Substrate cleaning equipment

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a substrate cleaning device for cleaning and drying a substrate used for a semiconductor, a liquid crystal display, and the like, and more particularly to an improvement of a substrate chuck structure for surely and easily attaching and detaching a substrate.

【0002】

[Conventional technology]

The semiconductor manufacturing process and the liquid crystal display manufacturing process include a photo process for forming a desired pattern on a substrate, an etching process for etching an oxide film on the substrate surface, and a peeling process for removing a resist used in the photo process. Includes. In these treatment steps, a predetermined treatment liquid is supplied onto the substrate to perform each treatment. Therefore, when moving to the next step, it is necessary to perform a substrate cleaning step of cleaning the substrate so that the treatment liquid used in the previous step is sufficiently removed and does not remain. As a device for performing such cleaning, while supplying a cleaning liquid to the surface of the substrate, the treatment liquid of the previous step that adheres to and remains on the surface of the substrate is cleaned with a brush or the like, and then the surface of the substrate is free of nitrogen or the like. A device is widely used in which the substrate is rotated at high speed while spraying an active gas, and the cleaning liquid remaining adhered is shaken off by the wind pressure and centrifugal force of the inert gas.

【0003】

Here, when the substrate has a rectangular shape, if the substrate is rotated at high speed as described above, rotational spots and turbulent flow are likely to occur, and good cleaning liquid cannot be shaken off and removed. Therefore, in Japanese Patent Application Laid-Open No. 7-106233 previously proposed by the applicant of the present application, the substrate is fitted into a substantially disk-shaped straightening vane in which the substrate shape is hollowed out in the center to form a substrate storage area, and the substrate is rotated. There is. With this configuration, stable high-speed rotation can be obtained by rotating the substrate together with the straightening vane, and good cleaning liquid can be shaken off and removed.

【0004】

In the straightening vane, the dimension of the substrate storage area is formed larger than the substrate dimension (clearance of several mm) to hold the entire substrate on the wall surface, or the hollow dimension is formed to be one size larger than the substrate dimension and erected in the hollow portion. A substrate storage area is formed by the plurality of fixing pins provided to hold the corners and sides of the substrate.

【0005】

[Problems to be Solved by the Invention]

However, conventionally, in the substrate holding structure of the substrate cleaning device, the dimension of the substrate storage area is formed larger than that of the substrate in order to facilitate mounting of the substrate on the straightening vane. Therefore, the substrate is held in a loosely fitted state that can be easily moved in the substrate storage area of the straightening vane. As a result, the substrate moves in the inertial direction at the same time as the rotation of the straightening vane starts, and collides with the wall surface or the fixing pin. In particular, in the case of a rectangular substrate for liquid crystal formed of glass having a thickness of about 1 mm, there is a problem that the peripheral portion of the substrate is damaged or the substrate is cracked due to collision.

【0006】

On the other hand, in order to minimize the movement of the board and reduce the impact due to collision, it is conceivable to make the size of the board storage area of the straightening vane as close as possible to the board size to reduce the clearance. There is a problem that high positioning accuracy is required when mounting the board on the board, and there is a risk that the straightening vane and the substrate mesh with each other after high-speed rotation and the board is broken when the substrate is removed from the straightening vane.

【0007】

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to ensure that the substrate is fixed during rotation, prevent damage due to collision of the substrate, and easily attach / detach the substrate. The purpose is to provide a substrate cleaning device.

【0008】

[Means for solving problems]

In order to achieve the above object, the first invention is a substrate to be cleaned in a substrate cleaning apparatus that cleans a substrate by supplying a cleaning liquid to the surface of the substrate while rotating the substrate in a plane formed by the substrate. Is placed and can be rotated together with the mounted substrate, and is arranged at least opposite to the substrate table mounted on the substrate table and the substrate mounted on the substrate table, and opens and closes substantially horizontally with respect to the substrate surface. In addition to being possible, there are multiple open / close chuck pins that sandwich the board in the closed state and fix it to the board table, and when the board table is in the lowered position, the board is sandwiched by the open / close chuck pins and fixed to the board table, and the board table is in the raised position. It is characterized by having a chuck pin operating means for releasing the fixing of the substrate by the opening / closing chuck pin when it is in the above position.

【0009】

According to the above configuration, the substrate is sandwiched and fixed in a substantially horizontal direction with respect to the substrate surface by the opening / closing chuck pins arranged at opposite side positions only when the substrate is in the descending position in a rotatable state. Further, when the substrate is in the raised position where the substrate is attached / detached, the fixing of the opening / closing chuck pin is released. Therefore, since the substrate is firmly fixed before the rotation of the substrate, it is possible to surely prevent the substrate from moving and colliding with the peripheral portion to be damaged, and the fixation is released when the substrate is attached or detached. The substrate can be easily attached and detached.

【0010】

Further, in order to achieve the above object, the second invention is the substrate cleaning apparatus of the first invention, wherein the chuck pin operating means includes an urging means for urging the opening / closing chuck pin in the opening direction and a substrate. It is characterized by having an interlocking mechanism that drives the opening / closing chuck pin in the opening direction by the urging force of the urging means at the same time as the table is raised to release the fixation of the substrate.

【0011】

According to the above configuration, the interlocking mechanism is operated by the urging means at the same time as the substrate table holding the substrate is raised to open the open / close chuck pin. Therefore, the fixing / releasing operation of the substrate can be easily performed without using a complicated mechanism.

【0012】

Further, in order to achieve the above object, the third invention is the substrate cleaning apparatus of the second invention, wherein the chuck pin operating means is a stopper to which the lower end of the opening / closing chuck pin comes into contact with the lower end of the opening / closing chuck pin when the substrate table is lowered. When the lower end of the opening / closing chuck pin comes into contact with the stopper when the board table is lowered, the opening / closing chuck pin is moved in the closing direction against the urging force of the urging means to sandwich the board and fix it to the board table. It is characterized by doing.

【0013】

According to the above arrangement, drop of the substrate table holding the substrate, the lower end of the opening and closing the chuck pins comes into contact with the stopper, the open-close feature in accordance with the contact state Kkupin performs the closing operation. Therefore, the substrate can be sandwiched and fixed without using a complicated mechanism. Further, the pinching strength can be adjusted by adjusting the height of the stopper, and the pinching amount can be easily changed, so that substrates of different sizes can be easily fixed.

【0014】

In order to achieve the above object, the fourth invention is the substrate cleaning apparatus of the first invention, wherein the chuck pin operating means is a detecting means for detecting an elevating state of a substrate table and a detection result of the detecting means. Based on the above, it is characterized by having an actuator that opens and closes the open / close chuck pin.

【0015】

According to this configuration, for example, a detection means such as an optical sensor or a proximity sensor accurately recognizes the ascending / descending state of the substrate table, and the opening / closing chuck pin is opened / closed based on the detection result. The control system can easily and surely recognize the elevating state of the board table and the open / closed state of the open / close chuck pin, and can surely hold the board.

【0016】

In order to achieve the above object, the fifth invention is characterized in that, in the substrate cleaning apparatus of the first invention, the portion of the opening / closing chuck pin that comes into contact with the substrate is formed of an elastic material.

【0017】

According to the above configuration, since the elastic member can absorb the pressing force of the opening / closing chuck pin more than necessary, it is possible to surely prevent the substrate from being damaged due to the pinching and fixing.

【0018】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a perspective view in which a part of the substrate cleaning device 10 according to the present embodiment is broken. Further, FIGS. 2 and 3 show a vertical sectional view of FIG. 1, FIG. 2 shows a state in which the substrate table is in the lowered position, and FIG. 3 shows a state in which the substrate table is in the raised position.

【0019】

The characteristic matter of this embodiment is that the board table on which the board is placed can be moved up and down in order to facilitate the attachment and detachment of the board, and the chuck structure for fixing the board can be opened and closed as the board table is moved up and down. It is performed in conjunction with each other, and the substrate can be reliably held when the chuck structure is closed, and the substrate can be easily attached and detached when the chuck structure is opened.

【0020】

As shown in the figure, the substrate 12 is mounted substantially horizontally on a plurality of mounting pins 16 provided on a substantially disk-shaped substrate table 14, and is fixed by a substrate chuck structure described later. Further, the board table 14 can be raised and lowered with the board 12 mounted by a table raising and lowering mechanism described later. As shown in FIG. 1, when the substrate 12 is rectangular, it has a substantially disk shape around the substrate in order to prevent rotation unevenness and airflow turbulence at the corners of the substrate 12 when the substrate 12 is rotated. A straightening vane 18 is provided. The straightening vane 18 is hollowed out in a rectangular shape according to the shape of the substrate 12 so that the substrate 12 can be accommodated in the same plane. The straightening vane 18 is preferably a disk having a thickness substantially equal to that of the substrate 12, and by making the substrate 12 and the straightening vane 18 have a disk shape as a whole, the rotation spots and turbulence as described above can be prevented. Occurrence can be prevented satisfactorily. Further, a base table 20 is arranged below the substrate table 14, and the straightening vane 18 is fixedly supported by a plurality of support columns 22.

【0021】

The base table 20 is fixed to a rotatable rotary cylinder 26 having a spline shaft 24 inside. Further, a ball spline 28 is inserted between the spline shaft 24 and the inner wall of the rotary cylinder 26 (in this embodiment, two places, the upper part and the lower part of the spline shaft 24), and the spline shaft 24 smoothly moves up and down. It is designed to be slidable. On the other hand, the rotary cylinder 26 is rotatably held by a holding cylinder 34 fixed to the frame 32 via a plurality of bearings 30. Since the ball spline 28 is fixed to the inner wall of the rotary cylinder 26, the spline shaft 24 can be rotated together with the rotary cylinder 26 by rotating the rotary cylinder 26 with respect to the frame 32. That is, by driving the rotary cylinder drive motor 38 connected to the rotary cylinder 26 via the drive belt 36, the rotary cylinder 26 and the spline shaft 24 can be rotationally driven at the same time. As described above, the base table 20 is fixed to the rotary cylinder 26, and the substrate table 14 is fixed to the spline shaft 24. Therefore, by rotationally driving the rotary cylinder 26, the base table 20 and the rectifying plate 18 are fixed. , The board table 14 and the board 12 can be integrally rotationally driven. As a result, the substrate 12 can be rotated at high speed to shake off and remove the remaining cleaning liquid. A rotary encoder 40 is connected to the lower end of the spline shaft 24 to detect the rotational displacement and rotational speed of the spline shaft 24 and feed back the detection results to a control unit (not shown) to perform optimum rotational control. ..

【0022】

On the other hand, as described above, the spline shaft 24 is slidable in the vertical direction by the ball spline 28. Hereinafter, the elevating mechanism of the spline shaft 24 will be described. A support column 42 is erected on the frame 32 in parallel with the spline shaft 24, and a rod-shaped screw shaft 44 that can rotate in parallel with the support column 42 is provided. An elevating motor 48 is connected to the lower end of the screw shaft 44 via a drive belt 46. Further, a nut member 50 is screwed onto the screw shaft 44 so as to move up and down as the screw shaft 44 rotates. Further, a support member 52 is fixed to the nut member 50 and is connected to an elevating guide plate 56 that supports the rotary encoder 40 via a floating joint 54. Therefore, the spline shaft 24 to which the rotary encoder 40 is connected can be moved in the vertical direction by rotationally driving the screw shaft 44 by the lifting motor 48 and raising and lowering the nut member 50. A guide rod 58 is provided in parallel with the screw shaft 44, and a floating joint 54 is provided between the support member 52 fixed to the nut member 50 and the elevating guide plate 56 to which the rotary encoder 40 is fixed. Since it is interposed, the elevating guide plate 56 can be smoothly ascended and lowered. FIG. 2 shows a state in which the elevating mechanism is lowered to lower the spline shaft 24, that is, a state in which the substrate table 14 is lowered and can be rotated by driving the rotary cylinder drive motor 38, and FIG. 3 shows a state in which the spline shaft 24 is lowered. This indicates that the board table 14 is raised and the board 12 can be attached to and detached from the board cleaning device 10.

【0023】

As described above, the substrate 12 needs to be rotated at a high speed in order to shake off the cleaning liquid remaining on the substrate 12, and it is necessary to securely fix the substrate 12 to the substrate table 14 during rotation. Hereinafter, the chuck structure of the substrate will be described in detail. As shown in FIGS. 1 to 3, a plurality of chuck pins 60 are provided at opposite sides of the substrate table 14 as opening / closing chuck pins for gripping and fixing the substrate 12. As shown in FIG. 2, the chuck pin 60 performs a closing operation in which the substrate table 14 stands up substantially vertically when the substrate table 14 is in the lowered position, sandwiches the substrate 12 and fixes the chuck pin 60 at a predetermined position. Further, when the substrate table 14 is in the raised position, as shown in FIG. 3, the chuck pin 60 opens by tilting outward to release the substrate 12.

【0024】

The structure and opening / closing operation of the chuck pin 60 will be described with reference to FIGS. 4 and 5. The chuck pin 60 has a substantially L-shape, and is rotatably supported around a rotation shaft 60a by a bracket 62 provided around a peripheral portion of the substrate table 14. The bracket 62 is provided on the back surface side of the substrate table 14, and the substrate grip portion 64, which is one end of the chuck pin 60, projects toward the front surface side of the substrate table 14 through the opening 14a of the substrate table 14. Further, a stopper bolt 68 is erected on the arm portion 66 on the other end side of the chuck pin 60, the stopper head 68a protrudes on the lower surface side of the chuck pin 60, and when the substrate table 14 descends, it comes into contact with the stopper block described later. It has become like. Further, for example, a spring 70 is provided around the stopper bolt 68 as an urging means. One end of the spring 70 is engaged with the upper surface of the arm portion 66 of the chuck pin 60, and the other end is engaged with the spring receiver 14b of the substrate table 14. The arm portion 66 and the stopper block form an interlocking mechanism, and further, the spring 70 and the interlocking mechanism form a chuck pin operating means. Therefore, the urging force of the spring 70 causes the chuck pin 60 to rotate in the direction of arrow A in FIG. 4 around the rotation shaft 60a, and as a result, the substrate grip portion 64 opens in the direction of arrow B in FIG. Since the amount of opening and closing of the chuck pin 60 for attaching and detaching the substrate 12 is sufficient to be several mm, the amount of rotation of the chuck pin 60 is very small, and the substrate grip portion 64 is substantially in the horizontal direction (arrow B). Open and close in the direction).

【0025】

As described above, when the board table 14 is raised by the drive of the elevating motor 48 (see FIG. 3) (the state shown in FIG. 3), the board 12 is in the released state supported only by the mounting pin 16 and is not shown. It can be easily gripped by an arm or the like (for example, a shuttle transport device), and the substrate 12 can be easily attached to and detached from the substrate cleaning device 10.

【0026】

Next, when the lifting motor 48 (see FIG. 2) is driven to lower the board table 14 and the chuck pin 60 passes through the opening 20a provided in the base table 20, the stopper head 68a of the stopper bolt 68 is used as the base. It comes into contact with the stopper block 72 provided on the back surface side of the table 20. When the stopper head 68a comes into contact with the stopper block 72, the stopper bolt 68 is raised against the urging force of the spring 70. That is, the chuck pin 60 closes in the direction of arrow C in FIG. 5 and is pressed against the substrate 12 supported by the mounting pin 16. As described above, since a plurality of chuck pins 60 are provided at positions opposite to each other on the substrate 12, the substrate 12 can be sandwiched and fixed.

【0027】

The substrate grip portion 64 of the chuck pin 60 is formed of an elastic member, for example, fluororesin, and absorbs an unnecessary pressing force when sandwiching and fixing the substrate 12, so that the substrate 12 is damaged by the unnecessary pressing. It is preventing. Further, the rotation angle (raising angle) of the chuck pin 60 can be easily adjusted by adjusting the height of the contact surface 72a of the stopper block 72, so that the pressing force may be changed depending on the type of the substrate. Even when fixing substrates of different sizes, it is possible to easily change and adjust the pressing force and pressing amount, improving versatility.

【0028】

Next, the procedure for removing the cleaning liquid from the substrate by the substrate cleaning device will be described. First, as shown in FIG. 3, the substrate cleaning device 10 raises the substrate table 14 by driving the elevating motor 48, for example, in the forward rotation direction, and waits for the substrate 12 to be supplied from a substrate transport device (not shown). .. At this time, since the board table 14 is in the raised position, the chuck pin 60 is opened by the urging force of the spring 70 and waits for the supply of the board 12. When it is confirmed by a sensor or the like (not shown) that the substrate 12 is supplied on the substrate table 14, the elevating motor 48 rotates in the direction opposite to that at the time of ascending, and lowers the substrate table 14. When the lowering of the board table 14 progresses and the stopper head 68a of the stopper bolt 68 comes into contact with the stopper block 72, the chuck pin 60 starts to close, the board 12 starts to be pinched, and the board 12 starts to be pinched before the board 12 rotates. Securely fix. At this time, since the closing operations of the chuck pins 60 are performed at the same time, the mounting position of the board 12 is automatically corrected to the center even if the mounting position on the board 12 on the board table 14 deviates from the predetermined position. To. The driving amount of the elevating motor 48 is recognized by a rotary encoder or sensor (not shown) so that the chuck pin 60 does not press the substrate 12 more than necessary.

【0029】

As shown in FIG. 1, the holding cylinder 34 has a lower flange 34a at the bottom, which is fixed to the frame 32. Further, the holding cylinder 34 also has an upper flange 34b at the upper portion, and the outer cup 76 is fixed to the holding cylinder 34. The outer cup 76 is arranged so as to house the substrate 12, the substrate table 14, and the annular hood 78, which will be described later, inside the outer cup 76, so that the cleaning liquid shaken off from the substrate 12 can be collected. That is, a drain pipe 80 is provided at the bottom of the bottom of the outer cup 76, and the cleaning liquid accumulated at the bottom of the outer cup 76 is discharged from here. Further, the cleaning liquid shaken off from the substrate 12 collides with the inner wall of the annular hood 78, and as a result of the high-speed rotation of the substrate 12, it becomes fine particles and scatters in the air inside the outer cup 76. The droplets of this cleaning liquid are sucked into the suction blower 82 together with air from the suction pipe 84. That is, there is an opening (suction hole 84a) of the suction pipe 84 near the bottom of the outer cup 76, and air is sucked from here. Due to this suction, the approximate air flow in the outer cup 76 becomes a flow from top to bottom, which stabilizes the air flow for collecting the cleaning liquid.

【0030】

In the present embodiment, as shown in FIG. 1, when the mounting and fixing of the substrate 12 is completed, the nozzle 86 for supplying the cleaning liquid that supplies the cleaning liquid protrudes, and further, the brush 88 that brushes the surface of the substrate 12 protrudes. The brush 88 is provided at the tip of the brush arm 90 and is rotationally driven by a power transmission mechanism provided in the brush arm 90. In the cleaning step, the cleaning liquid is supplied from the nozzle 86 and brushed with the brush 88. The brush arm 90 cleans the substrate 12 while moving the brush 88 by a moving mechanism (not shown) so that the entire surface of the substrate 12 is brushed.

【0031】

Further, in the present embodiment, after the cleaning work of the substrate 12 is completed, the upper gas injection nozzle 92 and the lower gas injection nozzle 94 for drying the substrate 12 are provided. The upper gas injection nozzle 92 and the lower gas injection nozzle 94 supply a gas having a low activity such as nitrogen from above and below the substrate 12. The upper gas injection nozzle 92 projects from above the substrate 12 to inject gas, and the lower gas injection nozzle 94 is formed at the upper end of the spline shaft 24. Gas is supplied to the lower gas injection nozzle 94 from the gas supply path 94a provided on the spline shaft 24, and the gas is sprayed on the lower surface of the substrate 12. Although a considerable part of the cleaning liquid of the substrate is blown off by this gas injection, the cleaning liquid may remain on the substrate 12 in a portion not directly exposed to the air flow. Therefore, by rotating the substrate 12 at high speed, the remaining cleaning liquid is completely shaken off. At this time, since the substrate 12 is securely sandwiched by the chuck pins 60, the substrate 12 does not move during rotation and collide with other members to be damaged.

【0032】

A dust collecting duct 96 is arranged around the upper part of the holding cylinder 34. The dust collecting duct 96 is connected to the suction blower 82 via a dust collecting pipe 96a, and dust near the upper part of the holding cylinder 34 from the dust collecting hole 96b provided on the inner peripheral surface of the dust collecting duct 96. And drain it out of the outer cup 76.

【0033】

As described above, when the removal of the cleaning liquid remaining on the substrate 12 is completed, the elevating motor 48 is driven again in the forward rotation direction to raise the spline shaft 24, raise the substrate table 14, and use the chuck pin 60 to raise the substrate. Release the 12 pinch locks. As described above, since the substrate 12 is supported only by the mounting pins 16, it can be easily taken out from the substrate cleaning device 10 by a transfer arm or the like of the substrate transfer mechanism. At this time, by increasing the height of the above-mentioned mounting pin 16 and increasing the distance between the mounting position of the board 12 and the board table 14, the transfer arm or the like can be easily inserted and the mounting / detaching efficiency of the board 12 is improved. be able to. Since the substrate 12 is securely fixed by the chuck pins 60 when the substrate table 14 is rotated, increasing the height of the mounting pins 16 does not affect the high-speed rotation of the substrate 12 and the like. In this embodiment, an example in which two chuck pins 60 are arranged on one side of the substrate 12 has been described, but the same applies even if the number of chuck pins 60 is increased or decreased or the arrangement position is changed as necessary. The effect of pinching and fixing can be obtained.

【0034】

In the above-described embodiment, an example is shown in which the chuck pin 60 mechanically opens and closes by the action of the spring 70 and the stopper block 72 interlocked with the raising and lowering operation of the board table 14, but for example, the board table 14 A detection means for detecting the ascending position and the descending position of the chuck pin 60 may be provided, and the actuator may be operated based on the detection result so that the chuck pin 60 electrically opens and closes.

【0035】

When, for example, an optical sensor or a proximity sensor is used as the detection means, the mounting position of the detection means is a position along the spline axis 24 or a screw axis even if the position of the board table 14 can be directly detected in the vicinity of the board table 14. The position along 44 may be a position where the position of the board table 14 can be indirectly recognized. Further, the position of the substrate table 14 may be recognized by using a detector that detects the rotation speed and the rotation direction of the elevating motor 48. Based on the detection results of these detection means, the chuck pin 60 opens and closes by driving an actuator such as a motor or a cylinder. In this case, the chuck pin 60 may be operated directly by the drive shaft of the actuator, but since the substrate table 14 to which the chuck pin 60 is attached rotates at high speed, it is indirectly operated by using a shaft or a wire operated by a motor or a cylinder. It is desirable to open and close the chuck pin 60.

【0036】

With such a configuration, the control system of the board cleaning device can easily electrically recognize the ascending / descending state of the board table 14 and the opening / closing operation of the chuck pin 60, so that the board can be securely fixed. It can be carried out.

【0037】

[Effect of the invention]

As described above, according to the present invention, the substrate is sandwiched and fixed in a substantially horizontal direction with respect to the substrate surface by the opening / closing chuck pins arranged in opposite positions only when the substrate is in the descending position in a rotatable state. To. Further, when the substrate is in the raised position where the substrate is attached / detached, the fixing of the opening / closing chuck pin is released. Therefore, when the substrate is rotated, the substrate is firmly fixed, and it is possible to surely prevent the substrate from moving and colliding with the peripheral portion to be damaged, and when the substrate is attached / detached, the fixation is released, so that the substrate is attached / detached. The work can be done easily.

[Simple explanation of drawings]

[Figure 1]

It is a partially broken perspective view of the embodiment of the substrate cleaning apparatus which concerns on this invention.

[Figure 2]

It is sectional drawing when the substrate is in the descending position in embodiment of the substrate cleaning apparatus which concerns on this invention.

[Fig. 3]

It is sectional drawing when the substrate is in the raised position in embodiment of the substrate cleaning apparatus which concerns on this invention.

[Fig. 4]

It is an enlarged view explaining the open state of the chuck structure in embodiment of the substrate cleaning apparatus which concerns on this invention.

[Fig. 5]

It is an enlarged view explaining the closed state of the chuck structure in embodiment of the substrate cleaning apparatus which concerns on this invention.

[Explanation of symbols]

10 board cleaning device, 12 boards, 14 board table, 16 mounting pins, 18 rectifying plate, 20 base table, 24 spline shaft, 26 rotary cylinder, 34 holding cylinder, 38 rotary cylinder drive motor, 48 elevating motor, 60 chuck Pins, 64 board grips, 70 springs, 72 stopper blocks.