Silicon dioxide-containing glass ceramic wafer substrate and preparation method thereof

Abstract

The invention relates to the technical field of glass ceramics, in particular to a silicon dioxide-containing glass ceramic wafer substrate and a preparation method thereof. The preparation method comprises the following steps: weighing aluminum oxide, hydroxyethyl urea, chromium dioxide, lithium oxide, magnesium oxide, titanium dioxide, a clarifying agent, a toughening agent and silicon dioxide; preparing an aqueous solution from hydroxyethyl urea, and putting the powder, a clarifying agent, a toughening agent and the aqueous solution into a ball milling tank to obtain slurry; carrying out vacuum defoaming, tape casting, drying, glue removal heat treatment, glass melting, rolling and annealing treatment to obtain a glass plate; and polishing, ultrasonically cleaning and drying the glass plate to obtain the wafer substrate. According to the preparation method, hydroxyethyl urea and chromium dioxide are combined under a specific controlled heat treatment system, so that the functions of a conventional dispersing agent are exceeded, a unique toughening phase existing in a grain boundary is generated through in-situ reaction, uniform formation of a superfine nanocrystalline structure is realized synergistically, and thus the fracture toughness and the surface flatness of the material are synchronously and remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of glass-ceramic technology, and more specifically, to a glass-ceramic wafer substrate containing silicon dioxide and its preparation method. Background Technology

[0002] A wafer substrate, often simply called a wafer, is a core raw material in the semiconductor manufacturing process. It refers to a circular semiconductor wafer that serves as the basic platform for integrated circuit (chip) manufacturing. All tiny electronic circuits are formed on the surface of the wafer through precision processes such as photolithography and etching.

[0003] However, the intrinsic properties of traditional mainstream substrate materials such as single-crystal silicon are gradually becoming performance bottlenecks when dealing with specific high-end applications such as radio frequency devices and power devices, particularly their dielectric constant and coefficient of thermal expansion. Microcrystalline glass, a material obtained through controlled crystallization and possessing the excellent properties of both glass and ceramics, has been introduced as a candidate material for novel wafer substrates. Its core advantage lies in the ability to achieve extremely low dielectric constants and dielectric losses through compositional design, meeting the requirements for high-speed, low-loss transmission of high-frequency signals. Simultaneously, its coefficient of thermal expansion is adjustable, allowing it to be matched with various key semiconductor materials (such as gallium arsenide), thereby reducing thermal stress and improving device reliability.

[0004] However, the application of glass-ceramic in the field of wafer substrates still faces two major fundamental material defects.

[0005] Firstly, there is a lack of surface flatness and microscopic uniformity. The photolithography process in wafer fabrication requires the substrate surface to be atomically flat; any nanoscale undulations or defects will lead to circuit pattern distortion. During the crystallization process of glass-ceramics, due to the coexistence of crystalline and amorphous phases, and the differences in growth rates and orientations of different crystalline phases, microscopic grain boundary protrusions or phase separation pits are easily formed on the surface. This inherent microscopic inhomogeneity is difficult to completely eliminate even through subsequent polishing, becoming a fundamental obstacle affecting photolithography accuracy and thin film deposition quality.

[0006] Secondly, the material has lower intrinsic toughness. Compared to monocrystalline silicon, glass-ceramic typically has poorer fracture toughness. It is more sensitive to microcracks during wafer thinning, dicing, packaging, and subsequent thermal cycling, and its impact and thermal shock resistance is insufficient. This results in a higher breakage rate during manufacturing, raising questions about its long-term reliability and limiting its application in scenarios requiring high mechanical reliability.

[0007] Therefore, when existing microcrystalline glass materials are used as high-performance wafer substrates, the inherent defects in their surface micro-flatness and macro-mechanical toughness are intertwined, which seriously hinders the full realization of their performance advantages and practical applications. Summary of the Invention

[0008] The purpose of this invention is to address the inherent defects of glass-ceramic materials, such as insufficient surface flatness and low intrinsic toughness, and to overcome the material bottleneck of using them as high-performance wafer substrates.

[0009] The purpose of this invention is to provide a silicon dioxide-containing microcrystalline glass wafer substrate and its preparation method. Through the synergistic effect of hydroxyethyl urea and inorganic components, the entire process from slurry uniformity to the final crystal phase structure is optimized, thereby improving the surface flatness and fracture toughness of the microcrystalline glass.

[0010] To achieve the above objectives, one objective of this invention is to provide a silicon dioxide-containing microcrystalline glass wafer substrate, comprising the following raw materials in the following mass percentages: The composition is as follows: 18-22% aluminum oxide, 1.5-3.0% hydroxyethyl urea, 0.8-1.8% chromium dioxide, 2.5-4.5% lithium oxide, 3-6% magnesium oxide, 1.0-2.0% titanium dioxide, 0.1-0.4% clarifying agent, 0.5-1.5% toughening agent, with the balance being silicon dioxide.

[0011] In this invention, silicon dioxide serves as a glass network forger, constructing the basic structure and providing chemical stability and low dielectric properties; aluminum oxide serves as a network intermediate, participating in the formation of the main crystalline phase; lithium oxide serves as the main flux and crystallization regulator, lowering the melting temperature and promoting the formation of the main crystalline phase; magnesium oxide serves as an auxiliary flux and grain refiner, reducing melt viscosity, promoting densification, and inhibiting excessive grain growth; titanium dioxide serves as an auxiliary nucleating agent, synergistically lowering the nucleation barrier with chromium oxide. The hydroxyethyl urea is used as a dispersant in wet ball milling to achieve uniform nanoscale mixing of raw materials. In subsequent heat treatment, the reducing atmosphere and intermediate products generated by its controlled decomposition can partially reduce chromium dioxide and combine with it, generating a layered chromate urea complex derivative at the grain boundary in situ. This derivative acts as a grain boundary lubricating phase, effectively passivating the crack tip to improve fracture toughness. The chromium dioxide, as a multifunctional nucleating agent and toughening synergist, is partially converted into chromium trioxide under the action of hydroxyethyl urea to provide nucleation sites, and the other part participates in the generation of the grain boundary toughening phase. The clarifying agent is used to remove air bubbles from the melt during the high-temperature melting stage; the toughening agent is used to stabilize the toughening phase and dissolve it in the glass network to strengthen the glass phase.

[0012] As a further improvement to this technical solution, the clarifying agent is antimony trioxide, and the toughening agent is yttrium trioxide.

[0013] A second objective of this invention is to provide a method for preparing the aforementioned silicon dioxide-containing microcrystalline glass wafer substrate, comprising the following steps: Step S1: Weigh the raw materials according to the mass ratio; Hydroxyethyl urea was dissolved in deionized water to prepare an aqueous solution. Then, silicon dioxide, aluminum oxide, chromium dioxide, lithium oxide, magnesium oxide, titanium dioxide powder, clarifying agent, toughening agent and aqueous solution were added together into a ball mill jar and wet ball milled to obtain a homogeneous slurry. Step S2: After vacuum degassing, the homogeneous slurry is cast into a wet film, which is then dried and subjected to heat treatment to obtain a raw sheet. The unfinished glass blanks are melted and homogenized to obtain molten glass. Step S3: Roll and anneal the molten glass to obtain a glass plate; The annealed glass plate is held at 720-780℃ for 1.5-3 hours, and then the temperature is raised to 880-950℃ and held for 0.5-1.5 hours. Step S4: Polish the glass plate on both sides, then perform ultrasonic cleaning and drying to obtain the wafer substrate product.

[0014] As a further improvement to this technical solution, in step S1, hydroxyethyl urea is dissolved in deionized water to prepare an aqueous solution with a concentration of 25-35 wt%.

[0015] As a further improvement to this technical solution, in step S1, zirconium oxide balls are used as the grinding medium during wet ball milling, and the balls are milled at a speed of 300-400 rpm for 18-24 hours in a ball mill.

[0016] As a further improvement to this technical solution, in step S2, after the wet film is dried at 40-60℃, it is sent into a programmable temperature controlled furnace for segmented glue removal heat treatment. The heat treatment for debinding involves holding the product at a temperature range of 180-400℃ for 2-4 hours at a heating rate of 0.5-1℃ / min.

[0017] As a further improvement to this technical solution, in step S2, the blank sheet is placed in a platinum crucible and melted in a high-temperature silicon molybdenum rod electric furnace at 1550-1650℃ for 3-5 hours, and mechanical stirring is used to obtain glass melt.

[0018] As a further improvement to this technical solution, in step S3, the molten glass is poured into a preheated alloy mold and rolled into a glass plate of uniform thickness using a precision twin-roll rolling mill at 1150-1250℃.

[0019] As a further improvement to this technical solution, in step S3, the rolled glass plate is transferred into an annealing furnace, kept at a temperature higher than its glass transition temperature, and then cooled to room temperature at a rate of 1-2℃ / min.

[0020] As a further improvement to this technical solution, in step S4, diamond polishing slurry is first used for rough polishing and fine polishing, and finally colloidal silica polishing slurry is used for chemical mechanical polishing to make its surface roughness <0.5nm.

[0021] In this invention, by combining hydroxyethyl urea and chromium dioxide under a specific controlled heat treatment regime, the urea surpasses the function of conventional dispersants, and generates a unique toughening phase existing at the grain boundaries through in-situ reaction. This synergistically achieves the uniform formation of an ultrafine nanocrystalline structure, thereby simultaneously and significantly improving the fracture toughness and surface smoothness of the material.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: In this silica-containing microcrystalline glass wafer substrate and its preparation method, hydroxyethyl urea is first used as a highly efficient dispersant in the wet ball milling stage to achieve extremely uniform mixing of raw materials at the submicron scale, laying the foundation for compositional uniformity for subsequent reactions and crystallization. Subsequently, in the controlled decomposition stage, it is not only safely removed as an organic carrier, but its decomposition products also serve as reactants and precursors, synergistically constructing a tough network that strengthens grain boundaries with chromium dioxide. Finally, through precision rolling, annealing, and controlled crystallization, the highly homogeneous glass precursor is transformed into a microcrystalline glass body with small grain size, uniform distribution, and strong grain boundaries. This fundamentally overcomes the technical contradiction of traditional microcrystalline glass, which is difficult to balance high flatness and high reliability due to its intrinsic brittleness and uneven microstructure, and successfully prepares a high-performance microcrystalline glass wafer substrate that meets the requirements of high-end semiconductor photolithography processes. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the preparation process of the present invention; Figure 2 This is a schematic diagram showing the fracture toughness of a wafer substrate when hydroxyethyl urea has different mass percentages. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] One objective of this invention is to provide a silicon dioxide-containing microcrystalline glass wafer substrate, comprising the following raw materials in the following mass percentages: The composition is as follows: 18-22% aluminum oxide, 1.5-3.0% hydroxyethyl urea, 0.8-1.8% chromium dioxide, 2.5-4.5% lithium oxide, 3-6% magnesium oxide, 1.0-2.0% titanium dioxide, 0.1-0.4% clarifying agent, 0.5-1.5% toughening agent, with the balance being silicon dioxide.

[0026] In this invention, silicon dioxide is used as the glass network forging body, providing the basic structure, chemical stability, and the required low dielectric properties. This range ensures good glass-forming ability and a low coefficient of thermal expansion. Aluminum oxide, as a network intermediate, improves the material's hardness, elastic modulus, and thermal shock resistance, and participates in the formation of the main crystalline phase to regulate properties. Lithium oxide serves as the main flux and crystallization regulator, lowering the melting temperature and promoting the formation of a low-expansion β-quartz or β-spodumene solid solution main crystalline phase. Magnesium oxide acts as an auxiliary flux and grain refiner, reducing the viscosity of the high-temperature melt, promoting densification, and inhibiting excessive grain growth, thereby improving surface polishability. Titanium dioxide, as an auxiliary nucleating agent, works synergistically with chromium oxide to further lower the nucleation barrier and promote the formation of a uniform, fine grain structure. In this invention, the clarifying agent is preferably antimony trioxide, which is used to remove bubbles in the melt during the high-temperature melting stage to ensure that the glass body is macroscopically defect-free; and the toughening agent is preferably yttrium trioxide, which stabilizes the toughening phase provided by zirconium oxide or chromium oxide and dissolves in the glass network to strengthen the glass phase.

[0027] Hydroxyethyl urea is a key component of this invention, and its effect surpasses that of conventional dispersants: (1) It is used as a strong dispersant and viscosity modifier in wet ball milling to achieve uniform mixing of raw materials at the nanoscale; (2) During subsequent heat treatment, the reducing atmosphere (such as NH3, CO) and intermediate products generated by its controlled decomposition (180-400℃) can partially reduce chromium dioxide (CrO2) to Cr2O3 and combine with it to generate trace amounts of urea chromate complex derivatives with layered structures in situ at the grain boundaries. This derivative can act as a "grain boundary lubricating phase," effectively passivating crack tips and consuming fracture energy, thereby producing an unexpected toughness improvement effect (the fracture toughness improvement exceeds 20% more than that expected by only improving dispersibility).

[0028] Chromium dioxide acts as a multifunctional nucleating agent and toughening synergist. A portion of it is converted to Cr2O under the action of hydroxyethyl urea. 3 One part provides nucleation sites, while the other part reacts with the decomposition products of hydroxyethyl urea to participate in the formation of the aforementioned grain boundary toughening phase, which is the core of achieving synergistic toughening.

[0029] Please see Figure 1As shown, a second objective of this invention is to provide a method for preparing the aforementioned silicon dioxide-containing microcrystalline glass wafer substrate, comprising the following steps: Step S1: Accurately weigh the raw materials according to the mass ratio, and dissolve hydroxyethyl urea in deionized water to prepare an aqueous solution with a concentration of 25-35wt%.

[0030] Silica, aluminum oxide, chromium dioxide, lithium oxide, magnesium oxide, titanium dioxide powders, clarifying agents, toughening agents, and an aqueous solution of hydroxyethyl urea are added to a ball mill jar. Zirconia balls are used as the grinding media, and the mixture is ball-milled at 300-400 rpm for 18-24 hours. During this process, hydroxyethyl urea, as a highly efficient dispersant, effectively breaks up powder agglomerations, achieving uniform dispersion at the submicron or even nanometer scale, forming a stable homogeneous slurry with high solids content (≥50%), low viscosity, and excellent rheological properties. This is the primary prerequisite for obtaining uniform microstructure.

[0031] Step S2: After vacuum degassing, the above slurry is formed on a polished film carrier by a casting machine, and the blade gap is controlled to obtain a wet film of the required thickness (usually 0.5-1.0 mm).

[0032] After the wet film is slowly dried at 40-60℃, it is sent to a programmable temperature-controlled furnace for segmented debinding heat treatment. The key is to use an extremely low heating rate, such as 0.5-1℃ / min, within the temperature range of 180-400℃, and hold it at that temperature for 2-4 hours to ensure the slow and complete decomposition and release of hydroxyethyl urea and other organic compounds. At the same time, this provides sufficient time and a suitable temperature environment for their reduction-complexation reaction with CrO2, thereby generating a uniformly distributed grain boundary toughening phase precursor in situ and avoiding cracking or porosity in the green body due to rapid volatilization.

[0033] After debinding, the unfinished sheet is placed in a platinum crucible and melted in a high-temperature silicon molybdenum rod electric furnace at 1550-1650℃ for 3-5 hours, with mechanical stirring (such as platinum agitator) to obtain a highly homogenized and clear glass melt.

[0034] Step S3: Quickly pour the homogenized molten glass into a preheated alloy mold, and use a precision twin-roll mill to roll it into a glass sheet of uniform thickness at 1150-1250℃. Rapidly cool it below the glass transition temperature to "freeze" the high-temperature disordered glass structure.

[0035] The rolled glass plate is immediately transferred into an annealing furnace and held at a temperature slightly above its glass transition temperature (Tg) for a period of time. Then it is cooled to room temperature at a preset slow rate, such as 1-2℃ / min, to eliminate internal thermal stress.

[0036] The annealed glass plate is held at 720-780℃ for 1.5-3 hours. At this temperature, the nucleation sites provided by CrO2 / TiO2 and the grain boundary phase precursor region formed in step two will induce the generation of crystal nuclei with the highest density.

[0037] The temperature is then raised to 880-950℃ and held for 0.5-1.5 hours. During this stage, the crystal nuclei grow in a controlled manner, and the main crystalline phase (such as β-quartz solid solution) precipitates. Due to the extremely high nucleation density, the final grain size is limited to below 50 nanometers and is extremely uniformly distributed, which is the structural basis for achieving atomic-level surface smoothness.

[0038] Step S4: Perform double-sided ultra-precision polishing on the microcrystalline glass substrate. First, rough polishing and fine polishing are performed using diamond polishing slurry. Finally, chemical mechanical polishing (CMP) is performed using colloidal silica polishing slurry to achieve a surface roughness (Ra) of <0.5nm, meeting the requirements of the photolithography process. This is followed by rigorous ultrasonic cleaning and drying to obtain the final wafer substrate product.

[0039] The following specific embodiments will further illustrate the silicon dioxide-containing microcrystalline glass wafer substrate and its preparation method provided by the present invention.

[0040] Example 1 Step S1: Accurately weigh the following components according to the mass ratio: 18% aluminum oxide, 3.0% hydroxyethyl urea, 0.8% chromium dioxide, 4.5% lithium oxide, 3% magnesium oxide, 2.0% titanium dioxide, 0.1% clarifying agent, 1.5% toughening agent, with the remainder being silicon dioxide. Dissolve the hydroxyethyl urea in deionized water to prepare an aqueous solution with a concentration of 25 wt%.

[0041] Silica, aluminum oxide, chromium dioxide, lithium oxide, magnesium oxide, titanium dioxide powder, clarifying agent, toughening agent, and hydroxyethyl urea aqueous solution were added together into a ball mill jar. Zirconia balls were used as the grinding media, and the mixture was ball-milled at 400 rpm for 18 hours.

[0042] Step S2: After vacuum degassing, the above slurry is formed on a polished film carrier by a casting machine, and the blade gap is controlled to obtain a wet film of the required thickness.

[0043] After the wet film is slowly dried at 60℃, it is sent to a programmable temperature controlled oven for segmented glue removal heat treatment. The key is to use an extremely low heating rate, such as 1℃ / min, within the temperature range of 180-400℃, and hold at that temperature for 2 hours.

[0044] The unbound blanks after debinding are placed in a platinum crucible and melted in a high-temperature silicon molybdenum rod electric furnace at 1650℃ for 3 hours, with mechanical stirring, to obtain molten glass.

[0045] Step S3: Quickly pour the homogenized molten glass into a preheated alloy mold, and use a precision twin-roll calender to roll it into a glass sheet of uniform thickness at 1250°C.

[0046] The rolled glass plate is immediately transferred into an annealing furnace and held at a temperature slightly above its glass transition temperature (Tg) for a period of time. Then it is cooled to room temperature at a preset slow rate, such as 1°C / min, to eliminate internal thermal stress.

[0047] The annealed glass plate was held at 780℃ for 1.5 hours. Then the temperature was increased to 950℃ and held for 0.5 hours.

[0048] Step S4: Perform double-sided ultra-precision polishing on the microcrystalline glass substrate. First, rough polishing and fine polishing are performed using diamond polishing slurry. Finally, chemical mechanical polishing (CMP) is performed using colloidal silica polishing slurry to achieve a surface roughness (Ra) of <0.5nm, meeting the requirements of the photolithography process. This is followed by rigorous ultrasonic cleaning and drying to obtain the final wafer substrate product.

[0049] Example 2 Step S1: Accurately weigh the following components according to the mass ratio: 20% aluminum oxide, 2.0% hydroxyethyl urea, 1.2% chromium dioxide, 3.5% lithium oxide, 4% magnesium oxide, 1.5% titanium dioxide, 0.3% clarifying agent, 1.0% toughening agent, with the remainder being silicon dioxide. Dissolve the hydroxyethyl urea in deionized water to prepare an aqueous solution with a concentration of 30 wt%.

[0050] Silica, aluminum oxide, chromium dioxide, lithium oxide, magnesium oxide, titanium dioxide powder, clarifying agent, toughening agent, and hydroxyethyl urea aqueous solution were added together into a ball mill jar. Zirconia balls were used as the grinding media, and the mixture was ball-milled at 350 rpm for 21 hours.

[0051] Step S2: After vacuum degassing, the above slurry is formed on a polished film carrier by a casting machine, and the blade gap is controlled to obtain a wet film of the required thickness.

[0052] After the wet film is slowly dried at 50°C, it is sent to a programmable temperature-controlled oven for segmented adhesive removal heat treatment. The key is to use an extremely low heating rate, such as 1°C / min, within the temperature range of 180-400°C, and hold at that temperature for 3 hours.

[0053] The unbound blanks after debinding are placed in a platinum crucible and melted in a high-temperature silicon molybdenum rod electric furnace at 1600℃ for 4 hours, with mechanical stirring, to obtain molten glass.

[0054] Step S3: Quickly pour the homogenized molten glass into a preheated alloy mold, and use a precision twin-roll calender to roll it into a glass sheet of uniform thickness at 1200℃.

[0055] The rolled glass plate is immediately transferred into an annealing furnace and held at a temperature slightly above its glass transition temperature (Tg) for a period of time. Then it is cooled to room temperature at a preset slow rate, such as 1°C / min, to eliminate internal thermal stress.

[0056] The annealed glass plate was held at 760℃ for 2 hours. Then the temperature was increased to 900℃ and held for 1 hour.

[0057] Step S4: Perform double-sided ultra-precision polishing on the microcrystalline glass substrate. First, rough polishing and fine polishing are performed using diamond polishing slurry. Finally, chemical mechanical polishing (CMP) is performed using colloidal silica polishing slurry to achieve a surface roughness (Ra) of <0.5nm, meeting the requirements of the photolithography process. This is followed by rigorous ultrasonic cleaning and drying to obtain the final wafer substrate product.

[0058] Example 3 Step S1: Accurately weigh the following components according to the mass ratio: 22% aluminum oxide, 1.5% hydroxyethyl urea, 1.8% chromium dioxide, 2.5% lithium oxide, 6% magnesium oxide, 1.0% titanium dioxide, 0.4% clarifying agent, 0.5% toughening agent, with the remainder being silicon dioxide. Dissolve the hydroxyethyl urea in deionized water to prepare an aqueous solution with a concentration of 35 wt%.

[0059] Silica, aluminum oxide, chromium dioxide, lithium oxide, magnesium oxide, titanium dioxide powder, clarifying agent, toughening agent, and hydroxyethyl urea aqueous solution were added together into a ball mill jar. Zirconia balls were used as the grinding media, and the mixture was ball-milled at 300 rpm for 24 hours.

[0060] Step S2: After vacuum degassing, the above slurry is formed on a polished film carrier by a casting machine, and the blade gap is controlled to obtain a wet film of the required thickness.

[0061] After the wet film is slowly dried at 40℃, it is sent to a programmable temperature controlled oven for segmented adhesive removal heat treatment. The key is to use an extremely low heating rate, such as 0.5℃ / min, within the temperature range of 180-400℃, and hold at that temperature for 4 hours.

[0062] The unbound sheet after debinding is placed in a platinum crucible and melted in a high-temperature silicon molybdenum rod electric furnace at 1550℃ for 5 hours, with mechanical stirring, to obtain molten glass.

[0063] Step S3: Quickly pour the homogenized molten glass into a preheated alloy mold, and use a precision twin-roll calender to roll it into a glass sheet of uniform thickness at 1150°C.

[0064] The rolled glass plate is immediately transferred into an annealing furnace and held at a temperature slightly above its glass transition temperature (Tg) for a period of time. Then it is cooled to room temperature at a preset slow rate, such as 2°C / min, to eliminate internal thermal stress.

[0065] The annealed glass plate was held at 720℃ for 3 hours. Then the temperature was increased to 880℃ and held for 1.5 hours.

[0066] Step S4: Perform double-sided ultra-precision polishing on the microcrystalline glass substrate. First, rough polishing and fine polishing are performed using diamond polishing slurry. Finally, chemical mechanical polishing (CMP) is performed using colloidal silica polishing slurry to achieve a surface roughness (Ra) of <0.5nm, meeting the requirements of the photolithography process. This is followed by rigorous ultrasonic cleaning and drying to obtain the final wafer substrate product.

[0067] Wafer substrates were prepared according to Examples 1-3, and then the flatness and fracture toughness of the wafer substrates were tested.

[0068] Flatness inspection: The surface flatness inspection is conducted in accordance with the national standard GB / T 25994-2010 "Microcrystalline Glass Plates" and general specifications of the semiconductor industry. Non-contact optical profilometer and atomic force microscope (AFM) are used to quantitatively evaluate the surface roughness of the substrate to verify whether it meets the requirements of high-end photolithography process.

[0069] 1. Sample preparation At least three wafers (≥100mm in diameter) are randomly selected from the same batch of finished microcrystalline glass wafer substrates as test samples. The samples must undergo rigorous cleaning (e.g., RCA standard cleaning process) and drying to ensure the surface is free of particulate contamination, water stains, or organic residue. Testing should be conducted in a Class 100 cleanroom environment.

[0070] 2. Testing Environment and Equipment The test should be conducted in a constant temperature and humidity laboratory at (20±1)℃ and (45±5)% relative humidity. The main equipment includes: White light interferometer / optical profilometer: used for rapid, large-area surface topography scanning, with a vertical resolution better than 0.1nm.

[0071] Atomic force microscopy (AFM): used for nanoscale high-resolution surface morphology and roughness analysis of critical areas.

[0072] 3. Test Procedures and Data Processing a) Large-area scanning: Using a white light interferometer, scan 1mm × 1mm areas at the center and four symmetrical points 10mm from the edge of each sample surface. Measure and record the arithmetic mean roughness (Ra) and root mean square roughness (Rq) of each area.

[0073] b) Nanoscale precision measurement: In each sample, the most uniformly appearing region, as determined in step a), is scanned using AFM in tapping mode at two scales: 10 μm × 10 μm and 1 μm × 1 μm. High-resolution 3D topographic images are obtained, and the Ra values ​​for the corresponding scales are calculated.

[0074] c) Result determination: The average Ra value of all samples and all measuring points is taken as the final surface roughness characterization value of the batch of substrates, and the result is recorded in Table 1.

[0075] Fracture toughness testing: Fracture toughness testing is conducted in accordance with the national standard GB / T 23806-2009 "Test Method for Fracture Toughness of Fine Ceramics - Single-sided Pre-cracked Beam Method". The toughness improvement effect is quantitatively evaluated by measuring the material's ability to resist crack propagation.

[0076] 1. Sample preparation From the same batch of microcrystalline glass substrate blanks (after crystallization and before polishing), rectangular test strips with dimensions of length (L) ≥ 20 mm, width (W) = 4.0 ± 0.2 mm, and thickness (B) = 3.0 ± 0.2 mm were cut and precision ground using an internal circular cutter and a diamond wheel. The long side of the test strip should be parallel or perpendicular to its rolling direction and recorded. At least 10 valid test samples were prepared for each batch. A straight-through notch with a depth (a) approximately half the width (W) was introduced at the center of the test strip in the width direction using an ultra-thin diamond saw blade, and a sharp pre-crack was prepared using the bridge pressing method or fatigue pre-crack method.

[0077] 2. Testing Environment and Equipment The tests were conducted in a standard laboratory environment (temperature 23±5℃, relative humidity 50±10%). A universal testing machine equipped with a three-point bending fixture was used, with a fixed span (S) of 16 mm. The load cell range of the testing machine should be suitable for the sample being tested.

[0078] 3. Test Procedures and Calculations a) Installation and Loading: Place the specimen symmetrically on the three-point bending fixture, ensuring the pre-crack is located on the vertical plane between the two lower support rollers. Apply a load to the specimen at a constant displacement rate of 0.5 mm / min until it fractures. Record the load-displacement curve throughout the process.

[0079] b) Crack length measurement: After the specimen breaks, the accurate length a of the pre-existing crack on the fracture surface is measured using an optical microscope.

[0080] c) Fracture toughness calculation: Based on the measured maximum fracture load P and crack length a, as well as the specimen's geometric dimensions, the fracture toughness K is calculated using the standard formula. The fracture toughness value is equal to the maximum fracture load multiplied by the three-point bending span, then divided by the product of the specimen thickness and the cube of the specimen width, and finally multiplied by a shape factor function related to the ratio of crack length to specimen width. The shape factor function (f(a / W)) is a dimensionless shape factor related to the geometric dimensions, and its specific expression is given in standard GB / T 23806-2009.

[0081] c) Result Determination: Calculate the arithmetic mean of the K values ​​of all valid samples, and use this as the fracture toughness value for the batch of material. The result is recorded in Table 1. (The K value for traditional microcrystalline glass without the addition of key components such as hydroxyethyl urea is typically 1.0-1.5 MPa·m.) 1 / 2 ).

[0082] Table 1. Flatness and fracture toughness of wafer substrates in Examples 1-3

[0083] Table 1 shows that the flatness of the wafer substrates prepared in Examples 1-3 is as follows: Ra < 0.5 nm as measured by white light interferometer; Ra < 0.3 nm as measured by AFM at a scale of 1 μm × 1 μm; and the fracture toughness is not less than 2.0 MPa·m. 1 / 2 This demonstrates that the method provided by the present invention can yield microcrystalline glass wafer substrates with satisfactory flatness and fracture toughness.

[0084] In this invention, an in-situ reduction-complexation reaction occurs between hydroxyethyl urea and chromium dioxide within a specific segmented debinding heat treatment temperature window, generating a grain boundary lubricating phase mainly composed of layered urea chromate derivatives. This achieves a functional leap from conventional physical dispersion to interfacial chemical modification, and produces a synergistic effect with a uniform nucleation and grain refinement system composed of titanium dioxide, magnesium oxide, etc. Simultaneously, the macroscopic uniformity of the blank ensured by tape casting and the microstructure regulation achieved by a two-step crystallization heat treatment with precise temperature control (low-temperature high-density nucleation and high-temperature restricted grain growth) fundamentally suppress the surface undulations and internal stress concentration caused by the expansion difference between crystalline and amorphous phases and abnormal grain growth. In the preparation process, hydroxyethyl urea first acts as a highly efficient dispersant in the wet ball milling stage, achieving extremely uniform mixing of raw materials at the submicron scale, laying the foundation for compositional uniformity for subsequent reactions and crystallization. Subsequently, in the controlled decomposition stage, it is not only safely removed as an organic carrier, but its decomposition products also act as reactants and precursors, synergistically constructing a tough network that strengthens grain boundaries with chromium dioxide. Finally, through precision rolling, annealing, and controlled crystallization, the highly homogeneous glass precursor is transformed into a microcrystalline glass with fine grain size (<50nm), uniform distribution, and strong grain boundaries. This fundamentally overcomes the technical contradiction of traditional microcrystalline glass, which is difficult to balance high flatness and high reliability due to its intrinsic brittleness and uneven microstructure, and successfully prepares a high-performance microcrystalline glass wafer substrate that meets the requirements of high-end semiconductor photolithography processes.

[0085] Test case In this invention's formulation, hydroxyethyl urea serves as a key functional additive. During the wet ball milling stage, it acts as a highly efficient dispersant and viscosity modifier, achieving extremely uniform mixing of raw materials at the submicron to nanoscale, laying the foundation for obtaining a uniform microstructure. More importantly, during the subsequent specific segmented debinding heat treatment (180-400℃), the reducing atmosphere (such as NH3, CO) and intermediate products generated by its controlled decomposition can undergo in-situ chemical reactions with chromium dioxide in the formulation, partially reducing CrO2 to Cr2O3. This CrO3 then combines with Cr2O3 at the grain boundaries to generate trace amounts of chromate urea complex derivatives with a unique layered structure. This derivative, acting as a "grain boundary lubricating phase," effectively passivates crack tips, induces crack deflection and branching, thereby significantly consuming fracture energy and resulting in an unexpected improvement in fracture toughness. Simultaneously, the extremely high nucleation density it promotes limits the final grain size to below 50 nanometers, which is the fundamental guarantee for achieving atomic-level surface smoothness (Ra < 0.5 nm).

[0086] To verify that hydroxyethyl urea is an indispensable key component for the microcrystalline glass wafer substrate prepared in this invention to possess both high flatness and high toughness, this experimental example, based on Example 2 above, only changes the composition of hydroxyethyl urea, and designs the following comparative experiment: Control group A: Hydroxyethyl urea was completely removed from the formula.

[0087] Control group B: The hydroxyethyl urea in the formula was replaced in equal amounts with the conventional polymeric dispersant ammonium polyacrylate (ammonium salt).

[0088] Control group C: Hydroxyethyl urea in the formula was replaced with an equal amount of the conventional dispersant polyvinyl alcohol (PVA).

[0089] Under the condition that other raw materials, proportions and preparation methods are exactly the same, a comparative sample was prepared, and its surface smoothness (Ra) and fracture toughness (K) were tested using the aforementioned detection methods. The results are recorded in Table 2.

[0090] Table 2 Comparison of the effects of hydroxyethyl urea on wafer substrate performance

[0091] As shown in Table 2, compared with Comparative Example A, Example 2 has a significant advantage in terms of flatness and toughness, proving that the addition of hydroxyethyl urea plays a decisive role in solving the two major defects.

[0092] Compared to Comparative Examples B and C, Example 2 still demonstrates a significant performance advantage. This indicates that the effect of hydroxyethyl urea far exceeds its physical dispersing function; while conventional dispersants can only improve slurry uniformity to a limited extent and cannot trigger a synergistic chemical reaction with chromium dioxide during heat treatment to generate a grain boundary toughening phase, thus failing to achieve the same level of structural refinement and a leap in toughness.

[0093] In summary, the specific chemical functions of hydroxyethyl urea and its synergistic effect with chromium dioxide are the non-obvious technical key to achieving the superior performance of this invention.

[0094] In addition, in the formulation of this invention, the mass ratio of hydroxyethyl urea is precisely controlled at 1.5-3.0%. If its content deviates from this range, it will lead to a significant deterioration of key properties such as the flatness and toughness of the wafer substrate.

[0095] When the hydroxyethyl urea content is too low, its dispersion ability during the wet ball milling stage is insufficient, failing to adequately break up the agglomeration of inorganic powders, leading to a decrease in slurry uniformity. This can cause compositional fluctuations in the subsequent glass matrix, becoming the source of microscopic inhomogeneities. More importantly, during the debinding heat treatment stage, insufficient hydroxyethyl urea decomposition products are insufficient to undergo a sufficient reduction-complexation reaction with chromium dioxide, resulting in an insufficient quantity and uneven distribution of the chromate toughening phase generated in situ at the grain boundaries. When the hydroxyethyl urea content is too high, its decomposition during heat treatment becomes difficult to control. Excessive organic matter decomposes in the 180-400℃ range, producing a large amount of gas, which easily forms closed pores or interconnected channels with a size exceeding 10 micrometers inside the green blank. These macroscopic defects are difficult to completely eliminate in subsequent melting and will act as stress concentration points, severely impairing the mechanical strength and reliability of the material.

[0096] To verify that the 1.5-3.0% mass ratio of hydroxyethyl urea is also an indispensable key factor in ensuring both high flatness and high toughness of the microcrystalline glass wafer substrate prepared in this invention, this experimental example, based on Example 1 above, only changed the mass ratio of hydroxyethyl urea, setting it to 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%. Then, the fracture toughness of the prepared wafer substrate was tested using the detection method provided in the above examples. The results are as follows... Figure 2 As shown.

[0097] according to Figure 2 It can be seen that when the mass percentage of hydroxyethyl urea in the formula is 0.5%, 1.0%, 3.5%, 4.0%, 4.5%, or 5.0%, which is not 1.5-3.0%, the fracture toughness value of the prepared wafer substrate is significantly lower than that of the wafer substrate prepared when the mass percentage of hydroxyethyl urea in the formula is 1.5%, 2.0%, 2.5%, or 3.0%.

[0098] Therefore, it can be shown that the 1.5-3.0% mass ratio of hydroxyethyl urea is also an indispensable key factor for the microcrystalline glass wafer substrate prepared by this invention to have both high flatness and high toughness.

[0099] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a silica-containing microcrystalline glass wafer substrate, characterized in that, Includes the following steps: Step S1: Weigh out 18-22% aluminum oxide, 1.5-3.0% hydroxyethyl urea, 0.8-1.8% chromium dioxide, 2.5-4.5% lithium oxide, 3-6% magnesium oxide, 1.0-2.0% titanium dioxide, 0.1-0.4% clarifying agent, and 0.5-1.5% toughening agent according to the mass ratio, with the balance being silicon dioxide; dissolve hydroxyethyl urea in deionized water to prepare an aqueous solution, and then add the silicon dioxide, aluminum oxide, chromium dioxide, lithium oxide, magnesium oxide, titanium dioxide powder, clarifying agent, toughening agent and aqueous solution together into a ball mill jar, and obtain a homogeneous slurry by wet ball milling; Step S2: After vacuum degassing, the homogenized slurry is cast into a wet film. After drying the wet film, it is subjected to heat treatment to remove the binder and obtain a green sheet. The green sheet is then subjected to glass melting and homogenization to obtain molten glass. Step S3: Roll and anneal the molten glass to obtain a glass plate; keep the annealed glass plate at 720-780℃ for 1.5-3 hours, then raise the temperature to 880-950℃ and keep it at that temperature for 0.5-1.5 hours. Step S4: Polish the glass plate on both sides, then perform ultrasonic cleaning and drying to obtain the wafer substrate product.

2. The method for preparing a silicon dioxide-containing microcrystalline glass wafer substrate according to claim 1, characterized in that: In step S1, the clarifying agent is antimony trioxide, and the toughening agent is yttrium trioxide.

3. The method for preparing a silicon dioxide-containing microcrystalline glass wafer substrate according to claim 1, characterized in that: In step S1, hydroxyethyl urea is dissolved in deionized water to prepare an aqueous solution with a concentration of 25-35 wt%.

4. The method for preparing a silicon dioxide-containing microcrystalline glass wafer substrate according to claim 1, characterized in that: In step S1, zirconium oxide balls are used as the grinding medium during wet ball milling, and the balls are milled at a speed of 300-400 rpm for 18-24 hours.

5. The method for preparing a silicon dioxide-containing microcrystalline glass wafer substrate according to claim 1, characterized in that: In step S2, after the wet film is dried at 40-60°C, it is sent to a programmable temperature controlled furnace for segmented glue removal heat treatment. The heat treatment for debinding involves holding the product at a temperature range of 180-400℃ for 2-4 hours at a heating rate of 0.5-1℃ / min.

6. The method for preparing a silica-containing microcrystalline glass wafer substrate according to claim 1, characterized in that: In step S2, the blank sheet is placed in a platinum crucible and melted in a high-temperature silicon molybdenum rod electric furnace at 1550-1650℃ for 3-5 hours, with mechanical stirring to obtain molten glass.

7. The method for preparing a silicon dioxide-containing microcrystalline glass wafer substrate according to claim 1, characterized in that: In step S3, the molten glass is poured into a preheated alloy mold and rolled into a glass sheet of uniform thickness using a precision twin-roll calender at 1150-1250℃.

8. The method for preparing a silicon dioxide-containing microcrystalline glass wafer substrate according to claim 7, characterized in that: In step S3, the rolled glass plate is transferred into an annealing furnace, kept at a temperature higher than its glass transition temperature, and then cooled to room temperature at a rate of 1-2℃ / min.

9. The method for preparing a silicon dioxide-containing microcrystalline glass wafer substrate according to claim 1, characterized in that: In step S4, during polishing, diamond polishing slurry is first used for rough polishing and fine polishing, and finally colloidal silica polishing slurry is used for chemical mechanical polishing to make its surface roughness <0.5nm.

10. A silica-containing microcrystalline glass wafer substrate prepared by the preparation method according to any one of claims 1-9, characterized in that, Including the following raw materials: Silicon dioxide, aluminum oxide, hydroxyethyl urea, chromium dioxide, lithium oxide, magnesium oxide, titanium dioxide, clarifying agent, and toughening agent, wherein: The silicon dioxide acts as a glass network forger, constructing the basic structure and providing chemical stability and low dielectric properties; the aluminum oxide acts as a network intermediate, participating in the formation of the main crystalline phase; the lithium oxide acts as a major flux and crystallization regulator, lowering the melting temperature and promoting the formation of the main crystalline phase; the magnesium oxide acts as an auxiliary flux and grain refiner, reducing melt viscosity, promoting densification, and inhibiting excessive grain growth; and the titanium dioxide acts as an auxiliary nucleating agent, synergistically lowering the nucleation barrier with chromium oxide. The hydroxyethyl urea is used as a dispersant in wet ball milling to achieve uniform nanoscale mixing of raw materials. In subsequent heat treatment, the reducing atmosphere and intermediate products generated by its controlled decomposition can partially reduce chromium dioxide and combine with it, generating a layered chromate urea complex derivative at the grain boundary in situ. This derivative acts as a grain boundary lubricating phase, effectively passivating the crack tip to improve fracture toughness. The chromium dioxide, as a multifunctional nucleating agent and toughening synergist, is partially converted into chromium trioxide under the action of hydroxyethyl urea to provide nucleation sites, and the other part participates in the generation of the grain boundary toughening phase. The clarifying agent is used to remove air bubbles from the melt during the high-temperature melting stage; the toughening agent is used to stabilize the toughening phase and dissolve it in the glass network to strengthen the glass phase.

Images