A MEMS gas sensor device and a preparation method thereof

Abstract

Relating to the field of semiconductor gas detection technology, especially relating to a MEMS gas sensor device and a preparation method thereof. A MEMS gas sensor device comprises a first substrate, a second substrate and a third substrate. The third substrate is arranged between the first substrate and the second substrate. The first substrate, the second substrate and the third substrate enclose a front cavity and a back cavity. A heating electrode is arranged on the front surface of the first substrate. A test electrode is arranged on the front surface of the second substrate. A support layer is arranged on the front surface of the third substrate. A heating element and a test element are arranged on the support layer. A gas-sensitive element is formed on the upper surfaces of the support layer, the heating element and the test element. The present invention prepares a MEMS gas sensor device through a series of preparation methods, solves the problems of low mechanical strength and high power consumption of a semiconductor metal oxide MEMS gas sensor, and saves the manufacturing cost and reduces the volume of the device.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor gas detection technology, and in particular to a MEMS gas sensor device and a preparation method thereof. Background Art

[0002] In the prior art, semiconductor metal oxide MEMS gas sensors have developed into the most frequently used sensors. Traditionally, semiconductor metal oxides require a micro-heating platform to allow sensitive materials to work at a suitable temperature. Micro-heating platforms can be divided into suspended membrane type and closed membrane type according to different types of supporting membrane structures. The suspended membrane type micro-heating platform is composed of silicon substrate, supporting layer, heating layer, insulating layer and sensitive layer from bottom to top. The typical suspended membrane type structure includes silicon substrate, electrode, cavity, supporting layer and supporting beam. The supporting layer needs to be supported by the supporting beam, but the corner position of the supporting beam is prone to large deformation, which makes the supporting beam easy to break during repeated work. The closed membrane type micro-heating platform is composed of silicon substrate, supporting layer, heating layer, insulating layer and sensitive layer from bottom to top. The closed membrane type micro-heating platform has stronger mechanical strength, but the closed membrane type micro-heating platform has stronger heat dissipation effect and greater power loss.

[0003] In order to obtain a semiconductor metal oxide MEMS gas sensor with stable operation and lower power loss, the researchers have proposed many solutions, such as changing the structure of the supporting layer and changing the heating wire structure, such as changing the supporting layer to a circular suspended membrane structure or a double-arm suspended membrane structure, and changing the heating wire structure to an S-shaped heating wire or a circular heating wire.

[0004] Typical suspended membrane MEMS gas sensors require the support of a support beam, so they have low mechanical strength, are easy to break, and have low stability. The manufacturing process from silicon wafers to gas sensors is complex, and the yield of finished products is low. The front etching method or the back etching method is used to make the cavity, which requires the production of additional masks, which invisibly increases the cost. In addition, the front etching method is used to make the cavity, and the etching angle must be considered to avoid leaving silicon islands under the cantilever arm, which increases the area of ​​heat conduction and thus increases power consumption. Summary of the invention

[0005] In order to solve the problems of low mechanical strength and high power consumption of semiconductor metal oxide MEMS gas sensors, the present invention provides a MEMS gas sensor device and a preparation method.

[0006] In a first aspect, a MEMS gas sensor device provided by the present invention includes a substrate, which is composed of a first substrate, a second substrate, and a third substrate. The third substrate is arranged between the first substrate and the second substrate. The first substrate, the second substrate, and the third substrate enclose a front cavity and a back cavity. A heating electrode is provided on the front surface of the first substrate, a test electrode is provided on the front surface of the second substrate, and a functional element is provided on the front surface of the third substrate.

[0007] Further, the functional element includes a heating element, a test element, and a gas-sensitive element. The heating element is connected to the heating electrode, and the test element is connected to the test electrode.

[0008] Further, a support layer is deposited on the front surface of the third substrate. The heating element and the test element are arranged on the support layer, and the heating element and the test element are surrounded by the first substrate and the second substrate in the front cavity.

[0009] Further, the support layer includes a two-layer composite structure composed of silicon oxide and silicon nitride.

[0010] Further, the heating element and the test element are in a convex shape. The heating element is patterned on the upper surface of the support layer, the test element is patterned on the upper surface of the support layer, and the gas-sensitive element is formed on the upper surfaces of the support layer, the heating element, and the test element.

[0011] Further, the cross-section of the back cavity is any one or a combination of a trapezoid, a triangle, a rectangle, and a square.

[0012] In a second aspect, a method for manufacturing a MEMS gas sensor provided by the present invention includes the following steps:

[0013] S1. Provide a substrate, and clean and spin-dry the surface of the substrate;

[0014] S2. Etch the front surface of the substrate by using an ICP-RIE inductively coupled plasma reactive ion etching method;

[0015] S3. Use PECVD and LPCVD methods to alternately deposit a silicon oxide thin film and a silicon nitride thin film on the front surface of the substrate to form a support layer;

[0016] S4. Use a magnetron sputtering method and a lift-off method to fabricate a heating element on the support layer in sequence, and use a magnetron sputtering technique and a lift-off method to fabricate a test element on the support layer in sequence;

[0017] S5. Etch the back surface of the substrate by using a deep silicon etching method to obtain a back cavity;

[0018] S6. Fabricate a gas sensor element on the heating element and the test element by magnetron sputtering method.

[0019] Further, the etching depth of the front side is 5 - 200 um, the thickness of the silicon oxide thin film is 500 - 700 nm, the thickness of the silicon nitride thin film is 1300 - 1500 nm, the thickness of the heating element is 100 - 500 nm, the thickness of the test element is 100 - 300 nm, and the depth of the back cavity is 300 - 600 um.

[0020] Further, the material of the heating element is platinum, the material of the test element is platinum, and the material of the gas sensor element is SnO2.

[0021] Further, the substrate is any one or combination of silicon and silicon on insulator.

[0022] In summary, the present invention has the following beneficial technical effects:

[0023] 1. A MEMS gas sensor device of the present invention includes etching two cavities on the front and back sides of a silicon substrate. The cavity on the front side serves as the cavity of the micro - hot - plate, reducing the heat dissipated by thermal convection. The cavity on the back side reduces the heat dissipated by thermal conduction, enabling more heat to be concentrated on the support layer of the micro - hot - plate, reducing the power of the gas sensor. At the same time, using the front - side etching method to fabricate the cavity does not require considering the etching angle, avoiding the problem of leaving silicon islands and increasing the heat - conduction area, thus reducing the power of the bulk sensor.

[0024] 2. In a MEMS gas sensor device of the present invention, the support platform at the corner position of the micro - hot - plate is directly connected to the substrate, increasing the mechanical strength of the gas sensor and ensuring the stability of the gas sensor during operation.

[0025] 3. A method for fabricating a MEMS gas sensor of the present invention includes using deep silicon etching process and inductively coupled plasma etching process to fabricate the back cavity and the front cavity, which can use one mask, saving the manufacturing cost. Making the electrodes of the heating element and the test element on the same plane can effectively reduce the number of electrodes, enabling the heating element and the test element to share one electrode, which can greatly reduce the volume of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a typical structural diagram of the suspended - membrane type MEMS gas sensor of Embodiment 1 of the present invention;

[0027] Figure 2 is a typical structural diagram of the closed - membrane type MEMS gas sensor of Embodiment 1 of the present invention;

[0028] Figure 3Schematic diagram of a typical closed - film - type micro - hot - plate in the prior art of Embodiment 1 of the present invention;

[0029] Figure 4 Main structure of the existing heating wire in Embodiment 1 of the present invention;

[0030] Figure 5 Schematic diagram of a MEMS gas sensor device in Embodiment 1 of the present invention;

[0031] Figure 6 The first variant structure of the MEMS gas sensor device in Embodiment 1 of the present invention;

[0032] Figure 7 The second variant structure of the MEMS gas sensor device in Embodiment 1 of the present invention;

[0033] Figure 8 The third variant structure of the MEMS gas sensor device in Embodiment 1 of the present invention;

[0034] Figure 9 Simulation comparison diagram of traditional - structure and new - structure micro - hot - plate gas sensors in Embodiment 1 of the present invention;

[0035] Figure 10 Schematic diagram of displacement distribution of traditional micro - hot - plate gas sensor and new - structure micro - hot - plate gas sensor in Embodiment 1 of the present invention;

[0036] Figure 11 Process verification diagram of the support film in Embodiment 1 of the present invention;

[0037] Figure 12 Flowchart of a method for fabricating a MEMS gas sensor in Embodiment 2 of the present invention.

[0038] Among them, 1. Suspended - film type; 101. Substrate; 102. Electrode; 103. Cavity; 104. Support layer; 105. Support beam; 2. Closed model; 201. Silicon substrate; 202. Silicon nitride; 203. Silicon oxide; 204. Platinum; 3. MEMS gas sensor device; 301. First substrate; 302. Second substrate; 303. Third substrate; 304. Front - side cavity; 305. Back - side cavity; 306. Heating electrode; 307. Test electrode; 308. Heating element; 309. Test element; 310. Gas - sensitive element. Detailed implementation manners

[0039] The present invention will be further described in detail below with reference to the accompanying drawings.

[0040] Embodiment 1

[0041] Refer to Figure 1, the suspended film type 1 in the prior art includes a silicon substrate 101, an electrode 102, a cavity 103, a support beam 105 and a support layer 104. The support layer 104 needs to be supported by the support beam 105. However, large deformations are likely to occur at the corner positions of the support beam 105, making the support beam 105 prone to breakage during repeated operation. Refer to Figure 2 , there are also two common cantilever film type structures for the support layer of the suspended film type.

[0042] Refer to Figure 3 , in the prior art, the micro hot platform of the typical closed film type 2 includes a silicon substrate, a support layer, a heating layer, an insulating layer and a sensitive layer from bottom to top, including a silicon substrate 201, silicon nitride 202, silicon oxide 203, and platinum 204.

[0043] Refer to Figure 4 , the main structures of the heating wire also include an S-shaped heating wire structure or a circular heating wire structure.

[0044] Refer to Figure 5 , a MEMS gas sensor device 3 of this embodiment includes a substrate, which is composed of a first substrate 301, a second substrate 302 and a third substrate 303. The third substrate 303 is arranged between the first substrate 301 and the second substrate 302. The first substrate 301, the second substrate 302 and the third substrate 303 enclose a front cavity 304 and a back cavity 305. A heating electrode 306 is provided on the front surface of the first substrate 301, a test electrode 307 is provided on the front surface of the second substrate 302, and a functional element is provided on the front surface of the third substrate 303.

[0045] The functional element includes a heating element 308, a test element 309 and a gas-sensitive element 310. The heating element 308 is connected to the heating electrode 306, and the test element 309 is connected to the test electrode 307.

[0046] A support layer is deposited on the front surface of the third substrate 303. The heating element 308 and the test element 309 are arranged on the support layer, and the heating element 308 and the test element 309 are surrounded by the first substrate 301 and the second substrate 302 in the front cavity 304.

[0047] The support layer includes a two-layer composite structure composed of silicon oxide and silicon nitride or a three-layer composite structure composed of alternating silicon oxide and silicon nitride. The support layer can also use polyimide materials.

[0048] The heating element 308 and the test element 309 are convex. The heating element 308 is patterned on the upper surface of the support layer, the test element 309 is patterned on the upper surface of the support layer, and the gas-sensitive element 310 is formed on the upper surfaces of the support layer, the heating element 308 and the test element 309.

[0049] Reference Figure 6 and Figure 7 The heating element 308 and the test element 309 are convex. The top view shape of the heating element 308 includes various shapes such as S-shaped, circular, interdigitated or elliptical structures, and the shape of the test element 309 includes various shapes such as interdigitated electrodes, single electrodes or three-electrode structures.

[0050] The cross-sectional shape of the back cavity is any one or a combination of a trapezoid, a triangle, a rectangle and a square.

[0051] The depth of the back cavity is 300-600um, and the depth of the front cavity is 5-200um.

[0052] Reference Figure 7 and Figure 8 This embodiment also includes a similar structure, wherein the back cavity includes a cavity structure that is through-through from front to back, through-through on one side, or not through-through from front to back, and the front cavity includes a cavity structure that is through-through from front to back, through-through on one side, or not through-through from front to back. It can also be an approximate variant structure. This embodiment can also be any combination of the cross-sectional shapes and structures of the back cavity and the front cavity.

[0053] As described in this embodiment, the typical suspended membrane type MEMS gas sensor needs the support of a supporting beam, so it has low mechanical strength, is easy to break, and has low stability. The manufacturing process from silicon wafer to gas sensor is complicated and the yield of the finished product is low. The front etching method or the back etching method is used to make the cavity, which requires the production of additional masks, which invisibly increases the cost. In addition, the front etching method is used to make the cavity, and the etching angle must be considered to avoid leaving silicon islands under the cantilever arm, which increases the area of ​​heat conduction and thus increases power consumption.

[0054] The present embodiment proposes a MEMS gas sensor device, which proposes a semiconductor metal oxide MEMS gas sensor structure with strong stability and low power consumption, and solves the problems of low mechanical strength and high power consumption of semiconductor metal oxide MEMS gas sensors. Figure 9 The simulation comparison of the traditional structure on the left and the new structure micro-hot plate gas sensor on the right shows that when a 5V voltage is applied, the new structure micro-hot plate gas sensor has a higher temperature, less heat loss, and lower power consumption. Figure 10 , The left figure shows the displacement distribution of the traditional micro-hotplate gas sensor and the new structure micro-hotplate gas sensor. The displacement generated by the new structure is smaller. Figure 11 From the support film process verification diagram, it can be seen that the structure of the novel micro-hot plate gas sensor of this embodiment is more stable.

[0055] Example 2

[0056] Referring to Figure 12 , a method for fabricating a MEMS gas sensor according to this embodiment includes the following steps:

[0057] S1. Provide a substrate, and clean and spin-dry the surface of the substrate;

[0058] S2. Use the ICP-RIE inductively coupled plasma reactive ion etching method to etch the front side of the substrate, and the etching depth of the front side is 5 - 200 um;

[0059] S3. Use the PECVD and LPCVD methods to alternately deposit a silicon oxide thin film S31 and a silicon nitride thin film on the front side of the substrate to form a support layer S32. The thickness of the silicon oxide thin film is 500 - 700 nm, and the thickness of the silicon nitride thin film is 1300 - 1500 nm;

[0060] S4. Use the magnetron sputtering method and the lift-off method to fabricate a heating element on the support layer in sequence, and use the magnetron sputtering method and the lift-off method to fabricate a test element on the support layer in sequence. The thickness of the heating element is 100 - 500 nm, and the thickness of the test element is 100 - 300 nm;

[0061] S5. Use the deep silicon etching method to etch the back side of the substrate to obtain a back cavity, and the depth of the back cavity is 300 - 600 um;

[0062] S6. Use the magnetron sputtering method to fabricate a gas-sensitive element on the heating element and the test element.

[0063] The heating element is any one or a combination of gold, platinum, tungsten, or polysilicon. The test element is any one or a combination of gold, platinum, or palladium. The gas-sensitive element is any one or a combination of SnO2 or ZnO.

[0064] The substrate is any one or a combination of silicon and silicon-on-insulator.

[0065] In this embodiment, the deep silicon etching process and the inductively coupled plasma etching process are used to fabricate the back cavity and the front cavity, and one mask can be used, which saves the manufacturing cost. Making the electrodes of the heating element and the test element on the same plane can effectively reduce the number of electrodes, so that the heating element and the test element share one electrode, which can greatly reduce the volume of the device.

[0066] The above are all the preferred embodiments of the present invention. The protection scope of the present invention is not limited hereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present invention shall be covered within the protection scope of the present invention.

Claims

1. A MEMS gas sensor device, characterized in that: The invention comprises a substrate, wherein the substrate is composed of a first substrate, a second substrate and a third substrate, wherein the third substrate is arranged between the first substrate and the second substrate, wherein the first substrate, the second substrate and the third substrate enclose a front cavity and a back cavity, wherein a heating electrode is arranged on the front of the first substrate, a test electrode is arranged on the front of the second substrate, and a functional element is arranged on the front of the third substrate, wherein the functional element comprises a heating element, a test element and a gas-sensitive element, wherein the heating element is connected to the heating electrode, and the test element is connected to the test electrode, wherein the heating element and the test element are in a convex shape, wherein the heating element is patterned on the upper surface of the supporting layer, wherein the test element is patterned on the upper surface of the supporting layer, wherein the gas-sensitive element is formed on the upper surfaces of the supporting layer, the heating element and the test element, wherein a supporting layer is deposited on the front of the third substrate, wherein the heating element and the test element are arranged on the supporting layer, wherein the heating element and the test element are surrounded by the first substrate and the second substrate in the front cavity, wherein the supporting layer comprises a two-layer composite structure composed of silicon oxide and silicon nitride, wherein the depth of the front cavity is 5-200 um, and the depth of the back cavity is 300-600 um.

2. A MEMS gas sensor device according to claim 1, characterized in that: The cross section of the back cavity is any one or a combination of a trapezoid, a triangle, a rectangle and a square.

3. A method for preparing a MEMS gas sensor device as claimed in claim 1 or 2, characterized in that: The following steps are involved: S1. Providing a substrate, cleaning and drying the surface of the substrate; S2. The front side of the substrate is etched by ICP-RIE inductively coupled plasma reactive ion etching method; S3. Using PECVD and LPCVD methods, silicon oxide films and silicon nitride films are alternately deposited on the front side of the substrate to form a support layer; S4. Sequentially using a magnetron sputtering method and a stripping method to produce a heating element on the support layer, and sequentially using a magnetron sputtering method and a stripping method to produce a test element on the support layer; S5. Etching the back side of the substrate by a deep silicon etching method to obtain a back side cavity; S6. Using magnetron sputtering method to make gas sensing elements on the heating element and the testing element.

4. The method for preparing a MEMS gas sensor device according to claim 3, characterized in that: The thickness of the silicon oxide film is 500-700 nm, the thickness of the silicon nitride film is 1300-1500 nm, the thickness of the heating element is 100-500 nm, and the thickness of the testing element is 100-300 nm.

5. The method for preparing a MEMS gas sensor device according to claim 3, characterized in that: The material of the heating element is platinum, the material of the testing element is platinum, and the material of the gas sensor is SnO2.

6. The method for preparing a MEMS gas sensor device according to claim 3, characterized in that: The substrate is silicon on insulator.

Images