CN116534788A - MEMS bridge type palladium alloy hydrogen sensing chip based on suspended membrane structure and preparation method thereof - Google Patents
MEMS bridge type palladium alloy hydrogen sensing chip based on suspended membrane structure and preparation method thereof Download PDFInfo
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- 229910001252 Pd alloy Inorganic materials 0.000 title claims abstract description 83
- 239000001257 hydrogen Substances 0.000 title claims abstract description 55
- 229910052739 hydrogen Inorganic materials 0.000 title claims abstract description 55
- 238000002360 preparation method Methods 0.000 title claims abstract description 28
- 239000012528 membrane Substances 0.000 title claims abstract description 23
- 125000004435 hydrogen atom Chemical class [H]* 0.000 title claims abstract description 13
- 239000010410 layer Substances 0.000 claims abstract description 148
- 239000000463 material Substances 0.000 claims abstract description 93
- 239000007789 gas Substances 0.000 claims abstract description 89
- 238000012360 testing method Methods 0.000 claims abstract description 57
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 47
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- FFUAGWLWBBFQJT-UHFFFAOYSA-N hexamethyldisilazane Chemical compound C[Si](C)(C)N[Si](C)(C)C FFUAGWLWBBFQJT-UHFFFAOYSA-N 0.000 claims description 52
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 34
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- 238000004519 manufacturing process Methods 0.000 claims description 23
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- 229910052757 nitrogen Inorganic materials 0.000 claims description 17
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- 239000013077 target material Substances 0.000 claims description 6
- WABPQHHGFIMREM-UHFFFAOYSA-N lead(0) Chemical compound [Pb] WABPQHHGFIMREM-UHFFFAOYSA-N 0.000 claims description 5
- 239000010409 thin film Substances 0.000 claims description 3
- 230000004044 response Effects 0.000 abstract description 11
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- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 42
- 150000002431 hydrogen Chemical class 0.000 description 30
- 229910004298 SiO 2 Inorganic materials 0.000 description 18
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- 230000002829 reductive effect Effects 0.000 description 9
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 6
- 238000001514 detection method Methods 0.000 description 6
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Classifications
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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
- B81C1/00134—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems comprising flexible or deformable structures
- B81C1/00158—Diaphragms, membranes
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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
- B81C1/00134—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems comprising flexible or deformable structures
- B81C1/00166—Electrodes
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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
- B81C1/00349—Creating layers of material on a substrate
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
- G01N27/122—Circuits particularly adapted therefor, e.g. linearising circuits
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
- G01N27/125—Composition of the body, e.g. the composition of its sensitive layer
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B2201/00—Specific applications of microelectromechanical systems
- B81B2201/02—Sensors
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Abstract
The invention discloses a MEMS bridge palladium alloy hydrogen sensing chip based on a suspended membrane structure and a preparation method thereof. Firstly, preparing a front insulating layer and a back masking layer on a silicon substrate; secondly, sequentially sputtering and depositing a palladium alloy gas-sensitive material with a bridge structure, a test electrode, a heating electrode, a lead disc and a protective layer on the insulating layer; and finally, forming a suspended film structure by etching the back masking layer and the silicon substrate. The invention builds the Wheatstone bridge based on the palladium alloy material, improves the response recovery speed on the basis of ensuring the strength of the film, and has the characteristics of high sensitivity, good selectivity and stable output signal.
Description
Technical Field
The invention relates to a MEMS bridge type palladium alloy hydrogen sensing chip based on a suspended membrane structure and a preparation method thereof.
Background
With the rapid development of socioeconomic performance, energy and environmental problems have become increasingly of concern, and thus new energy sources that are ideal, efficient and clean are urgently needed, thereby effectively completing the sustainable development of the environment. The hydrogen is an ideal novel energy source, has the advantages of safety, high efficiency, sustainability and the like, and is widely developed and applied; however, hydrogen has the characteristics of inflammability, explosiveness and easy leakage, is not easy to control in the production, transportation and use processes, and can explode when encountering open fire or electric spark when the hydrogen content in the air is within the range of 4-74.2%. Therefore, the development of the hydrogen sensor for detecting hydrogen leakage and controlling hydrogen has important research significance and application value, and has wide application in the fields of hydrogen production and storage, industrial agriculture, chemical food, electronic medical treatment and the like.
There have been many different types of hydrogen sensors currently under intensive study, which can be classified into catalytic combustion type, electrochemical type, metal oxide semiconductor type, palladium alloy type, optical type, and the like. The catalytic combustion type hydrogen sensor has high detection limit, the electrochemical type hydrogen sensor has short service life, the metal oxide semiconductor type hydrogen sensor has poor selectivity, the optical type hydrogen sensor has complex structure and high cost, and the long-term high-precision detection requirement of trace hydrogen is difficult to meet. The palladium material has high dissolution rate and good selectivity to hydrogen, and is widely selected as a gas-sensitive material of a hydrogen sensor, but a pure palladium film is easy to generate hydrogen embrittlement, so that the stability of the sensor is greatly influenced; the hydrogen sensor based on palladium and an alloy system thereof can work at room temperature, has good selectivity, high stability and wide range, and is widely researched and applied.
However, the response sensitivity of the palladium alloy type hydrogen sensor is low, the accuracy of the sensor needs to be improved, and the output resistance signal also needs to be converted, so that the further application development of the palladium alloy type hydrogen sensor is limited. The output signals can be amplified and converted by utilizing the bridge structure, and the four palladium alloy hydrogen sensing chips are integrated into a bridge circuit for testing, so that the problems of high power consumption, unbalanced initial bridge, large device size and the like are solved; therefore, the preparation of the bridge type palladium alloy gas-sensitive material on a single palladium alloy hydrogen sensing chip is considered, and the gas-sensitive film is deposited on a suspended film type micro-hotplate consisting of a heating resistor and a temperature measuring resistor through MEMS compatible processes such as magnetron sputtering deposition, so that the method has the characteristics of miniaturization, batch production, low power consumption, high consistency and repeatability, can meet the hydrogen detection in various application scenes, and realizes large-scale application.
Disclosure of Invention
In order to solve the defects in the prior art, the invention aims to solve the problem of lower sensitivity of the traditional palladium alloy hydrogen sensor, and provides a MEMS electric bridge type palladium alloy hydrogen sensor chip based on a suspended membrane structure and a preparation method thereof, wherein a Wheatstone bridge is constructed based on a palladium alloy material, and an output signal is amplified; meanwhile, the MEMS compatible technology is utilized to integrate and prepare the bridge type palladium alloy material on the suspended membrane type micro-hotplate, so that the preparation technology of the sensing chip is simplified, the response recovery speed is improved on the basis of guaranteeing the strength of the film, and the MEMS integrated micro-hotplate has the characteristics of high sensitivity, good selectivity, stable output signal, accurate temperature control and mass production.
The invention is realized by the following technical scheme.
In one aspect of the invention, a preparation method of a MEMS bridge type palladium alloy hydrogen sensing chip based on a suspended membrane structure is provided, comprising the following steps:
1) Preparation of SiO on the front and back of Si substrate 2 -Si 3 N 4 The double-layer composite film is respectively a front insulating layer and a back masking layer, and is annealed;
2) Manufacturing a gas-sensitive material mask on the annealed front insulating layer through a photoresist-uniformizing photoetching developing process, and defining a gas-sensitive material pattern;
3) Sequentially depositing a Ti adhesion layer and a Pd alloy gas-sensitive material by direct-current sputtering;
4) Obtaining Pd alloy gas-sensitive material through a stripping process;
5) Manufacturing an electrode layer mask on the front insulating layer through a photoresist-homogenizing photoetching developing process, defining patterns of a test electrode, a heating electrode and a lead disc of the heating electrode, and performing front alignment by using an alignment mark in the photoetching process;
6) Sequentially depositing a Cr adhesion layer and an Au electrode layer by electron beam evaporation;
7) Obtaining an Au electrode layer through a stripping process;
8) On the front insulating layer, a protective layer mask is manufactured through a photoresist-uniformizing photoetching developing process, and Si is defined 3 N 4 A protective layer pattern, wherein alignment marks are used for front surface alignment in the photoetching process;
9) Deposition of Si by radio frequency sputtering 3 N 4 A protective layer;
10 Through a stripping process, si is obtained 3 N 4 A protective layer and annealing treatment;
11 Manufacturing a back heat insulation groove mask on the back masking layer through a photoresist-uniformizing photoetching developing process, and performing back alignment by using an alignment mark in the photoetching process;
12 Back side SiO sequentially by plasma dry etching 2 -Si 3 N 4 Etching the masking layer and circularly etching the deep silicon to form a suspended film structure;
13 Cleaning the whole wafer; dicing is carried out through laser hidden cutting, and a sensing chip is obtained.
The further scheme in the method is as follows:
in the step 1), the SiO is prepared by a thermal oxidation method 2 Thin film, and then preparing Si by adopting a plasma enhanced chemical vapor deposition method 3 N 4 Film, siO 2 The thickness of the film is 500+/-10 nm, si 3 N 4 The thickness of the film is 250+/-10 nm; annealing for 5-6h in 500-600 deg.C air environment.
In the steps 2), 5) and 8), the photoresist homogenizing and photoetching developing process comprises the steps of respectively homogenizing and coating the adhesive hexamethyldisilazane at the low speed of 450-550r/min, 5-7s and the high speed of 1400-1600r/min and 38-42s, and drying at 120 ℃ for 8-12min; uniformly coating a photoresist EPG535 at low speed of 450-550r/min, 5-7s and high speed of 900-1100r/min and 38-42s, and drying at 95 ℃ for 4-6min; aligning the mask plate and the silicon wafer, and exposing for 6-8s; developing for 17-25s, and drying at 110 ℃ for 18-22min.
In the step 3), a Pd alloy target material is used for sequentially depositing a 20-30nm Ti adhesion layer and 40-80nm Pd alloy, the sputtering current is 200-250mA, and the sputtering time is 4-8min.
In the steps 4), 7) and 10), the stripping process comprises soaking in acetone solution for 1-2h and ultrasonic treatment for 5-10min; soaking in absolute ethanol for 4-6min; soaking in deionized water for 4-6min; drying with nitrogen, and drying at 110 ℃ for 18-22min; annealing for 2h under nitrogen environment at 200-300 ℃.
In the step 6), the thickness of the deposited Cr adhesion layer is 30-50nm, and the thickness of the Au electrode layer is 150-200nm.
In step 9), si is deposited 3 N 4 The thickness of the protective layer is 200-250nm.
In the step 11), a heat insulation groove mask is manufactured through a photoresist homogenizing photoetching developing process, photoresist EPG535 is homogenized on the front surface of a silicon wafer, the speed is 450-550r/min for 5-7s, the speed is 900-1100r/min, the speed is 38-42s, and the temperature is 95 ℃ for 4-6min; uniformly coating photoresist AZ4620 on the back of the silicon wafer, drying at a low speed of 450-550r/min for 5-7s and a high speed of 2800-3200r/min for 45-55s at 95 ℃ for 4-6min; aligning the mask plate with the back of the silicon wafer, then performing back exposure for 28-32s and front full exposure for 6-8s, developing for 75-110s, cleaning residual photoresist on the front of the silicon wafer, drying for 18-22min at 110 ℃, and hardening for 55-65min at 135 ℃.
In another aspect of the invention, a MEMS electric bridge palladium alloy hydrogen sensing chip based on a suspended membrane structure prepared by the method is provided, which comprises a Si substrate, wherein SiO is respectively distributed on the front and the back of the Si substrate 2 -Si 3 N 4 A front insulating layer and a back masking layer which are formed by the composite film, wherein the back masking layer and the silicon substrate are provided with heat insulation grooves; the method comprises the steps that an electric bridge type palladium alloy gas-sensitive material and an electrode layer are arranged on a front insulating layer, and the electrode layer comprises a test electrode, a heating electrode and a lead disc thereof; the bridge arm of the test electrode is connected with the resistance strip of the gas sensitive material to form a Wheatstone bridge, and Si is covered on the gas sensitive material and the electrode layer 3 N 4 And (3) a protective layer.
The further scheme in the above-mentioned structure still lies in:
the palladium alloy gas-sensitive material is four fold line surrounding type resistor strips, two test gas-sensitive material resistor strips and a lead wire disc are exposed in the air, and the other two fixed gas-sensitive material resistor strips are covered under the protective layer; the bridge arm of the test electrode is connected with the resistance strip of the gas sensitive material through a square contact disc; the heating electrodes are in two groups of spiral structures and are arranged on the left side and the right side of the Wheatstone bridge.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
1. the Wheatstone bridge is constructed based on the palladium alloy gas-sensitive material, and the gas-sensitive film based on the bridge structure has the characteristics of high sensitivity, good selectivity and stable output signal.
2. The palladium alloy gas-sensitive material with the thickness of 40-80nm is deposited by controlling direct current sputtering, and the palladium alloy target material is directly sputtered in the preparation process, so that an alloy system is easy to form, and the process repeatability is high and the consistency is good; in addition, the thickness of the gas-sensitive material is thinner, which is favorable for the rapid stabilization of the hydrogen atom diffusion process and improves the response recovery speed on the basis of ensuring the film strength.
3. The test electrode, the heating electrode and the lead wire disc are all made of 150-200nm Au electrode layers, have high conductivity, chemical stability and thermal stability, and are suitable for alloy wire ball welding of leads; the preparation is carried out simultaneously through electron beam evaporation and deposition, so that the process cost can be reduced, the working procedures can be reduced, and the yield can be improved; in addition, a square contact disc is designed at the joint of the test electrode and the gas sensitive material, so that the test electrode and the gas sensitive material can be connected smoothly; the spiral layout of the heating electrode can ensure the rapid and uniform heating process.
4. By Si 3 N 4 The protective layer can effectively prevent hydrogen from passing through and improve the stability of the electrode layer, and ensure that the bridge circuit effectively works in a hydrogen atmosphere; the preparation method has the characteristics of uniformity and compactness through magnetron sputtering deposition, can directly prepare the patterned protective layer, and is easy to control and higher in yield compared with the traditional process of defining the pattern through deposition and etching.
5. Compared with the traditional wet etching, the method for preparing the suspended film structure by the back dry etching has the advantages of high etching efficiency and easiness in control, can vertically transfer the thermally-insulated groove pattern defined by photoetching onto the suspended film, and has higher yield.
6. The suspended membrane bridge type palladium alloy hydrogen sensing chip prepared by the MEMS compatible process has the advantages of smaller size, lower power consumption, mass production and good hydrogen response characteristic, and meets the requirements of the current market on hydrogen sensors.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate and do not limit the invention, and together with the description serve to explain the principle of the invention:
FIG. 1 is a three-dimensional perspective view of a MEMS bridge type palladium alloy hydrogen sensor chip of the present invention;
FIG. 2 is a three-dimensional exploded view of a MEMS bridge palladium alloy hydrogen sensor chip of the present invention;
FIGS. 3 (a) - (e) are two-dimensional plan view/reticle patterns of four defined patterns of the MEMS bridge palladium alloy hydrogen sensor chip of the present invention;
FIGS. 4 (a) - (d) are schematic diagrams of two-dimensional planes during the preparation of the MEMS bridge palladium alloy hydrogen sensor chip of the present invention;
fig. 5 (a) - (m) are process flow diagrams for preparing the MEMS bridge palladium alloy hydrogen sensor chip of the present invention.
In the figure: 1. si (Si) 3 N 4 A masking layer; 2. SiO (SiO) 2 A masking layer; 3. a Si substrate; 4. a heat insulation groove; 5. SiO (SiO) 2 An insulating layer; 6. si (Si) 3 N 4 An insulating layer; 7. pd alloy gas-sensitive material; 8. Cr-Au heating electrode; 9. Cr-Au test electrode; 10. si (Si) 3 N 4 A protective layer; 8-1 to 8-4 are four lead plates of the heating electrode; 9-1 to 9-4 are four lead pads of the test electrode.
Detailed Description
The present invention will now be described in detail with reference to the drawings and the specific embodiments thereof, wherein the exemplary embodiments and descriptions of the present invention are provided for illustration of the invention and are not intended to be limiting.
As shown in FIG. 1 and FIG. 2, the MEMS bridge palladium alloy hydrogen sensing chip based on the suspended membrane structure comprises Si which are distributed on the back surface of a Si substrate 3 in sequence 3 N 4 Masking layer 1 and SiO 2 A back mask layer formed by compounding mask layer 2, si 3 N 4 Masking layer 1, siO 2 The back surfaces of the masking layer 2 and the Si substrate 3 are provided with heat insulation grooves 4 for forming a suspended film structure; the front surface of the Si substrate 3 is made of SiO 2 Insulating layer 5 and Si 3 N 4 Front insulating layer formed by compounding insulating layers 6, si 3 N 4 The insulating layer 6 is provided with a Pd alloy gas-sensitive material 7 and an electrode layer, the electrode layer comprises two pairs of Cr-Au heating electrodes 8 and four lead discs 8-1 to 8-4 of the heating electrodes, four groups of Cr-Au test electrodes 9 and four lead discs 9-1 to 9-4 of the test electrodes, the Cr-Au heating electrodes and the Cr-Au test electrodes are positioned on the same plane, the same materials are adopted, and the preparation is based on the same procedure; covering the gas sensitive material and the electrode layer with Si 3 N 4 And a protective layer 10 for protecting the electrodes and fixing the gas sensitive material, exposing only the electrode lead pad and the test gas sensitive material.
FIGS. 3 (a) - (e) are schematic diagrams of a reticle embodiment of the present invention, on which cross-shaped coarse alignment marks and fine alignment marks are designed, wherein the coarse alignment marks are conveniently found and aligned in the alignment process, then the positions of the fine alignment marks are adjusted, and the alignment is performed after the magnification of a microscope is adjusted, so that the relative positions of material layers prepared for multiple times can be ensured to be fixed; the size of the scribing channel reserved between the two chip elements is 600 mu m, so that the upper material layer can not be damaged in the scribing process, and 1600 sensing chips can be obtained on the whole wafer after scribing.
Fig. 3 (b) - (e) are schematic partial views of a mask plate with four defined patterns of a sensing chip, fig. 3 (b) is a palladium alloy gas-sensitive material 7, and the mask plate is composed of four broken line surrounding resistor strips, wherein two upper and lower opposite resistor strips are test gas-sensitive materials, and are exposed to air to detect the change of hydrogen concentration; the left and right opposite resistance strips are made of fixed gas-sensitive materials and are covered under the protective layer.
As shown in fig. 3 (c), the electrode layer consists of the heating electrode 8 and the test electrode 9, and is arranged symmetrically at the center, the electrode width is 20 μm, and the lead pad size is 200 μm×200 μm; the heating electrode 8 consists of two pairs of heating electrodes on the left side and the right side, and the corresponding lead wire discs 8-1 to 8-4 are in spiral surrounding type, fully surround the bridge circuit and ensure the rapid and uniform heating process. The test electrode 9 is composed of four groups of electrodes corresponding to the upper and lower lead pads 9-1 to 9-4, wherein one pair of diagonally distributed electrodes (lead pads 9-1, 9-4) is used for providing input direct current voltage to the bridge, and the other pair of diagonally distributed electrodes (lead pads 9-2, 9-3) is tested.
As shown in FIG. 3 (d), si 3 N 4 The protective layer 10 has windows of 4 lead pads on the left and right sides, and a window for testing gas sensitive material in the middle.
As shown in FIG. 3 (e), the heat insulating groove 4 is at the center of the chip and has a size of 460. Mu.m.times.460. Mu.m.
Fig. 4 (a) -4 (d) are two-dimensional schematic plan views of the sensor chip of the present invention during the processing process, showing the preparation flow and the relative positional relationship of four defined patterns, and first preparing a Pd alloy gas-sensitive material 7, as shown in fig. 4 (a); secondly, preparing a heating electrode 8 and a testing electrode 9, wherein four groups of testing electrodes and four gas-sensitive material resistor strips are connected through square contact plates to form a Wheatstone bridge, and the size of the Wheatstone bridge is 40 mu m multiplied by 40 mu m, as shown in fig. 4 (b); then Si is prepared 3 N 4 A protective layer 10, the other areas except for the eight lead pads and the test gas sensitive material are covered, as shown in fig. 4 (c); finally, an insulating trench 4 is prepared from the back side to form a suspended film structure comprising a wheatstone bridge circuit and heating electrodes thereon, as shown in fig. 4 (d).
In the invention, the test electrode and the heating electrode are made of the same materials and parameters based on the same process, the test electrode is connected with the gas-sensitive material to form a Wheatstone bridge, the protective layer is used for protecting the electrode and fixing the gas-sensitive material, and only the electrode lead disc and the test gas-sensitive material are exposed; the back masking layer and the silicon substrate are provided with heat insulation grooves for forming a suspended film structure.
Wherein, the front insulating layer and the back masking layer adopt SiO 2 -Si 3 N 4 Composite film, siO prepared by thermal oxidation 2 The film is compressive stress, si prepared by PECVD 3 N 4 The thin films are tensile stress, and stress compensation can be realized by mutually overlapping proper film thicknesses.
The palladium alloy gas-sensitive material 7 is four fold line surrounding resistor strips, the structure of the palladium alloy gas-sensitive material is four symmetrically arranged arc bending resistor strips, the outer parts of the bending resistor strips are flush, the extending parts of the middle bending resistor strips are oppositely arranged, two ends of each arc bending resistor strip are respectively opened, and the two ends of each arc bending resistor strip are connected with a square contact disc of the test electrode 9.
The test electrode 9 consists of four groups of bridge arms, and is connected with four gas sensitive material resistor bars to form a Wheatstone bridge; in consideration of alignment and processing errors, the square contact disc is arranged at the joint, so that the gas-sensitive material can be effectively covered, and meanwhile, the basic resistance values of the four resistor strips are ensured to be equal, and the bridge is initially balanced. One pair of the test electrodes is used for providing input direct-current voltage for the bridge, the other pair of the test electrodes is used for testing, and the heating electrode is used for providing stable working temperature for the chip.
The heating electrodes 8 are designed into two groups of spiral structures, are arranged on the left side and the right side of the Wheatstone bridge, fully surround the bridge circuit, and ensure the rapid and uniform heating process.
The gas-sensitive material and the electrode are provided with round corners at the transition positions of the fold lines, so that the phenomenon of stress concentration is avoided, and meanwhile, an adhesive layer is designed between the gas-sensitive material and the electrode and the insulating layer for enhancing the connection strength; the gas-sensitive material arrangement is compatible with the electrode arrangement in a matching way, the length of the gas-sensitive material arrangement is increased as much as possible, the line width is designed to be 10 micrometers, the gas-sensitive material arrangement is used for improving the base resistance, and the signal response and the anti-interference capability of the gas-sensitive film are enhanced.
The protective layer is Si 3 N 4 Compact and uniform, can effectively prevent diffusion of hydrogen, ensure stable resistance of the fixed gas-sensitive material, ensure stability of the heating electrode and the testing electrode, and ensure stable and reliable testing process.
Referring to fig. 5 (a) -5 (m), the preparation method of the MEMS bridge palladium alloy hydrogen sensing chip based on the suspended membrane structure of the present invention is as follows:
1) As shown in FIGS. 5 (a) and (b), siO is prepared on the front and back surfaces of Si substrate 3 by thermal oxidation and plasma enhanced chemical vapor deposition 2 -Si 3 N 4 Double-layer composite film, double-sided thermal oxidation of 500+/-10 nm SiO 2 Double-sided PECVD (plasma Low pressure chemical vapor deposition) 250+ -10 nm Si 3 N 4 And annealing at 500-600deg.C for 5-6h to form a composition comprising SiO 2 Insulating layer 5, si 3 N 4 Insulating layer 6 and Si 3 N 4 Masking layer 1, siO 2 SiO of masking layer 2 2 -Si 3 N 4 Double-layer composite thinA membrane;
2) As shown in FIG. 5 (c), siO is present on the front side 2 -Si 3 N 4 And manufacturing a gas sensitive material mask on the double-layer composite film through a photoresist-homogenizing photoetching developing process, and defining a pattern of the Pd alloy gas sensitive material 7.
Firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 450-550r/min at low speed and 5-7s, the speed is 1400-1600r/min at high speed and 38-42s, and drying at 120 ℃ for 8-12min; then evenly coating the photoresist (EPG 535), and drying at the low speed of 450-550r/min, 5-7s, the high speed of 900-1100r/min, 38-42s and the temperature of 95 ℃ for 4-6min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 6-8s; finally, developing in 5 per mill NaOH solution for 17-25s, and drying at 110 ℃ for 18-22min;
3) As shown in fig. 5 (d), a Ti adhesion layer and a Pd alloy material are sequentially deposited by direct current sputtering, a 40-80nm Pd alloy film is directly sputtered and deposited on a palladium alloy target, the thickness of the Ti adhesion layer is 20-30nm, and the response speed is improved on the basis of ensuring the strength of the film; wherein the Pd alloy target is directly used for preparation, the sputtering current is 200-250mA, and the sputtering time is 4-8min;
4) As shown in fig. 5 (e), ultrasonic treatment is performed for 5-10min after soaking in an acetone solution for 1-2h through a stripping process; soaking in absolute ethanol for 4-6min; soaking in deionized water for 4-6min; finally, drying with nitrogen for 18-22min at 110 ℃ to obtain Pd alloy gas-sensitive material 7, which is divided into a fixed gas-sensitive material and a test gas-sensitive material;
5) As shown in FIG. 5 (f), si is present on the front surface 3 N 4 Manufacturing an electrode layer mask on the insulating layer 6 through a photoresist-homogenizing photoetching development process, defining patterns of a Cr-Au test electrode 9, lead discs 9-1 to 9-4 of the Cr-Au test electrode, a Cr-Au heating electrode 8 and lead discs 8-1 to 8-4 of the Cr-Au heating electrode, and performing front alignment by using an alignment mark in the photoetching process to determine the relative positions of the electrode layer and the gas sensitive material, so that the test electrode and the gas sensitive material can be connected;
manufacturing an electrode layer mask according to the same scheme as that of the step 2) spin-coating adhesive HMDS (hexamethyldisilazane) and spin-coating photoresist (EPG 535);
6) As shown in fig. 5 (g), a 30-50nm Cr adhesion layer and a 150-200nm Au electrode layer were sequentially deposited by electron beam evaporation; the stable peeling-off in the process of lead wire can be ensured, and the power consumption is reduced;
7) As shown in fig. 5 (h), according to the stripping process of step 4), a Cr-Au test electrode 9 and its lead pads 9-1 to 9-4, a Cr-Au heating electrode 8 and its lead pads 8-1 to 8-4 are obtained; the test electrode 9 and the Pd alloy gas-sensitive material 7 form a Wheatstone bridge;
8) As shown in fig. 5 (i), si is present on the front surface 3 N 4 On the insulating layer 6, a protective layer mask is manufactured by a photoresist-uniformizing photoetching developing process, and Si is defined 3 N 4 The pattern of the protective layer 10 is subjected to front surface alignment by using an alignment mark in the photoetching process, the relative positions of the protective layer, the electrode layer and the gas sensitive material are determined, the protective layer can be ensured to effectively cover the electrode and fix the gas sensitive material, and the lead disc and the test gas sensitive material are exposed;
manufacturing a protective layer mask according to the same scheme as that of the step 2) of uniformly coating adhesive HMDS (hexamethyldisilazane) and uniformly coating photoresist (EPG 535);
9) As shown in FIG. 5 (j), 200-250nm Si is deposited by RF sputtering 3 N 4 A protective layer;
10 As shown in FIG. 5 (k), si is obtained according to the lift-off process of step 4) 3 N 4 A protective layer 10; deposition of Si by radio frequency sputtering 3 N 4 The protective layer is directly prepared, and compared with the traditional process of defining patterns by deposition and etching, the method is easy to control and has higher yield;
11 As shown in FIG. 5 (l), si is provided on the back surface 3 N 4 Masking layer 1 and SiO 2 On the masking layer 2, a mask of the heat insulation groove 4 is manufactured through a photoresist-homogenizing photoetching developing process, and alignment marks are used for back surface alignment in the photoetching process, so that the heat insulation groove 4 is ensured to be positioned at the center of the chip;
firstly, uniformly coating photoresist (EPG 535) on the front surface of a silicon wafer, wherein the speed is 450-550r/min at low speed and 5-7s, the speed is 900-1100r/min at high speed and 38-42s, and drying is carried out at 95 ℃ for 4-6min; secondly, uniformly coating photoresist (AZ 4620) on the back of the silicon wafer, drying at a low speed of 450-550r/min, 5-7s, a high speed of 2800-3200r/min and 45-55s for 4-6min at a temperature of 95 ℃; then aligning the mask plate and the back of the silicon wafer by utilizing a microscope under a photoetching machine, and then exposing the back for 28-32s and exposing the front for 6-8s; finally developing in 7 per mill NaOH solution for 75-110s, cleaning residual photoresist on the front surface of the silicon wafer, drying at 110 ℃ for 18-22min, and hardening at 135 ℃ for 55-65min;
12 As shown in FIG. 5 (m), back side SiO is sequentially performed by Inductively Coupled Plasma (ICP) dry etching 2 -Si 3 N 4 Masking layer etching and deep silicon etching, firstly etching 200+ -10 s Si 3 N 4 Layer and 200+ -10 sSiO 2 The layer is then circularly etched for a plurality of times until the insulating layer is stopped, and a suspended film structure is formed;
13 Cleaning the whole wafer, soaking in acetone solution for 5-10min, soaking in absolute ethanol for 4-6min, soaking in deionized water for 4-6min, and oven drying at 110deg.C for 18-22min. Finally, scribing is carried out through laser hidden cutting, and a sensing chip is obtained.
The preparation of the sensor chip of the present invention is further illustrated by the following examples.
Example 1
1) SiO preparation by thermal oxidation and plasma enhanced chemical vapor deposition on front and back sides of 4 inch 400 micron thick Si substrates 2 -Si 3 N 4 Double-layer composite film, double-sided thermal oxidation of 510nm SiO 2 Double-sided PECVD (plasma Low pressure chemical vapor deposition) 260nm Si 3 N 4 And annealing for 6h in 500 ℃ air environment to form SiO 2 -Si 3 N 4 A double-layer composite film;
2) On the front side Si 3 N 4 Manufacturing a gas sensitive material mask on the insulating layer through a photoresist-homogenizing photoetching developing process, and defining Pd alloy gas sensitive material patterns;
firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 450r/min at low speed and 7s, the speed is 1400r/min at high speed and 42s, and drying is carried out at 120 ℃ for 12min; then evenly coating photoresist (EPG 535), drying at a low speed of 450r/min, 7s, a high speed of 900r/min and 42s at 95 ℃ for 6min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 8s; finally, developing for 20s in 5 per mill NaOH solution, and drying for 20min at 110 ℃;
3) Sequentially depositing a 30nm Ti adhesion layer and an 80nm Pd alloy material by direct current sputtering, wherein the material is directly prepared by using a Pd alloy target material, the sputtering current is 250mA, and the sputtering time is 8min;
4) Soaking in acetone solution for 1h by a stripping process, and performing ultrasonic treatment for 8min; soaking in absolute ethanol for ultrasonic treatment for 6min; soaking in deionized water for 5min; finally, drying by nitrogen for 22min at 110 ℃ to obtain the Pd alloy gas-sensitive material;
5) On the front side Si 3 N 4 And manufacturing an electrode layer mask on the insulating layer through a photoresist-homogenizing photoetching development process, defining a Cr-Au test electrode and a lead disc thereof, a Cr-Au heating electrode and a lead disc pattern thereof, and performing front alignment by using an alignment mark in the photoetching process.
Firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 450r/min at low speed and 7s, the speed is 1400r/min at high speed and 42s, and drying is carried out at 120 ℃ for 12min; then evenly coating photoresist (EPG 535), drying at a low speed of 450r/min, 7s, a high speed of 900r/min and 42s at 95 ℃ for 6min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 8s; finally, developing 25s in 5 per mill NaOH solution, and drying at 110 ℃ for 22min;
6) Sequentially depositing a 50nm Cr adhesion layer and a 200nm Au electrode layer by electron beam evaporation;
7) Soaking in acetone solution for 1.5h by a stripping process, and then performing ultrasonic treatment for 5min; soaking in absolute ethanol for ultrasonic treatment for 6min; soaking in deionized water for 5min; finally, drying by nitrogen for 22min at 110 ℃ to obtain a Cr-Au test electrode and a lead disc thereof, and a Cr-Au heating electrode and a lead disc thereof; the test electrode and the Pd alloy gas-sensitive material form a Wheatstone bridge;
8) On the front side Si 3 N 4 On the insulating layer, a protective layer mask is manufactured through a photoresist-uniformizing photoetching developing process, and Si is defined 3 N 4 And (3) carrying out front surface alignment on the protective layer pattern by using an alignment mark in the photoetching process, and determining the relative positions of the protective layer, the electrode layer and the gas-sensitive material.
Firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 450r/min at low speed and 7s, the speed is 1400r/min at high speed and 42s, and drying is carried out at 120 ℃ for 12min; then evenly coating photoresist (EPG 535), drying at a low speed of 450r/min, 7s, a high speed of 900r/min and 42s at 95 ℃ for 6min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 8s; finally, developing 25s in 5 per mill NaOH solution, and drying at 110 ℃ for 22min;
9) Deposition of 250nm Si by radio frequency sputtering 3 N 4 A protective layer;
10 Through a stripping process, soaking in an acetone solution for 2 hours, and then carrying out ultrasonic treatment for 10 minutes; soaking in absolute ethanol for ultrasonic treatment for 6min; soaking in deionized water for 6min; finally drying with nitrogen, drying at 110 ℃ for 22min, and annealing for 2h in a nitrogen environment at 300 ℃ to obtain Si 3 N 4 A protective layer;
11 At the back Si) 3 N 4 Masking layer and SiO 2 Manufacturing a mask of the heat insulation groove on the masking layer through a photoresist-homogenizing photoetching developing process, and performing back surface alignment by using an alignment mark in the photoetching process to ensure that the heat insulation groove is positioned at the center of the chip;
firstly, uniformly coating photoresist (EPG 535) on the front surface of a silicon wafer, wherein the low speed is 450r/min, the low speed is 7s, the high speed is 1000r/min, the high speed is 40s, and the drying is carried out for 6min at 95 ℃; secondly, uniformly coating photoresist (AZ 4620) on the back of the silicon wafer, drying at a low speed of 450r/min, 7s and a high speed of 2800r/min, 55s and a temperature of 95 ℃ for 6min; then aligning the mask plate and the back of the silicon wafer by utilizing a microscope under a photoetching machine, and then exposing the back for 32s and exposing the front for 8s; finally, developing for 100s in 7 per mill NaOH solution, cleaning residual photoresist on the front surface of the silicon wafer, drying for 22min at 110 ℃, and hardening for 55min at 135 ℃;
12 Back side SiO sequentially by Inductively Coupled Plasma (ICP) dry etching 2 -Si 3 N 4 Masking layer etching and deep silicon etching, first etching 210s Si 3 N 4 Layer and 210s SiO 2 The layer is then circularly etched for a plurality of times until the insulating layer is stopped, and a suspended film structure is formed;
13 Cleaning the whole wafer, soaking in acetone solution for 10min, soaking in absolute ethanol for 5min, soaking in deionized water for 6min, and drying at 110 ℃ for 18min. Finally, dicing is carried out through laser hidden cutting, and 1600 sensing chips with the size of 2mm multiplied by 2mm can be obtained on a 4-inch wafer.
In the chip test process, the bridge type palladium alloy gas-sensitive material can form a Wheatstone bridge circuit, the output resistance signal is converted and amplified into a voltage signal, the sensitivity can be improved by 5 times under the voltage of a 10V direct current power supply, and the detection limit is reduced to 2ppm. Meanwhile, the heat dissipation is carried out through the suspended film type micro-heat plate structure, and the power consumption can be reduced to 10mw. The response recovery time of the sensing chip is 20s/40s.
Example 2
1) SiO preparation by thermal oxidation and plasma enhanced chemical vapor deposition on front and back sides of 4 inch 400 micron thick Si substrates 2 -Si 3 N 4 Double-layer composite film, double-sided thermal oxidation of 500nm SiO 2 Double-sided PECVD (plasma Low pressure chemical vapor deposition) 250nm Si 3 N 4 And annealing at 550 ℃ for 5.5h to form SiO 2 -Si 3 N 4 A double-layer composite film;
2) On the front side Si 3 N 4 And manufacturing a gas sensitive material mask on the insulating layer through a photoresist-uniformizing photoetching developing process, and defining Pd alloy gas sensitive material patterns.
Firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 500r/min at a low speed and 6s, the speed is 1500r/min at a high speed and 40s, and drying is carried out at 120 ℃ for 10min; then evenly coating the photoresist (EPG 535), drying at a low speed of 500r/min for 6s and a high speed of 1000r/min for 40s at 95 ℃ for 5min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 7s; finally, developing 25s in 5 per mill NaOH solution, and drying at 110 ℃ for 18min;
3) Sequentially depositing a 25nm Ti adhesion layer and a 60nm Pd alloy material by direct current sputtering, wherein the material is directly prepared by using a Pd alloy target material, the sputtering current is 220mA, and the sputtering time is 6min;
4) Soaking in acetone solution for 1h by a stripping process, and then performing ultrasonic treatment for 7min; soaking in absolute ethanol for 5min; soaking in deionized water for 4min; finally, drying by nitrogen for 20min at 110 ℃ to obtain the Pd alloy gas-sensitive material;
5) On the front side Si 3 N 4 On the insulating layer, an electrode layer mask is manufactured through a photoresist-homogenizing photoetching development process, a Cr-Au test electrode and a lead disc thereof, a Cr-Au heating electrode and a lead disc pattern thereof are defined, and an alignment mark is used in the photoetching processRecording and carrying out front overlay;
firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 500r/min at a low speed and 6s, the speed is 1500r/min at a high speed and 40s, and drying is carried out at 120 ℃ for 10min; then evenly coating the photoresist (EPG 535), drying at a low speed of 500r/min for 6s and a high speed of 1000r/min for 40s at 95 ℃ for 5min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 7s; finally, developing for 20s in 5 per mill NaOH solution, and drying for 20min at 110 ℃;
6) Sequentially depositing a 40nm Cr adhesion layer and a 180nm Au electrode layer by electron beam evaporation;
7) Soaking in acetone solution for 1h by a stripping process, and then performing ultrasonic treatment for 7min; soaking in absolute ethanol for 5min; soaking in deionized water for 5min; finally, drying by nitrogen for 20min at 110 ℃ to obtain a Cr-Au test electrode and a lead disc thereof, and a Cr-Au heating electrode and a lead disc thereof; the test electrode and the Pd alloy gas-sensitive material form a Wheatstone bridge;
8) On the front side Si 3 N 4 On the insulating layer, a protective layer mask is manufactured through a photoresist-uniformizing photoetching developing process, and Si is defined 3 N 4 The pattern of the protective layer 10 is etched on the front surface by using an alignment mark in the photoetching process, and the relative positions of the protective layer, the electrode layer and the gas-sensitive material are determined;
firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 500r/min at a low speed and 6s, the speed is 1500r/min at a high speed and 40s, and drying is carried out at 120 ℃ for 10min; then evenly coating the photoresist (EPG 535), drying at a low speed of 500r/min for 6s and a high speed of 1000r/min for 40s at 95 ℃ for 5min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 7s; finally, developing for 20s in 5 per mill NaOH solution, and drying for 20min at 110 ℃;
9) Deposition of 225nm Si by radio frequency sputtering 3 N 4 A protective layer;
10 Through a stripping process, soaking in an acetone solution for 2 hours, and then carrying out ultrasonic treatment for 10 minutes; soaking in absolute ethanol for 5min; soaking in deionized water for 5min; finally drying with nitrogen, and drying at 110 ℃ for 20min to obtain Si 3 N 4 Protecting the layer, and annealing for 2 hours in a nitrogen environment at 250 ℃;
11 At least one of the above-mentioned positions)Back Si 3 N 4 Masking layer and SiO 2 Manufacturing a mask of the heat insulation groove on the masking layer through a photoresist-homogenizing photoetching developing process, and performing back surface alignment by using an alignment mark in the photoetching process to ensure that the heat insulation groove is positioned at the center of the chip;
firstly, uniformly coating photoresist (EPG 535) on the front surface of a silicon wafer, wherein the low speed is 550r/min and 6s, the high speed is 900r/min and 42s, and the drying is carried out for 5min at 95 ℃; secondly, uniformly coating photoresist (AZ 4620) on the back of the silicon wafer, drying at a low speed of 500r/min for 5s and a high speed of 3200r/min for 45s at a temperature of 95 ℃ for 5min; then aligning the mask plate and the back of the silicon wafer by utilizing a microscope under a photoetching machine, and then exposing the back for 30s and exposing the front for 6s; finally, developing for 75 seconds in 7 per mill NaOH solution, cleaning the residual photoresist on the front surface of the silicon wafer, drying for 20 minutes at 110 ℃, and hardening for 65 minutes at 135 ℃;
12 Back side SiO sequentially by Inductively Coupled Plasma (ICP) dry etching 2 -Si 3 N 4 Masking layer etching and deep silicon etching, first 200s Si is etched 3 N 4 Layer and 200s SiO 2 The layer is then circularly etched for a plurality of times until the insulating layer is stopped, and a suspended film structure is formed;
13 Cleaning the whole wafer, soaking in acetone solution for 8min, soaking in absolute ethanol for 6min, soaking in deionized water for 5min, and drying at 110 ℃ for 20min. Finally, dicing is carried out through laser hidden cutting, and 1600 sensing chips with the size of 2mm multiplied by 2mm can be obtained on a 4-inch wafer.
In the chip test process, the bridge type palladium alloy gas-sensitive material can form a Wheatstone bridge circuit, the output resistance signal is converted and amplified into a voltage signal, the sensitivity can be improved by 4 times under the voltage of an 8V direct current power supply, and the detection limit is reduced to 3ppm. Meanwhile, the heat dissipation is carried out through the suspended film type micro-heat plate structure, and the power consumption can be reduced to 7mw. The response recovery time of the sensing chip is 15s/30s.
Example 3
1) SiO preparation by thermal oxidation and plasma enhanced chemical vapor deposition on front and back sides of 4 inch 400 micron thick Si substrates 2 -Si 3 N 4 Double-layer composite film, double-sided thermal oxidation 490nm SiO 2 Double-sided PECVD (plasma Low pressure)Chemical vapor deposition) 240nm Si 3 N 4 And annealing for 5h at 600 ℃ in the air environment to form SiO 2 -Si 3 N 4 A double-layer composite film;
2) On the front side Si 3 N 4 And manufacturing a gas sensitive material mask on the insulating layer through a photoresist-uniformizing photoetching developing process, and defining Pd alloy gas sensitive material patterns.
Firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 550r/min at a low speed and 5s, the speed is 1600r/min at a high speed and 38s, and drying at 120 ℃ for 8min; then evenly coating photoresist (EPG 535), drying at a low speed of 550r/min, 5s, a high speed of 1100r/min and 38s and a temperature of 95 ℃ for 4min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 6s; finally, developing for 17s in 5 per mill NaOH solution, and drying for 22min at 110 ℃;
3) Sequentially depositing a 20nm Ti adhesion layer and a 50nm Pd alloy material by direct current sputtering, wherein the material is directly prepared by using a Pd alloy target material, the sputtering current is 200mA, and the sputtering time is 4min;
4) Soaking in acetone solution for 2h by stripping process, and then performing ultrasonic treatment for 10min; soaking in absolute ethanol for 4min; soaking in deionized water for 6min; finally, drying by nitrogen for 18min at 110 ℃ to obtain the Pd alloy gas-sensitive material;
5) On the front side Si 3 N 4 Manufacturing an electrode layer mask on the insulating layer through a photoresist-homogenizing photoetching developing process, defining a Cr-Au test electrode and a lead disc thereof, a Cr-Au heating electrode and a lead disc pattern thereof, and performing front alignment by using an alignment mark in the photoetching process;
firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 550r/min at a low speed and 5s, the speed is 1600r/min at a high speed and 38s, and drying at 120 ℃ for 8min; then evenly coating photoresist (EPG 535), drying at a low speed of 550r/min, 5s, a high speed of 1100r/min and 38s and a temperature of 95 ℃ for 4min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 6s; finally, developing for 17s in 5 per mill NaOH solution, and drying for 18min at 110 ℃;
6) Sequentially depositing a 30nm Cr adhesion layer and a 150nm Au electrode layer by electron beam evaporation;
7) Soaking in acetone solution for 2h by stripping process, and then performing ultrasonic treatment for 10min; soaking in absolute ethanol for 4min; soaking in deionized water for 6min; finally, drying by nitrogen for 18min at 110 ℃ to obtain a Cr-Au test electrode and a lead disc thereof, and a Cr-Au heating electrode and a lead disc thereof; the test electrode and the Pd alloy gas-sensitive material form a Wheatstone bridge;
8) On the front side Si 3 N 4 On the insulating layer, a protective layer mask is manufactured through a photoresist-uniformizing photoetching developing process, and Si is defined 3 N 4 And (3) carrying out front surface alignment on the protective layer pattern by using an alignment mark in the photoetching process, and determining the relative positions of the protective layer, the electrode layer and the gas-sensitive material.
Firstly, uniformly coating an adhesive HMDS (hexamethyldisilazane), wherein the speed is 550r/min at a low speed and 5s, the speed is 1600r/min at a high speed and 38s, and drying at 120 ℃ for 8min; then evenly coating photoresist (EPG 535), drying at a low speed of 550r/min, 5s, a high speed of 1100r/min and 38s and a temperature of 95 ℃ for 4min; then aligning the mask plate and the silicon wafer by a microscope under a photoetching machine, and then exposing for 6s; finally, developing for 17s in 5 per mill NaOH solution, and drying for 18min at 110 ℃;
9) Deposition of 200nm Si by radio frequency sputtering 3 N 4 A protective layer;
10 Through a stripping process, soaking in an acetone solution for 2 hours, and then carrying out ultrasonic treatment for 10 minutes; soaking in absolute ethanol for 4min; soaking in deionized water for 4min; finally drying with nitrogen, and drying at 110 ℃ for 18min to obtain Si 3 N 4 Protecting the layer, and annealing for 2 hours in a nitrogen environment at 200 ℃;
11 At the back Si) 3 N 4 Masking layer and SiO 2 Manufacturing a mask of the heat insulation groove on the masking layer through a photoresist-homogenizing photoetching developing process, and performing back surface alignment by using an alignment mark in the photoetching process to ensure that the heat insulation groove is positioned at the center of the chip;
firstly, uniformly coating photoresist (EPG 535) on the front surface of a silicon wafer, drying at a low speed of 500r/min for 5s and a high speed of 1100r/min for 38s for 4min at a temperature of 95 ℃; secondly, uniformly coating photoresist (AZ 4620) on the back of the silicon wafer, carrying out low-speed 550r/min and 5s, high-speed 3000r/min and 45s, and drying at 95 ℃ for 4min; then aligning the mask plate and the back of the silicon wafer by utilizing a microscope under a photoetching machine, and then exposing the back for 28s and exposing the front for 6s; finally developing for 75 seconds in 7 per mill NaOH solution, cleaning the residual photoresist on the front surface of the silicon wafer, drying for 18 minutes at 110 ℃, and hardening for 60 minutes at 135 ℃;
12 Back side SiO sequentially by Inductively Coupled Plasma (ICP) dry etching 2 -Si 3 N 4 Masking layer etching and deep silicon etching, first 190s Si is etched 3 N 4 Layer and 190s SiO 2 The layer is then circularly etched for a plurality of times until the insulating layer is stopped, and a suspended film structure is formed;
13 Cleaning the whole wafer, soaking in acetone solution for 5min, soaking in absolute ethanol for 4min, soaking in deionized water for 4min, and drying at 110 ℃ for 22min. Finally, dicing is carried out through laser hidden cutting, and 1600 sensing chips with the size of 2mm multiplied by 2mm can be obtained on a 4-inch wafer.
In the chip test process, the bridge type palladium alloy gas-sensitive material can form a Wheatstone bridge circuit, the output resistance signal is converted and amplified into a voltage signal, the sensitivity can be improved by 3 times under the voltage of a 6V direct current power supply, and the detection limit is reduced to 5ppm. Meanwhile, the heat dissipation is carried out through the suspended film type micro-heat plate structure, and the power consumption can be reduced to 5mw. The response recovery time of the sensing chip is 10s/20s.
The method adopts magnetron sputtering to deposit the bridge type palladium alloy gas-sensitive film, can convert and amplify the resistance signal into the voltage signal for output, and has a faster response recovery speed; meanwhile, the preparation process is compatible with the MEMS process, and the gas-sensitive material is integrated on the suspended membrane type micro-hotplate to be produced in a large scale, so that the method has good consistency and lower power consumption, and lays a foundation for popularization and application of the hydrogen sensing chip.
The invention is not limited to the above embodiments, and based on the technical solution disclosed in the invention, a person skilled in the art may make some substitutions and modifications to some technical features thereof without creative effort according to the technical content disclosed, and all the substitutions and modifications are within the protection scope of the invention.
Claims (10)
1. The preparation method of the MEMS bridge type palladium alloy hydrogen sensing chip based on the suspended membrane structure is characterized by comprising the following steps of:
1) Preparation of SiO on the front and back of Si substrate 2 -Si 3 N 4 The double-layer composite film is respectively a front insulating layer and a back masking layer, and is annealed;
2) Manufacturing a gas-sensitive material mask on the annealed front insulating layer through a photoresist-uniformizing photoetching developing process, and defining a gas-sensitive material pattern;
3) Sequentially depositing a Ti adhesion layer and a Pd alloy gas-sensitive material by direct-current sputtering;
4) Obtaining Pd alloy gas-sensitive material through a stripping process;
5) Manufacturing an electrode layer mask on the front insulating layer through a photoresist-homogenizing photoetching developing process, defining patterns of a test electrode, a heating electrode and a lead disc of the heating electrode, and performing front alignment by using an alignment mark in the photoetching process;
6) Sequentially depositing a Cr adhesion layer and an Au electrode layer by electron beam evaporation;
7) Obtaining an Au electrode layer through a stripping process;
8) On the front insulating layer, a protective layer mask is manufactured through a photoresist-uniformizing photoetching developing process, and Si is defined 3 N 4 A protective layer pattern, wherein alignment marks are used for front surface alignment in the photoetching process;
9) Deposition of Si by radio frequency sputtering 3 N 4 A protective layer;
10 Through a stripping process, si is obtained 3 N 4 A protective layer and annealing treatment;
11 Manufacturing a back heat insulation groove mask on the back masking layer through a photoresist-uniformizing photoetching developing process, and performing back alignment by using an alignment mark in the photoetching process;
12 Back side SiO sequentially by plasma dry etching 2 -Si 3 N 4 Etching the masking layer and circularly etching the deep silicon to form a suspended film structure;
13 Cleaning the whole wafer; dicing is carried out through laser hidden cutting, and a sensing chip is obtained.
2. MEMS bridge palladium alloy hydrogen sensing chip preparation method based on suspended membrane structure as claimed in claim 1The method is characterized in that in the step 1), the SiO is prepared by adopting a thermal oxidation method 2 Thin film, and then preparing Si by adopting a plasma enhanced chemical vapor deposition method 3 N 4 Film, siO 2 The thickness of the film is 500+/-10 nm, si 3 N 4 The thickness of the film is 250+/-10 nm; annealing for 5-6h in 500-600 deg.C air environment.
3. The preparation method of the MEMS bridge palladium alloy hydrogen sensing chip based on the suspended membrane structure, which is disclosed in the steps 2), 5) and 8), comprises the steps of uniformly coating adhesive hexamethyldisilazane at the low speed of 450-550r/min, the high speed of 1400-1600r/min and the high speed of 38-42s respectively, and drying at 120 ℃ for 8-12min; uniformly coating a photoresist EPG535 at low speed of 450-550r/min, 5-7s and high speed of 900-1100r/min and 38-42s, and drying at 95 ℃ for 4-6min; aligning the mask plate and the silicon wafer, and exposing for 6-8s; developing for 17-25s, and drying at 110 ℃ for 18-22min.
4. The preparation method of the MEMS bridge palladium alloy hydrogen sensing chip based on the suspended membrane structure, which is disclosed in claim 1, is characterized in that in the step 3), a Pd alloy target material is used for sequentially depositing a 20-30nm Ti adhesion layer and a 40-80nm Pd alloy, the sputtering current is 200-250mA, and the sputtering time is 4-8min.
5. The method for preparing the MEMS bridge palladium alloy hydrogen sensing chip based on the suspended membrane structure according to claim 1, wherein in the steps 4), 7) and 10), the stripping process comprises soaking in acetone solution for 1-2h and ultrasonic treatment for 5-10min; soaking in absolute ethanol for 4-6min; soaking in deionized water for 4-6min; drying with nitrogen, and drying at 110 ℃ for 18-22min; annealing for 2h under nitrogen environment at 200-300 ℃.
6. The method for preparing the MEMS bridge palladium alloy hydrogen sensor chip based on the suspended membrane structure according to claim 1, wherein in the step 6), the thickness of the deposited Cr adhesion layer is 30-50nm, and the thickness of the Au electrode layer is 150-200nm.
7. Root of Chinese characterThe method for manufacturing a MEMS bridge palladium alloy hydrogen sensor chip based on a suspended membrane structure as claimed in claim 1, wherein in the step 9), si is deposited 3 N 4 The thickness of the protective layer is 200-250nm.
8. The preparation method of the MEMS bridge palladium alloy hydrogen sensing chip based on the suspended membrane structure, which is characterized in that in the step 11), a heat insulation groove mask is manufactured through a photoresist homogenizing photoetching development process, photoresist EPG535 is homogenized on the front surface of a silicon chip, the speed is 450-550r/min and 5-7s, the speed is 900-1100r/min and 38-42s, and the temperature is 95 ℃ and dried for 4-6min; uniformly coating photoresist AZ4620 on the back of the silicon wafer, drying at a low speed of 450-550r/min for 5-7s and a high speed of 2800-3200r/min for 45-55s at 95 ℃ for 4-6min; aligning the mask plate with the back of the silicon wafer, then performing back exposure for 28-32s and front full exposure for 6-8s, developing for 75-110s, cleaning residual photoresist on the front of the silicon wafer, drying for 18-22min at 110 ℃, and hardening for 55-65min at 135 ℃.
9. A MEMS bridge palladium alloy hydrogen sensor chip based on a suspended membrane structure prepared by the method as claimed in any one of claims 1-8 comprises a Si substrate, wherein SiO is distributed on the front and back of the Si substrate 2 -Si 3 N 4 A front insulating layer and a back masking layer which are formed by the composite film, wherein the back masking layer and the silicon substrate are provided with heat insulation grooves; the method comprises the steps that an electric bridge type palladium alloy gas-sensitive material and an electrode layer are arranged on a front insulating layer, and the electrode layer comprises a test electrode, a heating electrode and a lead disc thereof; the bridge arm of the test electrode is connected with the resistance strip of the gas sensitive material to form a Wheatstone bridge, and Si is covered on the gas sensitive material and the electrode layer 3 N 4 And (3) a protective layer.
10. The MEMS bridge type palladium alloy hydrogen sensing chip based on the suspended membrane structure according to claim 9, wherein the palladium alloy gas sensitive material is four fold line surrounding type resistance strips, two test gas sensitive material resistance strips and a lead wire disc are exposed in the air, and the other two fixed gas sensitive material resistance strips are covered under the protective layer; the bridge arm of the test electrode is connected with the resistance strip of the gas sensitive material through a square contact disc; the heating electrodes are in two groups of spiral structures and are arranged on the left side and the right side of the Wheatstone bridge.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117401643A (en) * | 2023-10-20 | 2024-01-16 | 扬州国宇电子有限公司 | MEMS micro-hotplate and preparation method thereof |
| CN118032877A (en) * | 2024-04-10 | 2024-05-14 | 广东迈能欣科技有限公司 | Electronic hydrogen sensor chip and preparation method thereof |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117401643A (en) * | 2023-10-20 | 2024-01-16 | 扬州国宇电子有限公司 | MEMS micro-hotplate and preparation method thereof |
| CN118032877A (en) * | 2024-04-10 | 2024-05-14 | 广东迈能欣科技有限公司 | Electronic hydrogen sensor chip and preparation method thereof |
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