JP2015198182A - Processing method of optical device wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of an optical device wafer capable of easily breaking a device wafer.SOLUTION: The method includes: a modified layer forming step of forming a modified layer (25) along a predetermined dividing line (17) inside an optical device wafer by irradiating with a laser beam (L) which is transparent with respect to an optical device wafer (11) while positioning a light condensing point (P) inside the optical device wafer; and a dividing step of dividing the optical device wafer into optical device chips including individual optical devices by applying external force to the optical device wafer on which the modified layer forming step is performed and breaking along the predetermined dividing line using the modified layer as a starting point of breaking. In the modified layer forming step, a laser beam condensed by a condenser (14) is used, in which the maximum value of a spherical aberration is +5 μm or more and +20 μm or less in a single crystal substrate forming the optical device wafer.

Description

  The present invention relates to a processing method for dividing an optical device wafer into a plurality of chips.

  A so-called optical device wafer in which an optical device such as a light emitting element is provided on the surface of a substrate made of a material such as sapphire is, for example, fractured starting from a modified layer formed along a street (scheduled division line). Divided into chips (optical device chips) (see, for example, Patent Document 1).

  This modified layer is formed inside the substrate by utilizing multiphoton absorption generated by condensing the laser beam, and is more fragile than other regions. Therefore, if an external force is applied in the vicinity of the modified layer, the optical device wafer can be broken along the street and divided into a plurality of chips.

JP 2013-105847 A

  By the way, the easiness of fracture of an optical device wafer largely fluctuates according to the state of the above-mentioned modified layer. Until now, it has been considered that a modified layer suitable for fracture of an optical device wafer can be formed by gathering laser beams to one point inside the substrate without deviation. That is, it has been regarded as important to reduce the aberration of the condenser that collects the laser beam.

  However, even if a modified layer is formed using a condenser with sufficiently small aberration, for example, an optical device wafer composed of a single crystal substrate (sapphire substrate) made of sapphire cannot always be easily broken. Had occurred.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical device wafer processing method capable of easily breaking an optical device wafer.

  According to the present invention, processing of an optical device wafer that divides an optical device wafer in which an optical device including a light-emitting layer is formed in a plurality of regions partitioned by lattice-shaped scheduled division lines formed on the surface of a single crystal substrate. A method of irradiating a laser beam having transparency to an optical device wafer with a condensing point positioned inside the optical device wafer, and forming a modified layer along the division line inside the optical device wafer. A modified layer forming step to be formed, and an external force is applied to the optical device wafer on which the modified layer forming step has been performed, and the modified layer is ruptured along the planned dividing line as a starting point of rupture. Dividing into optical device chips including individual optical devices, and in the modified layer forming step, the maximum value of spherical aberration is +5 in the single crystal substrate. Method of processing an optical device wafer, comprising the use of a condensed by laser radiation in the condenser to be more than + 20 [mu] m or less m is provided.

  In the present invention, the condenser comprises a birefringent lens that separates the laser beam into ordinary light and extraordinary light, and an objective lens that condenses the ordinary light and extraordinary light separated by the birefringent lens, respectively. Preferably, in the modified layer forming step, two modified layers are formed by ordinary light and extraordinary light.

  In the present invention, the single crystal substrate is preferably a sapphire substrate.

  In the method for processing an optical device wafer according to the present invention, a laser beam focused by a condenser having a maximum spherical aberration of +5 μm or more and +20 μm or less in a single crystal substrate is used. The laser beam is not collected too much in the single crystal substrate. As a result, a modified layer suitable for breaking can be formed to easily break the optical device wafer.

FIG. 1A is a perspective view schematically showing a configuration example of an optical device wafer according to the present embodiment, and FIG. 1B schematically shows an optical device wafer supported by an annular frame. It is a perspective view shown. It is a figure which shows a modified layer formation step typically. FIG. 3A is a diagram schematically showing an optical path of each light beam included in the laser beam, and FIG. 3B is an enlarged view showing a part of FIG. Graph showing the relationship between the position where the light beam that has passed through the collector intersects the optical axis (horizontal axis) and the height of the light beam that enters the collector (vertical axis) (vertical aberration display of spherical aberration) is there. It is a figure which shows typically the collector which concerns on a modification.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The optical device wafer processing method according to the present embodiment includes a modified layer forming step (FIGS. 2 to 5) and a dividing step.

  In the modified layer forming step, a street (divided) is formed inside the optical device wafer by using a laser beam condensed by a condenser in which the maximum spherical aberration is +5 μm or more and +20 μm or less in the substrate constituting the optical device wafer. A modified layer is formed along the planned line.

  In the dividing step, the optical device wafer is broken by applying an external force and divided into a plurality of optical device chips. Hereinafter, the processing method of the optical device wafer according to the present embodiment will be described in detail.

  FIG. 1A is a perspective view schematically showing a configuration example of the optical device wafer according to the present embodiment. As shown in FIG. 1A, the optical device wafer 11 is constituted by a substrate (single crystal substrate) having a thickness of about 100 μm to 1 mm made of a material such as sapphire or SiC, and the surface 11a is a central device. The area 13 is divided into an outer peripheral surplus area 15 surrounding the device area 13.

  The device region 13 is further divided into a plurality of regions by a plurality of streets (division lines) arranged in a lattice pattern, and each region includes a light emitting layer made of, for example, a GaN-based semiconductor material. Is formed. The outer periphery 11c of the optical device wafer 11 is chamfered, and the cross-sectional shape is an arc shape.

  FIG. 1B is a perspective view schematically showing an optical device wafer supported by an annular frame. A protective tape 21 having a diameter larger than that of the optical device wafer 11 is attached in advance to the surface 11 a side of the optical device wafer 11 described above. An annular frame 23 is fixed to the outer peripheral portion of the protective tape 21. As a result, the optical device wafer 11 is held on the annular frame 23 via the protective tape 21.

  In the optical device wafer processing method according to the present embodiment, first, a modified layer forming step of forming a modified layer along the street 17 inside the optical device wafer 11 is performed. FIG. 2 is a diagram schematically showing the modified layer forming step.

  This modified layer forming step is performed by, for example, the laser processing apparatus 2 shown in FIG. The laser processing apparatus 2 includes a chuck table 4 that holds the optical device wafer 11 by suction. Around the chuck table 4, there is provided a clamp 6 that holds and fixes the frame 23 holding the optical device wafer 11 from four directions.

  The chuck table 4 is connected to a rotation mechanism (not shown) such as a motor, and rotates around a rotation axis extending in the vertical direction. A moving mechanism (not shown) is provided below the chuck table 4, and the chuck table 4 is moved in the horizontal direction by the moving mechanism.

  The upper surface of the chuck table 4 is a holding surface 4 a that sucks and holds the surface 11 a side of the optical device wafer 11. A negative pressure of a suction source acts on the holding surface 4a through a flow path formed inside the chuck table 4, and a suction force for sucking the optical device wafer 11 is generated.

  A laser irradiation unit 8 for irradiating the optical device wafer 11 with the laser beam L is disposed above the chuck table 4. The laser irradiation unit 8 includes a laser oscillator 10 that oscillates a laser beam L having a wavelength that is difficult to be absorbed by the optical device wafer 11 (wavelength having transparency).

  The laser beam L oscillated by the laser oscillator 10 enters the condenser 14 through an optical element such as a mirror 12. The concentrator 14 is composed of, for example, a convex lens, and the inside of the optical device wafer 11 (the substrate constituting the optical device wafer 11) sucked and held by the chuck table 4 with the laser beam L oscillated by the laser oscillator 10. The light is condensed at a condensing point P inside. Further, the condenser 14 is configured to condense the laser beam L with a predetermined aberration.

  Specifically, the concentrator 14 is configured such that the maximum value of the spherical aberration generated when the laser beam L is collected is +5 μm or more and +20 μm or less in the substrate of the optical device wafer 11. More specifically, the maximum value of the spherical aberration viewed in the optical axis direction is +5 μm or more and +20 μm or less in the substrate.

  3A is a diagram schematically showing the optical path of each light beam constituting the laser beam L, and FIG. 3B is an enlarged view showing a part of FIG. 3A in an enlarged manner. 3A and 3B show representative optical paths L0, L1, L2, L3, and L4 in order from the optical axis A of the condenser 14. FIG.

  As described above, the condenser 14 according to the present embodiment is configured to generate a predetermined spherical aberration in the direction of the optical axis A. Therefore, as shown in FIGS. 3A and 3B, the optical paths L1, L2, L3, and L4 of the light beams constituting the laser light L intersect with each other at a position slightly shifted from the optical axis A.

  The spherical aberration in the direction along the optical axis A can be represented by a shift between a position where a paraxial light beam sufficiently close to the optical axis A intersects the optical axis A and a position where each light beam intersects the optical axis A. For example, it is assumed that the light beam passing through the optical path L1 is a paraxial light beam sufficiently close to the optical axis A. In this case, as shown in FIG. 3B, the spherical aberration SA of the light beam passing through the optical path L4 is a position where the light beam passing through the optical path L1 intersects with the optical axis A, and the position where the light beam passing through the optical path L4 intersects with the optical axis A. It is expressed by the deviation.

  FIG. 4 is a graph showing an example of the relationship between the position (horizontal axis) where the light beam that has passed through the collector 14 intersects the optical axis and the height of the light beam incident on the collector 14 (vertical axis). That is, FIG. 4 corresponds to a longitudinal aberration display of spherical aberration. The height of the light beam shown on the vertical axis in FIG. 4 is obtained by standardizing the distance from the optical axis A to the incident position of the light beam (the distance in the direction perpendicular to the optical axis A) by the diameter of the condenser 14. It is. Further, the sign of + (plus) on the horizontal axis indicates a shift toward the optical device wafer 11 side (front of the traveling direction of the light beam), and the sign of − (minus) indicates the collector 14 side (backward of the traveling direction of the light beam). ).

  In the example shown in FIG. 4, the maximum value of the spherical aberration (typically, the deviation of the light beam passing through the position farthest from the optical axis A (vertical axis: 1.00)) is about +8 μm. If the concentrator 14 is configured in this way, the laser beam L is not excessively collected in the substrate constituting the optical device wafer 11. Thereby, a modified layer suitable for breaking the optical device wafer 11 can be formed.

  In the modified layer forming step, first, the surface 11 a side of the optical device wafer 11 is sucked and held on the chuck table 4. Thereby, the back surface 11b side of the optical device wafer 11 is exposed upward. In this embodiment, an aspect in which the laser beam L is irradiated on the back surface 11b side of the optical device wafer 11 is shown, but the laser beam L may be irradiated on the surface 11a side of the optical device wafer 11.

  Next, the chuck table 4 is moved and rotated to align the laser irradiation unit 8 with the street 17 to be processed. After the alignment, the laser irradiation unit 8 irradiates the laser beam L toward the back surface 11b of the optical device wafer 11, and moves the chuck table 4 in a first direction parallel to the processing target street 17 (processing feed). Let That is, the optical device wafer 11 and the laser irradiation unit 8 are relatively moved in parallel with respect to the street 17 to be processed.

  When the laser beam L described above is condensed inside the optical device wafer 11, the vicinity of the condensing point P is modified. Therefore, by applying the laser beam L while relatively moving as described above, it is possible to form the modified layer 25 that is the starting point of the fracture of the optical device wafer 11 along the street 17 to be processed.

  After forming the modified layer 25 along the processing target street 17 as described above, the irradiation of the laser beam L is stopped, and the chuck table 4 is moved (indexed) in the second direction perpendicular to the processing target street 17. Feed).

  That is, the optical device wafer 11 and the laser irradiation unit 8 are relatively moved vertically with respect to the street 17 to be processed. Thereby, the laser irradiation unit 8 is aligned with the adjacent street 17.

  After the alignment, a similar modified layer 25 is formed along the adjacent street 17. After repeating this operation and forming the modified layer 25 along all the streets 17 extending in the first direction, the chuck table 4 is rotated by 90 ° around the rotation axis extending in the vertical direction, The modified layer 25 is formed along the street 17 extending in the second direction orthogonal to the direction. When the modified layer 25 is formed along all the streets 17, the modified layer forming step ends.

  After the modified layer forming step, the dividing step of applying an external force to break the optical device wafer and dividing it into a plurality of optical device chips including each optical device 19 is performed. In this division step, for example, an external force is applied to the optical device wafer 11 by using a method of expanding the tape attached to the optical device wafer 11 or a method of pressing the optical device wafer 11 along the street 17. .

  The modified layer 25 is formed on the street 17 of the optical device wafer 11, and the strength of the optical device wafer 11 is low in the street 17. Therefore, by applying an external force using the above-described method or the like, the optical device wafer 11 can be broken along the street 17 and divided into a plurality of optical device chips.

  Next, an experiment conducted to confirm the effectiveness of the optical device wafer processing method according to the present embodiment will be described. In this experiment, the modified layer 25 was formed using a plurality of concentrators having different spherical aberration maximum values as viewed in the optical axis direction, and the easiness to break the optical device wafer 11 was verified.

  The concentrator used in this experiment had a maximum value of spherical aberration in the optical axis direction of 0 μm, +5 μm, +10 μm, +15 μm, +20 μm, and +25 μm, respectively. In this experiment, an optical device wafer 11 composed of a sapphire substrate was used.

  The ease of breaking was confirmed by a method of pressing the optical device wafer 11 along the street 17. There are two types of pressing force for pressing the optical device wafer 11. The experimental results are shown in the following table. In the table below, a circle (◯) indicates that the fracture was possible with a weak pressing force, a triangle (Δ) indicates that the fracture was possible with a strong pressing force, and a cross (×) indicates a fracture. Indicates that it was not possible.

  From the above table, it can be seen that the optical device wafer 11 can be easily broken by using a condenser having a maximum spherical aberration of +5 μm to +20 μm as viewed in the optical axis direction. On the other hand, at 0 μm, the width of the modified layer 25 becomes too narrow (thin) with respect to the thickness of the optical device wafer 11, and the optical device wafer 11 cannot be broken. In addition, when the width is +25 μm, the width of the modified layer 25 can be sufficiently widened, but the energy density becomes too low to form the modified layer 25 suitable for fracture.

  From the above experimental results, it can be said that in order to easily break the optical device wafer, it is necessary to use a condenser having a maximum spherical aberration value of +5 μm to +20 μm (+5 μm or more and +20 μm or less). Further, it is more preferable to use a condenser having a maximum spherical aberration of +5 μm to +10 μm (+5 μm or more and +10 μm or less).

  As described above, in the method of processing an optical device wafer according to the present embodiment, the laser beam L collected by the condenser 14 having a maximum spherical aberration of +5 μm to +20 μm in the substrate (single crystal substrate). Therefore, the laser beam L used for forming the modified layer 25 is not condensed too much in the substrate. Thereby, the modified layer 25 suitable for breakage is formed, and the optical device wafer 11 can be easily broken.

  In addition, this invention is not limited to description of the said embodiment, A various change can be implemented. For example, the condenser 14 may be configured to be able to separate the laser beam L into ordinary light and abnormal light. In this case, in the modified layer forming step, it is possible to simultaneously form the two modified layers 25 by ordinary light and extraordinary light.

  FIG. 5 is a diagram schematically illustrating a light collector 14 according to a modification. As shown in FIG. 5, the condenser 14 according to the modification includes a birefringent lens 16 that separates the laser beam L into ordinary light La and extraordinary light Lb. The birefringent lens 16 includes, for example, a first optical element 18 and a second optical element 20 made of different materials.

  The first optical element 18 is made of, for example, LASF35 glass or the like, and has a convex surface 18a. The second optical element 20 is made of, for example, YVO4 crystal and has a concave surface 20a having a curvature corresponding to the convex surface 18a. The convex surface 18a of the first optical element 18 and the concave surface 20a of the second optical element 20 are joined.

  When the laser beam L is incident on the birefringent lens 16, the laser beam L is separated into ordinary light La and extraordinary light Lb according to an angle formed by the laser beam L and the second optical element 20 (crystal axis of the YVO4 crystal). . That is, the birefringent lens 16 transmits the ordinary light La without being refracted and refracts the extraordinary light Lb.

  Both the laser beam L separated into the ordinary light La and the extraordinary light Lb are collected by the objective lens 22. The objective lens 22 is typically a convex lens, and is configured, for example, such that the maximum value of spherical aberration is +5 μm or more and +20 μm or less.

  Thus, by using the lens unit constituted by the birefringent lens 16 and the objective lens 22 as the condenser 14, for example, as shown in FIG. 5, the condensing point Pa of the ordinary light La and the abnormal light Lb are obtained. The condensing point Pb can be shifted in the depth direction of the optical device wafer 11. As a result, two modified layers 25 having different depths can be formed simultaneously.

  The configuration of the birefringent lens 16 is not limited to the configuration shown in FIG. For example, the shape, material, etc. of the first optical element 18 and the second optical element 20 are changed, and the condensing point Pa of the ordinary light La and the condensing point Pb of the abnormal light Lb are changed to the front surface 11a (or the back surface) of the optical device wafer 11. It may be shifted in a direction parallel to 11b). In that case, two parallel modified layers 25 can be formed at the same depth.

  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 Optical device wafer 11a Front surface 11b Back surface 11c Outer periphery 13 Device area | region 15 Outer periphery excess area | region 17 Street (division plan line)
DESCRIPTION OF SYMBOLS 19 Optical device 21 Protective tape 23 Frame 25 Modified layer 2 Laser processing apparatus 4 Chuck table 4a Holding surface 6 Clamp 8 Laser irradiation unit 10 Laser oscillator 12 Mirror 14 Condenser 16 Birefringence lens 18 First optical element 18a Convex surface 20 First 2 Optical element 20a Concave surface 22 Objective lens A Optical axis L Laser beam L0, L1, L2, L3, L4 Optical path La Normal light Lb Abnormal light P, Pa, Pb Condensing point

Claims (3)

An optical device wafer processing method for dividing an optical device wafer in which an optical device including a light emitting layer is formed in a plurality of regions partitioned by lattice-shaped division lines formed on a surface of a single crystal substrate,
A modified layer that irradiates a laser beam having transparency to the optical device wafer with a focusing point positioned inside the optical device wafer, and forms a modified layer along the division line inside the optical device wafer. Forming step;
An optical device that includes an individual optical device by applying an external force to the optical device wafer that has undergone the modified layer forming step, breaking the modified layer along the planned dividing line using the modified layer as a starting point of breakage Dividing step of dividing into chips,
In the modified layer forming step, a laser beam collected by a condenser having a maximum spherical aberration of +5 μm or more and +20 μm or less in the single crystal substrate is used. The concentrator is a lens unit comprising a birefringent lens that separates the laser beam into ordinary light and extraordinary light, and an objective lens that condenses the ordinary light and extraordinary light separated by the birefringent lens, respectively.
2. The method of processing an optical device wafer according to claim 1, wherein in the modified layer forming step, two modified layers are formed by ordinary light and extraordinary light.   The method for processing an optical device wafer according to claim 1, wherein the single crystal substrate is a sapphire substrate.

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