CN112897456B - Preparation method of back suspension film gas sensor compatible with MEMS (micro electro mechanical systems) process - Google Patents

Preparation method of back suspension film gas sensor compatible with MEMS (micro electro mechanical systems) process Download PDF

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CN112897456B
CN112897456B CN202110082943.3A CN202110082943A CN112897456B CN 112897456 B CN112897456 B CN 112897456B CN 202110082943 A CN202110082943 A CN 202110082943A CN 112897456 B CN112897456 B CN 112897456B
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silicon wafer
gas sensor
layer
etching
drying
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CN112897456A (en
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王海容
田鑫
王久洪
李剑
曹慧通
金成�
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Shenzhen Tianditong Electronics Co ltd
Xian Jiaotong University
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Shenzhen Tianditong Electronics Co ltd
Xian Jiaotong University
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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
    • B81C1/00436—Shaping materials, i.e. techniques for structuring the substrate or the layers on the substrate
    • B81C1/00523—Etching material
    • B81C1/00531—Dry etching
    • 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
    • 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
    • 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
    • B81C1/00436—Shaping materials, i.e. techniques for structuring the substrate or the layers on the substrate
    • B81C1/00444—Surface micromachining, i.e. structuring layers on the substrate
    • B81C1/00468—Releasing structures
    • 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
    • B81C1/00436—Shaping materials, i.e. techniques for structuring the substrate or the layers on the substrate
    • B81C1/00523—Etching material
    • B81C1/00539—Wet etching
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/08—Oxides
    • C23C14/086—Oxides of zinc, germanium, cadmium, indium, tin, thallium or bismuth
    • 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
    • G01N27/127—Composition of the body, e.g. the composition of its sensitive layer comprising nanoparticles
    • 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
    • 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
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

The invention discloses a preparation method of a back suspension film gas sensor compatible with MEMS technology, which prepares SiO on the front surface of a silicon wafer 2 And Si (Si) 3 N 4 Annealing and photoetching to obtain a sensitive material pattern; sputtering sensitive materials; stripping annealing photoetching to obtain heating wires, lead discs, test electrodes and lead disc patterns; evaporating Cr adhesive layer and Au layer, and uniformly coating photoresist by heat treatment; and then dry etching Si is adopted on the back suspension film of the silicon wafer 3 N 4 Wet etching of SiO 2 And preparing Si by a dry etching process, and finishing the preparation of the back suspension film gas sensor. The method releases Si with good heat conduction at the back suspension film structure, greatly reduces heat dissipation when the gas sensor works, can work under low power consumption, is energy-saving and environment-friendly, reduces the use cost, is easy to package, and solves the problem that the low power consumption gas sensor is incompatible with MEMS technology.

Description

Preparation method of back suspension film gas sensor compatible with MEMS (micro electro mechanical systems) process
Technical Field
The invention relates to a MEMS (Micro-Electro-mechanical System) processing technology, in particular to a back suspension film gas sensor preparation method compatible with MEMS technology.
Background
With the rapid development of world economies, increasing gas emissions create serious air pollution. These gases come from various sources such as by-products of factories, automobile exhaust and the like, and most of the gases are toxic, harmful, flammable and explosive gases, which seriously threatens the production and living safety of people. Therefore, on-line detection and early warning of various flammable and explosive, toxic and harmful gas are vital to ensuring production and life safety of people. The gas sensor is used as a direct device for collecting and analyzing gas information and plays an important role in environmental protection, industrial production and life safety. The method is characterized in that the sensitive material is used for adsorbing the target gas, and the concentration information of the target gas can be converted into a resistance signal due to the change of the carrier concentration of the target gas.
The development of MEMS technology has led to the development of gas sensors towards miniaturization, low power consumption, integration and intellectualization. The miniaturized gas sensor based on the MEMS technology not only ensures the consistency of the gas-sensitive film, but also greatly reduces the price of the gas sensor, and has become the development trend of future gas sensors. The current method for reducing the power consumption is to remove a large amount of silicon on the back of the silicon wafer, and the formed structure has two types, namely a suspended film structure based on the wet etching of the back of the silicon wafer and a cantilever beam structure based on the wet etching of the front of the silicon wafer. Because the etching rate is not easy to control in the wet etching process, the pattern distortion is easy to cause, the consistency is not present, and more importantly, the process needs to be protected on the front surface and cannot be compatible with the MEMS process. On the other hand, because the silicon substrate with the front structure is largely removed, the heating plate is supported by only four suspended beams, the structure is extremely unstable due to uncontrollable corrosion rate and thermal deformation, and the yield is not high and the mass production is not possible.
Low power consumption and low cost are the development direction, high consistency and high yield based on MEMS technology are the guarantee of low cost, miniaturization is the basis of low power consumption and integration, and integration is the premise of intellectualization. Therefore, the most central problem in the development of gas sensors is to produce gas sensors with high uniformity, high yield, low power consumption and mass production under MEMS technology.
Disclosure of Invention
The invention aims to provide a preparation method of a back suspension film gas sensor compatible with an MEMS (micro electro mechanical System) process, and aims to thoroughly solve the problem that the gas sensor is incompatible with low power consumption, yield and mass production. The gas sensor has the advantages that the structure is simple, the prepared gas sensor can be kept to have high consistency based on the MEMS technology under the condition of mass production, meanwhile, the gas sensor miniaturized based on the MEMS technology reduces the power consumption, reduces the size and has the characteristic of low price, the whole production process does not need manual interference, and the mechanical automatic production is realized, so that the back suspension film gas sensor compatible with the MEMS technology is prepared in mass in industrial production.
The invention is realized by the following technical scheme.
The preparation method of the back suspension film gas sensor compatible with the MEMS technology is characterized by comprising the following steps of:
1) Selecting a silicon wafer subjected to double-sided thermal oxidation and nitridation treatment;
2) SiO on the front surface of the silicon wafer 2 -Si 3 N 4 On the double-layer composite film, a PECVD method is adopted to prepare SiO 2 And Si (Si) 3 N 4 And annealing;
3) Processing the front side of the annealed silicon wafer by adopting a photoetching process to obtain a sensitive material pattern;
4) Sputtering sensitive materials on the surface of the silicon wafer obtained in the step 3);
5) Stripping sensitive materials by adopting a stripping process, and carrying out annealing treatment;
6) Adopting photoetching technology to treat the front surface of the annealed silicon wafer to obtain heating wires, lead wire discs, test electrodes and lead wire disc patterns;
7) Carrying out electron beam evaporation of a Cr bonding layer on the front surface of the silicon wafer obtained in the step 6), and then evaporating an Au layer on the Cr bonding layer;
8) Stripping the Cr bonding layer and the Au layer by adopting a stripping process, and performing heat treatment;
9) Uniformly coating EPG535 photoresist on the surface of the silicon wafer obtained by heat treatment, and drying;
10 Uniformly coating AZ4620 photoresist on the back of the silicon wafer treated in the step 1), and drying;
11 Exposing, developing and drying the surface of the silicon wafer obtained in the step 10);
12 Performing oxygen plasma bombardment on the surface of the silicon wafer obtained after exposure, development and drying;
13 Silicon is removed from the surface of the silicon wafer obtained in the step 12) by dry etching 3 N 4 The layers are then stripped of SiO by BOE standard solution 2 A layer;
14 And (3) removing Si through dry etching to obtain a back heat insulation groove, and removing photoresist and scribing to finish the preparation of the back suspended film gas sensor.
Preferably, in the step 1), siO is prepared by double-sided thermal oxidation 2 The layer is 400nm-600nm, and Si prepared by double-sided nitridation 3 N 4 The layer is 100nm-200nm.
Preferably, in the step 2), siO 2 The layer is 400nm-600nm, si 3 N 4 The layer is 100nm-200nm.
Preferably, in the step 10), the AZ4620 photoresist is uniformly coated for 6s to 10s at the rotating speed of the spin coater of 500r/min to 600 r/min; then uniformly coating AZ4620 photoresist for 50s-60s at the rotating speed of 1000r/min-1500r/min, and drying for 3min-5min at the temperature of 90-95 ℃.
Preferably, in the step 11), the exposure time is 35s-40s, the development is carried out for 30-50s by using 5% -10%o NaOH solution, and the drying is carried out for 30-60 min at the temperature of 130-150 ℃.
Preferably, in the step 12), the oxygen plasma bombardment power is 200-300W, and the bombardment time is 30-40 s.
Preferably, in the step 13), the Si is etched by using a reactive plasma etching process 3 N 4 Layer, etching gas is SF 6 The etching power is 120W-160W, and the etching time is 140s-160s.
Preferably, in the step 13), the standard BOE solution is 49% HF aqueous solution and 40% NH 4 F, preparing an aqueous solution according to the mass ratio of 1:6, and removing Si 3 N 4 The silicon wafer of the layer is soaked for 50s-120s.
Preferably, in the step 14), the reactive coupling plasma process is used to etch Si, the etching power is 2kW-2.5kW, and the etching time is 1.2h-2h.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
1. the dry etching Si preparation process is adopted, so that front protection in wet etching is avoided, and the whole preparation process is compatible with the MEMS process.
2. The sputtering method is adopted to uniformly and mechanically coat the whole wafer, the film forming consistency is good, and the mass production can be realized, and meanwhile, the high consistency of a plurality of gas sensors in the wafer is ensured.
3. Etching SiO with BOE solution 2 The layer has the advantage of automatic stop compared with the dry etching, the dry etching cannot be ensured due to factors such as unstable machine equipment, residual or excessive etching can influence the subsequent wet etching process, and the corrosion selectivity of the BOE solution can well ensure SiO 2 And the gas sensor is just removed, so that the whole preparation process parameters of the gas sensor are stable.
4. The back cantilever structure has more reliable performance than the front cantilever structure, the last step of dry etching Si is performed in a dry environment, photoresist and scribing can be removed after etching is finished, subsequent manual operation is not needed, the possibility of film damage is reduced, and the yield of the gas sensor is improved.
5. The back film suspending structure releases Si with good heat conduction, so that heat dissipation is greatly reduced when the gas sensor works, the gas sensor can work under low power consumption, the energy is saved, the environment is protected, and the use cost is reduced.
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 cross-sectional view of a backside cantilever gas sensor compatible with MEMS technology in accordance with the present invention;
FIG. 2 is a plan view structure diagram of a heating wire, a heating wire lead disc, a test electrode lead disc and a sensitive material of the back suspension film gas sensor compatible with the MEMS technology;
FIG. 3 is a flow chart of a back suspension film gas sensor compatible with MEMS technology according to the present invention;
FIGS. 4 (a) -4 (m) are process flow diagrams illustrating the fabrication of a MEMS process compatible back side suspended film gas sensor according to the present invention;
in the figure: 1.5, 7, a silicon nitride layer; 2. 4, 6, a silicon oxide layer; 3, a silicon wafer; 8, heating wires; 9, a sensitive material layer; 10, testing an electrode; 11, a heating wire lead disc; and 12, testing an electrode lead disc.
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 2, the invention relates to a back suspension film gas sensor compatible with an MEMS technology, which comprises a silicon wafer 3, silicon oxide layers 2, 4 and 6, silicon nitride layers 1, 5 and 7, a heating wire 8, a sensitive material layer 9, a test electrode 10, a heating wire lead disc 11 and a test electrode lead disc 12; the test electrode 10 and the sensitive material layer 9 are arranged above the front silicon nitride layer 7 in a central lamination manner; the test electrode 10 with the comb-gear shaping composite structure is arranged above the sensitive material layer 9; the heating wire 8 is in a scissor shape and surrounds two layers at the periphery of the test electrode 10; the leading-out end of the comb-gear shaping composite test electrode 10 is arranged at the scissor mouth of the heating wire 8; the heating wire 8 and the test electrode 10 are respectively connected with symmetrically distributed lead wire discs 11 and 12; the silicon nitride layer 1, the silicon oxide layer 2 and the silicon wafer 3 are provided with a rectangular groove in the middle part, and materials in the groove are completely released to the silicon oxide layer 5.
The following provides a preparation method of a back suspension film gas sensor compatible with MEMS technology, as shown in FIG. 3, comprising the following steps:
1) Selecting a silicon wafer with the thickness of 400-500um which is subjected to double-sided thermal oxidation and nitridation treatment, and preparing SiO (silicon oxide) by double-sided thermal oxidation 2 The layer is 400nm-600nm, and Si prepared by double-sided nitridation 3 N 4 The layer is 100nm-200nm, see FIG. 4 (a);
2) SiO on the front surface of the silicon wafer 2 -Si 3 N 4 On the double-layer composite film, a PECVD method is adopted to prepare SiO 2 And Si (Si) 3 N 4 And annealed at 400-700 ℃ for 5-8 h, see fig. 4 (b);
3) Processing the front surface of the silicon wafer obtained in the step 2) through a photoetching process, uniformly coating EPG535 type photoresist on the front surface of the silicon wafer at low speed of 500r/min-600r/min and 6s and high speed of 1000r/min-1200r/min and 30s-40s respectively, baking the silicon wafer at 95-120 ℃ for 5min, then exposing the silicon wafer to light for 7s-9s by using a designed sensitive material mask plate, placing the exposed silicon wafer in 3 per mill-5 per mill NaOH solution for developing for 30s-40s, drying by nitrogen at 100-120 ℃ for 10min-20min after drying by blowing, and obtaining a sensitive material graph, see (c) of FIG. 4;
4) Performing front sputtering on the silicon wafer obtained in the step 3) to obtain a sensitive material, wherein the power is 100W-150W, the sputtering time is 20min-25min, the argon flow is 20-25sccm, and the rotating speed of the silicon wafer substrate is 20r/min-25r/min to obtain SnO 2 The thickness is 70-80nm; see fig. 4 (d);
5) Treating the silicon wafer obtained in the step 4) through a stripping process, sequentially soaking the silicon wafer in acetone for 12-20 min, performing ultrasonic treatment for 30-40 s, and circulating for 2-4 times; soaking in absolute ethanol for 30s-40s, flushing with deionized water, drying with nitrogen, drying at 100-120deg.C for 10min-20min, and annealing at 400-700deg.C for 2h-4h, as shown in figure 4 (e);
6) Processing the front surface of the silicon wafer obtained in the step 5) through a photoetching process, uniformly coating EPG535 type photoresist on the front surface of the silicon wafer at low speed of 400r/min-500r/min, 6s-8s and high speed of 1000r/min-1200r/min and 30s-40s respectively, baking the silicon wafer at 90-95 ℃ for 5min-7min, exposing the photoresist for 7s-9s through a designed mask plate of a heating wire, a test electrode and the like, placing the exposed silicon wafer in 3 permillage-5 permillage NaOH solution for developing for 20s-30s, drying the silicon wafer at 100-120 ℃ for 10min-20min after nitrogen blow-drying, and obtaining the heating wire, a lead disc, the test electrode and the lead disc, as shown in fig. 4 (f);
7) Carrying out electron beam evaporation of a Cr bonding layer on the front surface of the silicon wafer obtained in the step 6), and then evaporating an Au layer on the Cr layer, wherein the thickness of the Cr layer is 50-60 nm, and the thickness of the Au layer is 220-250 nm; see fig. 4 (g);
8) The silicon wafer obtained in the step 7) is treated through a stripping process, is sequentially soaked in acetone for 10min-15min, is subjected to ultrasonic treatment for 30s-40s, and is circulated for 3-4 times; soaking in absolute ethanol for 8s-10s, flushing with deionized water, drying with nitrogen, drying at 90-100deg.C for 10min-15min, and annealing at 300-400deg.C for 10min-20min, as shown in figure 4 (h);
9) Uniformly coating EPG535 photoresist on the front surface of the silicon wafer obtained in the step 8) at low speed of 500r/min-600r/min, 5s-8s, high speed of 1000r/min-1200r/min and 30s-40s, and drying at 90-100 ℃ for 4-6 min, as shown in fig. 4 (i);
10 Uniformly coating AZ4620 photoresist on the back surface of the silicon wafer obtained in the step 9) for 6s-10s at the rotating speed of a spin coater of 500r/min-600 r/min; then uniformly coating AZ4620 photoresist for 50s-60s at the rotating speed of 1000r/min-1500r/min, and drying at the temperature of 90-95 ℃ for 3min-5min, as shown in fig. 4 (j);
11 Exposing, developing and drying the back of the silicon wafer obtained in the step 10), wherein the exposure time is 35s-40s, developing for 30s-50s by using 5-10 per mill NaOH solution, and drying for 30min-60min at 130-150 ℃ as shown in fig. 4 (k);
12 Carrying out oxygen plasma bombardment on the back surface of the silicon wafer obtained in the step 11), wherein the bombardment power is 200-300W, and the bombardment time is 30-40 s;
13 The Si on the back of the silicon wafer obtained in the step 12) is removed by dry etching 3 N 4 The layers are then stripped of SiO by BOE standard solution 2 The layer, standard BOE solution according to mass ratio 49% HF aqueous solution: 40% NH 4 The aqueous solution F is prepared in a ratio of 1:6, and Si is removed 3 N 4 The silicon wafer of the layer is soaked for 50s-120s. Etching Si using Reactive Ion Etching (RIE) process 3 N 4 Layer, etching gas is SF 6 The etching power is 120W-160W, and the etching time is 140s-160s, see FIG. 4 (l);
14 And (3) etching Si on the silicon wafer obtained in the step (13) through a reactive coupling plasma (ICP) process, wherein the etching power is 2kW-2.5kW, the etching time is 1.2h-2h, a back heat insulation groove is obtained, and photoresist stripping and scribing are carried out, so that the back suspension film gas sensor compatible with the MEMS process is prepared, and the preparation is shown in fig. 4 (m).
The process according to the invention is further illustrated by the following examples.
Example 1
1) Selecting a silicon wafer with N-type doping, crystal orientation of 100, resistance of 1-5ohm.cm and thickness of 500um, and then performing double-sided thermal oxidation to formThe thickness of the oxide layer is 400nm, and Si is deposited by double-sided LPCVD 3 N 4 The thickness of the formed nitride layer is 150nm;
2) On the front side SiO 2 -Si 3 N 4 On the double-layer composite film, 500nmSiO is prepared by adopting a PECVD method 2 And 150nmSi 3 N 4 Annealing at 500 ℃ for 6 hours;
3) Uniformly coating EPG535 type photoresist on the front surface of a silicon wafer at low speed of 600r/min and 6s and high speed of 1200r/min and 40s, baking the silicon wafer at 120 ℃ for 5min, exposing the silicon wafer on the photoresist for 8s by using a designed sensitive material mask, placing the exposed silicon wafer in 4 permillage NaOH solution for developing for 30s, drying the silicon wafer at 120 ℃ for 20min after nitrogen blowing, and obtaining a designed sensitive material pattern;
4) Putting the silicon wafer obtained in the step 3) into a sputtering machine to perform front sputtering of SnO 2 The sensitive material is subjected to radio frequency sputtering, the power is 100W, the sputtering time is 25min, the argon flow is 20sccm, the rotating speed of the silicon wafer substrate is 20r/min, and SnO is obtained 2 The thickness is 70nm;
5) Sequentially soaking the silicon wafer obtained in the step 4) in acetone for 20min, performing ultrasonic treatment for 40s, and circulating for 4 times; peeling, soaking in absolute ethanol for 30s, flushing with deionized water, drying with nitrogen, drying at 100 ℃ for 20min, and annealing at 700 ℃ for 2h;
6) Uniformly coating EPG535 type photoresist on the front surface of the silicon wafer obtained in the step 5) at low speed of 500r/min, 6s, high speed of 1000r/min and 40s, baking the silicon wafer at 95 ℃ for 5min, exposing the photoresist for 7s by using a mask plate of a designed heating wire, a test electrode and the like, placing the exposed silicon wafer in 5 permillage NaOH solution for developing for 20s, drying the silicon wafer at 110 ℃ for 10min after nitrogen blow-drying, and obtaining the designed patterns with the heating wire, the test electrode and the like;
7) Evaporating Cr and Au on the front surface of the silicon wafer obtained in the step 6) by electron beams, wherein the thickness of a Cr layer is 50nm, and the thickness of an Au layer is 230nm;
8) Sequentially soaking the silicon wafer obtained in the step 7) in acetone for 10min, performing ultrasonic treatment for 40s, and circulating for 4 times; peeling, soaking in absolute ethanol for 10s, flushing with deionized water, drying with nitrogen, drying at 100deg.C for 15min, and heat treating at 300deg.C for 15 min;
9) Uniformly coating EPG535 type photoresist on the front surface of a silicon wafer at low speed of 500r/min and 8s and at high speed of 1000r/min and 40s, and drying the silicon wafer at 95 ℃ for 5min;
10 Uniformly coating AZ4620 photoresist on the back surface of the silicon wafer in the step 9) at low speed of 600r/min for 6s and high speed of 1500r/min for 55s, and drying at 95 ℃ for 4min.
11 Exposing the back of the silicon wafer in the step 10) under the etching mask for 38s, developing for 30s by using 7 per mill NaOH solution, and drying for 40min at 150 ℃.
12 The silicon wafer obtained in step 11) was bombarded with oxygen plasma at 260W for 40s.
13 Silicon wafer obtained in step 12) is etched with Si by using a reactive plasma etching (RIE) process 3 N 4 Layer, etching gas is SF 6 The etching power is 140W, and the etching time is 150s; according to 49% aqueous HF: 40% NH 4 F, preparing a standard BOE solution with the ratio of the aqueous solution F to the aqueous solution F being 1:6, and removing Si 3 N 4 Soaking the silicon wafer of the layer for 70s, removing SiO 2 。
14 And (3) etching Si on the silicon wafer obtained in the step 13) by using a reactive coupling plasma (ICP) process, wherein the etching power is 2.5kW, and the etching time is 1.5h.
The chip is placed in the gas to be tested, voltage is applied to the two ends of the heating wire, the heating wire instantaneously generates high temperature, the sensitive material area instantaneously generates high temperature, and the power consumption of the back suspension film gas sensor prepared by the process method is 36mW under the condition that the generation of 300 ℃ high temperature is ensured, so that the power consumption of the back suspension film gas sensor is reduced by 85 percent compared with that of a gas sensor without a suspension film structure.
Example 2
1) Selecting a silicon wafer with N-type doping, crystal orientation of 100, resistance of 1-5ohm.cm and thickness of 450um, then performing double-sided thermal oxidation to form an oxide layer with thickness of 600nm, and performing double-sided LPCVD to deposit Si 3 N 4 The thickness of the formed nitride layer is 200nm;
2) On the front side SiO 2 -Si 3 N 4 On the double-layer composite film, 600nmSiO is prepared by adopting a PECVD method 2 And 100nmSi 3 N 4 Annealing at 700℃for 5h.
3) Uniformly coating EPG535 type photoresist on the front surface of a silicon wafer at low speed of 550r/min and 6s and high speed of 1000r/min and 30s, baking the silicon wafer at 95 ℃ for 5min, exposing the photoresist for 7s by using a designed sensitive material mask, placing the exposed silicon wafer in 5 permillage NaOH solution for developing for 30s, drying the silicon wafer at 100 ℃ for 15min after nitrogen blow-drying, and obtaining a designed sensitive material pattern;
4) Putting the silicon wafer obtained in the step 3) into a sputtering machine to perform front sputtering of SnO 2 The sensitive material is subjected to radio frequency sputtering, the power is 120W, the sputtering time is 20min, the argon flow is 25sccm, the rotating speed of the silicon wafer substrate is 25r/min, and SnO is obtained 2 The thickness is 80nm;
5) Sequentially soaking the silicon wafer obtained in the step 4) in acetone for 12min, performing ultrasonic treatment for 30s, and circulating for 3 times; peeling, soaking in absolute ethanol for 30s, flushing with deionized water, drying with nitrogen, drying at 110 ℃ for 10min, and annealing at 400 ℃ for 4h;
6) Uniformly coating EPG535 type photoresist on the front surface of the silicon wafer obtained in the step 5) at low speed of 450r/min, 6s and high speed of 1200r/min and 30s, baking the silicon wafer at 90 ℃ for 5min, exposing the photoresist for 7s by using a mask plate of a designed heating wire, a test electrode and the like, placing the exposed silicon wafer in 4 permillage NaOH solution for developing for 30s, drying the silicon wafer at 120 ℃ for 20min after nitrogen blow-drying, and obtaining the designed patterns with the heating wire, the test electrode and the like;
7) Evaporating Cr and Au on the front surface of the silicon wafer obtained in the step 6) by electron beams, wherein the thickness of a Cr layer is 50nm, and the thickness of an Au layer is 250nm;
8) Sequentially soaking the silicon wafer obtained in the step 7) in acetone for 12min, performing ultrasonic treatment for 30s, and circulating for 4 times; peeling, soaking in absolute ethanol for 8s, flushing with deionized water, drying with nitrogen, drying at 100deg.C for 10min, and heat treating at 400deg.C for 10 min;
9) Uniformly coating EPG535 type photoresist on the front surface of a silicon wafer at low speed of 500r/min and 8s and at high speed of 1200r/min and 30s, and baking the silicon wafer at 100 ℃ for 4min;
10 Uniformly coating AZ4620 photoresist on the back surface of the silicon wafer in the step 9) at low speed of 600r/min for 6s and high speed of 1200r/min for 50s, and drying at 90 ℃ for 5min;
11 Exposing the back of the silicon wafer in the step 10) under the etching mask for 35s, developing for 40s by using 10 per mill NaOH solution, and drying for 30min at 130 ℃;
12 Bombarding the silicon wafer obtained in the step 11) for 30 seconds under the condition of 300W by using oxygen plasma;
13 Silicon wafer obtained in step 12) is etched with Si by using a reactive plasma etching (RIE) process 3 N 4 Layer, etching gas is SF 6 The etching power is 120W, and the etching time is 160s; according to 49% aqueous HF: 40% NH 4 F, preparing a standard BOE solution with the ratio of the aqueous solution F to the aqueous solution F being 1:6, and removing Si 3 N 4 Soaking the silicon wafer of the layer for 120s, removing SiO 2 ；
14 And (3) etching Si on the silicon wafer obtained in the step 13) by using a reactive coupling plasma (ICP) process, wherein the etching power is 2.0kW, and the etching time is 2 hours.
The chip is placed in the gas to be tested, voltage is applied to the two ends of the heating wire, the heating wire instantaneously generates high temperature, the sensitive material area instantaneously generates high temperature, and the power consumption of the back suspension film gas sensor prepared by the process method is 38mW under the condition that the generation of 300 ℃ high temperature is ensured, so that the power consumption of the back suspension film gas sensor is reduced by 84 percent compared with that of a gas sensor without a suspension film structure.
Example 3
1) Selecting a silicon wafer with N-type doping, crystal orientation of 100, resistance of 1-5ohm.cm and thickness of 400um, then performing double-sided thermal oxidation to form an oxide layer with thickness of 500nm, and performing double-sided LPCVD to deposit Si 3 N 4 The thickness of the formed nitride layer is 100nm;
2) On the front side SiO 2 -Si 3 N 4 On the double-layer composite film, 400nmSiO is prepared by adopting a PECVD method 2 And 200nmSi 3 N 4 Annealing at 400 ℃ for 8 hours;
3) Uniformly coating EPG535 type photoresist on the front surface of a silicon wafer at low speed of 500r/min and 6s and at high speed of 1100r/min and 40s, baking the silicon wafer at 100 ℃ for 5min, exposing the silicon wafer to light for 9s by using a designed sensitive material mask, placing the exposed silicon wafer in a 3 permillage NaOH solution for developing for 40s, drying the silicon wafer at 110 ℃ for 10min after nitrogen blowing, and obtaining a designed sensitive material pattern;
4) Putting the silicon wafer obtained in the step 3) into a sputtering machine to perform front sputtering of SnO 2 The sensitive material is subjected to radio frequency sputtering, the power is 150W, the sputtering time is 20min, the argon flow is 25sccm, the rotating speed of the silicon wafer substrate is 20r/min, and SnO is obtained 2 The thickness is 75nm;
5) Sequentially soaking the silicon wafer obtained in the step 4) in acetone for 15min, performing ultrasonic treatment for 35s, and circulating for 2 times; peeling, soaking in absolute ethanol for 40s, flushing with deionized water, drying with nitrogen, drying at 120 ℃ for 15min, and annealing at 500 ℃ for 3h;
6) Uniformly coating EPG535 type photoresist on the front surface of the silicon wafer obtained in the step 5) at low speed of 400r/min, 8s, high speed of 1200r/min and 30s, baking the silicon wafer at 90 ℃ for 7min, exposing the photoresist for 9s by using a mask plate of a designed heating wire, a test electrode and the like, placing the exposed silicon wafer in 5 permillage NaOH solution for developing for 30s, drying the silicon wafer at 120 ℃ for 20min after nitrogen blow-drying, and obtaining the designed patterns with the heating wire, the test electrode and the like;
7) Evaporating Cr and Au on the front side of the silicon wafer obtained in the step 6) by electron beams, wherein the thickness of a Cr layer is 60nm, and the thickness of an Au layer is 220nm;
8) Sequentially soaking the silicon wafer obtained in the step 7) in acetone for 15min, performing ultrasonic treatment for 30s, and circulating for 3 times; peeling, soaking in absolute ethanol for 9s, flushing with deionized water, drying with nitrogen, drying at 90 ℃ for 15min, and performing heat treatment at 350 ℃ for 20 min;
9) Uniformly coating EPG535 photoresist on the front surface of the silicon wafer at low speed of 550r/min and 5s and at high speed of 1100r/min and 40s, and baking the silicon wafer at 90 ℃ for 6min;
10 Uniformly coating AZ4620 photoresist on the back surface of the silicon wafer in the step 9) at a low speed of 550r/min for 10s and at a high speed of 1000r/min for 60s, and drying at 95 ℃ for 3min.
11 Exposing the back of the silicon wafer in the step 10) under the etching mask for 40s, developing for 50s by using 5%o NaOH solution, and drying for 60min at 140 ℃.
12 The silicon wafer obtained in step 11) was bombarded with oxygen plasma at 200W for 35s.
13 Silicon wafer obtained in step 12) is etched with Si by using a reactive plasma etching (RIE) process 3 N 4 Layer, etching gas is SF 6 The etching power is 160W, and the etching time is 140s; according to 49% aqueous HF: 40% NH 4 F, preparing a standard BOE solution with the ratio of the aqueous solution F to the aqueous solution F being 1:6, and removing Si 3 N 4 Soaking the silicon wafer of the layer for 50s, removing SiO 2 。
14 And (3) etching Si on the silicon wafer obtained in the step 13) by using a reactive coupling plasma (ICP) process, wherein the etching power is 2.2kW, and the etching time is 1.2h.
The chip is placed in the gas to be tested, voltage is applied to the two ends of the heating wire, the heating wire instantaneously generates high temperature, the sensitive material area instantaneously generates high temperature, and the power consumption of the back suspension film gas sensor prepared by the process method is 40mW under the condition that the generation of 300 ℃ high temperature is ensured, so that the power consumption of the back suspension film gas sensor is reduced by 83% compared with that of a gas sensor without a suspension film structure.
The back suspension film gas sensor compatible with the MEMS technology, which is prepared by adopting the method disclosed by the invention, has the excellent performances of low power consumption, high yield and mass production, and compared with the prior art, the power consumption of the back suspension film gas sensor is reduced by not less than 83%, so that the method disclosed by the invention is a method for preparing the back suspension film gas sensor compatible with the MEMS technology, and the back suspension film gas sensor is excellent in performance.
The invention has the advantages of simple structure, local high temperature, easy packaging, thorough solving of the problem that the low-power consumption gas sensor is incompatible with the MEMS technology, and being capable of keeping the prepared gas sensor to have very high consistency and yield based on the MEMS technology under the condition of mass production, reducing the power consumption, reducing the size and having the characteristic of low price based on the miniaturized gas sensor of the MEMS technology, and the whole production process does not need manual interference, and is mechanically and automatically produced so as to carry out the preparation of the back suspension film gas sensor compatible with the MEMS technology in mass in industrial production.
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 (9)

1. The preparation method of the back suspension film gas sensor compatible with the MEMS technology is characterized by comprising the following steps of:
1) Selecting a silicon wafer subjected to double-sided thermal oxidation and nitridation treatment;
2) SiO on the front surface of the silicon wafer 2 -Si 3 N 4 On the double-layer composite film, a PECVD method is adopted to prepare SiO 2 And Si (Si) 3 N 4 And annealing;
3) Processing the front side of the annealed silicon wafer by adopting a photoetching process to obtain a sensitive material pattern;
4) Sputtering sensitive materials on the surface of the silicon wafer obtained in the step 3);
5) Stripping sensitive materials by adopting a stripping process, and carrying out annealing treatment;
6) Adopting photoetching technology to treat the front surface of the annealed silicon wafer to obtain heating wires, lead wire discs, test electrodes and lead wire disc patterns;
7) Carrying out electron beam evaporation of a Cr bonding layer on the front surface of the silicon wafer obtained in the step 6), and then evaporating an Au layer on the Cr bonding layer;
8) Stripping the Cr bonding layer and the Au layer by adopting a stripping process, and performing heat treatment;
9) Uniformly coating EPG535 photoresist on the surface of the silicon wafer obtained by heat treatment, and drying;
10 Uniformly coating AZ4620 photoresist on the back of the silicon wafer treated in the step 1), and drying;
11 Exposing, developing and drying the surface of the silicon wafer obtained in the step 10);
12 Performing oxygen plasma bombardment on the surface of the silicon wafer obtained after exposure, development and drying;
13 Silicon is removed from the surface of the silicon wafer obtained in the step 12) by dry etching 3 N 4 The layers are then stripped of SiO by BOE standard solution 2 A layer;
14 And (3) removing Si through dry etching to obtain a back heat insulation groove, and removing photoresist and scribing to finish the preparation of the back suspended film gas sensor.
2. The method for preparing a backside suspended film gas sensor compatible with MEMS process according to claim 1, wherein in said step 1), siO is prepared by double-sided thermal oxidation 2 The layer is 400nm-600nm, and Si prepared by double-sided nitridation 3 N 4 The layer is 100nm-200nm.
3. The method for preparing a backside suspension film gas sensor compatible with MEMS process according to claim 1, wherein in said step 2), siO 2 The layer is 400nm-600nm, si 3 N 4 The layer is 100nm-200nm.
4. The method for preparing the back suspension film gas sensor compatible with the MEMS process according to claim 1, wherein in the step 10), the AZ4620 photoresist is uniformly coated for 6s-10s at the rotating speed of a spin coater of 500r/min-600 r/min; then uniformly coating AZ4620 photoresist for 50s-60s at the rotating speed of 1000r/min-1500r/min, and drying for 3min-5min at the temperature of 90-95 ℃.
5. The method for preparing the back suspension film gas sensor compatible with the MEMS process according to claim 1, wherein in the step 11), the exposure time is 35s-40s, the development is performed for 30-50s by using 5% -10%o NaOH solution, and the baking is performed for 30-60 min at 130-150 ℃.
6. The method for preparing a backside film suspension gas sensor compatible with MEMS process according to claim 1, wherein in the step 12), the oxygen plasma bombardment power is 200W-300W, and the bombardment time is 30s-40s.
7. The method for preparing a backside suspended film gas sensor compatible with MEMS process as claimed in claim 1, wherein in said step 13), the reactive plasma etching process is used to etch Si 3 N 4 Layer, etching gas is SF 6 The etching power is 120W-160W, and the etching time is 140s-160s.
8. The method for preparing a MEMS-process-compatible back suspension gas sensor according to claim 1, wherein in step 13), the standard BOE solution is 49% hf aqueous solution and 40% nh 4 F, preparing an aqueous solution according to the mass ratio of 1:6, and removing Si 3 N 4 The silicon wafer of the layer is soaked for 50s-120s.
9. The method for preparing a backside suspended film gas sensor compatible with MEMS process according to claim 1, wherein in the step 14), the reactive coupling plasma process is used for etching Si, the etching power is 2kW-2.5kW, and the etching time is 1.2h-2h.
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