Monolithic integrated multifunctional composite sensor and preparation method thereof

Abstract

The invention provides a monolithic integrated multifunctional composite sensor and a preparation method thereof, a single silicon wafer single-sided bulk silicon micro-manufacturing technology is adopted, a first microgroove of a gas flow sensing unit is pre-defined and covered, a pressure reference cavity and a pressure sensitive diaphragm are firstly formed, and then through protection of the first microgroove and a side wall, the gas flow sensing unit and the pressure reference cavity are combined. A monocrystalline silicon thermocouple arm and a heating resistor pattern are pre-defined, then a pressure sensing unit is protected through a heat insulation medium layer, then a heat insulation cavity and a temperature sensing unit are formed, and finally the gas flow sensing unit, the pressure sensing unit and the temperature sensing unit are integrated on the same single chip. The structure that the heat insulation cavity and the pressure reference cavity are located in the same monocrystalline silicon substrate is achieved. According to the method, the traditional double-sided processing technology is replaced, the problem that the small size of the traditional composite chip is difficult to realize is solved, the complex process caused by the traditional silicon-silicon or silicon-glass bonding structure is avoided, the process difficulty and cost are greatly reduced, the yield of the composite chip is improved, and the reliability of the sensor is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon micromechanical sensors and relates to a monolithic integrated multifunctional composite sensor and a preparation method thereof. Background Art

[0002] With the continuous development of MEMS micromachining technology, silicon-based MEMS flow sensors prepared based on silicon-based micromachining technology are widely used in aerospace, industrial process monitoring, biochemical medicine and other fields due to their advantages such as small chip size, low preparation cost and high performance. Especially in recent years, with the increasing demand for miniaturization and high precision of flow sensors in analytical instruments or equipment such as fine chemical industry and biomedicine, traditional flow measurement devices are difficult to meet the requirements in terms of performance, manufacturing cost, chip size and other aspects. Miniaturization, high performance and low cost of flow sensors have become the future development trend.

[0003] In addition, since gas flow is greatly affected by pressure and temperature, during the micro-flow measurement process, slight temperature changes or pressure fluctuations will cause changes in gas density, heat capacity and other parameters, which will lead to measurement errors. In order to improve the measurement accuracy, external thermistors and pressure sensors are generally used to monitor the pressure and temperature of the environment in which the gas to be measured is located in real time, and the detection accuracy of gas micro-flow is ensured by temperature and pressure compensation. However, since the temperature and pressure detection points are far away from the flow sensitive chip, there are usually problems such as response hysteresis, deviation between the temperature and pressure values ​​and the pressure and temperature at the flow location, which is not suitable for air tightness detection scenarios with rapid temperature changes and large pressure fluctuations. Therefore, in order to eliminate the influence of temperature hysteresis and pressure deviation, the development of a multifunctional composite sensor chip with integrated pressure, flow and temperature detection on a single chip is of great significance for improving micro-flow detection accuracy, reducing chip size, and reducing chip cost. In 1992, Euisik Yoon et al. from the University of Michigan in the United States developed a mass flow sensor chip with integrated temperature, pressure and flow detection based on double-sided micromachining technology. Among them, the combination of polysilicon heating resistor and Cr / Au temperature measuring resistor realizes the measurement of gas flow, and two pairs of orthogonally arranged polysilicon-gold thermopiles realize the detection of gas flow direction; the pressure sensor uses polysilicon as a piezoresistor, and uses concentrated boron doping corrosion self-stop to prepare the pressure sensitive diaphragm structure. Although this monolithic integrated structure realizes the single-chip integration of three sensors: pressure, temperature and flow, it has the following shortcomings: (1) The back side wet etching is used to release the flow sensor sensitive detection unit and the pressure sensitive diaphragm structure. Due to the limitation of the angle of 54.74 degrees between the (111) crystal plane and the (100) crystal plane, the chip size after processing is relatively large; (2) Polysilicon piezoresistors are used as the detection resistors of the pressure sensor. Since the polysilicon piezoresistance coefficient is about half of the single-crystal silicon piezoresistance coefficient, the sensitivity of the pressure sensor based on polysilicon piezoresistors is less than that of the single-crystal silicon piezoresistance under the same pressure sensitive diaphragm size; (3) Double-sided micromachining and concentrated boron corrosion self-stop are used, the process is complex and the manufacturing cost is high.

[0004] Therefore, how to provide a monolithic integrated multifunctional composite sensor and its preparation method, so that the composite sensor chip integrates flow sensor, pressure sensor and temperature sensor into one, while ensuring that the composite sensor has sufficiently high sensitivity, overcome the problems of complex manufacturing process, large size and high manufacturing cost in the prior art, has become an important technical problem that needs to be urgently solved by technical personnel in this field.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a monolithic integrated multifunctional composite sensor and a preparation method thereof, so as to solve the problems of complex manufacturing process, large size and high cost of composite sensors in the prior art.

[0007] To achieve the above-mentioned and other related purposes, the present invention provides a method for preparing a monolithic integrated multifunctional composite sensor, which is characterized by comprising the following steps:

[0008] Providing a single crystal silicon substrate with a first conductivity type, the single crystal silicon substrate comprising a piezoresistor region of a pressure sensing unit and a single crystal silicon thermocouple arm and a heating resistor region in a gas flow sensing unit, and forming a hard mask layer on the single crystal silicon substrate;

[0009] Forming a second conductive type doping region in the varistor region and the single crystal silicon thermocouple arm and heating resistor region;

[0010] forming predefined microgrooves of single crystal silicon thermocouple arms and heating resistors in the second conductive type doped region;

[0011] A first passivation layer is formed on the hard mask layer to cover the predefined micro grooves, and then a plurality of micro release holes are formed in the first passivation layer to define the size of the pressure sensitive membrane. The depth of the micro release holes is the thickness of the pressure sensitive membrane.

[0012] A second passivation layer and a sidewall protection layer are formed on the first passivation layer to protect the sidewalls of the micro-release holes, and then the single crystal silicon is etched to a certain depth along the bottom of the micro-release holes, where the etching depth is the pressure reference cavity depth, and the pressure reference cavity is released to form a pressure sensitive diaphragm at the same time;

[0013] removing the remaining first passivation layer and the second passivation layer on the hard mask layer to expose the predefined microgrooves;

[0014] Continue etching along the bottom of the predefined microgroove to a certain depth to form a first microgroove, wherein the depth of the first microgroove is the thickness of the single crystal silicon thermocouple arm and the heating resistor;

[0015] forming a third passivation layer on the sidewall of the first microgroove, and forming a sacrificial layer to fill the micro release hole and the first microgroove, and then removing the excess sacrificial layer on the front side of the single crystal silicon substrate to achieve planarization;

[0016] Removing the hard mask layer on the front side of the single crystal silicon substrate, and then forming a heat-insulating dielectric layer on the surface of the single crystal silicon substrate;

[0017] forming connection holes, lead pads, metal thermocouple arms, metal interconnection layers, heating resistors and ambient temperature resistors on the thermal insulation medium layer;

[0018] A second microgroove of a certain depth is formed in the gas flow sensor area, wherein the etching depth is equal to the height of the heat insulation cavity;

[0019] The second microgroove is released to form a heat-insulating groove and a heat-insulating cavity, and the metal thermocouple arm and the single crystal silicon thermocouple arm form a single crystal silicon-metal thermocouple pair through a metal interconnection layer.

[0020] Optionally, the surface of the single crystal silicon substrate is a (111) crystal plane, and the single crystal silicon-metal thermocouple is along <211> Crystal arrangement, heating resistor along <110> Crystal arrangement.

[0021] Optionally, the pressure reference cavity and the thermal insulation cavity are released by TMAH etching to remove part of the single crystal silicon substrate and the sacrificial layer, and the six peripheral surfaces and the upper and lower surfaces of the pressure reference cavity and the thermal insulation cavity are all (111) crystal planes.

[0022] Optionally, the first conductivity type and the second conductivity type are opposite conductivity types, and the first conductivity type is P type or N type.

[0023] Optionally, the thermal insulation medium layer includes a composite film layer composed of a silicon oxide layer and a silicon nitride layer or a single-layer low-stress silicon nitride layer.

[0024] Optionally, the temperature sensing unit includes one of a Pt resistor, a single crystal silicon resistor and a polycrystalline silicon resistor.

[0025] At the same time, the present invention also provides a monolithic integrated multifunctional composite sensor, characterized in that the monolithic integrated multifunctional composite sensor comprises:

[0026] A single crystal silicon substrate having a first conductivity type;

[0027] A gas flow sensing unit, the gas flow sensing unit comprising a single crystal silicon heating resistor, a single crystal silicon thermocouple arm-metal thermocouple pair, a thermal insulation groove, a thermal insulation medium layer and a thermal insulation cavity; the thermal insulation cavity is located directly below the single crystal silicon-metal thermocouple pair and buried inside the single crystal silicon substrate; the thermal insulation groove is located between the single crystal silicon-metal thermocouple pairs and on both sides of the single crystal silicon heating resistor;

[0028] A pressure sensing unit, the pressure sensing unit comprising a piezoresistor, a pressure sensitive diaphragm and a pressure reference cavity; the piezoresistor is located above the pressure sensitive diaphragm, and the pressure sensitive resistor constitutes a Wheatstone pressure detection circuit; the pressure reference cavity is located directly below the pressure sensitive diaphragm and buried inside the single crystal silicon substrate;

[0029] Temperature sensing unit;

[0030] The gas flow sensing unit, the pressure sensing unit and the temperature sensing unit are integrated on the same surface of the single crystal silicon substrate.

[0031] Optionally, the single crystal silicon-metal thermocouple pair includes a single crystal silicon thermocouple arm and a metal thermocouple arm, the single crystal silicon thermocouple arm is suspended below the thermal insulation medium layer, and the metal thermocouple arm is located above the thermal insulation medium layer; the single crystal silicon thermocouple arm and the metal thermocouple arm are interconnected at the hot end through a metal via.

[0032] Optionally, the thermal insulation cavity has a hexagonal prism structure, and the side surfaces and upper and lower surfaces of the thermal insulation cavity are (111) crystal planes.

[0033] Optionally, the thermal insulation medium layer includes one of a composite film layer composed of a silicon oxide layer and a silicon nitride layer or a single-layer low-stress silicon nitride layer.

[0034] As described above, the present invention provides a monolithic integrated multifunctional composite sensor and a preparation method thereof, which adopts a single silicon wafer single-sided silicon micro-manufacturing technology, and after predefining and covering the first microgroove of the gas flow sensing unit, first forms a pressure reference cavity and a pressure sensitive diaphragm, and then protects the first microgroove and the sidewall, predefines the single crystal silicon thermocouple arm and the heating resistor thickness pattern, and then protects the pressure sensing unit through a heat insulation medium layer, and then forms a heat insulation cavity and a temperature sensing unit, and finally realizes the integration of the gas flow sensing unit, the pressure sensing unit and the temperature sensing unit on the same monolithic chip, and realizes the structure of the heat insulation cavity and the pressure reference cavity inside the same monocrystalline silicon substrate. This method replaces the traditional double-sided processing technology, which not only solves the problem that the traditional composite chip is difficult to achieve small size, but also avoids the complex process brought by the traditional silicon-silicon or silicon-glass bonding structure, greatly reduces the process difficulty and manufacturing cost, and at the same time improves the yield of the composite sensor chip, and improves the performance and reliability of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Shown is a schematic diagram of the three-dimensional structure of the monolithic integrated multifunctional composite sensor of the present invention.

[0036] Figure 2 The monolithic integrated multifunctional composite sensor of the present invention is shown Figure 1 Schematic diagram of the ABC section structure along the middle.

[0037] Figure 3 Display as Figure 2 A partial enlarged schematic diagram of the structure.

[0038] Figure 4 Shown is a schematic diagram of the process flow of the method for preparing a monolithic integrated multifunctional composite sensor in the present invention.

[0039] Figure 5 It is a schematic structural diagram of providing a single crystal silicon substrate and forming a hard mask layer on the surface of the single crystal silicon substrate in the present invention.

[0040] Figure 6 It is a schematic diagram of the structure after the second conductive type doping region is formed in the present invention.

[0041] Figure 7 It is a schematic diagram of the structure after forming predefined micro grooves in the present invention.

[0042] Figure 8 It is a schematic structural diagram showing the present invention after micro-release holes are formed in the first passivation layer from top to bottom.

[0043] Figure 9a It is a schematic structural diagram showing the formation of a sidewall protection layer in the micro-release hole in the present invention.

[0044] Figure 9b It is a schematic diagram of the structure after etching a certain depth along the micro-release hole when defining the pressure reference cavity thickness in the present invention.

[0045] Fig.9c It is a schematic diagram of the structure after the pressure reference cavity is formed in the present invention.

[0046] Fig.10 It is a schematic diagram of the structure after the passivation layer is removed to form a pressure sensitive membrane and the predefined micro grooves are exposed in the present invention.

[0047] Fig.11 It is a schematic diagram of the structure after the first microgroove is formed in the present invention.

[0048] Fig.12a It is a schematic diagram of the structure after the third passivation layer is formed on the side walls of the first micro groove and the micro release hole in the present invention.

[0049] Figure 12b It is a schematic diagram of the structure after the sacrificial layer is filled in the micro-releasing hole and the first micro-groove in the present invention.

[0050] Fig.12c It is a schematic diagram of the structure after the hard mask layer is removed in the present invention.

[0051] Fig.13It is a schematic diagram of the structure after a heat-insulating dielectric layer is formed on the surface of a single crystal silicon substrate in the present invention.

[0052] Fig.14 It is a schematic diagram of the structure after a metal interconnection layer, a metal thermocouple arm, a heating resistor and an ambient temperature resistor are formed on the thermal insulation medium layer in the present invention.

[0053] Fig.15 It is a schematic diagram showing the structure after the second micro groove is formed in the gas flow sensor area in the present invention.

[0054] Fig.16 It is a schematic diagram of the structure after the heat insulation groove and the heat insulation cavity are formed in the present invention.

[0055] Description of Reference Numerals

[0056] 100 Single crystal silicon substrate

[0057] 110 Hard mask layer

[0058] 120 second conductivity type doping region

[0059] 130a Predefined microgrooves

[0060] 131a Predefined single crystal silicon thermocouple arm microgroove

[0061] 132a Predefined heating resistor microgroove

[0062] 130b First microgroove

[0063] 130c Second micro groove

[0064] 140 First passivation layer

[0065] 141 Second passivation layer

[0066] 150 Third passivation layer

[0067] 160 Sacrificial Layer

[0068] 200 Gas flow sensing unit

[0069] 210 Heating resistor

[0070] 230 Single crystal silicon thermocouple arm

[0071] 240 Insulation Tank

[0072] 250 Insulation medium layer

[0073] 251 Connection hole

[0074] 260 Metal Thermocouple Arm

[0075] 270 Insulated cavity

[0076] 300 Pressure Sensing Units

[0077] 310 Varistor

[0078] 320 Micro Release Hole

[0079] 330 Pressure reference chamber

[0080] 340 Pressure sensitive diaphragm

[0081] 400 Temperature Sensing Units

[0082] 401 Ambient temperature resistor

[0083] 500 Lead Pad DETAILED DESCRIPTION

[0084] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0085] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0086] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0087] Embodiment 1

[0088] This embodiment provides a method for preparing a monolithic integrated multifunctional composite sensor. Figure 1 to Figure 3 , showing a schematic diagram of the global and local three-dimensional structure of a monolithic integrated multifunctional composite sensor. The monolithic integrated multifunctional composite sensor comprises a single crystal silicon substrate 100, a gas flow sensing unit 200, a pressure sensing unit 300 and a temperature sensing unit 400; the gas flow sensing unit 200, the pressure sensing unit 300 and the temperature sensing unit 400 are integrated on the same surface of the single crystal silicon substrate 100; Figure 4 The process flow chart of the preparation of a monolithic integrated multifunctional composite sensor is shown in this embodiment. Figures 5 to 16 For reference in each step of the preparation process Figure 1 The cross section along ABC is Figure 2 The schematic diagram of the unfolded structure of the cross section along ABC in FIG. 1 is a schematic diagram of the unfolded structure of the cross section along ABC in FIG. 1 , and the specific preparation steps of the monolithic integrated multifunctional composite sensor are as follows:

[0089] See also Figure 4 and Figure 5 , perform step S1, provide a single crystal silicon substrate 100 with a first conductivity type, the single crystal silicon substrate includes the varistor 310 region of the pressure sensing unit 300 and the single crystal silicon thermocouple arm 230 and the heating resistor 210 region in the gas flow sensing unit 200, and form a hard mask layer 110 on the single crystal silicon substrate 100.

[0090] Specifically, the surface of the single crystal silicon substrate 100 is a (111) crystal plane, the first conductivity type can be a P-type conductivity type or an N-type conductivity type, preferably, the present embodiment adopts an N-type conductivity type, and the thickness of the single crystal silicon substrate 100 is about 450 μm, and the resistivity is 1 to 10 Ωcm. The single crystal silicon substrate 100 can be single-sided polished single crystal silicon or double-sided polished single crystal silicon.

[0091] Specifically, the material of the hard mask layer 110 includes one or a combination of a silicon nitride layer and a silicon oxide layer. In this embodiment, silicon oxide is formed as the hard mask layer 110 by a thermal oxidation process. The thickness of the silicon oxide in this embodiment is The thickness of the silicon oxide layer is not specifically limited and can be set according to actual needs.

[0092] See also Figure 4 and Figure 6 , executing step S2, forming a second conductive type doping region 120 in the region of the varistor 310 and the region of the single crystal silicon thermocouple arm 230 and the heating resistor 210.

[0093] Specifically, the surface of the hard mask layer 110 is patterned by reactive ion etching technology to form a second conductive type ion implantation window, and the second conductive type ion implantation is performed and an annealing process is performed to form a second conductive type doped region 120. The second conductive type is the opposite conductive type to the first conductive type of the single crystal silicon substrate 100. In this embodiment, the second conductive type doped region 120 is a boron ion doped region, and the boron ion doped region includes the varistor 310 pattern of the -pressure sensing unit 300 and the single crystal silicon thermocouple arm 230 and the heating resistor 210 in the gas flow sensing unit 200.

[0094] Furthermore, the heating resistor 210 is <110> The single crystal silicon thermocouple arm 230 is arranged along <211> Arranged in crystal direction, a plurality of the single crystal silicon thermocouple arms 230 and the subsequent metal thermocouple arms 260 form a single crystal silicon-metal thermocouple pair, and the single crystal silicon-metal thermocouple pair is located on both sides of the heating resistor 210, and is symmetrically distributed, that is, the upstream and downstream positions, respectively forming two independent thermopile detection circuits in the upstream and downstream, and the potential difference is obtained by detecting the temperature difference between the two independent thermopile detection circuits in the upstream and downstream. Among them, the single crystal silicon-metal thermocouple pair is a group or more than two groups, which are set according to actual needs. When the single crystal silicon-metal thermocouple pair is more than two groups, the single crystal silicon-metal thermocouple pair groups are connected end to end to form a complete detection circuit.

[0095] See also Figure 4 and Figure 7 , executing step S3 , forming the predefined micro groove 130 a of the single crystal silicon thermocouple arm 230 and the heating resistor 210 in the second conductive type doping region 120 .

[0096] Specifically, by forming a predefined microgroove 130a, the single crystal silicon is exposed to define the single crystal silicon thermocouple arm 230 and the heating resistor 210. The predefined microgroove 130a includes a predefined single crystal silicon thermocouple arm microgroove 131a and a predefined heating resistor microgroove 132a, and the predefined single crystal silicon thermocouple arm microgroove 131a is symmetrically distributed on both sides of the single crystal silicon thermocouple arm. The single crystal silicon thermocouple arm 230 and the heating resistor 210 are referred to Figure 3 and Fig.16 .

[0097] See also Figure 4 and Figure 8 , execute step S4, form a first passivation layer 140 on the hard mask layer 110 and cover the predefined micro groove 130a, and then form a plurality of micro release holes 320 in the single crystal silicon substrate 100 to define the morphology size of the pressure sensitive membrane 340, and the depth of the micro release holes 320 is the thickness of the pressure sensitive membrane 340.

[0098] Specifically, the first passivation layer 140 is deposited by low stress chemical vapor deposition (LPCVD), the material of the first passivation layer 140 includes a TEOS (tetraethyl orthosilicate) passivation layer, the first passivation layer 140 is patterned, and a plurality of the micro release holes 320 with a certain depth h1 are etched by a reactive ion deep etching (Deep-RIE) process, and the thickness of the first passivation layer 140 is There is no limitation here.

[0099] Furthermore, the thickness of the pressure sensitive membrane 340 is in the range of 3 to 30 μm, for example, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or 30 μm.

[0100] See also Figure 4 and Figures 9a to 9c , perform step S5, form a second passivation layer 141 on the first passivation layer 140 to protect the side wall of the micro-release hole 320, and pattern the second passivation layer 141, and then continue to etch the single crystal silicon substrate 100 along the bottom of the micro-release hole 320 to a certain depth, the etching depth is the depth of the pressure reference cavity 330, and release to form a pressure sensitive membrane 340 at the same time, the morphology of the pressure sensitive membrane 340 is referenced Figure 2 .

[0101] Specifically, a second passivation layer 141 is deposited on the surface of the first passivation layer 140 to cover the sidewall and bottom of the micro-release hole 320, and then the second passivation layer 141 at the bottom of the micro-release hole 320 is etched away, leaving the second passivation layer 141 at the sidewall, and then the single crystal silicon substrate 100 is further etched to a certain depth along the bottom of the micro-release hole 320 using a reactive ion deep etching (Deep-RIE) technique. By using a KOH solution or a TMAH etching solution to etch inside the single crystal silicon substrate 100, the particularity of the crystal orientation arrangement of the (111) crystal plane of the single crystal silicon substrate 100 can be fully utilized, combined with the anisotropic etching characteristics of the TMAH etching solution, and then the bottom single crystal silicon substrate 100 is fully etched and then stopped automatically, thereby finally forming a vacuum chamber constructed by the eight (111) crystal planes, namely, the pressure reference chamber 330. In some other embodiments, the etching solution may also be a KOH solution, which will not be described in detail here.

[0102] Further, the material of the first passivation layer 140 and the second passivation layer 141 includes a TEOS (tetraethyl orthosilicate) passivation layer, and the depth of the pressure reference cavity 330 is ≥ 20 μm, such as 20 μm, 30 μm, etc. Preferably, the depth in this embodiment is 20 μm. The structure of the pressure reference cavity 330 is a hexagonal prism structure, and the six side faces and the upper and lower two faces of the pressure reference cavity 330 are (111) crystal planes.

[0103] See also Figure 4 and Fig.10 , performing step S6, removing the first passivation layer 140 and the second passivation layer 141 remaining on the hard mask layer 110, and exposing the predefined micro groove 130a.

[0104] Specifically, dry etching or wet etching is used to remove the remaining TEOS passivation layer on the hard mask layer 110. The wet etching includes etching with a BOE solution.

[0105] See also Figure 4 and Fig.11 , execute step S7, continue etching along the bottom of the predefined microgroove 130a to a certain depth to form a first microgroove 130b, and the depth of the first microgroove 130b is the thickness of the single crystal silicon thermocouple arm 230 and the heating resistor 210.

[0106] Specifically, the first micro groove 130 b is formed by etching using the Deep-RIE technology, and the depth of the first micro groove 130 b is at least greater than 3 μm.

[0107] See also Figure 4 and Figures 12a to 12c , execute step S8, form a third passivation layer 150 on the side wall of the first microgroove 130b, and form a sacrificial layer 160 to fill the micro release hole 320 and the first microgroove 130b, and then remove the excess sacrificial layer 160 on the front side of the single crystal silicon substrate 100 to achieve planarization.

[0108] Specifically, a third passivation layer 150 is deposited on the surface of the first microgroove 130b by LPCVD, and the material of the third passivation layer 150 includes a TEOS (tetraethyl orthosilicate) passivation layer. The third passivation layer 150 covers the sidewalls and bottom of the first microgroove 130b. By etching away the passivation layer at the bottom of the first microgroove 130b, the third passivation layer 150 covering the sidewalls of the first microgroove 130b is formed.

[0109] Furthermore, the material of the sacrificial layer 160 deposited by LPCVD is low stress polysilicon. After the sacrificial layer 160 fills the micro release holes 320 and the first micro grooves 130b, the excess sacrificial layer 160 scattered on the surface of the single crystal silicon substrate 100 during the filling process is removed by dry etching.

[0110] See also Figure 4 and Fig.13 , executing step S9 , after removing the hard mask layer 110 on the front side of the single crystal silicon substrate 100 , a heat insulating dielectric layer 250 is formed on the surface of the single crystal silicon substrate 100 .

[0111] Specifically, the hard mask layer 110 on the front side of the single crystal silicon substrate 100 is removed by dry etching. In some other embodiments, a BOE wet etching solution may also be used to remove the hard mask layer 110. The thermal insulation dielectric layer 250 includes a composite film layer composed of a silicon oxide layer and a silicon nitride layer, or a single low stress silicon nitride layer. The thickness of the thermal insulation dielectric layer 250 can be set as required.

[0112] See also Figure 4 and Fig.14 , execute step S10, graph the thermal insulation medium layer 250, form a connection hole 251, and form a lead pad 500, a metal interconnection layer, the metal thermocouple arm 260, the heating resistor 210 and the ambient temperature resistor 401 in the temperature sensing unit 400 on the thermal insulation medium layer 250.

[0113] Specifically, as this embodiment, after etching the connection hole 251 on the thermal insulation medium layer 250, a Cr / Pt metal thin layer is sputtered, and then a plasma etching process is used to prepare the connection hole 251, the lead pad 500, the metal interconnection layer, the metal thermocouple arm 260, the heating resistor 210 and the ambient temperature resistor 401 in the temperature sensing unit 400. The metal thin layer may also include Ti / Pt, etc.

[0114] Further, the ambient temperature resistor 401 is referenced Figure 1 and Figure 2 The ambient temperature resistor 401 may also include a platinum resistor, a single crystal silicon resistor or a polycrystalline silicon resistor.

[0115] See also Figure 4 and Fig.15 , executing step S11, patterning the thermal insulation medium layer 250, forming a second micro groove 130c of a certain depth in the gas flow sensor 200 area, and the etching depth is the height of the thermal insulation cavity 270.

[0116] Specifically, the second microgroove 130c is formed by using a deep reactive ion etching (Deep-RIE) technique to form a groove to a certain depth in the area between the first microgroove 130b and the area of ​​the non-single-crystal silicon thermocouple arm 230 and the heating resistor 210. At the same time, the second microgroove 130c serves as a release groove for the subsequent TMAH wet etching of the single-crystal silicon thermocouple arm 230 and the heating resistor 210.

[0117] For further reference, Figure 3 The thermal insulation cavity 270 is a hexagonal prism structure, and the side surface and the upper and lower surfaces of the thermal insulation cavity 270 are (111) crystal planes. The thermal insulation cavity 270 is located directly below the single crystal silicon-metal thermocouple pair and buried inside the single crystal silicon substrate 100. Generally, the height of the thermal insulation cavity 270 is greater than or equal to 50 μm, such as 50 μm, 60 μm, 80 μm, and 150 μm. In this embodiment, the height of the thermal insulation cavity 270 is 80 μm.

[0118] Furthermore, the front etching process is adopted, which not only makes the size smaller, but also makes the three-layer structure of the metal thermocouple arm, the single crystal silicon thermocouple arm and the thermal insulation film can be completed simultaneously. First of all, the prior art can only adopt the method of stacking three-layer structures, and its manufacturing process is complicated. The front etching of the present application makes the process simpler. Secondly, in the prior art, although the back dry etching can maintain the size, for devices with high requirements for manufacturing process and cost, if the back wet etching is adopted, due to the angle between the two crystal phases, the etching morphology is trapezoidal, resulting in the same size of the single crystal silicon substrate 100. When the back etching is adopted, the support size on both sides is reduced. If the same strength is maintained, the size needs to be increased, which makes the size of the single crystal silicon substrate 100 required by the back etching larger, while the present application adopts the front etching, which reduces the size of the single crystal silicon substrate 100.

[0119] See also Figure 4 and Fig.16 , execute step S12, release the second micro groove 130c to form the thermal insulation groove 240 and the thermal insulation cavity 270, and the metal thermocouple arm 260 and the single crystal silicon thermocouple arm 230 form a single crystal silicon-metal thermocouple pair through the metal interconnection layer.

[0120] Specifically, TMAH solution is used to corrode and release the silicon-metal thermocouple, the heating resistor 210 and the heat-insulating cavity 270. In some other embodiments, the corrosive solution may also be a KOH solution.

[0121] Furthermore, the heat-insulating groove 240 is formed between the two pairs of the single crystal silicon-metal thermocouples. Similarly, the heat-insulating groove 240 is also formed between the two sides of the heating resistor 210 .

[0122] Embodiment 2

[0123] This embodiment also provides a monolithic integrated multifunctional composite sensor, which is manufactured by the manufacturing method described in the first embodiment or other suitable similar methods. The manufacturing method, material and structure of the monolithic integrated multifunctional composite sensor can be referred to in the first embodiment. Figure 1 to Figure 3 and Fig.16 , which is a schematic diagram of the structure of the monolithic integrated multifunctional composite sensor, wherein the monolithic integrated multifunctional composite sensor comprises:

[0124] A single crystal silicon substrate 100 having a first conductivity type;

[0125] A gas flow sensing unit 200, the gas flow sensing unit 200 comprises a single crystal silicon heating resistor 210, a single crystal silicon thermocouple arm-metal thermocouple pair, a heat insulation groove 240, a heat insulation medium layer 250 and a heat insulation cavity 270; the heat insulation cavity 270 is located directly below the single crystal silicon metal thermocouple pair and buried inside the single crystal silicon substrate 100; the heat insulation groove 240 is located between the single crystal silicon-metal thermocouple pairs and on both sides of the single crystal silicon heating resistor 210;

[0126] A pressure sensing unit 300, the pressure sensing unit 300 comprises a piezoresistor 310, a pressure sensitive membrane 340 and a pressure reference cavity 330; the piezoresistor 310 is located above the pressure sensitive membrane 340, and the pressure sensitive resistor 310 constitutes a Wheatstone pressure detection circuit; the pressure reference cavity 330 is located directly below the pressure sensitive membrane 340 and buried inside the single crystal silicon substrate 100;

[0127] Temperature sensing unit 400;

[0128] The gas flow sensing unit 200 , the pressure sensing unit 300 , and the temperature sensing unit 400 are integrated on the same surface of the single crystal silicon substrate 100 .

[0129] As an example, the surface of the single crystal silicon substrate 100 is a (111) crystal plane, the first conductivity type can be a P-type conductivity type, or an N-type conductivity type, preferably, the present embodiment adopts an N-type conductivity type, and the thickness of the single crystal silicon substrate 100 is about 450 μm, and the resistivity is 1 to 10 Ω·cm. The single crystal silicon can be single-sided polished single crystal silicon, or double-sided polished single crystal silicon.

[0130] For example, see Figure 3 The single crystal silicon-metal thermocouple pair includes a single crystal silicon thermocouple arm 230 and a metal thermocouple arm 260, wherein the single crystal silicon thermocouple arm 230 is suspended below the thermal insulation medium layer 250, and the metal thermocouple arm 260 is located above the thermal insulation medium layer 250; the single crystal silicon thermocouple arm 230 and the metal thermocouple arm 260 are interconnected at the hot end through a connecting hole 251.

[0131] As an example, the heating resistor 210 is arranged along <110> The single crystal silicon thermocouple arm 230 is arranged along <211> Crystal arrangement.

[0132] As an example, the thermal insulation medium layer 250 includes a composite film layer composed of a silicon oxide layer and a silicon nitride layer or a single layer of low stress silicon nitride layer, and the thermal insulation cavity 270 is a hexagonal prism structure, and the side and upper and lower surfaces of the thermal insulation cavity 270 are (111) crystal planes.

[0133] As an example, the pressure reference cavity 330 is a hexagonal prism structure, and the side surface and the upper and lower surfaces of the pressure reference cavity 330 are (111) crystal planes.

[0134] As an example, the temperature sensing unit 400 includes an ambient temperature resistor 401 , and the ambient temperature resistor 401 includes one of a platinum resistor, a single crystal silicon resistor, or a polycrystalline silicon resistor.

[0135] In summary, the present invention provides a monolithic integrated multifunctional composite sensor and a preparation method thereof, which adopts a single silicon wafer single-sided silicon micro-manufacturing technology, and after predefining and covering the first microgroove of the gas flow sensing unit, first forms a pressure reference cavity and a pressure sensitive diaphragm, and then protects the first microgroove and the sidewall, predefines the thickness of the single crystal silicon thermocouple arm and the heating resistor, and then protects the pressure sensing unit through a heat-insulating medium layer, and then forms a heat-insulating cavity and a temperature sensing unit, and finally realizes the integration of the gas flow sensing unit, the pressure sensing unit and the temperature sensing unit on the same monolithic chip, and realizes the structure of the heat-insulating cavity and the pressure reference cavity inside the same monocrystalline silicon substrate. This method replaces the traditional double-sided processing technology, which not only solves the problem that the traditional composite chip is difficult to achieve a small size, but also avoids the complex process brought by the traditional silicon-silicon or silicon-glass bonding structure, greatly reduces the process difficulty and manufacturing cost, and at the same time improves the yield of the composite sensor chip, and improves the performance and reliability of the sensor. Therefore, the present invention effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0136] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a monolithic integrated multifunctional composite sensor, characterized in that: The following steps are involved: Providing a single crystal silicon substrate with a first conductivity type, the single crystal silicon substrate comprising a piezoresistor region of a pressure sensing unit and a single crystal silicon thermocouple arm and a heating resistor region in a gas flow sensing unit, and forming a hard mask layer on the single crystal silicon substrate; Forming a second conductive type doping region in the varistor region and the single crystal silicon thermocouple arm and heating resistor region; forming predefined microgrooves of single crystal silicon thermocouple arms and heating resistors in the second conductive type doped region; A first passivation layer is formed on the hard mask layer to cover the predefined micro grooves, and then a plurality of micro release holes are formed in the first passivation layer to define the size of the pressure sensitive membrane. The depth of the micro release holes is the thickness of the pressure sensitive membrane. A second passivation layer and a sidewall protection layer are formed on the first passivation layer to protect the sidewalls of the micro-release holes, and then the single crystal silicon is etched to a certain depth along the bottom of the micro-release holes, where the etching depth is the pressure reference cavity depth, and the pressure reference cavity is released to form a pressure sensitive diaphragm at the same time; removing the remaining first passivation layer and the second passivation layer on the hard mask layer to expose the predefined microgrooves; Continue etching along the bottom of the predefined microgroove to a certain depth to form a first microgroove, wherein the depth of the first microgroove is the thickness of the single crystal silicon thermocouple arm and the heating resistor; forming a third passivation layer on the sidewall of the first microgroove, and forming a sacrificial layer to fill the micro release hole and the first microgroove, and then removing the excess sacrificial layer on the front side of the single crystal silicon substrate to achieve planarization; Removing the hard mask layer on the front side of the single crystal silicon substrate, and then forming a heat-insulating dielectric layer on the surface of the single crystal silicon substrate; forming connection holes, lead pads, metal thermocouple arms, metal interconnection layers, heating resistors and ambient temperature resistors on the thermal insulation medium layer; A second microgroove of a certain depth is formed in the gas flow sensor area, wherein the etching depth is equal to the height of the heat insulation cavity; The second microgroove is released to form a heat-insulating groove and a heat-insulating cavity, and the metal thermocouple arm and the single crystal silicon thermocouple arm form a single crystal silicon-metal thermocouple pair through a metal interconnection layer.

2. The method for preparing a monolithic integrated multifunctional composite sensor according to claim 1, characterized in that: The surface of the single crystal silicon substrate is a (111) crystal plane, and the single crystal silicon-metal thermocouple is along <211> Crystal arrangement, heating resistor along <110> Crystal arrangement.

3. The method for preparing a monolithic integrated multifunctional composite sensor according to claim 1, characterized in that: The pressure reference cavity and the thermal insulation cavity are released by TMAH etching to remove part of the single crystal silicon substrate and the sacrificial layer, and the six peripheral surfaces and the upper and lower surfaces of the pressure reference cavity and the thermal insulation cavity are all (111) crystal planes.

4. The method for preparing a monolithic integrated multifunctional composite sensor according to claim 1, characterized in that: The first conductivity type and the second conductivity type are opposite conductivity types to each other, and the first conductivity type is P type or N type.

5. The method for preparing a monolithic integrated multifunctional composite sensor according to claim 1, characterized in that: The heat-insulating medium layer includes a composite film layer composed of a silicon oxide layer and a silicon nitride layer or a single-layer low-stress silicon nitride layer.

6. The method for preparing a monolithic integrated multifunctional composite sensor according to claim 1, characterized in that: The temperature sensing unit includes one of a Pt resistor, a single crystal silicon resistor and a polycrystalline silicon resistor.

7. A monolithic integrated multifunctional composite sensor, the monolithic integrated multifunctional composite sensor comprising: A single crystal silicon substrate having a first conductivity type; A gas flow sensing unit, the gas flow sensing unit comprising a single crystal silicon heating resistor, a single crystal silicon thermocouple arm-metal thermocouple pair, a thermal insulation groove, a thermal insulation medium layer and a thermal insulation cavity; the thermal insulation cavity is located directly below the single crystal silicon-metal thermocouple pair and buried inside the single crystal silicon substrate; the thermal insulation groove is located between the single crystal silicon-metal thermocouple pairs and on both sides of the single crystal silicon heating resistor; A pressure sensing unit, the pressure sensing unit comprising a piezoresistor, a pressure sensitive diaphragm and a pressure reference cavity; the piezoresistor is located above the pressure sensitive diaphragm, and the pressure sensitive resistor constitutes a Wheatstone pressure detection circuit; The pressure reference cavity is located directly below the pressure sensitive diaphragm and buried inside the single crystal silicon substrate; Temperature sensing unit; The gas flow sensing unit, the pressure sensing unit and the temperature sensing unit are integrated on the same surface of the single crystal silicon substrate.

8. The monolithic integrated multifunctional composite sensor according to claim 7, characterized in that: The single crystal silicon-metal thermocouple pair comprises a single crystal silicon thermocouple arm and a metal thermocouple arm, wherein the single crystal silicon thermocouple arm is suspended below the thermal insulation medium layer, and the metal thermocouple arm is located above the thermal insulation medium layer; the single crystal silicon thermocouple arm and the metal thermocouple arm are interconnected at the hot end through a metal via.

9. The monolithic integrated multifunctional composite sensor according to claim 7, characterized in that: The pressure reference cavity and the thermal insulation cavity have a hexagonal prism structure. The side surfaces and upper and lower surfaces of the thermal insulation cavity are (111) crystal planes, and the side surfaces and upper and lower surfaces of the pressure reference cavity are (111) crystal planes.

10. The method for preparing a monolithic integrated multifunctional composite sensor according to claim 7, characterized in that: The heat-insulating medium layer includes a composite film layer composed of a silicon oxide layer and a silicon nitride layer or a single-layer low-stress silicon nitride layer.

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