JP2009034694A - Laser beam machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining method capable of efficiently removing distortion caused by the heat of laser beams in the cut surface of a substrate in the laser beam machining method by which the substrate is irradiated with laser beams to cut the substrate one by one. <P>SOLUTION: A protective film 5 containing fluoride is deposited on a surface of a wafer 1. The wafer 1 with the protective film 5 being deposited thereon is held on a chuck table of a laser beam machining apparatus 10, and laser beams L are passed through the protective film 5 and applied to a division-scheduled line 2 on the surface of the wafer 1. Since the wafer 1 and the protective film 5 on the division-scheduled line 1 are melted and evaporated, a slit S is formed in the wafer 1. In this condition, fluoride in the protective film 5 is sublimed into plasma, and chemically reacted with silicon as a component of the wafer 1, and a cut surface 6 is etched. Thus, an area 7 where thermal distortion is caused is removed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser processing method suitable for use when, for example, irradiating a laser beam along a division line formed on a substrate such as a semiconductor wafer to separate the substrate.

  In the semiconductor device chip manufacturing process, a plurality of rectangular areas are defined on the surface of a substantially disk-shaped semiconductor wafer by dividing lines arranged in a lattice pattern, and electronic circuits such as ICs and LSIs are formed in these rectangular areas. After forming the wafer, the wafer is cut along the planned dividing line to obtain a rectangular region as a semiconductor chip.

  As a means for cutting the wafer, a dicing method is generally used in which a thin disk-shaped blade rotated at a high speed is cut into the wafer. This dicing method has an advantage that a flat and sharp cut surface can be obtained. However, the width of the line to be divided between chips needs to be larger than the thickness of the blade to be used (mainly about 10 to 30 μm). Therefore, the cutting allowance is relatively large, which is disadvantageous in terms of improving the productivity by obtaining as many chips as possible per wafer.

  On the other hand, in recent years, a laser method has been adopted in which a transparent laser beam is irradiated along a planned division line, and a slit is formed in the wafer by a thermal evaporation phenomenon called ablation to obtain individual chips. Yes. In this laser method, the cutting allowance is much smaller than that in the dicing method, which is advantageous in terms of productivity.

  However, distortion remains due to heat on the cut surface of the wafer cut by the laser method. Since this thermal strain lowers the bending strength of the chip, it must be removed. In view of this, there is known a method of removing the thermal strain and improving the bending strength by performing chemical etching treatment such as plasma etching on the side surface of the chip after laser processing (see Patent Document 1).

Special table 2006-520534

In order to perform the chemical etching process as described above, a large facility is required in which a reactive gas is supplied and retained around the wafer, and plasma is generated by applying a high voltage to the reactive gas. Further, as a gas capable of etching silicon used for a wafer, there is a fluoride gas such as SF ₆ . The fluorinated gas such as SF ₆ is a warming gas and is expensive. Thus, in order to perform a chemical etching process, since a large-scale installation and expensive gas are used, much expense will be started.

  Therefore, the present invention provides a laser processing method for efficiently removing the distortion generated by the heat of the laser beam on the cut surface of the substrate in a laser processing method for irradiating the substrate with a laser beam and separating the substrate into individual pieces. It is an object.

  The present invention is a laser processing method for forming a groove or a slit in a substrate by irradiating a laser beam along a predetermined division line on the surface of the substrate, wherein a protective film containing fluoride is formed on the surface of the substrate. The substrate is irradiated with a laser beam through a protective film.

  In the present invention, the laser beam passes through the protective film and irradiates the substrate, and the substrate and the protective film on the division line are evaporated by the thermal energy of the laser beam. At this time, the fluoride in the protective film is sublimated and converted into plasma by thermal energy, and the cut surface of the substrate is etched. By etching the cut surface, the distortion formed on the cut surface by the heat of the laser beam is removed. In this way, since the protective film contains fluoride, the cut surface of the substrate is etched simultaneously with the cutting of the substrate by a normal laser method, so that cutting can be performed without using conventional etching equipment. The strain formed on the surface can be removed. As a result, etching efficiency and cost can be reduced.

  Examples of the method for forming the protective film include a method of spin-coating a liquid serving as a protective film on the surface of the substrate. Moreover, the method of forming a protective film by sticking an adhesive film on the surface of a board | substrate is mentioned. The protective film is used to prevent a component of the substrate evaporated by laser processing from reattaching to the cut substrate. Since the protective film is not necessary after laser processing, a protective film that can be easily removed is preferably used. Therefore, when the protective film is formed by spin coating, it is preferable to use a water-soluble liquid as the protective film because it can be easily removed by supplying water after laser processing. Moreover, when forming a protective film with an adhesive film, what the adhesive material of an adhesive film peels by heating or optical irritation | stimulation is used suitably. Such an adhesive material is peeled off by an external stimulus such as heating. Therefore, the adhesive film can be easily removed from the substrate only by applying an external stimulus to the adhesive film after laser processing.

  According to the present invention, by containing fluoride in the protective film formed on the surface of the substrate, grooves or slits are formed by irradiating a laser beam to the division lines of the substrate, and at the same time, the cut surface of the substrate is Since the etching is performed, the strain formed on the cut surface can be easily removed. As a result, there is an effect that the etching efficiency and cost can be reduced.

[1] Semiconductor Wafer Reference numeral 1 in FIG. 1 indicates a disk-shaped semiconductor wafer (hereinafter abbreviated as a wafer) irradiated with a laser beam by the laser processing method of one embodiment of the present invention. The wafer 1 is a silicon wafer or the like. A plurality of rectangular semiconductor chips (devices) 3 are defined on the surface of the wafer 1 by grid-like division lines 2, and on the surface of the semiconductor chips 3, an unillustrated electronic device such as an IC or LSI is provided. A circuit is formed. A V-shaped notch 4 indicating the crystal orientation of the semiconductor is formed at a predetermined location on the peripheral surface of the wafer 1.

When laser processing the wafer 1, for the purpose of preventing the transpiration component generated during the laser processing from reattaching to the wafer 1, the side on which the electronic circuit is formed as shown in FIG. A protective film 5 is formed on the surface. The protective film 5 is formed by applying a water-soluble photoresist containing water-soluble polymer such as casein, polyvinyl alcohol, gelatin, etc., ammonium dichromate used as a photosensitizer, and a fluoride for etching the wafer 1 to the surface of the wafer 1. It is formed by spin coating. As this fluoride, for example, NaF (sodium fluoride), MFP (sodium monofluorophosphate), CaF ₂ (calcium fluoride), KF (potassium fluoride) and the like are used. The thickness of the protective film 5 is appropriately selected within a range of about 50 to 500 μm. Moreover, the content rate of the fluoride contained in the water-soluble photoresist of this embodiment is appropriately selected within a range of about 5 to 70%.

  FIG. 2 shows a state in which a dicing tape 60 is adhered to the back surface of the wafer 1. The dicing tape 60 is, for example, a pressure-sensitive adhesive tape in which a polyvinyl chloride having a thickness of about 100 μm is used as a base material and an acrylic resin-based pressure-sensitive adhesive is applied to a thickness of about 5 μm on one side. An annular dicing frame 61 having an inner diameter larger than the diameter of the wafer 1 is attached to the outer peripheral portion of the adhesive surface (the upper surface in FIG. 2) of the dicing tape 60. The dicing frame 61 is made of a rigid metal plate or the like, and the wafer 1 is handled via the dicing tape 60 and the dicing frame 61.

  The wafer 1 adhered to the dicing tape 60 is irradiated with a laser beam along the planned division line 2 by the laser processing method according to one embodiment of the present invention, so that slits are formed, and the semiconductor chips 3 are separated into individual pieces. Is done. The laser processing method of one embodiment is suitably implemented using the laser processing apparatus 10 shown in FIG.

[2] Configuration and Operation of Laser Processing Apparatus The wafer 1 attached to the dicing tape 60 is held on a horizontal chuck table (not shown) provided in the laser processing apparatus 10. A laser head 21 that irradiates a laser beam vertically downward is disposed above the chuck table. The chuck table is installed on an XY moving table 13 provided on the base 12 of the apparatus 10 so as to be movable in the horizontal X-axis direction and the Y-axis direction. By moving in the direction, a laser beam is irradiated from the laser head 21 onto the planned division line 2.

  The XY moving table 13 includes an X-axis base 30 provided on the base 12 so as to be movable in the X-axis direction, and a Y-axis base 40 provided on the X-axis base 30 so as to be movable in the Y-axis direction. It consists of a combination. The X-axis base 30 is slidably attached to a pair of parallel guide rails 31 that are fixed on the base 12 and extend in the X-axis direction, and an X-axis drive mechanism 34 that operates a ball screw 33 by a motor 32. Is moved in the X-axis direction. On the other hand, the Y-axis base 40 is slidably attached to a pair of parallel guide rails 41 extending in the Y-axis direction fixed on the X-axis base 30, and the Y-axis that operates the ball screw 43 by the motor 42. It is moved in the Y-axis direction by the drive mechanism 44.

  The chuck table is of a generally known vacuum chuck type that holds a workpiece (in this case, the wafer 1) by vacuum action and is rotatably supported on the Y-axis base 40, not shown. It is rotated in one direction or both directions by a rotation drive mechanism. The chuck table is moved in the X-axis direction and the Y-axis direction as the X-axis base 30 and the Y-axis base 40 move.

  The wafer 1 held on the chuck table is rotated by rotating the chuck table so that each division line 2 extending in one direction is parallel to the X-axis direction and each division line 2 extending in the other direction perpendicular to the X-axis direction. Is parallel to the Y-axis direction, and this state is fixed by stopping the chuck table. While maintaining this state, the X-axis base 30 and the Y-axis base 40 of the XY moving table 13 are appropriately moved, and the laser beam emitted from the laser head 21 is projected from the surface side along the scheduled division line 2. The surface of the wafer 1 is irradiated. In the present embodiment, the focal position of the laser beam is set immediately below the planned division line 2, and a slit is formed at the focal position.

  The laser head 21 is provided at the tip of a casing 22 that extends in the Y-axis direction toward the chuck table. The casing 22 is provided on the column 14 erected on the upper surface of the base 12 so as to be movable up and down along the vertical direction (Z-axis direction), and is driven up and down (not shown) housed in the column 14. It is moved up and down by the mechanism.

  The laser head 21 is connected to a pulse laser oscillator composed of a YAG laser oscillator or a YVO4 laser oscillator so that the laser oscillated by the laser oscillator is irradiated as a laser beam vertically downward from the laser head 21. It has become. The laser oscillated by the laser oscillator has a good transparency to the wafer surface and can form a slit reliably. For example, the output is 1 to 5 W, and the wavelength is selected according to the light transmittance of the workpiece.

  The irradiation position of the laser beam from the laser head 21 is controlled based on the imaging of the microscope 24 attached to one side of the casing 22 via the arm 23. The microscope 24 moves up and down together with the laser head 21 as the casing 22 moves up and down to adjust the focus. Prior to laser beam irradiation, the wafer 1 held on the chuck table is moved below the microscope 24 and a surface pattern image is taken by the microscope 24. Then, the imaged pattern image of the wafer surface is captured by an image processing means (not shown), and the division line 2 to be cut is detected by the image processing means, and the rotation of the chuck table described above is controlled and divided. This is a reference for adjusting the planned line 2 and the XY axes in parallel. Further, based on the data of the scheduled division line 2 detected by the image processing means, the movement operation of the chuck table and the XY movement table 13 and the operation of laser beam irradiation from the laser head 21 are controlled.

  In the laser processing apparatus 10 described above, the laser beam is irradiated from the laser head 21 onto the planned division line 2 while moving the X-axis base 30 in the X-axis direction, thereby causing the wafer along the planned division line 2 parallel to the X-axis direction. 1 and the protective film 5 are melted and evaporated, and a slit S is formed in the wafer 1. Also, by irradiating the laser beam to the division line 2 from the laser head 21 while moving the Y-axis base 40 in the Y-axis direction, the wafer 1 and the protective film 5 along the division line 2 parallel to the Y-axis direction. Melts and evaporates, and a slit S is formed in the wafer 1. Alternatively, after processing the planned division line 2 in the X-axis direction, the chuck table may be rotated 90 degrees, and the planned division line 2 in the X-axis direction may be processed again. When irradiating the laser beam, the casing 22 is moved up and down to adjust the vertical position of the laser head 21, and the focal position of the laser beam is set directly below the planned division line 2.

  As described above, when the laser beam is irradiated along the division line 2 in the X-axis direction and the Y-axis direction and the slit S is formed in the wafer 1, the cut surface of the wafer 1 (side surface of the semiconductor chip 3). In addition, distortion is generated by the heat of the laser beam. This thermal strain reduces the bending strength of the semiconductor chip 3. However, in this embodiment, thermal strain is removed in the following manner.

  As shown in FIG. 4, the wafer 1 and the protective film 5 are melted and evaporated by the heat of the laser beam L, and at the same time the slit S is formed in the wafer 1, the fluoride contained in the protective film 5 is sublimated. Turn into plasma. The sublimated and plasmad fluoride F stays in the slit S and contacts the cut surface 6. The fluoride F in contact with the cut surface 6 chemically reacts with silicon, which is a component of the wafer 1, and the cut surface 6 is etched. Thereby, the region 7 where the thermal strain is generated is removed. The etching of the cut surface 6 is performed at the same time as the slit S is formed. As a result, it is possible to prevent the bending strength of the semiconductor chip 3 from being lowered.

  As described above, the laser beam is applied to all the division lines 2 to separate the wafer 1 into the semiconductor chips 3, and then water is supplied to the surface of the wafer 1 to remove the protective film 5. Thereby, the semiconductor chip 3 from which the thermal strain generated on the cut surface 6 and the protective film 5 are removed is obtained.

  According to this embodiment, simultaneously with the cutting of the wafer 1 by a normal laser processing method, the fluoride contained in the protective film 5 is sublimated and turned into plasma. At this time, the fluoride F stays in the slit S formed in the wafer 1 and causes a chemical reaction with silicon that is a component of the wafer 1 to etch the cut surface 6. The distortion formed on the cut surface 6 can be removed. As a result, since it is not necessary to use a conventional etching facility, etching efficiency and cost can be reduced.

[3] Other Embodiments In the above embodiment, the protective film 5 is formed by spin-coating a water-soluble photoresist on the surface of the wafer 1, but by sticking an adhesive film on the surface of the wafer 1, Even if the protective film 5 is formed, the same effect as the above-described embodiment can be obtained. The adhesive film is formed of a base material containing fluoride and an adhesive material. As this base material, Teflon tape (manufactured by DuPont, Teflon is a registered trademark), nitoflon (manufactured by Nitto Denko Corporation) and the like are preferably used. Further, since the protective film 5 is not necessary after laser processing as in the above embodiment, a film that can be easily removed is preferably used. Therefore, in this embodiment, an adhesive film that is peeled off by heating or optical stimulation is preferably used. Such an adhesive material is peeled off by an external stimulus such as heating. As this adhesive material, Ribaalpha (manufactured by Nitto Denko Corporation), a heat-peelable adhesive material, and Selfa (manufactured by Sekisui Chemical Co., Ltd.), an ultraviolet-peelable adhesive material, are preferably used. By using such an adhesive material, the adhesive film can be easily removed from the wafer 1 simply by applying an external stimulus to the adhesive film after laser processing.

1A is a perspective view of a wafer separated into a plurality of semiconductor chips according to an embodiment of the present invention, and FIG. It is a perspective view which shows the state which affixed the wafer on the dicing tape. 1 is an overall perspective view of a laser processing apparatus that can suitably perform a method according to an embodiment of the present invention. It is sectional drawing which shows the state which has irradiated the laser beam to the wafer with the method of one Embodiment.

Explanation of symbols

1 ... wafer (substrate)
2 ... Scheduled line
5 ... Protective film F ... Sublimation, plasma fluoride L ... Laser beam S ... Slit

Claims (4)

A laser processing method for forming grooves or slits in a substrate by irradiating a laser beam along a division line on the surface of the substrate,
A laser processing method, comprising: forming a protective film containing fluoride on a surface of the substrate; and irradiating the substrate with a laser beam through the protective film.   The laser processing method according to claim 1, wherein the protective film is formed by spin-coating a liquid serving as the protective film on the surface of the substrate.   The laser processing method according to claim 1, wherein the protective film is formed by sticking an adhesive film to the surface of the substrate.   The laser processing method according to claim 3, wherein the adhesive material of the adhesive film is peeled off by heating or optical stimulation.

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