JP5995545B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a method for processing a wafer in which protruding electrodes called bumps are mounted on the surface of a semiconductor device.

  A workpiece such as a semiconductor wafer having a plurality of semiconductor devices formed on the surface is thinly ground by a grinding device that rotates a grinding wheel called a wheel at high speed and is divided into individual devices, and then an electronic substrate and The device or the electrodes of the devices are connected and mounted.

  When a semiconductor wafer is divided into individual devices, a cutting device called a dicing saw is used, and it is known that the semiconductor wafer is crushed and cut by forming cutting grooves in the semiconductor wafer with a cutting blade that rotates at high speed.

  On the other hand, the cutting grooves are becoming narrower, and there are cases where it is difficult to divide with a cutting blade due to the appearance of a technique for coating a semiconductor wafer with a brittle material.

  Therefore, as disclosed in Patent Document 1, it is known that a laser processing apparatus that performs division processing using a laser beam is used. According to Patent Document 1, a modified layer is formed along a planned dividing line (scheduled cutting line) in the thickness direction of the semiconductor wafer, and is expanded by applying an external force to the semiconductor wafer, and is ruptured starting from the modified layer. A processing method is disclosed.

Japanese Patent No. 3408805

  In the process of forming a semiconductor wafer modified layer as disclosed in Patent Document 1, the modified layer is formed at an accurate position in the thickness direction of the semiconductor wafer by a laser beam, and then an external force is applied to ensure It is important to expand.

  Here, when bumps serving as electrodes are formed on the surface of the semiconductor wafer, the bump surface side is adhered to an adhesive tape, the adhesive tape is held by a chuck table, and a laser beam is irradiated from the back surface.

  However, if there are variations in the height of the bumps, the focal point of the laser beam in the thickness direction of the semiconductor wafer will vary, and the position at which the modified layer will be formed also varies, resulting in poor division due to this variation. There is concern.

  Furthermore, since the adhesive tape is attached to the bump surface where unevenness is formed due to the presence of the bump, the contact area between the bump surface and the adhesive tape is small. For this reason, when the adhesive tape is expanded by applying external force after forming the modified layer, the adhesive state of the bump surface and adhesive tape cannot be maintained and they are displaced from each other, and external force cannot be transmitted to the semiconductor wafer. There is a problem that defective division occurs.

  That is, there is a problem in that the holding force on the bump surface side by the adhesive tape is weak, and the bump surface is not attracted to the adhesive tape, resulting in failure of the modified layer.

  The present invention has been made in view of the above problems, and its object is to provide a wafer processing method in which a plurality of devices in which a plurality of spherical electrodes protrude from the surface are formed on the surface. It is to provide a technique for enabling division more reliably.

According to the first aspect of the present invention, there is provided a wafer processing method in which a plurality of devices each having a plurality of spherical electrodes projecting from a surface partitioned by a plurality of division lines formed in a lattice shape are formed on the surface. The upper surface of the electrode of the wafer held on the holding surface of the chuck table is exposed by cutting the upper surface of the electrode on which the electrode is disposed with a cutting tool rotating on a rotation axis orthogonal to the holding surface, and a flat portion is formed on the upper end of the electrode. A frame unit is formed by sticking the surface of the wafer having a flat part formed on the electrode and the surface of the wafer with the expandable adhesive tape attached to the annular frame while contacting the flat part. The frame unit forming step to be performed and the back side of the wafer of the frame unit are exposed and held on the chuck table, and transmitted from the back side of the wafer to the wafer. A modified layer forming step for forming a modified layer inside the wafer by irradiating a laser beam of a wavelength having a wavelength along the division line, and expanding the adhesive tape in the radial direction to apply an external force to the wafer, seen containing an expansion step to break along the modified layer, and the byte cutting step, the area of the flat portion so stuck state is maintained between the electrode and the adhesive tape in extending the adhesive tape extended step A method of processing a wafer to ensure the above is provided.

  According to the present invention, since the flat portion (flat surface) is formed by cutting the upper end of the electrode with a cutting tool in advance, it becomes possible to dramatically increase the holding force on the electrode surface side by the adhesive tape. When expanded, the wafer can be reliably divided.

  Furthermore, the thickness of the entire wafer including the electrodes becomes uniform at the time of cutting with a bite, and the variation of the modified layer forming position due to the laser beam is eliminated, and the effect of reducing the division failure due to the variation is also achieved.

It is a perspective view of the cutting tool suitable for implementation of the present invention. It is a perspective view of the wafer used as the process target of this invention. It is a side view explaining cutting of an electrode (bump) by a cutting tool unit. (A) is a side view which shows about the state before the upper end part of an electrode (bump) is cut. (B) is a side view showing a state after the upper end portion of the electrode (bump) is cut. (A) is sectional drawing of a frame unit. (B) is a perspective view of a frame unit. It is side surface sectional drawing shown about a modified layer formation step. It is side surface sectional drawing shown about an expansion step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an embodiment of a cutting tool 2 suitable for carrying out the present invention. Reference numeral 4 denotes a base (housing) of the cutting tool 2, and a column 6 is erected at the rear of the base 4. A pair of guide rails (only one is shown) 8 extending in the vertical direction is fixed to the column 6.

  A cutting tool unit 10 is mounted along the pair of guide rails 8 so as to be movable in the vertical direction. The cutting tool unit 10 is attached to a moving base 12 whose housing 20 moves in the vertical direction along a pair of guide rails 8.

  The cutting tool unit 10 is detachably attached to a housing 20, a spindle 22 (see FIG. 3) rotatably accommodated in the housing 20, a mount 24 fixed to the tip of the spindle 22, and the mount 24. And a bite wheel 25. A bite unit 26 is detachably attached to the bite wheel 25.

  The cutting tool unit 10 includes a cutting tool feed mechanism 18 including a ball screw 14 and a pulse motor 16 that move the cutting tool unit 10 in the vertical direction along a pair of guide rails 8. When the pulse motor 16 is pulse-driven, the ball screw 14 rotates and the moving base 12 is moved in the vertical direction.

  A chuck table mechanism 28 having a chuck table 30 is disposed at an intermediate portion of the base 4, and the chuck table mechanism 28 is moved in the Y-axis direction by a chuck table moving mechanism (not shown). Reference numeral 33 denotes a bellows, which covers the chuck table moving mechanism.

  In the front portion of the base 4, a first wafer cassette 32, a second wafer cassette 34, a wafer transfer robot 36, a positioning mechanism 38 having a plurality of positioning pins 40, and a wafer carry-in mechanism (loading arm) 42, a wafer unloading mechanism (unloading arm) 44, and a spinner cleaning unit 46 are disposed.

  Further, a cleaning water spray nozzle 48 for cleaning the chuck table 30 is provided at the approximate center of the base 4. The cleaning water spray nozzle 48 sprays cleaning water toward the chuck table 30 in a state where the chuck table 30 is positioned in the wafer loading / unloading area on the front side of the apparatus.

  FIG. 2 is a perspective view showing an embodiment of a wafer W that is a workpiece in the implementation of the present invention. The wafer W to be processed is made of, for example, a silicon wafer having a thickness of 100 μm, and a plurality of intersecting division lines (streets) S1 and S2 are formed in a lattice shape on the surface Wa. A device D is formed in each of a plurality of regions partitioned by the planned division lines S1 and S2. Spherical bumps B serving as electrodes are disposed on the surface of each device D. In the wafer W configured in this way, a device region W1 where the device D is formed and an annular outer peripheral region W2 surrounding the device region W1 are formed.

  Note that the shape of the wafer W to be processed is not limited to a disk shape as shown in FIG. 2, and a rectangular shape such as a quadrangular shape (regular quadrangle, rectangular shape) is also assumed. In the case of a rectangle, it is assumed that the outer peripheral surplus area also forms a rectangular ring. In addition to semiconductor wafers, optical device wafers and the like are assumed to be processed.

  Next, a characteristic wafer dividing method in the present invention will be described. As shown in FIG. 2, the wafer is partitioned by a plurality of division lines S1 and S2 formed in a lattice shape, and a plurality of devices D on which bumps B as a plurality of spherical electrodes protrude from the surface Wa are formed on the surface. For W, the present invention is implemented.

  First, as shown in FIGS. 3 and 4A and 4B, the surface Wa side where the bumps B are disposed is exposed and the bumps B of the wafer W held on the holding surface 31 of the chuck table 30 are exposed. The upper end is cut with a cutting tool 27 that rotates on a rotating shaft (spindle 22) orthogonal to the holding surface 31, and a cutting tool step for forming a flat portion on the upper end of the bump B is performed.

  As shown in FIG. 3, the back surface Wb of the wafer W is sucked and held by the holding surface 31 by placing it on the holding surface 31 so that the front surface Wa of the wafer W is on the upper side. The bumps B are arranged so as to protrude from the surface Wa of the wafer W.

  The chuck table 30 is processed and fed in the Y-axis direction below the cutting tool unit 10. A cutting tool 27 for cutting the bump B is attached to the tip of the cutting tool unit 26, and the cutting tool 27 rotates together with the cutting tool unit 26 by the rotation of the spindle 22.

  Then, the tool 27 is positioned at a predetermined position (height position) in the Z-axis direction, the spindle 22 is rotated, and the chuck table 30 is processed and fed, whereby the upper end portion of the bump B is cut.

  FIG. 4 (A) shows a state before the upper end portion of the bump B is cut. From this state, the upper end of the bump B is cut as shown in FIG. 4 (B). The part is removed by cutting.

  Then, as shown in FIG. 4 (B), the flat portion Ba is formed in each bump B by removing the upper end portion of the spherical bump B after the cutting process. Then, by forming the flat portion Ba, a series of flat flat surfaces Bf composed of the flat portions Ba are formed. The flat surface Bf constitutes a surface substantially parallel to the back surface Wb of the wafer W.

  Next to the above bite cutting step, as shown in FIGS. 5 (A) and 5 (B), the surface Wa of the wafer W having the flat portions Ba formed on the bumps B is attached to the annular frame F so as to be expandable. A frame unit forming step for forming the frame unit U is performed by bringing the flat portion Ba into contact with the adhesive tape T having the adhesive tape T and sticking it.

  The adhesive tape T is composed of a sheet-like member having stretchability in which an adhesive layer Tb is formed on a sheet base material Ta, and the adhesive layer Tb is adhered to the lower surface Fb of the annular frame F on the ring. Thus, the adhesive tape T and the frame F are integrated.

  By arranging the adhesive layer Tb of the adhesive tape T so as to cover the surface Wa of the wafer W, the bumps B are arranged between the wafer W and the adhesive layer Tb. As a result, the wafer W is adhered to the adhesive tape T via the bumps B.

  Here, since the flat portion Ba of the bump B is adhered to the adhesive layer Tb of the adhesive tape T, the contact between the bump B and the adhesive tape T compared to the case where the flat portion Ba is not formed. A large area is secured, and the bumps B and consequently the wafer W are firmly attached to the adhesive tape T.

  Further, since the flat portion Ba of the bump B is adhered to the adhesive layer Tb of the adhesive tape T, the wafer W has a higher level of level than the case where the flat portion Ba is not formed. As will be described later, in the state where the frame unit U is placed on the horizontal holding surface of the chuck table, the wafer W can be placed in a state that is closer to the horizontal.

  Following the above frame unit formation step, as shown in FIG. 6, the back surface Wb side of the wafer W of the frame unit U is exposed and held on the chuck table 60, and transmitted from the back surface Wb side of the wafer W to the wafer W. A modified layer forming step of forming a modified layer K inside the wafer W by irradiating a laser beam LB having a wavelength with the property along the division lines S1 and S2 (see FIG. 2) is performed.

  This modified layer forming step can be performed using a laser processing apparatus including the laser irradiation unit 50 and the chuck table 60. The frame F of the frame unit U is held by a clamp 62 provided around the chuck table 60 so that the wafer W is positioned above the holding surface 61 of the chuck table 60.

  Above the chuck table 60, a laser irradiation unit 50 having a condenser 51 for irradiating the laser beam LB is positioned. The laser beam LB is condensed at a predetermined position in the thickness direction of the wafer W from the back surface Wb side of the wafer W to form a modified layer K inside the wafer W. Further, the condenser 51 is processed and fed in the Y-axis direction, so that the modified layer K is continuously formed along the planned division line.

  In forming the modified layer K, as described above, since the wafer W is placed on the chuck table 60 in a higher level, the entire wafer W including the bumps B is formed. Accordingly, the thickness of the modified layer K becomes uniform, and the variation in the formation position of the modified layer K due to the laser beam is eliminated. That is, the modified layer K can be formed without variation in the thickness direction of the wafer W.

  Following the above modified layer forming step, as shown in FIG. 7, the adhesive tape T is expanded in the radial direction to apply an external force to the wafer W, and an expanding step for breaking the wafer W along the modified layer K is performed. To be implemented.

  This expansion step includes an expansion drum 70 and a dividing device that is provided around the expansion drum 70 and that moves relative to the axial direction of the expansion drum 70 (up and down movement) by an air cylinder (not shown) or the like. Can be implemented.

  The frame F of the frame unit U is held by the clamp 73 of the holding frame 72, and the adhesive tape T is placed on the holding surface 71 of the expansion drum 70. The expansion drum 70 is formed of a cylindrical member, and the wafer W is disposed in a region surrounded by the holding surface 71 on the ring.

  Next, when the holding frame 72 is moved downward with the position of the expansion drum 70 fixed, the adhesive tape T expands and expands. Along with the expansion of the adhesive tape T, stress is transmitted to the modified layer K of the wafer W via the bumps B, and the wafer W breaks starting from the modified layer K. By this breakage, the wafer W is divided into individual chips C.

  And as above-mentioned, since the bump B has the flat part Ba firmly attached with respect to the adhesive tape T, when the adhesive tape T is expanded, it adheres with the bump B. The sticking state of the tape T is maintained, and it does not shift | deviate mutually (bump B does not peel from the adhesive tape T).

  That is, the holding force for the adhesive tape T to hold the bump B firmly is secured, and the bump B is moved by the adhesive tape T as the adhesive tape T is expanded. Thus, the wafer W is reliably transmitted to the quality layer K, and the wafer W is reliably broken from the modified layer K.

  According to the above embodiment, since the flat portion Ba (flat surface Bf) is formed by cutting the upper end of the bump B with a cutting tool in advance, the holding force on the bump B surface side by the adhesive tape T is greatly increased. Therefore, when the adhesive tape T is expanded, the wafer W can be surely divided.

  Furthermore, the thickness of the entire wafer W including the bumps B becomes uniform during the cutting of the cutting tool, and there is no variation in the position where the modified layer is formed by the laser beam. This also has the effect of reducing division defects caused by the variation. Will play.

  In the above embodiment, the case where the bump B is completely exposed on the surface Wa of the wafer W has been described. However, a step of sealing the bump B with resin may be added. In this case, for example, in the cutting tool step, a part of the bump B sealed with the resin is cut and exposed together with the resin to form the flat portion Ba, so that the adhesive tape T is used as in the above embodiment. The effect of improving the holding force on the bump B surface side and reducing the variation in the modified layer forming position can be obtained. In this case, a step of removing the resin may be added before the frame unit forming step.

2 cutting tool 27 cutting tool 30 chuck table 31 holding surface 50 laser irradiation unit 60 chuck table 61 holding surface 70 expansion drum B bump Ba flat part Bf flat surface C chip D device K modified layer T adhesive tape Ta sheet substrate U frame Unit W Wafer

Claims (1)

A method of processing a wafer in which a plurality of devices in which a plurality of spherical electrodes protrude from the surface are partitioned by a plurality of division lines formed in a lattice shape and formed on the surface,
The upper end of the electrode of the wafer held on the holding surface of the chuck table with the surface side where the electrode is disposed is cut with a cutting tool rotating on a rotation axis orthogonal to the holding surface, and the upper end of the electrode is cut A bite cutting step for forming a flat portion on
A frame unit forming step of forming a frame unit by adhering the surface of the wafer having the flat portion formed on the electrode to an adhesive tape having expandability attached to an annular frame while contacting the flat portion. When,
The back side of the wafer of the frame unit is exposed and held on a chuck table, and a laser beam having a wavelength having transparency to the wafer is irradiated along the division line from the back side of the wafer. A modified layer forming step for forming a modified layer inside
The external force is applied to the wafer to the adhesive tape extends radially, seen containing an expansion step, the breaking along the wafer reforming layer,
In the cutting tool step, a wafer processing method for securing an area of the flat portion so that a sticking state between the electrode and the adhesive tape is maintained when the adhesive tape is expanded in the expansion step .

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