TWI832451B - Wafer fixing mechanism and wafer fixture comprising thereof - Google Patents

Abstract

The present invention discloses a wafer fixing mechanism, comprising a main body, a device positioning portion, and a wafer alignment groove. The device positioning portion is combined with the bottom side of the main body. The device positioning part is combined with one side of a platform. The wafer alignment groove is an open groove that extends in the horizontal direction from the main body. The shape of the wafer alignment groove matches the shape of the outer edge of one of the sidewalls of the wafer, so that the outer edge of one of the sidewalls of the wafer is aligned to precisely position the wafer.

Description

Wafer positioning mechanism and wafer positioning jig including same

The present invention relates to a wafer positioning mechanism and a wafer positioning fixture, and in particular, to a wafer positioning mechanism and a wafer positioning fixture that are convenient, fast and precise for positioning.

In an era of advanced technological innovation and rapid technological changes, integrated circuit components have the characteristics of small size and powerful functions, so they are widely used in various fields or types of electronic products. In order to realize more miniaturized and high-performance electronic products, there is an increasing demand for thin wafers. While reducing the size of the wafers, it is necessary to ensure that the performance of subsequent fabricated memories or power devices is not affected or even possible. It has better electrical performance, heat dissipation performance, etc., giving electronic products more advantages.

At present, the most common wafer thinning method is grinding, which means that during the wafer manufacturing process, a wafer grinding and thinning process is required to reduce the thickness of the wafer and flatten the surface. In general, wafer grinding During the procedure, tape is first attached to the surface of the wafer for protection, and then the wafer is placed on the grinder table with the back side facing up, and the grinder is allowed to grind the back side of the wafer to achieve the purpose of thinning the wafer. thickness.

When performing the wafer thinning process, accurately positioning the wafer on the carrying platform is a very important step. For example, in wafer thinning equipment that uses a vacuum suction cup as a carrying platform, the operator must visually adjust the wafer positioning to complete the wafer positioning operation. This method not only takes too much time for calibration, resulting in low efficiency, but also reduces the positioning accuracy. There will be differences depending on the experience of the operator. Therefore, the wafer positioning mechanism of the present invention and the wafer positioning jig including the same are proposed to solve the above problems.

The main purpose of the present invention is to provide a wafer positioning mechanism, which includes a body part, a device positioning part combined with the bottom side of the body part, and a wafer alignment groove. The device positioning part is used to be assembled on one side of the platform. The wafer alignment groove is an open groove formed by extending in the horizontal direction from the body part. The shape of the wafer alignment groove is consistent with the shape of the outer edge of one of the side walls of the wafer to provide space for one of the wafer's side walls. The outer edges of the sidewalls are aligned to accurately position the wafer.

Further, the wafer alignment groove is an arc-shaped opening groove, the outer edge of one of the side walls is the circumferential area of the wafer, and the arc-shaped opening groove conforms to the curvature of the circumferential area for the outer edge of the side wall to pass Depend on.

Furthermore, the arc-shaped opening groove further includes a protruding portion, the protruding portion conforms to the shape of the notch of the wafer for leaning against the notch on the outer edge of the side wall.

Further, the wafer alignment groove is a trapezoidal opening groove, the outer edge of one of the side walls is a flat edge area of the wafer, and the trapezoidal opening groove conforms to the shape of the flat edge area for the outer edge of the side wall. Depend on fate.

Further, the material of the wafer positioning mechanism is metal, metal alloy, ceramic, silicon carbide, metal nitride, metal oxide, rubber, plastic, glass fiber composite material, carbon fiber composite material, organic fiber composite material or the above materials. combination.

Another object of the present invention is to provide a wafer positioning fixture, which includes a wafer positioning mechanism as described above and at least one of the platforms. The platform includes a platform body, a wafer setting table on the top side of the platform body, and a fixing unit provided on one side of the platform body. The fixing unit is used for corresponding combinations of the device positioning parts of the wafer positioning mechanism to fix the wafer positioning mechanism on the platform body, and when the wafer positioning mechanism is fixed on the platform, the wafer alignment groove The wafer is placed on the table with the bottom side abutting against the top side of the platform body, so that the wafer alignment groove is supported by the outer edge of one of the side walls of the wafer in the horizontal direction.

Further, the platform body includes a base and a wafer suction disk disposed on the base, and the wafer setting table is disposed on the top side of the wafer suction disk.

Further, the fixing unit includes a plurality of rivet posts disposed on the top side of the base and distributed on the outer circumferential side of the wafer suction disk, and the device positioning part includes at least one rivet post provided on the bottom side of the body part for each of the rivet posts. Embedded limit groove, the limit groove opens in the direction close to the center of the wafer suction disk for the rivet posts to be embedded in the horizontal direction, and the rivet posts are respectively fixed in the corresponding limit grooves to form horizontal positioning , and the fixing unit includes an annular locking groove arranged on the horizontal peripheral wall of the wafer suction disk, and the device positioning part is at least one locking convex part provided on the bottom side of the body part and protruding in the horizontal direction , the latching protrusion is inserted into the annular latching groove to further form vertical positioning.

Further, the fixing unit is at least one positioning groove provided on the horizontal peripheral wall of the wafer suction disk, and the device positioning part is a positioning bump provided on the bottom side of the body part and protruding in the horizontal direction, The number of the positioning protrusions corresponds to the number of the positioning grooves and are respectively inserted into the positioning grooves to form horizontal and vertical positioning.

Further, the fixing unit includes at least one fitting groove provided on the outer peripheral side of the wafer suction disk and open on the top side, and the device positioning part includes a groove provided on the bottom side of the body part and protruding in the horizontal direction. The fitting post is used to be inserted into the fitting groove to form horizontal positioning. The fixing unit includes an annular latching groove arranged on the horizontal peripheral wall of the wafer suction plate. The device positioning part is at least one latching convex part provided on the bottom side of the body part and protruding in the horizontal direction. The latching protrusion is inserted into the annular latching groove to further form vertical positioning.

Therefore, the wafer positioning mechanism and the wafer positioning fixture of the present invention help to position the wafer quickly and accurately, and help improve the work efficiency. In addition, the wafer positioning mechanism of the present invention has a simple structure, is easy to process and manufacture, and is convenient to operate. In addition, the wafer positioning structure of the present invention can be used in equipment with a low degree of automation and can also be used in automated equipment, and its application range is wide.

The detailed description and technical content of this creation are described below with reference to the drawings. Furthermore, the figures in this creation are for convenience of explanation, and their proportions may not be drawn according to actual proportions, but may be exaggerated. These figures and their proportions are not intended to limit the scope of this creation.

Please refer to "Fig. 1" to "Fig. 3", which are schematic appearance views of the first to ninth embodiments of the wafer positioning mechanism of the present invention, and "Fig. 4", which are schematic appearance views of different embodiments of the wafer alignment groove of the present invention. , as shown in the figure.

The present invention discloses a wafer positioning mechanism 100, which is used to be combined with a platform to accurately position the wafer WF to facilitate processing of the wafer WF. The material of the wafer positioning mechanism 100 may be, for example but not limited to, metal, ceramics, rubber, or any other single material or composite material used to make a solid structure. In one embodiment, the processing includes, for example, wafer polishing and thinning procedures, which are not limited in the present invention.

The wafer positioning mechanism 100 includes a body part 10, a device positioning part 20, and a wafer alignment groove 30. The device positioning part 20 is combined with the bottom side of the body part 10 for combination with a platform. On the other hand, the wafer alignment groove 30 is an open groove extending from the main body 10 in the horizontal direction D1 (as shown in FIGS. 8 to 10 ). The shape of the wafer alignment groove 30 is consistent with the shape of the wafer alignment groove 30 The shape of the outer edge LS of one side wall of the wafer WF (as shown in "Figure 4", "Figure 8" to "Figure 10") conforms to the shape, so that the outer edge LS of one side wall of the wafer WF can be aligned , thereby accurately positioning the wafer WF. Specifically, the wafer alignment groove 30 is opened in the horizontal direction D1 (that is, the direction parallel to the surface of the platform 200 ), and the shape of the opening is consistent with the outer edge LS of the side wall of the wafer WF. In addition to being completely consistent, the shapes described above may also be partially consistent. For example, the wafer alignment groove 30 may be in a zigzag shape (such as (A) in "Figure 4") or a wavy shape (such as in "Figure 4"). (B)) or other similar shapes, when a chord is determined by two points on the circumference, the shape is consistent if at least the two most protruding points form a stop (interference) with the wafer WF. This is explained first.

In one embodiment, as shown in (A) in "Fig. 1" to "Fig. 3" (first, fourth and seventh embodiments of the wafer positioning mechanism 100), the wafer alignment groove 30 It is an arc-shaped opening groove, and the outer edge LS of one of the side walls is the circumferential area of the wafer WF, and the arc-shaped opening groove conforms to the curvature of the circumferential area for the outer edge LS of the side wall to lean.

In another embodiment, as shown in (B) in "Fig. 1" to "Fig. 3" (the third, sixth and ninth embodiments of the wafer positioning mechanism 100), the wafer alignment groove 30 is It is a trapezoidal opening groove, and the outer edge LS of one of the side walls is the flat edge area (Flat) of the wafer WF, and the trapezoidal opening groove conforms to the shape of the flat edge area to provide space for the outer edge LS of the side wall. Rely on.

In another embodiment, as shown in (C) in "Fig. 1" to "Fig. 3" (second, fifth, and eighth embodiments of the wafer positioning mechanism 100), the wafer alignment groove 30 is an arc-shaped opening slot, and the outer edge LS of one of the side walls is the circumferential area of the wafer WF, and the arc-shaped opening slot conforms to the curvature of the circumferential area for the outer edge of the side wall to lean, where The arc-shaped opening groove 30 further includes a protruding portion 31, which is consistent with the shape of the notch NT (Notch) of the wafer WF and is used for the notch NT on the outer edge LS of the side wall (as shown in "Fig. 9 ” shown) Reliance. The following paragraphs will describe the specific implementation of the wafer positioning mechanism 100 using the device positioning part 20 to be combined with the platform, which will be described here first.

Continuing, please refer to "Fig. 5" to "Fig. 7" together, which are schematic diagrams of the appearance of different embodiments of the wafer positioning jig of the present invention, and refer to "Fig. 1" to "Fig. 3" as well, as shown in the figure Show.

The present invention also discloses a wafer positioning fixture 300. The wafer positioning fixture 300 includes a wafer positioning mechanism 100 of any of the aforementioned embodiments and at least one of the platforms 200. The platform 200 includes a platform body 40 , a wafer placement table P on the top side of the platform body 40 , and a fixing unit F disposed on one side of the platform body 40 .

The platform body 40 includes a base 41 and a wafer suction disc 42 disposed on the base 41 . The wafer setting table P is disposed on the top side of the wafer suction disc 42 . The fixing unit F is used for corresponding combinations of the device positioning part 20 of the wafer positioning mechanism 100 to fix the wafer positioning mechanism 100 on the platform body 40, and the wafer positioning mechanism 100 is fixed on the platform 200, the bottom side of the wafer alignment groove 30 is against the wafer setting table P on the top side of the platform body 40, so that the wafer alignment groove 30 provides the wafer WF in the horizontal direction D1. One of the outer edges of one side wall leans against LS.

The bottom side of the wafer alignment groove 30 is against what is referred to as "resistance" on the wafer setting table P on the top side of the platform body 40. For example, but not limited to, the bottom side of the wafer alignment groove 30 Closely adhere to the wafer setting table P, or partially contact, or the bottom side of the wafer alignment groove 30 and the wafer setting table P still maintain a fine distance. If the distance is maintained, the distance is at least smaller than the thickness of the wafer WF , ensuring that the wafer alignment groove 30 is supported by the outer edge LS of the side wall of the wafer WF.

In one embodiment, as shown in "Figure 5" and (A) in "Figure 1" to "Figure 3", the fixing unit F includes a plurality of rivet posts F1 (or studs, hereinafter collectively referred to as rivet post), and an annular retaining groove F2. The device positioning portion 20 includes at least one limiting groove 21 for the rivet post F1 to be embedded, and at least one retaining convex portion 22 inserted into the annular retaining groove F2. The plurality of rivet posts F1 are provided on the top side of the base 41 and distributed on the outer peripheral side of the wafer suction plate 42. The at least one limiting groove 21 is provided on the bottom side of the body part 10 for the rivet posts F1 respectively. Embedding, the limiting groove 21 opens in a direction close to the center of the wafer suction plate 42 for the rivet posts F1 to be embedded in the horizontal direction. The rivet posts F1 are respectively fixed in the corresponding limiting grooves 21 to form Horizontally positioned; and the annular groove F2 is ring-shaped on the horizontal peripheral wall of the wafer suction plate 42, and the at least one protruding portion 22 is provided on the bottom side of the body portion 10 and protrudes along the horizontal direction D1, and the The latching protrusion 22 is inserted into the annular latching groove F2 to further form vertical positioning. As shown in "Fig. 5", the wafer positioning mechanism 100 is based on (A) in Fig. 1 as an example. The positioning part 20 of the device includes three limiting grooves 21 for the rivets F1 to be embedded, and two A latching protrusion 22 is inserted into the annular latching groove F2, and the height of the latching protrusion 22 is equal to or slightly less than the height of the annular latching groove F2, thereby assembling and fixing the wafer positioning mechanism 100 to the platform 200 . In another embodiment, the device positioning part 20 includes a single or more than one limiting groove 21 for the rivet post F1 to be embedded, and a single or more than one limiting groove 21 . The invention does not intend to limit the number, size, shape or position of the combination of the fixing unit F and the device positioning part 20 of the latching protrusion 22 inserted into the annular latching groove F2, which will be described in advance.

In another embodiment, as shown in "Fig. 6" and (B) in "Fig. 1" to "Fig. 3", the fixing unit F is at least one positioning groove F3, and the device positioning part 20 It is the positioning protrusion 23 inserted into the positioning groove F3. The at least one positioning groove F3 is provided on the horizontal peripheral wall of the wafer suction plate 42, and the positioning bump 23 is provided on the bottom side of the body part 10 and protrudes along the horizontal direction D1. The positioning bump 23 and the The number of positioning grooves F3 corresponds to each other and is inserted into the positioning grooves F3 respectively to form horizontal and vertical positioning. As shown in "Fig. 6", the wafer positioning mechanism 100 is taken as an example in (B) of Fig. 2. The positioning part 20 of the device is a single positioning bump 23, and the shape of the positioning bump 23 corresponds to The shape of the positioning groove F3 and the size of the positioning bump 23 are equal to or slightly smaller than the size of the positioning groove F3. The positioning bump 23 is inserted into the positioning groove F3 to assemble and fix the wafer positioning mechanism 100. 200 on the platform. In another embodiment, the shapes of the positioning bumps and the positioning grooves are, for example, but not limited to triangles, squares (as shown in Figure 6), or other polygonal forms, which are not included in the present invention. Without wishing to limit it, let me explain it first.

In another embodiment, as shown in "Fig. 7" and (C) in "Fig. 1" to "Fig. 3", the fixing unit F includes at least one fitting groove F4 and an annular card. groove F5, the device positioning part 20 includes a fitting post 24 for the fitting groove F4 to be inserted into, and at least one latching protrusion 25 inserted into the annular latching groove F5. The at least one fitting groove F4 is provided on the outer peripheral side of the wafer suction disk 42 and opens on the top side. The fitting post 24 is provided on the bottom side of the body part 10 and protrudes along the horizontal direction D1. The fitting post 24 is used to be inserted into the fitting groove F4 to form a horizontal positioning; and the annular groove F5 is arranged on the horizontal peripheral wall of the wafer suction plate 42, and the at least one engaging convex portion 25 is provided on the body The protruding portion 25 protrudes from the bottom side of the portion 10 along the horizontal direction D1, and is inserted into the annular retaining groove F5 to further form vertical positioning. As shown in "Fig. 7", the wafer positioning mechanism 100 is shown in (C) in Fig. 3 as an example. The positioning part 20 of the device is a single fitting post 24, and the shape of the fitting post 24 corresponds to The shape of the fitting groove F4 and the size of the fitting post 24 are equal to or slightly smaller than the size of the fitting groove F4. When the fitting post 24 is inserted into the fitting groove F4, the locking protrusion 25 is inserted into the fitting groove F4. The wafer positioning mechanism 100 is assembled and fixed to the platform 200 in the annular groove F5 and the height of the convex portion 25 is equal to or slightly smaller than the height of the annular groove F5 . In another embodiment, the shape of the fitting post and the fitting groove is, for example, but not limited to, triangular, square (as shown in Figure 7), or other polygonal forms. In the present invention, Without intending to limit it, I will explain it here first.

Continuing, please refer to "Fig. 8" to "Fig. 10" together, which are schematic diagrams of the combination of the wafer positioning jig and the wafer according to different embodiments of the present invention, as shown in the figures.

As shown in "Figure 8", in this embodiment, the wafer positioning mechanism 100 is based on (A) in Figure 1 as an example. In actual application, the wafer positioning mechanism 100 is first assembled on the The platform 200, after the wafer positioning mechanism 100 is positioned, places the wafer WF on the wafer setting table P, and moves the wafer WF in the direction of the wafer alignment groove 30, so that the side walls of the wafer WF The outer edge LS (referring to the circumferential area) relies on the wafer alignment groove 30 which is an arc-shaped opening groove to complete the positioning of the wafer WF.

As shown in "Fig. 9", in this embodiment, the wafer positioning mechanism 100 is taken as an example in (B) of Fig. 2. The wafer positioning mechanism 100 is first assembled on the platform 200, and then Place the wafer WF on the wafer setting table P, and move the wafer WF in the direction of the wafer alignment groove 30 so that the outer edge LS (referring to the flat edge area) of the side wall of the wafer WF leans against the trapezoidal opening. The wafer of the groove is aligned with the groove 30 to complete the positioning of the wafer WF.

As shown in "Figure 10", in this embodiment, the wafer positioning mechanism 100 is based on (A) in Figure 1 as an example. The wafer positioning mechanism 100 is first assembled on the platform 200, and then Place the wafer WF on the wafer setting table P, and move the wafer WF in the direction of the wafer alignment groove 30 so that the notch NT of the wafer WF is aligned with the protrusion 31 and the The outer edge LS (referring to the circumferential area) of the side wall relies on the wafer alignment groove 30 which is an arc-shaped opening groove to complete the positioning of the wafer WF.

In summary, the wafer positioning mechanism and the wafer positioning fixture of the present invention help to position the wafer quickly and accurately, and help improve the work efficiency. In addition, the wafer positioning mechanism of the present invention has a simple structure, is easy to process and manufacture, and is convenient to operate. In addition, the wafer positioning structure of the present invention can be used in equipment with a low degree of automation, and can also be used in automated equipment, with a wide range of applications.

The invention has been described in detail above. However, the above is only one of the preferred embodiments of the invention. This should not be used to limit the scope of the invention, that is, any work based on the scope of the patent application for this invention is equivalent. Changes and modifications should still fall within the scope of the patent for this creation.

100: Wafer positioning mechanism 10: Ontology part 20:Device positioning department 30: Wafer alignment groove 31:Protrusion D1: horizontal direction WF: wafer LS: outer edge of side wall NT: notch 300: Wafer positioning fixture 200:Platform P: Wafer setting table F: fixed unit 40:Platform ontology 41:Base 42: Wafer suction disc F1: Rivet post F2: Annular stuck groove 21:Limit slot 22: stuck convex part F3: Positioning slot 23: Positioning bumps F4: Fitting slot F5: Ring groove 24: Chimeric column 25: stuck convex part

Figure 1, (A) to (C) are schematic appearance views of the first to third embodiments of the wafer positioning mechanism of the present invention.

Figure 2, (A) to (C) are schematic appearance views of the fourth to sixth embodiments of the wafer positioning mechanism of the present invention.

Figure 3, (A) to (C) are schematic appearance views of the seventh to ninth embodiments of the wafer positioning mechanism of the present invention.

Figure 4, (A) to (B) are schematic top views of the wafer alignment groove of the present invention.

FIG. 5 is a schematic view of the appearance of the first embodiment of the wafer positioning jig of the present invention.

FIG. 6 is a schematic view of the appearance of the second embodiment of the wafer positioning jig of the present invention.

FIG. 7 is a schematic view of the appearance of the third embodiment of the wafer positioning jig of the present invention.

FIG. 8 is a schematic view of the appearance of the first embodiment of the combination of the wafer positioning fixture and the wafer according to the present invention.

FIG. 9 is a schematic view of the appearance of a second embodiment of the combination of a wafer positioning fixture and a wafer according to the present invention.

FIG. 10 is a schematic view of the appearance of a third embodiment of the combination of a wafer positioning fixture and a wafer according to the present invention.

100: Wafer positioning mechanism

10: Ontology part

20:Device positioning department

30: Wafer alignment groove

D1: horizontal direction

300: Wafer positioning fixture

200:Platform

P: Wafer setting table

F: fixed unit

40:Platform ontology

41:Base

42: Wafer suction disc

F1: Rivet post

F2: Annular stuck groove

21:Limit slot

22: stuck convex part

Claims (10)

A wafer positioning mechanism includes: a body part; a device positioning part combined with the bottom side of the body part for combination with one side of a platform; and a wafer alignment groove formed along the body part. An open groove is formed extending in the horizontal direction. The shape of the wafer alignment groove is consistent with the shape of the outer edge of one side wall of a wafer, so that the outer edge of one of the side walls of the wafer can be aligned to position the wafer. . The wafer positioning mechanism of claim 1, wherein the wafer alignment groove is an arc-shaped opening groove, the outer edge of one of the side walls is the circumferential area of the wafer, and the arc-shaped opening groove is in contact with the circumference The curvature of the area conforms to the outer edge of the side wall. The wafer positioning mechanism as claimed in claim 2, wherein the arc-shaped opening groove further includes a protrusion that matches the shape of the notch of the wafer for the notch on the outer edge of the side wall to lean against. . The wafer positioning mechanism according to claim 1, wherein the wafer alignment groove is a trapezoidal opening groove, the outer edge of one of the side walls is the flat edge area of the wafer, and the trapezoidal opening groove is in contact with the trapezoidal opening groove. The flat area is shaped to rest on the outer edge of the side wall. The wafer positioning mechanism as described in claim 1, wherein the material of the wafer positioning mechanism is metal, metal alloy, ceramic, silicon carbide, metal nitride, metal oxide, rubber, plastic, glass fiber composite material, Carbon fiber composites, organic fiber composites or a combination of the above materials. A wafer positioning fixture, including: a wafer positioning mechanism as described in any one of claims 1 to 5; and at least one platform, which includes a platform body and a wafer setting on the top side of the platform body The table top, and the fixing unit provided on one side of the platform body, the fixing unit is for corresponding combination of the device positioning part of the wafer positioning mechanism, so as to fix the wafer positioning mechanism on the platform body, and the wafer When the positioning mechanism is fixed on the platform, the bottom side of the wafer alignment groove is against the wafer placement table on the top side of the platform body, so that the wafer alignment groove provides space for the wafer in the horizontal direction. Lean against the outer edge of one side wall. The wafer positioning jig as claimed in claim 6, wherein the platform body includes a base and a wafer suction disc disposed on the base, and the wafer setting table is disposed on the top side of the wafer suction disc. . The wafer positioning jig according to claim 7, wherein the fixing unit includes a plurality of rivet posts disposed on the top side of the base and distributed on the outer peripheral side of the wafer suction plate, and the device positioning part includes at least one Limiting grooves are provided on the bottom side of the body part for the riveting posts to be embedded respectively. The limiting grooves open in a direction close to the center of the wafer suction disk for the riveting posts to be embedded in the horizontal direction. The riveting posts are respectively fixed on The corresponding limiting groove forms a horizontal positioning; and The fixing unit includes an annular locking groove arranged on the horizontal peripheral wall of the wafer suction plate, and the device positioning part is at least one locking convex part provided on the bottom side of the body part and protruding in the horizontal direction. The latching protrusion is inserted into the annular latching groove to further form vertical positioning. The wafer positioning jig according to claim 7, wherein the fixing unit is at least one positioning groove provided on the horizontal peripheral wall of the wafer suction disk, and the device positioning part is provided on the bottom side of the body part And there are positioning bumps protruding in the horizontal direction. The positioning bumps correspond to the number of the positioning grooves and are respectively inserted into the positioning grooves to form horizontal and vertical positioning. The wafer positioning jig according to claim 7, wherein the fixing unit includes at least one fitting groove provided on the outer peripheral side of the wafer suction plate and open on the top side, and the device positioning part includes A fitting post protruding from the bottom side of the body part in a horizontal direction, the fitting post is used to be inserted into the fitting groove to form a horizontal positioning; and The fixing unit includes an annular locking groove arranged on the horizontal peripheral wall of the wafer suction plate, and the device positioning part is at least one locking convex part provided on the bottom side of the body part and protruding in the horizontal direction. The latching protrusion is inserted into the annular latching groove to further form vertical positioning.

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