A micro variable stiffness cantilever beam structure, a preparation method and a sensor

Abstract

The application discloses a micro variable stiffness cantilever beam structure, a preparation method and a sensor, and the preparation method of the micro variable stiffness cantilever beam structure can realize accurate preparation of the variable stiffness cantilever beam structure, the stiffness can be adjusted by adjusting the size of the front and rear cantilever beam structures, the dynamic detection range and the sensitivity of the complete cantilever beam structure can be adjusted, and the problem that only the size of a single-stage cantilever beam is changed in the prior art cannot realize the double promotion of the sensitivity and the range of the optical reflection type sensor can be effectively solved. The micro variable stiffness micro cantilever beam can be miniaturized and prepared on demand through the micro-nano processing mode, the application range of the cantilever beam sensor is further widened, and a solid foundation is laid for the miniaturization of the optical reflection type sensor. The application can further expand the application range by changing the existing variable stiffness cantilever beam structure, such as preparing a needle tip structure at the top of the cantilever.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a micro variable stiffness cantilever structure, a preparation method and a sensor. BACKGROUND

[0002] Atomic force microscope (AFM) is a new surface analysis instrument with atomic level high resolution. It can not only observe the surface phenomena of conductors and semiconductor materials like scanning tunneling microscope (STM), but also can be used to observe the microstructure of non-conductor surfaces such as glass and ceramic.

[0003] Atomic force microscope is to realize surface imaging by using the interaction force between the force-sensitive probe tip and the sample. Referring to Figure 1 One end of an elastic micro-cantilever which is extremely sensitive to weak force is fixed, and the other end has a tiny tip. The tip is in light contact with the surface of the sample. Due to the extremely weak force between the atoms of the tip and the atoms of the sample surface, the micro-cantilever will have a slight elastic deformation. The laser hitting the cantilever will be deflected. Through photoelectric conversion, the optical signal is converted into an electrical signal, thereby realizing the imaging of the sample surface, and the precision can reach nanometer level.

[0004] Inspired by the detection principle of atomic force probe, the sensor based on cantilever optical detection has the following detection principle: the sensitive cantilever beam deforms elastically under the change of external environment (such as acceleration), and the laser reflected by the cantilever is deflected in turn, thereby realizing the extraction of electrical signal of external environment information through photoelectric conversion. However, the thickness of the common detection cantilever is uniform, and the overall elastic deformation cannot reach the order of magnitude difference, thereby causing that the sensor based on this detection method cannot realize the detection of dynamic range across orders of magnitude.

[0005] At present, most of the sensors based on cantilever optical reflection principle are in the stage of theoretical verification and principle prototype building, and the volume is large. Referring to Figure 2 The principle is mainly to irradiate an external light beam into the cantilever, and realize the amplification of driving displacement through multiple reflections of the cantilever and the external mirror.

[0006] In the comparative document "Research on High Precision Optical Lever Micro-accelerometer[D], Zhejiang University, 2007", the cantilever beam is composed of a rectangular steel sheet in the model system. The plane mirror is pasted on the aluminum block, and the two together constitute the mass block. The plane mirror is also part of the displacement detection system. One end of the cantilever beam is fixed on the support on the bottom plate, and the other end is the free end, pasting the mass block.

[0007] In the comparative document "On the design of piezoresistive silicon cantilevers with stress concentration regions for scanning probe microscopy applications[J] 2000", a piezoresistive cantilever with a thin bottom is prepared by a silicon epitaxy process, which can increase the detection sensitivity of the piezoresistive cantilever.

[0008] Referring to Figure 3 In the comparative document "Tapered cantilever beam type micro mass sensor design and analysis[J] 2012", the material of the cantilever beam is a high spring steel sheet, and the piezoelectric layer is PZT-5, which is prepared by a wire cutting process.

[0009] It can be seen that most of the existing variable cross-section micro cantilevers have uniform thickness, and the size mainly changes in the length and width directions. When stressed, the cantilever beam cannot realize cross-order elastic deformation, resulting in a small dynamic measurement range of the sensitive unit, and the sensitivity and detection range cannot be improved.

[0010] At present, the sensing elements based on light reflection principle are not prepared based on micro-nano processing technology, such as the existing optical lever accelerometer, the cantilever sensing unit of which has a large volume and cannot realize the miniaturization of the sensor. SUMMARY

[0011] The technical problem to be solved by the present application is to provide a preparation method of a micro variable stiffness cantilever beam which is miniaturized, high in sensitivity and adjustable in dynamic detection range.

[0012] In order to solve the above problems, the present application provides a preparation method of a micro variable stiffness cantilever beam, comprising the following steps:

[0013] S1, providing a double buried layer SOI substrate;

[0014] S2, forming a first photoresist layer on the double buried layer SOI substrate, and performing photoetching on the first photoresist layer;

[0015] S3, taking the first photoresist layer as a protective layer, etching the double buried layer SOI substrate to prepare a front-end cantilever beam structure, and removing the first photoresist layer;

[0016] S4, providing a silicon wafer, and bonding the silicon wafer with the front-end cantilever beam structure;

[0017] S5, thinning the bottom of the double buried layer SOI substrate to the silicon oxide layer below the front-end cantilever beam structure;

[0018] S6, a first silicon nitride layer is prepared on the silicon wafer, and a second silicon nitride layer is prepared on the back of the silicon oxide layer under the front cantilever beam structure;

[0019] S7, a second photoresist layer is formed on the first silicon nitride layer, and the second photoresist layer is subjected to photolithography;

[0020] S8, the second photoresist layer is used as a protective layer, and the first silicon nitride layer and the silicon wafer are etched to the silicon oxide layer on the top of the double buried layer SOI substrate to prepare a back cantilever beam structure and a cantilever beam support structure, and the second photoresist layer is removed; the rigidity of the back cantilever beam structure is higher than that of the front cantilever beam structure, and the thickness of the back cantilever beam structure is greater than that of the front cantilever beam structure;

[0021] S9, the silicon oxide layer under the front cantilever beam structure, the silicon oxide layer above the back cantilever beam structure and the remaining silicon nitride layer on the silicon wafer are removed, the release of the cantilever beam is completed, and a complete cantilever beam structure is formed;

[0022] S10, a metal reflection layer is deposited on the complete cantilever beam structure.

[0023] In an embodiment of the present application, the following steps are further included:

[0024] The rigidity of the front cantilever beam structure is adjusted by adjusting the length, thickness and width of the front cantilever beam structure, and the rigidity of the back cantilever beam structure is adjusted by adjusting the length, thickness and width of the back cantilever beam structure, so as to adjust the dynamic detection range and sensitivity of the complete cantilever beam structure.

[0025] In an embodiment of the present application, in step S4, the silicon wafer is bonded to the front cantilever beam structure by bonding glue.

[0026] In an embodiment of the present application, in step S6, a silicon nitride layer is prepared on the silicon wafer and on the back of the silicon oxide layer under the front cantilever beam structure by low-pressure chemical vapor deposition.

[0027] In an embodiment of the present application, in step S8, the second photoresist layer is used as a protective layer, and the silicon nitride layer on the silicon wafer and the silicon wafer are etched to the second silicon oxide layer of the double buried layer SOI substrate to prepare a back cantilever beam structure and a cantilever beam support structure.

[0028] In an embodiment of the present application, in step S9, the silicon oxide layer under the front cantilever beam structure, the silicon oxide layer above the back cantilever beam structure and the remaining silicon nitride layer on the silicon wafer are removed by chemical etching.

[0029] In one embodiment of the present application, the double buried layer SOI substrate comprises, from top to bottom, a first silicon oxide layer, a first single crystal silicon layer, a second silicon oxide layer, a second single crystal silicon layer, a third silicon oxide layer, and a third single crystal silicon layer.

[0030] In one embodiment of the present application, the crystal direction of the silicon wafer is <100>.

[0031] The present application also provides a micro variable stiffness cantilever structure prepared by the preparation method of the micro variable stiffness cantilever as described above.

[0032] The present application also provides a sensor comprising a laser and a laser displacement sensor, which further comprises the micro variable stiffness cantilever structure as described above, the laser being used to emit laser to the front end cantilever structure or the rear end cantilever structure, and the laser displacement sensor being used to receive the laser reflected by the front end cantilever structure or the rear end cantilever structure.

[0033] The present application has the following beneficial effects:

[0034] The preparation method of the micro variable stiffness cantilever can realize the accurate preparation of the variable stiffness cantilever structure, the stiffness can be adjusted by adjusting the size of the front and rear cantilever structures, the dynamic detection range and the sensitivity of the complete cantilever structure can be adjusted, and the problem that the sensitivity and the range of the optical reflection type sensor cannot be improved simultaneously by only changing the size of the single stage cantilever in the prior art can be effectively solved.

[0035] The micro variable stiffness micro cantilever can be miniaturized and controlled on demand by the micro-nano processing method in the present application, which further widens the application range of the cantilever sensor and lays a solid foundation for the miniaturization of the optical reflection type sensor.

[0036] The present application can further expand the application range by changing the existing variable stiffness cantilever structure, such as preparing a needle tip structure at the top of the cantilever.

[0037] The above description is only a summary of the technical solutions of the present application, in order to more clearly understand the technical means of the present application, the content of the specification can be implemented, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following preferred embodiments are described in detail, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is the principle diagram of the existing atomic force microscope;

[0039] Figure 2 is the schematic diagram of the existing sensor based on the cantilever type optical reflection principle;

[0040] Figure 3is a schematic diagram of an existing trapezoidal variable cross-section cantilever beam type micro mass sensor;

[0041] Figure 4 is a flow chart of a preparation method of a micro variable stiffness cantilever beam in the embodiment one of the present application;

[0042] Figure 5 is a schematic diagram of a preparation method of a micro variable stiffness cantilever beam in the embodiment one of the present application;

[0043] Figure 6 is a schematic diagram of a sensor in the embodiment three of the present application.

[0044] Labeling instructions:

[0045] 1, cantilever beam support structure; 2, rear end cantilever beam structure; 3, front end cantilever beam structure; 4, laser displacement sensor; 5, laser. DETAILED DESCRIPTION

[0046] The present application will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not as a limitation on the present application.

[0047] Embodiment one

[0048] As shown in Figures 4-5 , the present embodiment discloses a preparation method of a micro variable stiffness cantilever beam, comprising the following steps:

[0049] Step S1, providing a double buried layer SOI substrate; referring to Figure 5 Fig. (a), the double buried layer SOI substrate comprises first silicon oxide layer, first single crystal silicon layer, second silicon oxide layer, second single crystal silicon layer, third silicon oxide layer and third single crystal silicon layer stacked in order from top to bottom.

[0050] Step S2, forming a first photoresist layer on the double buried layer SOI substrate, and performing photoetching on the first photoresist layer; referring to Figure 5 Fig. (b).

[0051] Step S3, taking the first photoresist layer as a protective layer, etching the double buried layer SOI substrate to prepare a front end cantilever beam structure, and removing the first photoresist layer; referring to Figure 5 Fig. (c).

[0052] Step S4, providing a silicon wafer, and bonding the silicon wafer with the front end cantilever beam structure; referring to Figure 5 Fig. (d), the top layer in Fig. (d) is a silicon wafer. Specifically, the silicon wafer is bonded with the front end cantilever beam structure by bonding glue.

[0053] Step S5, thinning the bottom of the double buried layer SOI substrate to the silicon oxide layer under the front cantilever beam structure; refer to Figure 5 Fig. (e).

[0054] Step S6, preparing a first silicon nitride layer on the silicon wafer and a second silicon nitride layer on the back of the silicon oxide layer under the front cantilever beam structure; refer to Figure 5 Fig. (f). Specifically, the silicon nitride layers are prepared on the silicon wafer and the back of the silicon oxide layer under the front cantilever beam structure by low pressure chemical vapor deposition (LPCVD). Optionally, the crystal direction of the silicon wafer is <100>.

[0055] Step S7, forming a second photoresist layer on the first silicon nitride layer and performing photolithography on the second photoresist layer; refer to Figure 5 Fig. (g).

[0056] Step S8, using the second photoresist layer as a protective layer, etching the first silicon nitride layer and the silicon wafer to the silicon oxide layer on the top of the double buried layer SOI substrate to prepare a back cantilever beam structure and a cantilever beam support structure, and removing the second photoresist layer; the rigidity of the back cantilever beam structure is higher than that of the front cantilever beam structure, and the thickness of the back cantilever beam structure is greater than that of the front cantilever beam structure; refer to Figure 5 Fig. (h). Optionally, using the second photoresist layer as a protective layer, etching the silicon nitride layer on the silicon wafer and the silicon wafer to the second silicon oxide layer of the double buried layer SOI substrate by KOH solution or TMAH solution to prepare a back cantilever beam structure and a cantilever beam support structure.

[0057] Step S9, removing the silicon oxide layer under the front cantilever beam structure, the silicon oxide layer above the back cantilever beam structure, and the remaining silicon nitride layer on the silicon wafer to complete the release of the cantilever beam and form a complete cantilever beam structure; refer to Figure 5 Fig. (i). Optionally, the silicon oxide layer under the front cantilever beam structure, the silicon oxide layer above the back cantilever beam structure, and the remaining silicon nitride layer on the silicon wafer are removed by chemical etching.

[0058] Step S10, depositing a metal reflective layer on the complete cantilever beam structure to improve the light reflection efficiency; refer to Figure 6 Fig. (j).

[0059] Further, the following steps are also included:

[0060] The rigidity of the front end cantilever beam structure is adjusted by adjusting the length, thickness and width of the front end cantilever beam structure, and the rigidity of the rear end cantilever beam structure is adjusted by adjusting the length, thickness and width of the rear end cantilever beam structure, so as to adjust the dynamic detection range and sensitivity of the complete cantilever beam structure. Specifically, before the preparation of the micro variable rigidity cantilever beam, the length, thickness and width of the front end cantilever beam structure and the length, thickness and width of the rear end cantilever beam structure are calculated according to the target dynamic detection range and sensitivity of the micro variable rigidity cantilever beam, and the front end cantilever beam structure and the rear end cantilever beam structure are prepared according to the calculated length, thickness and width of the front end cantilever beam structure and the length, thickness and width of the rear end cantilever beam structure. Alternatively, the dynamic detection range and sensitivity of the complete cantilever beam structure corresponding to different lengths, thicknesses and widths of the front end cantilever beam structure and the rear end cantilever beam structure are obtained through multiple experiments.

[0061] The preparation method of the micro variable rigidity cantilever beam can realize accurate preparation of the variable rigidity cantilever beam structure, and can adjust the rigidity by adjusting the size of the front and rear cantilever beam structures, so as to adjust the dynamic detection range and sensitivity of the complete cantilever beam structure. The problem that the sensitivity and range of the optical reflection sensor cannot be improved simultaneously by only changing the size of the single-stage cantilever beam in the prior art can be effectively solved.

[0062] The micro variable rigidity cantilever beam can be miniaturized and prepared on demand by the micro-nano processing method in the application, which further widens the application range of the cantilever beam sensor and lays a solid foundation for the miniaturization of the optical reflection sensor.

[0063] The application can further expand the application range by changing the existing variable rigidity cantilever beam structure, such as preparing a needle tip structure at the top of the cantilever.

[0064] Embodiment two

[0065] The embodiment discloses a micro variable rigidity cantilever beam structure, which is prepared by the preparation method of the micro variable rigidity cantilever beam in embodiment one, and the structure can refer to Figure 6 , which comprises a cantilever beam support structure 1, a rear end cantilever beam structure 2 and a front end cantilever beam structure 3. The rigidity of the rear end cantilever beam structure 2 is higher than that of the front end cantilever beam structure 3, and the thickness of the rear end cantilever beam structure 2 is greater than that of the front end cantilever beam structure 3.

[0066] Embodiment three

[0067] Referring to ​The embodiment discloses a sensor, comprising a laser 5 and a laser displacement sensor 4, which further comprises the micro-variable stiffness cantilever beam structure in the second embodiment, the laser 5 is used for emitting laser to the front-end cantilever beam structure 3 or the rear-end cantilever beam structure 2, and the laser displacement sensor 4 is used for receiving the laser reflected by the front-end cantilever beam structure 3 or the rear-end cantilever beam structure 2. When the cantilever beam is elastically deformed due to external environmental change (such as acceleration), the laser reflected by the cantilever beam is deflected in turn, so that the electrical signal extraction of external environmental information can be realized through photoelectric conversion.

[0068] The above embodiments are only preferred embodiments for fully illustrating the present application, and the protection scope of the present application is not limited thereto. Any equivalent replacement or transformation made by the skilled in the art on the basis of the present application is within the protection scope of the present application. The protection scope of the present application is subject to the claims.

Claims

1. A method of fabricating a micro variable stiffness cantilever beam, characterized by, The method comprises the following steps: S1, providing a double buried layer SOI substrate; S2, forming a first photoresist layer on the double buried layer SOI substrate, and performing photoetching on the first photoresist layer; S3, taking the first photoresist layer as a protective layer, etching the double buried layer SOI substrate to prepare a front end cantilever beam structure, and removing the first photoresist layer; S4, providing a silicon wafer, and bonding the silicon wafer with the front end cantilever beam structure; S5, thinning the bottom of the double buried layer SOI substrate to a silicon oxide layer below the front end cantilever beam structure; S6, preparing a first silicon nitride layer on the silicon wafer, and preparing a second silicon nitride layer on the back of the silicon oxide layer below the front end cantilever beam structure; S7, forming a second photoresist layer on the first silicon nitride layer, and performing photoetching on the second photoresist layer; S8, taking the second photoresist layer as a protective layer, etching the first silicon nitride layer and the silicon wafer to the silicon oxide layer on the top of the double buried layer SOI substrate to prepare a rear end cantilever beam structure and a cantilever beam support structure, and removing the second photoresist layer; the rigidity of the rear end cantilever beam structure is higher than that of the front end cantilever beam structure, and the thickness of the rear end cantilever beam structure is greater than that of the front end cantilever beam structure; S9, removing the silicon oxide layer below the front end cantilever beam structure, the silicon oxide layer above the rear end cantilever beam structure, and the remaining silicon nitride layer on the silicon wafer, completing the release of the cantilever beam, and forming a complete cantilever beam structure; S10, depositing a metal reflecting layer on the complete cantilever beam structure.

2. The method of claim 1, wherein the micro variable stiffness cantilever beam is prepared by the steps of: The method further comprises the following steps: The rigidity of the front end cantilever beam structure is adjusted by adjusting the length, thickness and width of the front end cantilever beam structure, and the rigidity of the rear end cantilever beam structure is adjusted by adjusting the length, thickness and width of the rear end cantilever beam structure, so as to adjust the dynamic detection range and sensitivity of the complete cantilever beam structure.

3. The method for fabricating a micro-variable stiffness cantilever beam as described in claim 1, characterized in that, In step S4, the silicon wafer is bonded with the front end cantilever beam structure by bonding glue.

4. The method for fabricating a micro-variable stiffness cantilever beam as described in claim 1, characterized in that, In step S6, the silicon nitride layer is prepared on the silicon wafer and the back of the silicon oxide layer below the front end cantilever beam structure by low pressure chemical vapor deposition method.

5. The method for preparing a micro-variable stiffness cantilever beam as described in claim 1, characterized in that, In step S8, the silicon nitride layer on the silicon wafer and the silicon wafer are etched to the second silicon oxide layer of the double buried layer SOI substrate by taking the second photoresist layer as a protective layer and using KOH solution or TMAH solution to prepare a rear end cantilever beam structure and a cantilever beam support structure.

6. The method for fabricating a micro-variable stiffness cantilever beam as described in claim 1, characterized in that, In step S9, the silicon oxide layer below the front end cantilever beam structure, the silicon oxide layer above the rear end cantilever beam structure, and the remaining silicon nitride layer on the silicon wafer are removed by chemical etching.

7. The method for fabricating a micro-variable stiffness cantilever beam as described in claim 1, characterized in that, The double buried layer SOI substrate comprises, from top to bottom, a first silicon oxide layer, a first single crystal silicon layer, a second silicon oxide layer, a second single crystal silicon layer, a third silicon oxide layer and a third single crystal silicon layer.

8. The method for fabricating a micro-variable stiffness cantilever beam as described in claim 1, characterized in that, The crystal direction of the silicon wafer is <100>.

9. A micro variable stiffness cantilever beam structure, characterized by, The micro variable stiffness cantilever beam is prepared by the method of any one of claims 1-8.

10. A sensor comprising a laser and a laser displacement sensor, characterized in that, Also included is the micro variable stiffness cantilever beam structure of claim 9, the laser for emitting laser light to the front or back end cantilever beam structure, the laser displacement sensor for receiving the laser light reflected by the front or back end cantilever beam structure.

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