Ultrasonic stripping method and ultrasonic stripping equipment adopting low surface tension medium

Abstract

The invention relates to the technical field of semiconductor processing, in particular to an ultrasonic stripping method and ultrasonic stripping equipment adopting a low-surface-tension medium, and mainly solves the technical problem that ultrasonic vibration energy is relatively low in capacity of expanding cracks in a crystal. According to the ultrasonic stripping method adopting the low-surface-tension medium, the low-surface-tension medium is adopted as ultrasonic coupling liquid, and the laser-modified crystal is stripped through ultrasonic vibration. When the laser-modified crystal is placed in an ultrasonic pool, the low-surface-tension medium can be in contact with the crystal with the initial microcrack, and the low-surface-tension medium can reduce the strength and hardness of the crystal according to the Labinet effect, so that the front end of the crack can be promoted to extend, and meanwhile, the low-surface-tension medium can be more easily immersed into the crack and reaches the front edge of the crack; in this way, the capacity of ultrasonic vibration energy for expanding cracks in the crystal can be effectively improved, on one hand, stripping efficiency can be improved, and on the other hand, the requirement for the width of initial microcracks can be lowered.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor processing technology, and in particular to an ultrasonic stripping method and ultrasonic stripping equipment using a low surface tension medium. Background Art

[0002] In the semiconductor industry, hard and brittle crystalline materials such as silicon carbide, sapphire, and diamond, due to their excellent physical and chemical properties, show great potential for application in electronic device manufacturing. However, due to the hard and brittle nature of these materials, processing them into high-quality wafers faces numerous technical challenges, such as high cutting losses, low efficiency, and brittle edges. Combined laser and ultrasonic slicing methods, compared to mechanical contact slicing methods, are widely used because they significantly reduce residual stress and damage to the crystal.

[0003] The combined laser and ultrasonic slicing method is mainly divided into two steps: the first step is laser modification, that is, the initial microcracks are formed inside the crystal by laser; the second step is ultrasonic peeling, that is, the laser-modified crystal is placed in an ultrasonic tank, and the ultrasonic vibration energy is transmitted to the front end of the crack with the help of liquid media such as water in the tank, thereby achieving the expansion of the initial microcracks and then achieving peeling and slicing.

[0004] However, the ultrasonic peeling method still has some significant shortcomings, mainly manifested in the low ability of ultrasonic vibration energy to propagate cracks inside the crystal. In order to achieve effective separation of wafers, there are currently two main methods: the first is to cause a greater degree of initial microcracks in the crystal during the previous laser modification process, but this method will increase the risk of fragmentation during wafer peeling on the one hand, and on the other hand, it will also lead to a thicker laser modified damage layer, and a thicker damage layer will cause greater damage to the cutting piece, so it is not very applicable; the second is to optimize the frequency, power and other parameters of the ultrasonic vibration, but the adjustment space of these parameters is limited, and it is difficult to fundamentally solve the problems of crack propagation efficiency and separation success rate. Therefore, there is an urgent need to develop a method that can effectively improve the ability of ultrasonic vibration energy to propagate cracks inside the crystal. Summary of the Invention

[0005] In order to overcome the technical defect of the existing ultrasonic stripping method that the ultrasonic vibration energy has a low ability to propagate cracks inside the crystal, the present invention provides an ultrasonic stripping method and ultrasonic stripping equipment using a low surface tension medium.

[0006] The ultrasonic stripping method using a low surface tension medium provided by the present invention adopts the low surface tension medium as an ultrasonic coupling liquid and strips the laser-modified crystal through ultrasonic vibration.

[0007] Optionally, the low surface tension medium is a single-component liquid or a surfactant solution with low surface tension.

[0008] Optionally, the single-component liquid with low surface tension is one of ethanol, isopropanol, acetone or ethyl acetate.

[0009] Optionally, the surfactant solution is an aqueous solution to which a surfactant is added.

[0010] Optionally, the surfactant is one of fatty acid salts, sulfonates, sulfates, quaternary ammonium salts or amino acids.

[0011] Optionally, the frequency range used in ultrasonic peeling is 15kHz to 150kHz, and the power range used in ultrasonic peeling is 30W to 3000W.

[0012] The ultrasonic stripping device provided by the present invention is used to implement the aforementioned ultrasonic stripping method using a low surface tension medium, and the ultrasonic stripping device includes: an ultrasonic pool with an open top and filled with the low surface tension medium; An ultrasonic vibration generator is installed at the bottom of the ultrasonic pool; The holding assembly includes a holding body and a driving member. The holding body is suspended in the ultrasonic pool through the driving member. The holding body is used to hold the crystal to be peeled on its lower surface, and the driving member is used to drive the holding body to move horizontally.

[0013] Optionally, the driving member is further used to drive the holding body to move up and down to control the distance between the crystal to be peeled and the ultrasonic vibration generator to range from 0.5 mm to 5 mm.

[0014] Optionally, the ultrasonic stripping device further includes a liquid inlet pipe and a liquid outlet pipe both connected to the ultrasonic pool, the liquid inlet pipe is provided with a first flow valve, and the liquid outlet pipe is provided with a second flow valve.

[0015] The technical solution provided by the present invention has the following advantages compared with the prior art: The ultrasonic stripping method provided by the present invention adopts a low surface tension medium as an ultrasonic coupling liquid. When the laser-modified crystal is placed in an ultrasonic tank, the low surface tension medium will contact the crystal with initial microcracks. According to the Leppingie effect, the low surface tension medium will reduce the strength and hardness of the crystal, thereby promoting the extension of the front end of the crack. At the same time, the low surface tension medium is also more likely to penetrate the crack and reach the crack front. This can effectively enhance the ability of ultrasonic vibration energy to expand cracks inside the crystal. On the one hand, it can improve the efficiency of stripping, and on the other hand, it can also reduce the width requirements of the initial microcracks modified by laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0018] Figure 1 Schematic diagram showing the structure of an ultrasonic peeling device in an embodiment of the present invention.

[0019] In the picture: 1. Ultrasonic tank; 2. Low surface tension medium; 3. Crystal to be peeled; 4. Initial microcrack; 5. Ultrasonic vibration generator; 6. Holding component; 7. Liquid inlet pipe; 8. Liquid outlet pipe; 9. First flow valve; 10. Second flow valve. DETAILED DESCRIPTION

[0020] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features therein can be combined with each other.

[0021] In the description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance. It should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, removable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms based on specific circumstances.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all the embodiments.

[0023] The following combination Figure 1 Specific embodiments of the present invention are described in detail. Example 1

[0024] This embodiment provides an ultrasonic exfoliation method using a low surface tension medium, wherein the low surface tension medium 2 is used as an ultrasonic coupling liquid, and the laser-modified crystal is exfoliated by ultrasonic vibration.

[0025] It is easy to understand that the so-called ultrasonic coupling liquid, that is, the liquid medium filled in the ultrasonic tank 1, is mainly used to transmit ultrasonic energy, so that the ultrasonic energy is efficiently transmitted from the ultrasonic vibration generator 5 to the crystal 3 to be peeled.

[0026] Specifically, the low surface tension medium 2 is a single-component liquid or a surfactant solution having low surface tension.

[0027] More specifically, the single-component liquid with low surface tension is one of ethanol, isopropyl alcohol, acetone, or ethyl acetate. Of course, the single-component liquid with low surface tension is not limited thereto, and other single-component liquids with low surface tension can also be used as the low surface tension medium 2.

[0028] More specifically, the surfactant solution is an aqueous solution to which a surfactant is added. Of course, the surfactant solution is not limited thereto, and other solutions to which a surfactant is added may also be used as the low surface tension medium 2 .

[0029] Specifically, the surfactant is one of fatty acid salt, sulfonate, sulfate, quaternary ammonium salt or amino acid. Of course, the surfactant is not limited thereto, and other commonly used surfactants in this area can also be used.

[0030] It should be noted that when a surfactant solution is used as the low-surface-tension medium 2, the concentration of the solution must be controlled within an appropriate range. If the concentration is too low, crack extension and liquid penetration into the cracks will be insufficient. If the concentration is too high, excessive foaming or excessive viscosity may occur during ultrasonic vibration, hindering efficient ultrasonic vibration wafer separation. The concentration range of the surfactant solution depends on the type of solvent and solute used, and can be easily designed by those skilled in the art or determined through limited experimentation. For example, when a quaternary ammonium salt is used as the solute and pure water is used as the solvent, the concentration range of the surfactant solution should be designed to be between 0.1 g / L and 2 g / L.

[0031] It's important to note that when a surfactant solution is used as the low-surface-tension medium 2, the selection of a surfactant with a specific affinity that matches the surface energy of the material is based on the chemical composition of the different crystal materials. This can be easily designed by those skilled in the art or determined through limited experimentation. For example, for single-crystal silicon carbide, the use of a quaternary ammonium salt, a cationic surfactant, can significantly improve the wettability of the silicon carbide surface, facilitating the ultrasonic coupling fluid's penetration into the crack and reaching the crack front.

[0032] Specifically, the frequency range used in ultrasonic peeling is 15 kHz to 150 kHz, and the power range used in ultrasonic peeling is 30 W to 3000 W.

[0033] More specifically, the frequency used in ultrasonic peeling is 15 kHz, 28 kHz, 40 kHz, 80 kHz, or 100 kHz; the power range used in ultrasonic peeling is 30 W, 300 W, or 3000 W.

[0034] The effect of the method of this embodiment is verified through two groups of experiments below.

[0035] Experiment 1 S1. Select a conductive 8-inch silicon carbide ingot modified by laser as the crystal to be peeled 3; S2. The crystals to be peeled off 3 were placed in an aqueous solution of a quaternary ammonium salt as an ultrasonic coupling liquid in an ultrasonic cell 1, the concentration of the aqueous solution of a quaternary ammonium salt was added to 0.5g / L; S3. Set the ultrasonic frequency to 28 kHz, the ultrasonic output power to 500 W, the distance between the ultrasonic vibration generator 5 and the crystal 3 to be peeled to 3 mm, and perform ultrasonic peeling.

[0036] S4. Observe the microcracks inside the crystal with the human eye. When the microcracks have fully expanded and penetrated, turn off the ultrasonic vibration generator 5.

[0037] Result: After 1.8 minutes, the wafer was completely separated.

[0038] Comparison 1 S1. Select a conductive 8-inch silicon carbide ingot modified by laser as the crystal to be peeled 3, and the laser modification and the same parameters as in Experiment 1 are used; S2. The crystal to be peeled 3 is placed in an ultrasonic pool 1 with pure water as an ultrasonic coupling liquid; S3. Set the ultrasonic frequency to 28 kHz, the ultrasonic output power to 500 W, the distance between the ultrasonic vibration generator 5 and the crystal 3 to be peeled to 3 mm, and perform ultrasonic peeling.

[0039] S4. Observe the microcracks inside the crystal with the human eye. When the microcracks have fully expanded and penetrated, turn off the ultrasonic vibration generator 5.

[0040] Result: After 3.2 minutes, the wafer was separated.

[0041] The comparison of the results of Experiment 1 and Comparison 1 shows that the ultrasonic peeling method can shorten the peeling time and improve the peeling efficiency.

[0042] Experiment 2 S1. Select a conductive 8-inch silicon carbide ingot that has been laser-modified as crystal 3 to be peeled, and the laser power is reduced by 20% compared to Experiment 1; S2. The crystals to be peeled off 3 were placed in an aqueous solution of a quaternary ammonium salt as an ultrasonic coupling liquid in an ultrasonic cell 1, the concentration of the aqueous solution of a quaternary ammonium salt was added to 0.5g / L; S3. Set the ultrasonic frequency to 28 kHz, the ultrasonic output power to 500 W, the distance between the ultrasonic vibration generator 5 and the crystal 3 to be peeled to 3 mm, and perform ultrasonic peeling.

[0043] S4. Observe the microcracks inside the crystal with the human eye. When the microcracks have fully expanded and penetrated, turn off the ultrasonic vibration generator 5.

[0044] Result: After 5.4 minutes, the wafer was separated.

[0045] Comparison 2 S1. Select a conductive 8-inch silicon carbide ingot modified by laser as the crystal to be peeled 3, and the laser modification uses the same parameters as Experiment 2; S2. The crystal to be peeled 3 is placed in an ultrasonic pool 1 with pure water as an ultrasonic coupling liquid; S3. Set the ultrasonic frequency to 28 kHz, the ultrasonic output power to 500 W, the distance between the ultrasonic vibration generator 5 and the crystal 3 to be peeled to 3 mm, and perform ultrasonic peeling.

[0046] S4. Observe the microcracks inside the crystal with the human eye. When the microcracks have fully expanded and penetrated, turn off the ultrasonic vibration generator 5.

[0047] Result: After 15 minutes, the wafer was still not separated.

[0048] Comparing the results of Experiment 2 and Comparison 2 shows that when the laser power is reduced, resulting in narrower initial microcracks in the crystal, ultrasonic exfoliation of the crystal is not possible using conventional methods, but is possible using this method. This indicates that ultrasonic exfoliation using this method can reduce the required width of the initial microcracks created by laser exfoliation, thereby minimizing material loss during laser exfoliation.

[0049] The ultrasonic stripping method using a low surface tension medium in this embodiment has the following effects: In terms of processing efficiency, this method, under the action of ultrasonic vibration energy and in conjunction with the low-surface-tension medium 2, can more efficiently promote the expansion of cracks within hard and brittle crystalline materials after laser modification. Compared to traditional ultrasonic vibration peeling methods such as those using pure water, there is no need to wait for crack expansion, greatly shortening the time required for wafer separation. Taking the peeling of 6-8 inch silicon carbide ingots as an example, this method can shorten the peeling time by 20%-50%, significantly improving the overall processing efficiency of laser peeling technology and meeting the modern semiconductor industry's demand for large-scale, high-efficiency production.

[0050] From the perspective of improving material utilization, the use of low-surface-tension medium 2 as an ultrasonic coupling fluid enhances the ultrasonic vibration peeling capability and efficiency, thereby reducing the necessary initial crack propagation within the crystal caused by laser modification. This can be achieved by reducing the laser modification scanning power, reducing the number of repeated scans, and reducing the spacing between scan lines, thereby reducing the thickness of the laser-modified damage layer, thereby effectively reducing cutting blade loss and improving semiconductor raw material utilization. Taking silicon carbide as an example, in large-scale production, the use of the present invention can reduce the thickness of the raw materials required to process each silicon carbide wafer by 10%-25% compared to traditional methods, significantly saving raw material costs and improving the economic benefits of the enterprise.

[0051] From the perspective of product quality stability, the present invention uses a low-surface-tension ultrasonic liquid medium, which can achieve stable and efficient chip separation by reasonably selecting and adjusting the type and concentration of surfactants while appropriately reducing the loss of laser stripping materials. This reduces the probability of quality failure in the laser stripping process, including the inability to separate the ingot wafer due to insufficient laser modification, and cracking due to excessive ultrasonic power, thereby improving the overall quality and consistency of the laser stripping process.

[0052] Furthermore, this method is highly practical and economical in practical application. Single-component liquids or surfactants with low surface tension are relatively easy to obtain, and the process of adding and controlling their concentration is straightforward, eliminating the need for expensive additional equipment. Furthermore, this method can utilize existing ultrasonic vibration peeling equipment, eliminating the need for large-scale equipment replacement, reducing technology upgrade costs for companies and facilitating widespread adoption within the industry. Example 2

[0053] This embodiment provides an ultrasonic stripping device for implementing the ultrasonic stripping method using a low surface tension medium described in Example 1. The ultrasonic stripping device includes an ultrasonic tank 1, an ultrasonic vibration generator 5, and a holding assembly 6.

[0054] The top of the ultrasonic pool 1 is open, and the ultrasonic pool 1 is filled with a low surface tension medium 2.

[0055] Specifically, the size of the ultrasonic pool 1 is determined by the size of the crystals 3 to be peeled, and it needs to be made of chemically resistant and high-strength materials, such as stainless steel, to ensure long-term stable use in low surface tension liquid media.

[0056] The ultrasonic vibration generator 5 is installed at the bottom of the ultrasonic pool 1 .

[0057] The holding assembly 6 includes a holding body and a driving member. The holding body is suspended in the ultrasonic pool 1 through the driving member. The holding body is used to hold the crystal 3 to be peeled off on its lower surface, and the driving member is used to drive the holding body to move horizontally.

[0058] Specifically, the holding body can be a mechanical clamping type, using the auxiliary structure on the upper surface of the crystal 3 to be peeled for clamping; or it can be a vacuum adsorption type, directly adsorbing the upper surface of the crystal 3 to be peeled.

[0059] It is easy to understand that the driving member drives the main body to move horizontally, thereby driving the crystal 3 to be peeled off to move horizontally, so that it receives ultrasonic vibration more evenly.

[0060] Furthermore, the driving member is also used to drive the main body to rise and fall to control the distance between the crystal to be peeled 3 and the ultrasonic vibration generator 5 to be within a range of 0.5mm to 5mm. By controlling the distance between the crystal to be peeled 3 and the ultrasonic vibration generator 5 within this range, the ultrasonic vibration energy can be more fully utilized.

[0061] Specifically, the driving part can use common linear power elements such as electric push rods and linear motors to achieve horizontal movement or lifting.

[0062] In addition, the ultrasonic peeling apparatus of this embodiment further includes an inlet pipe 7 and an outlet pipe 8, both of which are connected to the ultrasonic tank 1. The inlet pipe 7 is provided with a first flow valve 9, and the outlet pipe 8 is provided with a second flow valve 10. The inlet pipe 7 is used to inject the low-surface tension medium 2 into the ultrasonic tank 1, and the outlet pipe 8 is used to discharge the low-surface tension medium 2 from the ultrasonic tank 1. The first flow valve 9 is used to control the inlet flow rate, and the second flow valve 10 is used to control the outlet flow rate.

[0063] The method of using the ultrasonic peeling device of this embodiment is as follows: S1. Inject the low surface tension medium 2 into the ultrasonic tank 1 through the liquid inlet pipe 7. The liquid level needs to be adjusted according to the size of the crystal 3 to be peeled off to ensure that the crystal 3 to be peeled off can be completely immersed in the low surface tension medium 2. At the same time, the size of the ultrasonic tank 1 should also ensure that there is enough liquid space around the crystal; S2. The crystal to be peeled is held on the holding body 3 and is immersed in the low surface tension medium 2 by the driving member, and the distance between the crystal to be peeled and the ultrasonic vibration generator 5 is controlled to be in the range of 0.5 mm to 5 mm; S3 starts the ultrasonic vibration generator 5, sets the frequency range of ultrasonic peeling used in the range of 15kHz to 150kHz, the power range of ultrasonic peeling used in the range of 30W to 3000W, while the crystal is driven by the drive member to move horizontally for ultrasonic peeling; S4. When the microcracks inside the crystal are found to have fully expanded and penetrated through the human eye or camera monitoring, and the crystal separation is achieved, the ultrasonic vibration generator 5 is turned off; S5. Remove the separated wafer and remaining crystal material, and rinse them with deionized water manually or using automated equipment to remove the low surface tension medium 2 remaining on the surface and any crystal residue that may be attached.

[0064] S6. After cleaning, the wafers are fully inspected, including thickness, defects, surface shape, internal cracks, etc. Only wafers that pass the inspection can enter the subsequent processing and manufacturing links.

[0065] It should be noted that in step S3, if a surfactant solution is used as the low surface tension medium, since the surfactant may undergo volatilization, decomposition, and other changes under long-term ultrasonic vibration, it is necessary to regularly use liquid chromatography or spectrophotometry to detect the composition and concentration of the surfactant in the ultrasonic pool 1. If it is found that the concentration deviates from the preset value, the liquid medium in the ultrasonic pool 1 is replaced or its composition is adjusted in time.

[0066] It should be noted that in step S5, if necessary, pure water or other cleaning agents can be used to further clean the wafer and the remaining crystal material to ensure that their surfaces are clean.

[0067] The above is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions have been made with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents; and such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments, and they should all be covered by the scope of protection of the claims.

Claims

1. An ultrasonic stripping method using a low surface tension medium, characterized in that: A low surface tension medium (2) is used as an ultrasonic coupling liquid, and the laser-modified crystal is peeled off by ultrasonic vibration.

2. The ultrasonic stripping method using a low surface tension medium according to claim 1, characterized in that: The low surface tension medium (2) is a single-component liquid or a surfactant solution with low surface tension.

3. The ultrasonic stripping method using a low surface tension medium according to claim 2, characterized in that: The single-component liquid with low surface tension is one of ethanol, isopropyl alcohol, acetone or ethyl acetate.

4. The ultrasonic stripping method using a low surface tension medium according to claim 2, characterized in that: The surfactant solution is an aqueous solution to which a surfactant is added.

5. The ultrasonic stripping method using a low surface tension medium according to claim 4, characterized in that: The surfactant is one of fatty acid salt, sulfonate, sulfate, quaternary ammonium salt or amino acid.

6. The ultrasonic stripping method using a low surface tension medium according to any one of claims 1 to 5, characterized in that: The frequency range used in ultrasonic peeling is 15kHz to 150kHz, and the power range used in ultrasonic peeling is 30W to 3000W.

7. An ultrasonic peeling device, characterized in that: It is used to implement the ultrasonic stripping method using a low surface tension medium as described in claims 1 to 6, and the ultrasonic stripping equipment includes: An ultrasonic pool (1) with an open top, wherein the ultrasonic pool (1) is filled with the low surface tension medium (2); An ultrasonic vibration generator (5) installed at the bottom of the ultrasonic pool (1); A holding assembly (6) comprises a holding body and a driving member, wherein the holding body is suspended in the ultrasonic pool (1) via the driving member, the holding body is used to hold the crystal (3) to be peeled off on its lower surface, and the driving member is used to drive the holding body to move horizontally.

8. The ultrasonic peeling device according to claim 7, characterized in that The driving member is also used to drive the holding body to move up and down to control the distance between the crystal to be peeled (3) and the ultrasonic vibration generator (5) to be within a range of 0.5 mm to 5 mm.

9. The ultrasonic peeling device according to claim 7 or 8, characterized in that: The ultrasonic stripping device further comprises a liquid inlet pipe (7) and a liquid outlet pipe (8) both of which are connected to the ultrasonic pool (1); the liquid inlet pipe (7) is provided with a first flow valve (9), and the liquid outlet pipe (8) is provided with a second flow valve (10).

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