JP2016201453A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method capable of cancelling nonuniformity of a modified layer caused by pulling a chamfered part of a wafer obliquely downwards.SOLUTION: The present invention relates to the processing method for the wafer including a device region and an outer peripheral marginal region surrounding the device region on a front face. In the device region, devices are formed in regions that are separated by a plurality of predetermined dividing lines which are formed while crossing each other. The wafer comprises an arcuate chamfered part 11e from the front face to a rear face at an outer edge. On either the front face or the rear face of the wafer, an adhesive tape T is bonded and then held by a holding surface of a chuck table. The wafer is processed along the outer peripheral marginal region while using a laser beam 28 or a cutting blade, and the device region and the chamfered part are separated. The adhesive tape is then sucked and held by the holding surface of the chuck table and while positioning a convergence point within the wafer, the wafer is irradiated on its exposed surface with the laser beam, and a modified layer along the predetermined dividing line is formed within the wafer.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a wafer processing method for dividing a wafer such as a semiconductor wafer into individual device chips.

  To divide a wafer with multiple devices on the surface into multiple device chips, position the laser beam condensing point inside the wafer and irradiate the wafer with the laser beam along the planned division line. A wafer processing method in which a modified layer serving as a starting point of the wafer is formed inside the wafer has been proposed and implemented (see, for example, JP-A-2005-86161).

  The laser beam is irradiated from the edge of the wafer along the planned dividing line (street) to form a modified layer inside the wafer, and the modified starting point when the modified layer divides the wafer into device chips. It becomes.

  The wafer has a flat front surface and a back surface, and an arc-shaped chamfered portion formed on the outer peripheral edge from the front surface to the back surface. The wafer is sucked and held on a chuck table via an adhesive tape, and laser processing is performed. .

JP 2005-86161 A

  When the adhesive tape with the wafer attached is sucked and held on the chuck table, the chamfered part formed on the outer periphery is slightly attached to the adhesive tape. Pulled by the power of. If the modified layer is formed inside the wafer by irradiating the wafer with the laser beam in this state, the modified layer is unstablely formed in the vicinity of the chamfered portion and other regions.

  That is, in the region where the oblique downward force is applied, the extension of the crack from the modified layer is long, and in the region where the oblique downward force is not applied, the extension of the crack from the modified layer is short. As a result, there is a problem that the formation of the modified layer becomes non-uniform inside the wafer.

  The present invention has been made in view of these points, and the object of the present invention is to eliminate the nonuniformity of the modified layer caused by the wafer chamfered portion being pulled obliquely downward. Is to provide a simple wafer processing method.

  According to the present invention, the device has a device region where a device is formed in each region defined by a plurality of division lines formed intersecting and an outer peripheral surplus region surrounding the device region, and the outer peripheral edge A method of processing a wafer having an arc-shaped chamfer from the front surface to the back surface, the adhesive tape attaching step for attaching an adhesive tape to either the front surface or the back surface of the wafer, and the adhesive tape attaching step After performing the above, the adhesive tape is held by the holding surface of the chuck table, the wafer is processed along the outer peripheral surplus area using a laser beam or a cutting blade, and the device area and the chamfered part are separated. After carrying out the steps and the separating step, the adhesive tape is sucked and held by the holding surface of the chuck table, and the focusing point is positioned inside the wafer. A modified layer forming step of irradiating a laser beam from the exposed surface of the wafer and forming a modified layer along the division line inside the wafer, and separating the device region and the chamfered portion. Thus, when the adhesive tape adhered to the chamfered portion is sucked and held by the chuck table, even if the chamfered portion is pulled obliquely downward in the outer peripheral direction by the adhesive tape toward the holding surface, the device There is provided a wafer processing method characterized in that it is possible to suppress an influence on a crack extending from the modified layer formed in a region.

  Preferably, in the adhesive tape attaching step, the outer peripheral portion of the adhesive tape to which the wafer is attached so as to cover the opening of the annular frame is attached to the annular frame to form a frame unit.

  Preferably, the wafer processing method further includes a grinding step of thinning the wafer by grinding the back surface of the wafer with a grinding wheel before performing the adhesive tape attaching step.

  According to the wafer processing method of the present invention, since the separation step for separating the chamfered portion from the device region is performed before the modified layer forming step is performed, the chamfered portion is pulled obliquely downward through the adhesive tape. It is possible to eliminate the non-uniformity of the modified layer caused by the above.

It is a surface side perspective view of a semiconductor wafer. It is a back surface side perspective view of the semiconductor wafer which affixed the protective tape on the surface. It is a partial cross section side view which shows a grinding step. 4A is a perspective view of the frame unit, and FIG. 4B is a partial cross-sectional view of the frame unit. FIG. 5A is a perspective view showing the first embodiment of the separation step, and FIG. 5B is a sectional view after the separation step is performed. It is a perspective view which shows 2nd Embodiment of a separation step. It is sectional drawing which shows a modified layer formation step. It is a perspective view of the frame unit after execution of a modified layer formation step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, a perspective view of a semiconductor wafer (hereinafter simply referred to as a wafer) 11 is shown. A semiconductor wafer 11 shown in FIG. 1 is formed of, for example, a silicon wafer having a thickness of 700 μm. A plurality of division lines (streets) 13 are formed in a lattice shape on the surface 11a, and a plurality of division lines 13 are formed. A device 15 such as an IC or an LSI is formed in each of the areas partitioned by.

  The wafer 11 thus formed includes a device region 17 in which a plurality of devices 15 are formed, and an outer peripheral surplus region 19 surrounding the device region 17 on the surface 11a. Further, an arc-shaped chamfered portion 11e extending from the front surface 11a to the back surface 11b is formed on the outer peripheral edge of the semiconductor wafer 11, and a notch as a mark indicating the crystal orientation of the silicon wafer is formed on a part of the chamfered portion 11e. 21 is formed.

  In grinding the back surface 11 b of the wafer 11, the protective tape 23 is attached to the front surface 11 a of the wafer 11 by the protective tape attaching step. Accordingly, the front surface 11a of the wafer 11 is protected by the protective tape 23, and the back surface 11b is exposed as shown in FIG.

  As described above, after the protective tape 23 is attached to the front surface 11a of the wafer 11, a grinding step is performed in which the back surface of the wafer 11 is ground to process the wafer 11 to a predetermined thickness. In the grinding step, as shown in FIG. 3, the protective tape 23 adhered to the front surface 11 a of the wafer 11 is sucked and held by the chuck table 10 of the grinding device, and the back surface 11 b of the wafer 11 is exposed.

  In FIG. 3, a grinding wheel 18 is detachably attached to a wheel mount 16 fixed to the tip of a spindle 14 of a grinding unit 12 by a screw (not shown). The grinding wheel 18 is configured by attaching a plurality of grinding wheels 22 to the outer periphery of a free end (lower end) of an annular wheel base 20 in an annular shape.

  In the grinding step, while rotating the chuck table 10 in the direction indicated by the arrow a at, for example, 300 rpm, the grinding wheel 18 is rotated in the direction indicated by the arrow b, for example, at 6000 rpm, and the grinding unit feed mechanism is driven to The grinding wheel 22 is brought into contact with the back surface 11 b of the wafer 11.

  Then, grinding is performed while the grinding wheel 18 is ground and fed downward at a predetermined grinding feed speed. While measuring the thickness of the wafer 11 with a contact type or non-contact type thickness measurement gauge, the wafer 11 is ground to a predetermined thickness, for example, 100 μm.

  After the grinding step, an adhesive tape sticking step is performed. In the adhesive tape attaching step, as shown in FIG. 4A, the outer peripheral portion of the dicing tape T, which is an adhesive tape, is attached to the annular frame F so as to close the opening of the annular frame F, and the wafer is attached to the dicing tape T. The frame unit 25 is formed by sticking the front surface side of 11. In the frame unit 25, the back surface 11b of the wafer 11 is exposed upward.

  In the modified layer forming step to be described later, a laser beam is generally irradiated from the back surface 11b side of the wafer 11. However, the wafer processing method of the present invention is not limited to this. In some cases, the laser beam is irradiated from the surface side. In this case, the back surface 11b of the wafer 11 is adhered to the dicing tape T of the frame unit 25 to expose the front surface 11a of the wafer 11.

  As shown in FIG. 4B, the dicing tape T is formed by applying an adhesive layer 29 to the surface of a base material 27 such as polyolefin. When the surface 11a of the wafer 11 is adhered to the dicing tape T, the chamfered portion 11e formed on the outer peripheral edge of the wafer 11 is slightly adhered to the adhesive layer 29 of the dicing tape T. It will be pulled with a downward force in the direction.

  In the wafer processing method of the present invention, the chamfered portion 11e is separated from the device region 17 of the wafer 11 so that the obliquely downward force acting on the chamfered portion 11e does not affect the device region 17. Perform the steps. A first embodiment of the device region separation step will be described with reference to FIG.

  FIG. 5A is a perspective view showing a first embodiment of the separation step, and FIG. 5B is a partial sectional view thereof. In the first embodiment of the separation step, the dicing tape T of the frame unit 25 is sucked and held by the holding surface of the suction holding unit 26 of the chuck table 24, and is then applied from the condenser (laser head) 28 of the laser beam irradiation unit to the wafer 11. On the other hand, a laser beam having an absorptive wavelength (for example, 355 nm) is irradiated on the back surface 11b of the wafer 11 corresponding to the boundary between the device region 17 and the outer peripheral surplus region 19, and the chuck table 24 is rotated at a low speed in the direction of arrow a. On the other hand, a circular separation groove 31 for completely cutting the wafer 11 by ablation processing is formed. With this separation groove 31, the device region 17 of the wafer 11 is separated from the chamfered portion 11e.

  Referring to FIG. 6, a perspective view of a second embodiment of the separation step is shown. In the separation step of the second embodiment, the cutting blade 32 of the cutting unit 30 is rotated at a high speed while cutting from the back surface 11b of the wafer 11 which is the boundary between the device region 17 and the outer peripheral surplus region 19 until the dicing tape T is reached. By rotating 24A at least once in the direction of arrow a, a circular separation groove 31 for completely cutting the wafer 11 is formed.

  After performing the separation step, as shown in FIG. 7, the dicing tape T is sucked and held by the holding surface of the suction holding portion 26 of the chuck table 24, and the condensing point is moved from the condenser 28 of the laser beam irradiation unit to the inside of the wafer. The laser beam LB having a wavelength that is transparent to the wafer 11 (for example, 1064 nm) is irradiated on the back surface 11b of the wafer 11 corresponding to the division line 13 extending in the first direction, and the chuck table 24 Then, the laser beam LB is irradiated from the end to the end of the wafer 11 along the scheduled division line 13 to form the modified layer 33 inside.

  After this modified layer forming step is performed along all the division lines 13 extending in the first direction, the chuck table 24 is rotated by 90 °, and then the second direction orthogonal to the first direction. A similar modified layer forming step is performed along all the division lines 13 extending in the same manner.

  The processing conditions in this modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Average output: 0.2W
Repetition frequency: 80 kHz
Condensing spot diameter: φ1μm
Processing feed rate: 100 mm / s

  Referring to FIG. 8, a perspective view of the frame unit 25 after performing the modified layer forming step is shown. In the wafer processing method of this embodiment, since the separation step of separating the chamfered portion 11e from the device region 17 of the wafer 11 is performed before the modified layer forming step, the chamfering adhered to the dicing tape T is performed. Even if the portion 11e is pulled in the outer peripheral direction by a diagonally downward force, this pulling force can be blocked by the separation groove 31, and the uniform modified layer 33 is formed along all the planned dividing lines 13 in the device region 17. Can be formed.

11 Semiconductor wafer 13 Scheduled division line (street)
DESCRIPTION OF SYMBOLS 15 Device 17 Device area | region 18 Grinding wheel 19 Peripheral surplus area | region 22 Grinding wheel 23 Protective tape 25 Frame unit 27 Base material 28 Condenser (laser head)
29 Adhesive layer 30 Cutting unit 31 Separation groove 32 Cutting blade 33 Modified layer T Dicing tape (adhesive tape)

Claims (3)

A device region in which a device is formed in each region partitioned by a plurality of division lines formed in an intersecting manner and an outer peripheral surplus region surrounding the device region are provided on the surface, and the outer periphery extends from the surface to the back surface. It is a processing method of a wafer provided with a circular chamfered part,
An adhesive tape attaching step for attaching an adhesive tape to either the front surface or the back surface of the wafer;
After performing the adhesive tape adhering step, the adhesive tape is held on a holding surface of a chuck table, and a wafer is processed along the outer peripheral surplus area using a laser beam or a cutting blade, and the device area and the chamfer are chamfered. A separation step for separating the parts,
After carrying out the separation step, the adhesive tape is sucked and held by the holding surface of the chuck table, a condensing point is positioned inside the wafer, a laser beam is irradiated from the exposed surface of the wafer, and the division is performed inside the wafer. A modified layer forming step for forming a modified layer along a predetermined line, and
By separating the device region and the chamfered portion, when the adhesive tape adhered to the chamfered portion is sucked and held by the chuck table, the chamfered portion is surrounded by the adhesive tape toward the holding surface. A wafer processing method characterized in that, even when pulled obliquely downward in a direction, it is possible to suppress an influence on a crack extending from the modified layer formed in the device region.   2. The wafer processing method according to claim 1, wherein in the adhesive tape attaching step, a frame unit is formed by attaching an outer peripheral portion of the adhesive tape to the annular frame so as to cover an opening of the annular frame.   The wafer processing method according to claim 1, further comprising a grinding step of thinning the wafer by grinding the back surface of the wafer with a grinding wheel before performing the adhesive tape attaching step.

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