WAFER MANUFACTURING PROCESS

Abstract

Wafer manufacturing process for producing a wafer (W) from an ingot (2) after forming a separating layer (28) inside the ingot (2) by setting a focal point (FP) of a laser beam (LB) having a transmission wavelength for the ingot (2) onto a predetermined depth inside the ingot (2) from an end face (4) of the ingot (2), wherein the predetermined depth corresponds to a thickness of the wafer (W) to be produced, and next applying the laser beam (LB) to the ingot (2), wherein the wafer manufacturing process comprises: a first ultrasonic vibration application step involving the application of ultrasonic vibrations of a first density to a predetermined area of ​​the ingot (2) in order to form a partially fractured section (29) where part of the separating layer (28) is fractured; After performing the first ultrasonic vibration application step, a second ultrasonic vibration application step is performed, applying the ultrasonic vibrations with a second density lower than the first density to an entire area of ​​the ingot (2) larger than the predetermined area, in order to form a fully fractured section (29') in which the interface (28) is completely fractured in such a way that the fracture begins from the partially fractured section (29); and a separation step involving the separation of the wafer (W) along the fully broken section (29') from the ingot (2).

Description

BACKGROUND OF THE INVENTION AREA OF THE INVENTION

[0001] The present invention relates to a wafer manufacturing process for producing a wafer from an ingot after forming a separating layer inside the ingot by setting a focal point of a laser beam having a transmission wavelength for the ingot at a predetermined depth inside the ingot from an end face of the ingot, wherein the predetermined depth corresponds to the thickness of the wafer to be produced, and next applying the laser beam to the ingot. DESCRIPTION OF THE RELATED STATE OF THE ART

[0002] A wide variety of electronic components, such as integrated circuits (ICs), large scale integrations (LSIs) and light-emitting diodes (LEDs), are formed by creating a functional layer on the front side of a wafer made of silicon (Si), sapphire (Al2O3) or similar materials and dividing this functional layer into a multitude of separate areas along a multitude of intersecting dividing lines.

[0003] The dividing lines of the wafer containing these components are processed by a machining device, such as a cutting device or a laser processing device, to separate the wafer into a multitude of individual component chips, each corresponding to a specific component. The resulting component chips are used in a wide variety of electronic equipment, such as mobile phones and personal computers. Furthermore, power components or optical components, such as LEDs, are formed by creating a functional layer on the front face of a wafer made of hexagonal silicon carbide single crystal (SiC single crystal) and dividing this functional layer into a multitude of separate regions along a multitude of intersecting dividing lines.

[0004] Generally, the wafer on which the devices are formed is produced by cutting an ingot with a wire saw. Both sides of the wafer cut from the ingot are then polished to a high gloss (see, for example, JP 2000-94 221 A). However, when the ingot is cut with a wire saw and both sides of each wafer are polished to obtain the product, 70% to 80% of the ingot becomes scrap, resulting in poor economics. In particular, a hexagonal SiC single-crystal ingot has high hardness and is therefore difficult to cut with a wire saw. Consequently, a considerable amount of time is required to cut the ingot, leading to reduced productivity. Furthermore, since this ingot has high unit costs, there is the problem of efficiently producing a wafer using this prior art.

[0005] A technique for solving this problem has been proposed by the present applicant. This technique includes the steps of focusing the focal point of a laser beam, having a transmission wavelength suitable for hexagonal SiC single crystals, into the interior of a SiC ingot; next, applying the laser beam to the ingot by scanning the laser beam across the ingot to form a separation layer in a predetermined parting plane within the ingot; and next, separating a wafer from the ingot along the separation layer (see, for example, patent application JP 2016-111143A). Furthermore, a similar technique has also been proposed.This technique includes the steps of adjusting the focal point of a laser beam, which has a transmission wavelength for hexagonal Si single crystal, to a predetermined depth inside the ingot from an end face of the ingot, the predetermined depth corresponding to the thickness of a wafer to be produced; next, applying the laser beam to the ingot by scanning the laser beam across the ingot to form a modified section at this predetermined depth inside the ingot; and next, separating the wafer from the ingot along this modified section (see, for example, patent application JP 2011 - 060 862 A).

[0006] Furthermore, patent application JP 2018 - 133 484 A discloses a process for producing a wafer from a silicon carbide single-crystal ingot using a laser beam to form a peelable layer inside the ingot and ultrasonic waves of a predetermined frequency to detach the wafer via the peelable layer. Patent application DE 10 2017 222 047 A1 also deals with such a process. SUMMARY OF THE INVENTION

[0007] In accordance with the techniques described in German patent applications JP 2016-111143A and JP 2011-060862A, the amount of ingot that becomes scrap when manufacturing the wafer from the ingot is reduced compared to using a wire saw to cut the ingot, thus mitigating the problem of poor economics. However, separating the wafer from the ingot along the parting line or modified section formed by applying a laser beam inside the ingot is not straightforward, so efficient manufacturing remains a challenge.

[0008] It is therefore an object of the present invention to provide a wafer manufacturing process that can efficiently produce a wafer from a hexagonal SiC single crystal ingot.

[0009] In accordance with one aspect of the present invention, a wafer manufacturing method is provided for producing a wafer from an ingot after forming a separating layer inside the ingot by setting a focal point of a laser beam having a transmission wavelength for the ingot at a predetermined depth inside the ingot from an end face of the ingot, wherein the predetermined depth corresponds to a thickness of the wafer to be produced, and next applying the laser beam to the ingot, wherein the wafer manufacturing method comprises: a first ultrasonic vibration application step with applying an ultrasonic vibration with a first density to a predetermined area of ​​the ingot in order to form a partially fractured section where part of the separating layer is fractured;After performing the first ultrasonic vibration application step, a second ultrasonic vibration application step is performed, applying the ultrasonic vibration with a second density lower than the first density to an entire area of ​​the ingot larger than the predetermined area, thereby forming a fully fractured section where the interface is so completely fractured that fracture originates from the partially fractured section; and a separation step is performed, separating the wafer from the ingot along the fully fractured section.

[0010] Preferably, the ultrasonic vibration is applied to the ingot by a layer of water during the first and second ultrasonic vibration application steps.

[0011] Preferably, the ingot encloses a hexagonal SiC single-crystal ingot with a c-axis and a c-plane perpendicular to the c-axis, and the separating layer is constructed with a modified section and cracks extending isotropically from the modified section along the c-plane, wherein the modified section is formed by setting a focal point of a laser beam having a transmission wavelength suitable for hexagonal SiC single crystal on a predetermined depth inside the SiC ingot from one end face of the SiC ingot, the predetermined depth corresponding to the thickness of the wafer to be produced, and next applying the laser beam to the SiC ingot to decompose SiC into Si and C.

[0012] Preferably, the c-axis is inclined with a deviation angle with respect to a perpendicular to one end face of the SiC ingot, wherein the deviation angle is formed between the c-plane and the one end face, the focal point of the laser beam is moved in a direction perpendicular to a formation direction of the deviation angle in order to continuously form the modified section in the direction perpendicular to the formation direction of the deviation angle, and the focal point of the laser beam is further moved in the formation direction of the deviation angle in a region that is not larger than a formation region of the cracks, whereby a plurality of linear modified sections in the formation direction of the deviation angle are arranged side by side in such a way that the cracks extending from any adjacent of the plurality of linear modified sections overlap.

[0013] In accordance with the wafer manufacturing process of the present invention, the amount of ingot that becomes scrap when producing the wafer from the ingot can be greatly reduced compared to using a wire saw to cut the ingot. Furthermore, the first ultrasonic vibration application step is performed at a high density on a portion of the ingot, thereby forming the partially fractured section. Subsequently, the second ultrasonic vibration application step is performed at a low density to apply ultrasonic vibration to the entire ingot, thereby forming the fully fractured section by spreading from the partially fractured section. Consequently, the fully fractured section is formed from the separation layer that was previously formed within the interior of the ingot.Accordingly, the wafer to be produced can be separated from the ingot in a simple and efficient manner along the completely broken section.

[0014] The above and other problems, features and advantages of the present invention and the manner of its implementation will become clearer by studying the following description and the attached claims with reference to the attached drawings, which show a preferred embodiment of the invention, and the invention itself will be best understood by this. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a side view of an ingot formed from a hexagonal SiC single crystal; Fig. 1B is a top view of the Fig. 1A depicted ingots; Fig. Figure 2 is a perspective view showing a way of attaching a substrate to the surface shown in the Fig. 1A and Fig. 1B shows the ingot shown and the subsequent placement of the ingot with the substrate on a clamping table; Fig. 3A is a perspective view showing a formation step of a separating layer inside the ingot; Fig. 3B is a side view showing the Fig. 3A represents the step shown; Fig. 4A is a top view of the ingot in the state where the separating layer is formed by performing the in Fig. 3A shows the step that has been formed inside the ingot; Fig. 4B is a section view along line BB from Fig. 4A; Fig. 5A is a perspective view showing a first ultrasonic vibration application step using a high-density ultrasonic vibration generating device; Fig. 5B is a sectional view showing the Fig. 5A represents the first ultrasonic vibration application step; Fig. Figure 6A is a perspective view showing a second ultrasonic vibration application step using a low-density ultrasonic vibration generating agent; Fig. 6B is a sectional view showing the Fig. 6A represents the second ultrasonic vibration application step; Fig. 7A is a perspective view representing a separation step; and Fig. 7B is a sectional view showing the Fig. 7A represents the separation step shown. DETAILED DESCRIPTION OF THE PREFERRED EXECUTION FORM

[0015] A wafer manufacturing process in accordance with a preferred embodiment of the present invention will now be described in detail with reference to the attached drawings. Fig. 1A and Fig. Figure 1B represents an ingot 2 in accordance with this preferred embodiment. The ingot 2 is a hexagonal SiC single-crystal ingot of this preferred embodiment, having a substantially cylindrical shape. For example, the ingot 2 has a diameter of approximately 100 mm. The ingot 2 has a substantially circular first end face 4, a substantially circular second end face 6 opposite the first end face 4, a substantially cylindrical surface 8 configured to connect the first end face 4 and the second end face 6, and a c-axis ( <0001> -direction), extending from the first end face 4 to the second end face 6, and a c-plane ({0001}-plane) perpendicular to the c-axis. In ingot 2, the c-axis is inclined with respect to a perpendicular 10 to the first end face 4 by a deviation angle α (for example, α equal to 1°, 3°, or 6°).The angle of deviation α is formed between the c-plane and the first end surface 4. The direction of formation of the angle of deviation α, that is, the inclination direction of the c-axis, is shown in the . Fig. 1A and Fig. 1B is represented by an arrow A. Furthermore, the cylindrical surface 8 of the ingot 2 is formed with a first alignment plane 12 and a second alignment plane 14, which are perpendicular in the side view and serve to indicate a crystal orientation. The first alignment plane 12 is parallel to the formation direction A of the deviation angle α, and the second alignment plane 14 is perpendicular to the formation direction A of the deviation angle α. As in Fig. As shown in Figure 1B, which is a top view of the ingot 2, the length L2 of the second alignment plane 14 is shorter than the length L1 of the first alignment plane 12 (L1 > L2). Accordingly, the orientation A of the deviation angle α can be determined independently of whether the first end face 4 is the front face of the ingot 2 or not. The ingot to be used for the wafer manufacturing process in accordance with the present invention is not limited to the hexagonal SiC single-crystal ingot mentioned above, but the usable ingot can be an ingot whose c-axis is not inclined relative to the perpendicular to the first end face, that is, an ingot that has a structure such that the deviation angle α between the c-plane and the first end face is 0° (that is, an ingot that has a structure such that the perpendicular to the first end face coincides with the c-axis).

[0016] In the wafer manufacturing process according to this preferred embodiment, a separation layer formation step is first carried out to form a separation layer by adjusting the focal point of a laser beam having a transmission wavelength for the ingot 2 to a predetermined depth within the ingot 2, the predetermined depth corresponding to the thickness of a wafer to be produced, and next the laser beam is applied to the ingot 2. The separation layer formation step is now described with reference to the Fig. 2 to 4B described.

[0017] During the execution of the separation layer formation step, a circular substrate 16, as shown in Fig. 2, is attached to the second end face 6 of the ingot 2 via an adhesive or similar substance. The ingot 2 with the substrate 16 is then transferred to a laser processing device 18, from which a part is Fig. Figure 2 shows the laser processing device 18, which includes a clamping table 20. The clamping table 20 has an upper surface formed with a circular vacuum clamping element 24. The vacuum clamping element 24 is made of a porous ceramic that allows air to pass through. The size (diameter) of the vacuum clamping element 24 is slightly smaller than that of the substrate 16. A suction element (not shown) is connected to the vacuum clamping element 24. The ingot 2 with the substrate 16, thus transferred to the laser processing device 18, is placed on the vacuum clamping element 24 of the clamping table 20 in such a way that the substrate 16 is in contact with the upper surface of the vacuum clamping element 24. Accordingly, the first end face 4 of the ingot 2 is oriented upwards on the clamping table 20. The suction device is then activated to hold the ingot 2 with the substrate 16 against the vacuum clamp 24 via a vacuum.In the present invention, the substrate 16 to be attached to the ingot 2 is not essential. That is to say, the substrate 16 can be omitted, provided that the vacuum clamping device 24 of the clamping table 20 has a size and shape capable of holding the ingot 2 directly against the vacuum clamping device 24 by means of a vacuum.

[0018] After the ingot 2 is held on the clamping table 20, a focal point of a laser beam, having a transmission wavelength suitable for the SiC single crystal forming the ingot 2, is focused at a predetermined depth from the first end face 4 of the ingot 2 within the ingot 2, the predetermined depth corresponding to the thickness of a wafer to be produced. The laser beam is then applied to the first end face 4 of the ingot 2, forming a separation layer in which SiC decomposes into Si and carbon (C), and cracks form isotropically in the c-plane. The first end face 4 is a mirror surface that has been previously prepared by grinding and polishing to remove roughness. The separation layer formation step is now described with reference to the Fig. Sections 3A to 4B are described in more detail.

[0019] As in Fig. As shown in Figure 3A, the laser processing device 18, a part of which is shown, includes, in addition to the clamping table 20, a focusing device 22. The focusing device 22 serves to apply a pulsed laser beam LB to the ingot 2. The clamping table 20 is configured to be rotated about its vertical axis by a motor (not shown). Furthermore, the clamping table 20 is configured to be moved by an X-movement mechanism (not shown) in the direction indicated by an arrow X in Fig. The clamping table 20 is to be moved in the X-direction shown in Figure 3A with respect to the focusing device 22. This means that the clamping table 20 is configured to be fed or moved in the X-direction. Furthermore, the clamping table 20 is configured to be moved by a Y-movement mechanism (not shown) in the direction indicated by an arrow Y in Figure 3A. Fig. The focusing device 22 is to be moved in the Y-direction shown in Figure 3A with respect to the focusing device 22, where the Y-direction is perpendicular to the X-direction. This means that the clamping table 20 is configured to be moved or fed in the Y-direction. The focusing device 22 includes a focusing lens (not shown) for focusing the pulsed laser beam LB inside the ingot 2 and applying it to the ingot 2. The pulsed laser beam LB is generated and its power adjusted by a laser beam application unit (not shown).

[0020] During the formation of the separation layer in the ingot 2, which is held on the clamping table 20 under a vacuum, the ingot 2 is imaged by an imaging unit (not shown) belonging to the laser processing device 18. This means that the first end face 4 of the ingot 2 is captured by the imaging unit to obtain an image of the ingot 2. In accordance with the first alignment plane 12 and the second alignment plane 14, which are distinguished from each other by viewing the image of the ingot 2, the clamping table 20 is rotated by the motor and also moved by the X-axis and Y-axis movements. This sets the orientation of the ingot 2 to a predetermined position and also establishes the positional relationship between the ingot 2 and the focusing device 22 in the XY plane, which is defined by the X and Y directions.

[0021] When setting the orientation of ingot 2 to a predetermined orientation, the second alignment plane 14 is used, as shown in Fig. 3 shown, aligned parallel to the X-direction. Accordingly, the direction perpendicular to the formation direction A of the deviation angle α is aligned parallel to the X-direction, and the formation direction A of the deviation angle α is aligned parallel to the Y-direction. Thereafter, the focal point position adjusting means belonging to the laser processing device 18 (not shown) is actuated to move the focusing means 22 in a vertical direction, thereby establishing a focal point FP, as shown in Fig. As shown in Figure 3B, the focuser 22 focuses the laser beam onto the ingot 2 at a predetermined depth (for example, 300 µm) from the first end face 4 of the ingot 2, where the predetermined depth corresponds to the thickness of a wafer to be produced. The pulsed laser beam LB, which has a transmission wavelength suitable for the SiC forming the ingot 2, is then directed onto the ingot 2 by the focuser 22 while the clamping table 20 is moved at a predetermined feed rate in the X-direction, i.e., in the direction perpendicular to the formation direction A of the deviation angle α. This laser processing operation forms a modified section or region 26.

[0022] As in Fig. 4A as a top view of ingot 2 and in Fig. 4B as a section view along line BB from Fig. As shown in Figure 4A, the modified section 26 is continuously formed by applying the pulsed laser beam LB in the direction perpendicular to the formation direction A of the deviation angle α. In this laser processing process, the pulsed laser beam LB is initially applied to the ingot 2 to decompose SiC into Si and C. The pulsed laser beam LB is then applied to the ingot 2 and absorbed by the previously generated C. Subsequently, with the movement of the clamping table 20 in the X-direction, SiC is decomposed into Si and C in a chain reaction. Simultaneously, cracks 27 are also formed, propagating isotropically from the modified section 26 along the c-plane.Although the clamping table 20 is moved in the X-direction during the laser processing operation to form the modified section 26, the focusing device 22 can be moved in the X-direction at a predetermined feed rate without moving the clamping table 20.

[0023] After executing the laser processing operation to form the modified section 26, which, as mentioned above, extends in the predetermined direction (X-direction) inside the ingot 2, the clamping table 20 is moved by a predetermined increment Li in the Y-direction, i.e., in the formation direction A of the deviation angle α, by actuating the Y-movement mechanism. Accordingly, the ingot 2 and the focal point FP are moved relative to each other in the Y-direction. The predetermined increment Li (for example, 250 to 400 µm) is set so that it does not exceed the diameter of a circular area defined by the multiple isotropically extending cracks 27. Consequently, an increment operation is performed to further move the clamping table 20 in the Y-direction. Afterward, the laser processing operation and the increment operation are performed.The movement process is repeated to form several modified sections 26 spaced apart by the predetermined division amount Li in the formation direction A of the deviation angle α, and also to form several cracks 27 extending isotropically from each modified section 28 along the c-plane. In this preferred embodiment, the c-axis is inclined with respect to the perpendicular to the first end face 4 of the hexagonal SiC single-crystal ingot 2, such that the deviation angle α is formed which is greater than 0°. Accordingly, the cracks 27 and the cracks 27 that are formed next to each other in the formation direction A of the deviation angle α overlap in plan view.Consequently, a separation layer 28 is formed inside the ingot 2 at a predetermined depth from the first end face 4 of the ingot 2, wherein the predetermined depth corresponds to the thickness of a wafer to be produced and the separation layer 28 is composed of the several modified sections 26 and the several cracks 27. Accordingly, the separation layer 28 has reduced strength for separating the wafer from the ingot 2.

[0024] For example, the separating layer formation step for forming separating layer 28 is carried out under the following processing conditions. Wavelength: 1064 nm Repetition rate: 60 kHz Average power consumption: 1.5 watts Pulse width: 4 ns Numerical aperture (NA) of the focusing lens: 0.65 Feed speed: 200 mm / s

[0025] By performing the separating layer formation step, the ingot 2, which has the separating layer 28, can be obtained, wherein the separating layer 28 is formed inside the ingot 2 at a depth that corresponds to the thickness of a wafer to be produced.

[0026] After preparing the ingot 2 with the separating layer 28 by performing the separating layer formation step, a fractured section is formed from the separating layer 28 as the fracture start point, and the wafer to be produced is then separated from the ingot 2 along this fractured section. The process for forming the fractured section in the ingot 2 and separating the wafer from the ingot 2 along the fractured section is now described with reference to the Fig. Described in sections 5A to 7B. (First ultrasonic vibration application step)

[0027] First, an initial ultrasonic vibration application step is performed to apply high-density ultrasonic vibrations to a predetermined area of ​​the ingot 2, which encloses the wafer to be produced, thereby forming a partially fractured section where part of the separating layer 28 is fractured. In the first ultrasonic vibration application step, as described in Fig. Figure 5A shows an ultrasonic vibration generation device 40, including a water bath 30. A holding table 32 is provided on the bottom of the water bath 30. The holding table 32 has a flat upper surface for holding the ingot 2. After preparing the water bath 30, the ingot 2 with the substrate 16 is placed on the holding table 32 in such a way that the first end face 4 of the ingot 2 is facing upwards, with the separating layer 28 already formed in the ingot 2. After placing the ingot 2 on the holding table 32, water 34 is poured into the water bath 30 until the height of the surface of the water 34 in the water bath 30 is sufficiently higher than the height of the first end face 4 of the ingot 2. Fig. 5B depicted ingots 2. During Fig. Figure 5B is a sectional view showing the first ultrasonic vibration application step; the water bath 30 is shown as a vertical section for simple illustration purposes only.

[0028] The ultrasonic vibration generation device 40 includes a high-density ultrasonic vibration generator 42. The high-density ultrasonic vibration generator 42 has an ultrasonic transducer (not shown) for generating an ultrasonic vibration S. The lower end section of the high-density ultrasonic vibration generator 42 tapers to form a high-density ultrasonic vibration application section 43. The high-density ultrasonic vibration application section 43 is a circular section with a diameter of, for example, 8 mm.

[0029] The ultrasonic vibration S generated by the high-density ultrasonic vibration generator 42, for example, has a power of 100 watts and a frequency of 400 kHz. In accordance with the high-density ultrasonic vibration generator 42, the ultrasonic vibration S generated by the ultrasonic transducer is focused by the high-density ultrasonic vibration delivery section 43, which has a tapered shape, thus increasing the density of the ultrasonic vibration S. Consequently, the high-density ultrasonic vibration S can be delivered towards a target area.

[0030] With the ingot 2 held on the holding table 32 and immersed in water 34 in the water bath 30, the high-density ultrasonic vibration generator 42 is lowered towards the first end face 4 of the ingot 2. Then, the high-density ultrasonic vibration application section, formed at the lower end of the high-density ultrasonic vibration generator 42, is immersed in the water 34 in the water bath 30 and positioned near the center of the first end face 4 of the ingot 2. At this point, a small gap (for example, several mm) is defined between the high-density ultrasonic vibration application section 42 and the first end face 4 of the ingot 2.

[0031] After the aforementioned positioning of the high-density ultrasonic vibration application section 43 near the center of the first end face 4 of the ingot 2, the high-density ultrasonic vibration S is applied by the high-density ultrasonic vibration application section 43 across the layer of water 34 for a predetermined period (for example, approximately 10 seconds) in the direction of the first end face 4 of the ingot 2. As described in Fig. As shown in Figure 5B, the high-density ultrasonic vibration S is accordingly concentrated on the specified area of ​​the first end face 4 of the ingot 2, which encloses the wafer to be produced, thereby stimulating part of the separating layer 28. As a result, as shown in Fig. Figure 5B shows that a partially fractured section 29 is formed in this part of the separating layer 28. This means that this part of the separating layer 28 is fractured in the partially fractured section 29. In this way, the first ultrasonic vibration application step is completed. (Second ultrasonic vibration application step)

[0032] After completion of the first ultrasonic vibration application step, a second ultrasonic vibration application step is performed. The second ultrasonic vibration application step is now carried out with reference to the Fig. 6A and Fig. 6B described.

[0033] During the execution of the second ultrasonic vibration application step, the high-density ultrasonic vibration generating medium 42 used in the first ultrasonic vibration application step is converted into a Fig. The ultrasonic vibration generating device 45 shown in Figure 6A has been modified. As a method for changing the ultrasonic vibration generating device 42 from the high-density ultrasonic vibration generating device 42 to the low-density ultrasonic vibration generating device 45, the high-density ultrasonic vibration generating device 42 can first be removed from the ultrasonic vibration generating device 40 and the low-density ultrasonic vibration generating device 45 can then be attached.Alternatively, the ultrasonic vibration generating device 40 can have a holder (not shown) for mounting both the high-density ultrasonic vibration generating device 42 and the low-density ultrasonic vibration generating device 45, the holder being configured so that either the high-density ultrasonic vibration generating device 42 or the low-density ultrasonic vibration generating device 45 can be selected as required. In this case, the high-density ultrasonic vibration generating device 42 can be moved away from the position above the ingot 2 first, and the low-density ultrasonic vibration generating device 45 can be positioned above the ingot 2 next.

[0034] As in the Fig. 6A and Fig. As shown in Figure 6B, the low-density ultrasonic vibration generating means 45 has a lower end section configured as a low-density ultrasonic vibration application section 46. The low-density ultrasonic vibration application section 46 is opposite the first end face 4 of the ingot 2. The low-density ultrasonic vibration application section 46 has a region that is larger than the region of the high-density ultrasonic vibration application section 43, which is used in the first ultrasonic vibration application step. In particular, the low-density ultrasonic vibration application section 46 is a circular section with a diameter of, for example, 100 mm, which is essentially the same as the diameter of the ingot 2.

[0035] The low-density ultrasonic vibration generator 45 is configured to generate an ultrasonic vibration S'. Similar to the high-density ultrasonic vibration generator 42, the low-density ultrasonic vibration generator 45 has an ultrasonic transducer (not shown) for generating the ultrasonic vibration S'. For example, the ultrasonic vibration S' has a power of 100 watts and a frequency of 400 kHz. As described above, the area of ​​the low-density ultrasonic vibration application section 46 is larger than the area of ​​the high-density ultrasonic vibration application section 43. Accordingly, the density of the ultrasonic vibration S' applied by the low-density ultrasonic vibration application section 46 is lower than the density of the ultrasonic vibration S applied by the high-density ultrasonic vibration application section 43.

[0036] As in Fig. Figure 6A shows the low-density ultrasonic vibration generator 45 positioned directly above the ingot 2, which is placed on the holding table 32 and immersed in the water bath 30. During the second ultrasonic vibration application step, the low-density ultrasonic vibration generator 45 is lowered towards the first end face 4 of the ingot 2 until the low-density ultrasonic vibration application section 46 of the generator is immersed in the water 34 contained in the water bath 30 and comes close to the first end face 4 of the ingot 2. Accordingly, the entire first end face 4 of the ingot 2 is covered by the low-density ultrasonic vibration application section 46.At this point, a small gap (for example, several mm) is defined between the application section for low density ultrasonic vibrations 46 and the first end surface 4 of the ingot 2.

[0037] In the state in which the application section for low-density ultrasonic vibrations 46 is set up near the first end face 4 of the ingot 2 as mentioned above, the low-density ultrasonic vibration S' is applied by the application section for low-density ultrasonic vibrations 46 over the layer of water 34 in the direction of the entire first end face 4 of the ingot 2 over a predetermined period (for example, in about 30 seconds).By applying the low-density ultrasonic vibration S' to the entire first end face 4 of the ingot 2, as mentioned above, the entire separating layer 28 formed inside the ingot 2 is stimulated by the low-density ultrasonic vibration S', causing the cracks 27 in the separating layer 28 to extend from the partially fractured section 29 formed during the first ultrasonic vibration application step, and the adjacent cracks 27 to connect accordingly, forming a fully fractured section 29' in which the separating layer 28 is completely fractured. As in . Fig. As shown in Figure 6B, the fully fractured section 29' is continuous throughout the entire separating layer 28 formed inside the ingot 2. Accordingly, the wafer to be produced can be reliably separated from the ingot 2 along the fully fractured section 29'. In this way, the second ultrasonic vibration deposition step is completed. (Separation step)

[0038] After performing the first and second ultrasonic vibration application steps to form the fully fractured section 29' from the separating layer 28 formed inside the ingot 2, a separation step is performed to separate a wafer W from the ingot 2 along the fully fractured section 29', with the ingot 2 remaining immersed in the water 34 in the water bath 30. Accordingly, the wafer W exhibits, as shown in the Fig. 7A and Fig.Figure 7B shows the first end face 4 of the ingot 2 as a front face Wa. During the separation step, the wafer W can be held and lifted directly by an operator. Alternatively, the wafer W can be held by a vacuum using a suction device (not shown) and lifted from the water bath 30 by the suction device, the size of which corresponds to the size of the wafer W.

[0039] In the state where wafer W has been separated from ingot 2 by performing the separation step as described above, the parting surface of wafer W, as a back surface Wb, is a rough surface, and the parting surface of ingot 2, as a new first end surface 4', is also a rough surface. Accordingly, the back surface Wb of wafer W and the first end surface 4' of ingot 2 are next polished to become flattened (not shown). Afterward, the wafer W separated from ingot 2 is received in a suitable housing or similar and then transferred to any device for performing a subsequent step. Alternatively, ingot 2 with the flattened first end surface 4' is transferred to the laser processing device 18 to repeat the parting line formation step.After forming a separating layer in the ingot 2 by using the laser processing device 18, the first ultrasonic vibration application step, the second ultrasonic vibration application step and the separation step are repeated in order to efficiently produce another wafer W from the ingot 2.

[0040] In accordance with this preferred embodiment, the amount of ingot 2 that becomes rejects during wafer W fabrication can be greatly reduced compared to when a wire saw is used to cut the ingot 2. Furthermore, the first ultrasonic vibration application step is performed to apply the high-density ultrasonic vibration S to a portion of the ingot 2, thereby forming the partially fractured section 29. Subsequently, the second ultrasonic vibration application step is performed to apply the low-density ultrasonic vibration S' to the entire ingot 2, thereby forming the fully fractured section 29' by spreading out from the partially fractured section 29. Consequently, the fully fractured section 29' is formed from the previously formed separating layer 28 in the ingot 2.Accordingly, the wafer W to be produced can be separated from the ingot 2 in a simple and efficient manner along the completely fractured section 29'.

[0041] The present invention is not limited to the preferred embodiment described above, but various modifications are possible. Although in the preferred embodiment described above the c-axis in the ingot 2 is inclined with respect to the perpendicular 10 to the first end face 4 of the ingot 2, and the angle of deviation α between the c-plane and the first end face 4 is formed, the present invention is not limited to this configuration, for example. That is to say, the present invention is also applicable to an ingot configured such that the c-axis is not inclined with respect to the perpendicular 10 to the first end face 4.

[0042] Although in the first and second ultrasonic vibration application steps of the above preferred embodiment an ultrasonic vibration is applied from the ultrasonic vibration generation device 40 to the ingot 2 via the layer of water 34, the layer of water 34 can furthermore be replaced by a layer of air or a layer of a liquid other than water.

[0043] 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 appended claims, and all modifications and adaptations that fall within the equivalent scope of protection of the claims are therefore included in the invention.

Claims

[1] A wafer manufacturing method for manufacturing a wafer (W) from an ingot (2) after forming a separation layer (28) inside the ingot (2) by setting a focal point (FP) of a laser beam (LB) having a transmission wavelength for the ingot (2) to a predetermined depth inside the ingot (2) from an end face (4) of the ingot (2), the predetermined depth corresponding to a thickness of the wafer (W) to be manufactured, and next applying the laser beam (LB) to the ingot (2), the wafer manufacturing method comprising: a first ultrasonic vibration application step of applying ultrasonic vibrations of a first density to a predetermined area of the ingot (2) to thereby form a partially broken portion (29) where a part of the separation layer (28) is broken; after performing the first ultrasonic vibration application step, a second ultrasonic vibration application step comprising applying the ultrasonic vibrations at a second density lower than the first density to an entire area of the ingot (2) larger than the predetermined area, to thereby form a fully fractured portion (29') in which the separation layer (28) is fully fractured in such a manner that fracture starts from the partially fractured portion (29); and a separation step comprising separating the wafer (W) along the completely broken portion (29') from the ingot (2). [2] A wafer manufacturing method according to claim 1, wherein the ultrasonic vibration is applied to the ingot (2) through a layer of water (34) in the first ultrasonic vibration applying step and the second ultrasonic vibration applying step. [3] A wafer manufacturing method according to claim 1 or 2, wherein the ingot (2) comprises a hexagonal SiC single-crystal ingot with a c-axis and a c-plane perpendicular to the c-axis, and the separation layer (28) is constructed with a modified portion (26) and cracks (27) extending isotropically from the modified portion (26) along the c-plane, wherein the modified portion (26) is formed by setting a focal point (FP) of a laser beam (LB) having a transmission wavelength for hexagonal SiC single crystal to a predetermined depth inside the SiC ingot (2) from one end face (4) of the SiC ingot (2), the predetermined depth corresponding to the thickness of the wafer (W) to be produced, and next applying the laser beam (LB) to the SiC ingot (2) to thereby decompose SiC into Si and C. [4] A wafer manufacturing method according to claim 3, wherein the c-axis is inclined by a deviation angle (α) with respect to a perpendicular to the one end face (4) of the SiC ingot (2), the deviation angle (α) being formed between the c-plane and the one end face (4), the focal point (FP) of the laser beam (LB) is moved in a direction perpendicular to a forming direction of the deviation angle (α), thereby continuously forming the modified portion (26) in the direction perpendicular to the forming direction of the deviation angle (α), and the focal point (FP) of the laser beam (LB) is moved further in the direction of formation of the deviation angle (α) in an area which is not larger than a formation area of the cracks (27), wherein a plurality of linear modified portions (26) are arranged side by side in the formation direction of the deviation angle (α) such that the cracks (27) extending from any adjacent ones of the plurality of linear modified portions (26) overlap.

Images