JP2014165338A - Laser processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing method in which a reformed layer is formed in a wafer by emitting a laser beam from the back side of the wafer without using an annular frame.SOLUTION: A laser processing method comprises: an adhering step in which the back side 11b of a wafer is attached to an adhesive tape 12 having the same size as the wafer 11 or a larger size; a holding step in which the adhesive tape with the wafer attached thereto is brought into close contact with the holding surface of a plate 14, which is transparent with respect to a laser beam emitted to the wafer, via a liquid and the wafer is thereby held by the plate via the adhesive tape; and a reformed layer formation step in which after the holding step, while a light condensing point P is located in the wafer held by the plate from the back side of the holding surface of the plate, a laser beam of transmissive wavelength is emitted to the wafer from the back side of the wafer via the plate along a predetermined division line, thereby forming a reformed layer 19 in the wafer.

Description

  The present invention relates to a wafer laser processing method.

  As a method of dividing a wafer such as a semiconductor wafer or an optical device wafer into individual chips, as disclosed in Japanese Patent No. 3408805, a laser beam with a wavelength (for example, 1064 nm) that is transparent to the wafer is condensed. A point is positioned inside the wafer corresponding to the division line, and a laser beam is irradiated along the division line to form a modified layer inside the wafer, and then an external force is applied to the wafer to apply the wafer to the modified layer. There is a method of dividing into individual chips by using as a division starting point.

  Japanese Patent Laid-Open No. 2010-034250 discloses a method in which a tape attached to a wafer having a modified layer formed therein is expanded to apply an external force to the wafer, and the wafer is divided into individual layers starting from the modified layer. A method of dividing into chips is disclosed.

  In general, films of various materials are laminated or uneven on the wafer surface side, so it is possible to irradiate the laser beam from the wafer surface side by positioning the condensing point of the laser beam inside the wafer. In general, a modified layer is generally formed inside the wafer by irradiating a laser beam from the back side of the wafer.

  In this case, the front side of the wafer is attached to the adhesive tape, the outer periphery of the adhesive tape is attached to the annular frame, and the wafer is sucked and held by the chuck table of the laser processing apparatus via the adhesive tape. A method of irradiating a laser beam from the side is often used.

  However, in this method, since an external force is applied to the wafer to divide the wafer into individual chips and then the chips are picked up from the back side, it is necessary to invert the front and back of the chips in later handling.

  In order to solve this problem, in Japanese Patent Application Laid-Open No. 2010-029927, the back side of the wafer is attached to the adhesive tape, and the front side of the wafer is sucked and held by the chuck table of the laser processing apparatus via the adhesive tape. There has been proposed a method of irradiating a laser beam from the back side of a wafer to form a modified layer inside the wafer. In this case, in order to facilitate handling, laser processing is performed with the outer peripheral portion of the adhesive tape attached to the annular frame.

Japanese Patent No. 3408805 JP 2010-034250 A JP 2010-029927 A

  However, when an annular frame is used, even if an attempt is made to expand the adhesive tape to apply external force to the wafer, the amount of expansion is limited, so the adhesive tape cannot be expanded sufficiently and the division is insufficient. There is a fear.

  In addition, there is a problem that the adhesive tape extended and loosened loosens, and chips formed by dividing the wafer come into contact with each other to damage the outer periphery of the chip.

  The present invention has been made in view of the above points, and its object is to form a modified layer inside the wafer by irradiating a laser beam from the back side of the wafer without using an annular frame. It is to provide a laser processing method.

  According to the present invention, a laser that performs laser processing by irradiating a wafer having a device with a wavelength having transparency to each region formed by a plurality of intersecting scheduled lines formed on the surface. A processing method, an adhesion step of adhering the back side of a wafer to an adhesive tape having a size equal to or larger than that of the wafer, and transparent to a laser beam irradiated to the wafer after the adhesion step is performed. Holding the adhesive tape having the wafer attached thereto on a holding surface of a plate having a property via a liquid, and holding the wafer via the adhesive tape on the plate, and carrying out the holding step After that, with the focusing point positioned inside the wafer held on the plate from the back side of the holding surface of the plate, A modified layer forming step of forming a modified layer inside the wafer by irradiating a laser beam of a wavelength having a transient wavelength from the back side of the wafer along the division line through the plate; There is provided a laser processing method comprising the above.

  Preferably, in the laser processing method of the present invention, after the modified layer forming step is performed, the outer peripheral edge of the adhesive tape is sandwiched by the sandwiching means to expand the adhesive tape, and the wafer is separated into individual chips from the modified layer as a starting point. And a dividing step of dividing the image into two.

  Preferably, in the laser processing method of the present invention, after performing the dividing step, the outer peripheral portion of the adhesive tape is attached to the annular frame, and the wafer is supported by the annular frame via the adhesive tape. The method further includes a process.

  Preferably, the plate has a suction portion that opens to the holding surface, and a suction path having one end communicating with the suction portion and the other end communicating with the suction source, and the holding step is performed via a liquid on the holding surface of the plate. After placing the wafer and placing the wafer, the suction source is activated and the wafer on the plate is sucked through the adhesive tape so that the adhesive tape to which the wafer is attached is adhered to the plate. And a suction stop step of stopping the operation of the suction source after performing the contact step.

  In the laser processing method of the present invention, the wafer is held on the transparent plate via the adhesive tape in order to bring the adhesive tape to which the wafer is attached via the liquid into close contact with the transparent plate. Furthermore, a modified layer is formed inside the wafer by irradiating a laser beam from the back side of the wafer through a transparent plate, so there is no need to use an annular frame and the amount of expansion of the adhesive tape is limited in the subsequent dividing step. The wafer can be reliably divided into chips by sufficiently expanding the adhesive tape.

  Furthermore, since the annular frame can be attached after the expansion of the adhesive tape, there is no possibility of chip damage resulting from contact between the chips due to the expanded adhesive tape.

It is a disassembled perspective view which shows a sticking step. It is a perspective view explaining a holding step. It is a partial cross section side view which shows a modified layer formation step. It is a block diagram of a laser beam generation unit. It is a partial cross section side view explaining a division | segmentation step. It is sectional drawing which shows an annular frame sticking step. It is sectional drawing which shows a mounting step. It is sectional drawing which shows a contact | adherence step. It is sectional drawing which shows a suction stop step. It is sectional drawing which shows the modified layer formation step of 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, an exploded perspective view showing a sticking step according to an embodiment of the present invention is shown. On a surface 11a of a semiconductor wafer (hereinafter sometimes simply referred to as a wafer) 11, devices 15 such as ICs and LSIs are formed in respective regions partitioned by a plurality of division lines 13 formed in a lattice shape. ing.

  In the attaching step of this embodiment, the back surface 11b side of the wafer 11 is attached to the adhesive tape 12 having a size equal to or larger than that of the wafer 11, and the front surface 11a of the wafer 11 is exposed.

  After performing the sticking step, as shown in FIG. 2A, from the nozzle 16 on the plate 14 such as glass having transparency to the laser beam irradiated on the wafer, the holding surface 14a of the plate 14 is moved. The liquid 17 is dropped to cover the holding surface 14a with the liquid. In the present embodiment, pure water is used as the liquid.

  Next, as shown in FIG. 2 (B), the adhesive tape 12 with the wafer 11 adhered thereto is brought into intimate contact with the holding surface 14a of the plate 14 via the liquid 17, and the wafer is adhered to the plate 14 via the adhesive tape 12. A holding step of holding 11 is performed.

  In this holding step, since the wafer 11 is held by the plate 14 with the liquid 17 interposed between the holding surface 14a of the plate 14 and the back surface 11b of the wafer 11, a certain level of holding force is exhibited although it is not strong. And the wafer 11 can be held in a fixed position.

  After carrying out the holding step, a modified layer 19 is formed inside the wafer 11 using a laser beam irradiation unit including a condenser (laser head) 18 shown in FIG. 3 and a laser beam generation unit 20 shown in FIG. A modified layer forming step of forming is performed.

  As shown in the block diagram of FIG. 4, the laser beam generating unit 20 includes a laser oscillator 22 that oscillates a YAG laser or YVO 4 laser having a wavelength that is transmissive to the wafer 11, a repetition frequency setting means 24, a pulse width, The adjusting means 26 and the power adjusting means 28 are included.

  In the modified layer forming step, a pulsed laser beam having a wavelength (for example, 1064 nm) having transparency to the wafer 11 adjusted to a predetermined power by the power adjusting means 28 of the laser beam generating unit 20 as shown in FIG. In the state where the condensing point P is positioned inside the wafer 11 from the condenser 18 arranged on the lower side of the plate 14, the plate 14 is irradiated from the back surface 11b side through the plate 14, and the plate 14 is irradiated with the arrow X1. The modified layer 19 is formed inside the wafer 11 along the planned dividing line 13 by processing and feeding in the direction.

  After carrying out this modified layer forming step along all the planned dividing lines 13 extending in the first direction, the plate 14 is rotated by 90 degrees, and then in the second direction orthogonal to the first direction. A similar modified layer forming step is performed along all the planned dividing lines 13 that extend.

  Thus, after forming the reforming layer 19 inside the wafer 11 along all the planned dividing lines 13, as shown in FIG. 5, the adhesive tape 12 is expanded in the radial direction by clamping the clamping means 30 with the clamping means 30 and moving the clamping means 30 in the direction of the arrow A. When the adhesive tape 12 is sufficiently expanded, the wafer 11 is divided into individual device chips 15 using the modified layer 19 as a starting point (division step).

  Before performing the dividing step, the dividing step of evaporating the liquid 17 by heating, for example, peeling the wafer 11 from the plate 14 and then expanding the adhesive tape 12 is performed.

  In the dividing step of the present embodiment, the amount of expansion of the adhesive tape 12 performed by the clamping means 30 is not limited, and the adhesive tape 12 can be sufficiently expanded. Therefore, the wafer 11 is not divided sufficiently, and the wafer 11 It is surely divided into individual device chips 15.

  After carrying out the dividing step, as shown in FIG. 6, the annular frame F is attached to the outer periphery of the adhesive tape 12, and the wafer 11 is supported by the annular frame F via the adhesive tape 12. Perform the sticking step.

  In the present embodiment, since the annular frame F can be adhered to the adhesive tape 12 after the adhesive tape 12 is sufficiently expanded, the device chip 15 is damaged due to the contact between the device chips 15 caused by the expanded adhesive tape 12. There is no fear.

  After performing the annular frame sticking step, a pickup step for picking up the device chip 15 divided from the wafer 11 from the adhesive tape 12 is performed. When this pickup step is performed, the adjacent device chips 15 are sufficiently spaced apart from each other, so that damage to the device chips 15 due to contact between the device chips 15 can be prevented.

  Next, a second embodiment of the holding step will be described with reference to FIGS. In the holding step of the present embodiment, a plate 14A having an annular suction groove 32 that acts as a suction portion that opens to the holding surface 14a is used. The annular suction groove (suction part) 32 is selectively connected to a vacuum suction source 36 or an ejection air source 38 via a suction path 33 and an electromagnetic switching valve 34.

  In the holding step of this embodiment, first, as shown in FIG. 7, a mounting step of mounting the rear surface 11b side of the wafer 11 on the holding surface 14a of the plate 14A via a liquid 17 such as pure water is performed. At this time, the electromagnetic switching valve 34 is in the cutoff position.

  Next, as shown in FIG. 8, the electromagnetic switching valve 34 is switched so that the vacuum suction source 36 communicates with the annular suction groove 32 via the suction path 33, and the wafer 11 on the plate 14A is adhered by the operation of the vacuum suction source 36. An adhesion step is performed in which the pressure-sensitive adhesive tape 12 to which the wafer 11 is adhered is adhered onto the plate 14A by suction through the tape 12.

  After performing the contact step, as shown in FIG. 9, the suction switching step for switching the electromagnetic switching valve 34 to the shut-off position and stopping the suction by the suction source 36 is performed. Since the wafer 11 is in close contact with the holding surface 14a of the plate 14A via the adhesive tape 12, even if the suction by the suction source 36 is stopped, this close contact state is not hindered.

  Therefore, after carrying out the holding step of the present embodiment, the wafer 11 adhered to the adhesive tape 12 is sufficiently in contact with the holding surface 14a of the plate 14A via the adhesive tape 12, so that FIG. As shown in the figure, the wafer 11 does not fall from the plate 14A even when the upper and lower sides are determined and the surface 11a of the wafer 11 faces downward with the plate 14A facing upward.

  Therefore, since the conventional laser processing apparatus in which the condenser 18 is disposed on the upper side of the wafer 11 can be used, the holding surface 14a of the plate 14A is held by holding the surface side of the wafer 11 with the chuck table of the laser processing apparatus. The wafer 11 is irradiated with a laser beam with the condenser 18 positioned inside the wafer 11 by the condenser 18 from the back side of the wafer, and the chuck table is processed and sent in the direction of the arrow X1, thereby dividing the wafer 11 to be divided. 13, the modified layer 19 can be formed inside the wafer 11.

  In the present embodiment, when it is necessary to peel the adhesive tape 12 from the plate 14A, the electromagnetic switching valve 34 is switched to connect the annular suction groove 32 to the ejection air source 38 via the suction path 33, and the annular suction groove The adhesive tape 12 is peeled from the plate 14 </ b> A by ejecting air from 32.

11 Wafer 12 Adhesive Tape 13 Scheduled Divided Line 15 Device 17 Liquid 18 Concentrator 19 Modified Layer 20 Laser Beam Generation Unit 30 Nipping Means 32 Annular Suction Groove 33 Suction Path 34 Electromagnetic Switching Valve 36 Vacuum Suction Source 38 Blowout Air Source

Claims (4)

A laser processing method in which laser processing is performed by irradiating a wafer having a device with a wavelength having transparency to each region defined by a plurality of intersecting scheduled lines formed on a surface. ,
An adhering step of adhering the back side of the wafer to an adhesive tape having a size equal to or larger than the wafer;
After carrying out the adhering step, the adhesive tape having the wafer attached thereto is brought into intimate contact with the holding surface of the plate having transparency with respect to the laser beam applied to the wafer through the liquid. A holding step for holding the wafer via the adhesive tape;
After carrying out the holding step, a laser having a wavelength that is transparent to the wafer in a state where a condensing point is positioned inside the wafer held on the plate from the back side of the holding surface of the plate A modified layer forming step of forming a modified layer inside the wafer by irradiating a beam along the planned dividing line from the back side of the wafer through the plate;
A laser processing method comprising: In the attaching step, the wafer is attached to an adhesive tape having a size larger than the wafer,
After performing the modified layer forming step, the dividing step of expanding the adhesive tape by sandwiching the outer peripheral edge of the adhesive tape with a clamping means, and dividing the wafer into individual chips starting from the modified layer. The laser processing method according to claim 1, further provided.   After carrying out the dividing step, further comprising an annular frame attaching step in which the outer peripheral portion of the adhesive tape is attached to the annular frame, and the wafer is supported by the annular frame via the adhesive tape. The laser processing method according to claim 2. The plate has a suction part that opens to the holding surface, and a suction path having one end communicating with the suction part and the other end communicating with a suction source,
The holding step includes placing a wafer on the holding surface of the plate via the liquid; and
After carrying out the placing step, the suction source is operated to suck the wafer on the plate through the adhesive tape so that the adhesive tape to which the wafer is adhered adheres to the plate. When,
A suction stop step of stopping the operation of the suction source after performing the contact step;
The laser processing method in any one of Claims 1-3 containing.

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