Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a substrate cleaning apparatus, and more particularly to a substrate cleaning apparatus suitable for cleaning a substrate which requires a high level of cleanliness, such as a semiconductor wafer, a glass substrate, a liquid crystal panel, etc. 
     2. Description of the Related Art 
     Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are spaced by a distance of at most 0.5 μm, it requires that surface on which pattern images are to be focused by a stepper is as flat as possible because the depth of focus of the optical system is relatively small. If particles larger than the distance between adjacent interconnections are present on a substrate, then they tend to cause a short circuit between the interconnections. Therefore, it is important that the substrate is cleaned as well as planarized in its fabrication process. The same processing requirements apply to other substrates including glass substrates, liquid crystal panels, etc. In view of these requirements, there has been a demand for cleaning techniques for removing smaller particles, i.e., submicrons, from semiconductor substrates or the like. 
     According to a known process of cleaning a polished semiconductor substrate to a high level of cleanliness, the surface to be cleaned of the substrate is scrubbed by a cleaning member such as a brush or a sponge that is rubbed against the substrate (primary cleaning), and then a stream of water under high pressure, i.e., a high-speed jet of water, is ejected toward the substrate to produce air bubbles due to cavitation to clean the substrate (secondary cleaning). 
     FIG. 9A of the accompanying drawings shows a conventional general arrangement of a substrate cleaning apparatus for use in scrubbing a substrate. The substrate cleaning apparatus has a plurality of upstanding substrate-holding rollers  100  openably and closably disposed around a substrate W. The substrate-holding rollers  100  has holding grooves  102  defined in upper ends thereof for holding the edge of the substrate W and rotating the substrate W upon rotation of the rollers  100 . As shown in FIG. 9B of the accompanying drawings, a pair of cleaning devices  108  is disposed in sandwiching relationship to the substrate W. The cleaning devices  108  are rotatable about respective axes thereof and movable into and out of contact with the substrate W. Each of the cleaning devices  108  comprises a solid shaft  104  and a cleaning member  106  in the form of a tubular sponge, brush, or the like disposed on the surface of the solid shaft  104 . As shown in FIG. 9C of the accompanying drawings, nozzles  110  which supply a cleaning liquid, pure water, or the like to the face and back of the substrate W are provided. 
     While the substrate W is being held and rotated by the rollers  100 , the cleaning liquid is supplied from the nozzles  110  to the face and back of the substrate W, and the cleaning members  106  are rubbed against the substrate W to scrub the substrate W (primary cleaning) for thereby removing deposits of an abrasive liquid, a polishing residue, etc. from the entire face and back of the substrate W. 
     Since the scrubbing process is carried out while the cleaning members  106  are being held in contact with the substrate W, the contamination of the cleaning members  106  themselves governs the cleaning effect. If the contamination of the cleaning members  106  progresses, then the contaminant attached to the cleaning members  106  tends to contaminate the substrate W. Therefore, as shown in FIG. 9C, a cleaning tank  114  filled with a cleaning liquid  112  is disposed in a retracted position of the cleaning devices  108 , and each of the cleaning devices  108  is cleaned by being dipped and rotated in the cleaning liquid  112  in the cleaning tank  114 . 
     SUMMARY OF THE INVENTION 
     With the above conventional arrangement, it is necessary to supply the cleaning liquid to the entire surface of the substrate in order to uniformly clean the substrate, and hence a large amount of cleaning liquid is required. Particularly, if the substrate is rotated at a high speed, then the cleaning liquid is quickly removed from the surface of the substrate, and hence is utilized with low efficiency, resulting in a need for a greater amount of the cleaning liquid which is supplied from nozzles  110 . 
     Furthermore, since the cleaning devices  108  are dipped in the cleaning liquid  112  in the cleaning tank  114  to clean the cleaning members  106  themselves, the cleaning devices  108  may be contaminated by contaminants contained in the cleaning liquid and ions released into the cleaning liquid. 
     The shafts  104  of the cleaning devices  108  are rotatably supported by bearings at ends held by the shaft end holders thereof remote from drive ends that are connected to a drive mechanism such as a motor. Therefore, particles are produced and metal and grease are released from the bearings, seals that protect the bearings from corrosive fluids, and springs which bias the cleaning devices in the axial direction. When not in operation, the cleaning liquid is dried to allow the cleaning agent to be solidified, preventing the cleaning devices from operating smoothly. Because the ends of the shafts held by the shaft end holders are combined with a complex mechanism, the diameter of the cleaning devices is so large that it takes a long period of time to impregnate the entire cleaning members of the cleaning devices with the cleaning liquid, and a large amount of cleaning liquid is required. 
     The present invention has been made in view of the above drawbacks. It is an object of the present invention to provide a substrate cleaning apparatus which has an increased cleaning efficiency of a cleaning liquid and maintains a sufficient cleaning capability, includes durable bearings of a simple structure, and can be operated stably at a low cost. 
     To achieve the above object, there is provided in accordance with an invention described in claim  1 , a substrate cleaning apparatus comprising a substrate holder for holding a substrate while rotating the substrate in a substantially horizontal plane, a cleaning device for scrubbing a surface to be cleaned of the substrate, a cleaning device holder for holding the cleaning device rotatably about its own axis, the cleaning device having a shaft and a cleaning member disposed around the shaft, the cleaning member being permeable to a cleaning liquid, the shaft having an axially extending shaft hole and a cleaning liquid ejection port extending radially therethrough from the shaft hole, and a fluid-lubricated bearing disposed between the shaft and the cleaning device holder in at least one end thereof and lubricated by a cleaning liquid as a lubricating fluid. The cleaning member which is permeable to a cleaning liquid may be a sponge that is liquid-permeable by itself, a brush which has gaps, or a hydrophobic tube with holes defined at suitable intervals. 
     Since the cleaning liquid is ejected via the shaft hole in the shaft from the cleaning liquid ejection port and supplied via the cleaning member to the surface to be cleaned of the substrate, the cleaning liquid concentrates on a region to be cleaned of the substrate. Therefore, no wasteful cleaning liquid is supplied to the substrate, which is cleaned efficiently. Because the cleaning member itself is cleaned steadily by the cleaning liquid passing through the cleaning member, the substrate is prevented from being contaminated by the cleaning member which would otherwise be contaminated. Furthermore, inasmuch as the cleaning device is supported by the fluid-lubricated bearing which employs the cleaning liquid as the lubricating fluid, a stable contamination-free support structure of simple arrangement is achieved. 
     According to an invention described in claim  2 , in the invention described in claim  1 , the cleaning device holder has a shaft end holding member biased toward an end of the shaft, the shaft end holding member and the shaft having complementarily shaped abutting sliding surfaces. By guiding the cleaning liquid to the abutting sliding surfaces, a fluid-lubricated bearing which employs the cleaning liquid as a lubricating fluid is provided. The abutting sliding surfaces may usually be tapered surfaces, but may be arbitrary surfaces created by rotating quadratic curves or the like. The pressure between the abutting sliding surfaces can be adjusted by adjusting the biasing force of a spring or the like which urges the shaft end holding member. 
     According to an invention described in claim  3 , in the invention described in claim  2 , the abutting sliding surfaces are disposed at an open end of the shaft hole. With this arrangement, the cleaning liquid is supplied directly to the abutting sliding surfaces, not via a special passage. 
     According to an invention described in claim  4 , in the invention described in claim  1 , the fluid-lubricated bearing is made of a material which does not release metal ions into the cleaning liquid and is highly slidable. The fluid-lubricated bearing thus constructed provides a sliding assembly with good slidability and free of metal contamination. 
     The cleaning device may be arranged so as to be movable between a substrate cleaning position and a standby position, so that the cleaning device does not interfere when the substrate is fed. A cleaning tank having a cleaning liquid ejection nozzle may be disposed in the standby position of the cleaning device for cleaning the cleaning device itself. 
     According to an invention described in claim  5 , in the invention described in claim  1 , the cleaning device holder has a shaft end holding member biased toward an end of the shaft, the shaft end holding member housing therein a centering pusher rotatable in unison with the cleaning device and rotatably supported by a roller bearing. The cleaning liquid is introduced into the roller bearing disposed in the shaft end holding member, thus providing a fluid-lubricated bearing that employs the cleaning liquid as a lubricating fluid. Since the centering pusher is rotatably supported by the roller bearings, particles are prevented from being produced which would otherwise occur due to sliding movement between the centering pusher and the cleaning device. 
     According to an invention described in claim  6 , in the invention described in claim  5 , the roller bearing is made of a material which does not release metal ions into the cleaning liquid and/or an etching liquid and does not produce particles. The roller bearing may comprise a ceramics bearing, and may be made of ceramics, Teflon, or the like. Therefore, metal contamination and particles are prevented from being produced by the roller bearings. 
     According to an invention described in claim  7 , there is provided an apparatus for polishing a substrate, comprising a substrate housing unit, a substrate polishing assembly, a substrate cleaning apparatus according to any one of claims  1  through  6 , and a substrate feeding mechanism for feeding a substrate between the substrate housing unit, the substrate polishing assembly, and the substrate cleaning apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing an overall arrangement of a polishing apparatus according to an embodiment of the present invention; 
     FIG. 2A is a perspective view showing a general arrangement of a substrate cleaning apparatus according to an embodiment of the present invention, FIGS. 2B and 2C are views illustrative of the manner in which the substrate cleaning apparatus operates; 
     FIG. 3 is a front elevational view, partly in cross section, of the substrate cleaning apparatus shown in FIG. 2; 
     FIG. 4 is an enlarged view of a portion shown in FIG. 3; 
     FIG. 5 is a cross-sectional view of a polishing assembly; 
     FIG. 6A is a perspective view of a substrate cleaning apparatus for secondary cleaning, and FIG. 6B is a view illustrative of the manner in which the substrate cleaning apparatus for secondary cleaning operates; 
     FIG. 7 is a front elevational view, partly in cross section, of a substrate cleaning apparatus according to another embodiment of the present invention; 
     FIG. 8 is an enlarged view of a portion shown in FIG. 7; and 
     FIG. 9A is a perspective view showing a general arrangement of a conventional substrate cleaning apparatus, and FIGS. 9B and 9C are views illustrative of the manner in which the conventional substrate cleaning apparatus operates. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing a polishing apparatus according to an embodiment of the present invention. The polishing apparatus comprises a polishing assembly  10  having a single polishing machine, a loading/unloading unit  12 , two feeding machines  14   a,    14   b,  a substrate cleaning apparatus  16  for primary cleaning, two substrate cleaning apparatuses  18   a,    18   b  for secondary cleaning, and a reversing machine  20 . The polishing assembly  10  and the substrate cleaning apparatus  16 ,  18   a,    18   b  are in the form of units separated by partitions, and are evacuated independently of each other so that their atmospheres will not interfere with each other. 
     As shown in FIG. 2A, the substrate cleaning apparatus  16  for primary cleaning comprises a plurality of upstanding substrate-holding rollers  30  openably and closably disposed around a substrate W. The substrate-holding rollers  30  has holding grooves  32  defined in upper ends thereof for holding the edge of the substrate W and rotating the substrate W upon rotation of the rollers  30 . As shown in FIG. 2B, a pair of cleaning devices  38  is disposed in sandwiching relationship to the substrate W. The cleaning devices  38  are rotatable about respective axes thereof and movable into and out of contact with the substrate W. Each of the cleaning devices  38  comprises a solid shaft  34  and a cleaning member  36  in the form of a tubular sponge, brush, or the like disposed on the surface of the solid shaft  34 . As shown in FIG. 2C, a cleaning tank  42  filled with a cleaning liquid  40  is disposed and a cleaning liquid nozzle  44  is disposed above the cleaning tank  42 . 
     As shown in FIG. 3, the shaft  34  has a shaft hole  46  extending axially substantially the full length of the shaft  34 . The shaft hole  46  is closed at an end that is coupled to a driver of the shaft  34  and open at an opposite end with an outward taper. To the shaft hole  46 , there are formed a plurality of cleaning liquid ejection ports  48  extending radially and having ends open at the outer surface of the shaft  34 . The cleaning liquid ejection ports  48  are spaced in the axial direction. The shaft  34  is made of a material having predetermined flexibility, slidability, and corrosion resistance, such as Teflon, for example. 
     The cleaning device  38  has both ends supported by a frame  50  extending parallel thereto. When the frame  50  is vertically moved by a support mechanism (not shown), the cleaning device  38  can be brought into and out of contact with the substrate W. A motor  52  and a pair of bevel gears  54   a,    54   b  for converting the direction of rotary output power of the motor  52  into a horizontal direction are disposed at the end of the frame  50 . The driven bevel gear  54   b  is fixed to a transmission shaft  58  that is supported by a bearing  56 . The transmission shaft  58  is coupled to the closed end of the shaft  34  of the cleaning device  38  by a coupling  68 , for rotating the cleaning device  38  upon rotation of the motor  52 . 
     A box-shaped shaft end holder  60  is attached to the other end of the frame  50 . The shaft end holder  60  houses therein a shaft end holding member  62  that is slidable toward the transmission shaft  58  but locked against rotation. The shaft end holding member  62  has a centering pusher  66  having a tapered portion on its distal end. The centering pusher  66  has a shank projecting from a hole defined in the shaft end holder  60 . A helical compression spring  64  is disposed between the shaft end holding member  62  and a rear wall of the shaft end holder  60  for normally urging the shaft end holding member  62  toward the transmission shaft  58 . The shaft end holding member  62  is pressed toward the transmission shaft  58  under the bias of the helical compression spring  64 , inserting the tapered portion of the centering pusher  66  into the shaft hole  46  in the shaft  34  for thereby centering the shaft  34  and supporting the cleaning device  38 . 
     The centering pusher  66  of the shaft end holding member  62  is made of a material which is highly hard and does not release metal ions, such as ceramics, for example. The shaft  34  is made of Teflon, for example, as described above. Therefore, the centering pusher  66  and the shaft  34  make up a sliding assembly in which they are well slidable against each other, and which is highly resistant to chemicals and free of metal contamination. 
     The shaft end holding member  62  has a cleaning liquid passage  70  that opens at the distal end of the centering pusher  66 . As shown in FIG. 4, a cleaning liquid supply joint  72  that communicates with the cleaning liquid passage  70  is attached to an upper end of the shaft end holding member  62 . A cleaning liquid that is supplied from a pipe or the like connected to the cleaning liquid supply joint  72  flows from the cleaning liquid passage  70  into the shaft hole  46  in the shaft  34  of the cleaning device  38 , and is ejected from the cleaning liquid ejection ports  48 . The cleaning liquid supply joint  72  is flexible so as not to block axial movement of the shaft end holding member  62 . The cleaning device  38  can be moved toward the shaft end holding member  62  and detached from the coupling  68  for easy replacement. 
     As shown in FIG. 5, the polishing assembly  10  comprises a polishing table  82  with a cloth (polishing cloth)  80  attached to an upper surface thereof, a top ring  84  for holding and pressing a semiconductor wafer (substrate) W against the polishing table  82 , and an abrasive liquid nozzle  86  for supplying an abrasive liquid Q between the cloth  80  and the substrate W. 
     As shown in FIG. 6, each of the substrate cleaning apparatus  18   a,    18   b  for secondary cleaning comprises a cleaning machine of the high-speed-rotation type having a turntable  92  comprising radial arms  90  mounted on the upper end of a rotatable shaft for gripping the substrate W. The cleaning machine is rotatable at a high speed ranging from 1500 to 5000 r.p.m. Each of the substrate cleaning apparatus  18   a,    18   b  has a swing arm  96  having a cleaning liquid nozzle  94  for supplying a cleaning liquid that is ultrasonically vibrated onto the upper surface of the substrate W. Each of the substrate cleaning apparatus  18   a,    18   b  also has a nozzle  98  for supplying an inactive gas for increasing the process performance and shortening the tact time. 
     Operation of the polishing apparatus shown in FIG. 1 will be described below. The substrate W which is supplied from the loading/unloading unit  12  via the reversing machine  20  to the polishing assembly  10  is supplied with the abrasive liquid Q from the abrasive liquid nozzle  86 . At the same time, the polishing table  82  and the top ring  84  are rotated, and the substrate W is normally polished by being pressed against the cloth  80 . Thereafter, pure water is used as an abrasive liquid to polish the substrate W with water under a pressure lower than the pressure in the normal polishing stage and/or at a speed lower than the speed in the normal polishing stage. In the water polishing stage, small scratches produced on the polished surface of the substrate W in the normal polishing stage are reduced, and at the same time a polishing residue and abrasive particles that remain on the polished surface are removed. Instead of the water polishing stage, or between the normal polishing stage and the water polishing stage, the substrate W may be cleaned with an abrasive liquid containing abrasive particles of smaller diameter than those used in the normal polishing stage. 
     The polished substrate W is fed via a substrate transfer table  22  to the substrate cleaning apparatus  16  for primary cleaning by the feeding machines  14   a,    14   b,  and held by the rollers  30  of the substrate cleaning apparatus  16 . The rollers  30  are then rotated to rotate the substrate W, while at the same time the cleaning devices  38  are moved from standby positions to cleaning positions. In the cleaning position, the motors  52  are energized to rotate the cleaning devices  38 , and the cleaning members  36  are rubbed against the face and back of the substrate W to scrub the substrate W (primary cleaning). 
     The cleaning liquid is supplied from a cleaning liquid source under a predetermined pressure via the cleaning liquid supply joint  72  into the cleaning liquid passage  70  in the shaft end holding member  62 , flows from the tip end of the centering pusher  66  into the shaft hole  46  in the shaft  34 , and is ejected from the cleaning liquid ejection ports  48 . The cleaning liquid enters into the cleaning members  36  and oozes out of its surface and is supplied to the surface to be cleaned of the substrate W. Since the cleaning liquid is supplied to only the region of the surface of the substrate W which needs and effectively uses the cleaning liquid, the substrate W can efficiently cleaned. For example, the same cleaning effect can be achieved even if the amount of cleaning liquid is used from 30 to 50 percent smaller than the amount of cleaning liquid that has heretofore been used. The cleaning members  36  are prevented from being contaminated because the cleaning liquid that oozes out of the cleaning members  36  steadily removes contaminants attached to the cleaning members  36 . 
     Part of the cleaning liquid supplied to each of the cleaning devices  38  flows out of the gap between the tapers between the centering pusher  66  of the shaft end holding member  62  and the shaft  34 , thus providing a fluid-lubricated bearing that is lubricated by the cleaning liquid, so that the cleaning device  38  can stably be supported by a simple structure without producing contaminants. Insofar as the pressure in the cleaning liquid in the shaft hole  46  is higher than the external pressure, no particles go into the cleaning liquid, and hence the cleaning liquid is not contaminated. Because the shaft  34  is made of Teflon and the centering pusher  66  of the shaft end holding member  62  is made of ceramics, there is provided a sliding assembly in which they are well slidable against each other, and which is highly resistant to chemicals and free of metal contamination. 
     After the substrate W has been scrubbed (primary cleaning), the cleaning devices  38  are retracted to the retracted positions where the cleaning liquid is ejected from the cleaning liquid nozzle  44  to the cleaning device  38  and the cleaning device  38  is simultaneously rotated to clean the cleaning member  36 , regularly or if necessary. Since the cleaning device  38  is not dipped in the cleaning liquid, the cleaning device  38  is prevented from being contaminated by contact with the cleaning liquid which would otherwise be contaminated. At this time, the cleaning liquid may be introduced from the shaft end holding member  62  into the shaft hole  46  in the shaft  34  and ejected from the cleaning liquid ejection ports  48  for increased cleaning efficiency. 
     After the primary cleaning, the substrate W is supplied with pure water or the like, and then delivered to the substrate cleaning apparatus  18   a  or  18   b  for secondary cleaning. In the substrate cleaning apparatus  18   a  or  18   b,  the substrate W is gripped by the arms  90  of the turntable  92 , and rotated at a low speed ranging from about 100 to 500 r.p.m. At the same time, the swing arm  96  is angularly moved over the entire surface of the substrate W and ultrasonically vibrated pure water is supplied from the cleaning liquid nozzle  94  on the distal end of the swing arm  96  to clean the surface of the substrate W (secondary cleaning). The supply of the pure water is stopped, and the swing arm  96  is moved to a standby position, after which the rotational speed of the substrate W is changed to a higher rotational speed ranging from 1500 to 5000 min −1 . While a clean inactive gas is being supplied, if necessary, the substrate W is dried. The substrate W which has been cleaned and dried is returned to the loading/unloading unit  12  by clean hands of the feeding machines  14   a,    14   b.    
     FIGS. 7 and 8 show a substrate cleaning apparatus according to another embodiment of the present invention. The substrate cleaning apparatus according to the other embodiment differs from the substrate cleaning apparatus according to the previous embodiment as follows: 
     A box-shaped shaft end holder  160  which is open on one side is attached to the other end of the frame  50 . The shaft end holder  160  houses therein a shaft end holding member  162  that is slidable toward the transmission shaft  58  but locked against rotation. A helical compression spring  164  is disposed between the shaft end holding member  162  and a rear wall of the shaft end holder  160  for normally urging the shaft end holding member  162  toward the transmission shaft  58 . The shaft end holding member  162  houses therein a tube holder  174  with its ends fixed in position. The tube holder  174  holds a tube  172  that is bent at a right angle and extends from the cleaning liquid supply joint  72 . A centering pusher  166  is rotatably supported on a shaft of the tube holder  174  by a pair of roller bearings  176  within the shaft end holding member  162 . The centering pusher  166  has a shank fitted in a large-diameter hole in the end of the shaft hole  46  in the shaft  34 . The centering pusher  166  and the shaft end holding member  162  are pushed toward the transmission shaft  58  by the helical compression spring  164 , the shank of the centering pusher  166  fits in the large-diameter hole in the end of the shaft hole  46  in the shaft  34  thereby to support the cleaning device  38 . When the motor  52  is energized to rotate the cleaning device  38 , the centering pusher  166  is rotated in unison with the shaft  34  while being supported by the roller bearings  176 . 
     The shaft end holding member  162  has the cleaning liquid passage  70  that opens at the distal end of the centering pusher  166 . The tube  172  extends in the tube holder  174  to the open end of the cleaning liquid passage  70 . 
     In the substrate cleaning apparatus according to the other embodiment, the cleaning liquid flows from a cleaning liquid source under a predetermined pressure via the cleaning liquid supply joint  72  and the tube  172  into the shaft hole  46  in the shaft  34 . Part of the cleaning liquid supplied to the cleaning device  38  flows out of a gap  170  between the cleaning liquid passage  70  in the centering pusher  166  and the tube  172 , thus providing a fluid-lubricated bearing that is lubricated by the cleaning liquid, so that the cleaning device  38  can stably be supported by a simple structure without producing contaminants. 
     With the substrate cleaning apparatus according to the other embodiment, the cleaning liquid is introduced into the roller bearings  176  disposed in the shaft end holding member  162 , thus providing a fluid-lubricated bearing that is lubricated by the cleaning liquid. Since the centering pusher  166  is rotatably supported by the roller bearings  176 , particles are prevented from being produced which would otherwise occur due to sliding movement between the centering pusher  166  and the cleaning device  38 . 
     The roller bearings  176  should preferably be made of a material which does not release metal ions into the cleaning liquid and etching liquids and does not produce particles. For example, the roller bearings  176  may comprise ceramics bearings, and may be made of ceramics, Teflon, or the like. Therefore, metal contamination and particles are prevented from being produced by the roller bearings  176 . 
     According to the present invention, as described above, since the cleaning liquid oozes out of the cleaning member and is supplied to the surface to be cleaned of the substrate so as to concentrate on a region to be cleaned, the substrate is cleaned without wasting the cleaning liquid. Because the cleaning member itself is cleaned steadily by the cleaning liquid passing through the cleaning member, the substrate is prevented from being contaminated by the cleaning member which would otherwise be contaminated. Furthermore, inasmuch as the cleaning device is supported by the fluid-lubricated bearing which employs the cleaning liquid as the lubricating fluid, the diameter of the cleaning device may be reduced. Thus, a replacement speed for switching from a chemical to pure water or from pure water to a chemical can be increased. For example, when pure water used to prevent the cleaning device from becoming dry is switched to a chemical for etching or cleaning the substrate, the pure water in the cleaning device is quickly replaced with the chemical for stable performance. Moreover, a stable contamination-free support structure of simple arrangement is achieved, providing a substrate cleaning apparatus which is stable and operable at a low cost.

Technology Category: 5