Wafer-to-tray leveling method and apparatus

Abstract

The application provides a wafer-to-tray leveling method and device, which comprises the following steps: placing the contact ends of at least three displacement sensors, which are not collinear, in a target plane that is coplanar with the upper bearing surface of a lower tray, and zeroing the sensing values of the displacement sensors to calibrate the displacement sensors; driving the displacement sensors to extend until the contact ends thereof contact the lower bearing surface of an upper tray located above the lower tray, and obtaining the sensing values of the displacement sensors respectively; judging whether the upper bearing surface and the lower bearing surface are parallel according to the corresponding sensing values of the displacement sensors; when it is judged that the upper bearing surface and the lower bearing surface are not parallel, adjusting the relative height of the lower tray or the upper tray to make the upper bearing surface and the lower bearing surface parallel. Based on the technical scheme of the application, the direct contact type measurement of the displacement sensors can achieve an accuracy of within 3 microns, has the advantage of high precision, and is not affected by other environmental factors, and is simple and direct.

Description

Technical Field

[0001] This invention relates to the field of wafer bonding and leveling technology, and particularly to a wafer-to-pallet leveling method and apparatus. Background Technology

[0002] As the demands for chip functionality continue to increase, it becomes increasingly difficult to improve performance by shrinking transistor size. Therefore, integrated circuit technology is gradually evolving from 2D planar integration to 3D integration. In 3D integration technology, wafer-level bonding is one of the most crucial steps, and wafer-level bonding first requires ensuring that two opposing wafer trays remain parallel.

[0003] Most current equipment manufacturers use a method of detecting the distance between two trays by blowing air onto the upper tray to provide feedback pressure, and then determine whether they are parallel. This method requires a very close spacing, and the accuracy of fluid measurement is difficult to guarantee.

[0004] Therefore, in view of the tray parallelism requirement in the wafer stacking process of semiconductor wafer-level packaging, the present invention proposes a wafer-to-tray leveling method and apparatus. Summary of the Invention

[0005] In view of the limitations and inaccuracies of the existing pallet parallel detection and adjustment methods, this application proposes a wafer-to-pallet leveling method and apparatus.

[0006] In a first aspect, the present invention proposes a wafer-to-pallet leveling method, comprising:

[0007] The contacts of at least three non-collinear displacement sensors are positioned in a target plane coplanar with the upper bearing surface of the lower tray, and the sensing values ​​of the displacement sensors are set to zero to calibrate the displacement sensors.

[0008] Drive the displacement sensor to extend until its contact tip contacts the lower bearing surface of the upper tray located above the lower tray, and obtain the sensing values ​​of the displacement sensor respectively;

[0009] Based on the sensing value corresponding to the displacement sensor, it is determined whether the upper bearing surface and the lower bearing surface are parallel;

[0010] When it is determined that the upper bearing surface and the lower bearing surface are not parallel, the lower tray or the upper tray is driven to adjust their relative height so that the upper bearing surface and the lower bearing surface are parallel.

[0011] In one embodiment, positioning the contacts of at least three non-collinear displacement sensors within a target plane coplanar with the upper bearing surface of the lower tray includes:

[0012] Place the calibration tool on the upper support surface of the lower tray, so that the lower surface of the calibration tool is in contact with and coplanar with the upper support surface;

[0013] The displacement sensor extends from under the lower tray until its top contact point touches the lower surface of the calibration tool, and then the calibration tool is removed.

[0014] In one embodiment, determining whether the upper bearing surface and the lower bearing surface are parallel includes:

[0015] Compare the numerical values ​​of at least three displacement sensors to obtain a comparison result.

[0016] If the comparison result meets the parallel condition, it is determined that the upper bearing surface and the lower bearing surface are parallel. The parallel condition is that the magnitudes of the sensing values ​​are the same or the maximum difference between any two values ​​is not greater than a preset value.

[0017] Otherwise, it is determined that the upper bearing surface and the lower bearing surface are not parallel.

[0018] In one embodiment, driving the lower tray or the upper tray to adjust their relative height so that the upper bearing surface is parallel to the lower bearing surface includes:

[0019] Based on the magnitude of the difference between each pair of the sensing values, the adjustment value of the corresponding target drive component among the multiple lifting drive components that are respectively set to correspond to the displacement sensor is determined;

[0020] The target drive component is adjusted to raise or lower the lower tray or the upper tray according to the adjustment value, so that the upper bearing surface is parallel to the lower bearing surface.

[0021] In one embodiment, after the target drive unit causes the lower tray to rise or fall according to the adjustment value, the method further includes:

[0022] The sensing values ​​of the displacement sensors are reacquired respectively;

[0023] The comparison result of the numerical value comparison is determined based on the reacquired sensor value, and it is determined again whether the comparison result satisfies the parallel condition.

[0024] If the parallel condition is still not met, the lower tray is readjusted using the lifting assembly.

[0025] In one implementation, it further includes:

[0026] After confirming that the upper bearing surface is parallel to the lower bearing surface, the displacement sensor is reset and retracted to below the lower tray, and a leveling completion signal is output.

[0027] Secondly, the present invention provides a wafer-to-pallet leveling device, comprising:

[0028] The upper pallet has its lower surface as the lower load-bearing surface.

[0029] The lower tray is disposed opposite to the upper tray, and the upper surface of the lower tray is the upper bearing surface;

[0030] A sensor assembly comprising at least three non-collinear displacement sensors, each displacement sensor having a contact tip at its tip and being retractable in a direction in which the upper and lower trays are opposite to each other;

[0031] The lifting assembly includes multiple lifting drive components connected to the upper tray or the lower tray, and each lifting drive component is configured to correspond one-to-one with a displacement sensor in the sensor assembly;

[0032] The contacts of the at least three displacement sensors can determine a target plane that is coplanar with the lower or upper bearing surface and serves as the starting point for the extension.

[0033] In one embodiment, the displacement sensor assembly is disposed below the lower tray, which has a plurality of through holes corresponding to the respective displacement sensors.

[0034] In one implementation, it further includes:

[0035] A calibration tool having a calibration plane that meets flatness requirements, the calibration tool being able to be placed on the upper bearing surface or the lower bearing surface;

[0036] The calibration plane of the calibration tool placed on the upper or lower bearing surface is coplanar with the corresponding bearing surface, and the projection of the contact end of the displacement sensor onto the plane where the calibration plane is located falls within the range of the calibration plane.

[0037] In one implementation, it further includes:

[0038] The upper support mechanism includes an upper support platform and an upper moving platform that is slidably engaged with the upper support platform, and the upper tray is disposed on the upper moving platform;

[0039] The lower support mechanism includes a lower support platform and a lower moving platform that is slidably fitted to the lower support platform, and the lower tray is disposed on the lower moving platform.

[0040] The above-mentioned technical features can be combined in various suitable ways or replaced by equivalent technical features, as long as the purpose of the present invention can be achieved.

[0041] The wafer-to-pallet leveling method and apparatus provided by the present invention have at least the following advantages compared with the prior art:

[0042] The present invention discloses a wafer-to-pallet leveling method and apparatus that utilizes direct contact measurement with a displacement sensor, achieving an accuracy within 3μm. Compared to existing air pressure feedback measurement methods, which require close spacing and are easily affected by environmental factors affecting airflow and pressure, the measurement method of the present invention has the advantages of being more direct, less affected by environmental factors, and more accurate. Compared to existing visual focus measurement methods, which require precise adjustment to ensure the measured point is located at the center of the field of view, and the focused image within the depth of field of visual recognition will reflect a clear result, this depth of field itself has a travel of several μm, thus introducing height errors. The measurement method of the present invention does not require additional adjustment, is simple and direct, does not actively introduce errors, and the measurement results are more accurate and reliable. Attached Figure Description

[0043] The invention will now be described in more detail with reference to embodiments and the accompanying drawings.

[0044] Figure 1 The main flowchart of the method of the present invention is shown;

[0045] Figure 2 An exploded view of the overall structure of the device of the present invention is shown;

[0046] Figure 3 A schematic diagram of the lower support mechanism of the device of the present invention is shown;

[0047] Figure 4 An assembly diagram showing the overall structure of the device of the present invention is displayed;

[0048] Figure 5 A schematic diagram of the device of the present invention with a calibration tool placed thereon is shown;

[0049] Figure 6 The image shows a frontal projection view of the device of the present invention.

[0050] In the accompanying drawings, the same parts use the same reference numerals. The drawings are not to scale.

[0051] Figure label:

[0052] 1-Upper support mechanism, 11-Upper tray, 12-Upper motion table, 13-Upper support platform, 2-Lower support mechanism, 21-Lower tray, 211-Perforation, 22-Lower motion table, 23-Lower support platform, 3-Displacement sensor, 4-Lifting drive component, 5-Calibration tool. Detailed Implementation

[0053] The invention will now be further described with reference to the accompanying drawings.

[0054] Example 1

[0055] Embodiments of the present invention provide a wafer-to-pallet leveling method, which can be referred to in the accompanying drawings. Figures 2 to 6 The leveling method of this embodiment can be understood by referring to the device structure shown in the accompanying drawings, but the method is not limited to the device structure shown in the drawings. The method proposed in this embodiment includes the following steps:

[0056] Step S100: Position the contacts of at least three non-collinear displacement sensors in a target plane coplanar with the upper bearing surface of the lower tray, and set the sensing values ​​of the displacement sensors to zero to calibrate the displacement sensors.

[0057] Specifically, based on the principle that three non-collinear points determine a plane, the contacts of the displacement sensors are used as measurement points. At least three contacts of the displacement sensors define a target plane, which is then coplanar with the upper bearing surface of the lower tray. The sensor readings are set to zero, serving as the starting point for the measurement. Alternatively, this target plane can initially be coplanar with the lower bearing surface of the upper tray, also serving as the starting point for the measurement.

[0058] Step S110: Place the calibration tool on the upper support surface of the lower tray, so that the lower surface of the calibration tool is in contact with and coplanar with the upper support surface;

[0059] Specifically, there are many methods to make the target plane coplanar with the upper bearing surface of the lower tray. This also depends on the position of the displacement sensor. If the displacement sensor is positioned relative to the upper bearing surface of the lower tray, then the target plane and the upper bearing surface only need to be in contact with the sensor's contact point to achieve coplanarity. However, considering the rationality of the structural design, in this embodiment, the displacement sensor is positioned on the same side as the lower tray, as shown in the attached figure. Figure 3 As shown, the contact point of the displacement sensor cannot directly contact the upper bearing surface of the lower tray, requiring the use of a calibration tool. The lower surface of the calibration tool and the upper bearing surface of the lower tray have good flatness, and they remain coplanar when in contact.

[0060] Step S120: Extend the displacement sensor from under the lower tray until its top contact touches the lower surface of the calibration tool, then remove the calibration tool.

[0061] Specifically, after the calibration tool is placed in the lower tray, the lower surface of the calibration tool covers the top of the displacement sensor, driving the displacement sensor to extend a portion to contact the lower surface of the calibration tool. This indirectly achieves that the target plane determined by the contact end of the displacement sensor is coplanar with the upper bearing surface of the lower tray.

[0062] Step S200: Drive the displacement sensor to extend until its contact tip contacts the lower bearing surface of the upper tray located above the lower tray, and obtain the sensing values ​​of the displacement sensor respectively.

[0063] Specifically, after determining that the target plane determined by the displacement sensor is coplanar with the upper bearing surface of the lower tray, the corresponding displacement sensor extends simultaneously until its contact tip contacts the lower bearing surface of the upper tray located above the lower tray, and the sensing value of each displacement sensor can be obtained separately.

[0064] Step S300: Determine whether the upper bearing surface and the lower bearing surface are parallel based on the sensing value corresponding to the displacement sensor;

[0065] Specifically, the values ​​of each displacement sensor are compared. Based on the principle, the contacts of multiple displacement sensors are initially located in a target plane coplanar with the upper bearing surface of the lower tray. Therefore, after extending and contacting the lower bearing surface of the upper tray, if the upper bearing surface of the lower tray is parallel to the lower bearing surface of the upper tray, the values ​​of the multiple displacement sensors should be consistent, or the data difference should be within the error range; otherwise, they are not parallel.

[0066] Step S310: Compare the values ​​of at least three sensors corresponding to at least three displacement sensors to obtain the comparison results;

[0067] Step S320: If the comparison result meets the parallel condition, it is determined that the upper bearing surface and the lower bearing surface are parallel. The parallel condition is that the magnitude of the sensing values ​​is the same or the maximum difference between any two is not greater than the preset value.

[0068] Step S330: Otherwise, it is determined that the upper bearing surface and the lower bearing surface are not parallel.

[0069] Specifically, based on the comparison results of at least three sensing values ​​corresponding to at least three displacement sensors, and depending on whether the values ​​are consistent or whether the maximum difference between them is greater than a preset value (error range), it can be directly determined whether the upper bearing surface and the lower bearing surface are parallel.

[0070] Step S400: When it is determined that the upper bearing surface and the lower bearing surface are not parallel, drive the lower pallet or the upper pallet to adjust the relative height so that the upper bearing surface and the lower bearing surface are parallel.

[0071] Step S410: Based on the difference between each pair of sensing values, determine the adjustment value of the corresponding target drive component among the multiple lifting drive components that are respectively set to correspond to the displacement sensor;

[0072] Step S420: The target drive component moves the lower or upper tray up or down according to the adjustment value so that the upper bearing surface is parallel to the lower bearing surface;

[0073] Specifically, when the upper and lower bearing surfaces are not parallel, the lower or upper pallet is adjusted; in this embodiment, the lower pallet is adjusted. The lifting drive component and the displacement sensor are correspondingly positioned in the plane but offset vertically. The target drive component to be adjusted is determined based on the difference in their values, thereby adjusting the local relative height of the lower pallet at the corresponding position. There are many ways to determine the target drive component.

[0074] For example, please refer to the attached diagram. Figure 6 The lifting drive unit corresponds to three displacement sensors, Z0, Z1, and Z2. If their sensor values ​​are Z0 = 10, Z1 = 11, and Z2 = 12, and the preset value (error range) is 0.2, then the maximum difference = Z2 - Z0 = 2, which is greater than the preset value of 0.2. Therefore, it is determined that the upper and lower bearing surfaces are not parallel. Adjustment can be made using the following methods, including but not limited to:

[0075] (1) First, an adjustment base point Z0 (the lifting drive with the smallest sensing value) can be determined. The lifting drive Z0 is not moved. The lifting drive Z1 and Z2 are taken as the target drive to be adjusted. Then the adjustment value of Z1 is Z1-Z0=1 and the adjustment value of Z2 is Z2-Z0=2. Adjust (retract) the lifting drive Z1 and Z2 according to the adjustment value so that the sensing values ​​of the lifting drive Z1 and Z2 are consistent with Z0, thereby realizing that the upper bearing surface is parallel to the lower bearing surface.

[0076] Of course, you can also first determine the lifting drive with the largest sensor value as the adjustment base point, such as Z2 in the example above; or determine the lifting drive with an intermediate sensor value as the adjustment base point, such as Z1 in the example above. The subsequent adjustment method is the same as the method described above.

[0077] (2) Based on the distance requirement between the upper and lower trays, the upper tray can be used as a fixed reference to determine the target position of the lower tray in the height direction when it is in a parallel state. The height of the target position is converted into the target value of the displacement sensor. For example, if the target value Z = 11.5, then based on the above example, the lifting drive components Z0, Z1, and Z2 need to be adjusted and thus all serve as target drive components. Their adjustment values ​​are the corresponding differences of -1.5 (retract), -0.5 (retract), and 0.5 (extend).

[0078] Furthermore, in this embodiment, based on the technical requirements for wafer stacking, the preset value (error range) for parallelism is determined to be 3μm.

[0079] Step S430: Reacquire the sensing values ​​of the displacement sensors respectively;

[0080] Step S440: Determine the comparison result of the numerical values ​​based on the reacquired sensor values, and determine again whether the comparison result meets the parallel condition.

[0081] Step S450: If the parallel condition is still not met, readjust the lower tray using the lifting assembly;

[0082] Specifically, after the adjustment is completed, the adjustment result needs to be further determined. Then, after the adjustment, the contact of the displacement sensor is brought back into contact with the lower bearing surface of the upper tray (or the contact between the contact of the displacement sensor and the lower bearing surface of the upper tray is maintained throughout the adjustment process) to obtain the sensing value again. The parallel requirement is then determined again based on the sensing value. If it is not met, the adjustment is carried out again according to the aforementioned adjustment method.

[0083] Step S500: After confirming that the upper bearing surface and the lower bearing surface are parallel, reset the displacement sensor to the bottom of the lower tray and output a leveling completion signal.

[0084] It should be noted that the attached diagram can be used as a reference. Figure 2 In practical applications, the device containing the tray usually has two stations: the transfer station and the calibration station. The upper and lower trays correspond to each other at the calibration station and are staggered at the transfer station. The lower tray is used for loading and unloading calibration tools at the transfer station.

[0085] Example 2

[0086] An embodiment of the present invention provides a wafer-to-pallet leveling device, comprising:

[0087] Upper pallet 11, the lower surface of which is the lower bearing surface;

[0088] The lower tray 21 is disposed opposite to the upper tray 11, and the upper surface of the lower tray 21 is the upper bearing surface;

[0089] A sensor assembly comprising at least three non-collinear displacement sensors 3, each displacement sensor 3 having a contact tip at its top and being extendable and retractable in a direction in which the upper tray 11 and the lower tray 21 are opposite to each other.

[0090] The lifting assembly includes multiple lifting drive components 4 connected to the upper tray 11 or the lower tray 21, and the lifting drive components 4 are configured to correspond one-to-one with the displacement sensors 3 in the sensor assembly.

[0091] Among them, the contacts of at least three displacement sensors 3 can determine a target plane that is coplanar with the lower or upper bearing surface and serves as the starting point of the extension.

[0092] Specifically, as shown in the attached diagram. Figures 2 to 6As shown, the upper tray 11 is positioned above the lower tray 21, the lifting assembly is supported on the lower tray 21, and the displacement sensor 3 is positioned on the lower tray 21. The displacement sensor 3 and the lifting drive component 4 correspond to each other and their positions on the horizontal plane coincide.

[0093] Furthermore, the displacement sensor 3 assembly is disposed below the lower tray 21, which has a plurality of through holes 211 corresponding to the respective displacement sensors 3.

[0094] Furthermore, it also includes:

[0095] The calibration tool 5 has a calibration plane that meets the flatness requirements, and the calibration tool 5 can be placed on the upper bearing surface or the lower bearing surface.

[0096] Among them, the calibration plane of the calibration tool 5 placed on the upper or lower bearing surface is coplanar with the corresponding bearing surface, and the projection of the contact end of the displacement sensor 3 in the plane where the calibration plane is located falls within the range of the calibration plane.

[0097] Specifically, refer to the attached diagram. Figure 3 The displacement sensor 3 is integrated into the lower tray 21 and passes through the perforation 211 on the lower tray 21. When the calibration tool 5 is placed on the lower tray 21, the calibration plane on its lower surface covers the opening of the perforation 211, thereby enabling the projection of the contact of the displacement sensor 3 in the plane of the calibration plane to fall within the range of the calibration plane. In this way, the contact of the displacement sensor 3 can accurately contact the calibration plane of the calibration tool 5.

[0098] Furthermore, it also includes:

[0099] The upper support mechanism 1 includes an upper support platform 13 and an upper motion platform 12 that is slidably engaged with the upper support platform 13, and an upper tray 11 is disposed on the upper motion platform 12;

[0100] The lower support mechanism 2 includes a lower support platform 23 and a lower motion platform 22 that is slidably fitted to the lower support platform 23, and a lower tray 21 is disposed on the lower motion platform 22.

[0101] Specifically, the upper tray 11 and the lower tray 21 are respectively included in the upper support mechanism 1 and the lower support mechanism 2, and the support platform and the motion platform in the upper support mechanism 1 and the lower support mechanism 2 respectively realize the movement of the upper tray 11 and the lower tray 21 in the horizontal plane.

[0102] In the description of this invention, it should be understood that the terms "upper", "lower", "bottom", "top", "front", "rear", "inner", "outer", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0103] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A wafer-to-tray leveling device, characterized in that, include: The upper pallet has its lower surface as the lower load-bearing surface. The lower tray is disposed opposite to the upper tray, and the upper surface of the lower tray is the upper bearing surface; A sensor assembly comprising at least three non-collinear displacement sensors, each displacement sensor having a contact tip at its top and being retractable in a direction in which the upper and lower trays are opposite to each other; the displacement sensor assembly is disposed below the lower tray, which has a plurality of through holes corresponding to the respective displacement sensors; The lifting assembly includes multiple lifting drive components connected to the upper tray or the lower tray, and each lifting drive component is configured to correspond one-to-one with a displacement sensor in the sensor assembly; The contacts of the at least three displacement sensors can determine a target plane that is coplanar with the lower or upper bearing surface and serves as the starting point for the extension.

2. The wafer-to-pallet leveling device according to claim 1, characterized in that, Also includes: A calibration tool having a calibration plane that meets flatness requirements, the calibration tool being able to be placed on the upper bearing surface or the lower bearing surface; Wherein, the calibration plane of the calibration tool placed on the upper or lower bearing surface is coplanar with the corresponding bearing surface, and the projection of the contact end of the displacement sensor in the plane where the calibration plane is located falls within the range of the calibration plane.

3. The wafer-to-pallet leveling device according to claim 1, characterized in that, Also includes: The upper support mechanism includes an upper support platform and an upper moving platform that is slidably engaged with the upper support platform, and the upper tray is disposed on the upper moving platform; The lower support mechanism includes a lower support platform and a lower moving platform that is slidably fitted to the lower support platform, and the lower tray is disposed on the lower moving platform.

4. A wafer-to-pallet leveling method, applied in claim 1 3. The wafer-to-tray leveling device according to any one of the claims, characterized in that, include: The contacts of at least three non-collinear displacement sensors are positioned in a target plane coplanar with the upper bearing surface of the lower tray, and the sensing values ​​of the displacement sensors are set to zero to calibrate the displacement sensors. Drive the displacement sensor to extend until its contact tip contacts the lower bearing surface of the upper tray located above the lower tray, and obtain the sensing values ​​of the displacement sensor respectively; Based on the sensing value corresponding to the displacement sensor, it is determined whether the upper bearing surface and the lower bearing surface are parallel; When it is determined that the upper bearing surface and the lower bearing surface are not parallel, the lower tray or the upper tray is driven to adjust their relative height so that the upper bearing surface and the lower bearing surface are parallel.

5. The wafer-to-pallet leveling method according to claim 4, characterized in that, To ensure that the contacts of at least three non-collinear displacement sensors are located in a target plane coplanar with the upper bearing surface of the lower tray, including: Place the calibration tool on the upper support surface of the lower tray, so that the lower surface of the calibration tool is in contact with and coplanar with the upper support surface; The displacement sensor extends from under the lower tray until its top contact point touches the lower surface of the calibration tool, and then the calibration tool is removed.

6. The wafer-to-pallet leveling method according to claim 4, characterized in that, Determining whether the upper bearing surface and the lower bearing surface are parallel includes: Compare the numerical values ​​of at least three displacement sensors to obtain a comparison result. If the comparison result meets the parallel condition, it is determined that the upper bearing surface and the lower bearing surface are parallel. The parallel condition is that the magnitudes of the sensing values ​​are the same or the maximum difference between any two values ​​is not greater than a preset value. Otherwise, it is determined that the upper bearing surface and the lower bearing surface are not parallel.

7. The wafer-to-pallet leveling method according to claim 6, characterized in that, Driving the lower tray or the upper tray to adjust their relative height so that the upper bearing surface is parallel to the lower bearing surface includes: Based on the magnitude of the difference between each pair of the sensing values, the adjustment value of the corresponding target drive component among the multiple lifting drive components that are respectively set to correspond to the displacement sensor is determined; The target drive component is adjusted to raise or lower the lower tray or the upper tray according to the adjustment value, so that the upper bearing surface is parallel to the lower bearing surface.

8. The wafer-to-pallet leveling method according to claim 7, characterized in that, After the target drive unit causes the lower tray to rise or fall according to the adjustment value, it further includes: The sensing values ​​of the displacement sensors are reacquired respectively; The comparison result of the numerical value comparison is determined based on the reacquired sensor value, and it is determined again whether the comparison result satisfies the parallel condition. If the parallel condition is still not met, the lower tray is readjusted using the lifting assembly.

9. The wafer-to-pallet leveling method according to claim 4, characterized in that, Also includes: After confirming that the upper bearing surface is parallel to the lower bearing surface, the displacement sensor is reset and retracted to below the lower tray, and a leveling completion signal is output.

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