JP6116421B2 - Circular wafer processing method - Google Patents

Description

  The present invention relates to a processing method for a circular wafer in which a mark indicating a crystal orientation is formed on a back surface.

  For example, a wafer having devices formed on the front surface is divided into a plurality of chips after the back surface is ground. After grinding of the wafer and before separation, a dicing tape is attached to the back surface of the wafer to support the wafer on an annular frame, and a protective tape attached to the surface of the wafer for the purpose of device protection during grinding is applied. Peeling and removing are performed (for example, refer to Patent Document 1).

  A cutting device or a laser processing device used for dividing a wafer recognizes the rough position and orientation of the wafer based on the outer periphery of the frame. Therefore, if the position and orientation of the wafer with respect to the frame are greatly deviated, a defect occurs in the alignment (alignment) of the wafer in the cutting apparatus or laser processing apparatus.

  Therefore, conventionally, the position and orientation of the wafer with respect to the frame have been matched with reference to marks such as notches and orientation flats provided on the wafer to indicate the crystal orientation.

  The above-described marks such as notches and orientation flats are formed by cutting out the wafer. Therefore, a device cannot be formed in a region where these marks are provided.

  In particular, if an orientation flat is provided, the wafer is greatly cut out, which is disadvantageous in terms of the number of devices. For these reasons, in recent years, notches with relatively small notches are often used so as to ensure the maximum device formation region.

JP 2005-86074 A

  By the way, when a heat treatment is performed on a wafer provided with a notch, the wafer may be cracked starting from the notch. In view of this, a method for forming a mark on the back surface of the wafer that does not require the wafer to be cut out has been studied in place of the notch for cutting the wafer.

  However, marks formed by this method are removed when the back surface of the wafer is ground. That is, after grinding the back surface of the wafer, the mark is already lost at the timing when the dicing tape is attached and the wafer is supported on the frame, and therefore this mark cannot be used as a reference for alignment.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a circular wafer processing method capable of determining the crystal orientation even after the marks are removed by grinding the back surface. is there.

  According to the present invention, there is provided a processing method for a circular wafer in which a mark indicating a crystal orientation is formed on the back surface, and a bonding step of bonding a surface protection tape comprising a base material and a glue layer on the surface of the circular wafer; The surface protection tape at a position corresponding to the mark of the circular wafer is irradiated with a laser beam having a wavelength that is transmissive to the substrate and absorbable to the glue layer after the attaching step. And forming a mark indicating the crystal orientation of the circular wafer on the surface protective tape by altering the adhesive layer of the surface protective tape, and after performing the mark forming step, A grinding step of holding the surface protection tape by a holding means and grinding the back surface of the circular wafer by a grinding means, and forming the surface protection tape after the marks are removed by the grinding step Processing method of a circular wafer, comprising the possible to identify the crystal orientation of the circular wafer is provided with indicia that.

  In the present invention, the circular wafer is preferably a silicon wafer, and the laser beam irradiated in the mark forming step is preferably a laser beam oscillated using carbon dioxide gas as a laser medium.

  In the processing method of the circular wafer of the present invention, the adhesive layer is altered by irradiating a position corresponding to the mark on the circular wafer with a laser beam having a wavelength that absorbs the adhesive layer of the surface protection tape. A mark indicating the crystal orientation of the wafer is formed on the surface protection tape.

  Thereby, even after the mark indicating the crystal orientation is removed from the circular wafer by grinding the back surface, the crystal orientation of the circular wafer can be determined based on the mark formed on the surface protective tape.

  As other methods for forming a mark on the surface protection tape, for example, laser marking using ablation, printing using an ink jet printer, or the like can be considered.

  However, for example, in laser marking using ablation, irregularities are formed on the surface protection tape by ablation. Further, even in printing using an ink jet printer, unevenness is formed on the surface protection tape due to adhesion of ink.

  When the back surface of the circular wafer is ground with such unevenness formed on the surface protective tape, the thickness of the circular wafer after grinding varies due to the unevenness of the surface protective tape.

  On the other hand, in the processing method of the circular wafer of the present invention, since the paste layer is altered to form a mark indicating the crystal orientation, the surface protective tape is not formed with irregularities, and the circular wafer after grinding is formed. Flatten with high accuracy.

It is a perspective view which shows a sticking step typically. 2A is a partial cross-sectional side view schematically showing the mark forming step, and FIG. 2B is an enlarged view of the vicinity of the region irradiated with the laser beam in FIG. 2A. It is an enlarged view. It is a top view which shows typically the aspect of the mark formed at a mark formation step. It is a perspective view which shows a grinding step typically. It is a perspective view which shows a flame | frame mounting step typically.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The circular wafer processing method according to the present embodiment includes a sticking step (see FIG. 1), a mark forming step (see FIGS. 2 and 3), and a grinding step (see FIG. 4).

  In the adhering step, a surface protection tape composed of a base material and an adhesive layer is adhered to the surface of the circular wafer having a crystal orientation mark formed on the back surface. In the mark forming step, the surface protection tape is irradiated with a laser beam to change the quality of the adhesive layer, and a mark corresponding to the mark on the circular wafer is formed.

  In the grinding step, the surface protection tape attached to the circular wafer is held by the holding means, and the back surface of the circular wafer is ground by the grinding means. Hereinafter, the processing method of the circular wafer concerning this embodiment is explained in full detail.

  FIG. 1 is a perspective view schematically showing an attaching step according to the present embodiment. As shown in FIG. 1, a circular wafer 11 to be processed is, for example, a semiconductor wafer such as a silicon wafer having a disk-like outer shape, and its surface 11a has streets (scheduled division lines) arranged in a lattice pattern. 13 is divided into a plurality of regions.

  A device 15 such as an IC is formed in each region of the surface 11 a partitioned by the street 13. A mark 17 indicating the crystal orientation of the circular wafer 11 is provided in the vicinity of the outer periphery of the back surface 11b.

  The mark 17 is formed without cutting out the wafer, unlike marks formed by cutting out the wafer such as notches and orientation flats. That is, the shape of the outer peripheral edge of the circular wafer 11 is a circular shape without a notch.

  As described above, in the present embodiment, a semiconductor wafer having a circular outer periphery without a notch such as a notch or an orientation flat is particularly referred to as a “circular wafer”.

  In the attaching step, a surface protective tape 19 for protecting the device 15 is attached to the surface 11a of the circular wafer 11 described above. As shown in FIG. 1, the surface protection tape 19 includes a film-like base material 21 and an adhesive paste layer 23 provided on the base material 21.

  The base material 21 is a resin film, and shows a transparency that transmits a laser beam irradiated in a later mark forming step. In the substrate 21, the absorption rate of the laser beam is 2% or less, preferably 1% or less. Such a base material 21 is formed using materials, such as a cycloolefin polymer, a polypropylene, polymethyl methacrylate, for example.

  The adhesive layer 23 exhibits adhesiveness to the wafer 11 and absorbs a laser beam irradiated in a later mark forming step. In the glue layer 23, the absorption rate of the laser beam is higher than 2%.

  Further, the glue layer 23 is configured to change its color due to alteration when it absorbs the laser beam. A visible mark can be formed on the surface protection tape 19 by utilizing the change in the color of the glue layer 23 due to the absorption of the laser beam. Such a glue layer 23 is formed using, for example, an epoxy resin, an acrylic resin, or the like.

  In addition, this sticking step can be implemented using the tape mounter (not shown) which sticks various tapes to a wafer etc., for example. However, the processing method of the circular wafer of this invention is not limited to the aspect which uses a tape mounter.

  After the attaching step, a mark forming step for forming a mark corresponding to the mark 17 on the circular wafer 11 by irradiating the surface protection tape 19 with a laser beam is performed. FIG. 2A is a partial cross-sectional side view schematically showing the mark forming step according to the present embodiment, and FIG. 2B is a view of the region irradiated with the laser beam in FIG. It is an enlarged view which expands and shows the vicinity. FIG. 3 is a plan view schematically showing an aspect of the mark formed in the mark forming step.

  The mark forming step is performed using, for example, a laser irradiation apparatus 2 shown in FIG. However, the mark forming step may be performed in a tape mounter or other apparatus in which the attaching step is performed.

  As shown in FIG. 2A, the laser irradiation apparatus 2 includes a chuck table 4 that holds the circular wafer 11 by suction. Below the chuck table 4, an imaging unit 6 that images the back surface 11 b side of the circular wafer 11 is provided. A laser irradiation unit 8 that irradiates a laser beam L toward the surface protective tape 19 attached to the circular wafer 11 is disposed above the chuck table 4.

  The laser irradiation unit 8 includes a laser oscillator (not shown) that oscillates a laser beam L having a wavelength that is absorbed by the adhesive layer 23 of the surface protection tape 19, and a condenser lens that condenses the laser beam L oscillated by the laser oscillator. 10 and the like.

  As the laser oscillator, for example, a carbon dioxide laser oscillator using carbon dioxide as a laser medium is used. This carbon dioxide laser oscillator oscillates a laser beam L having a center wavelength of 10.6 μm. Since the laser beam L having such a wavelength can be selectively absorbed only by the adhesive layer 23, it is suitable for forming a mark.

  In the mark forming step, first, the back surface 11b side of the wafer 11 is sucked and held on the chuck table 4 described above. Then, the back surface 11 b side of the wafer 11 is imaged by the imaging unit 6 disposed below the chuck table 4 to detect the position of the mark 17.

  Thereafter, the laser irradiation unit 8 is positioned above the mark 17 detected by the imaging unit 6, and the laser beam L is irradiated toward the surface protection tape 19 attached to the circular wafer 11. Further, the chuck table 4 and the laser irradiation unit 8 are relatively moved in accordance with the shape of the mark to be formed.

  In the present embodiment, as described above, the laser beam L having a center wavelength of 10.6 μm oscillated using carbon dioxide gas as a laser medium is irradiated with an output of 10 W or less. Since the base material 21 of the surface protection tape 19 is configured to transmit such a laser beam L, the irradiated laser beam L is absorbed by the glue layer 23 through the base material 21.

  The glue layer 23 that has absorbed the laser beam L is altered (for example, chemically changed) by the energy of the laser beam L. As a result, in the irradiation region of the laser beam L, as shown in FIGS. 2B and 3A, a visually distinguishable mark 25 having a color different from other regions is formed. Here, the mark is formed by relatively moving the chuck table 4 and the laser irradiation unit 8, but the mark may be formed by changing (deflecting) the direction of the optical axis, for example.

  The circular wafer 11 made of a semiconductor material such as silicon does not absorb the laser beam L oscillated using carbon dioxide as a laser medium. Therefore, even if the laser beam L having a high power density is irradiated, the device 15 provided on the circular wafer 11 is not damaged. Therefore, it is not necessary to adjust the position of the condensing point (focal point) L1 so that the laser beam L is not condensed on the circular wafer 11.

  In this embodiment, as shown in FIG. 2B, the condensing lens 10 is adjusted so that the condensing point L1 of the laser beam L is positioned above the surface protective tape 19. Thereby, the irradiation range of the laser beam L becomes wider compared with the case where the condensing point L1 is positioned inside the surface protection tape 19.

  In this way, the laser beam L is defocused, and the condensing point L1 of the laser beam L is positioned in the region between the condensing lens 10 and the surface protective tape 19, whereby the mark formed on the surface protective tape 19 is formed. The line width of 25 can be increased. In the present embodiment, the line width of the mark 25 is about 0.1 μm. However, the line width of the mark 25 formed by the circular wafer processing method of the present invention is not limited to this.

  Moreover, the shape of the mark 25 to be formed is not limited to that shown in FIG. If the crystal orientation of the circular wafer 11 can be recognized, the shape of the mark 25 is arbitrary. For example, as shown in FIG. 3B, a mark 25 having a shape in which two long straight lines 25a and 25b intersect may be formed.

  After the mark forming step, a grinding step for grinding the back surface 11b of the circular wafer 11 is performed. FIG. 4 is a perspective view schematically showing the grinding step. This grinding step is performed using, for example, a grinding apparatus 12 shown in FIG.

  The grinding device 12 includes a spindle 14 that rotates around a rotation axis that extends in the vertical direction. The spindle 14 is lifted and lowered by a lifting mechanism (not shown). A disc-shaped wheel mount 16 is provided on the lower end side of the spindle 14, and a grinding wheel (grinding means) 18 is fixed to the wheel mount 16 with a plurality of bolts 20.

  The grinding wheel 18 includes a wheel base 18a formed of a metal material such as aluminum or stainless steel. A plurality of grinding wheels 18b are fixed to the annular lower surface of the wheel base 18a over the entire circumference.

  A holding table (holding means) 22 is disposed below the grinding wheel 18. The holding table 22 is connected to a rotation mechanism (not shown) such as a motor and rotates around a rotation axis extending in the vertical direction, like the spindle 14.

  The surface of the holding table 22 is a holding surface for sucking and holding the circular wafer 11 and the like. A negative pressure of a suction source (not shown) acts on the holding surface through a flow path (not shown) formed inside the holding table 22 to generate a suction force for sucking the circular wafer 11 and the like.

  In the grinding step, first, the surface protection tape 19 attached to the circular wafer 11 is brought into contact with the surface of the holding table 22 to apply a negative pressure of the suction source. Thereby, the circular wafer 11 is sucked and held on the holding table 22 via the surface protection tape 19.

  Next, the spindle 14 is lowered while rotating the spindle 14 and the holding table 22, and the grinding wheel 18 b is brought into contact with the back surface 11 b of the circular wafer 11. The rotation speed of the spindle 14 is set to, for example, 6000 rpm, and the rotation speed of the holding table 22 is set to, for example, 300 rpm. However, the rotation speeds of the spindle 14 and the holding table 22 are not limited to these.

  By lowering the spindle 14 at a predetermined feed rate, the back surface 11b of the circular wafer 11 is ground. This grinding is performed while measuring the thickness of the circular wafer 11 with a contact-type or non-contact-type thickness measurement sensor. When the circular wafer 11 has a predetermined thickness (for example, 100 μm), the grinding step ends.

  After performing the grinding step, a frame mounting step for mounting an annular frame on the circular wafer 11 via a dicing tape is performed. FIG. 5 is a perspective view schematically showing the frame mounting step.

  In the frame mounting step, the positions and orientations of the annular frame 27 and the circular wafer 11 are aligned based on the mark 25 formed on the surface protection tape 19, and the dicing tape 29 is attached to the back surface 11 b of the circular wafer 11 and the frame 27. To wear.

  Thereby, the circular wafer 11 is supported by the frame 27 via the dicing tape 29. In this frame mounting step, the position and orientation of the frame 27 and the circular wafer 11 are aligned with reference to the mark 25 on the surface protection tape 19, so that the alignment of the circular wafer 11 is appropriately performed in the subsequent division step and the like. Can be implemented.

  As described above, in the method for processing a circular wafer according to the present embodiment, the laser beam L having a wavelength that is absorptive with respect to the adhesive layer 23 of the surface protection tape 19 is placed at a position corresponding to the mark 17 on the circular wafer 11. The surface layer 25 is formed with marks 25 indicating the crystal orientation of the circular wafer 11 by irradiating and altering the paste layer 23.

  Thereby, even after the mark 17 indicating the crystal orientation is removed from the circular wafer 11 by grinding the back surface 11b, the crystal orientation of the circular wafer 11 can be determined based on the mark 25 formed on the surface protective tape 19. .

  As other methods for forming a mark on the surface protection tape 19, for example, laser marking using ablation, printing using an ink jet printer, or the like can be considered.

  However, for example, in laser marking using ablation, irregularities are formed on the surface protection tape 19 by ablation. Further, even in printing using an ink jet printer, unevenness is formed on the surface protection tape 19 due to adhesion of ink.

  If the back surface 11 b of the circular wafer 11 is ground with such unevenness formed on the surface protection tape 19, the thickness of the circular wafer 11 after grinding varies due to the unevenness of the surface protection tape 19.

  On the other hand, in the processing method of the circular wafer according to the present embodiment, the adhesive layer 23 is altered to form the mark 25 indicating the crystal orientation. The subsequent circular wafer 11 can be flattened with high accuracy.

  In addition, this invention is not limited to description of the said embodiment, A various change can be implemented. For example, in the above embodiment, the laser beam L is irradiated from the surface 11a side (surface protection tape 19 side) of the circular wafer 11 in the mark forming step, but the present invention is not limited to this. Since the laser beam L is not absorbed by the circular wafer 11, the mark 25 may be formed on the protective tape by irradiating the laser beam L from the back surface 11 b side of the circular wafer 11.

  In the above embodiment, the frame mounting step is performed after the grinding step, but the present invention is not limited to this. After the grinding step, any step utilizing the mark 25 can be performed.

  In addition, the configurations, methods, and the like according to the above-described embodiments can be changed as appropriate without departing from the scope of the object of the present invention.

11 circular wafer 11a front surface 11b back surface 13 street (division planned line)
15 Device 17 Mark 19 Surface protection tape 21 Base material 23 Adhesive layer 25 Mark 25a, 25b Straight line 27 Frame 29 Dicing tape L Laser beam L1 Condensing point (focal point)
DESCRIPTION OF SYMBOLS 2 Laser irradiation apparatus 4 Chuck table 6 Imaging unit 8 Laser irradiation unit 10 Condensing lens 12 Grinding apparatus 14 Spindle 16 Wheel mount 18 Grinding wheel (grinding means)
18a Wheel base 18b Grinding wheel 20 Bolt 22 Holding table (holding means)

Claims (2)

A processing method of a circular wafer in which a mark indicating a crystal orientation is formed on the back surface,
An adhering step of adhering a surface protection tape comprising a base material and a glue layer on the surface of the circular wafer;
After performing the adhering step, a laser beam having a wavelength that is transparent to the substrate and absorbable to the glue layer is applied to the surface protection tape at a position corresponding to the mark on the circular wafer. A mark forming step of forming a mark indicating the crystal orientation of the circular wafer on the surface protective tape by irradiating and altering the adhesive layer of the surface protective tape;
A grinding step of holding the surface protection tape of the circular wafer with a holding means and grinding the back surface of the circular wafer with a grinding means after performing the mark forming step;
A method of processing a circular wafer, wherein the crystal orientation of the circular wafer can be discriminated by the mark formed on the surface protection tape even after the mark is removed in the grinding step. A circular wafer is a silicon wafer,
2. The method for processing a circular wafer according to claim 1, wherein the laser beam irradiated in the mark forming step is a laser beam oscillated using a carbon dioxide gas as a laser medium.

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