Abstract:
A cleaning apparatus comprises a holder for holding a substrate such as a semiconductor wafer horizontally and rotating the substrate about its central axis, while conducting a cleaning operation of the substrate by supplying a cleaning liquid thereto. The apparatus further comprises a cleaning vessel including a side wall encircling the substrate rotated by the holder to intercept the cleaning liquid supplied to and scattered from the rotating substrate and then finally drain the cleaning liquid. There is provided a vent duct for carrying gas from the inside of the cleaning vessel to the outside of the same. The vent duct includes an inlet provided at substantially the same level as that of the substrate for introducing the gas into the vent duct. The side wall may include an inner surface along which the cleaning liquid scattered from the substrate flows downward in a spiral manner, with the inner surface, being of a construction which impedes the spiral movement of the liquid in a circumferential or peripheral direction.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cleaning apparatus for cleaning a substrate, such as a semiconductor wafer or substrate, a liquid crystal panel, and a glass substrate, all of which are required to have a high degree of cleanliness. 
     With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit-wiring patterns have been becoming increasingly fink with spaces between wiring patterns also decreasing. Consequently, it is required for semiconductor substrates to be subjected to fine cleaning in such a manner as to remove sub-micron particles from surfaces on which wiring patterns are formed, which particles might otherwise form short circuits between adjacent wiring patterns. Such fine cleaning is also required in processing a glass substrate to be used as a masking member, or a liquid crystal panel or the like. 
     An apparatus for conducting fine cleaning is generally provided with a rotary substrate holder which holds and rotates a substrate in a horizontal plane, while the substrate is supplied with a cleaning liquid and scrubbed with a brush or sponge member. If fine cleaning is conducted without scrubbing, a cleaning liquid may be supplied in the form of a jet imparted with megasonic or supersonic vibration energy or a jet under high pressure. 
     The apparatus is further provided with a cleaning vessel which has a side wall and a bottom wall provided at the lower end thereof, and is movable between a raised position where the side wall encircles a substrate held and rotated by the holder to prevent a cleaning liquid supplied to the rotating substrate from scattering, and a lowered position where the substrate holder is exposed or positioned above the vessel to enable the substrate to be replaced with a subsequent one. 
     In such an apparatus, there is generally provided a means for producing a stream of clean air or inert gas flowing in the cleaning vessel down around the rotating substrate so as to carry out mist of a cleaning liquid, which may be generated during cleaning, from the cleaning vessel through an exit provided in the bottom wall of the vessel, whereby any mist generated is prevented from being deposited on the substrate. 
     After completion of cleaning, the apparatus continues to rotate the substrate, and in place of the cleaning liquid, an inert gas is supplied to the substrate to effect drying thereof. 
     The stated apparatus involves the following problem: 
     In a cleaning operation, a jet of cleaning liquid is directed to either or both of the opposite sides or upper and lower surfaces of a rotating substrate and the liquid supplied to the upper or lower surface is then scattered outside the rotating substrate under centrifugal force whereby it impinges on the inner surface of the side wall of the cleaning vessel. Consequently, a cleaning liquid mist is generated around the substrate, i.e., in areas above and/or below the substrate and adjacent to the inner surface of the side wall of the cleaning vessel. Such a mist is, as stated above, intended to be carried out from the apparatus by a gas stream. However, there is a tendency for some of the mist carried in the gas stream to become deposited on the lower surface of the rotating substrate, around which a negative pressure is generated due to a centrifugal force caused by rotation of the substrate, and/or on the inner surface of the cleaning vessel. Agitation of the gas stream caused by rotation of the substrate increases the tendency of a cleaning liquid mist to become deposited on the lower surface of a rotating substrate. Further, such a mist may arise from a cleaning liquid which flows downward in a spiral manner along the inner surface of the side wall after splashing from the rotating substrate and being intercepted by the inner surface of the side wall of the cleaning vessel. Any mist which has become deposited as described above dries during the drying operation following the cleaning operation, and forms an adhesive residue. 
     SUMMARY OF THE INVENTION 
     In view of the above-described circumstances, the present invention is directed to prevention of deposition of a cleaning liquid mist in a cleaning apparatus. 
     In accordance with the present invention, a cleaning apparatus comprises: a rotary holder for holding a substrate such as a semiconductor wafer horizontally and rotating the substrate about its central axis, while conducting a cleaning operation of the substrate by supplying a cleaning liquid thereto; a cleaning vessel including a side wall encircling the substrate rotated by the rotary holder to intercept the cleaning liquid supplied to and scattered from the rotating substrate and then finally drain the cleaning liquid; and a vent duct for carrying gas from the inside of the cleaning vessel to the outside of the same. The vent duct includes an inlet provided at substantially the same level as that of the substrate for introducing the gas into the vent duct. 
     In accordance with another aspect of the present invention, a cleaning apparatus comprises: a holder for holding a substrate horizontally and rotating the substrate about its central axis, while conducting a cleaning operation of the substrate by supplying a cleaning liquid to the substrate; a cleaning vessel comprising a side wall encircling the substrate rotated by the holder; and a vent duct for carrying a gas from the inside of the cleaning vessel to the outside of the same. The vent duct includes an inlet provided in the side wall to introduce the gas into the duct. 
     The cleaning vessel is provided with an inner wall, separated from and located inwardly of the side wall, and surrounding the wafer to intercept the cleaning liquid scattered from the substrate rotated by the holder, and the vent inlet is provided behind the inner wall relative to the substrate. 
     The vent inlet may be provided in the side wall to fluidly communicate with the inside of the cleaning vessel. 
     The vent duct may include a duct portion provided on the inner surface of the side wall and extending in a circumferential direction, with the vent inlet provided on the vent duct portion. 
     In accordance with another aspect of the present invention, a cleaning apparatus comprises a rotary holder for holding a substrate such as a semiconductor wafer horizontally and rotating the substrate about its central axis, while conducting a cleaning operation of the substrate by supplying a cleaning liquid to the substrate; and a cleaning vessel comprising a side wall encircling the substrate rotated by the rotary holder to intercept the cleaning liquid supplied to and scattered from the rotating substrate and then direct the liquid downward. The side wall includes an inner surface along which the cleaning liquid intercepted by the side wall flows downward in a spiral manner. The inner surface is provided with means for impeding the spiral movement of the liquid in a circumferential or peripheral direction. 
     Specifically, the side wall may be provided with a polygonal cross-sectional configuration. Alternatively, the side wall may be provided on its inner surface with a vertically extending obstacle such as a vertical groove or a vertical ridge which impedes the spiral movement of the cleaning liquid. 
     The apparatus may further include a nozzle for supplying a liquid to the inner surface of the side wall to prevent the inner surface from being dried. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a cleaning apparatus in accordance with the present invention; 
     FIG. 2 is a sectional view taken along a line II—II in FIG. 1; 
     FIG. 3 is a side elevational viewed from a line III—III in FIG. 1; 
     FIG. 4 is a sectional view taken along a line IV—IV in FIG. 1; 
     FIG. 5 is a schematic view of the apparatus of FIG. 1 showing a function of the apparatus; and 
     FIG. 6 is a sectional view taken along a line VI—VI in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the cleaning apparatus according to the present invention will be described below in detail with reference to FIGS. 1 to  6 . 
     The cleaning apparatus comprises a rotary substrate holder  10  for horizontally holding a semiconductor substrate or wafer W to be cleaned, a motor  12  for drivingly rotating the holder  10 , a cleaning liquid supply device  16  having a nozzle  14  for directing a cleaning liquid to the upper surface of the substrate W, a liquid supply nozzle  18  for supplying a liquid such as pure water, a cleaning agent or a gas such as pure nitrogen gas, and a casing  20  covering the above-stated elements. The cleaning liquid may be supplied in the form of, for example, a jet of pure water delivered at a speed sufficiently high to generate cavitation therein when it impinges on the upper surface of the wafer, or a jet of pure water imparted with ultrasonic vibration. 
     The rotary substrate holder  10  includes a disc  22  secured at the top end of an output shaft  11  of the motor  12  and a plurality of chucks  23  provided on the disc  22 , which chucks  23  are adapted to be engaged with the peripheral edge of the wafer W for securely holding the substrate W. The motor  12  rotates the disc  22  about its central axis. 
     The cleaning liquid supply device  16  includes a pivotal arm  24  which is provided at its distal end with the nozzle  14  and is pivotable about a strut  24 ′ provided at the proximal end thereof between a retracted rest position shown by a solid line in FIG. 1 and a work position wherein the nozzle  14  is positioned over the substrate W held on the holder  10 . In a variation of the cleaning liquid supply device  16 , the arm  24  is provided at its distal end with a brush, sponge member or the like to be brought into contact with the upper surface of the substrate W in addition to or in place of the nozzle  14  to effect so-called scrub cleaning. 
     The cleaning apparatus further includes a cleaning vessel  26  provided in the housing  20  and comprises a side wall  26 ′ surrounding the rotary substrate holder  10  and a bottom wall  26 ″. The bottom wall  26 ″ includes a center hole  27  through which the motor output shaft  11  extends vertically and a cleaning liquid discharge port  28  connected to a drainage pipe. The bottom wall  26 ″ is inclined as a whole towards the liquid discharge port  28 . The cleaning vessel  26  is connected to a piston/cylinder type actuator  44 , whereby the cleaning vessel  26  is moved vertically between a raised position as shown in FIGS. 2-5 and a lowered position where the chucks  23  extend above the top end of the cleaning vessel  26  to enable the substrate W held by the chucks  23  to be replaced with another one. The replacement of wafers is effected through an opening  32  (FIG. 3) formed in the side wall of the casing  20  at the same level as the chucks  23  and which, when the cleaning vessel  26  is at its raised position, is closed by the raised cleaning vessel  26 . 
     As is best shown in FIGS. 2 and 5, the cleaning vessel  26  is provided along its upper peripheral edge with an annular cover  33  including an annular horizontal portion  33 ′ having an outer peripheral edge engaged with the upper peripheral edge of the side wall  26 ′ and an inner peripheral edge defining a central opening  15 , and a conical portion or wall  33 ″ extending from the inner peripheral edge of the annular horizontal portion  33 ′. When the cleaning vessel  26  is positioned at its raised position as shown, the conical wall  33 ″ reaches a level corresponding to that of the wafer W held by the rotary substrate holder  10 . Relative to the rotary substrate holder  10 , behind the conical wall  33 ′ there is provided a vent duct  34  in the aide wall  26 ′ of the cleaning vessel  26 . The vent duct  34  is positioned adjacent to the upper peripheral edge of the side wall  26 ′ and extends in a circumferential direction to assume an annular form. The vent duct  34  is, as best shown in FIGS. 5 and 6, fluidly communicated with the interior of the cleaning vessel  26  through a plurality of vent holes  36  formed in the vent duct  34  and with an external vent duct  40  through a vent opening  38  formed in the side wall  26 ′. In this embodiment, the side wall  26 ′ is, as seen in a planar view, generally rectangular and the vent duct  34  accordingly assumes a rectangular shape. The vent duct  34  defines corner sections  34 ′ interconnected by an intermediate section. As shown in Fi.  6 , a relatively large number of vent holes  36  per unit area is provided in corner sections  34 ′ as compared with the intermediate section that interconnects the corner sections, and accordingly, the vent holes  36  are arranged in the corner sections  34 ′ along a peripheral direction of the vent duct  34  in a non-equal density fashion with respect to the vent holes  36  in the intermediate section. 
     As shown in FIGS. 2 and 5, the motor output shaft  12  is provided along its central axis with a gas supply pipe  42 . The top end opening of the gas supply pipe  42  is directed towards the lower surface of the substrate W held by the holder  10  and the lower end (not shown) is connected to a pure nitrogen gas source with the nitrogen gas jet being directed to the lower surface of the wafer W to prevent any deposition on the surface of a mist of the cleaning liquid. It is possible for the pipe  42  to supply other kinds of liquid such as pure water, a cleaning agent or the like to the lower surface of the substrate W as required. 
     The side wall  26 ′ of the cleaning vessel  26  is further provided on its inner surface under the vent duct  34  with a drying prevention nozzle  54  including a small diameter pipe  50  extending in a circumferential direction to assume a ring form. The pipe  50  is fluidly connected to a water source (not shown) and includes a plurality of holes  52  directed towards the inner surface of the side wall  26 ′, whereby water is supplied to the inner surface of the side wall  26  to prevent it from being dried. 
     In operation, the cleaning vessel  26  is first lowered. A robot arm (not shown) supplies a substrate W to be cleaned through the substrate supply opening  32  formed in the casing  20  to the rotary substrate holder  10 . When the wafer W is held by the chucks  23  in a horizontal position, the cleaning vessel  26  is raised to the work position, whereby the substrate W held by the holder  10  is surrounded by the side wall  26 ′ of the cleaning vessel  26  and, simultaneously the substrate supply opening  32  is closed by the side wall  26 ′. A stream of pure gas which flows downward through the cleaning vessel is supplied during the operation. 
     Next, the motor  12  is actuated to rotate the rotary substrate holder  10  and the pivotal arm  24  of the cleaning liquid supply device  16  is pivoted about the strut  24 ′ so that the nozzle  14  provided at the distal end of the arm  24  directs a jet of cleaning liquid to the upper surface of the rotating substrate W. When cleaning of the wafer W has been completed, supply of the cleaning liquid is halted and, in its place, a rinsing liquid such as pure water is supplied through the nozzle  18  to the upper surface of the rotating wafer W to effect rinsing of the surface. During these operations, a liquid supplied to the upper surface of the substrate W is scattered outside the wafer under a centrifugal force generated by rotation of the wafer and impinges on the conical wall  33  and/or inner surface of the side wall of the cleaning vessel  26 . The liquid is finally discharged from the exit opening  28  formed in the bottom wall of the cleaning vessel. 
     When a liquid impinges on the conical wall  33  and/or the inner surface of the side wall  26 ′, a mist is generated. In this embodiment, the mist is carried by a gas which is drawn into the vent duct  34  through holes  36  positioned at the same level as that of the wafer W, whereby the mist is prevented from being carried by a gas stream flowing down in the cleaning vessel and finally flowing out from the exit hole  28 . Accordingly, any likelihood of deposition of the mist on the wafer W greatly decreases. 
     Further, since the side wall  26 ′ of the cleaning vessel  26  has a rectangular cross section, the movement of the liquid discharged from the rotating substrate W and then spirally flowing down along the inner surface of the side wall  26 ′ is impeded by the corner portions of the side wall  26 ′ so that the component of movement in a circumferential or peripheral direction is depleted in a relatively short time. Consequently, the liquid reaches the exit opening  28  through a short path so that the possibility of generation of the mist from the liquid flowing down along the inner surface of the side wall  26 ′ decreases. 
     When a predetermined time for rinsing of the substrate W has expired, the supply of rinsing liquid from the nozzle  18  is halted and, in its place, a jet of clear gas such as nitrogen is directed from the nozzle  18  to the center of the substrate W with rotation of the substrate being maintained to effect a spin dry operation. During the drying operation, the vent gas flowing through the vent duct  34  is maintained so that particles of a liquid which may be discharged from the substrate and a mist which may be generated are caused to exit immediately. 
     Following completion of the drying operation, the cleaning vessel  26  is lowered, and the cleaned and dried substrate W is replaced with a new one by means of the robot arm which operates through the opening  32  formed in the housing. 
     The drying prevention nozzle  54  supplies water to the inner surface of the side wall  26 ′ of the cleaning vessel  26  to prevent the inner surface from being dried, thereby preventing particles of for example, a cleaning agent from becoming deposited and drying on the inner surface of the side wall. 
     In this embodiment, the side wall has a rectangular cross section. However, the side wall may have any other form of cross section so long as the form employed can bring about a reduction in speed of a liquid flowing down on the inner surface of the side wall, to thereby reduce a speed component in a circumferential or peripheral direction of the liquid. For example, the cross section configuration of the side wall  26  may be in the form of a triangle, pentagon, or other polygon. The above-stated speed reduction function can be brought about by the provision of vertical ridges, grooves or the like formed on the inner surface of the side wall, with such a provision permitting the side wall to have a circular or oval cross sectional configuration and not a polygonal configuration. 
     In the embodiment shown in the drawings, vent holes  36  are generally uniformly provided along the entire length of the annular vent duct  34 , with a relatively large number of vent holes  36  being provided in the corner portions  34 ′ of the annular vent duct  34 . However, the arrangement of the holes  36  may be adapted as required, and the holes may be provided in the form of slits. Further, in place of an annular vent duct, the vent duct may be formed only at the corners of the rectangular side wall  26 . 
     It should be noted that the present invention is not necessarily limited to the foregoing embodiments but can be modified in a variety of ways without departing from the gist of the present invention.