JP6598702B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer processing method for dividing a wafer into a plurality of device chips.

  For example, when a wafer having a relatively large thickness of 300 [μm] or more is diced with a cutting blade, there is a problem that the back surface chipping becomes large. For this reason, a method using SDBG (Stealth Dicing Before Grinding) in which laser processing and grinding processing are combined has been proposed (see, for example, Patent Document 1). In SDBG, a laser beam having a wavelength that is transmissive to the wafer is irradiated along the planned dividing line of the wafer to form a modified layer having reduced strength at a predetermined depth of the wafer. Thereafter, by grinding the back surface of the wafer, the wafer is thinned to the finished thickness, and the wafer is divided into individual device chips by the grinding pressure using the modified layer as a division starting point.

International Publication No. 2003/077295

  However, it is necessary to irradiate the wafer with a high-power laser beam in order to form a modified layer inside the wafer by SDBG and cause cracks to reach the front and back surfaces of the wafer from the modified layer. As described above, a laser beam having transparency to the wafer is irradiated, so that some of the beam leaks to the device side of the wafer, and the electrical characteristics of the device chip after singulation may deteriorate. There is. On the other hand, if the wafer is irradiated with a low-power laser beam in fear of deterioration of the electrical characteristics of the device chip, there is a problem that the wafer cannot be separated into pieces.

  This invention is made | formed in view of this point, and it aims at providing the processing method of the wafer which can divide | segment a wafer, without deteriorating the electrical property of the device chip after singulation.

  The wafer processing method of the present invention is a wafer processing method for processing a wafer having a device region having a plurality of devices and a plurality of scheduled division lines formed on a surface thereof and an outer peripheral surplus region surrounding the device region, A laser beam having a wavelength that is transparent to the wafer is positioned inside the wafer and irradiated with a first output from the back surface of the wafer along the division line to form a modified layer inside the wafer. After performing the first modified layer forming step and the first modified layer forming step, a laser beam having a wavelength that is transmissive to the wafer is positioned inside the wafer, and a second output that is higher in output than the first output. Irradiation is performed from the back surface of the wafer along the planned division line of the outer peripheral surplus area of the wafer, and a modified layer is further formed inside the outer peripheral surplus area of the wafer. After performing the two modified layer forming step and the second modified layer forming step, a division is performed in which an external force is applied along the planned division line and the wafer is divided along the planned division line starting from the modified layer. And steps.

  According to this configuration, the laser beam is irradiated to the inside of the wafer with the first output along the planned division line of the wafer, and the laser beam is irradiated with the second output along the planned division line of the outer peripheral area of the wafer. It is irradiated inside. As a result, a modified layer is formed in the device region of the wafer with a first output laser beam having a relatively low output, and a modified layer is formed in the outer peripheral region of the wafer with a second output laser beam having a relatively high output. A quality layer is formed. When an external force is applied along the planned dividing line, the cracks from the modified layer in the outer peripheral surplus area where the breaking strength is greatly reduced are extended, and the wafer is divided along the planned dividing line. As described above, since the device region of the wafer can be divided without irradiating a high-power laser beam, the electrical characteristics of the device chip after singulation are not deteriorated.

  According to the present invention, the modified layer is formed with a relatively low-power laser beam in the device region of the wafer and a relatively high-power laser beam in the outer peripheral region of the wafer, and the outer peripheral surplus with low strength is applied by applying external force. Cracks from the modified layer in the region are elongated. Therefore, since the device region of the wafer can be divided without irradiating a high-power laser beam, the electrical characteristics of the device chip after singulation are not deteriorated.

It is the perspective view and sectional drawing of the wafer of this Embodiment. It is explanatory drawing of the processing method of the wafer of a comparative example. It is a figure which shows an example of the 1st modified layer formation step of this Embodiment. It is a figure which shows an example of the 2nd modified layer formation step of this Embodiment. It is a figure which shows an example of the division | segmentation step of this Embodiment. It is a figure which shows the fracture | rupture result of the sapphire wafer of an experiment example. It is a figure which shows an example of the 1st, 2nd modified layer formation step of a modification.

  Hereinafter, the wafer processing method of the present embodiment will be described with reference to the accompanying drawings. FIG. 1 is a perspective view and a cross-sectional view of a wafer according to the present embodiment. FIG. 2 is an explanatory view of a wafer processing method of a comparative example. In this embodiment, an example in which the wafer processing method is applied to SDBG will be described. However, the present invention can be applied to other methods in which a modified layer is divided from the inside of the wafer.

  As shown in FIGS. 1A and 1B, the wafer W is formed in a substantially disk shape, and is partitioned into a plurality of regions by division lines L (see FIG. 3B) arranged in a lattice at the center of the surface. Yes. A device D is formed in each region partitioned by the planned division lines. The surface of the wafer W is divided into a device area A1 where a plurality of devices D and division lines L are formed, and an outer peripheral surplus area A2 surrounding the device area A1. On the outer edge of the wafer W, a notch N indicating a crystal orientation is formed. A protective tape T for protecting the device D is attached to the surface of the wafer W.

  The wafer W has a thickness of, for example, 300 [μm] or more, and is divided into individual device chips by SDBG that combines laser processing and grinding processing. In this case, after the modified layer is formed in the wafer W by laser processing, the wafer W is divided by the modified layer as a starting point while being ground to the finished thickness by grinding. The wafer W may be a semiconductor wafer in which a semiconductor device such as IC or LSI is formed on a semiconductor substrate such as silicon or gallium arsenide, or an optical device such as an LED is formed on an inorganic material substrate such as sapphire or silicon carbide. An optical device wafer may be used.

  By the way, as shown in FIG. 2A, when a thick wafer W is laser processed, the inside of the wafer W is usually irradiated with a high-power laser beam, and the breaking strength along the division line L (see FIG. 3B). As a result, the modified layer 16 having a sufficiently reduced value is formed. For this reason, when the wafer W is ground, cracks extend from the modified layer 16 to the front and back surfaces of the wafer W due to the grinding pressure, and the wafer W is appropriately divided. However, since the wavelength of the laser beam is transparent to the wafer W, a part of the high-power laser beam reaches the device D (see FIG. 1) side of the wafer W, and the electrical characteristics of the device D are changed. It will deteriorate.

  On the other hand, as shown in FIG. 2B, the wafer W is laser-processed with a low-power laser beam used for a thin wafer, thereby minimizing the deterioration of the electrical characteristics of the device D of the wafer W (see FIG. 1). To the limit. However, the modified layer 18 formed with a low-power laser beam does not have a sufficiently low breaking strength, and cracks can extend from the modified layer 18 to the front and back surfaces of the wafer W even when grinding pressure is applied. Can not. Thus, since the splitting property of the wafer W and the electrical characteristics of the device D are in a trade-off relationship, it is difficult to split the wafer W without deteriorating the electrical characteristics of the device chip after singulation. It was.

  Here, the inventors of the present invention irradiated a low-power laser beam over the entire length of the planned division line, and irradiated a high-power laser beam only to the outer peripheral surplus area A2 at both ends of the planned division line (FIG. 4). It was discovered that when the wafer W was ground, the modified layer could be divided satisfactorily. This is because cracks tend to extend from a modified layer whose fracture strength is sufficiently reduced by irradiation with a high-power laser beam to a modified layer whose fracture strength is not sufficiently lowered by irradiation with a low-power laser beam. It is thought that. In this way, by irradiating the high-power laser beam only on the outer peripheral surplus area A2 where the device D does not exist, it is possible to divide the wafer W well without deteriorating the electrical characteristics of the device D.

  Hereinafter, a wafer processing method will be described with reference to FIGS. FIG. 3 shows an example of the first modified layer forming step of the present embodiment, FIG. 4 shows an example of the second modified layer forming step of the present embodiment, and FIG. 5 shows an example of the dividing step. 3A is a view of the first modified layer forming step as viewed from the side, and FIG. 3B is a view of the first modified layer forming step as viewed from above. 4A is a view of the second modified layer forming step as viewed from the side, and FIG. 4B is a view of the second modified layer forming step as viewed from above. FIG. 5A is a view of the dividing step as viewed from the side, and FIG. 5B is a view of the dividing step as viewed from above.

  As shown in FIGS. 3A and 3B, a first modified layer forming step is first performed. In the first modified layer forming step, the wafer W is held via the protective tape T on the chuck table 21 of the laser processing apparatus. Further, the irradiation port of the laser irradiation nozzle 22 is positioned on the division line L of the wafer W, and the laser beam is irradiated from the back surface 11 side of the wafer W by the laser irradiation nozzle 22. The laser beam has a wavelength that is transmissive to the wafer W, and is adjusted to a first output that does not deteriorate the electrical characteristics of the device D (see FIG. 1) on the surface 12 side of the wafer W.

  The laser beam is positioned inside the wafer W, and the first modified layer 13 having a predetermined thickness is formed inside the wafer W. In this case, the first modified layer 13 is formed on the back surface 11 side with respect to the finished thickness H of the wafer W, and the depth of the condensing point of the laser beam is reduced after the wafer W is thinned. It is adjusted not to remain. Then, by moving the laser irradiation nozzle 22 relative to the wafer W, a laser beam is irradiated from the back surface 11 of the wafer W along the planned division line L, and along the planned division line L inside the wafer W. A first modified layer 13 is formed.

  In this way, the first modified layer 13 is formed with the laser beam having the first output over the entire length of the division line L from one end side to the other end side of the wafer W. Since the device region A1 is irradiated with the laser beam with the first output having a low output, the electrical characteristics of the device D are not deteriorated. The modified layer refers to a region where the density, refractive index, mechanical strength, and other physical characteristics inside the wafer W become different from the surroundings due to the irradiation of the laser beam, and the strength is lower than the surroundings. The modified layer is, for example, a melt treatment region, a crack region, a dielectric breakdown region, or a refractive index change region, and may be a region in which these are mixed.

  As shown in FIGS. 4A and 4B, after the first modified layer forming step is performed, the second modified layer forming step is performed. In the second modified layer forming step, the laser beam is irradiated from the back surface 11 side of the wafer W by the laser irradiation nozzle 22 to the dividing line on which the modified layer 13 is formed in the first modified layer forming step. The laser beam has a wavelength that is transmissive to the wafer W, and is adjusted to a second output that is higher than the first output. The condensing point of the second output laser beam is positioned at the same depth as the first modified layer 13 formed by the first output laser beam.

  Further, an ON section and an OFF section of the laser beam are set so that the laser beam is irradiated only on the outer peripheral surplus area A2 of the wafer W. In other words, the outer peripheral surplus area A2 at both ends of the planned division line L on the wafer W is set as an ON section of the laser beam, and the device area A1 other than both ends of the planned split line L is set as an OFF section of the laser beam. Then, by moving the laser irradiation nozzle 22 relative to the wafer W, the laser beam is irradiated from the back surface 11 of the wafer W along the scheduled division line L, and only in the outer peripheral surplus area A2 of the wafer W. A second modified layer 14 is further formed.

  In this way, the second modified layer 14 is formed by the laser beam of the second output on both end sides of the division line L of the wafer W. Since the outer peripheral surplus area A2 other than the device area A1 is irradiated with the laser beam with the second output having a high output, the electrical characteristics of the devices D in the device area A1 are not affected, and the inner peripheral surplus area A2 is not affected. The second modified layer 14 having a sufficiently low breaking strength is formed. Further, since the second modified layer 14 formed by the laser beam having the second output is connected to the first modified layer 13 formed by the laser beam having the first output, the second modified layer 14 is formed. From this, cracks tend to extend toward the first modified layer 13. The first and second modified layer forming steps are repeated, and the first and second modified layers 13 and 14 are formed along all the division lines L.

  As shown in FIGS. 5A and 5B, the dividing step is performed after the second modified layer forming step is performed. In the dividing step, the wafer W is held via the protective tape T on the chuck table 31 of the grinding apparatus. The grinding wheel 32 is brought close to the chuck table 31 while rotating, and the grinding wheel 32 and the back surface 11 of the wafer W are in rotational contact with each other, whereby the wafer W is ground. At this time, the grinding pressure from the grinding wheel 32 acts on the second modified layer 14 in the outer peripheral surplus region A2, and cracks extend from the second modified layer 14 to the first modified layer 13 in the device region A1. Cracks extend from the back surface 11 to the front surface 12 of the wafer W starting from the first and second modified layers 13 and 14.

  That is, since the breaking strength of the second modified layer 14 in the outer peripheral surplus region A2 is sufficiently reduced, even if the breaking strength of the first modified layer 13 in the device region A1 is not sufficiently reduced, The crack extends along the division line L starting from the second modified layer 14. Therefore, the wafer W can be divided into individual device chips even if laser processing is performed with a low laser beam output for the device region A1. In this manner, the wafer W is thinned to the desired finish thickness H by the grinding wheel 32, and is divided into individual device chips along the division line L.

  Hereinafter, an experimental example will be described with reference to FIG. In the experimental example, the first and second modified layer forming steps are performed on a sapphire wafer having a wafer size of 20 [mm] and a thickness of 100 [μm], and the second modified layer is formed in the second modified layer forming step. The breaking strength of sapphire wafers when the amount of layer formation was changed was compared. In this case, the formation amount (formation length) of the second modified layer from both ends of the sapphire wafer is 0 [mm], 2.5 [mm] × 2, 1.0 [mm] × 2, 0.5 [ mm] × 2, and four types of sapphire wafers AD were prepared in which the ratio of the formation amount of the second modified layer to the wafer size was 0%, 25%, 10%, and 5%, respectively.

  Further, the processing conditions of the first modified layer forming step are set to a focal depth of 15 [μm], an output of 0.1 [W], and a feed rate of 400 [mm / s]. The processing conditions were set to a focal depth of 15 [μm], an output of 0.2 [W], and a feed rate of 400 [mm / s]. The breaking strength was measured by braking the laser-processed sapphire wafer AD using a braking device (DBM-801NR manufactured by Daito Electron Co., Ltd.).

  As a result, as shown in FIG. 6, the breaking strength of the sapphire wafer A is about 44.0 [N], the breaking strength of the sapphire wafer B is about 14.0 [N], and the breaking strength of the sapphire wafer C is about 18. 0 [N], the breaking strength of the sapphire wafer D was about 20.0 [N]. And it was confirmed that the breaking strength of the sapphire wafer BD on which the second modified layer is formed is not more than half the breaking strength of the sapphire wafer A on which the second modified layer is not formed. In addition, from the breaking strength of the sapphire wafer BD, it was confirmed that the breaking strength tends to decrease according to the amount of the second modified layer formed.

  As described above, according to the wafer processing method of the present embodiment, the laser beam is irradiated to the inside of the wafer W with the first output along the scheduled division line of the wafer W, and the outer peripheral surplus area A2 of the wafer W is obtained. The laser beam is irradiated to the inside of the wafer W with the second output along the scheduled dividing line. As a result, the first modified layer 13 is formed in the device region A1 of the wafer W by the laser beam having the relatively low output and the first output, and the relatively high output second region is formed in the outer peripheral surplus region A2 of the wafer W. The second modified layer 14 is formed with a laser beam with the output of. Then, when an external force is applied along the planned dividing line, the crack from the second modified layer 14 in the outer peripheral surplus area A2 whose strength is greatly reduced extends, and the wafer W is divided along the planned dividing line. Is done. As described above, since the device region A1 of the wafer W can be divided without irradiating a high-power laser beam, the electrical characteristics of the device chip after singulation are not deteriorated.

  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 above-described embodiment, the first modified layer forming step is configured to form the first modified layer in the wafer, but the present invention is not limited to this configuration. For example, as shown in FIG. 7, in the first modified layer forming step, two stages of the first modified layer 13 may be formed inside the wafer W. In this case, in the second modified layer forming step, the second modified layer 14 is formed only on both ends of the upper first modified layer 13. If the second modified layer 14 is formed on both ends of the uppermost first modified layer 13 in the second modified layer forming step, two steps are formed inside the wafer W in the first modified layer forming step. The above first modified layer 13 may be formed.

  In the above-described embodiment, the example in which the wafer processing method is applied to SDBG has been described. However, the present invention is not limited to this configuration. It is also possible to apply the wafer processing method to SD (Stealth Dicing: registered trademark). In SD, the first and second modified layer forming steps are performed on a thin wafer instead of the thick wafer used in SDBG. As described above, even if the laser beam applied to the device region in the first modified layer forming step is further suppressed to a low output, the breaking strength of the wafer can be sufficiently reduced by the second modified layer forming step. (See FIG. 6). Therefore, deterioration of the electrical characteristics of the device can be suppressed during SD processing of a thin wafer.

  In the above-described embodiment, the dividing step is configured to divide the wafer with the modified layer as a starting point by the grinding pressure, but is not limited to this configuration. The dividing step may be configured to apply an external force along the planned dividing line and divide the wafer along the planned dividing line from the modified layer. For example, in the case of a configuration in which a modified layer is formed on a thin wafer such as SD, the wafer may be divided along the planned division line by expanding or breaking.

  In the above-described embodiment, the modified layer is formed in the first and second modified layer forming steps, but a crack layer may be formed in addition to the modified layer. That is, cracks along the planned dividing line may be formed inside the wafer after the first and second modified layer forming steps.

  Further, in the above-described embodiment, the entire length of the planned division line is irradiated with a low-power laser beam in the first modified layer formation step, and only the division planned line in the outer peripheral surplus area is increased in the second modified layer formation step. Although the configuration is such that the output laser beam is irradiated, the present invention is not limited to this configuration. In the first modified layer forming step, a low-power laser beam is irradiated only on the planned division line in the device region, and in the second modified layer forming step, a high-power laser beam is irradiated only on the planned division line in the outer peripheral region. May be.

  In the above-described embodiment, the first modified layer 13 is formed on the back surface 11 side of the finished thickness H of the wafer W in the first modified layer forming step. However, the present invention is not limited to this configuration. The first modified layer 13 may be formed on the surface 12 side of the finished thickness H of the wafer W in the first modified layer forming step. That is, the first modified layer 13 may be formed at a position where the first modified layer 13 remains after the wafer W is thinned (after SDBG).

  As described above, the present invention has an effect that a wafer can be divided without deteriorating electrical characteristics of a device chip after singulation, and in particular, a semiconductor wafer or an optical device wafer is divided. This is useful for wafer processing methods.

11 Wafer back surface 12 Wafer surface 13 First modified layer (modified layer)
14 Second modified layer (modified layer)
A1 Device area A2 Peripheral surplus area D Device L Divided line W Wafer

Claims (1)

A wafer processing method for processing a wafer having a device region having a plurality of devices and a plurality of division lines formed on a surface and an outer peripheral surplus region surrounding the device region,
A laser beam having a wavelength that is transparent to the wafer is positioned inside the wafer and irradiated with a first output from the back surface of the wafer along the planned dividing line to form a modified layer inside the wafer. 1 modified layer forming step;
After performing the first modified layer forming step, a laser beam having a wavelength that is transmissive to the wafer is positioned inside the wafer, and a second output higher than the first output is applied to the wafer from the back surface of the wafer. A second modified layer forming step of irradiating along the planned division line of the outer peripheral surplus region to further form a modified layer inside the outer peripheral surplus region of the wafer;
A division step of applying an external force along the planned dividing line and dividing the wafer along the planned dividing line starting from the modified layer after the second modified layer forming step;
For processing a wafer comprising:

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