Transportation device

Abstract

The application provides a transport device. The transport device is used for transporting a wafer to a preset position, and comprises: a bearing structure used for bearing the wafer; an electromagnetic assembly located at the periphery of at least part of the bearing structure, the electromagnetic assembly being used for applying an electromagnetic force to the bearing structure after being powered on, so that the bearing structure is in a suspended state; and a driving assembly connected with the bearing structure, the driving assembly being used for driving the bearing structure to move to the preset position when the bearing structure is in the suspended state. The application effectively solves the problem that the operation instability of a lower platform affects the alignment precision of upper and lower wafers in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, and in particular, to a transportation device. BACKGROUND

[0002] At present, wafer bonding technology is used to tightly bond two polished wafers together, and is widely used in 3D integrated circuits and micro mechanical systems. Specifically, in the process flow of wafer bonding, after the upper wafer is aligned, the lower platform is used to drive the lower wafer to move to a specified position for bonding with the upper wafer. Among them, the lower platform is usually driven to move by rollers. Specifically, an electric motor drives the rollers to rotate, and the rollers are in contact with the lower platform to drive the lower platform to slide.

[0003] However, since the rollers are in direct contact with the lower platform, long-term use can cause wear and tear of the rollers and the lower platform, affecting the normal use of the lower platform, and even affecting the alignment accuracy of the lower wafer and the upper wafer. SUMMARY

[0004] The main purpose of the present application is to provide a transportation device and a wafer transportation method to solve the problem of unstable operation of the lower platform in the prior art, which affects the alignment accuracy of the upper and lower wafers.

[0005] In order to achieve the above purpose, the present application provides a transportation device for transporting a wafer to a predetermined position, the transportation device comprising: a bearing structure for bearing the wafer; an electromagnetic assembly located at least partially around the bearing structure, the electromagnetic assembly being used to apply an electromagnetic force to the bearing structure after being energized, so that the bearing structure is in a suspended state; a driving assembly connected to the bearing structure; the driving assembly is used to drive the bearing structure to move to the predetermined position when the bearing structure is in the suspended state.

[0006] Further, the transportation device further comprises a rack, and the electromagnetic assembly is arranged on the rack.

[0007] Further, the electromagnetic assembly comprises: a first electromagnetic structure located below the bearing structure, the first electromagnetic structure applying an upward electromagnetic force to the bearing structure; a second electromagnetic structure located above the bearing structure and arranged opposite to the first electromagnetic structure, the second electromagnetic structure applying an upward or downward electromagnetic force to the bearing structure.

[0008] Further, each group of electromagnetic assemblies further comprises: a third electromagnetic structure located on one side of the bearing structure, the third electromagnetic structure applying an electromagnetic force to the first side of the bearing structure towards or away from the second side of the bearing structure; the first side and the second side are arranged opposite to each other.

[0009] Further, the electromagnetic assemblies are two groups, one group of electromagnetic assemblies covers at least a first side of the bearing structure, and the other group of electromagnetic assemblies covers at least a second side of the bearing structure; wherein the first side and the second side are oppositely arranged.

[0010] Further, the racks are two, the two racks are arranged in one-to-one correspondence with the two groups of electromagnetic assemblies, and the two racks are respectively located at the two sides of the bearing structure; wherein the driving assembly drives the bearing structure to move along a preset direction, and each rack extends along the preset direction.

[0011] Further, the rack comprises: a first plate body, the first electromagnetic structure is arranged on the first plate body; a second plate body, one end of the first plate body is connected with the second plate body, the first plate body and the second plate body are arranged at a first included angle, and the third electromagnetic structure is arranged on the second plate body; a third plate body, the other end of the second plate body is connected with the third plate body, the third plate body and the second plate body are arranged at a second included angle, and the second electromagnetic structure is arranged on the third plate body.

[0012] Further, the transport device further comprises a control module, the control module is connected with the electromagnetic assembly to control the on-off of the circuit where the electromagnetic assembly is located, and the driving assembly comprises: a driving device connected with the bearing structure, the driving device drives the bearing structure to move; the control module is connected with the driving device to control the start-stop action of the driving device.

[0013] Further, the control module is further used for controlling the circuit where the electromagnetic assembly is located to be in the on-state and controlling the driving device to be in the stop running state, so that the transport device is in the receiving state, and the bearing structure bears the wafer; after the bearing structure bears the wafer, the control module controls the driving device to be in the start state, and the driving device drives the bearing structure to move the wafer.

[0014] Further, the driving device is a pneumatic cylinder or a hydraulic cylinder, a piston rod of the pneumatic cylinder or the hydraulic cylinder is connected with the bearing structure to drive the bearing structure to move through the piston rod. According to the technical scheme of the application, when the transport device needs to transport the wafer, the wafer is placed on the bearing structure, the electromagnetic assembly is powered on, the electromagnetic assembly applies electromagnetic force to the bearing structure to make the bearing structure in a suspended state. Then, the driving assembly is started, the driving assembly drives the bearing structure to move to a preset position to align the upper and lower wafers, so as to facilitate the bonding of the upper and lower wafers.

[0015] Compared with the unstable operation of the lower platform in the prior art, the transport device in the application uses magnetic levitation technology to support the bearing structure and the wafer, so that the suspended state of the bearing structure is more stable, and the operation of the bearing structure is more stable, thereby solving the problem that the unstable operation of the lower platform in the prior art affects the alignment accuracy of the upper and lower wafers, improving the alignment accuracy of the upper and lower wafers, and thereby improving the wafer bonding quality. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application, and are incorporated into and constitute a part of this specification. The drawings illustrate an exemplary embodiment of the application and, together with the description, serve to explain the application without imposing undue limitation thereon. In the drawings:

[0017] Figure 1 A front view of an embodiment of the transport device according to the present application is shown.

[0018] Wherein, the above-mentioned drawings include the following reference signs:

[0019] 10, wafer; 20, bearing structure; 30, electromagnetic assembly; 31, first electromagnetic structure; 32, second electromagnetic structure; 33, third electromagnetic structure; 50, rack; 51, first plate body; 52, second plate body; 53, third plate body. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0021] It should be noted that, unless otherwise specified, all the technical and scientific terms used in the present application have the same meaning as that generally understood by the ordinary skilled person in the technical field to which the present application belongs.

[0022] In the present application, unless otherwise specified, the orientation words such as "upper" and "lower" are generally directed to the directions shown in the drawings, or are directed to the vertical, perpendicular or gravity directions; similarly, for the convenience of understanding and description, "left" and "right" are generally directed to the left and right shown in the drawings; "inner" and "outer" refer to the inner and outer relative to the contour of each component itself, but the above-mentioned orientation words are not used to limit the present application.

[0023] In order to solve the problem that the running instability of the lower platform affects the alignment accuracy of the upper and lower wafers in the prior art, the present application provides a transport device.

[0024] As shown in Figure 1 The transport device is used to transport the wafer 10 to a preset position, and the transport device comprises a bearing structure 20, an electromagnetic assembly 30 and a driving assembly. The bearing structure 20 is used to carry the wafer 10. The electromagnetic assembly 30 is located at least partially on the periphery of the bearing structure 20, and the electromagnetic assembly 30 is used to apply an electromagnetic force to the bearing structure 20 after being energized, so that the bearing structure 20 is in a suspended state. The driving assembly is connected with the bearing structure 20. The driving assembly is used to drive the bearing structure 20 to move to the preset position when the bearing structure 20 is in the suspended state.

[0025] When the wafer 10 (lower wafer) needs to be transported by the transportation device, the wafer 10 is placed on the bearing structure 20, the electromagnetic assembly 30 is powered, the electromagnetic assembly 30 applies electromagnetic force to the bearing structure 20, so that the bearing structure 20 is in a suspended state. Then, the driving assembly is started, and the driving assembly drives the bearing structure 20 to move to a preset position, so that the upper and lower wafers are aligned, facilitating the bonding of the upper and lower wafers.

[0026] Compared with the instability of the lower platform in the prior art, the transportation device in the embodiment uses magnetic levitation technology to support the bearing structure 20 and the wafer 10, thereby making the suspended state of the bearing structure 20 more stable and the operation of the bearing structure 20 more stable, thereby solving the problem of instability of the lower platform in the prior art affecting the alignment accuracy of the upper and lower wafers, improving the alignment accuracy of the upper and lower wafers, and thereby improving the wafer bonding quality.

[0027] In the embodiment, when the bearing structure 20 is in a suspended state, the bearing structure 20 does not contact the electromagnetic assembly 30 under the action of electromagnetic force, and has a preset gap between the electromagnetic assembly 30.

[0028] It should be noted that the items transported by the transportation device are not limited thereto, and can also be used to transport other objects other than wafers.

[0029] In the embodiment, the bearing structure 20 is made of metal material. The driving assembly drives the bearing structure 20 to move accurately, thereby realizing high-precision, contactless suspended movement. In this way, the bearing structure 20 is controlled by magnetic levitation, which is contactless, frictionless, does not need lubrication, has high precision, long service life, and the like, thereby improving the alignment accuracy of the upper and lower wafers. Compared with the airflow control in the prior art which is not accurate enough, the magnetic levitation control is adopted in the embodiment, so that the transportation of the wafer 10 by the transportation device is more accurate and efficient.

[0030] As shown in Figure 1 The transportation device further includes a rack 50, and the electromagnetic assembly 30 is arranged on the rack 50. The electromagnetic assembly 30 is two groups, one group of electromagnetic assembly 30 covers at least part of the first side of the bearing structure 20, and the other group of electromagnetic assembly 30 covers at least part of the second side of the bearing structure 20. The first side and the second side are oppositely arranged. In this way, the electromagnetic assembly 30 simultaneously applies electromagnetic force to the first side and the second side of the bearing structure 20, so that the bearing structure 20 is uniformly stressed, facilitating the driving assembly to drive the bearing structure 20 to move, and making the movement of the bearing structure 20 more stable, thereby improving the transportation efficiency of the transportation device. At the same time, the above structure is simple in structure, easy to process and realize, and reduces the processing cost of the transportation device.

[0031] Specifically, the bearing structure 20 is a plate-shaped structure, a group of electromagnetic assemblies 30 apply electromagnetic force to a first side of the bearing structure 20, and another group of electromagnetic assemblies 30 apply electromagnetic force to a second side of the bearing structure 20, so that the bearing structure 20 is more uniformly stressed, and the bearing structure 20 is in a suspended state under the action of the electromagnetic force. Then, the driving assembly drives the bearing structure 20 to move the wafer 10, so as to realize the conveying of the wafer 10 by the conveying device. Wherein, after the electromagnetic assemblies 30 are powered, the electromagnetic force of the electromagnetic assemblies 30 acting on the bearing structure 20 is relatively constant, so as to ensure that the bearing structure 20 is always at a preset height position, avoiding the collision between the bearing structure 20 and the electromagnetic assemblies 30 during the movement of the bearing structure 20, and affecting the normal use of the conveying device.

[0032] As shown in Figure 1 , the electromagnetic assembly 30 comprises a first electromagnetic structure 31. Wherein, the first electromagnetic structure 31 is located below the bearing structure 20, and the first electromagnetic structure 31 applies upward electromagnetic force to the bearing structure 20. In this way, after the first electromagnetic structure 31 is powered, the first electromagnetic structure 31 applies upward electromagnetic force to the bearing structure 20, so that the bearing structure 20 overcomes its own gravity and the gravity of the wafer 10 and is in a suspended state, thereby improving the use reliability of the conveying device.

[0033] As shown in Figure 1 , the electromagnetic assembly 30 further comprises a second electromagnetic structure 32. Wherein, the second electromagnetic structure 32 is located above the bearing structure 20 and is oppositely arranged with the first electromagnetic structure 31, and the second electromagnetic structure 32 applies upward electromagnetic force to the bearing structure 20. In this way, along the height direction of the bearing structure 20, the first electromagnetic structure 31 and the second electromagnetic structure 32 both apply upward electromagnetic force to the bearing structure 20, so as to reduce the electromagnetic force applied by the first electromagnetic structure 31 and the second electromagnetic structure 32 to the bearing structure 20, that is, even if the current on the circuit where the first electromagnetic structure 31 and the second electromagnetic structure 32 are located is small, the suspension of the bearing structure 20 can also be realized, and the energy consumption of the conveying device is reduced.

[0034] In other embodiments not shown in the drawings, the second electromagnetic structure applies downward electromagnetic force to the bearing structure. In this way, along the height direction of the bearing structure, the first electromagnetic structure applies upward electromagnetic force to the bearing structure, and the second electromagnetic structure applies downward electromagnetic force to the bearing structure, so as to ensure that the bearing structure is in a suspended state and will not contact the first electromagnetic structure or the second electromagnetic structure to affect the movement of the bearing structure, thereby improving the use reliability of the conveying device.

[0035] As shown in Figure 1As shown, the electromagnetic component 30 also includes a third electromagnetic structure 33. The third electromagnetic structure 33 is located on one side of the support structure 20, and applies an electromagnetic force toward or away from the second side of the support structure 20 to the first side. The first side and the second side are arranged back-to-back. Thus, during the movement of the wafer 10 driven by the support structure 20, the aforementioned arrangement of the third electromagnetic structure 33 can prevent the support structure 20 from shifting during movement, thereby affecting its normal operation and improving the operational reliability of the transport equipment.

[0036] Specifically, after the electromagnetic component 30 is energized, the first electromagnetic structure 31 applies an upward electromagnetic force to the supporting structure 20, the second electromagnetic structure 32 applies an upward electromagnetic force to the supporting structure 20, and the third electromagnetic structure 33 applies an electromagnetic force to the first side of the supporting structure 20 toward or away from the second side of the supporting structure 20. On the one hand, this ensures that the supporting structure 20 can be levitated, and on the other hand, it prevents the supporting structure 20 from shifting left or right during movement and colliding with the third electromagnetic structure 33, thereby ensuring that the supporting structure 20 can slide along the preset direction.

[0037] In this embodiment, there are two racks 50, each corresponding to one of the two sets of electromagnetic components 30. The two racks 50 are located on opposite sides of the support structure 20. The drive assembly drives the support structure 20 to move along a preset direction, and each rack 50 extends along the preset direction. This arrangement avoids structural interference between the racks 50 and the wafer 10, thus preventing disruption to the normal operation of the transport equipment and improving its reliability. Furthermore, the structure is simple, easy to manufacture and implement, and reduces the processing cost of the transport equipment.

[0038] In this embodiment, the length of the frame 50 is the same as the length of the support structure 20 to ensure that the support structure 20 is always suspended in a horizontal position.

[0039] like Figure 1 As shown, the rack 50 includes a first plate 51, a second plate 52, and a third plate 53. A first electromagnetic structure 31 is disposed on the first plate 51. The first plate 51 is connected to one end of the second plate 52, and the first plate 51 and the second plate 52 are arranged at a first angle. A third electromagnetic structure 33 is disposed on the second plate 52. The third plate 53 is connected to the other end of the second plate 52, and the third plate 53 and the second plate 52 are arranged at a second angle. The second electromagnetic structure 32 is disposed on the third plate 53. Thus, the rack 50 has a U-shaped cross-section, further preventing structural interference between the rack 50 and the wafer 10 and the supporting structure 20, which could affect the operational reliability of the transport equipment. Simultaneously, the above configuration simplifies the structure of the rack 50, making it easy to manufacture and implement, and reducing the manufacturing cost of the rack 50.

[0040] As shown in Figure 1 The transportation device further comprises a control module connected with the electromagnetic assembly 30 to control the on-off of the circuit where the electromagnetic assembly 30 is located, and the driving assembly comprises a driving device. The driving device is connected with the bearing structure and drives the bearing structure to move. The control module is connected with the driving device to control the start-stop action of the driving device. In this way, the control module controls the electromagnetic assembly 30 and the driving device, which reduces the operation difficulty of the transportation device for the workers, reduces the labor intensity of the workers, and also realizes the intelligent control of the transportation device.

[0041] In this embodiment, the control module is further configured to control the circuit where the electromagnetic assembly 30 is located to be in the on state and control the driving device to be in the stop state, so that the transportation device is in the receiving state, and the bearing structure 20 bears the wafer 10. After the bearing structure 20 bears the wafer 10, the control module controls the driving device to be in the start state, and the driving device drives the bearing structure 20 to move the wafer 10.

[0042] Optionally, the driving device is a pneumatic cylinder or a hydraulic cylinder, and a piston rod of the pneumatic cylinder or the hydraulic cylinder is connected with the bearing structure 20 to drive the bearing structure 20 to move through the piston rod. In this way, the above-mentioned arrangement makes the movement of the bearing structure 20 more easy and convenient, and reduces the processing cost of the transportation device.

[0043] In this embodiment, the driving device is a pneumatic cylinder. The piston rod of the pneumatic cylinder is connected with the bearing structure 20 to drive the bearing structure 20 to slide along the preset direction through the piston rod.

[0044] It should be noted that the type of the driving device is not limited to this. Optionally, the driving device is a hydraulic cylinder or an electric cylinder.

[0045] In other embodiments not shown in the drawings, the driving assembly further comprises a traction member. The traction member is connected with the driving device and the bearing structure, the driving end of the driving device is connected with one end of the traction member, and the other end of the traction member is connected with the bearing structure to drive the bearing structure to slide along the preset direction.

[0046] Specifically, when the wafer 10 needs to be transported by the transportation device, the electromagnetic assembly 30 can be powered first to make the circuit where the electromagnetic assembly 30 is located in a pass-through state, and the bearing structure 20 is in a suspended state. Then, the wafer 10 is placed on the bearing structure 20. The control module controls the driving device to be in an activated state, and the driving device drives the bearing structure 20 to move the wafer 10 through the transmission device. Alternatively, when the wafer 10 needs to be transported by the transportation device, the wafer 10 is placed on the bearing structure 20 first, and then the electromagnetic assembly 30 is powered to make the circuit where the electromagnetic assembly 30 is located in a pass-through state, and the bearing structure 20 is in a suspended state. Then, the control module controls the driving device to be in an activated state, and the driving device drives the bearing structure 20 to move the wafer 10 through the transmission device.

[0047] The application also provides a wafer transportation method suitable for the above-mentioned transportation device, and the wafer transportation method comprises the following steps:

[0048] The circuit where the electromagnetic assembly of the transportation device is located is controlled to be in a pass-through state, so that the bearing structure of the transportation device is in a suspended state, and the bearing structure bears the wafer.

[0049] After the bearing structure bears the wafer, the driving assembly of the transportation device is controlled to be in a running state, and the driving assembly drives the bearing structure and the wafer to move to a preset position.

[0050] Specifically, when the wafer 10 needs to be transported by the transportation device, the wafer 10 is placed on the bearing structure 20, the electromagnetic assembly 30 is powered, and the electromagnetic assembly 30 applies an electromagnetic force to the bearing structure 20 to make the bearing structure 20 in a suspended state. Then, the driving assembly is started, and the driving assembly drives the bearing structure 20 to move to a preset position to align the upper and lower wafers, so as to facilitate the bonding of the upper and lower wafers. Since the transportation device in the embodiment uses magnetic levitation technology to support the bearing structure 20 and the wafer 10, the suspended state of the bearing structure 20 is more stable, and the operation of the bearing structure 20 is more stable, thereby solving the problem that the operation of the lower platform in the prior art is unstable and affects the alignment accuracy of the upper and lower wafers, improving the alignment accuracy of the upper and lower wafers, and thereby improving the wafer bonding quality.

[0051] From the above description, it can be seen that the above-mentioned embodiments of the application achieve the following technical effects:

[0052] When the wafer needs to be transported by the transportation device, the wafer is placed on the bearing structure, the electromagnetic assembly is powered, and the electromagnetic assembly applies an electromagnetic force to the bearing structure to make the bearing structure in a suspended state. Then, the driving assembly is started, and the driving assembly drives the bearing structure to move to a preset position to align the upper and lower wafers, so as to facilitate the bonding of the upper and lower wafers.

[0053] Compared with the unstable operation of the lower platform in the prior art, the transport device in the application uses magnetic suspension technology to support the bearing structure and the wafer, so that the suspension state of the bearing structure is more stable, and the operation of the bearing structure is more stable, thereby solving the problem that the unstable operation of the lower platform in the prior art affects the alignment accuracy of the upper and lower wafers, improving the alignment accuracy of the upper and lower wafers, and thereby improving the wafer bonding quality.

[0054] Obviously, the above-described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0055] It should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a feature, step, work, device, component and / or combination thereof.

[0056] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0057] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A transport device for conveying wafers to a preset position, characterized in that, The transportation device comprises: a bearing structure for bearing the wafer; an electromagnetic assembly located at least partially on the periphery of the bearing structure, the electromagnetic assembly being used to apply electromagnetic force to the bearing structure after being powered on, so that the bearing structure is in a suspended state; a driving assembly connected with the bearing structure, the driving assembly being used to drive the bearing structure to move to the preset position when the bearing structure is in the suspended state; the electromagnetic assembly comprises: a first electromagnetic structure located below the bearing structure, the first electromagnetic structure applying upward electromagnetic force to the bearing structure; a second electromagnetic structure located above the bearing structure and oppositely arranged with the first electromagnetic structure, the second electromagnetic structure applying upward or downward electromagnetic force to the bearing structure; the transportation device further comprises a control module connected with the electromagnetic assembly to control the on-off of the circuit where the electromagnetic assembly is located, and the driving assembly comprises: a driving device connected with the bearing structure, the driving device driving the bearing structure to move, and the control module is connected with the driving device to control the start-stop action of the driving device; the control module is further used to control the circuit where the electromagnetic assembly is located to be in the on state and control the driving device to be in the stop running state, so that the transportation device is in a receiving state, and the bearing structure bears the wafer; after the bearing structure bears the wafer, the control module controls the driving device to be in the start state, and the driving device drives the bearing structure to move the wafer.

2. The transport apparatus of claim 1, wherein, The transportation device further comprises a rack, and the electromagnetic assembly is arranged on the rack.

3. The transport apparatus of claim 2, wherein, The electromagnetic assembly further comprises: a third electromagnetic structure located on one side of the bearing structure, the third electromagnetic structure applying electromagnetic force to the first side of the bearing structure towards or away from the second side of the bearing structure; the first side is oppositely arranged with the second side.

4. The transport apparatus of claim 2, wherein, The electromagnetic assembly is two groups, one group of the electromagnetic assembly covers at least part of the first side of the bearing structure, and the other group of the electromagnetic assembly covers at least part of the second side of the bearing structure; wherein, the first side and the second side are oppositely arranged.

5. The transport apparatus of claim 4, wherein, The rack is two, two racks are arranged one-to-one corresponding to two groups of electromagnetic assemblies, and two racks are respectively located on two sides of the bearing structure; wherein, the driving assembly drives the bearing structure to move in a preset direction, and each rack extends along the preset direction.

6. The transport apparatus of claim 3, wherein, The rack comprises: a first plate body, the first electromagnetic structure is arranged on the first plate body; a second plate body, one end of the first plate body is connected with the second plate body, the first plate body and the second plate body are arranged at a first included angle, and the third electromagnetic structure is arranged on the second plate body; a third plate body, the other end of the second plate body is connected with the third plate body, the third plate body and the second plate body are arranged at a second included angle, and the second electromagnetic structure is arranged on the third plate body.

7. The transport apparatus of claim 1, wherein, The drive device is a gas cylinder or a hydraulic cylinder, a piston rod of the gas cylinder or the hydraulic cylinder being connected with the load-bearing structure to drive the load-bearing structure in motion by means of the piston rod.

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