Wafer separation method and wafer separation apparatus

Abstract

A method for separating a wafer includes: forming one or more ablation layers in a crystal ingot based on one or more target planes in the crystal ingot that are perpendicular to an axial direction of the crystal ingot; and separating the crystal ingot into at least two portions based on the one or more ablation layers; wherein forming each ablation layer includes: focusing a laser at a target plane to form a plurality of first focal spots in the crystal ingot, each first focal spot having a center at the target plane, each first focal spot having a dimension in the axial direction that is greater than a dimension in another direction, the plurality of first focal spots forming a grid array, and each first focal spot forming a portion of a boundary of each grid; forming a plurality of second focal spots in the crystal ingot, each second focal spot having a center at the target plane, at least one second focal spot being formed in each grid, and each second focal spot initiating a cleave crack in the crystal ingot that extends along a cleave plane of the crystal ingot. A device for separating a wafer is also provided.

Description

Technical Field

[0001] This application relates to the semiconductor field, and more specifically to a wafer separation method and a wafer separation apparatus. Background Technology

[0002] Semiconductor wafers (hereinafter referred to as wafers) are the cornerstone of chips. Chips are formed by using wafers as carriers and forming device structures through multiple processes such as deposition, photolithography, and etching, and then fabricating them through dicing and packaging.

[0003] Currently, most computer processors, memory, and mobile phone chips are made from silicon wafers. Silicon wafers can be obtained by slicing silicon ingots.

[0004] One possible wafer separation method is to use multi-wire dicing technology. Specific preparation methods include, for example, obtaining cylindrical silicon single crystals by methods such as Czochralski, with the length of the cylindrical silicon single crystals being approximately 100mm to 200mm and the diameter approximately 100mm to 450mm; removing both ends and rounding to obtain a standard cylinder with a uniform outer diameter, i.e., an ingot; and then dicing the cylindrical silicon ingot into wafers of uniform thickness using multi-wire dicing.

[0005] Figure 1 and Figure 2 A schematic diagram is shown of cutting a cylindrical ingot using a multi-wire dicing process. The multi-wire dicing process uses a row of equally spaced dicing wires C moving back and forth at high speed. The dicing wires C cut into the cylindrical side of the ingot B perpendicular to the axis f. After passing through the entire cylinder, the cylindrical ingot B is separated into individual silicon wafers.

[0006] Reference Figure 2 In the above scheme, to ensure the strength of the dicing wire C, C is configured with a sufficiently large wire diameter, typically on the order of several hundred micrometers. Furthermore, to enhance the dicing wire's cutting ability, its surface is coated with diamond particles. The dicing process of ingot B essentially involves cutting away the silicon material in contact with the dicing wire C. The removed silicon single crystal portion represents material loss due to the multi-wire dicing process. For example, for a commonly used wafer with a thickness d1 of 350 micrometers, the thickness d2 of the material loss layer produced by multi-wire dicing technology is approximately 200 to 300 micrometers, representing a material loss percentage of 30% to 45%.

[0007] The aforementioned material losses account for a significant portion of the cost in chip manufacturing. For example, SiC, a wide-bandgap semiconductor material widely used in power devices, is expensive—approximately ten times the price of a silicon wafer of the same size—due to advancements in SiC single-crystal growth methods and technologies. Furthermore, SiC single-crystal material has a Mohs hardness of 9.2, much harder than silicon. This necessitates larger wire diameters during multi-wire cutting to avoid breakage, leading to greater SiC single-crystal material loss. In such cases, the cost waste associated with traditional multi-wire cutting techniques is substantial. Summary of the Invention

[0008] In view of this, this application provides a wafer separation method and a wafer separation apparatus.

[0009] In a first aspect, embodiments of this application provide a wafer separation method.

[0010] In a first possible implementation of the first aspect, the wafer separation method includes:

[0011] One or more ablation layers are formed with reference to one or more target planes perpendicular to the ingot's axis within the ingot: and

[0012] The ingot is divided into at least two parts by one or more ablation layers;

[0013] The formation of each ablation layer includes:

[0014] Focus a laser on a target plane.

[0015] Multiple first focal spots are formed within the ingot, with the center of each first focal spot located on the target plane. The size of the first focal spot in the axial direction is larger than the size of the first focal spot in other directions. The multiple first focal spots are arranged in a grid-like array, and each first focal spot forms part of the boundary of each grid.

[0016] Multiple second focal spots are formed within the ingot, with the center of each second focal spot located on the target plane. At least one second focal spot is formed within each grid, and each second focal spot induces the formation of a cleavage crack extending along the cleavage plane of the ingot.

[0017] The first focal spot acts as a crack-inhibiting point at the boundary of each grid. Cleavage cracks formed by the second focal spot stop propagating when they reach the location of the first focal spot, or in other words, the extension of the cleavage crack terminates at and connects with the first focal spot. Therefore, the cleavage cracks formed within each grid are approximately the same shape as the grid, and these cracks connect with the first focal spot located at the boundary of each grid, resulting in the entire ablation layer forming a series of definite cleavage cracks. In summary, the first focal spot defines the propagation area of ​​the cleavage cracks induced by each second focal spot, and it also connects the cleavage cracks in adjacent grids. Thus, according to this application, a complete ablation layer can be formed, with a regular shape, low surface roughness, and the separated wafer is less prone to breakage, resulting in less crystal material loss.

[0018] According to the first possible implementation of the first aspect, in the second possible implementation of the wafer separation method, a plurality of first focal spots are formed prior to a plurality of second focal spots, or

[0019] At least some of the first focal spots and at least some of the second focal spots are formed simultaneously.

[0020] The first focal spot forms before the second focal spot, or the first and second focal spots form simultaneously. The cleavage cracks induced by the second focal spot terminate at the first focal spot, so that the adjacent cleavage cracks formed are connected by the first focal spot, and the shape of the ablation layer is controllable.

[0021] Secondly, embodiments of this application provide another wafer separation method.

[0022] In the first possible implementation of the second aspect, the wafer separation method includes:

[0023] One or more ablation layers are formed with reference to one or more target planes perpendicular to the axial direction of the ingot; and

[0024] The ingot is divided into at least two parts by one or more ablation layers;

[0025] The formation of each ablation layer includes:

[0026] Focus a laser on a target plane.

[0027] Multiple second focal spots are formed within the ingot, with the center of each second focal spot located on the target plane. Each second focal spot induces the formation of a cleavage crack extending along the cleavage plane of the ingot.

[0028] Multiple first focal spots are formed within the ingot, with the center of each first focal spot located on the target plane. The size of the first focal spot in the axial direction is larger than the size of the first focal spot in other directions. The multiple first focal spots are arranged in a grid-like array, with each first focal spot forming part of the boundary of each grid. Each grid has at least one second focal spot.

[0029] The wafer separation method according to this implementation provides another way of forming focal spots, which is flexible in operation during laser focusing.

[0030] In the third possible implementation of the first aspect, based on any of the possible implementations of the first aspect, or in the second possible implementation of the second aspect, based on the first possible implementation of the second aspect,...

[0031] The method for forming either the first focal spot or the second focal spot includes:

[0032] Place the ingot on the movable platform, focus the laser onto a target plane, and move the movable platform to change the focusing position in the circumferential and / or radial direction of the ingot.

[0033] This implementation method uses a stationary optical system and a moving crystal ingot. This method can improve the size and positional accuracy of the first and second focal spots, ensure the stability and accuracy of the optical system, make the focusing process convenient, and can efficiently and accurately focus the laser to form a focal spot with a predetermined pattern.

[0034] In the fourth possible implementation of the first aspect, or in the third possible implementation of the second aspect, based on any possible implementation of the first aspect,

[0035] The size of the second focal spot in the direction parallel to the cleavage plane of the ingot is larger than the size of the second focal spot in other directions.

[0036] Based on the internal structural characteristics of the crystal, the length direction of the second focal spot is parallel to the cleavage plane, which makes it easy for the second focal spot to coincide with the crack on the cleavage plane, resulting in a relatively smooth ablation layer and less loss of crystal material.

[0037] According to any of the possible implementations of the first aspect above, in the fifth possible implementation of the first aspect, or according to any of the possible implementations of the second aspect above, in the fourth possible implementation of the second aspect,

[0038] The first and / or second focal spot are formed by connecting multiple circular focal spots end to end to create an elongated shape.

[0039] The optical system required for a circular focal spot has a simple structure, and the focal spot according to this implementation can be formed by a simple optical system.

[0040] According to any of the possible implementations of the first aspect above, in the sixth possible implementation of the first aspect, or according to any of the possible implementations of the second aspect above, in the fifth possible implementation of the second aspect,

[0041] Two adjacent cleavage surface cracks are respectively connected to the two ends of at least one first focal spot in the axial direction.

[0042] According to this implementation, adjacent cleavage surface cracks are closely connected, making it easy to form a complete ablation layer. Furthermore, the length of the first foci can be kept as short as possible, reducing the surface roughness of the ablation layer and minimizing material loss.

[0043] According to any of the possible implementations of the first aspect above, in the seventh possible implementation of the first aspect, or according to any of the possible implementations of the second aspect above, in the sixth possible implementation of the second aspect,

[0044] The numerical aperture of the optical system used to generate the first focal spot is larger than the numerical aperture of the optical system used to generate the second focal spot.

[0045] According to any possible implementation of the first aspect above, in the eighth possible implementation of the first aspect, or according to any possible implementation of the second aspect above, in the seventh possible implementation of the second aspect,

[0046] Dividing the ingot into at least two parts, with one or more ablation layers as boundaries, includes:

[0047] Using an ablation layer as the separation boundary, the wafer located on one side of the ablation layer is separated from the ingot located on the other side of the ablation layer.

[0048] Since the morphology of the ablation layer is controllable and the surface is relatively flat, the wafer separation method according to this implementation can easily separate individual wafers.

[0049] According to any of the possible implementations of the first aspect above, in the ninth possible implementation of the first aspect, or according to any of the possible implementations of the second aspect above, in the eighth possible implementation of the second aspect,

[0050] Dividing the ingot into at least two parts, with one or more ablation layers as boundaries, includes:

[0051] Multiple wafers and ingots, defined by multiple ablation layers, are continuously separated.

[0052] Multiple ablation layers are formed sequentially within the ingot. For multiple ablation layers formed from the same laser source location, the later-formed ablation layer is closer to the laser source location than the earlier-formed ablation layer.

[0053] The wafer separation method according to this implementation separates the repetitive laser ablation step from the repetitive wafer removal step, which can improve wafer separation efficiency and is suitable for large-scale production organization.

[0054] According to the eighth or ninth possible implementation of the first aspect above, in the tenth possible implementation of the first aspect, or according to the seventh or eighth possible implementation of the second aspect above, in the ninth possible implementation of the second aspect,

[0055] Removing the wafer includes:

[0056] Cut the outer edge of the ablation layer to separate the outer periphery of the wafer from the ingot.

[0057] The wafer separation method according to this implementation can eliminate the problem of incomplete ablation that may exist at the edge of the ingot, making the operation of separating the wafer from the ingot easier to implement.

[0058] Based on the tenth possible implementation of the first aspect above, in the eleventh possible implementation of the first aspect, or based on the ninth possible implementation of the second aspect above, in the tenth possible implementation of the second aspect,

[0059] The outer peripheral edge of the ablation layer includes:

[0060] The ingot is rotated around its axis, and the crystal material at the outer periphery of the ablation layer is removed by a cutting device.

[0061] The wafer separation method according to this implementation is accurate, precise, simple and efficient in cutting the outer peripheral edge of the ablation layer.

[0062] In the twelfth possible implementation of the first aspect, based on the tenth or eleventh possible implementation of the first aspect, or in the eleventh possible implementation of the second aspect, based on the ninth or tenth possible implementation of the second aspect,

[0063] Removing the wafer also includes:

[0064] The chuck is attached to the axial end face of the wafer, allowing the chuck to carry the wafer away from the ingot.

[0065] The wafer separation method according to this implementation is convenient for wafer removal, has a large contact area between the chuck and the wafer, and the wafer is subjected to uniform force, making it less prone to breakage or other damage.

[0066] Thirdly, embodiments of this application provide a wafer separation apparatus.

[0067] In a first possible implementation of the third aspect, the wafer separation apparatus is used to separate one or more wafers from an ingot using any possible wafer separation method according to the first aspect above or any possible wafer separation method according to the second aspect above, the wafer separation apparatus comprising:

[0068] A laser generating mechanism for forming a first and second focal spot;

[0069] The moving platform is used to support the crystal ingot and drive it to translate and / or rotate about its own axis; and

[0070] The wafer removal mechanism is used to separate the wafer from the ingot.

[0071] The wafer separation device according to this implementation method has a simple structure and can separate wafers in an efficient and material-saving manner.

[0072] According to the first possible implementation of the third aspect, in the second possible implementation of the wafer separation device, the wafer removal mechanism includes a cutting device for cutting the ingot at the outer peripheral edge of the ablation layer.

[0073] The wafer separation device according to this implementation can effectively separate the outer periphery of the wafer, which is beneficial for separating wafers with regular surfaces and reduces waste of crystal material.

[0074] According to the second possible implementation of the third aspect, in the third possible implementation of the wafer separation device, the cutting device is a laser scalpel or a grinding wheel.

[0075] The wafer separation device according to this implementation method has good cutting accuracy and high efficiency for the outer periphery of the wafer.

[0076] According to any possible implementation of the third aspect above, in a fourth possible implementation of the third aspect, the wafer removal mechanism includes a chuck that can move to the axial end of the ingot to pick up and transfer the wafer.

[0077] The wafer separation device according to this embodiment can conveniently and efficiently separate wafers from wafer ingots. The large contact area between the suction cup and the wafer ensures uniform force on the wafer, reducing the risk of breakage or other damage.

[0078] According to any possible implementation of the third aspect above, in a fifth possible implementation of the third aspect, the wafer separation device further includes a polishing mechanism.

[0079] The polishing mechanism is used to polish the axial end face of the wafer where the ablation layer is located, and / or

[0080] The polishing mechanism is used to polish the axial end face where the ablation layer of the crystal ingot is located.

[0081] The wafer separation apparatus according to this implementation can obtain wafers with smooth surfaces that can be used for epitaxy. Attached Figure Description

[0082] Figure 1 and Figure 2 This is a schematic diagram of a possible method for separating wafers using multi-wire dicing technology;

[0083] Figure 3 and Figure 4 This is a schematic diagram of a possible method for separating wafers using lasers;

[0084] Figure 5 This is a schematic diagram of separating a wafer from a crystal ingot according to one embodiment of this application;

[0085] Figure 6 This is a cross-sectional schematic diagram of an ablation layer formed through a first foil and a second foil according to an embodiment of this application;

[0086] Figure 7 This is a schematic cross-sectional view of a crystal ingot with a first focal spot formed according to an embodiment of this application;

[0087] Figure 8 This is a schematic cross-sectional view of a crystal ingot having a first and a second focal spot formed according to an embodiment of this application;

[0088] Figure 9 This is a cross-sectional schematic diagram of a laser forming an ablation layer in a crystal ingot according to an embodiment of this application;

[0089] Figure 10 and Figure 11 This is a schematic diagram of cutting the edge of a crystal ingot with a grinding wheel to separate a wafer according to one embodiment of this application;

[0090] Figure 12 This is a schematic diagram of cutting the edge of a crystal ingot with a laser cutter to separate a wafer according to one embodiment of this application;

[0091] Figure 13 This is a cross-sectional view of a wafer being removed using a chuck according to an embodiment of this application;

[0092] Figure 14 This is a cross-sectional view of a wafer end face being polished with a polishing wheel according to an embodiment of this application;

[0093] Figure 15 This is a cross-sectional view of a wafer end face being polished with a chemical mechanical polishing disc according to an embodiment of this application;

[0094] Figure 16 This is a cross-sectional view of the end face of a crystal ingot being polished with a polishing wheel according to an embodiment of this application.

[0095] Figure 17 This is a wafer separation method according to an embodiment of the present application.

[0096] Explanation of reference numerals in the attached figures:

[0097] B-crystal ingot; B0 wafer; Bf crystal plane;

[0098] C-cutting line; f-axis; a-angle of deviation; Fc-cleavage plane;

[0099] L-laser; L0 focal spot; L1 first focal spot; L2 second focal spot; Lk laser scalpel;

[0100] S-ablation layer; K1 cleavage surface crack; K2 induced crack;

[0101] P activity platform; D suction cup; W cutting wheel; Po1 polishing wheel; Po2 chemical mechanical polishing disc;

[0102] A is the axial direction; R is the radial direction; D1 is the first direction. Detailed Implementation

[0103] Unless otherwise specified, refer to Figure 5 , Figure 11 and Figure 12 A represents the axial direction of the wafer separation device, which is aligned with the axial direction of the ingot; R represents the radial direction of the wafer separation device, which is aligned with the radial direction of the ingot.

[0104] Unless otherwise specified, this application uses the vertical relationship shown in the figure to illustrate the positional relationship of each component. It should be understood that this vertical relationship is not absolute, and the spatial orientation of the components may change accordingly depending on the product application scenario and working posture.

[0105] Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following related objects are in an "or" relationship.

[0106] Laser separation technology is a wafer separation method with high separation accuracy.

[0107] like Figure 3 As shown, laser wafer separation technology uses a laser L (or laser beam) focused at a certain depth within ingot B. The focal point forms a focal spot, which ablates the ingot. Multiple focal spots connect to form an ablation layer S. After the material of the ablation layer S is lost, ingot B can be separated into a wafer B0 located on one side of the ablation layer S and the remaining ingot B located on the other side of the ablation layer S (for convenience, the part that can be further separated will still be referred to as the ingot).

[0108] Figure 4 A schematic diagram is shown illustrating the formation of an easily separable ablation layer S using focal spots. This diagram uses a SiC single crystal as an example. The laser ablation effect causes a small cleavage crack K1 to form at each focal spot L0. Since the crystal plane Bf (the axial end face of ingot B) of a typical SiC single crystal ingot B typically forms a 4-degree angle with the cleavage plane, the cleavage cracks K1 formed by multiple focal spots L0 at the same depth within ingot B are all inclined relative to the crystal plane Bf. These multiple cleavage cracks K1 are essentially parallel and do not intersect each other. Furthermore, the multiple cleavage cracks K1 exhibit uneven coverage and uneven height.

[0109] To form a damage layer that can separate the wafer, one possible method is to apply an external force to the ingot after laser ablation, such as rotating the ingot, warping the edges, or applying ultrasound, thereby forming induced cracks K2 between adjacent cleavage surface cracks K1. The induced cracks K2 and the cleavage surface cracks K1 connect together to form a damage layer that can separate the wafer B0.

[0110] However, due to the inhomogeneity of the cleavage crack K1 and the uncertainty of the orientation of the induced crack K2, traditional laser wafer separation technology suffers from problems such as uneven and inhomogeneous damaged layer surfaces and uncontrollable dimensions, leading to the fragility of the prepared wafer B0. In addition, the loss of single-crystal materials is also relatively large.

[0111] The applicant has made this application after considering several factors, including those mentioned above.

[0112] Reference Figures 5 to 16 Taking SiC single crystal ingot B as an example, the wafer separation method and wafer separation apparatus according to this application are introduced.

[0113] Reference Figure 5 In this embodiment, the ingot B is cylindrical in shape, and its axis f (parallel to the axial direction A) forms an angle α with the perpendicular direction of the crystallization direction. In this embodiment, the angle α is approximately 4°.

[0114] When a crystalline mineral is subjected to stress, its own structure causes the crystal to cleave along a certain crystallographic direction, forming smooth planes. This process is also called cleavage, and the smooth planes formed are called cleavage planes. The following will use cleavage planes to explain the method of separating the ingot B and the wafer B0 from ingot B.

[0115] In this embodiment, the cleavage surface Fc is <0001> The plane (parallel to directions <1-100> and <11-20>) has an axis f that forms an angle α with the perpendicular line to the cleavage plane Fc.

[0116] The two end faces (also called crystal faces, referring to the end faces formed after polishing and cleaning) on ​​the axial direction A of the wafer B0 separated from the ingot B also form an angle a with the cleavage plane Fc.

[0117] Reference Figure 6 This application employs a laser ablation method to separate wafers. This method uses a laser to form an ablation layer S within the wafer ingot B, with a target plane as the reference. The target plane is a virtual plane perpendicular to the axial direction A. Using the target plane as the reference means that the centers (focusing positions of the laser) of the first and second focal spots, as described below, are located within this target plane. It should be understood that because the first and second focal spots have specific dimensions and extension directions, they are not entirely located within the target plane. For ease of description, it is sometimes stated that the first and second focal spots are located within the target plane; in reality, this means that the centers of the first and second focal spots are located within the target plane.

[0118] The target plane is, for example, approximately 350 micrometers away from one axial end face (hereinafter referred to as the upper surface) of ingot B. This depth is slightly greater than the thickness of the finished wafer B0 along axis A. This is because, for a given finished wafer B0, considering that wafer B0 still needs to be polished and cleaned after separation, a margin can be left for polishing.

[0119] With the ablation layer S as the boundary, one side of its axial direction can be used to form wafer B0. For the sake of convenience, the remaining part on the other side will still be called ingot B.

[0120] It should be understood that in other possible applications, the ablation layer S may also be used simply to divide the ingot B into two parts, both of which may have large axial dimensions rather than directly forming the wafer B0.

[0121] To achieve a regular surface in the ablation layer S, this application uses laser focusing to form two types of focal spots: a first focal spot L1 and a second focal spot L2. The second focal spot L2 utilizes the cleavage properties of the crystal to form multiple cleavage cracks K1 within the ingot B that are parallel to (or extend along) the cleavage plane Fc. The first focal spot L1 connects these multiple cleavage cracks K1 together and prevents further propagation of the cleavage cracks K1. Thus, the ablation layer S is essentially defined only by the area covered by the cleavage cracks K1 and the first focal spot L1.

[0122] (Formation of the ablation layer)

[0123] Combination Figures 6 to 9 This paper introduces the method for forming the ablation layer S.

[0124] First, refer to Figure 6 and Figure 7 The structure of the first focal spot L1 is introduced.

[0125] The first focal spot L1 is used to define the boundary of crack K1 on each cleavage plane, and the first focal spot L1 is not used to cause cleavage in the crystal. The first focal spot L1 is also called the crack suppression point.

[0126] Each first focal spot L1 is elongated, with its dimension along the axial direction A of ingot B being larger than its dimension in other directions. This makes it less likely for the first focal spot L1 to induce cleavage within ingot B; that is, the first focal spot L1 will not induce unwanted cracks in the crystal.

[0127] Multiple first focal spots L1 are arranged in a grid-like array, with each first focal spot L1 forming part of the grid boundary. The multiple grids divide the region where the ablation layer S is desired into multiple sub-regions (each grid representing one sub-region), which makes each cleavage crack K1 described below occupy only a small area, facilitating the formation of the ablation layer S and resulting in a low surface roughness of the ablation layer S. Optionally, the maximum size of each grid in each direction is 50 to 1000 micrometers.

[0128] It should be understood that by changing the distance between adjacent first focal spots L1, i.e., changing the size of each grid in the grid array, the surface smoothness (or roughness) of the ablation layer S can be adjusted, thereby controlling the amount of material loss during wafer separation. This is because, for example, the smaller the distance between adjacent first focal spots L1 (in short, the denser the first focal spots L1), the shorter the propagation distance of the cleavage crack K1 generated by the second focal spot L2, and thus the smaller the surface undulation of the ablation layer S. Of course, the denser the first focal spots L1, the higher the laser scanning speed is usually required, and the greater the laser ablation cost. In practical applications, a balance can be struck between the cost of laser use and the loss of crystal material.

[0129] In this embodiment, each grid (except for the grids that are adjacent to the edge of ingot B) is approximately square in shape. It should be understood that in other possible embodiments, a single grid may also be other shapes, such as triangles, quadrilaterals, or hexagons, and the grid array may include a variety of different grid shapes.

[0130] Next, refer to Figure 6 and Figure 8 The structure of the second focal spot L2 is introduced.

[0131] The second focal spot L2 is used to induce cleavage crack K1 in the crystal. It should be understood that the cleavage crack K1 is formed spontaneously along with the formation of the second focal spot L2, and no other external force needs to be applied to the ingot B during this process.

[0132] To ensure that the second focal spot L2 can induce cleavage cracks K1 in ingot B, the second focal spot L2 is elongated, with its dimension in the first direction D1 being larger than its dimensions in other directions, and the first direction D1 is not parallel to the axial direction A. In this embodiment, the first direction D1 is parallel to the axial end face of ingot B. However, preferably, the first direction D1 is parallel to the cleavage surface Fc.

[0133] In a grid-like array constructed from multiple first focal spots L1, at least one (one in this embodiment) second focal spot L2 is formed within each grid.

[0134] Optionally, the cleavage crack K1 formed by the second focal spot L2 within each grid is connected to the first focal spot L1 surrounding the grid. According to the formation mechanism of the cleavage crack K1, the boundary of the cleavage crack K1 terminates at the first focal spot L1 it contacts, thus forming a shaped split region by the first focal spot L1 around each grid and the second focal spot L2 inside.

[0135] Optionally, two adjacent cleavage cracks K1 are respectively connected to the two ends of at least one first focal spot L1 along the axial direction A. Alternatively, each end of the first focal spot L1 along the axial direction A is connected to a cleavage crack K1. This connected structure can be achieved, for example, by reasonably calculating the length of the first focal spot L1 along the axial direction A and the size of the grid. This allows the split regions formed by each grid to connect together, thereby forming a complete ablation layer S that can divide the ingot B.

[0136] It should be understood that, due to various reasons (such as errors in actual operation), at least part of the first focal spot L1 may not be connected to the adjacent cleavage surface crack K1, for example, there may be a very small gap between the first focal spot L1 and the adjacent cleavage surface crack K1. Such a small-sized (e.g., less than 5 micrometers) connection region may be destroyed subsequently by applying a very small external force.

[0137] In this embodiment, for each ablation layer, all first foci L1 are formed before second foci L2. Thus, the boundary of the cleavage surface cracks K1 induced by the second foci L2 can be defined according to the position of the first foci L1, or in other words, adjacent cleavage surface cracks are connected by the first foci L1, making the shape of the ablation layer S controllable.

[0138] It should be understood that in other possible implementations, at least a portion of the second focal spot L2 may form before the first focal spot L1, or at least a portion of the second focal spot L2 may form simultaneously with at least a portion of the first focal spot L1. According to this formation method, cleavage cracks K1 may occur at the second focal spot L2 that are not formed later, extending beyond the adjacent first focal spot L1. It should be understood that as long as the cleavage cracks K1 are contiguous with the first focal spot L1, or very close to it, a relatively regular ablation layer S can still be formed.

[0139] The following describes the method for forming the first focal spot L1 and the second focal spot L2 according to this embodiment.

[0140] Optionally, the upper surface of ingot B (the surface through which the laser passes) is first polished to form an optically grade (e.g., surface roughness less than 5 nanometers) smooth surface. This facilitates laser passage and subsequent wafer separation.

[0141] The ingot B is placed on the movable platform P. A first laser source is used to focus the laser on the target plane (e.g., 350 micrometers away from the upper end face) along the axial direction of the ingot B. The movable platform P is moved so that the focusing position changes along the first preset path in the circumferential and / or radial directions of the ingot B, thereby forming a grid-like array constructed by the first focal spot L1 in the target plane.

[0142] Optionally, the numerical aperture of the optical system used to form the first focal spot L1 is 1.3 to 1.5.

[0143] Then, using a second laser source, the laser is focused on the target plane along the axial direction of ingot B. The movable platform P is moved so that the focusing position changes along the second preset path in the circumferential and / or radial directions of ingot B, thereby forming a second focal spot L2 in each grid.

[0144] Optionally, the numerical aperture of the optical system used to form the second focal spot L2 is smaller than the numerical aperture of the optical system used to form the first focal spot L1, and the numerical aperture of the optical system used to form the second focal spot L2 is 0.4 to 0.3.

[0145] Optionally, the elongated focal spot (first focal spot L1 and / or second focal spot L2) can be formed at once by a specific or combined focusing lens; or it can be formed by forming one circular focal spot at a time and connecting multiple circular focal spots together to form the elongated focal spot.

[0146] (Remove the wafer)

[0147] Next, refer to Figures 9 to 16 This paper introduces the steps involved in wafer separation, including wafer removal and subsequent steps.

[0148] Using the aforementioned ablation layer S as a boundary, the wafer B0, separated from the ingot B by the ablation layer S, is removed from the ingot B. Two methods for removing the wafer are described here.

[0149] The first method involves removing a wafer B0 after each ablation layer S is formed, and then forming the next ablation layer S, and so on.

[0150] The second method is to continuously form multiple ablation layers S at different depths within the ingot B, and then continuously remove the multiple wafers B0 separated by these multiple ablation layers S one by one.

[0151] In the second method, in order to ensure the quality of the focal spot formation, optionally, for multiple ablation layers S formed from the same laser source location, the later-formed ablation layer S is closer to the laser source location than the earlier-formed ablation layer S, so that the earlier-formed ablation layer S will not hinder or affect the later-formed ablation layer S.

[0152] Here, "laser source location" refers to the incident position of the laser on ingot B. For example, if the laser is incident from the top of ingot B, the later-formed ablation layer S will be closer to the top of ingot B than the earlier-formed ablation layer S; in other words, the ablation layer S near the bottom will form first, followed by the ablation layer S near the top. As another example, if the laser can be incident from both ends of ingot B, the ablation layer S located in the middle along axis A will form first, followed by the ablation layers S near the two ends.

[0153] The following mainly introduces the wafer separation method after the formation of the ablation layer S.

[0154] Optionally, the separation method includes: step (a), cutting the outer peripheral edge of the ablation layer S.

[0155] Because the laser focusing efficiency is limited at the edge of ingot B, the ablation layer S may not extend completely to the edge of ingot B (this phenomenon is also known as the edge effect of laser ablation). Therefore, alternatively, a cutting device can be used to cut the outer peripheral edge of the ablation layer S.

[0156] Alternatively, the ingot B can be rotated about its axis f, and the crystal material at the outer peripheral edge of the ablation layer S can be removed by a cutting device.

[0157] Optionally, during the cutting and ablation of the layer S, a vacuum adsorption stage (e.g., a porous ceramic vacuum adsorption stage) is used to position the ingot B. The ingot B is fixed by the adsorption device on the stage, allowing the ingot B to rotate with the stage with high motion accuracy.

[0158] Alternatively, the cutting device may be a laser cutter Lk or a grinding wheel W.

[0159] Figure 10 and Figure 11 The diagram illustrates a method of cutting the outer peripheral edge of the ablation layer S using a grinding wheel W. Optionally, the grinding wheel W rotates in the same direction as the ingot B, so that at the point of contact, the contact portions of the two can move in opposite directions. Optionally, the thickness of the cutting portion of the grinding wheel W in the axial direction A is 150 to 300 micrometers, and the depth of the grinding wheel W extending into the ingot B in the radial direction R is 20 to 500 micrometers.

[0160] Figure 11 The method of cutting ingot B using a laser cutter Lk is shown. That is, the laser is focused on the outer peripheral edge of the ablation layer S, and the crystalline material at the outer peripheral edge of the ablation layer S is removed by laser ablation.

[0161] Optionally, the separation method further includes step (b), using a chuck to remove wafer B0.

[0162] Optionally, the chuck D is attached to the axial end face of the wafer B0 away from the ablation layer S, and carries the wafer B0 away from the ingot B.

[0163] Optionally, the separation method further includes: step (c), polishing the two axial end faces of wafer B0, and / or polishing the axial end face where the ablation layer S of ingot B is located.

[0164] Optionally, polishing the axial end face of wafer B0 includes mechanical polishing and chemical mechanical polishing of the axial end face of wafer B0. Optionally, the polishing mechanism includes a polishing wheel Po1 (see reference). Figure 14 (for mechanical polishing) and chemical mechanical polishing disc Po2 (refer to) Figure 15 (used for chemical mechanical polishing).

[0165] Optionally, the axial end face where the ablation layer S of the polished ingot B is located includes mechanical polishing of that end face. Optionally, refer to Figure 16 Mechanical polishing was performed using a polishing wheel Po1.

[0166] Optionally, after polishing wafer B0, wafer B0 is cleaned to obtain a wafer that can be used for epitaxy.

[0167] (Wafer separation device)

[0168] It should be understood that this application also provides a wafer separation apparatus for separating wafers using the above-described separation method. The apparatus includes a laser generating mechanism, a movable platform P, a wafer removal mechanism, and a polishing mechanism.

[0169] The laser generating mechanism is used to form the first focal spot L1 and the second focal spot L2.

[0170] The active platform P is used to support the crystal ingot B and drive the crystal ingot B to perform translational motion and / or rotation around its own axis f.

[0171] The wafer removal mechanism is used to separate wafer B0 from ingot B. Optionally, the wafer removal mechanism includes a dicing device and a suction cup D. Optionally, the dicing device is selected from a laser cutter Lk or a grinding wheel W.

[0172] Optionally, the polishing mechanism includes a polishing wheel Po1 and a chemical mechanical polishing disc Po2.

[0173] Optionally, suction cup D is a porous ceramic vacuum suction cup.

[0174] Next, using two embodiments as examples, we will describe the specific steps of separating a wafer using the wafer separation method according to this application.

[0175] (Example 1)

[0176] Step 1: A SiC ingot with a height of 15 mm and a diameter of 6 inches along the axial direction A is grown using PVT (Physical Vapor Transport). The ingot is then oriented, and the <11-20> face and a face offset of 4 degrees towards the <11-20> direction are ground out. <0001> Noodles; will <0001> A standard cylinder is machined from one of the circular end faces; the height of the standard cylinder of the resulting ingot along axis A is 12mm.

[0177] Step 2: Polish the upper surface of the ingot with a 10000# grinding wheel to obtain an optically smooth end face (the surface roughness of the upper surface is 2nm).

[0178] Step 3: Fix the crystal ingot on a precision moving platform that can move horizontally, so that the lower end face of the crystal ingot is in close contact with the moving platform, and keep the cross-section (upper surface) of the crystal ingot parallel to the surface of the moving platform.

[0179] Step 4: A laser with a wavelength of 1064 nanometers and a pulse width of 1 nanosecond is used as the laser generating mechanism. The laser is turned on, and a first focusing lens with an NA value (numerical aperture of the optical system) of 1.3 is used to set the focusing depth to 350 micrometers from the upper surface of the crystal ingot. The first preset path of the moving platform is set so that the laser forms multiple first focal spots arranged in a grid array in the target plane 350 micrometers from the upper surface of the crystal ingot. The spacing between adjacent first focal spots is 200 micrometers in the <1-100> direction and 200 micrometers in the <11-20> direction.

[0180] Step 5: Switch the laser to the second focusing lens with an NA value of 0.4 and set the focusing depth to 350 micrometers from the upper surface of the ingot; set the second preset path of the moving platform so that the laser forms multiple second focal spots in the target plane 350 micrometers from the upper surface of the ingot, wherein at least one second focal spot is formed in each grid of the grid array formed by the first focal spot; the multiple second focal spots form multiple cleavage surface cracks that extend along the cleavage surface, and each cleavage surface crack stops extending when it encounters the first focal spot around it.

[0181] Step 6: Transfer the ingot to a porous ceramic vacuum adsorption stage and rotate the stage at 100 rpm. Use a grinding wheel with a blade thickness of 0.3 mm and a rotation speed of 30,000 rpm to cut the outer periphery of the ablation layer. The grinding wheel is set on the side of the ingot. In the initial state, the grinding wheel does not contact the ingot. The grinding wheel slowly approaches the ingot at a speed of approximately 0.5 mm / s. After contacting the ingot, it extends 1 mm into the ingot in the radial direction R.

[0182] Step 7: Use a porous ceramic vacuum chuck to adhere to the upper surface of the ingot, move the vacuum chuck slightly, separate and remove the wafer.

[0183] Step 8: First, use an 8000# grinding wheel to mechanically polish the end face of the removed wafer where the ablation layer is located (referred to as the ablation surface); then use silica sol with a particle size of 20nm to perform chemical mechanical polishing on the end face of the wafer, so that the surface roughness of the end face is less than 0.3nm; then, through the RCA cleaning process, a wafer that can be used for epitaxy is obtained.

[0184] Step 9: Use a 10000# grinding wheel to mechanically polish the ablation surface of the ingot after laser ablation separation to obtain an optically smooth end face with a roughness of 2nm.

[0185] Then, steps 3 to 9 above are repeated 28 times (assuming that the ingots remaining after the last separation can directly correspond to a wafer), which can produce 30 epi-ready SiC wafers that can be used for epitaxial growth.

[0186] (Example 2)

[0187] Step 1: A SiC ingot with a height of 25 mm and a diameter of 6 inches along the axial direction A is grown using the PVT method; the ingot is then oriented, and the <11-20> face and a face offset of 4 degrees towards the <11-20> direction are ground out. <0001> Noodles; will <0001> A standard cylinder is machined from one of the rounded end faces; the height of the standard cylinder of the resulting ingot along axis A is 23 mm.

[0188] Step 2: Polish the upper surface of the crystal ingot with a 20000# grinding wheel to obtain an optically smooth end face (the surface roughness of the upper surface is 1nm).

[0189] Step 3: Fix the crystal ingot on a precision moving platform that can move horizontally, so that the lower end face of the crystal ingot is in close contact with the moving platform, and keep the cross-section (upper surface) of the crystal ingot parallel to the surface of the moving platform.

[0190] Step 4: A laser with a wavelength of 1064 nm and a pulse width of 150 femtoseconds is used as the laser generating mechanism. The laser is turned on, and a first focusing lens with an NA (numerical aperture) of 1.5 is used. The focusing depth is set to 350 micrometers from the upper surface of the crystal ingot. A first preset path is set for the moving platform, causing the laser to form multiple first focal spots arranged in a grid array within the target plane 350 micrometers from the upper surface of the crystal ingot. The spacing between adjacent first focal spots is 400 micrometers in the <1-100> direction and 400 micrometers in the <11-20> direction.

[0191] Step 5: Switch the laser to the second focusing lens with an NA value of 0.3 and set the focusing depth to 350 micrometers from the upper surface of the ingot; set the second preset path of the moving platform so that the laser forms multiple second focal spots in the target plane 350 micrometers from the upper surface of the ingot, wherein at least one second focal spot is formed in each grid of the grid array formed by the first focal spot; the multiple second focal spots form multiple cleavage surface cracks that extend along the cleavage surface, and each cleavage surface crack stops extending when it encounters the first focal spot around it.

[0192] Step 6: Transfer the ingot to a porous ceramic vacuum adsorption stage and rotate the stage at 150 rpm. Use a grinding wheel with a blade thickness of 0.2 mm and a rotation speed of 20,000 rpm to cut the outer periphery of the ablation layer. The grinding wheel is set on the side of the ingot. Initially, the grinding wheel does not contact the ingot. The grinding wheel slowly approaches the ingot at a speed of approximately 0.5 mm / s. After contacting the ingot, it extends 0.5 mm into the ingot in the radial direction R.

[0193] Step 7: Use a porous ceramic vacuum chuck to adhere to the upper surface of the ingot, move the vacuum chuck slightly, separate and remove the wafer.

[0194] Step 8: First, use a 20000# abrasive wheel to mechanically polish the end face of the removed wafer where the ablation layer is located (referred to as the ablation surface); then use silica sol with a particle size of 10nm to perform chemical mechanical polishing on the end face of the wafer, so that the surface roughness of the end face is less than 0.2nm; then, through the RCA cleaning process, a wafer that can be used for epitaxy is obtained.

[0195] Step 9: Use a 20000# grinding wheel to mechanically polish the ablation surface of the ingot after laser ablation separation to obtain an optically smooth end face with a roughness of 1nm.

[0196] Then, steps 3 to 9 above were repeated 56 times (assuming that the ingots remaining after the last separation can directly correspond to a wafer), to process 58 epi-ready SiC wafers that can be used for epitaxial growth.

[0197] It should be understood that, for either of the two embodiments described above, the step numbers are not intended to completely define the execution order of the steps, and the execution order of some steps can be adjusted. For example, steps 4 and 5 can be executed simultaneously, or step 5 can be executed before step 4. When step 5 is executed before step 4, the first focal spot has not yet formed when the cleavage crack is formed. Therefore, after the first focal spot is formed, it may appear that some cleavage cracks extend beyond the adjacent first focal spot. Alternatively, steps 3 to 5 can be repeated several times to continuously form multiple ablation layers, and then steps 6 to 9 can be repeated several times to separate the multiple wafers defined by the previously continuously formed multiple ablation layers.

[0198] Figure 17 A wafer separation method according to an embodiment of this application is illustrated. It includes:

[0199] One or more ablation layers are formed with reference to one or more target planes perpendicular to the axial direction of the ingot; and

[0200] The ingot is divided into at least two parts by one or more ablation layers.

[0201] The formation of each ablation layer includes:

[0202] A laser is focused onto a target plane to form multiple first focal spots within the ingot. The center of each first focal spot is located on the target plane. The size of the first focal spot in the axial direction is larger than the size of the first focal spot in other directions. The multiple first focal spots are arranged in a grid-like array, and each first focal spot forms part of the boundary of each grid.

[0203] Keeping the target plane focused by the laser unchanged, multiple second focal spots are formed in the ingot. The center of each second focal spot is located in the target plane. At least one second focal spot is formed in each grid. Each second focal spot induces the formation of a cleavage crack in the ingot that extends along the cleavage plane of the ingot.

[0204] The following is a brief description of some of the beneficial effects of the above-described embodiments of this application.

[0205] (i) In the process of ablation of the ingot, this application introduces a first focal spot that can suppress cracks, thereby controlling the size of the cleavage surface cracks generated by the second focal spot, so that the final ablation surface shape is controllable and the roughness is small, the wafer is not easy to break, and the material loss during the processing is small.

[0206] (ii) Because the ablation layer has a smaller roughness, it can reduce the amount of consumables (e.g., grinding wheels) used in the polishing process and save time costs in the polishing process.

[0207] (iii) Considering that the laser does not completely ablate the edge of the ingot, a step of cutting the outer periphery of the ablation layer is added, which facilitates the complete separation of the wafer and the ingot and avoids the edge cracks from being torn or fragmented under external force due to incomplete splitting.

[0208] (iv) According to experiments, for a SiC ingot with an axial thickness of 23 mm, if the multi-wire processing technology described in the background art is used, the SiC material loss per wafer is approximately 300 μm, and the ingot can be processed into 35 SiC wafers with a final thickness of 350 μm; if the laser separation technology described in the background art is used, the SiC material loss per wafer is approximately 150 μm, and the ingot can be processed into 50 SiC wafers with a final thickness of 350 μm; while using the separation method according to this application, the SiC material loss per wafer is approximately 50 μm, and therefore 57 SiC wafers with a final thickness of 350 μm can be processed. Furthermore, compared to the previous two methods, the material loss during the polishing step is reduced by approximately 40% when using the separation method according to this application.

[0209] The scope of protection of this application should be determined by the scope of the claims. The specific embodiments described above are not intended to limit the scope of protection of this application. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, for example:

[0210] (i) This application is not limited to processing SiC ingots, but can also be used to process other single crystal materials whose cleavage planes are at an angle to the end face of the ingot, such as, but not limited to, GaN, AlN, Ga2O3 and diamond.

[0211] (ii) This application is not limited to separating wafers from ingots, but can also be used for, for example, other cutting of ingots or thinning of wafers.

Claims

1. A wafer separation method, characterized in that, The wafer separation method includes: One or more ablation layers are formed with reference to one or more target planes within the ingot that are perpendicular to the axial direction of the ingot; and The ingot is divided into at least two parts, with one or more ablation layers as boundaries; The formation of each of the ablation layers includes: The laser is focused onto one of the target planes. Multiple first focal spots are formed within the ingot, the center of each first focal spot is located on the target plane, the size of the first focal spot in the axial direction is larger than the size of the first focal spot in other directions, the multiple first focal spots are arranged in a grid-like array, and each first focal spot is formed as part of the boundary of each grid; While keeping the target plane focused by the laser unchanged, a plurality of second focal spots are formed in the ingot. The center of each second focal spot is located on the same target plane as the center of the first focal spot. At least one second focal spot is formed in each grid. Each second focal spot causes the ingot to form a cleavage crack extending along the cleavage plane of the ingot. The cleavage crack is inclined relative to the crystal plane.

2. The wafer separation method according to claim 1, characterized in that, The plurality of first focal spots are formed before the plurality of second focal spots, or At least a portion of the first focal spots and at least a portion of the second focal spots are formed simultaneously.

3. The wafer separation method according to claim 1 or 2, characterized in that, The method for forming either the first focal spot or the second focal spot includes: The ingot is placed on a movable platform, and the laser is focused on a target plane. The movable platform is moved so that the focusing position changes in the circumferential and / or radial direction of the ingot.

4. The wafer separation method according to claim 1 or 2, characterized in that, The size of the second focal spot in the direction parallel to the cleavage plane of the ingot is larger than the size of the second focal spot in other directions.

5. The wafer separation method according to claim 1 or 2, characterized in that, The first focal spot and / or the second focal spot are formed into an elongated shape by connecting multiple circular focal spots end to end.

6. The wafer separation method according to claim 1 or 2, characterized in that, Two adjacent cleavage surface cracks are respectively connected to the two ends of at least one of the first focal spots in the axial direction.

7. The wafer separation method according to claim 1 or 2, characterized in that, The numerical aperture of the optical system used to generate the first focal spot is larger than the numerical aperture of the optical system used to generate the second focal spot.

8. The wafer separation method according to claim 1 or 2, characterized in that, The division of the ingot into at least two parts, using the one or more ablation layers as boundaries, includes: Using one of the ablation layers as a separation boundary, the wafer located on one side of the ablation layer is separated from the ingot located on the other side of the ablation layer.

9. The wafer separation method according to claim 1 or 2, characterized in that, The division of the ingot into at least two parts, using the one or more ablation layers as boundaries, includes: Multiple wafers, defined by multiple ablation layers, are continuously separated from the ingot, wherein, The multiple ablation layers are formed sequentially and continuously within the ingot. For multiple ablation layers formed from the same laser source location, the later-formed ablation layer is closer to the laser source location than the earlier-formed ablation layer.

10. The wafer separation method according to claim 8, characterized in that, Removing the wafer includes: Cut the outer peripheral edge of the ablation layer to separate the outer periphery of the wafer from the ingot.

11. The wafer separation method according to claim 10, characterized in that, The cutting of the outer peripheral edge of the ablation layer includes: The ingot is rotated about its axis, and the crystal material at the outer peripheral edge of the ablation layer is removed by a cutting device.

12. The wafer separation method according to claim 10, characterized in that, Removing the wafer also includes: The suction cup is attached to the axial end face of the wafer, allowing the suction cup to carry the wafer away from the ingot.

13. A wafer separation method, characterized in that, The wafer separation method includes: One or more ablation layers are formed with reference to one or more target planes within the ingot that are perpendicular to the axial direction of the ingot; and The ingot is divided into at least two parts, with one or more ablation layers as boundaries; The formation of each of the ablation layers includes: The laser is focused onto one of the target planes. Multiple second focal spots are formed within the ingot, the center of each second focal spot being located on the target plane, and each second focal spot inducing the formation of a cleavage crack extending along the cleavage plane of the ingot, the cleavage crack being inclined relative to the crystal plane; While keeping the target plane focused by the laser unchanged, a plurality of first focal spots are formed within the ingot. The center of each first focal spot is located on the same target plane as the center of the second focal spot. The size of the first focal spot in the axial direction is larger than the size of the first focal spot in other directions. The plurality of first focal spots are arranged in a grid-like array. Each first focal spot is formed as part of the boundary of each grid. Each grid has at least one second focal spot.

14. The wafer separation method according to claim 13, characterized in that, The method for forming either the first focal spot or the second focal spot includes: The ingot is placed on a movable platform, and the laser is focused on a target plane. The movable platform is moved so that the focusing position changes in the circumferential and / or radial direction of the ingot.

15. The wafer separation method according to claim 13 or 14, characterized in that, The size of the second focal spot in the direction parallel to the cleavage plane of the ingot is larger than the size of the second focal spot in other directions.

16. The wafer separation method according to claim 13 or 14, characterized in that, The first focal spot and / or the second focal spot are formed into an elongated shape by connecting multiple circular focal spots end to end.

17. The wafer separation method according to claim 13 or 14, characterized in that, Two adjacent cleavage surface cracks are respectively connected to the two ends of at least one of the first focal spots in the axial direction.

18. The wafer separation method according to claim 13 or 14, characterized in that, The numerical aperture of the optical system used to generate the first focal spot is larger than the numerical aperture of the optical system used to generate the second focal spot.

19. The wafer separation method according to claim 13 or 14, characterized in that, The division of the ingot into at least two parts, using the one or more ablation layers as boundaries, includes: Using one of the ablation layers as a separation boundary, the wafer located on one side of the ablation layer is separated from the ingot located on the other side of the ablation layer.

20. The wafer separation method according to claim 13 or 14, characterized in that, The division of the ingot into at least two parts, using the one or more ablation layers as boundaries, includes: Multiple wafers, defined by multiple ablation layers, are continuously separated from the ingot, wherein, The multiple ablation layers are formed sequentially and continuously within the ingot. For multiple ablation layers formed from the same laser source location, the later-formed ablation layer is closer to the laser source location than the earlier-formed ablation layer.

21. The wafer separation method according to claim 19, characterized in that, Removing the wafer includes: Cut the outer peripheral edge of the ablation layer to separate the outer periphery of the wafer from the ingot.

22. The wafer separation method according to claim 21, characterized in that, The cutting of the outer peripheral edge of the ablation layer includes: The ingot is rotated about its axis, and the crystal material at the outer peripheral edge of the ablation layer is removed by a cutting device.

23. The wafer separation method according to claim 21, characterized in that, Removing the wafer also includes: The suction cup is attached to the axial end face of the wafer, allowing the suction cup to carry the wafer away from the ingot.

24. A wafer separation device, characterized in that, The wafer separation apparatus is used to separate one or more wafers from the ingot using the wafer separation method according to any one of claims 1 to 23, the wafer separation apparatus comprising: A laser generating mechanism for forming the first focal spot and the second focal spot; An active platform is used to support the crystal ingot and drive the crystal ingot to perform translational motion and / or rotation about the crystal ingot's own axis; and A wafer removal mechanism is used to separate the wafer from the ingot.

25. The wafer separation apparatus according to claim 24, characterized in that, The wafer removal mechanism includes a cutting device for cutting the ingot at the outer peripheral edge of the ablation layer.

26. The wafer separation apparatus according to claim 25, characterized in that, The cutting device is a laser cutter or a grinding wheel.

27. The wafer separation apparatus according to any one of claims 24 to 26, characterized in that, The wafer removal mechanism includes a suction cup that can move to the axial end of the ingot to pick up and transfer the wafer.

28. The wafer separation apparatus according to any one of claims 24 to 26, characterized in that, The wafer separation device also includes a polishing mechanism. The polishing mechanism is used to polish the axial end face of the wafer where the ablation layer is located, and / or The polishing mechanism is used to polish the axial end face where the ablation layer of the ingot is located.

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