Self-supporting amorphous carbon thin film NEMS acceleration sensor chip and preparation method thereof

Abstract

The application belongs to the technical field of nanoelectromechanical system acceleration sensor, and discloses a self-supporting amorphous carbon thin film NEMS acceleration sensor chip and a preparation method thereof. The acceleration sensor chip comprises a chip substrate, a graphene interdigital electrode, an amorphous carbon sensitive thin film and a metal electrode. The chip substrate comprises a silicon substrate, a silicon oxide layer and a silicon nitride layer arranged in sequence from bottom to top. The metal electrode and the amorphous carbon sensitive thin film are deposited on the silicon nitride layer. The amorphous carbon sensitive thin film comprises an amorphous carbon sensitive beam suspended on a groove, a first sensitive thin film area covering a mass block on the silicon nitride layer and a second sensitive thin film area covering a fixed outer frame on the silicon nitride layer. The graphene interdigital electrode is transferred on the metal electrode and the amorphous carbon sensitive thin film. The technical scheme of the application can reduce the ohmic contact resistivity of the existing amorphous carbon sensor, and the sensitivity of the sensor can be improved through the nanoscale thickness of the sensitive beam and the interdigital electrode structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanoelectromechanical system (NEMS) acceleration sensor, and particularly relates to a self-supporting amorphous carbon thin film NEMS acceleration sensor chip and a preparation method thereof. BACKGROUND

[0002] As an important product of nanoelectromechanical system, the micro high-sensitivity acceleration sensor has broad application requirements in civil industry, national defense and military industry and other fields.

[0003] At present, the existing acceleration sensors are mainly silicon diffusion type piezoresistive acceleration sensors, and the process thereof is relatively mature. However, in order to improve the sensitivity of the sensor, the mass block volume of the acceleration sensor is generally large. The sensitivity of the acceleration sensor with a small volume is not high, and cannot meet the accurate acceleration measurement in the fields of marine environment, industrial automation, automobile electronics, medical equipment and the like. In addition, the silicon-based acceleration sensor processed based on the MEMS (Micro-Electro-Mechanical System) process can only be made to 10 μm in the thinnest sensitive beam, and is easy to break and fail.

[0004] In summary, with the continuous development and progress of the acceleration sensor, there are still the following technical problems to be solved, including:

[0005] 1) At present, the methods for increasing the sensitivity of the sensor are to thin the thickness of the beam and to increase the volume of the mass block. However, the conventional MEMS process (such as wet etching, dry etching and the like) is very limited for further thinning the thickness of the beam and increasing the volume of the mass block.

[0006] 2) At present, the volume of the high-sensitivity sensor is large, and cannot meet the requirements of miniaturization and small size;

[0007] 3) As a new sensitive material, the piezoresistive coefficient of amorphous carbon is low. When it is deposited on a silicon substrate as a pressure-sensitive material, the sensitivity is much smaller than that of the traditional silicon-based sensor;

[0008] 4) The adhesion of amorphous carbon to metal is poor. When in large-area contact, the metal is easy to peel off from the amorphous carbon substrate, resulting in electrical connection failure. The ohmic contact resistivity of metal-semiconductor (amorphous carbon) is high, and cannot meet the requirements of the sensor. In the high radiation and corrosion environment such as the ocean, the Schottky contact is easy to form, which directly limits the use of the sensor. SUMMARY

[0009] The self-supporting amorphous carbon thin film NEMS acceleration sensor chip and the preparation method aim to solve one or more of the above technical problems.

[0010] To achieve the above-mentioned purposes, the application adopts the following technical solutions:

[0011] The self-supporting amorphous carbon thin film NEMS acceleration sensor chip provided by the application comprises a chip substrate, a graphene interdigital electrode, an amorphous carbon sensitive thin film and a metal electrode.

[0012] The chip substrate comprises a silicon substrate, a silicon oxide layer and a silicon nitride layer arranged in sequence from bottom to top.

[0013] The metal electrode and the amorphous carbon sensitive thin film are transferred with the graphene interdigital electrode.

[0014] The metal electrode and the amorphous carbon sensitive thin film are transferred with the graphene interdigital electrode.

[0015] The amorphous carbon sensitive thin film is rectangular, and only one pair of edges covers part of the groove.

[0016] Further improvement of the present application is that the metal electrode comprises a metal electrode first electrode and a metal electrode second electrode arranged on the fixed outer frame of the silicon nitride layer; the metal electrode first electrode comprises a first metal pad and a first lead connected with each other, and the metal electrode second electrode comprises a second metal pad and a second lead connected with each other; wherein the first lead and the second lead are arranged on two sides of a pair of edges of the amorphous carbon sensitive film uncovered groove respectively, and the first lead and the second lead are parallel to the pair of edges of the amorphous carbon sensitive film uncovered groove; neither the first metal pad nor the second metal pad is in contact with the amorphous carbon sensitive film.

[0017] Further improvement of the present application is that the graphene interdigital electrode comprises a graphene interdigital electrode first electrode and a graphene interdigital electrode second electrode; the graphene interdigital electrode first electrode and the graphene interdigital electrode second electrode both comprise a comb handle and a comb tooth, the comb teeth of the graphene interdigital electrode first electrode and the graphene interdigital electrode second electrode form an interdigital structure, the comb handle of the graphene interdigital electrode first electrode covers the first lead completely or partially, and the comb handle of the graphene interdigital electrode second electrode covers the second lead completely or partially.

[0018] Further improvement of the present application is that the fixed outer frame is arranged on the chip substrate, and the fixed outer frame is arranged on the chip substrate through a silicon oxide layer.

[0019] The mass block is rectangular, and the groove is a rectangular frame; wherein the size of the mass block is 15 μm-3000 μm, and the width of the groove is 1 μm-200 μm.

[0020] Alternatively, the mass block is circular, and the groove is a circular ring; wherein the diameter of the mass block is 15 μm-30000 μm, and the width of the groove is 1 μm-200 μm.

[0021] Wherein the inner edge of the groove corresponds to the outer edge of the mass block, and the outer edge of the groove corresponds to the inner edge of the fixed outer frame.

[0022] Further improvement of the present application is that the thickness of the amorphous carbon sensitive beam is 1 nm-500 nm.

[0023] Further improvement of the present application is that the self-supporting amorphous carbon film NEMS acceleration sensor chip is rectangular, and the side length is 50 μm-4000 μm; the thickness of the chip substrate is 100 μm-600 μm; the thickness of the silicon nitride layer is 100 nm-300 nm; and the thickness of the silicon oxide layer is 100 nm-300 nm.

[0024] Further improvements of the present application are that the graphene sensitive thin film comprises a single atomic layer, two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers or ten atomic layers of graphene thin film.

[0025] The application provides a preparation method of a self-supporting amorphous carbon thin film NEMS acceleration sensor chip.

[0026] Step 1, depositing a silicon dioxide and silicon nitride thin film layer on the upper surface of a silicon wafer and a silicon oxide layer on the lower surface of the silicon wafer by a low-pressure chemical vapor deposition method and a plasma-enhanced chemical vapor deposition method to obtain a chip substrate;

[0027] Step 2, spin-coating photoresist on the upper surface of the chip substrate, and performing photolithography by selecting a metal electrode mask plate; performing magnetron sputtering by using a metal target to sputter a metal thin film covering the upper surface of the wafer; performing metal electrode stripping by using acetone to obtain a metal electrode covering a fixed frame, and preparing a first process wafer;

[0028] Step 3, spin-coating photoresist on the upper surface of the first process wafer, and performing photolithography by selecting a front mass etching mask plate; etching the silicon nitride layer on the wafer surface spin-coated with photoresist in an atmosphere of 50-100 sccm SF6 and 30-60 sccm Ar by plasma dry etching; etching the silicon oxide layer on the wafer surface not covered with photoresist in an atmosphere of 80-120 sccm CHF3 and 30-60 sccm Ar by plasma dry etching; etching the silicon layer not covered with photoresist to the transparent silicon oxide layer by deep silicon dry etching, and stopping etching; removing the photoresist on the wafer surface after dry etching by using acetone to prepare a second process wafer;

[0029] Step 4, depositing 1-100 nm amorphous carbon thin film on the surface of a target substrate by a PVD process and a CVD process to obtain an amorphous carbon thin film with high sp 3 content and piezoresistive coefficient; transferring the amorphous carbon thin film to the second process wafer by a polymer-assisted transfer process or a direct wet transfer process after sacrificing the target substrate; removing the polymer-assisted material on the surface of the amorphous carbon thin film by using acetone and ethanol, and immersing the wafer in deionized water, and blowing the silicon wafer dry in nitrogen to complete cleaning to prepare a third process wafer;

[0030] Step 5, spin-coating photoresist on the surface of the third process wafer, and performing photolithography by selecting an amorphous carbon patterning mask plate; patterning the amorphous carbon thin film by using plasma to remove the amorphous carbon thin film not protected by the photoresist to prepare a fourth process wafer;

[0031] Step 6, graphene films are prepared by a mechanical exfoliation method and a chemical vapor deposition method, and the prepared graphene films are transferred to the upper surface of the fourth process wafer by a polymer assisted transfer method, and cover the metal electrode and the region of the patterned amorphous carbon sensitive film layer; the polymer assisted material on the surface of the graphene film is removed by acetone and ethanol, the wafer is soaked in deionized water, and the silicon wafer is blown dry in nitrogen, so that cleaning is completed; photoresist is spin-coated on the upper surface of the graphene, and photolithography is performed by selecting a graphene internal toothed electrode mask; graphene interdigital electrodes are processed by removing graphene in the exposed region through oxygen plasma etching; the photoresist on the surface of the patterned graphene film is removed by acetone, ethanol and deionized water, and a fifth process wafer is prepared;

[0032] Step 7, in an atmosphere of 80-120sccm CHF3 and 30-60sccm Ar, the oxide layer on the back surface of the wafer is etched by a plasma dry etching method, so as to release the mass block, and the mass block is suspended on the lower surface of the amorphous carbon film, and a self-supporting amorphous carbon film NEMS acceleration sensor chip is prepared.

[0033] Further improvement of the application is that in step 4, the third process wafer directly generates the amorphous carbon film suspended in the groove on the second process wafer by a focused ion beam process and a CVD process, and is directly prepared.

[0034] Compared with the prior art, the application has the following beneficial effects:

[0035] The application discloses a micro high-sensitivity self-supporting amorphous carbon film NEMS acceleration sensor chip based on a graphene interdigital electrode, which comprises a graphene interdigital electrode, an amorphous carbon sensitive film, a metal electrode, a silicon nitride layer, a silicon oxide layer and a silicon substrate; wherein the sensitive beam is composed of the amorphous carbon sensitive film, and the electrode is composed of the graphene interdigital electrode; the nanometer-thickness sensitive beam structure and the interdigital electrode structure greatly improve the sensitivity of a traditional silicon-based amorphous carbon acceleration sensor. In addition, the bonding force between the graphene interdigital electrode and the amorphous carbon sensitive film is much greater than that between other metal electrodes, and the two-dimensional electrode material can also reduce the ohmic contact resistance between the amorphous carbon and the electrode. In summary, under the premise of ensuring the miniaturization of the acceleration sensor, the sensitivity is maximally improved by optimizing the sensitive structure and the electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following briefly introduces the drawings needed to be used in the embodiments or prior art description; obviously, the drawings in the following description are some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0037] Figure 1 is the axial side schematic view of the self-supporting amorphous carbon thin film NEMS acceleration sensor chip in the embodiment of the present application;

[0038] Figure 2 is the exploded schematic view of the self-supporting amorphous carbon thin film NEMS acceleration sensor chip in the embodiment of the present application;

[0039] Figure 3 is the top view schematic view of the self-supporting amorphous carbon thin film NEMS acceleration sensor chip in the embodiment of the present application;

[0040] Figure 4 is the Figure 3 cross-sectional view at A-A in the embodiment;

[0041] Figure 5 is the front view schematic view of the self-supporting amorphous carbon thin film NEMS acceleration sensor chip in the embodiment of the present application;

[0042] Figure 6 is the Figure 5 cross-sectional view at B-B in the embodiment;

[0043] Figure 7 is the Figure 5 cross-sectional view at C-C in the embodiment;

[0044] Figure 8 is the schematic view of the metal electrode mask in the embodiment of the present application;

[0045] Figure 9 is the schematic view of the front mass etching mask in the embodiment of the present application;

[0046] Figure 10 is the schematic view of the amorphous carbon sensitive thin film patterning mask in the embodiment of the present application;

[0047] Figure 11 is the schematic view of the graphene interdigital electrode mask in the embodiment of the present application;

[0048] Figure 12 is the schematic view of the graphene interdigital electrode structure principle in the embodiment of the present application;

[0049] The figure mark explanation is as follows:

[0050] 1, graphene interdigital electrode; 2, amorphous carbon sensitive thin film; 3, metal electrode; 4, silicon nitride layer; 5, silicon oxide layer; 6, silicon substrate;

[0051] 1-1, graphene interdigital electrode first electrode; 1-2, graphene interdigital electrode second electrode; 3-1, metal electrode first electrode; 3-2, metal electrode second electrode. DETAILED DESCRIPTION

[0052] In order to better understand the technical scheme of the present application, the technical scheme in the embodiments of the present application will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts should fall within the protection scope of the present application.

[0053] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but can include other steps or units that are not clearly listed or inherent to the process, method, product or device.

[0054] The present application will be described in further detail below in conjunction with the accompanying drawings:

[0055] Please refer to Figures 1 to 7 The embodiment of the present application provides a self-supporting amorphous carbon thin film NEMS acceleration sensor chip, in particular to a micro high-sensitivity self-supporting amorphous carbon thin film NEMS acceleration sensor chip based on a graphene interdigital electrode, which comprises a graphene interdigital electrode 1, an amorphous carbon sensitive thin film 2, a metal electrode 3, a silicon nitride layer 4, a silicon oxide layer 5 and a silicon substrate 6, wherein,

[0056] The silicon substrate 6, the silicon oxide layer 5 and the silicon nitride layer 4 are sequentially arranged from bottom to top; the silicon substrate 6, the silicon oxide layer 5 and the silicon nitride layer 4 are consistent in shape and all comprise a fixed outer frame and a mass block, the mass block is surrounded by the fixed outer frame, and the fixed outer frame and the mass block are isolated by a groove;

[0057] The metal electrode 3 and the amorphous carbon sensitive thin film 2 are deposited on the silicon nitride layer 4; the metal electrode 3 includes a metal electrode first electrode 3-1 and a metal electrode second electrode 3-2, both of which are arranged in a fixed outer frame; the metal electrode first electrode 3-1 includes a first metal pad and a first lead, and the first metal pad is connected with the first lead; the metal electrode second electrode 3-2 includes a second metal pad and a second lead, and the second metal pad is connected with the second lead; the amorphous carbon sensitive thin film 2 is rectangular, and only one pair of edges covers part of the groove; the amorphous carbon sensitive thin film 2 includes an amorphous carbon sensitive beam suspended on the groove, a first sensitive thin film area covering the mass block, and a second sensitive thin film area covering the fixed outer frame; the first lead and the second lead are arranged on both sides of the pair of edges of the amorphous carbon sensitive thin film 2 which does not cover the groove, and the leads are parallel to the direction of the amorphous carbon sensitive thin film and do not overlap, and the first metal pad and the second metal pad are not in contact with the amorphous carbon sensitive thin film 2; further explanatory, the length of the amorphous carbon sensitive beam is the width of the groove, and the width of the amorphous carbon is 1 μm to the length of the mass block edge, and the thickness is 1-500 nm;

[0058] The graphene interdigital electrode 1 is transferred on the metal electrode 3 and the amorphous carbon sensitive thin film 2; the graphene interdigital electrode 1 includes a graphene interdigital electrode first electrode 1-1 and a graphene interdigital electrode second electrode 1-2, both of which include a comb handle and a comb tooth, and the comb teeth of the graphene interdigital electrode first electrode 1-1 and the graphene interdigital electrode second electrode 1-2 form an interdigital structure; the comb handle of the graphene interdigital electrode first electrode 1-1 covers the first lead completely or partially, and the comb handle of the graphene interdigital electrode second electrode 1-2 covers the second lead completely or partially.

[0059] In the embodiment of the application, the shapes of the graphene interdigital electrode first electrode 1-1 and the graphene interdigital electrode second electrode 1-2 are symmetrical, but the positions are asymmetrical, and the comb teeth of the two do not overlap each other, but differ by half the tooth spacing, to form an interdigital structure; specifically, the number of comb teeth in the comb tooth structure is 2-100, the comb tooth width is 1-100 μm, and the length is composed of the edge length of the mass block, the groove width and the part on the fixed mass block; in addition, the length on the fixed mass block is the distance between the edge of the comb handle close to the fixed inner frame and the fixed inner frame, which is 10-200 μm.

[0060] In the embodiment of the present application, the mass block is rectangular or circular; when the mass block is rectangular, the groove is a rectangular frame; when the mass block is circular, the groove is a circular ring; wherein the inner edge of the groove corresponds to the outer edge of the mass block, and the outer edge of the groove corresponds to the inner edge of the fixed outer frame; in specific examples, when the mass block is rectangular, the groove is a rectangular frame, the mass block has a size of 15-3000 μm, and the groove has a width of 1-200 μm; when the mass block is circular, the groove is a circular ring, the mass block has a diameter in the range of 15-30000 μm, and the groove has a width of 1-200 μm.

[0061] In the embodiment of the present application, the thickness of the silicon nitride layer 4 is 100-300 nm; the thickness of the silicon oxide layer 5 is 100-300 nm; the thickness of the chip substrate composed of the silicon substrate 6, the silicon oxide layer 5 and the silicon nitride layer 4 is 100-600 μm; and the overall acceleration sensor chip is rectangular with a side length of 50-4000 μm.

[0062] In the embodiment of the present application, the material of the metal electrode 3 is one metal or a combination of several metals selected from Au, Cr, Ti, Cu, Ni and Pt.

[0063] In the embodiment of the present application, the graphene sensitive film comprises a single atomic layer, two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers and a thicker graphene film (0.35-100 nm).

[0064] Compared with silicon material, amorphous carbon has higher hardness and Young's modulus, and has characteristics such as wear resistance, corrosion resistance and biocompatibility. In the present application, the amorphous carbon film is used as a sensitive film, and due to its stable mechanical properties, the thickness thereof can reach 1-100 nm, the thinning of the sensitive beam can improve the sensitivity of the sensor, and at the same time, the volume of the mass block can be further reduced while ensuring high sensitivity. In addition, graphene as an electrode has the following advantages compared with traditional electrodes: 1) low ohmic contact resistivity, better linear proportional output curve; 2) good adhesion between graphene and amorphous carbon, not easy to fall off; 3) the work function of graphene is adjustable under gate bias, which can reduce the Schottky barrier and form a good ohmic contact; 4) due to the high mechanical properties of graphene, such as fracture toughness, it can be applied to flexible substrates, and under large strain, it still has good electrical connection. Since the high-sensitivity self-supporting amorphous carbon film is very thin, under the same external loading condition, the strain is large, and the metal electrode is prone to peeling and cracking under large strain. The present application selects graphene as the electrode, which can avoid the occurrence of this problem.

[0065] The embodiment of the present application is further explained. The two edges of the whole chip are located in the x direction, and the two edges are located in the y direction. The long edge length direction of the amorphous carbon sensitive film is along the y direction, and the amorphous carbon sensitive film is symmetrical along the x and y directions. The amorphous carbon sensitive film includes an amorphous carbon sensitive beam suspended on two grooves along the x direction, an amorphous carbon sensitive film covering the mass block, and a sensitive film covering the fixed frame. The length of the amorphous carbon sensitive beam is the width of the groove, and the width of the amorphous carbon is 1 μm to the length of the mass block edge. The length of the amorphous carbon sensitive film is the length of the inner edge of the fixed frame to the overall length of the chip. The metal electrode is composed of a lead and a pad. The lead is along the y direction, parallel to the amorphous carbon film direction and does not overlap, including a first lead and a second lead, and the lead width is 10-300 μm. The pad is arranged on both sides of the x axis center line of the chip, including a first metal pad and a second metal pad, and the metal pad does not contact the amorphous carbon sensitive film. The first metal pad is connected with the first lead to form the first external electrode of the chip. The second metal pad is connected with the second lead to form the second external electrode of the chip. The material of the external electrode is not limited, including one of Au, Cr, Ti, Cu, Ni, Pt or a combination of several. Further, the amorphous carbon sensitive film and the metal electrode are transferred with a graphene internal electrode. The graphene internal electrode includes a first graphene internal electrode and a second graphene internal electrode, which are respectively arranged on both sides of the y axis center line of the sensor. The first and second graphene internal electrodes have the same structure and are composed of a comb tooth part and a comb handle part. The comb tooth part connects the amorphous carbon sensitive film and the comb handle part, one end of which is located on the amorphous carbon sensitive film and the other end of which is located on the fixed frame, crossing the groove along the y axis direction. The comb handle part connects all the comb tooth electrodes on one side and is connected with the external metal lead on one side. Specifically, the amorphous carbon sensitive film is connected with the graphene internal comb tooth electrode and the graphene internal comb handle electrode through the graphene internal comb tooth electrode. The graphene comb handle electrode is connected with the external metal pad through the external metal lead. Finally, the two sides of the amorphous carbon sensitive film are electrically connected with the first and second metal pads. Specifically, the first and second graphene internal electrodes form a comb structure, and the first and second graphene internal electrodes are symmetrical in shape along the y axis direction but asymmetric in position. The comb tooth parts of the two do not overlap each other, and the comb tooth parts of the two are different by half the tooth spacing along the y axis direction. The number of comb teeth in the comb structure is 2-100, and the width of the comb tooth is 1-100 μm. The length is composed of the length of the mass block along the x direction, the width of the groove and the part on the fixed mass block. The length on the fixed mass block is the distance between the edge of the comb handle close to the fixed inner frame and the fixed inner frame, which is 10-200 μm. The graphene sensitive film includes a single atomic layer, two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers and thicker graphene film (0.35-100 nm).

[0066] Referring to Figures 8 to 11 The embodiment of the present application discloses a manufacturing method of a micro high-sensitivity self-supporting amorphous carbon film NEMS acceleration sensor chip based on a graphene interdigital electrode, and specifically comprises the following steps:

[0067] Step 1, depositing a silicon dioxide and silicon nitride film layer on the upper surface of a silicon wafer and a silicon oxide layer on the lower surface of the silicon wafer by a low pressure chemical vapor deposition (LPCVD) and a plasma enhanced chemical vapor deposition (PECVD), wherein the thickness of the upper surface silicon oxide layer and the silicon nitride film layer is 100-300 nm, and the thickness of the lower surface silicon oxide layer is 500 nm-2 μm, to obtain a wafer;

[0068] Step 2, spin-coating photoresist on the upper surface of the silicon nitride film layer, and performing photoetching by using an external metal electrode mask, to obtain a wafer;

[0069] Step 3, performing magnetron sputtering by using a metal target, to sputter a metal film covering the upper surface of the wafer, and obtaining an external metal electrode (metal solder pad and metal lead wire) covering a fixed external frame by using acetone for metal electrode stripping, wherein the substrate is a first process wafer;

[0070] Step 4, spin-coating photoresist on the upper surface of the first process wafer, and performing photoetching by using a positive mass block etching mask, to obtain a wafer;

[0071] Step 5, etching the silicon nitride layer on the surface of the wafer spin-coated with photoresist obtained in step 4 by plasma dry etching in an atmosphere of 50-100 sccm SF6 and 30-60 sccm Ar, then etching the silicon oxide layer on the surface of the wafer not covered by the photoresist by plasma dry etching in an atmosphere of 80-120 sccm CHF3 and 30-60 sccm Ar, and finally etching the silicon layer not covered by the photoresist by deep silicon dry etching until the transparent silicon oxide layer, to obtain a wafer;

[0072] Step 6, removing the photoresist on the surface of the wafer after dry etching by using acetone, to obtain a second process wafer;

[0073] Step 7, depositing an amorphous carbon film with a thickness of 1-100 nm on the surface of a target substrate by a PVD process and a CVD process, to obtain an amorphous carbon film with high sp 3 content and piezoresistive coefficient, and then transferring the amorphous carbon film to the second process wafer by a polymer assisted transfer process or a direct wet transfer process after sacrificing the target substrate; alternatively, the amorphous carbon film can be directly generated on the second process wafer by a focused ion beam process and a CVD process, to obtain a wafer, thereby omitting the amorphous carbon wet transfer process;

[0074] Exemplary preferred, the PVD process includes magnetron sputtering deposition, high power impulse magnetron sputtering (HiPIMS) deposition, vacuum cathodic arc deposition, plasma deposition, laser pulse deposition, electron cyclotron resonance plasma sputtering (ECR), etc.; the CVD process includes plasma enhanced chemical vapor deposition (PECVD), linear ion beam chemical vapor deposition (LIBCVD), hot wire chemical vapor deposition, direct photochemical vapor deposition, electron cyclotron resonance deposition and laser-assisted chemical deposition (LCVD), etc.;

[0075] Step 8, by wet etching process, i.e. by removing the polymer auxiliary material on the surface of the amorphous carbon film through acetone, ethanol; then immerse the wafer in deionized water for 5 min; finally, dry the silicon wafer in nitrogen, complete the cleaning, get the third process wafer; wherein, the amorphous carbon transferred by direct transfer method and deposited directly on the second process wafer can skip this step;

[0076] Step 9, spin coating photoresist on the surface of the third process wafer, and selecting amorphous carbon patterning mask for photoetching, to get the wafer;

[0077] Step 10, patterning the amorphous carbon film by plasma, removing the part of amorphous carbon film not protected by photoresist to get the fourth process wafer;

[0078] Step 11, prepare the graphene film layer by mechanical exfoliation method and chemical vapor deposition method, the graphene film layer contains single atomic layer, two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, ten atomic layers and thicker graphene film (optionally, the thickness can be 0.35-100 nm);

[0079] Step 12, transfer the graphene film prepared in step 11 to the upper surface of the fourth process wafer by polymer assisted transfer method, and cover the area of the external metal electrode prepared in step 2 and the patterned amorphous carbon sensitive film layer prepared in step 10;

[0080] Step 13, by wet etching process, i.e. by removing the polymer auxiliary material on the surface of the graphene film through acetone, ethanol; then immerse the wafer in deionized water for 5 min; finally, dry the silicon wafer in nitrogen, complete the cleaning, get the wafer;

[0081] Step 14, spin coating photoresist on the graphene upper surface, selecting graphene internal toothed electrode mask for photoetching to obtain a wafer;

[0082] Step 15, removing graphene in the exposed area by oxygen plasma etching to process graphene internal electrode structure and obtain a wafer;

[0083] Step 16, removing photoresist on the surface of the patterned graphene film by acetone, ethanol and deionized water to obtain a fifth process wafer;

[0084] Step 17, etching the oxide layer on the back surface of the wafer by plasma dry etching in an atmosphere of 80-120sccm CHF3 and 30-60sccm Ar to release the mass block, so that the mass block is suspended under the lower surface of the amorphous carbon film to obtain a sensor chip.

[0085] In the embodiment of the application, the amorphous carbon film preparation process in step 7 is described in detail:

[0086] The substrate pulse positive bias of the ECR plasma sputtering process is 0-200V, and the deposition time is 20-120min;

[0087] The substrate pulse negative bias of the direct current sputtering process is -600-0V, the pressure in the reaction chamber is 1-2mTorr, the deposition temperature is 20-30℃, and the deposition time is 20-120min, and the graphite target is pretreated for 5-20min;

[0088] The voltage of the high-power pulse power supply is 800-1000V, and the pulse duty cycle is 1%-5%;

[0089] The radio frequency bias of the PECVD is 500-800V, the pressure in the reaction chamber is 15-30mTorr, the deposition time is 20-120min, and the deposition temperature is 20-30℃;

[0090] The substrate pulse negative bias of the ion vapor deposition process is -5--1kV, the working pressure is 1-15mTorr, the deposition time is 100-300min, and the deposition temperature is 150-250℃.

[0091] In the embodiment of the application, the amorphous carbon film polymer assisted transfer process in step 8 is described in detail:

[0092] (1) spin coating the polymer on the amorphous carbon film with the target substrate;

[0093] (2) placing the amorphous carbon film with the spin-coated polymer in the etching liquid to remove the target substrate;

[0094] (3) The amorphous carbon is fished out from the etching solution with a clean PET substrate and transferred to clean water to rinse the etching solution;

[0095] (4) Finally, the amorphous carbon is transferred to the surface of a test chip, soaked in an acetone solution to remove the polymer, and soaked for 20 min; then clean acetone solution is taken again, and the process is repeated twice to ensure that the polymer is completely removed; finally, the amorphous carbon is rinsed with anhydrous ethanol to completely remove the residual acetone.

[0096] Further preferably, the material of the polymer in step (1) is not limited, including PDMS, PMMA and TRT, etc.

[0097] Further preferably, the material of the target substrate in step (1) is not limited, including a silicon substrate on which silk fibroin and dextran are spin-coated as water-soluble materials, metals such as chromium, copper and nickel, silicon oxide, silicon, aluminum oxide, glass, PDMS, PE, PI, etc.

[0098] Further preferably, in step (3), the spin-coated amorphous carbon with the polymer on the target substrate is placed in clean water for 30 min, then the deionized water is replaced, and the process is repeated three times to completely remove the etching solution; then it is placed in air for 30 min; finally, it is heated on a hot plate at 90℃ for 30 min to completely remove the moisture between the amorphous carbon and the substrate.

[0099] Further preferably, in step (4), after the spin-coated amorphous carbon with the polymer is transferred to the test chip substrate, it is left to stand in air for 10-60 min; and dried in an oven for 10-60 min, with the oven temperature being 60-200℃, to increase the bonding force between the amorphous carbon and the chip substrate and prevent the amorphous carbon from peeling off during the removal of the polymer.

[0100] In the embodiment of the present application, the direct transfer process of the amorphous carbon film in step 8 is described in detail:

[0101] (1) An amorphous carbon film is deposited on a target substrate;

[0102] (2) The amorphous carbon film is placed in an etching solution to remove the target substrate;

[0103] (3) The amorphous carbon is fished out from the etching solution with a clean PET substrate and transferred to clean water to rinse the etching solution;

[0104] (4) Finally, the amorphous carbon is transferred to the surface of a test chip, left to stand in air for 10-60 min; and dried in an oven for 10-60 min, with the oven temperature being 60-200℃, to increase the bonding force between the amorphous carbon and the chip substrate.

[0105] In the embodiment of the present application, the patterning process of the amorphous carbon film is described:

[0106] (1) spin the photoresist on the surface of the amorphous carbon film, the photoresist is selected as AZ4620 with a rotation speed of 2000 rpm for 40 s;

[0107] (2) the sample after spin coating is placed on an oven at 85-120 DEG C for 20 min to evaporate the solvent in the photoresist;

[0108] (3) the wafer is exposed to ultraviolet light using a mask, and the exposure time is 20-30 s;

[0109] (4) the photoresist after exposure is developed using a 0.5% NaOH solution, and the developing time is 1-2 min;

[0110] (5) the wafer is baked on an oven at 120-140 DEG C to remove the moisture on the surface of the wafer;

[0111] (6) the amorphous carbon film after photoetching is selectively etched using plasma to remove the part of the amorphous carbon film not protected by the photoresist; the plasma material is not limited, including but not limited to one or a combination of Ar plasma, O2 plasma and C4F8 plasma.

[0112] In the embodiment of the present application, the graphene film preparation process comprises:

[0113] (S1) preparing a substrate: selecting a catalytic metal for graphene growth, and cutting it into a square of 2x2 cm, and sending the copper foil into a quartz boat of a tube furnace and placing it at the heating center position;

[0114] (S2) discharging air: vacuumizing the tube furnace and introducing nitrogen gas during the process, and repeatedly introducing nitrogen gas three times to ensure that the oxygen and other gas molecules in the furnace are completely discharged;

[0115] (S3) heating and annealing stage: introducing hydrogen gas into the tube furnace at a flow rate of 100 sccm to stabilize the gas pressure at 0.15 Kpa; opening the heating unit to heat it, and making the temperature rise from room temperature to 1060 DEG C. After reaching 1060 DEG C, the gas pressure and temperature are kept unchanged, and the gas is continuously introduced for 30 minutes to anneal the catalytic metal to improve its surface morphology;

[0116] (S4) growth stage: maintaining the temperature in the furnace unchanged, and introducing the carbon source and the auxiliary gas hydrogen into the tube furnace after being fully mixed, and the carbon source is decomposed to release carbon atoms under high temperature conditions, and the carbon atoms are deposited on the catalytic metal to form a graphene film, and the process lasts for 20 minutes;

[0117] (S5) cooling stage: after the growth is completed, the heating system of the tube furnace is turned off, and the temperature in the furnace naturally decreases to room temperature, and then the catalytic metal is taken out to complete the preparation of graphene.

[0118] Further preferably, the material of the catalytic metal in step (S1) is not limited, including Cu, Ni, Ru and alloys thereof, etc.

[0119] Further preferably, the carbon source in step (S4) includes gaseous carbon sources such as methane, ethylene, acetylene, etc.; liquid carbon sources such as benzene, xylene, etc.; and solid carbon sources such as naphthalene, pentacene, etc.

[0120] In the embodiment of the present application, the graphene film transfer process is the same as the amorphous carbon transfer process; and the graphene film patterning process is the same as the amorphous carbon transfer process.

[0121] Please refer to Figure 12 The principle of the technical solution provided by the embodiment of the present application is explained as follows: the stress of the amorphous carbon sensitive film / strip is composed of the stress of the amorphous carbon on the fixed outer frame and the mass and the stress of the amorphous carbon suspended in the groove, and the stress concentration area is the amorphous carbon suspended in the groove; the stress caused by the input acceleration from the outside is converted into the change of the resistance value by using the piezoresistive effect of the amorphous carbon, and the proportional relationship between the change of the resistance value and the stress is

[0122]

[0123] In the formula, π is the piezoresistive coefficient of the amorphous carbon; σ is the total strain of the amorphous carbon sensitive film / strip; R is the initial resistance; and ΔR is the resistance change value.

[0124] In the embodiment of the present application, the graphene interdigital electrode is used, the initial resistance of the interdigital electrode is reduced by increasing the aspect ratio and density of the interdigital electrode, and the sensitivity and response speed of the sensor can be increased; at this time, In the formula, R 局部 is the resistance between two adjacent combs; and ΔR 局部 is the direct change of the resistance between two adjacent combs.

[0125] Since the amorphous carbon only suspended in the area of the groove has a larger strain, the amorphous carbon covering on the fixed frame and the mass has a smaller strain, therefore, the interdigital electrode can greatly increase the output of the sensor. Since the sensitive beam of the sensor is composed of amorphous carbon, the thickness of the amorphous carbon film is 1-100 nm, and the thickness of the sensitive beam of the sensor is nanoscale, which greatly increases the sensitivity of the sensor. When the sensor is subjected to acceleration perpendicular to the plane of the mass, the mass is displaced under the action of external force, which causes the amorphous carbon film suspended in the groove to have large deflection deformation. Under the large deflection theory, the amorphous carbon suspended in the groove is only subjected to tensile stress, and the resistance value is increased. In summary, the embodiment of the present application proposes a micro high-sensitivity self-supporting amorphous carbon film NEMS acceleration sensor chip based on graphene interdigital electrode. By changing the sensitive material, a nanometer-thick beam structure is proposed by using the characteristics of the sensitive material. At the same time, the graphene interdigital electrode is introduced, which increases the bonding force between the electrode and the amorphous carbon, and reduces the ohmic contact between the electrode and the amorphous carbon, thereby further improving the sensitivity of the sensor.

[0126] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it, although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: the specific embodiments of the present application can still be modified or replaced by the equivalent, without departing from the spirit and scope of the present application. Any modification or equivalent replacement, which should be covered in the protection scope of the claims of the present application.

Claims

1. A self-supporting amorphous carbon thin film NEMS accelerometer chip, characterized in that, include: The chip substrate, graphene interdigitated electrodes (1), amorphous carbon sensitive film (2), and metal electrodes (3) are used; among them, The chip substrate includes a silicon substrate (6), a silicon oxide layer (5), and a silicon nitride layer (4) arranged sequentially from bottom to top; the silicon substrate (6), the silicon oxide layer (5), and the silicon nitride layer (4) have the same shape and each includes a fixed outer frame and a mass block; wherein the mass block is surrounded by the fixed outer frame, and the fixed outer frame and the mass block are isolated by a trench; The silicon nitride layer (4) is deposited with the metal electrode (3) and the amorphous carbon sensitive film (2); wherein the metal electrode (3) is disposed on the fixed outer frame of the silicon nitride layer (4) and does not directly contact the amorphous carbon sensitive film (2); the amorphous carbon sensitive film (2) includes an amorphous carbon sensitive beam suspended on the trench, a first sensitive film region covering the mass block of the silicon nitride layer (4) and a second sensitive film region covering the fixed outer frame of the silicon nitride layer (4); The graphene interdigitated electrode (1) is transferred onto the metal electrode (3) and the amorphous carbon sensitive film (2); wherein the amorphous carbon sensitive film (2) is connected to the metal electrode (3) through the graphene interdigitated electrode (1).

2. The self-supporting amorphous carbon thin film NEMS accelerometer chip according to claim 1, characterized in that, The amorphous carbon sensitive film (2) is rectangular, with only one set of opposite sides covering part of the groove.

3. The self-supporting amorphous carbon thin film NEMS accelerometer chip according to claim 2, characterized in that, The metal electrode (3) includes a first metal electrode (3-1) and a second metal electrode (3-2) disposed on the fixed outer frame of the silicon nitride layer (4); the first metal electrode (3-1) includes a first metal pad and a first lead connected together, and the second metal electrode (3-2) includes a second metal pad and a second lead connected together; wherein, the first lead and the second lead are respectively disposed on both sides of a set of opposite sides of the amorphous carbon sensitive film (2) that are not covered by the trench, and the first lead and the second lead are parallel to the set of opposite sides of the amorphous carbon sensitive film (2) that are not covered by the trench; neither the first metal pad nor the second metal pad is in contact with the amorphous carbon sensitive film (2).

4. The self-supporting amorphous carbon thin film NEMS accelerometer chip according to claim 3, characterized in that, The graphene interdigitated electrode (1) includes a first graphene interdigitated electrode (1-1) and a second graphene interdigitated electrode (1-2); both the first graphene interdigitated electrode (1-1) and the second graphene interdigitated electrode (1-2) include a comb handle and comb teeth. The comb teeth of the first graphene interdigitated electrode (1-1) and the second graphene interdigitated electrode (1-2) form an interdigitated structure. The comb handle of the first graphene interdigitated electrode (1-1) covers all or part of the first lead wire, and the comb handle of the second graphene interdigitated electrode (1-2) covers all or part of the second lead wire.

5. The self-supporting amorphous carbon thin film NEMS accelerometer chip according to claim 1, characterized in that, The mass block is rectangular, and the groove is a rectangular frame; wherein the size of the mass block is 15μm to 3000μm, and the width of the groove is 1μm to 200μm; Alternatively, the mass block is circular, and the groove is annular; wherein the diameter of the mass block is 15μm to 30000μm, and the width of the groove is 1μm to 200μm; The inner edge of the groove corresponds to the outer edge of the mass block, and the outer edge of the groove corresponds to the inner edge of the fixed outer frame.

6. The self-supporting amorphous carbon thin film NEMS accelerometer chip according to claim 1, characterized in that, The thickness of the amorphous carbon sensitive beam is 1 nm to 500 nm.

7. The self-supporting amorphous carbon thin film NEMS accelerometer chip according to claim 1, characterized in that, The self-supporting amorphous carbon thin film NEMS accelerometer chip is rectangular with a side length of 50μm to 4000μm; the thickness of the chip substrate is 100μm to 600μm; the thickness of the silicon nitride layer (4) is 100nm to 300nm; and the thickness of the silicon oxide layer (5) is 100nm to 300nm.

8. The self-supporting amorphous carbon thin film NEMS accelerometer chip according to claim 1, characterized in that, The graphene sensitive film includes graphene films with one atomic layer, two atomic layers, three atomic layers, four atomic layers, five atomic layers, six atomic layers, seven atomic layers, eight atomic layers, nine atomic layers, or ten atomic layers.

9. A method for fabricating a self-supporting amorphous carbon thin film NEMS accelerometer chip as described in claim 1, characterized in that, Includes the following steps: Step 1: Deposit silicon dioxide and silicon nitride thin film layers on the upper surface of a silicon wafer and deposit a silicon oxide layer on the lower surface using low-pressure chemical vapor deposition and plasma-enhanced chemical vapor deposition to obtain a chip substrate; Step 2: Spin-coat photoresist onto the upper surface of the chip substrate and perform photolithography using a metal electrode mask; Magnetron sputtering is performed using a metal target to sputter a thin metal film covering the entire surface of the wafer; the metal electrodes are then stripped with acetone to obtain metal electrodes covering the fixed outer frame, thus preparing the first-process wafer. Step 3: Spin-coat photoresist onto the upper surface of the wafer in the first process, and perform photolithography using a front-side mass block etching mask; in an atmosphere of 50-100 sccm SF6 and 30-60 sccm Ar, etch the silicon nitride layer on the wafer surface with spin-coated photoresist using plasma dry etching; in an atmosphere of 80-120 sccm CHF3 and 30-60 sccm Ar, etch the silicon oxide layer on the wafer surface not covered by photoresist using plasma dry etching; etch away the silicon layer not covered by photoresist using deep silicon dry etching, and stop etching when the transparent silicon oxide layer is reached; The photoresist on the wafer surface after dry etching is removed with acetone to prepare the second-process wafer. Step 4: Deposit 1–100 nm amorphous carbon thin films on the target substrate surface using PVD and CVD processes to obtain high sp2. 3 Amorphous carbon thin films with specific content and piezoresistive coefficients are prepared. The amorphous carbon thin films are transferred to the second process wafer via a polymer-assisted transfer process or a direct wet transfer process after sacrificing the target substrate. The polymer auxiliary materials on the surface of the amorphous carbon thin films are removed by acetone and ethanol, and the wafers are immersed in deionized water and dried in nitrogen to complete the cleaning process and prepare the third process wafer. Step 5: Spin-coat photoresist onto the wafer surface in the third process, and perform photolithography using an amorphous carbon patterned mask; Amorphous carbon thin films are patterned using plasma to remove amorphous carbon thin films not protected by photoresist, thus preparing a fourth-process wafer. Step 6: Graphene films are prepared using mechanical exfoliation and chemical vapor deposition. The prepared graphene films are then transferred to the upper surface of the wafer in the fourth process using a polymer-assisted transfer method, covering the metal electrodes and the patterned amorphous carbon sensitive film layer area. The polymer auxiliary material on the surface of the graphene film is removed using acetone and ethanol. The wafer is then immersed in deionized water and dried in nitrogen to complete the cleaning process. Photoresist is spin-coated onto the graphene surface, and photolithography is performed using a graphene internal toothed electrode mask. The graphene in the exposed areas is removed by oxygen plasma etching to fabricate graphene interdigitated electrodes. The photoresist on the surface of the patterned graphene film is removed using acetone, ethanol, and deionized water to prepare the wafer in the fifth process. Step 7: In an atmosphere of 80–120 sccm CHF3 and 30–60 sccm Ar, the oxide layer on the back side of the wafer is etched by plasma dry etching to release the mass block, which is then suspended on the lower surface of the amorphous carbon thin film, thus preparing a self-supporting amorphous carbon thin film NEMS accelerometer chip.

10. The preparation method according to claim 9, characterized in that, In step 4, the third process wafer is directly prepared by generating an amorphous carbon thin film suspended in the trench on the second process wafer through focused ion beam technology and CVD technology.

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