JP2015071198A - Grinding method of plate-like object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grinding method of a plate-like object which can suppress a possibility of breakage due to internal stress.SOLUTION: A grinding method of a plate-like object 11 includes: a stress detection step of detecting internal stress of a plate-like object by propagating an ultrasonic wave U to the plate-like object; a grinding condition setting step of setting a grinding condition in accordance with the internal stress of the plate-like object detected by the stress detection step; and a grinding step of grinding the plate-like object with grinding means by using the grinding condition set by the grinding condition setting step.

Description

  The present invention relates to a grinding method for a plate-like object represented by a semiconductor wafer or an optical device wafer.

  In recent years, in order to realize a small and lightweight device, it is required to thinly grind a plate-like object such as a semiconductor wafer or an optical device wafer. A plate-like object can be ground by holding the plate-like object on a holding table of a grinding apparatus and pressing a rotating grinding wheel against a work surface of the plate-like object (see, for example, Patent Document 1).

JP 2011-41991 A

  By the way, inside a semiconductor wafer having a device formed on the surface, an optical device wafer having an epitaxial film formed thereon, a WL-CSP (Wafer Level-Chip Size Package) wafer in which the device is sealed with a molding material, etc. are laminated. A large stress (internal stress) due to the structure is generated.

  Therefore, when these plate-like objects are thinly ground, the plate-like objects warp due to internal stress, and in some cases, the plate-like objects are damaged. Usually, since many devices are formed in these plate-shaped objects, if one plate-shaped object is damaged, many devices will be defective and loss will become very large.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a method for grinding a plate-like object that can suppress the possibility of damage due to internal stress.

  According to the present invention, there is provided a grinding method for a plate-like object, in which an ultrasonic wave is propagated through the plate-like object to detect an internal stress of the plate-like object, and the plate-like shape detected in the stress detection step. A grinding condition setting step for setting grinding conditions according to the internal stress of the object, and a grinding step for grinding the plate-like object by a grinding means using the grinding conditions set in the grinding condition setting step. A plate-like object grinding method is provided.

  In the present invention, it is preferable to further include a determination step of determining that grinding is not performed when the internal stress of the plate-like object detected in the stress detection step exceeds a predetermined value.

  The plate-like object grinding method of the present invention detects internal stress by propagating ultrasonic waves to the plate-like object, and grinds the plate-like object under the grinding conditions corresponding to the detected internal stress. The possibility of breakage of the plate-like object can be kept low.

It is a figure which shows typically the stress detection step which concerns on this Embodiment. It is a perspective view which shows typically the grinding step which concerns on this Embodiment.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The plate-like object grinding method according to the present embodiment includes a stress detection step (see FIG. 1), a grinding condition setting step, and a grinding step (see FIG. 2).

  In the stress detection step, stress (internal stress) is detected using a birefringent acoustoelastic method (acoustoelastic method) in which ultrasonic waves are propagated through the plate-like object. In the grinding condition setting step, grinding conditions are set such that the plate-like object is not easily damaged according to the detected stress. In the grinding step, the plate-like object is ground under the set grinding conditions. Hereinafter, the grinding method of the plate-shaped object which concerns on this Embodiment is explained in full detail.

  In the plate-like object grinding method of the present embodiment, first, a stress detection step of detecting the stress of the plate-like object is performed. FIG. 1 is a diagram schematically showing a stress detection step according to the present embodiment. As shown in FIG. 1, the stress detection step is performed using a stress detection device 2.

  The stress detection device 2 includes a piezoelectric element 4 that oscillates an ultrasonic wave U that vibrates in a direction perpendicular to the propagation direction and can detect the reflected wave R. The piezoelectric element 4 is disposed on the surface of the workpiece 11 so that the ultrasonic wave U can propagate in the thickness direction of the plate-like object 11.

  The plate-like object 11 is an optical device wafer in which an epitaxial film 15 constituting an optical device is provided on the surface side of the sapphire wafer 13. However, the configuration of the plate-like object 11 is not limited to this. For example, a semiconductor wafer having a device formed on the surface, a WL-CSP (Wafer Level-Chip Size Package) wafer in which the device is sealed with a molding material, or the like may be used as the plate-like object 11.

  A sound speed measuring device 6 is connected to the piezoelectric element 4. The sound velocity measuring device 6 is a device that measures the sound velocity by, for example, a single-around method, and integrates the time (propagation time) required from the oscillation of the ultrasonic wave U to the detection of the reflected wave R to obtain the ultrasonic wave U ( And the propagation speed (sound speed) of the reflected wave R) is calculated.

An arithmetic device 8 is connected to the sound speed measuring device 6. The computing device 8 calculates the acoustic anisotropy a corresponding to the stress of the plate-like object 11 based on the following formula (1), for example. In the following formula (1), v ₁ indicates the propagation speed of the ultrasonic wave U (or reflected wave R) that vibrates in the first direction perpendicular to the propagation direction, and v ₂ indicates the propagation direction and the first direction. The propagation speed of the ultrasonic wave U (or reflected wave R) oscillating in the second direction perpendicular to the direction is shown.

  In the stress detection step according to the present embodiment, the stress of the plate-like object 11 is detected by the birefringent acoustoelastic method using the stress detection device 2 described above. Here, the birefringent acoustoelastic method is a stress detection method that uses a phenomenon in which the velocity difference between two elastic vibration waves (sound waves) deflected in directions orthogonal to each other is proportional to the main stress difference.

In the birefringence acoustoelastic method, as shown in the above formula (1), the stress inside the object is quantified as a non-dimensionalized acoustic anisotropy (acoustic birefringence) a. Therefore, in the stress detection step, first, the ultrasonic wave U deflected in the first direction perpendicular to the thickness direction of the plate-like object 11 is oscillated by the piezoelectric element 4, the reflected wave R is detected, and the sound speed measuring device is detected. 6, the propagation velocity v ₁ is calculated.

In addition, the ultrasonic wave U deflected in the thickness direction of the plate-like object 11 and the second direction perpendicular to the first direction is oscillated by the piezoelectric element 4, the reflected wave R is detected, and the propagation velocity is detected by the sound velocity measuring device 6. v to calculate the _2. The ultrasonic wave U deflected in the second direction is oscillated, for example, by rotating the piezoelectric element 4 by 90 degrees in a plane parallel to the surface of the workpiece 11. After calculating the propagation velocities v ₁ and v ₂ , the calculation unit 8 calculates the acoustic anisotropy a of the plate-like object 11.

  As described above, the birefringent acoustoelastic method is suitable for the stress detection step according to the present embodiment because the acoustic anisotropy a corresponding to stress such as residual stress can be measured nondestructively. Further, according to this birefringent acoustoelastic method, the acoustic anisotropy a corresponding to the stress of the opaque plate-like object 11 can also be detected.

  The acoustic anisotropy a obtained as described above may be converted into stress. For example, the acoustic anisotropy a can be converted into stress by preparing in advance a table showing the relationship between the stress and the acoustic anisotropy a. This table may be stored, for example, in a memory (not shown) in the arithmetic device 8.

  After the stress detection step, a grinding condition setting step for setting grinding conditions for the plate-like object 11 according to the detected stress is performed. For example, the following table is stored in a memory (not shown) of the grinding apparatus 10 (see FIG. 2) for grinding the plate-like object 11 in the subsequent grinding step.

  The stress (or acoustic anisotropy a) of the plate-like object 11 detected in the stress detection step is sent from the stress detection device 2 to the grinding device 10. A controller (not shown) of the grinding apparatus 10 sets (selects) grinding conditions with reference to the stress received from the stress detection apparatus 2 and the table.

  That is, the controller of the grinding apparatus 10 sets the grinding feed speed (the descending speed of the spindle 16 (see FIG. 2)) to 2 (μm / s) when the stress of the plate-like object 11 is 100 to 200 (MPa). When the stress of the plate-like object 11 is 200 to 300 (MPa), the grinding feed rate is set to 1 (μm / s). When the stress of the plate-like object 11 is 300 to 400 (MPa), the grinding feed rate is set to 0.5 (μm / s), and the stress of the plate-like object 11 is 400 to 500 (MPa) In addition, the grinding feed rate is set to 0.3 (μm / s).

  Furthermore, the controller of the grinding device 10 determines that grinding is impossible when the stress of the plate-like object 11 exceeds 500 (MPa), and avoids grinding of the plate-like object 11. As described above, in the grinding condition setting step, when the stress of the plate-like object 11 exceeds a predetermined value, the plate-like object is determined in the grinding apparatus 10 by determining that grinding is impossible (grinding is not performed). The possibility that 11 will break can be reduced. Thereby, the maintenance of the grinding apparatus 10 becomes easy.

  In this grinding condition setting step, the grinding feed speed is set according to the stress of the plate-like object 11, but the grinding condition set in the grinding condition setting step is not limited to the grinding feed speed. For example, grinding conditions such as the amount of water to be supplied, the number of rotations of the chuck table 12 (see FIG. 2), and the number of rotations of the spindle 16 may be set in the grinding condition setting step.

  After the grinding condition setting step (including the determination step), a grinding step for grinding the plate-like object 11 under the set grinding conditions is performed. FIG. 2 is a perspective view schematically showing the grinding step.

  As shown in FIG. 2, the grinding apparatus 10 includes a holding table 12 that sucks and holds the plate-like object 11. A rotating mechanism (not shown) is provided below the holding table 12, and the holding table 12 rotates around the vertical axis by this rotating mechanism. Further, a moving mechanism (not shown) is provided below the holding table 12, and the holding table 12 moves in the horizontal direction by this moving mechanism.

  The surface of the holding table 12 is a holding surface for sucking and holding the plate-like object 11. 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 12, and a suction force for sucking the plate-like object 11 is generated.

  A grinding mechanism (grinding means) 14 is disposed above the holding table 12. The grinding mechanism 14 includes a spindle 16 that rotates about a vertical axis. The spindle 16 is lifted and lowered by a lifting mechanism (not shown).

  A disc-shaped wheel mount 18 is fixed to the lower end side of the spindle 16, and a grinding wheel 20 is attached to the wheel mount 18. The grinding wheel 20 includes a wheel base 20a formed of a metal material such as aluminum or stainless steel. A plurality of grinding wheels 20b are fixed to the annular lower surface of the wheel base 20a over the entire circumference.

  In the grinding step, first, the protective tape 21 is attached to the surface side (epitaxial film side) of the plate-like object 11. Next, the side of the protective tape 21 is brought into contact with the holding surface of the holding table 12 to apply a negative pressure of the suction source. Thereby, the plate-like object 11 is sucked and held by the holding table 12 via the protective tape 21. In this state, the back side of the plate-like object 11 is exposed upward.

  Next, the spindle 16 is lowered while rotating the holding table 12 and the spindle 16 in predetermined rotation directions, and the grinding wheel 20b is brought into contact with the back surface side of the plate-like object 11 as shown in FIG.

  The spindle 16 descends at a predetermined grinding feed speed set in the grinding condition setting step. Thereby, it can grind, without damaging the plate-shaped object 11. FIG. When the plate-like object 11 is ground to the finished thickness, the grinding step is finished. In addition, the thickness of the plate-like object 11 is measured in real time by a thickness measuring device (not shown).

  As described above, the plate-like object grinding method according to the present embodiment detects the stress (internal stress) by propagating the ultrasonic wave U to the plate-like object 11, and the grinding condition corresponding to the detected stress. Since the plate-like object 11 is ground by this, the possibility of damage to the plate-like object 11 due to stress can be kept low.

  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 ultrasonic wave U is propagated to the plate-like object 11 in the stress detection step, but the frequency (frequency) of the sound wave (elastic vibration wave) propagated to the plate-like object 11 is not particularly limited. . For example, sound waves in the audible range may be propagated to the plate-like object 11.

  Further, in the above embodiment, the ultrasonic wave U deflected in the first direction and the second direction is oscillated by rotating one piezoelectric element 4 by 90 degrees, but the ultrasonic wave deflected in the first direction is oscillated. A piezoelectric element that oscillates and a piezoelectric element that oscillates an ultrasonic wave deflected in the second direction may be provided separately. Similarly, an oscillation piezoelectric element and a detection piezoelectric element can be provided separately.

  In the above embodiment, the grinding condition is selected from a table prepared in advance in the grinding condition setting step (including the determination step). However, the grinding condition can be set by any method. For example, the grinding conditions may be set based on the detected stress and operator experience.

  Further, the stress detection step and the grinding condition setting step (including the determination step) may be repeated a plurality of times. For example, when grinding the plate-like object 11 whose stress changes with the progress of grinding, the stress detection step can be performed again at an arbitrary timing to reset the grinding conditions. Thereby, since it can respond to the change of the stress accompanying the progress of grinding, the possibility of breakage of the plate-like object 11 can be further reduced. Of course, in the grinding of the plate-like object 11 where the stress does not change, the stress detection step and the grinding condition setting step need only be performed once.

  Moreover, in the said embodiment, although the stress detection apparatus 2 and the grinding apparatus 10 are provided separately, the stress detection apparatus 2 may be integrated in the grinding apparatus 10. FIG. 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.

DESCRIPTION OF SYMBOLS 11 Plate-like object 13 Sapphire wafer 15 Epitaxial film 21 Protective tape 2 Stress detector 4 Piezoelectric element 6 Sonic measuring device 8 Arithmetic device 10 Grinding device 12 Holding table 14 Grinding mechanism (grinding means)
16 Spindle 18 Wheel mount 20 Grinding wheel 20a Wheel base 20b Grinding wheel U Ultrasonic wave R Reflected wave

Claims (2)

A method for grinding a plate-like object,
A stress detection step for detecting the internal stress of the plate-like object by propagating ultrasonic waves to the plate-like object;
A grinding condition setting step for setting grinding conditions according to the internal stress of the plate-like object detected in the stress detection step;
And a grinding step of grinding the plate-like object by a grinding means using the grinding condition set in the grinding condition setting step. 2. The plate-like object according to claim 1, further comprising a judgment step of judging that grinding is not performed when the internal stress of the plate-like object detected in the stress detection step exceeds a predetermined value. Grinding method.

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