WO2023028920A1

WO2023028920A1 - Wafer separation method and wafer separation apparatus

Info

Publication number: WO2023028920A1
Application number: PCT/CN2021/115989
Authority: WO
Inventors: 黄维; 陈丙振; 张浩东
Original assignee: 华为技术有限公司
Priority date: 2021-09-01
Filing date: 2021-09-01
Publication date: 2023-03-09
Also published as: CN117813178A

Abstract

A wafer separation method, comprising: forming one or more ablation layers by using, as a reference, one or more target planes in a crystal ingot that are perpendicular to the axial direction of the crystal ingot; and dividing the crystal ingot into at least two portions by using the one or more ablation layers as a boundary, wherein the formation of each ablation layer comprises: focusing laser light on a target plane; forming a plurality of first focal spots in the crystal ingot, wherein the center of each first focal spot is located in the target plane, the size of the first focal spot in the axial direction is greater than the size thereof in another direction, the plurality of first focal spots are arranged in a grid array, and each first focal spot is formed as a portion of a boundary of each grid; and forming a plurality of second focal spots in the crystal ingot, wherein the center of each second focal spot is located in the target plane, at least one second focal spot is formed in each grid, and each second focal spot causes the crystal ingot to form a cleavage plane crack which extends along a cleavage plane of the crystal ingot. Further provided in the present application is a wafer separation apparatus.

Description

Wafer separation method and wafer separation device

technical field

The present application relates to the semiconductor field, and more specifically relates to a wafer separation method and a wafer separation device.

Background technique

Semiconductor wafers (hereinafter also referred to as wafers) are the cornerstone of chips. The chip is based on the wafer as the carrier, and the device structure is formed through multiple processes such as deposition, photolithography, and etching, and then prepared by dicing and packaging.

At present, most of the chips in computer processors, memory and mobile phones use silicon wafer materials to prepare semiconductor wafers. Silicon wafers can be sliced from silicon boules.

One possible method of wafer separation is to use multi-wire dicing. The specific preparation method includes, for example: obtaining a cylindrical silicon single crystal by pulling or other methods. The length of the cylindrical silicon single crystal is approximately 100 mm to 200 mm, and the diameter is approximately 100 mm to 450 mm; A standard cylinder with a consistent diameter, that is, an ingot; and then the cylindrical silicon ingot is cut into a wafer-shaped wafer with a uniform thickness by multi-wire cutting.

Figures 1 and 2 show schematic diagrams of cutting a cylindrical ingot by a multi-wire cutting process. The multi-wire cutting process uses a row of equally spaced cutting lines C to move back and forth at high speed. The cutting line C cuts in from the side of the cylinder of the ingot B perpendicular to the axis f. After passing through the entire cylinder, the cylindrical ingot B is cut Separated into silicon wafers one by one.

Referring to FIG. 2 , in the above solution, in order to ensure the strength of the cutting line C, the cutting line C is configured to have a sufficiently thick wire diameter, generally on the order of hundreds of microns. And, in order to make the cutting wire have better cutting ability, its surface will be coated with diamond particles. The essence of the cutting process of the ingot B is to remove the silicon material in contact with the cutting line C, and the removed silicon single crystal part is the material loss caused by the multi-wire cutting process. For example, for a commonly used wafer with a thickness d1 of 350 microns, the thickness d2 of the material loss layer produced by the multi-wire cutting technology is about 200 microns to 300 microns, and the lost material accounts for 30% to 45%.

The above-mentioned material loss accounts for a relatively high cost in chip production. For example, for SiC, a wide-bandgap semiconductor material that has wide application requirements in the field of power devices, due to SiC single crystal growth methods and technological developments, the price of SiC wafers is relatively high. , which is about ten times that of a silicon wafer of the same size. Moreover, the Mohs hardness of SiC single crystal material is 9.2, which is much harder than silicon material. When multi-wire cutting is used, a larger wire diameter is required to avoid the problem of wire breakage, which will bring more SiC single crystal material loss. In this case, the cost waste caused by the traditional multi-wire cutting technology is very large.

Contents of the invention

In view of this, the present application provides a wafer separation method and a wafer separation device.

In a first aspect, embodiments of the present application provide a wafer separation method.

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

forming one or more ablative layers relative to one or more target planes within the ingot perpendicular to the axis of the ingot; and

dividing the ingot into at least two portions bounded by one or more ablative layers;

Wherein, the formation of each ablation layer includes:

Focusing the laser on a target plane,

A plurality of first focal spots are formed in the crystal 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, and the plurality of first focal spots the focal spots are arranged in a grid-like array, and each first focal spot forms part of a boundary of each grid;

A plurality of second focal spots are formed in the crystal ingot, the center of each second focal spot is located on the target plane, at least one second focal spot is formed in each grid, and each second focal spot induces the crystal ingot to form an along-grain A cleavage plane crack extending from the cleavage plane of the ingot.

The first focal spot can be used as a crack suppression point at the boundary of each mesh, and the cleavage surface crack formed by the second focal spot stops expanding when it extends to the position of the first focal spot, or the extension of the cleavage surface crack stops. At the first focal spot and connected to the first focal spot. Therefore, the cleavage plane crack formed in each grid is roughly the same shape as the grid, and the cleavage plane crack is connected with the first focal spot located at the boundary of each grid, so that the entire ablation layer is formed Cleavage plane cracks for a definite shape next to each other. In summary, the first focal spot limits the expansion area of the cleavage plane cracks induced by each second focal spot, and the first focal spot plays a role in connecting the cleavage plane cracks in adjacent grids, so that According to the application, a complete ablation layer can be formed, the ablation layer has regular shape and small surface roughness, the separated wafer is not easy to break, and the loss of crystal material is small.

According to the first possible implementation of the first aspect, in the second possible implementation of the wafer separation method, the multiple first focal spots are formed before the multiple second focal spots, or

At least some of the first focal spots of the plurality of first focal spots are formed simultaneously with at least some of the second focal spots of the plurality of second focal spots.

The first focal spot is formed before the second focal spot, or the first focal spot and the second focal spot are formed at the same time, and the cleavage surface crack caused by the second focal spot terminates at the first focal spot, so the adjacent The cracks on the cleavage plane are just connected by the first focal spot, and the shape of the ablation layer is controllable.

In a second aspect, the embodiments of the present application provide another wafer separation method.

In a first possible implementation of the second aspect, the wafer separation method includes:

Wherein, the formation of each ablation layer includes:

Focusing the laser on a target plane,

forming a plurality of second focal spots in the crystal ingot, the center of each second focal spot is located on the target plane, and each second focal spot causes the crystal ingot to form a cleavage plane crack extending along the cleavage plane of the crystal ingot;

A plurality of first focal spots are formed in the crystal 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, and the plurality of first focal spots The focal spots are arranged in a grid-like array, each first focal spot forms part of the boundary of each grid, and each grid has at least one second focal spot within it.

The wafer separation method according to this implementation mode provides another focal spot formation mode, and the operation is flexible when the laser is focused.

According to any possible implementation of the first aspect above, in the third possible implementation of the first aspect, or according to the first possible implementation of the second aspect above, in the second possible implementation of the second aspect Among the possible implementations,

The method for forming any one of the first focal spot and the second focal spot includes:

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

This implementation method adopts the method of not moving the optical system and moving the crystal ingot. This implementation method can improve the size and position accuracy of the first focal spot and the second focal spot, ensure the stability and accuracy of the optical system, and make the focusing process easy to operate. And it can efficiently and accurately focus the laser and form a predetermined pattern of focal spots.

According to any possible implementation of the first aspect above, in the fourth possible implementation of the first aspect, or according to any possible implementation of the second aspect above, in the third possible implementation of the second aspect Among the possible implementations,

The size of the second focal spot in a direction parallel to the cleave plane of the ingot is larger than the size of the second focal spot in other directions.

According to the internal structure characteristics of the crystal, the length direction of the second focal spot is parallel to the cleavage plane, so it is easy to make the second focal spot coincide with the crack on the cleavage plane, so that the ablation layer is relatively smooth and the loss of crystal material is small.

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

The first focal spot and/or the second focal spot are connected end to end by a plurality of circular focal spots to form a long strip.

The structure of the optical system required for a circular focal spot is simple, and the focal spot according to this implementation manner can be formed by a simple optical system.

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

The two adjacent cleavage plane cracks are respectively connected to the two ends of the at least one first focal spot in the axial direction.

According to this implementation mode, adjacent cleavage plane cracks are closely connected, and a complete ablation layer is easily formed. In addition, the length of the first focal spot can be made as short as possible to reduce the surface roughness of the ablation layer and reduce material loss.

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

The numerical aperture of the optical system used to generate the first focal spot is greater than the numerical aperture of the optical system used to generate the second focal spot.

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 Among the possible implementations,

Dividing the ingot into at least two parts bounded by one or more ablative layers includes:

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

Since the shape of the ablation layer is controllable and the surface is relatively smooth, the wafer separation method according to this implementation can separate a single wafer relatively easily.

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

Continuously separating a plurality of wafers divided by a plurality of ablation layers from an ingot, wherein,

Multiple ablation layers are successively formed in the ingot. For multiple ablation layers formed by the same laser source position, the ablation layer formed later is closer to the laser source position than the ablation layer formed earlier. .

The wafer separation method according to the implementation mode separates the repeated laser ablation step and the repeated wafer removal step, which can improve the efficiency of wafer separation and is suitable for large-scale production organization.

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 In the ninth possible implementation of the second aspect,

Wafer removal includes:

The peripheral edge of the ablative layer is cut to separate the peripheral portion of the wafer from the ingot.

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

According to the tenth possible implementation manner of the first aspect above, in the eleventh possible implementation manner of the first aspect, or according to the ninth possible implementation manner of the second aspect above, in the first possible implementation manner of the second aspect Among the ten possible implementations,

Cutting the peripheral edge of the ablative layer includes:

The ingot is rotated about its axis and the crystalline material is removed from the peripheral edge of the ablative layer with a cutting device.

According to the wafer separation method of the implementation, the cutting position of the peripheral edge of the ablation layer is accurate, high in precision, simple and efficient.

According to the tenth or eleventh possible implementation of the first aspect above, in the twelfth possible implementation of the first aspect, or according to the ninth or tenth possible implementation of the second aspect above , in an eleventh possible implementation of the second aspect,

Wafer removal also includes:

The suction cup is adsorbed on the axial end surface of the wafer, so that the suction cup takes the wafer away from the ingot.

According to the wafer separation method of this implementation mode, the wafer removal operation is convenient, the contact area between the suction cup and the wafer is large, the force on the wafer is uniform, and damage such as fragmentation is not easy to occur.

In a third aspect, embodiments of the present application provide a wafer separation device.

In the first possible implementation of the third aspect, the wafer separation device is used to use any possible wafer separation method according to the above first aspect or any possible wafer separation method according to the above second aspect The method is to separate one or more wafers from an ingot, and the wafer separation device includes:

a laser generating mechanism for forming a first focal spot and a second focal spot;

a movable platform for carrying the ingot and driving the ingot for translation and/or rotation about the axis of the ingot itself; and

Wafer removal mechanism for separating the wafer from the ingot.

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

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 wafer at the peripheral edge of the ablation layer. ingot.

The wafer separation device according to this implementation mode can effectively separate the peripheral part of the wafer, which is beneficial to separate the wafer with a regular surface, and there is less waste of crystal material.

According to the second possible implementation manner of the third aspect, in the third possible implementation manner of the wafer separation device, the cutting device is a laser knife or a grinding wheel.

The wafer separation device according to this implementation mode cuts the outer peripheral portion of the wafer with good precision and high efficiency.

According to any possible implementation of the above third aspect, in a fourth possible implementation of the third aspect, the wafer removal mechanism includes a suction cup that can move to the axial end of the ingot to suck and transfer wafers.

The wafer separation device according to this implementation mode can conveniently and efficiently separate the wafer from the crystal ingot. The contact area between the suction cup and the wafer is large, the force on the wafer is uniform, and it is not easy to break and other damage.

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

a polishing mechanism for polishing the axial end face of the wafer where the ablative layer is located, and/or

The polishing mechanism is used to polish the axial end surface of the crystal ingot where the ablation layer is located.

The wafer separation device according to this implementation mode can obtain wafers with flat surfaces that can be used for epitaxy.

Description of drawings

Figures 1 and 2 are schematic diagrams of a possible wafer separation using multi-wire dicing technology;

Figures 3 and 4 are schematic diagrams of a possible use of lasers to separate wafers;

5 is a schematic diagram of separating a wafer from an ingot according to an embodiment of the present application;

6 is a schematic cross-sectional view of forming an ablation layer through a first focal spot and a second focal spot according to an embodiment of the present application;

7 is a schematic cross-sectional view of an ingot with a first focal spot formed according to an embodiment of the present application;

8 is a schematic cross-sectional view of an ingot formed with a first focal spot and a second focal spot according to an embodiment of the present application;

9 is a schematic cross-sectional view of forming an ablation layer in an ingot using a laser according to an embodiment of the present application;

10 and 11 are schematic diagrams of cutting the edge of an ingot with a grinding wheel to separate a wafer according to an embodiment of the present application;

12 is a schematic diagram of cutting the edge of an ingot with a laser knife to separate wafers according to an embodiment of the present application;

13 is a cross-sectional view of removing a wafer with a suction cup according to an embodiment of the present application;

FIG. 14 is a cross-sectional view of polishing a wafer end face with a polishing wheel according to an embodiment of the present application;

15 is a cross-sectional view of polishing the end face of a wafer with a chemical mechanical polishing disc according to an embodiment of the present application;

FIG. 16 is a cross-sectional view of polishing an end face of an ingot with a polishing wheel according to an embodiment of the present application.

FIG. 17 is a wafer separation method according to one embodiment of the present application.

Explanation of reference signs:

B ingot; B0 wafer; Bf crystal face;

C cutting line; f axis; a declination; Fc cleavage plane;

L laser; L0 focal spot; L1 first focal spot; L2 second focal spot; Lk laser knife;

S ablation layer; K1 cleavage plane crack; K2 induced crack;

P movable platform; D suction cup; W cutting wheel; Po1 polishing wheel; Po2 chemical mechanical polishing disc;

A axial; R radial; D1 first direction.

Detailed ways

Unless otherwise specified, referring to Fig. 5, Fig. 11 and Fig. 12, A represents the axial direction of the wafer separation device, and the axial direction A is consistent with the axial direction of the ingot; R represents the radial direction of the wafer separation device, and the radial direction R Consistent with the radial direction of the crystal ingot.

Unless otherwise specified, the present application uses the up-down relationship shown in the figure to describe the positional relationship of each component. It should be understood that the upper-lower relationship is not absolute, and the spatial orientations corresponding to the components may change accordingly with different product application scenarios and working postures.

In addition, "and/or" in the description and claims means at least one of the connected objects, and the character "/" generally means that the related objects are an "or" relationship.

Laser separation wafer technology is a wafer separation method with high separation precision.

As shown in Figure 3, the laser separation wafer technology uses laser L (or laser beam) to focus at a certain depth in the ingot B, and the focal point forms a focal spot, which ablates the ingot, and multiple focal spots are connected together An ablation layer S is formed. After the material loss of the ablation layer S, the ingot B can be separated into the wafer B0 on one side of the ablation layer S and the remaining ingot B on the other side of the ablation layer S (for the convenience of expression, the energy The further separated parts are called boules).

FIG. 4 shows a schematic diagram of using a focal spot to form an ablation layer S for easy separation. The figure shows a SiC single crystal as an example. The ablation effect of the laser makes a small piece of cleavage plane crack K1 formed at each focal spot L0. Since the crystal face Bf (the axial end face of the ingot B) of the SiC single crystal ingot B usually forms an off angle of 4 degrees with the cleavage plane, the multiple focal spots L0 at the same depth in the ingot B are caused by The formed cleavage plane cracks K1 are all inclined relative to the crystal plane Bf, and the multiple cleavage plane cracks K1 are substantially parallel to each other and do not intersect each other. Moreover, the multiple cleavage plane cracks K1 also have non-uniform coverage areas and heights.

In order to form a damaged layer with the effect of separating the wafer, one possible method is to apply an external force to the ingot after laser ablation, such as rotating the ingot, warping, or applying ultrasonic waves, so that the crack K1 on the adjacent cleavage plane An induced crack K2 is formed between them. The induced crack K2 and the cleavage plane crack K1 are connected together to form a damaged layer capable of separating the wafer B0.

However, due to the inhomogeneity of the crack K1 on the cleavage plane and the uncertainty of the direction of the induced crack K2, the traditional laser separation technology has the problems of uneven surface, unevenness and uncontrollable size of the damaged layer, which leads to the B0 is brittle. In addition, the loss of single crystal material is also relatively large.

The applicant made the present application in consideration of some circumstances including the above-mentioned ones.

Referring to FIG. 5 to FIG. 16 , taking SiC single crystal ingot B as an example, the wafer separation method and wafer separation device according to the present application are introduced.

Referring to Fig. 5, the crystal ingot B in this embodiment is in the shape of a cylinder, and its axis f (parallel to the axial direction A) forms an off-angle a with the vertical direction of the crystallization direction. In this embodiment, the off-angle a is approximately 4 °.

After the crystalline mineral is stressed, due to its own structure, the crystal will crack into a smooth plane along a certain crystallization direction. This process is also called cleavage, and the cracked smooth plane is called a cleavage plane. The ingot B and the method of decomposing the wafer B0 from the ingot B will be described below with the aid of the cleavage plane.

The cleavage plane Fc in this embodiment is the <0001> plane (which is parallel to the direction <1-100> and the direction <11-20>), and the axis f forms an off-angle a with the perpendicular to the cleavage plane Fc.

The two end surfaces (also called crystal planes, referring to the end surfaces formed after separation, polished and cleaned) of the wafer B0 separated from the ingot B in the axial direction A also form an off angle a with the cleavage plane Fc.

Referring to FIG. 6 , the present application uses laser ablation to separate wafers. In this method, a laser is used to form an ablation layer S in the crystal ingot B with a target plane as a reference. The target plane is a virtual plane perpendicular to the axis A. Taking the target plane as the reference means that the centers of the first focal spot and the second focal spot described below (the focus position of the laser light) are located on the target plane. It should be understood that since the first focal spot and the second focal spot have a certain size and extension direction, the first focal spot and the second focal spot are not completely located in the target plane. For the convenience of expression, sometimes it is also called that the first focal spot and the second focal spot are located in the target plane, which actually means that the centers of the first focal spot and the second focal spot are located in the target plane.

The target plane is, for example, approximately 350 microns away from one axial end surface of the ingot B (hereinafter referred to as the upper surface). This depth is slightly greater than the thickness of the finished wafer B0 in the axial direction A. This is because, for a certain finished wafer B0, considering that the wafer B0 needs to be polished and cleaned after separation, a margin can be reserved for polishing.

With the ablation layer S as the boundary, one side in the axial direction can be used to form a wafer B0 , and the remaining part on the other side is still referred to as the ingot B for convenience of expression.

It should be understood that, in other possible applications, the ablative layer S may also be used only to divide the ingot B into two parts, and the two parts may both have larger axial dimensions instead of correspondingly directly forming the wafer B0.

In order to make the ablation layer S have a regular surface, the present application uses laser focusing to form two types of focal spots, ie, the first focal spot L1 and the second focal spot L2. The second focal spot L2 utilizes the cleavage characteristics of the crystal to form a plurality of cleavage plane cracks K1 parallel to the cleavage plane Fc (or extending along the cleavage plane) in the ingot B; the first focal spot L1 is used for The multiple cleavage plane cracks K1 are connected together and the further expansion of the cleavage plane cracks K1 is prevented. The ablative layer S is thus delimited substantially only by the area covered by the cleavage plane crack K1 and the first focal spot L1.

(formation of ablative layer)

The method for forming the ablation layer S is introduced with reference to FIG. 6 to FIG. 9 .

First, referring to FIG. 6 and FIG. 7 , the structure of the first focal spot L1 will be introduced.

The first focal spot L1 is used to define the boundary of each cleavage plane crack K1, and the first focal spot L1 is not used to cause crystal cleavage. The first focal spot L1 is also called a crack inhibition point.

Each first focal spot L1 is elongated, and its size in the axial direction A of the ingot B is larger than that in other directions. This makes it difficult for the first focal spot L1 to induce cleavage in the ingot B, that is, the first focal spot L1 will not induce undesired cracks in the crystal.

A plurality of first focal spots L1 are arranged in a grid-like array, and each first focal spot L1 forms a part of a boundary of the grid. Multiple grids divide the area where the ablation layer S is expected to be generated into multiple sub-areas (each grid represents a sub-area), which makes each cleavage plane crack K1 described below occupy only a small area, and the ablation The layer S is easy to form, and the surface roughness of the ablative layer S is small. Optionally, each mesh has a maximum dimension in each direction of 50 to 1000 microns.

It should be understood that by changing the distance between adjacent first focal spots L1, that is, by changing the size of each grid in the grid-like array, the flatness (or roughness) of the surface of the ablation layer S can be adjusted, so that Control the amount of material loss during wafer separation. This is because, for example, the smaller the distance between adjacent first focal spots L1 (referred to as the denser the first focal spot L1), the shorter the propagation distance of the cleavage plane crack K1 generated by the second focal spot L2 , so that the surface relief of the ablation layer S is smaller. Of course, the denser the first focal spot L1, the higher the scanning speed of the laser is generally required, and the higher the ablation cost of the corresponding laser. In practical applications, a balanced choice can be made between the cost of laser use and the loss of crystal materials.

In the present embodiment, each grid (except the grid contacting the edge of the ingot B) has a substantially square shape. It should be understood that, in other possible implementation manners, a single grid may also be in other shapes, such as triangle, quadrangle, or hexagon, etc., and the grid-like array may include multiple grids of different shapes.

Next, referring to FIG. 6 and FIG. 8 , the structure of the second focal spot L2 will be introduced.

The second focal spot L2 is used to induce the crystal to produce cleavage plane cracks K1. It should be understood that the cleavage plane crack K1 is spontaneously formed with the generation of the second focal spot L2, and no other external force is required to be applied to the crystal ingot B during this process.

In order to ensure that the second focal spot L2 can induce the cleavage surface crack K1 of the crystal ingot B, the second focal spot L2 is in the shape of a long strip, and its size in the first direction D1 is larger than that in other directions, and the first direction D1 is not parallel to axis A. In this embodiment, the first direction D1 is parallel to the axial end surface of the crystal ingot B. As shown in FIG. But preferably, the first direction D1 is parallel to the cleavage plane Fc.

In the grid-like array constructed by a plurality of first focal spots L1, at least one (in this embodiment, one) second focal spot L2 is formed in each grid.

Optionally, the cleavage plane crack K1 formed by the second focal spot L2 in each grid is connected to the first focal spot L1 around the grid. According to the formation mechanism of the cleavage plane crack K1, the boundary of the cleavage plane crack K1 will terminate at the first focal spot L1 that it touches, so that the first focal spot L1 around each grid and the second focal spot inside each mesh L2 can form a split region with a defined shape.

Optionally, two adjacent cleavage plane cracks K1 are connected to two ends of at least one first focal spot L1 in the axial direction A respectively. Alternatively, both ends of each first focal spot L1 on the axis A are respectively connected to a cleavage plane crack K1. The aforementioned just-connected structure can be realized, for example, by determining the length of the first focal spot L1 in the axial direction A and the size of the grid through reasonable calculations. As a result, the split regions formed by each grid can be connected together, thereby forming a complete ablation layer S capable of splitting the crystal ingot B.

It should be understood that due to various reasons (such as errors in actual operation, etc.), at least part of the first focal spot L1 may not be connected to the adjacent cleavage plane crack K1, for example, the first focal spot L1 and the adjacent There is a very small gap between the cracks K1 on the physical surface. Connection regions of such small dimensions (for example less than 5 micrometers) can be subsequently broken, for example, by applying a small external force.

In this embodiment, for each ablation layer, all the first focal spots L1 are formed before the second focal spots L2. Therefore, the boundary of the cleavage plane crack K1 induced by the second focal spot L2 can be defined according to the position of the first focal spot L1, or in other words, adjacent cleavage plane cracks are just connected by the first focal spot L1, so that the ablated layer The shape of S is controllable.

It should be understood that, in other possible implementation manners, at least part of the second focal spot L2 may also be formed before the first focal spot L1, or at least part of the second focal spot L2 is formed simultaneously with at least part of the first focal spot L1. According to this formation method, there may be a situation where the cleavage plane crack K1 exceeds the adjacent first focal spot L1 at the second focal spot L2 which is not formed later. It should be understood that as long as the cleavage plane crack K1 and the first focal spot L1 are in contact, or the distance is very small, a relatively regular ablation layer S can still be formed.

Next, the method for forming the first focal spot L1 and the second focal spot L2 according to this embodiment will be introduced.

Optionally, firstly, the upper end surface of the ingot B (the end surface for passing the laser light) is polished, so that the upper end surface is formed into a smooth end surface of an optical level (for example, the surface roughness is less than 5 nanometers). In order to facilitate the passage of laser light and facilitate the subsequent separation of wafers.

Place the crystal ingot B on the movable platform P, use the first laser source, make the focus position of the laser be located on the target plane in the axial direction of the crystal ingot B (for example, 350 microns from the upper end surface), move the movable platform P, and make the focus position along the The first preset path changes in the circumferential direction and/or radial direction of the ingot B, so as to form a grid-like array constructed by the first focal spot L1 in the target plane.

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

Afterwards, using the second laser source, the focus position of the laser is located on the target plane in the axial direction of the crystal ingot B, and the movable platform P is moved so that the focus position is on the circumference and/or radial direction of the crystal ingot B along the second preset path. upwards to form a second focal spot L2 in each grid.

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.

Optionally, the strip-shaped focal spots (the first focal spot L1 and/or the second focal spot L2) can be formed once by a specific or combined focusing lens; it is also possible to form a circular focal spot each time spot, and connect multiple circular focal spots together to form a strip-shaped focal spot.

(Remove the wafer)

Next, referring to FIG. 9 to FIG. 16 , the steps of removing the wafer and subsequent steps in the wafer separation method will be described.

Using the above-mentioned ablation layer S, the wafer B0 separated by the ablation layer S is separated from the ingot B, or the wafer B0 is removed from the ingot B by using the ablation layer S as a boundary. There are two ways to remove the wafer described here.

In the first method, after each ablation layer S is formed, a wafer B0 is removed, and then the next ablation layer S is formed, and the cycle repeats.

The second method is to continuously form a plurality of ablation layers S at different depths in the ingot B, and then continuously remove the plurality of wafers B0 separated by the ablation layers S one by one.

For the second method, in order to ensure the formation quality of the focal spot, optionally, for multiple ablation layers S formed by the same laser source position, the ablation layer S formed later is larger than the ablation layer S formed earlier. It is closer to the laser source, so that the ablation layer S formed earlier will not hinder or affect the ablation layer S formed later.

Here, the "laser source position" refers to the incident position of laser light on the ingot B. For example, if the laser is incident from the upper end of the ingot B, then the ablation layer S formed later is closer to the upper end of the ingot B than the ablation layer S formed earlier, or in other words, the ablation layer S near the lower end is formed first, and then An ablation layer S is formed near the upper end. For another example, the laser can be incident from both ends of the ingot B, then the ablation layer S located in the middle in the axial direction A is formed first, and then the ablation layer S near the two ends is formed.

The wafer separation method after the formation of the ablation layer S is mainly introduced below.

Optionally, the separation method includes: step (a), cutting the peripheral edge of the ablative layer S.

Since the focusing efficiency of the laser light is limited at the edge of ingot B, the ablation layer S may not fully extend to the edge of ingot B (this phenomenon is also known as the edge effect of laser ablation). Optionally, therefore, the peripheral edge of the ablative layer S is cut using a cutting device.

Alternatively, the ingot B is rotated about its axis f, and the crystalline material at the peripheral edge of the ablative layer S is removed with a cutting device.

Optionally, during the process of cutting the ablative layer S, the ingot B is positioned using a vacuum adsorption stage (for example, a porous ceramic vacuum adsorption stage). The crystal ingot B is fixed by the adsorption device on the stage, so that the crystal ingot B can rotate with the stage with high motion accuracy.

Optionally, the cutting device is a laser knife Lk or a grinding wheel W.

10 and 11 show the manner in which the outer peripheral edge of the ablation layer S is cut using a grinding wheel W. As shown in FIG. Optionally, the rotation direction of the grinding wheel W is the same as that of the crystal ingot B, so that where the two are in contact, the contact parts of the two can move toward each other. Optionally, the thickness of the cutting part of the grinding wheel W in the axial direction A is 150 to 300 microns, and the depth of the grinding wheel W protruding into the ingot B in the radial direction R is 20 to 500 microns.

FIG. 11 shows the manner in which the ingot B is cut using the laser knife Lk. That is, the laser is focused on the outer peripheral edge of the ablation layer S, and the crystal material on the outer peripheral edge of the ablation layer S is removed by laser ablation.

Optionally, the separation method further includes: step (b), using a suction cup to remove the wafer B0.

Optionally, the suction cup D is adsorbed on the axial end surface of the wafer B0 away from the ablation layer S, and leaves the ingot B with the wafer B0.

Optionally, the separation method further includes: step (c), polishing the two axial end surfaces of the wafer B0, and/or polishing the axial end surface of the ingot B where the ablative layer S is located.

Optionally, polishing the axial end surface of the wafer B0 includes performing mechanical polishing and chemical mechanical polishing on the axial end surface of the wafer B0. Optionally, the polishing mechanism includes a polishing wheel Po1 (refer to FIG. 14, used for mechanical polishing) and a chemical mechanical polishing disc Po2 (refer to FIG. 15, used for chemical mechanical polishing).

Optionally, polishing the axial end surface of the ingot B where the ablative layer S is located includes performing mechanical polishing on the end surface. Optionally, referring to FIG. 16 , mechanical polishing is performed using a polishing wheel Po1.

Optionally, after the wafer B0 is polished, the wafer B0 is cleaned, so as to obtain a wafer that can be used for epitaxy.

(wafer separation device)

It should be understood that the present application also provides a wafer separation device that uses the above separation method to separate wafers. The device includes a laser generating mechanism, a movable platform P, a wafer removing mechanism and a polishing mechanism.

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

The movable platform P is used to carry the crystal ingot B, and drive the crystal ingot B to do translation and/or rotate around the axis f of the crystal ingot B itself.

The wafer removal mechanism is used to separate the wafer B0 from the ingot B. Optionally, the wafer removing mechanism includes a cutting device and a suction cup D. Optionally, the cutting device is selected from a laser knife Lk or a grinding wheel W.

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

Optionally, the suction cup D is a porous ceramic vacuum suction cup.

Next, by taking two embodiments as examples, specific steps for separating wafers using the wafer separation method according to the present application will be introduced.

(Embodiment 1)

Step 1, use the PVT (Physical Vapor Transport) method to grow a SiC ingot with a height of 15mm in the axial direction A and a diameter of 6 inches; orient the ingot, grind out the <11-20> face and the <11 -20> the <0001> surface with a 4 degree deviation in the direction; use the <0001> surface as one of the round end surfaces to process a standard cylinder; the height of the obtained standard cylinder of the ingot in the axial direction A is 12 mm.

In step 2, use a 10000# grinding wheel to polish the upper end face of the crystal ingot to obtain an optical-grade smooth end face (the surface roughness of the upper end face is 2nm).

Step 3, fixing the crystal ingot on a precision mobile platform that can move in the horizontal direction, making the lower end surface of the crystal ingot closely fit the mobile platform, and keeping the section (upper surface) of the crystal ingot parallel to the surface of the mobile platform.

In step 4, a laser with a wavelength of 1064 nanometers and a pulse width of 1 nanosecond is used as the laser generating mechanism. Turn on the laser, use the first focusing lens whose NA value (numerical aperture of the optical system) is 1.3, and set the depth of focus to be 350 microns away from the upper surface of the crystal ingot; A plurality of first focal spots arranged in a grid-like array are formed in the target plane of 350 microns on the upper surface of the ingot, and the distance between adjacent first focal spots in the <1-100> direction is 200 microns, and in The pitch in the 20> direction is 200 microns.

Step 5, switch the laser to the second focusing lens with an NA value of 0.4, set the depth of focus to 350 microns from the upper surface of the ingot; set the second preset path of the mobile platform, so that the laser is on the ingot at this distance A plurality of second focal spots are formed in the target plane of 350 microns on the surface, wherein at least one second focal spot is formed in each grid in the grid-like array formed by the first focal spots; a plurality of second focal spots are formed Multiple cleavage-plane cracks propagating along the cleavage plane, each cleavage-plane crack stopping when it reaches its surrounding first focal spot.

Step 6, transfer the crystal ingot to the porous ceramic vacuum adsorption stage, and make the stage rotate at a speed of 100rpm; use a grinding wheel with a blade thickness of 0.3mm and a rotation speed of 30000rpm to cut the outer peripheral part of the ablation layer; the grinding wheel is set on the crystal ingot In the initial state, the grinding wheel is not in contact with the crystal ingot, and the grinding wheel slowly approaches the crystal ingot at a speed of about 0.5mm/s, and after touching the crystal ingot, it extends 1mm into the crystal ingot in the radial direction R.

In step 7, the porous ceramic vacuum chuck is used to adsorb to the upper surface of the crystal ingot, and the vacuum chuck is slightly moved to separate and remove the wafer.

Step 8, first use the 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 chemically mechanically polish the end face of the wafer , so that the surface roughness of the end face is less than 0.3nm; and then through the RCA cleaning process, a wafer that can be used for epitaxy is obtained.

Step 9, using a 10000# grinding wheel to mechanically polish the ablation surface of the crystal ingot separated by laser ablation to obtain an optical-grade smooth end surface with a roughness of 2 nm.

Afterwards, the above steps 3 to 9 are repeated 28 times (assuming that the remaining ingot after the last separation can directly correspond to a wafer), and an epi-ready (out of the box) wafer that can be used for epitaxial growth can be processed. 30 SiC wafers.

(Example 2)

Step 1, use the PVT method to grow a SiC crystal ingot with a height of 25mm in the axial direction A and a diameter of 6 inches; orient the crystal ingot, grind out the <11-20> plane and the <11-20> direction The <0001> surface of 4 degrees; the <0001> surface is used as one of the circular end faces to process a standard cylinder; the height of the standard cylinder of the obtained crystal ingot in the axial direction A is 23 mm.

In step 2, use a 20000# grinding wheel to polish the upper end surface of the crystal ingot to obtain an optical-grade smooth end surface (the surface roughness of the upper end surface is 1 nm).

In step 4, a laser with a wavelength of 1064 nanometers and a pulse width of 150 femtoseconds is used as the laser generating mechanism. Turn on the laser, use the first focusing lens whose NA value (numerical aperture of the optical system) is 1.5, and set the depth of focus to be 350 microns away from the upper surface of the crystal ingot; A plurality of first focal spots arranged in a grid-like array are formed in the target plane 350 microns away from the upper surface of the ingot, and the distance between adjacent first focal spots in the <1-100> direction is 400 microns. The pitch in the -20> direction is 400 microns.

Step 5, switch the laser to the second focusing lens with an NA value of 0.3, set the depth of focus to 350 microns from the upper surface of the ingot; set the second preset path of the mobile platform, so that the laser is on the ingot at this distance A plurality of second focal spots are formed in the target plane of 350 microns on the surface, wherein at least one second focal spot is formed in each grid in the grid-like array formed by the first focal spots; a plurality of second focal spots are formed Multiple cleavage-plane cracks propagating along the cleavage plane, each cleavage-plane crack stopping when it reaches its surrounding first focal spot.

Step 6, transfer the crystal ingot to the porous ceramic vacuum adsorption stage, and make the stage rotate at a speed of 150rpm; use a grinding wheel with a blade thickness of 0.2mm and a rotation speed of 20000rpm to cut the outer peripheral part of the ablation layer; the grinding wheel is set on the crystal ingot In the initial state, the grinding wheel is not in contact with the crystal ingot, and the grinding wheel slowly approaches the crystal ingot at a speed of about 0.5mm/s, and after touching the crystal ingot, it extends into the crystal ingot by 0.5mm in the radial direction R.

Step 8, first use a 20000# 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 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; and then through the RCA cleaning process, a wafer that can be used for epitaxy is obtained.

Step 9, using a 20000# grinding wheel to mechanically polish the ablation surface of the crystal ingot separated by laser ablation to obtain an optical-grade smooth end surface with a roughness of 1 nm.

After that, the above steps 3 to 9 are repeated 56 times (assuming that the remaining ingot after the last separation can directly correspond to a wafer), and epi-ready (out of the box) SiC that can be used for epitaxial growth is processed. 58 wafers.

It should be understood that, for any of the above two embodiments, the sequence numbers of the steps are not used to completely limit the execution order of the steps, and the execution order of some steps can be adjusted. For example, step 4 and step 5 can be performed at the same time, or step 5 can be performed before step 4. When step 5 is performed before step 4, the first focal spot has not been formed when the cleavage plane crack is formed, so at the first focal point After the spot is formed, it may appear as a partial cleavage plane crack extending beyond the adjacent first focal spot. For another example, steps 3 to 5 may be repeated several times to continuously form a plurality of ablation layers, and then steps 6 to 9 may be repeated several times to remove the multiple ablation layers defined by the previously continuously formed ablation layers. wafers are separated.

FIG. 17 illustrates a wafer separation method according to one embodiment of the present application. It includes:

The ingot is divided into at least two portions bounded by one or more ablative layers.

Wherein, the formation of each ablation layer includes:

Use the laser to focus on a target plane to form multiple first focal spots in the ingot, the center of each first focal spot is located on the target plane, and the size of the first focal spot in the axial direction is larger than that of the first focal spot in other directions The size on , a plurality of first focal spots are arranged in a grid-like array, and each first focal spot forms a part of the boundary of each grid;

Keep the target plane focused by the laser unchanged, form a plurality of second focal spots in the ingot, the center of each second focal spot is located on the target plane, and form at least one second focal spot in each grid, and each second focal spot The bifocal spot induces the ingot to form a cleavage plane crack extending along the cleavage plane of the ingot.

Part of the beneficial effects of the above-mentioned embodiments of the present application will be briefly described below.

(i) In the process of ablation of the crystal ingot, the present application introduces the first focal spot that can suppress cracks, so that the size of the cleavage plane cracks produced by the second focal spot can be controlled, so that the final ablation The shape of the etched surface is controllable and the roughness is small, the wafer is not easy to break, and the material loss during processing is small.

(ii) Since the roughness of the ablation layer is small, the number of consumables (such as grinding wheels) in the polishing process can be reduced, and the time cost of the polishing process can be saved.

(iii) In consideration of the incomplete ablation of the edge of the ingot by the laser, the step of cutting the peripheral part of the ablation layer is added, so that the complete separation of the wafer and the ingot can be facilitated, and edge cracks are avoided due to incomplete splitting And it is torn or broken under the action of external force.

(iv) According to the test, for a SiC crystal ingot with an axial thickness of 23mm, if the multi-line processing technology introduced in the background technology is used, the SiC material thickness consumed by processing a single wafer is about 300um, then the crystal ingot can be 35 pieces of SiC wafers with a final thickness of 350 microns are processed; if the laser separation technology introduced in the background technology is used, the thickness of the SiC material lost in processing a single wafer is about 150um, and the ingot can be processed to obtain 50 pieces SiC wafers with a final thickness of 350 microns; and using the separation method according to this application, the thickness of SiC material lost in processing a single wafer is about 50um, so 57 SiC wafers with a final thickness of 350 microns can be processed . And compared with the previous two methods, the material loss in the polishing step is reduced by about 40% during the processing process using the separation method according to the present application.

The protection scope of the present application shall be based on the protection scope of the claims. The above specific implementation methods are not intended to limit the scope of protection of this application. Anyone skilled in the art within the technical scope disclosed in this application can easily think of changes or replacements, which should be covered within the scope of protection of this application. . So, for example:

(i) This application is not limited to processing SiC crystal ingots, but can also be used to process other single crystal materials whose direction of the cleavage plane is off-angle with the direction of the end face of the crystal ingot, such as but not limited to GaN, AlN, Ga ₂ O ₃ and diamonds etc.

(ii) The application is not limited to separating wafers from boules, but can also be used for other cutting of boules or thinning of wafers, for example.

Claims

A wafer separation method, characterized in that the wafer separation method comprises:

forming one or more ablative layers relative to one or more target planes within the ingot perpendicular to the axis of the ingot; and

dividing the ingot into at least two portions bounded by the one or more ablative layers;

Wherein, the formation of each ablative layer comprises:

Focusing the laser on one of said target planes,

A plurality of first focal spots are formed in the ingot, the center of each of the first focal spots is located on the target plane, and the size of the first focal spots in the axial direction is larger than that of the first focal spots. The size of the spot in other directions, the plurality of first focal spots are arranged in a grid-like array, and each of the first focal spots forms part of the boundary of each of the grids;

A plurality of second focal spots are formed in the crystal ingot, the center of each of the second focal spots is located on the target plane, at least one of the second focal spots is formed in each of the grids, and each of the second focal spots is formed in the grid. The second focal spot induces the ingot to form a cleavage plane crack extending along the cleavage plane of the ingot.
The wafer separation method according to claim 1, wherein the plurality of first focal spots are formed prior to the plurality of second focal spots, or

At least part of the plurality of first focal spots and at least part of the plurality of second focal spots are formed simultaneously.
A wafer separation method, characterized in that the wafer separation method comprises:

forming one or more ablative layers relative to one or more target planes within the ingot perpendicular to the axis of the ingot; and

dividing the ingot into at least two portions bounded by the one or more ablative layers;

Wherein, the formation of each ablative layer comprises:

Focusing the laser on one of said target planes,

A plurality of second focal spots are formed within the ingot, each of the second focal spots is centered on the target plane, and each of the second focal spots induces the ingot to form a Cleavage plane cracks extending from the cleavage plane;

A plurality of first focal spots are formed in the ingot, the center of each of the first focal spots is located on the target plane, and the size of the first focal spots in the axial direction is larger than that of the first focal spots. The size of the spot in other directions, the plurality of first focal spots are arranged in a grid-like array, each of the first focal spots is formed as a part of the boundary of each of the grids, and each of the grids has at least one said second focal spot therein.
The wafer separation method according to any one of claims 1 to 3, wherein the method for forming any one of the first focal spot and the second focal spot comprises:

The crystal ingot is placed on the movable platform, the laser is focused on one of the target planes, and the movable platform is moved to change the focus position in the circumferential direction and/or radial direction of the crystal ingot.
The wafer separation method according to any one of claims 1 to 4, wherein the size of the second focal spot in a direction parallel to the cleavage plane of the crystal ingot is larger than that of the second focal spot. The size of the spot in other directions.
The wafer separation method according to any one of claims 1 to 5, characterized in that, the first focal spot and/or the second focal spot are formed by connecting a plurality of circular focal spots end-to-end to form a long strip.
The wafer separation method according to any one of claims 1 to 6, characterized in that two adjacent cleavage plane cracks are respectively connected to at least one of the first focal spots in the axial direction The two ends meet.
The wafer separation method according to any one of claims 1 to 7, wherein the numerical aperture of the optical system used to generate the first focal spot is larger than the optical system used to generate the second focal spot the numerical aperture.
The wafer separation method according to any one of claims 1 to 8, characterized in that, dividing the ingot into at least two parts with the one or more ablation layers as a boundary comprises:

Taking one ablation layer as a separation boundary, separating the wafer on one side of the ablation layer from the crystal ingot on the other side of the ablation layer.
The wafer separation method according to any one of claims 1 to 8, characterized in that, dividing the ingot into at least two parts with the one or more ablation layers as a boundary comprises:

Continuously separating a plurality of wafers divided by the plurality of ablative layers from the ingot, wherein,

The plurality of ablation layers are successively formed in the ingot, and for the plurality of ablation layers formed by the same laser source position, the ablation layer formed later is larger than the ablation layer formed earlier. The formed ablation layer is closer to the laser source.
The wafer separation method according to claim 9 or 10, wherein taking off the wafer comprises:

cutting the peripheral edge of the ablative layer to separate the peripheral portion of the wafer from the ingot.
The wafer separation method according to claim 11, wherein the cutting the peripheral edge of the ablation layer comprises:

The ingot is rotated about its axis and crystalline material is removed from the peripheral edge of the ablative layer with a cutting device.
The wafer separation method according to claim 11 or 12, wherein taking off the wafer further comprises:

The suction cup is adsorbed on the axial end surface of the wafer, so that the suction cup takes the wafer away from the crystal ingot.
A wafer separation device, characterized in that the wafer separation device is used to separate one or more wafers from the ingot using the wafer separation method according to any one of claims 1 to 13 , the wafer separation device includes:

a laser generating mechanism for forming the first focal spot and the second focal spot;

a movable platform, used to carry the crystal ingot and drive the crystal ingot to do translation and/or rotate around the axis of the crystal ingot itself; and

A wafer removal mechanism is used to separate the wafer from the ingot.
The wafer separation device according to claim 14, wherein the wafer removal mechanism comprises a cutting device for cutting the crystal ingot at the peripheral edge of the ablative layer.
The wafer separation device according to claim 15, wherein the cutting device is a laser knife or a grinding wheel.
The wafer separation device according to any one of claims 14 to 16, wherein the wafer removal mechanism includes a suction cup, and the suction cup can move to the axial end of the crystal ingot to suck and transfer the wafer.
The wafer separation device according to any one of claims 14 to 17, wherein the wafer separation device further comprises a polishing mechanism,

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

The polishing mechanism is used for polishing the axial end surface of the crystal ingot where the ablation layer is located.