Wafer inventory detection device

Abstract

To provide a wafer inventory detection device capable of reliably detecting the presence of wafers even when the wafers are transparent, without being affected by water droplets.SOLUTION: A wafer inventory detection device detects whether a wafer W is placed on a tray 41, and includes an ultrasonic sensor 43 provided on the opposite side of the tray 41 from the placement side of the dray 41 on which the wafer W is placed, and which emits ultrasonic waves from a detection surface 43a and receives the ultrasonic waves by the detection surface 43a; and a reflector 44 provided on the opposite side of the tray 41 from the placement side, and which has an ultrasonic reflecting surface 44a that refracts and reflects the ultrasonic waves emitted from the detection surface 43a toward an opening 42 in the tray 41 and refracts and reflects the ultrasonic waves returning from the opening 42 toward the detection surface 43a.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a workpiece (e.g., wafer) presence detection device, and more particularly to a wafer presence detection device that detects whether or not a wafer is placed on a tray in a wafer polishing device that performs CMP processing on the wafer. [Background technology]

[0002] 2. Description of the Related Art In the field of semiconductor manufacturing, wafer polishing apparatuses are known that polish the surfaces of semiconductor wafers such as silicon wafers (hereinafter simply referred to as "wafers").

[0003] The polishing apparatus described in Patent Document 1 is a polishing apparatus that applies chemical mechanical polishing (CMP) technology. In this polishing apparatus, a waiting unit relays the transfer of wafers between a load / unload section, where wafers are removed from a cassette and transported, and a polishing head, which polishes the wafers.

[0004] The waiting unit is a wafer loading table with a two-tiered structure. The upper tier is a loading-only wafer loading table (in-table) with a tray that transfers wafers before polishing to the polishing head, and the lower tier is an unloading-only wafer placement table (out-table) with a tray that receives wafers from the polishing head after polishing.

[0005] In this polishing device, when the in-table tray moves to a predetermined position (load position) where the wafer is handed over to the polishing head, the polishing head with a retainer attached descends, suction-holds the wafer to the retainer, and carries it onto the polishing platen, where the wafer is polished.

[0006] After polishing, the wafers are moved onto the tray on the out-table, and the processed wafers are handed over to the tray on the out-table. The out-table is transported to a designated position together with the processed wafers, and then moved to an unload cassette by a transport robot. By repeating this process, multiple wafers can be polished continuously.

[0007] In a method of transporting wafers using a waiting unit, in order to prevent mistakes such as double-feeding of wafers, the in-table must receive wafers from the transport robot or the out-table must receive polished wafers from the polishing head when there are no wafers in the in-table tray or the out-table tray. For this reason, a wafer presence detection device is provided in the in-table tray and the out-table tray to detect whether or not wafers are present. Conventional wafer presence detection devices use optical sensors to detect the presence of wafers.

[0008] As shown in Fig. 7, an optical sensor 101 in a conventional wafer presence detection device has a light-emitting unit 102 and a light-receiving unit 103. Meanwhile, an opening 105 that penetrates vertically is provided in a tray 104 of an in-table (or out-table) on which wafers W are placed. The optical sensor 101 is also provided such that the light-emitting unit 102 is disposed on the lower surface (or upper surface) of the tray 104, corresponding to the opening 105 of the tray 104, and the light-receiving unit 103 is disposed on the upper surface (or lower surface) of the tray 104.

[0009] When a wafer W is placed on the in-table (or out-table) tray 104, the opening 105 is closed by the wafer W, and the light from the light-emitting unit 102 is blocked by the wafer W, preventing the light from reaching the light-receiving unit 103. This causes the optical sensor 101 to recognize that a wafer W is present on the tray 104. Conversely, when a wafer W is not placed on the in-table or out-table tray 104, the opening 105 is open, and the light from the light-emitting unit 102 reaches the light-receiving unit 103 through the opening 105, thereby recognizing that no wafer W is present on the tray 104. In other words, the presence of a wafer W on the in-table or out-table tray 104 is detected depending on whether or not light from the light-emitting unit 102 enters the light-receiving unit 103. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 3510177 Summary of the Invention [Problem to be solved by the invention]

[0011] However, in the conventional structure in which the optical sensor 101 is used to detect the presence of wafers W, if water droplets adhere to the optical sensor 101, the presence of wafers W may be erroneously detected.

[0012] Furthermore, nowadays, there are transparent wafers W made of transparent glass, but in the case of transparent wafers W, the light from the light projecting unit 102 passes through the wafer W and enters the light receiving unit 103, which causes a problem that the optical sensor 101 cannot be used when handling transparent wafers W.

[0013] Therefore, a technical problem arises that must be solved in order to provide a wafer presence detection device that can reliably detect the presence of wafers, even transparent wafers, without being affected by water droplets, and the present invention aims to solve this problem. [Means for solving the problem]

[0014] In order to achieve the above-mentioned object, the wafer presence detection device of the present invention is a wafer presence detection device that detects whether or not a wafer is placed on a tray, and is equipped with an ultrasonic sensor that is provided on the opposite side of the tray from the placement side on which the wafer is placed, and that emits ultrasonic waves from a transmission surface and receives the ultrasonic waves with a receiving surface, and an ultrasonic refraction means that is provided on the opposite side of the tray from the placement side and has an ultrasonic reflection surface that refracts and reflects the ultrasonic waves emitted from the transmission surface toward an opening of the tray, and refracts and reflects the ultrasonic waves returning from the opening toward the receiving surface.

[0015] In the wafer presence detection device according to the present invention, it is preferable that the transmitting surface and the receiving surface are disposed at approximately right angles to the rear surface of the tray.

[0016] In the wafer presence detection device according to the present invention, it is preferable that the transmitting surface and the receiving surface are inclined toward the ultrasonic refraction means. [Effects of the Invention]

[0017] According to the present invention, ultrasonic waves are emitted toward the wafers and the ultrasonic waves reflected by the wafers are received, so the presence of wafers can be reliably detected even for transparent wafers made of transparent glass, for example, thereby improving detection accuracy. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a plan view schematically showing the overall structure of a wafer polishing apparatus using a wafer presence detection device of the present invention; [Figure 2]3A and 3B are diagrams showing a schematic configuration of a main part of a waiting unit in the wafer polishing apparatus, in which FIG. 3A is a front view of the waiting unit, and FIG. 3B is a plan view of the waiting unit seen from above. [Figure 3] 1 is a vertical cross-sectional side view schematically showing the configuration of a main part of a wafer presence detection device according to a first embodiment of the present invention. [Figure 4] FIG. 10 is a vertical cross-sectional side view schematically showing the configuration of the main part of a wafer presence detection device according to a second embodiment of the present invention. [Figure 5] FIG. 10 is a vertical cross-sectional side view schematically showing the configuration of a main part of a wafer presence detection device according to a third embodiment of the present invention. [Figure 6] FIG. 10 is a vertical cross-sectional side view schematically showing the configuration of the main part of a wafer presence detection device according to a fourth embodiment of the present invention. [Figure 7] FIG. 1 is a vertical cross-sectional side view schematically showing a configuration of a main part of a conventional wafer presence detection device. DETAILED DESCRIPTION OF THE INVENTION

[0019] In order to achieve the object of providing a wafer presence detection device that can reliably detect the presence of wafers even if the wafers are transparent, without increasing the size of the device, the present invention has been realized by providing a wafer presence detection device that detects whether or not a wafer is placed on a tray, comprising: an ultrasonic sensor that is provided on the opposite side of the tray from the placement side on which the wafers are placed, and that emits ultrasonic waves from a transmission surface and receives the ultrasonic waves with a receiving surface; and ultrasonic refraction means that is provided on the opposite side of the tray from the placement side, and has an ultrasonic reflection surface that refracts and reflects the ultrasonic waves emitted from the transmission surface toward an opening in the tray, and refracts and reflects the ultrasonic waves returning from the opening toward the receiving surface. [Example]

[0020] Examples of embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that in each of the following examples, when referring to the number, numerical value, amount, range, etc. of components, unless otherwise specified or when it is clearly limited to a specific number in principle, the number is not limited to the specific number and may be more or less than the specific number.

[0021] Furthermore, when referring to the shape or positional relationship of components, etc., it includes things that are substantially similar or approximate to those shapes, etc., unless otherwise specified or when it is clearly considered otherwise in principle.

[0022] In addition, the drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional proportions of the components may not be the same as in reality. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

[0023] In the following description, expressions indicating directions such as up, down, left, and right are not absolute, but are appropriate when each part of the wafer presence detection device of the present invention is in the posture shown in the drawing, but if the posture changes, they should be interpreted accordingly. Furthermore, the same elements are given the same symbols throughout the description of the embodiments.

[0024] 1 is a plan view showing a schematic diagram of the overall configuration of a wafer polishing apparatus 10 using a wafer presence detection device according to the present invention. In FIG. 1, the wafer polishing apparatus 10 is a CMP apparatus that polishes the surface of a wafer W to make it flat.

[0025] The wafer polishing apparatus 10 includes a load cassette 11, a transfer robot 12, an aligner 13, a waiting unit 14, a polishing table 15, and an unload cassette 16. The waiting unit 14 includes an in-table 17, a polishing head 18, and an out-table 19.

[0026] The load cassette 11 is used to temporarily store wafers W before polishing.

[0027] The transport robot 12 is used for loading the wafers W, and receives the wafers W before polishing from the load cassette 11, transports them in the order of the aligner 13, the in-table 17, the polishing head 18, the polishing surface plate 15, and the out-table 19, and then transports them to the unload cassette 16 where the wafers W after polishing are temporarily stored.

[0028] The aligner 13 adjusts the orientation of the wafer W after it is removed from the load cassette 11 and before it is transferred to the waiting unit 14 .

[0029] The polishing platen 15 is formed in a disk shape, and a polishing pad (not shown) is replaceably attached to the upper surface. The polishing platen 15 rotates integrally with the polishing pad about its axis by driving a rotation drive mechanism. The polishing platen 15, together with the polishing head 18, polishes the surface of the wafer W pressed against it to a flat surface using the polishing pad.

[0030] 2 is a diagram showing a schematic configuration of the waiting unit 14, where (a) is a front view of the waiting unit 14 and (b) is a plan view of the waiting unit 14 seen from above. In Fig. 2, the waiting unit 14 is a wafer placement table with a two-tiered structure. The waiting unit 14 is provided with a wafer presence detection device 40 according to the present invention.

[0031] The wafer placement table on the upper side of the waiting unit 14 is an in-table 17, which serves as a wafer placement table dedicated to loading and delivering wafers W before polishing to the polishing head 18. On the other hand, the wafer placement table on the lower side is an out-table 19, which serves as a wafer placement table dedicated to unloading and receiving wafers W after polishing from the polishing head 18. Trays 41 on which wafers W are placed and held are provided on the in-table 17 and out-table 19, respectively. The tray 41 provided on the in-table 17 moves integrally with the in-table 17, and the tray 41 provided on the out-table 19 moves integrally with the out-table 19.

[0032] The in-table 17 and the out-table 19 of the weighting unit 14 are connected to rodless cylinders 21a and 21b via connecting members 20a and 20b, respectively. When the rodless cylinders 21a and 21b of the weighting unit 14 are driven, the in-table 17 and the out-table 19 can move in the direction of arrow Y in FIG. 2(b).

[0033] The polishing head 18 is slidable above the tray 41 on the in-table 17 and the tray 41 on the out-table 19, and is also movable up and down in the vertical direction Z. The polishing head 18 receives the wafer W from the tray 41 on the in-table 17, moves to above the polishing platen 15, and, when polishing, descends to press the wafer W against a polishing pad (not shown) affixed to the upper surface of the polishing platen 15 to perform polishing. During polishing, CPM slurry, which is a mixture of abrasives and chemicals, is supplied onto the polishing pad from a nozzle (not shown).

[0034] After polishing, the wafer W is moved onto the out-table 19, and the processed wafer W is delivered onto the tray 41 of the out-table 19. The out-table 19 is transported to a predetermined position together with the processed wafer W, and then moved to the unload cassette 16 by the transport robot 12.

[0035] In this way, in the wafer polishing apparatus 10 in which wafers W are transferred via the trays 41 on the in-table 17 and the trays 41 on the out-table 19, in order to prevent serious errors such as double feeding of wafers W and to perform movement and processing smoothly, it is necessary to detect the state of wafers W in the trays 41 on the in-table 17 and the state of wafers W in the trays 41 on the out-table 19 and then perform the required operation. Therefore, in the wafer polishing apparatus 10 of this embodiment, wafer presence detection devices 40 that detect the state of wafers W in each tray 41 on the in-table 17 and the out-table 19 are provided corresponding to each of the in-table 17 and the out-table 19.

[0036] The wafer presence detection device 40 according to the first embodiment of the wafer polishing apparatus 10 of this embodiment is provided on the in-table 17 and the wafer presence detection device 40 provided on the out-table 19, and their structures are substantially the same. Therefore, in the following explanation, for the sake of simplicity, the wafer presence detection device 40 on the out-table 19 side will be explained as a representative. Therefore, it should be understood that the in-table 17 side is also provided with a wafer presence detection device 40 that is the same as the wafer presence detection device 40 provided on the in-table 17 on the out-table 19 side.

[0037] 3, the wafer presence detection device 40 according to the first embodiment has an opening 42 that penetrates from the tray front surface 41a to the tray back surface 41b at approximately the center of a tray 41 on which wafers W are placed and covered by the wafers W. The wafer presence detection device 40 also has an ultrasonic sensor 43 disposed on the tray back surface 41b of the tray 41 at a position corresponding to the opening 42, with its detection surface 43a facing the opening 42.

[0038] The ultrasonic sensor 43 is a well-known sensor that alternately transmits ultrasonic waves from a transmitting portion of the detection surface 43a and receives the ultrasonic waves reflected by one surface of the wafers W at a receiving portion of the detection surface 43a, and detects the presence or absence of ultrasonic waves reflected by one surface of the wafers W and returning to the detection surface 43a, thereby detecting the presence or absence of wafers W on the tray 41. Note that, depending on the ultrasonic sensor 43, the detection surface 43a may be separated into an ultrasonic wave transmitting surface that emits ultrasonic waves and an ultrasonic wave receiving surface that receives the reflected ultrasonic waves.

[0039] 3, when wafers W are placed on a tray 41 and the opening 42 is covered by the wafers W, ultrasonic waves are emitted from the transmitter on the detection surface 43a of the ultrasonic sensor 43. The ultrasonic waves pass through the opening 42 and strike one side of the wafers W. The ultrasonic waves are reflected by the one side of the wafers W, enter the receiver on the detection surface 43a, and are received by the detection surface 43a within a predetermined time. This alternating transmission and reception of ultrasonic waves makes it possible to detect whether or not a wafer W is present on the tray 41. Furthermore, since the wafers W are detected by detecting ultrasonic waves reflected by one side of the wafers W, even if the wafers W are transparent wafers W made of, for example, transparent glass, the wafers W placed on the tray surface 41a can be reliably detected.

[0040] On the other hand, when no wafers W are placed on the tray 41 and the opening 42 is not covered by the wafers W, if ultrasonic waves are emitted from the transmitter on the detection surface 43a of the ultrasonic sensor 43, the ultrasonic waves pass through the opening 42 and escape upward without being reflected. Even if the ultrasonic waves are reflected by other members, they are incident on the receiver on the detection surface 43a for a time period different from the predetermined time, and it is possible to detect that no wafers W are present on the tray 41.

[0041] 3, the ultrasonic sensor 43 can be incorporated with the ultrasonic transmitter and receiver located on one side (the rear side in this embodiment) of the tray 41, shortening the height distance L. This allows the wafer presence detection device 40 to be made more compact, and also allows the wafer polishing apparatus 10 to be made smaller overall.

[0042] Furthermore, since ultrasonic waves are emitted toward one surface of the wafers W and the ultrasonic waves reflected by the surface of the wafers W are received, the presence of the wafers W can be reliably detected even for transparent wafers made of transparent glass, for example, and the detection accuracy is improved.

[0043] 4 shows a wafer presence detection device 40 of the second embodiment. The wafer presence detection device 40 of the second embodiment has a reflector 44 serving as ultrasonic refraction means having an ultrasonic reflecting surface 44a provided between an opening 42 of a tray 41 and an ultrasonic sensor 43. The reflector 44 is a member that reflects sound waves, such as a metal or plastic plate, and has the ultrasonic reflecting surface 44a provided on its surface. The ultrasonic sensor 43 is disposed below the tray back surface 41b of the tray 41 with its detection surface 43a facing the reflector 44, and is configured to emit ultrasonic waves from the transmitting portion of the detection surface 43a of the ultrasonic sensor 43 in a direction substantially parallel (horizontal) to the tray back surface 41b of the tray 41.

[0044] The ultrasonic reflecting surface 44a of the reflector 44 refracts and reflects ultrasonic waves transmitted horizontally from the transmitter of the detection surface 43a of the ultrasonic sensor 43 toward the tray 41 at approximately a right angle, and also refracts and reflects reflected light from the tray 41 side toward the detection surface 43a of the ultrasonic sensor 43 at approximately a right angle, returning it toward the detection surface 43a.

[0045] That is, in the wafer presence detection device 40 of the second embodiment shown in FIG. 4, when wafers W are placed on a tray 41 and the opening 42 is covered by the wafers W, ultrasonic waves are emitted from the transmitter on the detection surface 43a of the ultrasonic sensor 43. The ultrasonic waves are directed toward the ultrasonic reflecting surface 44a of the reflector 44. The ultrasonic waves directed toward the ultrasonic reflecting surface 44a are reflected by the ultrasonic reflecting surface 44a, pass through the opening 42, and strike one side of the wafer W. The ultrasonic waves that strike one side of the wafer W are then reflected by the other side of the wafer W, pass through the ultrasonic reflecting surface 44a of the reflector 44, enter the receiver on the detection surface 43a, and are received within a predetermined time. Therefore, in this embodiment, the presence of wafers W in the tray 41 can be detected by alternately transmitting and receiving ultrasonic waves. Furthermore, because the wafers W are detected by detecting ultrasonic waves reflected by one side of the wafers W, detection is reliable even if the wafers W are transparent wafers, such as those made of transparent glass.

[0046] On the other hand, when no wafers W are placed on the tray 41 and the opening 42 is not covered by the wafers W, if ultrasonic waves are emitted from the transmitting portion of the detection surface 43a of the ultrasonic sensor 43, the ultrasonic waves pass through the opening 42 and exit upward without being reflected, as in the first embodiment. Furthermore, even if the ultrasonic waves are reflected by other members, they will not be incident on the receiving portion of the detection surface 43a within a predetermined time, making it possible to detect that no wafers W are present on the tray 41.

[0047] 4, the ultrasonic sensor 43 can be incorporated while the ultrasonic transmitter and receiver are located on one side (the rear surface in this embodiment) of the tray 41, shortening the height distance L. This allows the wafer presence detection device 40 to be made more compact, thereby enabling the entire wafer polishing apparatus 10 to be made smaller. Furthermore, by placing a reflector 44 between the opening 42 and the detection surface 43a of the ultrasonic sensor 43, the ultrasonic sensor 43 can be positioned closer to the tray rear surface 41b of the tray 41, thereby shortening the height distance L between the ultrasonic sensor 43 and the tray 41, thereby further reducing the size. Although the shortest detection distance of the ultrasonic sensor 43 is long, approximately 50 mm or more, by providing a reflector 44 between the opening 42 and the ultrasonic sensor 43 and reflecting the ultrasonic waves from the ultrasonic reflecting surface 44a, the ultrasonic sensor 43 can be easily incorporated.

[0048] Furthermore, as in the first embodiment, ultrasonic waves are emitted toward one surface of the wafer W and the ultrasonic waves reflected by the surface of the wafer W are received. Therefore, even if the wafer W is a transparent wafer made of transparent glass, for example, the presence of the wafer W can be reliably detected, improving the detection accuracy.

[0049] 5 shows a wafer presence detection device 40 of the third embodiment. As in the second embodiment, the wafer presence detection device 40 of the third embodiment is provided with a reflector 44 having an ultrasonic reflection surface 44a as ultrasonic refraction means between the opening 42 of the tray 41 and the ultrasonic sensor 43. The ultrasonic sensor 43 is disposed below the tray back surface 41b of the tray 41 with the detection surface 43a facing the reflector 44, and is configured to be able to emit ultrasonic waves from the transmitting portion of the detection surface 43a of the ultrasonic sensor 43 and receive reflected ultrasonic waves, which is substantially the same as the wafer presence detection device 40 of the second embodiment.

[0050] The difference between the wafer presence detection device 40 of the third embodiment and the wafer presence detection device 40 of the second embodiment is that in the second embodiment, the detection surface 43a of the ultrasonic sensor 43 is positioned approximately perpendicular to the tray back surface 41b of the tray 41, whereas in the third embodiment, the detection surface 43a of the ultrasonic sensor 43 is tilted diagonally downward.

[0051] That is, if water droplets or the like are scattered and adhere to the detection surface 43a of the ultrasonic sensor 43 during cleaning of the wafer W, ultrasonic waves may be refracted by the water droplets or the like, resulting in a decrease in detection performance. However, if the detection surface 43a of the ultrasonic sensor 43 is provided facing diagonally downward as in the third embodiment, it is possible to prevent water droplets or the like from adhering to the detection surface 43a, thereby stabilizing detection accuracy.

[0052] 6 shows a wafer presence detection device 40 according to a fourth embodiment of the present invention. Similar to the wafer presence detection device 40 according to the second embodiment, the wafer presence detection device 40 according to the fourth embodiment is provided with a reflector 44 having an ultrasonic reflecting surface 44a as ultrasonic refraction means between the opening 42 of the tray 41 and the ultrasonic sensor 43, and with blowers 45a and 45b for blowing air onto the ultrasonic reflecting surface 44a and the detection surface 43a of the ultrasonic sensor 43, respectively.

[0053] In a structure such as the fourth embodiment, which includes a blower 45a that blows air onto the ultrasonic reflecting surface 44a and a blower 45b that blows air onto the detection surface 43a of the ultrasonic sensor 43, if water droplets or dust adhere to the ultrasonic reflecting surface 44a or the detection surface 43a, the air from the blowers 45a and 45b can blow away the water droplets or dust on the ultrasonic reflecting surface 44a or the detection surface 43a, cleaning them. This stabilizes the ultrasonic path and makes it possible to maintain stable detection accuracy for the presence of wafers.

[0054] Although the first, second, third, and fourth embodiments disclose a structure in which the ultrasonic sensor 43 is provided on the tray rear surface 41b side of the tray 41, it may also be provided on the tray front surface 41a side of the tray 41. It may also be provided on both the tray front surface 41a side and the tray rear surface 41b side of the tray 41.

[0055] Furthermore, in the second, third and fourth embodiments, depending on the structure of the tray 41, if a recess or cavity in which the reflector 44 having the ultrasonic reflecting surface 44a and the ultrasonic sensor 43 are placed is provided in a part of the tray 41, and the reflector 44 and the ultrasonic sensor 43 are respectively placed in the recess or cavity, it becomes possible to absorb part of the height dimensions of the reflector 44 and the ultrasonic sensor 43 within the thickness dimension of the tray 41.

[0056] Furthermore, although the above embodiments have been described as being applied to the waiting unit 14 of the wafer polishing apparatus 10, the present invention is not limited to being applied to the waiting unit 14 of the wafer polishing apparatus 10, but can also be applied within semiconductor manufacturing equipment in which wafers W are placed on trays and work is performed.

[0057] Furthermore, the present invention can be modified in various ways without departing from the spirit of the present invention, and it is natural that the present invention also covers such modifications. [Explanation of symbols]

[0058] 10: Wafer polishing equipment 11: Road cassette 12: Transport robot 13: Alaina 14: Waiting unit 15: Polishing plate 16: Unload cassette 17: In-table 18: Polishing head 19:Out table 20a: connecting member 20b: connecting member 21a: Rodless cylinder 21b: Rodless cylinder 40: Cargo detection device 41: Tray 41a: Tray surface 41b: Back of tray 42: Opening 43: Ultrasonic sensor 43a: Detection surface 44:Reflector 44a: Ultrasonic reflective surface 45a: Blower 45b: Blower L: Height distance W: wafer Y: Arrow Z: Vertical direction

Claims

1. A wafer presence detection device that detects whether or not a wafer is placed on a tray, an ultrasonic sensor provided on the tray opposite to the side on which the wafer is placed, the ultrasonic sensor transmitting ultrasonic waves from a transmitting surface and receiving the ultrasonic waves with a receiving surface; an ultrasonic refraction means provided on the opposite side of the tray from the placement side, the ultrasonic refraction means having an ultrasonic reflection surface that refracts and reflects the ultrasonic waves transmitted from the transmission surface toward the opening of the tray and refracts and reflects the ultrasonic waves returning from the opening toward the reception surface; A wafer presence detection device comprising:

2. 2. The wafer presence detection device according to claim 1, wherein the transmitting surface and the receiving surface are disposed at a substantially right angle to the rear surface of the tray.

3. 2. The wafer presence detection device according to claim 1, wherein the transmitting surface and the receiving surface are inclined toward the ultrasonic refraction means.

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