Silicon nitride ceramic substrate and preparation method thereof, metallized substrate and semiconductor device

Abstract

The invention relates to the technical field of semiconductor manufacturing, in particular to a silicon nitride ceramic substrate and a preparation method thereof, a metalized substrate and a semiconductor device. Silicon nitride crystal grains are distributed on the surface of the silicon nitride ceramic substrate, and the silicon nitride crystal grains comprise complete silicon nitride crystal grains; in an observation area selected on the surface of the silicon nitride ceramic substrate, the proportion of the number of the complete silicon nitride crystal grains to the total number of all the silicon nitride crystal grains in the observation area is between 30% and 60%; the complete silicon nitride crystal grains are defined as silicon nitride crystal grains which are continuous in crystal grain outline and free of fracture or crack and crystal grain form loss. Through the design of the silicon nitride ceramic substrate, the heat conductivity and the reliability of the substrate can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to a silicon nitride ceramic substrate, a preparation method thereof, a metalized substrate and a semiconductor device. BACKGROUND

[0002] The silicon nitride ceramic substrate has become a key basic material in the fields of high-power electronic device packaging, aerospace electronic components, medical device core components, etc. due to its excellent thermal conductivity, high strength and weather resistance. In the electronic field, with the rapid development of chips towards high power and high integration, a large amount of heat generated by electronic devices during operation needs to be conducted and dissipated efficiently through the silicon nitride ceramic substrate for packaging to avoid damage to the devices due to overheating.

[0003] However, the thermal conductivity of the conventional silicon carbide ceramic substrate in the prior art is insufficient, which is difficult to stably meet the higher core needs of electronic device packaging, and is prone to damage or packaging failure during use, thereby affecting the overall performance of the device. SUMMARY

[0004] The present application provides a silicon nitride ceramic substrate, a preparation method thereof, a metalized substrate and a semiconductor device, which can improve the thermal conductivity and reliability of the substrate and meet the higher performance needs of electronic device packaging.

[0005] In a first aspect, the present application provides a silicon nitride ceramic substrate, wherein the surface of the silicon nitride ceramic substrate is distributed with silicon nitride grains, and the silicon nitride grains contain complete silicon nitride grains. In an observation area selected on the surface of the silicon nitride ceramic substrate, The proportion of the number of the complete silicon nitride grains to the total number of all silicon nitride grains in the observation area is between 30% and 60%. The complete silicon nitride grain is defined as a silicon nitride grain with continuous grain outline without cracks or fractures and without missing grain morphology.

[0006] In a second aspect, the present application provides a metalized silicon nitride substrate, which comprises the silicon nitride ceramic substrate according to the first aspect of the present application, and the surface of the silicon nitride ceramic substrate is covered with a metal conductive layer.

[0007] In a third aspect, the present application provides a preparation method of a silicon nitride ceramic substrate, which comprises the step of cleaning the silicon nitride ceramic intermediate after grinding treatment by using a cleaning solution to obtain the silicon nitride ceramic substrate according to the first aspect of the present application. The cleaning solution comprises the following components by weight: 20-30 parts of fluoride, 10-15 parts of surfactant, 6-10 parts of PH buffer, 2-5 parts of oxidizing agent, 1-3 parts of chelating agent and 40-60 parts of water.

[0008] Fourthly, embodiments of the present invention also provide a semiconductor device, including a silicon nitride ceramic substrate provided in the first aspect embodiment above, or a metallized silicon nitride substrate provided in the second aspect embodiment above.

[0009] Based on the above, the silicon nitride ceramic substrate provided in this embodiment of the invention can effectively improve thermal conductivity by limiting the proportion of complete silicon nitride grains on its surface, ensuring that the heat generated during the operation of electronic devices is quickly conducted and dissipated, and avoiding overheating damage to the devices; at the same time, the complete grain structure can reduce the residual stress inside the substrate, so that the substrate can maintain structural stability under complex working conditions such as mechanical vibration and temperature cycling, reduce performance degradation, and reduce the risk of cracking during use.

[0010] Other features and beneficial effects of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a conceptual schematic diagram of a complete silicon nitride grain; Figure 2 , Figure 3 This is a conceptual diagram of an incomplete silicon nitride grain; Figure 4 This is a SEM image of a silicon nitride ceramic substrate composed of complete silicon nitride grains. Figure 5 This is a SEM image of a silicon nitride ceramic substrate composed of incomplete silicon nitride grains. Figure 6 This is a cross-sectional schematic diagram of a metallized silicon nitride substrate provided in an embodiment of the present invention.

[0013] Figure label: 1. Silicon nitride ceramic substrate; 2. Metal conductive layer; 10. Intact silicon nitride grain; 20. Incomplete silicon nitride grain; 21. Fracture point; 22. Crack point; 3. Connecting layer. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0015] It should also be noted that the schematic diagrams of complete and incomplete silicon nitride grains and silicon nitride grains provided in this invention are for the purpose of expressing the conceptual features of silicon nitride grain structure, but are not fabricated to scale.

[0016] This invention provides a silicon nitride ceramic substrate 1, comprising: silicon nitride grains distributed on the surface of the silicon nitride ceramic substrate 1, wherein the silicon nitride grains include complete silicon nitride grains 10; and selected on the surface of the silicon nitride ceramic substrate 1... Within the observation area, the number of complete silicon nitride grains 10 accounts for 30% to 60% of the total number of silicon nitride grains in the observation area; the complete silicon nitride grain 10 is defined as a silicon nitride grain with a continuous grain outline without breaks or cracks and without missing grain morphology.

[0017] The above settings can effectively improve thermal conductivity, ensuring that the heat generated by electronic devices during operation is quickly conducted and dissipated, avoiding overheating damage to the devices; at the same time, the complete grain structure can reduce residual stress on the substrate, allowing the substrate to maintain structural stability under complex working conditions such as mechanical vibration and temperature cycling, reducing performance degradation and lowering the risk of cracking during use.

[0018] In one embodiment, the outline of the complete silicon nitride grain 10 is long rod-shaped, and the aspect ratio is between 10 and 50. The aspect ratio is defined as the ratio of the longest axial extension dimension to the largest radial dimension of the complete silicon nitride grain 10, which effectively ensures the axial rigidity of the grain and avoids the risk of brittle fracture caused by an excessive aspect ratio.

[0019] In one embodiment, the longest axial extension dimension of the complete silicon nitride grain 10 is between 30 and 80 μm, and the maximum radial dimension of the complete silicon nitride grain 10 is between 2 and 8 μm.

[0020] In one embodiment, the silicon nitride ceramic substrate 1 has a bending strength of 800 MPa or higher to ensure the structural strength of the substrate.

[0021] In one embodiment, the surface roughness of the silicon nitride ceramic substrate 1 is between 0.2 μm and 0.6 μm, or between 0.3 μm and 0.5 μm, which significantly improves the bonding force with the metallization interface in the metallized silicon nitride substrate and prevents the metal conductive layer 2 from falling off.

[0022] In one embodiment, the residual tensile stress on the surface of the silicon nitride ceramic substrate 1 is less than 10 MPa, so as to significantly reduce the risk of substrate structure.

[0023] This invention also provides a metallized silicon nitride substrate, comprising a silicon nitride ceramic substrate 1 as described in any of the preceding claims, wherein the surface of the silicon nitride ceramic substrate 1 is covered with a metal conductive layer 2.

[0024] This invention also provides a method for preparing a silicon nitride ceramic substrate 1, comprising a step of cleaning the milled silicon nitride ceramic intermediate with a cleaning solution to obtain the silicon nitride ceramic substrate 1 as described in any of the above embodiments; the cleaning solution comprises the following components by weight: 20-30 parts of fluoride, 10-15 parts of surfactant, 6-10 parts of pH buffer, 2-5 parts of oxidant, 1-3 parts of chelating agent and 40-60 parts of water.

[0025] In one embodiment, the fluoride is selected from at least one of hydrofluoric acid and ammonium fluoride; the surfactant is selected from at least one of sodium alkylbenzene sulfonate, phosphate esters, and sulfosuccinate; the pH buffer is selected from at least one of citric acid, acetic acid, and phosphoric acid; the oxidant is selected from at least one of hydrogen peroxide, nitric acid, and potassium persulfate; and the chelating agent is selected from at least one of polyacrylic acid (PAA), hydroxyethylidene diphosphonic acid (HEDP), and acrylamide methylpropanesulfonic acid copolymer (AMPS).

[0026] This invention also provides a semiconductor device comprising a silicon nitride ceramic substrate 1 as described in any of the preceding embodiments, or a metallized silicon nitride substrate as described in the preceding embodiments.

[0027] The technical solution of the present invention will now be described and explained in detail through various specific embodiments and accompanying drawings.

[0028] Example 1 Silicon nitride ceramic substrates require high thermal conductivity and high reliability, but existing polishing processes can introduce microcracks into the silicon nitride grains, which can lead to grain breakage in severe cases. Figure 2 , Figure 3 and Figure 5 As shown, the local cumulative residual stress is 50~150 MPa, which leads to a reduction in its bending strength of 50~200 MPa. Usually, high-temperature annealing can eliminate microcracks, but the interior of silicon nitride ceramic materials will undergo chemical reactions at high temperatures, which will cause changes in its material composition and grain size, further reducing its thermal conductivity and bending strength.

[0029] To address the aforementioned problems, Embodiment 1 of the present invention provides a silicon nitride ceramic substrate 1, which improves the substrate's performance by limiting the number of complete silicon nitride grains on the surface of the silicon nitride ceramic substrate 1. Specifically, the surface of the silicon nitride ceramic substrate 1 is distributed with silicon nitride grains, and the silicon nitride grains include complete silicon nitride grains 10.

[0030] Among them, a complete silicon nitride grain 10 is defined as a silicon nitride grain with a continuous grain outline without breaks or cracks, and without any missing grain morphology. That is, as shown in the figure... Figure 1 , Figure 4 As shown, if the edge lines of a silicon nitride grain are continuous and uninterrupted, and the overall grain morphology is intact (without local missing parts or obvious defects), it is determined to be a "complete silicon nitride grain 10". In contrast, the surface of the silicon nitride ceramic substrate 1 also contains incomplete silicon nitride grains 20. Incomplete silicon nitride grains 20 are silicon nitride grains with defects other than the complete silicon nitride grains 10, such as... Figure 5 As shown, it is defined as the presence of fractures or cracks at the grain edges, or the occurrence of localized chipping or incomplete morphology, such as... Figure 2 The crack 22 shown at the edge of the silicon nitride grain is as follows: Figure 3 The silicon nitride grain shown has a fracture point 21 at its edge.

[0031] In this embodiment, the surface of the silicon nitride ceramic substrate 1 is selected as... Within the observation area, the number of complete silicon nitride grains 10 accounts for 30% to 60% of the total number of silicon nitride grains in the observation area.

[0032] By controlling the proportion of intact silicon nitride grains 10, the reliability of the substrate structure can be significantly improved. The absence of fractures and cracks in the intact silicon nitride grains 10 avoids stress concentration points caused by grain damage. Compared to existing substrates with localized residual stress of 50-150 MPa due to microcracks in the grains, the 30%-60% intact grain proportion in this embodiment significantly disperses the mechanical and thermal stresses borne by the substrate, reducing the risk of cracking caused by stress concentration during use and providing a foundation for a bending strength exceeding 800 MPa. Furthermore, intact grains without morphological defects maintain the excellent properties of the silicon nitride ceramic material itself, preventing interruptions in thermal conductivity pathways due to grain defects and improving the substrate's thermal conductivity. Simultaneously, the orderly distribution of intact grains optimizes the substrate surface microstructure, providing suitable interface conditions for subsequent metallization processing. Compared to existing substrates with a surface roughness of only 0.1~0.3μm after grinding, which makes the metal conductive layer 2 easy to fall off, this embodiment limits the reasonable proportion of complete silicon nitride grains 10 on the surface of the silicon nitride ceramic substrate 1, which can form a surface state suitable for metallization, enhance the bonding force between the metal layer and the ceramic substrate, and reduce the risk of encapsulation failure.

[0033] Furthermore, the design of 30%~60% complete silicon nitride grains 10 avoids the problem of insufficient performance due to too low a proportion, and does not require pursuing too high a proportion to increase the difficulty and cost of preparation. It effectively solves the contradiction in the existing technology that using high temperature annealing to eliminate cracks will damage thermal conductivity and grinding to control roughness will damage the grains, providing technical support for the large-scale and high-reliability production of silicon nitride ceramic substrate 1.

[0034] In practice, silicon nitride grains on the surface of the silicon nitride ceramic substrate 1 are observed using a pre-set magnification, such as with an OM microscope. The method for testing the percentage of intact silicon nitride grains 10 can be as follows: n (e.g., 3) representative observation areas are randomly selected on the surface of the silicon nitride ceramic substrate 1 (each area is spaced at least 2 mm apart to avoid overlap or concentration in the same microscopically uneven area). The size of each observation area is precisely controlled to be 500 μm (length) × 500 μm (width). The silicon nitride grains in each observation area are counted: the number of intact silicon nitride grains 10 is counted separately from the total number of silicon nitride grains in that area (which may include both intact silicon nitride grains 10 and incomplete silicon nitride grains 20), and the percentage of intact grains is calculated as "number of intact grains / total number of grains × 100%". The percentage of intact silicon nitride grains 10 across the n observation areas is then averaged to determine if the average falls within the range of 30% to 60%.

[0035] It should be noted that the selection of the observation area, the determination of complete grains, and the calculation of the proportion in the above embodiments are all routine operations that can be repeatedly performed by those skilled in the art; and the embodiments only list typical cases where the proportion of complete grains is in the range of 30% to 60%. All silicon nitride ceramic substrates 1 that have a complete grain proportion between 30% and 60% and whose complete silicon nitride grains 10 meet the definition of "continuous outline without breakage or cracks, and no morphological defects" fall within the protection scope of this embodiment.

[0036] Furthermore, the outline of the complete silicon nitride grain 10 is long rod-shaped. That is, in the microstructure of the surface of the silicon nitride ceramic substrate 1, if the silicon nitride grain as a whole has an elongated shape that is "axially extended and radially narrow" (i.e., the extension length of the grain along a certain direction is significantly greater than the width perpendicular to that direction), and the outline is continuous without breakage or missing shape, it is determined to be a long rod-shaped complete silicon nitride grain 10.

[0037] In this embodiment, the aspect ratio of the long, rod-shaped complete silicon nitride grain 10 is between 10 and 50, where the aspect ratio is defined as the ratio of the longest axial extension dimension to the maximum radial dimension of the complete silicon nitride grain 10. The "longest axial extension dimension" refers to the distance between the farthest vertices at both ends of the grain along its extension direction (i.e., the grain length direction). The "maximum radial dimension" refers to the maximum value among a series of cross-sections selected perpendicular to the aforementioned axial direction in the middle region of the grain (avoiding dimensional deviations caused by end chamfers or sharp points), measured as the straight-line distance between two points on the grain profile within each cross-section.

[0038] By limiting the aspect ratio of the intact silicon nitride grains 10, the axial rigidity of the grains is effectively guaranteed, while avoiding the risk of brittle fracture caused by excessive aspect ratio. Simultaneously, it facilitates rapid heat conduction and diffusion along the axial direction of the long, rod-shaped grains, preventing interruptions or detours in heat conduction pathways due to short grain shapes. This type of intact grain can suppress crack initiation and propagation through interlocking and stress conduction between grains when the substrate is subjected to external forces or temperature fluctuations, further enhancing the substrate's bending strength.

[0039] As an example, the longest axial extension dimension of the complete silicon nitride grain 10 is between 30 and 80 μm; the maximum radial dimension of the complete silicon nitride grain 10 is between 2 and 8 μm.

[0040] It should be understood that this aspect ratio range can be achieved by optimizing and adjusting conventional process parameters such as sintering temperature and holding time, without the need to introduce complex equipment or special raw materials, thus ensuring the high performance of the substrate while taking into account the feasibility of large-scale production.

[0041] Optionally, the flexural strength of the silicon nitride ceramic substrate 1 is above 800 MPa. Specifically, the flexural strength of the silicon nitride ceramic substrate 1 can be obtained through three-point bending measurements. Compared to conventional grinding processes that reduce the flexural strength of the silicon nitride substrate to 50-200 MPa, this embodiment, through the above-described defined structure of the complete silicon nitride grains 10, can design the flexural strength of the silicon nitride ceramic substrate 1 to be above 800 MPa, thereby ensuring the structural strength of the substrate, meeting the high reliability protection requirements of electronic device packaging, and preventing device damage due to insufficient substrate strength.

[0042] Furthermore, the surface roughness of the silicon nitride ceramic substrate 1 is between 0.2 μm and 0.6 μm, preferably between 0.3 μm and 0.5 μm. Specifically, in existing conventional polishing processes, in order to avoid excessively deep microcracks, small-diameter polishing particles are usually used, resulting in a surface roughness of only 0.1 to 0.2 μm for the silicon nitride substrate. However, excessively small roughness leads to limited contact area at the metallization interface, weak mechanical interlocking, and easy detachment of the metal conductive layer 2. In this embodiment, a roughness of 0.2 μm to 0.6 μm or 0.3 μm to 0.5 μm is designed. While ensuring a certain degree of integrity of the silicon nitride grains 10, the appropriate micro-uneven structure on the substrate surface increases the contact area between the substrate and the metal conductive layer 2 in the metallized silicon nitride substrate, significantly improving the metallization interface adhesion and preventing the metal conductive layer from detaching.

[0043] In other embodiments, the residual tensile stress on the surface of the silicon nitride ceramic substrate 1 is below 10 MPa. Residual tensile stress refers to the tensile stress (not generated by external force) that remains inside the silicon nitride ceramic substrate 1 after processing such as grinding and cleaning, extending along the surface or internally. Excessive stress can easily lead to problems such as crack propagation and decreased bending strength during subsequent use. In the prior art, conventional grinding processes can cause localized accumulation of 50-150 MPa of residual tensile stress on the substrate surface. However, this embodiment, through the above-described structural design, can control the residual tensile stress below 10 MPa, significantly reducing the structural risk of the substrate and meeting the higher performance requirements of the device.

[0044] Example 2 Embodiment 2 of the present invention also provides a metallized silicon nitride substrate, which adopts the silicon nitride ceramic substrate 1 as described in Embodiment 1 above. The specific design, function and role of the silicon nitride ceramic substrate 1 can be referred to the description in Embodiment 1 above, and will not be repeated here.

[0045] The surface of the silicon nitride ceramic substrate 1 is covered with a metal conductive layer 2. In specific implementations, the material of the metal conductive layer 2 is selected from one or more metals or alloys such as silver and copper, to ensure low resistivity and good high-temperature compatibility, thus avoiding interfacial reactions with the silicon nitride ceramic. Preferably, please refer to... Figure 6 A connecting layer 3 is provided between the silicon nitride ceramic substrate 1 and the metal conductive layer 2 to improve the adhesion strength between them. The connecting layer 3 is made of a material with relatively strong adhesion. Of course, depending on the actual functional requirements, the connecting layer 3 can also be made of transition materials that can alleviate the difference in thermal expansion coefficients between the silicon nitride ceramic substrate 1 and the metal conductive layer 2 and enhance interfacial bonding, such as Ti or TiN. The specific material can be reasonably designed according to actual needs, and this embodiment does not limit it.

[0046] Given that the surface roughness of silicon nitride ceramic substrates prepared by conventional grinding processes in the existing technology is only 0.1~0.2μm, the small interface contact area with the metal layer during metallization and the weak mechanical interlocking result in insufficient metal layer adhesion, making them prone to detachment during use. At the same time, conventional grinding will also cause the substrate surface to accumulate residual tensile stress of 50~150MPa. If high-temperature annealing is used to eliminate stress, it will trigger internal chemical reactions in silicon nitride ceramics, causing changes in material composition and grain size, thereby reducing the thermal conductivity and bending strength of the substrate. Ultimately, this leads to poor reliability and short service life of the metallized substrate, making it difficult to meet the high-performance requirements of high-power electronic devices.

[0047] In this second embodiment, the metallized silicon nitride substrate using a silicon nitride ceramic substrate 1 can fundamentally solve the problem of insufficient adhesion of existing metal layers by designing a surface roughness of 0.2~0.6μm or 0.3~0.5μm, thus preventing metal layer detachment. By designing the substrate with low residual tensile stress below 10MPa and bending strength above 800MPa, the risk of stress concentration can be avoided without high-temperature annealing. This protects the high thermal conductivity of the silicon nitride ceramic itself (avoiding the decrease in thermal conductivity caused by changes in composition and grain size) and ensures that the substrate is not prone to cracking or breakage during metallization sintering and subsequent processes. In addition, the combination of 30%~60% complete silicon nitride grains 10 and the low resistivity of the metal conductive layer 2 can efficiently conduct the heat and current generated during the operation of electronic devices, reducing local overheating and current loss, ultimately achieving a metallized substrate with high conductivity, high thermal conductivity, and long-term durability.

[0048] Example 3 Embodiment 3 of the present invention also provides a method for preparing a silicon nitride ceramic substrate 1, including a step of cleaning the milled silicon nitride ceramic intermediate with a cleaning solution to obtain the silicon nitride ceramic substrate 1 as described in Embodiment 1 above. That is, the core of the method for preparing the silicon nitride ceramic substrate 1 provided in this embodiment is to remove the damaged layer on the surface of the substrate after milling with a special cleaning solution, and finally obtain the silicon nitride ceramic substrate 1 described in Embodiment 1, which has a complete silicon nitride grain 10 ratio of 30% to 60%, a bending strength of 800 MPa or more, a surface roughness of 0.3 to 0.5 μm, and a residual tensile stress of 10 MPa or less.

[0049] The cleaning solution comprises the following components by weight: 20-30 parts of fluoride, 10-15 parts of surfactant, 6-10 parts of pH buffer, 2-5 parts of oxidant, 1-3 parts of chelating agent, and 40-60 parts of water.

[0050] Preferably, the fluoride is selected from at least one of hydrofluoric acid and ammonium fluoride; the surfactant is selected from at least one of sodium alkylbenzene sulfonate, phosphate esters, and sulfosuccinate; the pH buffer is selected from at least one of citric acid, acetic acid, and phosphoric acid; the oxidant is selected from at least one of hydrogen peroxide, nitric acid, and potassium persulfate; and the chelating agent is selected from at least one of polyacrylic acid (PAA), hydroxyethylidene diphosphonic acid (HEDP), and acrylamide methylpropanesulfonic acid copolymer (AMPS).

[0051] For example, Table 1 shows the types of raw material components in the cleaning solution.

[0052] Table 2 shows the cleaning effect of the cleaning solution on silicon nitride ceramic substrates.

[0053] The above experiments show that the core properties of the substrates in Comparative Example 1 (no fluoride) and Comparative Example 2 (no surfactant) are far from meeting the standards, such as the proportion of intact grains and the bending strength. Examples 1 to 6 use the cleaning solution with the specified ratio in this example, and the proportion of intact grains, residual tensile stress, surface roughness, and bending strength of the substrate all meet the performance requirements of Example 1, verifying the effectiveness of the cleaning solution formulation range of this invention. Among them, Example 3 (fluoride compound) has the best cleaning effect, and the various auxiliary components can be flexibly combined within the specified types and ratios to meet the requirements.

[0054] Silicon nitride ceramics are chemically very stable and resistant to common acids, alkalis and oxidants. However, after existing grinding processes, microcracks and defective grains will be generated on the substrate surface, and residual stress will accumulate locally. This residual stress will significantly increase the surface energy of the substrate, resulting in a slight decrease in surface stability, which provides the possibility of chemical cleaning to remove the damaged layer.

[0055] The cleaning solution using the above-described formulation in this embodiment can precisely remove the polishing damage layer. This not only ensures that the proportion of intact silicon nitride grains reaches 30% to 60%, completely solving the problem of reduced performance (such as decreased thermal conductivity) caused by grain breakage and numerous microcracks resulting from existing polishing methods, but also reduces the residual surface tensile stress from 50 to 150 MPa in existing technologies to below 10 MPa, avoiding the risk of substrate cracking due to stress concentration. Furthermore, it eliminates the need for "high-temperature annealing" (avoiding changes in material composition and abnormal grain size caused by annealing), balancing stress relief and substrate stability. Simultaneously, it can improve the surface roughness from 0.1 to 0.3 μm after existing polishing to 0.3 to 0.5 μm. The moderately textured microstructure formed by the exposure of intact silicon nitride grains increases the contact area and mechanical interlocking with the metal layer, solving the problem of "insufficient metal layer adhesion and easy detachment," and improving long-term service life.

[0056] Specifically, the cleaning principle of the cleaning solution mainly utilizes an oxidant in an acidic environment to oxidize the surface silicon nitride (Si3N4) whose stability has decreased after grinding, generating silicon dioxide (SiO2), which provides a "soluble target" for subsequent removal of the damaged layer. Simultaneously, the added fluoride reacts with the generated silicon dioxide (SiO2) to form water-soluble fluorosilicates, thereby dissolving and peeling off the oxidized damaged layer (containing microcracks and broken grains), exposing the intact silicon nitride grains underneath. The surfactant in the cleaning solution reduces the surface tension of the solution, enhancing the penetration of the agent into the microcracks and grain gaps on the substrate surface, ensuring sufficient contact between the damaged area and the cleaning solution. The pH buffer stabilizes the pH of the cleaning solution within the acidic range of 3.0~4.0, ensuring both the oxidizing activity of the oxidant and maintaining the reaction rate between the fluoride and SiO2, preventing reaction interruption or excessive corrosion due to pH fluctuations. The chelating agent chelates residual metal impurities from grinding, preventing impurities from depositing on the substrate surface or interfering with the oxidation and dissolution reactions, ensuring a clean substrate surface after cleaning. Once the damaged layer (including microcracks and incomplete grains) is completely dissolved and peeled off, the chemical stability of the exposed intact silicon nitride grains is restored (without significant residual stress), and they are no longer further corroded by the cleaning solution. The reaction stops automatically, achieving the goal of precisely removing damage and preserving intact grains.

[0057] In the specific implementation of the preparation method, silicon carbide ceramic intermediates are first prepared according to conventional processes. For example, silicon nitride ceramic intermediates with a grinding damage layer (including microcracks and defective grains) on the surface are obtained by sequentially going through the steps of "mixing-ball milling-flow milling-degreasing-sintering-grinding". Then, ultrasonic cleaning is used to remove grinding dust from the surface, and drying is performed to ensure that the surface is free of oil and dust.

[0058] Next, the cleaning solution prepared according to the above ratio is diluted with deionized water to obtain a working cleaning solution, which is then used for ultrasonic cleaning. Preferably, the dilution ratio of the cleaning solution is between 5 and 20 times, so that the diluted concentration can effectively remove the damaged layer without corroding the intact grains. In addition, in this embodiment, ultrasonic cleaning is preferably performed for 5 to 30 minutes at a temperature between 20 and 40 degrees Celsius and an ultrasonic frequency between 10 kHz and 500 kHz to obtain a silicon nitride ceramic substrate. This process eliminates damaged grains on the surface of the silicon nitride ceramic substrate, exposing the intact silicon nitride grains and effectively improving the bending strength and roughness.

[0059] In addition, after cleaning, the substrate can be removed immediately and ultrasonically cleaned multiple times with deionized water to thoroughly remove any residual cleaning solution from the surface (to avoid secondary corrosion of the substrate surface caused by fluoride residue). Finally, it should be dried to ensure that the substrate surface is dry.

[0060] Example 4 This fourth embodiment provides a semiconductor device that utilizes a silicon nitride ceramic substrate as described in Embodiment 1 above to effectively improve device performance. The semiconductor device can be a light-emitting device, such as a light-emitting diode (LED) or a semiconductor laser. Alternatively, the semiconductor device may utilize a metallized silicon nitride substrate as described in Embodiment 2 above.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon nitride ceramic substrate, characterized by: The surface of the silicon nitride ceramic substrate is distributed with silicon nitride grains, and the silicon nitride grains include complete silicon nitride grains; Selected on the surface of the silicon nitride ceramic substrate Within the observation area, the proportion of complete silicon nitride grains to the total number of silicon nitride grains in the observation area is between 30% and 60%; a complete silicon nitride grain is defined as a silicon nitride grain with a continuous grain outline without breaks or cracks and without missing grain morphology.

2. The silicon nitride ceramic substrate according to claim 1, characterized by: The complete silicon nitride grains have a long rod shape, and a length-width ratio of 10-50, wherein the length-width ratio is defined as the ratio of the longest axial extension size of the complete silicon nitride grains to the largest radial size.

3. The silicon nitride ceramic substrate according to claim 2, characterized by: The longest axial extension size of the complete silicon nitride grains is 30-80 μm, and the largest radial size of the complete silicon nitride grains is 2-8 μm.

4. The silicon nitride ceramic substrate of claim 1, wherein: The bending strength of the silicon nitride ceramic substrate is 800 MPa or more.

5. The silicon nitride ceramic substrate of claim 1, wherein: The surface roughness of the silicon nitride ceramic substrate is 0.2-0.6 μm, or 0.3-0.5 μm.

6. The silicon nitride ceramic substrate of claim 1, wherein: The residual tensile stress on the surface of the silicon nitride ceramic substrate is 10 MPa or less.

7. A metallized silicon nitride substrate, characterized by: The silicon nitride ceramic substrate is covered with a metal conductive layer.

8. A method of producing a silicon nitride ceramic substrate, characterized by: The step of cleaning the ground silicon nitride ceramic intermediate with a cleaning solution to obtain the silicon nitride ceramic substrate of any one of claims 1-6 is included. The cleaning solution includes the following components by weight: 20-30 parts of fluoride, 10-15 parts of surfactant, 6-10 parts of PH buffer, 2-5 parts of oxidant, 1-3 parts of chelating agent, and 40-60 parts of water.

9. The method of producing a silicon nitride ceramic substrate according to claim 8, characterized by: The fluoride is selected from at least one of hydrofluoric acid and ammonium fluoride; the surfactant is selected from at least one of sodium alkyl benzene sulfonate, phosphate ester, and sulfosuccinic acid ester; the PH buffer is selected from at least one of citric acid, acetic acid, and phosphoric acid; the oxidant is selected from at least one of hydrogen peroxide, nitric acid, and potassium persulfate; and the chelating agent is selected from at least one of polyacrylic acid, hydroxyethylidene diphosphonic acid, and acrylamidomethylpropane sulfonic acid copolymer.

10. A semiconductor device, characterized by: The silicon nitride ceramic substrate of any one of claims 1-6, or the metallized silicon nitride substrate of claim 7 is included.

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