Wafer picking device
By setting supports of different heights in the wafer picking device, the wafers in the wafer box are tilted evenly, ensuring that the spacing between adjacent wafers is equal. This solves the problem of scratches during wafer picking and ensures wafer quality.
Patent Information
- Application Number
- CN202422639542.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-30
- Publication Date
- 2025-10-24
- Estimated Expiration
- 2034-10-30
AI Technical Summary
During the wafer picking process, existing technologies can easily cause scratches on the wafer surface, affecting wafer quality.
Design a wafer picking device that uses supports of different heights in the carrier box to ensure that the wafers in the wafer box are tilted evenly and that the spacing between adjacent wafers is equal. The wafer picking assembly lifts up the wafers to avoid damage to adjacent wafers.
It effectively reduces or eliminates scratches on wafers during the pick-up process, ensuring wafer quality and has a wide range of applications.
Smart Images
Figure CN223471573U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to the technical field of semiconductor manufacturing, especially relates to a wafer picking device. BACKGROUND
[0002] In the process of semiconductor manufacturing, the wafer processed in the front process is transferred by a wafer box, and when a wafer is inspected, the wafer is taken out of the wafer box by a suction pen according to the position of the wafer in the wafer box. When the operator inserts the suction pen into the wafer box to suck the back of the wafer, the wafer is taken out by the suction pen. Since the wafers are closely spaced, the front of the spacer wafer is easily scratched when the suction pen is inserted or taken out, which may cause abnormal scratching of the wafer surface pattern, thereby causing quality problems.
[0003] Currently, a wafer picker is usually used to pick a wafer from the wafers in the wafer box, and then the required wafer is taken out by the suction pen. However, the wafer surface is often scratched when the wafer picker lifts the wafer, causing abnormal quality of the wafer.
[0004] However, how to reduce the damage to the wafer during the lifting of the wafer picker is a technical problem that needs to be solved at present. UTILITY MODEL CONTENTS
[0005] The utility model solves the technical problem of providing a wafer picking device that can effectively reduce or eliminate the problem of wafer scratching during picking, ensure the quality of the wafer, and have a wide range of applications.
[0006] To solve the above problems, the utility model provides a wafer picking device, which comprises: a bearing box, the bearing box has a containing cavity, the containing cavity is used for placing a wafer box, the bearing box comprises a first connecting plate and a second connecting plate arranged opposite in a first direction, a third connecting plate and a fourth connecting plate arranged opposite in a second direction, a first bearing plate connected with the third connecting plate, and a second bearing plate connected with the fourth connecting plate, the first connecting plate, the second connecting plate, the third connecting plate, the fourth connecting plate, the first bearing plate and the second bearing plate are connected to enclose the containing cavity, there is a gap area between the first bearing plate and the second bearing plate, and the second direction is perpendicular to the first direction; a picking assembly located in the gap area, the picking assembly is connected with the first connecting plate and the second connecting plate, and the picking assembly is used for lifting the wafer in the wafer box; a first support and a second support located at the bottom of the bearing box, the first support is connected with the first connecting plate, the second support is connected with the second connecting plate, and the height of the first support is different from the height of the second support.
[0007] Optionally, after the bearing box is placed on a horizontal plane, the included angle between the surface of the first bearing plate or the surface of the second bearing plate and the horizontal plane is 10° to 15°.
[0008] Optionally, the height of the first support is greater than the height of the second support.
[0009] Optionally, the wafer box comprises a first end face and a second end face opposite to each other, the first end face is shaped as H, and the second end face is shaped as U; after the wafer box is placed into the carrying box, the first end face faces the second connecting plate, and the second end face faces the first connecting plate.
[0010] Optionally, the carrying box further comprises a positioning module in the accommodating cavity, the positioning module is used for positioning the wafer box after the wafer box is placed into the accommodating cavity.
[0011] Optionally, the positioning module comprises a first positioning module on the surface of the first carrying plate and a second positioning module on the surface of the second carrying plate.
[0012] Optionally, the first support is integrally connected or detachably connected with the first connecting plate, and the second support is integrally connected or detachably connected with the second connecting plate.
[0013] Optionally, the first support is clamped or screw-connected with the first connecting plate, and the second support is clamped or screw-connected with the second connecting plate.
[0014] Optionally, the wafer picking assembly comprises a rotating shaft and a plurality of wafers arranged along the first direction, one end of the wafer is connected with the rotating shaft, two ends of the rotating shaft are connected with the first connecting plate and the second connecting plate respectively, the rotating shaft is close to the first carrying plate, the rotating shaft has a first spacing with the first carrying plate, and the other end of the wafer has a second spacing with the second carrying plate.
[0015] Optionally, the wafer picking assembly further comprises a picking rod connected with one end of the rotating shaft, the picking rod is located outside the accommodating cavity, the picking rod moves along the first direction and drives the wafer to move along the first direction, and the picking rod lifts and drives the wafer to lift.
[0016] Optionally, the carrying box further comprises a gear disc on the outer wall of the accommodating cavity, the gear disc has gear grooves of different gears, the gear grooves have sliding grooves communicating with different gear grooves at the bottom, and the picking rod slides in the sliding grooves to different gear grooves.
[0017] Optionally, the wafer box has a plurality of tooth grooves, the picking rod slides to different gear grooves, and drives the wafer to move to the bottom of the corresponding tooth groove.
[0018] Compared with the prior art, the technical scheme of the utility model has the following advantages:
[0019] In the technical solution of the present invention, the wafer box is placed in the accommodating cavity of the carrier box, and the accommodating cavity is surrounded by a first connecting plate, a second connecting plate, a third connecting plate, a fourth connecting plate, a first carrier plate and a second carrier plate, wherein the first connecting plate and the second connecting plate are arranged relative to each other in a first direction, the third connecting plate and the fourth connecting plate are arranged relative to each other in a second direction, and there is a gap area between the first carrier plate and the second carrier plate, and the second direction is perpendicular to the first direction; a pick-up assembly is located in the gap area, the pick-up assembly connects the first connecting plate and the second connecting plate, and the pick-up assembly is used to lift the wafer in the wafer box; the first connecting plate located at the bottom of the carrier box A support member and a second support member, the first support member is connected to the first connecting plate, and the second support member is connected to the second connecting plate. The height of the first support member is different from the height of the second support member. When the carrier box is placed on a horizontal surface, the difference in height between the first support member and the second support member is utilized to enable the wafers in the wafer box to tilt in the same direction, and the spacing between adjacent wafers is equal, avoiding adjacent wafers from getting close to each other and causing the spacing to decrease, thereby effectively avoiding damage to adjacent wafers in the process of lifting the wafer, effectively ensuring the quality of the wafer, and having a wider range of uses. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 This is a schematic structural diagram of a wafer picking device in one embodiment of the present invention;
[0021] Figure 2 for Figure 1 The main view;
[0022] Figure 3 for Figure 1 A schematic structural diagram of a wafer picking device in another direction;
[0023] Figure 4 This is a top view of a wafer picking device after placing a wafer box in one embodiment of the present invention;
[0024] Figure 5 This is a schematic structural diagram of a wafer box in one embodiment of the present invention;
[0025] Figure 6 for Figure 5 Rear view;
[0026] Figure 7 FIG. 1 is a schematic structural diagram of a wafer picking device in another embodiment of the present invention. DETAILED DESCRIPTION
[0027] As mentioned in the background art, there are still many problems in the process of lifting the wafer by the wafer picker.
[0028] The inventors find that after the wafer is placed in the wafer box, the tilting directions of the wafers in the wafer box are not consistent, some adjacent wafers tilt towards opposite directions respectively, which will cause the adjacent wafers to be too close, and then cause damage to the adjacent wafers which are too close in the process of lifting the wafer by the pick-up, thereby affecting the normal use of the wafer.
[0029] The inventors find that after the wafer is placed in the wafer box, the tilting directions of the wafers in the wafer box are not consistent, some adjacent wafers tilt towards opposite directions respectively, which will cause the adjacent wafers to be too close, and then cause damage to the adjacent wafers which are too close in the process of lifting the wafer by the pick-up, thereby affecting the normal use of the wafer.
[0030] In order to make the above-mentioned purposes, characteristics and advantages of the utility model more obvious and easy to understand, the specific embodiments of the utility model will be described in detail below with reference to the drawings.
[0031] First, please refer to Figure 1 , Figure 2 , Figure 3 and Figure 4 , a wafer pick-up device 100, including a bearing box 101, a pick-up assembly and a support 103.
[0032] In the embodiment, the bearing box 101 has a containing cavity 101a, the containing cavity 101a is used to place the wafer box 200, the bearing box 101 includes the first connecting plate 101b and the second connecting plate 101c oppositely arranged in the first direction, the third connecting plate 101d and the fourth connecting plate 101e oppositely arranged in the second direction, the first bearing plate 108 connected with the third connecting plate 101d and the second bearing plate 109 connected with the fourth connecting plate 101e, the first connecting plate 101b, the second connecting plate 101c, the third connecting plate 101d, the fourth connecting plate 101e, the first bearing plate 108 and the second bearing plate 109 are connected to enclose the containing cavity 101a, and the first bearing plate 108 and the second bearing plate 109 have a gap area 110 in the second direction; the pick-up assembly located in the gap area 110, the pick-up assembly is connected to the first connecting plate 101b and the second connecting plate 101c, and the pick-up assembly is used to lift the wafer in the wafer box 200; the first support 103a and the second support 103b located at the bottom of the bearing box 101, the first support 103a is connected with the first connecting plate 101b, the second support 103b is connected with the second connecting plate 101c, and the height (H1) of the first support 103a and the height (H2) of the second support 103b are different.
[0033] In the embodiment, the wafer picking assembly comprises a rotating shaft 111 and a plurality of wafers 102 arranged along a first direction, one end of the wafer 102 is connected with the rotating shaft 111, two ends of the rotating shaft 111 are connected with the first connecting plate 101b and the second connecting plate 101c respectively, the rotating shaft 111 is close to the first bearing plate 108, the rotating shaft 111 has a first spacing with the first bearing plate 108, the other end of the wafer 102 has a second spacing with the second bearing plate 109.
[0034] In the embodiment, since the height of the first support 103a is different from the height of the second support 103b, after the wafer box is placed in the accommodating cavity of the bearing box 101, the wafers in the wafer box can be inclined towards the same direction, and the spacing between the adjacent wafers is equal, avoiding the adjacent wafers from approaching each other to reduce the spacing, thereby effectively avoiding the damage to the adjacent wafers caused by the wafer picking 102 in the process of lifting the wafers, effectively ensuring the quality of the wafers, and having a wide range of use.
[0035] In the embodiment, please refer to Figure 5 , the wafer box 200 comprises a first end surface 201 and a second end surface 202 which are parallel to the wafers, the first end surface 201 is opposite to the second end surface 202, the shape of the first end surface 201 is H-shaped, and the shape of the second end surface 202 is U-shaped.
[0036] In the embodiment, the first direction is X direction, and the second direction is Y direction.
[0037] In the embodiment, generally, the front surface (i.e. the surface facing the second end surface 202) of the wafer has a designed pattern, and the back surface (i.e. the surface facing the first end surface 201) of the wafer does not have a pattern.
[0038] Specifically, the height of the first support 103a is greater than the height of the second support 103b, or the height of the second support 103b is greater than the height of the first support 103a.
[0039] In the embodiment, the height of the first support 103a is greater than the height of the second support 103b, so that after the wafer box 200 is placed into the carrier box 101, the first end surface 201 faces the second connecting plate 101c and the second end surface 202 faces the first connecting plate 101b. Since the front surface of the wafer has patterns, the patterns are set according to actual process requirements, so the patterns cannot be damaged. At this time, when the height of the first support 103a is greater than the height of the second support 103b, the wafers in the wafer box 200 are all inclined toward the first end surface 201, thereby ensuring the effective spacing between adjacent wafers and making the spacing between adjacent wafers equal. In this way, during the process of lifting the target wafer by the pick-up piece 102, the spacing between the target wafer and the adjacent wafers is greater than the spacing between the pick-up piece 102 and the adjacent wafers, so the pick-up piece 102 will not contact the adjacent wafers, and thus will not damage the patterns on the surface of the adjacent wafers, further ensuring that the wafers are not damaged.
[0040] In the embodiment, the height H1 of the first support 103a is 4 cm, and the height H2 of the second support 103b is 2.5 cm.
[0041] In the embodiment, after the wafer box 200 is placed into the carrier box 101, the spacing between the adjacent two wafers is equal and greater than 2.75 mm, specifically 5 mm, thereby effectively avoiding the risk of scratching the adjacent wafers during the process of lifting the wafers.
[0042] In the embodiment, the surface of the first carrier plate 108 and the surface of the second carrier plate 109 are flush, which is to ensure that after the wafer box 200 is placed into the carrier box 101, the wafers in the wafer box 200 can only be inclined along the second direction, and will not be inclined toward the first direction, thereby ensuring the effective spacing between adjacent wafers, thereby effectively avoiding damage to the adjacent wafers caused by the pick-up piece 102 during the process of lifting the wafers.
[0043] In the embodiment, please refer to Figure 2 After the carrier box 101 is placed on the horizontal plane, the included angle between the horizontal plane where the surface of the first carrier plate 108 or the surface of the second carrier plate 109 is located and the ground is 10° to 15°. On the one hand, this included angle enables the wafers to be inclined toward a direction, while achieving the maximum spacing between adjacent wafers. On the other hand, it can avoid the wafers from being too inclined due to the too large included angle, thereby causing the wafers in the wafer box 200 to slide out and cause irreversible damage to the wafers.
[0044] Figure 1 and Figure 4The pivot 111 is shown close to the third connecting plate 101d, and of course in some embodiments, the pivot 111 is close to the fourth connecting plate 101e, and there is a gap between the other end of the pick piece 102 and the first bearing plate 108.
[0045] Figure 1 And Figure 4 The pivot 111 is shown close to the third connecting plate 101d, and of course in some embodiments, the pivot 111 is close to the fourth connecting plate 101e, and there is a gap between the other end of the pick piece 102 and the first bearing plate 108. Figure 7 The pivot 111 is connected to the first bearing plate 108, and of course in some embodiments, the pivot 111 is connected to the second bearing plate 109, and there is a gap between the other end of the pick piece 102 and the first bearing plate 108.
[0046] Figure 7 The pivot 111 is connected to the first bearing plate 108, and of course in some embodiments, the pivot 111 is connected to the second bearing plate 109, and there is a gap between the other end of the pick piece 102 and the first bearing plate 108.
[0047] In this embodiment, the pick pieces 102 are uniformly arranged along the first direction X, and the number of pick pieces 102 is 5, and the width d of the pick piece 102 is 5.5 mm.
[0048] In some embodiments, the number and width value of the pick piece 102 can also be other numerical values, which can be designed according to actual needs.
[0049] In this embodiment, the middle of the pick piece 102 is a groove, and the center position of the groove is used to lift the wafer.
[0050] In this embodiment, the first support 103a and the first connecting plate 101b are integrally connected; in some embodiments, the first support 103a and the first connecting plate 101b can be detachably connected, such as clamping or threaded connection.
[0051] In this embodiment, the second support 103b and the second connecting plate 101c are integrally connected; in some embodiments, the second support 103b and the second connecting plate 101c can be detachably connected, such as clamping or threaded connection.
[0052] In this embodiment, please continue to refer to Figure 5The wafer box 200 further comprises opposite side surfaces 203 connected to the first end surface 201 and the second end surface 202 respectively, and the first end surface 201, the second end surface 202 and the opposite side surfaces 203 enclose a wafer accommodating cavity 205, and the surface of the side surface 203 in the wafer accommodating cavity 205 is provided with a plurality of tooth grooves 204, and the tooth grooves 204 of the opposite side surfaces 203 are in one-to-one correspondence.
[0053] In the embodiment, please continue to refer to Figure 1 and Figure 4 Further comprising: a positioning module 104 located in the accommodating cavity, the positioning module 104 is used for positioning the wafer box 200 after the wafer box 200 is placed in the accommodating cavity 101a, and specifically, the positioning module 104 comprises a first positioning module 104a located in the accommodating cavity 101a and on the surface of the first bearing plate 108 and a second positioning module 104b located in the accommodating cavity 101a and on the surface of the second bearing plate 109.
[0054] In the embodiment, please refer to Figure 5 and Figure 6 The bottom of the side surface 203 is provided with an extension part 205, and specifically, the extension part 205 comprises a first extension part 205a and a second extension part 205b, and the first extension part 205a and the second extension part 205b are oppositely distributed.
[0055] When the wafer box 200 is placed into the bearing box 101, the wafer box 200 is located between the first positioning module 104a and the second positioning module 104b, the first extension part 205a is located on the first bearing plate 108, and the second extension part 205b is located on the second bearing plate 109, so as to prevent the wafer box 200 from being placed in error during the process of being placed into the bearing box 101, thereby preventing the wafer from being accidentally damaged when the pick piece 102 is lifted.
[0056] In the embodiment, please continue to refer to Figure 1 One end of the rotating shaft 111 extends to the outside of the accommodating cavity 101a through the first connecting plate 101b.
[0057] In some embodiments, one end of the rotating shaft 111 extends to the outside of the accommodating cavity through the second connecting plate 101c.
[0058] In the embodiment, the pick lever 105 fixedly connected to one end of the rotating shaft 111 is further included, the pick lever 105 is located outside the accommodating cavity, the pick lever 105 moves along the first direction to drive the pick piece 102 to move along the first direction, the pick lever 105 is lifted to drive the rotating shaft 111 to rotate, thereby driving the pick piece 102 to be lifted.
[0059] In the embodiment, the gear disc 106 is arranged on the outer wall of the accommodating cavity 101a, and the gear disc 106 is connected with the first connecting plate 101b. The gear disc 106 has gear slots 106a of different gears, and the bottom of each gear slot 106a has a sliding channel communicating with the gear slots 106a of different gears. The pick rod 105 slides in the sliding channel and enters the gear slots 106a of different gears. The pick rod 105 slides into the gear slots 106a of different gears, and drives the pick piece 102 to move to the bottom of the corresponding tooth groove 204.
[0060] In some embodiments, the gear disc 106 is connected with the first connecting plate 101b.
[0061] In the embodiment, the gear slots 106a are arranged uniformly along the first direction X.
[0062] In the embodiment, please continue to refer to Figure 1 The gear display panel 107 is further included, which is used to display the gears of the gear slots 106a and the wafer box tooth grooves 204 corresponding to each gear. According to the selection of the display panel 107, the pick rod 105 is located in which gear and picks up which wafer at the corresponding position.
[0063] In the embodiment, the display panel 107 is connected with the third connecting plate 101d.
[0064] In the embodiment, there are five gear slots 106a, the pick rod 105 is lifted up in any gear slot 106a, the position of the wafer lifted up is consistent with the position displayed by the display panel 107, specifically, there are 25 tooth slots 204 in the wafer box 200, which are sequentially marked by numbers 1-25 (204-1, 204-2, 204-3…204-25), the gear slots 106a are five, which are sequentially marked by A gear, B gear, C gear, D gear and E gear along the first direction X (106a-A, 106a-B, 106a-C, 106a-D, 106a-E), wherein the A gear slot 106a-A corresponds to the tooth slots 204-1, 204-6, 204-11, 204-16 and 204-21; the B gear slot 106a-B corresponds to the tooth slots 204-2, 204-7, 204-12, 204-17 and 204-22; the C gear slot 106a-C corresponds to the tooth slots 204-3, 204-8, 204-13, 204-18 and 204-23; the D gear slot 106a-D corresponds to the tooth slots 204-4, 204-9, 204-14, 204-19 and 204-24; and the E gear slot 106a-E corresponds to the tooth slots 204-5, 204-10, 204-15, 204-20 and 204-25; when the pick rod 105 moves to the A gear slot 106a-A, the pick rod 105 is lifted up to drive the pick piece 102 to be lifted up, so that the wafers in the tooth slots 204-1, 204-6, 204-11, 204-16 and 204-21 are simultaneously picked up; similarly, when the pick rod 105 moves to the B gear slot 106a-B, the pick rod 105 is lifted up to drive the pick piece 102 to be lifted up, so that the wafers in the tooth slots 204-2, 204-7, 204-12, 204-17 and 204-22 are simultaneously picked up; similarly, when the pick rod 105 moves to the C gear slot 106a-C, the pick rod 105 is lifted up to drive the pick piece 102 to be lifted up, so that the wafers in the tooth slots 204-3, 204-8, 204-13, 204-18 and 204-23 are simultaneously picked up; similarly, when the pick rod 105 moves to the D gear slot 106a-D, the pick rod 105 is lifted up to drive the pick piece 102 to be lifted up, so that the wafers in the tooth slots 204-4, 204-9, 204-14, 204-19 and 204-24 are simultaneously picked up; and similarly, when the pick rod 105 moves to the E gear slot 106a-E, the pick rod 105 is lifted up to drive the pick piece 102 to be lifted up, so that the wafers in the tooth slots 204-5, 204-10, 204-15, 204-20 and 204-25 are simultaneously picked up.
[0065] Although the utility model discloses as above, the utility model is not limited to this. Any person skilled in the art, without departing from the spirit and scope of the utility model, can make various changes and modifications, therefore the protection scope of the utility model should be the range defined by the claims.
Claims
1. A wafer picking device, characterized by, The utility model relates to a wafer carrier, which comprises: a carrier box having a receiving cavity for placing a wafer box, the carrier box comprising a first connecting plate and a second connecting plate arranged oppositely in a first direction, a third connecting plate and a fourth connecting plate arranged oppositely in a second direction, a first carrier plate connected with the third connecting plate, and a second carrier plate connected with the fourth connecting plate, the first connecting plate, the second connecting plate, the third connecting plate, the fourth connecting plate, the first carrier plate and the second carrier plate being connected to enclose the receiving cavity, and a gap region being present between the first carrier plate and the second carrier plate, the second direction being perpendicular to the first direction; a wafer lifting assembly located in the gap region, the wafer lifting assembly being connected with the first connecting plate and the second connecting plate, and being used for lifting wafers in the wafer box; a first support and a second support located at the bottom of the carrier box, the first support being connected with the first connecting plate, the second support being connected with the second connecting plate, and the height of the first support being different from the height of the second support.
2. The wafer picking apparatus of claim 1, wherein After the carrier box is placed on a horizontal plane, the included angle between the surface of the first carrier plate or the surface of the second carrier plate and the horizontal plane is 10° to 15°.
3. The wafer picking apparatus of claim 1, wherein The height of the first support is greater than the height of the second support.
4. The wafer picking apparatus of claim 3, wherein The wafer box comprises a first end face and a second end face oppositely, the shape of the first end face is H-shaped, the shape of the second end face is U-shaped, after the wafer box is placed into the carrier box, the first end face faces the second connecting plate, and the second end face faces the first connecting plate.
5. The wafer picking apparatus of claim 1, wherein Further comprising a positioning module located in the receiving cavity, the positioning module being used for positioning the wafer box after the wafer box is placed in the receiving cavity.
6. The wafer picking apparatus of claim 5, wherein The positioning module comprises a first positioning module located on the surface of the first carrier plate and a second positioning module located on the surface of the second carrier plate.
7. The wafer picking apparatus of claim 1, wherein The first support and the first connecting plate are integrally connected or detachably connected, and the second support and the second connecting plate are integrally connected or detachably connected.
8. The wafer picking apparatus of claim 7, wherein The first support and the first connecting plate are clamped or threadedly connected, and the second support and the second connecting plate are clamped or threadedly connected.
9. The wafer picking apparatus of claim 1, wherein The wafer lifting assembly comprises a rotating shaft and a plurality of wafers arranged in the first direction, one end of the wafer being connected with the rotating shaft, two ends of the rotating shaft being connected on the first connecting plate and the second connecting plate respectively, the rotating shaft being close to the first carrier plate, the rotating shaft having a first spacing with the first carrier plate, and the other end of the wafer having a second spacing with the second carrier plate.
10. The wafer picking apparatus of claim 9, wherein, The wafer lifting assembly further comprises a lifting rod connected with one end of the rotating shaft, the lifting rod being located outside the receiving cavity, the lifting rod moving along the first direction and driving the wafer to move along the first direction, and the lifting rod lifting the wafer.
11. The wafer picking apparatus of claim 10, wherein, Also include: the gear disc in the outer wall of the accommodation cavity, the gear disc has different gear slots, the bottom of the gear slot has a sliding channel connected to different gear slots, the pick rod slides in the sliding channel to different gear slots.
12. The wafer picking apparatus of claim 11, wherein, The wafer box has several tooth slots, the pick rod slides to different gear slots, and the pick rod moves to the corresponding tooth slot bottom.