Wafer manufacturing process

Abstract

Wafer fabrication method for producing a hexagonal single-crystal wafer (27) from a hexagonal single-crystal ingot (11) having a first face (11a), a second face (11b) opposite the first face, a c-axis extending from the first face (11a) to the second face (11b), and a c-plane perpendicular to the c-axis, wherein the wafer fabrication method comprises: a separation start point formation step with setting a focal point (P) of a laser beam (LB) having a transmission wavelength for the ingot (11) at a predetermined depth inside the ingot (11) by the first face (11a), the depth corresponding to a thickness of the wafer to be produced, and nextly, applying the laser beam (LB) to the first face (11a) while moving the focal point (P) and the ingot (11) relative to each other to form a modified layer (23) parallel to the first face (11a) and cracks (25) form,which extend from the modified layer (23) along the c-plane to form a separation start point; and a wafer separation step comprising separating a plate-shaped element having a thickness corresponding to the thickness of the wafer (27) from the ingot (11) at the separation start point after performing the separation start point formation step to produce the wafer (27) from the ingot (11); wherein the separation start point formation step includes: a formation step for a modified layer (23) comprising a relative movement of the focal point (P) of the laser beam (LB) in a first direction perpendicular to a second direction, where the c-axis is inclined with respect to a perpendicular to the first surface (11a) by a deviation angle (α) and the deviation angle is formed between the first surface (11a) and the c-plane, thereby forming the modified layer (23) extending in the first direction linearly,and a division step with a relative movement of the focal point (P) in the second direction in order to move the focal point (P) by a predetermined amount; wherein the separation start point formation step includes a first separation start point formation step with scanning the laser beam (LB) from a scan start point to a scan end point on the ingot (11) and a second separation start point formation step with scanning the laser beam (LB) from the scan end point to the scan start point, wherein the first separation start point formation step and the second separation start point formation step are repeated alternately several times in order to separate the cracks (25) from the modified layer (23).

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The present invention relates to a wafer manufacturing process for cutting a hexagonal single-crystal ingot to produce a wafer. Description of the relevant state of the art

[0002] Various electronic components, such as integrated circuits (ICs) and low-level interconnects (LSIs), are fabricated by forming a functional layer on the front face of a wafer made of silicon or a similar material. This functional layer is then divided into numerous regions along a multitude of intersecting dividing lines. These dividing lines are processed by a tool, such as a cutting machine or laser cutter, to divide the wafer into a multitude of individual component chips. These component chips are widely used in a variety of devices, including mobile phones and personal computers.Furthermore, power components or optical components, such as LEDs and LDs, are formed by creating a functional layer on the front face of a wafer made from a hexagonal single crystal, such as SiC and GaN, and dividing this functional layer into a multitude of regions along a multitude of intersecting dividing lines.

[0003] Generally, the wafer on which the components are to be formed is produced by cutting an ingot with a wire saw. Both sides of the resulting wafer are polished to a mirror finish or a high gloss, respectively; see, for example, the disclosed Japanese patent number 2000-94 221. This wire saw is configured such that a single wire, similar to piano wire and with a diameter of approximately 100 to 300 μm, is wound around numerous grooves, usually formed on two to four guide rollers, to create a multitude of cutting sections spaced parallel to each other at a predetermined pitch. The wire is actuated so that it runs in one or opposite directions, thereby cutting the ingot into a multitude of wafers.

[0004] 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, raising the issue of inefficient production. In particular, a hexagonal single-crystal ingot made of SiC or GaN, for example, has a high Mohs hardness, making it difficult to cut with a wire saw. Consequently, a significant amount of time is required to cut the ingot, resulting in reduced productivity. In other words, there is a problem with efficiently producing a wafer using state-of-the-art technology.

[0005] A technique for solving this problem is described in Japanese patent no. 2013-49461. This technique includes the steps of focusing the focal point of a laser beam, having a transmission wavelength suitable for SiC, onto the interior of a hexagonal single-crystal ingot; next, applying the laser beam to the ingot by scanning the laser beam on the ingot to form a modified layer and cracks in a parting plane within the ingot; and next, applying an external force to the ingot to fracture the ingot along the parting plane where the modified layer and cracks are formed, thus separating a wafer from the ingot.In this technique, the laser beam is scanned spirally or linearly along the parting line, so that a first laser beam application point and a second laser beam application point, which is closest to the first application point, have a predetermined positional relationship to each other. As a result, the modified layer and the cracks are formed with a very high density in the parting line of the ingot. SUMMARY OF THE INVENTION

[0006] However, in the ingot cutting method described in the aforementioned Japanese patent no. 2013-49461, the laser beam is scanned or sweeps across the ingot in a spiral or linear pattern. In the case of linear scanning, the scanning direction of the laser beam is not defined. In the ingot cutting method described in Japanese patent no. 2013-49461, the pitch, i.e., the distance, between the first and second application points of the laser beam is set to 1 to 10 μm, as mentioned above. This pitch corresponds to the pitch of the cracks extending from the modified layer along a c-plane defined in the ingot.

[0007] In this way, the division of the application points of the laser beam applied to the ingot is very small. Regardless of whether the laser beam is scanned spirally or linearly, the laser beam must therefore be applied with a very small division, and the improvement in productivity is not yet sufficient.

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

[0009] In accordance with one aspect of the present invention, a wafer fabrication method is provided for producing a hexagonal single-crystal wafer from a hexagonal single-crystal ingot, the ingot having a first face, a second face opposite the first face, a c-axis extending from the first face to the second face, and a c-plane perpendicular to the c-axis, wherein the wafer fabrication method includes: a separation start point formation step with setting a focal point of a laser beam having a transmission wavelength for the ingot at a predetermined depth inside the ingot from the first face, the depth corresponding to a thickness of the wafer to be produced, and nextly, applying the laser beam to the first face with a relative movement of the focal point and the ingot to form a modified layer and cracks parallel to the first face.which extend from the modified layer along the c-plane to form a separation start point; and a wafer separation step after performing the separation start point formation step by separating a plate-shaped element with a thickness equal to the thickness of the wafer from the ingot at the separation start point to produce the wafer from the ingot.

[0010] The separation start point formation step includes: a formation step for a modified layer with a relative movement of the focal point of the laser beam in a first direction perpendicular to a second direction, where the c-axis is inclined with respect to a perpendicular to the first surface by a deviation angle, and the deviation angle between the first surface and the c-plane is formed, thereby forming the modified layer extending in the first direction linearly; and a division step with a relative movement of the focal point in the second direction, in order to move the focal point further by a predetermined amount.The separation start point training step includes a first separation start point training step with scanning the laser beam from a scan start point to a scan end point on the ingot and a second separation start point training step with scanning the laser beam from the scan end point to the scan start point, wherein the first separation start point training step and the second separation start point training step are repeated alternately several times in order to separate the cracks from the modified layer.

[0011] In accordance with the wafer fabrication method of the present invention, the separation start point formation step comprises the first separation start point formation step with scanning the laser beam from the scan start point to the scan end point and the second separation start point formation step with scanning the laser beam from the scan end point to the scan start point, wherein the first separation start point formation step and the second separation start point formation step are repeated alternately several times in order to separate the cracks from the modified layer. Preferably, the repetition frequency and the feed rate in the second separation start point formation step are the same as in the first separation start point formation step.There is a possibility that diffuse reflection of the laser beam occurs near the scan start point on the hexagonal single-crystal ingot, causing the modified layer and cracks to form improperly. However, by performing the first and second separation start point formation steps as described above, the modified layer and cracks can be properly formed in the edge region of the ingot. Consequently, productivity can be significantly improved, and the amount of ingot scrap can be reduced to approximately 30%.

[0012] The above and other problems, features and advantages of the present invention and the manner of its realization will become clearer, and the invention itself will best be understood by studying the following description and attached claims with reference to the attached drawings, which show a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. Figure 1 is a perspective view of a laser processing device suitable for use in carrying out a wafer manufacturing process of the present invention;

[0014] Fig. 2 is a block diagram of a laser beam generation unit;

[0015] Fig. 3A is a perspective view of a hexagonal single-crystal ingot;

[0016] Fig. 3B is a view of the in Fig. 3A shown ingots;

[0017] Fig. Figure 4 is a perspective view to illustrate a separation point training step;

[0018] Fig. 5 is a top view of the in Fig. 3A shown ingots;

[0019] Fig. Figure 6 is a schematic sectional view to illustrate a training step of a modified layer;

[0020] Fig. Figure 7 is a schematic top view to illustrate the formation step of a modified layer;

[0021] Fig. Figure 8A is a schematic top view to illustrate a classification step;

[0022] Fig. Figure 8B is a schematic top view to illustrate a classification amount;

[0023] Fig. Figure 9 is a perspective view to illustrate a wafer separation step;

[0024] Fig. Figure 10 is a perspective view of a hexagonal single-crystal wafer produced from the ingot;

[0025] the Fig. 11A to Fig. Figures 11C are schematic sectional views to illustrate the separation start point formation step in accordance with a preferred embodiment of the present invention; and

[0026] the Fig. 12A and Fig. Figure 12B shows schematic top views to illustrate a laser beam scanning process during the separation start point formation step. DETAILED DESCRIPTION OF THE PREFERRED EXECUTION FORM

[0027] A preferred embodiment of the present invention will now be described in detail with reference to the drawings. Fig. Figure 1 shows a perspective view of a laser processing device 2shown, which is suitable for use in carrying out a wafer manufacturing process of the present invention. The laser processing device 2 includes a stationary base 4 and a first sliding or cam block 6 one who is so at the stationary base 4 It is mounted in such a way that it can be moved in the X direction. The first scenery block 6 is provided by a feeding mechanism 12 , which consists of a ball screw spindle 8 and a stepper motor 10 is set up in a feed direction or in the X direction along a pair of guide rails 14 moved.

[0028] A second set of scenery 16 is at the first set block 6 It is mounted so that it can be moved in the Y direction. The second scenery block 16 is determined by a classification mechanism 22 , which consists of a ball screw spindle 18and a stepper motor 20 is constructed in a division direction or in the Y-direction along a pair of guide rails 24 moved. A support table 26 is on the second set block 16 mounted. The support table 26 is through the feeding mechanism 12 and the classification mechanism 22 movable in the X and Y directions and also by a block in the second scenery block 16 The housed motor is rotatable.

[0029] A pillar 28 is so at the stationary base 4 It is designed to protrude upwards from this point. A laser beam delivery mechanism (laser beam delivery device) 30 is on the pillar 28 Assembled. The laser beam application mechanism. 30 is made from a case 32 , one inside the case 32 housed laser beam generation unit 34 (see Fig. 2) and a focusing device (laser head) 36 constructed so that it is movable in the Z-direction at the front end of the housing 32 is mounted. An imaging unit 38 , which features a microscope and a camera, is also located at the front end of the housing 32 mounted so that it is compatible with the focusing device 36 is aligned in the X direction.

[0030] As in Fig. As shown in 2, the laser beam generation unit is enclosed. 34 a laser oscillator 40 for generating a pulsed laser beam, such as a YAG laser and YVO4 laser, a repetition rate setting device 42 to adjust the repetition rate of the laser oscillator 40 pulsed laser beam to be generated, a pulse width adjustment device 44 to adjust the pulse width of the laser oscillator 40 pulsed laser beam to be generated and a power adjustment device 46to adjust the power of the laser oscillator 40 to generate a pulsed laser beam. Although not specifically shown, the laser oscillator features 40 a Brewster window opens, so that the laser oscillator 40 The generated laser beam is a laser beam consisting of linearly polarized light. After the power of the pulsed laser beam is adjusted by the power control device... 46 the laser beam generation unit 34 When set to a predetermined power level, the pulsed laser beam is reflected by a mirror. 48 , which is part of the focusing device 36 heard, reflected upon, and next, through a focusing device 36 included focusing lens 50 focused. The focusing lens 50 is positioned such that the pulsed laser beam is contained within a hexagonal single-crystal ingot 11 as one at the support table 26 The fixed workpiece is focused on.

[0031] Referring to Fig. Figure 3A shows a perspective view of the hexagonal single-crystal ingot. 11 shown as the workpiece to be machined. Fig. 3B is a view of the in Fig. 3A hexagonal single-crystal ingots shown 11 The hexagonal single-crystal ingot 11 The ingot, which will be referred to hereafter simply as the ingot, is selected from a SiC single-crystal ingot or a GaN single-crystal ingot. 11 has a first surface (upper surface) 11a and one of the first areas 11a opposite second surface (lower surface) 11b up. The first area 11a of the ingot 11 It is polished to a high gloss beforehand, as the laser beam is directed at the first surface. 11A is applied.

[0032] The ingot 11 indicates a first alignment level 13 and one to the first alignment level 13vertical second alignment plane 15 The length of the first alignment plane 13 is greater than the length of the second alignment plane 15 The ingot 11 has a c-axis 19 on, which in relation to a vertical 17 to the upper surface 11a by a deviation angle α in the direction of the second alignment plane 15 is inclined, and also has a tilt relative to the c-axis 19 perpendicular c-plane 21 on. The c-level 21 is in relation to the upper surface 11a inclined by the deviation angle α. In general, in the hexagonal single-crystal ingot 11 the direction of extension of the shorter second alignment plane 15 vertical direction, the inclination direction of the c-axis 19 The c-plane 21 is countless at the molecular level of the ingot 11In this preferred embodiment, the deviation angle α is set to 4°. However, the deviation angle α is not limited to the 4° of the present invention. For example, the deviation angle α can be set during the production of the ingot. 11 can be freely adjusted to a range of 1° to 6°.

[0033] Referring again to Fig. 1 is a pillar 52 on the left side of the stationary base 4 attached. The column 52 is equipped with an elongated opening extending in a vertical direction 53 formed and a pressure mechanism 54 It is movable in a vertical direction on the column. 52 mounted so that it is visible from the opening 53 stands out.

[0034] As in Fig. As shown in 4, the ingot 11 using a wax or an adhesive in the state on the upper surface of the support table 26attached, where the second alignment plane 15 of the ingot 11 parallel to the X-direction. In other words, the direction of formation of the deviation angle α is as shown in Fig. Figure 5 is shown, indicated by an arrow Y1. This means that the direction of arrow Y1 is the direction in which the intersection occurs. 19a between the c-axis 19 and the upper surface 11a of the ingot 11 in relation to the vertical 17 to the upper surface 11a is present. Furthermore, the direction perpendicular to the direction of arrow Y1 is shown by an arrow A. Then the ingot 11 at the support table 26 fixed in the state in which the direction of arrow A becomes parallel to the X direction.

[0035] Accordingly, the laser beam is scanned in the direction of arrow A, perpendicular to the direction of arrow Y1 or the direction in which the deviation angle α is formed. In other words, the direction of arrow A, perpendicular to the direction of arrow Y1 where the deviation angle α is formed, is the feed direction of the support table. 26 defined.

[0036] In the wafer manufacturing process of the present invention, it is important that the scanning direction of the focusing means 36 The laser beam to be applied is set to the direction of arrow A perpendicular to the direction of arrow Y1, where the deviation angle α of the ingot 11 is formed. That is, it was found that by adjusting the scanning direction of the laser beam to the direction of arrow A, as mentioned above in the wafer manufacturing process of the present invention, cracks originating from within the ingot are formed. 11The modified layer formed by the laser beam spreads out over a very long distance along the c-plane. 21 extend.

[0037] When carrying out the wafer manufacturing process in accordance with this preferred embodiment, a separation start point formation step is carried out in such a way that the focal point of the laser beam, which has a transmission wavelength, such as 1064 nm, is located on the support table 26 fixed hexagonal single-crystal ingot 11 exhibits, on one of the first surfaces 11a (upper surface) from a predetermined depth inside the ingot 11 The laser beam is set to correspond to the thickness of a wafer to be produced, and then, during a relative movement of the focal point and the ingot, the laser beam moves relative to the ingot. 11 on the upper surface 11a is applied to create a modified layer 23 parallel to the upper surface 11a and cracks25 to develop those that differ from the modified layer 23 along the c-plane 21 extend and thus form a separation starting point (separation plane) where the modified layer 23 and the cracks 25 be trained.

[0038] This separation start point training step includes a training step for a modified layer with a relative movement of the focal point of the laser beam in the direction of arrow A, which is perpendicular to the direction of arrow Y1, where the c-axis 19 with regard to the vertical 17 to the upper surface 11a is inclined by the angle of deviation α and the angle of deviation α between the c-plane 21 and the upper surface 11a is formed, whereby the modified layer 23 within the ingot 11 and the cracks 25 , which differ from the modified layer 23 along the c-plane 21extend, be formed, and also include a division step for the relative movement of the focal point in the formation direction of the deviation angle α, i.e. in the Y-direction, in order to thereby position the focal point as in Fig. 7 and the Fig. 8A and Fig. 8B is shown to advance a predetermined amount.

[0039] As in the Fig. 6 and Fig. As shown in 7, the modified layer 23 so linearly formed that it extends in the X-direction, so that the cracks 25 from the modified layer 23 in opposite directions along the c-plane 21 extend. In the wafer manufacturing process according to this preferred embodiment, the separation point formation step further comprises a division amount setting step with a measurement of the crack width. 25 , which are on one side of the modified layer 23along the c-plane 21 to be formed, and then an adjustment of the focal point's division value according to the width measurement above. With W1, the width of the cracks. 25 characteristic, which is on one side of the modified layer 23 be trained so that they can distinguish themselves from the modified layer 23 along the c-plane 21 To spread out, the division amount W2 of the focal point is more precisely set in the range from W1 to 2W1.

[0040] For example, the separation start point training step is carried out with the following laser processing conditions. Light source: pulsed Nd:YAG laser Wavelength: 1064 nm Repetition rate: 80 kHz Average power consumption: 3.2 W Pulse width: 4 ns Spot diameter: 10 μm Numerical aperture (NA) of the focusing lens: 0.45 Division amount: 400 μm

[0041] Under the laser processing conditions mentioned above, the width W1 of the cracks 25 , which differ from the modified layer 23 along the c-plane 21 in a Fig. The cracks spread in the direction shown in Figure 6, are set to approximately 250 μm, and the division value W2 is set to 400 μm. However, the average power of the laser beam is not limited to 3.2 W. Good results were achieved in the preferred embodiment when the average power of the laser beam was set to 2 to 4.5 W. In the case where the average power was set to 2 W, the width W1 of the cracks was... 25 approximately 100 μm. In the event that the average power was set to 4.5 W, the width W1 of the cracks was 25 approximately 350 μm.

[0042] In the event that the average power is less than 2 W or greater than 4.5 W, the modified layer can 23 not good within the ingot 11 to be trained. Accordingly, the average power of the laser beam to be applied is preferably set to a range of 2 to 4.5 W. For example, the average power of the laser beam applied to the ingot was... 11 The laser beam to be applied is set to 3.2 W in this preferred embodiment. As in Fig. Figure 6 shows the depth D1 of the focal point for forming the modified layer. 23 from the upper surface 11a set to 500 μm.

[0043] Referring to Fig. Figure 8A shows a schematic top view to illustrate the scanning direction of the laser beam. The separation start point formation step is shown as in Fig. Figure 8A shows the process running on a forward path X1 and a reverse path X2. This means that the modified layer... 23 in the hexagonal single-crystal ingot 11 The modified layer is formed on the forward path X1. Then the focal point of the laser beam is moved by the predetermined amount. After that, the modified layer is formed again. 23 on the reverse path X2 in the ingot 11 trained.

[0044] In the event that the division value of the focal point of the laser beam is set in a range from W to 2 W, where W is the width of the cracks 25 is that which is on one side of the modified layer 23 along the c-plane 21 Furthermore, the division value of the focal point is preferably set to W or less until the modified layer is formed. 23 for the first time after the focal point of the laser beam was set on the inside of the ingot 11is being trained.

[0045] In the event that the division value of the laser beam focal point is 400 μm, the division value is set to, for example, 200 μm until the modified layer 23 for the first time within the ingot 11 is trained, and then the laser beam is scanned several times with this division amount of 200 μm, as in Fig. 8B shown. That is, the first part of the multitude of scan phases of the laser beam is an idle phase, and if it has been determined that the modified layer 23 for the first time within the ingot 11 Once trained, the division amount is set to 400 μm and then the modified layer is applied. 23 inside the ingot 11 trained.

[0046] In this way, the focal point of the laser beam is moved successively to create a large number of modified layers. 23at depth D1 throughout the entire area of ​​the ingot 11 to develop and also the cracks 25 to train those who differ from each modified layer 23 along the c-plane 21 extend. Then a wafer separation step is performed in such a way that an external force is applied to the ingot. 11 is applied to thereby at the separation starting point, which consists of the modified layers 23 and the cracks 25 consists of separating a plate-shaped element with a thickness that corresponds to the thickness of the ingot 11 to be trained wafers corresponds to thus a in Fig. 10 hexagonal single-crystal wafers shown 27 to produce.

[0047] This wafer separation step is performed in the following manner. As shown in Fig. Figure 9 shows an ultrasonic vibration generating device. 62 in a water tank 60 set up and the hexagonal single-crystal ingot11 , in which the separation start point has been formed by the previous step, is applied to the ultrasonic vibration generation device 62 installed. Then the water tank 60 with pure water 64 filled to form the hexagonal single-crystal ingot 11 in the pure water 64 to immerse. Then a voltage is applied to the ultrasonic vibration generating device. 62 applied to generate an ultrasonic vibration with a frequency of, for example, 40 kHz.

[0048] This ultrasonic vibration is converted into the hexagonal single-crystal ingot. 11 transferred, whereby the plate-shaped element with a thickness corresponding to the thickness of the wafer is transferred at the separation start point located in the ingot 11 is formed from the ingot 11 is separated. Accordingly, a situation like this can occur, as in Fig. 10 hexagonal single-crystal wafers shown 27from the hexagonal single-crystal ingot 11 are produced. Although the pure water 64 in this preferred embodiment in the water tank 60 Although it is included, any other type of container can be used.

[0049] As an ultrasonic vibration generating device 62 For example, an AS Ultrasonic Cleaner US-2R, provided by AS ONE Corporation, can be used to generate ultrasonic vibrations. In this case, the ultrasonic vibration generation device can 62 to generate an ultrasonic vibration with a frequency of 40 kHz and a power of 80 W. The ultrasonic vibration to be applied during the wafer separation step preferably has a frequency of 30 to 50 kHz and even more preferably of 35 to 45 kHz.

[0050] The separation start point training step in accordance with this preferred embodiment is now described in more detail with reference to the Fig. 11A to Fig. 11C described. As in Fig. As shown in 11A, the focal point P of a laser beam LB is focused on the depth inside the ingot corresponding to the thickness of the wafer to be produced. 11 adjusted, and the laser beam LB will next be directed onto the upper surface. 11a of the ingot 11 applied. As a result, the modified layer is created. 23 formed at focal point P and the cracks 25 are thus around the modified layer 23 They are designed to extend radially from this point along the c-plane. That is, once the laser beam LB is applied, the modified layer 23 formed at focal point P and the cracks 25 , which differ from the modified layer 23 spread, become, as in Fig. 11B shown to illustrate the modified layer 23in the c-plane. In the separation start point formation step in accordance with this preferred embodiment, the focal point P is formed at the modified layer already formed as mentioned above. 23 adjusted and the laser beam will next be directed at the upper surface 11a of the ingot 11 applied. This laser beam application step is repeated several times.

[0051] In this laser beam application step, the laser beam is applied from one end of the ingot. 11 The ingot is scanned at the other end, and this scanning process is repeated several times at the same repetition rate and feed rate as the previous cycle. For example, the laser beam scanning process is repeated approximately every 5 to 7 cycles, and the laser beam is directed at the ingot in that state. 11 applied by directing the focal point of the laser beam onto each previously formed modified layer23 is adjusted. As a result, the cracks are... 25 of each modified layer 23 separated and on opposite sides of each modified layer 23 , as in Fig. 11C shown, interconnected. Since the cracks 25 , as described above, from each modified layer 23 Once the two elements have been separated and joined together, the subsequent separation step can be carried out very simply. This means that the plate-shaped element, with a thickness corresponding to the thickness of the wafer, can be easily separated from the hexagonal single-crystal ingot. 11 at the separation starting point, the hexagonal single-crystal wafer can be separated. 27 simply from the ingot 11 is manufactured.

[0052] Regarding the separation start point training step, which refers to the Fig. 11A to Fig. As described in section 11C, a more preferred laser beam application method is now described with reference to the Fig. 12A and Fig. 12B described. The laser beam scanning method in this preferred embodiment is based on the knowledge that diffuse reflection of the laser beam near the scan start point occurs at the hexagonal single-crystal ingot. 11 occurs, which causes the problem that the modified layers 23 and the cracks 25 cannot be formed in a simple way. Accordingly, this laser beam scanning method is a solution to this problem. More precisely, in this preferred embodiment, this laser beam scanning method is carried out as a separation start point formation step in the following manner. As in Fig. As shown in Figure 12A, the scanning of the laser beam is started at a scan start point P1 and ends at a scan end point P2 on the hexagonal single crystal ingot. 11in such a way that the scanning is repeated alternately on a forward path X1 and a backward path X2 (first separation start point training step).

[0053] As in Fig. As shown in Figure 12B, the laser beam scanning is then started at scan endpoint P2 and terminated at scan start point P1, in such a way that the scanning is repeated alternately on a forward path X3 corresponding to the reverse path X2 and a reverse path X4 corresponding to the forward path X1 (second separation start point formation step). The first separation start point formation step and the second separation start point formation step mentioned above are repeated alternately several times to modify the layers. 23 and the cracks 25to separate them from each other. By alternately repeating the first separation point formation step and the second separation point formation step mentioned above, it is possible to solve the problem mentioned above that the modified layers and the cracks are not easily formed due to the occurrence of diffuse reflection of the laser beam near the scan start point on the hexagonal single crystal ingot.

[0054] 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, and all modifications and adaptations that fall within the equivalent scope of protection of the claims are therefore included in the invention. QUOTES INCLUDED IN THE DESCRIPTION

[0055] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0056] JP 2000-94221

[0003] JP 2013-49461 [0005, 0006, 0006]

Claims

[1] Wafer manufacturing process for producing a hexagonal single-crystal wafer from a hexagonal single-crystal ingot having a first face, a second face opposite the first face, a c-axis extending from the first face to the second face and a c-plane perpendicular to the c-axis, wherein the wafer manufacturing process comprises: a parting point formation step comprising setting a focal point of a laser beam having a transmission wavelength for the ingot at a depth predetermined by the first face inside the ingot, the depth corresponding to a thickness of the wafer to be produced, and nextly applying the laser beam to the first face while moving the focal point and the ingot relative to each other, thereby forming a modified layer parallel to the first face and cracks extending from the modified layer along the c-plane to form a parting point; and a wafer separation step involving the separation of a plate-shaped element with a thickness equal to the thickness of the wafer from the ingot at the separation start point after the execution of the separation start point formation step, in order to produce the wafer from the ingot; including the separation start point training step: a training step for a modified layer with a relative movement of the focal point of the laser beam in a first direction that is perpendicular to a second direction, where the c-axis is inclined with respect to a perpendicular to the first surface by a deviation angle and the deviation angle is formed between the first surface and the c-plane, whereby the modified layer extending in the first direction is formed linearly, and a division step involving a relative movement of the focus in the second direction, in order to move the focus by a predetermined amount; wherein the separation start point formation step includes a first separation start point formation step with scanning the laser beam from a scan start point to a scan end point on the ingot and a second separation start point formation step with scanning the laser beam from the scan end point to the scan start point, wherein the first separation start point formation step and the second separation start point formation step are repeated alternately several times in order to separate the cracks from the modified layer. [2] Wafer manufacturing method according to claim 1, wherein the wafer separation step includes the steps of immersing the hexagonal single-crystal ingot in water and then applying an ultrasonic vibration to the ingot, thereby separating the plate-shaped element from the ingot to produce the hexagonal single-crystal wafer. [3] Wafer manufacturing process according to claim 1 or 2, wherein the hexagonal single crystal ingot is selected from a SiC single crystal ingot and a GaN single crystal ingot.

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