Optical micro-electro-mechanical structure and method for manufacturing same

Abstract

The application provides an optical micro-electro-mechanical structure and a manufacturing method thereof. The structure comprises a detection mass, a plurality of lower-layer support ropes, a plurality of upper-layer support ropes, a suspended waveguide and an optical resonant cavity. The detection mass comprises a bottom layer, an intermediate layer and a top layer which are stacked in sequence in the Z direction. The plurality of lower-layer support ropes are distributed on both sides of the detection mass in the X direction and connected with the bottom layer. The plurality of upper-layer support ropes are distributed on both sides of the detection mass in the X direction and connected with the top layer. The suspended waveguide is located on one side of the detection mass in the Y direction. The optical resonant cavity comprises a first optical crystal strip connected with the detection mass and a second optical crystal strip connected with the suspended waveguide. The detection mass in the optical micro-electro-mechanical structure is a three-layer structure, which can greatly increase the mass of the detection mass and reduce the influence caused by thermal-mechanical noise. The double-layer support ropes can enhance the structural stability. The manufacturing method has high compatibility and can realize more accurate patterns.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) technology, and relates to an optical MEMS structure and its fabrication method. Background Technology

[0002] Over the past few decades, Microelectromechanical Systems (MEMS) technology has been considered one of the most promising technologies of our time and has been widely used in various fields. MEMS technology, by combining silicon-based microelectronics with micromachining, has revolutionized research and industry. Among these, optical MEMS (optoMEMS) sensors integrate optical elements into traditional MEMS technology, combining the advantages of MEMS sensors with the characteristics of optical detection.

[0003] Compared to traditional MEMS sensors, optoMEMS sensors possess irreplaceable characteristics, including fast response, high accuracy, and immunity to electromagnetic interference (EMI). Therefore, optoMEMS sensors have been extensively studied in a wide range of applications, including but not limited to gyroscopes, sensors, and accelerometers. However, due to the miniaturization of optoMEMS devices, noise management has become one of the most critical factors in improving the performance of optoMEMS sensors.

[0004] Thermomechanical noise plays a dominant role in limiting the performance of opto-MEMS sensors. Therefore, reducing the mechanical and thermal noise in opto-MEMS sensors is crucial for achieving high-sensitivity opto-MEMS systems. Notably, introducing a large-mass detection mass in an opto-MEMS system can significantly reduce thermal noise levels. Furthermore, by increasing the size of the measurement mass, extremely high mechanical-thermal noise resolution can be maintained even at lower mechanical quality factors (Q), increasing the flexibility of opto-MEMS device design and fabrication and reducing process requirements. Adding a measurement mass allows for packaging at atmospheric pressure, reducing the complexity of commonly used low-pressure packaging, and increasing yield as lower mechanical quality factors become more demanding.

[0005] Fabrication of suspended detection mass blocks involves photolithography, multi-purpose wet etching, plasma etching, and micromachining techniques. Typically, a simple fabrication method tends to increase the mass block's size in the XY direction to increase its mass, but this method is inefficient, time-consuming, and lacks accuracy. Furthermore, increasing the area of ​​the detection mass block in the XY direction can also reduce the stability of the photoelectric sensor, thus affecting its performance.

[0006] Therefore, how to provide an optical microelectromechanical structure with a large mass detection block and its fabrication method, so as to improve sensor performance through the large mass detection block and improve the manufacturing process compatibility of the large mass detection block to facilitate large-scale manufacturing, has become an important technical problem that needs to be solved by those skilled in the art.

[0007] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0008] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an optical microelectromechanical structure and its fabrication method, which solves the problems of low sensitivity, poor stability, complex fabrication process, and low precision of existing optical microelectromechanical structures.

[0009] To achieve the above and other related objectives, the present invention provides an optical microelectromechanical structure, comprising:

[0010] The quality block to be inspected includes a bottom layer, a middle layer, and a top layer stacked sequentially in the Z direction;

[0011] Multiple lower-level support ropes are distributed on both sides of the detection mass block in the X direction and connected to the bottom layer;

[0012] Multiple upper-level support ropes are distributed on both sides of the detection mass block in the X direction and connected to the top layer;

[0013] A suspended waveguide is located on one side of the detection mass block in the Y direction;

[0014] An optical resonant cavity includes a first optical crystal strip and a second optical crystal strip arranged and spaced apart along the Y direction. The first optical crystal strip is connected to the detection mass block, and the second optical crystal strip is connected to the suspended waveguide. The X direction, the Y direction, and the Z direction are perpendicular to each other.

[0015] Optionally, the length of the detection mass block along the X direction ranges from 40 micrometers to 200 micrometers, and the width along the Y direction ranges from 40 micrometers to 200 micrometers.

[0016] Optionally, the thickness of the bottom layer along the Z direction ranges from 100 nanometers to 300 nanometers, the thickness of the middle layer along the Z direction ranges from 300 micrometers to 500 micrometers, and the thickness of the top layer along the Z direction ranges from 100 nanometers to 300 nanometers.

[0017] Optionally, the bottom layer includes a silicon nitride layer, the middle layer includes a silicon layer, and the top layer includes a silicon nitride layer.

[0018] Optionally, the lower support rope is a straight line extending in the X direction, and the upper support rope is a straight line extending in the X direction.

[0019] Optionally, the number of lower support ropes on each side of the detection mass block in the X direction is 30 to 5000, and the number of upper support ropes on each side of the detection mass block in the X direction is 30 to 5000.

[0020] Optionally, the length of the lower support rope in the X direction ranges from 300 mm to 700 mm, the width in the Y direction ranges from 300 nm to 500 nm, and the thickness in the Z direction ranges from 100 nm to 300 nm; the length of the upper support rope in the X direction ranges from 300 mm to 700 mm, the width in the Y direction ranges from 300 nm to 500 nm, and the thickness in the Z direction ranges from 100 nm to 300 nm.

[0021] Optionally, the optical resonant cavity includes a defect region and a mirror region, with the mirror region distributed on both sides of the defect region in the X direction.

[0022] Optionally, the mirror area is also distributed on both sides of the defect area in the Y direction.

[0023] Optionally, the optical microelectromechanical structure is applied to an accelerometer or a gyroscope.

[0024] This invention also provides a method for fabricating an optical microelectromechanical structure, comprising the following steps:

[0025] A laminated structure is provided, the laminated structure comprising a first material layer, a second material layer and a third material layer stacked sequentially in the Z direction;

[0026] The third material layer is graphically represented to obtain the top layer of the detection mass block, and a suspended waveguide, an optical resonant cavity, and multiple upper support tethers are obtained. The suspended waveguide is located on one side of the detection mass block in the Y direction, and the multiple upper support tethers are distributed on both sides of the detection mass block in the X direction and connected to the top layer. The optical resonant cavity includes a first optical crystal strip and a second optical crystal strip arranged and spaced apart along the Y direction. The first optical crystal strip is connected to the detection mass block, and the second optical crystal strip is connected to the suspended waveguide. The X direction, the Y direction, and the Z direction are perpendicular to each other.

[0027] The first material layer is graphically represented to obtain the bottom layer of the detection mass block, and multiple lower support ropes are obtained. The lower support ropes and the upper support ropes are positioned at the same vertical projection position on the XY plane.

[0028] The second material layer is etched from the side of the laminated structure having the first material layer to remove the portion of the second material layer not covered by the lower support tether;

[0029] The portion of the second material layer located between the lower support rope and the upper support rope is removed, and the portion of the second material layer located between the top layer and the bottom layer that is not removed is used as the intermediate layer of the detection mass block.

[0030] Optionally, the first material layer includes a silicon nitride layer, the second material layer includes a silicon layer, and the third material layer includes a silicon nitride layer.

[0031] Optionally, the method for patterning the third material layer includes inductively coupled plasma etching (ICP-C), with the etching gas comprising a mixture of C4F8 and SF6; the method for patterning the first material layer includes ICP-C, with the etching gas comprising a mixture of C4F8 and SF6; the method for etching the second material layer from the side of the stacked structure having the first material layer to remove the portion of the second material layer not obscured by the lower support tether includes Bosch etching, with the etching gas comprising alternating use of C4F8 and SF6; the method for removing the portion of the second material layer located between the lower support tether and the upper support tether includes isotropic dry etching, with the etching gas comprising XeF2.

[0032] As described above, the optical microelectromechanical structure (MEMS) of the present invention includes a detection mass block, multiple lower-layer support tethers, multiple upper-layer support tethers, a levitating waveguide, and an optical resonant cavity. The detection mass block comprises a bottom layer, a middle layer, and a top layer stacked sequentially in the Z-direction. Multiple lower-layer support tethers are distributed on both sides of the detection mass block in the X-direction and connected to the bottom layer. Multiple upper-layer support tethers are distributed on both sides of the detection mass block in the X-direction and connected to the top layer. The levitating waveguide is located on one side of the detection mass block in the Y-direction. The optical resonant cavity includes a first optical crystal strip and a second optical crystal strip arranged and spaced apart along the Y-direction. The first optical crystal strip is connected to the detection mass block, and the second optical crystal strip is connected to the levitating waveguide. The detection mass block of the optical MEMS of the present invention has a three-layer structure. The size of the detection mass block is increased in the Z-direction, which greatly increases the mass of the detection mass block while maintaining a fixed area. This reduces the impact of thermo-mechanical noise and improves the performance and sensitivity of the optical MEMS. Furthermore, as the size of the detection mass increases in the XY direction, the single-layer nano-tether system is prone to losing its stability, leading to interference from various mechanical modes. This invention enhances stability through multiple lower and upper support tethers, which is beneficial for single-mode operation. Moreover, the lower and upper support tethers, combined with the detection mass, allow for flexible adjustment of the mechanical resonant frequency from hundreds to tens of thousands of hertz. The fabrication method of the optical microelectromechanical structure of this invention is compatible with CMOS processes, facilitates large-scale manufacturing, and enables more precise patterning. Attached Figure Description

[0033] Figure 1 The image shown is a top view of the optical microelectromechanical structure of the present invention.

[0034] Figure 2 The image shown is a front view of the optical microelectromechanical structure of the present invention.

[0035] Figure 3 The diagram shown is an enlarged schematic of the optical resonant cavity in the optical microelectromechanical structure of the present invention.

[0036] Figure 4 The diagram shows the process flow of the fabrication method of the optical microelectromechanical structure of the present invention.

[0037] Figure 5 The diagram shows a stacked structure provided by the method for fabricating the optical microelectromechanical structure of the present invention.

[0038] Figure 6 The diagram shown illustrates the structure obtained after forming a photoresist layer on the top surface of the third material layer, which is a method for fabricating the optical microelectromechanical structure of the present invention.

[0039] Figure 7The diagram shows a method for fabricating an optical microelectromechanical structure according to the present invention, in which a designated area of ​​the photoresist layer on the top surface of the third material layer is exposed.

[0040] Figure 8 The diagram shown illustrates the structure obtained after developing the photoresist layer on the top surface of the third material layer, as part of the fabrication method of the optical microelectromechanical structure of the present invention.

[0041] Figure 9 The diagram shown is a schematic of the structure obtained after transferring the pattern to the third material layer in the fabrication method of the optical microelectromechanical structure of the present invention.

[0042] Figure 10 The diagram shown illustrates the structure obtained after forming a photoresist layer on the surface of the first material layer, according to the fabrication method of the optical microelectromechanical structure of the present invention.

[0043] Figure 11 The diagram shown illustrates the structure obtained after developing the photoresist layer on the surface of the first material layer, as described in the fabrication method of the optical microelectromechanical structure of the present invention.

[0044] Figure 12 The diagram shown is a schematic of the structure obtained after transferring a pattern into the first material layer, which is a method for fabricating the optical microelectromechanical structure of the present invention.

[0045] Figure 13 The diagram shown illustrates a method for fabricating the optical microelectromechanical structure of the present invention, which involves etching a second material layer from one side of a stacked structure having a first material layer.

[0046] Figure 14 The diagram shown is a schematic of the structure obtained after removing the portion of the second material layer located between the lower and upper support ropes, which is the fabrication method of the optical microelectromechanical structure of the present invention.

[0047] Component designation explanation

[0048] 1. Quality Inspection Block

[0049] 101 Bottom Layer

[0050] 102 Intermediate Layer

[0051] 103 Top Floor

[0052] 104 gap

[0053] 2 Lower layer support ropes

[0054] 3. Upper support ropes

[0055] 4. Suspended waveguide

[0056] 5 Optical resonant cavity

[0057] 501 First Optical Crystal Strip

[0058] 502 Second Optical Crystal Strip

[0059] 6 cantilever

[0060] 7 Photoresist layer

[0061] 8 Photomask template

[0062] 9. Photoresist layer

[0063] 10 Photomask template

[0064] A Defect Area

[0065] 1a First material layer

[0066] 1b Second material layer

[0067] 1c Third material layer Detailed Implementation

[0068] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0069] Please see Figures 1 to 14 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0070] Example 1

[0071] This embodiment provides an optical microelectromechanical structure. Please refer to [link / reference]. Figure 1 and Figure 2The images show a top view and a front view of the optical microelectromechanical structure, respectively. The structure includes a detection mass block 1, multiple lower support tethers 2, multiple upper support tethers 3, a suspended waveguide 4, and an optical resonant cavity 5. The detection mass block 1 comprises a bottom layer 101, a middle layer 102, and a top layer 103 stacked sequentially in the Z direction. Multiple lower support tethers 2 are distributed on both sides of the detection mass block 1 in the X direction and connected to the bottom layer 102. Multiple upper support tethers 3 are distributed on both sides of the detection mass block 1 in the X direction and connected to the top layer 103. The suspended waveguide 4 is located on one side of the detection mass block 1 in the Y direction. The optical resonant cavity 5 includes a first optical crystal strip 501 and a second optical crystal strip 502 arranged and spaced apart along the Y direction. The first optical crystal strip 501 is connected to the detection mass block 1, and the second optical crystal strip 502 is connected to the suspended waveguide 4. The X, Y, and Z directions are perpendicular to each other.

[0072] As an example, the bottom layer 101 includes a silicon nitride layer, the middle layer 102 includes a silicon layer, and the top layer 103 includes a silicon nitride layer. In this embodiment, the detection mass block 1 is generally rectangular and suspended by high-stress silicon nitride nanowires. Here, high-stress silicon nitride refers to silicon nitride material with a stress greater than 1 GPa. Using high-stress silicon nitride as the material for the support tether can improve the mass factor Q of the optomechanical sensing structure, thereby reducing the impact of noise and improving device performance. Simultaneously, as the mass block in the optomechanical sensing structure increases, the mechanical resonant frequency of the optomechanical sensing structure decreases. By using high-stress silicon nitride support tethers, the elastic coefficient can be increased, thereby compensating for the frequency loss caused by the increase in the detection mass block.

[0073] Specifically, the support ropes mainly serve to fix the detection mass block 1. The number of ropes and the size and weight of the detection mass block can be adjusted according to the required frequency.

[0074] As an example, the length of the detection mass block 1 along the X direction ranges from 40 micrometers to 200 micrometers, and the width along the Y direction ranges from 40 micrometers to 200 micrometers.

[0075] As an example, the thickness of the bottom layer 101 along the Z direction ranges from 100 nanometers to 300 nanometers, the thickness of the middle layer 102 along the Z direction ranges from 300 micrometers to 500 micrometers, and the thickness of the top layer 103 along the Z direction ranges from 100 nanometers to 300 nanometers. Because the detection mass block 1 has a three-layer structure, its size in the Z direction is significantly increased, resulting in a greatly increased mass, potentially more than 10,000 times that of a traditional single-layer mass block of the same area.

[0076] It should be noted that as the mass of the detection mass block in the optomechanical sensing structure increases, the mechanical resonant frequency of the optomechanical sensing structure will also decrease. At this time, by increasing the number of support tethers, the frequency loss caused by the increase of the detection mass block can be compensated, so that the mechanical resonant frequency remains constant in the range of hundreds of hertz to tens of thousands of hertz (e.g., 100Hz-100000Hz).

[0077] As an example, the lower support rope 2 is a straight line extending in the X direction, and the upper support rope 3 is a straight line extending in the X direction.

[0078] As an example, depending on the desired frequency of the photoelectric sensor, the number of lower support ropes 2 on each side of the detection mass block 1 in the X direction is 30-5000, and the number of upper support ropes 3 on each side of the detection mass block 1 in the X direction is 30-5000, in order to maintain the stability and frequency range of the photoelectric device.

[0079] As an example, the lower support rope 2 and the bottom layer 101 are made of the same material and have the same thickness (the thickness range along the Z direction is 100 nanometers-300 nanometers), and the upper support rope 3 and the top layer 103 are made of the same material and have the same thickness (the thickness range along the Z direction is 100 nanometers-300 nanometers).

[0080] As an example, according to the design of the optical device, the length of the lower support tether 2 in the X direction ranges from 300 mm to 700 mm, and the width in the Y direction ranges from 300 nm to 500 nm; the length of the upper support tether 3 in the X direction ranges from 300 mm to 700 mm, and the width in the Y direction ranges from 300 nm to 500 nm.

[0081] As an example, the detection mass block 1 has a notch 104 on the side facing the suspended waveguide 4, the first optical crystal strip 501 is located in the notch 104, and the two ends of the second optical crystal strip 502 are connected to the suspended waveguide 4 by cantilever 6, the cantilever 6 and the top layer 103 are made of the same material layer.

[0082] For example, please refer to Figure 3 The image shows an enlarged schematic diagram of the optical resonant cavity 5. In this embodiment, the optical resonant cavity 5 includes a defect region A and a mirror region. The mirror region is distributed on both sides of the defect region A in the X direction to confine the light field in the X direction. In this embodiment, the mirror region is also distributed on both sides of the defect region A in the Y direction, thereby confining the light field in both the X and Y directions.

[0083] Specifically, the first optical crystal strip 501 and the second optical crystal strip 502 are placed in each other's near field range. The strong coupling between the two optical crystal strips forms a band structure, which, combined with total internal reflection, confines the optical mode to the defect region of the optical resonant cavity, i.e., the center position of the optical resonant cavity.

[0084] As an example, the first optical crystal strip 501 and the second optical crystal strip 502 can be two identical photonic crystal structure optical crystal strips, mirror-symmetric about the X direction. Both the first optical crystal strip 501 and the second optical crystal strip 502 have multiple air holes. The shape of the air holes can be elliptical or other suitable shapes. The distance between two adjacent air holes is the lattice period. The defect region A can be achieved by regularly changing the structure of the air holes, such as changing the lattice period and aperture size of the air holes. For the mirror region, it consists of air holes with the same aperture size and lattice period.

[0085] It should be noted that, based on the requirements of different devices, the specific arrangement of the air holes in the first optical crystal strip 501 and the second optical crystal strip 502 can be flexibly adjusted, and no special restrictions are imposed here.

[0086] The detection principle of the optical microelectromechanical structure in this embodiment is as follows: when the external force causes the detection mass block 1 to be displaced, the mode of the optical resonant cavity 5 will change and couple with the suspended waveguide 4, and then be transmitted to the detection instrument.

[0087] The optical microelectromechanical structure of this embodiment, by introducing large mass detection blocks with tethers on the top and bottom sides, can be widely used in accelerometers, gyroscopes, and other suitable optomechanical sensors.

[0088] Specifically, for optical microelectromechanical accelerometers, the fluctuations in the detected mass caused by thermo-mechanical resonance are defined as thermal acceleration noise a. th It satisfies the following formula:

[0089]

[0090] Where, k B It is Boltzmann's constant, T is temperature, and ω is... m / 2π is the mechanical frequency, and m is the mass of the detection mass block.

[0091] Reducing the impact of thermal noise can further improve the performance of opto-microelectromechanical accelerometers. According to the above formula, k B And T remains constant at room temperature, ω m This is determined by the requirements of the designed opto-microelectromechanical accelerometer. Therefore, by directly increasing the mass m, thermal noise fluctuations can be effectively reduced.

[0092] Specifically, the detection principle of the optical microelectromechanical accelerometer is as follows: When the optical microelectromechanical accelerometer is subjected to a force in the Y direction, the detection mass block 1 will be displaced in the Y direction, further causing a change in the size of the optical resonant cavity 5 (a change in the distance between the first optical crystal strip 501 and the second optical crystal strip 502), and the cavity resonant frequency ω c The magnitude of the displacement of the detection mass block changes as the size of the optical resonant cavity 5 changes. The levitation waveguide 4 is coupled to the optical resonant cavity 5 using an evanescent field. Changes in the mode in the optical resonant cavity 5 will further cause changes in the transmission mode in the levitation waveguide 4, which will be transmitted to the detection end. When the detection end receives this mode change (such as wavelength information), it will further reflect the acceleration of the detection mass block.

[0093] In this embodiment of the optical microelectromechanical structure (MEMS), the detection mass block has a three-layer structure. The size of the detection mass block is increased in the Z-direction, which greatly increases the mass of the detection mass block while maintaining a fixed area. This reduces the impact of thermo-mechanical noise and improves the performance and sensitivity of the MEMS. Furthermore, when the size of the detection mass block increases in the XY direction, a single-layer nano-tether system is prone to loss of stability, leading to interference from various mechanical modes. The MEMS structure in this embodiment enhances stability through multiple lower and upper support tethers, which is beneficial for single-mode operation. Moreover, the lower and upper support tethers, combined with the detection mass block, allow for flexible adjustment of the mechanical resonant frequency from hundreds of hertz to tens of thousands of hertz.

[0094] Example 2

[0095] This embodiment provides a method for fabricating an optical microelectromechanical structure, which can be used to fabricate the optical microelectromechanical structure described in Embodiment 1. Please refer to [link / reference needed]. Figure 4 The diagram shows the process flow of this method, which includes the following steps:

[0096] S1: A stacked structure is provided, the stacked structure comprising a first material layer, a second material layer and a third material layer stacked sequentially in the Z direction;

[0097] S2: The third material layer is patterned to obtain the top layer of the detection mass block, and a floating waveguide, an optical resonant cavity, and multiple upper support ropes are obtained. The floating waveguide is located on one side of the detection mass block in the Y direction. The multiple upper support ropes are distributed on both sides of the detection mass block in the X direction and connected to the top layer. The optical resonant cavity includes a first optical crystal strip and a second optical crystal strip arranged and spaced apart along the Y direction. The first optical crystal strip is connected to the detection mass block, and the second optical crystal strip is connected to the floating waveguide. The X direction, the Y direction, and the Z direction are perpendicular to each other.

[0098] S3: Graphicalize the first material layer to obtain the bottom layer of the detection mass block, and obtain multiple lower support ropes, wherein the lower support ropes and the upper support ropes are at the same vertical projection position on the XY plane;

[0099] S4: Etch the second material layer from the side of the stacked structure having the first material layer to remove the portion of the second material layer not covered by the lower support tether;

[0100] S5: Remove the portion of the second material layer located between the lower support rope and the upper support rope. The portion of the second material layer that is not removed between the top layer and the bottom layer serves as the intermediate layer of the detection mass block.

[0101] Please refer to the following first. Figure 5 Perform step S1: Provide a stacked structure, the stacked structure including a first material layer 1a, a second material layer 1b and a third material layer 1c stacked sequentially in the Z direction.

[0102] As an example, the first material layer 1a includes a silicon nitride layer, the second material layer 1b includes a silicon layer, and the third material layer 1c includes a silicon nitride layer. In this embodiment, the second material layer 1b is a silicon layer with a thickness of 300 micrometers to 500 micrometers, and both the second material layer 1b and the third material layer 1c are high-stress silicon nitride layers with a thickness of 100 nanometers to 300 nanometers.

[0103] As an example, the silicon nitride layer is grown on the upper and lower surfaces of the silicon layer by low-pressure chemical vapor deposition (LPCVD) while maintaining operating conditions in the range of 700MPa-900MPa.

[0104] Please see again Figures 6 to 9Step S2 is executed: the third material layer 1c is graphically patterned to obtain the top layer 103 of the detection mass block 1, and a suspended waveguide 4, an optical resonant cavity 5, and multiple upper support ropes 3 are obtained. The suspended waveguide 4 is located on one side of the detection mass block 1 in the Y direction. The multiple upper support ropes 3 are distributed on both sides of the detection mass block 1 in the X direction and connected to the top layer 103. The optical resonant cavity 5 includes a first optical crystal strip 501 and a second optical crystal strip 502 arranged along the Y direction and spaced apart. The first optical crystal strip 501 is connected to the detection mass block 1, and the second optical crystal strip 502 is connected to the suspended waveguide 4.

[0105] It should be noted that, for the sake of illustration, in Figures 6 to 9 The subsequent figures only show the area where the detection mass block 1 and the supporting tether are located; the suspended waveguide 4 is not shown, the optical resonant cavity 5 is only shown in part, and the number of supporting tethers is not drawn according to the actual number. The top side pattern of the optical microelectromechanical structure can be seen in conjunction with the aforementioned figures. Figure 1 .

[0106] Specifically, such as Figure 6 As shown, a photoresist layer 7 with a thickness of 200nm-1000nm is first spin-coated onto the top surface of the third material layer 1c. In this embodiment, photoresist is dropped onto the surface of the third material layer 1c, and the stacked structure is placed on a vacuum chuck and rotated at a high speed of about 2000rpm using a rotator to form a uniformly covered photoresist layer on the surface of the third material layer 1c.

[0107] Specifically, such as Figure 7 As shown, the stacked structure is transported to a photolithography scanner, which exposes the photoresist layer 7 to ultraviolet (UV) radiation. Simultaneously, a photomask 8 with an optical resonant cavity pattern is inserted between the UV light source and the photoresist layer 7, thereby exposing a designated area of ​​the photoresist layer 7. Figure 7 The middle arrow indicates ultraviolet light.

[0108] Specifically, such as Figure 8 As shown, the photoresist layer 7 exhibits a top-side pattern through development.

[0109] Specifically, such as Figure 9As shown, inductively coupled plasma etching (ICP-RIE) is used to transfer patterns into the third material layer 1c. In this embodiment, a stacked structure is placed on a silicon carrier wafer, and then octafluorocyclobutane (C4F8) and sulfur hexafluoride (SF6) are introduced as etching gases into a vacuum chamber to achieve isotropic dry etching of the third material layer 1c. By excitation with a radio frequency power source, the etchant gas is ionized into plasma and pushed towards the surface of the third material layer 1c by a DC bias voltage placed between the plasma and the silicon nitride surface to achieve patterning of the third material layer 1c. Figure 9 The middle arrow indicates plasma. In this embodiment, after constructing the designed structure in the third material layer 1c, the photoresist layer 7 on the surface of the third material layer 1c is further removed by cleaning with low-pressure O2 plasma.

[0110] Please see again Figures 10 to 12 Execute step S3: Graphicalize the first material layer 1a to obtain the bottom layer 101 of the detection mass block 1, and obtain multiple lower support ropes 2, wherein the lower support ropes 2 and the upper support ropes 3 have the same vertical projection position on the XY plane.

[0111] Specifically, in order to construct the designed pattern in the first material layer 1a, the stacked structure is first flipped, and the first material layer 1a is graphically represented using a method that is essentially the same as that used to graphically represent the third material layer 1c.

[0112] Specifically, such as Figure 10 As shown, photoresist is first uniformly coated on the surface of the first material layer 1a to obtain photoresist layer 9. Simultaneously, to align the positions of the nano-tethers at the top and bottom of the chip, an optical calibration method is introduced. The top-side pattern is imaged for alignment with the bottom-side photomask 10, and then exposed to ultraviolet light. Figure 10 The middle arrow indicates ultraviolet light.

[0113] It is worth noting that the photomask 10 used on the bottom side is basically the same as the photomask 8 used on the top side pattern, except that the photomask 10 on the bottom side does not have an optical resonant cavity.

[0114] Specifically, such as Figure 11 As shown, a pattern is constructed in the photoresist layer 9 by development.

[0115] Specifically, such as Figure 12 As shown, the pattern of the photoresist layer 9 is transferred to the first material layer 1a using the same inductively coupled plasma etching method as described above for etching the third material layer 1c.

[0116] Please see again Figure 13Step S4 is performed: the second material layer 1b is etched from the side of the stacked structure having the first material layer 1a to remove the portion of the second material layer 1b that is not covered by the lower support tether 2.

[0117] Specifically, since the thickness of the second material layer 1b is a thousand times that of the first material layer 1a, the Bosch etching method of deep reactive ion etching (DRIE) is introduced, wherein... Figure 13 The middle arrow indicates plasma. In this embodiment, the etching gas includes alternating use of C4F8 and SF6. C4F8 is used to deposit a passivation film on the sidewalls and bottom surfaces of the etched trench, while SF6 is used to selectively etch the passivation film on the bottom of the trench in the next step, and further etch the silicon at the bottom. By alternating use of C4F8 and SF6 for anisotropic dry etching, the thick silicon layer is completely etched away.

[0118] Specifically, such as Figure 13 As shown, silicon is etched between the top and bottom silicon nitride patterns, and tens to thousands of silicon flakes are formed in the same locations as the silicon nitride nanowires (only three nanowires and three silicon flakes are shown in the illustration for simplicity).

[0119] Please see again Figure 14 Execute step S5: Remove the portion of the second material layer 1b located between the lower support rope 2 and the upper support rope 3, and use the portion of the second material layer 1b that was not removed between the top layer 103 and the bottom layer 101 as the intermediate layer 102 of the detection mass block 1.

[0120] Specifically, isotropic dry etching is used to etch away the silicon wafer. In this embodiment, the etching gas includes XeF2. Taking advantage of the extremely high selectivity of xenon difluoride (XeF2) for silicon and silicon nitride, the remaining silicon wafer can be easily and thoroughly removed by XeF2. Finally, tens to thousands of silicon nitride nanowires are suspended on the left and right sides of the top and bottom layers of a large mass detection mass block.

[0121] The fabrication method of the optical microelectromechanical structure in this embodiment introduces a large-mass detection mass to reduce the impact of thermo-mechanical noise, thereby improving the performance and sensitivity of the opto-MEMS accelerometer. The single-layer design of the detection mass in traditional opto-MEMS accelerometers limits the fabrication process, tending to increase the size of the detection mass in the XY direction using single-sided photolithography. However, increasing the area of ​​the detection mass in the XY plane reduces the stability of the optical system and thus affects the performance of the opto-MEMS sensor. The fabrication method of the optical microelectromechanical structure in this embodiment uses double-sided photolithography for high-performance opto-mechanical sensors, incorporating the intermediate silicon layer as part of the detection mass. Furthermore, the size of the detection mass is increased in the Z direction using double-sided photolithography, and incorporating the silicon layer as part of the detection mass enables mass production. In this way, the detection mass can be easily scaled up tens of thousands of times while maintaining a constant area of ​​the detection mass in the XY direction. In the single-layer detection mass design, the support tether is only fixed to both sides of the single-layer silicon nitride. As the size of the detection mass increases in the XY direction, the single-layer nanotether system is prone to losing its stability, leading to interference from various mechanical modes. In contrast, the fabrication method of the optical microelectromechanical structure in this embodiment introduces thousands of tethers into both the top and bottom silicon nitride layers to enhance stability, which is beneficial for single-mode operation. Furthermore, the tethers on the top and bottom sides of the silicon nitride layer can be combined with a large detection mass block to achieve flexible adjustment of the mechanical resonant frequency from hundreds of hertz to tens of thousands of hertz.

[0122] The fabrication method for optical microelectromechanical structures in this embodiment can also achieve more precise patterns. Wet etching is commonly used in the fabrication of optoMEMS; however, wet etching technology has significant drawbacks, including low repeatability, unavoidable toxic byproducts, and insufficient precision. Since optoMEMS devices typically include precision structures such as optical resonant cavities as core sensing components, critical point drying is also necessary to prevent the collapse of these fragile structures. To overcome these problems, the fabrication method for optical microelectromechanical structures in this embodiment employs dry etching in a double-sided photolithography process. By changing the etchant, more precise patterns can be introduced into both the silicon and silicon nitride layers.

[0123] In summary, the optical microelectromechanical structure of the present invention includes a detection mass block, multiple lower-layer support tethers, multiple upper-layer support tethers, a levitating waveguide, and an optical resonant cavity. The detection mass block comprises a bottom layer, a middle layer, and a top layer stacked sequentially in the Z-direction. Multiple lower-layer support tethers are distributed on both sides of the detection mass block in the X-direction and connected to the bottom layer. Multiple upper-layer support tethers are distributed on both sides of the detection mass block in the X-direction and connected to the top layer. The levitating waveguide is located on one side of the detection mass block in the Y-direction. The optical resonant cavity includes a first optical crystal strip and a second optical crystal strip arranged and spaced apart along the Y-direction. The first optical crystal strip is connected to the detection mass block, and the second optical crystal strip is connected to the levitating waveguide. The detection mass block of the optical microelectromechanical structure of the present invention has a three-layer structure. The size of the detection mass block is increased in the Z-direction, which greatly increases the mass of the detection mass block while maintaining a fixed area. This reduces the impact of thermo-mechanical noise and improves the performance and sensitivity of the optical microelectromechanical structure. Furthermore, as the size of the detection mass increases in the XY direction, the single-layer nano-tether system easily loses its stability and becomes susceptible to interference from various mechanical modes. This invention enhances stability through the design of multiple lower and upper support tethers, which is beneficial for single-mode operation. Moreover, the lower and upper support tethers, combined with the detection mass, allow for flexible adjustment of the mechanical resonant frequency from hundreds to tens of thousands of hertz. The fabrication method of the optical microelectromechanical structure of this invention is compatible with CMOS technology, facilitates large-scale manufacturing, and enables more precise patterning. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0124] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can 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 those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An optical microelectromechanical structure, characterized in that, include: The quality block for testing includes a bottom layer, an intermediate layer, and a top layer stacked sequentially in the Z direction, wherein the thickness of the intermediate layer in the Z direction is greater than the thickness of the bottom layer and the top layer in the Z direction. Multiple lower-level support ropes are distributed on both sides of the detection mass block in the X direction and connected to the bottom layer; Multiple upper support ropes are distributed on both sides of the detection mass block in the X direction and connected to the top layer. The upper support ropes and the lower support ropes are located on opposite sides of the middle layer in the Z direction, spaced apart in the Z direction, and have the same vertical projection position on the XY plane. A suspended waveguide is located on one side of the detection mass block in the Y direction; An optical resonant cavity includes a first optical crystal strip and a second optical crystal strip arranged and spaced apart along the Y direction. The first optical crystal strip is connected to the detection mass block, and the second optical crystal strip is connected to the suspended waveguide. The X direction, the Y direction, and the Z direction are perpendicular to each other.

2. The optical microelectromechanical structure according to claim 1, characterized in that: The length of the detection mass block along the X direction ranges from 40 micrometers to 200 micrometers, and the width along the Y direction ranges from 40 micrometers to 200 micrometers.

3. The optical microelectromechanical structure according to claim 1, characterized in that: The thickness of the bottom layer along the Z direction ranges from 100 nanometers to 300 nanometers, the thickness of the middle layer along the Z direction ranges from 300 micrometers to 500 micrometers, and the thickness of the top layer along the Z direction ranges from 100 nanometers to 300 nanometers.

4. The optical microelectromechanical structure according to claim 1, characterized in that: The bottom layer includes a silicon nitride layer, the middle layer includes a silicon layer, and the top layer includes a silicon nitride layer.

5. The optical microelectromechanical structure according to claim 1, characterized in that: The lower support rope is a straight line extending in the X direction, and the upper support rope is a straight line extending in the X direction.

6. The optical microelectromechanical structure according to claim 1, characterized in that: The number of lower support ropes on each side of the detection mass block in the X direction is 30-5000, and the number of upper support ropes on each side of the detection mass block in the X direction is 30-5000.

7. The optical microelectromechanical structure according to claim 1, characterized in that: The lower support rope has a length ranging from 300 micrometers to 700 micrometers along the X direction, a width ranging from 300 nanometers to 500 nanometers along the Y direction, and a thickness ranging from 100 nanometers to 300 nanometers along the Z direction; the upper support rope has a length ranging from 300 micrometers to 700 micrometers along the X direction, a width ranging from 300 nanometers to 500 nanometers along the Y direction, and a thickness ranging from 100 nanometers to 300 nanometers along the Z direction.

8. The optical microelectromechanical structure according to claim 1, characterized in that: The optical resonant cavity includes a defect region and a mirror region, with the mirror region distributed on both sides of the defect region in the X direction.

9. The optical microelectromechanical structure according to claim 8, characterized in that: The mirror area is also distributed on both sides of the defect area in the Y direction.

10. The optical microelectromechanical structure according to claim 1, characterized in that: The optical microelectromechanical structure is used in accelerometers or gyroscopes.

11. A method for fabricating an optical microelectromechanical structure, characterized in that, Includes the following steps: A laminated structure is provided, the laminated structure comprising a first material layer, a second material layer and a third material layer stacked sequentially in the Z direction, wherein the thickness of the second material layer in the Z direction is greater than the thickness of the first material layer and the third material layer in the Z direction; The third material layer is graphically represented to obtain the top layer of the detection mass block, and a suspended waveguide, an optical resonant cavity, and multiple upper support tethers are obtained. The suspended waveguide is located on one side of the detection mass block in the Y direction, and the multiple upper support tethers are distributed on both sides of the detection mass block in the X direction and connected to the top layer. The optical resonant cavity includes a first optical crystal strip and a second optical crystal strip arranged and spaced apart along the Y direction. The first optical crystal strip is connected to the detection mass block, and the second optical crystal strip is connected to the suspended waveguide. The X direction, the Y direction, and the Z direction are perpendicular to each other. The first material layer is graphically represented to obtain the bottom layer of the detection mass block, and multiple lower support ropes are obtained. The lower support ropes and the upper support ropes are positioned at the same vertical projection position on the XY plane. The second material layer is etched from the side of the laminated structure having the first material layer to remove the portion of the second material layer not covered by the lower support tether; The portion of the second material layer located between the lower support rope and the upper support rope is removed, and the portion of the second material layer located between the top layer and the bottom layer that is not removed is used as the intermediate layer of the detection mass block.

12. The method for fabricating an optical microelectromechanical structure according to claim 11, characterized in that: The first material layer includes a silicon nitride layer, the second material layer includes a silicon layer, and the third material layer includes a silicon nitride layer.

13. The method for fabricating an optical microelectromechanical structure according to claim 12, characterized in that: The method for patterning the third material layer includes inductively coupled plasma etching (ICP-C), with the etching gas including a mixture of C4F8 and SF6; the method for patterning the first material layer includes ICP-C, with the etching gas including a mixture of C4F8 and SF6; the method for etching the second material layer from the side of the stacked structure having the first material layer to remove the portion of the second material layer not obscured by the lower support tether includes Bosch etching, with the etching gas including alternating use of C4F8 and SF6; the method for removing the portion of the second material layer located between the lower support tether and the upper support tether includes isotropic dry etching, with the etching gas including XeF2.

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