JP6198618B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a processing method for thinly processing a wafer made of a material such as silicon.

  In recent years, in order to realize a small and lightweight device, it is required to thinly process a wafer made of a material such as silicon. The wafer is thinned by, for example, forming a device such as an IC in each region partitioned by streets (division planned lines) on the front surface and then grinding the back surface side.

  By the way, when the wafer is thinned by grinding, the rigidity is greatly lowered and handling in a later process becomes difficult. Therefore, a processing method has been proposed in which only the back surface side of the wafer corresponding to the central device region is ground to maintain the thickness of the outer peripheral portion, thereby leaving a predetermined rigidity on the ground wafer (for example, Patent Documents). 1).

  In this processing method, for example, the back surface side of the wafer is ground using a grinding wheel having a diameter smaller than that of the wafer to form a recess corresponding to the device region. The rigidity of the wafer is maintained by an annular reinforcing portion (annular convex portion) remaining on the back side of the outer peripheral surplus region surrounding the device region. The annular reinforcing portion is removed by a method such as cutting after the end of the post-process.

JP 2007-19379 A

  The concave portion corresponding to the device region described above is often formed in a shape in which the bottom surface and the side surface are connected by a curved surface. The concave portion having such a shape is formed because the corner portion of the grinding wheel mounted on the grinding wheel is worn and rounded as the grinding progresses. That is, the roundness formed at the corners of the grinding wheel due to wear is transferred to the wafer, and a curved surface shape (R shape) is generated at the connection portion between the bottom surface and the side surface of the recess.

  The annular reinforcing portion is usually removed by cutting a cutting blade into a connecting portion between the bottom surface and the side surface of the recess. However, if the cutting blade is cut into the connecting portion having the curved surface shape as described above, a force in the bending direction due to the curved surface shape is applied, and the cutting blade is curved.

  When a wafer is cut with a curved cutting blade, the processing width may be widened and the device may be damaged. Further, the wafer or the cutting blade may be damaged by the force in the bending direction.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a wafer processing method capable of preventing damage to a wafer, a device, and a cutting blade.

  According to the present invention, there is provided a wafer processing method having a device region in which a plurality of devices are formed on a surface and an outer peripheral surplus region surrounding the device region, and grinding a back surface of the wafer corresponding to the device region Grinding with a grindstone to reduce the thickness to a predetermined finish thickness, forming a recess corresponding to the device region on the back side of the wafer, and forming an annular protrusion corresponding to the outer peripheral surplus region, and the grinding step Before carrying out, the laser beam is irradiated with the condensing point of a laser beam having a wavelength transparent to the wafer positioned on the back side of the wafer from the depth position corresponding to the finished thickness, A modified layer forming step for forming an annular modified layer having a predetermined width from the boundary with the outer peripheral surplus region toward the center of the wafer, and the grinding step are performed. And a cutting step of cutting the boundary into a ring shape with a cutting blade to form a dividing groove for dividing the device region and the outer peripheral surplus region, and a wafer processing method comprising: .

  In the present invention, it is preferable that the predetermined width of the annular modified layer corresponds to an R-shaped width formed by the grinding wheel at the intersection between the bottom surface and the side surface of the recess in the grinding step.

  Further, in the present invention, the grinding step includes rough grinding for forming a first recess on the back surface of the wafer by grinding the back surface of the wafer corresponding to the device region with a rough grinding wheel and reducing the thickness to the first thickness. And after performing the rough grinding step, the center of the first recess is ground with a finishing grinding wheel containing abrasive grains finer than the rough grinding wheel, and is thinned to the predetermined finishing thickness. And finishing grinding to form a second recess having a diameter smaller than the diameter.

  The wafer processing method of the present invention is a modified layer in which an annular modified layer having a predetermined width is formed at a boundary between a device region and an outer peripheral surplus region before performing a grinding step for forming a recess on the back side of the wafer. Since the forming step is performed, the boundary between the device region and the outer peripheral surplus region is weakened by the annular reforming layer in the stage of performing the cutting step for dividing the device region and the outer peripheral surplus region.

  Therefore, when the cutting blade is cut at the boundary between the device region and the outer peripheral surplus region in the cutting step, the R shape formed in the grinding step is easily scraped off, and no bending force is applied to the cutting blade. Thereby, damage of a wafer, a device, or a cutting blade can be prevented.

FIG. 1A is a partial cross-sectional side view schematically showing the modified layer forming step, and FIG. 1B is a cross-sectional view schematically showing a cross section of the wafer on which the modified layer is formed. is there. It is a perspective view which shows a grinding step typically. It is a partial cross section side view which shows a cutting step typically. 4A is a cross-sectional view schematically showing a cross section of the wafer after the rough grinding step is performed, and FIG. 4B is a schematic cross section of the wafer after the finish grinding step is performed. It is sectional drawing shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The wafer processing method according to the present embodiment includes a modified layer forming step (see FIG. 1), a grinding step (see FIG. 2), and a cutting step (see FIG. 3).

  In the modified layer forming step, the annular modified layer (annular modified layer) is irradiated by irradiating the boundary between the device region and the outer peripheral surplus region with a laser beam having a wavelength that is difficult to be absorbed by the wafer (transmitting laser beam). Form.

  In the grinding step, the back surface side of the wafer is ground to form a concave portion corresponding to the device region, and an annular reinforcing portion (annular convex portion) is left. In the cutting step, the boundary between the device region and the outer peripheral surplus region is cut with a cutting blade to divide the device region and the outer peripheral surplus region. Hereinafter, the wafer processing method according to the present embodiment will be described in detail.

  FIG. 1A is a partial cross-sectional side view schematically showing the modified layer forming step, and FIG. 1B is a cross-sectional view schematically showing a cross section of the wafer on which the modified layer is formed. is there. As shown in FIGS. 1A and 1B, the wafer 11 is a disk-shaped semiconductor wafer made of a material such as silicon, for example, and the surface 11a includes a central device region 13 and a device region 13. It is divided into the outer peripheral surplus area 15 surrounding the area.

  The device area 13 is further divided into a plurality of areas by streets (division planned lines) 17 arranged in a lattice pattern, and a device 19 such as an IC is formed in each area. The outer periphery 11c of the wafer 11 is chamfered, and the cross-sectional shape is an arc shape. In the wafer processing method of this embodiment, the back surface 11b side of the wafer 11 is ground and processed to a thin finish thickness T.

  Here, the planned grinding region 21 of the wafer 11 corresponding to the device region 13 is ground from the back surface 11b side to form a recess 23 (see FIG. 2) and an annular reinforcing portion (annular) corresponding to the outer peripheral surplus region 15. A conventional processing method for leaving the (convex portion) 25 will be considered.

  When the wafer 11 is processed by this processing method, the recess 23 is formed in a shape in which a bottom surface 23a (see FIG. 3) and a side surface 23b (see FIG. 3) are connected by a curved surface. In this way, the connecting portion (intersection) 23c (see FIG. 3) between the bottom surface 23a and the side surface 23b has a curved surface shape (R shape) because the corner of the grinding wheel 16b (see FIG. 2) used for grinding is used. This is because the portion is worn and rounded as the grinding progresses.

  When the connecting portion 23c between the bottom surface 23a and the side surface 23b has a curved shape, a force in the bending direction (direction perpendicular to the depth direction) is applied to the cutting blade 20 when the cutting blade 20 (see FIG. 3) is cut in the cutting step. And the cutting blade 20 is curved. Such a force in the bending direction causes various problems on the wafer 11, the device 19, and the cutting blade 20.

  Therefore, in the wafer processing method of the present embodiment, first, the laser beam L having a wavelength that is difficult to be absorbed by the wafer 11 is supplied to the second boundary surface 21a that becomes the bottom surface 23a of the recess 23 and the second side surface 23b of the recess. A modified layer forming step of forming an annular modified layer (annular modified layer) 27 is performed by irradiating the connecting portion (intersection portion) 21c with the boundary surface 21b.

  Since the modified portion 27 weakens the connecting portion 23c formed in the subsequent grinding step, the curved surface shape is easily scraped off by the cut blade 20, and a force in the bending direction is applied to the cutting blade 20. Can be prevented.

  This modified layer forming step is performed by, for example, the laser processing apparatus 2 shown in FIG. The laser processing apparatus 2 includes a chuck table (not shown) that holds the wafer 11 by suction. The chuck table is connected to a rotation mechanism such as a motor, and rotates around a rotation axis extending in the vertical direction. Further, a moving mechanism is provided below the chuck table, and the chuck table moves in the horizontal direction by the moving mechanism.

  The upper surface of the chuck table is a holding surface for sucking and holding the surface 11 a side of the wafer 11. A negative pressure of a suction source acts on the holding surface through a flow path formed inside the chuck table, and a suction force for sucking the wafer 11 is generated.

  A laser processing head 4 is disposed above the chuck table. The laser processing head 4 focuses the laser beam L oscillated by a laser oscillator (not shown) inside the wafer 11 sucked and held by the chuck table. The laser oscillator is configured to be able to oscillate a laser beam L having a wavelength that is difficult to be absorbed by the wafer 11 (a laser beam L having a wavelength having transparency).

  In the modified layer forming step, first, the surface 11a side of the wafer 11 is sucked and held on the chuck table. Thereby, the back surface 11b side of the wafer 11 is exposed upward. Before placing the wafer 11 on the chuck table, it is preferable to attach a protective member 31 (see FIG. 2) to the surface 11a side of the wafer 11.

  Next, the chuck table is moved and rotated to position the laser processing head 4 on the boundary between the device region 13 and the outer peripheral surplus region 15. Further, the laser processing head 4 is adjusted so that the condensing point P of the laser beam L is positioned slightly above the depth position corresponding to the finished thickness T of the wafer 11 (on the back surface 11b side of the wafer 11). .

  Thereafter, the laser beam L is irradiated from the laser processing head 4 toward the back surface 11b of the wafer 11, and the chuck table is rotated. Accordingly, the annular modified layer 27 can be formed by irradiating the boundary between the device region 13 and the outer peripheral surplus region 15 with the laser beam L.

  The modified layer 27 is formed to have a predetermined width at least from the boundary between the device region 13 and the outer peripheral surplus region 15 toward the center of the wafer 11. That is, the modified layer 27 has a predetermined width in the radial direction of the wafer 11. The width of the modified layer 27 preferably corresponds to the width of the curved surface formed at the connecting portion 23c between the bottom surface 23a and the side surface 23b of the recess 23 in the subsequent grinding step. Of course, the width of the modified layer 27 may be larger than the width of the curved surface shape.

  By forming the modified layer 27 having such a width, the entire curved surface formed in the connection portion 23c can be weakened. As a result, the curved shape of the connecting portion 23c can be appropriately scraped off by the cutting blade 20, and a bending force can be prevented from being applied to the cutting blade 20.

  After the modified layer forming step, the back surface 11b side of the wafer 11 is ground to form a recess 23 corresponding to the device region 13, and a grinding step for leaving the annular reinforcing portion 25 is performed. FIG. 2 is a perspective view schematically showing the grinding step.

  The grinding step is performed by, for example, the grinding device 6 shown in FIG. The grinding device 6 includes a holding table 8 that holds the wafer 11 by suction. The holding table 8 is connected to a rotation mechanism (not shown) such as a motor, and rotates around a rotation axis extending in the vertical direction. A moving mechanism (not shown) is provided below the holding table 8, and the holding table 8 moves in the horizontal direction by this moving mechanism.

  The surface (upper surface) of the holding table 8 is a holding surface that holds the wafer 11 by suction. A negative pressure of a suction source (not shown) acts on the holding surface through a flow path (not shown) formed inside the holding table 8 to generate a suction force for sucking the wafer 11.

  A grinding mechanism 10 is disposed above the holding table 8. The grinding mechanism 10 includes a spindle housing 12 supported by an elevating mechanism (not shown). A spindle 14 connected to a rotation mechanism (not shown) such as a motor is rotatably supported on the spindle housing 12. The spindle 14 rotates around a rotating shaft extending in the vertical direction by the rotational force transmitted from the rotating mechanism, and moves up and down together with the spindle housing 12 by the lifting mechanism.

  A grinding wheel 16 having a diameter smaller than that of the wafer 11 is mounted on the lower end side of the spindle 14. The grinding wheel 16 includes a wheel base 16a formed of a metal material such as aluminum or stainless steel. A plurality of grinding wheels 16b are fixed to the annular lower surface of the wheel base 16a over the entire circumference.

  In the grinding step, first, the surface 11 a side of the wafer 11 is sucked and held by the holding table 8. Thereby, the back surface 11b side of the wafer 11 is exposed upward. Note that the surface 11 a side of the wafer 11 is protected by a protective member 31.

  Next, the holding table 8 is moved to position the outer peripheral edge of the grinding wheel 16 b on the boundary between the device region 13 and the outer peripheral surplus region 15. Thereafter, the grinding wheel 16 and the holding table 8 are rotated to lower the spindle 14. The descending amount of the spindle 14 is set such that the lower surface of the grinding wheel 16b is pressed against the back surface 11b of the wafer 11.

  As described above, the planned grinding region 21 of the wafer 11 corresponding to the device region 13 is ground from the back surface 11b side to form the concave portion 23, and the annular reinforcing portion (annular convex portion) 25 corresponding to the outer peripheral surplus region 15 is formed. It can be left. That is, in the grinding step, the concave portion 23 and the annular reinforcing portion 25 are formed on the back surface 11 b side of the wafer 11.

  This grinding step ends when the wafer 11 (the portion corresponding to the device region 13 of the wafer 11) is ground to the finished thickness T. After grinding the wafer 11 to the finished thickness T, the wafer 11 may be taken out of the holding table 8 and the protective member 31 adhered to the surface 11a side may be removed.

  After the grinding step, the cutting step of cutting the boundary between the device region 13 and the outer peripheral surplus region 15 with the cutting blade 20 and dividing the device region 13 and the outer peripheral surplus region 15 is performed. FIG. 3 is a partial cross-sectional side view schematically showing the cutting step.

  The cutting step is performed by, for example, the cutting device 18 shown in FIG. The cutting device 18 includes a chuck table (not shown) that holds the wafer 11 by suction. The chuck table is connected to a rotation mechanism such as a motor, and rotates around a rotation axis extending in the vertical direction. A machining feed mechanism (not shown) is provided below the chuck table, and the chuck table is moved in the machining feed direction by the machining feed mechanism.

  The upper surface of the chuck table is a holding surface for sucking and holding the surface 11 a side of the wafer 11. A negative pressure of a suction source acts on the holding surface through a flow path formed inside the chuck table, and a suction force for sucking the wafer 11 is generated.

  An annular cutting blade 20 for cutting the wafer 11 is disposed above the chuck table. The cutting blade 20 is mounted on one end side of a spindle 22 that rotates around a rotation axis that extends in the horizontal direction.

  The cutting blade 20 is formed in an annular shape having a predetermined thickness, for example, by mixing abrasive grains such as diamond and CBN (Cubic Boron Nitride) in a bond material (bonding material) such as metal or resin. A motor (not shown) is connected to the other end side of the spindle 22, and the cutting blade 20 mounted on the spindle 22 rotates by the rotational force of this motor.

  The spindle 22 and the cutting blade 20 are supported by an elevating mechanism (not shown) and move (elevate) in the vertical direction. Further, an index feed mechanism (not shown) is provided below the lifting mechanism, and the cutting blade 20 moves in the index feed direction by this index feed mechanism.

  In the cutting step, first, a dicing tape 33 having a diameter larger than that of the wafer 11 is attached to the surface 11 a side of the wafer 11. An annular frame 35 is fixed to the outer peripheral portion of the dicing tape 33. Next, the surface 11a side of the wafer 11 is sucked and held on the chuck table. Thereby, the back surface 11b side of the wafer 11 is exposed upward.

  Next, the chuck table is moved and rotated to position the cutting blade 20 on the boundary between the device region 13 and the outer peripheral surplus region 15. Thereafter, the cutting blade 20 is rotated to cut into the wafer 11 and the chuck table is rotated. Thereby, an annular dividing groove for dividing the device region 13 and the outer peripheral surplus region 15 can be formed. When the device region 13 and the outer peripheral surplus region 15 are divided, the cutting step ends.

  As described above, in the wafer processing method according to the present embodiment, before the grinding step for forming the recess 23 on the back surface 11 b side of the wafer 11 is performed, a predetermined boundary is formed between the device region 13 and the outer peripheral surplus region 15. A modified layer forming step for forming an annular modified layer (annular modified layer) 27 having a width of 5 mm is performed. Therefore, the boundary between the device region 13 and the outer peripheral surplus region 15 is weakened by the modified layer 27 at the stage of performing the cutting step for dividing the device region 13 and the outer peripheral surplus region 15.

  Therefore, when the cutting blade 20 is cut at the boundary between the device region 13 and the outer peripheral surplus region 15 in the cutting step, the curved surface shape (R shape) formed in the connection portion 23c in the grinding step is easily crushed, and the cutting blade No force in the bending direction is applied to 20. Thereby, damage to the wafer 11, the device 19, and the cutting blade 20 can be prevented.

  In addition, this invention is not limited to description of the said embodiment, A various change can be implemented. For example, the grinding step may include a plurality of processes for grinding the wafer 11. In the following modification, a grinding step including two steps of a rough grinding step and a finish grinding step will be described.

  FIG. 4A is a cross-sectional view schematically showing a cross section of the wafer 11 after performing the rough grinding step, and FIG. 4B is a schematic cross section of the wafer 11 after performing the finish grinding step. FIG.

  In the grinding step according to the modified example, first, a rough grinding step of rough grinding the back surface 11b side of the wafer 11 is performed. This rough grinding step can be performed by a grinding device similar to the grinding device 6 described above. However, as the grinding wheel 16b, a rough grinding wheel (not shown) including coarse abrasive grains is used.

  In the rough grinding step, the back surface 11b side of the wafer 11 is ground with the rough grinding wheel described above, and the region corresponding to the device region 13 is processed to a first thickness larger than the finished thickness T. Thereby, the first concave portion 41 is formed in the region corresponding to the device region 13, and the annular reinforcing portion (annular convex portion) 43 remains in the region corresponding to the outer peripheral surplus region 15.

  After the rough grinding step, a finish grinding step for grinding the center of the first recess 41 is performed. This finish grinding step can also be performed by a grinding apparatus similar to the grinding apparatus 6 described above. However, as the grinding wheel 16b, a finish grinding wheel (not shown) including abrasive grains finer than the coarse grinding wheel used in the rough grinding step is used.

  In the finish grinding step, the center of the bottom surface of the first recess 41 is ground with the finish grinding wheel described above, and processed to the finish thickness T. Thereby, the second recess 45 having a diameter slightly smaller than that of the device region 13 can be formed.

  After the above-described grinding step, a cutting step for dividing the device region 13 and the outer peripheral surplus region 15 may be performed. In this modification, the wafer 11 can be divided into an inner region and an outer region of the second recess 45. In this case, it is preferable to form the annular modified layer 27 in a region corresponding to the contour of the second recess 45.

  In addition, the configurations, methods, and the like according to the above-described embodiments can be modified as appropriate without departing from the object of the present invention.

DESCRIPTION OF SYMBOLS 2 Laser processing apparatus 4 Laser processing head 6 Grinding apparatus 8 Holding table 10 Grinding mechanism 12 Spindle housing 14 Spindle 16 Grinding wheel 16a Wheel base 16b Grinding wheel 18 Cutting apparatus 20 Cutting blade 22 Spindle 11 Wafer 11a Surface 11b Back surface 11c Outer periphery 13 Device Area 15 Peripheral surplus area 17 Street (division planned line)
19 Device 21 Planned grinding region 21a First boundary surface 21b Second boundary surface 21c Connection portion (intersection)
23 Concave part 23a Bottom face 23b Side face 23c Connection part (intersection part)
25 Reinforcement part (annular convex part)
27 Modified layer (annular modified layer)
31 Protective member 33 Dicing tape 35 Frame 41 First concave portion 43 Reinforcement portion (annular convex portion)
45 Second recess L Laser beam P Focus point T Finish thickness

Claims (3)

A wafer processing method having a device region in which a plurality of devices are formed on a surface and an outer peripheral surplus region surrounding the device region,
The back surface of the wafer corresponding to the device region is ground with a grinding wheel and thinned to a predetermined finish thickness to form a concave portion corresponding to the device region on the back surface side of the wafer and an annular convex portion corresponding to the outer peripheral surplus region Forming a grinding step;
Before carrying out the grinding step, the laser beam focusing point of the laser beam having a wavelength transparent to the wafer is positioned on the back side of the wafer from the depth position corresponding to the finished thickness, and the laser beam is irradiated. A modified layer forming step of forming an annular modified layer having a predetermined width from the boundary between the device region and the outer peripheral surplus region toward the center of the wafer;
A cutting step of forming a dividing groove for cutting the boundary in an annular shape with a cutting blade and dividing the device region and the outer peripheral surplus region after performing the grinding step. Processing method.   The predetermined width of the annular modified layer corresponds to an R-shaped width formed by the grinding wheel at an intersection between a bottom surface and a side surface of the recess in the grinding step. The processing method of the wafer as described. The grinding step is a rough grinding step of forming a first recess on the back surface of the wafer by grinding the back surface of the wafer corresponding to the device region with a rough grinding wheel and thinning to a first thickness;
After performing the rough grinding step, the center of the first recess is ground with a finish grinding wheel containing finer grains than the rough grinding wheel to reduce the thickness to the predetermined finish thickness. The method for processing a wafer according to claim 1, further comprising: a finish grinding step for forming a second concave portion having a small diameter.

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