JP2018063986A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new wafer processing method capable of appropriately dividing a wafer including a metal layer overlapping with an intersection region with which division schedule lines intersect.SOLUTION: A wafer processing method includes: a modified layer forming step of forming a first modified layer along a first division schedule line and a second modified layer along a second division schedule line inside a wafer except a non-processing region in an intersection region with which the first division schedule line and the second division schedule line intersect by irradiating the wafer with a laser beam of a wavelength having permeability to the wafer along the first division schedule line and the second division schedule line; and a division-promoting modified layer forming step of forming a division-promoting modified layer for promoting division in a portion overlapping with a metal layer in the non-processing region by irradiating the portion overlapping with the metal layer with the laser beam of the wavelength having the permeability to the wafer.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a wafer processing method for modifying the inside of a wafer with a laser beam.

  In an electronic device typified by a mobile phone or a personal computer, a device chip including a device such as an electronic circuit is an essential component. The device chip is, for example, a method in which the surface of a wafer made of a semiconductor material such as silicon is partitioned by a plurality of planned division lines (streets), a device is formed in each region, and then the wafer is divided along the planned division lines. Manufactured by.

  One method of dividing the wafer is SD (Stealth Dicing), which forms a modified layer (modified region) modified by multiphoton absorption by focusing a transparent laser beam inside the wafer. The method called is known (for example, refer patent document 1). After forming the modified layer along the division line, the wafer can be divided starting from the modified layer by applying a force to the wafer.

  By the way, in this SD, the modified layer remains in the device chip to be formed, and the bending strength of the device chip cannot often be sufficiently increased. Therefore, a method called SDBG (Stealth Dicing Before Grinding) in which the rear surface of the wafer is ground after forming the modified layer and the wafer is divided into a plurality of device chips while removing the modified layer has been put into practical use. (For example, refer to Patent Document 2).

JP 2002-192370 A International Publication No. 2003/77295

  In the above-mentioned SDBG, the wafer is divided using the force applied during grinding, so that a separate process for dividing the wafer is not necessarily required. On the other hand, in SDBG, the corners of the device chip are in contact with each other by grinding that continues even after the division into device chips, and the device chips are easily cracked or chipped.

  In order to solve this problem, a method of grinding without dividing the wafer until a certain thickness has been studied by not forming a modified layer in the intersecting region where the planned dividing lines intersect. According to this method, it is possible to shorten the grinding time that continues after being divided into device chips, and to suppress the occurrence of cracks and chips due to the contact between the corners of the device chips.

  However, for example, if a metal layer constituting a TEG (Test Elements Group) or the like is overlapped in an intersecting region where the planned dividing lines intersect, the wafer cannot be appropriately divided by this method. In this case, an irregularly shaped device chip was easily formed.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a new wafer that is processed so that a wafer including a metal layer that overlaps an intersecting region where scheduled division lines intersect can be appropriately divided. It is to provide a processing method.

  According to one aspect of the present invention, each region partitioned by a plurality of first division planned lines extending in the first direction and a plurality of second division planned lines extending in the second direction intersecting the first direction. In which a device is formed and a metal layer is formed on the first division line or the second division line, and a laser beam having a wavelength that is transparent to the wafer is applied to the wafer. Irradiation is performed along one scheduled split line and the second scheduled line, and inside the wafer excluding a non-processed area in an intersecting region where the first scheduled split line and the second scheduled line intersect, A modified layer forming step for forming a first modified layer along the first division line and a second modified layer along the second division line; and a wafer on a portion overlapping the metal layer in the non-processed region. Wavelengths that are transparent to the Irradiating the Zabimu method of processing a wafer comprising a dividing promoting modified layer forming step of forming a split promote reforming layer to promote the division of the portion overlapping with the metal layer, it is provided.

  In the wafer processing method according to one aspect of the present invention, the division that promotes the division of the portion that overlaps the metal layer in the portion that overlaps the metal layer in the non-processed region where the first modified layer and the second modified layer are not formed. Since the modified layer for promotion is formed, the wafer can be appropriately divided even when the metal layer overlaps the non-processed region.

FIG. 1A is a perspective view schematically illustrating a configuration example of a wafer, and FIG. 1B is a perspective view schematically illustrating a state where a protective member is attached to the wafer. 2A is a partially sectional side view schematically showing the first modified layer forming step, and FIG. 2B is a partially sectional side view schematically showing the second modified layer forming step. FIG. It is a figure which shows typically the wafer in which the 1st modified layer and the 2nd modified layer were formed. FIG. 4A is a partial cross-sectional side view schematically showing the division promoting modified layer forming step, and FIG. 4B is a diagram illustrating the first modified layer, the second modified layer, and the division promoting layer. It is a figure which shows typically the wafer in which the modified layer was formed. It is a partial cross section side view which shows a grinding step typically.

  Embodiments according to one aspect of the present invention will be described with reference to the accompanying drawings. The wafer processing method according to the present embodiment includes a first modified layer forming step (see FIG. 2A), a second modified layer forming step (see FIG. 2B), and a division promoting modified layer. Forming step (see FIG. 4A).

  In the first modified layer forming step, the wafer is irradiated with a laser beam along a first division planned line (first street) extending (extending) in the first direction to form the first modified layer inside the wafer. To do. In the second modified layer forming step, the wafer is irradiated with a laser beam along a second division planned line (second street) extending (extending) in the second direction, and the first division planned line and the second division planned line are irradiated. A second modified layer is formed inside the wafer excluding the non-processed region in the intersecting region where the and intersect.

  In the division promoting modified layer forming step, the laser beam is irradiated to a portion overlapping the metal layer in the non-processed region where the second modified layer (and the first modified layer) is not formed, and the portion overlapping the metal layer is divided. A reforming layer for promoting division is formed. Hereinafter, the wafer processing method according to the present embodiment will be described in detail.

  FIG. 1A is a perspective view schematically showing a configuration example of a wafer processed in this embodiment. As shown in FIG. 1A, the wafer 11 is formed in a disk shape using a semiconductor material such as silicon (Si). The surface 11a side of the wafer 11 has a plurality of first division planned lines (first streets) 13a extending in the first direction D1 and a plurality of second division planned lines (second streets) 13b extending in the second direction D2. Are divided into a plurality of areas, and each area is provided with a device 15 such as an IC or an LSI.

  In this embodiment, the disk-shaped wafer 11 made of a semiconductor material such as silicon is used, but the material, shape, structure, size, etc. of the wafer 11 are not limited. For example, a wafer 11 made of a material such as ceramics can be used. Similarly, the type, quantity, size, arrangement, etc. of the device 15 are not limited. Further, the first direction D1 in which the first planned division line 13a extends and the second direction D2 in which the second planned division line 13b extends need only intersect each other, and do not need to be perpendicular to each other.

  Before carrying out the wafer processing method according to the present embodiment, a protective member made of resin or the like is attached to the surface 11a side of the wafer 11 described above. FIG. 1B is a perspective view schematically showing how a protective member is attached to the wafer 11. The protective member 21 is, for example, a circular film (tape) having a diameter equivalent to that of the wafer 11, and a glue layer having adhesive force is provided on the surface 21a side.

  Therefore, as shown in FIG. 1B, the protective member 21 can be attached to the surface 11 a side of the workpiece 11 by bringing the surface 21 a side of the protective member 21 into close contact with the surface 11 a side of the workpiece 11. By attaching the protective member 21 to the surface 11a side of the workpiece 11, it is possible to reduce the impact applied in each subsequent step and protect the device 15 provided on the surface 11a side of the wafer 11.

  After affixing the protective member 21 to the surface 11a side of the wafer 11, a first modified layer is formed by irradiating a laser beam along the first division line 13a to form a first modified layer inside the wafer 11. Do step. FIG. 2A is a partial cross-sectional side view schematically showing the first modified layer forming step. The first modified layer forming step is performed using, for example, a laser processing apparatus 2 shown in FIG.

  The laser processing apparatus 2 includes a chuck table 4 for sucking and holding the wafer 11. The chuck table 4 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel to the vertical direction. A moving mechanism (not shown) is provided below the chuck table 4, and the chuck table 4 is moved in the horizontal direction by the moving mechanism.

  A part of the upper surface of the chuck table 4 serves as a holding surface 4 a that sucks and holds the protective member 21 attached to the wafer 11. The holding surface 4 a is connected to a suction source (not shown) through a suction path (not shown) formed inside the chuck table 4. By applying the negative pressure of the suction source to the holding surface 4 a, the wafer 11 is held on the chuck table 4 via the protection member 21.

  A laser irradiation unit 6 is disposed above the chuck table 4. The laser irradiation unit 6 irradiates and condenses a laser beam L pulsed by a laser oscillator (not shown) at a predetermined position. The laser oscillator is configured to be able to pulse-oscillate a laser beam L having a wavelength that is transparent to the wafer 11 (wavelength that is difficult to be absorbed).

  In the first modified layer forming step, first, the back surface 21b of the protective member 21 attached to the wafer 11 is brought into contact with the holding surface 4a of the chuck table 4 to apply a negative pressure of the suction source. Thereby, the wafer 11 is held on the chuck table 4 with the back surface 11b side exposed upward.

  Next, the chuck table 4 is moved and rotated to align the laser irradiation unit 6 on, for example, an extension line of the target first division planned line 13a. Then, as shown in FIG. 2A, the chuck table is irradiated in a direction parallel to the target first division line 13a while irradiating the laser beam L from the laser irradiation unit 6 toward the back surface 11b of the wafer 11. 4 is moved.

  The laser beam L is condensed at a predetermined depth inside the wafer 11. Thus, by condensing the laser beam L having a wavelength transmissive to the wafer 11 inside the wafer 11, the inside of the wafer 11 is modified and the first modified layer serving as a starting point of the division. 17a can be formed.

  The first modified layer 17a is desirably formed at a position where the depth is removed by subsequent grinding. For example, when the wafer 11 is later ground from the back surface 11b side to a thickness of about 30 μm, the first modified layer 17a may be formed at a depth of about 70 μm from the front surface 11a.

  The first modified layer 17a is also formed continuously and integrally in, for example, an intersecting area A (see FIG. 3) where the first scheduled division line 13a and the second scheduled division line 13b intersect. When the operation as described above is repeated and the first modified layer 17a is formed along all the first division planned lines 13a, the first modified layer forming step ends. The first modified layer 17a is desirably formed under the condition that the crack reaches the surface 11a. Further, a plurality of first modified layers 17a may be formed at different depth positions with respect to each first division planned line 13a.

  After the first modified layer forming step, a second modified layer forming step of irradiating the wafer with the laser beam L along the second division line 13b to form the second modified layer inside the wafer 11 is performed. Do. FIG. 2B is a partial cross-sectional side view schematically showing the second modified layer forming step. The second modified layer forming step is subsequently performed using the laser processing apparatus 2.

  In the second modified layer forming step, first, the chuck table 4 is moved and rotated to align the laser irradiation unit 6 on, for example, an extension line of the target second division planned line 13b. Then, as shown in FIG. 2B, while irradiating the laser beam L from the laser irradiation unit 6 toward the back surface 11b of the wafer 11, the chuck table in a direction parallel to the target second division planned line 13b. 4 is moved.

  The laser beam L is condensed at a predetermined depth inside the wafer 11. As a result, the inside of the wafer 11 can be modified to form the second modified layer 17b serving as a starting point for the division. The second modified layer 17b is desirably formed at a position having the same depth as the first modified layer 17a. In addition, the second modified layer 17b is desirably formed under the condition that the crack reaches the surface 11a.

  In the second modified layer forming step, the second modified layer 17b is not formed in a part of the intersecting region A where the first division planned line 13a and the second division planned line 13b intersect. FIG. 3 is a diagram schematically showing the wafer 11 on which the first modified layer 17a and the second modified layer 17b are formed. In FIG. 3, for convenience of explanation, the device 15 formed on the surface 11 a side of the wafer 11 and the first modified layer 17 a and the second modified layer 17 b formed inside the wafer 11 are both solid lines. It is represented by

  As shown in FIG. 3, the second modified layer 17b is formed inside the wafer 11 excluding the non-processed region B in the intersecting region A where the first division planned line 13a and the second division planned line 13b intersect. The That is, in the second modified layer forming step, the discontinuous and discrete second modified layer 17b divided by the non-processed region B is formed.

  The size, arrangement, etc. of the non-processed region B are arbitrary, but for example, a region having a length of 150 μm or more and 250 μm or less extending in the second direction D2 around the center position in the width direction of the first division planned line 13a is not It is desirable to set the processing region B, and it is more desirable to set a region having a length of about 200 μm as the non-processing region B. In this case, the non-processed region B is set substantially symmetrically with respect to the first modified layer 17a.

  Thus, by not forming the second modified layer 17b in the non-processed region B of the intersecting region A, the wafer 11 can be ground without being divided at least in the initial stage of subsequent grinding (the non-processed region B). Can be ground while being connected). Therefore, the probability that the corners of the chips (device chips) divided from the wafer 11 come into contact with each other in the intersecting region A and the cracks and chips are generated can be reduced.

  When the second modified layer 17b is formed along all the second scheduled division lines 13b by repeating the above-described operation, the second modified layer forming step ends. In this second modified layer forming step, a plurality of second modified layers 17b may be formed at different depth positions with respect to each second scheduled division line 13b. In this embodiment, the second modified layer forming step is performed after the first modified layer forming step. However, the first modified layer forming step may be performed after the second modified layer forming step. .

  By the way, a metal layer used for a TEG (Test Elements Group) or the like may be formed at a position overlapping the non-processed region B of the wafer 11 described above. When such a metal layer exists, the wafer 11 cannot be appropriately broken in the non-processed region B, and there is a high possibility that an irregularly shaped chip is formed. Therefore, in the present embodiment, after the first modified layer forming step and the second modified layer forming step, a division promoting modified layer forming step for forming a division promoting modified layer for promoting division is performed. .

  FIG. 4A is a partial cross-sectional side view schematically showing the division promoting modified layer forming step, and FIG. 4B shows the first modified layer 17a, the second modified layer 17b, and the divided layers. It is a figure which shows typically the wafer 11 in which the modified layer for promotion was formed. In FIG. 4B, for convenience of explanation, the device 15 formed on the surface 11a side of the wafer 11, the first modified layer 17a, the second modified layer 17b, and the division formed in the wafer 11 are illustrated. Both of the promotion reforming layers are represented by solid lines. The division promoting modified layer forming step is subsequently performed using the laser processing apparatus 2.

  In the division promoting modified layer forming step, first, the chuck table 4 is moved and rotated to align the laser irradiation unit 6 above the metal layer 19 (FIG. 4B) overlapping the non-processed region B, for example. 4A, the chuck table 4 is moved in accordance with the size and shape of the metal layer 19 while irradiating the laser beam L from the laser irradiation unit 6 toward the back surface 11b of the wafer 11.

  The laser beam L is condensed at a predetermined depth inside the wafer 11. As a result, the inside of the wafer 11 can be modified to form the division promoting modified layer 17c for promoting the division of the portion overlapping the metal layer 19, as shown in FIG. 4B. The division promoting modified layer 17c is desirably formed at a depth equivalent to that of the second modified layer 17b.

  When the operation as described above is repeated and the division promoting reforming layer 17c is formed in the portion that overlaps the metal layer 19 in all the non-processed regions B, the division promoting reforming layer forming step is completed. In this division promotion modified layer forming step, a plurality of division promotion modified layers 17c may be formed at different depth positions.

  Further, in the present embodiment, the division promoting promotion modified layer forming step is performed after the first modified layer forming step and the second modified layer forming step. However, the first modified layer forming step and the second modified layer forming step are performed. A division promoting modified layer forming step may be performed before the layer forming step. In addition, the division promoting modified layer forming step may be performed in the middle of the second modified layer forming step.

  After the first modified layer forming step, the second modified layer forming step, and the division promoting modified layer forming step, for example, the back surface 11b is ground to make the wafer 11 thinner and divided into a plurality of chips. A grinding step should be performed. FIG. 5 is a partial cross-sectional side view schematically showing the grinding step.

  The grinding step is performed using, for example, a grinding apparatus 12 shown in FIG. The grinding device 12 includes a chuck table 14 for sucking and holding the wafer 11. The chuck table 14 is connected to a rotation drive source (not shown) such as a motor, and rotates around a rotation axis substantially parallel to the vertical direction. A moving mechanism (not shown) is provided below the chuck table 14, and the chuck table 14 is moved in the horizontal direction by the moving mechanism.

  A part of the upper surface of the chuck table 14 serves as a holding surface 14 a that sucks and holds the protective member 21 attached to the wafer 11. The holding surface 14 a is connected to a suction source (not shown) through a suction path (not shown) formed inside the chuck table 14. By applying the negative pressure of the suction source to the holding surface 14 a, the wafer 11 is held on the chuck table 14 via the protection member 21.

  A grinding unit 16 is disposed above the chuck table 14. The grinding unit 16 includes a spindle housing (not shown) supported by an elevating mechanism (not shown). A spindle 18 is accommodated in the spindle housing, and a disc-shaped mount 20 is fixed to the lower end portion of the spindle 18.

  A grinding wheel 22 having the same diameter as that of the mount 20 is mounted on the lower surface of the mount 20. The grinding wheel 22 includes a wheel base 24 formed of a metal material such as stainless steel or aluminum. A plurality of grinding wheels 26 are annularly arranged on the lower surface of the wheel base 24.

  A rotary drive source (not shown) such as a motor is connected to the upper end side (base end side) of the spindle 18, and the grinding wheel 22 is substantially parallel to the vertical direction by the force generated by this rotary drive source. Rotate around the axis of rotation. A nozzle (not shown) for supplying a grinding liquid such as pure water to the wafer 11 or the like is provided in or near the grinding unit 16.

  In the grinding step, first, the wafer 11 carried out from the chuck table 4 of the laser processing apparatus 2 is sucked and held by the chuck table 14 of the grinding apparatus 12. Specifically, the back surface 21b of the protective member 21 affixed to the wafer 11 is brought into contact with the holding surface 14a of the chuck table 14 to apply a negative pressure of the suction source. Thus, the wafer 11 is held on the chuck table 14 with the back surface 11b side exposed upward.

  Next, the chuck table 14 is moved below the grinding unit 16. Then, as shown in FIG. 5, the chuck table 14 and the grinding wheel 22 are rotated, and the spindle housing (spindle 18 and grinding wheel 22) is lowered while supplying the grinding liquid to the back surface 11b and the like of the wafer 11.

  The descending speed (falling amount) of the spindle housing is adjusted so that the lower surface of the grinding wheel 26 is pressed against the back surface 11 b side of the wafer 11. Thereby, the back surface 11b side can be ground and the wafer 11 can be made thin. When the wafer 11 is thinned to a predetermined thickness (finished thickness), for example, when divided into a plurality of chips starting from the first modified layer 17a, the second modified layer 17b, and the division promoting modified layer 17c, The grinding step ends.

  In the present embodiment, the back surface 11b side of the wafer 11 is ground using one set of grinding units 16 (grinding grindstone 26), but the wafer 11 is ground using two or more sets of grinding units (grinding grindstones). It may be ground. For example, rough grinding is performed using a grinding wheel composed of abrasive grains having a large diameter, and finishing grinding is performed using a grinding wheel composed of abrasive grains having a small diameter, thereby greatly reducing the time required for grinding. The flatness of the back surface 11b can be improved without increasing the length.

  As described above, in the wafer processing method according to the present embodiment, the metal layer 19 and the portion that overlaps the metal layer 19 in the non-processed region B where the first modified layer 17a and the second modified layer 17b are not formed. Since the division promoting modified layer 17c that promotes the division of the overlapping portion is formed, the wafer 11 can be appropriately divided even when the metal layer 19 overlaps the non-processed region B.

  In addition, this invention is not restrict | limited to description of the said embodiment, A various change can be implemented. For example, in the above-described embodiment, the non-processed region in the intersecting region where the first division planned line and the second division planned line intersect is set along the second direction, and is discontinuous in the second modified layer forming step. Discrete second modified layers are formed, but the first direction and the second direction, the first division planned line and the second division planned line, the first modified layer and the second modified layer, etc. are distinguished. Is just a convenience and these relationships can be interchanged.

  For example, a non-processed area in an intersecting area where the first division planned line and the second division planned line intersect is set along the first direction, and the first modified layer forming step performs discontinuous and discrete first processes. One modified layer may be formed.

  In addition, a non-working region in an intersecting region where the first division planned line and the second division planned line intersect is set along both the first direction and the second direction, so that the non-continuous and discrete first modification is performed. A quality layer and a second modified layer may be formed. That is, in the present invention, it is sufficient that the first modified layer and the second modified layer are not formed in the non-processed region in the intersection region where the first division planned line and the second division planned line intersect.

  In addition, the structure, method, and the like according to the above-described embodiment can be appropriately modified and implemented without departing from the scope of the object of the present invention.

11 Wafer 11a Front surface 11b Back surface 13a First division planned line (first street)
13b Second division planned line (second street)
DESCRIPTION OF SYMBOLS 15 Device 17a 1st modified layer 17b 2nd modified layer 17c Modified layer for promotion of division 21 Protective member 21a Front surface 21b Back surface 2 Laser processing device 4 Chuck table 4a Holding surface 6 Laser irradiation unit 12 Grinding device 14 Chuck table 14a Holding Surface 16 Grinding unit 18 Spindle 20 Mount 22 Grinding wheel 24 Wheel base 26 Grinding wheel

Claims (1)

A device is formed in each region partitioned by a plurality of first division planned lines extending in the first direction and a plurality of second division planned lines extending in the second direction intersecting the first direction, A method of processing a wafer having a metal layer on one scheduled division line or on the second scheduled division line,
A laser beam having a wavelength that is transmissive to the wafer is irradiated along the first scheduled division line and the second scheduled division line, and the first scheduled division line and the second scheduled division line intersect. A modified layer forming step of forming a first modified layer along the first planned division line and a second modified layer along the second planned division line inside the wafer excluding the non-processed region in the intersection region When,
A portion for promoting division that irradiates a portion of the non-working region that overlaps the metal layer with a laser beam having a wavelength that is transmissive to the wafer to form a division promoting modification layer that promotes the division of the portion that overlaps the metal layer. And a modified layer forming step.