This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. JP2006-090097 filed Mar. 29, 2006, the entire content of which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a processing method in which a peripheral reinforcing portion of a wafer (for example, a semiconductor wafer), which is formed around a device region of the wafer having devices (for example, semiconductor chips) formed thereon and is thicker than the device region, is removed from the wafer. 
   2. Description of the Related Art 
   In general, semiconductor chips, which are used in various electronic apparatuses, are produced by the following method. That is, grid-like rectangular regions are defined by predetermined division lines on a disc-shaped semiconductor wafer, and electronic circuits are formed on surfaces of the rectangular regions. Next, a rear surface of the wafer is ground so as to be thinned. The wafer is divided along the predetermined division lines. As a result, semiconductor chips are produced. In recent years, electronic apparatuses have been greatly improved in compactness and thinness. In accordance with this, semiconductor chips are required to be even thinner, and semiconductor wafers are required to be thinner than previously. 
   When a semiconductor wafer is thinned, the rigidity of the semiconductor wafer is decreased. Due to this, it is difficult to handle the semiconductor wafer after the thinning, and cracking easily occurs in the semiconductor wafer. In order to solve these problems caused by the thinning, only the rear surface of circular device region, which has semiconductor chips formed on the surface, is ground so as to be thinned, and a ring-shaped peripheral extra region around the device region is thereby formed as a relatively thick reinforcing portion. In this case, since the rear surface is ground, the thick peripheral reinforcing portion projects on the rear surface, and the entire semiconductor wafer has a recessed shape in cross section. The technique, in which only the peripheral portion is allowed to be thick, has been disclosed in Japanese Unexamined Patent Applications Publication Nos. 2004-281551 and 2005-123425. 
   In conventional techniques, in order to easily handle a thinned semiconductor wafer, a protective tape was applied to a surface of the semiconductor wafer so as to provide rigidity thereto. However, when a metal film composed of gold is provided by a method (for example, deposition or sputtering) on a rear surface of the semiconductor wafer after thinning, the protective tape has insufficient heat-resistance, so that the processing temperature needs to be lower. Due to this, processing is more time-consuming in this case than in normal cases. In contrast, in the above rigidity improvement technique by formation of a peripheral reinforcing portion, since the rigidity is maintained even when the protective tape is peeled from the semiconductor wafer after the thinning, the above rigidity improvement technique by formation of a peripheral reinforcing portion is superior in that deposition or sputtering can be performed without consideration of heat effects. 
   In the above manner, the semiconductor wafer is finally divided into plural semiconductor chips. In this case, a typical dividing method for semiconductor wafer is a method in which a semiconductor wafer, which is chucked and held on a vacuum chuck-type table, is cut off by a cutting blade. In this method, a rear surface of the semiconductor wafer is applied to and supported by an adhesive surface of a dicing tape which is provided to a ring-shaped dicing frame, and the dicing tape is chucked on the chuck table. As a result, the semiconductor wafer is supported by the chuck table. 
   In this case, if the semiconductor wafer has a typical plate shape, the entire rear surface of the semiconductor wafer closely contacts the chuck table, so that the semiconductor wafer is stably held. However, when the semiconductor wafer has the above peripheral reinforcing portion, it is difficult to stably hold the semiconductor wafer. In order to solve this problem, it was conceived that the chuck table could be modified to have a shape to which the recessed rear surface of the semiconductor wafer having the above peripheral reinforcing portion is fitted. However, since this modification of the chuck table is not practical, the above peripheral reinforcing portion of the semiconductor wafer is removed, so that the entire semiconductor wafer is processed to have a plate shape. 
   In a method for removing a peripheral reinforcing portion, as shown in  FIGS. 9 and 10 , a semiconductor wafer  1  applied on a dicing tape  501  is held on a rotating chuck table, and a cutting blade  502  for dividing the semiconductor wafer  1  into semiconductor chips cuts a circular boundary between a device region  4  and a peripheral reinforcing portion  5   a . Next, for example, the semiconductor wafer  1  is rotated by rotating the chuck table  501 , so that the peripheral reinforcing portion  5   a  is cut off. However, in this method, since a cut width  502   a  by the cutting blade  502  is wider than an edge thickness of the cutting blade  502  due to difference between an inner circumference and an outer circumference of the cutting blade  502 , a peripheral portion of the device region  4  is also subjected to the cutting, so that outer diameter of the device region  4  becomes small. As a result, the number of the obtained semiconductor chip becomes small, that is, the yield of the semiconductor chips becomes small. 
   In order to solve the above problem, as shown in  FIGS. 11 and 12 , in another method for removing a peripheral reinforcing portion, while a semiconductor wafer  1  is rotated by rotating a chuck table  503 , and a grinding wheel  504  having a rotational shaft parallel to that of the chuck table  503  is rotated, plural grinding stones  505  are pressed on a peripheral reinforcing portion  5   a , so that the peripheral reinforcing portion  5   a  is cut and removed. It was conceived that this method was advantageous since the above problem due to the difference between the inner circumference and the outer circumference of the cutting blade  502  was not caused. However, in this method, it is necessary to control the center distance between the chuck table  503  and the grinding wheel  504  with high precision. That is, it is necessary that outermost circumferential edge of rotation locus of the rotating grinding stones  505  corresponds to a boundary between the device region  4  and the peripheral reinforcing portion  5   a  of the semiconductor wafer  1 . Even if the outermost circumferential edge thereof is positioned slightly insider than the boundary between the device region  4  and the peripheral reinforcing portion  5   a  on the semiconductor wafer  1 , the peripheral portion of the device region  4  is ground. Due to this, semiconductor chips on the cut peripheral portion thereof cannot be used, and the yield of the semiconductor chips is decreased. However, this method does not have a function for recognizing and controlling the position of rotation locus of edges of the grinding stones  505 , and the grinding stones  505  are away from the rotational shaft of the grinding wheel  504 . As a result, in practice, it is difficult to control grinding points of the grinding stones  505  with high precision and fineness, and grinding of the device region  4  cannot be avoided. 
   In addition, in this method, a case in which the semiconductor wafer  1  is concentric with the rotation center of the chuck table  503  does not cause a problem. However, in a case in which the semiconductor wafer  1  is not concentric with the rotation center of the chuck table  503 , this case often occurring, the semiconductor wafer  1  is eccentric. Due to this, when the entire peripheral reinforcing portion  5   a  is ground, the grinding stones  505  overlap with a portion of the device region  4 , so that this portion cannot be used, and the yield of the semiconductor chips is decreased. As shown in  FIG. 12 , when the center of the semiconductor wafer  1  rotating eccentrically is the most remote from the grinding stones  505  as shown by a broken line, the only peripheral reinforcing portion  5   a  is ground by the grinding stones  505 . However, when the center of the semiconductor wafer  1  rotating eccentrically is proximate to the grinding stones  505  as shown by a two-dot chain line, the grinding stones  505  overlap with the device region  4 , and the device region  4  is ground by the grinding stones  505 . 
   SUMMARY OF THE INVENTION 
   Therefore, an object of the present invention is to provide a processing method for a wafer, which can reliably obtain a device region of the wafer as large as possible by precisely removing only peripheral reinforcing portion of the wafer and thereby does not decrease yield of semiconductor chips when the peripheral reinforcing portion is processed around the device region so that the wafer has a plate shape. 
   According to one aspect of the present invention, a processing method for a wafer includes: preparing a wafer which has a device region having plural devices formed on a surface of the wafer; and a peripheral reinforcing portion which is integrally formed around the device region and has a projection projecting outwardly on a rear surface of the wafer. The processing method further includes: holding the wafer on a holding surface of a rotatable holding table such that the rear surface of the wafer is exposed and the surface of the wafer closely contacts the holding table. The processing method further includes: thinning the peripheral reinforcing portion by cutting and removing at least the projection of the peripheral reinforcing portion of the wafer by using a cutting tool having a rotational shaft parallel to the holding surface, while rotating the wafer by rotating the holding table after the holding of the wafer. The peripheral reinforcing portion is thinned so as to have a thickness equal to or thinner than that of the device region by the thinning. 
   In the processing method of the present invention, the cutting tool having the rotational shaft parallel to the holding surface is appropriately moved in a predetermined direction parallel to the holding surface and in a direction perpendicular to the predetermined direction, and the cutting tool cuts the projection of the peripheral reinforcing portion, so that the projection is removed and the rear surface of the wafer has a plate shape. In the processing method, since the rotational shaft of the cutting tool is parallel to the holding surface of the holding table, the cutting point of the cutting tool corresponds to a position of the rotational shaft at which the cutting tool is mounted. Therefore, since the cutting position of the cutting tool with respect to the projection is easily controlled, the peripheral reinforcing portion can be reliably removed. As a result, the device region can be secured as large as possible. 
   Examples of devices and actions for cutting the peripheral reinforcing portion of the wafer by the cutting tool can be used as follows. In one method example, the cutting tool has a width equal to or wider than that of the projection, and the cutting tool is pressed toward a top end surface of the projection of the rotating wafer in a thickness direction of the wafer, and the cutting tool cuts the projection. In this method, the projection is removed by one movement of the cutting tool which presses the entire width of the top end surface of the projection in a thickness direction of the projection. In another method example, entry amount of the cutting tool with respect to the wafer in a thickness direction of the wafer is set such that an edge of the cutting tool corresponds to the rear surface of the device region, and the cutting tool faces the projection and moves parallel to the holding surface toward a side of the projection. In this method, the projection is removed by one movement of the cutting tool which presses the side of the projection so as to cut the projection. 
   In another method example, the cutting tool moves relatively to the wafer parallel to the holding surface, so that the cutting tool cuts and removes at least the projection. In this method, in particular, the cutting tool may move parallel to an axial direction of the rotational shaft. In the relative movement, at least one of the cutting tool and the holding table may move parallel to the holding surface. In this case, while the wafer may be reciprocated, the cutting tool may be pressed on the top end surface of the projection, thereby cutting the projection. As a result, the projection can be removed efficiently. 
   In the wafer of which the projection of the peripheral reinforcing portion will be removed in the above processing method of the present invention, the rigidity can be secured by the peripheral reinforcing portion, so that the handleability and the durability can be improved. Therefore, since heat due to deposition, sputtering, or the like cause no problem, a metal film may be provided to a region of the rear surface which corresponds to the device region. 
   In the present invention, the processing is performed by using the cutting tool having the rotational shaft parallel to the holding surface such that at least the projection of the peripheral reinforcing portion is cut and removed and the peripheral reinforcing portion is thinned so as to have a thickness equal to or thinner than that of the device region. Therefore, only the peripheral reinforcing portion can be reliably removed, so that the device region can be secured as large as possible. As a result, the wafer can be processed to have a plate shape without decreasing the yield of semiconductor chips. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A to 1C  are a surface side perspective view, a rear surface side perspective view, and a cross sectional view which show a wafer processed in an embodiment according to the present invention. 
       FIG. 2  is an overall perspective view of a wafer processing apparatus of the embodiment according to the present invention. 
       FIG. 3  is a plan view of the wafer processing apparatus shown in  FIG. 2 . 
       FIG. 4  is a plan view which shows a wafer hand of wafer supply section of the wafer processing apparatus. 
       FIGS. 5A to 5D  are side views which show actions of the wafer hand in turn. 
       FIGS. 6A and 6B  are a plan view and a cross sectional view which show a dicing tape and a dicing frame. 
       FIGS. 7A to 7H  are side views which show an action example of the cutting blade in turn, the cutting blade cutting a peripheral reinforcing portion of the wafer. 
       FIGS. 8A to 8C  are side views which show a process in turn, in which the dicing tape is applied to the rear surface of the wafer by a pressing roller. 
       FIG. 9  is one example of conventional method for removing a peripheral reinforcing portion. 
       FIG. 10  is a cross sectional view of the method shown in  FIG. 9 . 
       FIG. 11  is another example of conventional method for removing a peripheral reinforcing portion. 
       FIG. 12  is an enlarged view of the method shown in  FIG. 11 . 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   An embodiment of the present invention will be explained hereinafter with reference to the drawings. 
   1. Semiconductor Wafer 
   In  FIGS. 1A to 1C , reference numeral  1  denotes a disc-shaped semiconductor wafer (hereinafter referred to simply as “wafer”) which is processed in the embodiment. The wafer  1  is a silicon wafer or the like. As shown in  FIG. 1A , grid-like predetermined division lines  2  are formed on a surface of the wafer  1 , and plural rectangular semiconductor chips  3  are defined by the predetermined division lines  2  on the surface of the wafer  1 . Electronic circuits (for example, Integrated Circuits (ICs) and Large Scale Integrations (LSIs)), which are not shown in  FIGS. 1A to 1C , are formed on surfaces of the semiconductor chips  3 . The plural semiconductor chips  3  are formed on a device region  4  which is almost circular so as to be concentric with the wafer  1 . A ring-shaped peripheral extra region  5 , which has no semiconductor chip  3  formed thereon, is formed around the device region  4 . 
     FIGS. 1B and 1C  are views in which a rear surface of the wafer  1  faces upward. As shown in  FIGS. 1B and 1C , the rear surface of the wafer  1  has a ring-shaped peripheral edge portion (hereinafter referred to simply as “ring-shaped projection  6 ”) which projects outwardly thereon. A recess  4   a  is formed inside the ring-shaped projection  6 . A portion of the rear surface which corresponds to the device region  4  is ground and removed by a grinding stone or the like, so that the recess  4   a  is formed. The peripheral extra region  5  is not ground and remains as it is, and it is thereby used as a peripheral reinforcing portion  5   a . The peripheral reinforcing portion  5   a  has the ring-shaped projection  6  projecting on the rear surface of the wafer  1 . For example, in the wafer  1 , the peripheral reinforcing portion  5   a  has a thickness of about 600 μm. For example, the device region  4  which is thinned by formation of the recess  4   a  has a thickness of about 50 to 100 μm. 
   The wafer  1  may have a metal film on a region of the rear surface corresponding to the device region  4 , that is, a bottom of the recess  4   a . For example, the metal film is composed of Au and is formed by a method (for example, deposition or sputtering). The wafer  1  may be subjected to a predetermined heating process for ion implantation from the rear surface of the wafer  1 . As shown in  FIGS. 1A to 1C , a protective tape  7  for protecting the electronic circuits of the semiconductor chips is applied on the surface of the wafer  1 . Next, this wafer  1  is transferred to the following processing. 
   2. Wafer Processing Apparatus 
   A wafer processing apparatus, which is desirably used for a processing method of the present invention, will be explained hereinafter with reference to  FIGS. 2 to 8C .  FIGS. 2 and 3  are a perspective view and a plan view which show a processing apparatus  10 . The processing apparatus  10  is equipped with a pedestal  11 . From the right side to the left side in the X direction on the pedestal  11  shown in  FIG. 3 , a wafer supply section  100 , a wafer cutting section  200 , a dicing tape applying section (holding tape applying device)  300 , and a dicing tape carrying section  400  are provided in turn. These sections will be explained hereinafter. 
   2-a. Wafer Supply Section 
   The wafer supply section  100  is equipped with a wafer carrier  101 , a pair of carrying belts  102 , a first stopper  111 , a second stopper  112 , a wafer hand  120 , and a wafer hand driving mechanism  140 . The wafer carrier  101  is disposed at one end side (lower end side in  FIG. 3 ) of the Y direction on the pedestal  11 . The carrying belts  102  extend from the wafer carrier  101  to the other side of the Y direction. The first stopper  111  and the second stopper  112  are provided at a middle portion and a downstream portion (upper end portion in  FIG. 3 ) of the carrying belts  102  between the carrying belts  102 . The wafer hand  120  picks up a wafer  1  and carries it to the wafer cutting section  200 . The wafer hand driving mechanism  140  moves the wafer hand  120  in the X, Y and Z directions. 
   Plural wafers  1  are provided in the wafer carrier  101  so as to be stored horizontally such that rear surfaces of the wafers  1  face upward. The wafer carrier  101  has an elevating mechanism therein. The wafer carrier  101  moves wafers  1 , which are provided therein, vertically by one step by using the elevating mechanism. The wafer  1  moved to the lowest step by the elevating mechanism is mounted on the carrying belts  102 , and it is moved by the carrying belts  102  toward the stoppers  111  and  112 . The first stopper  111  is a vertical moving type stopper or a retractable type stopper so as to stop at a stopper position and a non-stop position. At the stopper position of the first stopper  111 , the wafer  1  carried by the carrying belts  102  abuts to the first stopper  111 . From the stopper position to the non-stop position, the first stopper  111  moves downwardly so that the wafer  1  passes therethrough. The second stopper  112  is securing type stopper for stopping the wafer  1 . 
   As shown in  FIGS. 4 to 5D , the wafer hand  120  is equipped with a disc-shaped base  121 , plural hand picks  122 , a disc-shaped gear plate  123 , and a hand shaft  124 . The hand picks  122  are provided on the base  121 . The gear plate  123  is disposed above the base  121 . The hand shaft  124  is secured at the center of the gear plate  123  and extends upward. Plural (in the embodiment, four) pick shafts  125  which extend in the Z direction (vertical direction) are provided at a circumferential portion of the base  121  so as to be equally spaced from each other. The pick shafts  125  penetrate the circumferential portion so as to be rotatable and so as not to be movable in the axial direction. The hand picks  122  are provided at end portions of the pick shafts  125  which project downwardly from the base  121 . The hand picks  122  are relatively flat conical so as to broaden outwardly in the lower direction. 
   On the other hand, gear portions  125   a  are formed at end portions of the pick shafts  125  which project upwardly from the base  121 . Gear portions  123   a , which are formed on a peripheral surface of the gear plate  123 , mesh with the gear portions  125   a  of the pick shafts  125 . The gear plate  123  and the pick shafts  125  are concentric with the hand shaft  124 . When the gear plate  123  rotates together with the hand shaft  124  in one direction, the rotation thereof is transmitted to each pick shaft  125  via the gear portions  123   a  and  125   a , and the hand pick  122  rotates in cooperation therewith. 
   Each hand pick  122  has a teardrop shape in plan view. The hand picks  122  are provided on the pick shafts  125  such that leading end portions  122   a  of all hand picks  122 , which are sharply angled, face the rotational axis of the hand shaft  124  when they are positioned at a predetermined rotation angle. When the leading end portions  122   a  of all hand picks  122  face the rotational axis of the hand shaft  124  in the above manner, as shown in  FIG. 5C , the wafer  1  can be received on the leading end portions  122   a  of the hand picks  122 . As shown in  FIG. 5B , when the hand picks  122  are rotated by about 180 degrees from the above pick-up positions, the wafer  1  cannot be received on the hand picks  122 , so that the wafer  1  can pass through the inside of each hand pick  122 . 
   As shown in  FIGS. 2 and 3 , the hand shaft  124  of the wafer hand  120  is rotatably and elevatably supported by a Z axis driving mechanism  170  of the wafer hand driving mechanism  140 . In the Z axis driving mechanism  170 , a driving mechanism for rotating and vertically elevating of the hand shaft  124  is provided. The wafer hand driving mechanism  140  has a Y axis driving mechanism  150 , an X axis driving mechanism  160 , and the Z axis driving mechanism  170 . The Y axis driving mechanism  150  is provided proximate to the carrying belts  102  on the pedestal  11  via a column  130 , and it extends in the Y direction. The X axis driving mechanism  160  is provided so as to engage with the Y axis driving mechanism  150  and cross above the carrying belts  102  in the X direction. The Z axis driving mechanism  170  engages with the X axis driving mechanism  160  and extends in the Z direction. 
   The Y axis driving mechanism  150  and the X axis driving mechanism  160  are screw rod type driving mechanisms. The Y axis driving mechanism  150  moves the X axis driving mechanism  160  in the Y direction. The X axis driving mechanism  160  moves the Z axis driving mechanism  170  in the X direction. The wafer hand  120  is moved in the X, Y and Z directions by the Y axis driving mechanism  150 , the X axis driving mechanism  160 , and the Z axis driving mechanism  170 . Next, the wafer hand  120  picks up the wafer  1  which is stopped by the first stopper  111  or the second stopper  112 , and it moves the wafer  1  to the wafer cutting section  200 . 
   2-b. Wafer Cutting Section 
   The wafer cutting section  200  is equipped with a first chuck table  201 , a second chuck table  202 , and a cutting unit  220 . The first chuck table  201  and the second chuck table  202  are provided proximate to wafers  1  stopped by the stoppers  111  and  112 . The cutting unit  220  moves so as to cross above the chuck tables  201  and  202  in the Y direction. The chuck tables  201  and  202  are typical vacuum chuck type tables. The chuck tables  201  and  202  have holding surfaces  201   a  and  202   a  which are flat upper surfaces for chucking and holding the wafers  1 . The chuck tables  201  and  202  are rotated by rotation driving mechanisms (not shown in the drawings) around each center which is a rotational axis. The chuck tables  201  and  202  are rotatably supported by table bases  211  and  212  which reciprocate in the X direction. A cornice-shaped cover  215  is stretchably provided on both sides of the moving direction of each table base  211  and  212  so as to cover the moving path of each table base  211  and  212  in order to prevent intrusion of cut waste or the like thereinto. 
   Each chuck table  201  and  202  reciprocates together with the table bases  211  and  212  from the neighborhood of the wafer supply section  100  to the dicing tape applying section  300  in the X direction. The wafer  1  is carried onto the chuck table  201  ( 202 ) by the wafer hand  120  such that the rear surface of the wafer  1 , on which the ring-shaped projection  6  of the peripheral reinforcing portion  5   a  projects, faces upward. Next, while the wafer  1  is held on the chuck table  201  ( 202 ), the peripheral reinforcing portion  5   a  including the ring-shaped projection  6  is cut and removed by the cutting unit  220 . 
   The cutting unit  220  is equipped with a cylindrical spindle housing  221  and a cutting blade  222 . The spindle housing  221  has an axial direction parallel to the Y direction. The cutting blade  222  is provided on a spindle which is a rotation driving shaft provided in the spindle housing  221 . The spindle housing  221  is supported by a frame (not shown in the drawings) provided on the pedestal  11  so as to reciprocate in the Y direction and move vertically in the Z direction while the axial direction of the spindle housing  221  is parallel to the Y direction. A driving mechanism (not shown in the drawings) for moving the cutting unit  220  in these directions is provided on the frame. The cutting blade  222  has an axial direction parallel to the Y direction. That is, the axial direction of the cutting blade  222  is parallel to the holding surfaces  201   a  and  202   a  of the chuck tables  201  and  202 . 
   As shown in  FIG. 2 , a blade cover  223  is provided at an end portion (lower end portion in  FIG. 3 ) of the spindle housing  221  which is proximate to the cutting blade  222 . Cutting water nozzles  224  and  225  are provided on the blade cover  223 , and they supply cutting water onto processed points of the wafer  1 . The cutting water is used for lubricating, cooling, cleaning, and the like during the cutting. The cutting unit  220  is provided so as to cross above the chuck tables  201  and  202  in the Y direction, so that cutting unit  220  can cut the wafer  1  held on the first chuck table  201  and the second chuck table  202 . 
   2-c. Dicing Tape Carrying Section 
   The movable ranges of the chuck tables  211  and  212  in the X direction are about 2 to 3 times as long as the lengths (widths) of the chuck tables  211  and  212 . An area which extends from a middle point of the movable range and is proximate to the wafer supply section  100  is set as an area of the wafer cutting section  200 . An area which extends from the middle point of the movable range and is proximate to the dicing tape carrying section  400  is set as an area of the dicing tape applying section  300 . A cleaning water shower nozzle  230  and an air nozzle  240  are arranged next to each other at a boundary portion between the wafer cutting section  200  and the dicing tape applying section  300 . The cleaning water shower nozzle  230  sprays cleaning water onto the wafer  1  disposed on the chuck table  201 . The air nozzle  240  blows high pressure air onto the wafer  1  on which the cleaning water is sprayed, thereby removing the water therefrom. The nozzles  230  and  240  are long tubular nozzles which extend in the Y direction, and they have plural spraying openings which are dotted in the longitudinal direction thereof and face downward. The cleaning water shower nozzle  230  is disposed on the side of the wafer cutting section  200 , and the air nozzle  240  is disposed on the side of the dicing tape applying section  300 . The nozzles  230  and  240  are provided so as to cross above the moving paths of the table bases  211  and  212  via a column  250  which stands on the pedestal  11 . 
   The dicing tape applying section  300  is equipped with a pressing roller  310  and a roller driving mechanism  320 . The pressing roller  310  presses and applies the dicing tape  31 , which is shown in  FIGS. 6A and 6B , on the wafer  1 . The roller driving mechanism  320  moves the pressing roller  310  in the Y and Z directions. The pressing roller  310  has a surface composed of elastic body (for example, rubber) which is appropriately elastic. The pressing roller  310  is rotatably supported by an X direction rotation shaft of roller frame  311 . The roller frame  311  is elevatably supported by a Z axis driving mechanism  370  of the roller driving mechanism  320  via a shaft  312  which extends in the Z direction. The Z axis driving mechanism  370  has an elevating mechanism therein. The elevating mechanism elevates the shaft  312  and the pressing roller  310 . 
   The roller driving mechanism  320  is equipped with a Y axis driving mechanism  350  and the Z axis driving mechanism  370 . The Y axis driving mechanism  350  is supported by a column  340  which stands on the pedestal  11 . In this case, the Y axis driving mechanism  350  is provided so as to cross above the moving paths of the table bases  211  and  212  in the Y direction. The Z axis driving mechanism  370  is provided proximate to the dicing tape carrying section  400  of the Y axis driving mechanism  350 . The Z axis driving mechanism  370  engages with the Y axis driving mechanism  350  and extends in the Z direction. The Y axis driving mechanism  350  is a screw rod type driving mechanism and moves the Z axis driving mechanism  370  in the Y direction. The pressing roller  310  is reciprocated on the moving paths of the table bases  211  and  212  by the Y axis driving mechanism  350 . The pressing roller  310  is elevated by the Z axis driving mechanism  270 . 
   2-d. Dicing Tape Carrying Section 
   The dicing tape carrying section  400  carries the dicing tape  31 , which is shown in  FIGS. 6A and 6B , to the dicing tape applying section  300 . For example, the dicing tape  31  is an adhesive tape which has a base film and an adhesive coated on a surface of the base film. For example, the base film of the dicing tape  31  is composed of polyvinylchloride and has a thickness of about 100 μm. The adhesive is composed of acrylic resin and has a thickness of about 5 μm. A ring-shaped dicing frame  32  is applied to the adhesive surface of the dicing tape  31 . The dicing frame  32  has an inner diameter larger than the diameter of the wafer  1 . The dicing frame  32  is composed of a rigid member (for example, a metal plate). The wafer  1  is applied to the dicing tape  31 , and handling (for example, carrying) of the wafer  1  is performed by holding the dicing frame  32 . 
   The dicing tape carrying section  400  is equipped with a cassette  405 , a drawing clamp  410 , a carrying clamp portion  420 , and a clamp driving mechanism  430 . The cassette  405  is disposed at an end portion (lower end portion in  FIG. 3 ) of the Y direction on the pedestal  11 . The drawing clamp  410  is disposed proximate to the other end portion of the cassette  405  in the Y direction, and draws a dicing frame  32 , which has one dicing tape, from the cassette  405 . The carrying clamp portion  420  carries the dicing frame  32 , which is held by the drawing clamp  410 , to the dicing tape applying section  300 . The clamp driving mechanism  430  moves the carrying clamp portion  420  in the X, Y and Z directions. 
   Plural dicing frames  32  which have dicing tapes are stored and provided in the cassette  405  such that adhesive surfaces of the dicing tapes  31  face downward and are disposed horizontally. The clamp driving mechanism  430  is equipped with a Y axis driving mechanism  450 , an X axis driving mechanism  460  and a Z axis driving cylinder  470 . The Y axis driving mechanism  450  has the same construction as that of the Y axis driving mechanism  150  of the wafer supplying section  100 . The X axis driving mechanism  460  has the same construction as that of the X axis driving mechanism  160  of the wafer supplying section  100 . The cassette  405  moves the dicing frame  32  vertically by one step by using an elevating mechanism provided therein in the same manner as the wafer carrier  101 . The dicing frame  32 , which is moved to a predetermined drawing position, is drawn from the cassette  405  by the drawing clamp  410 . 
   The Y axis driving mechanism  450  of the clamp driving mechanism  430  is provided via a column  480  at a side (left side in  FIG. 3 ) which is appropriately away from the cassette  405  in the other side of the Y direction. The disposed position of the Y axis driving mechanism  450  corresponds to a line extending from the direction in which the second chuck table  202  moves toward the dicing tape carrying section  400 . The X axis driving mechanism  460  extending to the dicing tape applying section  300  engages with the Y axis driving mechanism  450 . 
   The drawing clamp  410  holds one dicing frame  32  provided in the cassette  405 . The drawing clamp  410  is provided in a groove  411  which is formed on the upper surface of the pedestal  11  and extends in the Y direction. The drawing clamp  410  is movable along the groove  411  and is reciprocated between the cassette  405  and the X axis driving mechanism  460  by using a driving mechanism which is not shown in the drawings. 
   The Z axis driving cylinder  470  engages with the X axis driving mechanism  460  via a base plate  471 . As shown in  FIGS. 8A to 8C , the Z axis driving cylinder  470  has a piston  473  which is stretchable downwardly. The carrying clamp portion  420  has a stay  421  and a pair of carrying clamps  422 . The stay  421  has an end portion which is secured at a lower end of the piston  473  of the Z axis driving cylinder  470 , and the stay  421  extends in the X direction toward the dicing tape applying section  300 . The carrying clamps  422  are provided on a surface of the stay  421 , which faces the cassette  405 , so as to be spaced a predetermined distance from each other in the X direction. The carrying clamp  422  holds the dicing frame  32  in the same manner as the drawing clamp  410 . 
   In the clamp driving mechanism  430 , the Y axis driving cylinder  450  moves the X axis driving mechanism  460  in the Y direction, and the X axis driving mechanism  460  moves the Z axis driving cylinder  470  in the X direction. Therefore, the carrying clamp portion  420  is moved together with the X axis driving mechanism  460  in the Y direction, and is moved together with the Z axis driving cylinder  470  in the X direction. The carrying clamp portion  420  is moved vertically (in the Z direction) by the piston  473  of the Z axis driving cylinder  470 . 
   3. Action of Wafer Processing Apparatus 
   Next, an action example of the above constructed wafer processing apparatus  10  will be explained hereinafter. 
   One wafer  1  is drawn from the wafer carrier  101  of the wafer supply section  100  by the carrying belts  102 . The wafer  1  is carried to the first stopper  111  by the carrying belts  102 , and the carrying belts  102  stop. The wafer  1  is abutted to the first stopper  111  and is stopped thereby. In this case, the rear surface of the wafer  1 , which has the recess  4   a  formed thereon, faces upward. Next, the wafer hand  120  picks up the wafer  1 . 
   As shown in  FIG. 5A , the wafer hand  120  is moved directly above the wafer  1  by the wafer hand driving mechanism  140  in the condition that the leading end portion  122   a  of the hand pick  122  faces outwardly. As shown in  FIG. 5B , the wafer hand  120  is moved downwardly by the Z axis driving mechanism  170 , so that the lower surface of the hand pick  122  is positioned lower than the lower surface of the wafer  1 . Next, the gear plate  123  is rotated by rotating of the hand shaft  124 , in cooperation with the gear plate  123 , and the hand pick  122  is rotated together with each pick shaft  125  by about 180 degrees. As shown in  FIG. 5C , the leading end portion  122   a  of the hand pick  122  moves under the lower surface of the wafer  1 . While this condition shown in  FIG. 5C  is maintained, as shown in  FIG. 5D , the wafer hand  120  is moved upwardly, so that the wafer  1  is held upwardly. Since a peripheral portion of the surface of the wafer  1 , which corresponds to the peripheral reinforcing portion  5   a , is received by the hand pick  122 , the wafer  1  can be carried without an excessive load being applied on the wafer  1 . 
   Next, the wafer hand  120  is appropriately carried in the X and Y directions by the wafer hand driving mechanism  140  and is moved downwardly, so that the wafer  1  is mounted on the first chuck table  201  of the wafer cutting section  200  which is moved proximate to the wafer supply section  100  beforehand and is under vacuum operation. The wafer  1  is chucked and held on the chuck table  201 . The wafer hand  120  is moved upwardly from the wafer  1  and is returned to the front side of the wafer carrier  101  in order to carry a next wafer  1 . The wafer  1  is desirably concentric with the rotation center of the first chuck table  201 . Alternatively, the center of the wafer  1  may be shifted slightly from the rotation center of the first chuck table  201 . 
   The first chuck table  201  holding the wafer  1  is rotated, and the table base  211  is moved toward the dicing tape applying section  300 , so that the rotation center of the first chuck table  201  corresponds to the rotational shaft of the cutting unit  220 . The cutting unit  220  is moved in the Y direction and is positioned above the wafer  1 . While the cutting blade  222  is rotated at a high speed, the cutting unit  220  is moved downwardly. The cutting blade  222  cuts the ring-shaped projection  6  of the peripheral reinforcing portion  5   a  of the wafer  1 , and it repeatedly reciprocates in the Y direction. As a result, at least the ring-shaped projection  6  of the peripheral reinforcing portion  5   a  is cut and removed. For example, the position of the cutting blade  220  in the Y direction is a position at which the cutting blade  220  cuts the other end portion (upper portion in  FIG. 3 ) of the Y direction on the peripheral reinforcing portion  5   a.    
     FIGS. 7A to 7H  show an action example of the cutting blade  222  which cuts the peripheral reinforcing portion  5   a . In this case, the cutting blade  222  has an edge thickness which is almost half of the width of the peripheral reinforcing portion  5   a.    
   As shown in  FIGS. 7A and 7B , first, the cutting blade  222  moves from the upside, and it cuts an inner circumferential side of the ring-shaped projection  6  of the peripheral reinforcing region  5   a . As shown in  FIG. 7C , the cutting blade  222  moves to an outer circumferential side of the ring-shaped projection  6  along the rotational shaft of the cutting blade  222 , so that the height of the ring-shaped projection  6  is reduced by one step. Next, as shown in  FIG. 7D , the cutting blade  222  moves downwardly, so that the cutting blade  222  cuts the outer circumferential side of the ring-shaped projection  6 . As shown in  FIG. 7E , the cutting blade  222  moves to the inner circumferential side of the ring-shaped projection  6 , so that the height of the ring-shaped projection  6  is further reduced by one step. Next, as shown in  FIG. 7F , the cutting blade  222  moves downwardly, and it cuts the inner circumferential side of the ring-shaped projection  6  slightly more deeply than the device region  4 . As shown in  FIG. 7G , the cutting blade  222  moves to the outer circumferential side of the ring-shaped projection  6 , the height of the ring-shaped projection  6  is further reduced by one step, and the cutting blade  222  moves away from the wafer  1 . As shown in  FIG. 7H , the wafer  1  is obtained such that the peripheral reinforcing region  5   a  is thinner than the device region  4 . The whole horizontal reciprocation direction of the cutting blade  222  extends along the rotational shaft of the cutting blade  222 , and the cutting direction of the cutting blade  222  is the Z direction (vertical direction). In the cutting of the wafer  1 , the appropriate amount of the cutting water is supplied from the cutting water nozzles  224  and  225  onto the processed points of the wafer  1 . 
   In the above manner, after the reinforcing region  5   a  is processed by the wafer cutting section  200 , the table base  211  is moved, so that the processed wafer  1  is disposed on the dicing tape applying section  300 . In the moving of the table base  211 , the cleaning water is sprayed from the cleaning water shower nozzle  230  onto the wafer  1 , so that ground waste and the like are cleaned. The high pressure air is blown from the air nozzle  240 , so that the water clinging on the wafer  1  is removed. 
   When the peripheral reinforcing portion  5   a  of the wafer  1  is processed by the wafer cutting section  200  and the processed wafer  1  is carried to the dicing tape applying section  300 , in the dicing tape carrying section  400 , one dicing frame  32  having the dicing tape  31  provided thereon is drawn from the cassette  405 , and the dicing frame  32  is carried to the dicing tape applying section  300 . 
   In the above action in the dicing tape carrying section  400 , first, the drawing clamp  410  holds one dicing frame  32  provided in the cassette  405 , it moves toward the X axis driving mechanism  460 , and it draws the dicing frame  32 . Next, the drawing clamp  410  moves the dicing frame  32  proximate to the first chuck table  201  disposed on the dicing tape applying section  300  as shown in  FIG. 3 . The carrying clamp portion  420  is disposed proximate to the other end side (upper end side in  FIG. 3 ) of the Y direction on the drawn dicing frame  32 , and the piston  473  is moved downwardly. The carrying clamp  422  holds the dicing frame  32 , and the holding of the dicing frame  32  by the drawing clamp  410  is stopped, so that the dicing frame  32  is received to the carrying clamp  422 . Next, the dicing frame  32  is held upwardly by moving the piston  473  upwardly, and the carrying clamp portion  420  is moved to the dicing tape applying section  300 . Therefore, the dicing tape  31 , which is provided on the dicing frame  32  held by the carrying clamp  422 , is moved directly above the wafer  1  disposed on the dicing tape applying section  300 . The dicing tape  31  is desirably disposed proximate to the wafer  1  so as to be spaced about several millimeters therefrom. 
   Next, the dicing tape  31  is applied on the rear surface of the wafer  1  by the pressing roller  310 . As shown in  FIG. 3 , the pressing roller  310  is waiting in advance at the end portion side (lower side in  FIG. 3 ) of the Y axis driving mechanism  350  in the Y direction. First, the pressing roller  310  is moved onto the dicing tape  31  by the Y axis driving mechanism  350 . Next, as shown in  FIG. 8A , after the pressing roller  310  is moved downwardly so as to abut to the surface of the dicing tape  31  by the Z axis driving mechanism  370 , the pressing roller  310  is further moved downwardly, so that the end portion of the dicing tape  31  is pressed on the rear surface of the wafer  1  by the pressing roller  310 . Next, as shown in  FIGS. 8B to 8C , while the pressing roller  310  presses the dicing tape  31 , the pressing roller  310  rolls toward the carrying clamp  422 . As a result, the dicing tape  31  is pressed on the rear surface of the wafer  1 , thereby being applied thereon. In this manner, the pressing roller  310  moves from one end side to the other end side on the rear surface of the wafer  1 , and the dicing tape  31  is pressed thereon by the pressing roller  310 , so that the dicing tape  31  can be applied without the air entering between the wafer  1  and the dicing tape  31 . 
   In the final stage of the above applying, an end portion of the dicing tape  31  is not applied on the wafer  1  due to a vertical gap between the dicing frame  32  and the wafer  1 , thereby being rolled up. Due to this, it is difficult to apply the end portion of the dicing tape  31  on the wafer  1  smoothly. In order to solve this difficulty, for example, the Z axis driving cylinder  470  is elastically supported with respect to the base plate  471  so as to be movable vertically by using a cushion spring, so that the carrying clamp  422  moves downwardly in accordance with the dicing tape  31 . Thus, the adhesion of the dicing tape  31  can be improved, so that the above technique is desirable. 
   In the above manner, the wafer  1  is processed such that the peripheral reinforcing portion  5   a  is thinner than the device region  4 , and the dicing tape  31  is applied onto the rear surface of the wafer  1 . Next, the dicing tape carrying section  400  operates in reverse of the above operation, so that the above wafer  1  is provided into the cassette  405 . Finally, the wafer  1  applied on the dicing tape  31  is cut along the predetermined division lines  2  by a cutting apparatus or the like, thereby being divided into plural semiconductor chips  3 . The above cutting and removing of the peripheral reinforcing portion  5   a  by the wafer cutting section  200  is performed in order that the ring-shaped projection  6  on the rear surface of the wafer  1  is removed and the rear surface becomes flat and can be held by a typical chuck table when the wafer  1  is divided into plural semiconductor chips  3 . 
   In the wafer cutting section  200  of the wafer processing apparatus  10 , while the cutting blade  222  reciprocates parallel to the rotational shaft of the cutting blade  222 , the cutting blade  222  cuts the ring-shaped projection  6  of peripheral reinforcing portion  5   a  of the wafer  1 . As a result, the ring-shaped projection  6  is cut off and removed. In this method, the axial movement of the cutting blade  222  (in practice, the cutting unit  220 ) is appropriately controlled so that the cutting blade  222  does not enter the device region  4 . Therefore, only the peripheral reinforcing portion  5   a  can be reliably removed, and the device region  4  can be secured as large as possible. As a result, the rear surface of the wafer  1  can be processed to be flat for applying the dicing tape  31  thereon without decreasing the yield of the semiconductor chips  3 . 
   If the wafer  1  is held such that the center of the wafer  1  corresponds to that of the chuck table  201  and the wafer  1  is concentric with the chuck table  201 , the reciprocation of the cutting blade  222  has an amplitude which simply corresponds to the width of the peripheral reinforcing portion  5   a . If the wafer  1  is held to be eccentric with the chuck table  201 , in one rotation of the chuck table  201 , the cutting blade  222  may enter the device region  4 . This case was one conventional problem. However, this problem can be relatively easily solved by the control method in which the cutting blade  222  reciprocates in the axial direction. This method can be realized as follows. For example, the mounted position of the wafer  1  on the chuck table  201  is recognized by using a microscope for alignment before the processing. The reciprocation of the cutting blade  222  is synchronized with the rotation of the chuck table  201 . 
   In the above embodiment, only the case in which the wafer  1  is cut on the first chuck table  201  is explained above. Alternatively, for example, in the wafer processing apparatus  10 , the chuck tables  201  and  202  may be used. In this case, the one of the chuck tables  201  and  202  may be used for the cutting, and the other of the chuck tables  201  and  202  may be used for the applying of the dicing tape  31 , so that the operation of the wafer processing apparatus  10  can be efficient. In the above embodiment, the wafer processing apparatus  10  has one cutting unit  220 . Alternatively, as shown in  FIG. 3 , another cutting unit  220  (shown by a broken line) may be provided to face the cutting unit  220 . In this case too, the peripheral reinforcing portion  5   a  may be cut by the axial reciprocation of the another cutting unit  220 . In this structure, since one peripheral reinforcing portion  5   a  of one wafer  1  can be cut by using the two cutting units  220 , the processing speed can be greatly reduced. 
   In the above embodiment, in the wafer cutting section  200 , the cutting unit  220  is reciprocated in the axial direction. Alternatively, the chuck table  201  and the table base  211  may be reciprocated in the axial direction of the cutting blade  222 , and the wafer  1  may be reciprocated with respect to the cutting blade  222  which is secured, and the peripheral reinforcing portion  5   a  may be cut. That is, the cutting unit  220  and the chuck table  201  may be relatively moved in the axial direction of the cutting blade  222 . In this case, at least one of the cutting unit  220  and the chuck table  201  may be moved.
A processing method for a wafer includes: preparing a wafer which has a device region having plural devices formed on a surface of the wafer; and a peripheral reinforcing portion which is integrally formed around the device region and has a projection projecting outwardly on a rear surface of the wafer. The processing method further includes: holding the wafer on a holding surface of a rotatable holding table such that the rear surface of the wafer is exposed and the surface of the wafer closely contacts the holding table. The processing method further includes: thinning the peripheral reinforcing portion by cutting and removing at least the projection of the peripheral reinforcing portion of the wafer by using a cutting tool having a rotational shaft parallel to the holding surface, while rotating the wafer by rotating the holding table after the holding of the wafer. The peripheral reinforcing portion is thinned so as to have a thickness equal to or thinner than that of the device region by the thinning.