JP6101468B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer processing method for dividing a semiconductor wafer or an optical device wafer into individual chips.

  2. Description of the Related Art Conventionally, as a processing method for dividing a wafer into individual chips, a technique for dividing the wafer by laser processing has attracted attention. As a laser processing, a processing method is proposed in which a fragile layer (modified layer) is formed inside the wafer by irradiating a laser beam having transparency to the wafer, and the modified layer having a reduced strength is used as a starting point. (For example, refer to Patent Document 1). In this processing method, a laser beam is irradiated along the first and second division lines orthogonal to each other, and a linear modified layer is formed inside the wafer. Then, when an external force is applied to the fragile modified layer, the wafer is divided into individual chips along the modified layer. In this laser processing, unlike mechanical dicing using a dicing saw or the like, there is no generation of cutting waste and there is almost no cutting allowance, so that it is possible to cope with the reduction in street size.

  By the way, when the thickness of the wafer is reduced to several tens of μm or less, the laser beam is transmitted through the wafer, and it becomes difficult to form an appropriate modified layer at an appropriate position inside the wafer. In view of this, there has been proposed a processing method in which a modified layer is formed inside the wafer before thinning and is ground to a finished thickness after the modified layer is formed (see, for example, Patent Document 2). In the processing method of Patent Document 2, a modified layer is formed on the surface to be ground that is higher than the finished thickness. Therefore, an appropriate modified layer can be formed at an appropriate position inside the wafer, and the modified layer is also removed, so that the luminance is improved when processing an optical device wafer, and the bending strength is increased when processing a semiconductor wafer. Is improved.

Japanese Patent No. 3408805 JP 2012-49164 A

  According to the above processing method, when the first modified layer is formed along the first scheduled dividing line among the first and second scheduled dividing lines perpendicular to each other, the first modified layer is appropriately formed inside the wafer. It is possible to form a modified layer. However, when the second modified layer is formed along the second planned division line, the intersection of the first and second divided lines is caused by the influence of the first modified layer formed previously. The second modified layer may be insufficiently formed in the vicinity of the location. For this reason, in the subsequent grinding process, the wafer is divided efficiently from the first modified layer, but the division from the second modified layer is incomplete, causing corner cracks and chipping. There was a problem of becoming.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a wafer processing method capable of appropriately dividing a wafer along orthogonal dividing lines.

The wafer processing method of the present invention includes a plurality of first division planned lines extending on a surface in a predetermined direction and a plurality of second division planned lines formed so as to intersect the plurality of first division planned lines. A modified layer is formed inside a wafer in which devices are formed in a plurality of partitioned regions, and the modified layer is thinned to a finished thickness, and the first scheduled dividing line and the second scheduled divided line are started from the modified layer. A wafer processing method for dividing the wafer along the expanded tape attaching step of attaching the expanded tape to the front surface side of the wafer, and after the expanding tape attaching step, holding the expanded tape side, A laser beam having a wavelength that is transparent to the wafer is positioned from the back side of the wafer to the focal point on the back side rather than the position corresponding to the finished thickness inside the wafer. A first modified layer forming step of irradiating along the first planned division line and forming a first modified layer along the first planned division line inside the wafer; After the quality layer forming step, the first modified layer is formed on the back surface side of the condensing point of the laser beam having a wavelength transmissive to the wafer from the back surface side of the wafer from the position corresponding to the finished thickness . A second modified layer forming step of forming a second modified layer along the second scheduled dividing line closer to a position corresponding to the finished thickness than the formed region, and the first modified layer After performing the forming step and the second modified layer forming step, the expanded tape side is held and ground from the back surface of the wafer by a grinding means to reduce the finished thickness, and the first modification is performed by a grinding operation. Reaching the surface of the wafer starting from the quality layer and the second modified layer A grinding step for growing a rack along the first division line and the second division line, and after the grinding step, an external force is applied to the first division line and the second division line. And an expanding step for separating the chips along a predetermined line.

  According to this configuration, after the first modified layer is formed inside the wafer, the second modified layer is formed between the first modified layer and a position corresponding to the finished thickness. In this case, since the first modified layer is formed inside the wafer prior to the second modified layer, the first modified layer is not affected by the second modified layer. Further, since the second modified layer is formed inside the wafer after the first modified layer, the second modified layer is affected by the first modified layer near the intersection of the first and second division lines. In some cases, it is insufficiently formed near the intersection of the first and second division lines. On the other hand, the second modified layer is formed at a position where it is easier to crack near the finished thickness than the first modified layer. For this reason, the second modified layer is easily cracked at a point other than the intersection of the first and second scheduled division lines, and is dragged by a crack other than the intersection to easily break the vicinity of the intersection. Therefore, it is possible to divide the wafer into individual chips with the same ease of cracking of the first and second modified layers.

  According to the present invention, after the first modified layer is formed inside the wafer, the second modified layer is formed between the first modified layer and the position corresponding to the finished thickness. The wafer can be appropriately divided along the orthogonal dividing lines.

It is a figure which shows an example of the expand tape sticking process which concerns on this Embodiment. It is a perspective view of the wafer which concerns on this Embodiment. It is a figure which shows an example of the 1st, 2nd modified layer formation process which concerns on this Embodiment. It is a fragmentary sectional view of the wafer after the modification layer formation concerning this embodiment. It is a figure which shows an example of the grinding process which concerns on this Embodiment. It is a figure which shows an example of the expanding process which concerns on this Embodiment.

  Hereinafter, a wafer processing method according to the present embodiment will be described. The wafer processing method according to the present embodiment is a method of dividing a wafer into individual chips along intersecting first and second division lines, and an expanding tape attaching process using a tape attaching device, a laser. The first and second modified layer forming steps by the processing device, the grinding step by the grinding device, and the expanding step by the tape expansion device are performed. In the expand tape attaching step, the expand tape is attached to the surface side of the wafer on which the device is formed.

  In the first modified layer forming step, the first modified layer is formed on the back surface side (upper side) of the finished thickness inside the wafer along the first scheduled dividing line. In the second modified layer forming step, the second modified layer is formed between the region where the first modified layer is formed inside the wafer and the finished thickness along the second division line. The At this time, the second modified layer is influenced by the first modified layer formed in the vicinity of the intersection of the first and second division lines, but is close to the finished thickness. It is easy to break even near the intersection.

  In the grinding process, the wafer is thinned to the finished thickness by the grinding means, and the wafer is divided into individual chips along the planned division line starting from the first and second modified layers by the grinding operation. The At this time, even in the vicinity of the intersection of the first and second division planned lines, the first and second modified layers are equalized by being dragged by the crack of the second modified layer formed at a position where it is easily broken. Divided. In the expanding step, an external force is applied to the expanding tape, and the wafers are separated from each other along the first and second division lines.

  Details of the wafer processing method according to the present embodiment will be described below. With reference to FIG.1 and FIG.2, an expanded tape sticking process is demonstrated. FIG. 1 is a diagram showing an example of an expanding tape attaching process according to the present embodiment. FIG. 2 is a perspective view of the wafer according to the present embodiment.

  As shown in FIG. 1 and FIG. 2, in the expanding tape attaching step, the expanding tape 16 stretched on the ring frame 15 is attached to the surface 11 side of the substantially disk-shaped wafer W. By sticking the expanded tape 16, the back surface 12 of the wafer W that becomes the irradiated surface side is exposed at the time of laser processing in the subsequent process, and the front surface 11 of the wafer W that becomes the held surface is protected by the expanded tape 16. . The wafer W after the expansion tape 16 is attached is carried into a laser processing apparatus (not shown). The expanded tape 16 only needs to be stretchable, and is formed, for example, by applying an adhesive to one surface of a sheet base material made of polyvinyl chloride.

  On the surface 11 of the wafer W covered with the expanding tape 16, a first division planned line 14a extending in a predetermined direction and a second division planned line 14b extending intersecting the first division planned line 14a are formed. ing. A device 13 is formed in a region partitioned by the first and second division planned lines 14a and 14b. The wafer W may be a semiconductor wafer in which devices such as IC and LSI are formed on a semiconductor substrate such as silicon or gallium arsenide, or an optical device such as an LED is formed on a ceramic, glass or sapphire inorganic material substrate. An optical device wafer may be used.

  An example of the first and second modified layer forming steps will be described with reference to FIGS. FIG. 3 is an explanatory diagram of the first and second modified layer forming steps according to the present embodiment. FIG. 4 is a partial cross-sectional view of the wafer after forming the modified layer according to the present embodiment. 3A and 3B show the first modified layer forming step, and FIGS. 3C and 3D show the second modified layer forming step. 3A and 3B, it is assumed that the first planned division line extends in the Y-axis direction and the second planned division line extends in the X-axis direction. 3C and 3D, it is assumed that the second planned division line extends in the Y-axis direction and the first planned division line extends in the X-axis direction.

  As shown in FIG. 3A, a first modified layer forming step is performed after the above-described expanding tape attaching step. In the first modified layer forming step, the wafer W is held on the chuck table 21 of a laser processing apparatus (not shown) via the expanded tape 16. Further, the exit of the processing head 22 is positioned on the first scheduled division line 14a (see FIG. 2) of the wafer W, and the processing head 22 irradiates a laser beam from the back surface 12 side of the wafer W. The laser beam has a wavelength having transparency to the wafer W, and is adjusted so as to be condensed at the first height position H1 on the back surface 12 side with respect to the finished thickness L inside the wafer W.

  Then, the processing head 22 is relatively moved in the Y-axis direction with respect to the wafer W, so that the first modification along the first division line 14a at the first height position H1 inside the wafer W is achieved. Layer 25a is formed. This laser processing is repeated along all the first division planned lines 14a. When the first modified layer 25a is formed at the first height position H1, as shown in FIG. 3B, the condensing point of the laser beam is moved up so as to be condensed at the second height position H2. Adjusted to Similarly, the first modified layer 25a is also formed at the second height position H2 along all the first planned dividing lines 14a.

  As shown in FIG. 3C, the second modified layer forming step is performed after the first modified layer forming step. In the second modified layer forming step, the chuck table 21 is rotated 90 degrees, and the second scheduled division line 14b orthogonal to the first scheduled division line 14a is aligned with the Y-axis direction. Further, the exit of the processing head 22 is positioned on the second scheduled division line 14b (see FIG. 2) of the wafer W, and the processing head 22 irradiates a laser beam from the back surface 12 side of the wafer W. The laser beam has a wavelength that is transparent to the wafer W, and is adjusted so as to be focused at a third height position H3 between the finished thickness L inside the wafer W and the first height position H1. Is done.

  Then, when the processing head 22 is moved relative to the wafer W in the Y-axis direction, the second modification along the second division planned line 14b is performed at the third height position H3 inside the wafer W. Layer 25b is formed. This laser processing is repeated along all the second scheduled division lines 14b. When the second modified layer 25b is formed at the third height position H3, as shown in FIG. 3D, the condensing point of the laser beam is moved up, and the third height position H3 and the first height layer Hb are moved. It adjusts so that it may condense to the 4th height position H4 between height positions H1. Similarly, at the fourth height position H4, the second modified layer 25b is formed along all the second scheduled division lines 14b.

  In this case, the second modified layer 25b is favorably improved in the vicinity of the intersection 17 between the first and second scheduled division lines 14a and 14b due to the influence of the first modified layer 25a formed earlier. Not quality. On the other hand, since the first modified layer 25a is formed inside the wafer W prior to the second modified layer 25b, it is good even at the intersection 17 of the first and second scheduled division lines 14a and 14b. Has been modified. Therefore, in the present embodiment, as shown in FIG. 4A, the first and second modified layers 25a are moved closer to the finished thickness L than the first modified layer 25a. 25b is adjusted to the same level of cracking.

  The second modified layer 25b is close to the finished thickness L inside the wafer W, and is formed at the optimum height position for division. The first modified layer 25a is harder to crack than the second modified layer 25b by the distance from the finished thickness L to the back surface 12 side than the second modified layer 25b. For this reason, the second modified layer 25b is easier to crack than the first modified layer 25a except at the intersection 17 of the first and second scheduled division lines 14a and 14b. In addition, the second modified layer 25b is not modified well in the vicinity of the intersection 17 of the first and second scheduled division lines 14a and 14b, but is modified to such an extent that it can be cracked by cracks other than in the vicinity of the intersection 17. Has been.

  For this reason, the first and second modified layers 25a and 25b are equally cracked, and the wafer W is favorably divided along the first and second scheduled division lines 14a and 14b. In contrast, as in the comparative example shown in FIG. 4B, when the first and second modified layers 25a and 25b are formed at the same height, the first and second modified layers 25a and 25b are formed. Is not properly divided even if it is formed at the optimum position. In the comparative example, when the second modified layer 25b is formed, the laser beam is scattered due to the presence of the first modified layer 25a previously formed, and the vicinity of the intersection 17 is insufficiently modified. Thus, in the comparative example, the vicinity of the intersection 17 of the second modified layer 25b is insufficiently modified, while the vicinity of the intersection 17 of the first modified layer 25a is appropriately modified. For this reason, when the first planned division line 14a is divided first, the vicinity of the intersection 17 of the second planned division line 14b is difficult to break, and the corner edge of the chip after division may be chipped. .

  By the way, if the wafer W does not have a thickness of several tens of μm or more, the laser beam may pass through the wafer W too much and the inside of the wafer W may not be satisfactorily modified. Therefore, in the present embodiment, the first and second modified layers are formed inside the wafer W by performing the first and second modified layer forming steps before the wafer W is thinned by the grinding step. The quality layers 25a and 25b can be formed.

  The first and second modified layers 25a and 25b are exposed to a laser beam so that the internal density, refractive index, mechanical strength and other physical characteristics of the wafer W are different from the surroundings, and the strength is higher than the surroundings. Refers to the area where the drop occurs. The first and second modified layers 25a and 25b are, for example, a melt treatment region, a crack region, a dielectric breakdown region, and a refractive index change region, and may be a region in which these are mixed.

  The grinding process will be described with reference to FIG. FIG. 5 is a diagram illustrating an example of a grinding process according to the present embodiment.

  As shown in FIG. 5, a grinding process is performed after the second modified layer forming process. As shown in FIG. 5A, in the grinding process, the wafer W is held on the chuck table 31 of a grinding apparatus (not shown) via the expanded tape 16. Further, the grinding means 32 is positioned above the wafer W held on the chuck table 31. Then, the grinding wheel 33 of the grinding means 32 approaches the chuck table 31 while rotating around the Z axis, and the grinding wheel 33 and the back surface 12 of the wafer W are in rotational contact with each other in parallel to grind the wafer W. During grinding, the thickness of the wafer W is measured in real time by a height gauge (not shown). Then, the feed amount of the grinding means 32 is controlled so that the measurement result of the height gauge approaches the finished thickness L.

  As shown in FIG. 5B, a grinding load acts strongly on the first and second modified layers 25a and 25b from the grinding wheel 33 by the grinding operation. Thereby, the crack which reaches the surface 11 of the wafer W from the first and second modified layers 25a and 25b is generated. Cracks generated inside the wafer W are grown along the first and second division lines 14a and 14b, whereby the wafer W is divided into individual chips C. Then, when the wafer W is thinned to the finished thickness L, the grinding operation is stopped.

  In this way, the wafer W is divided into individual chips C along the first and second scheduled division lines 14a and 14b while being thinned to a desired finish thickness L. In this case, when the wafer W is thinned to the finished thickness L, the first and second modified layers 25a and 25b formed on the back surface 12 side with respect to the finished thickness L are removed from the wafer W. Thereby, the brightness is improved when the wafer W is an optical device wafer, and the bending strength is improved when the wafer W is a semiconductor wafer.

  The expanding process will be described with reference to FIG. FIG. 6 is a diagram illustrating an example of an expanding process according to the present embodiment.

  As shown in FIG. 6, an expanding process is performed after the above-described grinding process. As shown in FIG. 6A, the ring frame 15 is placed on the annular table 41 of the tape expansion device (not shown), and the ring frame 15 is held on the annular table 41 by the clamp portion 42. Further, the outer diameter of the expansion drum 43 is smaller than the inner diameter of the ring frame 15, and the inner diameter of the expansion drum 43 is larger than the outer diameter of the wafer W. Therefore, the upper end portion of the expansion drum 43 is brought into contact with the expanded tape 16 between the wafer W and the ring frame 15.

  As shown in FIG. 6B, the expansion drum 43 is raised relative to the annular table 41 by lowering the ring frame 15 together with the annular table 41. As a result, the expanding tape 16 is expanded in the radial direction, and the chip interval is widened so that the chip C is easily peeled off from the expanding tape 16. When the chip interval is widened, the chip C is attracted to the pickup collet (not shown) and peeled off from the expanded tape 16.

  As described above, according to the wafer processing method of the present embodiment, after the first modified layer 25a is formed inside the wafer W, the first modified layer 25a and the finish thickness L are equivalent. The second modified layer 25b is formed between the first and second positions. In this case, since the first modified layer 25a is formed inside the wafer W prior to the second modified layer 25b, it is not affected by the second modified layer 25b. Further, since the second modified layer 25b is formed inside the wafer W after the first modified layer 25a, the first modified layer 25b is formed near the intersection 17 of the first and second scheduled division lines 14a and 14b. Under the influence of the modified layer 25a, it may be insufficiently formed near the intersection 17. On the other hand, the 2nd modified layer 25b is formed in the position which is easy to be cracked near the finishing thickness L rather than the 1st modified layer 25a. For this reason, the second modified layer 25b is easily cracked at portions other than the intersection 17 of the first and second scheduled division lines 14a and 14b, and is dragged by cracks other than the intersection 17, and the vicinity of the intersection 17 is also easily broken. Therefore, it is possible to divide the wafer into individual chips with the same ease of cracking of the first and second modified layers 25a and 25b.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, in the present embodiment, the first and second modified layers 25a and 25b are continuously formed along the first and second scheduled division lines 14a and 14b in the modified layer forming step. However, it is not limited to this configuration. If the wafer W can be divided along the first and second scheduled division lines 14a and 14b, the first and second modified layers 25a and 25b are formed on the first and second scheduled division lines 14a and 14b. It may be formed intermittently along.

  Further, in the present embodiment, the condensing point of the laser beam is moved up to form the first and second modified layers 25a and 25b having a predetermined thickness. However, the present invention is not limited to this configuration. The first and second modified layers 25a and 25b can also be formed by one-time laser beam irradiation by adjusting the processing conditions of laser processing. In addition, a plurality of first and second modified layers 25a and 25b are formed in the thickness direction inside the wafer W, but one first and second modified layers 25a are formed in the thickness direction. 25b may be formed.

  In this embodiment, the expanding tape attaching process is performed by the tape attaching apparatus, the first and second modified layer forming processes are performed by the laser processing apparatus, the grinding process is performed by the grinding apparatus, and the expanding process is performed by the tape expanding apparatus. However, some or all of the steps may be performed in one apparatus.

  As described above, the present invention has an effect that a wafer can be appropriately divided along orthogonal dividing lines, and in particular, a wafer processing method for dividing a semiconductor wafer or an optical device wafer into individual chips. Useful.

DESCRIPTION OF SYMBOLS 11 Front surface 12 Back surface 13 Device 14a 1st division | segmentation planned line 14b 2nd division | segmentation planned line 16 Expanding tape 17 Crossing 25a 1st modified layer 25b 2nd modified layer 32 Grinding means W Wafer C Chip

Claims (1)

A device is provided in a plurality of regions partitioned by a plurality of first division planned lines extending in a predetermined direction on the surface and a plurality of second division planned lines formed intersecting with the plurality of first division planned lines. A modified layer is formed inside the formed wafer, thinned to a finished thickness, and the wafer is divided along the first scheduled dividing line and the second scheduled divided line from the modified layer as a starting point. A processing method,
An expanding tape attaching process for attaching an expanding tape to the front surface side of the wafer;
After the expanding tape sticking step, the expanding tape side is held, and a laser beam having a wavelength transmissive to the wafer is focused from the position corresponding to the finished thickness inside the wafer from the back side of the wafer. And a first modified layer forming step of irradiating along the first division planned line and forming a first modified layer along the first division planned line inside the wafer;
After the first modified layer forming step, a laser beam having a wavelength that is transmissive to the wafer is focused from the back side of the wafer on the back side with respect to the position corresponding to the finished thickness . A second modified layer forming step of forming the second modified layer along the second division line closer to the position corresponding to the finished thickness than the region where the modified layer is formed;
After carrying out the first modified layer forming step and the second modified layer forming step, the expanded tape side is held and ground from the back surface of the wafer by grinding means to reduce the thickness to the finished thickness. A grinding step of growing a crack reaching the surface of the wafer from the first modified layer and the second modified layer as a starting point along the first planned division line and the second planned division line by operation; ,
After the grinding step, an expanding step of applying an external force to separate the chips along the first scheduled dividing line and the second scheduled dividing line;
A method for processing a wafer, comprising:

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