JP2014209523A - Wafer processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer processing method which can grind a wafer while measuring a thickness of the wafer without contacting a gauge with a device chip.SOLUTION: A wafer processing method comprises: a modifying layer forming step of forming a modifying layer K along a split scheduled line except in a circumferential surplus area CA; a protection member arranging step of arranging a protection member PT on a surface side of a wafer W on which devices D are formed; and a grinding step of grinding the wafer W from a rear face Wb by grinding means 22 while holding the protection member PT side by a chuck table 21 to thin the wafer W to a predetermined thickness, and splitting a device area DA of the wafer W along the modifying layer K into individual devices D. In the grinding step, the wafer W is grounded while a thickness being measured by contacting a contact-type thickness measurement gauge 30 which measures a thickness of the wafer W in contact with the rear face Wb of the wafer W, with the circumferential surplus area CA of the wafer W where the modifying layer K is not formed.

Description

  The present invention relates to a wafer processing method.

  In the semiconductor device manufacturing process for manufacturing semiconductor devices widely used in electronic equipment, a wafer with devices formed on the surface is ground to a predetermined thickness, and the wafer is divided along the planned dividing line (street). Individual device chips. A grinding device that rotates a grinding wheel is used for grinding a wafer, and a cutting device that rotates a cutting blade at a high speed and a laser processing device that emits a pulsed laser beam are generally used for dividing the wafer.

  Device chips tend to be smaller and thinner for downsizing of electronic devices, but a technique called DBG (Dicing Before Grinding) is used to achieve the device chip (see, for example, Patent Document 1). . In addition, in order to achieve further narrowing of the street and less chipping on the device side, a wafer processing method that combines laser processing to form a modified layer inside the wafer and grinding processing to grind the wafer is also proposed. (For example, refer to Patent Document 2).

  When a wafer on which a groove or a modified layer has been formed in advance by dicing is ground, the wafer is ground until a predetermined thickness is obtained while measuring the thickness of the wafer. At that time, the thickness of the wafer is measured while bringing the gauge of the thickness measuring means into contact with the upper surface of the rotating wafer held by the chuck table. As grinding progresses, the wafer is divided into device chips by pre-formed grooves or modified layers.

JP-A-5-335411 JP 2004-111428 A

  Device chips that have been made into chips and have a small contact area with the protective tape are easy to move, so when the gauge is brought into contact with the wafer, the device chip and the gauge come into contact with each other, and the device chips come into contact with each other or are scattered. There is a risk of doing.

  The present invention has been made in view of the above, and an object of the present invention is to provide a wafer processing method capable of grinding while measuring the thickness of the wafer without contacting the gauge and the device chip. .

  In order to solve the above-described problems and achieve the object, a wafer processing method according to the present invention surrounds a device region in which a device is formed in a region partitioned by a plurality of intersecting scheduled lines, and the device region. A method of processing a wafer having an outer peripheral surplus area on a surface thereof, wherein a condensing point of a laser beam having a wavelength transmissive to the wafer is positioned inside the planned dividing line and irradiated with a laser beam, and the outer peripheral surplus area is removed. A modified layer forming step for forming a modified layer along the planned dividing line, and a protective member for disposing a protective member on the surface side of the wafer on which the device is formed before or after the modified layer forming step is performed. After performing the disposing step, the modified layer forming step, and the protective member disposing step, the protective member side is held on the chuck table and held on the back surface of the wafer. And a grinding step in which the device region of the wafer is divided into individual devices along the modified layer, and the grinding step contacts the back surface of the wafer. The contact type thickness measurement gauge that measures the thickness of the wafer is brought into contact with the back surface of the outer peripheral surplus area of the wafer on which the modified layer is not formed and is ground while measuring the thickness of the wafer. To do.

  In the wafer processing method, the wafer is preferably a transparent body.

  According to the wafer processing method of the present invention, in the grinding step, the contact-type thickness measurement gauge is brought into contact with the back surface of the outer peripheral surplus region that remains without being divided into individual devices, so that it is divided into individual devices. There is an effect that the wafer can be ground while measuring the thickness of the wafer without bringing the device chip and the contact-type thickness measurement gauge into contact with each other. For this reason, it is possible to suppress contact between device chips due to contact of the contact-type thickness measurement gauge and scattering of the device chips.

Drawing 1 is an explanatory view of a protection member arrangement step of a processing method of a wafer concerning an embodiment. FIG. 2 is a schematic configuration diagram of a wafer to which a protective tape is attached in the protective member disposing step. FIG. 3 is an explanatory diagram of a modified layer forming step of the wafer processing method according to the embodiment. FIG. 4 is an explanatory diagram of the condensing point of the laser beam. FIG. 5 is an explanatory diagram of the modified layer formed inside the wafer. FIG. 6 is an explanatory diagram of a grinding step of the wafer processing method according to the embodiment. FIG. 7 is an explanatory view of a wafer to be ground while the thickness is measured. FIG. 8 is an explanatory view of a wafer divided into individual devices by a grinding step. FIG. 9 is a schematic cross-sectional view of the wafer shown in FIG.

  DESCRIPTION OF EMBODIMENTS Embodiments (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the structures described below can be combined as appropriate. In addition, various omissions, substitutions, or changes in the configuration can be made without departing from the scope of the present invention.

Embodiment
Drawing 1 is an explanatory view of a protection member arrangement step of a processing method of a wafer concerning an embodiment. FIG. 2 is a schematic configuration diagram of a wafer to which a protective tape is attached in the protective member disposing step. FIG. 3 is an explanatory diagram of a modified layer forming step of the wafer processing method according to the embodiment. FIG. 4 is an explanatory diagram of the condensing point of the laser beam. FIG. 5 is an explanatory diagram of the modified layer formed inside the wafer. FIG. 6 is an explanatory diagram of a grinding step of the wafer processing method according to the embodiment. FIG. 7 is an explanatory view of a wafer to be ground while the thickness is measured. FIG. 8 is an explanatory view of a wafer divided into individual devices by a grinding step. FIG. 9 is a schematic cross-sectional view of the wafer shown in FIG.

  This embodiment relates to a wafer processing method. As shown in FIG. 1, the wafer processing method according to the present embodiment includes a device area DA in which a device D is formed in an area partitioned by a plurality of intersecting scheduled lines S, and an outer periphery surrounding the device area DA. This is a method for processing a wafer W having a surplus area CA on the surface Wa. Further, in the wafer processing method according to the present embodiment, the wafer W is ground while measuring the thickness of the wafer W to be thinned to a predetermined thickness t (see FIG. 9) and is divided into individual devices D. A method includes a modified layer forming step, a protective member disposing step, and a grinding step.

  Here, the wafer W as a processing target is, for example, a transparent body such as glass, sapphire, or quartz, and is an optical device wafer or the like using the transparent body as a base material. The wafer W has, on the surface Wa, a device area DA in which the device D is formed in an area defined by a plurality of intersecting scheduled lines S, and an outer peripheral surplus area CA surrounding the device area DA. The plurality of division planned lines S that intersect each other are orthogonal, for example. The area defined by the plurality of division lines S that intersect each other is, for example, a square.

(Protective member placement step)
The protective member disposing step is a step of disposing the protective member PT on the surface Wa side of the wafer W on which the device D is formed before or after the modified layer forming step described later. In the present embodiment, the protective member PT is disposed on the surface Wa side of the wafer W before performing the modified layer forming step.

  The protective member PT is, for example, an adhesive tape that is attached to the surface Wa of the wafer W, and is a member that protects the device D. The protective member PT may have the same diameter as that of the wafer W, or may have a diameter larger than that of the wafer W and an outer peripheral edge attached to the opening peripheral edge of the annular frame. In that case, the wafer W is supported by the annular frame via the protective member PT.

  As shown in FIG. 2, when the protective member PT is disposed on the surface Wa side of the wafer W, the protective member disposing step ends.

(Modified layer formation step)
In the modified layer forming step, as shown in FIG. 3 to FIG. 5, the condensing point P of the laser beam L having a wavelength transmissive to the wafer W is positioned inside the planned division line S and irradiated with the laser beam L. This is a step of forming the modified layer K along the planned division line S except for the outer peripheral surplus area CA. In the present embodiment, after the protective member disposing step is performed, the modified layer K along the planned division line S is formed except for the outer peripheral surplus area CA. The modified layer forming step is performed by the laser processing unit 10 as shown in FIG. The laser processing unit 10 includes a chuck table 11, a laser beam irradiation unit 12, an imaging unit 13, and a laser processing unit moving unit (not shown).

  The chuck table 11 is a holding unit that holds the wafer W, and for example, sucks and holds the wafer W with a suction force by a negative pressure. The chuck table 11 has a disk shape in which a portion constituting the holding surface 11a is formed of porous ceramic or the like, and is connected to a vacuum suction source (not shown). On the holding surface 11a, the protective member PT side disposed on the wafer W in the protective member disposing step is placed. That is, the chuck table 11 sucks and holds the wafer W via the protective member PT, and the wafer W is placed on the holding surface 11a with the surface Wa side facing the holding surface 11a.

  As shown in FIGS. 3 and 4, the laser beam irradiation means 12 includes a condenser 12 a that irradiates a laser beam L, and a casing 12 b that houses a laser beam oscillation means (not shown). The condenser 12 a irradiates the wafer W held on the chuck table 11 with a laser beam L having a wavelength having transparency. Further, the condenser 12 a positions the condensing point P of the laser beam L within the division planned line S and irradiates the laser beam L.

  The condensing point P is set on the back surface Wb side with respect to a predetermined thickness t (see FIG. 9) at which the wafer W is thinned in a grinding step described later. That is, the condensing point P is set such that the depth d from the back surface Wb of the wafer W is shallower than the depth from the back surface Wb of the wafer W before the grinding step to the predetermined thickness t. Moreover, the laser beam L irradiated from the laser beam irradiation means 12 is a pulse laser, for example.

  In the present embodiment, the laser beam L is irradiated from the back surface Wb side of the wafer W. When the protective member PT is not disposed on the surface Wa of the wafer W, for example, when a modified layer forming step is performed before the protective member disposing step, a laser beam is emitted from the surface Wa side of the wafer W. L may be irradiated.

  The imaging means 13 is, for example, a camera using a CCD (Charge Coupled Device) image sensor. The imaging means 13 images a plurality of division lines S that the wafer W intersects to generate alignment adjustment image data.

  The laser processing unit moving means moves the chuck table 11 in the X-axis direction (corresponding to the machining feed direction), and moves the laser beam irradiation means 12 in the Y-axis direction (corresponding to the index feed direction). The laser beam irradiation means 12 is moved relative to each other. The laser processing unit moving means can also rotate the chuck table 11 around its central axis. The laser processing unit moving means irradiates the laser beam L irradiated from the condenser 12a along the planned division line S by moving the chuck table 11 in the processing feed direction. The laser processing unit moving means irradiates the laser beam L along the planned division line S in the device area DA as shown in FIGS. The modified layer K is formed.

  Further, the laser processing unit moving means irradiates the laser beam L with respect to all the division lines S in the same direction in the device area DA, and then rotates the chuck table 11 by 90 degrees so that the laser beam L from the laser beam irradiation means 12 is emitted. By repeating the irradiation in the same manner, the modified layer K is formed along all of the plurality of division lines S that intersect except for the outer peripheral surplus area CA.

  When the modified layer K is formed by irradiating the laser beam L along all of the plurality of scheduled division lines S that intersect except for the outer peripheral surplus area CA, the modified layer forming step ends. In the present embodiment, the X-axis direction is a direction orthogonal to the vertical direction. The Y-axis direction is a direction orthogonal to the X-axis direction and the vertical direction.

  Here, the modified layer K is a region where the density, refractive index, mechanical strength, and other physical characteristics are different from those in the surrounding area. The modified layer K is, for example, a melt treatment region, a crack region, a dielectric breakdown region, a refractive index change region, a region where these regions are mixed, or the like. In the present embodiment, the modified layer K has a condensing point P of the laser beam L set on the back surface Wb side with respect to a predetermined thickness t (see FIG. 9) at which the wafer W is thinned in a grinding step to be described later. Therefore, it is removed in the grinding step. Further, the modified layer K has a starting point that causes cracks CK (see FIG. 8) along the plurality of division lines S that intersect when the wafer W is thinned to a predetermined thickness t in the grinding step. It will be.

(Grinding step)
The grinding step is a step performed after performing the modified layer forming step and the protective member disposing step, and the protective member PT side is held by the chuck table 21 as shown in FIGS. In this step, the wafer W is ground from the back surface Wb of the wafer W by the grinding means 22 and thinned to a predetermined thickness t, and the device area DA of the wafer W is divided into individual devices D along the modified layer K. . The grinding step is performed by the grinding unit 20 as shown in FIG. Further, in the grinding step, the contact-type thickness measuring gauge 30 is ground while measuring the thickness of the wafer W by bringing it into contact with the back surface Wb of the outer peripheral surplus area CA of the wafer W on which the modified layer K is not formed.

  The grinding unit 20 includes a chuck table 21, a grinding unit 22, and a grinding unit moving unit (not shown). The grinding unit 20 is also provided with a contact-type thickness measurement gauge 30 that measures the thickness of the wafer W by contacting the back surface Wb of the wafer W.

  Similar to the chuck table 11 of the laser processing unit 10, the chuck table 21 sucks and holds the protection member PT side of the wafer W with a negative pressure. That is, the chuck table 21 sucks and holds the wafer W via the protective member PT, and the wafer W is placed on the holding surface 21a with the surface Wa side facing the holding surface 21a.

  The grinding means 22 includes a spindle housing 22a, a rotating spindle 22b that is rotatably supported by the spindle housing 22a and rotated by a rotation driving mechanism (not shown), a mounter 22c that is mounted on the rotating spindle 22b, and a mounter 22c. A grinding wheel 22d, a base 22e of the grinding wheel 22d, a grinding wheel 22f disposed on the lower surface of the base 22e, and a grinding water supply nozzle (not shown) for supplying grinding water are configured. The grinding means 22 contacts the back surface Wb side of the wafer W while rotating the grinding wheel 22 f in the same direction as the chuck table 21 to grind the wafer W.

  The grinding unit moving means rotates the chuck table 21 around its central axis, and moves the grinding means 22 in the Z-axis direction (corresponding to the grinding feed direction). The grinding unit moving means moves the grinding wheel 22 f rotating in the same direction as the chuck table 21 in the grinding feed direction, and brings the grinding wheel 22 f into contact with the back surface Wb of the wafer W. The grinding unit moving means feeds the grinding wheel 22f downward at a predetermined grinding feed speed, and grinds and thins the wafer W from the back surface Wb side. The grinding unit moving means grinds the grinding means 22 until the wafer W is thinned to a predetermined thickness t and the device area DA of the wafer W is divided into individual devices along the modified layer K. To send. That is, the grinding unit moving means stops the grinding feed of the grinding means 22 when the contact-type thickness measurement gauge 30 detects that the wafer W has been thinned to a predetermined thickness t. In the present embodiment, the Z-axis direction is the vertical direction.

  The contact-type thickness measurement gauge 30 is a thickness measurement unit that measures the thickness of the wafer W by contacting the back surface Wb of the wafer W in the grinding step. The contact-type thickness measuring gauge 30 uses a known thickness measuring means. Since the contact-type thickness measurement gauge 30 is not easily affected by the grinding water supplied from the grinding means 22 when the wafer W is ground, the non-contact-type thickness gauge 30 is being ground during the grinding of the wafer W by the grinding means 22. The thickness of the wafer W can be measured with higher accuracy than the measurement means. Moreover, even if the contact-type thickness measurement gauge 30 is a transparent body that cannot measure the thickness of the wafer W by the non-contact-type thickness measurement means, the thickness can be measured.

  The contact-type thickness measurement gauge 30 has a measurement head 31 for measuring the thickness of the wafer W. The measuring head 31 is provided with a probe 31a that contacts the back surface Wb of the outer peripheral surplus area CA of the wafer W on which the modified layer K is not formed. The measuring element 31a contacts the back surface Wb of the outer peripheral surplus area CA between the center side of the wafer W with respect to the notch Wc formed on the outer periphery of the wafer W and the outer peripheral side of the wafer W with respect to the device area DA. For this reason, for example, since the notch Wc is formed about 1.5 mm from the outer periphery to the inner side, the measuring element 31 a contacts the back surface Wb of the outer peripheral surplus area CA in a range of about 3 to 10 mm from the outer periphery to the inner side of the wafer W. To do.

  When the back surface Wb side of the wafer W is ground by the grinding means 22 while measuring the thickness of the wafer W by the contact-type thickness measuring gauge 30, a grinding load is applied to the modified layer K from the grinding wheel 22f. As shown in FIG. 8 and FIG. 9, a crack CK starting from the modified layer K and reaching the surface Wa is formed along the division line S.

  The modified layer K is ground and removed from the wafer W thinned to the predetermined thickness t. Further, in the wafer W thinned to a predetermined thickness t, the device area DA is divided into individual devices D by cracks CK along a plurality of division lines S except for the outer peripheral surplus area CA. The That is, the wafer W is divided into individual devices D along the modified layer K.

  When the wafer W is thinned to a predetermined thickness t and the device area DA is divided into individual devices D, the grinding step ends.

  Note that, after the grinding step, the device chip DC is formed by dividing the device area DA into the individual devices D, but the outer peripheral surplus area CA and the device chip DC are supported by the protective member TP. The form of the wafer W is maintained.

  In the device chip DC, since the modified layer K is removed when the back surface Wb of the wafer W is ground and thinned to a predetermined thickness t, the strength is not reduced by the modified layer K. .

  The outer peripheral surplus area CA remaining in the ring shape after the grinding step is removed by removal by a ring removal device (not shown) or excision by edge trimming, or the above-mentioned modification is applied to a modified layer that causes cracks during expansion processing by an expansion device (not shown). It may be divided at the time of expansion by forming it separately from the layer K.

  As described above, according to the wafer processing method according to the present embodiment, in the grinding step, the protective member PT side is held by the chuck table 21 of the grinding unit 20 and ground from the back surface Wb of the wafer W by the grinding means 22. The wafer W is thinned to a predetermined thickness t, and the device area DA of the wafer W is divided into individual devices D along the modified layer K. In the grinding step, a contact-type thickness measurement gauge 30 that contacts the back surface Wb of the wafer W and measures the thickness of the wafer W is used as a back surface of the outer peripheral surplus area CA of the wafer W on which the modified layer K is not formed. Grinding while measuring the thickness of the wafer W in contact with Wb. For this reason, the wafer W can be ground while measuring the thickness of the wafer W.

  Further, since the contact-type thickness measurement gauge 30 is brought into contact with the back surface Wb of the outer peripheral surplus area CA and the device chip DC is formed in the device area DA, the contact between the device chip DC and the contact-type thickness measurement gauge 30 is reduced. Can be avoided.

  Since contact between the device chip DC and the contact-type thickness measurement gauge 30 can be avoided, contact between the device chips DC due to contact with the contact-type thickness measurement gauge 30 and scattering of the device chip DC can be suppressed.

  In addition, the start point and the end point of the modified layer K formed inside the wafer W by irradiation with the laser beam L can be easily controlled. For this reason, the modified layer K can be easily formed in the device area DA while leaving the outer peripheral surplus area CA, and the outer peripheral surplus area CA can be left after the cutting step.

  Further, according to the wafer processing method of the present embodiment, since the wafer W is a transparent body, it is difficult to measure with a non-contact type thickness measuring means using reflected light. Although the thickness of the wafer W cannot be measured in the first place due to the influence of the above, etc., while measuring the thickness of an optical device wafer or the like having a transparent material such as glass, sapphire, quartz, etc. as a base material by the contact-type thickness measurement gauge 30 The wafer W can be ground and thinned to a predetermined thickness t.

  Since the wafer W can be ground while measuring the thickness of the transparent body and the wafer W can be thinned to a predetermined thickness t, when the wafer W is a transparent body, the wafer according to the present embodiment This processing method is indispensable.

  In the above embodiment, the wafer W is an optical device wafer or the like whose base material is glass, sapphire, quartz or the like, but the wafer W is not limited to a transparent body, and silicon, gallium arsenide (GaAs) or the like is used. It may be a semiconductor wafer or the like as a base material, and may be various processing materials such as an inorganic material substrate, a metal material, or a resin material.

21 Chuck table 22 Grinding means 30 Contact-type thickness measurement gauge CA Peripheral surplus area D Device DA Device area K Modified layer L Laser beam P Condensing point PT Protective member W Wafer Wa Surface Wb Back surface S Scheduled line t Predetermined thickness

Claims (2)

A method of processing a wafer having a device area in which devices are formed in an area partitioned by a plurality of intersecting scheduled lines and an outer peripheral surplus area surrounding the device area on a surface,
A condensing point of a laser beam having a wavelength having transparency to the wafer is positioned inside the planned division line and irradiated with the laser beam to form a modified layer along the planned division line except for the outer peripheral surplus region. A modified layer forming step;
Before or after performing the modified layer forming step, a protective member disposing step of disposing a protective member on the surface side of the wafer on which the device is formed;
After carrying out the modified layer forming step and the protective member disposing step, the protective member side is held by a chuck table and ground from the back surface of the wafer by a grinding means and thinned to a predetermined thickness, Grinding the device region of the wafer into individual devices along the modified layer; and
In the grinding step, a contact-type thickness measurement gauge that contacts the back surface of the wafer to measure the thickness of the wafer is brought into contact with the back surface of the outer peripheral surplus area of the wafer on which the modified layer is not formed. A method of processing a wafer, characterized by grinding while measuring the thickness.   The wafer processing method according to claim 1, wherein the wafer is a transparent body.

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