A pressure sensor and a method of manufacturing the same

Abstract

The application discloses a pressure sensor and a preparation method thereof, and belongs to the field of semiconductor technology and manufacturing. The pressure sensor comprises, from bottom to top, a silicon substrate, a buffer layer, a GaN layer and an AlGaN layer, and the AlGaN layer is provided with a gate, a source and a drain; the silicon substrate comprises a base, and a first support body, a second support body and a third support body are sequentially arranged on the base from left to right; the upper surfaces of the second support body and the third support body are attached to the lower surface of the buffer layer, and a cavity is formed between the second support body and the third support body; the height of the first support body is smaller than that of the second support body, and a gap is formed between the first support body and the buffer layer. According to the application, when pressure is applied, the resistance of the current sensing channel in the drain increases, so that the current decreases, and pressure sensing is realized. Simulation results prove that the pressure sensor has high sensitivity and a larger range.

Description

TECHNICAL FIELD

[0001] The present application relates to a pressure sensor and its preparation method, belonging to the field of semiconductor technology and manufacturing. BACKGROUND

[0002] The basic principle of the gallium nitride pressure sensor is to use the good piezoresistive property of gallium nitride material. When the material is subjected to external force, the resistance value will change. This change can be measured by an external circuit and converted into a pressure value.

[0003] Specifically, when the gallium nitride material is subjected to pressure, lattice distortion occurs, causing the difficulty of electron movement within the material to change, resulting in a change in resistance. This change in resistance is proportional to the pressure received and can be measured by an external circuit.

[0004] The gallium nitride pressure sensor can achieve high precision, high speed and long-term stable pressure measurement, which can help enterprises to timely discover pressure abnormalities in equipment or products, avoid product quality problems and safety accidents, and reduce detection cost and equipment maintenance cost, thereby improving the economic benefit of enterprises.

[0005] Currently, the sensitive element of the gallium nitride pressure sensor usually uses a gallium nitride thin film, which is usually several microns to tens of microns thick, and its shape can be a diaphragm, a beam or a column. When subjected to external force, the gallium nitride thin film will undergo a small deformation, thereby causing a change in electrical properties and outputting an electrical signal. However, the gallium nitride pressure sensor prepared by using the gallium nitride thin film as the sensitive element can measure a pressure range from several thousand pascals to several hundred megapascals, but the sensitivity is low and the actual measurement range cannot reach the range required by actual engineering. SUMMARY

[0006] In order to solve the problem of low sensitivity and small measurement range of the existing gallium nitride pressure sensor, the present application provides a pressure sensor and its preparation method, and the technical solution is as follows:

[0007] The first object of the present application is to provide a pressure sensor, which comprises, from bottom to top, a silicon substrate, a buffer layer, a GaN layer and an AlGaN layer, and the AlGaN layer has a gate, a source and a drain;

[0008] The silicon substrate comprises a base, and a first support, a second support and a third support are arranged on the base from left to right; the upper surfaces of the second support and the third support are attached to the lower surface of the buffer layer, and a cavity is formed between the second support and the third support; the height of the first support is less than that of the second support, and there is a gap between the first support and the buffer layer.

[0009] Optionally, the thickness of the silicon substrate is 350-1000um.

[0010] Optionally, the gap between the first support body and the buffer layer is 10-130um.

[0011] Optionally, the thickness of the buffer layer is 2-15um.

[0012] Optionally, the thickness of the GaN layer is 1-5um.

[0013] Optionally, the thickness of the AlGaN layer is 10-20nm.

[0014] The second object of the present application is to provide a pressure sensing method, which is realized based on the pressure sensor of any one of the above-mentioned embodiments, and includes: when pressure is applied at the source electrode or the drain electrode, the pressure sensor appears a bending deformation on the left side, which causes the resistance of the current sensing channel between the source electrode and the drain electrode to increase, thereby causing the current to decrease, and further realizing pressure sensing, wherein the current sensing channel between the source electrode and the drain electrode is a two-dimensional electron gas (2D-EDGE) existing at the interface between the GaN layer and the AlGaN layer.

[0015] The third object of the present application is to provide a preparation method of a pressure sensor, which is used for preparing the pressure sensor of any one of the above-mentioned embodiments, and includes:

[0016] Step 1: cleaning the silicon wafer;

[0017] Step 2: growing a buffer layer on the cleaned silicon substrate;

[0018] Step 3: preparing a GaN layer, growing a GaN thin film on the buffer layer by a metal organic chemical vapor deposition method;

[0019] Step 4: preparing an AlGaN layer, growing an AlGaN thin film on the GaN layer by a metal organic chemical vapor deposition method;

[0020] Step 5: preparing a source electrode, a drain electrode and a gate electrode on the AlGaN layer;

[0021] Step 6: etching and bonding the silicon substrate;

[0022] On the back of the pressure sensor, after coating photoresist on the corresponding position of the second support body, etching is performed to a reserved depth of 10-20um, and then all the photoresist is washed away; photoresist is coated on the corresponding position of the third support body, and then etching is performed, and the photoresist is washed away after etching is completed;

[0023] The silicon-silicon direct bonding technology is used to bond the matched silicon-based abutment prepared in advance with the back surface of the pressure sensor;

[0024] Optionally, the step 5 comprises: forming the source and the drain on the AlGaN layer by using the ohmic contact principle, and then forming the gate by using the Schottky contact principle.

[0025] Optionally, the source and the drain adopt Ti / Al / Ni / Au 4-layer metal, and the gate adopts Ni / Au 2-layer metal.

[0026] The present application has the following advantages:

[0027] The pressure sensor of the present application is designed as a "rocker structure", when pressure is applied at the source and the drain, the bending deformation of the two sides of the sensor will cause the resistance of the current sensing channel inside the drain to increase significantly, thereby causing the current to decrease, and thus realizing pressure sensing.

[0028] In addition, due to the support of the bottom support body, the destruction of the gallium nitride pressure sensor caused by the sudden increase of the stress and the change of the stress is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description, and obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0030] Figure 1 It is a structure diagram of the pressure sensor of the present application.

[0031] Figure 2 It is a preparation process flow chart of the pressure sensor of the present application.

[0032] Figure 3 It is a stress generation diagram of the sensor under the condition of 500kpa stress pressure in the embodiment of the present application.

[0033] Figure 4 It is a stress generation diagram of the sensor under the condition of 250kpa stress pressure in the embodiment of the present application.

[0034] Figure 5is a stress generation diagram of a sensor under a stress pressure of 50 kpa in an embodiment of the present application.

[0035] Figure 6 is a sensitivity characteristic curve diagram of a pressure sensor.

[0036] Figure 7 is a sensitivity characteristic curve diagram of a gallium nitride pressure sensor of the present application.

[0037] Figure 8 is a relationship curve diagram of a maximum range and a gap size of a gallium nitride pressure sensor of the present application. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application more clear, the following will make further detailed description to the embodiments of the present application in combination with the drawings.

[0039] Embodiment one:

[0040] The embodiment provides a pressure sensor, referring to Figure 1 The pressure sensor comprises, from bottom to top, a silicon substrate, a buffer layer, a GaN layer and an AlGaN layer, and the AlGaN layer is provided with a gate, a source and a drain.

[0041] The silicon substrate comprises a base, and a first support body, a second support body and a third support body are sequentially arranged on the base from left to right; the upper surfaces of the second support body and the third support body are attached to the lower surface of the buffer layer, and a cavity is formed between the second support body and the third support body; the height of the first support body is less than that of the second support body, and there is a gap between the first support body and the buffer layer.

[0042] Embodiment two:

[0043] The embodiment provides a pressure sensor, referring to Figure 1 The pressure sensor comprises, from bottom to top, a silicon substrate, a buffer layer, a GaN layer and an AlGaN layer, and the AlGaN layer is provided with a gate, a source and a drain.

[0044] The silicon substrate comprises a base, and a first support body, a second support body and a third support body are sequentially arranged on the base from left to right; the upper surfaces of the second support body and the third support body are attached to the lower surface of the buffer layer, and a cavity is formed between the second support body and the third support body; the height of the first support body is less than that of the second support body, and there is a gap between the first support body and the buffer layer.

[0045] The thickness of the silicon substrate is 350-1000 um; the gap between the first support body and the buffer layer is 10-130 um; the thickness of the buffer layer is 2-15 um; the thickness of the GaN layer is 1-5 um; and the thickness of the AlGaN layer is 10-20 nm.

[0046] The thickness of the silicon substrate in the simulation experiment of the embodiment is 500 um, the gap between the first support body and the buffer layer is 130 um, the thickness of the buffer layer is 7 um, the thickness of the GaN layer is 3 um, and the thickness of the AlGaN layer is 10 nm. The width of the entire pressure sensor is 100 um, and the length is 2000 um.

[0047] When 0.01 N (500 kPa) is applied to the left side of the pressure sensor (the area is only 0.02 mm 2 ), a stress of 2830 Mpa is generated in the middle. The embodiment of the application realizes pressure sensing by the resistance change caused by the change of the two-dimensional electron gas at the gallium nitride / aluminum gallium nitride interface under pressure. The specific sensing process is analyzed as follows:

[0048] The change of the lattice constant is obtained by the formula Δa / a0=(1 / E)σ, wherein Δa is the change of the lattice constant, a is the lattice constant without stress, σ is the stress, and E is the elastic modulus. The elastic modulus of gallium nitride is 280 Gpa. According to the formula, Δa / a0=12.1*10 -3 / 280

[0049] According to the formula, the polarization charge density is calculated as follows:

[0050]

[0051] a(x)=(−0.077x+3.189)10 -10 m

[0052] c 13 (x)=(5x+103)*10^9Pa

[0053] c 33 (x)=(−32x+405)10^9Pa

[0054] e 31 (x)=(−0.11x−0.49)C / m 2

[0055] e 33 (x)=(0.73x+0.73)C / m 2

[0056] wherein Δδ(x) is the polarization charge density, c 13 and c 33 are elastic constants, e 31 and e 33 are piezoelectric constants, x is the Al component ratio in the AlGaN barrier layer, and is generally 20%-30%, is the spontaneous polarization charge density of AlGaN, where a0is the GaN lattice constant.

[0057] The two-dimensional electron gas surface density formula is:

[0058]

[0059] q = 1.6 * 10 -19 C

[0060] where ε0= 8.85 * 10 -12 F / m (dielectric constant in air), ε r (x) = 4.82 F / m (dielectric constant of 30% aluminum gallium nitride), d AlGaN is the barrier layer thickness, d AlGaN = 17 nm = 17 * 10 -6 m, is the barrier height of AlGaN, ranging from a few hundred millielectron volts to a few electron volts (1.5 electron volts); E F (x) is the Fermi level in the GaN material at equilibrium, which is 1.7 electron volts.

[0061] The doping of aluminum element in the gallium nitride material realizes the band gap width of 3.4-6.2eV, the band gap width of the gallium nitride in the embodiment is 3.4eV, the band gap width of the aluminum gallium nitride containing 30% is 3.96eV; ΔE C (x) = 0.56eV, representing the conduction band difference of gallium nitride and aluminum gallium nitride.

[0062] The two-dimensional electron gas surface density n s (x) (the unit of surface density and bulk density) and the resistance r (ohm) can be represented by the following formula:

[0063] r = 1 / (eμn)

[0064] where n is the two-dimensional electron gas surface density, e is the elementary charge, and μ is the mobility of the two-dimensional electron flow. In gallium nitride, the mobility μ is usually around 0.2 m^2 / Vs.

[0065] The calculation formula of the resistance R of the gallium nitride pressure sensor is as follows:

[0066]

[0067] where L is the length of the gallium nitride pressure sensor, d is the width of the gallium nitride pressure sensor, and R≈320Ω*20=6400Ω under the condition of 0N pressure.

[0068] The structure of the sensor of the embodiment is similar to a seesaw. The metal has ductility similar to a rubber band. When pressure is applied at both the source and the drain, the bending deformation of the two sides of the sensor will cause the resistance of the current sensing channel inside the drain (a two-dimensional electron gas 2D-EDGE exists at the gallium nitride / aluminum gallium nitride interface, thereby realizing electrical conductivity, but the resistivity of the two-dimensional electron gas is related to the stress on its surface) to increase significantly, thereby causing the current to decrease, thereby realizing pressure sensing.

[0069] According to the force, it can be known that when the source is subjected to a small force, the source has a certain speed. Since the slit in the middle is small, the source will soon contact the lower support. Since the drain is connected to the silicon-based abutment column, the lower support column of the gate, the source, the drain, and the gate all deform (compared to the general gallium nitride pressure sensor, only the source and the drain deform, compared to the general gallium nitride pressure sensor, more deformation occurs, and therefore the sensitivity is higher), the two-dimensional electron gas changes greatly, and the resistance changes quickly, that is, the sensor has high sensitivity characteristics, and since the bottom support supports, the force can be increased, and therefore the measurement range of the pressure sensor is large.

[0070] The simulation experiment of the measurement range of the pressure sensor of the embodiment is as follows:

[0071] Simulation 1: The range is (0-0.01N), as shown in Figure 3 When the pressure is 0.01N (500kPa), the intermediate stress of gallium nitride produces 2.83Gpa, and the resistance reaches 3200Ω at this time, ΔR≈3200Ω, and the sensitivity: ΔR / R≈0.50.

[0072] Simulation 2: When the pressure is 0.005N (250kPa), as shown in Figure 4 The intermediate stress of gallium nitride produces 1.41Gpa, and the sensitivity: ΔR / R≈0.33.

[0073] Simulation 3: When the pressure is 0.001N (50kPa), as shown in Figure 5 The intermediate stress of gallium nitride produces 0.28Gpa, and the sensitivity: ΔR / R≈0.08.

[0074] Comparative Example: Invention Patent “Flexible Piezoresistive Pressure Sensor with Adjustable Range and Sensitivity” CN201911277053.7 of Nanjing University of Science and Technology

[0075] Figure 6 The effect diagram of the invention patent of Nanjing University of Science and Technology is shown in Figure 6 The maximum sensitivity of the scheme under the conditions of pressure of 500kpa, 250kpa, and 50kpa is about 0.23, 0.16, and 0.1, respectively.

[0076] The pressure sensor sensitivity and pressure relationship curve of the embodiment is shown in Figure 7 As can be seen from the comparative experimental data, the maximum sensitivity of the embodiment is 0.50, 0.33, and 0.08 under the conditions of 500kpa, 250kpa, and 50kpa, which is greater than that of the prior art.

[0077] Figure 8 The figure is the relationship between the maximum range of the gallium nitride pressure sensor of the embodiment and the gap size.

[0078] As can be seen from Figure 8 , the smaller the gap, the greater the range of the pressure sensor, and it can be seen that the measurement range of the pressure sensor of the embodiment can reach the MPa level, while the range of the comparative patent can only reach the Kpa level, so the embodiment significantly expands the range of the pressure sensor while improving the sensitivity.

[0079] Embodiment three:

[0080] The embodiment provides a preparation method of a pressure sensor, comprising:

[0081] Step 1: cleaning of the silicon wafer;

[0082] The cleaning of the new wafer is the first step in the sensor process flow of the embodiment, and the purpose is to remove organic matter and oxides on the heterojunction surface. The cleaning of the organic matter on the heterojunction surface mainly uses acetone, isopropyl alcohol, and oxygen plasma. The oxides are mainly cleaned by acidic and alkaline solutions such as HF, HCL, NH4OH, (NH4)2S, TMAH, stripping solution, etc.

[0083] Step 2: preparation of a buffer layer; the function of this layer is to make the gallium nitride and Si lattice more matched, and to improve the growth quality.

[0084] Step 3: preparation of a GaN layer;

[0085] Reaction furnace preheating: the reaction furnace is preheated to an appropriate temperature (generally 1000-1100℃) to ensure the temperature stability and reaction rate during the growth process.

[0086] Growth gas preparation: high-purity nitrogen and raw material gases such as trimethyl gallium are injected into the reaction furnace, and the flow rate and proportion are adjusted by the flow controller to control the stability and composition of the reaction atmosphere during the growth process.

[0087] Gallium nitride growth: the cleaned substrate is placed in the reaction furnace, subjected to certain pretreatment (such as high-temperature drying), and then a layer of gallium nitride film is grown on the substrate by methods such as metal organic chemical vapor deposition (MOCVD).

[0088] Step 4: Preparation of AlGaN layer;

[0089] Preheating of the reactor: The reactor is preheated to an appropriate temperature (generally 800-1000°C) to ensure temperature stability and reaction rate during the growth process.

[0090] Preparation of growth gas: High-purity nitrogen and raw gas such as trimethylaluminum and trimethylgallium are injected into the reactor, and the flow rate and proportion are adjusted by the flow controller to control the stability and composition of the reaction atmosphere during the growth process.

[0091] AlGaN growth: The cleaned substrate is placed in the reactor, preheated (such as high-temperature drying), and then an AlGaN thin film is grown on the substrate by methods such as metal organic chemical vapor deposition (MOCVD).

[0092] Step 5: Preparation of source, drain and gate;

[0093] The source and drain are grown on the AlGaN layer using the principle of ohmic contact (high-temperature thermal annealing method (electron beam evaporation, four layers of metal (Ti / Al / Ni / Au 4 layers of metal) in sequence, and rapid annealing at 850°C in a nitrogen atmosphere for 35s)), and then the gate is grown by Schottky contact (electron beam evaporation, two layers of metal (gate metal is Ni / Au two layers of metal) in sequence, and annealing at 400°C in a nitrogen atmosphere for 5min).

[0094] Step 6: Preparation of silicon substrate;

[0095] On the back of the sensor, the Si of the support to be protected is protected with photoresist, and then etched to a reserved 10-20um (leaving enough space for bonding with the silicon base support) by deep silicon etching method (plasma etching of SF6 / O2 / CHF3 mixed gas, buffer is gallium nitride material, which needs to be etched with chlorine gas, SF6 gas cannot etch gallium nitride), then wash off all the photoresist, and then protect the right side silicon base support with photoresist, and again use the deep silicon etching method to complete the etching, and then wash the photoresist to complete the etching.

[0096] The last step is also the most important, and the matching silicon base support is prepared in advance, and a certain interval is reserved, and then the silicon-silicon direct bonding technology is used (two silicon wafers can be directly bonded together by high-temperature treatment without any adhesive and external electric field, and the process is simple.)(1) The three lower silicon wafers are polished (oxidized or unoxidized), and then subjected to appropriate surface cleaning and activation (OH-solution or plasma); (2) The three parts of the silicon wafer polishing surface are bonded together at room temperature; (3) The bonded silicon wafer is treated at high temperature for several hours in an oxygen or nitrogen environment, forming a good bond.

[0097] Part of the steps in the embodiments of the present application can be realized by software, and the corresponding software program can be stored in a readable storage medium, such as an optical disc or a hard disk.

[0098] The above merely describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A pressure sensor, characterized in that, The pressure sensor comprises, from bottom to top, a silicon substrate, a buffer layer, a GaN layer, and an AlGaN layer, wherein the AlGaN layer has a gate, a source, and a drain. The silicon substrate includes: a substrate, on which a first support, a second support, and a third support are disposed sequentially from left to right; the upper surfaces of the second support and the third support are attached to the lower surface of the buffer layer, and a cavity is formed between the second support and the third support; the height of the first support is less than that of the second support, and there is a gap between the first support and the buffer layer.

2. The pressure sensor according to claim 1, characterized in that, The thickness of the silicon substrate is 350-1000um.

3. The pressure sensor according to claim 1, characterized in that, The gap between the first support and the buffer layer is 10-130 μm.

4. The pressure sensor according to claim 1, characterized in that, The thickness of the buffer layer is 2-15 μm.

5. The pressure sensor according to claim 1, characterized in that, The thickness of the GaN layer is 1-5 μm.

6. The pressure sensor according to claim 1, characterized in that, The thickness of the AlGaN layer is 10-20 nm.

7. A pressure sensing method, characterized in that, The method is implemented based on the pressure sensor according to any one of claims 1-6, and includes: when pressure is applied at the source or drain, the left side of the pressure sensor undergoes bending deformation, which causes the resistance of the current sensing channel between the source and drain to increase, thereby causing the current to decrease, and thus realizing pressure sensing. The current sensing channel between the source and drain is: a two-dimensional electron gas 2D-EDGE existing at the interface of the GaN layer and the AlGaN layer.

8. A method for manufacturing a pressure sensor, characterized in that, For manufacturing the pressure sensor according to any one of claims 1-6, comprising: Step 1: Silicon wafer cleaning; Step 2: Grow a buffer layer on the cleaned silicon substrate; Step 3: Prepare a GaN layer by growing a GaN thin film on the buffer layer using metal-organic chemical vapor deposition. Step 4: Prepare an AlGaN layer by growing an AlGaN thin film on the GaN layer using metal-organic chemical vapor deposition. Step 5: Fabricate the source, drain, and gate on the AlGaN layer; Step 6: Etching and bonding of the silicon substrate; On the back of the pressure sensor, photoresist is applied to the position corresponding to the second support, and then etched until 10-20µm is left. Then all the photoresist is washed away. Photoresist is applied to the position corresponding to the third support, and then etched. After etching is completed, the photoresist is cleaned. The pre-prepared matching silicon-based pillars are bonded to the back of the pressure sensor using silicon-silicon direct bonding technology.

9. The method for preparing a pressure sensor according to claim 8, characterized in that, Step 5 includes: forming a source and a drain on the AlGaN layer using the ohmic contact principle, and then forming a gate using the Schottky contact principle.

10. The method for preparing a pressure sensor according to claim 8, characterized in that, The source and drain are made of four layers of metal (Ti / Al / Ni / Au), and the gate is made of two layers of metal (Ni / Au).

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