JP2006120851A - Substrate storing container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate storing container capable of suppressing and preventing a substrate from rotating to catch wearing scrap or the like, with easy alignment of substrates. <P>SOLUTION: The container comprises a container body 1 in which semiconductor wafers W are aligned and stored, a lid for opening/closing the opening front surface of the container body 1, and a pair of, left and right, rear retainers 20/20A which are attached to the inside surface of the rear surface wall 8 of the container body 1 to hold the rear periphery of the semiconductor wafer W. The rear retainers 20/20A are formed of a flexible inside piece 21, an outside piece 22 which faces the inside piece 21, and a support block 23 which is bridged between the inside piece 21 and the outside piece 22 to pinch the rear periphery of the semiconductor wafer W. The inside piece 21 is closer to a center line CL that penetrates the centroid C of the semiconductor wafer W than the outside piece 22 is to the center line, and the amount of flexure of the inside piece 21 is set larger than that of the outside piece 22, to regulate large rotation of the semiconductor wafer W. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a substrate storage container that stores a substrate made of silicon, glass, or the like, and more particularly to a retainer of a substrate storage container that is attached to a container body or a lid and holds a peripheral edge of the substrate.

  In recent years, with the increase in diameter of semiconductor wafers from 200 mm to 300 mm, front open box type substrate storage containers are manufactured and sold. This type of substrate storage container aligns and stores a plurality of semiconductor wafers (not shown). The container main body of the front open box and the detachable lid that opens and closes the front of the opening of the container main body (see Patent Document 1).

A pair of left and right rear retainers are mounted on the inner surface of the rear wall of the container body, and a front retainer facing the pair of rear retainers is mounted on the back surface of the lid, and the pair of rear retainers are disposed between the pair of rear retainers and the front retainer. The semiconductor wafer accommodated in the container body is horizontally held. Each rear retainer is formed of an inner piece, an outer piece facing the inner piece, and a support block that is spanned between the inner piece and the outer piece and sandwiches the rear periphery of the semiconductor wafer via a groove. Yes.
Japanese Patent Laid-Open No. 2003-174081

  The conventional substrate storage container is configured as described above, and the load of the semiconductor wafer should act on the inner piece and the outer piece of each rear retainer substantially evenly. Either the inner piece or the outer piece of each rear retainer If one side bends excessively, the semiconductor wafer is likely to rotate in the bending direction. And, for example, if the pair of rear retainers bend in the same direction due to vibration or impact during transport of the substrate storage container, there is a big problem that the semiconductor wafer rotates greatly in the bent direction and wear powder adheres. Arise.

  In addition, if the semiconductor wafer rotates at random, when the electronic circuit is formed on the surface of the semiconductor wafer, the positioning notch cut out on the peripheral edge of the semiconductor wafer must be realigned. There is also the problem of taking time.

  The present invention has been made in view of the above, and an object of the present invention is to provide a substrate storage container that can suppress and prevent the substrate from rotating and wear powder or the like from adhering to the substrate or can easily align the substrate.

In the present invention, in order to solve the above problems, a container main body for storing a substrate, a lid body for opening and closing the opening of the container main body, and at least one of the container main body and the lid body are provided at the opposing portion. A plurality of retainers for holding the peripheral edge of the substrate,
Each retainer includes a flexible inner piece, an outer piece facing the inner piece, and a support block provided between the inner piece and the outer piece to support the peripheral edge of the substrate. It is characterized in that the piece is brought closer to the center line passing through the center of gravity of the substrate than the outer piece, and the amount of bending of the inner piece is made larger than the amount of bending of the outer piece to suppress the rotation of the substrate.

In addition, the inner piece and the outer piece of each retainer can be brought into contact with at least one of the opposing portions of the container body and the lid, respectively, so that the inner piece can be formed thinner than the outer piece.
In addition, the outer piece of each retainer can be brought into contact with the facing portion of at least one of the container main body and the lid, and the inner piece can be made to face through the gap.
Further, a reinforcing member can be provided on the outer piece of each retainer.

In addition, the support block of each retainer can be positioned closer to the outer side than the center part of the inner and outer pieces.
Furthermore, the inner piece and the outer piece of each retainer are brought into contact with the facing portion of at least one of the container main body and the lid, respectively, and the angle θ1 formed by the facing portion and the inner piece is set to the angle between the facing portion and the outer piece. It is possible to make it smaller than the forming angle θ2.

  Here, the substrate in the claims includes at least a semiconductor wafer such as a silicon wafer of 200 mm, 300 mm, and 450 mm, mask glass, liquid crystal glass, and the like. The container body may be transparent, translucent, or opaque. The back wall of the container body can be a see-through window. The retainer includes a front retainer in addition to a rear retainer. The substrate storage container may be a front open box type, or may be a top open box type that vertically stores a plurality of semiconductor wafers having a diameter of 200 mm.

  In the case of the top open box type, the substrate storage container is a bottomed rectangular tube-shaped outer box, and a rectangular tube-shaped inner box that is detachably stored in the outer box and stores a plurality of substrates vertically aligned. The detachable lid body covers the upper surface of the opening of the outer box and presses the upper peripheral edge of the substrate by pressing the substrate. A retainer is provided on the inner bottom surface of the outer box and / or the substrate holder of the lid body.

  According to the present invention, since the inner piece of each retainer is more flexible than the outer piece, the substrate housed in the container body rotates clockwise in one retainer portion and counterclockwise in the other retainer portion. Try to rotate to. As a result, the movement in the rotation direction of the substrate is canceled, and the rotation of the substrate is restricted.

ADVANTAGE OF THE INVENTION According to this invention, there exists an effect that it can suppress that a board | substrate rotates and an abrasion powder etc. adhere and can align a board | substrate easily.
In addition, when the outer piece of each retainer is brought into contact with at least one of the opposing portions of the container main body and the lid, and the inner piece is made to face through the gap, the inner piece that is not in contact with the facing portion is obtained. It will bend and contact, and the amount of bending will increase.
Further, if a reinforcing member is provided on the outer piece of each retainer, the rigidity of the outer piece can be increased more than the inner piece without greatly changing the thickness and shape of the inner piece and the outer piece.

  Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. A substrate storage container in this embodiment includes a container main body 1 for storing a plurality of semiconductor wafers W, as shown in FIGS. A detachable lid 10 that opens and closes the opening front of the container body 1 and a pair of left and right rear retainers 20 and 20A that are attached to the rear wall 8 of the container body 1 and elastically hold the rear periphery of the semiconductor wafer W. The rear retainers 20 and 20A are provided with a function of restricting free rotation of the semiconductor wafer W.

  As shown in FIG. 4, each semiconductor wafer W is made of, for example, a round disk-shaped silicon wafer having a diameter of 300 mm. Both front and back surfaces are formed as mirror surfaces. In and out. At the periphery of the semiconductor wafer W, a notch N that facilitates discrimination and alignment of the crystal direction is cut out in a substantially semicircular plane.

  As shown in FIGS. 1 and 2, the container body 1 is formed into a transparent front open box having a front opening using a predetermined resin, and a plurality of (for example, 25) semiconductor wafers W are vertically arranged. Functions to store side by side. As shown in FIG. 3, a pair of left and right teeth 2 that support and mount the semiconductor wafer W substantially horizontally are formed on the inner surfaces of both side walls of the container main body 1. Are arranged at a predetermined pitch.

  The teeth 2 are formed in a substantially rectangular shape, a substantially square shape, or a substantially semicircular arc shape, and a flat plate 3 that is formed on the front inner side of the flat plate 3 and a flat plate 3 that extends along the peripheral edge of the semiconductor wafer W. The front middle wall region, the flat front thick region that is integrally formed on the front outer side of the flat plate 3 and located outside the front middle wall region, in other words, on the side wall side of the container body 1, and the flat plate A rear middle thickness region integrally formed at the rear portion of the flat plate 3, and a flat rear thick portion formed at the rear portion of the flat plate 3 and positioned in front of the rear middle thickness region and located in a small area near the side wall of the container body 1 Region.

  A slight vertical step contacting the side periphery of the semiconductor wafer W is formed between the front middle wall region and the front thick wall region. The front thick wall region is formed when the lid 10 is removed. It functions to restrict W from jumping out of the container body 1. A slightly recessed thin region is formed between the front middle region and the rear middle region, and this thin region is opposed to the peripheral edge of the side of the semiconductor wafer W with a slight gap.

  The teeth 2 having such a structure horizontally supports the peripheral edge of the semiconductor wafer W in a flat front middle region and rear middle region while maintaining high accuracy, and the semiconductor wafer W is inclined in the vertical direction. Thus, it functions to prevent the robot fork from being taken in and out.

  Positioning tools 4 that are positioned by a processing apparatus on which the substrate storage container is mounted are integrally formed on both the front side and the rear center of the bottom surface of the container body 1, and a thin and small plate is formed on the rear surface of the bottom surface of the container body 1. A bottom plate is detachably mounted from the rear, and a plurality of identifiers detachably fitted to the bottom plate from below are identified by the processing apparatus, so that the type of the substrate storage container and the semiconductor wafer W The number of sheets is grasped.

  Each positioning tool 4 is formed in a substantially M-shaped cross section, a substantially inverted Y shape, or a concave oval shape. The bottom plate is formed in a plane substantially concave shape, a substantially Y shape, or a polygonal shape, and is attached or changed in size as necessary.

  As shown in FIGS. 1 and 3, a flat rectangular robotic flange 5 is integrally or detachably attached to the center of the ceiling of the container body 1, and this robotic flange 5 is called an OHT and is not shown in the figure. As a result, the substrate container transports the inside of the process. Moreover, the peripheral part of the opening front of the container main body 1 is formed in a substantially L-shaped cross section so that it protrudes outward to form a rim part 6 (see FIGS. 2 and 3). A plurality of recesses for locking the lid are formed on the upper and lower sides.

  Thick disk-shaped or inverted U-shaped transport handles (not shown) are selectively mounted on both side walls of the container body 1, and the substrate storage container is transported by gripping the transport handles. .

  The container body 1, the teeth 2, the positioning tool 4, the bottom plate, the robotic flange 5, and the transport handle are molded using, for example, polycarbonate, polyetherimide, polyetheretherketone, or cyclic olefin resin. . Carbon black, acetylene black, carbon fiber, carbon nanotube, metal fiber, antistatic agent and the like can be appropriately added to these materials.

  As shown in FIGS. 1 to 3, the lid body 10 is set on a fitting body 11 that is detachably fitted into the rim portion 6 of the container body 1, and on both sides of the opening surface of the fitting body 11. A pair of left and right locking mechanisms 15 and a pair of cover plates 16 that are detachably attached to both sides of the opening surface of the fitting body 11 and cover the locking mechanism 15, respectively, and are the opening front of the container body 1. The rim portion 6 is detachably pressed and fitted and closed in a sealed state.

  The fitting body 11 is basically formed in a substantially dish-shaped or substantially hat-shaped cross section, is formed in a horizontally long frontal rectangular shape, and has a substantially H-shaped cross section, a substantially L-shaped cross section so that the peripheral wall can ensure rigidity, or The seal gasket 12 interposed between the container main body 1 and the cover body 10 is detachably fitted to the bent peripheral wall. The seal gasket 12 is formed endlessly using, for example, fluorine rubber, silicone rubber, or the like, is pressed and deformed to the inner periphery of the rim portion 6 when the lid body 10 is fitted, and contains dust from the outside to the inside of the container body 1. It functions to suppress and prevent the inflow of gas.

  An elastic front retainer 13 having a substantially U-shaped plane is mounted on the back surface of the fitting body 11 (the surface facing the back wall 8 of the container body 1, the facing portion), and the front retainer 13 is accommodated in the container body 1. The front peripheral edge of each semiconductor wafer W is clamped. The front retainer 13 includes a vertically long support frame that is attached to the center of the back surface of the fitting body 11, a plurality of elastic pieces that are installed between both sides of the support frame and are arranged in the vertical direction, and each elastic piece. And a guide block 14 that holds the front peripheral edge of the semiconductor wafer W through a groove, and the front peripheral edge of the semiconductor wafer W is formed in a groove on substantially both sides of each elastic piece. A guided block 14 is selectively formed so as to be sandwiched therebetween.

  Each locking mechanism 15 is pivotally supported on the surface side portion of the fitting body 11 and is rotated by an operation from the outside of a lid opening / closing device (not shown) and is slidably supported by the fitting body 11 and connected to the rotation reel. And a plurality of advancing / retracting bars that slide linearly in the up / down direction of the lid 10 based on the rotation of the rotary reel, and formed at the front end of each advancing / retracting bar, and protrudes and disappears from the opening of the peripheral wall of the fitting 11. And a locking claw that is engaged with and locked to the locking hole 7 of the rim portion 6 and locks the lid body 10 that is fitted and closed to the rim portion 6 of the container body 1.

  Each cover plate 16 is formed in a shape corresponding to the opening area of the fitting body 11, and a through operation hole 17 for the locking mechanism 15 facing the center of the surface of the rotary reel is formed in a front rectangle. The hole 17 is penetrated by the key of the lid opening / closing device.

  Note that the fitting body 11, the locking mechanism 15, the cover plate 16 and the like of the lid body 10 are formed using, for example, polycarbonate, polycarbonate containing fluorine, polybutylene terephthalate, polyetheretherketone, polyetherimide, polyacetal, or the like. The

  As shown in FIGS. 2 and 4, the pair of rear retainers 20, 20 </ b> A are mounted on the inner surface (opposing portion) of the back wall 8 of the container body 1 with a space therebetween and the center passing through the center of gravity C of the semiconductor wafer W. The semiconductor wafers W are arranged substantially symmetrically so as to sandwich the line CL, and are held substantially horizontally in a state where the semiconductor wafer W is slightly lifted from the pair of teeth 2 so as to face the front retainer 13 when the lid 10 is fitted and closed.

  As shown in FIG. 5, each of the rear retainers 20, 20 </ b> A has a flexible inner piece 21 that contacts the back wall 8 of the container body 1 and a gap between the inner piece 21 that contacts the back wall 8 of the container body 1. Are formed in a vertically long shape having a substantially U-shaped cross section from a flexible outer piece 22 facing each other and an elastic support block 23 sandwiched between the inner piece 21 and the outer piece 22 and sandwiching the semiconductor wafer W. , Oriented in the vertical direction of the container body 1 (see FIG. 8 for this point).

  Each of the rear retainers 20 and 20A is made of, for example, a polyolefin-based or polyester-based thermoplastic elastomer, fluorine rubber, rubber such as EPDM, polyurethane, polyolefin-based resin such as polyethylene or polypropylene, polyester-based resin such as polyethylene terephthalate or polybutylene terephthalate, poly It is formed as an ether ether ketone material.

  Each of the rear retainers 20, 20 </ b> A is formed with a plurality of fitting portions 24 formed of concave portions, convex portions, and the like at intervals between the inner piece 21 and the outer piece 22 in the vertical direction. It is fixed to the back wall 8 of the container body 1 by being fitted to the fitted portion 24 on the inner surface of the back wall. The inner piece 21 and the outer piece 22 are formed at the same height, and the front and rear length of the outer piece 22 is longer than the front and rear length of the inner piece 21 (length in the vertical direction in FIG. 5). The inner piece 21 is closer to the center line CL passing through the center of gravity C of the semiconductor wafer W than the outer piece 22, and is formed in a thin thickness of 30 to 90% of the outer piece 22. It is set larger than the deflection amount.

  The thickness of the inner piece 21 is in the range of 30 to 90% of the thickness of the outer piece 22. If the thickness is less than 30%, the strength of the inner piece 21 may be reduced and the semiconductor wafer W may not be safely held. Moreover, it is difficult to mold. Conversely, if it exceeds 90%, the rear retainers 20 and 20A may not bend in the direction of the center line CL of the container body 1.

  The support block 23 is obliquely installed between the end portions of the inner piece 21 and the outer piece 22, and a plurality of blocks 25 that sandwich the rear periphery of each semiconductor wafer W via the V-grooves are formed by the inner piece 21 and the outer piece 22. It is located near the middle part.

  According to the above configuration, since the inner piece 21 of each rear retainer 20 / 20A is formed to be more easily bent than the outer piece 22, when the semiconductor wafer W is sandwiched between the front retainer 13 and the rear retainer 20 / 20A, the semiconductor wafer The left rear retainer 20 shown in FIG. 4 attempts to rotate horizontally in the clockwise direction (see the arrow in FIG. 4), and the right rear retainer 20A attempts to rotate in the counterclockwise direction (see the arrow in the same figure). That is, reverse force is applied to the semiconductor wafer W from the left and right rear retainers 20 and 20A, respectively, and the rotation directions are reversed, so that they cancel each other and prevent the semiconductor wafer W from rotating significantly.

  Due to such a rotation restricting action, the problem that the semiconductor wafer W rotates greatly and wear powder adheres even if the pair of rear retainers 20 and 20A bends due to vibrations and shocks when the substrate storage container is transported is extremely effective. Can be resolved. In addition, since it is not necessary to realign the position of the notch N of the semiconductor wafer W, improvement in production efficiency and workability can be greatly expected. Further, even if vibration or impact acts on the semiconductor wafer W, the rear retainers 20 and 20A bend and absorb the impact, so that it is possible to effectively suppress and prevent the peripheral portion of the semiconductor wafer W from being damaged.

  Next, FIG. 6 shows a second embodiment of the present invention. In this case, the outer piece 22 of each of the rear retainers 20 and 20A is brought into contact with the inner surface of the rear wall 8 of the container body 1 and the inner side The piece 21 is opposed in a non-contact manner through the gap G, the inner piece 21 is formed thinner than the outer piece 22, and the inner piece 21 is bent on the inner surface of the back wall of the container body 1 when the semiconductor wafer W is sandwiched. To make contact.

  A gap G of 0.5 to 2 mm is formed between the inner surface of the rear wall of the container body 1 and the inner piece 21 of the rear retainer 20 / 20A. This is because when the gap G is less than 0.5 mm, the rotation regulation of the semiconductor wafer W becomes insufficient. On the other hand, if it exceeds 2 mm, the deformation stroke of the rear retainers 20 and 20A is too large, the load concentrates on the outer piece 22 and deformation easily occurs, and the mounting position of the semiconductor wafer W varies back and forth. The inner piece 21 of the rear retainer 20, 20 </ b> A may be thin, but may be the same thickness as the outer piece 22. The other parts are the same as those in the above embodiment, and the description thereof is omitted.

  In the present embodiment, it is obvious that the same effects as those in the above embodiment can be expected, and that it is significant when the above embodiment cannot be adopted.

  Next, FIG. 7 shows a third embodiment of the present invention. In this case, a reinforcing member 26 is insert-molded and integrated into the outer piece 22 of each rear retainer 20, 20 A, and the semiconductor wafer W is integrated. The inner piece 21 is bent and brought into contact with the inner surface of the back wall of the container body 1 when sandwiched.

The reinforcing member 26 is made of a resin having good rigidity made of various metals, polyetheretherketone, various thermoplastic resins to which carbon fibers are added, and the like, so that the rigidity of the outer piece 22 is improved as compared with the inner piece 21. Function. The inner piece 21 of the rear retainer 20, 20 </ b> A may be thin, but may be the same thickness as the outer piece 22. Other parts are the same as those in the above embodiment, and thus the description thereof is omitted.
In this embodiment, the same effect as the above embodiment can be expected, and it is clear that the inner piece 21 does not need to be particularly thin.

Next, FIG. 8 shows a fourth embodiment of the present invention. In this case, each block 25 of the support block 23 in each of the rear retainers 20 and 20A is connected to the central portion of the inner piece 21 and the outer piece 22. In this case, the inner piece 21 is deflected closer to the outer piece 22 to increase the amount of bending of the inner piece 21. Other parts are the same as those in the above embodiment, and thus the description thereof is omitted.
In this embodiment, the same effect as the above embodiment can be expected, and it is clear that the inner piece 21 does not need to be thinned and the configuration of the rear retainers 20 and 20A can be diversified.

Next, FIG. 9 shows a fifth embodiment of the present invention. In this case, the angle θ1 formed by the inner surface 21 of the back wall of the container body 1 and the inner piece 21 of each retainer is set to the inner surface of the rear wall and the outer surface. The angle θ2 formed by the piece 22 is made smaller, and the amount of bending of the inner piece 21 is increased. Other parts are the same as those in the above embodiment, and thus the description thereof is omitted.
In the present embodiment, it is obvious that the same effects as those of the above-described embodiment can be expected, and the configuration of the rear retainers 20 and 20A can be diversified.

  Note that the lock mechanism of the above-described embodiment includes a rotating body that is supported by the lid body 10 and rotates by an external operation, and is slidably supported by the lid body 10 and connected to the rotating body, and is based on rotation of the rotating body. A plurality of advancing and retracting bars that move forward and backward in and out of the lid body 10, and rotatably supported near the opening of the peripheral wall of the lid body and coupled to the tip of the advancing and retracting bar. The locking roller can be configured to protrude from the opening of the lid body 10.

  In the above embodiment, the pair of rear retainers 20 and 20A are directly mounted on the back wall 8 of the container body 1. However, the present invention is not limited to this. For example, a pair of rear retainers 20 and 20A may be indirectly attached to the back wall 8 of the container body 1 via a plate or the like. Moreover, it can also be set as the structure which connected a pair of rear retainer 20 * 20A to the substantially H shape, the substantially square shape, etc. via the one or several connection piece. In this case, since the rear retainers 20 and 20A can be made into one part, it becomes possible to attach and remove them in one operation.

  Further, the pair of rear retainers 20 and 20A may be arranged point-symmetrically with respect to the inner surface of the back wall of the container body 1, in other words, with respect to the center point of the attachment region. If arranged in a point-symmetric manner in this way, it can be attached to either the left or right side of the back wall 8 of the container body 1 simply by providing one rear retainer 20 or 20A. In this case, if the top and bottom marks for mounting on the left and right are marked, the mounting operation is really easy. Further, the front retainer 13 of the lid 10 may be configured as a pair of rear retainers 20 and 20A.

It is a whole perspective explanatory view showing an embodiment of a substrate storage container concerning the present invention. It is the II-II sectional view taken on the line of FIG. It is the III-III sectional view taken on the line of FIG. It is a plane explanatory view showing the relation between a semiconductor wafer and a pair of rear retainers in an embodiment of a substrate storage container concerning the present invention. It is explanatory drawing which shows the rear retainer in embodiment of the substrate storage container which concerns on this invention. It is explanatory drawing which shows the rear retainer in 2nd Embodiment of the substrate storage container which concerns on this invention. It is explanatory drawing which shows the rear retainer in 3rd Embodiment of the substrate storage container which concerns on this invention. It is a perspective explanatory view showing a pair of rear retainers in a 4th embodiment of a substrate storage container concerning the present invention. It is explanatory drawing which shows the rear retainer in 5th Embodiment of the substrate storage container which concerns on this invention.

Explanation of symbols

1 Container body 2 Teeth 6 Rim part 8 Back wall (opposite part)
10 Lid 13 Front Retainer 20 Rear Retainer (Retainer)
20A Rear retainer (Retainer)
21 Inner piece 22 Outer piece 23 Support block 25 Block 26 Reinforcement member C Center of gravity CL Center line G Clearance N Notch W Semiconductor wafer (substrate)

Claims (6)

A container main body for storing the substrate, a lid for opening and closing the opening of the container main body, and a plurality of retainers for holding the peripheral edge of the substrate provided at an opposing portion of at least one of the container main body and the lid. A substrate storage container comprising:
Each retainer includes a flexible inner piece, an outer piece facing the inner piece, and a support block provided between the inner piece and the outer piece to support the peripheral edge of the substrate. The board storage is characterized in that the piece is moved closer to the center line passing through the center of gravity of the board than the outer piece, and the amount of bending of the inner piece is made larger than the amount of bending of the outer piece to suppress the rotation of the board. container.   The substrate storage container according to claim 1, wherein an inner piece and an outer piece of each retainer are brought into contact with at least one of the container main body and the cover, respectively, and the inner piece is formed thinner than the outer piece.   The substrate storage container according to claim 1, wherein an outer piece of each retainer is brought into contact with at least one of the container main body and the lid, and the inner piece is opposed through a gap.   4. The substrate storage container according to claim 1, wherein a reinforcing member is provided on an outer piece of each retainer.   The substrate storage container according to claim 1, wherein the support block of each retainer is positioned closer to the outer side than the center part of the inner and outer pieces.   The inner piece and the outer piece of each retainer are brought into contact with at least one of the opposing portions of the container main body and the lid body, and the opposing portion and the outer piece form an angle θ1 formed by the opposing portion and the inner piece. The substrate storage container according to claim 1, wherein the substrate storage container is smaller than the angle θ2.

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