Dicing tape attaching apparatus and dicing tape attaching method

A dicing tape attaching apparatus (10) comprises a fixed table (38) for supporting a mount frame (36), a movable table (31) for supporting a wafer (20) with the reverse surface thereof ground, and a height adjusting unit (70) such as a screw jack for adjusting the height of the movable table. When the dicing tape (3) is attached on the mount frame and the wafer, the height adjusting unit such as the screw jack so operates that the height of the dicing tape attaching surface of the wafer supported on the movable table coincides with the height of the upper surface of the mount frame supported on the fixed table. As a result, the wafer is prevented from forming cuts, cracks and internal distortions.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Japanese Application Number 2005-340145, filed on Nov. 25, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a dicing tape attaching method, for attaching a dicing tape on the back surface of a wafer, and to a dicing tape attaching apparatus for carrying out the method.

2. Description of the Related Art

In the semiconductor fabrication field, wafers have increased in size every year, on the one hand, and, in order to increase the mounting density, the thickness of the wafer has been reduced. The thickness of the wafer is reduced by a back grind process which grinds the back surface of the semiconductor wafer. In the back grind process, a surface protective tape is attached on the front surface of the wafer to protect the semiconductor elements formed on the front surface.

FIG. 7is an enlarged sectional view of a circular wafer with a surface protective film attached on the front surface of the wafer. As can be understood fromFIG. 7, the edge portion25of the circular wafer20is originally chamfered. Also, a surface protective film11is attached on the front surface21of the wafer20. As shown inFIG. 7, in the case where the wafer20is back ground and reduced in thickness from Z0to Z1, the chamfered portion27on the back surface of the wafer20is cut off, and the new back surface22(ground surface) of the wafer20reaches the chamfered portion26of the front surface.

Next, as shown inFIG. 8, the wafer20is inverted with the back surface22up and arranged in a mount frame36somewhat larger than the wafer20. By moving an attaching roll146, such as a rubber roll, from one end to the other of the mount frame36, the dicing tape3is attached on both the wafer20and the mount frame36. As a result, the back ground wafer20is integrated with the mount frame36for an improved handling characteristic of the wafer20in the subsequent processes.

FIGS. 9aand9bare sectional views taken along the attaching roll146and shown by the dotted line and the solid line, respectively. Specifically,FIG. 9ashows the state in which the dicing tape3begins to be attached at the end portion28of the wafer20.FIG. 9b, on the other hand, shows the state in which the dicing tape is attached to about central portion of the wafer20. As can be understood from these drawings, the wafer20and the mount frame36are supported on tables131,138, respectively.

As can be understood by reference toFIG. 7, the thickness of the wafer20is reduced by back grinding and, therefore, the end portion28of the wafer20after back grinding corresponds to the chamfered portion26. At the time of starting to attach the dicing tape3as shown inFIG. 9a, therefore, a force is exerted in the direction of arrow in such a way that the central portion, or thereabouts, of the attaching roll146is deformed and the chamfered portion26of the wafer20lacking a surface protective film11is pressed. Also, immediately before the end of the process of attaching the dicing tape3, a similar force is exerted at the end portion29opposite of the end portion28.

Also, at about the central portion of the wafer20, as shown inFIG. 9b, the attaching roll146is deformed at the edges of the wafer20, and the ends of the wafer20perpendicular to the moving direction the attaching roll146are curved downward. This force may form cuts or cracks at the ends of the wafer20, so that the yield of the products is reduced. Even in the case where cuts or cracks do not occur, internal distortions of the wafer is caused and may appear as cuts or cracks in the subsequent processes.

This invention has been achieved in view of this situation, and the object thereof is to provide a dicing tape attaching method in which the dicing tape can be attached on the mount frame and the wafer without forming cuts or cracks or internal distortions of the wafer, and a dicing tape attaching apparatus for carrying out the method.

SUMMARY OF THE INVENTION

In order to achieve the object described above, according to a first aspect of the invention, there is provided a dicing tape attaching apparatus for attaching a dicing tape on a mount frame and a wafer, comprising a fixed table for supporting the mount frame, a movable table for supporting the wafer, a height adjusting means for adjusting the height of the movable table, and a dicing tape attaching means to move in parallel to the dicing tape attaching surface of the wafer for attaching the dicing tape on the mount frame and the wafer, wherein when the dicing tape is attached on the mount frame and the wafer, the height adjusting means coincides the height of the dicing tape attaching surface of the wafer supported on the movable table with the height of the upper surface of the mount frame supported on the fixed table.

Specifically, in the first aspect, at the time of attaching the dicing tape, the wafer on the movable table and the mount frame on the fixed table can be made flush with each other by the height adjusting means. Thus, an unnecessary force, from the dicing tape attaching means, is not exerted on the edges of the wafer. As a result, the dicing tape can be attached on the mount frame and the wafer without forming cuts, cracks and internal distortions in the wafer.

According to a second aspect of the invention, there is provided a dicing tape attaching apparatus in the first aspect, wherein the height adjusting means is a screw jack.

Specifically, in the second aspect, the use of the screw jack prevents the position of the movable table from being changed by the force exerted at the time of attaching the dicing tape.

According to a third aspect of the invention, there is provided a dicing tape attaching apparatus in the first or second aspect, wherein the dicing tape attaching surface of the wafer is formed by grinding the back surface of the wafer.

Specifically, in the third aspect, even in the case where the wafer is back ground and the ground back surface reaches the chamfered portion of the front surface, the wafer is prevented from forming cuts or cracks and internal distortions. The thickness of the back ground wafer may be not more than, for example, 100 micrometers.

According to a fourth aspect of the invention, there is provided a dicing tape attaching apparatus in any one of the first to third aspects, further comprising a height detection means for detecting the height of the dicing tape attaching surface of the wafer supported on the movable table and/or the height of the upper surface of the mount frame supported on the fixed table, wherein the height adjusting means adjusts the height of the movable table based on the height of the dicing tape attaching surface and/or the height of the upper surface of the mount frame detected by the height detection means.

Specifically, in the fourth aspect, the height of the movable table can be automatically adjusted based on the height of the dicing tape attaching surface and/or the height of the upper surface of the mount frame.

According to a fifth aspect of the invention, there is provided a dicing tape attaching apparatus in any one of the first to fourth aspects, further comprising an input means for inputting the thickness of the wafer, the thickness of the film attached on the surface of the wafer opposite to the dicing tape attaching surface of the wafer and/or the thickness of the mount frame, wherein the height adjusting means adjusts the height of the movable table based on the thickness of the wafer and the film and/or the thickness of the mount frame input by the input means.

Specifically, in the fifth aspect, the height of the movable table can be accurately adjusted in accordance with the degree to which the wafer is back ground and/or the thickness of the used surface protective film.

According to a sixth aspect of the invention, there is provided a dicing tape attaching apparatus in any one of the first to fifth aspects, further comprising a pressing means for applying the pressing force by pressing the dicing tape attaching surface of the wafer supported on the movable table against the dicing tape attaching means through the dicing tape, a dicing tape attaching means distance calculation means for detecting the distance covered by the dicing tape attaching means when the dicing tape attaching means is moved from one end of the wafer in parallel to the dicing tape attaching surface of the wafer, and a movable table pressing force setting means for setting the pressing force of the movable table using the covered distance of the dicing tape attaching means detected by the dicing tape attaching means distance calculation means in such a manner that the pressure applied at the contact point of the wafer to the dicing tape is kept substantially constant during the movement of the dicing tape attaching means from one end to the other end of the wafer.

Specifically, in the sixth aspect, the pressing force of the movable table is set in accordance with the covered distance of the tape attaching means calculated by the tape attaching means distance calculation means and, therefore, the surface pressure applied to the wafer can be substantially accurately equalized over the whole wafer. As a result, an unnecessary force from the dicing tape attaching means is not exerted over the whole outer periphery of the wafer. Thus, cuts, cracks and internal distortions can be further prevented. The surface pressure is defined as the pressure exerted on the wafer per unit area thereof.

According to a seventh aspect of the invention, there is provided a dicing tape attaching apparatus in the sixth aspect, wherein the pressing means is an air cylinder and includes a stopper adapted to stop the rod of the air cylinder before the stroke end thereof.

Specifically, in the seventh aspect, the movable table can be held before the stroke end of the movable table and therefore can be smoothly moved.

According to an eighth aspect of the invention, there is provided a dicing tape attaching apparatus in the sixth or seventh aspect, wherein the dicing tape attaching means is a roll, and at least a part of the roll is formed of a material not substantially deformed when the pressing force is applied by the pressing means.

Specifically, in the eighth aspect, the roll is not substantially deformed, and therefore an unnecessary force is not exerted especially on the edges of the wafer. The hardness of the roll rubber is desirably about 40 to 45 degrees. Also, the diameter of the roll can be increased as much as possible.

According to a ninth aspect of the invention, there is provided a dicing tape attaching method, for attaching a dicing tape on a mount frame and a wafer, comprising the steps of supporting the mount frame on the fixed table, supporting the wafer on the movable table, adjusting the height of the movable table in such a manner that the height of the dicing tape attaching surface of the wafer supported on the movable table coincides with the height of the upper surface of the mount frame supported on the fixed table when the dicing tape is attached on the mount frame and the wafer, and moving a dicing tape attaching means in parallel to the dicing tape attaching surface of the wafer thereby to attach the dicing tape on the mount frame and the wafer.

Specifically, in the ninth aspect, the wafer on the movable table and the mount frame on the fixed table can be arranged flush with each other by the height adjusting means at the time of attaching the dicing tape. As a result, the unnecessary force from the dicing tape attaching means is prevented from being exerted on the edges of the wafer. As a result, the dicing tape can be attached on the mount frame and the wafer without forming cuts or cracks and internal distortions in the wafer.

According to a tenth aspect of the invention, there is provided a dicing tape attaching method in the ninth aspect, further comprising the steps of detecting the height of the dicing tape attaching surface of the wafer supported on the movable table and/or the height of the upper surface of the mount frame supported on the fixed table and adjusting the height of the movable table based on the detected height of the dicing tape attaching surface and/or the detected upper surface of the mount frame.

Specifically, in the tenth aspect, the height of the movable table can be automatically adjusted based on the height of the dicing tape attaching surface and/or the height of the upper surface of the mount frame.

According to an 11th aspect of the invention, there is provided a dicing tape attaching method in the ninth or tenth aspect, further comprising the steps of inputting the thickness of the wafer, the thickness of the film attached on the surface opposite to the dicing tape attaching surface and/or the thickness of the mount frame and adjusting the height of the movable table based on the input thickness of the wafer and the film and/or the input thickness of the mount frame.

Specifically, in the 11th aspect, the height of the movable table can be accurately adjusted in accordance with the degree to which the wafer is back ground and/or the thickness of the used surface protective film.

According to a 12th aspect of the invention, there is provided a dicing tape attaching method in any one of the ninth to 11th aspects, further comprising the steps of supplying the dicing tape between the dicing tape attaching surface of the wafer and the dicing tape attaching means by a dicing tape supply means moving the movable table toward the dicing tape attaching means so as to exert the pressing force to the dicing tape attaching surface of the wafer supported on the movable table against the dicing tape attaching means through the dicing tape calculating the distance covered by the dicing tape attaching means from one end of the wafer and setting the pressing force of the movable table using the covered distance of the dicing tape attaching means detected by the dicing tape attaching means distance calculation means in such a manner that the pressure at the contact point of the wafer to the dicing tape is kept substantially constant during the movement of the dicing tape attaching means moves from one end to the other end of the wafer.

Specifically, in the 12th aspect, the pressing force of the movable table is set in accordance with the covered distance of the dicing tape attaching means as calculated and, therefore, the surface pressure applied to the wafer is kept substantially and accurately equal over the whole wafer. As a result, the unnecessary force from the dicing tape attaching means is prevented from being exerted over the whole outer periphery of the wafer, thereby preventing the forming of cuts, cracks and internal distortions.

These and other objects, features and advantages of the present invention will be more apparent in light of the detailed description of exemplary embodiments thereof as illustrated by the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are explained below with reference to the accompanying drawings. In the drawings, the same component members are designated by the same reference numerals, respectively. To facilitate the understanding, the scale of the drawings has been appropriately changed.

FIG. 1is a sectional view schematically showing a dicing tape attaching apparatus according to this invention. The back surface of a wafer20supplied to a dicing tape attaching apparatus10, as explained with reference toFIG. 7, is ground by back grinding to a chamfered portion26on the front surface thereof, and the thickness of the wafer20is not more than 100 micrometers. Also, as is well known, a surface protective film11for protecting the semiconductor elements is already attached on the front surface of the wafer20.

The dicing tape attaching apparatus10shown inFIG. 1includes a housing15containing therein a supply unit42for supplying a dicing tape3to be attached on a circular silicon wafer20and a take-up unit43for taking up the tape from the supply unit42. As shown inFIG. 1, a plurality of castors18and a plurality of stoppers19are arranged on the bottom surface of the housing15. The dicing tape attaching apparatus10is moved to the desired position on a floor L by the castors18and can be fixed at the desired position by the stoppers19. Also, doors17are arranged in the lower part of the dicing tape attaching apparatus10. By opening the doors17, a control unit9such as a digital computer and other members described later, arranged in the lower part of the dicing tape attaching apparatus10, can be accessed.

As shown inFIG. 1, a guide roll47for guiding the dicing tape3and applying a predetermined tension to the dicing tape3is arranged downstream of the supply unit42. Further, a pair of peeling rolls44are arranged downstream of the guide roll47. The peeling rolls44function to peel a release6of the dicing tape3, so that the release6is taken up on the a release take-up unit45. Guide rolls51for guiding the dicing tape3and a take-up unit43for taking up the dicing tape3are arranged downstream of the peeling rolls44. Also, a dancer roll59adapted to move in accordance with the amount of the supplied dicing tape3is arranged between the guide rolls51and the take-up unit43.

As shown inFIG. 1, on a rack12arranged in the intermediate portion of the dicing tape attaching apparatus10a movable table31adapted to move up and down is arranged. The wafer20is supported on the movable table31with the front surface21on which a surface protective film11is attached, down, i.e. with a back ground surface22up.

Further, a fixed table38having an opening corresponding to the outer periphery of the movable table31is arranged around the movable table31. The wafer20and the movable table31are adapted to move up and down through the opening of the fixed table38. As shown inFIG. 1, a mount frame36is arranged on the upper surface around the opening of the fixed table38. The mount frame36functions to hold each of parts of wafer20which are cut in the dicing process. The wafer20and the mount frame36are supported by well-known means such as vacuum adsorption on the movable table31and the fixed table38, respectively.

FIG. 2is an partially enlarged view showing a part of the dicing tape attaching apparatus in enlarged form. Poles77extending downward from the rack12are connected to a base71of the housing15. A shaft32extending from the bottom surface of the movable table31is guided by a guide93arranged on the rack12, and the forward end of the shaft32is formed as a spline shaft92. An outer side portion91formed with a groove for engaging with the spline shaft92is connected to the forward end of a rod83of an air cylinder80. As a result, the shaft32having the spline shaft92can be accurately slid in vertical direction along the outer side portion91.

The rod83moved up and down by the operation of the air cylinder80extends through a hole82formed in the upper surface of an air cylinder casing81. As shown inFIG. 2, a flange85is fixed midway of the rod83. The diameter of the flange85is larger than the hole82of the air cylinder casing81, and the flange85functions as a stopper to restrict the movement of the rod83. Though not shown, the rod83is connected to the piston in the air cylinder80. Further, the air cylinder80is driven by a motor86.

A gear74is arranged on the lower surface of the air cylinder casing81. This gear74is engaged with another gear75driven by the motor76. Also, the gear74is integrated with the threaded shaft73of a screw jack70. The threaded shaft73is engaged with a female screw72arranged on a base71. Upon rotation of the gear75by the motor76driven, the threaded shaft73rotates through the gear74, so that the air cylinder80and the movable table31located above the gear74are moved up and down integrally. In other words, the screw jack70functions as a height adjusting means for adjusting the height of the movable table31.

A motor76may be arranged under the screw jack70to drive the screw jack70. Also, the screw jack motor76and the air cylinder motor86are connected to a control unit90.

As shown inFIG. 2, a roll46adapted to reciprocate horizontally in the housing15is arranged on the movable table31. The length of the roll46is larger than the maximum width of the wafer20and the mount frame36(see the roll146shown inFIG. 8). Though not shown, the roll46is connected to an endless chain suspended on two pulleys, which in turn are connected to a motor not shown. By driving the motor in forward and backward directions, the roll46can be reciprocated horizontally between the pulleys.

The roll46may, of course, be reciprocated horizontally by another drive mechanism. As can be understood fromFIG. 2, the dicing tape3is supplied between the roll46and the wafer20and the mount frame36. Then, the roll46moves horizontally from the end of the mount frame36near the end28of the wafer20to the end of the mount frame36near the other end29of the wafer through the diameter of the wafer20, so that the dicing tape3can be attached on the wafer20and the mount frame36.

Also, the whole of the roll46may be formed of a rubber material or the peripheral surface of the roll46may be covered with a rubber material. The roll46used in the dicing tape attaching apparatus10according to this invention is formed of a material hardly deformed under the pressing force exerted thereon as described later. A rubber material having the rubber hardness of about 40 to 45 may be used.

Referring again toFIG. 1, a cutter unit65is arranged above the movable table31and the roll46. The cutter unit65has a rotatable cutter64adapted to reciprocate vertically. After attaching the dicing tape, the cutter unit65is moved to the wafer20, and then the cutter64is rotated along the peripheral edge of the mount frame36. In this way, the dicing tape3attached on the wafer20and the mount frame36can be cut.

Further, a height detector95is arranged in the housing15. The height detector95detects at least one of the height of the grinding back surface22of the wafer20supported on the movable table31and the height of the upper surface of the mount frame36supported on the fixed table38. This height detector95is connected to the control unit90.

An input unit96such as a keyboard or a mouse is also connected to the control unit90. The operator can appropriately input the thickness of the wafer20after being back ground and/or the thickness of the surface protective film11from the input unit96.

During the operation of the dicing tape attaching apparatus10according to the invention, as described above, the wafer20and the mount frame36are supported on the movable table31and the fixed table38, respectively. Then, the height of the grinding surface22of the wafer20supported on the movable table31and the height of the upper surface of the mount frame36supported on the fixed table38are detected by the height detector95. The height of the wafer20and the mount frame36thus detected are supplied to the control unit90, which in turn drives the screw jack70through the motor76based on the detected heights.

As a result, the threaded shaft73of the screw jack70is appropriately rotated, and the movable table31moves up and down integrally with the gear74, the air cylinder80and the shaft32thereby to adjust the height of the movable table31. Thus, the height of the grinding surface22of the wafer20comes to coincide with the height of the upper surface of the mount frame36(seeFIG. 2). In the case where one of the height of the wafer20and the mount frame36is known, the operation of detecting the height thereof may be omitted.

The degree to which the wafer20is back ground and/or the thickness of the surface protective film11may be varied from one wafer20or lot to another. In such a case, the thickness of the wafer20ground and/or the thickness of the surface protective film11is input using the input unit96. The control unit90, taking the input value into consideration, drives the screw jack70so that the height of the grinding surface22of the wafer20and the height of the upper surface of the mount frame36coincide with each other. In other words, even in the case where the degree to which the wafer20is back ground and/or the thickness of the surface protective film11is varied, the height of the movable table31is accurately adjusted to the height of the upper surface of the mount frame36.

InFIG. 2, an initial position46′ of the roll46for attaching the dicing tape3is shown. As shown inFIG. 2, the roll46at the initial position46′ is located substantially just above the end portion28of the wafer20. At this time, the dicing tape3is partially attached under a predetermined pressing force against the mount frame in the neighborhood of the end portion28. The grinding surface22of the wafer20and the upper surface of the mount frame36are substantially flush with each other, and therefore the opposite ends of the roll46are placed on the mount frame36at the initial position46′. As a result, an unnecessary force, from the roll46, is not exerted on the grinding surface22of the wafer20. Therefore, cuts, cracks or internal distortions are not formed under the pressure applied to the wafer20by the force from the roll46. Also, according to this invention, the roll46is formed of a material which is hardly deformed, and therefore cuts or cracks can be further prevented.

Also, at the time of attaching the dicing tape3by the dicing tape attaching apparatus10, the roll46moves diametrically from the end portion28of the wafer20toward the end portion of the mount frame36near the end portion29. While the roll46moves in the neighborhood of the central portion of the wafer20, the ends of the roll46remain supported on the mount frame36as shown inFIG. 6. Therefore, the roll46is not deformed at the edges of the wafer20perpendicular to the direction of movement of the roll46. Thus, cuts, cracks or the like are not formed in the wafer20.

When the roll46is moved on the wafer20to attach the dicing tape3, the appropriate pressing force is generated between the movable table31and the roll46by the air cylinder80.

FIG. 3is a flowchart showing the operation program for the tape attaching apparatus according to the invention. The program100shown inFIG. 3is stored in a storage unit such as a ROM or a RAM of the control unit90and is executed by the control unit90. This program100is executed at the same time that the roll46(designated by dotted line as a reference numeral46′ inFIG. 2) at a position corresponding to the end portion28of the wafer20begins to move in the direction of arrow (diametrical direction) along the tape attaching surface20′ of the wafer20.

In step101of the program100shown inFIG. 3, the size D such as the diameter of the used wafer20is detected. The size of the wafer20is detected by a sensor (not shown) arranged diametrically or concentrically on the table31. As an alternative, in step101, the operator of the dicing tape attaching apparatus10may directly input the size D of the wafer20from the input unit96of the control unit90.

Next, in step102, the ratio of the size D of the wafer20to a predetermined size D0, i.e. the coefficient D/D0is determined. The predetermined size D0may be the maximum size of the wafer20that can be supported on the table31of the dicing tape attaching apparatus10. Then, the process proceeds to step103in which the distance x0from an origin0(seeFIG. 4described later) at a certain position to an end28of the wafer20is measured using an encoder or the like not shown. The end28of the wafer20located at a position the distance x0from the origin0is set as a measurement starting point00.

Next, in step104, the distance (x−x0) covered by the roll46from the measurement starting point00is calculated. As can be understood fromFIG. 4described later, the covered distance (x−x0) is the distance covered by the roll46on the wafer20. The measurement starting point00coincides with the end28of the wafer20for each size. During the movement of the roll46in one direction from the end28to the other end29of the wafer20, the distance (x−x0) covered by the roll46is calculated from the speed of the motor coupled to the pulley described above relating to the roll46.

Next, using the distance (x−x0) covered by the roll46, the contact width W, in which the wafer20contacts with the roll46via the dicing tape3, is calculated in step105.FIG. 4is a diagram for explaining the contact width W. InFIG. 4, the wafer20is viewed from above. InFIG. 4, the end28of the wafer20is the measurement starting point00, and the y axis extending horizontally crosses at right angles to the x axis at the origin0. As shown inFIG. 4, the center C of the circular wafer20is located on the x axis. The wafer20is in line contact with the roll46in the direction parallel to the y axis. In this specification, this line contact area is called the contact width W. In the embodiments shown in the accompanying drawings, the origin0is located outside of the wafer20. In the case where the wafer20of maximum size is used, however, the end28of the wafer20may be the origin0. In this case, the origin0and the measurement starting point00are equal to each other and therefore x0=0.

The contact width W, in which the wafer20contacts with the roll46, when the roll46is advanced by the distance (x−x0) is determined in the manner described below. InFIG. 4, if the contact width W crosses the peripheral edge of the wafer20at a crossing point S and if the line extending in parallel to the x axis through the crossing point S crosses the line perpendicular to the x axis through the center C of the wafer20at a crossing point Q and if the line extending in parallel to the x axis through the crossing point S crosses the line of x=x0at a crossing point D, as shown inFIG. 4, the line segment SC is equal to the radius r of the wafer20. Also, the wafer20is symmetric about the x axis, and therefore the line segment QC is equal to one half of the contact width W. Further, the line segment DQ is equal to the line segment00-C (=r) on the x axis, and the line segment DS is equal to the distance (x−x0). Therefore, the line segment SQ is equal to r−x+x0. As a result, taking note of the triangle SQC shown inFIG. 4, the contact width W is expressed by the equation below.
W=2√{square root over (r2−(r−x+x0)2)}  (1)

The behavior of the contact width W at the time of movement of the roll46will be explained.FIG. 5ais a diagram showing the relation between the distance (x−x0) covered by the roll46from the measurement starting point00and the contact width W of the wafer20with the roll46through the dicing tape3. InFIG. 5a, the abscissa represents the distance (x−x0) covered by the roll46from the measurement starting point00, and the ordinate represents the contact width W described above. As shown inFIG. 5a, at the initial position where the center of the roll46corresponds to the end28of the wafer20(see the roll46′ shown by dotted line inFIG. 2), the contact width W is substantially zero and the roll46and the end28of the wafer20are in point contact with each other. With the increase in the covered distance x, the contact width W increases in accordance with the equation described above, and when the covered distance x coincides with the radius r of the wafer20, the contact width W assumes the maximum value 2r (=D). After that, the contact width W gradually decreases and, when, the covered distance x is 2r, the contact width W becomes substantially zero again. According to this embodiment, a circular wafer20is used and therefore the contact width W behaves symmetrically about a line associated with the covered distance x equal to the radius r.

Referring again toFIG. 3, in step106, the target value of the pressing force F(x), under which the wafer20is pressed against the roll46through the dicing tape3by the table31, is calculated from the coefficient D/D0calculated in step102and the contact width W calculated in step105. The target pressing force F(x) is calculated on the basis of a predetermined pressing force F0. The predetermined pressing force F0is the maximum value of the force exerted on the wafer20when the wafer20of the maximum size installable on the table3is supported on the table31of the table lift30and the distance (x−x0) covered by the roll46corresponds to the radius r, i.e. the axis of the roll46is located at the center of the wafer20. When the distance (x−x0) covered by the roll46reaches the radius r, the contact width W is equal to the diameter D (=2r) of the wafer20. This contact width W may correspond to the contact area A of the portion of the wafer20in contact with the roll46through the dicing tape3.

The contact between the wafer20and the roll46through the dicing tape3is not a line contact and, strictly speaking, the contact is a surface contact with a minor distance along x direction. Thus, the contact area A can be calculated more accurately by multiplying the coefficient corresponding to this minor distance by the contact width W.

According to this invention, the pressing force F(x) under which the wafer20is in contact with the roll46is determined in such a manner that the pressure P(x) exerted on the contact area A is constant.FIG. 5bis a diagram showing the relation between the distance (x−x0) covered by the roll46and the pressing force F(x), andFIG. 5ca diagram showing the relation between the distance (x−x0) covered by the roll46and the pressure P(x). In these drawings, the abscissa represents the covered distance (x−x0), and the ordinate represents the pressing force F(x) and the pressure P(x), respectively. As shown inFIG. 5c, in order that the pressure P(x) may be constant during the movement of the roll46on the wafer20(0≦x−x0≦2r), the pressing force F(x) is required to be increased with the increase in the contact width W or the contact area A when the covered distance (x−x0) is smaller than the radius r (0≦x−x0<r), while the pressing force F(x) is required to be decreased with the decrease in the contact width W when the covered distance (x−x0) is not less than the radius r and not more than twice the radius r (r≦x−x0≦2r). Taking into the consideration the fact that pressure is a force exerted on the unit area, the pressing force F(x) according to the invention is expressed by equation below (see alsoFIG. 5b).
F(x)=F0×W×D/D0=(2F0·D/D0)√{square root over (r2−(r−x+x0)2)}  (2)

By applying this pressing force F(x) to the wafer20, the pressure P(x) remains at a constant value (=F0·D/D0) regardless of the distance (x−x0) covered by the roll46during the movement of the roll46from one end28to the other end29of the wafer20.

In this equation, the coefficient D/D0is multiplied in order to exert the pressing force F(x) corresponding to the size of the wafer20on the wafer20. Specifically, the pressing force F(x) exerted on the wafer20having the size D is always D/D0times smaller than the force exerted on the wafer20of maximum size D0. In the case where the dicing tape3is attached on a plurality of wafers20of various sizes by the same tape attaching apparatus, the initial setting such as the maximum pressing force is required to be changed in accordance with the size of the wafer20. According to the invention, however, the pressing force F(x) is calculated after multiplying the coefficient D/D0, and therefore, even in the case where the dicing tape3is attached on the wafer20of a different size, the initial setting is not required to be changed in accordance with the size of the wafer20. As a result, the dicing tape3can be continuously attached on the wafer20without work suspension. The value of the pressure P can of course be changed by multiplying F0by a predetermined value.

As an alternative, coefficients are predetermined in accordance with the hardness, thickness and adhesive temperature of the bonding agent used with the dicing tape3and stored in the storage unit of the control unit90, and the target pressing force F(x) may be calculated by appropriately multiplying these coefficients. In this case, the target pressing force F(x) can be calculated with higher accuracy.

The process then proceeds to step107, in which the air cylinder80of the table lift30is adjusted through the control unit90in such a manner that the pressing force F(x) corresponding to the covered distance (x−x0) can be exerted on the wafer20by the table31. The force exerted on the air cylinder80is varied with the value of the target pressing force F(x) and the type of the dicing tape3used. For this reason, the force exerted on the air cylinder80is determined experimentally, and stored in the form of a map, as a function of the target pressing force F(x) and the type of the dicing tape3, in a storage unit such as a ROM or a RAM of the control unit90. In step107, the force exerted on the air cylinder80is determined from this map, thereby making it possible for the table31to exert the pressing force F(x) on the wafer20.

As will be understood from the relation between the pressing force F(x) and the covered distance (x−x0) shown inFIG. 5b, the pressing force F(x) exerted on the wafer20increases when the covered distance (x−x0) is between zero and the radius r (0≦x−x0<r), while the pressing force F(x) exerted on the wafer20is decreased when the covered distance (x−x0) is between the radius r and twice the radius r (r≦x−x0≦2r) (see Equation (2)). In this way, the pressing force F(x) is adjusted to remain a constant value of the pressure P(x) regardless of the distance (x−x0) covered by the roll46. Specifically, according to the invention, the pressing force F(x) of the table31is adjusted to remain a constant pressure exerted on the contact portion of the wafer20taking the change of the contact width W with the covered distance (x−x0) into consideration.

Next, in step109, it is determined whether the distance (x−x0) covered by the roll46calculated in step104is larger than the diameter D, i.e. twice the radius r of the wafer20or not. In the case where the covered distance (x−x0) is not larger than or equal to the diameter D, the process proceeds to step103, the process is repeated. In the case where it is determined that the covered distance (x−x0) is larger than the diameter D, on the other hand, it can be determined that the roll46has passed the other end29of the wafer20, and therefore the dicing tape3is attached with a predetermined pressing force up to the end of the mount frame near the end portion29, after which the process is ended. After that, a cutter unit65is rotated so that the dicing tape3attached on the wafer20and the mount frame36is appropriately cut off along the periphery of the mount frame36.

In this way, a substantially equal pressure can be exerted over the whole wafer20by the dicing tape attaching apparatus10in the present invention. Specifically, according to this invention, the pressing force is adjusted so that the neighborhood of the end portions28,29of the wafer20may not be locally pressed. In the present invention, the surface pressure, i.e. the pressure per unit area of the wafer is substantially equal over the whole wafer. Due to the foregoing, an unnecessary force from the roll46is not exerted on the end portions28,29and the outer peripheral portion of the wafer20, thereby making it possible to further prevent cuts, cracks or internal distortions from being generated.

Further, according to the prior art in which the pressing force is exerted using an air cylinder80, the movable table31and the air cylinder80may be pushed back by the repulsive force of the roll46. According to the invention, however, the use of the screw jack70prevents the movable table31and the air cylinder80from being pushed back by the repulsive force even when the repulsive force is generated from the roll46. In other words, the use of the screw jack70prevents the position of the movable table31from being changed when attaching the dicing tape3.

As described above, the flange85is arranged midway of the rod83of the air cylinder80. This flange85engages the outer peripheral portion of the hole82of the air cylinder casing81and restricts the extension of the rod83to the maximum stroke thereof. Thus, the rod83extends only to the point where the flange85engages the outer peripheral portion of the hole82.

In the case where the attaching operation is performed with the air cylinder rod extended to the neighborhood of the maximum stroke thereof as in the prior art, the large sliding resistance and the variation thereof occurring during the operation of the air cylinder makes it difficult to move the movable table31smoothly from the position of maximum stroke during the attaching process. According to this invention, on the other hand, the fact that the extension of the rod83is restricted by the flange85makes it possible to slide the movable table31smoothly when attaching the dicing tape3, with the result that the dicing tape can be attached in stable fashion. Specifically, according to this invention, it is apparent that the flange85is arranged at a position where the sliding resistance and the variation thereof when operating the air cylinder are comparatively small.

Depending on the material used form the roll46, the grinding surface22of the wafer20and the upper surface of the mount frame36are not necessarily flush with each other. In the case where the roll46is formed of rubber liable to be deformed with comparative ease, for example, the grinding surface22of the wafer20is desirably set slightly lower than the upper surface of the mount frame36. This configuration for attaching the dicing tape3with the height of the grinding surface22and the height of the upper surface of the mount frame36displaced from each other by a predetermined distance as described above is also included in the scope of the invention.

Although the invention has been shown and described with exemplary embodiments thereof, it should be understood, by those skilled in the art, that the foregoing and various other changes, omissions and additions may be made therein and thereto without departing from the scope of the invention.