A method for automated ultrasonic delamination of a crystal ingot

Abstract

The present application relates to a kind of crystal ingot automated ultrasonic stripping method, it includes the following steps, S1: first ultrasonic treatment is carried out on the edge of laser modification obtained crystal ingot, to make the modification layer of the crystal ingot form edge separation starting point, obtain edge pre-separation crystal ingot;S2: fixed region is respectively arranged at the two ends of the edge pre-separation crystal ingot, at least one fixed region is forced, while carrying out second ultrasonic treatment, until the stripping force of the feedback of at least one fixed region reduces to preset threshold, obtains wafer and remaining crystal ingot.The present application has the advantages of accurate judgment stripping end point, avoid wafer out of control drift, improve stripping yield and degree of automation.

Description

Technical Field

[0001] This invention relates to the technical field of semiconductor processing, and in particular to an automated ultrasonic stripping method for crystal ingots. Background Technology

[0002] After laser modification of silicon carbide ingots, water is typically used as the sound and force transmission medium, combined with ultrasonic assistance, to further propagate the laser-induced microcracks within the ingot, thereby achieving efficient and non-destructive wafer separation. This process is known as ultrasonic ablation. Currently, a common industrial ultrasonic ablation method involves applying high-frequency vibration energy to the ingot using an ultrasonic transducer or other ultrasonic transducer on the laser incident side. Utilizing the propagation and cavitation effects of ultrasound in water, cracks are excited and guided to extend along a predetermined path, ultimately separating the target wafer from the parent ingot. However, this method presents a key technical challenge in practice: because the entire ablation process occurs inside the ingot and is difficult to observe directly, operators often cannot accurately determine when the wafer has completely separated from the ingot. This uncertainty may lead to two adverse consequences: First, if the wafer is not completely detached from the ingot after the ultrasonic treatment ends, the target wafer cannot be successfully removed, resulting in process failure or the need for repeated processing, which affects production efficiency. Second, if the wafer falls off the ingot prematurely during the ultrasonic process, while the ultrasonic waves are still being applied, the detached wafer may drift or rotate uncontrollably under the combined action of water flow disturbance and ultrasonic cavitation force, thus deviating from the originally set wafer removal position. In severe cases, it may even collide with other structures or container walls, causing irreversible damage such as scratches and cracks on the wafer surface, which directly affects product yield and subsequent processing quality.

[0003] Chinese Patent CN110277349B discloses a method for generating a wafer from a hexagonal single crystal ingot. The method includes the following steps: a release layer formation step, in which a laser beam of a wavelength transparent to the hexagonal single crystal ingot is positioned at a depth equivalent to the thickness of the wafer to be generated at a distance from the end face of the ingot, and the ingot is irradiated with the laser beam to form a release layer; an ultrasonic generation step, in which an ultrasonic generation unit is positioned facing the wafer to be generated, separated by a water layer, and the ultrasonic generation unit generates ultrasonic waves, which are transmitted to the hexagonal single crystal ingot to destroy the release layer; and a release detection step, in which a height detection unit is positioned on the upper surface of the wafer to be generated, separated by a water layer, and the release of the wafer from the hexagonal single crystal ingot is detected based on the change in height of the upper surface of the wafer, and the temperature of the water layer is set to a temperature that can suppress the formation of cavitation.

[0004] The existing technical solutions described above have the following drawbacks: The methods described use a ranging head to detect height changes on the ingot surface to determine whether the wafer has been successfully separated. However, in practice, this method has certain limitations: because the ranging head can only acquire height information at a specific point on the ingot surface in a single measurement, it cannot simultaneously cover the entire ingot area. Therefore, if the edge of the ingot or a small local area inside is not completely separated and is still adhered to the substrate, and the ranging head happens not to sample and measure this unseparated area, it may incorrectly conclude that the entire wafer has been successfully separated. This judgment deviation caused by insufficient sampling points or improper location selection can easily lead to misjudgments, resulting in the inability to perform subsequent wafer removal processes normally, and may even affect the processing efficiency and yield of the entire batch of products. Summary of the Invention

[0005] The problem this invention aims to solve is that existing ultrasonic peeling techniques are prone to failing to accurately determine whether the wafer has been completely separated, which can easily lead to wafer removal failure or wafer damage. The invention provides an automated ultrasonic peeling method for wafer ingots, which has the advantages of accurately determining the peeling endpoint, avoiding uncontrolled wafer drift, improving peeling yield, and increasing automation.

[0006] The above-mentioned objective of this invention is achieved through the following technical solutions: An automated ultrasonic stripping method for crystal ingots includes the following steps: S1: Perform a first ultrasonic treatment on the edge of the ingot obtained by laser modification so that the modified layer of the ingot forms an edge separation starting point, and obtain an edge pre-separated ingot; S2: Fixing regions are set at both ends of the pre-separated crystal ingot at the edge. Force is applied to at least one fixing region, and a second ultrasonic treatment is performed until the peeling force fed back by the at least one fixing region is reduced to a preset threshold, thereby obtaining a wafer and the remaining crystal ingot.

[0007] Specifically, in the "Automated Ultrasonic Stripping Method for Crystal Ingots" of the present invention, The specific meaning of "laser modification" is that a laser beam of a specific wavelength is focused inside the ingot to generate a localized damaging layer, namely the modification layer. The modification layer is mainly composed of a high dislocation density layer and cracks. The modification layer is the starting point for subsequent crack propagation. By optimizing the laser and optical path system, the modification layer can be confined inside the ingot, without causing thermal damage to the surface of the ingot. Then, external force is used to guide the cracks toward the circumferential surface and / or end face of the ingot, thereby separating the ingot into the required size. The specific meaning of "ingot" refers to a cylindrical or blocky solid material grown from one or more of the following materials: single crystals, polycrystalline materials, and amorphous materials, through a specific process (such as the Czochralski method, zone melting method, PVT method, etc.). The material is not limited to, for example, materials containing at least one element from Group IIIA, Group IVA, Group VA, and Group IIB of the periodic table. It is not limited to, for example, silicon (Si), silicon carbide (SiC), silicon nitride (Si3N4), silicon oxide (SiO2), silicon germanide (SiGe), germanium (Ge), gallium arsenide (GaAs), gallium nitride (GaN), indium phosphide (InP), indium arsenide (InAlSb), zinc oxide (ZnO), aluminum nitride (AlN), gallium trioxide (Ga2O3), aluminum oxide (Al2O3), gallium phosphide (GaP), indium arsenide (InAs), and indium nitride (In). N, aluminum arsenide (AlAs), diamond, cubic boron nitride (CBN), magnesium silicate (Mg2SiO4), lead titanate (PbTiO3), barium titanate (BaTiO3), lithium niobate (LiNbO3), Al2O3CrNd glass, cadmium telluride (CdTe), tungsten oxide (WO3), zinc ferrite (ZnFe2O), gamma iron oxide (γ-Fe2O3), strontium ferrite (SrO·6Fe2O3), cadmium sulfide (CdS), calcium polysulfide (Ca2Sx), vanadium oxide (VO2), nickel oxide (NiO), lanthanum boride (LaB6), barium oxide (BaO), lead magnesium niobate (PMN), barium titanate (BaTiO3), lithium titanate (LiTiO3), yttrium aluminum garnet (YAG), lithium niobate (LiNbO3), gallium phosphate (GaPO4), calcium titanate (CaTiO3), rare earth ketoates (YBa2Cu3O7), and / or metallic materials, etc. The specific meaning of "fixed area" refers to the area formed on the surface of the crystal ingot by installing the crystal ingot through methods such as fastener fixing, welding fixing, pressing fixing (interference fit), riveting fixing, heat fitting fixing, cold expansion fixing, clamping fixing, bonding fixing, magnetic adsorption, and / or vacuum adsorption. This area can be a continuous area of ​​contact or a dispersed area of ​​intermittent contact. The size and shape of this area will affect the interaction force between objects during the subsequent crack propagation process. The specific meaning of "applying force" refers to the force applied to the ingot through the aforementioned fixed area, such as tensile force, pressure, thrust, support force, driving force, resistance, centripetal force, restoring force, gravity, elastic force, magnetic force, nuclear force, frictional force, and / or shear force. The method of applying force is not limited, for example, it can be continuous force or intermittent force. The magnitude of the applied force is not limited, for example, it can be constant, regularly changing, or irregularly changing. The direction of the applied force is not limited, for example, it can be a straight line direction, a broken line direction, a circumferential direction, a curved direction, and / or a spiral direction that is approximately parallel, perpendicular, and / or intersecting with the plane where the modified layer is located. The specific meaning of "peeling force" refers to the interaction force from the unseparated ingots experienced by the force-applying end during the separation process. When the modified layer region is not completely separated, the wafer part to be separated from the remaining ingot part is still adhered to the whole, and the peeling force is insufficient to mechanically peel the wafer and will not cause the wafer to crack. As the second ultrasonic treatment proceeds, the cracks in the modified layer continue to expand, the area of ​​the adhered region gradually decreases, and the peeling force will gradually decrease accordingly. When the wafer is completely peeled from the remaining ingot, the adhesion structure completely disappears, and the force-applying end can easily remove the peeled wafer. It is only necessary to overcome the weight of the wafer. The fixed force applied disappears, and at this time the peeling force will drop abruptly, which indicates that the peeling is complete.

[0008] Furthermore, in S1, the first ultrasonic treatment is either non-immersion ultrasonic or immersion ultrasonic, with the ultrasonic waves directed toward the edge of the ingot near the modified layer.

[0009] Furthermore, in S1, the ultrasonic action area of ​​the first ultrasonic treatment moves relative to the edge of the crystal ingot so that the ultrasonic action path passes through the edge of the crystal ingot at least once.

[0010] Furthermore, in S1, the relative motion is performed by moving the ultrasonic wave action area of ​​the first ultrasonic treatment relative to the edge of the crystal ingot in a planar manner, and / or by rotating the crystal ingot.

[0011] Furthermore, in S1, the first ultrasonic treatment employs a high-power-density and small-area ultrasonic transducer.

[0012] Furthermore, in S1, the ultrasonic power of the first ultrasonic treatment is 80~120W, the ultrasonic frequency is 80~120kHz, the ultrasonic time increases by 0.8~1.2min for every 50mm increase in the crystal ingot diameter, the ultrasonic action area is within a range of 20~40mm from the edge of the crystal ingot, and the distance between the ultrasonic transducer and the surface of the crystal ingot is 1~3mm.

[0013] Furthermore, in S2, the second ultrasonic treatment is immersion ultrasonic, with the ultrasonic waves directed toward the periphery of the ingot.

[0014] Furthermore, in S2, the second ultrasonic treatment employs a high-power and large-area ultrasonic transducer.

[0015] Furthermore, in S2, the ultrasonic power of the second ultrasonic treatment is 800~1200W, and the ultrasonic frequency is 20~40kHz.

[0016] Furthermore, in S2, force is applied to at least one fixed area until the peeling force reaches 20~60N, the force is maintained, and the peeling force on at least one fixed area is monitored in real time. When the peeling force suddenly decreases and falls below a preset threshold, it is determined that the wafer has been separated from the remaining ingot, the force application and the second ultrasonic treatment are stopped.

[0017] In summary, the beneficial technical effects of the present invention are as follows: 1. Because the present invention uses a two-step ultrasonic processing method: the first step is to construct the separation starting point at the edge of the ingot, and the second step is to carry out a second ultrasonic processing while applying peeling force, and to use the real-time monitoring of the sudden decrease in peeling force as the basis for determining the completion of separation, it makes up for the shortcomings of the traditional method that relies on single-point distance measurement and is prone to misjudgment. Thus, it achieves the effect of accurately judging the moment when the wafer is completely separated, and avoids wafer removal failure or wafer damage due to stopping ultrasonication too early or too late. 2. In this invention, it is preferable to make the ultrasonic action area relative to the edge of the ingot move (e.g., the ingot rotates or the ultrasonic head moves) during the first ultrasonic treatment to ensure that the ultrasonic path covers at least one circumference of the edge of the ingot. Since this operation can effectively form a reliable separation starting point throughout the entire edge, it provides a uniform crack propagation entrance for the second ultrasonic treatment, thus achieving the effect that even if the ingot is not separated locally, it can be reliably pre-opened, and the crack propagation is more uniform during the subsequent peeling process. 3. The method of the present invention first uses high-power-density, small-area ultrasound to pre-expose the separation starting point at the edge of the ingot, then transfers the ingot to an ultrasonic bath for immersion and fixes both ends. While applying tensile force, immersion ultrasound is performed using a sidewall ultrasonic transducer array, and the peeling force is monitored in real time until it suddenly decreases. This achieves the effects of controllable peeling process, immediate cessation of ultrasound and stretching after complete wafer separation, effective prevention of damage to the wafer from water flow and cavitation force after detachment, and significant improvement in ultrasonic peeling yield and automation level. Attached Figure Description

[0018] Figure 1 This is a partial structural schematic diagram of the ingot obtained by laser modification in Embodiment 1 of the present invention.

[0019] Figure 2 This is a schematic diagram of the ultrasonic device for the first ultrasonic treatment provided in Embodiment 1 of the present invention.

[0020] Figure 3 This is a partial cross-sectional view of the modified layer of the crystal ingot in Embodiment 1 of the present invention.

[0021] Figure 4 This is a schematic diagram of the ultrasonic device for the second ultrasonic treatment provided in Embodiment 1 of the present invention.

[0022] Figure 5This is a partial cross-sectional view of the modified layer of the crystal ingot in Embodiment 1 of the present invention.

[0023] Figure 6 This is a schematic diagram of the ultrasonic device for the first ultrasonic treatment provided in Embodiment 2 of the present invention. Detailed Implementation

[0024] To make the technical means, creative features, objectives and effects of this invention clearer and easier to understand, the invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0025] Example 1: An automated ultrasonic stripping method for crystal ingots disclosed in this invention includes the following steps: S1: The edge of the laser-modified ingot is subjected to a first ultrasonic treatment to form an edge separation starting point in the modified layer of the ingot, resulting in an edge-pre-separated ingot; the specific implementation method is as follows: S11: Reference Figure 1 Prepare a laser-modified crystal ingot. The crystal ingot has a modifier layer and opposing first and second end faces. The first end face is the end face of the crystal ingot that is close to the modifier layer. S12: Reference Figure 2 The second end face of the crystal ingot is adsorbed and fixed to the rotating end of the rotary displacement stage, and a high power density and small area ultrasonic transducer plate is installed at a height of 2mm away from the first end face of the crystal ingot with the working end facing the first end face. S13: Start the rotary displacement stage and ultrasonic transducer plate to perform the first ultrasonic treatment, and control the ultrasonic power to 100W, the ultrasonic frequency to 100kHz, and the ultrasonic time to increase by 1.0min for every 50mm increase in the crystal ingot diameter. The ultrasonic action area is within 30mm of the edge of the crystal ingot. S14: Reference Figure 3 During the first ultrasonic treatment, the ingot rotates and the ultrasonic action area moves relative to the edge of the ingot so that the ultrasonic action path passes through the edge of the ingot at least once. The strong cavitation effect generated by the high power density ultrasonic waves forces the edge cracks of the ingot to connect and obvious cracks to form the edge separation starting point of the modified layer of the ingot, providing a force point for the second ultrasonic treatment, and obtaining an edge pre-separated ingot. S2: Fixed regions are set at both ends of the pre-separated ingot at the edge. Force is applied to at least one fixed region, and a second ultrasonic treatment is performed simultaneously until the peeling force fed back by at least one fixed region is lower than a preset threshold, thus obtaining a wafer and the remaining ingot; Specific implementation method is as follows: S21: Reference Figure 4The edge pre-separated crystal ingot obtained in S1 is transferred to the ultrasonic cell. The second end face of the crystal ingot is adsorbed and fixed on the tooling at the bottom of the ultrasonic cell, and the first end face is adsorbed and fixed on the vacuum chuck at the moving end of the robot arm. The active end of the high-power and large-area ultrasonic transducer on the side wall of the ultrasonic cell faces the periphery of the crystal ingot. S22: Inject pure water into the ultrasonic bath to immerse the crystal ingot and the robot arm, start the rotating displacement stage, the robot arm and the high-power and large-area ultrasonic transducer to perform the second ultrasonic treatment, and control the robot arm to stretch upward until the peeling force reaches 50N, then maintain the stretching force. The ultrasonic power is 1000W and the ultrasonic frequency is 30kHz. S13: Reference Figure 5 During the second ultrasonic treatment, the modified layer is subjected to the upward pulling force applied by the robotic arm. The high power and large area of ​​the ultrasonic transducers on the sidewall of the ultrasonic pool apply ultrasonic vibration and cavitation effect through the separation starting point at the edge of the modified layer, which can easily cause the cracks inside the modified layer to gradually expand. S14: During the second ultrasonic treatment, the peeling force (i.e. the force fed back by the moving end of the robot) on the first end face is monitored in real time. That is, the robot is subjected to the reverse pull of the modified layer. When the peeling force suddenly decreases and is lower than the preset threshold of 5N, it is determined that the wafer has been separated from the remaining ingot, the force application and the second ultrasonic treatment are stopped, and the wafer and the remaining ingot are obtained.

[0026] Example 2: This invention discloses an automated ultrasonic stripping method for crystal ingots. The difference from Example 1 is that in S1, the first ultrasonic treatment is immersion ultrasonic. The specific implementation is as follows: S12: Reference Figure 6 The second end face of the crystal ingot is adsorbed and fixed to the rotating end of the rotating displacement stage at the bottom of the ultrasonic pool, and the high power density and small area ultrasonic transducer plate is installed at a height of 2mm away from the first end face of the crystal ingot with the working end facing the first end face. S13: Inject pure water into the ultrasonic bath to immerse the crystal ingot and the ultrasonic transducer plate, start the rotating displacement stage and the ultrasonic transducer plate to perform the first ultrasonic treatment, and control the ultrasonic power to be 100W, the ultrasonic frequency to be 100kHz, and the ultrasonic time to be increased by 1.0min for every 50mm increase in the crystal ingot diameter. The ultrasonic action area is within 30mm of the edge of the crystal ingot.

[0027] Example 3: This is an automated ultrasonic stripping method for crystal ingots disclosed in this invention. The difference from Example 1 is that the technical parameters of the first ultrasonic treatment and the second ultrasonic treatment in S1 and S2 are shown in Table 1.

[0028] Example 4: This is an automated ultrasonic stripping method for crystal ingots disclosed in this invention. The difference from Example 3 is that in S1, the first ultrasonic treatment is immersion ultrasonic.

[0029] Example 5: This is an automated ultrasonic stripping method for crystal ingots disclosed in this invention. The difference from Example 1 is that the technical parameters of the first ultrasonic treatment and the second ultrasonic treatment in S1 and S2 are shown in Table 1.

[0030] Example 6: This is an automated ultrasonic stripping method for crystal ingots disclosed in this invention. The difference from Example 5 is that in S1, the first ultrasonic treatment is immersion ultrasonic.

[0031] Example 7: This is an automated ultrasonic stripping method for crystal ingots disclosed in this invention. The difference from Example 1 is that the technical parameters of the first ultrasonic treatment and the second ultrasonic treatment in S1 and S2 are shown in Table 1.

[0032] Example 8: This is an automated ultrasonic stripping method for crystal ingots disclosed in this invention. The difference from Example 7 is that in S1, the first ultrasonic treatment is immersion ultrasonic.

[0033] Example 9: This is an automated ultrasonic stripping method for crystal ingots disclosed in this invention. The difference from Example 1 is that the technical parameters of the first ultrasonic treatment and the second ultrasonic treatment in S1 and S2 are shown in Table 1.

[0034] Example 10: This is an automated ultrasonic stripping method for crystal ingots disclosed in this invention. The difference from Example 9 is that in S1, the first ultrasonic treatment is immersion ultrasonication.

[0035] Table 1 Ingot size / inches 8 8 6 4 6 First ultrasound power / W 100 120 100 80 80 First ultrasound frequency / kHz 100 120 120 80 90 First ultrasound time / min 4 4 3 2 3 Diameter of the first ultrasonic treatment / mm 30 30 20 10 20 Peel force / N 50 40 60 20 30 Second ultrasound power / W 1000 1200 800 800 1200 Second ultrasonic frequency / kHz 28 40 25 28 25 Experimental Example 1: The technical parameters used in Examples 1 to 10 can all achieve automatic wafer separation. After the silicon carbide wafers prepared in Examples 1 to 10 were thinned, crack detection was performed. The detection results are shown in Table 2. The wafers were all intact and no breakage or edge chipping occurred, and the separation yield was high.

[0036] Table 2 wafer size 8 8 8 8 6 6 4 4 6 6 Wafer Integrity whole whole whole whole whole whole whole whole whole whole Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An automated ultrasonic stripping method for crystal ingots, characterized in that: Includes the following steps, S1: Perform a first ultrasonic treatment on the edge of the ingot obtained by laser modification so that the modified layer of the ingot forms an edge separation starting point, and obtain an edge pre-separated ingot; S2: Fixing regions are set at both ends of the pre-separated crystal ingot at the edge. Force is applied to at least one fixing region, and a second ultrasonic treatment is performed until the peeling force fed back by the at least one fixing region is reduced to a preset threshold, so as to obtain a wafer and the remaining crystal ingot. In S1, the first ultrasonic treatment is either non-immersion ultrasonic or immersion ultrasonic, and the ultrasonic wave is directed toward the edge of the ingot near the modified layer. In S1, the ultrasonic power of the first ultrasonic treatment is 80~120W, the ultrasonic frequency is 80~120kHz, the ultrasonic time increases by 0.8~1.2min for every 50mm increase in crystal ingot diameter, the ultrasonic action area is within 20~40mm of the edge of the crystal ingot, and the distance between the ultrasonic transducer and the crystal ingot surface is 1~3mm. In S2, the second ultrasonic treatment is immersion ultrasonic, and the ultrasonic waves are directed toward the circumferential surface of the ingot. In S2, the ultrasonic power of the second ultrasonic treatment is 800~1200W, and the ultrasonic frequency is 20~40kHz.

2. The automated ultrasonic stripping method for crystal ingots according to claim 1, characterized in that: In S1, the ultrasonic action area of ​​the first ultrasonic treatment moves relative to the edge of the crystal ingot so that the ultrasonic action path passes through the edge of the crystal ingot at least once.

3. The automated ultrasonic stripping method for crystal ingots according to claim 2, characterized in that: In S1, the relative motion is achieved by moving the ultrasonic wave action area of ​​the first ultrasonic treatment relative to the edge of the crystal ingot in a planar manner, and / or by causing the crystal ingot to rotate.

4. The automated ultrasonic stripping method for crystal ingots according to claim 2, characterized in that: In S1, the first ultrasonic treatment uses a high power density and small area ultrasonic transducer.

5. The automated ultrasonic stripping method for crystal ingots according to claim 1, characterized in that: In S2, the second ultrasonic treatment employs a high-power and large-area ultrasonic transducer.

6. The automated ultrasonic stripping method for crystal ingots according to claim 1, characterized in that: In S2, force is applied to at least one fixed area until the peeling force reaches 20~60N. The applied force is maintained, and the peeling force on at least one fixed area is monitored in real time. When the peeling force suddenly decreases and falls below a preset threshold, it is determined that the wafer has been separated from the remaining ingot, and the application of force and the second ultrasonic treatment are stopped.

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