Large-size MEMS (Micro Electro Mechanical System) micro hot plate as well as preparation method and application thereof

Abstract

The invention provides a large-size MEMS (Micro Electro Mechanical System) micro hot plate as well as a preparation method and application thereof, and relates to the technical field of gas sensors. The large-size MEMS micro hot plate comprises a suspension working platform, through holes, a supporting assembly and a cantilever beam assembly, wherein the size of a working area of the suspension working platform is (200-500) mu m * (200-500) mu m; the through holes are formed in the periphery of the suspension working platform; the supporting assembly is used for supporting the suspension working platform; the suspension working platform comprises a silicon nitride layer, a spiral heating electrode, an insulating layer and a circular interdigital electrode which are stacked in sequence; one end of the cantilever beam is connected with the suspension working platform, and the other end of the cantilever beam is connected with the supporting assembly. According to the large-size MEMS micro hot plate provided by the invention, the problem that a traditional MEMS micro hot plate is not matched with a sensitive material film forming process due to the fact that the working area is too small is solved, the performance and compatibility of a sensor can be improved, and a reliable technical scheme is provided for large-scale production of a high-performance gas sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas sensor, in particular to a large-size MEMS micro-hotplate and a preparation method and application thereof. BACKGROUND

[0002] Gas detection is widely used in the fields of industrial production, medical monitoring, air pollution prevention and control, air quality detection in enclosed space, fuel vehicle tail gas detection and new energy vehicle safety protection. With the continuous progress of science and technology, gas sensors are developing towards miniaturization, intelligentization and low power consumption. Among them, MEMS (Micro Electro Mechanical System) technology as a key technology to realize the miniaturization, intelligentization and low power consumption of sensors has been widely concerned and researched.

[0003] Although the traditional metal oxide semiconductor (MOS) gas sensor based on MEMS technology has made significant progress in device size and power consumption, in actual application, due to the too small working area (micro-hotplate) of the MEMS gas sensor chip, it is not matched with the powder printing technology, thereby limiting the selection of the sensitive layer material of the gas sensor, which not only affects the performance of the sensor, but also restricts the potential of the gas sensor in large-scale production and application. Therefore, developing a MEMS gas sensor chip with a large working area has important practical significance to meet the growing demand for gas detection. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a large-size MEMS micro-hotplate and a preparation method and application thereof. The MEMS micro-hotplate provided by the present application has the advantages of large working area (micro-hotplate-effective heating area), low power consumption, uniform temperature distribution, stable mechanical performance and high reliability, and solves the problem of mismatching with the sensitive material film forming process caused by the too small working area of the traditional MEMS micro-hotplate.

[0005] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0006] The present application provides a large-size MEMS micro-hotplate, which comprises a suspended working platform, through holes located around the suspended working platform, a support assembly and a cantilever beam assembly for supporting the suspended working platform.

[0007] The working area size of the suspended working platform is 200-500 μm x 200-500 μm; the suspended working platform comprises silicon nitride, a spiral heating electrode, an insulating layer and a circular interdigital electrode which are stacked in sequence.

[0008] The cantilever beam assembly has 8 cantilever beams, one end of the cantilever beam is connected to the suspended working platform, and the other end is connected to the support assembly.

[0009] Preferably, the spiral micro-heating electrode comprises a Ti layer and a Pt layer stacked in sequence, the Pt layer has a spiral structure; the thickness of the Ti layer is 20-40 nm; the thickness of the Pt layer is 200-500 nm.

[0010] Preferably, the circular interdigital electrode comprises a Ti layer and a Pt layer stacked in sequence; the thickness of the Ti layer is 20-40 nm; the thickness of the Pt layer is 200-500 nm.

[0011] Preferably, the thickness of the silicon nitride layer is 200-600 nm.

[0012] Preferably, the insulating layer comprises a silicon oxide layer and a silicon nitride layer stacked in sequence; the thickness of the silicon oxide layer is 600-1200 nm; the thickness of the silicon nitride layer is 200-600 nm.

[0013] Preferably, the support assembly comprises a silicon oxide layer, a silicon substrate layer, a silicon oxide layer, a silicon nitride layer, a heating electrode pad block, an insulating layer and an interdigital electrode pad block stacked in sequence, and the insulating layer on the surface of the heating electrode pad block is provided with an electrode hole.

[0014] The silicon substrate layer has a prism-shaped through hole.

[0015] Preferably, one end of the cantilever beam is connected to a suspended working platform, that is, one end of two cantilever beams is connected to the spiral heating electrode, one end of two cantilever beams is connected to the circular interdigital electrode, and one end of four cantilever beams is connected to the silicon nitride layer and the insulating layer.

[0016] The application also provides a preparation method of the large-size MEMS micro-hot plate.

[0017] A silicon oxide layer and a silicon nitride layer are deposited on the upper surface of the substrate in sequence, a spiral heating electrode is formed by patterning treatment after depositing a heating electrode layer, an electrode hole is etched, an insulating layer is deposited, a circular interdigital electrode is formed by patterning treatment after depositing an interdigital electrode layer, the microstructure is released, and a large-size MEMS micro-hot plate is obtained.

[0018] Preferably, the preparation method further comprises depositing a back medium layer on the lower surface of the substrate.

[0019] The application also provides an application of the large-size MEMS micro-hot plate or the large-size MEMS micro-hot plate prepared by the preparation method as a MEMS gas sensor chip.

[0020] Compared with the traditional serpentine electrode structure, the heating electrode is designed into a spiral configuration, which has multiple advantages: the annular current path design significantly improves the temperature field uniformity of the large-size MEMS micro-hotplate; the symmetric topology structure not only improves the heat transfer efficiency, but also enhances the compactness of the MEMS micro-hotplate structure; the optimized current distribution effectively reduces the edge heat loss; the circular arc transition feature can alleviate the stress concentration phenomenon at the right-angle bending position, thereby improving the reliability of the MEMS micro-hotplate.

[0021] For the widely used rectangular interdigital electrode architecture, the present application finds that there are inherent limitations in geometric compatibility: when applied to a circular micro-hotplate, the linear arrangement characteristics of the rectangular electrode will cause the edge sensing area of the circular micro-hotplate to be unable to form effective electrode coverage, resulting in an electric signal collection blind area. The present application uses a conformal design of a circular interdigital electrode to break through this technical bottleneck, and its advantages are reflected in: the curvature-matched electrode arrangement increases the effective contact area and reduces the baseline resistance; the annular electric field distribution reduces the edge effect, significantly improving the detection sensitivity of the large-size MEMS micro-hotplate.

[0022] The present application uses 8 suspension beam arms to support the suspended working platform, which can ensure that the large-size MEMS micro-hotplate is not easy to deform, and the overall structure stability is excellent.

[0023] The large-size MEMS micro-hotplate provided by the present application ensures low power consumption, uniform temperature distribution, stable mechanical performance and high reliability, improves the film formation efficiency and quality of metal oxide sensitive materials such as tin dioxide and zinc oxide, and realizes effective compatibility of MEMS technology and metal oxide ceramic powder material film formation process. The large-size MEMS micro-hotplate provided by the present application solves the problem of mismatching between the working area of the traditional MEMS micro-hotplate and the film formation process of the sensitive material, can improve the performance and compatibility of the sensor, and provides a reliable technical scheme for the large-scale production of high-performance gas sensors. As shown in the test results of the embodiment, the large-size MEMS micro-hotplate provided by the present application has good performance consistency, the temperature reaches 301 DEG C when the input voltage is 3.5V, the power consumption is 56.4mW, the temperature distribution is uniform, the heat loss is small, and the power consumption is low. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a schematic diagram of the substrate in Example 1;

[0025] Figure 2 It is a preparation process flow chart of the silicon oxide layer, silicon nitride layer and back medium layer in Example 1;

[0026] Figure 3 It is a preparation process flow chart of the heating electrode in Example 1;

[0027] Figure 4Optical microscope image of the spiral heating electrode in Example 1;

[0028] Figure 5 Process flow chart for the preparation of the insulating layer in Example 1;

[0029] Figure 6 Process flow chart for the preparation of the interdigital electrode in Example 1;

[0030] Figure 7 Optical microscope image of the circular interdigital electrode after the patterning process in Example 1;

[0031] Figure 8 Process flow chart for the preparation of the electrode hole in Example 1;

[0032] Figure 9 Process flow chart for the preparation of the via hole in Example 1;

[0033] Figure 10 Optical microscope image of the micro-hotplate after etching the via hole in Example 1;

[0034] Figure 11 Process flow chart for the etching of the backside dielectric layer in Example 1;

[0035] Figure 12 Process flow chart for the etching of the via hole on the backside in Example 1;

[0036] Figure 13 Schematic diagram of the backside etching of the via hole of the large-size MEMS micro-hotplate prepared in Example 1;

[0037] Figure 14 Optical microscope image of the large-size MEMS micro-hotplate prepared in Example 1;

[0038] Figure 15 Frontside (left) and backside (right) optical microscope images of the working area of the large-size MEMS micro-hotplate prepared in Example 1;

[0039] Figure 16 Voltage-temperature test result graph of the eight large-size MEMS micro-hotplates prepared in Example 1;

[0040] Figure 17 Temperature-power consumption test result graph of the large-size MEMS micro-hotplate prepared in Example 1;

[0041] Figure 18 Temperature distribution graph of the large-size MEMS micro-hotplate prepared in Example 1 under different input voltages.

[0042] Figure 19 Schematic diagram of the three-dimensional structure of the working area of the large-size MEMS micro-hotplate in the present application, Figure 19Two layers of Ti layer are omitted; DETAILED DESCRIPTION

[0043] The application provides a large-size MEMS micro-hotplate (see schematic diagram of section structure Figure 12 , see front perspective view Figure 13 , and see schematic diagram of three-dimensional structure of working area Figure 19 ), which comprises a suspended working platform, through holes around the suspended working platform, a support assembly for supporting the suspended working platform and a cantilever beam assembly.

[0044] In the application, the working area size of the suspended working platform is 200-500 μm*200-500 μm, and in specific embodiments, can be 200 μm*200 μm, 250 μm*250 μm, 300 μm*300 μm, 350 μm*350 μm, 400 μm*400 μm, 450 μm*450 μm or 500 μm*500 μm. In the application, the shape of the suspended working platform preferably comprises a circle or a square.

[0045] In the application, the suspended working platform comprises a silicon nitride layer, a spiral heating electrode, an insulating layer and a circular interdigital electrode which are sequentially stacked.

[0046] In the application, the thickness of the silicon nitride layer is preferably 200-600 nm, and in specific embodiments, can be 200 nm, 300 nm, 400 nm, 500 nm or 600 nm.

[0047] In the application, the spiral micro-heating electrode preferably comprises a Ti layer and a Pt layer which are sequentially stacked; the thickness of the Ti layer is preferably 20-40 nm, and in specific embodiments, can be 20 nm, 25 nm, 30 nm, 35 nm or 40 nm; the thickness of the Pt layer is preferably 200-500 nm, and in specific embodiments, can be 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm. In the application, the Ti layer serves as an adhesion layer, which can improve the adhesion of the Pt layer and avoid peeling of the Pt layer at high temperature; the Pt layer serves as a heating resistance and signal resistance material.

[0048] Compared with a traditional snake-shaped electrode structure, the application has multiple advantages in that the spiral configuration of the heating electrode significantly improves the temperature field uniformity of the large-size MEMS micro-hotplate through a ring-shaped current path design; the symmetrical topological structure not only improves the heat energy transmission efficiency but also enhances the compactness of the MEMS micro-hotplate structure; the optimized current distribution effectively reduces the edge heat loss; and the circular arc transition feature can relieve the stress concentration phenomenon at the right-angle bending position, thereby improving the reliability of the MEMS micro-hotplate.

[0049] In the present application, the insulating layer comprises a silicon oxide (SiO2) layer and a silicon nitride layer which are stacked in sequence; the thickness of the silicon oxide layer is preferably 600-1200 nm, and in specific embodiments can be 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm or 1200 nm; the thickness of the silicon nitride layer is preferably 200-600 nm, and in specific embodiments can be 200 nm, 300 nm, 400 nm, 500 nm or 600 nm.

[0050] In the present application, the circular interdigital electrode comprises a Ti layer and a Pt layer which are stacked in sequence; the thickness of the Ti layer is preferably 20-40 nm, and in specific embodiments can be 20 nm, 25 nm, 30 nm, 35 nm or 40 nm; the Ti layer serves as an adhesion layer, which can improve the adhesion of the Pt layer and prevent the Pt layer from peeling off at high temperatures; the thickness of the Pt layer is preferably 200-500 nm, and in specific embodiments can be 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm.

[0051] For the widely used rectangular interdigital electrode architecture, the present application has found that there are inherent limitations in geometric compatibility: when applied to a circular micro-hotplate, the linear arrangement characteristics of the rectangular electrode will result in the edge sensing area of the circular micro-hotplate being unable to form effective electrode coverage, causing an electric signal collection blind area. The circular interdigital electrode with conformal design used in the present application can break through this technical bottleneck, and its advantages are reflected in: the curvature-matched electrode arrangement increases the effective contact area and reduces the baseline resistance; the annular electric field distribution reduces the edge effect, and significantly improves the detection sensitivity of large-size MEMS micro-hotplates.

[0052] In the present application, the cantilever beam assembly has 8 cantilever beams, one end of the cantilever beams is connected to the suspended working platform, specifically, one end of 2 cantilever beams is connected to the spiral heating electrode, one end of 2 cantilever beams is connected to the circular interdigital electrode, and one end of 4 cantilever beams is connected to the silicon nitride layer and the insulating layer; the other end of the 8 cantilever beams is connected to the support assembly. The present application uses 8 cantilever beams to support the suspended working platform, which can ensure that the large-size MEMS micro-hotplate is not easily deformed and has excellent overall structural stability. In the present application, the materials of 2 cantilever beams among the 8 cantilever beams include the silicon nitride layer, the pins of the spiral heating electrode and the insulating layer, and the materials of 2 cantilever beams include the silicon nitride layer, the insulating layer and the pins of the circular interdigital electrode; the materials of the remaining 4 cantilever beams include the silicon nitride layer and the insulating layer.

[0053] In the present application, the support assembly preferably comprises a silicon oxide layer, a silicon substrate layer, a silicon nitride layer, a heating electrode pad block, an insulating layer and an interdigital electrode pad block which are sequentially stacked, and an electrode hole is arranged in the insulating layer on the surface of the heating electrode pad block.

[0054] In the present application, the silicon substrate layer has a prism-shaped through hole; the upper bottom edge length of the silicon substrate layer is greater than the lower bottom edge length; the material of the silicon substrate layer is preferably silicon, more preferably n-type silicon, and in specific embodiments, it can be an n-type silicon wafer with a (100) crystal orientation; the thickness of the silicon substrate layer is preferably 300-600 μm, and in specific embodiments, it can be 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm or 600 μm; the resistivity of the silicon is preferably 3-10 Ω·cm.

[0055] In the present application, the thickness of the silicon oxide layer in the support assembly is preferably 600-1200 nm, and in specific embodiments, it can be 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm or 1200 nm. In the present application, the size of the electrode hole is preferably the same as that of the heating electrode pad block. In the present application, the size of the electrode hole is preferably 50-300 μm, and in specific embodiments, it can be 50 μm, 100 μm, 150 μm, 200 μm, 250 μm or 300 μm.

[0056] The present application also provides a preparation method of the large-size MEMS micro-hotplate described in the above technical solution, which comprises the following steps: sequentially depositing a silicon oxide layer and a silicon nitride layer on the upper surface of a substrate, patterning the heating electrode layer after deposition to form a spiral-shaped heating electrode, depositing an insulating layer, patterning the interdigital electrode layer after deposition to form a circular interdigital electrode, releasing the microstructure, and obtaining a large-size MEMS micro-hotplate.

[0057] In the present application, the silicon oxide layer and the silicon nitride layer are sequentially deposited on the upper surface of the substrate, specifically, the silicon oxide layer is grown (denoted as first growth) and the silicon nitride layer is deposited (denoted as first deposition) on the upper surface of the substrate. In the present application, the substrate is preferably cleaned before use, and the cleaning preferably comprises sequentially cleaning with acetone and deionized water, and the purpose of the cleaning is to remove surface impurities and contaminants.

[0058] In the present application, the thickness of the silicon oxide layer is preferably 600-1200 nm, and in specific embodiments can be 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm or 1200 nm. In the present application, the first growth is preferably thermal oxidation growth, and the first growth is preferably performed in an oxidation furnace, and the first growth is preferably performed using a dry-oxygen-wet-oxygen-dry-oxygen alternating process; the conditions of the dry-oxygen-wet-oxygen-dry-oxygen alternating process preferably include: a temperature of 900-1100°C, and in specific embodiments can be 900°C, 950°C, 1000°C, 1050°C or 1100°C; a humidity of dry oxygen of 1-10%, and in specific embodiments can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%; a humidity of wet oxygen of 40-100%, and in specific embodiments can be 40%, 50%, 60%, 70%, 80%, 90% or 100%; a dry-oxygen growth time of 0.5-3 h, and in specific embodiments can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h; a wet-oxygen growth time of 2-6 h, and in specific embodiments can be 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h or 6 h. In the present application, the reaction principle of the thermal oxidation growth is as follows: dry-oxygen oxidation: Si (solid) + O2 (gas) → SiO2 (solid); wet-oxygen oxidation: Si (solid) + 2H2O (gas) → SiO2 (solid) + 2H2 (gas).

[0059] In the present application, the preparation method preferably further includes growing (denoted as second growth) a back surface medium layer on the lower surface of the substrate. In the present application, the back surface medium layer is preferably a silicon oxide layer. In the present application, the silicon oxide layer on the upper surface of the substrate and the back surface medium layer on the lower surface of the substrate are preferably deposited simultaneously. In the present application, the thickness of the back surface medium layer is preferably 600-1200 nm, and in specific embodiments can be 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm or 1200 nm.

[0060] The first deposition is not particularly limited in the present application and can be performed by a deposition method known to those skilled in the art, such as low pressure chemical vapor deposition (LPCVD). In the present application, the low pressure chemical vapor deposition is preferably performed in an LPCVD device. In the present application, the conditions of the first deposition preferably include a temperature of 700-850°C, which in specific embodiments can be 700°C, 750°C, 800°C or 850°C; a pressure of 133-1330 Pa, which in specific embodiments can be 133 Pa, 200 Pa, 300 Pa, 400 Pa, 500 Pa, 600 Pa, 700 Pa, 800 Pa, 900 Pa, 1000 Pa, 1100 Pa, 1200 Pa, 1300 Pa or 1330 Pa; and the time of the first deposition is not particularly limited in the present application and can be any time that can provide a silicon nitride layer having a thickness of 200-600 nm. In the present application, the reaction principle of the first deposition is as follows: 3SiCl2H2(gas)+4NH3(gas)→Si3N4(solid)+6HCl(gas)+6H2(gas).

[0061] After obtaining the silicon nitride layer, the present application deposits a heating electrode layer (referred to as the second deposition) on the surface of the silicon nitride layer and then performs a patterning process to form a spiral heating electrode. Specifically, a Ti layer and a Pt layer are sequentially deposited on the surface of the silicon nitride layer to form a heating electrode layer, and then the heating electrode layer is subjected to a patterning process (referred to as the first patterning process) to form a spiral heating electrode.

[0062] The second deposition is not particularly limited in the present application and can be performed by a deposition method known to those skilled in the art, such as evaporation or sputtering, more preferably electron beam evaporation. In the present application, the conditions of the second deposition preferably include a sputtering power of 400-600 W, which in specific embodiments can be 400 W, 450 W, 500 W, 550 W or 600 W; an inert gas flow rate of 20-50 seem, which in specific embodiments can be 20 seem, 30 seem, 40 seem or 50 seem; the inert gas preferably includes argon or helium; and the time of the second deposition is not particularly limited in the present application and can be any time that can provide a Ti layer having a thickness of 20-40 nm and a Pt layer having a thickness of 200-500 nm.

[0063] In the present application, the first patterning process preferably includes sequentially performing coating of photoresist, ultraviolet exposure, development, hardening, etching and photoresist removal.

[0064] In the present application, before the photoresist is coated, the substrate with the silicon nitride layer is preferably cleaned and dried; the cleaning preferably comprises cleaning with acetone and / or deionized water; the drying temperature is preferably 60-65°C, and in specific embodiments can be 60°C, 61°C, 62°C, 63°C, 64°C or 65°C; the drying time is preferably 120-180 seconds, and in specific embodiments can be 120 seconds, 130 seconds, 140 seconds, 150 seconds, 160 seconds, 170 seconds or 180 seconds.

[0065] The present application does not have special limitations on the photoresist, and a positive photoresist known to those skilled in the art can be used, such as AZ1500 photoresist. The present application does not have special limitations on the coating, and a photoresist layer with a thickness of 0.8-1.0 μm can be obtained, such as spin coating, the spin coating speed is preferably 4000-5000 r / min, and in specific embodiments can be 4000 r / min, 4200 r / min, 4500 r / min, 4800 r / min or 5000 r / min; the thickness of the photoresist layer can be specifically 0.8 μm, 0.9 μm or 1 μm.

[0066] In the present application, the conditions for the ultraviolet exposure preferably comprise: light intensity of 60-80 mJ / cm 2 , and in specific embodiments can be 60 mJ / cm 2 , 65 mJ / cm 2 , 70 mJ / cm 2 , 75 mJ / cm 2 or 80 mJ / cm 2 ; exposure power of 5-15 mW / cm 3 , and in specific embodiments can be 5 mW / cm 3 , 8 mW / cm 3 , 10 mW / cm 3 , 12 mW / cm 3 or 15 mW / cm 3 ; exposure time of 2-3 seconds.

[0067] The present application does not have special limitations on the developer used for the development, and a developer known to those skilled in the art can be used. In the present application, the development time is preferably 40-50 seconds, and in specific embodiments can be 40 seconds, 42 seconds, 45 seconds, 48 seconds or 50 seconds.

[0068] In the present application, the temperature of the hard film is preferably 100-160℃, and in specific embodiments can be 100℃, 110℃, 120℃, 130℃, 140℃, 150℃ or 160℃; the time of the hard film is preferably 12-16min, and in specific embodiments can be 12min, 13min, 14min, 15min or 16min.

[0069] In the present application, the etching preferably comprises reactive ion etching (RIE) and / or inductively coupled etching (ICP); the present application does not have special limitations on the conditions of the etching, as long as a spiral heating electrode can be obtained.

[0070] The present application does not have special limitations on the stripping, and any stripping method known to those skilled in the art can be used, such as placing in a dry stripping machine to remove photoresist.

[0071] After the spiral heating electrode is formed, the present application deposits an insulating layer (denoted as the third deposition) on the surface of the spiral heating electrode, specifically, sequentially deposits a silicon oxide layer and a silicon nitride layer on the surface of the spiral heating electrode. The present application does not have special limitations on the third deposition, and any deposition process known to those skilled in the art can be used to sequentially obtain a silicon oxide layer with a thickness of 600-1200nm and a silicon nitride layer with a thickness of 200-600nm, such as plasma enhanced chemical vapor deposition (PECVD). In the present application, the reaction principle of the PECVD is as follows: SiH4+O2→SiO2+2H2; 3SiH4+4NH3→Si3N4+12H2.

[0072] After the insulating layer is obtained, the present application deposits an interdigital electrode layer on the surface of the insulating layer and then performs a patterning treatment to form a circular interdigital electrode (denoted as a Ti / Pt layer), specifically, sequentially deposits (denoted as the fourth deposition) a Ti layer and a Pt layer on the surface of the insulating layer to form an interdigital electrode layer, and then performs a patterning treatment (denoted as the second patterning treatment) on the interdigital electrode layer to form a circular interdigital electrode.

[0073] The present application does not have special limitations on the fourth deposition, and any deposition method known to those skilled in the art can be used to sequentially obtain a Ti layer with a thickness of 20-40nm and a Pt layer with a thickness of 200-500nm. In the present application, the conditions of the fourth deposition are preferably the same as those of the second deposition, which will not be repeated here.

[0074] In the present application, the Ti layer and the Pt layer in the insulating layer are etched during the patterning treatment, and the conditions of the second patterning treatment are preferably the same as those of the first patterning treatment, which will not be repeated here.

[0075] After the circular interdigital electrode is formed, the application preferably further comprises etching electrode holes in the insulating layer to obtain lead-out electrodes; the lead-out electrodes are heating electrode pad blocks and interdigital electrode pad blocks.

[0076] In the application, the etching of the electrode holes in the insulating layer preferably comprises, in sequence, coating photoresist on the surface of the insulating layer, ultraviolet exposure, development, hardening, etching and photoresist removal. The application does not have special limitations on the preparation conditions of the electrode holes, and electrode holes with a size of 50-300 μm can be obtained.

[0077] In the application, before the photoresist is coated, the substrate with the circular interdigital electrode is preferably dried after being cleaned; the cleaning preferably comprises cleaning with acetone and / or deionized water. In the application, the drying temperature is preferably 60-65°C, and in specific embodiments can be 60°C, 61°C, 62°C, 63°C, 64°C or 65°C; the drying time is preferably 120-180 s, and in specific embodiments can be 120 s, 130 s, 140 s, 150 s, 160 s, 170 s or 180 s.

[0078] The application does not have special limitations on the photoresist, and a positive photoresist known to those skilled in the art can be used, such as AZ1500 photoresist. The application does not have special limitations on the coating, and a photoresist layer with a thickness of 1.5-2 μm can be obtained, such as spin coating, the rotation speed of which is preferably 2000-4000 r / min, and in specific embodiments can be 2000 r / min, 2500 r / min, 3000 r / min, 3500 r / min or 4000 r / min; the thickness of the photoresist layer can be specifically 1.5 μm, 1.8 μm or 2 μm.

[0079] In the application, the conditions of the ultraviolet exposure preferably comprise: light intensity of 60-80 mJ / cm 2 , and in specific embodiments can be 60 mJ / cm 2 , 65 mJ / cm 2 , 70 mJ / cm 2 , 75 mJ / cm 2 or 80 mJ / cm 2 ; exposure power of 5-15 mW / cm 3 , and in specific embodiments can be 5 mW / cm 3 , 8 mW / cm 3 , 10 mW / cm 3 , 12 mW / cm 3 or 15 mW / cm 3 ; exposure time of 2-3 s.

[0080] The present application is not limited to the developing agent used for the developing, and any developing agent known to those skilled in the art can be used. In the present application, the time for the developing is preferably 40-50 s, and in specific embodiments, can be 40 s, 42 s, 45 s, 48 s or 50 s.

[0081] In the present application, the temperature for the hardening is preferably 100-160 ℃, and in specific embodiments, can be 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃ or 160 ℃; the time for the hardening is preferably 12-16 min, and in specific embodiments, can be 12 min, 13 min, 14 min, 15 min or 16 min.

[0082] The present application is not limited to the etching, and any etching method known to those skilled in the art can be used, such as reactive ion etching (RIE). In the present application, the conditions for the reactive ion etching preferably include: the gaseous etchant includes CF4 gas; the flow rate of the gaseous etchant is 30-60 sccm, and in specific embodiments, can be 30 sccm, 40 sccm, 50 sccm or 60 sccm; the etching mask is a patterned photoresist. In the present application, the reaction principle of the gaseous etchant with silicon nitride and silicon oxide during the etching is as follows: plasma: CF4→CF3+F; plasma: F+SiO2→SiF4+O; plasma: F+Si3N4→SiF4+N.

[0083] The present application is not limited to the removing of the photoresist, and any removing method known to those skilled in the art can be used, such as placing in a dry removing machine.

[0084] After the formation of the circular interdigital electrode, the present application releases the microstructure to obtain a large-size MEMS micro-hotplate. In the present application, the releasing of the microstructure preferably includes sequentially performing front etching of the via, etching of the back medium layer and back etching of the via to obtain a large-size MEMS micro-hotplate.

[0085] In the present application, the etching of the via is preferably etching of the insulating layer, the silicon oxide layer and the silicon nitride layer on the upper surface of the substrate; the method and conditions for the etching of the via are preferably the same as those for the etching of the electrode hole in the insulating layer, which will not be described herein again.

[0086] In the present application, the method and conditions for the etching of the back medium layer are preferably the same as those for the etching of the electrode hole in the insulating layer, which will not be described herein again.

[0087] ​​​​​​​In the present application, the structure layer releasing preferably comprises a wet etching, which preferably comprises KOH etching and tetramethylammonium hydroxide (TMAH) etching in sequence; the thickness of the wet etching is the same as the thickness of the substrate. In the present application, the conditions of the KOH etching preferably comprise: the etchant is KOH aqueous solution, the mass fraction of the KOH aqueous solution is preferably 20-40%, and in specific embodiments, can be 20%, 25%, 30%, 35% or 40%; the temperature is 60-80℃, and in specific embodiments, can be 60℃, 65℃, 70℃, 75℃ or 80℃; the time of KOH etching is preferably 2-3h, and in specific embodiments, can be 2h, 2.5h or 3h. In the present application, the conditions of the tetramethylammonium hydroxide etching preferably comprise: the etchant is TMAH aqueous solution, the mass fraction of the TMAH aqueous solution is preferably 15-25%, and in specific embodiments, can be 15%, 18%, 22% or 25%; the temperature is 60-80℃, and in specific embodiments, can be 60℃, 65℃, 70℃, 75℃ or 80℃; the time of TMAH etching is 3-4h, and in specific embodiments, can be 3h, 3.5h or 4h.

[0088] The present application improves the effective working area of the micro-hotplate to 200-500μm×200-500μm by innovative micro-hotplate structure design and optimized manufacturing process, successfully solves the compatibility problem of the traditional MEMS micro-hotplate and the metal oxide sensitive material film forming process, and provides a reliable technical solution for the large-scale production of high-performance MEMS gas sensors.

[0089] The present application also provides the application of the large-size MEMS micro-hotplate prepared by the preparation method to a MEMS gas sensor chip. In the present application, the gas detected by the MEMS gas sensor chip preferably comprises one or more of hydrogen, carbon monoxide and methane.

[0090] In order to further illustrate the present application, the large-size MEMS micro-hotplate, the preparation method and the application thereof provided by the present application are described in detail below in combination with embodiments, but they should not be understood as limiting the protection scope of the present application.

[0091] Example 1

[0092] 1. Substrate pretreatment

[0093] A six-inch double-throw silicon wafer (structure diagram see Figure 1 ), crystal direction (100), thickness 400μm, resistivity 3-10Ω·cm. The silicon wafer was cleaned with acetone and deionized water in sequence.

[0094] 2. Thermal oxidation to form SiO2 layer on both sides of the wafer (see Figure 2 )

[0095] The cleaned wafer was placed in an oxidation furnace and grown for 2h in dry oxygen (2% RH), 4h in wet oxygen (40% RH), and 2h in dry oxygen (2% RH) to form a 1.0 μm thick SiO2 layer on both sides of the wafer. The dry oxygen was 2% RH and the wet oxygen was 40% RH. The oxidation temperature was 1050°C.

[0096] 3. LPCVD deposition of Si3N4 layer (see Figure 2 )

[0097] The wafer with the SiO2 layer was placed in an LPCVD apparatus and a 0.4 μm thick Si3N4 layer was deposited on the SiO2 layer on the top side of the wafer at a temperature of 650°C.

[0098] 4. Sputtering of Ti / Pt layer (heating electrode, see Figure 3 )

[0099] The wafer with the Si3N4 layer was placed in a sputtering apparatus and a 30 nm thick Ti layer and a 500 nm thick Pt layer were sputtered on the Si3N4 layer in that order to form a heating electrode. The sputtering power was 500 W and the argon flow rate was 30 seem.

[0100] 5. Lithography and etching of the heating electrode (patterned processing, spiral heating electrode)

[0101] Cleaning and drying: The wafer with the Ti / Pt layer was cleaned with acetone and deionized water in that order and dried at 60°C for 120s.

[0102] Gluing: AZ1500 photoresist was used at a rotation speed of 5000 r / min and a photoresist layer thickness of 1 μm.

[0103] Exposure: The light intensity was 75 mJ / cm 2 , the exposure power was 10 mW / cm 3 , and the exposure time was 2s.

[0104] Developing: The time was 45s.

[0105] Hardening: The time was 15 min.

[0106] Etching: The Ti / Pt layer was etched in an inductively coupled etching device. The etching thickness of the Ti layer was 30 nm, and the etching thickness of the Pt layer was 500 nm, forming a spiral heating electrode, as shown in FIG. 1. Figure 4 .

[0107] Removal of photoresist: The etched silicon wafer was placed in a dry photoresist removal machine to remove the photoresist.

[0108] 6. PECVD deposition of an insulating layer (see FIG. 2) Figure 5

[0109] The silicon wafer after removal of the photoresist was placed in a PECVD device to deposit a 600 nm thick SiO2 layer and a 500 nm thick Si3N4 layer on the side of the silicon wafer having the spiral heating electrode, forming an insulating layer.

[0110] 7. Sputtering of a Ti / Pt layer (interdigital electrode, see FIG. 3) Figure 6

[0111] The silicon wafer with the deposited insulating layer was placed in a sputtering device to sputter a 20 nm thick Ti layer and a 200 nm thick Pt layer on the surface of the insulating layer, forming an interdigital electrode. The sputtering power was 500 W, and the argon flow rate was 30 sccm.

[0112] 8. Photolithography and etching of the signal electrode (patterning, circular interdigital electrode, see FIG. 4) Figure 7

[0113] Cleaning and drying: The silicon wafer with the interdigital electrode was cleaned with acetone and deionized water, respectively, and dried at 60°C for 120 s.

[0114] Photoresist coating: AZ1500 photoresist was used at a rotation speed of 5000 r / min, and the coating thickness was 1 μm.

[0115] Exposure: The light intensity was 75 mJ / cm 2 , the exposure power was 10 mW / cm 3 , and the exposure time was 2 s.

[0116] Development: The time was 45 s.

[0117] Hardening: The time was 15 min.

[0118] Etching: The Ti / Pt layer was etched in an RIE device to form a circular interdigital electrode. The etching thickness of the Ti layer was 20 nm, and the etching thickness of the Pt layer was 200 nm. The shape of the circular interdigital electrode is shown in FIG. 5. Figure 7

[0119] Removal of photoresist: The etched silicon wafer was placed in a dry photoresist removal machine to remove the photoresist.

[0120] ​​​​9. Etching the electrode hole, forming the heating electrode pad block and the interdigital electrode pad block (see Figure 8 )

[0121] Cleaning and drying: the silicon wafer with the circular interdigital electrode was cleaned with acetone and deionized water in sequence, and dried at 60°C for 120s.

[0122] Gluing: AZ1500 photoresist was used, the rotation speed was 3000r / min, and the coating thickness was 2μm.

[0123] Exposure: the light intensity was 75mJ / cm 2 , the exposure power was 10mW / cm 3 , and the exposure time was 2s.

[0124] Developing: the time was 45s.

[0125] Hardening: the time was 15min.

[0126] Etching: the silicon wafer was placed in the RIE device to etch the insulating layer (SiO2 / Si3N4 layer), the etching thickness of the SiO2 layer was 0.6μm, and the etching thickness of the Si3N4 layer was 0.5μm. The gaseous etchant used was CF4 gas, the flow rate was 800sccm, and the etching mask was the patterned photoresist, thereby obtaining the heating electrode pad block and the interdigital electrode pad block.

[0127] 10. Etching the through hole on the front side (see Figure 9 )

[0128] Cleaning and drying: the silicon wafer with the circular interdigital electrode was cleaned with acetone and deionized water in sequence, and dried at 60°C for 120s.

[0129] Gluing: AZ1500 photoresist was used, the rotation speed was 3000r / min, and the coating thickness was 2μm.

[0130] Exposure: the light intensity was 75mJ / cm 2 , the exposure power was 10mW / cm 3 , and the exposure time was 2s.

[0131] Developing: the time was 45s.

[0132] Hardening: the time was 15min.

[0133] The exposed silicon wafer was placed in the RIE device to etch the insulating layer, the silicon oxide layer and the silicon nitride layer (SiO2 / Si3N4 / SiO2 / Si3N4 layer), and the etching thickness of the SiO2 / Si3N4 / SiO2 / Si3N4 layer was 1.0μm / 0.4μm / 0.6μm / 0.5μm in sequence. The gaseous etchant used was CF4 gas, and the flow rate was 800sccm.

[0134] Photoresist stripping: The etched silicon wafer was placed in a dry photoresist stripping machine to remove the photoresist.

[0135] 11. Etching of the backside dielectric layer (SiO2 layer) (see Figure 11 )

[0136] Cleaning and drying: The front side etched via silicon wafer was cleaned with acetone and deionized water, respectively, and dried at 60 °C for 120 s.

[0137] Photoresist coating: AZ1500 photoresist was used, with a rotation speed of 3000 r / min, and a coating thickness of 2 μm.

[0138] Exposure: The light intensity was 75 mJ / cm 2 , the exposure power was 10 mW / cm 3 , and the exposure time was 2 s.

[0139] Developing: The time was 45 s.

[0140] Hardening: The time was 15 min.

[0141] The exposed silicon wafer was placed in a RIE device to etch the SiO2 layer, with a thickness of 1.0 μm. The gaseous etchant used was CF4 gas, with a flow rate of 800 sccm, and the etching mask was a patterned photoresist.

[0142] Photoresist stripping: The etched silicon wafer was placed in a dry photoresist stripping machine to remove the photoresist.

[0143] 12. Etching of the backside via (see Figure 12-13 )

[0144] The silicon wafer after etching of the backside dielectric layer was placed in a wet etching device, and the silicon wafer was etched with 20 wt% KOH aqueous solution and 25 wt% TMAH aqueous solution, respectively, to release the micro-hotplate structure layer, to obtain a large-size MEMS micro-hotplate (with a working area size of 300 μm x 300 μm). The total etching thickness was 400 μm. The KOH etching temperature was 60 °C, and the time was 2 h; the TMAH etching temperature was 80 °C, and the time was 3 h. Through this etching method, the micro-hotplate structure layer was released.

[0145] Figure 4 An optical microscope image of the spiral heating electrode, Figure 7 an optical microscope image of the circular interdigital electrode, Figure 10 an optical microscope image of the micro-hotplate after via etching, which shows that the spiral heating electrode and the circular interdigital electrode have clear trends, and the electrode edges are clear, and electrical parameter measurement can be performed from the heating electrode pad block and the interdigital electrode pad block.

[0146] Optical microscope image of the large-size MEMS micro-hotplate Figure 14-15 , Figure 15 The left image in the middle is the front optical microscope image of the working area, Figure 15 The right image in the middle is the back optical microscope image of the working area, and it can be seen that the large-size MEMS micro-hotplate has a complete structure, smooth edges, and a clear shape, and the eight-suspension-arm suspended membrane structure is obvious.

[0147] A batch of large-size MEMS micro-hotplates are prepared according to the above method, and 8 of them are randomly taken out for voltage-temperature test, temperature-power consumption test and temperature distribution under different input voltages, and the specific test steps are as follows: a bench power supply is used to apply voltage to the large-size MEMS micro-hotplate from 0.5V to 4V, and when the temperature is stable, the power supply will display the current at this time, and the power consumption is calculated as voltage x current.

[0148] The voltage-temperature test results are shown in Figure 16 The temperature-power consumption test results are shown in Figure 17 The temperature distribution under the same input voltage is shown in Figure 18 The test results show that the large-size MEMS micro-hotplate has good performance consistency, the temperature reaches 301℃ when the input voltage is 3.5V, the power consumption is 56.4mW, the temperature distribution is uniform, the heat loss is small, and the power consumption is low. It is shown that the large-size MEMS micro-hotplate provided by the present application solves the problem of mismatching with the sensitive material film forming process caused by the too small working area of the traditional MEMS micro-hotplate, can improve the performance and compatibility of the sensor, and provides a reliable technical scheme for the large-scale production of high-performance gas sensors.

[0149] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the technical field, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A large-size MEMS micro-hotplate, characterized in that: It includes a suspended working platform, through holes located around the suspended working platform, and a support assembly and a cantilever beam assembly for supporting the suspended working platform; The working area size of the suspended working platform is 200-500 μm×200-500 μm; the suspended working platform comprises a silicon nitride layer, a spiral heating electrode, an insulating layer and a circular interdigital electrode stacked in sequence; The cantilever beam assembly includes 8 cantilever beams, one end of each cantilever beam is connected to the suspended working platform, and the other end is connected to the support assembly.

2. The large-size MEMS micro-hotplate according to claim 1, characterized in that: The spiral micro-heating electrode comprises a Ti layer and a Pt layer stacked in sequence, wherein the Pt layer has a spiral structure; the thickness of the Ti layer is 20 to 40 nm; and the thickness of the Pt layer is 200 to 500 nm.

3. The large-scale MEMS micro-hotplate according to claim 1, characterized in that: The circular interdigital electrode includes a Ti layer and a Pt layer stacked in sequence; the thickness of the Ti layer is 20 to 40 nm; the thickness of the Pt layer is 200 to 500 nm.

4. The large-scale MEMS micro-hotplate according to claim 1, characterized in that: The thickness of the silicon nitride layer is 200-600 nm.

5. The large-scale MEMS micro-hotplate according to claim 1, characterized in that: The insulating layer includes a silicon oxide layer and a silicon nitride layer stacked in sequence; the thickness of the silicon oxide layer is 600 to 1200 nm; the thickness of the silicon nitride layer is 200 to 600 nm.

6. The large-scale MEMS micro-hotplate according to claim 1, characterized in that: The support assembly includes a silicon oxide layer, a silicon substrate layer, a silicon oxide layer, a silicon nitride layer, a heating electrode pad block, an insulating layer and an interdigital electrode pad block stacked in sequence, and an electrode hole is provided in the insulating layer on the surface of the heating electrode pad block; The silicon substrate layer has a prism-shaped through hole.

7. The large-scale MEMS micro-hotplate according to claim 1, characterized in that: One end of the cantilever beam is connected to the suspended working platform: one end of two cantilever beams is connected to the spiral heating electrode, one end of two cantilever beams is connected to the circular interdigital electrode, and one end of four cantilever beams is connected to the silicon nitride layer and the insulating layer.

8. The method for preparing the large-size MEMS micro-hotplate according to any one of claims 1 to 7, characterized in that: The following steps are involved: A silicon oxide layer and a silicon nitride layer are sequentially deposited on the upper surface of the substrate. A heating electrode layer is deposited and then patterned to form a spiral heating electrode. An insulating layer is deposited. An interdigital electrode layer is deposited and then patterned to form a circular interdigital electrode. The microstructure is released to obtain a large-size MEMS micro-hotplate.

9. The preparation method according to claim 8, characterized in that The preparation method further comprises depositing a back dielectric layer on the lower surface of the substrate.

10. Use of the large-scale MEMS micro-hotplate according to any one of claims 1 to 8 or the large-scale MEMS micro-hotplate prepared by the preparation method according to claim 9 as a MEMS gas sensor chip.

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