Patent Publication Number: US-9421662-B2

Title: Polishing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2013-0114143, filed on Sep. 25, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The inventive concepts relate to polishing apparatuses, and more particularly, to polishing apparatuses capable of polishing a peripheral portion of a wafer. 
     During manufacturing processes of a semiconductor device, an undesired film or a rough surface may be formed on a peripheral portion of a wafer. When the semiconductor device is manufactured, the peripheral portion of the wafer is held by an arm to deliver the wafer. Accordingly, the above-described undesired film formed on the wafer during the manufacturing processes of the semiconductor device may operate as particles and/or the above-described rough surface may operate as an obstacle to a photolithography process. In order to remove the undesired film and/or to relieve the rough surface, polishing the peripheral portion of the wafer by using a polishing apparatus is desired. 
     SUMMARY 
     At least some example embodiments provide polishing apparatuses capable of polishing a peripheral portion of a wafer while preventing particles from falling on the wafer. 
     According to an example embodiment, a polishing apparatus may include a chuck for supporting a wafer while exposing a peripheral portion of the wafer, a polishing head for polishing the peripheral portion of the wafer, and a polishing solution supplying assembly provided above the wafer for spraying a polishing solution on the wafer and to form a liquid curtain on the chuck to protect the wafer when the wafer is polished. 
     The polishing head may include a side surface and a top surface polishing portion capable of polishing a side surface and a top surface of the peripheral portion of the wafer. The polishing head may include a rear surface polishing portion capable of polishing a rear surface of the peripheral portion of the wafer. 
     The polishing solution supplying assembly may include a slit nozzle for spraying the polishing solution. The polishing solution supplying assembly may include a nozzle block that horizontally rotates with respect to the wafer. 
     The polishing solution supplying assembly may include a nozzle supporting block having an internal groove connected to a polishing solution supplying line, through which the polishing solution is supplied, a nozzle block including a distributing plate for distributing the polishing solution and coupled to (e.g., inserted into and fastened to) the internal groove of the nozzle supporting block and, and a slit nozzle for spraying the polishing solution and positioned between the nozzle supporting block and the nozzle block. 
     The distributing plate may include a through nozzle passing through the nozzle block and for supplying the polishing solution to a center of the wafer. The distributing plate may include a central through hole provided at a center and a distributing groove for radially distributing the polishing solution around an upper surface of the central through hole. The distributing groove may be connected to the slit nozzle. The internal groove of the nozzle supporting block may include an inclined groove and the slit nozzle may be formed along a surface of the inclined groove. 
     According to another example embodiment, a polishing apparatus may include a chuck for supporting a wafer while exposing a peripheral portion of the wafer, a polishing head for polishing the peripheral portion of the wafer, and a polishing solution supplying assembly for spraying a polishing solution to form a liquid curtain on the chuck to protect the wafer when the wafer is polished. The polishing solution supplying assembly may include a nozzle supporting block provided on the chuck and may include an internal groove configured to receive a polishing solution supplying line, a nozzle block coupled to (e.g., inserted into and fastened to) the internal groove of the nozzle supporting block, and a slit nozzle positioned between the nozzle supporting block and the nozzle block. The nozzle bock may include a distributing plate for distributing the polishing solution and a through nozzle connected to the distributing plate. 
     The through nozzle of the polishing solution supplying assembly may include a first sub-through nozzle having a first diameter and connected to the distributing plate and a second through nozzle having a second diameter larger than the first diameter and connected to the first through nozzle. 
     The internal groove of the nozzle supporting block may include a multistage groove connected to the polishing solution supplying line and an inclined groove connected to the multistage groove. A curvature of the liquid curtain may be determined in accordance with a radial angle of the inclined groove. A diameter of the slit nozzle may be determined in accordance with a diameter of the through nozzle. 
     According to still another example embodiment, a polishing apparatus may include a chuck configured to at least partially support a wafer while exposing a peripheral portion thereof, a polishing pad configured to polish the exposed peripheral portion of the wafer, and a polishing solution supplying assembly above the chuck, the polishing solution supplying assembly configured to spray a polishing solution to form a liquid curtain on the chuck. 
     The polishing solution supplying assembly may includes a nozzle supporting block on the chuck, a nozzle block coupled to the nozzle supporting block, and a slit nozzle between the nozzle supporting block and the nozzle block. The nozzle supporting block may include an internal groove, and the nozzle block is coupled to the nozzle supporting block by coupling the nozzle block to the internal groove of the nozzle supporting block. The nozzle block may include a distributing plate configured to distribute the polishing solution and a through nozzle connected to the distributing plate. The nozzle block may be partially disposed in the internal groove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various example embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a plan view schematically illustrating an entire structure of a substrate processing system including a polishing apparatus according to an example embodiment; 
         FIG. 2  is a plan view schematically illustrating a polishing apparatus that may be used for the substrate processing system of  FIG. 1 ; 
         FIGS. 3 and 4  are vertical cross-sectional views of  FIG. 2 ; 
         FIG. 5  is a cross-sectional view illustrating a peripheral portion of a wafer W; 
         FIG. 6  is a view schematically illustrating a tape supplying and recovering mechanism and a polishing head of  FIG. 2 ; 
         FIGS. 7 and 8  are views illustrating a wafer polishing process using a pressing mechanism of the polishing head of  FIG. 6 ; 
         FIGS. 9 and 10  are cross-sectional views illustrating that a rear surface of a peripheral portion of a wafer is polished by using the polishing apparatus of  FIGS. 2 to 4 ; 
         FIG. 11  is a cross-sectional view illustrating a polishing solution supplying assembly of  FIGS. 2 to 4 ; 
         FIG. 12  is a cross-sectional view illustrating a nozzle supporting block of  FIG. 11 ; 
         FIG. 13  is a cross-sectional view illustrating a nozzle block of  FIG. 11 ; 
         FIG. 14  is a plan view of a distributing plate included in the nozzle block of  FIG. 13 ; 
         FIG. 15  is a view illustrating a bottom surface of the nozzle block of  FIG. 13 ; 
         FIG. 16A  is a particle map diagram of a wafer when the wafer is polished using a liquid curtain according to one of the example embodiments illustrated in  FIGS. 9 and 10 ; 
         FIG. 16B  is a particle map diagram of a wafer when the wafer is polished without using a liquid curtain according to a comparative example; 
         FIG. 17A  is a view illustrating particles observed on a surface of a wafer when the wafer is polished using a liquid curtain according to one of the example embodiments illustrated in  FIGS. 9 and 10 ; and 
         FIG. 17B  is a view illustrating particles observed on a surface of a wafer when the wafer is polished without using a liquid curtain according to a comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings, in which some example embodiments are shown. The same elements in the drawings are denoted by the same reference numerals and a repeated explanation thereof will not be given. 
     Example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which elements of the inventive concepts are shown. The inventive concepts may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example embodiments to one of ordinary skill in the art. 
     It will be understood that when an element or layer is referred to as being “on,” “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of example embodiments. For example, a first element may be named a second element and similarly a second element may be named a first element without departing from the scope of example embodiments. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Example embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized example embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     A specific order of processes according to some example embodiments may be changed. For example, two processes consecutively described herein may be simultaneously performed or may be performed in an opposite order. 
     Variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments should not be construed as limited to the particular shapes of regions illustrated herein but may be construed to include deviations in shapes that result, for example, from manufacturing. 
     Hereinafter, some example embodiments will be explained in further detail with reference to the accompanying drawings. 
       FIG. 1  is a plan view schematically illustrating an entire structure of a substrate processing system including a polishing apparatus according to an example embodiment. 
     For example, a substrate processing system  1000  may include a wafer loading/unloading port  400 , a transfer rail  410 , a first transfer robot  430 , and a first wafer station  450  on which a wafer is arranged. The first transfer robot  430  may be used for transferring a wafer W between the wafer loading/unloading port  400  and the first wafer station  450 . The first transfer robot  430  may move on the transfer rail  410 . 
     A substrate processing system  1000  may include two polishing apparatuses  500 , two centering loaders  470 , a second transfer robot  520 , and a second wafer station  540 . The polishing apparatus  500  may polish a peripheral portion of the wafer W. 
     The wafer W loaded on the first wafer station  450  may be transferred to the centering loader  470 . The centering loader  470  may hold the wafer W to mechanically or optically align a center of the wafer W. The wafer W whose center is aligned may be loaded on the polishing apparatus  500 . The wafer W polished by the polishing apparatus  500  may be transferred to the second wafer station  540  by using the second transfer robot  520 . The polishing apparatus  500  will be described in detail later. 
     The substrate processing system  1000  may include a third transfer robot  560 , a washing unit  580 , a fourth transfer robot  600 , and a drying unit  620 . The wafer loaded on the second wafer station  540  may be transferred to the washing unit  580  by using the third transfer robot  560  so that the wafer is to be washed. The washed wafer may be transferred to the drying unit  620  by using the fourth transfer robot  600  so that the washed wafer is to be dried. The dried wafer may be transferred to the wafer loading/unloading port  400  by using the first transfer robot  430 . 
       FIG. 2  is a plan view schematically illustrating a polishing apparatus that may be used for the substrate processing system of  FIG. 1 .  FIGS. 3 and 4  are vertical cross-sectional views of  FIG. 2 .  FIG. 5  is a cross-sectional view illustrating a peripheral portion of a wafer W. 
     For example, the polishing apparatus  500  may be used for polishing a surface, a side surface, and a rear surface of the peripheral portion of the wafer W. A diameter of the wafer W may be 300 mm and semiconductor device forming films may be formed on a surface of the wafer W. In  FIG. 5 , the enlarged peripheral portion of the wafer W is illustrated. 
     In the wafer W, a device forming region D is a flat portion positioned several millimeters inward from an edge surface G. Another flat portion outside the device forming region D may be defined as a near upper edge portion E. In the wafer W, an upper inclined portion F, the edge surface G, and a lower inclined portion F′ may collectively define an inclined portion B. A lower surface of the wafer W corresponding to the near upper edge portion E may be defined as a near lower edge portion E′. 
     The peripheral portion may be defined by the near upper edge portion E, the inclined portion B, and the near lower edge portion E′. Top and side surfaces of the peripheral portion may include the near upper edge portion E, the upper inclined portion F, and the edge surface G. A rear surface of the peripheral portion may include the near lower edge portion E′ and the lower inclined portion F′. 
     The polishing apparatus  500  may include a chuck  3  for horizontally providing the wafer W (e.g., an object to be polished) and rotating the wafer W. The chuck  3  may be positioned in a center of the polishing apparatus  500 . The wafer W may be provided on the chuck  3 . The top surface, the side surface, and the rear surface of the peripheral portion of the wafer W provided on the chuck  3  may be exposed. A cup  85  for protecting the wafer W may be positioned around the wafer W on the chuck  3 . 
     The chuck  3  may include a dish-shaped stage  4  capable of holding the lower surface of the wafer W by a vacuum suction power, a shaft  5  coupled to a center of the stage  4 , and a motor M 1  for rotating the shaft  5 . The shaft  5  may be a hollow shaft. The wafer W may be arranged on the stage  4  so that the center of the wafer W is aligned with a rotation axis of the shaft  5 . 
     The shaft  5  may be supported by ball spline bearings  6  that allow the shaft  5  to vertically move. The ball spline bearings  6  may be linear motion bearings. The stage  4  may include an upper surface having a groove  4   a . The groove  4   a  may be connected to a communication line  7  extended through the shaft  5 . The communication line  7  may be coupled to a vacuum line  9  through a rotation joint  8  provided at a lower end of the shaft  5 . The communication line  7  may be connected to a nitrogen gas supplying line  10  used for discharging the processed wafer W from the stage  4  to the outside of the polishing apparatus. 
     The vacuum line  9  or the nitrogen gas supplying line  10  may be selectively coupled to the communication line  7  so that the wafer W may be attached to the upper surface of the stage  4  by vacuum suction or may be discharged from the upper surface of the stage  4 . 
     The shaft  5  may be rotated by the motor M 1  through a pulley p 1  coupled to the shaft  5 , a pulley p 2  attached to a rotation shaft of the motor M 1 , and a belt b 1  mounted on the pulleys p 1  and p 2 . The rotation shaft of the motor M 1  may be extended to run parallel with the shaft  5 . Through the above-described configuration, the wafer W positioned on the upper surface of the stage  4  may be rotated by the motor M 1 . 
     The ball spline bearings  6  may allow the shaft  5  to freely move in a vertical direction. The ball spline bearings  6  may be mounted in a first casing  12 . The shaft  5  may linearly move up and down with respect to the first casing  12  and the shaft  5  and the first casing  12  may integrally rotate. The shaft  5  may be coupled to an air cylinder  15 . The air cylinder  15  may be an elevating mechanism. The shaft  5  and the stage  4  may be ascended and descended by the air cylinder  15 . 
     A second casing  14  may be provided to surround the first casing  12 . The first casing  12  and the second casing  14  may be concentrically arranged. Radial bearings  18  may be provided between the first casing  12  and the second casing  14  so that the first casing  12  is rotatably supported by the radial bearings  18 . In such a structure, the chuck  3  may rotate the wafer W around a central axis Cr and may ascend and descend the wafer W along the central axis Cr. 
     When the shaft  5  ascends with respect to the first casing  12 , in order to separate the ball spline bearings  6  and the radial bearings  18  from a polishing chamber  21 , upper ends of the hollow shaft  5  and the first casing  12  may be coupled to a bellows  19  elongated in a vertical direction as illustrated in  FIGS. 3 and 4 .  FIGS. 3 and 4  illustrate that the shaft  5  is lowered and the state  4  is in a polishing position. After a polishing process, the air cylinder  15  may lift the wafer W to a delivery position together with the stage  4  and the shaft  5 . At this time, the wafer W may be discharged from the stage  4 . 
     As illustrated in  FIG. 2 , the polishing apparatus  500  may include polishing head assemblies  1 A,  1 B,  1 C, and  1 D. The polishing head assemblies  1 A,  1 B,  1 C, and  1 D may be arranged to be around the wafer W, which will be mounted on the chuck  3 . The polishing head assemblies  1 A and  1 D may include top surface and side surface polishing heads  30  used for polishing the top surface and/or the side surface of the peripheral portion of the wafer W. The polishing head assemblies  1 B and  1 C may include rear surface polishing heads  30  used for polishing the rear surface of the peripheral portion of the wafer W. 
     Tape supplying and recovering mechanisms  2 A,  2 B,  2 C, and  2 D for supplying or recovering polishing tapes  23  used for polishing the wafer W may be provided outside the polishing head assemblies  1 A,  1 B,  1 C, and  1 D in radial directions, respectively. The polishing head assemblies  1 A,  1 B,  1 C, and  1 D may be separated from the tape supplying and recovering mechanisms  2 A,  2 B,  2 C, and  2 D by a division wall  20 . An internal space of the division wall  20  may provide the polishing chamber  21 . 
     The four polishing head assemblies  1 A,  1 B,  1 C, and  1 D and the stage  4  may be positioned in the polishing chamber  21 . The tape supplying and recovering mechanisms  2 A,  2 B,  2 C, and  2 D may be positioned outside the division wall  20  (e.g., outside the polishing chamber  21 ). The polishing head assemblies  1 A,  1 B,  1 C, and  1 D may have a same structure and the tape supplying and recovering mechanisms  2 A,  2 B,  2 C, and  2 D may have a same structure. 
     The polishing head assemblies  1 A,  1 B,  1 C, and  1 D may include the polishing heads  30  capable of polishing the peripheral portion of the wafer W as described above. The polishing heads  30  may press the polishing tapes  23  supplied by the tape supplying and recovering mechanisms  2 A,  2 B,  2 C, and  2 D to the peripheral portion of the wafer W. The four polishing head assemblies  1 A,  1 B,  1 C, and  1 D and the four tape supplying and recovering mechanisms  2 A,  2 B,  2 C, and  2 D may be provided in this example embodiment. However, the inventive concepts are not limited to such an arrangement. For example, two, three, or no less than four pairs of polishing head assemblies and tape supplying and recovering mechanisms may be provided. 
     Here, among the polishing head assemblies  1 A,  1 B,  1 C, and  1 D of the same structure and the tape supplying and recovering mechanisms  2 A,  2 B,  2 C, and  2 D of the same structure, as an example, the polishing head assembly  1 A and the tape supplying and recovering mechanism  2 A will be described. 
     The tape supplying and recovering mechanism  2 A may include a supplying rill  24  for supplying the polishing tape  23  (e.g., a polishing tool) to the polishing head assembly  1 A and a recovering rill  25  for recovering the polishing tape  23  used for polishing the wafer W. The supplying rill  24  may be arranged on the recovering rill  25 . A motor M 2  may be coupled to the supplying rill  24  and the recovering rill  25  through a coupling ring  27 . In  FIG. 2 , for convenience sake, only the motor M 2  coupled to the supplying rill  24  and the coupling ring  27  is illustrated. The motor M 2  may be formed to apply a uniform torque in a desired (or alternatively, predetermined) rotation direction in order to apply a desired (or alternatively, predetermined) tension to the polishing tape  23 . 
     The polishing tape  23  may be a long tape-shaped polishing tool and one of surfaces of the polishing tape forms a polishing surface. The polishing tape  23  may be wound around the supplying rill  24  mounted on the tape supplying and recovering mechanism  2 A. The both surfaces of the wound polishing tape  23  may be supported by a rill plate (not shown), which is configured to not be folded. One end of the polishing tape  23  may be attached to the recovering rill  25  so that the recovering rill  25  winds the polishing tape  23  supplied to the polishing head assembly  1 A to recover the polishing tape  23 . 
     The polishing head assembly  1 A may include the polishing head  30  capable of pressing the polishing tape  23  supplied by the tape supplying and recovering mechanism  2 A to the peripheral portion of the wafer W to polish the peripheral portion of the wafer W. The polishing tape  23  may be supplied to the polishing head  30  so that the polishing surface of the polishing tape  23  faces the peripheral portion of the wafer W. 
     The tape supplying and recovering mechanism  2 A may include a plurality of guide rollers  31 ,  32 ,  33 , and  34 . The polishing tape  23  supplied to the polishing head assembly  1 A and recovered from the polishing head assembly  1 A may be guided by the guide rollers  31 ,  32 ,  33 , and  34 . The polishing tape  23  may be supplied from the supplying rill  24  to the polishing head  30  through openings  20   a  formed in the division wall  20  and the used polishing tape  23  may be recovered by the recovering rill  25  through the openings  20   a.    
     The polishing head  30  may be fixed to one end of a rotatable arm  60  with respect to an axis Ct, which runs parallel with a tangent line of the wafer W as illustrated in  FIG. 2 . The other end of the arm  60  may be coupled to a motor M 4  through pulleys p 3  and p 4  and a belt b 2 . When the motor M 4  rotates in a clockwise direction and a counter clockwise direction by a desired (or alternatively, predetermined) angle, the arm  60  may rotate around the axis Ct by a desired (or alternatively, predetermined) angle. In this example embodiment, the motor M 4 , the arm  60 , the pulleys p 3  and p 4 , and the belt b 2  may form a tilt mechanism that tilts the polishing head  30 . 
     The tilt mechanism may be mounted on a plate-shaped movable base  61 . The movable base  61  may be movably coupled to a movable plate  65  through a guide unit  62  and a rail  63 . The rail  63  may be linearly extended in a radial direction of the wafer W mounted on the chuck  3  so that the movable base  61  may move in the radial direction of the wafer W. A coupling plate  66  that passes through the movable plate  65  may be attached to the plate-shaped movable base  61 . A linear actuator  67  may be coupled to the coupling plate  66  through a joint  68 . The linear actuator  67  may be directly or indirectly fixed to the movable plate  65 . 
     The linear actuator  67  may include, for example, a combination of a position setting motor and a ball screw or an air cylinder. The linear actuator  67 , the rail  63 , and the guide unit  62  may form a moving mechanism for linearly moving the polishing head  30  in the radial direction of the wafer W. For example, the moving mechanism may move the polishing head  30  along the rail  63  toward the wafer W and away from the wafer W. The tape supplying and recovering mechanism  2 A may be attached to the movable plate  65 . 
       FIG. 3  illustrates the polishing apparatus  500  configured to polish the side surface of the peripheral portion of the wafer W. When the polishing apparatus  500  polishes the surface of the peripheral portion of the wafer W, the chuck  3  on which the wafer W is mounted may descend to be positioned above the polishing head  30 .  FIG. 4  illustrates that the chuck  3  moves upward so that the polishing apparatus  500  polishes the rear surface of the peripheral portion of the wafer W. As described above, when the polishing head  30  is tilted, an inclined surface of the surface or rear surface of the peripheral portion of the wafer W may be polished. 
     In the polishing apparatus  500  according to the present example embodiment, when the wafer W is polished, a polishing solution supplying assembly  76  may supply a polishing solution to a center of the upper surface of the wafer W and form a liquid curtain above the wafer W for protecting the wafer W. The polishing solution supplying assembly  76  may include a nozzle supporting block  74  and a nozzle block  72  for spraying the polishing solution. 
     The nozzle block  72  may be connected to a motor M 5  and may horizontally rotate with respect to the wafer W. Rotation of the nozzle block  72  may be selective and the nozzle block  72  may not rotate. The polishing solution supplying assembly  76  will be described in detail later. 
     A lower nozzle block  37  may be provided to supply the polishing solution to a boundary between the rear surface (e.g., the lower surface) of the wafer W and the stage  4  of the chuck  3 . Pure water may be used as the polishing solution. When silica is used as polishing grains of the polishing tape  23 , ammonia may be used as the polishing solution. The polishing apparatus  500  may include a washing nozzle block  38  for washing the polishing head  30  after the polishing process. The washing nozzle block  38  may spray a washing solution to the polishing head  30  in order to wash the polishing head  30  used for the polishing process. 
       FIG. 6  is a view schematically illustrating a tape supplying and recovering mechanism and the polishing head of  FIG. 2 . 
     For example, the polishing head  30  may apply pressure to the rear surface of the polishing tape  23  in order to press the polishing tape  23  against the wafer W by a desired (or alternatively, predetermined) power. The polishing head  30  may further include a tape discharging mechanism  42  for discharging the polishing tape  23  from the supplying rill  24  to the recovering rill  25 . The polishing head  30  may include a plurality of guide rollers  43 ,  44 ,  45 ,  46 ,  47 , and  48  for guiding the polishing tape  23  to move to the peripheral portion of the wafer W. 
     The tape discharging mechanism  42  of the polishing head  30  may include a tape discharging roller  42   a , a tape holding roller  42   b , and a motor M 3  for rotating the tape discharging roller  42   a . The motor M 3  may be arranged on one surface of the polishing head  30 . The tape discharging roller  42   a  may be coupled to a rotation shaft of the motor M 3 . 
     The tape holding roller  42   b  may be adjacent to the tape discharging roller  42   a . The tape holding roller  42   b  may be supported by a mechanism (not shown) that applies power to the tape holding roller  42   b  in a direction indicated by NF (e.g., toward the tape discharging roller  42   a ) to press the tape holding roller  42   b  to the tape discharging roller  42   a.    
     The polishing tape  23  may pass between the tape discharging roller  42   a  and the tape holding roller  42   b  and may be held by the tape discharging roller  42   a  and the tape holding roller  42   b . The tape discharging roller  42   a  may have a contact surface that contacts the polishing tape  23 . The entire contact surface may be covered with urethane resin. Due to such a structure, friction between the tape discharging roller  42   a  and the polishing tape  23  may increase, and thus the tape discharging roller  42   a  may discharge the polishing tape  23  without sliding. 
     When the motor M 3  rotates, the tape discharging roller  42   a  may rotate to discharge the polishing tape  23  from the supplying rill  24  to the recovering rill  25  through the polishing head  30 . The tape holding roller  42   b  may freely rotate around its axis to rotate when the polishing tape  23  is discharged by the tape discharging roller  42   a.    
     In such a method, rotation of the motor M 3  may be switched into a tape discharging work by friction between the contact surface of the tape discharging roller  42   a  and the polishing tape  23 , a winding angle of the polishing tape  23 , and holding of the polishing tape  23  by the tape holding roller  42   b . The polishing tape  23  may be discharged downward from a position where the polishing tape  23  contacts the wafer W. 
       FIGS. 7 and 8  are views illustrating a wafer polishing process using a pressing mechanism of the polishing head of  FIG. 6 . 
     For example,  FIG. 7  illustrates that the rear surface of the peripheral portion of the wafer W is polished by using a pressing mechanism  41  and  FIG. 8  illustrates that the side surface of the peripheral portion of the wafer W is polished by using the pressing mechanism  41 . The pressing mechanism  41  of  FIGS. 7 and 8  may include a pressing pad  50  positioned on the back of the polishing tape  23 , which is provided on two guide rollers  46  and  47 , a pad holder  51  for holding the pressing pad  50 , and an air cylinder (an actuator)  52  for moving the pad holder  51  toward the wafer W. 
     The guide rollers  46  and  47  may be arranged in a front part of the polishing head  30 . The air cylinder  52  may be a single load cylinder. Two air pipes  53  may be coupled to the air cylinder  52  through two ports. Electropneumatic regulators  54  may be provided to the air pipes  53 , respectively. A first end (e.g., an entrance end) of the air pipe  53  may be coupled to an air supplying source  55  and a second end (e.g., an exit end) of the air pipe  53  may be coupled to a port of the air cylinder  52 . 
     The electropneumatic regulators  54  may be controlled by a signal in order to appropriately control the pressure of an air to be supplied to the air cylinder  52 . In such a method, a press force of the pressing pad  50  is controlled by the pressure of the air supplied to the air cylinder  52  and the polishing surface of the polishing tape  23  may press the wafer W by a controlled pressure. 
       FIGS. 9 and 10  are cross-sectional views illustrating that a rear surface of a peripheral portion of a wafer is polished by using the polishing apparatus of  FIGS. 2 to 4 . 
     For example, the wafer W may be horizontally mounted on the stage  4  of the chuck  3  that forms the polishing apparatus  500 . The diameter of the wafer W may be larger than that of the stage  4  so that the peripheral portion of the wafer W can be exposed to the outside of the stage  4 . The wafer W mounted on the stage  4  may be rotated by the rotation of the shaft  5 . 
     The polishing head  30  may be positioned on the rear surface of the peripheral portion of the wafer W. The polishing head  30  may be used for polishing the rear surface of the peripheral portion of the wafer W. The polishing solution supplying assembly  76  may be formed above the wafer W. 
     The polishing solution supplying assembly  76  may include the nozzle supporting block  74  and the nozzle block  72  for spraying a polishing solution  92 . The motor M 5  capable of rotating the nozzle block  72  may be connected to the nozzle block  72 . The polishing solution supplying assembly  76  may supply the polishing solution  92  to the center of the upper surface of the wafer W so that the polishing solution  92  is sprayed to form a liquid curtain  94 , which is capable of protecting the wafer W when the wafer W is polished. 
     The liquid curtain  94  may be a polishing solution curtain created by the polishing solution  92 . The liquid curtain  94  may be a pure water curtain when the polishing solution is pure water. A shape of the liquid curtain  94  may vary with a spray type of the polishing solution  92 . In  FIG. 9 , the liquid curtain  94  having a V-shape may be formed on the wafer W. In  FIG. 10 , the liquid curtain  94  having a U-shape may be formed. As illustrated in  FIGS. 9 and 10 , a curvature of the liquid curtain  94  may be controlled. 
     The liquid curtain  94  may prevent foreign substances that break off from the wafer W during polishing or the polishing solution  92  from bouncing by the cup  85  and/or contaminating the surface of the wafer W. In  FIG. 9 , it is illustrated that only the rear surface of the peripheral portion of the wafer W is polished. However, when the side surface or the top surface of the wafer W is polished, the foreign substances that break off from the wafer W or the polishing solution may also contaminate the surface of the wafer W. Therefore, the liquid curtain  94  may prevent the surface of the wafer W from being contaminated when the peripheral portion of the wafer W is polished. The polishing solution supplying assembly  76  will be described in detail later. 
       FIG. 11  is a cross-sectional view illustrating a polishing solution supplying assembly of  FIGS. 2 to 4 .  FIG. 12  is a cross-sectional view illustrating a nozzle supporting block of  FIG. 11 .  FIG. 13  is a cross-sectional view illustrating a nozzle block of  FIG. 11 .  FIG. 14  is a plan view of a distributing plate included in the nozzle block of  FIG. 13 .  FIG. 15  is a view illustrating a bottom surface of the nozzle block of  FIG. 13 . 
     For example, the polishing solution supplying assembly  76  may include a polishing solution supplying line  90  for supplying the polishing solution and the nozzle supporting block  74  including an internal groove  106  connected to the polishing solution supplying line  90 . A fastening unit  102  capable of connecting the polishing solution supplying line  90  and an external polishing solution supplying source line (not shown) may be provided on one side of the nozzle supporting block  74 . The internal groove  106  may include a multistage groove  100  connected to the polishing solution supplying line  90  and an inclined groove  104  connected to the multistage groove  100 . The multistage groove  100  provided in the nozzle supporting block  74  may be formed of grooves having different diameters. In the nozzle supporting block  74 , the curvature of the liquid curtain may be determined in accordance with a radial angle A of the inclined groove  104  based on a central line of the inclined groove  104 . The radial angle A may be, for example, between a range of about 95 to about 105 degrees. 
     The polishing solution supplying assembly  76  includes the nozzle block  72  inserted into and fastened to the internal groove  106  of the nozzle supporting block  74  and including the distributing plate  120  for distributing the polishing solution. The nozzle supporting block  74  and the nozzle block  72  may be fastened by a fastening unit  124 . The fastening unit  124  may be formed of a female screw  124   a  provided in the multistage groove  100  of the nozzle supporting block  74  and a male screw  124   b  provided in a leading end of the nozzle block  72 . In the nozzle block  72 , the curvature of the liquid curtain may be determined in accordance with a radial angle B of the nozzle block  72 . The radial angle B may be, for example, between a range of about 95 to about 105 degrees. 
     The nozzle block  72  may horizontally rotate with respect to the wafer W as described above. The distributing plate  120  may include a central through hole  126  provided in a center and a distributing groove  128  for radially distributing the polishing solution around an upper surface of the central through hole  126 . A through nozzle  134  that passes through the nozzle block  72  may be formed in the distributing plate  120 . 
     The polishing solution may be supplied to the center of the wafer W through the through nozzle  134 . The through nozzle  134  may include a first through nozzle  130  of a first diameter. The first through nozzle  130  may be connected to the distributing plate  120 , and a second through nozzle  132 , which has a second diameter larger than the first diameter of the first through hole nozzle  130 , may be connected to the first through nozzle  130 . A leading end of the second through nozzle  132  connected to the first through nozzle  130  may include an internal inclined groove  135 . A hole  136  may be formed in a lower surface of the nozzle block  72  so that a fastening tool may be used when the nozzle block  72  is fastened to the nozzle supporting block  74 . 
     The polishing solution supplying assembly  76  may include a slit nozzle  122  positioned between the nozzle supporting block  74  and the nozzle block  72  to spray the polishing solution. The slit nozzle  122  may be formed in a space between the nozzle supporting block  74  and the nozzle block  72 . The space between the nozzle supporting block  74  and the nozzle block  72  may be controlled in accordance with sizes of the nozzle supporting block  74  and the nozzle block  72 . 
     The distributing groove  128  of the distributing plate  120  included in the nozzle block  72  may be connected to the slit nozzle  122 . The slit nozzle  122  may be formed along a surface of the inclined groove  104  of the nozzle supporting block  74 . A diameter of the slit nozzle  122  may be determined in accordance with diameters of the through nozzles  130  and  132 , for example, a diameter of the first through nozzle  130 . The curvature of the liquid curtain sprayed from the slit nozzle  122  may be determined in accordance with the diameter of the slit nozzle  122 . 
     The polishing solution may be sprayed through the slit nozzle  122  so that the above-described liquid curtain may be formed. As described above, the internal groove  106  of the nozzle supporting block  74  may include the inclined groove  104 . Therefore, the U-shaped or V-shaped liquid curtain may be formed by the polishing solution sprayed through the slit nozzle  122 . 
     The above-described polishing solution supplying assembly  76  may form the liquid curtain by supplying the polishing solution through the polishing solution supplying line  90  and spraying the polishing solution through the slit nozzle  122 . 
       FIG. 16A  is a particle map diagram of a wafer when the wafer is polished using a liquid curtain according to one of example embodiments illustrated in  FIGS. 9 and 10 .  FIG. 16B  is a particle map diagram of a wafer when the wafer is polished without using a liquid curtain according to a comparative example. 
     For example, as illustrated in  FIG. 16A , when the peripheral portion of the wafer W is polished by the polishing apparatus using the liquid curtain according to some example embodiments, particle map diagrams before and after polishing are the same. 
     On the other hand, as illustrated in  FIG. 16B , when the peripheral portion of the wafer W is polished by the polishing apparatus without using the liquid curtain according to the comparative example, many particles may be observed in the particle map diagram of the wafer after polishing. The particles observed on the wafer may significantly reduce yield of a semiconductor device. 
       FIG. 17A  is a view illustrating particles observed on a surface of a wafer when the wafer is polished using a liquid curtain according to one of the example embodiments illustrated in  FIGS. 9 and 10 .  FIG. 17B  is a view illustrating particles observed on a surface of a wafer when the wafer is polished without using a liquid curtain according to a comparative example. 
     For example, as illustrated in  FIG. 17A , when the peripheral portion of the wafer W is polished by the polishing apparatus using the liquid curtain according to some example embodiments, angular particles may not be observed on the wafer W. 
     By contrast, as illustrated in  FIG. 17B , when the peripheral portion of the wafer W is polished by the polishing apparatus without using the liquid curtain according to the comparative example, angular particles may be observed on the wafer. The angular particles observed on the wafer may significantly reduce yield of a semiconductor device. 
     While example embodiments have been particularly shown and described with reference to some example embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the following claims.