Method and apparatus for manufacturing wafers by laser peeling of SiC ingots

Abstract

The present invention provides a wafer manufacturing method and apparatus for laser delamination of a SiC ingot, which controls the crack propagation path between modified layers by adjusting the scanning direction and incidence angle of the laser beam, and optimizes the crack propagation direction so that it propagates along the cleavage plane by setting a slip angle. [Solution] The method of the present invention adjusts the rotation angle of the SiC ingot and the scanning direction of the laser beam, thereby shifting the scanning direction of the laser beam within a specific angular range relative to the main cutting surface, improving the formation of the modified layer and the crack propagation path, reducing the persistence of wafer defects, and improving the acceptance rate of the finished product.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing wafers, and particularly to a method and apparatus for manufacturing wafers by laser peeling of SiC ingots.

Background Art

[0002] In the current manufacturing of semiconductors and optoelectronic devices, SiC (silicon carbide) wafers have become important materials because they have excellent physical properties such as high thermal conductivity, high electron mobility, and high heat resistance. However, the conventional SiC wafer cutting method mainly depends on wire saw technology, and there are significant problems of efficiency reduction and material loss when processing high-hardness SiC materials.

[0003] The wire saw technology usually slices a SiC ingot like sawing using a metal wire with a diameter of about 100 μm to 300 μm. This method not only requires long-time processing but also has a high material loss rate of 70% to 80%. In particular, in the case of a SiC ingot with a high Mohs hardness, the problem of requiring a long cutting time becomes more prominent, so the possibility of mass production and application is limited.

[0004] In recent years, laser processing technology has been introduced into the SiC wafer cutting process. By adjusting the output, wavelength, and focal position of the laser, a modified layer and cracks can be formed inside the SiC ingot to achieve efficient cutting of the wafer. Compared with the conventional mechanical cutting method, laser processing has the advantages of non-contact, high precision, and high controllability. By forming a modified layer in the SiC ingot, the wafer can be easily peeled along a predetermined cutting path. For example, Japanese Patent Laid-Open No. 2013-49161 describes a technique in which the focal point of a laser beam having a wavelength that is transmissive to SiC is positioned inside a SiC ingot and irradiated to form a modified layer and cracks on the planned cutting surface, and an external force is applied to cut the wafer along the planned cutting surface where the modified layer and cracks are formed to separate the wafer from the ingot.

[0005] To clearly explain the technical means of this application, the upper, lower, left, right, front, and rear sides shown in Figures 1 and 5, and the left, right, front, and rear sides shown in Figure 4 are defined.

[0006] As shown in Figure 1, in this method, there is an angle (for example, 4°) between the cleavage plane of SiC and the crystal surface. JPEG2026101614000002.jpg33155 Actual laser scanning is generally performed along path (1) or path (2). As shown in Figure 3, when the laser is scanned along path (1), the crack gradually extends upward along the cleavage plane, but it does not extend indefinitely. Once it reaches a certain height, the laser energy density drops below the modification threshold, causing the crack height to decrease. Because the dopant concentration in the ingot is non-uniform, a defect region a that extends upward occurs in some areas. If the defect is located on the wafer side after delamination, the defect may remain even after the wafer has been polished to a predetermined thickness, potentially leading to rejection.

[0007] As shown in Figure 3, the applicant discovered that when the laser is scanned along path (2), the cracks gradually extend downward along the cleavage plane, but do not extend indefinitely. Once a certain depth is reached, the laser energy density drops below the modification threshold, causing the crack height to increase. Due to the non-uniform dopant concentration within the ingot, a defect region b that extends downward occurs in some areas. If the defect is located on the ingot side after detachment, the amount of polishing required for the ingot may increase. The impact of increased ingot polishing is small compared to wafer rejection, and as the depth increases, the material's light absorption increases, so the upward-extending defect a becomes larger and the downward-extending defect b becomes smaller. [Overview of the Initiative]

[0008] To solve the above technical problems, the object of the present invention is to provide a wafer manufacturing method by laser peeling of a SiC ingot. This method adjusts the rotation angle of the SiC ingot and the incident angle of the laser beam to shift the scanning direction of the laser beam within a specific angular range relative to the main cutting surface, thereby improving the formation of the modified layer and the crack propagation path, reducing the persistence of wafer defects, and improving the acceptance rate of the finished product.

[0009] To achieve the above objective, the present invention employs the following technical means. A wafer manufacturing method by laser peeling of a SiC ingot, 1) A step of irradiating the ingot with a modification laser beam and positioning the focal point of the modification laser beam at a depth corresponding to the thickness of the wafer to be manufactured from the first surface, thereby forming a modified layer parallel to the first surface of the SiC ingot, 2) After forming the modified layer, the process includes extending the crack from the modified layer to the cleavage plane of the SiC ingot so as to peel the SiC wafer away from the ingot along the crack, The SiC ingot originally has a main cross-section perpendicular to the scanning direction of the modifying laser beam. By adjusting the rotation angle of the SiC ingot and the scanning direction of the modifying laser beam, when the scanning direction of the modifying laser beam is from rear to front, the scanning direction of the modifying laser beam is shifted clockwise by an angle of 1° to 15° relative to the main cross-section, and when the scanning direction of the modifying laser beam is from front to rear, the scanning direction of the modifying laser beam is shifted counterclockwise by an angle of 1° to 15° relative to the main cross-section.

[0010] Preferably, this method is 1) A step of irradiating the ingot with a base laser beam having a first output, and positioning the focal point of this base laser beam at a first depth corresponding to the thickness of the wafer to be manufactured from the first surface, thereby forming a base layer parallel to the first surface of the SiC ingot, 2) After forming the base layer, a modifying laser beam is used in accordance with the position of the base layer, and the focusing point of the modifying laser beam is further positioned at a deeper second depth in the ingot, and a modified layer is formed at the first depth, the rotation angle of the SiC ingot and the scanning direction of the modifying laser beam are adjusted, and when the scanning direction of the modifying laser beam is from rear to front, the scanning direction of the modifying laser beam is shifted clockwise by an angle of 1° to 15° with respect to the main cutting plane, and when the scanning direction of the modifying laser beam is from front to rear, the scanning direction of the modifying laser beam is shifted counterclockwise by an angle of 1° to 15° with respect to the main cutting plane, and 3) After forming the modified layer, the step of extending the crack from the modified layer to the cleavage plane of the SiC ingot so as to peel the SiC wafer away from the ingot along the crack.

[0011] In the above technical means, a low-energy base layer (black dotted line in Figure 6) is pre-processed inside the ingot using a base layer laser beam, and consistency in the depth of the base layer can be ensured by controlling parameters such as the energy of the base layer, the spot spacing, and the pulse width. Next, a second modification laser beam with a higher output than the first output processes the modified layer again along path (2), and the base layer inhibits downward propagation along the cleavage plane of the laser modified layer, ultimately making the depth of the delamination layer more stable.

[0012] Preferably, the base layer can employ multi-spot laser processing to improve the base layer width and more effectively prevent the laser-modified layer from expanding inside the ingot.

[0013] Preferably, the angle of deviation of the scanning direction of the modification laser beam relative to the main cutting surface is 5° to 10°.

[0014] Preferably, the wavelength of the laser beam used for the undercoat is penetrating to the SiC ingot.

[0015] Preferably, the laser beam for modification is irradiated onto the region of the base layer so as to induce the formation of a modified layer by multiphoton absorption and cause cracks to propagate along the cleavage plane.

[0016] Preferably, in the wafer peeling step, an external force is applied to the SiC ingot to separate the wafer from the ingot at the separation starting point between the modified layer and the crack.

[0017] Preferably, the laser beam for modification has a second output that is larger than the first output.

[0018] Preferably, the control parameters of the laser beam for the base are Wavelength: 1000 nm to 1100 nm, Pulse width: 0.0001 ns to 20 ns, Spot diameter: 0.5 μm to 3 μm, Numerical aperture (NA) of the condenser lens: 0.4 to 0.9.

[0019] More preferably, the control parameters of the laser beam for the base are Wavelength: 1000 nm to 1100 nm, Repetition frequency: 90 kHz to 110 kHz, Average output: 0.8 W to 1.2 W, Pulse width: 0.0001 ns to 0.0005 ns, Spot diameter: 1.5 μm to 2 μm, Numerical aperture (NA) of the condenser lens: 0.6 to 0.7.

[0020] Preferably, the control parameters of the laser beam for modification are Wavelength: 1000 nm to 1100 nm, Pulse width: 0.0001 ns to 20 ns Spot diameter: 0.5 μm to 10 μm, Numerical aperture (NA) of the condenser lens: 0.4 to 0.9.

[0021] More preferably, the control parameters of the laser beam for modification are Wavelength: 1000 nm to 1100 nm, Repetition frequency: 90 kHz to 110 kHz, Average output: 2.7 W to 3.3 W, Pulse width: 15 ns to 20 ns, Spot diameter: 1.5 μm to 2 μm, Numerical aperture (NA) of the condenser lens: 0.6 to 0.7.

[0022] Furthermore, the present invention further discloses an apparatus for realizing the above method. This apparatus adjusts the rotation angle of the SiC ingot and the scanning direction of the laser beam for modification. When the scanning direction of the laser beam for modification is from the rear to the front, the scanning direction of the laser beam for modification is shifted by a deviation angle of 1° to 15° clockwise with respect to the main cutting plane. When the scanning direction of the laser beam for modification is from the front to the rear, the scanning direction of the laser beam for modification is shifted by a deviation angle of 1° to 15° counterclockwise with respect to the main cutting plane.

Advantages of the Invention

[0023] By adopting the above technical means, the present invention has the following technical effects. 1. Improvement in the quality of the formed modification layer By controlling the scanning direction of the laser beam for modification to be a specific deviation angle (1° to 15°) with respect to the main cutting plane of the SiC ingot, the formation of the modification layer can be effectively controlled. By such control, the overlapping phenomenon between the modification layers can be reduced, and the quality of the modification layer can be improved by ensuring the uniformity and consistency of the modification layer. By forming such a precise modification layer, the wafer peeling in the subsequent process becomes more controllable and effective. 2. Improvement in the controllability of crack propagation By adjusting the scanning direction and incidence angle of the laser beam, the crack propagation path between modified layers can be controlled. By setting the slip angle, the direction of crack propagation can be optimized to propagate along the cleavage plane. Such optimized crack propagation paths help to form clear and controllable delamination paths within the SiC ingot, thereby achieving high-precision wafer delamination and reducing the risk of wafer residual defects and breakage due to non-uniform crack propagation. 3. Improvement of wafer manufacturing efficiency and yield By using a multi-step modified layer formation method and combining laser beams with different power levels and parameters, the formation depth and position of each modified layer can be precisely controlled. This effectively improves the efficiency of wafer delamination and reduces unnecessary processing steps. At the same time, by precisely controlling the formation of modified layers and cracks, the occurrence of defects and failures can be reduced, and wafer yield can be significantly improved. Such a highly efficient and high-yield manufacturing method is particularly important in industrial production. 4. Reduction of material loss and production costs By optimizing laser beam parameters (e.g., wavelength, pulse width, spot diameter, numerical aperture, etc.) and scanning direction, the present invention can significantly reduce material loss during the processing stage. Precise control of the modified layer and cracks allows for maximum utilization of raw materials when peeling wafers from SiC ingots, reducing material loss due to over-processing or errors. This improvement in material utilization directly reduces production costs and has significant implications for large-scale industrial applications. 5. Improvement of wafer surface processing quality By controlling the scanning direction of the laser beam and other laser processing parameters, micro-defects such as microcracks and increased surface roughness on the wafer surface and within can be reduced. A more stable modified layer and crack formation process can provide a smoother delamination surface, which has significant implications for subsequent wafer processing (e.g., grinding, polishing) and applications (e.g., semiconductor device manufacturing).

[0024] In summary, the present invention, through an innovative laser beam control method and modified layer formation strategy, achieves comprehensive optimization of the SiC wafer manufacturing process from modified layer formation and crack propagation to wafer delamination, significantly improving production efficiency, material utilization, and product quality, and has the potential for a wide range of industrial applications. [Brief explanation of the drawing]

[0025] [Figure 1] This is a schematic diagram of the principles of routes (1) and (2) of the present invention. [Figure 2] This is a right side view of routes (1) and (2) of the present invention. [Figure 3] This is a schematic diagram of the modified layer formed by the scanning direction of the modifying laser beams in path (1) and path (2). [Figure 4] This is a scanning direction diagram of the laser beam processed in Example 1 and Example 2 of the present invention. [Figure 5] This is a schematic diagram of the process used in Example 2. [Figure 6] This is a schematic diagram of the process used in Example 2. [Modes for carrying out the invention]

[0026] The following examples of the present invention will clearly and completely describe the technical means in the examples, but it is clear that the examples described are not all examples of the present invention, but only a selection of them. All other examples that can be obtained by those skilled in the art without any creative work based on the examples of the present invention are all within the scope of the protection of the present invention. Example 1

[0027] Step 1: Formation of the modified layer The SiC ingot is fixed to a support table with its first surface facing upwards, and aligned with the laser beam's incidence path. The ingot is then irradiated with a modification laser beam (wavelength 1064 nm). The focusing point of the modification laser beam is adjusted to a depth of 390 μm from the first surface of the SiC ingot, and this depth corresponds to the reference depth of the wafer thickness to be manufactured. The control parameters for the modification laser beam are set to a pulse width of 20 ns, a spot diameter of 2 μm, a numerical aperture (NA) of 0.7, a repetition rate of 100 kHz, and an average power output of 3 W. The rotation angle of the SiC ingot and the scanning direction of the modification laser beam are adjusted. When the scanning direction of the modification laser beam is from rear to front, the scanning direction of the modification laser beam is shifted 7° clockwise relative to the main cutting plane. When the scanning direction of the modification laser beam is from front to rear, the scanning direction of the modification laser beam is shifted 7° counterclockwise relative to the main cutting plane, ensuring that the shift angle is within an optimized range. The ingot is scanned with respect to the modification laser beam from left to right at a feed rate of 60 mm / s to form a uniform modification layer and to form cracks that propagate along the cleavage plane on both sides of it. Step 2: Wafer Detachment After forming the modified layer and cracks, an external force is applied using a mechanical device to extend the cracks along the direction of the cleavage plane, ultimately achieving the separation of the SiC wafer from the ingot. Example 2

[0028] Step 1: Formation of the sublayer The SiC ingot is fixed to a support table with its first surface facing upward, and aligned with the laser beam's incidence path. The ingot is then irradiated with a base laser beam (wavelength 1064 nm) having a first output. The focusing point of the undercoat laser beam is adjusted to a depth of 390 μm from the first surface of the SiC ingot, and this depth corresponds to the reference depth of the wafer thickness to be manufactured. The control parameters for the laser beam used for the base coat are set to a pulse width of 0.0003 ns, a spot diameter of 2 μm, a numerical aperture (NA) of 0.7, a repetition rate of 100 kHz, and an average power output of 1 W. The ingot is scanned from left to right in relation to the underlying laser beam at a feed rate of 60 mm / s to form a uniform underlying layer. Step 2: Formation of the modified layer After forming the base layer, the SiC ingot is continuously processed using a second-power modifying laser beam (wavelength 1064 nm). The output of the modifying laser beam is greater than that of the base layer laser beam. The focal point of the modifying laser beam is adjusted to a depth of 5 μm deeper than the first depth, i.e., a depth of 395 μm. This depth increases the spot size of the modifying laser beam in the first sublayer to improve the crack propagation efficiency. The control parameters for the modification laser beam are a pulse width of 20 ns, a spot diameter of 2 μm, a numerical aperture (NA) of 0.7, a repetition rate of 100 kHz, and an average power output of 3 W. The rotation angle of the SiC ingot and the scanning direction of the modification laser beam are adjusted. When the scanning direction of the modification laser beam is from rear to front, the scanning direction of the modification laser beam is shifted 7° clockwise relative to the main cutting plane. When the scanning direction of the modification laser beam is from front to rear, the scanning direction of the modification laser beam is shifted 7° counterclockwise relative to the main cutting plane, ensuring that the shift angle is within an optimized range. The ingot is scanned with respect to the modification laser beam from left to right at a feed rate of 60 mm / s to form a modified layer to the same depth as the underlying layer, and to form cracks that propagate along the cleavage plane on both sides of it. Step 3: Wafer Detachment After forming the modified layer and cracks, an external force is applied using a mechanical device to extend the cracks along the direction of the modified layer, ultimately achieving the separation of the SiC wafer from the ingot. Comparative Example 1

[0029] The processing is carried out according to the scanning direction of the laser beam in path (1) in the background art, and other technical features are as shown in Example 1. Comparative Example 2

[0030] In background technology JPEG2026101614000004.jpg8132 Other technical features are as shown in Example 1.

[0031] In the technical means of the examples and comparative examples, the laser processing depth of all ingots is the same, that is, the theoretical depth of focus of the beam inside the ingot is the same.

[0032] In the technical methods of the examples and comparative examples, all wafers are polished to a target thickness of 350 μm, and a microscope is used to observe whether any processing defects such as laser traces or cracks remain inside the wafer.

[0033] In the technical methods of the examples and comparative examples, if processing defects remain even after polishing the wafer to a target thickness of 350 μm, further polishing is not performed, and the number of wafers with residual defects is recorded as unacceptable.

[0034] In the technical means of the examples and comparative examples, all detached ingots must be polished until processing defects such as laser marks and cracks disappear, and the slice loss at this time is recorded as the slice loss when the ingot is cleanly polished.

[0035] In the technical means of the examples and comparative examples, the total removal amount = slice loss when the ingot is cleanly polished - target thickness after wafer polishing.

[0036] In the technical means of the examples and comparative examples, the pass rate = 1 - (number of wafers rejected due to residual traces ÷ number of wafers processed).

[0037] The statistical data on the processing effect is shown in Table 1. Table 1 Statistical data on processing effects JPEG2026101614000005.jpg70149

[0038] The above describes embodiments of the present invention, and by describing the disclosed embodiments, the invention will be realized or used by those skilled in the art. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be realized in other embodiments without departing from the spirit or scope of the invention. Accordingly, the invention is not limited to these embodiments shown herein, but should be given the broadest scope that conforms to the principles and novelty disclosed herein.

Claims

1. 1) A step of irradiating the ingot with a modification laser beam and positioning the focal point of the modification laser beam at a depth corresponding to the thickness of the wafer to be manufactured from the first surface, thereby forming a modified layer parallel to the first surface of the SiC ingot, 2) A wafer manufacturing method by laser peeling of a SiC ingot, comprising the step of forming a modified layer and then extending a crack from the modified layer to the cleavage plane of the SiC ingot so as to peel the SiC wafer from the ingot along the crack, The SiC ingot originally has a main cross-section perpendicular to the scanning direction of the modification laser beam. By adjusting the rotation angle of the SiC ingot and the scanning direction of the modification laser beam, when the scanning direction of the modification laser beam is from rear to front, the scanning direction of the modification laser beam is shifted clockwise by an angle of 1° to 15° relative to the main cross-section, and when the scanning direction of the modification laser beam is from front to rear, the scanning direction of the modification laser beam is shifted counterclockwise by an angle of 1° to 15° relative to the main cross-section, so that the crack gradually extends towards the ingot along the cleavage plane. A method characterized by scanning along a shifted path.

2. This delicious, 1) A step of irradiating the ingot with a base laser beam having a first output, and positioning the focal point of this base laser beam at a first depth corresponding to the thickness of the wafer to be manufactured from the first surface, thereby forming a base layer parallel to the first surface of the SiC ingot, 2) After forming the base layer, a modifying laser beam is used in accordance with the position of the base layer, and the focusing point of the modifying laser beam is further positioned at a deeper second depth in the ingot, and a modified layer is formed at the first depth, the rotation angle of the SiC ingot and the scanning direction of the modifying laser beam are adjusted, and when the scanning direction of the modifying laser beam is from rear to front, the scanning direction of the modifying laser beam is shifted clockwise by an angle of 1° to 15° with respect to the main cutting plane, and when the scanning direction of the modifying laser beam is from front to rear, the scanning direction of the modifying laser beam is shifted counterclockwise by an angle of 1° to 15° with respect to the main cutting plane, and 3) The method according to claim 1, characterized by comprising the step of extending a crack from the modified layer to the cleavage plane of the SiC ingot so as to peel the SiC wafer from the ingot along the crack after the modified layer has been formed.

3. The method according to 1 or 2, characterized in that the deviation angle of the scanning direction of the modifying laser beam with respect to the main cutting surface is 5° to 10°.

4. The method according to the previous invention, characterized in that the wavelength of the laser beam used for the base layer is penetrating to the SiC ingot.

5. The method according to the previous invention, characterized in that the modifying laser beam is irradiated onto the region of the underlying layer so as to induce the formation of a modified layer by multiphoton absorption and cause cracks to propagate along the cleavage plane.

6. The method according to claim 2, characterized in that, in the wafer peeling step, an external force is applied to the SiC ingot to separate the wafer from the ingot at the point of separation between the modified layer and the crack.

7. The method according to claim 2, characterized in that the modifying laser beam has a second output greater than the first output.

8. The control parameters for the laser beam used for the base coat are: Wavelength: 1000nm to 1100nm, Repetition frequency: 90 kHz to 110 kHz, Average output: 0.8W to 1.2W Pulse width: 0.0001 ns to 0.0005 ns Spot diameter: 1.5 μm to 2 μm The method according to claim 2, characterized in that the numerical aperture (NA) of the condensing lens is 0.6 to 0.

7.

9. The control parameters for the laser beam used for modification are: Wavelength: 1000nm to 1100nm, Repetition frequency: 90 kHz to 110 kHz, Average output: 2.7W to 3.3W Pulse width: 15 ns to 20 ns, Spot diameter: 1.5 μm to 2 μm The method according to claim 2, characterized in that the numerical aperture (NA) of the condensing lens is 0.6 to 0.

7.

10. An apparatus for realizing the method described in any one of claims 1 to 9, This apparatus is characterized by adjusting the rotation angle of the SiC ingot and the scanning direction of the modification laser beam, shifting the scanning direction of the modification laser beam by an angle of 1° to 15° clockwise with respect to the main cutting plane when the scanning direction of the modification laser beam is from rear to front, and shifting the scanning direction of the modification laser beam by an angle of 1° to 15° counterclockwise with respect to the main cutting plane when the scanning direction of the modification laser beam is from front to rear.

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