Workpiece transport device and mapping method

Abstract

To accurately detect an abnormal mount state in which a plurality of workpieces are mounted in one slot or a workpiece is mounted across adjacent slots when performing mapping for determining a load state of workpieces in an accommodation unit in which a plurality of slots arranged in a vertical direction are provided and one workpiece is mounted in each slot under a normal state.SOLUTION: Wafers as workpieces are accommodated in a cassette stage as an accommodation unit such that a normal mounting state and an abnormal mounting state appear at a plurality of locations (step 101), a sensor is moved in a vertical direction with respect to the cassette stage in that state to detect the workpieces (step 102), and a determination threshold to be used for detecting the abnormal mounting state is calculated based on the average value of wafer thicknesses detected for each mounting state and the average value of center positions of the wafers in a height direction detected for each mounting state (step 103).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to the transportation of workpieces using a transport device such as a transport robot, and in particular to a transport device and mapping method that improves the accuracy of detecting an abnormal loading state of a workpiece in a storage section when performing mapping to determine the inventory state of the workpieces in the storage section such as a cassette or cassette stage. [Background technology]

[0002] When a conveying device such as a conveying robot conveys a plate-shaped workpiece such as a semiconductor wafer or a glass substrate, the workpiece to be conveyed is accommodated in a container called a cassette or a cassette stage in advance, and the conveying device extends a hand provided at the tip of the conveying device into the container from which the workpiece is conveyed, picks up the workpiece, conveys the workpiece with the workpiece placed on the hand, and accommodates the workpiece in the container at the destination. An example of a conveying robot conveying a workpiece such as a semiconductor wafer is shown in Patent Document 1. Since a container can generally accommodate a plurality of workpieces, it is necessary to check the position of the workpiece in the container before actually conveying the workpiece, which is called mapping. Assuming that the container has a plurality of slots vertically stacked, by performing mapping, it is possible to know which slots the workpieces are in, and an optimal conveying sequence can be assembled according to the result. In the conveying sequence, it is specified which slot in the container from which the workpiece is to be picked up and which slot in the container at which the workpiece is to be accommodated is currently an empty slot.

[0003] Mapping is performed by detecting the workpiece in the storage section without contact using a sensor to determine its position. The sensors used for mapping include a transmission type sensor that detects the workpiece by blocking the light path with the workpiece, and a reflection type sensor that irradiates the workpiece with detection light, detects the light reflected by the edge (or end face) of the workpiece, and detects the workpiece based on the amount of reflection and the reflection position. In mapping, the presence or absence of the workpiece is determined for each slot while moving the sensor along the arrangement direction of the slots, and the thickness of the workpiece and the position of the workpiece in the height direction of the slot can be determined depending on the position at which the sensor detects light (transmitted light or reflected light) and the position at which the sensor does not detect light. The workpiece is, for example, a semiconductor wafer, and its thickness is, for example, 1 mm or less, and the interval between the slots in which the workpieces are placed one by one in the storage section is about 5 mm to 10 mm. For these reasons, whether a transmission type or a reflection type sensor is used, it is preferable that the detection light is laser light with a narrow beam diameter and sharp directionality. Examples of mapping using a transmission type sensor are described in Patent Documents 2 and 3.

[0004] When a plate-shaped workpiece is stored horizontally in a storage section in which slots are arranged vertically, one workpiece needs to be stored in each slot. However, for some reason, two or more workpieces may be placed overlapping each other in one slot, or a workpiece may be placed so as to straddle two slots. In the following description, a state in which one workpiece is stored in one slot is called "single", and a state in which two or more workpieces are stored in one slot is called "double". In each slot, both ends of the workpiece are held by rails provided at both ends of the horizontal direction of the slot, for example, so that the workpiece is horizontal. Therefore, the slot is a horizontally elongated area, and the height position within the slot can be determined in the height direction of the slot based on the position where the workpiece is held by the rail. To transport the workpiece, it is necessary to insert the hand of the transport device into the storage section and slightly raise the hand to place the workpiece stored in the slot on the hand. Therefore, except for the rails at both ends of the horizontal direction of the slot, there is no partition between adjacent slots in the vertical direction. Therefore, a workpiece may be placed diagonally so as to straddle two adjacent slots in the vertical direction. When one workpiece spans two slots, it is called a "cross."

[0005] "Single" is a normal storage or mounting state of a workpiece that can go into the storage section. In contrast, "double" and "cross" are abnormal mounting states in the storage section. If you try to remove a workpiece from the storage section when the workpiece is stored in the storage section in the form of "double" or "cross", that is, in a defective state, there is a risk that the workpiece will be damaged or will not be able to be removed. Therefore, in the mapping, it is necessary not only to determine the workpiece inventory state, but also to recognize such defective states and issue an alert, thereby preventing damage accidents, etc. Such abnormal mounting states are different from the "single" case in terms of the detected thickness of the workpiece and the position of the workpiece in the height direction of the slot, so they can be detected by setting a threshold value for the detected thickness of the workpiece and a threshold value for the position of the workpiece in the height direction. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-84651 A [Patent Document 2] JP 2004-327501 A [Patent Document 3] JP 2000-36528 A Summary of the Invention [Problem to be solved by the invention]

[0007] When detecting an abnormal workpiece mounting state during mapping, it is necessary to set two thresholds in advance: a threshold for the detection thickness of the workpiece and a threshold for the height direction position of the workpiece in the slot. Conventionally, these thresholds were set manually by actually measuring a workpiece in an abnormal mounting state and using the measurement data in a normal mounting state and the measurement data in an abnormal mounting state. However, this threshold setting work takes time and varies depending on who sets the thresholds, and as a result, there are cases where an abnormal mounting state cannot be detected properly when mapping is actually performed.

[0008] An object of the present invention is to provide a transport device and a mapping method that can quickly and accurately set a threshold value for determining an abnormal mounting state of a workpiece when mapping is performed. [Means for solving the problem]

[0009] The conveying device of the present invention is a conveying device that conveys workpieces to a storage section having a plurality of slots arranged in the vertical direction and capable of horizontally storing one plate-shaped workpiece in each slot, and has a hand that holds the workpiece when transporting the workpiece, a sensor that irradiates light on the workpiece to determine the presence status of the workpiece in the slot, a moving mechanism that moves the hand and sensor relative to the storage section, and a control means that drives and controls the moving mechanism.The control means performs a threshold detection operation to move the sensor in the vertical direction to detect the workpieces using the sensor for a storage section in which works are stored at multiple locations in a normal mounting state and in which works are stored at multiple locations in an abnormal mounting state, and calculates a threshold for distinguishing between a normal mounting state and an abnormal mounting state from the average detected thicknesses and the average height positions within the slots obtained from the works in the normal mounting state in the threshold detection operation, and the average detected thicknesses and the average height positions within the slots obtained from the works in the abnormal mounting state in the threshold detection operation.

[0010] In the conveying device of the present invention, a storage section is prepared that stores workpieces so that normal and abnormal mounting states appear in multiple locations, and a threshold detection operation similar to the mapping operation is performed on the storage section, and a threshold is calculated based on an average value obtained by the threshold detection operation. Therefore, the threshold used to determine the presence or absence of an abnormal mounting state when mapping is performed can be set automatically without manual intervention. As a result, there is no variation in the determination threshold due to differences in operators, and an abnormal mounting state can be accurately determined when mapping is performed.

[0011] In the transport device of the present invention, the abnormal loading state includes a first state in which two or more workpieces are accommodated in one slot (i.e., "double") and a second state in which at least one workpiece is accommodated across adjacent slots (i.e., "cross"), and it is preferable to use an accommodation unit in which workpieces are accommodated in multiple locations in the first state and in which workpieces are accommodated in multiple locations in the second state when calculating the threshold. By performing a threshold detection operation on an accommodation unit in which the first state and the second state each appear in multiple locations, a threshold value that makes it possible to distinguish between the first state and the second state can be obtained.

[0012] In the transport device of the present invention, the sensor is preferably attached to the hand. Although the sensor needs to be moved for mapping, by attaching the sensor to the hand that moves relative to the storage unit, the configuration of the movement mechanism in the transport device can be simplified.

[0013] In the transport device of the present invention, the sensor may be a transmission type sensor that includes a light emitting unit and a light receiving unit and detects a workpiece when light from the light emitting unit toward the light receiving unit is blocked by the workpiece, or a reflection type sensor that detects a workpiece by irradiating light toward the workpiece and detecting reflected light from the workpiece. In the present invention, both transmission type and reflection type sensors that are generally used for mapping can be used. However, the calculation procedure of the threshold value may differ depending on the type of sensor used.

[0014] When using a reflective sensor, workpiece detection may not be successful depending on the mapping position. Here, the mapping position refers to the position where the sensor is placed to perform mapping to determine the presence or absence of workpieces in the storage area. height The irradiation position is a position on the workpiece where light from the sensor is irradiated along a horizontal direction perpendicular to the depth direction of the storage section. Therefore, in the conveying device of the present invention, the control means moves the sensor to the position where light from the sensor is irradiated along a horizontal direction perpendicular to the depth direction of the storage section. heightIt is preferable to repeatedly perform the operation of moving the irradiation position along the direction to detect reflected light from the workpieces, targeting the storage section in a state where one workpiece is stored in each slot, moving the irradiation position to obtain detection distribution data, determining a mapping position based on the detection distribution data, and then performing a threshold detection operation at the determined mapping position.

[0015] In the conveying device of the present invention, when the control means controls the moving mechanism to convey the workpieces, it executes control to perform mapping to determine the loading state of the workpieces in the storage section, and can determine the presence or absence of an abnormal loading state using a threshold value. By using the threshold value determined based on the present invention, it becomes possible to accurately determine an abnormal loading state when performing mapping.

[0016] The mapping method of the present invention is a mapping method for determining the status of workpieces in a storage section that has a plurality of slots arranged in the height direction and can horizontally store one plate-shaped workpiece in each slot. Do The method involves performing a threshold detection operation in which a sensor is moved in the height direction to detect the workpieces using the sensor for a storage section in which workpieces are stored at multiple locations in a normal mounting state and in which workpieces are stored at multiple locations in an abnormal mounting state, and calculating a threshold for distinguishing between a normal mounting state and an abnormal mounting state from the average detected thickness values ​​and the average height positions within the slot obtained from the workpieces in a normal mounting state in the threshold detection operation, and the average detected thickness values ​​and the average height positions within the slot obtained from the workpieces in an abnormal mounting state in the threshold detection operation.

[0017] In the mapping method of the present invention, a storage section is prepared that stores workpieces so that normal and abnormal mounting states appear in multiple locations, a threshold detection operation similar to the mapping operation is performed on the storage section, and a threshold is calculated based on an average value obtained by the threshold detection operation. Therefore, the discrimination threshold used to determine the presence or absence of an abnormal mounting state when mapping is performed can be automatically set without manual intervention and without variation, and an abnormal mounting state can be accurately determined when mapping is performed.

[0018] In the mapping method of the present invention, the abnormal mounting state includes a first state in which two or more workpieces are accommodated in one slot (i.e., "double") and a second state in which at least one workpiece is accommodated across adjacent slots (i.e., "cross"), and it is preferable to use an accommodation unit in which workpieces are accommodated in multiple locations in the first state and in which workpieces are accommodated in multiple locations in the second state when calculating the threshold value. By performing a threshold detection operation on an accommodation unit in which the first state and the second state each appear in multiple locations, a threshold value that makes it possible to distinguish and discriminate between the first state and the second state can be obtained.

[0019] In the mapping method of the present invention, a transmission type sensor having a light emitting unit and a light receiving unit and detecting a workpiece when light directed from the light emitting unit to the light receiving unit is blocked by the workpiece can be used as the sensor, or a reflection type sensor that detects the workpiece by irradiating light toward the workpiece and detecting the light reflected from the workpiece can be used. However, when a reflection type sensor is used, it may not be possible to detect the workpiece successfully depending on the mapping position. Therefore, in the mapping method of the present invention, if the sensor is a reflection type sensor, the sensor is turned off before performing the threshold detection operation. height It is preferable to repeatedly perform the operation of moving the irradiation position along the direction to detect reflected light from the workpieces, targeting the storage section in a state where one workpiece is stored in each slot, moving the irradiation position to obtain detection distribution data, determining a mapping position based on the detection distribution data, and then performing a threshold detection operation at the determined mapping position.

[0020] In the mapping method of the present invention, after the threshold value is determined, mapping is performed on the accommodation unit when the workpiece is transported, and the presence or absence of an abnormal mounting state can be determined using the threshold value. By using the threshold value determined based on the present invention, it becomes possible to accurately determine an abnormal mounting state when mapping is performed. Effect of the Invention

[0021] According to the present invention, a transport device and a mapping method can be obtained that can quickly and accurately set a threshold value for determining an abnormal mounting state of a workpiece when mapping is performed. [Brief description of the drawings]

[0022] [Figure 1] 1 is a diagram showing a transport robot which is a transport device according to an embodiment of the present invention; [Diagram 2] FIG. 1A is a plan view illustrating mapping using a transmission type sensor, and FIGS. 1B and 1C are plan views illustrating mapping using a reflection type sensor. [Diagram 3] FIG. 4 is a front view illustrating a wafer mounting state. [Figure 4] 10 is a flowchart showing a procedure for determining a threshold value used to determine an abnormal mounting state. [Diagram 5] 13 is a front view illustrating a state in which a wafer is loaded into a container for determining a threshold value. FIG. [Figure 6] 10 illustrates the determination of a discrimination threshold TH1 for detected thickness. [Figure 7] 11 is a diagram for explaining the determination of a discrimination threshold TH2 for the detected thickness and a discrimination threshold TH3 for the detected position in the height direction. FIG. [Figure 8] 13 is a diagram for explaining the determination of a discrimination threshold value TH4 regarding the detection position in the height direction. FIG. [Figure 9] FIG. 13 is a diagram for explaining the determination of a mapping position, where (a) is a side view and (b) is a plan view. [Figure 10]FIG. 11 is a diagram illustrating an example of detection distribution data. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a transport robot which is a transport device according to an embodiment of the present invention. The transport robot 20 shown in FIG. 1 is used to transport a workpiece which is a plate-like object. In the following description, the workpiece is a wafer 50 such as a silicon wafer, and the wafer 50 is accommodated in a cassette stage 40 which is an accommodation section. The cassette stage 40 has a plurality of slots arranged vertically, and is configured so that one wafer 50 is accommodated horizontally in each slot. Before transporting the wafer 50, the transport robot 20 performs mapping to determine the presence state of the wafer 50 in the cassette stage 40.

[0024] The transport robot 20 shown in FIG. 1 is similar to the horizontal articulated robot described in Patent Document 1, for example, and includes three arms 22 to 24 attached in series to a base 21, and a hand 25 attached to the tip of the tip-side arm 24. FIG. 1 illustrates the arms 22 to 24 in a folded state, but the arms 22 to 24 can also be in an unfolded state, and in particular, the arms 22 and 23 form a link mechanism in which the tip of the arm 23 moves in a radial direction within a horizontal plane, centered on the attachment position of the arm 22 to the base 21. The arm 24 is rotatable within a horizontal plane relative to the arm 23, and the hand 25 is rotatable relative to the arm 24. The base 21 is provided with a lifting mechanism (not shown) for lifting and lowering the base-side arm 22, and a rotation mechanism (not shown) for rotating the arm 22 around a vertical axis. A sensor used for mapping is attached to the hand 25, as will be described with reference to FIG. 2. The transfer robot 20 is further connected to a robot controller 30 for driving and controlling the transfer robot 20. The robot controller 30 controls the lifting mechanism and rotation mechanism provided on the base 21, a link mechanism consisting of the arms 22 and 23, a mechanism for rotating the arm 24 relative to the arm 23, and a mechanism for rotating the hand 25 relative to the arm 24, and processes detection signals from sensors. In particular, the robot controller 30 executes control of the operation for determining a discrimination threshold, the operation for determining a mapping position, the mapping operation, and the operation for transporting a workpiece.

[0025] The transport robot 20 performs a process of taking out one wafer 50 from the cassette stage 40 at the transport source and transporting the wafer 50 to the device or cassette stage 40 at the transport destination, and a process of storing the wafer 50 transported from the device or cassette stage 40 at the transport source in an empty slot of the cassette stage 40 at the transport destination. The cassette stage 40, which is a storage section, is a front-opening type such as a FOUP (Front-Opening Unified Pod), which is a front-opening cassette integrated transport and storage box defined in SEMI (Semiconductor Equipment and Materials International) Standard E47.1. Therefore, when the transport robot 20 takes out the wafer 50 from the slot in the cassette stage 40 and stores the wafer 50 in an empty slot in the cassette stage 40, the hand 25 of the transport robot 20 enters the cassette stage 40 with the fork part 26 side at the tip, aiming for a predetermined slot through the front opening of the cassette stage 40.

[0026] Mapping is performed before the actual transfer of the wafer 50. Since the slots in the cassette stage 40 are arranged vertically, during mapping, the hand 25 is raised and lowered so that the sensor moves vertically. FIGS. 2(a) to 2(c) are plan views for explaining mapping by the sensor, and when mapping is performed, the hand 25 moves in a direction perpendicular to the paper surface in the figures. The hand 25 is a long and slender member having a fork portion 26 provided at one end. The fork portion 20 has a shape with two branches at the tip side, and is a part that holds the wafer 50, which is a workpiece, when the wafer 50 is transferred. When transferred, the wafer 50 is placed horizontally on the surface of the fork portion 26.

[0027] FIG. 2(a) shows mapping using a transmission type sensor. The transmission type sensor includes a light emitting unit 27 provided at one end of the fork part 26 of the hand 25 and a light receiving unit 28 provided at the other end, and emits a laser beam 60 from the light emitting unit 27 toward the light receiving unit 28. For example, a laser diode (LD) is used to generate the laser beam 60. When the hand 25 is raised and lowered, the laser beam 60 is blocked by the wafer 50 and does not enter the light receiving unit 28, so that the transmission type sensor can detect the workpiece 50 in the slot. From the amount of movement and the movement position of the hand 25 during the period when the laser beam 60 does not enter the light receiving unit 28, the thickness of the wafer 50 and the height direction position of the wafer 50 in the slot can be determined.

[0028] 2(b) shows mapping using a reflective sensor 29. The reflective sensor 29 is an integrated unit of a light emitter and a light receiver for laser light 60, and the light emitter irradiates the wafer 50 with laser light 60, and the light receiver detects the reflected light from the wafer 50. The laser light 50 is diffusely reflected at the end face (wafer edge) of the wafer, so that part of the reflected light enters the light receiver. From the amount and position of movement of the hand 25 during the period in which the reflected light is detected, the thickness of the wafer 50 and the heightwise position of the wafer 50 within the slot can be determined.

[0029] When a reflective sensor 29 is used, the direction and intensity of the reflected light from the wafer 50 change significantly depending on the surface condition of the end face of the wafer 50. When the end face of the wafer 50 is rough, the irradiated laser light 60 is diffusely reflected at the end face of the wafer 50 as shown in FIG. 2(b) above, and part of the reflected light due to the diffuse reflection reaches the light receiving portion of the sensor 29. As a result, the sensor 29 can detect the wafer 50 without depending on the mapping position. Here, the mapping position refers to a position on the wafer 50 where the light from the sensor 29 is irradiated along the horizontal direction perpendicular to the depth direction of the cassette stage 40 when mapping is performed by moving the sensor in the vertical direction in which the slots are arranged. In contrast, when the end face of the wafer 50 is, for example, a mirror surface, the irradiated laser light 60 is mirror-reflected in one direction by the end face of the wafer 50 as shown in FIG. 2(c). In this case, if the mapping position is inappropriate, even if the laser light 60 is irradiated to the wafer 50, the reflected light does not return to the sensor 29, and the sensor 29 may not be able to detect the wafer 50. The determination of the mapping position when using the reflective sensor 29 will be described later. The mapping position can be changed by actually moving the sensor 29 in the horizontal direction, or by changing the direction of irradiation of light from the sensor without changing the position of the sensor 29 in the horizontal direction.

[0030] When performing the mapping as described above, it is necessary to be able to determine an abnormal mounting state of the wafer 50 on the cassette stage 40. FIG. 3 is a diagram showing an example of an abnormal mounting state, and the left half of FIG. 3 is drawn as a front view of the cassette stage 40 containing the workpiece 50. The illustrated cassette stage 40 has eight slots arranged in a vertical direction, and they are numbered from the bottom up, such as slot 1, slot 2, .... In each slot, rails 41 are provided at both ends in the horizontal direction of the slot. The wafer 50 is contained in the slot by holding both ends of the wafer 50 with a pair of rails 41 of the slot, so that the position in the height direction of the upper surface of the rails 41, i.e., the surface of the rails 41 that should come into contact with the wafer 50, is used as the height reference for the slot. The height reference for each slot is indicated by a dashed line in the figure. The right half of Figure 3 shows the range in which the wafer 50 is detected in the slot height direction when mapping is performed when the wafer 50 is accommodated in the cassette stage 40 as shown in the left half of Figure 3, for both the case where the sensor is a transmissive type and the case where the sensor is a reflective type.

[0031] In FIG. 3, one wafer 50 is accommodated in slot 2, and therefore this wafer 50 is in a normal loading state, i.e., "single." In FIG. 3, two wafers 50 are accommodated in slot 4, and these wafers 50 are in a "double" state, which is one of the abnormal loading states. In the defective state of "double," the detected thickness of the wafer 50 is greater than in the case of "single," so the state can be determined based on the detected thickness. For example, whether the sensor is a transmissive type or a reflective type, it can be determined to be a "double" state when the detected thickness exceeds a certain threshold value.

[0032] In FIG. 3, the wafer 50 is placed so as to straddle the slots 6 and 7. Specifically, the left end of the wafer 50 is located at the left end of the slot 6, and the right end of the wafer 50 is located at the right end of the slot 7, so that the wafer 50 is accommodated at an angle. The wafer 50 is in a "cross" state, which is one of the abnormal loading states. When the defective state is "cross", the method of determining this state differs depending on whether the sensor type is a transmission type or a reflection type. When a transmission type sensor is used, the detected thickness of the wafer 50 is larger in the "cross" state than in the "single" state (even compared to the "double" state), and the wafer detection position in the height direction of the slot is also different from that in the "single" state. As the detection position of the wafer in the height direction of the slot, it is preferable to use the center position of the wafer in the height direction of the slot, taking into consideration the variation in the thickness of the wafer. Therefore, when a transmission type sensor is used, it can be determined that the wafer is "cross" when the detected thickness exceeds a certain threshold value and, further, when the difference between the center position of the detected wafer 50 in the height direction and the center position of the wafer 50 in the height direction that would be detected in the "single" state exceeds another threshold value. In contrast, when a reflective sensor is used, the detected thickness when it is a "cross" will be the same as when it is a "single", so when the difference between the detected center position of the workpiece in the height direction and the center position of the workpiece in the height direction that would be detected if it were a "single" exceeds a threshold value, it can be determined that it is a "cross".

[0033] Conventionally, two thresholds used to detect an abnormal mounting state (i.e., a threshold for the detected thickness of the workpiece and a threshold for the height direction position of the workpiece in the slot) were set manually. However, there is a problem that the threshold setting work takes time and varies depending on who sets the threshold. In order to solve such a problem, the transport device of this embodiment automatically finds and sets the threshold used to determine an abnormal mounting state when mapping is performed. FIG. 4 shows a procedure for determining the threshold used to determine an abnormal mounting state. Steps 102 to 103 of the procedure shown in FIG. 4 are executed by the robot controller 30 controlling the transport robot 20.

[0034] First, in step 101, the wafers 50 are accommodated in the cassette stage 40 so that the normal loading state of "single" appears in multiple locations, and the abnormal loading states of "double" and "cross" appear in multiple locations. FIG. 5 shows an example of the loading state of the wafers 50 in the cassette stage 40 at this time. The wafers 50 are accommodated in each of slots 1 and 2 as "single". Two wafers 50 are stacked and accommodated in slot 3, forming a "double". Similarly, the wafers 50 are arranged in slot 4 as "double". The wafers 50 are arranged so as to straddle the left end of slot 5 and the right end of slot 6, forming a "cross", and similarly, the wafers 60 are arranged so as to straddle the left end of slot 6 and the right end of slot 7, forming a "cross". In the example shown in FIG. 5, two "singles", two "doubles", and two "crosses" appear.

[0035] In step 102, the wafer 50 in the cassette stage 40 in which the wafer 50 is accommodated is detected by a sensor while moving the hand 25 in the vertical direction, similar to the mapping performed when a normal wafer 50 is transported. This detection operation is called a threshold detection operation. According to the threshold detection operation, the detected thickness and the detected height position in each slot are obtained for the wafer 50 in each accommodation location. Here, the height position is assumed to be the center position in the height direction of the wafer 50 in the corresponding slot. As a result, multiple measurement values ​​of the wafer thickness and the center position in the height direction of the wafer are obtained for each of the mounting states of "single", "double" and "cross". In the case of "cross", as described above, the measurement value differs depending on whether the sensor is a transmission type sensor or a reflection type sensor. Here, since it is known which wafer 50 or which slot is in which mounting state on the cassette stage 40, the threshold value for determining an abnormal mounting state when mapping is performed (i.e., the discrimination threshold value) is determined from the measurement value so as to match the known mounting state. That is, a discrimination threshold is calculated based on the average value of the measured wafer thickness for each mounting state and the average value of the measured wafer thickness at the center position in the height direction in step 103. The calculation of the discrimination threshold will be specifically described below.

[0036] In the threshold detection operation, the average thickness value of "single" wafers 50 detected by the sensor is a, and the average value of the center position in the height direction of the wafers 50 in each slot is b. Similarly, the average thickness value of "double" wafers 50 detected by the sensor is c. For "cross" wafers 50, the average thickness value when detected by the transmission sensor is d, the average value of the center position in the height direction of the slot when detected by the transmission sensor is e, and the average value of the center position in the height direction of the slot when detected by the reflective sensor is f.

[0037] The discrimination threshold value TH1 for discriminating the "double" among the abnormal mounting states is set to the intermediate value between the average value a of the detected thickness in the "single" state and the average value c of the detected thickness in the "double" state, as shown in FIG. 6. That is, TH1=(a+c) / 2 Let us assume that.

[0038] The discrimination thresholds for discriminating "cross" using a transmission sensor include a discrimination threshold TH2 based on the detected thickness and a discrimination threshold TH3 based on the center position in the height direction. As shown in Figure 7, the discrimination threshold TH2 based on the detected thickness is set to the intermediate value between the average detected thickness a for "single" and the average detected thickness d for "cross". That is, TH2=(a+d) / 2 The discrimination threshold value TH3 based on the center position in the height direction is set to the intermediate value between the average value b of the center position in the height direction in the case of "single" and the average value e of the center position in the height direction in the case of "cross". That is, TH3=(b+e) / 2 Let us assume that.

[0039] The discrimination threshold value TH4 for discriminating "cross" using a reflective sensor is set to the intermediate value between the average value b of the center position in the height direction for "single" and the average value f of the center position in the height direction for "cross", as shown in FIG. TH4=(a+f) / 2 Let us assume that.

[0040] In this embodiment, the discrimination threshold for discriminating whether or not the wafer 50 is abnormally mounted when mapping is performed is determined as described above. This discrimination threshold is stored in the robot controller 30 as a parameter, for example. Once the discrimination threshold is determined, when mapping is performed when the wafer 50 is actually transported, it is possible to discriminate whether or not the wafer 50 is abnormally mounted in the cassette cartridge 40 by comparing the detected wafer thickness and the height direction center position in the slot with the discrimination threshold. When a transmission type sensor is used, it is possible to determine that an abnormal mounting state has occurred when the detected wafer thickness is greater than either of the discrimination thresholds TH1 and TH2, or when the height direction center position of the wafer is greater than TH3. When it is necessary to distinguish between "double" and "cross", since TH2>TH1 is generally satisfied, when the detected thickness exceeds TH2 or the height direction center position in the slot exceeds TH3, it is possible to discriminate as "cross", and otherwise it is possible to discriminate as "double". When a reflective type sensor is used, it is possible to discriminate as "double" when the detected wafer thickness is greater than the discrimination threshold TH1, and it is possible to discriminate as "cross" when the height direction center position is greater than the discrimination threshold TH4.

[0041] However, when a reflective sensor 29 is used, as shown in FIG. 2(c), depending on the position on the wafer 50 where the laser light 60 is irradiated, the wafer 50 may not be detected. Therefore, when there is a risk that the wafer 50 may not be detected due to its shape or material, it is preferable to perform an operation to determine an appropriate mapping position before performing the operations of steps 101 to 103. The mapping position is also determined by the robot controller 30 controlling the transport robot 0. The determined mapping position is not only used for mapping during transport, but also when performing the threshold detection operation in step 102.

[0042] Since the mapping position needs to be determined for each shape and material of the wafer 50, in determining the mapping position, first, wafers 50 having the same shape and material as the wafer to be transported are accommodated one by one in all slots of the cassette stage 40 to be mapped. Then, the reflective sensor 29 attached to the hand 25 is directed toward the cassette stage 40, and the hand 25 is moved to a position in front of the cassette stage 40. Next, as in the case of performing the mapping operation and the threshold detection operation, the hand 25 is moved vertically as shown in FIG. 9(a) and the laser light 60 is irradiated toward the cassette stage 40 to detect the wafer 50. Then, such a detection operation of the wafer 50 is repeatedly performed while changing the horizontal position of the hand 25 (i.e., the reflective sensor 29) in front of the cassette stage 40 as shown in FIG. 9(b). The horizontal direction here is a horizontal direction perpendicular to the depth direction of the cassette stage 40. As a result, the wafer 50 in each slot is irradiated with the laser light 60 at a different position along the horizontal direction, and the light receiving portion of the sensor 29 detects the wafer thickness for each slot and for each irradiation position in the horizontal direction. In the example shown in Fig. 9, the laser light 60 is irradiated at 11 different positions A to K along the horizontal direction.

[0043] A series of detection results thus obtained can be expressed as two-dimensional detection distribution data, with the horizontal irradiation position being one dimension and the vertical slot position being the other dimension. FIG. 10 shows an example of detection distribution data obtained when the cassette stage 40 has 10 slots, the horizontal irradiation positions of the laser light 60 are 11 positions A to K as described above, and each slot stores a silicon wafer with a thickness of 0.9 mm as the wafer 50. The area shown in black in the figure is the area where the sensor 29 detected the wafer 50. The larger the vertical dimension of this area (the up-down direction in the figure) is, the thicker the wafer 50 is detected. The dotted line indicates that the wafer 50 could not be detected even though the wafer 50 is present.

[0044] In the results shown in FIG. 10, even though the wafer 50 of the same material and thickness was detected, the detected thickness differed greatly for each slot and each irradiation position. At positions A, B, and K, there were slots where the wafer 50 failed to be detected. At positions F, G, and H, the wafer 50 was detected as being about 2 to 4 times thicker than the actual thickness, and the detected thickness varied greatly. This is thought to be due to over-reflection occurring due to the reflection angle of the laser light 60 on the wafer 50. Therefore, in the process of determining the mapping position, after excluding irradiation positions including slots where the wafer 50 could not be detected and irradiation positions where excessive over-reflection occurs, a position suitable for mapping is found from among the irradiation positions, and the irradiation position is determined as the mapping position. The following (1) to (3) can be given as conditions for determining the mapping position.

[0045] (1) The average detected thickness is closest to a predetermined thickness (e.g., the thickness of the wafer 50); (2) The smallest variation in all detected thickness values; (3) The difference between the maximum and minimum detected thicknesses is the smallest.

[0046] When determining the mapping position, any one of the conditions (1) to (3) may be used, two of these conditions may be used, or all of the conditions (1) to (3) may be used. By determining the mapping position in this manner, even when a reflective sensor 29 is used, the wafer 50 can be reliably detected in the threshold detection operation and the mapping operation. In the example shown in FIG. 10, for example, the position D or the position I is determined as the mapping position.

[0047] In the transport robot 20 of the present embodiment described above, the cassette stage 40 containing the wafers 50 is prepared so that the normal mounting state and the abnormal mounting state appear at multiple locations, and the discrimination threshold is calculated based on the average value obtained by performing the threshold detection operation on the cassette stage 40. Therefore, the discrimination threshold used to discriminate the presence or absence of the abnormal mounting state when mapping is performed can be set automatically without manual intervention. As a result, there is no variation in the discrimination threshold due to differences in operators, and the abnormal mounting state can be accurately discriminated when mapping is performed. Furthermore, the detection distribution data is obtained using the cassette stage 40 containing the wafers 50 in all slots, and the mapping position is determined from the detection distribution data, so that the optimal mapping position can be automatically obtained without manual intervention, and a more appropriate discrimination threshold can be obtained by performing the threshold detection operation at this mapping position. According to this embodiment, the number of steps required for setting the discrimination threshold for discriminating between the abnormal mounting states of "double" and "cross" when mapping is performed can be reduced.

[0048] Here, the resetting of the discrimination threshold will be explained. When a reflective sensor is used, the threshold may change depending on the shape, material, surface condition, etc. of the workpiece. Therefore, it is necessary to reset the discrimination threshold when changing the workpiece lot. When changing the workpiece lot, it is common to stop the device, such as a semiconductor manufacturing device, in which the transport device is installed, and the discrimination threshold can be reset during the stop period. Similarly, when a transmission type sensor is used, if the level of a container part such as a cassette stage changes due to a change in setup, the detected thickness of the wafer changes, so it is necessary to reset the discrimination threshold at such a time. When changing the setup, it is common to stop the device, such as a semiconductor manufacturing device, in which the transport device is installed, and the discrimination threshold can be reset during the stop period. Therefore, even if the discrimination threshold is automatically set based on the present invention, the stop period of the device is not extended, which contributes to improving the productivity of the device.

[0049] When calculating the discrimination thresholds based on the present invention, it is necessary to load the wafer 50 on the cassette stage 40 as intended in step 101 above. In order to prevent errors in loading the wafer 50 at this time, for example, the variation or standard deviation of the detection values ​​when the wafer 50 is detected in each mounting state may be calculated, and an alarm may be issued to prompt confirmation if the variation is large. Alternatively, after calculating each discrimination threshold, the calculated discrimination thresholds may be used to judge the detection results remaining in the memory of the robot controller 30, and it may be determined whether a normal mounting state and an abnormal mounting state have been correctly distinguished, and if not, an alarm may be issued to prompt confirmation. [Explanation of symbols]

[0050] 20...transport robot; 21...base; 22-24...arm; 25...hand; 26...fork section; 27...light emitting section; 28...light receiving section; 29...sensor; 30...robot controller; 40...cassette stage; 41...rail; 50...wafer; 60...laser light.

Claims

1. A conveying device that conveys a workpiece to a storage section that has a plurality of slots arranged in a height direction and can horizontally accommodate one plate-shaped workpiece in each slot, A hand that holds the workpiece when transporting the workpiece; a sensor that irradiates light onto the workpiece to determine the presence or absence of the workpiece in the slot; a moving mechanism that moves the hand and the sensor relative to the storage unit; A control means for driving and controlling the moving mechanism, The control means performs a threshold detection operation for the storage section in which the workpieces are stored at multiple locations in a normal mounting state and in which the workpieces are stored at multiple locations in an abnormal mounting state, by moving the sensor in the height direction to cause the sensor to detect the workpieces, and calculates a threshold for distinguishing between the normal mounting state and the abnormal mounting state from the average value of the detected thicknesses and the average value of the height positions within the slot obtained from the workpieces in the normal mounting state in the threshold detection operation, and the average value of the detected thicknesses and the average value of the height positions within the slot obtained from the workpieces in the abnormal mounting state in the threshold detection operation, the conveying device.

2. The abnormal mounting state includes a first state in which two or more of the workpieces are accommodated in one of the slots, and a second state in which at least one of the workpieces is accommodated across adjacent slots, The conveying device according to claim 1 , wherein the storage section in which the workpiece is stored at multiple locations in the first state and in which the workpiece is stored at multiple locations in the second state is used when calculating the threshold value.

3. The conveying device according to claim 1 , wherein the sensor is attached to the hand.

4. The conveying device according to any one of claims 1 to 3, wherein the sensor is a transmission type sensor having a light emitting unit and a light receiving unit, and detects the workpiece when light directed from the light emitting unit to the light receiving unit is blocked by the workpiece.

5. 4. The conveying device according to claim 1, wherein the sensor is a reflective sensor that detects the workpiece by irradiating light toward the workpiece and detecting light reflected from the workpiece.

6. A position on the workpiece where the light from the sensor is irradiated along a horizontal direction perpendicular to the depth direction of the storage section is defined as an irradiation position, The control means, before performing the threshold detection operation, moves the sensor along the height direction to detect the reflected light from the workpiece, for the accommodation unit in which the workpiece is accommodated in each of the slots, moves the irradiation position, and repeatedly executes the operation to obtain detection distribution data, and determines a mapping position based on the detection distribution data; the control means performs the threshold detection operation at the determined mapping location; The transport device according to claim 5 , wherein the mapping position is the irradiation position when the sensor is moved in the height direction to perform mapping for determining the presence / absence state of the workpieces in the storage section.

7. The conveying device according to any one of claims 1 to 6, wherein the control means, when controlling the moving mechanism to transport the workpiece, executes control to perform mapping to determine the loading status of the workpiece in the storage section, and determines whether or not there is an abnormal loading status using the threshold value.

8. A mapping method for determining the inventory status of a workpiece in a storage section that has a plurality of slots arranged in a height direction and can horizontally store one workpiece that is a plate-like object in each slot, comprising: A threshold detection operation is performed for the accommodation unit in which the workpieces are accommodated at multiple locations in a normal mounting state and in which the workpieces are accommodated at multiple locations in an abnormal mounting state, by moving a sensor in the height direction and causing the sensor to detect the workpieces; A mapping method in which a threshold for distinguishing between the normal mounting state and the abnormal mounting state is calculated from the average value of the detected thickness and the average value of the height position within the slot obtained from the workpiece in the normal mounting state in the threshold detection operation, and the average value of the detected thickness and the average value of the height position within the slot obtained from the workpiece in the abnormal mounting state in the threshold detection operation.

9. The abnormal mounting state includes a first state in which two or more of the workpieces are accommodated in one of the slots, and a second state in which at least one of the workpieces is accommodated across adjacent slots, The mapping method according to claim 8, wherein when calculating the threshold value, a storage section in which the workpiece is stored at multiple locations in the first state and in which the workpiece is stored at multiple locations in the second state is used.

10. The sensor is a reflective sensor that detects the workpiece by irradiating light toward the workpiece and detecting reflected light from the workpiece, A position on the workpiece where the light from the sensor is irradiated along a horizontal direction perpendicular to the depth direction of the storage section is defined as an irradiation position, Before performing the threshold detection operation, an operation of moving the sensor along the height direction to detect the reflected light from the workpiece is performed for the accommodation unit in which the workpiece is accommodated in each of the slots, by moving the irradiation position and repeatedly executing the operation to obtain detection distribution data, and determining a mapping position based on the detection distribution data; The threshold detection operation is performed at the determined mapping location; 10. The mapping method according to claim 8, wherein the mapping position is the irradiation position when the sensor is moved in the height direction to perform the mapping.

11. A mapping method according to any one of claims 8 to 10, further comprising: when transporting the workpiece after determining the threshold value, performing the mapping for the storage section, and determining whether or not the abnormal mounting state exists using the threshold value.

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