Substrate processing system with vertically aligned structure

Abstract

A substrate processing system according to one embodiment includes: a cleaning device for cleaning a substrate and located in a first position; a drying device for drying a substrate and located in a second position; and a transfer unit for transferring the substrate from the cleaning device to the drying device, wherein the first position and the second position may be arranged in a vertical manner.

Description

Technical Field

[0001] The following embodiments relate to a substrate processing system having a vertically aligned structure. Background Technology

[0002] Semiconductors are typically manufactured through a series of processes including photolithography, vapor deposition, and etching. Due to these repeated processes, various contaminants, such as particles, metallic impurities, or organic matter, remain on the surface of the substrate that makes up these semiconductors. These contaminants on the substrate reduce the reliability of the manufactured semiconductors. Therefore, to mitigate this issue, the semiconductor manufacturing process involves cleaning and drying the substrate.

[0003] Previously, because the cleaning and drying units were arranged horizontally, the cleaning solution on the substrate tilted to one side during the horizontal movement of the substrate from the cleaning unit to the drying unit, resulting in cleaning solution loss. Furthermore, since the weight measuring device was located in the transfer section where the substrate was transferred, the accuracy of the weight measurement decreased due to shaking during transfer. Therefore, a substrate processing system is needed that minimizes the tilting phenomenon of the cleaning solution and the resulting cleaning solution loss when transferring the substrate from the cleaning unit to the drying unit. Additionally, a substrate processing system in which the transfer section and the weight measuring section are composed of separate structures is needed to accurately measure the weight of the substrate.

[0004] The aforementioned background technology is technology that the inventor possessed or mastered in the process of deriving the disclosure of this application, and is not necessarily publicly known technology that was disclosed to the general public before this application. Summary of the Invention

[0005] One embodiment aims to provide a substrate processing system that prevents the cleaning fluid on the substrate from tilting during the transfer of the substrate from a cleaning device to a drying device, and minimizes the loss of the cleaning fluid.

[0006] One embodiment aims to provide a substrate processing system in which the transfer unit and the weight measuring unit are separately configured to improve the accuracy of weight measurement.

[0007] A substrate processing system according to one embodiment includes: a cleaning device for cleaning a substrate and located in a first position; a drying device for drying a substrate and located in a second position; and a transfer unit for transferring the substrate from the cleaning device to the drying device, wherein the first position and the second position may be arranged in a vertical manner.

[0008] The first position can be higher than the second position.

[0009] It may also include a weight measuring unit, which measures the weight of the substrate once at a first position after the cleaning process is completed, and measures the weight of the substrate a second time at a second position after the substrate is transferred to a second position.

[0010] The weight measuring unit may include: a first weight measuring device located in a first position; and a second weight measuring device located in a second position.

[0011] The weight measuring unit may also include a hinge drive unit, which enables the first weight measuring device to be hinge-driven from the horizontal direction to the vertical direction.

[0012] After the cleaning process is completed, the transfer unit transfers the substrate from the cleaning device to the first weight measuring device. After the first weight measuring device completes a weight measurement, the hinge drive unit enables the first weight measuring device to be hinged from the horizontal direction to the vertical direction.

[0013] When the first weight measuring device is driven by the hinge in the vertical direction, the transfer unit moves the substrate from the first position to the second weight measuring device. When the second weight measuring device completes the second weight measurement, the transfer unit can transfer the substrate from the second weight measuring device to the drying device.

[0014] The weight measuring unit may include: a weight measuring device for measuring the weight of the substrate; a track connecting the first position and the second position; and a drive unit for moving the weight measuring device along the track.

[0015] After the cleaning process is completed, the transfer unit transfers the substrate from the cleaning device to the weight measuring device located at the first position. After the weight measuring device completes a weight measurement, the drive unit can move the weight measuring device from the first position to the second position.

[0016] When the weight measuring device moves to the second position, the transfer unit transfers the substrate from the first position to the weight measuring device located at the second position. After the weight measuring device completes the second weight measurement, the transfer unit can transfer the substrate from the weight measuring device to the drying device.

[0017] It may also include a control unit that adjusts the conveying speed of the conveying unit by comparing the weight in a primary weight measurement and a secondary weight measurement.

[0018] The weight measuring unit includes a first weight measuring unit and a second weight measuring unit respectively installed in the cleaning device and the drying device. The first weight measuring unit and the second weight measuring unit may include: a tunnel portion respectively installed in the opening of the cleaning device and the drying device; a load sensor disposed on the upper part of the tunnel portion; and a substrate mounting portion disposed inside the tunnel portion.

[0019] After the cleaning process is completed, the transfer unit transfers the substrate from the cleaning device to the substrate mounting section of the first weight measuring unit. After the load sensor of the first weight measuring unit completes a weight measurement, the transfer unit can transfer the substrate from the substrate mounting section of the first weight measuring unit to the substrate mounting section of the second weight measuring unit.

[0020] When the load sensor of the second weight measuring unit completes the second weight measurement, the transfer unit can transfer the substrate from the substrate mounting part of the second weight measuring unit to the drying device.

[0021] It may also include a control unit that adjusts the conveying speed of the conveying unit by comparing the weight in a primary weight measurement and a secondary weight measurement.

[0022] According to one embodiment of the substrate processing system, since the cleaning device and the drying device are arranged in a vertical direction, the tilting of the cleaning liquid on the substrate can be prevented during the transfer of the substrate, and the loss of the cleaning liquid can be minimized.

[0023] According to one embodiment of the substrate processing system, since the transfer unit and the weight measurement unit are separately configured, the accuracy of weight measurement can be improved.

[0024] The effects of the substrate processing system according to one embodiment are not limited to those mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the following description. Attached Figure Description

[0025] Figure 1 and Figure 2 As a schematic side view of a substrate processing system according to one embodiment, the process of transferring a substrate from a cleaning apparatus to a drying apparatus is shown.

[0026] Figure 3 This is a schematic side view of a substrate processing apparatus according to one embodiment.

[0027] Figure 4 This is a schematic front view of a substrate processing apparatus according to one embodiment.

[0028] Figure 5 This is a schematic side view of a substrate processing apparatus according to one embodiment.

[0029] Figure 6 This is a perspective view of the weight measuring unit according to one embodiment. Detailed Implementation

[0030] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, since various modifications can be made to the embodiments, the scope of the patent application is not limited or restricted by these embodiments. Rather, it should be understood that all modifications, equivalents, and even substitutions made to the embodiments are included within the scope of the claims.

[0031] The terminology used in the embodiments is for illustrative purposes only and should not be construed as intended to be limiting. Singular expressions include plural expressions unless the context clearly distinguishes them. In this specification, terms such as "comprising" or "having" should be understood to specify the presence of features, numbers, steps, actions, constituent elements, components, or combinations thereof described in the specification, and not to preclude the presence or additional possibilities of one or more other features or numbers, steps, actions, constituent elements, components, or combinations thereof.

[0032] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments pertain. Terms as defined in commonly used dictionaries should be interpreted as having the same meaning as they have in the context of the relevant art, and should not be construed as having an ideal or overly formal meaning unless expressly defined herein.

[0033] Furthermore, when describing the embodiments with reference to the accompanying drawings, regardless of the reference numerals, the same reference numerals are assigned to the same constituent elements, and repeated descriptions are omitted. When describing embodiments, detailed descriptions of related well-known technologies are omitted if it is determined that such detailed descriptions may unnecessarily obscure the essence of the embodiments.

[0034] Furthermore, when describing the constituent elements of the embodiments, terms such as first, second, A, B, (a), and (b) may be used. These terms are merely for distinguishing the constituent element from other constituent elements and do not limit the nature, order, or steps of the relevant constituent elements. When a constituent element is described as "connected," "combined," or "accessed" to other constituent elements, it should be understood that although the constituent element can be directly connected to or accessed to other constituent elements, there may also be other constituent elements that are "connected," "combined," or "accessed" between the constituent elements.

[0035] For a given embodiment, the constituent elements and constituent elements that share a common function are described using the same names in another embodiment. Unless otherwise stated, the descriptions described in any embodiment are also applicable to other embodiments, and specific details are omitted to the extent necessary for repetition.

[0036] Figure 1 and Figure 2 As a schematic side view of a substrate processing system according to one embodiment, the process of transferring a substrate from a cleaning apparatus to a drying apparatus is shown.

[0037] refer to Figure 1 and Figure 2According to one embodiment, the substrate processing system 1 can clean and dry the substrate W. During the cleaning process performed by the cleaning apparatus 11, a cleaning solution can be applied to the substrate W. The substrate W coated with the cleaning solution is transferred to the drying apparatus 12, where the cleaning solution is removed during the drying process.

[0038] According to one embodiment, the substrate processing system 1 may include a cleaning device 11, a drying device 12, a transfer unit 13, a weight measuring unit 14, and a control unit (not shown).

[0039] The cleaning apparatus 11 can perform a cleaning process on the substrate W. The cleaning apparatus 11 may include an opening through which the substrate W can enter and exit, and the opening may be opened and closed. The cleaning apparatus 11 may be located in a first position.

[0040] The drying apparatus 12 can perform a drying process on the substrate W. The drying apparatus 12 may include an opening through which the substrate W can enter and exit, and the opening may be opened and closed. The drying apparatus 12 may be located in a second position.

[0041] The first and second positions can be arranged perpendicularly. In other words, the washing device 11 and the drying device 12 can be arranged perpendicularly to each other. The first position can be higher than the second position. In other words, the washing device 11 can be located above the drying device 12. On the other hand, the second position can be higher than the first position. In this case, the drying device 12 can also be located above the washing device 11.

[0042] The transfer unit 13 can transfer the substrate W. The transfer unit 13 can transfer the substrate W between the cleaning device 11 and the drying device 12. In other words, the transfer unit 13 can transfer the substrate W from the cleaning device 11 to the drying device 12. Additionally, the transfer unit 13 can introduce the substrate W into the cleaning device 11 and the drying device 12, or remove it from them, respectively. For example, the transfer unit 13 may include a robot and a track. The robot moves vertically along the track and can transfer the substrate W to a first position and a second position. With the substrate W transferred to the first and second positions, the robot can move horizontally and introduce the substrate W into the cleaning device 11 and the drying device 12, or remove it from them, respectively.

[0043] The weight measuring unit 14 can measure the weight of the substrate W. Specifically, the weight measuring unit 14 can measure the weight of the substrate W once at a first position after the cleaning process is completed, and then measure the weight of the substrate W a second time at a second position after the substrate W is transferred to a second position.

[0044] According to one embodiment, the weight measuring unit 14 may include a first weight measuring device 141, a second weight measuring device 142, and a hinge drive unit 143.

[0045] The first weight measuring device 141 may be located in a first position. For example, the first weight measuring device 141 may be located at a predetermined distance below the opening of the cleaning device 11. The first weight measuring device 141 may measure the weight of the substrate W after the cleaning process has been completed in one measurement.

[0046] The second weight measuring device 142 may be located in a second position. For example, the second weight measuring device 142 may be located at a predetermined distance below the opening of the drying device 12. The second weight measuring device 142 may perform a second measurement on the weight of the substrate W transferred to the second position. The second weight measuring device 142 may be configured to have the same sensitivity as the first weight measuring device 141.

[0047] The hinge drive unit 143 enables the first weight measuring device 141 to be hinge-driven from the horizontal direction to the vertical direction. For example, the hinge drive unit 143 enables the first weight measuring device 141, which is arranged in the horizontal direction, to rotate downward about the hinge center, thereby changing to the vertical direction.

[0048] The following describes the operating sequence of the substrate processing system 1.

[0049] Reference Figure 1 The substrate W can be introduced into the cleaning apparatus 11 from a first position. A cleaning process can be performed on the substrate W in the cleaning apparatus 11. When the cleaning process is complete, the substrate W can be transported out of the cleaning apparatus 11 by means of the transfer unit 13, and then lowered and mounted on the first weight measuring device 141. The first weight measuring device 141 can measure the weight of the substrate W once. After completing one weight measurement, the substrate W is slightly raised upwards by means of the transfer unit 13, and the first weight measuring device 141 can be hinged from the horizontal direction to the vertical direction by the hinge drive unit 143. According to the structure described above, the substrate W transfer path of the transfer unit 13 and the first weight measuring device 141 do not interfere with each other. (Refer to...) Figure 2 The transfer unit 13 can descend to transfer the substrate W from the first position to the second weight measuring device 142, where the substrate W can be mounted. The second weight measuring device 142 can perform a second weight measurement on the substrate W. After the second weight measurement is completed, the substrate W is slightly raised by the transfer unit 13 and introduced into the drying device 12 for the drying process. The drying device 12 can perform the drying process. As described above, the cleaning device 11 and the drying device 12 are arranged in a vertical direction, so that the substrate W coated with cleaning liquid can be transferred and lowered in a vertical direction. Therefore, since the transfer direction of the substrate W is consistent with the downward airflow and gravity direction above, the loss of cleaning liquid can be minimized.

[0050] The control unit can adjust the transfer speed of the transfer unit 13 by comparing the weights measured in the first and second weight measurements. Specifically, the control unit can measure the amount of cleaning fluid loss by comparing the weights measured in the first and second weight measurements, thereby optimizing the transfer conditions by adjusting the transfer speed of the transfer unit 13, and determining whether there are any abnormalities in the process and equipment by using the detected weight data.

[0051] Figure 3 This is a schematic side view of a substrate processing apparatus according to one embodiment. Figure 4 This is a schematic front view of a substrate processing apparatus according to one embodiment.

[0052] Reference Figure 3 and Figure 4 According to one embodiment, the substrate processing system 2 may include a cleaning device 21, a drying device 22, a transfer unit 23, a weight measuring unit 24, and a control unit (not shown). The cleaning device 21, the drying device 22, the transfer unit 23, and the control unit have the same structure as described above, so detailed descriptions are omitted.

[0053] The weight measuring unit 24 can measure the weight of the substrate W. Specifically, the weight measuring unit 24 can measure the weight of the substrate W once at a first position after the cleaning process is completed, and then measure the weight of the substrate W a second time at a second position after the substrate W is transferred to a second position.

[0054] According to one embodiment, the weight measuring unit 24 may include a weight measuring device 241, a track 242, and a drive unit (not shown).

[0055] The weight measuring device 241 can measure the weight of the substrate W. The track 242 provides a movement path for the weight measuring device 241. The track 242 can be arranged vertically, passing through a first position and a second position. A drive unit allows the weight measuring device 241 to move along the track 242. Therefore, the weight measuring device 241 can be moved vertically along the track 242 between the first and second positions via the drive unit.

[0056] The following describes the operating sequence of the substrate processing system 2.

[0057] Reference Figure 3 and Figure 4The substrate W can be introduced into the cleaning apparatus 21 from a first position. A cleaning process can be performed on the substrate W in the cleaning apparatus 21. At this time, the weight measuring device 241 can be located in the first position. For example, the weight measuring device 241 can be located at a predetermined distance below the opening of the cleaning apparatus 21. When the cleaning process is completed, the substrate W can be transported out of the cleaning apparatus 21 via the transfer unit 23, and lowered and mounted on the weight measuring device 241 located in the first position. The weight measuring device 241 can measure the weight of the substrate W once. After completing one weight measurement, the substrate W is slightly raised upwards via the transfer unit 23, and the weight measuring device 241 can be lowered to a second position along the track 242 via the drive unit. For example, the weight measuring device 241 can be located at a predetermined distance below the opening of the drying apparatus 22. According to the structure described above, the substrate W transfer path of the transfer unit 23 and the weight measuring device 241 can be independent of each other. Subsequently, the transfer unit 23 can descend to transfer the substrate W from the first position to the weight measuring device 241 located at the second position, and the substrate W can be mounted on the weight measuring device 241 located at the second position. The weight measuring device 241 can perform a second weight measurement on the substrate W. After the second weight measurement is completed, the substrate W is slightly raised upward by the transfer unit 23 and introduced into the drying device 22 for the drying process. The drying device 22 can perform the drying process. As described above, the cleaning device 21 and the drying device 22 are arranged in a vertical direction, so that the substrate W coated with cleaning liquid can be transferred downward in a vertical direction. Therefore, since the transfer direction of the substrate W is consistent with the downward airflow and gravity direction above, the loss of cleaning liquid can be minimized. In addition, according to this structure, since the weight measuring device 241 is always located at a position lower than the transfer unit 13, there is no interference in the path, and since both the first and second measurements are performed using a single weight measuring device 241, the measurement error can be reduced compared to using multiple weight measuring devices.

[0058] Figure 5 This is a schematic side view of a substrate processing apparatus according to one embodiment. Figure 6 This is a perspective view of the weight measuring unit according to one embodiment.

[0059] Reference Figure 5 and Figure 6 According to one embodiment, the substrate processing system 3 may include a cleaning device 31, a drying device 32, a transfer unit 33, a weight measuring unit 34, and a control unit (not shown). The cleaning device 31, the drying device 32, the transfer unit 33, and the control unit have the same structure as described above, so specific descriptions are omitted.

[0060] The weight measuring unit 34 can measure the weight of the substrate W. Specifically, the weight measuring unit 34 can measure the weight of the substrate W once at a first position after the cleaning process is completed, and then measure the weight of the substrate W a second time at a second position after the substrate W is transferred to a second position.

[0061] According to one embodiment, the weight measuring unit 34 may include a first weight measuring unit 34a and a second weight measuring unit 34b. The first weight measuring unit 34a may be installed in the cleaning device 31. The second weight measuring unit 34b may be installed in the drying device 32.

[0062] The first weight measuring unit 34a and the second weight measuring unit 34b may respectively include a tunnel section 341, a load sensor 342, and a substrate mounting section 343.

[0063] The tunnel section 341 can be installed in the openings of the cleaning device 31 and the drying device 32 respectively. The tunnel section 341 may have a shape that surrounds the periphery of the opening. The tunnel section 341 may serve the purpose of preventing particles from entering.

[0064] The load sensor 342 can be installed on the upper part of the tunnel section 341. The load sensor 342 can connect the upper part of the tunnel section 341 to the openings of the cleaning device 31 and the drying device 32.

[0065] The substrate mounting portion 343 can be disposed inside the tunnel portion 341. For weight measurement, the substrate W can be mounted on the substrate mounting portion 343, and the load sensor 342 can measure the weight of the substrate W by measuring the weight increase before and after mounting. With this structure, the mounting space can be minimized, and the transfer time can be shortened. Furthermore, it does not interfere with the transfer path of the transfer portion 33.

[0066] The following describes the operating sequence of the substrate processing system 2.

[0067] Reference Figure 5 and Figure 6The substrate W can be introduced into the cleaning apparatus 31 from a first position. In the cleaning apparatus 31, a cleaning process can be performed on the substrate W. After the cleaning process is completed, the substrate W can be transported out of the cleaning apparatus 31 via the transfer unit 33, and simultaneously lowered and mounted on the substrate mounting portion 343 of the first weight measuring unit 34a. The load sensor 342 can perform a first weight measurement on the substrate W. After the first weight measurement is completed, the substrate W can be slightly raised upwards from the substrate mounting portion 343 of the first weight measuring unit 34a via the transfer unit 33 and transferred to the substrate mounting portion 343 of the second weight measuring unit 34b. The substrate W is mounted on the substrate mounting portion 343 of the second weight measuring unit 34b, and the load sensor 342 can perform a second weight measurement on the substrate W. After the second weight measurement is completed, the substrate W can be slightly raised upwards from the substrate mounting portion 343 of the second weight measuring unit 34b via the transfer unit 33 and introduced into the drying apparatus 32 for the drying process. The drying apparatus 32 can perform a drying process. As described above, the cleaning device 31 and the drying device 32 are arranged vertically, so that the substrate W coated with cleaning liquid can be moved downward in the vertical direction. Therefore, since the moving direction of the substrate W is consistent with the downward airflow and gravity direction above, the loss of cleaning liquid can be minimized.

[0068] As described above, although embodiments have been illustrated with limited figures, those skilled in the art can apply various technical modifications and variations based on the above. For example, appropriate results can be obtained even if the described techniques are performed in a different order than those described, and / or the described system, structure, device, circuit, and other constituent elements are combined or integrated in a different form than those described, or replaced or substituted with other constituent elements or equivalents.

[0069] Therefore, other embodiments, other implementations, and contents equivalent to those in the patent claims also fall within the scope of the claims.

Claims

1. A substrate processing system, characterized by, The substrate processing system comprises: a cleaning device for performing a cleaning process on a substrate and located at a first position; a drying device for performing a drying process on the substrate and located at a second position; and a transfer unit for transferring the substrate from the cleaning device to the drying device, the first position and the second position are arranged in a vertical manner; a weight measuring unit for measuring the weight of the substrate at the first position after the cleaning process and at the second position after the substrate is transferred to the second position; a first weight measuring device located at the first position; and a second weight measuring device located at the second position; the weight measuring unit further comprises a hinge driving unit for hinge driving the first weight measuring device from a horizontal direction to a vertical direction; wherein the weight measuring unit and the transfer unit are separately arranged and located on a path between the first position and the second position.

2. The substrate processing system according to claim 1, wherein the first position is higher than the second position.

3. The substrate processing system according to claim 1, wherein after the cleaning process, the transfer unit transfers the substrate from the cleaning device to the first weight measuring device, after the first weight measuring device completes the first weight measurement, the hinge driving unit hinge drives the first weight measuring device from the horizontal direction to the vertical direction.

4. The substrate processing system according to claim 3, wherein after the first weight measuring device is hinge driven in the vertical direction, the transfer unit transfers the substrate from the first position to the second weight measuring device, after the second weight measuring device completes the second weight measurement, the transfer unit transfers the substrate from the second weight measuring device to the drying device. The substrate processing system comprises:

5. A substrate processing system, characterized by, a cleaning device for performing a cleaning process on a substrate and located at a first position; a drying device for performing a drying process on the substrate and located at a second position; and a transfer unit for transferring the substrate from the cleaning device to the drying device, the first position and the second position are arranged in a vertical manner; a weight measuring unit for measuring the weight of the substrate at the first position after the cleaning process and at the second position after the substrate is transferred to the second position; the weight measuring unit comprises a weight measuring device for measuring the weight of the substrate; a track connecting the first position and the second position; and a driving unit for moving the weight measuring device along the track; wherein the weight measuring unit and the transfer unit are separately arranged and located on a path between the first position and the second position.

6. The substrate processing system according to claim 5, wherein after the cleaning process, the transfer unit transfers the substrate from the cleaning device to the weight measuring device located at the first position, after the weight measuring device completes the first weight measurement, the driving unit moves the weight measuring device from the first position to the second position.

7. The substrate processing system according to claim 6, wherein after the weight measuring device is moved to the second position, the transfer unit transfers the substrate from the first position to the weight measuring device located at the second position, after the weight measuring device completes the second weight measurement, the transfer unit transfers the substrate from the weight measuring device to the drying device. ​ ​ ​ 8. The substrate processing system of claim 7, wherein, Further comprising: a control unit that adjusts the transfer speed of the transfer unit by comparing the weight in the first weight measurement and the second weight measurement.

9. A substrate processing system, characterized by, Further comprising: a cleaning device that performs a cleaning process on the substrate and is located at the first position; a drying device that performs a drying process on the substrate and is located at the second position; and a transfer unit that transfers the substrate from the cleaning device to the drying device, the first position and the second position are arranged in a vertical manner; a weight measurement unit that measures the weight of the substrate at the first position after the cleaning process is completed and measures the weight of the substrate at the second position after the substrate is transferred to the second position; the weight measurement unit comprises a first weight measurement unit and a second weight measurement unit respectively installed on the cleaning device and the drying device, the first weight measurement unit and the second weight measurement unit comprise: a tunnel unit respectively installed on the opening of the cleaning device and the drying device; a load sensor arranged on the upper part of the tunnel unit; and a substrate mounting unit arranged in the interior of the tunnel unit; wherein the weight measurement unit and the transfer unit are separately arranged and are arranged on a path between the first position and the second position.

10. The substrate processing system according to claim 9, wherein: when the cleaning process is completed, the transfer unit transfers the substrate from the cleaning device to the substrate mounting unit of the first weight measurement unit, when the load sensor of the first weight measurement unit completes the first weight measurement, the transfer unit transfers the substrate from the substrate mounting unit of the first weight measurement unit to the substrate mounting unit of the second weight measurement unit.

11. The substrate processing system according to claim 10, wherein: when the load sensor of the second weight measurement unit completes the second weight measurement, the transfer unit transfers the substrate from the substrate mounting unit of the second weight measurement unit to the drying device.

12. The substrate processing system according to claim 11, further comprising: a control unit that adjusts the transfer speed of the transfer unit by comparing the weight in the first weight measurement and the second weight measurement. ​

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