Wafer processing method based on composite laser

Abstract

The invention discloses a wafer processing method based on composite laser, and relates to the technical field of wafers, in particular to the technical field of wafer manufacturing. According to the specific implementation scheme, two kinds of lasers with different wavelengths are introduced to carry out modification treatment on a to-be-cut crystal ingot, firstly, the laser with the first wavelength which is relatively short is used for carrying out modification treatment to obtain a primary modified layer, and the material of the primary modified layer of the to-be-cut crystal ingot is changed; due to the fact that the second-wavelength laser subjected to secondary modification treatment has poor permeability on the preliminary modified layer, the lowest damage position of the to-be-cut crystal ingot in the vertical direction can be limited; in addition, the laser with the second wavelength is used for carrying out secondary modification treatment on the primary modified layer, cracks in the Y direction can be further expanded on the basis of the cracks in the Y direction of the primary modified layer, and the subsequent wafer stripping requirement is met.

Description

Technical Field

[0001] The present disclosure relates to the field of wafer technology, and in particular to the field of wafer manufacturing based on composite laser. Background Art

[0002] Traditional semiconductor ingot cutting methods mainly include slurry cutting and diamond wire cutting, which first cut the ingot into multiple wafers of specified thickness, and then grind and thin it to a specific thickness. Traditional mechanical cutting technology has problems such as low efficiency and severe damage.

[0003] In recent years, laser modification and stripping has emerged. Laser modification and stripping technology uses the laser beam to modify the internal structure of the material for stripping. It has the advantages of high efficiency, high precision, and low damage. It has gradually become the preferred technology for cutting high-hardness and brittle materials such as silicon carbide.

[0004] However, the existing laser modification and stripping methods only use a single laser for laser modification processing and fail to take advantage of the characteristics of different wavelengths. Summary of the invention

[0005] The present disclosure provides a wafer processing method based on a composite laser, which is used to at least solve some of the problems of the prior art.

[0006] The present disclosure provides a wafer processing method based on a composite laser, the method comprising:

[0007] Based on a laser having a first wavelength that is transmissive to the ingot to be cut, performing a preliminary modification process on the ingot to be cut at a predetermined depth to form a preliminary modified layer;

[0008] Based on the laser with a second wavelength having good transmittance to the ingot to be cut but poor transmittance to the preliminary modified layer, the ingot to be cut is subjected to secondary modification at a predetermined depth to obtain a target modified layer.

[0009] Wherein, the wavelength of the first wavelength is smaller than the wavelength of the second wavelength.

[0010] Optionally, the ingot to be cut is a silicon carbide ingot.

[0011] Optionally, the laser with the first wavelength is a green laser, and the laser with the second wavelength is an infrared laser.

[0012] Optionally, the wavelength range of the first wavelength is 522nm-542nm, and the wavelength range of the second wavelength is 1054nm-1074nm.

[0013] Optionally, the first wavelength is 532 nm and the second wavelength is 1064 nm.

[0014] Optionally, the power of the laser generating the first wavelength laser is 0.5W, the pulse width is 20ps-20ns, and the frequency is 100KHZ-500KHZ; the power of the laser generating the second wavelength laser is 10W, the pulse width is 1ns-30ns, and the frequency is 100KHZ-500KHZ.

[0015] Optionally, the power of the laser generating the laser of the first wavelength is 0.5 W, the pulse width is 100 ps, ​​and the frequency is 200 KHZ; the power of the laser generating the laser of the second wavelength is 10 W, the pulse width is 20 ns, and the frequency is 100 KHZ.

[0016] Optionally, according to a predetermined laser scanning trajectory, the focal point of the laser light is controlled to be located at a predetermined depth from the end face of the ingot to be cut, and reciprocates to form parallel linear burning points;

[0017] The scanning trajectory of the laser beam of the first wavelength is the same as the scanning trajectory of the laser beam of the second wavelength;

[0018] The distance between parallel lines of cautery was 350-450 μm.

[0019] Optionally, the distance between the parallel burn lines is 400 microns.

[0020] Optionally, the method further comprises:

[0021] The target modified layer is laser cut from the side of the ingot to be cut based on a third wavelength of laser; the third wavelength is smaller than the first wavelength; the third wavelength of laser has the ability to cut the modified layer but has no ability to modify the non-modified part of the ingot to be cut.

[0022] The present disclosure provides a wafer processing method based on a composite laser, comprising: performing a preliminary modification treatment on the crystal ingot to be cut at a predetermined depth based on a laser having a first wavelength which is transparent to the crystal ingot to be cut, to form a preliminary modified layer; performing a secondary modification treatment on the crystal ingot to be cut at a predetermined depth based on a laser having a second wavelength which is transparent to the crystal ingot to be cut but has poor transparency to the preliminary modified layer, to obtain a target modified layer; wherein the wavelength of the first wavelength is smaller than that of the second wavelength. That is to say, two lasers of different wavelengths are introduced to perform modification treatment on the crystal ingot to be cut, and the laser having a first wavelength with a relatively short wavelength is first used to perform modification treatment to obtain a preliminary modified layer, so that the material of the preliminary modified layer of the crystal ingot to be cut changes, and since the second wavelength laser for the secondary modification treatment has poor transparency to the preliminary modified layer, the minimum damage position of the crystal ingot to be cut in the vertical direction can be limited; in addition, the secondary modification treatment on the preliminary modified layer using the laser having a second wavelength can further expand the crack in the Y direction on the basis of the crack in the Y direction of the preliminary modified layer, so as to meet the subsequent wafer peeling requirements.

[0023] It should be understood that the content described in this section is not intended to identify the key or important features of the embodiments of the present disclosure, nor is it intended to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to better understand the present solution and do not constitute a limitation of the present disclosure.

[0025] Figure 1 It is a schematic flow chart of a wafer processing method based on a composite laser provided in an embodiment of the present disclosure;

[0026] Figure 2 It is a schematic diagram of the processing direction of the first wavelength and the second wavelength laser;

[0027] Figure 3 This is a schematic diagram of cracks formed in the modified layer by the first wavelength laser;

[0028] Figure 4 This is a schematic diagram of cracks formed in the modified layer by the second wavelength laser;

[0029] Figure 5 This is a schematic diagram of the third wavelength laser processing direction. DETAILED DESCRIPTION

[0030] The following is a description of exemplary embodiments of the present disclosure in conjunction with the accompanying drawings, including various details of the embodiments of the present disclosure to facilitate understanding, which should be considered as merely exemplary. Therefore, it should be recognized by those of ordinary skill in the art that various changes and modifications may be made to the embodiments described herein without departing from the scope and spirit of the present disclosure. Similarly, for the sake of clarity and conciseness, descriptions of well-known functions and structures are omitted in the following description.

[0031] Embodiment 1

[0032] Laser modification and stripping technology uses the internal modification of the laser beam for stripping, which has the advantages of high efficiency, high precision, and low damage. It has gradually become the preferred technology for cutting high-hardness and brittle materials such as silicon carbide. Among them, the laser modification and stripping method mainly includes two steps: 1. Modification step; 2. Stripping step. The existing modification steps mainly use a single wavelength laser beam for modification, such as using a 1064nm wavelength infrared laser for modification.

[0033] Figure 1 A wafer processing method based on a composite laser provided by an embodiment of the present disclosure is shown, the method comprising:

[0034] Step S101 , based on a laser having a first wavelength that is transparent to the crystal ingot to be cut, a preliminary modification process is performed on the crystal ingot to be cut at a predetermined depth to form a preliminary modified layer.

[0035] Step S102, based on a laser of a second wavelength having a transmittance to the ingot to be cut but poor transmittance to the preliminary modified layer, the ingot to be cut is subjected to a secondary modification process at a predetermined depth to obtain a target modified layer, wherein the wavelength of the first wavelength is smaller than the wavelength of the second wavelength.

[0036] Specifically, the crystal ingot to be cut is a silicon carbide crystal ingot, or it can be other crystal ingots to which the method disclosed herein can be applied, as long as the crystal ingot is first preliminarily modified using a laser of a first wavelength, and the second wavelength laser has poor permeability to the modified material and cannot cause damage to the depth exceeding the preliminary modified layer, but the preliminary modified layer can be further modified.

[0037] Among them, the laser with poor transmittance to the preliminary modified layer refers to the laser that cannot pass through the preliminary modified layer, or the laser with a wavelength with low transmittance to the preliminary modified layer (such as 20% transmittance, or other transmittance values, which can be determined according to the specific processing requirements).

[0038] Specifically, the laser of the first wavelength is a green laser, and the laser of the second wavelength is an infrared laser. Specifically, the laser of the first wavelength may be a laser of a wavelength range of 522nm-542nm, and the laser of the second wavelength may be a laser of a wavelength range of 1054nm-1074nm.

[0039] Among them, Figure 2 , 3 , 4, the first wavelength laser and the second wavelength laser are in accordance with Figure 1 Laser scanning processing is performed in the processing direction shown. Figure 3 As shown, by using the first wavelength, a parallel linear laser burning point can be formed at a predetermined depth from the end face of the ingot to be cut according to a predetermined scanning trajectory to obtain a preliminary modified layer, wherein the crack width in the Y direction formed by the first wavelength laser is relatively narrow. Figure 4 As shown, after the initial laser modification by a laser of a first wavelength, a secondary modification treatment is performed by a laser of a second wavelength, which can further expand the width of the Y-direction crack based on the Y-direction crack formed by the laser modification treatment with the first wavelength.

[0040] The present disclosure provides a wafer processing method based on a composite laser, comprising: performing a preliminary modification treatment on the crystal ingot to be cut at a predetermined depth based on a laser having a first wavelength which is transparent to the crystal ingot to be cut, to form a preliminary modified layer; performing a secondary modification treatment on the crystal ingot to be cut at a predetermined depth based on a laser having a second wavelength which is transparent to the crystal ingot to be cut but has poor transparency to the preliminary modified layer, to obtain a target modified layer; wherein the wavelength of the first wavelength is smaller than that of the second wavelength. That is to say, two lasers of different wavelengths are introduced to perform modification treatment on the crystal ingot to be cut, and the laser having a first wavelength with a relatively short wavelength is first used to perform modification treatment to obtain a preliminary modified layer, so that the material of the preliminary modified layer of the crystal ingot to be cut changes, and since the second wavelength laser for the secondary modification treatment has poor transparency to the preliminary modified layer, the minimum damage position of the crystal ingot to be cut in the vertical direction can be limited; in addition, the secondary modification treatment on the preliminary modified layer using the laser having a second wavelength can further expand the crack in the Y direction on the basis of the crack in the Y direction of the preliminary modified layer, so as to meet the subsequent wafer peeling requirements.

[0041] The embodiment of the present disclosure provides a possible implementation method. Specifically, the ingot to be cut is a silicon carbide ingot (it can also be other ingots that can use the method of the present disclosure), the first wavelength is 532nm, and the second wavelength is 1064nm. According to a predetermined laser scanning trajectory, the focal point of the laser light can be controlled to be located at a predetermined depth from the end face of the ingot to be cut, and reciprocating motion can be performed to form parallel linear burning points; wherein the scanning trajectory of the laser of the first wavelength is the same as that of the laser of the second wavelength. wherein the power of the laser generating the first wavelength laser is 0.5W, the pulse width is 20ps-20ns, and the frequency is 100KHZ-500KHZ; the power of the laser generating the second wavelength laser is 10W, the pulse width is 1ns-30ns, and the frequency is 100KHZ-500KHZ.

[0042] Specifically, according to Spot size = 4M2*wavelength*f / ΠD, it can be known that under the same spot size, 532nm<1064nm, so the 532nm focused spot is smaller than the 1064nm spot, and because the focused spot is smaller, the thermal impact caused is also smaller than that of 1064. After the initial modification using a laser with a wavelength of 532nm, the modified layer forms C, Si and a composite. The infrared light with a wavelength of 1064 has a very poor transmittance to it, which is reduced from about 80% to 2%. Therefore, after the low-power 532nm laser forms an ablation point inside the material, it also determines the lowest damage position in the Z direction, that is, due to the poor transmittance of the 1064nm wavelength to the initial modified layer, it will not further penetrate the initial modified layer, causing losses to the depth exceeding the initial modified layer of the ingot to be cut.

[0043] Specifically, the power of the laser generating the first wavelength laser is 0.5W, the pulse width is 100ps, and the frequency is 200KHZ; the power of the laser generating the second wavelength laser is 10W, the pulse width is 20ns, and the frequency is 100KHZ. The predetermined depth can be a depth of 500 microns from the wafer surface.

[0044] Among them, the spot size of the 532nm laser after focusing is about 2 microns, which can form an ablation point of 10 microns to 20 microns at a predetermined depth and a 5-micron transverse crack in the Y direction; the spot size of the 1064nm laser after focusing is 10 microns, which can expand the crack formed by 532nm to 400 microns at the same position, so that the transverse cracks caused by laser ablation marks at different longitudinal positions are connected to each other; after two laser processings with different wavelengths at the same position, a transverse crack covering the entire wafer has been formed at a distance of 500 microns from the entire wafer surface, thereby meeting the requirements for subsequent wafer peeling.

[0045] Specifically, the distance between the parallel burning lines is 350-450 microns. Preferably, the distance between the parallel burning lines is 400 microns. Thus, the transverse cracks generated by the laser ablation marks at different longitudinal positions can be connected to each other to form a transverse crack covering the entire wafer, thereby meeting the requirements for subsequent wafer peeling.

[0046] In the disclosed embodiment, the crystal ingot to be cut is preliminarily modified by a 532nm laser, and then modified by a 1064nm laser. The laser scanning trajectories of the two wavelengths of lasers are the same, thereby forming a transverse crack covering the entire wafer, meeting the subsequent wafer peeling requirements.

[0047] The present disclosure provides a possible implementation method, wherein the method further includes:

[0048] Step 103 (not shown in the figure) is to perform laser cutting processing on the target modified layer from the side of the ingot to be cut based on a third wavelength laser; the wavelength of the third wavelength is smaller than the first wavelength; the third wavelength laser has the ability to cut the modified layer but has no modification ability on the non-modified part of the ingot to be cut.

[0049] Specifically, after the ingot to be cut is modified, the material nature of the modified layer of the ingot to be cut is changed, and the Mohs hardness of the modified layer is changed to be lower than the Mohs hardness of the non-modified layer. A second wavelength laser having the ability to cut the modified layer but not having the ability to modify the non-modified part of the ingot to be cut can be used to cut the ingot in the lateral direction (such as Figure 5 As shown in the figure, laser stripping is performed at a depth which is the same as the predetermined depth from the end face of the wafer to be cut, thereby obtaining a target wafer.

[0050] The laser of the third wavelength has the ability to cut the modified layer but has no ability to modify the non-modified part of the ingot to be cut. The laser of the third wavelength can be an ultraviolet laser, such as an ultraviolet laser with a wavelength of 355 nm.

[0051] Taking silicon carbide ingot as an example, the Mohs hardness of silicon carbide ingot reaches 9.5. It is difficult to cut silicon carbide using ultraviolet laser. However, after the ingot to be cut is modified using a first wavelength laser (such as green laser, infrared laser), the modified layer becomes C, SI and a composite, so that the ultraviolet laser has the ability to cut the modified layer.

[0052] In the disclosed embodiment, the crystal ingot to be cut is first modified using lasers of the first wavelength and the second wavelength to obtain a target modified layer. Then, at the same depth as the target modified layer on the side of the crystal ingot to be cut, a laser of the third wavelength that has the ability to strip the modified layer but has no ability to strip the non-modified layer is used to perform chip stripping, which can improve the efficiency of chip stripping and reduce the risk of fragmentation.

[0053] For example, taking a silicon carbide ingot as an example, the modification and stripping process of the ingot to be cut includes:

[0054] 1. The outline of the entire wafer / ingot is captured visually to determine the area to be processed. The wafer is driven by a linear motor to move under the 532nm laser processing head for scanning. The spacing in the Y direction of the scan can be 200-800 microns, preferably 400 microns. After the entire wafer is scanned, the wafer is driven by a linear motor to move under the 1064nm laser processing head for secondary processing according to the pre-generated trajectory line to ensure that the laser traces of the two scans are highly overlapped. The preferred linear motor has a motion accuracy of ±1 micron. Among them, the power of the 532nm laser is 0.5W, the pulse width is 100ps, the frequency is 200KHZ, the spot size after focusing is 2 microns, and at a depth of 500 microns from the wafer surface, a 10-20 micron ablation point and a 5-micron Y-direction transverse crack are formed.

[0055] 2. Use 1064nm laser to perform secondary modification on the static ingot to be cut at the same depth and with the same scanning trajectory. The spot size of the 1064nm laser after focusing is 10 microns, and the crack formed by 532nm is expanded to 400 microns at the same position, so that the transverse cracks generated by laser ablation marks at different longitudinal positions are connected to each other. Among them, the power of the 1064nm laser is 10W, the pulse width is 20ns, and the frequency is 100KHZ. After two laser processings at the same position with different wavelengths, a transverse crack covering the entire wafer has been formed at a distance of 500 microns from the entire wafer surface.

[0056] 3. The linear motor drives the wafer to move to the 355nm laser processing head, and the position of the crack is captured by vision. The wafer is driven to rotate by the stage to achieve laser cutting of the wafer. The power of the 355nm laser is 10W, the pulse width is 100fs, and the frequency is 500KHZ.

[0057] 4. Finally, a crystal ingot and a wafer with a specified thickness peeled off from the crystal ingot are formed.

[0058] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this disclosure can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solutions disclosed in this disclosure can be achieved, and this document does not limit this.

[0059] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A wafer processing method based on a composite laser, characterized in that: include: Based on a laser having a first wavelength that is transmissive to the ingot to be cut, performing a preliminary modification process on the ingot to be cut at a predetermined depth to form a preliminary modified layer; Based on a laser with a second wavelength that is transparent to the ingot to be cut but has poor transparency to the preliminary modified layer, the ingot to be cut is subjected to a secondary modification treatment at a predetermined depth to obtain a target modified layer; wherein the wavelength of the first wavelength is smaller than that of the second wavelength.

2. The method according to claim 1, characterized in that The ingot to be cut is a silicon carbide ingot.

3. The method according to claim 1, characterized in that: The laser with the first wavelength is a green laser, and the laser with the second wavelength is an infrared laser.

4. The method according to claim 1, characterized in that: The wavelength range of the first wavelength is 522nm-542nm, and the wavelength range of the second wavelength is 1054nm-1074nm.

5. The method according to claim 1, characterized in that The first wavelength is 532 nm, and the second wavelength is 1064 nm.

6. The method according to claim 5, characterized in that The power of the laser generating the first wavelength laser is 0.5W, the pulse width is 20ps-20ns, and the frequency is 100KHZ-500KHZ; the power of the laser generating the second wavelength laser is 10W, the pulse width is 1ns-30ns, and the frequency is 100KHZ-500KHZ.

7. The method according to claim 6, characterized in that The power of the laser generating the laser of the first wavelength is 0.5 W, the pulse width is 100 ps, ​​and the frequency is 200 KHZ; the power of the laser generating the laser of the second wavelength is 10 W, the pulse width is 20 ns, and the frequency is 100 KHZ.

8. The method according to claim 7, characterized in that The method includes: According to the predetermined laser scanning trajectory, the focal point of the laser light is controlled to be located at a predetermined depth from the end face of the crystal ingot to be cut, and reciprocates to form parallel linear burning points; the scanning trajectory of the first wavelength laser is the same as that of the second wavelength laser; the distance between the burning parallel lines is 350-450 microns.

9. The method according to claim 8, characterized in that The distance between the parallel lines of burning was 400 microns.

10. The method according to any one of claims 1 to 9, characterized in that: The method further includes: The target modified layer is laser cut from the side of the ingot to be cut based on a third wavelength of laser; the third wavelength is smaller than the first wavelength; the third wavelength of laser has the ability to cut the modified layer but has no ability to modify the non-modified part of the ingot to be cut.

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