Preparation Method of Gallium Nitride-based MEMS Pressure Sensor with Porous Graphene Insertion Layer Structure

Abstract

The present invention discloses a preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure, which relates to the field of microelectronics technology and mainly solves the problems of device peeling and improving the growth quality of the GaN epitaxial layer at the current stage. From bottom to top, it includes a stainless steel substrate layer, an Al2O3 layer, an AlN layer, a porous graphene layer, a GaN layer, a SiO2 protection layer, and an ohmic electrode layer; among them, the AlN layer and the Al2O3 layer form an AlN / Al2O3 composite layer, and the ohmic electrodes are located on both sides above the GaN layer. By adding a porous graphene interlayer, the MEMS pressure sensor can be peeled off integrally from the substrate; by adding a magnetron sputtered Al2O3 layer and an AlN layer, the growth quality of the GaN epitaxial layer is improved, and the resistivity of the substrate is increased.

Description

Technical Field

[0001] The present invention belongs to the field of microelectronic technology, and particularly relates to a preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure. Background Art

[0002] With the research on MEMS pressure sensors becoming a hot topic, how to transfer a large number of devices from the substrate has become a difficult problem. At present, methods include laser lift-off, chemical lift-off, and mechanical polishing, but these methods all have their own problems; GaN materials have excellent chemical and physical stability, high electron concentration, high electron mobility, strong anti-irradiation ability, small sensing response time, reaching milliseconds, and environmental friendliness, making them ideal resistor layer materials. However, due to the large lattice mismatch between the GaN epitaxial material and the substrate material, misfit dislocations are easily generated during the growth process, forming a high density of lattice defects, which will seriously affect the sensitivity and stability of the sensitive thin film resistor. Therefore, realizing the peeling of the device and growing GaN epitaxial materials with a low dislocation density are the key issues in the research of GaN-based MEMS pressure sensors.

[0003] Due to the effect of Π-Π electrons, the specific surface area of two-dimensional graphene decreases, but the specific surface area of porous graphene is less affected by Π-Π electrons and is very high. Moreover, the lattice mismatch between porous graphene and GaN is small, and introducing a porous graphene interlayer can effectively reduce the defects of GaN materials caused by lattice defects. In addition, due to its relatively high mechanical strength and weak van der Waals forces between layers, the introduction of a porous graphene interlayer can achieve the peeling of the MEMS pressure sensor from the substrate.

[0004] The patent "Monolithic Integrated Structure and Method of MEMS Devices for Realizing Pressure Sensing" (application number: CN202110267764.7, publication number: CN113044806A) jointly applied by Dalian University of Technology and Qiqihar University discloses a preparation method of a MEMS device for realizing pressure sensing. The specific steps of this method are as follows: (1) etching a sealed cavity on a silicon substrate and sealing the silicon substrate by a high-temperature and high-pressure bonding process; (2) oxidizing SiO on the silicon substrate 2Insulating layer, depositing SiN insulating layer; (3) Vacuum evaporating the electrode layer and transferring and etching to form a graphene pressure sensing layer covering the electrode; The advantage of this patent is that a single-layer graphene is used as the pressure sensing layer, which is sensitive, has high adhesion, fast response, no hysteresis, and the device is integrally formed on a single chip. However, the deficiencies still existing in this method are as follows: 1. The single-layer graphene prepared in the engineering is not ideal, and inevitably structural defects such as vacancies and grain boundaries will be generated. If exposed to air for a long time, the sensitivity will be affected and the underlying material will be corroded. 2. This method requires etching the sealing cavity and high-temperature and high-pressure bonding processes, with a complex structure and increased cost. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure to solve the above-mentioned defects in the prior art.

[0006] A preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure includes the following steps:

[0007] (1) Polishing and cleaning the stainless steel substrate;

[0008] (2) Magnetron sputtering an Al 2 O 3 film on the stainless steel substrate to obtain a substrate sputtered with Al 2 O 3 ;

[0009] (3) Continuing to magnetron sputter an AlN film on the Al 2 O 3 to obtain a substrate sputtered with an AlN / Al 2 O 3 composite layer;

[0010] (4) Growing porous graphene on a three-dimensional porous copper-nickel alloy substrate and transferring the porous graphene to the AlN to obtain a substrate covered with porous graphene;

[0011] (5) Placing the substrate covered with porous graphene in a metal-organic chemical vapor deposition (MOCVD) reaction chamber, introducing a mixed gas of hydrogen and ammonia into the reaction chamber, and heat-treating the substrate covered with porous graphene to obtain a heat-treated substrate;

[0012] (6) Controlling the reaction temperature, introducing a gallium source and a nitrogen source, depositing a GaN film at a low temperature, and then raising the temperature to deposit a GaN film at a high temperature, and growing for a period of time to obtain a substrate covered with a GaN resistance layer film.

[0013] (7) Selectively dry-etch the GaN layer and the porous graphene layer according to the designed pattern until the AlN layer is exposed, obtaining a substrate covered with the patterned porous graphene layer and the GaN layer;

[0014] (8) Grow a SiO 2 protective layer on the exposed parts of the GaN thin film and the AlN layer by chemical vapor deposition;

[0015] (9) Selectively dry-etch the SiO 2 protective layer until the GaN layer is exposed;

[0016] (10) Perform metal evaporation on the exposed part of the GaN layer to form ohmic contact electrodes, and perform high-temperature annealing alloying on the metal layer to complete the device preparation.

[0017] Preferably, the thickness of the stainless steel substrate in step (1) is 100 μm.

[0018] Preferably, in step (2), the argon flow rate is 800 - 1000 sccm, the temperature is 300 - 600 °C, the annealing time is about 40 minutes, and the deposited Al2O3 thickness is 100 - 150 nm.

[0019] Preferably, in step (3), the pressure of the radio frequency sputtering system is 10 -7 Torr, and the thickness of the magnetron sputtered aluminum nitride is 25 - 50 nm.

[0020] Preferably, in step (4), the electrochemical deposition voltage is 0.6 V, the deposition time is 800 s, the rapid annealing furnace temperature is raised to 1100 °C, the electrochemical corrosion voltage is 0.7 V, and the selective corrosion time is 1000 s.

[0021] Preferably, in step (5), the time for introducing the mixed gas of hydrogen and ammonia is 5 - 7 min, and the reaction chamber and the temperature are heated to 600 - 700 °C.

[0022] Preferably, in step (6), the GaN thickness is 80 nm, the gallium source is trimethylgallium, the ammonia source is ammonia, the gallium source flow rate is 10 - 200 μmol / min; the ammonia flow rate is 1000 - 10000 sccm.

[0023] Preferably, in step (8), the SiO 2 thickness is more than 300 nm.

[0024] Preferably, in step (10), the electrode layer is Ni / Au, where the growth thickness of metal Ni is 30 nm and the growth thickness of metal Au is 300 nm.

[0025] The present invention also discloses a GaN-based MEMS pressure sensor with a porous graphene intercalation layer structure prepared by the above method, which includes a stainless steel substrate layer, an AlN / Al 2 O 3 composite layer, a porous graphene layer, a GaN layer, a SiO 2 protective layer, and ohmic electrodes. Among them, a porous graphene interlayer is provided between the GaN layer and the AlN / Al 2 O 3 composite layer.

[0026] The advantages of the present invention are as follows:

[0027] 1. Since the porous graphene is less affected by Π-Π electrons, it has a higher specific surface area than graphene and will not agglomerate due to the influence of Π-Π electrons, resulting in good material uniformity, and thus can improve the resistance sensitivity of the GaN material.

[0028] 2. The porous graphene has good mechanical properties and is an ideal carrier. Moreover, since the atoms between the porous graphene layers are connected by covalent bonds, and the porous graphene layers and between the porous graphene layer and other material layers are connected by weak van der Waals forces, it is easy to integrally peel off the MEMS pressure sensor from the substrate.

[0029] 3. Since the present invention uses a porous graphene intercalation layer, it ensures the lattice mismatch degree between different materials, improves the growth quality of the GaN epitaxial layer, and plays a buffering role in the growth of the GaN epitaxial layer below.

[0030] 4. Since the present invention uses 17-4ph steel, which has good toughness and strength, the substrate can be made into a thin layer, which avoids operations such as etching cavities in the middle of the substrate and bonding the substrate, ensuring the supportability and bendability of the substrate while saving costs; this stainless steel material is resistant to heat and humidity, acid, and has good corrosion resistance, and can be applied to complex environments.

[0031] 5. In the present invention, a Wheatstone response circuit is integrally etched on a chip for the porous graphene layer and the GaN layer, and pressure sensing can be realized without relying on an external circuit, avoiding circuit offset caused by relying on an external resistor. Brief Description of the Drawings

[0032] Figure 1 is a schematic cross-sectional structure diagram of the GaN-based MEMS pressure sensor with a porous graphene intercalation layer structure of the present invention.

[0033] Figure 2 is a layout schematic diagram of the thin film resistance layer.

[0034] Figure 3 is a schematic diagram of a Wheatstone bridge circuit.

[0035] Figure 4 For the preparation of the present invention Figure 1 Process flow chart of the device. Specific embodiments

[0036] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0037] Referring to Figure 1 , the GaN-based MEMS pressure sensor with a porous graphene insertion layer structure of the present invention comprises a total of seven layers, namely a stainless steel substrate layer (17-4ph steel) 1, a magnetron sputtered Al 2 O 3 layer 2, a magnetron sputtered AlN layer 3, a porous graphene layer 4, a GaN layer 5, a SiO 2 protective layer 6, and ohmic electrodes 7 are sequentially arranged from bottom to top, and the ohmic electrodes 7 are located on both sides of the GaN layer 5.

[0038] Referring to Figure 2 , the following two specific embodiments are given for the preparation method of the GaN-based MEMS pressure sensor with a porous graphene insertion layer structure of the present invention:

[0039] Embodiment 1

[0040] Prepare a GaN-based MEMS pressure sensor with an Al 2 O 3 thin film thickness of 100 nm and an AlN thin film thickness of 25 nm.

[0041] Step (1). Stainless steel substrate treatment

[0042] Using ammonium persulfate solution at 68 g / L as the etching solution, prepare a polishing solution according to the ratio of 50 ml:10 ml:50 ml:1 g:100 ml of orthophosphoric acid to isopropanol to absolute ethanol to high-purity urea to deionized water. Ultrasonically clean the selected 17-4ph stainless steel substrate. First, ultrasonically clean with absolute ethanol for 5 minutes, then ultrasonically clean with deionized water for 5 minutes, and repeat the cleaning 5 times. After all the cleaning is completed, use a nitrogen gun to blow dry the water stains remaining on the surface, and set it aside after drying.

[0043] Perform polishing treatment on the stainless steel substrate. First, perform corrosion pretreatment on the substrate, immerse it in the etching solution, and slowly stir for 3 minutes. After the surface contamination is removed sufficiently, perform the cleaning operation again and dry it for standby.

[0044] Magnetically stir in the polishing solution at 300 revolutions per minute for 30 minutes and then let it stand. Using an electrochemical polishing device, place the stainless-steel substrate as the anode of the polishing device and a 99.99% platinum wire as the cathode of the polishing device in the polishing solution, and polish for 5 - 8 minutes.

[0045] Step (2). Magnetron sputtering deposition of Al 2 O 3 thin film:

[0046] Install the substrate, adjust the distance between the substrate and the target, close the vacuum chamber, evacuate the air, introduce high-purity argon gas into the vacuum chamber as the working gas, and adjust the vacuum pump to make the chamber reach the preset value.

[0047] Pre-anneal and adjust the crystal orientation of the target. Pre-sputter, close the baffle on the surface of the target, and pre-sputter the surface of the target to remove the attached oxides and contaminants for 10 minutes.

[0048] Adjust the crystal orientation of the sputtered material, and anneal at 300 °C for 20 minutes in an argon atmosphere of 800 sccm.

[0049] Al 2 O 3 After reaching a deposition thickness of 100 nm, wait for the temperature in the reaction chamber to reach room temperature and then inflate the inside, and take out the substrate sputtered with Al 2 O 3 film.

[0050] Step (3). Magnetron sputtering deposition of AlN thin film:

[0051] After the Al 2 O 3 layer thin film sputtering is completed, adjust the pressure of the RF sputtering system to 10 -7 Torr, and continue to deposit a 25-nm-thick AlN thin film in the RF sputtering system using an Al target with a purity of 99.99% and a nitrogen target at an RF power of 50 W following similar steps.

[0052] Step (4). Growth and transfer of porous graphene:

[0053] Substrate mold construction:

[0054] Deposit a layer of metallic copper on the nickel foam by an electrochemical modification process. The electrochemical deposition voltage is 0.6 V and the deposition time is 400 s. Use a rapid thermal annealing furnace (RTP) to alloy the nickel foam and copper at about 1100 °C to make them alloyed. The annealed copper-nickel alloy is selectively corroded at an electrochemical corrosion voltage of 0.7 V for 1000 s to form multi-level pores on the alloy surface and form a three-dimensional porous copper-nickel alloy substrate.

[0055] Growth and transfer of porous graphene:

[0056] First, grow porous graphene on the constructed copper-nickel alloy substrate using chemical vapor deposition. Then, remove the copper-nickel alloy substrate by acid-base etching of the copper-nickel alloy substrate and the porous graphene, and then transfer the porous graphene to the sputtered substrate to obtain a sputtered AlN / Al composite layer substrate covered with porous graphene. 2 O 3 composite layer substrate.

[0057] Step (5). Substrate heat treatment:

[0058] Place the sputtered AlN / Al 2 O 3 composite layer substrate covered with porous graphene into a metal-organic chemical vapor deposition (MOCVD) reaction chamber, introduce a mixed gas of hydrogen and ammonia into the reaction chamber for 5 minutes, and heat the reaction chamber and the temperature to 600 °C to perform heat treatment on the AlN / Al 2 O 3 composite layer substrate covered with porous graphene to obtain a heat-treated substrate;

[0059] Step (6). Grow GaN thin film:

[0060] Control the temperature at 550 °C, introduce trimethylgallium and ammonia source, and deposit a low-temperature GaN thin film. Then raise the temperature to 1050 °C and perform heating for 70 minutes to form a high-temperature GaN thin film. After the GaN thin film grows to 80 nm thick, the growth process is completed.

[0061] Step (7). Etch pattern

[0062] Use selective dry etching on the porous graphene and the GaN thin film until the AlN layer is exposed. The shape of the etched pattern is as Figure 2 shown. Etching into winding, narrow and thin lines can increase the initial resistance value of each resistor. Etching the lines with the axial direction the same as the bending direction is to maximize the deformation during bending to improve the accuracy of the MEMS pressure sensor.

[0063] Step (8). Grow a 200-nm-thick SiO 2 protective layer on the GaN layer by chemical vapor deposition.

[0064] Step (9). Dry etching to form a rough surface:

[0065] Use selective dry etching on the SiO 2 protective layer to etch the SiO 2 protective layer until a part of the GaN layer is exposed.

[0066] Step (10). Evaporate electrodes:

[0067] Metal evaporation is performed on the exposed part of the GaN layer to form an ohmic electrode layer. The ohmic electrode layer uses a 40-nm-thick metal Ni and a 600-nm-thick metal Au, and the metal layer is annealed at high temperature for alloying. The device fabrication of the GaN-based MEMS pressure sensor with a porous graphene insertion layer structure is completed.

[0068] Example 2

[0069] Prepare Al 2 O 3 A GaN-based MEMS pressure sensor with a 150-nm-thick AlO film and a 50-nm-thick AlN film.

[0070] Step (1). Stainless steel substrate treatment

[0071] The specific implementation of this step is the same as step (1) in Example 1.

[0072] Step (2). Magnetron sputtering deposition of Al 2 O 3 film:

[0073] Install the substrate, adjust the distance between the substrate and the target, close the vacuum chamber, evacuate, introduce high-purity argon gas into the vacuum chamber as the working gas, and adjust the vacuum pump to make the chamber reach the preset value.

[0074] Pre-anneal and adjust the target crystal orientation. Pre-sputter, close the baffle on the target surface, pre-sputter the target surface to remove the attached oxides and contaminants, and the time is 15 minutes.

[0075] By adjusting process parameters such as working pressure and power, sputter-deposit Al 2 O 3 insulating layer film.

[0076] Adjust the sputtering material crystal orientation, and anneal at 600 °C for 60 minutes in an argon atmosphere of 1000 sccm.

[0077] Al 2 O 3 After the deposition thickness of Al 2 O 3 reaches 150 nm, wait for the temperature in the reaction chamber to reach room temperature, inflate the inside, and take out the substrate sputtered with Al

[0078] Step (3). Magnetron sputtering deposition of AlN film:

[0079] After the sputtering of the Al 2 O 3 layer film is completed, adjust the pressure of the RF sputtering system to 10 -7Torr, continue to deposit a 50-nm-thick AlN film in a radio frequency sputtering system using Al targets and nitrogen targets with a purity of 99.99% at a radio frequency power of 50 W according to a similar procedure.

[0080] Step (4). Grow and transfer porous graphene:

[0081] Substrate mode construction:

[0082] Deposit a layer of metallic copper on nickel foam by an electrochemical modification process. The electrochemical deposition voltage is 0.6 V and the deposition time is 800 s. Use a rapid thermal annealing furnace (RTP) to alloy the nickel foam and copper at about 1100 °C. The annealed copper-nickel alloy is selectively corroded at an electrochemical corrosion voltage of 0.7 V for 1000 s to form a multi-level pore structure on the alloy surface, forming a three-dimensional porous copper-nickel alloy substrate.

[0083] Step (5). Substrate heat treatment:

[0084] Place the sputtered AlN / Al 2 O 3 composite layer substrate covered with porous graphene into a metal organic chemical vapor deposition (MOCVD) reaction chamber. Introduce a mixed gas of hydrogen and ammonia into the reaction chamber for 7 min, and control the reaction chamber temperature at 700 °C to perform heat treatment on the AlN / Al 2 O 3 composite layer substrate covered with porous graphene to obtain a heat-treated substrate;

[0085] Step (6). Grow GaN film:

[0086] Control the temperature at 550 °C, introduce trimethylgallium and ammonia sources to deposit a low-temperature GaN film. Then raise the temperature to 1050 °C and heat for 70 minutes to form a high-temperature GaN film. The growth process is completed after the GaN film grows to a thickness of 80 nm.

[0087] Step (7). Etch the pattern

[0088] The specific implementation of this step is the same as step (7) in Example 1.

[0089] Step (8). Grow a 250-nm-thick SiO 2 protective layer on the GaN layer by chemical vapor deposition.

[0090] Step (9). Dry etching to form a rough surface:

[0091] The specific implementation of this step is the same as step (9) in Example 1.

[0092] Step (10). Evaporate electrodes:

[0093] The specific implementation of this step is the same as step (10) in Embodiment 1.

[0094] As is known by common technical knowledge, the present invention can be implemented by other embodiments that do not depart from its spiritual essence or essential features. Therefore, the above-disclosed embodiments are illustrative in all aspects and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. A preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure, characterized in that, it includes the following steps: (1) Polish and clean the stainless steel substrate; (2) Magnetron sputter Al on a stainless steel substrate 2 O 3 thin film to obtain a substrate sputtered with Al 2 O 3 ; (3) Continue magnetron sputtering of AlN film on Al 2 O 3 to obtain a substrate sputtered with an AlN / Al 2 O 3 composite layer; (4) Grow porous graphene on the three-dimensional porous copper-nickel alloy substrate and transfer the porous graphene onto AlN to obtain a substrate covered with porous graphene; (5) Place the substrate covered with porous graphene in a metal-organic chemical vapor deposition reaction chamber, introduce a mixed gas of hydrogen and ammonia into the reaction chamber, and perform heat treatment on the substrate covered with porous graphene to obtain a heat-treated substrate; (6) Control the reaction temperature, introduce a gallium source and an ammonia source, deposit a GaN thin film at a low temperature, then increase the temperature and deposit a GaN thin film at a high temperature, and grow for a period of time to obtain a substrate covered with a GaN resistor layer thin film; (7) Perform selective dry etching on the GaN layer and the porous graphene layer to etch into a pattern with meandering, narrow and thin lines, and the axial direction of the lines is the same as the bending direction until the AlN layer is exposed, obtaining a substrate covered with a patterned porous graphene layer and a GaN layer; (8) A SiO protective layer is grown by chemical vapor deposition on the exposed portions of the GaN thin film and the AlN layer. 2 protective layer; (9) Selectively dry-etch the SiO 2 protective layer until the GaN layer is exposed; (10) Perform metal evaporation on the exposed part of the GaN layer to form an ohmic contact electrode, and perform high-temperature annealing alloying on the metal layer to complete the device preparation.

2. The preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure according to claim 1, characterized in that, the thickness of the stainless steel substrate described in step (1) is 100 um.

3. The preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure according to claim 1, characterized in that, The pressure of the magnetron sputtering system in step (3) is 10 -7 Torr, and the thickness of the magnetron sputtered aluminum nitride is 25 - 50 nm.

4. The preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure according to claim 1, characterized in that, the time for introducing the mixed gas of hydrogen and ammonia in step (5) is 5-7 min, and the reaction chamber and the temperature are heated to 600-700 °C.

5. The preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure according to claim 1, characterized in that, the thickness of the GaN in step (6) is 80 nm, the gallium source is trimethylgallium, the ammonia source is ammonia, the flow rate of the gallium source is 10-200 μmol / min; the flow rate of ammonia is 1000-10000 sccm.

6. The preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure according to claim 1, characterized in that, The SiO described in step (8) 2 has a thickness of 300 nm or more.

7. The preparation method of a gallium nitride-based MEMS pressure sensor with a porous graphene insertion layer structure according to claim 1, characterized in that, the electrode in step (10) is Ni / Au, wherein the growth thickness of the metal Ni is 30 nm and the growth thickness of the metal Au is 300 nm.

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