared absorbing layer.
In this step, for example, a layer of aluminum having a thickness of 100 nm to 300 nm is formed on the first infrared absorbing layer 130 and the first thermocouple strip 151 by using a sputtering process. The aluminum layer is then patterned by photolithography and etching processes, and a plurality of second thermocouple strips 152, electrode structures 140, and first reflective layers 161 are formed simultaneously.
Wherein, the first thermocouple strips 151 and the second thermocouple strips 152 are alternately arranged and are connected end to end. The thermopile 150 is arranged around the central region of the first infrared absorbing layer 130, wherein the end of the thermocouple strip near the central region of the absorbing layer 130 is a hot end and the end far from the central region of the first infrared absorbing layer 130 is a cold end.
The electrode structure 140 is electrically connected to the thermopile 150, and in particular, the electrode structure 140 includes a first electrode 141 and a second electrode 142 separated from each other, and the first electrode 141 and the second electrode 142 are respectively connected to two free ends of a thermocouple strip connected end to end in sequence. The first reflective layer 161 is separated from the thermopile 150 and the electrode structure 140, and the first reflective layer 161 is located at the periphery of the thermocouple strip cold end, surrounding the thermopile 150.
In this embodiment, the electrode structure 140, the thermopile 150 and the first reflective layer 161 are disposed on the same layer, and the electrode structure 140, one thermocouple strip (e.g. the second thermocouple strip 152) in the thermopile 150 and the first reflective layer 161 are made of the same material, so that the electrode structure 140, one thermocouple strip (e.g. the second thermocouple strip 152) in the thermopile 150 and the first reflective layer 161 can be formed through the same step, thereby saving the process steps. In other embodiments, the materials of the electrode structure 140, the thermopile 150, and the first reflective layer 161 may be selected, and the corresponding steps may be adaptively adjusted. In addition, in the present embodiment, two thermocouple strips of the thermopile 150 are arranged in the same layer, and in other embodiments, two thermocouple strips of the thermopile 150 are arranged in a stacked manner and are separated by an insulating layer, so that corresponding process steps can be adjusted accordingly, and the embodiments are not limited and are not repeated.
As shown in fig. 6a, 6b and 6c, a passivation layer and a second infrared absorption layer are formed.
In this step, a passivation layer 170 is formed on the first infrared absorbing layer 130, for example, using a deposition process, and the passivation layer 170 covers the thermopile 150, the electrode structure 140, and the first reflective layer 161. Next, a second infrared absorbing layer 180 is formed on the passivation layer 170, for example, using a deposition process. In the present embodiment, the passivation layer 170 is made of a silicon oxide layer, and the second infrared absorbing layer 180 is made of a silicon nitride layer, but not limited thereto.
As shown in fig. 7a, 7b and 7c, a through hole a is formed.
In this step, for example, photolithography and etching processes are used to etch the second infrared absorption layer 180 and the passivation layer 170, so as to form a via a, which penetrates the passivation layer 170 and the second infrared absorption layer 180 to expose the electrode structure 140.
As shown in fig. 8a, 8b, and 8c, a metamaterial structure 190 is formed.
In this step, for example, a layer of aluminum having a thickness of 10 nm to 200 nm is formed on the second infrared absorbing layer 180 using a sputtering process. The aluminum layer is then patterned using photolithography and etching processes to form a metal reflective layer 191 in the central region of the second infrared absorbing layer 180. Wherein, the projection of the metal reflective layer 191 on the first infrared absorbing layer 130 covers the hot end of the thermocouple strip. In other embodiments, the material of the metal reflective layer 191 may be any one or any combination of gold, silver, copper, aluminum, titanium, nickel, and chromium.
Next, an intermediate dielectric layer is formed.
In this step, for example, a silicon oxide layer having a thickness of 100 nm to 300 nm is formed on the surfaces of the second infrared absorbing layer 180 and the metal reflective layer 191 by a deposition process. And etching the silicon oxide layer by adopting photoetching and etching processes to remove the silicon oxide layer on the surface of the second infrared absorption layer 180, and reserving the silicon oxide layer on the surface of the metal reflection layer 191 to form an intermediate medium layer 192. In other embodiments, the material of the intermediate dielectric layer 192 may also be aluminum oxide, or a stack of a silicon oxide layer and an aluminum oxide layer.
Next, a metal microstructure layer 193 is formed.
In this step, an aluminum layer having a thickness of 50 nm to 200 nm is formed on the surfaces of the second infrared absorbing layer 180 and the intermediate dielectric layer 192, for example, by a sputtering process. The aluminum layer is then etched using photolithography and etching processes to remove the aluminum layer on the surface of second infrared absorbing layer 180 and form a metal microstructured layer 193 having one or more periodic structural elements, such as metal microstructured layer 193 shown in fig. 2a and 2b, on the surface of intermediate dielectric layer 192. In other embodiments, the material of the metal microstructured layer 193 may be any one or any combination of gold, silver, copper, aluminum, titanium, nickel, and chromium.
Wherein the stacked metal reflective layer 191, intermediate dielectric layer 192, and metal microstructure layer 193 form a metamaterial structure 190.
As shown in fig. 9a, 9b and 9c, isolation trenches are formed.
In this step, for example, the second infrared absorption layer 180, the passivation layer 170, the first infrared absorption layer 130, and the etching stopper layer 120 are sequentially etched by photolithography and etching processes to reach the first surface of the substrate 110 or the inside of the substrate 110, thereby forming the isolation trench S.
Next, with continued reference to fig. 9a, 9b, and 9c, a back cavity is formed.
In this step, for example, a photolithography and deep silicon etching process is used to etch the second surface of the substrate 110, and the back cavity 111 is formed by using the etching stop layer 120 as a stop layer, where the back cavity 111 penetrates through the substrate 110 to expose the etching stop layer 120.
Then, a second reflective layer is formed.
In this step, a second reflective layer 162 is formed on the second surface of the remaining substrate 110 and the surface of the etch stop layer 120 exposed by the back cavity 111, for example, using an evaporation process.
The preparation method of the MEMS thermopile infrared detector provided by the embodiment comprises the following steps of the common steps in the semiconductor field.
In the description of the present embodiment, the terms "first", "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated.
Embodiments in accordance with the present invention, as described above, are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and the full scope and equivalents thereof.
Claims (20)
1. A MEMS thermopile infrared detector comprising:
a substrate;
a first infrared absorbing layer on the substrate;
the thermopile is positioned on the first infrared absorption layer and comprises thermocouple strips which are arranged around the central area of the first infrared absorption layer, one end of each thermocouple strip, which is close to the central area of the first infrared absorption layer, is a hot end, and one end, which is far away from the central area of the first infrared absorption layer, is a cold end;
the first reflecting layer is positioned on the first infrared absorption layer and surrounds the thermopile at the periphery of the cold end of the thermocouple strip; and
and a passivation layer covering the thermopile and the first reflection layer.
2. The MEMS thermopile infrared detector of claim 1, wherein the thermopile comprises a plurality of sets of thermocouple strips with a blank area between adjacent sets of thermocouple strips;
the first reflective layer includes a first portion opposite the cold ends of the thermocouple strips and a second portion between adjacent sets of thermocouple strips and protruding toward the blank area.
3. The MEMS thermopile infrared detector of claim 2, wherein an etch stop layer is disposed between the substrate and the first infrared absorbing layer;
the substrate is provided with a back cavity, and the back cavity penetrates through the substrate and exposes the etching stop layer.
4. A MEMS thermopile infrared detector as set forth in claim 3 further including a second reflective layer overlying a surface of said substrate remote from said etch stop layer and overlying a surface of an etch stop layer exposed via said back cavity.
5. A MEMS thermopile infrared detector as set forth in claim 3 or 4 and further including an isolation trench located in said void region and surrounding said thermopile; the isolation groove penetrates through the passivation layer and the first infrared absorption layer and is communicated with the back cavity.
6. A MEMS thermopile infrared detector as set forth in claim 5 wherein said isolation trench includes a plurality of mutually separated stripe-shaped trenches parallel to the direction of extension of adjacent thermocouple strips in a direction parallel to the surface of the first infrared absorbing layer.
7. A MEMS thermopile infrared detector as set forth in claim 6 wherein said stripe slots are spaced from an outermost thermocouple strip of each set of thermocouple strips by a width of at least one of said thermocouple strips.
8. A MEMS thermopile infrared detector as set forth in any one of claims 1-7, further comprising an electrode structure on said first infrared absorbing layer, said electrode structure being electrically connected to said thermopile;
and a through hole is formed in the passivation layer so as to expose the electrode structure.
9. A MEMS thermopile infrared detector as set forth in any one of claims 1 to 8, further comprising:
a second infrared absorption layer on the passivation layer;
and a metamaterial structure positioned on the second infrared absorption layer.
10. The MEMS thermopile infrared detector of claim 9, wherein the metamaterial structure comprises:
a metal reflecting layer, wherein the projection of the metal reflecting layer on the first infrared absorption layer covers the central area of the first infrared absorption layer and the hot end of the thermocouple strip;
the intermediate dielectric layer is positioned on the metal reflecting layer; and
and the metal microstructure layer is positioned on the intermediate medium layer and comprises periodically arranged structural units.
11. The MEMS thermopile infrared detector of claim 10, wherein the metal microstructure layer comprises periodically arranged cross-shaped structures comprising a first stripe-shaped structure extending in a first direction and a second stripe-shaped structure extending in a second direction, wherein both the first direction and the second direction are perpendicular to the substrate thickness direction.
12. The MEMS thermopile infrared detector of claim 11, wherein a distance between adjacent cross-shaped structures is 2000 nm to 4000 nm; and/or
The first direction is perpendicular to the second direction, and the width of the first strip-shaped structure is 200-2000 nanometers; the length of the first strip-shaped structure is 1500-2000 nanometers; the width of the second strip-shaped structure is 200-2000 nanometers; the length of the second strip-shaped structure is 1500-2000 nanometers.
13. A preparation method of an MEMS thermopile infrared detector comprises the following steps:
forming a first infrared absorption layer on a substrate;
forming a thermopile on the first infrared absorption layer, wherein the thermopile comprises thermocouple strips which are arranged around the central area of the absorption layer, one end of each thermocouple strip, which is close to the central area of the first infrared absorption layer, is a hot end, and one end, which is far away from the central area of the first infrared absorption layer, is a cold end;
forming a first reflecting layer on the first infrared absorption layer, wherein the first reflecting layer surrounds the thermocouple strip at the periphery of the cold end of the thermocouple strip; and
a passivation layer is formed over the thermopile and the first reflective layer.
14. The method of manufacturing of claim 13, wherein the thermopile comprises a plurality of sets of thermocouple strips with a void region between adjacent sets of thermocouple strips;
the first reflective layer includes a first portion opposite the cold ends of the thermocouple strips and a second portion between adjacent sets of thermocouple strips and protruding toward the blank area.
15. The method of manufacturing according to claim 14, further comprising:
forming an etching stop layer on the substrate, and then forming the first infrared absorption layer on the etching stop layer; and
and forming a back cavity on the substrate, wherein the back cavity penetrates through the substrate and exposes the etching stop layer.
16. The method of manufacturing according to claim 15, further comprising: and forming a second reflecting layer on the surface of the substrate away from the etching stop layer and the surface of the etching stop layer exposed through the back cavity.
17. The method of any of claims 15 or 16, further comprising forming an isolation trench around the thermopile in the void region, the isolation trench extending through the passivation layer and the first infrared absorbing layer and communicating with the back cavity.
18. The method of manufacturing according to claim 17, wherein the isolation groove comprises a plurality of mutually separated stripe grooves parallel to the extending direction of the adjacent thermocouple strip in the extending direction parallel to the surface of the first infrared absorbing layer.
19. The method of any one of claims 14-18, further comprising:
forming a second infrared absorption layer on the passivation layer;
and forming a metamaterial structure on the second infrared absorption layer.
20. The method of manufacturing of claim 19, wherein forming the metamaterial structure comprises:
forming a metal reflecting layer on the second infrared absorption layer, wherein the projection of the metal reflecting layer on the first infrared absorption layer covers the hot end of the thermocouple strip;
forming an intermediate dielectric layer on the metal reflecting layer; and
and forming a metal microstructure layer on the intermediate dielectric layer, wherein the metal microstructure layer comprises periodically arranged structural units.
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| CN117500356A (en) * | 2024-01-03 | 2024-02-02 | 无锡芯感智半导体有限公司 | Gas sensor chip integrated with MEMS-CMOS and preparation method thereof |
| CN117500356B (en) * | 2024-01-03 | 2024-03-26 | 无锡芯感智半导体有限公司 | Gas sensor chip integrated with MEMS-CMOS and preparation method thereof |
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