JP2017084923A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method that is able to reduce the number of modified layers even when a plurality of modified layers are formed and a wafer is fully cut and is able to reduce processing time.SOLUTION: A wafer processing method comprises: a first grinding step in which a rear 11b of a wafer 11 is ground to thin the wafer to first thickness; a modified layer formation step in which a modified layer 19 is formed in the wafer by emitting a laser beam along a dividing line 13 from the rear of the wafer while positioning in the wafer the condensing point of a laser beam LB that is able to pass through the wafer; and a second grinding step in which a wafer is thinned to second thickness by grinding the rear of the wafer and also the wafer is divided into individual devices 15. The modified layer formation step includes a warpage restriction step in which a plurality of modified layers overlapping in the thickness direction of the wafer are formed along the dividing line, thereby restricting warpage of the wafer, resulting from expansion of a modified layer portion due to crack 21 developing in the surface 11a and rear.SELECTED DRAWING: Figure 3

Description

  The present invention generally relates to a wafer processing method, and more particularly, to a wafer processing method in which a wafer in which an interval between adjacent division lines is set to 3 mm or less is divided into individual device chips by laser beam irradiation.

  Conventionally, for example, as disclosed in Japanese Patent No. 3408805, a laser beam having a wavelength that is transmissive to a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) is focused on the inside of the wafer. A method is known in which irradiation is performed in a combined state to form a modified layer inside the wafer, and then an external force is applied to the wafer to divide the wafer into individual device chips.

  Japanese Patent Application Laid-Open No. 2005-086161 discloses a laser beam irradiation step of forming a modified layer having a predetermined thickness from the back surface of a wafer by irradiating the wafer with a laser beam having transparency to the wafer along the division line. And a dividing step of dividing the wafer with the protective sheet attached to the surface along the modified layer, and grinding the back surface of the wafer divided along the modified layer with the protective sheet attached. And a grinding process for removing the modified layer.

  In such a wafer processing method, the modified layer formed in a concentrated manner on the surface side of the wafer expands, so that there is a problem that the wafer is likely to warp. If the laser beam is irradiated while the wafer is warped, the relative position in the thickness direction of the wafer with respect to the converging point of the laser beam changes, so that the modified layer cannot be formed at a predetermined position. May be biased to the surface of the wafer.

  If the modified layer is biased to the front surface of the wafer, the modified layer remains on the side of the device chip even if the wafer is divided into individual device chips by grinding the back surface until the wafer has a predetermined thickness. The bending strength of the sheet may be lowered.

  Further, even if an attempt is made to place the warped wafer on the chuck table of the grinding apparatus for suction holding, the negative pressure may leak and the wafer may not be sucked and held. Therefore, JP-A-2015-37172 proposes a processing method in which a plurality of modified layers are formed and a wafer is divided by the modified layers to reduce warpage.

Japanese Patent No. 3408805 Japanese Patent Laying-Open No. 2005-086161 Japanese Patent Laying-Open No. 2015-37172

  However, in the case of a small chip device wafer in which the distance between the planned division lines is 3 mm or less, the warpage becomes very large when the modified layer is formed along all the planned division lines. It is necessary to form a plurality of modified layers to make the wafer into a full cut state, and there is a problem that the number of modified layers to be formed becomes enormous and the processing time becomes long.

  The present invention has been made in view of these points, and the object of the present invention is to form a plurality of modified layers along almost all the division lines and to bring the wafer into a full cut state. The present invention also provides a wafer processing method that can reduce the number of modified layers and shorten the processing time.

  According to the present invention, a device is formed in each region partitioned by a plurality of intersecting scheduled lines set on the surface, and the wafer is cut by setting the interval between the adjacent scheduled dividing lines to be 3 mm or less. A method comprising: a protective member adhering step for adhering a protective member to a surface of a wafer; and the protective member adhering step, and then grinding the back surface of the wafer to thin the wafer to a first thickness. After performing the first grinding step and the first grinding step, a condensing point of a laser beam having a wavelength that is transmissive to the wafer is positioned inside the wafer, and along the division planned line from the back side of the wafer The modified layer forming step for irradiating the laser beam to form a modified layer inside the wafer, and the modified layer forming step are performed, and then the wafer back surface is ground and the wafer is ground. And a second grinding step for dividing the wafer into individual device chips, and the modified layer forming step is performed in the thickness direction of the wafer along the division line. Wafer processing characterized in that it includes a warpage suppressing step for forming a plurality of overlapping reformed layers and suppressing warpage of the wafer due to expansion of the reformed layer portion by cracks extending from the modified layer to the front surface and the back surface. A method is provided.

  Preferably, the warp suppressing step is performed on a part of the planned division lines. You may make it implement a curvature suppression step in all the division | segmentation schedule lines.

  According to the wafer processing method of the present invention, even for a small chip device wafer, the wafer is first thinned to the first thickness in the first grinding step and then the modified layer forming step is performed. Even when a plurality of modified layers are formed to form a full cut state, the number of modified layers can be reduced and the processing time can be shortened.

It is a perspective view which shows a protection member sticking step. It is a perspective view which shows a 1st grinding step. 3A is a cross-sectional view showing a modified layer forming step, and FIG. 3B is a partially enlarged cross-sectional view of a wafer showing a warp suppressing step. It is a partial cross section side view which shows a 2nd grinding step. It is a perspective view of the wafer after 2nd grinding step implementation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, there is shown a perspective view of a protective member attaching step for attaching a protective member 17 to a surface 11a of a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) 11.

  A plurality of division lines 13 are formed in a lattice pattern on the surface 11 a of the semiconductor wafer 11, and devices 15 such as LSIs are formed in each area partitioned by the division lines 13. In the present embodiment, the interval between the division planned lines 13 adjacent in parallel is set to 3 mm or less.

  The wafer 11 is made of silicon and has a thickness of about 700 μm. In the wafer processing method of this embodiment, first, a protection member attaching step of attaching a protection member 17 such as a protection tape to the surface 11a of the wafer 11 is performed.

  After performing the protective member attaching step, the first grinding step is performed in which the back surface 11b of the wafer 11 is ground to thin the wafer to a first thickness (100 to 300 μm). In the first grinding step, as shown in FIG. 2, the protection member 17 is sucked and held by the chuck table 10 of the grinding apparatus, and the back surface 11 b of the wafer 11 is exposed.

  The grinding unit 12 includes a spindle 14 that is rotationally driven by a motor, a wheel mount 16 that is fixed to the tip (lower end) of the spindle 14, and a grinding wheel 20 that is detachably attached to the wheel mount 16 with a plurality of screws 18. Is included. The grinding wheel 20 includes an annular wheel base 22 and a plurality of grinding wheels 24 fixed to the outer periphery of the lower end of the wheel base 22.

  In the first grinding step, while rotating the chuck table 10 in the direction indicated by arrow a at, for example, 300 rpm, the grinding wheel 20 is rotated in the direction indicated by arrow b at, for example, 6000 rpm, and a grinding unit feed mechanism (not shown) is operated. The grinding wheel 24 of the grinding wheel 20 is brought into contact with the back surface 11 b of the wafer 11.

  Then, the wafer 11 is ground while the grinding wheel 20 is ground and fed 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 performing the first grinding step, a laser beam having a wavelength (for example, 1064 nm) having transparency to the wafer 11 is irradiated along the division line 13 from the back surface 11b side of the wafer 11, and the modified layer is formed inside the wafer. A modified layer forming step of forming is performed.

  That is, as shown in FIG. 3A, the wafer 11 thinned in the first grinding step is sucked and held through the protective member 17 by the chuck table 26 of the laser processing apparatus, and the back surface 11b of the wafer 11 is exposed. .

  Then, a laser beam LB having a wavelength (for example, 1064 nm) that is transmissive to the wafer 11 from the condenser 30 of the laser beam irradiation unit 28 is positioned inside the wafer 11 and the rear surface 11b side of the wafer 11 is located. The modified layer 19 is formed inside the wafer 11 along the division line 13 by processing and feeding the chuck table 26 that sucks and holds the wafer 11 in the direction of the arrow X1.

  While the chuck table 26 is indexed and fed by the pitch of the division lines 13, similar modified layers 19 are successively formed inside the wafer 11 along the division lines 13 extending in the first direction. Next, after the chuck table 26 is rotated by 90 °, similar modified layers 19 are successively formed in the wafer 11 along the planned dividing line 13 extending in the second direction orthogonal to the first direction. .

  In this modified layer forming step, a plurality of modified layers 19 that overlap in the thickness direction of the wafer 11 are formed along the scheduled dividing line 13 and modified by cracks extending from the modified layer 19 to the front surface and the back surface of the wafer 11. A warpage suppressing step for suppressing warpage of the wafer 11 due to expansion of the mass layer 19 portion is included.

  As shown in FIG. 3B, this warpage suppressing step irradiates the laser beam along the planned dividing line 13 by positioning the condensing point of the laser beam at a position of about 50 μm from the surface 11a of the wafer 11. In FIG. 3B, the lower modified layer 19 is formed. When this modified layer 19 is formed, a crack 21 extending from the modified layer 19 to the surface 11 a of the wafer 11 is formed.

  Next, the condensing point of the laser beam is positioned on the back surface 11b side of the wafer 11, and the laser beam is irradiated along the same scheduled dividing line 13. In FIG. 3B, the modified layer 19 is formed on the back surface 11b side of the wafer 11. Form. When this modified layer 19 is formed, a crack 21 extending from the upper modified layer 19 to the back surface 11 b of the wafer 11 is formed.

  As described above, in the warp suppressing step, the wafer 11 is fully formed by forming a plurality of modified layers 19 and cracks 21 extending from the modified layers 19 to the surfaces 11a and 11B of the wafer 11 along the planned dividing line 13. Make a cut state.

  The warpage of the wafer 11 due to the expansion of the modified layer portion can be reduced by performing the warp suppression step for some or all of the planned division lines 13 according to the distance between the planned division lines 13 (pitch of the planned division lines). Can be suppressed.

  Table 1 below shows the relationship between the distance between the lines to be divided, the full cut line (%), and the warp state.

  In Table 1, a circle indicates a state in which the wafer is not warped, a triangle indicates a state in which the wafer is slightly suppressed, and a cross indicates a state in which the wafer is not eliminated. For example, in the case of the wafer 11 with a distance between the planned division lines of 3 mm, the warped state of the wafer 11 is somewhat relaxed by setting the full cut line to 2% or 20% of the total division line, and 50% This indicates that the warpage of the wafer 11 is completely eliminated.

  In the case of a wafer having a distance between divided lines of 5 mm, the warped state of the wafer 11 is completely eliminated by setting the full cut line to 2%. On the other hand, in the case of a wafer with a distance of 1 mm between the planned division lines, the warp of the wafer 11 is somewhat suppressed by setting the line in the full cut state to 50%, and the warp of the wafer 11 is completely controlled by setting it to 80%. Indicates that it will be resolved.

  Depending on the thickness of the wafer 11 after the first grinding step, the number of the modified layers 19 formed in the warp suppressing step is different. For example, when the thickness of the wafer 11 after the first grinding step is about 200 to 300 μm, it is preferable to form about 3 to 5 modified layers that overlap in the thickness direction of the wafer 11.

  After performing the modified layer forming step, the back surface 11b of the wafer 11 is ground to thin the wafer 11 to the second thickness, and the second grinding step is performed to divide the wafer 11 into individual device chips by grinding pressure. .

  In the second grinding step, as shown in FIG. 4, the wafer 11 on which the modified layer forming step including the warpage suppressing step is performed is sucked and held by the chuck table 10 via the protective member 17, and the back surface 11 b of the wafer 11 is held. To expose.

  Then, while rotating the chuck table 10 in the direction indicated by the arrow a at 300 rpm, for example, the grinding wheel 20 is rotated in the direction indicated by the arrow b at, for example, 6000 rpm, and the grinding feed mechanism (not shown) is operated to grind the grinding wheel 20. The grindstone 24 is brought into contact with the back surface 11 b of the wafer 11.

  The back surface 11b of the wafer 11 is ground while the grinding wheel 20 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 desired thickness, for example, 30 μm.

  In this second grinding step, the wafer 11 is divided into individual device chips 23 with the modified layer 19 as a division starting point by the grinding pressure of the grinding wheel 20. Since the modified layer 19 is formed on the back surface 11b side from the position 11 μm from the front surface 11a of the wafer 11, the modified layer 19 is completely removed and divided by performing this second grinding step. The modified layer 19 does not remain on the side surface of the device chip 23. Thereby, the bending strength of the device chip 23 can be sufficiently maintained.

  Referring to FIG. 5, a perspective view of the wafer 11 after performing the second grinding step is shown. The wafer 11 is divided into individual device chips 23 by performing the second grinding step. However, since the surface 11a of the wafer 11 is adhered to the protective member 17, the individually divided device chips 23 are divided into wafers. 11 shapes are retained.

  In the above-described embodiment, the case where the wafer 11 has the square device 15 has been described. However, when the wafer has long devices having different vertical and horizontal lengths, the interval between the lines to be divided is divided. A plurality of modified layers 19 may be formed only in a shorter distance, and the wafer 11 may be in a full cut state.

DESCRIPTION OF SYMBOLS 10 Chuck table 11 Semiconductor wafer 12 Grinding unit 13 Scheduled division line 15 Device 17 Protective member 19 Modified layer 20 Grinding wheel 21 Crack 23 Device chip 24 Grinding wheel 26 Chuck table 28 Laser beam irradiation unit 30 Condenser

Claims (2)

A wafer processing method in which devices are formed in each region divided into a plurality of planned division lines intersecting each other set on the surface, and the interval between the division target lines adjacent in parallel is set to 3 mm or less,
A protective member attaching step for attaching a protective member to the surface of the wafer;
A first grinding step of grinding the back surface of the wafer and thinning the wafer to a first thickness after performing the protective member attaching step;
After performing the first grinding step, a condensing point of a laser beam having a wavelength that is transparent to the wafer is positioned inside the wafer, and the laser beam is irradiated from the back surface side of the wafer along the planned division line. A modified layer forming step for forming a modified layer inside the wafer;
After performing the modified layer forming step, the second grinding step of grinding the back surface of the wafer to thin the wafer to a second thickness and dividing the wafer into individual device chips,
The modified layer forming step forms a plurality of modified layers that overlap in the thickness direction of the wafer along the scheduled dividing line, and expands the modified layer portion by cracks extending from the modified layer to the front surface and the back surface. A method for processing a wafer, comprising: a warpage suppressing step for suppressing the warpage of the wafer caused by.   The wafer processing method according to claim 1, wherein the warpage suppressing step is performed on a part or all of the division planned lines.

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