A temperature compensation method and apparatus for optical measurement in micro / nano fabrication

Abstract

This invention provides a temperature compensation method and apparatus for optical measurement in micro-nano manufacturing. The temperature compensation method compensates for the thermal deformation of a connector between a camera assembly and a support frame. The connector is made of a material that exhibits the Invar effect at room temperature. The first intersection point is the point where the first optical axis of the camera assembly intersects the surface of the object being measured. The temperature compensation method includes: measuring the current temperature at at least three temperature measurement points on the connector surface; fitting the deformed surface of the connector surface after thermal deformation based on the current temperature at the temperature measurement points; obtaining the second intersection point between the second optical axis of the camera assembly and the surface of the object being measured based on the deformed surface; obtaining the thermal deformation vector based on the positional difference between the second and first intersection points; and performing thermal compensation on all points on the surface of the object being measured based on the thermal deformation vector. The temperature compensation method of this invention reduces the impact of thermal deformation on the accuracy of optical measurement and improves the repeatability accuracy of optical measurement.

Description

Technical Field

[0001] This invention relates to the field of micro-nano manufacturing measurement, and more particularly to a temperature compensation method and apparatus for optical measurement in micro-nano manufacturing. Background Technology

[0002] In today's micro-nano manufacturing field, especially in IC (Integrated Circuit) and optoelectronic manufacturing, with the rapid development of technology, IC devices are showing a trend of continuously shrinking physical dimensions and expanding into three-dimensional structures, and the corresponding process nodes are also continuously upgrading. Against this backdrop, the requirements for inspection technology in the IC manufacturing process have reached unprecedented levels. IC metrology and inspection occupy a crucial position in the entire IC manufacturing process, serving as a key link in achieving process control and yield management.

[0003] Optical measurement technology has been widely used in IC manufacturing process control and yield management due to its advantages such as high measurement speed, non-contact operation, non-destructive nature to the object being inspected, and ease of online integration. Optical metrology, based on optical principles and utilizing photoelectric technology, measures critical dimensions in micro- and nano-manufacturing to achieve yield control. This mainly includes critical dimension measurement, three-dimensional topography measurement, thin film thickness measurement, and overlay accuracy measurement. Chip position optical metrology, leveraging machine recognition, image processing, machine learning, and artificial intelligence technologies, can quickly and accurately identify defects and their locations in inspected samples. Specifically, it uses camera scanning machine vision to identify the entire wafer, thereby obtaining the integrity and positional information of the chips on the wafer. In practical applications, the camera is fixed on a marble gantry, and the wafer is placed on a chuck. Scanning of different parts of the wafer is achieved by movement along the x and y axes, and finally, the chip information on the entire wafer is obtained through stitching.

[0004] Furthermore, after identifying the chip's position information on the wafer using machine vision, a calibrated SVD (Singular Value Decomposition) matrix transformation step is required to obtain the chip's actual coordinate information. However, as chip size continues to shrink, the precision requirements for measurement equipment become increasingly stringent. In high-precision measurement environments, even minute environmental fluctuations can significantly impact measurement results. Although measurement equipment is typically used in cleanrooms (with constant temperature and humidity conditions), the presence of heat sources within the equipment, such as light sources and cameras, can affect the thermal stability of the measurement system in localized areas. Moreover, the thermal expansion of the measurement system's tooling cannot be ignored; this issue can adversely affect measurements and reduce repeatability accuracy. Summary of the Invention

[0005] The purpose of this invention is to provide a temperature compensation method and apparatus for optical measurement in micro-nano manufacturing, which has the advantage of being able to achieve thermal deformation compensation.

[0006] To achieve the above objectives, the present invention provides a temperature compensation method for optical measurement in micro / nano manufacturing. The temperature compensation method is used to compensate for thermal deformation of a connector between a camera assembly and a support frame. The connector has a connecting surface adjacent to the camera assembly. In a reference state where the connector has not undergone thermal deformation, the intersection point between the first optical axis of the camera assembly and the surface of the object being measured is designated as the first intersection point. The temperature compensation method includes:

[0007] S10. After the connector undergoes thermal deformation, the current temperature at at least three temperature measurement points on the connecting surface is measured.

[0008] S20. The deformed surface of the connecting surface after thermal deformation is obtained by fitting the current temperature at at least three temperature measurement points;

[0009] S30. Based on the deformed surface, obtain the second intersection point between the second optical axis of the camera assembly and the surface of the object being detected after the connector has deformed, and obtain the thermal deformation vector based on the position difference between the second intersection point and the first intersection point.

[0010] S40. Perform thermal compensation on all points on the surface of the detected object after the connector undergoes thermal deformation based on the thermal deformation vector.

[0011] Optionally, the material of the connector is a material that exhibits the Invar effect at room temperature.

[0012] Optionally, in step S10, the number of temperature measurement points is four, and the four temperature measurement points are located at the four corners of the square connecting surface.

[0013] Optionally, in step S20, fitting the deformed surface of the connecting surface after thermal deformation based on the current temperature at at least three temperature measurement points includes:

[0014] S201. Calculate the position of each temperature measurement point after thermal deformation;

[0015] S202. The deformation surface is obtained by fitting each of the temperature measurement points as a reference, and the vertical distance between the deformation surface and each of the temperature measurement points is minimized.

[0016] Optionally, the four temperature measurement points include a first measurement point and a second measurement point, and the line connecting the first measurement point and the second measurement point is parallel to the bottom edge of the connecting surface; in step S30, obtaining the second intersection point between the second optical axis of the camera assembly and the surface of the object being detected based on the deformed surface specifically includes:

[0017] S301. Obtain the center projection point by projecting the center point of the connecting surface onto the deformed surface;

[0018] S302. Find a line parallel to the optical axis that is parallel to the deformation surface and perpendicular to the line connecting the first measurement point and the second measurement point through the central projection point;

[0019] S303. Calculate the normal vector of the deformed surface, and move the parallel line of the optical axis along the normal vector of the deformed surface to the distance between the first optical axis and the connecting surface to obtain the second optical axis.

[0020] Optionally, in step S201, the position of each temperature measuring point after thermal deformation is calculated based on the temperature change of each temperature measuring point, the thickness of the connector, and the coefficient of thermal expansion of the connector.

[0021] Optionally, in step S40, the points on the surface of the detected object are thermally compensated using the thermal deformation vector to obtain the compensated physical coordinates. After step S40, step S50 is further included: multiplying the compensated physical coordinates with the camera imaging matrix to obtain the compensated image coordinates.

[0022] Optionally, after step S40, step S50 is further included: multiplying the compensated physical coordinates with the camera imaging matrix to obtain compensated image coordinates, wherein the camera imaging matrix includes scaling factors, rotation angles, and coordinate translation amounts.

[0023] The present invention also provides an apparatus for optical inspection in micro / nano manufacturing, the apparatus comprising:

[0024] A camera assembly used to acquire optical information about the surface of the object being inspected;

[0025] A support frame is used to support the camera assembly;

[0026] A connector is disposed between the camera assembly and the support frame to connect the camera assembly and the support frame;

[0027] At least three temperature sensors are disposed at different locations on the connector;

[0028] A temperature compensation controller is connected to the temperature sensor and the camera assembly, and has a memory and a processor therein. The memory stores a computer program, and when the computer program is executed by the processor, it implements the temperature compensation method as described above.

[0029] Optionally, the connector has a connecting surface adjacent to the camera assembly; the number of temperature sensors is four, and the four temperature sensors are respectively disposed at the four corners of the connecting surface; and / or, the material of the connector is an Invar material at room temperature.

[0030] In summary, compared with the prior art, the temperature compensation method and apparatus for optical measurement in micro-nano manufacturing provided by the present invention have the following beneficial effects:

[0031] The temperature compensation method of the present invention introduces the change in the optical axis position of the camera assembly caused by the thermal deformation of the connector due to temperature change, and quantitatively compensates for the thermal deformation, so as to reduce the impact of thermal deformation on the optical detection accuracy and improve the repeatability accuracy of optical measurement. Attached Figure Description

[0032] Figure 1 This is a flowchart of the temperature compensation method for optical measurement in micro / nano manufacturing according to the present invention.

[0033] Figure 2 This is a schematic diagram of the device for optical measurement in micro-nano manufacturing according to the present invention.

[0034] Figure 3 This is a schematic diagram of the structure of the device for optical measurement in micro-nano manufacturing according to the present invention, viewed from the front.

[0035] Figure 4 This is a schematic diagram of the camera assembly and connectors in their base state when no thermal deformation has occurred.

[0036] Figure 5 This is a schematic diagram of the camera assembly and connectors after thermal deformation.

[0037] Explanation of reference numerals in the attached figures:

[0038] Device 10 for optical inspection in micro / nano manufacturing

[0039] Camera component 100

[0040] Support frame 110

[0041] Connector 120

[0042] Connection surface P0

[0043] Deformation surface P i

[0044] Temperature sensor 130

[0045] First measurement point 131

[0046] Second measurement point 132

[0047] 20 objects being detected Detailed Implementation

[0048] The following will be combined with the appendix in the embodiments of the present invention. Figure 1 ~Attached Figure 5 The technical solutions, structural features, objectives and effects achieved in the embodiments of the present invention will be described in detail.

[0049] It should be noted that the accompanying drawings are in a very simplified form and use non-precise proportions. They are only used to facilitate and clarify the purpose of illustrating the embodiments of the present invention, and are not intended to limit the implementation conditions of the present invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationship, or adjustments to the size should still fall within the scope of the technical content disclosed in the present invention, provided that they do not affect the effects and objectives that the present invention can produce.

[0050] It should be noted that, in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only the expressly listed elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0051] This invention provides a temperature compensation method for optical measurement in micro / nano manufacturing. The temperature compensation method is used to compensate for thermal deformation of the connector 120 between the camera assembly 100 and the support frame 110 (e.g., ...). Figure 4 and Figure 5 (As shown). When inspecting an object 20, such as a wafer, the camera assembly 100 is mounted on the support frame 110 via the connector 120.

[0052] When the connector 120 has not undergone thermal deformation, the connecting surface P0 adjacent to the camera assembly 100 is adjusted to a vertical state by assembling the camera assembly 100 to the support frame 110 via the connector 120 at room temperature, and then adjusting the support frame 110 and the fasteners used for connection. Using this state as a reference state, the thickness L0, length a, and width b of the connector 120 are measured, and the coefficient of thermal expansion of the material used to make the connector 120 is α. The camera assembly 100 is mounted on the connector 120. In the reference state, the optical axis of the camera assembly 100 is the first optical axis l0, the distance between the first optical axis l0 and the connector 120 is d, and the intersection point between the projection point of the first optical axis l0 on the object 20 being detected and the surface of the object 20 being detected is the first intersection point, with physical coordinates (x0, y0).

[0053] like Figure 1 As shown, temperature compensation methods include:

[0054] S10. After the connector 120 undergoes thermal deformation, the current temperature at at least three temperature measurement points on the connecting surface P0 is measured. In this embodiment, the number of temperature measurement points is four. Under the baseline state where the camera assembly 100, connector 120, and support frame 110 are initially installed, the initial temperatures of the four temperature measurement points are measured and recorded as T. 01 T 02 T 03 and T 04 When the temperature of connector 120 changes, the current temperature at each temperature measuring point on the connecting surface P0 is measured and recorded as T. i1 T i2 T i3 and T i4 (where i ≥ 0).

[0055] In a preferred embodiment, the connecting surface P0 is a square plane, and four temperature measurement points are located at the four corners of the square connecting surface P0 to measure the temperature changes at different positions of the connector 120, so as to fit the position of the entire connecting surface P0 after thermal deformation as completely as possible. In this embodiment, four temperature measurement points are set on the connecting surface P0 to minimize the consumption of computing power while ensuring the fitting accuracy of the connecting surface P0 after deformation.

[0056] In other embodiments, the temperature measurement points on the connecting surface P0 may be five or other numbers, as long as there are more than three to fit the thermally deformed connecting surface P0; this is not a limitation. Furthermore, the connecting surface P0 may also be other shapes besides square, such as triangles; this is not a limitation either.

[0057] S20. Based on the current temperature at at least three temperature measurement points, obtain the deformed surface P after thermal deformation of the connecting surface P0. i Specifically, step S20 includes:

[0058] S201. Calculate the positions of each temperature measurement point after thermal deformation. The positions of each temperature measurement point after thermal deformation are calculated based on the temperature change at each temperature measurement point, the thickness L0 of the connector 120, and the coefficient of thermal expansion α of the connector 120. Since the connector 120 undergoes thermal strain after heating, especially the thermal strain in the thickness direction of the connector 120, which has the greatest impact on the imaging of the camera assembly 100, this invention mainly compensates for the thermal deformation in the thickness direction of the connector 120. Specifically, the thermal deformation of the four temperature measurement points is calculated according to the following formula:

[0059] ΔL i1 =(T i1 -T 01 )×α×L0

[0060] ΔL i2 =(T i2 -T 02 )×α×L0

[0061] ΔL i3 =(T i3 -T 03 )×α×L0

[0062] ΔL i4 =(T i4 -T 04 )×α×L0

[0063] S202. The deformation surface P is obtained by fitting the data based on each temperature measurement point. i And the deformed surface P i The vertical distance from the point where thermal deformation occurs at each temperature measurement point is the smallest. Deformation surface P i The plane obtained by fitting the deformation surface P0 after thermal deformation based on the temperature changes at multiple temperature measurement points is called the deformed surface P. i This indicates the position of the connecting surface P0 after thermal deformation.

[0064] S30, according to the deformation surface P i The second optical axis l of the camera assembly 100 after deformation of the connector 120 is obtained. i The second intersection point (x) with the surface of the object being tested 20 i0 y i0After the connector 120 deforms due to heat, the position of the camera assembly 100, which is in close contact with the connection surface P0 of the connector 120, will also change accordingly, and the first optical axis l0 of the camera assembly 100 in the reference state will also change with the deformation of the connection surface P0. In this scheme, the second optical axis l i This indicates the optical axis position of the connector 120 in the camera assembly 100 after thermal deformation. The object being detected 20 does not move with the thermal deformation of the connector 120; therefore, after the camera assembly 100 follows the thermal deformation of the connector 120, its second optical axis l... i The intersection point with the surface of the object being detected 20 will move relative to the first intersection point (x0, y0), thus shifting the second optical axis l of the camera assembly 100. i The intersection point with the surface of the object being tested 20 is set as the second intersection point (x). i0 y i0 According to the second intersection point (x) i0 y i0 The thermal deformation vector is obtained from the position difference between the first intersection point (x0, y0) and the first intersection point (x0, y0). In this embodiment, step S30 specifically includes:

[0065] S301, with the center point of the connecting surface P0 on the deformed surface P i The projection onto the center point is obtained by projecting onto the center point.

[0066] In this embodiment, the four temperature measurement points include a first measurement point 131 and a second measurement point 132 (e.g., ...). Figure 3 As shown in the figure, the line connecting the first measurement point 131 and the second measurement point 132 is parallel to the bottom edge of the connecting surface P0.

[0067] S302, Find the parallel surface P to the deformation surface through the center projection point. i And the optical axis parallel line l perpendicular to the line connecting the first measurement point 131 and the second measurement point 132 i0 .

[0068] S303, Calculate the deformation surface P i The normal vector, parallel to the optical axis line l i0 Along the deformation surface P i The normal vector is moved by the distance d between the first optical axis l0 and the connecting surface P0 to obtain the second optical axis l. i (like Figure 4 and Figure 5 (As shown). Second optical axis l i The intersection point with the surface of the object being tested, such as the wafer surface, is the second intersection point (x). i0 y i0 ).

[0069] S40. Thermal compensation is performed on all points on the surface of the object 20 after the connector 120 undergoes thermal deformation based on the thermal deformation vector. The thermal deformation vector is translated between the camera assembly 100 and the object 20. The original coordinates of the points on the surface of the object being tested are (x... i y i After thermal compensation, the compensated physical coordinates (x) are obtained. i -x i0 +x0, y i -y i0 +y0).

[0070] In this embodiment, after step S40, step S50 is further included: multiplying the compensated physical coordinates by the camera imaging matrix to obtain the compensated image coordinates. The camera imaging matrix includes a scaling factor K, a rotation angle θ, and coordinate translation (u, v). An image coordinate system is established for the image captured by the camera assembly 100, and the pixel coordinates corresponding to the object can be measured in the image coordinate system. There is a one-to-one correspondence between the pattern on the object plane and the pattern in the image captured by the camera assembly 100, and the image coordinate system and the physical coordinate system satisfy an affine transformation relationship. Without considering temperature compensation, assume that the coordinates of any point A measured by the camera in the image coordinate system at time i are (X... i Y i Point A in the physical coordinate system corresponds to point (x). i y i If ), then there exists a matrix H such that Matrix H is a scaling, rotation, and translation matrix that makes the corresponding points in the image coordinate system coincide with the corresponding points in the object coordinate system. Matrix H satisfies:

[0071]

[0072] Where K is the scaling factor, θ is the rotation angle, and (u, v) is the coordinate translation.

[0073] After thermal deformation compensation, the thermal deformation vector is translated between the camera assembly 100 and the detected object 20. The coordinates of point A after compensation in the object coordinate system are (x i -x i0 +x0, y i -y i0 After performing the corresponding coordinate transformation, the measured coordinates (X′) of point A in the image coordinate system can be obtained. i ,Y′ i That is, satisfying: After the above steps, thermal compensation is completed for the imaging offset of the camera assembly 100 caused by the thermal deformation of the connector 120.

[0074] In this embodiment, the object to be detected 20 is illustrated by a wafer. However, the object that the camera assembly 100 uses to detect may not be limited to a wafer, but may be other objects that can be optically detected. No limitation is made here.

[0075] In this embodiment, the support frame 110 is exemplified by a gantry frame made of marble. Marble has the advantage of small thermal deformation when the temperature changes, and the gantry frame has the advantage of stable support. The marble gantry frame can minimize the impact of thermal deformation of the support frame 110 caused by temperature changes on the camera assembly 100. However, the support frame 110 can also be made of other materials or have other structures that can support the camera assembly 100, and there are no restrictions here.

[0076] In this embodiment, the material of the connector 120 is selected to be a material that exhibits the Invar effect at room temperature. Materials with the Invar effect are those with a low coefficient of thermal expansion at room temperature. As a preferred embodiment, the connector 120 is made of Invar steel. Invar steel has the advantage of good thermal stability and can maintain a very small or even near-zero coefficient of thermal expansion over a wide temperature range near room temperature, minimizing the impact of thermal expansion deformation of the connector 120 on the optical detection accuracy of the camera assembly 100.

[0077] In other embodiments, the connector 120 can also be made of other materials, as long as it can connect the camera assembly 100 and the support frame 110. Of course, the smaller the coefficient of thermal expansion, the better, so as to minimize the impact of the thermal deformation of the connector 120 on the optical detection accuracy of the camera assembly 100.

[0078] In addition, such as Figure 2 and Figure 3 As shown, the present invention also provides an apparatus 10 for optical inspection in micro-nano manufacturing, the apparatus including a camera assembly 100, a support frame 110, a connector 120, at least three temperature sensors 130 and a temperature compensation controller (not shown in the figure).

[0079] The camera assembly 100 is used to photograph the object 20 to obtain optical information about the surface of the object 20. The object 20 may be a wafer or other object that can be optically inspected.

[0080] The support frame 110 is used to support the camera assembly 100, so as to securely install the camera assembly 100 on the ground. In this embodiment, the support frame 110 is a gantry frame made of marble. Marble has the advantage of small thermal deformation when the temperature changes, and the gantry frame has the advantage of stable support. The marble gantry frame can minimize the impact of thermal deformation of the support frame 110 caused by temperature changes on the camera assembly 100. However, the support frame 110 can also be made of other materials or have other structures that can support the camera assembly 100, and there is no limitation here.

[0081] A connector 120 is disposed between the camera assembly 100 and the support frame 110 to connect the camera assembly 100 and the support frame 110. In this embodiment, the connector 120 is made of a material that exhibits the Invar effect at room temperature, such as Invar steel.

[0082] Temperature sensors 130 are disposed at different positions on connector 120; connector 120 has a connection surface P0 adjacent to camera assembly 100; there are four temperature sensors 130, which are respectively disposed at the four corners of connection surface P0.

[0083] The temperature compensation controller is connected to the temperature sensor 130 and the camera assembly 100, and has a memory and a processor inside. The memory stores a computer program, and when the computer program is executed by the processor, it implements the temperature compensation method described above.

[0084] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A temperature compensation method for micro-nano fabricated optical metrology, characterized in that, The temperature compensation method is used for compensating thermal deformation of a connecting piece between a camera assembly and a support frame, the connecting piece having a connecting surface adjacent to the camera assembly; In a reference state in which the connecting piece does not have thermal deformation, an intersection between a first optical axis of the camera assembly and a surface of a detected object is a first intersection point; The temperature compensation method comprises: S10, measuring current temperatures at at least three temperature measuring points on the connecting surface after the connecting piece has thermal deformation; S20, fitting a deformed surface of the connecting surface after thermal deformation according to the current temperatures at the at least three temperature measuring points; S30, obtaining a second intersection point between a second optical axis of the camera assembly after deformation of the connecting piece and the surface of the detected object according to the deformed surface, and obtaining a thermal deformation vector according to a position difference between the second intersection point and the first intersection point; S40, compensating all points on the surface of the detected object after thermal deformation of the connecting piece based on the thermal deformation vector; In step S20, the fitting of the deformed surface of the connecting surface after thermal deformation according to the current temperatures at the at least three temperature measuring points comprises: S201, calculating positions of the temperature measuring points after thermal deformation; S202, fitting the deformed surface with the temperature measuring points as references, and the deformed surface has minimum perpendicular distances to the temperature measuring points; The temperature measuring points comprise a first measuring point and a second measuring point, and a line connecting the first measuring point and the second measuring point is parallel to a bottom edge of the connecting surface; In step S201, the positions of the temperature measuring points after thermal deformation are calculated according to temperature variation amounts of the temperature measuring points, a thickness of the connecting piece, and a thermal expansion coefficient of the connecting piece; In step S30, the obtaining of the second intersection point between the second optical axis of the camera assembly and the surface of the detected object according to the deformed surface comprises: S301, obtaining a center projection point by projecting a center point of the connecting surface on the deformed surface; S302, finding an optical axis parallel line parallel to the deformed surface and perpendicular to the line connecting the first measuring point and the second measuring point through the center projection point; S303, calculating a normal vector of the deformed surface, and moving the optical axis parallel line along the normal vector of the deformed surface by a distance between the first optical axis and the connecting surface to obtain a second optical axis.

2. The temperature compensation method for micro-nano fabricated optical metrology of claim 1, wherein, The connecting piece is made of a material having Invar effect at room temperature.

3. The temperature compensation method for micro-nano fabricated optical metrology of claim 1, wherein, In step S10, the number of the temperature measuring points is four, and the four temperature measuring points are located at four corners of the connecting surface.

4. The temperature compensation method for micro-nano fabricated optical metrology of claim 1, wherein, In step S40, the points on the surface of the detected object are compensated by the thermal deformation vector to obtain compensated physical coordinates.

5. The temperature compensation method for micro-nano fabricated optical metrology of claim 4, wherein, After step S40, step S50 is further included: multiplying the compensated physical coordinates by a camera imaging matrix to obtain compensated image coordinates, wherein the camera imaging matrix comprises a scaling coefficient, a rotation angle, and a coordinate translation amount.

6. An apparatus for micro-nano fabrication of optical metrology, characterized in that, The device comprises: a camera assembly configured to acquire optical information of a surface of a detected object; a support frame configured to support the camera assembly; a connecting piece arranged between the camera assembly and the support frame to connect the camera assembly and the support frame; at least three temperature sensors arranged at different positions on the connecting piece; a temperature compensation controller connected to the temperature sensors and the camera assembly, and having a memory and a processor therein, the memory storing a computer program, the computer program being executed by the processor to implement the temperature compensation method according to any one of claims 1-5.

7. The device for micro-nano fabrication of optical metrology of claim 6, wherein, the connecting piece has a connecting surface adjacent to the camera assembly; the number of the temperature sensors is four, and the four temperature sensors are arranged at four corners of the connecting surface, respectively; and / or the material of the connecting piece is a material having the Invar effect at normal temperature. the connecting piece has a connecting surface adjacent to the camera assembly; the number of the temperature sensors is four, and the four temperature sensors are arranged at four corners of the connecting surface, respectively; and / or the material of the connecting piece is a material having the Invar effect at normal temperature.

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