Withdrawal procedure

Abstract

Lifting method for transferring an optical component layer (12) of an optical component wafer (10) to a transfer substrate, in which the optical component layer (12) is formed over a front surface (11a) of an epitaxial substrate (11) by means of a buffer layer (13) containing a Ga-containing Ga compound, wherein the lifting method comprises: a transfer substrate joining step for joining the transfer substrate (20) to an area of ​​the optical component layer (12) of the optical component wafer (10) by means of a connecting metal layer (21); a separating layer formation step for forming a separating layer (19) at an interface between the epitaxial substrate (11) and the buffer layer (13) by irradiating with a pulsed laser beam having a wavelength such that it is transmitted through the epitaxial substrate (11) and absorbed by the buffer layer (13), from a back surface (11b) of the epitaxial substrate (11) of the optical device wafer (10) to which the transfer substrate (20) is connected; and an optical component layer transfer step to bring into contact an ultrasonic horn (42) oscillating ultrasonic vibrations with the epitaxy substrate (11) after the separation layer formation step has been carried out, in order to set the epitaxy substrate (11) into vibration and to separate the epitaxy substrate (11) from the optical component layer (12) in order to transfer the optical component layer (12) to the transfer substrate (20), wherein the ultrasound horn (42) is brought into contact with an outer circumferential part of the epitaxy substrate (11), which is curved upwards by a distortion, during the optical component layer transfer step, and a contact surface of the ultrasound horn is convexly curved downwards for contact.

Description

BACKGROUND OF THE INVENTION AREA OF THE INVENTION

[0001] The present invention relates to a lifting method for transferring an optical component layer, which is stacked or arranged over an area of ​​an epitaxial substrate by means of a buffer layer, to a transfer substrate. DESCRIPTION OF THE RELATED STATE OF THE ART

[0002] In an optical device fabrication process, an optical device layer, consisting of an n-doped semiconductor layer and a p-doped semiconductor layer composed of GaN (gallium nitride) or similar materials, is formed by means of a buffer layer over an area of ​​an epitaxial substrate, such as a sapphire or silicon carbide substrate, which has a substantially circular wafer shape. Furthermore, optical devices, such as light-emitting diodes or laser diodes, are formed in a plurality of regions marked by a plurality of tracks, which are arranged in a grid-like pattern to form an optical device wafer. The individual optical devices are then fabricated by sectioning the optical device wafer along the tracks (see, for example, German patent application JP H10-305420A).

[0003] Furthermore, a manufacturing process known as lift-off is disclosed in patent application JP 2004-72052A as a technique for improving the luminance of optical components. In this process, an optical component layer, consisting of an n-doped semiconductor layer and a p-doped semiconductor layer, and formed by means of a buffer layer over a front surface of an epitaxial substrate, such as a sapphire substrate or a silicon carbide substrate forming an optical component wafer, is bonded to a transfer substrate of molybdenum (Mo), copper (Cu), or silicon (Si) using a bonding material such as AuSn (gold tin). The buffer layer is then refracted by irradiating it with a laser beam.The wavelength is broken down so that it is transmitted through the epitaxial substrate and absorbed by the buffer layer on the back surface of the epitaxial substrate. The epitaxial substrate is then separated from the optical component layer, thereby transferring the optical component layer to the transfer substrate.

[0004] Furthermore, the patent application JP 2013 - 229 508 A deals with a lifting process for transferring an optical component layer from a wafer to a transfer substrate, in which an optical component layer is laminated onto the surface of an epitaxial substrate via a buffer layer.

[0005] The patent application JP 2006 - 114 535 A further presents a process for the production of a nitride semiconductor element with a semiconductor functional layer and a substrate with high thermal conductivity, in which, after the growth of a semiconductor functional layer on a growth substrate, a substrate with high thermal conductivity is bonded to the semiconductor functional layer and then the growth substrate and the semiconductor functional layer are separated by irradiating the interface between the growth substrate and the semiconductor functional layer with ultrasonic waves. SUMMARY OF THE INVENTION

[0006] In the process where the buffer layer is irradiated with the laser beam as described above, the buffer layer may not be sufficiently disrupted in some cases, resulting in a problem where the epitaxial substrate cannot be cleanly separated from the optical component layer. For example, German patent application JP 2011-103361A discloses a technique in which ultrasonic waves are emitted onto a silicon substrate via purified water in which the silicon substrate is immersed, and a metal film on the silicon substrate is separated and removed. However, it does not disclose the timing of the transfer of the optical component layer as described above.

[0007] Therefore, it is an object of the present invention to provide a lifting method by which an epitaxial substrate can be cleanly separated even if a buffer layer cannot be sufficiently broken up.

[0008] In accordance with one aspect of the present invention, a detachment method is provided for transferring an optical component layer of an optical component wafer to a transfer substrate, wherein the optical component layer is formed over a front surface of an epitaxial substrate by means of a buffer layer composed of a Ga-containing Ga compound. The detachment method includes a transfer substrate joining step for connecting the transfer substrate to a surface of the optical component layer of the optical component wafer by means of a compound metal layer, and a separation layer formation step for forming a separation layer at an interface between the epitaxial substrate and the buffer layer by irradiation with a pulsed laser beam having a wavelength such thatthat it is transferred through the epitaxy substrate and absorbed by the buffer layer from a back surface of the epitaxy substrate of the optical device wafer to which the transfer substrate is connected, and includes an optical device layer transfer step to connect an ultrasonic horn oscillating ultrasonic vibrations with the epitaxy substrate after the separation layer formation step has been performed, in order to cause the epitaxy substrate to vibrate and to separate the epitaxy substrate from the optical device layer in order to transfer the optical device layer to the transfer substrate.

[0009] In accordance with the above lifting procedure, the ultrasonic horn is brought into contact with the epitaxial substrate to propagate the ultrasonic vibrations. Consequently, the vibrations can be efficiently propagated from the ultrasonic horn to the epitaxial substrate, and the coupling between the epitaxial substrate and the optical component layer via the buffer layer can be sufficiently broken. This prevents damage to the optical component layer due to the separation of the epitaxial substrate and allows for a quick and clean separation of the epitaxial substrate from the optical component layer.

[0010] In the lifting process of the present invention, the ultrasonic horn is brought into contact with an outer circumferential portion of the epitaxial substrate, which is curved upwards by a distortion, during the optical component layer transfer step, wherein a contact surface of the ultrasonic horn is convexly curved downwards. In accordance with this method, the vibrations from the ultrasonic horn to the epitaxial substrate can be propagated more efficiently.

[0011] The ultrasonic horn according to the present invention is used for the above-mentioned lifting method and is characterized in that the contact surface provided at the tip of the ultrasonic horn, which comes into contact with the epitaxial substrate, is designed as a slightly curved surface. According to this design, the efficiency of vibration propagation from the ultrasonic horn to the epitaxial substrate can be improved due to the curved surface of the tip of the ultrasonic horn, even if distortion or curvature is caused in the epitaxial substrate.

[0012] In accordance with the present invention, the ultrasonic horn is brought into contact with the outer circumferential part of the epitaxial substrate in order to propagate the ultrasonic vibration. This allows the buffer layer to be sufficiently disrupted and the epitaxial substrate to be cleanly separated.

[0013] The above and other problems, features and advantages of the present invention and the manner of its realization will become clearer with reference to the following description and the attached claims, with reference to the accompanying drawings, which show a preferred embodiment of the invention, and the invention itself is best understood by studying them. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a perspective view of an optical component wafer; Fig. 1B is an enlarged detail view of the optical component wafer; The Fig. 2A and Fig. 2B are perspective views showing a transfer substrate connection step; Fig. 2C is an enlarged detail view of a state in which a transfer substrate is bonded to the optical device wafer; Fig. Figure 3 is a schematic perspective view showing a step in the formation of a separating layer; Fig. Figure 4 is a schematic diagram showing the separation layer formation step; Fig. Figure 5 is a top view showing the trajectory of the emission position of a laser beam during the interface formation step; Fig. Figure 6 is a schematic perspective view showing an optical component layer transition step; Fig. Figure 7 is a schematic diagram to explain the optical component layer transfer step. Fig. Figure 8 is a top view showing the position of contact between an ultrasonic horn or an ultrasonic transducer and an epitaxy substrate during the optical component layer transfer step; Fig. Figure 9 is an explanatory diagram that can be enlarged by viewing a portion of the Fig. 7 has been produced; and

[0014] The Fig. 10A and Fig. Figure 10B shows schematic perspective views illustrating the optical component layer transfer step. DETAILED DESCRIPTION OF THE PREFERRED EXECUTION FORM

[0015] An optical component wafer 10, which is in the Fig. 1A and Fig. Figure 1B shows a wafer for fabricating optical components. The optical component wafer 10 has an epitaxial substrate 11, which is formed from a sapphire substrate having a circular disk shape with a diameter of 50 mm and a thickness of 60 µm, and an optical component layer 12, which is stacked on or formed on the side of a front surface 11a of the epitaxial substrate 11. The optical component layer 12 consists of an n-doped gallium nitride semiconductor layer 12A and a Fig. 1A a p-doped gallium nitride semiconductor layer 12B (not shown) is formed above the front surface 11a of the epitaxial substrate 11 by an epitaxial growth process. By layering or stacking the optical component layer 12 above the epitaxial substrate 11, a buffer layer 13 is formed, which is not shown in Fig. Figure 1A shows a GaN-composed optical component layer 12 with a thickness of, for example, 1 µm, formed between the front surface 11a of the epitaxial substrate 11 and the n-doped gallium nitride semiconductor layer 12B. In the present embodiment, the thickness of the optical component layer 12 is set to, for example, 10 µm. Optical components 16 are formed in a plurality of regions of the optical component layer 12, which are marked by a plurality of planned division lines 15 formed as a lattice (not shown in the figure). Fig. 1B shown).

[0016] The following describes a lifting procedure in accordance with the present embodiment with reference to the Fig. 2A to 10B described. As in the Fig. Figures 2A to 2C show a transfer substrate joining step for connecting a transfer substrate 20 to the side of the optics component layer 12 of the optics component wafer 10. Fig. Figure 2A is a schematic perspective view of the optical component wafer 10 and the transfer substrate 20 before joining. Fig. Figure 2B is a schematic perspective view of the optical component wafer 10 and the transfer substrate 20 after joining. Fig. 2C is an enlarged detail view of the main part of the optical component wafer 10 and the transfer substrate 20, which are connected to each other.

[0017] In the transfer substrate joining step, the transfer substrate 20, which consists of a 1 mm thick copper substrate, is joined to an area 12a of the optical component layer 12 by means of a compound metal layer 21. Molybdenum (Mo), silicon (Si), or similar materials can be used as the transfer substrate 20. Gold (Au), platinum (Pt), chromium (Cr), indium (In), palladium (Pd), or similar materials can be used as the compound metal to form the compound metal layer 21. In the transfer substrate joining step, the aforementioned compound metal is vapor-deposited onto an area 12a of the optical component layer 12 or an area 20a of the transfer substrate 20 to form the compound metal layer 21 with a thickness of approximately 3 µm.The bonding metal layer 21 is then produced so that it faces the surface 20a of the transfer substrate 20 or the surface 12a of the optical component layer 12, and a bonding pressure is exerted between them. This forms a composite substrate 25 in which the optical component wafer 10 and the transfer substrate 20 are bonded together by means of the bonding metal layer 21.

[0018] After the transfer substrate connection step has been carried out, as described in the Fig. 3, Fig. 4 to Fig. As shown in section 5, a separation layer formation step has been carried out. Fig. Figure 3 is a schematic perspective view to explain the separation layer formation step. Fig. Figure 4 is a schematic diagram to explain the separation layer formation step. Fig. Figure 5 is an explanatory top view showing the trajectory of the irradiation position of a laser beam.

[0019] In the separation layer formation step, the side of the transfer substrate 20 is placed on the upper surface (holding surface) of a holding or clamping table 31 in the laser processing device 30, separating it from the composite substrate 25. The composite substrate 25 is then held on the clamping table 31 by suction (not shown) by a suction unit that draws a back surface 11b of the epitaxy substrate 11 upwards. After this suction hold, a motion unit (not shown) is actuated to move a laser beam irradiation unit 32 and adjust the laser beam emission position of the laser beam irradiation unit 32 to the outermost perimeter of the epitaxy substrate 11. The laser beam irradiation unit 32 then performs irradiation from the side of the back surface 11b of the epitaxy substrate 11 (an upper side in the diagram) using a pulsed laser beam.In the laser beam emission unit 32, a laser beam tuned to a wavelength such that it is transmitted through the epitaxial substrate 11 and absorbed by the buffer layer 13 is oscillated by a laser beam oscillator 32a. The laser beam oscillated by the laser beam oscillator 32a is then reflected by a mirror 32b so that it strikes a condenser lens 32c. The converging lens 32c focuses the light onto the buffer layer 13 in order to irradiate the buffer layer 13 with the laser beam.

[0020] The mirror 32b is made of a galvanic mirror or similar material, and its reflection angle can be adjusted. The mirror 32b is adjusted to allow scanning with the laser beam focused by the converging lens 32c in any direction along the surface direction of the buffer layer 13. In the present embodiment, the scanning is carried out such that in the Fig. In the top view shown in Figure 5, the focal point of the laser beam follows a spiral trajectory from the outermost perimeter of the epitaxial substrate 11 towards the center. This irradiates the area corresponding to the entire surface of the buffer layer 13 with the laser beam. This laser irradiation disrupts the Ga bond in the buffer layer 13 and forms a separating layer 19, consisting of a plurality of N2 gas layers arranged in the form of islands, and a Ga layer at the interface between the epitaxial substrate 11 and the buffer layer 13 (see Figure 5). Fig. 8) Although in some cases formed over the entire surface of the buffer layer 13, the N2 gas layers tend to be more uniformly formed over a larger area when their positions are, as in Fig. 8 shown, are arranged closer to the outer perimeter of the buffer layer 13.

[0021] The separation layer formation step described above is carried out, for example, under the following laser processing conditions. Light source: pulsed YAG laser Wavelength: 257 nm Repetition rate: 50 kHz Average output power: 0.12 W Pulse width: 100 ps Peak power output: 5 µJ to 3 µJ Spot diameter: 70 µm Movement speed of the laser emission unit: 50 mm / s to 100 mm / s

[0022] After the separation layer formation step has been carried out, as described in the Fig. Figures 6 to 10B show an optical component layer transfer step to separate the epitaxy substrate 11 from the optical component layer 12 in order to transfer the optical component layer 12 to the transfer substrate 20. Fig. Figure 6 is a schematic perspective view to illustrate the optical component layer transfer step. Fig. Figure 7 is a schematic diagram to explain the optical component layer transfer step. Fig. Figure 8 is an explanatory top view showing the position of the contact of an ultrasound horn with the epitaxy substrate during the optical component layer transfer step. Fig. Figure 9 is an explanatory diagram that can be enlarged by viewing a portion of the Fig. 7 has been produced. Fig. Figure 10A is a schematic perspective view to illustrate a state immediately before the transfer of the optical component layer. Fig. Figure 10B is a schematic perspective view to illustrate a state in which the optical component layer is being transferred.

[0023] In the optical component layer transfer step, the side of the transfer substrate 20 is placed on the upper surface (holding surface) of a holding table 41 at the transfer device 40. The composite substrate 25 is then held on the holding table 41 by suction (not shown) with the back surface 11b of the epitaxy substrate 11 facing upwards. Subsequently, a vibration generation unit 43 connected to an ultrasonic horn 42 is actuated to provide the ultrasonic horn 42 with an ultrasonic vibration. This vibration generation causes the ultrasonic horn 42, which has a circular cylindrical shape, to oscillate ultrasonic vibrations. Then, a tip surface 42a, or a surface at the tip of the ultrasonic horn 42, as shown in Fig. Figure 7 shows that in this state, the ultrasonic horn 42 is brought into contact with an arbitrary position on the outer circumferential part of the epitaxy substrate 11. The ultrasonic vibration of the ultrasonic horn 42 is thereby propagated to the epitaxy substrate, causing the epitaxy substrate 11 to vibrate. The contact position of the ultrasonic horn 42 can be set to any position on the back surface 11b of the epitaxy substrate 11. However, it is preferred to set the position at the outer circumferential part of the epitaxy substrate 11, and even more preferably, the outermost circumference of the epitaxy substrate 11 and the outermost circumference of the ultrasonic horn 42 are brought as close together as possible. Even more preferably, these outermost circumferences coincide.

[0024] As seen in the enlarged view in Fig. As shown in Figure 9, a distortion or warping occurs on the outer circumferential side of the composite substrate 25. In particular, when the composite substrate 25 is positioned such that the back surface 11b of the epitaxial substrate 11 faces upwards, a distortion occurs such that the outer circumference of the composite substrate 25 is curved upwards. This is due to the difference in the coefficient of thermal expansion between the transfer substrate 20 and the optical component wafer 10, which are bonded together, etc. Meanwhile, the tip surface, i.e., the contact surface, 42a of the ultrasonic horn 42, which has been brought into contact with the back surface 11b of the epitaxial substrate 11, is formed from a slightly curved surface.Therefore, the tip surface 42a of the ultrasound horn 42 achieves line or surface contact along the rear surface 11b of the epitaxial substrate 11, causing distortion, which can lead to an increase in the contact area between them. As a result, the ultrasonic vibration can be efficiently propagated by fixing the contact position of the tip surface 42a of the ultrasound horn 42 at the outer circumferential part of the epitaxial substrate 11. The curved surface formed by the tip surface 42a is shaped similarly to the lower part of the spherical surface with a predetermined diameter, for example, to obtain a downwardly convex curved surface.

[0025] It is assumed that the ultrasonic vibration is transmitted from the epitaxial substrate 11 via the N2 gas layers 19a of the separation layer 19, as in Fig. Figure 8 shows how the N2 gas layers are propagated. In the outer circumferential part of the epitaxial substrate 11, with which the ultrasonic horn 42 comes into contact, the N2 gas layers 19a are formed over a wide area in the separating layer 19, so that vibrations can oscillate from a position that is close to the N2 gas layer 19a, such as a position directly above the N2 gas layer 19a. This can also further improve the efficiency of the vibration propagation.

[0026] Furthermore, using a curved surface as the tip surface 42a of the ultrasonic horn 42 makes it possible to propagate the ultrasonic vibration radially from the tip surface 42a. In contrast, with a design where the tip surface of the ultrasonic horn 42 is flat, the vibration is only propagated in the direction perpendicular to this flat surface. Therefore, when a curved surface is used as the tip surface 42a, the ultrasonic vibration can be propagated diffusely, and the efficiency of the vibration propagation can be further improved.

[0027] The optical component layer transition step is carried out by adjusting the states of the ultrasonic horn 42, which has a circular cylindrical shape, and the vibration provision unit 43, for example as follows.

[0028] Diameter of the circular cylinder: 15 mm; Radius of curvature of the tip surface 42a: 300 mm; Ultrasonic frequency: 20 kHz; Ultrasonic amplitude: 20 µm

[0029] The above-mentioned respective states of the tip surface 42a are unrelated to the diameter size of the optical component wafer 10, and the shape of the ultrasonic horn 42 does not need to be changed even if the diameter size of the optical component wafer 10 changes. For example, it is possible to respond to a change in the diameter size of the optical component wafer 10 by changing the ultrasonic amplitude to a larger amplitude if the diameter size of the optical component wafer 10 increases.

[0030] After the ultrasonic vibrations have been supplied by the ultrasonic horn 42, as in Fig. As shown in Figure 10A, a movement unit 45 is actuated to lower a suction pad 146, and a suction surface, i.e., the lower surface, of the suction pad 46 is placed on the back surface 11b of the epitaxial substrate 11 at the composite substrate 25. Subsequently, the back surface 11b of the epitaxial substrate 11 is drawn against the suction surface of the suction pad 46 by actuating a suction source 47. As shown in Fig. As shown in Figure 10B, the motion unit 45 is then actuated to lift the suction pad 46 in such a direction as to detach it from the holding table 41. This separates the epitaxial substrate 11 from the optical component layer 12, thus completing the transfer of the optical component layer 12 to the transfer substrate 20.

[0031] As described above, in the detachment process according to the present embodiment, an ultrasonic vibration can be efficiently propagated by bringing the ultrasonic horn 42 into contact with the outer circumferential part of the epitaxial substrate 11. This can sufficiently break the coupling between the epitaxial substrate 11 and the optical component layer 12 through the buffer layer 13. As a result, damage to the optical component layer 12 due to the separation of the epitaxial substrate 11 can be avoided, and the epitaxial substrate 11 can be quickly and cleanly separated from the optical component layer 12. According to the method of the present embodiment, the epitaxial substrate 11 can be separated from the optical component layer 12 even in the case of a structured sapphire substrate (PSS), where separation is considered difficult, as well as in the case of a 4-inch wafer.

[0032] The present invention is not limited to the embodiment described above and can be carried out with various modifications. In the embodiment described above, the sizes, shapes, and so forth of the respective components are not limited to those shown in the attached drawings and can be appropriately modified within a range where effects of the present invention are achieved. Other factors can likewise be implemented with appropriate modifications without departing from the scope of protection of the object of the present invention. For example, in the embodiment described above, the respective steps described above can be carried out by different device parts or devices, or they can be carried out by the same device.

[0033] The present invention is not limited to the details of the preferred embodiment described above. The scope of protection of the invention is defined by the attached claims.

Claims

[1] Lifting method for transferring an optical component layer (12) of an optical component wafer (10) to a transfer substrate, in which the optical component layer (12) is formed over a front surface (11a) of an epitaxial substrate (11) by means of a buffer layer (13) containing a Ga-containing Ga compound, wherein the lifting method comprises: a transfer substrate joining step for joining the transfer substrate (20) to an area of ​​the optical component layer (12) of the optical component wafer (10) by means of a connecting metal layer (21); a separating layer formation step for forming a separating layer (19) at an interface between the epitaxial substrate (11) and the buffer layer (13) by irradiating with a pulsed laser beam having a wavelength such that it is transmitted through the epitaxial substrate (11) and absorbed by the buffer layer (13), from a back surface (11b) of the epitaxial substrate (11) of the optical device wafer (10) to which the transfer substrate (20) is connected; and an optical component layer transfer step to bring into contact an ultrasonic horn (42) oscillating ultrasonic vibrations with the epitaxy substrate (11) after the separation layer formation step has been carried out, in order to set the epitaxy substrate (11) into vibration and to separate the epitaxy substrate (11) from the optical component layer (12) in order to transfer the optical component layer (12) to the transfer substrate (20), wherein the ultrasound horn (42) is brought into contact with an outer circumferential part of the epitaxy substrate (11), which is curved upwards by a distortion, during the optical component layer transfer step, and a contact surface of the ultrasound horn is convexly curved downwards for contact.

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