JPH11330038A - Chemical processing device for substrate and the like - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a chemical processing device which is able to reduce the area of a work room and has good maintainability and make it hard to receive the effects by generation of impurities. SOLUTION: A chemical processing device has a chemical processing tank 3 arranged in a work room 1, a holding means 50 capable of holding a substrate W to be processed, an automatic carrying means 30 moving vertically the holding means 50 along the chemical processing tank 3, an upper machine room 7 which is partitioned by a closing plate 12 provided at the upper side of the work room 1 and is provided with a motor driving part constituting the automatic carrying means 30 and an exhaust port 9, a slit 12a made in the closing plate 12 for allowing an arm 36 to move, the upper end side of the arm 36 being rotatably pivoted by the motor driving part, and a gas supplying passage 10 capable of blowing out gas to the upper machine room 7 from the work room 1 side of the slit 12a and exhausting the gas from the exhaust port 9 of the upper machine room 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical processing apparatus for automatically transferring an object to be processed, such as a semiconductor substrate, to a chemical processing tank and performing surface treatment.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process or the like, when a substrate or the like is subjected to chemical treatment with various treatment liquids, see Japanese Patent Application Laid-Open No. 6-898.
As exemplified in Japanese Patent Publication No. 37, an automatic chemical processing is often performed while a chemical processing tank is installed in an isolated work room and a substrate or the like is transferred (horizontally and vertically moved) by a transfer robot. In such a chemical treatment, usually, a combination of chemicals is often used, and it is also essential to clean the deposits with pure water after the chemical treatment. Therefore, a plurality of chemical treatment tanks are provided as a set. Therefore, in the working room, in addition to the installation space for each chemical solution treatment tank, a transfer area for the transfer robot is also required. Also, many harmful chemicals such as sulfuric acid, hydrogen peroxide, and phosphoric acid are used, and ventilation equipment is indispensable. Becomes Therefore, in terms of design, in particular, as the number of chemical solution treatment tanks increases, the working room is made compact and space is not restricted, the transfer efficiency by the transfer robot and the maintainability are excellent, and the generation of impurities etc. in the working room Is required.

[0003]

However, in the conventional apparatus, as shown in the above-mentioned publication, the working space is ensured in a state where the installation area for each chemical solution treatment tank and the transfer area for the transfer robot are arranged side by side. In addition, since the transfer robot is configured to move along the side of the chemical treatment tank, the work chamber naturally needs to be large in area, thereby restricting the maintainability of each treatment tank and the like. In addition, since the transfer robot moves in the transfer area close to the chemical processing tank in the working room, various impurities (such as detachment of attached matter and dust of worn members) generated from the robot driving unit enter the chemical processing tank. Also, there is a fear that it may adhere to the object to be processed.

SUMMARY OF THE INVENTION The present invention has been developed to solve the above-mentioned conventional problems, and has as its object to reduce the size of a working chamber, to improve the maintainability, and to reduce the influence of impurity generation on chemical solutions. It is to provide a device. Still other objects will be sequentially clarified in the contents described below.

[0005]

According to a first aspect of the present invention, there is provided a work chamber 1 as shown in the drawings.
And a holding means 50 capable of supporting a substrate or the like which is an object to be processed W, and an automatic transport means 30 for moving the holding means 50 horizontally and vertically along the chemical processing tank 3. In the chemical treatment apparatus provided with:
A drive unit, such as a motor, which is partitioned by the upper closing plate 12 and constitutes the automatic transfer means 30 is provided, and the upper machine room 7 provided with the exhaust port 9 and the upper machine room 7 are provided in the closing plate 12. A slit 12a for allowing movement of an arm 36 rotatably supporting an upper end of the driving unit, and blowing out gas from the working chamber 1 side of the slit 12a to the upper machine chamber 7 so that the upper machine chamber 7 And a gas supply path 10 that can be exhausted from the exhaust port 9.

According to this device, the working space is
Since the upper machine room 7 is provided at the upper part of the work room 1, it is sufficient to secure a space corresponding to the installation of the chemical solution treatment tank 3, and the work room 1 is reduced in area and becomes vertically long corresponding to the upper machine room 7. Become. Therefore, as the working chamber 1, for example, when a plurality of chemical solution processing tanks 3 are arranged in a line and an opening / closing door 4 for maintenance is provided on one side surface of each chemical solution processing tank 3, Maintenance work and the like for the tank 3 are facilitated. At the same time, impurities generated from the drive unit of the automatic transport means 30 and the like are prevented from dropping from the upper machine chamber 7 by gas blown from the working chamber 1 side to the upper machine chamber 5 through the slit 12a. As described above, it is possible to structurally prevent the risk that impurities enter the chemical solution treatment tank 3 or adhere to the workpiece W. In this structure, a dispersion chamber 6 provided below the closed plate 12 is provided. The gas is introduced into the dispersion chamber 6, and the gas is introduced from the dispersion chamber 6 to the exhaust port 9 of the upper machine chamber 7, Room 1
It is preferable that the air is exhausted from an exhaust port 5 provided at the lower part. This is because the gas is discharged from the dispersion chamber 6 through the exhaust port 9 of the upper machine chamber 7 and the exhaust port 5 provided at the lower part of the working chamber 1, so that the gas inside the working chamber 1 is supplied by a single gas supply source. The ventilation function and the above-described impurity introduction prevention function can be combined.

Further, the second present invention provides a chemical processing tank 3 disposed in the working chamber 1, a holding means 50 capable of supporting a substrate or the like as an object W to be processed, and a holding means 50 comprising a chemical processing tank. And an automatic transfer means 30 that moves in the horizontal and vertical directions along 3
A rail member 31 provided in the upper part of the work chamber 1, a pair of traveling machines 32 movable along the rail member 31, and an arm 36 pivotally supported on the traveling machine 32 at an upper end thereof so as to be rotatable.
And the movable body 4 connected and held to the lower end side of the arm 36
0, and the holding means 50 is attached to the movable body 40.

According to this device, since the automatic transfer means 30 is moved along the rail member 31 provided at the upper part of the work chamber 1, only a portion corresponding to the installation of the chemical processing tank 3 is provided as a planar work space. As long as it is ensured, the same advantages as those of the first aspect of the present invention can be provided, and it can be simplified compared to the conventional transfer robot. In this structure, the traveling machine 3
It is preferable that the lower ends of the two arms 36 are pivotally supported by the movable body 40 and rotatably mesh via a gear 41. This is because the movable body 40 is
When moving vertically and horizontally, the movement of the movable body 40 can be maintained and stabilized by moving through the gear 41. Further, specific examples of the traveling machine 32 include a driving motor 33, bases 34 a and 34 b on which the motor 33 is mounted, and a driving shaft 33 of the motor 33.
a, and a pinion 35 provided on the rail member 31.
When the pinion 35 is moved while meshing with the rack 31b provided along, the automatic transport means 32 can be realized relatively easily.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. This embodiment is a preferred specific example of the present invention and does not limit the scope of the present invention. FIG. 1 is a schematic configuration diagram showing the entire apparatus to which the present invention is applied in a longitudinal cross-sectional state, and FIG. 2 is a schematic configuration diagram showing the movement of an automatic conveying means of the apparatus. FIG. 3 is a schematic external view showing a configuration of the automatic transport unit, FIG. 4A is a configuration diagram showing a relationship between the automatic transport unit and the dispersion chamber, and FIG. 4B is a modified example thereof. FIG. 5A is a vertical cross-sectional view showing the relationship between the lower ends of the arms of the automatic transfer means disposed in the movable body.
(B) is a longitudinal sectional view showing a driving mechanism of the holding means disposed in the movable body. FIG. 6 is a schematic configuration diagram showing details of FIG. 5A, and FIG. 7 is a schematic operation diagram of FIG. 5A. FIG.
Is a partially cutaway view showing details of the holding means, and FIG. 9 is an exploded schematic view of the holding means. In the following description, the overall arrangement of the present invention will be described with reference to FIGS. 1 and 2, and then the detailed configuration of each part will be described in detail with reference to the corresponding drawings.

(Overall Configuration) A chemical solution processing apparatus according to an embodiment is employed in a semiconductor manufacturing process. A working chamber 1 which is isolated from the outside extends in the front-rear direction of FIG. A substrate transfer section on which a substrate W to be processed is placed is located, a plurality of chemical processing tanks 3 are arranged in a line behind the tank, and a drying section and a substrate discharge section (not shown) are provided. ing. Further, the working chamber 1 includes a door 4 and an inner door 4a provided on one side so as to be openable and closable, an exhaust port 5 with a damper provided on a lower part on the other side, a dispersion chamber 6 provided on an upper part, and an upper machine. Chamber 7, an inlet 8 provided on one side of the dispersion chamber 6, and an exhaust port 9 provided with a damper provided on one side of the upper machine room 7.
And the gas supply path 1 connected to the inlet 8 and the outlet 9
0 and so on. Then, the drive unit of the automatic transfer means 30 is installed in the upper machine room 7, and the holding means 5 for the substrate W is provided.
Numeral 0 is attached via a movable body 40 to an arm 36 suspended in the working chamber 1 by being connected to the drive unit.

Here, the size of the working chamber 1 is smaller than that of the conventional structure, and the width of the working chamber 1 is smaller than that of the conventional structure.
It is longer up and down in response to. Practically, the width may be about 10 cm larger than the width or diameter of the substrate W. The chemical treatment tank 3 is fixedly disposed on a room-installed portion via a support base 11 as in the related art. Inside, a chemical solution such as sulfuric acid or pure water is supplied from a chemical solution supply source (not shown) via a supply piping system or discharged via a discharge piping system.
These are exchanged in batches. Maintenance work for the chemical solution treatment tank 3 and the like is performed by opening and closing the door 4 and the inner door 4a.

The dispersing chamber 6 has a lower part partitioned from the working chamber 1 by a dispersing plate 11, and an upper part has an upper machine room 7 by a closing plate 12.
Is provided in a state where it is partitioned between and. The dispersion plate 11 is formed with a large number of through holes 11a and a long hole 11b through which the arm 36 constituting the automatic transport means 30 passes. A slit 12a is formed in the closing plate 12 so as to face the long hole 11b. As shown in FIG. 4, the slit 12a has a hole width larger than the thickness of the arm 36, and has a guide half 13a standing on the closed plate 12 along the edge of the slit 12a and a guide member 31 described later. And a guide half 13b erected along the side surface of the rim. In addition,
Both the length of the long hole 11b and the length of the slit 12a substantially correspond to the guide member 31.

The gas supply path 10 is connected to the inlet 8 of the dispersion chamber 6.
Piping system 1 that connects between the exhaust port 9 of the upper machine room 7
4, a configuration is provided in which an outside air intake unit 15, a fan 16, and a eva filter 17 for gas filtration are provided.
Then, the fan 16 sends air or the like flowing from the outside air intake unit 15 to the hepa filter 17, and removes impurities therefrom and sends the air into the dispersion chamber 6 through the inlet 8. Part of the air pumped into the dispersion chamber 6 is formed in the through-hole 11 a of the dispersion plate 11.
The flow flows downward into the work chamber 1 through the like and forms a flow discharged from the exhaust port 5 at the lower part of the work chamber 1. That is, it is used for the ventilation action in the work room 1. At the same time, a part of the air flows into the upper machine room 7 while being blown up through the slits 12 a of the closing plate 12, and is circulated from the exhaust port 9 through the piping system 14. This circulation path prevents impurities generated in the upper machine chamber 7 from dropping into the working chamber 1 through the slits 12a due to the wind pressure (wind speed) of the air blown up to the upper machine chamber 7 through the slits 12a. To get the action. When the introduction of impurities is prevented by such a method, it is usually sufficient to set the wind speed in the slit 12a to about 0.2 to 0.5 m / sec.

(Detailed Configuration) The automatic transport means 30 includes a pair of traveling machines 32 movable along a rail member 31 as shown in FIG. 3 and FIG. And a movable body 40 connected and held to the lower end of the arm 36, and the holding means 50 is assembled to the movable body 40.

Here, the rail member 31 is
A is fixed on the closed plate 12 along a. The upper surface has a guide projection 31a projecting from both sides and a rack projection 31b projecting between the guide projections 31a to form rack teeth on the side surface. The traveling machine 32 includes a driving motor 33 mounted on a base portion 34a, and a pinion 35 provided on a driving shaft 33a of the motor 33 and protruding below the base portion 34a.
1 is movably assembled via a base portion 34b. The base portion 34b is a rectangular plate and has a pinion 3
5 through the through hole 34c, and has a bearing block 37 provided on both lower surfaces and having a concave cross section, and a bearing 38 provided on one side of the upper surface. And
When the bearing block 37 is movably fitted to the corresponding convex piece 31a, the pinion 35 meshes with the rack teeth of the rack piece 31b. For this reason, the traveling machine 32 can move along the rack piece 31b through the rotation of the pinion 35 by driving the motor 33, and can change the moving direction when the rotation of the pinion 35 is reversed.

The bearing 38 has a hole 38a on the side surface in the width direction. And the upper end side of the arm 36
It is arranged corresponding to the hole 38a, and is rotatably supported via a shaft 39 inserted into the hole 38a. This arm 36
Is suspended in the work chamber 1 through the slit 12a and the elongated hole 11b of the closing plate 12, and is moved back and forth along the slit 12a and the elongated hole 11b by the movement of the traveling machine 32. In the modification of FIG. 4B, the base portion 34b is formed to have a substantially L-shaped cross section, and the L-shaped vertical piece 34c is arranged to protrude from the slit 12a into the dispersion chamber 6, and the vertical piece 34c is On the other hand, the upper end side of the arm 36 is rotatably supported in the dispersion chamber 6. Also in this case, the arm 36
Is suspended in the work room 1 through the elongated hole 11b,
The traveling machine 32 is moved back and forth along the elongated hole 11b.

The lower ends of the arms 36 of the traveling machines 32 are inserted into the movable body 40 and connected to each other via a gear 41. FIGS. 5A, 6 and 7 show the connection structure and operation of the movable body 40 and the arm 36. FIG. Reference numeral 42 denotes a part of a gondola-shaped housing constituting the movable body 40. Inside the housing 42, the lower end of each arm 36 is provided with a shaft 4
It is rotatably assembled via 3 and the bearing 45.
In this case, each shaft 43 is fixed so as to penetrate the lower end side of each arm 36 and the gear 41, and both sides are pivotally supported via bearings 45 mounted in holes 44 of the housing 42. Gear 41 mounted on each shaft 43
Has a substantially sector shape, and teeth 41a formed on the outer periphery are in mesh with each other. In FIG. 5A, reference numerals 70a and 70
Reference numerals b and 70c denote covers for covering unnecessary portions on the outer surface of the housing 42.

Therefore, the movable body 40 (housing 42) described above includes the arm 36 of each traveling machine 32 and each gear 41.
And is supported in a suspended state via a. Then, for example, when both arms 36 are changed from the solid line position in FIG. 7 to the imaginary line position approaching by the movement of the corresponding traveling machine 32, each arm 36 is synchronously rotated by the meshing action of the gears 41, and The horizontal state of the housing 42 moved in the direction is maintained. Such a horizontal state of the movable body 40 occurs when each traveling machine 32 is moved to an imaginary line position separated from the solid line position as shown on the left side of FIG.
When the gears are horizontally moved while maintaining a constant interval, the arms 36 are synchronously rotated by the meshing action of the gears 41 and are constantly maintained.

The holding means 50 is incorporated in the movable body 40 (housing 42). 5 (b), 8 and 9
Shows a schematic structure of the holding means 50. The holding means 50 includes an air cylinder 51 mounted in the housing 42 and a piston rod 52 of the air cylinder 51.
And a pair of chucking members 53 which are opened and closed by the operation of the above, so that the plurality of substrates W are releasably held between the two chucking members 53. The supply and discharge of air to and from the air cylinder 51 are not shown, but an air pipe is arranged along the arm 36 from inside the housing 42 and connected to a drive unit provided in the upper machine room 7. And can be controlled from outside.

The air cylinder 51 is a single-acting type having a built-in spring 54, and is pivotally supported in the housing 42 via a shaft 46 and the like. Piston rod 5
2, two cylinder arms 55 are rotatably connected. Each cylinder arm 55 has a plurality of links 56.
And a link mechanism consisting of a rod 57 so that the piston rod 52 is rotated in a different direction as shown in FIG. keeping. In the airless state, the piston rod 52 is in a contracted state by the urging force of the spring 54, the two chucking members 53 are closed, and the substrate W is held by the urging force. When compressed air is sent to the air cylinder 51, the piston rod 52 extends, and each cylinder arm 55 and the chucking member 53 rotate in different directions to be in an open state,
The substrate W is released. With such a structure of the air sealing 51, the holding state of the substrate W is maintained even if the power is inadvertently cut off due to an accident or the supply of air is stopped.

As shown in FIG. 9, the chucking member 53 includes two side plates 58 formed in a substantially rectangular shape, and three rods 59a connecting the side plates 58 at a predetermined interval. , 59b. The upper rod 59a is fixed to the corresponding cylinder arm 55. The lower rod 59b is provided with a plurality of grooves omitted on the inner periphery thereof, and supports the substrate W in a state in which the grooves are fitted. Each chucking member 53 is opened and closed by the operation of the cylinder arm 55 described above, and can hold or release the substrate W by a total of four lower rods 59b located inside the rectangle. it can.

The holding means 50 can be variously modified depending on the size and shape of the substrate W. In FIGS. 2 and 8, reference numeral 60 denotes a substrate holding jig, which is also deformed as necessary similarly to the holding unit 50. The jig 60 of this embodiment is composed of two side plates 61 and three rods 62 connecting the both side plates 61 at a predetermined interval. Each rod 62 is arranged on a concentric circle corresponding to the outer diameter of the substrate W, and has a structure that supports the substrate W in a state where the substrate W is fitted into a plurality of grooves provided on the upper and outer circumferences.

(Example of Operation of Apparatus) In the above chemical solution processing apparatus,
During operation, the gas supply path 10 is driven, and the above-described ventilation action in the work chamber 1 and the action of preventing the introduction of impurities that prevent the impurities generated in the upper machine chamber 7 from falling into the work chamber 1 are performed. can get. From this state, the plurality of substrates W in the cassette moved to the transfer unit (not shown) are transported to the respective chemical processing tanks 3. That is, when the pair of traveling units 32 are moved on the substrate transfer unit and approach each other, the arms 36 are placed in a substantially parallel lower state, and the movable body 40 is moved to the lowermost position. At the lowermost position of the movable body 40,
The compressed air of the air cylinder 51 is discharged. Then, each chucking member 53 is switched from the open state to the closed state, and sandwiches the plurality of substrates W being moved upward from the cassette from both sides. This holding force is proportional to the urging force of the spring 54. Thereafter, the pair of traveling machines 32 is controlled to move in different directions. Then, the substrate W held by the movable body 40 and the holding member 50 is moved upward integrally as the arms 36 move in different directions. After reaching the predetermined height, the pair of traveling machines 32 is controlled to move at the same speed and in the same direction. This movement is performed by the movable body 40 and the holding member 5.
The process is performed until the substrate W held at 0 is transferred to the position right above the target chemical processing tank 3. Thereafter, when the movements of the two traveling machines 32 are controlled to approach each other, the movable body 4
0 is lowered, and the substrate W held by the holding member 50 is put into the chemical processing tank 3.

The substrate W held by the holding member 50
Are a plurality of chemical treatment tanks 3 determined in such a manner.
While being sequentially transferred to the inside, the surface treatment and the cleaning treatment are performed, and at the final stage of reaching the discharge section, the container is automatically released from the holding means 50 and is carried out of the work chamber 1. In addition, in the work such as maintenance and inspection, the piping and the chemical solution treatment tank 3 in the work room 1 can be efficiently performed via the opening / closing door 4 and the inner door 4a. The above description is of a so-called cassetteless type in which the chucking member 53 directly sandwiches a plurality of substrates W. However, a structure in which the chucking member 53 grips and transports a cassette containing the substrates W is described. It may be. Regardless of the structure, this structure or a similar chucking method can be applied according to the purpose and specifications.

[0025]

As described above, the present invention has the following effects. According to the first aspect, in terms of the working space, the upper machine room is provided at the upper part of the working room, so that it is sufficient to secure a portion corresponding to the installation of the chemical treatment tank, and the working room can be reduced in area. In addition, as the working chamber, for example, a plurality of chemical processing tanks are arranged in a line, and an opening / closing door for maintenance is provided on one side of each chemical processing tank, and maintenance work of each processing tank is performed through the door. Can be easily performed. At the same time, the impurities generated from the drive unit of the automatic transfer means and the like are not dropped from the upper machine chamber due to the gas blown from the working chamber side to the upper machine chamber, and the impurities enter the chemical solution treatment tank as in the related art. The risk of adhering to the workpiece can also be prevented. According to the third aspect, since the automatic transfer means is moved along the rail member provided at the upper part of the work chamber, it is sufficient to secure a surface work space corresponding to the installation of the chemical solution treatment tank,
In addition to the advantage of the first aspect, simplification can be made with respect to the conventional transfer robot.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a work chamber to which the device of the present invention is applied in a longitudinal section.

FIG. 2 is a schematic configuration diagram showing the working chamber of FIG. 1 in a cross section in a front-rear direction.

FIG. 3 is a schematic external view showing a configuration of an automatic transport unit of FIG.

FIG. 4 is a main part configuration diagram showing a relationship between the automatic transfer means and the dispersion chamber in FIG. 1;

FIG. 5 is a diagram showing a relationship between the movable body of FIG. 1 and an automatic transport unit and a holding unit.

FIG. 6 is a schematic configuration diagram showing a relationship between the movable body of FIG. 5 and automatic conveyance means.

FIG. 7 is a schematic operation view showing vertical movement of the movable body in FIG. 5;

FIG. 8 is a schematic operation view showing a relationship between the movable body and the holding means in FIG. 5;

FIG. 9 is a schematic diagram showing a configuration of a holding unit in FIG. 5;

[Explanation of symbols]

1 is a working room, 3 is a chemical treatment tank, 5 is an exhaust port, 6 is a dispersion chamber, 7 is an upper machine room, 9 is an exhaust port, 10 is a gas supply path,
12 is a closed plate, 12a is a slit, 30 is an automatic conveying means,
31 is a rail member, 32 is a traveling machine, 33 is a motor, 36
Is an arm, 40 is a movable body, 50 is holding means, W is a substrate (workpiece).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/68 H01L 21/68 A

Claims (5)

[Claims] 1. A chemical solution processing tank disposed in a working chamber, holding means capable of supporting a substrate or the like as an object to be processed, and an automatic moving means for moving the holding means horizontally and vertically along the chemical solution processing tank. A chemical solution processing apparatus provided with a transport unit, wherein the upper machine is provided with a drive unit such as a motor, which is partitioned by a closed plate on the upper side of the working chamber, and constitutes the automatic transport unit, and which is provided with an exhaust port. And a slit provided in the closed plate to allow movement of an arm rotatably supporting an upper end side of the driving unit, and blowing gas from the working chamber side of the slit to the upper machine chamber. A gas supply path that can be exhausted from an exhaust port of the upper machine room. 2. A dispersing chamber provided at a lower part of the closed plate, wherein the gas is introduced into the dispersing chamber, and an exhaust port of the upper machine room from the dispersing chamber and a lower part of the working chamber are provided. The chemical processing apparatus according to claim 1, wherein the liquid is discharged from the exhaust port provided. 3. A chemical solution processing tank disposed in a working chamber, holding means capable of supporting a substrate or the like as an object to be processed, and an automatic moving means for moving the holding means horizontally and vertically along the chemical solution processing tank. In the chemical liquid processing apparatus provided with a transport means, the automatic transport means, a rail member provided in the upper part of the work chamber, a pair of traveling machines movable along the rail member, and an upper end side to the traveling machine And a movable body connected and held at the lower end of the arm, and the holding means is attached to the movable body. 4. The chemical processing apparatus according to claim 3, wherein lower ends of both arms pivotally supported by the traveling machine are pivotally supported by the movable body and rotatably meshed via gears. 5. The traveling machine has a drive motor, a base on which the motor is mounted, and a pinion connected to a drive shaft of the motor, and is provided along the rail member. The chemical solution treatment device according to claim 3, wherein the chemical solution treatment device moves while meshing the pinion with a rack.