Abstract:
A substrate processing method of the present invention prevents the reattachment of particles to substrates, such as semiconductor wafers, when processing and cleaning the substrates by immersing the substrates held in a vertical attitude in a processing liquid and a cleaning liquid. After processing the substrates in the processing liquid, they are drawn out from the processing liquid. Then, lower parts of the processed substrates are immersed in the cleaning liquid and temporarily kept stationary in the cleaning liquid. Alternatively, the cleaning liquid is sprayed onto the lower parts of the processed substrates. After a predetermined time, the substrates are immersed entirely in the cleaning liquid.

Description:
This is a divisional of application Ser. No. 09/185,413 filed Nov. 3, 1998, now U.S. Pat. No. 6,199,564 which application is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a substrate processing method and a substrate processing apparatus. More specifically, the present invention relates to a substrate processing method and a substrate processing apparatus for processing objects, such as semiconductor wafers or LCD substrates, with a processing liquid and cleaning the objects with a cleaning liquid. 
     2. Description of the Related Art 
     Generally, a semiconductor wafer processing apparatus has prevalently been used in fabricating semiconductor devices to remove particles, organic substances, metallic contaminants and/or an oxide film from objects, such as semiconductor wafers, (hereinafter referred to as “wafers”) by sequentially conveying the wafers through processing tanks containing processing liquids (chemical liquids) and cleaning tanks containing cleaning liquids (rinsing liquids) to immerse the wafers in the processing liquids and the cleaning liquids and to dry the wafers. 
     A wafer processing apparatus of this kind comprises processing tanks respectively containing processing liquids (chemical liquids), such as HF+H 2 O (a hydrogen fluoride solution (hereinafter referred to as “HF”)), NH 4 OH+H 2 O 2 +H 2 O (an ammonia peroxide solution) and HCl+H 2 O 2 +H 2 O (a hydrochloric acid peroxide solution), cleaning tanks respectively containing cleaning liquids, such as rinsing liquids (pure water), wafer holders, such as wafer boats, for holding a plurality of wafers, for example, fifty wafers, in a vertical attitude, and lifting devices for immersing the wafer boat holding wafers in, and taking out the same from the processing tanks and the cleaning tanks. 
     The processing tanks, the cleaning tanks and the wafer boats are placed in a downflow atmosphere in which a clean gas, for example, clean air flows down to handle the wafers or the like in a clean atmosphere. 
     Generally, the wafers or the like made of silicon are provided on their surfaces with an oxide film serving as an insulating film, and a predetermined pattern or the like. When a silicon wafer provided on its surface with an oxide film is processed with a processing liquid, the processing liquid remains on the surface of the silicon wafer because the oxide film is hydrophilic while silicon is hydrophobic. Experiments were conducted to verify this fact. In the experiments, a wafer boat B holding coated silicon wafers Wa coated with an oxide film and bare silicon wafers Wb as shown in FIG. 18A was immersed in a processing liquid, such as HF, contained in a processing tank for processing, and then the wafer boat was taken out of the processing liquid. At this stage, the processing liquid (HF) remained on the surfaces of the coated silicon wafers Wa as shown in FIG.  18 B. When the coated silicon wafers Wa and the bear silicon wafers Wb were immersed in a processing liquid or a cleaning liquid for the subsequent process, particles P contained in the processing liquid (HF) remaining on the coated silicon wafers Wa adhered to the surfaces of the coated silicon wafers Wa and therefrom to the surfaces of the adjacent bare silicon wafers Wb as shown in FIG.  18 B. As is obvious from the results of the experiments, particles adhere to the surfaces of wafers when silicon wafers coated with an oxide film are processed with a processing liquid and cleaned with a cleaning liquid, and those particles reduces the yield of products. 
     When etching oxide films formed on the surfaces of wafers W with a processing liquid, such as HF, the wafers W are immersed in the processing liquid (HF) contained in a processing tank, the wafers W are taken out of the processing tank, and the wafers W are carried to a cleaning tank. While the wafers W are thus being carried to the cleaning tank, the processing liquid (HF) remaining on the wafers W flows downward along the surfaces of the wafers W held in a vertical attitude and, consequently, the oxide films coating the wafers W are exposed partly as shown in FIGS. 19A and 19B. Since the etching of the exposed parts of the oxide films is stopped, while the etching of the coated parts of the oxide films continues, the oxide films cannot uniformly be etched, which reduces the yield of products. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to prevent the reattachment of particles to wafers or substrates by removing dust contained in a processing liquid remaining on the surfaces of the substrates after the substrates have been processed with the processing liquid by recleaning the substrates when processing the substrates by immersing the same in the processing liquid and cleaning the substrates by immersing the same in a cleaning liquid, in order that the yield of products can be improved. 
     Another object of the present invention is to prevent the downward flow of a processing liquid remaining on substrates along the surfaces of the substrates after the substrates have been processed with the processing liquid in order that etching uniformity and the yield of products can be improved. 
     With the foregoing object in view, according to an aspect of the present invention, a substrate processing method, which processes substrates by immersing the substrates held in a vertical attitude in a processing liquid and a cleaning liquid, is characterized in cleaning lower parts of the substrates at at least one of the time when the substrates are immersed in one of the processing liquid and the cleaning liquid contained in a tank and the time when the substrates have been exposed to one of the processing liquid and the cleaning liquid contained in the tank. The term “subjected to one of the processing liquid and the cleaning liquid” refers to either an act of pulling out the substrates from the processing liquid or the cleaning liquid contained in the tank or an act of draining the processing liquid or the cleaning liquid from the tank. Immersing the substrates in the processing liquid or the cleaning liquid signifies either an act of immersing the substrates in the processing liquid or the cleaning liquid contained in the tank or an act of wetting the substrates with the processing liquid or the cleaning liquid. 
     In the substrate processing method of the present invention, the lower parts of the substrates can be cleaned by ejecting a cleaning liquid on the lower parts of the substrates or by immersing the lower parts of the substrates in a cleaning liquid contained in a tank for a predetermined time. The lower parts of the substrates may be immersed in and kept stationary in the cleaning liquid. When thus immersing the lower parts of the substrates in the cleaning liquid, it is preferable that the cleaning liquid is supplied to the tank so that the cleaning liquid overflows the tank. 
     The substrates are supposed to be made of a hydrophobic material to have surfaces coated with hydrophilic films. Hydrophilic substrates are, for example, bare silicon substrates and metal substrates. Hydrophilic films are, for example, oxide films or insulating films. 
     According to another aspect of the present invention, a substrate processing method, which brings substrates held in a vertical attitude into a processing liquid and a cleaning liquid to process the substrates, processes the substrates in an atmosphere in which a clean gas flows down, and reduces or stops the flow of the clean gas when carrying the substrates processed by the processing liquid to the next processing unit for processing the substrates with another processing liquid or the cleaning liquid. 
     According to a further aspect of the present invention, a substrate processing method, which brings substrates held in a vertical attitude into a processing liquid and a cleaning liquid to process the substrates, blows a clean gas upward from below the substrates against the substrates when carrying the substrates processed with the processing liquid to the next processing unit for processing the substrates with another processing liquid or the cleaning liquid. The clean gas may be, for example, clean air or clean nitrogen gas. 
     According to a still further aspect of the present invention, a substrate processing apparatus, which carries out a substrate processing method of the present invention, comprises a processing tank containing a processing liquid in which substrates are to be immersed, a cleaning tank containing a cleaning liquid in which the substrates are to be immersed, substrate holding means for holding the substrates in a vertical attitude, lifting means for vertically moving the substrate holding means holding the substrates relative to the processing tanks or the cleaning tanks, in which liquid ejecting means for ejecting a processing liquid or a cleaning liquid toward lower parts of the substrates is disposed above the processing tanks or above the cleaning tanks. 
     According to another aspect of the present invention, a substrate processing apparatus, which carries out a substrate processing method of the present invention, comprises a processing tank containing a processing liquid in which substrates are to be immersed, a cleaning tank containing a cleaning liquid in which the substrates are to be immersed, substrate holding means for holding the substrates in a vertical attitude, lifting means for vertically moving the substrate holding means holding the substrates relative to the processing tanks or the cleaning tank, in which a control means controls the lifting means so that the lifting means is stopped when lowering the substrate holding means holding the substrates to immerse the substrates in the cleaning liquid contained in the cleaning tank at a position where lower parts of the substrates are immersed in the cleaning liquid. 
     According to a further aspect of the present invention, a substrate processing apparatus, which carries out a substrate processing method of the present invention, comprises a processing tank in which substrates are brought into contact with a processing liquid, a cleaning tank in which the substrates are brought into contact with a cleaning liquid, substrate holding means for holding the substrates in a vertical attitude, and lifting means for vertically moving the substrate holding means holding the substrates relative to the processing tank or the cleaning tanks, in which the processing tanks are disposed in a downflow atmosphere in which a clean gas flows down, and a control means stops or reduces the downflow of the clean gas creating the atmosphere. Preferably, the control means stops or reduces the flow of the clean gas when the substrates are carried from the processing tank to another processing tank or the cleaning tank. 
     According to a still further aspect of the present invention, a substrate processing apparatus, which carries out a substrate processing method of the present invention, comprises a processing tank in which substrates are brought into contact with a processing liquid, a cleaning tank in which the substrates are brought into contact with a cleaning liquid, substrate holding means for holding the substrates in a vertical attitude, and lifting means for vertically moving the substrate holding means holding the substrates relative to the processing tank or the cleaning tank, in which a clean gas ejecting means ejects a clean gas upward from below the substrates when the substrates processed with the processing liquid are carried to another processing tank or the cleaning tank. The lifting means may include a carrying means for carrying the substrates between the processing tank and the cleaning tank. The substrate processing apparatus may further comprise, besides the lifting means, a carrying means for carrying the substrates between the processing tank and the cleaning tank. Although the cleaning tank may be of any type provided that the same are able to contain cleaning liquids, it is preferable that the cleaning tanks are overflow tanks that allow the overflow of the cleaning liquids. 
     In the present invention, the lower part of the substrate is a part having a region extending between the lower edge of the substrate and a region near a circuit region in which semiconductor devices are built. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic plan view of a substrate processing system including a substrate processing apparatus according to the present invention; 
     FIG. 2 is a schematic side view of a substrate processing apparatus in a first embodiment of the present invention; 
     FIG. 3 is a rear end view of the substrate processing apparatus of FIG. 2; 
     FIG. 4 is a vertical sectional view of the substrate processing apparatus of FIG. 2; 
     FIG. 5 is a vertical sectional view of an essential part of the substrate processing apparatus of FIG. 2; 
     FIG. 6 is a schematic front view of a wafer, in which a shaded region is a lower part of the wafer to be cleaned; 
     FIG. 7 is a schematic vertical sectional view of an essential part of a substrate processing apparatus in a second embodiment of the present invention; 
     FIG. 8 is a schematic vertical sectional view of an essential part of a substrate processing apparatus in a third embodiment of the present invention; 
     FIG. 9 is a schematic vertical sectional view of an essential part of a substrate processing apparatus in a fourth embodiment of the present invention; 
     FIGS. 10A and 10B are a side view and a front view, respectively, of a clean gas ejecting device in an arrangement different from that in the same shown in FIG. 9; 
     FIG. 11 is a schematic perspective view of a substrate carrying device in a modification of a substrate carrying device included in the substrate processing apparatus of FIG. 9; 
     FIG. 12 is a diagrammatic view explaining an experimental procedure for examining the number of particles adhering to a wafer processed by the substrate processing apparatus in the second embodiment; 
     FIG. 13 is a plan view showing the adhesion of particles to a wafer in a comparative example before the wafer is cleaned; 
     FIG. 14 is a plan view showing the adhesion of particles to the wafer of FIG. 13 after the wafer has been cleaned; 
     FIG. 15 is a plan view showing the adhesion of particles to a wafer before the wafer is cleaned; 
     FIG. 16 is a plan view showing the adhesion of particles to the wafer of FIG. 15 after the wafer has been cleaned; 
     FIG. 17 is a graph showing the effect on etching uniformity of blowing N 2  gas upward from below wafers after processing the wafers with a chemical liquid; 
     FIG. 18A is a schematic side view of an arrangement of silicon wafers coated with an oxide film and bare silicon wafers for experiments for examining the adhesion of a processing liquid and particles to the silicon wafers; 
     FIG. 18B is a schematic sectional view of wafers, a processing liquid remaining on one of the wafers and particles contained in the processing liquid remaining on the wafer; 
     FIG. 18C is a schematic sectional view of wafers and particles adhering to the wafers; 
     FIG. 19A is a schematic sectional view of wafers processed with a chemical liquid and wetted with the chemical liquid; and 
     FIG. 19B is a schematic front view indicating a downward flow of a chemical liquid remaining on a wafer. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be described hereafter with reference to the accompanying drawings as applied to semiconductor wafer processing systems. 
     FIG. 1 shows a substrate processing system including a wafer processing apparatus according to the present invention by way of example. The wafer processing system comprises, as principal components, a carrying station  2  for carrying a carrier containing semiconductor wafers W in a horizontal position, a processing station  3  for processing wafers W with processing liquids (chemical liquids) and cleaning liquids and drying the wafers W, and a transfer station  4  interposed between the wafer carrying station  2  and the processing station  3  to transfer the wafers W, to adjust the locations of the wafers W, to change the attitude of the wafers W, and to adjust intervals between the wafers W. 
     The carrying station  2  is disposed at one end of the wafer processing system and has a carrier receiving station  5   a , a carrier delivery station  5   b  disposed beside the carrier receiving station  5   a , and a wafer handling station  6 . The carrier receiving station  5   a  and the wafer handling station  6  are connected by a carrying mechanism, not shown to carry the carrier  1  from the carrier receiving station  5   a  to the wafer handling station  6 . 
     Carrier lifters, not shown, are installed at the carrier delivery station  5   b  and the wafer handling station  6  to transfer empty carriers  1  to a carrier storage station, not shown, above the carrying station  2  and to receive empty carriers  1  from the carrier storage station. A carrier carrying robot, not shown, capable of moving in horizontal directions (X-directions and Y-directions) and vertical directions (Z-directions) is installed in the carrier storage station. The carrier carrying robot arranges empty carriers  1  carried from the wafer handling station in rows and carries the empty carriers  1  to the carrier delivery station  5   b . Carriers  1  containing wafers W, as well as empty carriers  1 , can be stored in the carrier storage station. 
     The carrier  1  has a case  1   a  having an opening, and side walls provided in their inner surfaces with holding grooves, not shown, for holding a plurality of wafers W, such as twenty-five wafers W, in a horizontal attitude, and a lid  1   b  for covering the opening of the case  1   a.  The lid  1   b  is opened and closed by operating a lid locking device, not shown, incorporated into the lid  1   b  by a lid operating device  8 . 
     The wafer handling station  6  has an opening opening into the transfer station  4 , and the lid operating device  8  is disposed in the opening. The lid operating device  8  opens and closes the lid  1   b . The lid operating device  8  removes the lid  1   b  of a carrier  1  containing unprocessed wafers W and delivered to the wafer handling station  6  so that the unprocessed wafers W can be taken out. After all unprocessed wafers W have been taken out of the carrier  1 , the lid operating device  8  puts the lid  1   b  on the case  1   a  of the carrier  1  to close the opening of the case  1   a . The lid operating device  8  removes the lid  1   b  of an empty carrier  1  transferred from the carrier storage station to the wafer handling station  6  to open the opening of the case  1   a  of the case  1  of the empty carrier  1 . After the empty carrier  1  has been fully loaded with wafers W, the lid operating device  8  puts the lid  1   b  on the case  1   a  of the frilly loaded carrier  1 . A mapping sensor  9  for counting the number of wafers W loaded into a carrier  1  is disposed near an opening in the wafer handling station  6 . 
     The transfer station  4  comprises a wafer transfer device  10  capable of holding a plurality of wafers W, such as twenty-five wafers, in a horizontal attitude and of taking the wafers W from a carrier  1  placed in the wafer handling station  6  and delivering the same to a carrier  1  placed in the wafer handling station  6 , a pitch changing device, i.e., a pitch adjusting means, not shown, capable of holding a plurality of wafers W, such as fifty-two wafers, in a vertical attitude, an attitude changing device  12  capable of changing the attitude of a plurality of wafers W, such as twenty-five wafers, between a horizontal attitude and a vertical attitude, and a notch aligner  13  capable of detecting notches formed in wafers W set in a vertical attitude and of adjusting the attitudes of the wafers W. A carrying passage  14  is extended between the processing station  3  and the transfer station  4 . A wafer carrying chuck  15 , i.e., a wafer carrying means, moves along the carrying passage  14 . 
     The wafer transfer device  10  includes a first aim  10   a  and a second arm  10   b , i.e., holding means, capable of taking a plurality of wafers W out of a carrier  1  placed in the wafer handling station  6 , carrying the wafers W and putting a plurality of wafers W into a carrier  1 . The two arms  10   a  and  10   b  are mounted on a table  11  capable of moving in horizontal directions (X-directions, Y-directions) and vertical directions (Z-directions) and of turning in θ-directions. The arms  10   a  and  10   b  operate individually to hold wafers W in a horizontal attitude and to transfer wafers W between a carrier  1  placed in the wafer handling station  6  and the attitude changing device  12 . The first arm  10   a  is able to hold unprocessed wafers W, while the second arm  10   b  is holding processed wafers W. 
     A plurality of processing units  16  to  19  are arranged in a row in the processing station  3 . Each of the processing units  16  to  19  is provided with a wafer processing apparatus of the present invention for removing particles and organic substances adhering to wafers W or removing metal or oxide films from wafers W. The wafer carrying chuck  15  is capable of moving in horizontal directions (X-directions, Y-directions) and vertical directions (Z-directions) and of turning in θ-directions on the carrying passage  14 . The first processing unit  16  includes a chuck cleaning device  16   a . The chuck cleaning device  16   a  need not necessarily be included in the first processing unit  16 ; the chuck cleaning device  16   a  may be disposed outside the first processing unit  16  or the other processing units  17 ,  18  and  19 . 
     Wafer processing apparatus in preferred embodiments of the present invention will be described with reference to FIGS. 2 to  8 . 
     First Embodiment 
     FIG. 2 is a schematic side view of a wafer processing apparatus in a first embodiment of the present invention installed in the first processing unit  16 , FIG. 3 shows a rear end view of the wafer processing apparatus of FIG.  2  and FIG. 4 shows a vertical sectional view of an essential part of the wafer processing apparatus of FIG.  2 . 
     Referring to FIG. 2, a wafer processing apparatus  20  has a first vessel  22   a  having the shape of, for example, a rectangular tube and housing a processing tank  21  containing a processing liquid, such as HF (chemical liquid), in which wafers W are immersed, a second vessel  22   b  disposed contiguously with the first vessel  22   a , having the shape of, for example, a rectangular tube and housing a cleaning tank  21 A containing a cleaning liquid, such as a rinsing liquid (pure water), and a third vessel  22   c  disposed contiguously with the first vessel  22   a , as also shown in FIG. 3, having the shape of, for example, a rectangular tube and housing a chuck cleaning device  16   a . A space between the plurality of vessels  22   a ,  22   b  and  22   c , and a filter unit  70 , which will be described later, is sealed and isolated from the external atmosphere by outer walls of the wafer processing apparatus  20 . 
     As shown in FIGS. 3 and 4, the first vessel  22   a  and the second vessel  22   b  are substantially the same in construction, and hence only the first vessel  22   a  will be described. A processing chamber  23  is defined by a bottom plate  23   a  in the first vessel  22   a  and the processing tank  21  is placed in the processing chamber  23 . A side suction passage  24  and a bottom suction passage  25  connected to the side suction passage  24  are formed in the first vessel  22   a . The filter unit  70  for supplying a clean gas, such as clean air, into the processing chamber  23  is disposed above the processing chamber  23  of the first vessel  22   a . The filter unit  70  is provided with a motor-driven fan, not shown. 
     The side suction passage  24  is defined by a front wall  26  of the first vessel  22   a , and a first partition wall  28  consisting of an inner upright wall  27  extending upward from the bottom plate  23   a  defining the processing chamber  23  and a wall continuous with and extending downward from the upright wall  27 . The bottom suction passage  25  is defined by a bottom wall  30  of the first vessel  22   a , and a second partition wall  29  substantially horizontally extending from the lower end of the first partition wall  28 . 
     The bottom wall  30  of the first vessel  22   a  is provided with an outlet opening  33  and a drain port  34 , i.e., draining opening. A suction pipe  32  has one end connected to the outlet opening  33  and the other end connected to a vacuum pump  31 , i.e., suction means. A gas-liquid separating wall  35  is formed on the inner surface of the bottom wall  30  so as to surround the outlet opening  33  to prevent liquids including a chemical liquid, such as HF, and contained in air to be discharged through the outlet opening  33  from flowing into the suction pipe  32 . The position of the outlet opening  33  on the bottom wall  30  is optional. A drain pipe  37  provided with a drain valve  36  is connected to the drain port  34  to drain waste liquids collected on the bottom wall  30  of the first vessel  22   a.    
     An adjustable flow control plate  38  is disposed above the open upper end of the side suction passage  24  so as to cover the side suction passage  24  and an upper end part of the upright wall  27 , A space between the upright wall  27  and the flow control plate  28  is adjustable. As shown in FIG. 4, the flow control plate  38  has a horizontal part  38   a  covering the opening of the side suction passage  24 , and a vertical part  38   b  extending vertically downward from an end of the horizontal part  38   a  on the side of the processing tank. A bolt  39  is screwed through a slot, not shown, in the horizontal part  38   a  in a threaded hole formed in a bracket  40  projecting inward from the front wall  26  of the vessel  22   a  to fasten the flow control plate  28  at an appropriate position to the bracket  40  so that an appropriate space is secured between the vertical part  38   b  of the flow control plate  38  and the upright wall  27 . 
     Thus, the width of a space between the vertical part  38   b  of the flow control plate  38  and the upright wall  27  can be adjusted by adjusting the position of the horizontal part  38   a  of the flow control plate  38  on the bracket  40  to adjust the flow rate of air flowing through the processing tank  21  and the processing chamber  23  optionally. The flow rate of air flowing through the side suction passage  24  can be adjusted to the flow rate of clean air supplied through the filter unit  70  into the first vessel  22   a . The respective positions of the flow control plates  38  of the vessels  22   a ,  22   b  and  22   c  can be adjusted so that the quantity of clean air supplied into the respective processing chambers  23  of the vessels  22   a ,  22   b  and  22   c  is equal to the sum of the quantities of air that flows through the respective side suction passages  24  of the vessels  22   a ,  22   b  and  22   c.    
     Escape of the gas supplied into the processing chamber  23  through passages other than a discharge system can be prevented by balancing the quantity of clean air supplied into the processing chamber  23  and that of air discharged from the processing chamber  23 . 
     The pressures in the processing chambers  23  of the vessels  22   a ,  22   b  and  22   c  can be adjusted so that the pressure in the processing chamber  23  in which the processing tank  21  containing a chemical liquid, such as HF, is placed is lower than that in the processing chamber  23  in which the processing tank  21  containing a liquid other than chemical liquids is placed to prevent an atmosphere of the chemical liquid from flowing into the vessels in which any chemical liquids are not used. 
     Although the position of the flow control plate  38  is adjusted manually in this embodiment, the position of the flow control plate  38  may be adjusted by moving the flow control plate  38  by a driving device, such as a cylinder actuator or a motor. 
     A discharge pressure sensing device  41  is disposed between the upright wall  27  and the flow control plate  38  to measure the pressure of air discharged from the processing chamber  23 . As shown in FIG. 4, the discharge pressure sensing device  41  has a pipe  44   a  supported by a pipe fitting  43  hermetically inserted in holes formed in the front wall  26  and the upright wall  27  at corresponding positions, and a pressure gage  44   b  disposed outside the vessel  22   a  and connected to the pipe  44   a . The pipe  44   a  is exposed to air in the space between the upright wall  27  and the vertical part  38   b  of the flow control plate  38 . 
     A lower chamber  45  is defined in the lower part of the processing chamber  23  by the bottom plate  23   a  of the processing chamber  23 , side walls  26   a  adjacent to the front wall  26 , a back wall  26   b  and the upright wall  27 . The volume of the lower chamber  45  is not less than that of processing liquid, such as HF, or pure water contained in the processing tank  21 . Since the volume of the lower chamber  45  is not less than that volume of the processing liquid or the volume contained in the processing tank  21 , the processing liquid and the like can be stored in the lower chamber  45  to secure safety even if, by any chance, the processing tank  21  should be broken and the processing liquid and the like should spill. The bottom plate  23   a  of the processing chamber  23  is sloped in a decline toward the back wall  26   b . A drain port  46  is formed in the back wall  26   b  near the joint of the bottom plate  23   a  and the back wall  26   b , and a drain pipe  47  provided with a drain valve, not shown, is connected to the drain port  46 . 
     A machine chamber  48  having an open back end is defined by the bottom plate  23   a  of the processing chamber  23 , the first partition wall  28  and the second partition wall  29 . A processing liquid handling system for supplying and draining the processing liquid is installed in the machine chamber  48  to secure a neat space  53  behind the wafer processing apparatus. The processing liquid handling system includes a circulation pump  49 , a damper  50 , a heater  51 , and piping system  52  connecting the components of the processing liquid handling system. Only the piping system  52  is arranged in the space  53  for the effective use of the space. 
     Measuring instruments and operating devices, not shown, are disposed in a space  54  behind an upper part of the front wall  26  of the vessel  22   a  ( 22   b ). A cover  55  is attached removably to the upper part of the front wall  26  to cover the front open end  54   a  of the space  54 . The back wall  26   b  of the vessel  22   a  is provided with an observation hole  56  to enable the visual observation of the interior of the vessel  22   a.    
     When the first vessel  22   a , the second vessel  22   b  and the third vessel  22   c  are joined in a row so that the vessels  22   a ,  22   b  and  22   c  communicate with each other by means of at least either the side suction passages  24  or the bottom suction passages  25 , air flowing through the vessels  22   a ,  22   b  and  22   c  can be discharged outside through the outlet opening  33  of the first vessel  22   a . When processing wafers W for processing and cleaning, clean air supplied through the filter unit  70  into the processing tanks  21  and the processing chambers  23  of the wafer processing apparatus  20  is polluted with the chemical liquids and pure water scattered from the processing tanks  21 . Since the polluted air can be discharged outside through the side suction passages  24  and the bottom suction passages  25 , the accuracy of processes for processing and cleaning the wafers W can be improved. 
     The processing tank  21  has an inner tank  21   a  for receiving wafers W therein, and an outer tank  21   b  surrounding an open upper end part of the inner tank  21   a  and capable of storing the processing liquid overflowed the inner tank  21   a . A wafer boat  57 , i.e., a liftable holding means, capable of holding a plurality of wafers W in a vertical attitude is disposed in the inner tank  21   a . A plurality of wafers W, for example, fifty wafers W, are transferred between the wafer boat  57  and the wafer carrying chuck  15 . 
     As shown in FIG. 2, the wafer boat  57  comprises a pair of lower holding bars  57   a  on which lower parts of wafers W rest, and a pair of side holding bars  57   b  disposed above the lower holding bars  57   a  to hold the wafers W by their side parts. The wafer boat  57  is moved vertically by a lifting mechanism  80  shown in FIG. 4, comprising, for example, a ball-screw mechanism and a cylinder actuator and connected to the wafer boat  57 . The wafer boat  57  holding wafers W is lowered to immerse the wafers W in the processing liquid contained in the processing tank  21 , and is raised to pull the wafers W out of the processing liquid. The lifting mechanism  80  is controlled for a wafer boat moving operation by control signals provided by a lifting mechanism controller  81 . 
     Processing liquid ejecting pipes  58  (FIG. 2) are extended in a lower part of the interior of the inner tank  21   a  to supply the processing liquid into the inner tank  21   a . The inner tank  21   a  is provided in its bottom wall with a drain port  21   c . Drain pipes  59  each provided with a drain valve, not shown, are connected to the drain ports  21   c , respectively. The outer tank  21   b  is provided in its bottom wall with a drain port  21   d . A drain pipe  60  provided with a drain valve, not shown, has one end connected to the drain port  21   d  and the other end connected via a selector valve, now shown, to the piping system  52  included in the processing liquid handling system. The processing liquid overflowed the inner tank  21   a  can be returned through the drain port  21   d  of the outer tank  21   b  to the piping system  52  and can be circulated to use the same again for processing wafers W. 
     Referring to FIGS. 2 and 5, cleaning liquid ejecting pipes  58 A for supplying a cleaning liquid, such as pure water, into the cleaning tank  21 A are extended in a lower part of the interior of the cleaning tank  21 A placed in the second vessel  22   b . The cleaning liquid ejecting pipes  58 A are connected to a cleaning liquid source  63  via a first cleaning liquid supply pipe  62 . A pair of cleaning liquid spraying pipes  64  are disposed at positions above the cleaning tank  21 A and corresponding to opposite sides of the cleaning tank  21 A to spray lower parts of wafers W to be placed in the cleaning tank  21 A and held on a wafer boat  57  comprising a pair of lower holding bars  57   a  and a pair of upper holding bars  57   b , and the lower holding bars  57   a  with a cleaning liquid, such as pure water. The lower part of each wafer W is a part having a region extending between the lower edge of the wafer W and a region near a circuit region Wp in which semiconductor devices are built. In FIG. 6, a shaded part is the lower part of the wafer W. The cleaning liquid spraying pipes  64  are connected by second cleaning liquid supply pipes  65  to the cleaning liquid source  63 . The cleaning liquid can be supplied to either the cleaning liquid ejecting pipes  58 A or the cleaning liquid spraying pipes  64  or can be supplied simultaneously to the cleaning liquid ejecting pipes  58 A and the cleaning liquid spraying pipes  64 . 
     An on-off valve  67  is disposed between the selector valve  66  and the cleaning liquid source  63 . Each of the second cleaning liquid supply pipe  65  is connected through a restrictor  69  and an on-off valve  68  to the cleaning liquid spraying pipe  64 . The cleaning tank  21 A is provided in its bottom wall with a drain port  21   e , and a drain pipe  60   b  is connected through a drain valve  60   a  to the drain port  21   e . The wafer boat  57  similar to that used in the processing tank  21  is disposed in the cleaning tank  21 A and is moved vertically by a lifting mechanism, not shown, controlled by a lifting mechanism controller, not shown. 
     A cleaning liquid L, such as pure water, is sprayed on the lower holding bars  57   a  and the wafers W immersed in and processed with the chemical liquid, such as HF, contained in the processing tank  21  before immersing the thus processed wafers W in the cleaning liquid L contained in the cleaning tank  21 A to clear the wafers W of particles contained in the chemical liquid, i.e., the processing liquid, remaining on the surfaces of the lower parts of the wafer W. Thus, the processed wafers W are immersed for cleaning in the cleaning liquid L contained in the cleaning tank  21 A after removing particles contained in the chemical liquid (processing liquid) remaining on the surfaces of the lower parts of the wafer W. 
     In this embodiment, the cleaning liquid spraying pipes  64  are disposed at positions above the cleaning tank  21 A to clean the lower parts of the wafers W before immersing the wafers W in the cleaning liquid contained in the cleaning tank  21 A. However, the cleaning liquid spraying pipes  64  may be extended above the processing tank  21  to spray the cleaning liquid for cleaning on the lower parts of the wafers W and the lower holding bars  57   a  immediately after the wafers W and the lower holding bars  57   a  have been lifted out of the processing tank  21 . Cleaning liquid spraying pipes  64  may be extended above both the processing tank  21  and the cleaning tank  21 A, and the cleaning liquid may be sprayed on the wafers W and the lower holding bars  57   a  both immediately after the wafers W and the lower holding bars  57   a  have been lifted out of the processing tank  21  and before immersing the same in the cleaning liquid contained in the cleaning tank  21 A for the further perfect removal of particles adhering to the wafers W. 
     Second Embodiment 
     A wafer processing apparatus in a second embodiment of the present invention will be described with reference to FIG. 7 showing an essential part of the wafer processing apparatus in a schematic sectional view, in which parts like or corresponding to those of the first embodiment are designated by the same reference characters and the description thereof will be omitted. 
     The wafer processing apparatus in the second embodiment removes particles adhering to the lower parts of wafers W processed with a chemical liquid by a means different from that employed in the first embodiment. A wafer cleaning unit  20 A included in the wafer processing apparatus is not provided with any members corresponding to the cleaning liquid spraying pipes  64  of the first embodiment. A cleaning liquid ejecting pipes  58 A extended in the bottom of a cleaning tank  21 A is connected via a cleaning liquid supply pipe  62 A to a cleaning liquid source  63 . A wafer boat  57  having a pair of lower holding bars  57   a  and a pair of side holding bars  57   b  can be vertically moved by a lifting mechanism, not shown. The wafer processing apparatus in the second embodiment is the same in other respects as that in the first embodiment. 
     In the wafer processing apparatus  20 A, when lowering the wafer boat  57  holding wafers W immersed in and processed with a chemical liquid, such as HF, contained in the processing tank  21  to immerse the wafers W in a cleaning liquid L, such as pure water, contained in and overflowing the cleaning tank  21 A, the wafer boat  57  is stopped temporarily for a predetermined time, such as 0.5 sec, after the lower holding bars  57   a  and the lower parts of the wafers W have been immersed in the cleaning liquid L as shown in FIG. 7 by controlling the lifting mechanism (FIG.  4 ). Consequently, particles adhering to the lower parts of the wafers W are dispersed in the overflowing cleaning liquid L for quick cleaning. After thus removing the particles adhering to the lower parts of the wafers W, the wafers W are immersed in the cleaning liquid L contained in the cleaning tank  21 A for cleaning. Accordingly, the reattachment of the particles to the wafers W can be prevented. 
     Third Embodiment 
     A wafer processing apparatus in a third embodiment of the present invention will be described with reference FIG. 8 showing an essential part of the wafer processing apparatus in a schematic sectional view, in which parts like or corresponding to those of the first and the second embodiment are designated by the same reference characters and the description thereof will be omitted. 
     The wafer processing apparatus in the third embodiment is intended to prevent etching irregularity which is liable to occur when wafers W are processed with a chemical liquid and are cleaned with a cleaning liquid in a downflow atmosphere in which a clean gas, such as clean air, flows down. While wafers W processed with a chemical liquid are lifted out of a processing tank  21  and carried to another processing tank  21  or a cleaning tank  21 A, the chemical liquid, such as HF, remaining on the wafers W is forced to flow down along the surfaces of the wafers W by the agency of gravity and the downflow of the clean gas, such as clean air, so that the surfaces of the upper parts of the wafers W become dry whereas the lower parts of the same are wet. The third embodiment is designed to prevent etching irregularity attributable to such irregular wetting of the wafers W with the chemical liquid. 
     Referring to FIG. 8, a wafer processing unit  20 B included in the wafer processing apparatus in the third embodiment has a processing tank  21 , a filter unit  70  provided with a fan  71 , a motor  72  for driving the fan  71 , and a controller  73  for controlling the motor  72 . The configuration of a wafer cleaning unit included in the wafer processing apparatus and having a cleaning tank  21 A is substantially the same as that of the wafer processing unit  20 B. 
     When wafers W immersed in and processed with a chemical liquid, such as HF, contained in the processing tank  21  are lifted out of the processing tank  21  and are carried to another processing tank  21  or the cleaning tank  21 A, the controller  73  provides a control signal for reducing the operating speed of the motor  72  to reduce the downflow of clean air from a level indicated by the arrows of alternate long and short dash lines for a normal processing operation to a level indicated by the arrows of solid lines for a wafer carrying operation below the former level. Thus, the downward flow of the processing liquid, such as HF, remaining on the wafers W toward the lower parts of the wafers W can be suppressed and, consequently, the etching uniformity of oxide films or the like formed on the surfaces of the wafers W can be improved. While the wafers W are being processed or cleaned and the wafers W are not carried, clean air is blown at the normal flow rate to suppress increase in the particle content of the atmosphere of the processing unit. 
     The downward flow of the processing liquid remaining on the wafers W along the wafers W may be suppressed by stopping the operation of the fan motor  72  of the filter unit  70  to stop blowing clean air instead of reducing the operating speed of the motor  72  to reduce the flow rate of clean air. 
     Fourth Embodiment 
     A wafer processing apparatus in a fourth embodiment of the present invention will be described with reference FIG. 9 showing an essential part of the wafer processing apparatus in a schematic sectional view, in which parts like or corresponding to those of the first and the second embodiment are designated by the same reference characters and the description thereof will be omitted. 
     In the fourth embodiment, the downward flow of a chemical liquid, such as HF, remaining on wafers W toward the lower parts of the wafer W is suppressed positively when carrying the wafers W processed with the chemical liquid in a processing tank  21  to another processing tank  21  or a cleaning tank  21 A to improve the etching uniformity of oxide films or the like formed on the surfaces of the wafers W. 
     Referring to FIG. 9, a wafer processing unit  20 C included in the wafer processing apparatus in the fourth embodiment has a processing tank  21 , and a clean gas ejecting pipes  74  disposed at positions above the processing tank  21  and corresponding to opposite sides of the processing tank  21  to blow a clean gas, such as clean air or nitrogen gas, from below wafers W lifted out of the processing tank  21 . The cleaning gas ejecting pipes  74  are connected by clean gas supply pipes  75  through an on-off valve  77  to a clean gas source  76 . The configuration of a wafer cleaning unit included in the wafer processing apparatus and having a cleaning tank  21 A is substantially the same as that of the wafer processing unit  20 C. 
     When wafers W immersed in and processed with a chemical liquid, such as HF, contained in the processing tank  21  are lifted out of the processing tank  21  and are carried to another processing tank  21  or the cleaning tank  21 A, a clean gas, such as N 2  gas, is ejected upward by the clean gas ejecting pipes  74  from below the wafers W to suppress the downward flow of the processing liquid adhering to the wafers W, so that the etching uniformity of oxide films or the like formed on the surfaces of the wafers W can be improved. 
     The clean gas ejecting pipes  74  may be disposed at positions above the cleaning tank  21 A to eject the clean gas upward from below wafers W being lowered into the cleaning tank  21 A instead of disposing the same at the positions above the processing tank  21 . The clean gas ejecting pipes  74  may be disposed on a passage along which the wafers W are carried from the processing tank  21  to another processing tank or the cleaning tank  21 A to eject a clean gas upward from below the wafers being carried along the passage. A wafer carrying chuck  15  may be provided with clean gas ejecting pipes  74 A in its lower part, as indicated in FIGS. 10A and 10B. 
     In the foregoing embodiments, the wafers W are carried by the wafer carrying chuck  15 , and the wafer boat  57  holding the wafers W is lowered into and lifted out of the processing tank  21  or the cleaning tank  21 A. However, a wafer processing apparatus in accordance with the present invention may have a different configuration. 
     For example, the wafer processing apparatus may be provided with a wafer carrying chuck  15 A, i.e., wafer carrying means, as shown in FIG. 11 capable of moving in horizontal directions (X-directions) and vertical directions (Z-directions), and the wafers W may be carried to the processing tank  21  and the cleaning tank  21 A, and may be lowered into and lifted out of the processing tank  21  and the cleaning tank  21 A by the wafer carrying chuck  15 A. As shown in FIG. 11, the wafer carrying chuck  15 A has a pair of horizontal support rods  15   a  capable of being turned about their axes, and a pair of substantially U-shaped holding frames  15   b  attached respectively to the support rods  15   a , and each of the holding frames  15   b  has a lower holding bar  15   c  and a side holding bar  15   d  extended above the lower holding bar  15   c . The horizontal support rods  15   a  are turned about their axes by a driving device, not shown, to hold a plurality of wafers W, for example, fifth wafers W, between the holding frames  15   b , and the holding frames  15   b  holding the wafers W are moved in horizontal directions, i.e., X-directions, and vertical directions, i.e., Z-directions. 
     Although the present invention has been described as applied to the wafer processing apparatus to be employed in a semiconductor wafer processing system, the present invention may be applied to a processing apparatus for processing workpieces other than semiconductor wafers, such as LCD panels. 
     EXAMPLES 
     Experiment 1 
     Wafers WE in Example 1 processed by the wafer processing apparatus in the second embodiment and wafers WC in Comparative Example 1 processed by a conventional wafer processing apparatus were compared to verify the effect of the present invention on the reduction of reattachment of particles to wafers. 
     The wafers WC were immersed in a 25° C. dilute hydrogen fluoride solution (DHF: 1:50), and then the wafers WC were immersed in pure water for three minutes. Particles adhering to the wafer WC before cleaning and those adhering to the same wafer WC after cleaning were counted. The counted numbers of particles are tabulated in Table 1. FIG. 13 shows particles adhering to the wafer WC before cleaning, and FIG. 14 shows particles adhering to the wafer WC after cleaning. In FIGS. 13 and 14, indicated at P are particles and at N is a notch formed in the circumference of the wafer WC. 
     
       
         
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 NUMBER OF PARTICLES 
               
               
                   
                 (COMPARATIVE EXAMPLE) 
               
             
          
           
               
                 PARTICLE SIZE 
                 BEFORE 
                 AFTER 
                   
               
               
                 (μM) 
                 CLEANING 
                 CLEANING 
                 DIFFERENCE 
               
               
                   
               
               
                 0.16-0.20 
                 15  
                 200 
                 185 
               
               
                 0.20-0.25 
                 13  
                 199 
                 186 
               
               
                 0.25-0.30 
                 8 
                 105 
                  97 
               
               
                 0.30-0.50 
                 6 
                 113 
                 107 
               
               
                 0.50-1.00 
                 2 
                  64 
                  65 
               
               
                 1.00-    
                 2 
                  56 
                  54 
               
               
                 TOTAL 
                 46  
                 737 
                 691 
               
               
                   
               
             
          
         
       
     
     As shown in FIG. 12, the wafers WE in Example 1 were immersed in 25° C. dilute hydrogen fluoride solution (DHF: 1:50), were moved from a position P 1  to a position P 5  at a speed of 500 mm/sec, the wafers WE were moved from the position P 5  to a position P 6  at a speed of 250 mm/sec, the lower parts of the wafers WE were immersed in pure water for 0.5 sec to remove particles adhering to the lower parts of the wafers WE, and then the wafers WE were moved from the position P 6  to P 8  at a speed of 500 mm/sec to immerse the wafers WE in pure water. The counted numbers of particles are tabulated in Table 2. FIG. 15 shows particles adhering to the wafer WE before cleaning, and FIG. 16 shows particles adhering to the wafer WE after cleaning. 
     
       
         
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 NUMBER OF PARTICLES 
               
               
                   
                 (EXAMPLE) 
               
             
          
           
               
                 PARTICLE SIZE 
                 BEFORE 
                 AFTER 
                   
               
               
                 (μM) 
                 CLEANING 
                 CLEANING 
                 DIFFERENCE 
               
               
                   
               
               
                 0.16-0.20 
                 127  
                 157  
                 30 
               
               
                 0.20-0.25 
                 22 
                 44 
                 22 
               
               
                 0.25-0.30 
                 15 
                 27 
                 12 
               
               
                 0.30-0.50 
                 14 
                 27 
                 13 
               
               
                 0.50-1.00 
                 10 
                 17 
                  7 
               
               
                 1.00-    
                 15 
                 28 
                 13 
               
               
                 TOTAL 
                 203  
                 300  
                 97 
               
               
                   
               
             
          
         
       
     
     The total number of particles on the wafer WC in Comparative Example 1 was 46 before cleaning and increased by 691 to 737 after cleaning (about 1.5 times the number of particles before cleaning). On the other hand, the total number of particles on the wafer WE in Example 1 was 203 before cleaning and increased by only 97 to 300 after cleaning (about 0.48 times the number of particles before cleaning). It is known from the results of the experiment that the increase of the number of particles adhering to the wafer after cleaning can be effectively reduced by immersing the wafer in pure water after removing particles adhering to the wafer by immersing the lower part of the wafer for 0.5 sec in pure water. 
     Experiment 2 
     Experiments were conducted to examine the effect of ejecting a clean gas on wafers on depth of etch by a chemical liquid remaining on the wafers processed with the chemical liquid. Nitrogen gas was ejected on wafers WE in Example 2 coated with films and processed by the chemical liquid by the wafer processing apparatus in the fourth embodiment. Any clean gas was not ejected on wafers WC in Comparative Example 2 coated with the same films and processed by the same chemical liquid. 
     The wafers WC in Comparative Example 2 were prepared by immersing fifty wafers W coated with films in a dilute hydrogen fluoride solution (DHF: 1:50) for 1 min, rinsing the processed wafers W in ultrapure water for 5.5 min, and then drying the rinsed wafers W for 9 min. The twenty-sixth wafer WC was subjected to etching depth measurement. Values of the etching depth were determined by measuring the thickness of the film at measuring points before processing and after processing. Measured values of the etching depth are shown in Table 3 and FIG.  17 . 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 MEASURING 
                 COORDINATES 
                 SLOT 26 
               
             
          
           
               
                 POINT 
                 X 
                 Y 
                 BEFORE PROCESSING 
                 AFTER PROCESSING 
                 DIFFERENCE 
               
               
                   
               
             
          
           
               
                 1 
                 0 
                 0 
                 997.89 
                 223.18 
                 774.7 
               
               
                 2 
                 0 
                 0 
                 997.87 
                 223.13 
                 774.7 
               
               
                 3 
                 0 
                 0 
                 997.96 
                 223.1 
                 774.9 
               
               
                 4 
                 0 
                 0 
                 997.93 
                 223.13 
                 774.8 
               
               
                 5 
                 50 
                 0 
                 997.95 
                 229.28 
                 768.7 
               
               
                 6 
                 0 
                 50 
                 997.49 
                 235.71 
                 761.8 
               
               
                 7 
                 −50 
                 0 
                 997.67 
                 233.16 
                 764.5 
               
               
                 8 
                 0 
                 −50 
                 998.27 
                 224.85 
                 773.4 
               
               
                 9 
                 100 
                 0 
                 997.71 
                 226.93 
                 770.8 
               
               
                 10 
                 70.711 
                 70.711 
                 997.54 
                 234.94 
                 762.6 
               
               
                 11 
                 0 
                 100 
                 998.18 
                 243.21 
                 755.0 
               
               
                 12 
                 −70.711 
                 70.711 
                 997.52 
                 241.79 
                 755.7 
               
               
                 13 
                 −100 
                 0 
                 998.48 
                 233.37 
                 765.1 
               
               
                 14 
                 −70.711 
                 −70.711 
                 997.84 
                 230.97 
                 766.9 
               
               
                 15 
                 0 
                 −100 
                 998.82 
                 224.08 
                 774.7 
               
               
                 16 
                 70.711 
                 −70.711 
                 998.88 
                 225.91 
                 773.0 
               
               
                 17 
                 145 
                 0 
                 998.06 
                 215.73 
                 782.3 
               
               
                 18 
                 133.96 
                 55.49 
                 996.41 
                 236.87 
                 759.5 
               
               
                 19 
                 102.53 
                 102.53 
                 995.89 
                 306 
                 689.9 
               
               
                 20 
                 55.49 
                 133.96 
                 997.02 
                 230.15 
                 766.9 
               
               
                 21 
                 0 
                 145 
                 996.8 
                 237.97 
                 758.8 
               
               
                 22 
                 −55.49 
                 133.96 
                 996.76 
                 237.33 
                 759.4 
               
               
                 23 
                 −102.531 
                 102.53 
                 997.47 
                 237.4 
                 760.1 
               
               
                 24 
                 −133.96 
                 55.49 
                 997.57 
                 228.73 
                 768.8 
               
               
                 25 
                 −145 
                 0 
                 1039.2 
                 293.49 
                 745.7 
               
               
                 26 
                 −133.96 
                 −55.49 
                 997.58 
                 227.47 
                 770.1 
               
               
                 27 
                 −102.53 
                 −102.531 
                 994.79 
                 230.04 
                 764.8 
               
               
                 28 
                 −55.49 
                 −133.96 
                 995.69 
                 231.53 
                 764.2 
               
               
                 29 
                 0 
                 −145 
                 1005.5 
                 299.32 
                 706.2 
               
               
                 30 
                 55.49 
                 −133.96 
                 1030 
                 347.36 
                 682.6 
               
               
                 31 
                 102.531 
                 −102.53 
                 1005.2 
                 310.68 
                 694.5 
               
               
                 32 
                 133.96 
                 −55.49 
                 998.08 
                 274.53 
                 723.6 
               
             
          
           
               
                 Average Etching Depth 
                 755.9 
               
               
                 Maximum Etching Depth 
                 782.3 
               
               
                 Minimum Etching Depth 
                 682.6 
               
               
                 Range of etching depth variation 
                 99.7 
               
               
                 Standard Deviation (sigma) 
                 26.4 
               
               
                 Range/2Average 
                 6.6 
               
               
                 Sigma/Average 
                 3.5 
               
               
                   
               
             
          
         
       
     
     The wafers WE in Example 2 were prepared by immersing fifty wafers W coated with films in a dilute hydrogen fluoride solution (DHF: 1:50) for 5 min or in a dilute hydrogen fluoride solution (DHF: 5:1) for 1 min, rinsing the processed wafers W in ultrapure water for 5.5 min, and then drying the rinsed wafers W for 9 min. Nitrogen gas was ejected on the wafers W while the wafers W were being carried to the cleaning tank. The twenty-sixth wafer WE was subjected to etching depth measurement. Values of the etching depth were determined by measuring the thickness of the film at measuring points before processing and after processing. Measured values of the etching depth are shown in Table 4 and FIG.  17 . 
     
       
         
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 MEASURING 
                 COORDINATES 
                 SLOT 26 
               
             
          
           
               
                 POINT 
                 X 
                 Y 
                 BEFORE PROCESSING 
                 AFTER PROCESSING 
                 DIFFERENCE 
               
               
                   
               
             
          
           
               
                 1 
                 0 
                 0 
                 994.15 
                 235.57 
                 758.6 
               
               
                 2 
                 0 
                 0 
                 994 
                 235.58 
                 758.4 
               
               
                 3 
                 0 
                 0 
                 994.23 
                 235.54 
                 758.7 
               
               
                 4 
                 0 
                 0 
                 994.07 
                 235.59 
                 758.5 
               
               
                 5 
                 50 
                 0 
                 995.51 
                 238.55 
                 757.0 
               
               
                 6 
                 0 
                 50 
                 994.73 
                 242.36 
                 752.4 
               
               
                 7 
                 −50 
                 0 
                 994.42 
                 241.38 
                 753.0 
               
               
                 8 
                 0 
                 −50 
                 994.61 
                 230.75 
                 763.9 
               
               
                 9 
                 100 
                 0 
                 995.87 
                 235.99 
                 759.9 
               
               
                 10 
                 70.711 
                 70.711 
                 996.53 
                 242.18 
                 754.4 
               
               
                 11 
                 0 
                 100 
                 996.32 
                 249.19 
                 747.1 
               
               
                 12 
                 −70.711 
                 70.711 
                 995.84 
                 248.41 
                 747.4 
               
               
                 13 
                 −100 
                 0 
                 996.21 
                 240.41 
                 755.8 
               
               
                 14 
                 −70.711 
                 −70.711 
                 996.13 
                 228.82 
                 767.3 
               
               
                 15 
                 0 
                 −100 
                 996.12 
                 230.84 
                 765.3 
               
               
                 16 
                 70.711 
                 −70.711 
                 996.72 
                 233.33 
                 763.4 
               
               
                 17 
                 145 
                 0 
                 997.76 
                 241.46 
                 756.3 
               
               
                 18 
                 133.96 
                 55.49 
                 1027.2 
                 278.12 
                 749.1 
               
               
                 19 
                 102.53 
                 102.53 
                 998.65 
                 237.46 
                 761.2 
               
               
                 20 
                 55.49 
                 133.96 
                 996.19 
                 234.62 
                 761.6 
               
               
                 21 
                 0 
                 145 
                 992.57 
                 246.31 
                 746.3 
               
               
                 22 
                 −55.49 
                 133.96 
                 994.14 
                 243.65 
                 750.5 
               
               
                 23 
                 −102.531 
                 102.53 
                 994.97 
                 245.56 
                 749.4 
               
               
                 24 
                 −133.96 
                 55.49 
                 996.07 
                 240.63 
                 755.4 
               
               
                 25 
                 −145 
                 0 
                 996.77 
                 232.69 
                 764.1 
               
               
                 26 
                 −133.96 
                 −55.49 
                 999.71 
                 230.26 
                 769.5 
               
               
                 27 
                 −102.53 
                 −102.531 
                 996.45 
                 233.21 
                 763.2 
               
               
                 28 
                 −55.49 
                 −133.96 
                 996.26 
                 243.45 
                 752.8 
               
               
                 29 
                 0 
                 −145 
                 1005.1 
                 250.39 
                 754.7 
               
               
                 30 
                 55.49 
                 −133.96 
                 1047.3 
                 315.2 
                 732.1 
               
               
                 31 
                 102.531 
                 −102.53 
                 1013.5 
                 268.21 
                 745.3 
               
               
                 32 
                 133.96 
                 −55.49 
                 995.64 
                 237.14 
                 758.5 
               
             
          
           
               
                 Average Etching Depth 
                 756.0 
               
               
                 Maximum Etching Depth 
                 769.5 
               
               
                 Minimum Etching Depth 
                 732.1 
               
               
                 Range of etching depth variation 
                 37.4 
               
               
                 Standard Deviation (sigma) 
                 7.7 
               
               
                 Range/2Average 
                 2.5 
               
               
                 Sigma/Average 
                 1.0 
               
               
                   
               
             
          
         
       
     
     Results of the experiments proved that the etching uniformity can be improved by ejecting nitrogen gas upward from below the wafers W after the wafers W have been processed by a chemical liquid. 
     According to an aspect of the present invention, dust contained in the processing liquid remaining on the surfaces of substrates can be removed in a process of processing the substrates held in a vertical attitude by immersing the same in a processing liquid and immersing the same in a cleaning liquid, by cleaning the lower parts of the substrates with a cleaning liquid either before the substrates are immersed in the processing liquid or the cleaning liquid or after the same have been taken out from the processing liquid or the cleaning liquid. Accordingly, the reattachment of particles to the substrates can be prevented and the yield of products can be improved. 
     According to another aspect of the present invention, the downward flow of the processing liquid along the substrates after the substrates have been processed with the processing liquid can be prevented in a process of processing the substrates held in a vertical attitude by bringing the same into contact with a processing liquid and bringing the same into contact with a cleaning liquid, by processing the substrates in an atmosphere in which a clean gas flows down, and reducing or stopping the flow of the clean gas when carrying the substrates processed with the processing liquid to the next processing unit using another processing liquid or the cleaning liquid. Thus, the etching uniformity of the substrates etched with the processing liquid can be improved and the yield of products can be improved. 
     According to a further aspect of the present invention, the downward flow of the processing liquid along the substrates after the wafers have been processed with the processing liquid can be prevented in a process of processing the substrates held in a vertical attitude by bringing the same into contact with a processing liquid and bringing the same into contact with a cleaning liquid, by blowing a clean gas upward from below the substrates while the substrates are being carried to the next processing unit using another processing liquid or the cleaning liquid. Thus, the etching uniformity of the substrates etched with the processing liquid can be improved and the yield of products can be improved.