A laser stealth dicing method and wafer

Abstract

This application discloses a laser hidden dicing method and a wafer. The laser hidden dicing method includes: bonding individual crystal pillars to be processed in an array to a first surface of a transparent substrate using a refractive index matching adhesive; flipping the transparent substrate with the bonded crystal pillars so that a second surface of the transparent substrate faces upwards, using the second surface as a reference plane for laser incidence; the second surface being the surface opposite to the first surface; controlling a laser beam corresponding to each crystal pillar to be incident from the reference plane, sequentially passing through the transparent substrate and the refractive index matching adhesive, and focusing on the interior of the corresponding crystal pillar for laser modification; wherein, the refractive index matching adhesive is also used to reduce the refractive index difference at the crystal pillar bonding interface. Through the above method, the laser hidden dicing method provided by this application can perform parallel and efficient processing of polycrystalline pillar samples with highly inconsistent results, reduces the requirements for the surface roughness of each crystal pillar, saves pre-processing time for the crystal pillars, and greatly improves processing efficiency and quality.

Description

Technical Field

[0001] This application relates to the field of crystal pillar processing technology, and in particular to a laser hidden cutting processing method and a wafer. Background Technology

[0002] With the development of semiconductor technology, hard and brittle semiconductor materials such as single-crystal diamond and silicon carbide are widely used in the manufacture of high-frequency and high-power devices due to their excellent electrical and thermal properties. In the processing of hard and brittle semiconductor materials, slicing is a crucial step. Laser slicing, as a non-contact processing method, creates a modified layer inside the material by focusing a laser, followed by separation through slicing. It offers advantages such as narrow kerfs, no wear, and high efficiency.

[0003] However, the following defects currently exist in the laser slicing process of hard and brittle semiconductor materials such as single-crystal diamond: 1) Poor sample height consistency: In actual production, due to limitations in growth or pretreatment processes, there are often height differences between multiple crystal pillar samples to be processed. Existing laser slicing processes usually require individual surface inspection and focus adjustment for each sample, making it difficult to achieve uniform focusing. This results in the inability to achieve parallel and efficient processing of multiple samples, severely restricting mass production efficiency.

[0004] 2) Extremely high surface roughness requirements: Laser lithography requires the laser to efficiently penetrate the material surface and focus internally. Existing processes have very stringent requirements for the flatness (Ra value) of the surface to be processed (typically Ra < 10nm) to reduce surface scattering. To meet this requirement, the chemical mechanical polishing (CMP) pretreatment before entering the lithography process takes an extremely long time, which not only increases processing costs but also severely limits production cycle time.

[0005] 3) Optical loss and scattering: When the sample surface roughness is high, the huge refractive index difference between air and material (n≈1.0 to 2.4) will cause severe scattering and reflection of the laser at the interface, resulting in energy loss, affecting the energy density at the focal point, and thus leading to poor modification effect or processing failure. Summary of the Invention

[0006] This application provides a laser hidden dicing method and wafer to solve the problem of low efficiency in current laser hidden dicing of crystal pillars of different heights.

[0007] To address the aforementioned technical problems, this application provides a laser hidden cutting method. The laser hidden cutting method includes: bonding individual crystal pillars to be processed in an array to a first surface of a transparent substrate using a refractive index matching adhesive; flipping the transparent substrate with the bonded crystal pillars so that a second surface of the transparent substrate faces upwards, using the second surface as a reference plane for laser incidence; the second surface being the surface opposite to the first surface; controlling a laser beam corresponding to each crystal pillar to be incident from the reference plane, sequentially passing through the transparent substrate and the refractive index matching adhesive, and focusing on the interior of the corresponding crystal pillar for laser modification; wherein the refractive index matching adhesive is also used to reduce the refractive index difference at the crystal pillar bonding interface.

[0008] In some embodiments, the refractive index of the refractive index matching adhesive deviates from that of the crystal pillar by less than 3%.

[0009] In some embodiments, the refractive index of the refractive index matching adhesive is in the range of 2.20 to 2.45. In some embodiments, the viscosity of the refractive index matching adhesive is 500-2000 cPs.

[0010] In some embodiments, the transmittance of the transparent substrate to the laser beam is not less than 92%.

[0011] In some embodiments, the flatness deviation of the reference surface of the transparent substrate is controlled within 5 μm.

[0012] In some embodiments, the laser modification focused on the interior of the corresponding crystal pillar includes: A spatial light modulator is used to adjust the longitudinal distribution of the laser focus within the crystal pillar, so as to achieve simultaneous modification of layers at different depths within the crystal pillar.

[0013] In some embodiments, after controlling the laser beam corresponding to each of the crystal pillars to be incident from the reference plane, sequentially pass through the transparent substrate and the refractive index matching adhesive, and be focused inside the corresponding crystal pillar for laser modification, the method further includes: The adhesive force of the refractive index matching adhesive is removed by physical or chemical means, the crystal pillars and the transparent substrate are separated, and the crystal pillars are then cleaved.

[0014] In some embodiments, the adhesive force of the refractive index matching adhesive is removed by at least one of ultraviolet light curing and demolding, heating release, or chemical solvent dissolution.

[0015] To solve the above-mentioned technical problems, another technical solution adopted in this application is to provide a wafer. The wafer is prepared by processing a crystal pillar using the laser slicing method described above.

[0016] The beneficial effects of this application are: unlike the prior art, this application discloses a laser hidden cutting method and a wafer. This embodiment of the application bonds crystal pillars of varying heights onto a uniform transparent substrate and performs a flipping process. Utilizing the highly flat second surface of the transparent substrate as a unified reference plane for laser incident, the laser only needs to focus once based on this reference plane to overcome height errors between the individual crystal pillars below. This enables parallel processing of polycrystalline pillar samples, significantly improving production efficiency for polycrystalline pillars with poor height consistency. Furthermore, by introducing a refractive index matching adhesive, whose refractive index is similar to that of the crystal pillar material, the adhesive fills the microscopic irregularities on the crystal pillar surface, transforming the original "air-material" high refractive index difference interface into a "liquid-material" ultra-low refractive index difference interface. This significantly reduces scattering losses at the interface, allowing high-quality hidden cutting even for crystal pillar samples with a surface roughness Ra≥10nm. This drastically shortens or even eliminates the cumbersome CMP fine polishing pretreatment process, further improving efficiency and saving time. In addition, the presence of the refractive index matching liquid effectively eliminates interface bubbles and diffuse reflection, ensuring that laser energy can efficiently pass through the interface and accurately focus inside the crystal pillar, improving the uniformity and processing accuracy of the modified layer. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a schematic flowchart of an embodiment of the laser stencil method provided in this application; Figure 2 yes Figure 1 The diagram shows the structure of a crystal pillar processed using the laser hidden cutting method. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0019] The terms "first," "second," and "third" used in the embodiments of this application are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0020] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] This application provides a laser hidden cutting method, in conjunction with reference to [reference needed]. Figure 1 and Figure 2 , Figure 1 This is a schematic flowchart of an embodiment of the laser stencil method provided in this application. Figure 2 yes Figure 1 The diagram shows a structural schematic of a crystal pillar processed using the laser slicing method. This laser slicing method includes: Step 10: The crystal pillars to be processed are bonded to the first surface of the transparent substrate in an array using refractive index matching adhesive.

[0022] The crystal pillar 101 is a hard and brittle semiconductor material, including one or more of single-crystal diamond, silicon carbide, and gallium nitride. The heights of the crystal pillars 101 to be processed can be inconsistent. Crystal pillars 101 of uniform or inconsistent heights can be bonded to the transparent substrate 103 in an array using refractive index matching adhesive 102, facilitating subsequent parallel and efficient processing of each crystal pillar 101. The arrangement of the crystal pillars 101 can be configured in different array configurations, such as 2×2, 3×4, or 5×5, and the shapes of the crystal pillars 101 include, but are not limited to, cylindrical and cuboid shapes.

[0023] The transparent substrate 103 can be made of materials with high light transmittance and excellent optical uniformity, such as quartz glass, borosilicate glass, or sapphire substrate.

[0024] In this embodiment, the refractive index matching adhesive 102 has a dual function: first, it acts as an adhesive to fix each crystal pillar 101 onto the transparent substrate 103 through its adhesiveness; second, it acts as an optical medium to reduce the refractive index difference at the bonding interface of the crystal pillars 101.

[0025] This embodiment introduces a refractive index matching adhesive 102 to construct a highly efficient optical coupling layer between the crystal pillar 101 and the transparent substrate 103. In the prior art, the surface of the crystal pillar 101 typically has microscopic irregularities, resulting in a significant refractive index difference between air and the crystal pillar 101 during direct processing. For example, if the crystal pillar 101 is made of single-crystal diamond, the refractive index difference is n≈1.0, leading to severe laser scattering and Fresnel reflection at the interface, causing energy loss and surface damage. This embodiment fills the microscopic irregularities on the surface of the crystal pillar 101 with the refractive index matching adhesive 102, transforming the original "air-material" high refractive index difference interface (n≈1.0 to 2.4) into a "liquid-material" low refractive index difference interface (n≈2.3 to 2.4). This significantly reduces scattering losses at the interface and improves the laser energy transmission efficiency. In addition, this also reduces the stringent requirements on the surface roughness of the crystal pillar 101, enabling crystal pillar 101 with a surface roughness Ra≥10nm to be cut with high quality, which significantly shortens the time of the front-end chemical mechanical polishing (CMP) process and improves production efficiency.

[0026] In this embodiment, the transmittance of the transparent substrate 103 to the laser beam is not less than 92%; the transmittance of the transparent substrate 103 to the laser beam can be 92%, 93%, 94%, 95%, 96%, 97%, or 98%, etc.

[0027] By limiting the high transmittance of the transparent substrate 103, the laser energy is efficiently coupled into the crystal pillar 101. If the transmittance is too low, a large amount of laser energy will be absorbed or reflected by the transparent substrate 103, causing the transparent substrate 103 to heat up or even be damaged, while reducing the processing efficiency.

[0028] In this embodiment, the first surface of the transparent substrate 103 is the surface on which each crystal pillar 101 is bonded. The first surface and each crystal pillar 101 are completely filled by refractive index matching adhesive 102 to form a continuous, uniform and bubble-free optical coupling layer. During the inverted processing, the second surface is the reference surface for laser incidence. The flatness requirement of the second surface is higher than that of the first surface to ensure that the wavefront distortion of the laser beam is minimized when it is incident on the reference surface, thereby maintaining the high energy density and spatial consistency of the focused spot, which in turn helps to improve the efficiency of laser hidden cutting processing.

[0029] In this embodiment, the flatness deviation of the reference surface of the transparent substrate 103 is controlled within 5μm.

[0030] Specifically, controlling the flatness deviation of the reference surface to within 5μm is the basis for achieving high-precision parallel processing. Since this embodiment uses the reference surface of the transparent substrate 103 as a unified reference, any undulation of the reference surface will be converted into the position error of the laser focus. If the flatness deviation of the reference surface is too large, the laser will cause the focusing position to deviate between each crystal pillar 101 due to refraction or optical path difference after passing through the transparent substrate 103, affecting the consistency of the modification depth.

[0031] This embodiment ensures the consistency of the modified layer depth inside each crystal pillar 101 in the array during processing by strictly limiting the flatness of the reference surface of the transparent substrate 103, thereby ensuring the uniformity of batch processing.

[0032] Furthermore, the refractive index of the refractive index matching adhesive 102 should deviate from that of the crystal pillar 101 by less than 3%. If the deviation exceeds 3%, the interface reflection loss will increase significantly, severely affecting the hidden cutting quality. For example, when the crystal pillar 101 is made of single-crystal diamond, silicon carbide, or gallium nitride, the refractive index of the refractive index matching adhesive 102 ranges from 2.20 to 2.45. This difference is mainly determined by the actual quality differences of the crystal pillar 101.

[0033] The degree of refractive index matching between the refractive index matching adhesive 102 and the crystal pillar 101 directly determines the interface reflectivity and beam quality. According to Fresnel's formula, the interface reflectivity is proportional to the square of the refractive index difference. In this embodiment, by controlling the refractive index deviation between the refractive index matching adhesive 102 and the crystal pillar 101 to within 3%, and specifically setting it within the range of 2.20 to 2.45 for high refractive index semiconductor materials such as single-crystal diamond, the diffuse reflection and refraction effects at the interface can be eliminated to the greatest extent. This not only greatly reduces the ineffective loss of laser energy at the interface, but also prevents stray light generated by interface reflection from causing unexpected damage to the surface of the crystal pillar 101, ensuring the stability of processing quality. At the same time, the refractive index parameter range of the refractive index matching adhesive 102 has a wide adaptability and can be applied to various hard and brittle semiconductor materials such as diamond and silicon carbide.

[0034] Furthermore, the viscosity of the refractive index matching adhesive 102 is 500-2000 cPs.

[0035] If the viscosity of the refractive index matching adhesive 102 is too low (below 500 cPs), the adhesive of the refractive index matching adhesive 102 will be too fluid, making it difficult to form a stable support layer between the crystal pillar 101 and the transparent substrate 103. Furthermore, during the inverted processing, the adhesive layer thickness may be uneven or even run due to gravity, affecting the precise positioning of the laser focus.

[0036] If the viscosity of the refractive index matching adhesive 102 is too high (above 2000 cPs), the adhesive will be difficult to coat evenly and will easily trap air bubbles during the coating process. Air bubbles are a major problem in optical processing, as they will severely scatter the laser, leading to excessively high local energy density or focusing failure, and damaging the crystal pillar 101.

[0037] Therefore, in this embodiment, the viscosity of the refractive index matching adhesive 102 is controlled at 500-2000 cPs, which can ensure that the adhesive has good coating and filling properties, effectively remove air bubbles, and provide sufficient shear force and surface tension to ensure that the crystal pillar 101 is stable and does not fall off in the inverted state, thus achieving a balance between process operability and processing stability.

[0038] Furthermore, the refractive index matching adhesive 102 may also contain a photoinitiator or a thermal initiator to accommodate different curing and demolding requirements.

[0039] Step 20: Flip the transparent substrate with each crystal pillar bonded to it so that the second surface of the transparent substrate faces upward, and use the second surface as the reference surface for laser incident; the second surface is the surface opposite to the first surface.

[0040] This embodiment adopts an inverted processing strategy to use the second surface as a unified reference surface for laser hidden cutting of each crystal pillar 101, ensuring that the laser focus position in each crystal pillar 101 is highly consistent during processing, thus overcoming the difficulty of parallel processing caused by the poor consistency of the height of each crystal pillar 101.

[0041] In the existing technology, due to the difference in height of the crystal pillars 101 after growth or cutting, the upper surfaces of each crystal pillar 101 are not on the same horizontal plane; if the laser is incident from the upper surface of the crystal pillar 101, it is difficult to unify the laser focusing position, which makes it impossible to achieve parallel processing of multiple pieces.

[0042] In this embodiment, by flipping the transparent substrate 103, the extremely high flatness of the transparent substrate 103 itself is used as a unified laser incident reference surface. Thus, during laser processing, only the distance between the transparent substrate 103 and the reference surface needs to be identified and adapted to process each crystal pillar 101 in parallel, thereby overcoming the difficulty of parallel processing due to the height difference of each crystal pillar 101, and significantly improving mass production efficiency.

[0043] Step 30: Control the laser beam corresponding to each crystal pillar to enter from the reference plane, pass through the transparent substrate and refractive index matching adhesive in sequence, and focus on the interior of the corresponding crystal pillar for laser modification.

[0044] A laser beam corresponding to each crystal pillar 101 penetrates the transparent substrate 103 and the refractive index matching adhesive 102, and focuses on the preset hidden layer inside each crystal pillar 101 to process and form a modified layer.

[0045] Because the reference surface is uniform, the refractive index matching adhesive 102 largely eliminates the optical path distortion caused by the roughness and refractive index difference of the crystal pillar 101 and the transparent substrate 103, so that the laser beam maintains good wavefront quality and energy density during transmission, while ensuring the accuracy and consistency of forming the modified layer at a preset depth inside each crystal pillar 101, so as to obtain a high-quality slice surface in the subsequent dicing process.

[0046] Optionally, each crystal pillar 101 can be processed by a single-focus laser to gradually form a uniform modified layer at different depths inside each crystal pillar 101.

[0047] Optionally, laser modification can be performed by focusing on the interior of the corresponding column, including: using a spatial light modulator to adjust the longitudinal distribution of the laser focus within the crystal column, so as to achieve simultaneous modification of different depth layers within the crystal column.

[0048] For the thick crystal pillar 101 material, the traditional single-layer scanning processing method is inefficient, and the accumulated thermal effect during multi-layer processing may affect the material quality. In this embodiment, a spatial light modulator (SLM) is used to modulate the laser wavefront, causing the laser beam to split into multiple focal points in the longitudinal direction. Thus, a single laser scan can simultaneously form modified layers at different depths inside the crystal pillar 101, further significantly improving the processing efficiency.

[0049] After step 30, the process further includes: removing the adhesive force of the refractive index matching adhesive by physical or chemical means, separating each crystal pillar from the transparent substrate, and performing a cleaving process on each crystal pillar.

[0050] The methods for removing the adhesive force of the refractive index matching adhesive 102 include at least one of ultraviolet light curing and demolding, heating release, or chemical solvent dissolution.

[0051] The refractive index matching adhesive 102 used in this embodiment has both bonding and refractive index matching functions, but it must be able to be removed without damage after processing. The various debonding methods provided in this embodiment, such as UV curing demolding, heat release, and solvent dissolution, are all non-mechanical contact separation methods, avoiding edge chipping or cracking caused by mechanical stress on the brittle crystal pillar 101.

[0052] Specifically, by selecting a release method that matches the properties of the refractive index-matching adhesive 102, the crystal pillar 101 can be quickly and cleanly separated from the transparent substrate 103. The substrate can even be recycled and reused, reducing production costs. The subsequent cleaving process separates the crystal pillar 101 into individual chips or wafers along the laser-modified path, ultimately obtaining a finished product with high surface quality and a shallow damage layer.

[0053] Based on this, this application also provides a wafer (not shown), which is prepared by processing the crystal pillar 101 using the laser hidden cutting method described above.

[0054] Thanks to the aforementioned laser-guided dicing method, this wafer boasts extremely high surface quality, with a smooth and even cut surface and minimal chipping and microcracks. Furthermore, by reducing reliance on CMP polishing in the preceding processes, the wafer's fabrication cycle is short and cost-effective. Moreover, due to the small heat-affected zone during processing, the wafer retains the original excellent electrical and physical properties of the semiconductor material, significantly improving the yield and reliability of the final device.

[0055] Unlike existing technologies, this application discloses a laser hidden slicing method and a wafer. This embodiment of the application bonds crystal pillars of varying heights onto a uniform transparent substrate and performs a flipping process. Utilizing the highly flat second surface of the transparent substrate as a unified reference plane for laser incident, the laser only needs to focus once based on this reference plane to overcome height errors between the individual crystal pillars below. This enables parallel processing of polycrystalline pillar samples, significantly improving production efficiency for polycrystalline pillars with poor height consistency. Furthermore, by introducing a refractive index matching adhesive, whose refractive index is similar to that of the crystal pillar material, the adhesive fills the microscopic irregularities on the crystal pillar surface, transforming the original "air-material" high refractive index difference interface into a "liquid-material" ultra-low refractive index difference interface. This significantly reduces scattering losses at the interface, allowing high-quality hidden cutting even for crystal pillar samples with a surface roughness Ra≥10nm. This drastically shortens or even eliminates the cumbersome CMP fine polishing pretreatment process, further improving efficiency and saving time. In addition, the presence of the refractive index matching liquid effectively eliminates interface bubbles and diffuse reflection, ensuring that laser energy can efficiently pass through the interface and accurately focus inside the crystal pillar, improving the uniformity and processing accuracy of the modified layer.

[0056] The above descriptions are merely embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made based on the description and drawings of this application, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application. The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

Claims

1. A laser hidden cutting method, characterized in that, The laser hidden cutting method includes: Each crystal pillar to be processed is bonded to the first surface of the transparent substrate in an array using refractive index matching adhesive; The transparent substrate to which each crystal pillar is bonded is flipped so that the second surface of the transparent substrate faces upward, and the second surface is used as the reference surface for laser incident; the second surface is the surface opposite to the first surface; A laser beam corresponding to each of the crystal pillars is controlled to be incident from the reference plane, pass through the transparent substrate and the refractive index matching adhesive in sequence, and be focused inside the corresponding crystal pillar for laser modification; The refractive index matching adhesive is also used to reduce the refractive index difference at the crystal pillar bonding interface.

2. The laser hidden cutting method according to claim 1, characterized in that, The refractive index of the refractive index matching adhesive deviates from that of the crystal pillar by less than 3%.

3. The laser hidden cutting method according to claim 1 or 2, characterized in that, The refractive index of the refractive index matching adhesive is in the range of 2.20 to 2.

45.

4. The laser hidden cutting method according to claim 1, characterized in that, The viscosity of the refractive index matching adhesive is 500-2000 cPs.

5. The laser hidden cutting method according to claim 1, characterized in that, The transparent substrate has a transmittance of no less than 92% for the laser beam.

6. The laser hidden cutting method according to claim 5, characterized in that, The flatness deviation of the reference surface of the transparent substrate is controlled within 5μm.

7. The laser hidden cutting method according to claim 1, characterized in that, The laser modification focused on the interior of the corresponding crystal pillar includes: A spatial light modulator is used to adjust the longitudinal distribution of the laser focus within the crystal pillar, so as to achieve simultaneous modification of layers at different depths within the crystal pillar.

8. The laser hidden cutting method according to claim 1, characterized in that, The process of controlling the laser beam corresponding to each of the crystal pillars to enter from the reference plane, pass sequentially through the transparent substrate and the refractive index matching adhesive, and focus on the interior of the corresponding crystal pillar for laser modification, further includes: The adhesive force of the refractive index matching adhesive is removed by physical or chemical means, the crystal pillars and the transparent substrate are separated, and the crystal pillars are then cleaved.

9. The laser hidden cutting method according to claim 8, characterized in that, Methods for removing the adhesive force of the refractive index matching adhesive include at least one of ultraviolet light curing and demolding, heating release, or chemical solvent dissolution.

10. A wafer, characterized in that, The wafer is prepared by processing a crystal pillar using the laser hidden cutting method as described in any one of claims 1 to 9.

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