Synthesis method of hydrazine dicarboxylate modified cerium dioxide abrasive

Abstract

The invention discloses a synthesis method of a hydrazine dicarboxylate modified cerium dioxide abrasive, and belongs to the technical field of precise polishing materials. The method comprises the following steps: taking cerous nitrate as a raw material, and preparing a cerous carbonate precursor through an ammonium carbonate precipitation reaction; and grinding and calcining the obtained precursor and hydrazine dicarboxylate to obtain the CeO2 grinding material with the surface rich in oxygen vacancies. And Ce < 4 + > can be partially reduced into Ce < 3 + > by reducing fragments generated by decomposition of the hydrazine dicarboxylate in the calcining process, so that an oxygen vacancy structure is formed through induction, and the chemical activity and the reaction rate of the abrasive are improved. The obtained grinding material shows excellent performance in chemical mechanical polishing (CMP) of K9 glass, the material removal rate (MRR) is increased by about 3.6 times compared with that of unmodified CeO2, the surface roughness (Ra) is reduced to about 0.16 nm or below, and grinding material particles are good in dispersity and less in agglomeration. The used hydrazine dicarboxylate is stable, low in toxicity and mild in reaction, and the particle size can be prevented from excessively growing while the high oxygen vacancy concentration is kept.

Description

Technical Field

[0001] This invention belongs to the field of chemical mechanical polishing (CMP) materials technology, specifically relating to a polishing abrasive and its preparation method that utilizes nitrogen-containing reducing organic compounds to chemically modify the surface of cerium oxide (CeO2). More specifically, this invention relates to an oxygen-vacancy-rich CeO2 abrasive that enhances surface activity and regulates reactivity by introducing hydrazine dicarboxylic acid ester compounds to regulate the oxygen vacancy concentration in the CeO2 lattice. This abrasive exhibits excellent material removal rate and surface finish in the CMP process for K9 optical glass, and shows promising application prospects for high-precision, low-damage surface polishing of silicon wafers and crystal materials. Background Technology

[0002] With the rapid development of integrated circuit, optoelectronic device, and high-end optical component manufacturing technologies, the requirements for surface planarization of wafers and optical glass are constantly increasing. Especially under nanoscale process conditions, the precise control of global planarization, surface roughness (Ra), and polishing selectivity at multi-material interfaces on wafer surfaces has become a core challenge for chemical mechanical polishing (CMP) technology. In the CMP process, the performance of the polishing slurry directly determines the yield and surface quality of the final process, and the abrasive, as a key component for achieving mechanochemical coupling, plays a decisive role in polishing behavior due to its structure and surface properties.

[0003] Cerium oxide (CeO2) has unique Ce properties. 4+ / Ce 3+ Due to its reversible oxidation properties, high chemical reactivity, and good environmental stability, CeO2 has long been considered one of the most representative rare-earth abrasives in CMP processes. However, traditional CeO2 abrasives still have the following problems: (1) The strong agglomeration of nanoparticles leads to poor dispersion stability; (2) The surface oxygen vacancy concentration is low, the interfacial reaction activity is limited, and the polishing rate is low. (3) The electronic structure is simple, making it difficult to achieve differentiated control of the reactivity of different substrate interfaces; (4) The reaction layer forms slowly in an alkaline CMP environment, making it difficult to further improve the material removal rate (MRR).

[0004] To address these issues, researchers have explored various approaches to optimize the electronic structure and dispersion of CeO2, including metal ion doping, composite structure construction, and surface modification with organic functional groups. Among these, surface functionalization is considered an effective strategy for controlling oxygen vacancies and surface electronic states. Existing research primarily focuses on using organosilanes, carboxylic acids, or amines to achieve surface modification through electrostatic adsorption or condensation reactions. However, the reducing power of these functional groups is limited, making it difficult to significantly regulate CeO2.4+ / Ce 3+ The ratio has no significant effect on the generation of lattice oxygen vacancies in CeO2.

[0005] Therefore, how to utilize organic compounds with stronger reducing properties to induce the formation of stable oxygen vacancies in the CeO2 structure, thereby simultaneously improving the chemical reactivity and mechanical polishing performance of the material, has become a key technical problem urgently needing to be solved in this field. To address the above shortcomings, this invention proposes a method for preparing CeO2 by surface chemical modification using hydrazine dicarboxylic acid esters. This method achieves controllable generation of oxygen vacancies in CeO2 through low-temperature reduction-induced action, significantly improving its CMP performance. Summary of the Invention

[0006] This invention proposes a method for chemically modifying cerium oxide (CeO2) using hydrazine dicarboxylate compounds with reducing and complexing capabilities. This significantly improves the chemical mechanical polishing (CMP) performance of CeO2 abrasives by inducing the generation of lattice oxygen vacancies. The method involves introducing a controlled reducing atmosphere during the solid-state reaction between the cerium carbonate precursor and the hydrazine dicarboxylate, thereby achieving the desired reduction in CeO2. 4+ →Ce 3+ By partially converting the oxygen vacancy in CeO2, the surface electronic structure and oxygen vacancy concentration of CeO2 can be controlled, thereby obtaining oxygen-vacancy-rich CeO2 abrasives with high chemical activity, high material removal rate (MRR), and low surface roughness (Ra).

[0007] Unlike traditional silane coupling agents or amino organic modifications, this invention innovatively employs hydrazine dicarboxylic acid ester molecules. During the grinding process, these molecules can form coordination bonds with hydroxyl or carboxylate groups on the surface of cerium carbonate. Simultaneously, during subsequent inert atmosphere calcination, they decompose to generate reducing gaseous intermediates, producing a localized reduction effect on the CeO2 lattice and inducing the formation of high-concentration oxygen vacancies. This process not only enhances the reactivity of the CeO2 particle surface but also avoids the interfacial inerting problem caused by organic coatings.

[0008] The technical implementation path of this invention is as follows: (1) Precursor preparation and pretreatment Cerium nitrate was reacted with ammonium carbonate to generate a cerium carbonate precursor. After washing and low-temperature drying, a reaction matrix with uniform particle size distribution and high specific surface area was obtained, providing active sites for subsequent solid-phase reactions.

[0009] (2) Introduction of hydrazine dicarboxylate and solid-phase reaction Cerium carbonate is uniformly mixed with hydrazine dicarboxylic acid esters (including dimethyl hydrazine dicarboxylic acid, diethyl hydrazine dicarboxylic acid, diisopropyl hydrazine dicarboxylic acid, dibenzyl hydrazine dicarboxylic acid, ditert-butyl hydrazine dicarboxylic acid, or mixtures thereof) at a molar ratio of 0.05-0.50, and then thoroughly mixed and brought into microscopic contact by hand grinding for 20-40 minutes.

[0010] In step (2), grinding the mixture until the fineness reaches D 90 ≤10 μm and uniform powder color.

[0011] (3) Then, under an inert atmosphere (N2 or Ar), it is calcined at 450-650℃ for 2-4 hours. During the thermal decomposition process, hydrazine dicarboxylic acid ester releases reducing gas and induces the formation of oxygen vacancies in CeO2 lattice.

[0012] In step (3), the mixed powder is dried at 60-80℃ for 6-12 hours before calcination to remove adsorbed moisture. During calcination, the inert atmosphere is nitrogen or argon. The resulting CeO2 powder, after grinding, has a particle size distribution of D. 50 =0.2-0.5 μm.

[0013] The present invention also provides a cerium dioxide abrasive rich in oxygen vacancies prepared by the method described above, wherein the particle size distribution D of the abrasive is... 50 The range is 0.2–0.5 μm, and the oxygen vacancy concentration is determined by Ce. 3+ / Ce 4+ The ratio is represented by a proportion, and its value is not less than 0.15.

[0014] The obtained oxygen-rich CeO2 powder was dispersed and then prepared into an alkaline CMP slurry, which was then subjected to standardized polishing experiments on a K9 optical glass substrate.

[0015] Based on this, the present invention provides a chemical mechanical polishing fluid comprising the following components by weight percentage: (1) 5~15 wt% of the CeO2 abrasive as described in claim 5; (2) 0.1~2 wt% dispersant; (3) The remainder consists of deionized water and pH adjuster; (4) The pH of the polishing solution is 8~10.

[0016] A process for polishing the surface of optical glass, silicon wafers or crystal materials, using the aforementioned chemical mechanical polishing slurry, polishing for 5-10 minutes under the conditions of a load of 2 psi, a lower plate rotation speed of 50-60 rpm and an upper plate rotation speed of 50-80 rpm, to obtain a polishing effect with a surface roughness Ra≤0.5 nm.

[0017] The polishing object is K9 glass, silicon wafer, or sapphire substrate.

[0018] Taking K9 glass as an example, the material removal rate (MRR) of this abrasive in K9 glass polishing experiments is 200-700 nm / min, and the surface roughness (Ra) is ≤0.50 nm.

[0019] Compared with unmodified CeO2 and traditional amino-modified samples, the samples of this invention exhibit higher material removal rate (MRR increased by about 1.6 to 3.6 times) and lower surface roughness (Ra reduced by about 14–30%).

[0020] Use of the method in the preparation of cerium dioxide abrasives for chemical mechanical polishing.

[0021] The use of the cerium dioxide abrasive in ultra-precision polishing of optical components, semiconductor wafers or crystal materials.

[0022] The beneficial effects of this invention include: (1) Controllable generation of CeO2 oxygen vacancies is achieved through low-cost organic reducing agents.

[0023] (2) Significantly improves the chemical reactivity and mechanical polishing performance of abrasives.

[0024] (3) The process is simple and does not require additional reducing atmosphere or complex equipment.

[0025] (4) Improves dispersibility and slurry stability, suitable for various alkaline CMP systems.

[0026] (5) The intrinsic relationship between “organic reducing agent structure-oxygen vacancy concentration-CMP performance” was revealed.

[0027] This invention not only provides a new strategy for preparing high-performance, industrially scalable CeO2 abrasives, but also reveals the essential mechanism of oxygen vacancy generation induced by hydrazine dicarboxylic acid ester, providing new research ideas for the surface regulation and application expansion of CeO2-based functional materials. Detailed Implementation

[0028] The present invention will be further illustrated below through embodiments and comparative examples. The embodiments described herein are merely preferred embodiments used to illustrate the technical principles of the invention, and are not intended to limit the scope of protection of the invention. Any improvements, equivalent substitutions, or parameter optimizations made by those skilled in the art without departing from the spirit of the invention should be considered to fall within the scope of protection of the invention.

[0029] Experimental conditions: Polishing object: K9 glass, 100 mm in diameter; Polishing equipment: Rotary disc CMP machine; Load: 2 psi; Lower plate speed: 60 rpm; Upper plate speed: 50 rpm; Polishing time: 10 min; Polishing solution pH: 8; CeO2 slurry concentration: 5 wt%.

[0030] The preparation method of the present invention will be described in detail below with Example 1 as a representative example. The other examples can be made by adjusting the molar ratio of the modifier.

[0031] (1) Raw material preparation Cerium(III) nitrate hexahydrate Ce(NO3)3·6H2O and ammonium carbonate ((NH4)2CO3) are used to prepare cerium carbonate precursors; Dimethyl hydrazine dicarboxylate (DMHD); Deionized water, anhydrous ethanol; Grinding tools: Zirconia or agate mortars.

[0032] (2) Preparation of cerium carbonate precursor Weigh 0.05 mol (approximately 23.2 g) of Ce(NO3)3·6H2O into a beaker, dissolve it in 200 mL of deionized water, and stir until clear; Slowly add 0.5 M ammonium carbonate solution, maintaining pH 8–9, until a uniform white precipitate (cerium carbonate precursor) is formed. After standing for 30 minutes, filter and wash with deionized water 2–3 times; Dry powdered cerium carbonate precursor was obtained by drying at 60℃ for 8-12 h.

[0033] (3) Grind and mix with hydrazine dicarboxylate (by hand) Dry Ce-precursor and dimethyl hydrazine dicarboxylate were added to an agate or zirconium oxide mortar at a molar ratio of 0.05 mol hydrazine / mol Ce. Grind manually for 30 minutes at room temperature until the powder mixture is uniform in color (grind to D). 90 (4.5μm) (4) Drying and loading into crucibles The ground mixed powder was dried at 80 ℃ for 10 h to remove adsorbed moisture; Place the dry powder in a ceramic crucible and lightly cover it with a lid to facilitate partial volatilization and the formation of a micro-reducing environment.

[0034] (5) Calcination in a muffle furnace Place the crucible into a muffle furnace, raise the temperature at a rate of 10 °C / min until it reaches 550 °C, and hold it at that temperature for 2 hours. The preferred calcination atmosphere is nitrogen gas to ensure that the hydrazine-based reduction fragment promotes the formation of oxygen vacancies at high temperatures; After calcination, the furnace is cooled to room temperature.

[0035] (6) Preparation of polishing slurry Take 5 g of calcined modified CeO2 powder and add it to 100 mL of deionized water and stir. Add 0.2 wt% polyacrylic acid (PAA) or SDS as a dispersant; The pH was adjusted to 8.0±0.1 using a dilute NaOH solution, and the mixture was ultrasonically dispersed for 15~20 min to obtain a stable CMP polishing slurry. During the polishing process, the slurry pH is controlled at 8–10, and the abrasive mass fraction is 10 wt%.

[0036] Corresponding Implementation Examples: Examples 1–4: Dimethyl hydrazine dicarboxylate was used in molar ratios of 0.05, 0.15, 0.25, and 0.50, respectively. Examples 5–8: Diethyl hydrazine dicarboxylate, diisopropyl hydrazine dicarboxylate, dibenzyl hydrazine dicarboxylate, and ditert-butyl hydrazine dicarboxylate were used, all in a molar ratio of 0.25; Comparative Example 1: Unmodified pure CeO2.

[0037] The table below shows the material removal rate (MRR), surface roughness (Ra), and overall evaluation results of abrasive systems with different molar ratios: Table 1. Test results of the examples and comparative examples

[0038] The following conclusions can be drawn from the experimental results of the above embodiments and comparative examples: 1. Modification with hydrazine dicarboxylate significantly improves the CMP performance of CeO2. Compared with unmodified CeO2 abrasive (MRR = 180 nm / min, Ra = 0.570 nm), the material removal rate (MRR) and surface roughness (Ra) were significantly improved after modification with hydrazine dicarboxylate. The modified samples generally exhibited higher reactivity and better surface smoothness, with the highest MRR increase reaching approximately 3.6 times and the lowest Ra decreasing to 0.157 nm, fully demonstrating the synergistic regulatory effect of hydrazine dicarboxylate on the electronic structure and interfacial chemical activity of CeO2 surface.

[0039] 2. The amount of modifier has a significant impact on CMP performance. Within the molar ratio of hydrazine dicarboxylate (HDI) ranging from 0.05 to 0.50, the MRR of CeO2 gradually increased with increasing addition, reaching a peak at a molar ratio of 0.25 (MRR = 643 nm / min for the methyl ester sample). When the molar ratio further increased to 0.50, the MRR decreased somewhat, while Ra slightly rebounded. This phenomenon indicates that an appropriate amount of HDI can effectively promote the generation of surface oxygen vacancies and enhance interfacial reactions, while excessive addition may reduce the exposure of active sites due to organic residue coverage or local aggregation, thereby leading to a decrease in polishing efficiency.

[0040] 3. The modification effects of hydrazine dicarboxylic acid esters are similar. Under a 0.25 molar ratio, a comparison of the five types of modifiers shows that dimethyl hydrazine dicarboxylate exhibits relatively small differences in polishing performance compared to diethyl hydrazine dicarboxylate, diisopropyl hydrazine dicarboxylate, dibenzyl hydrazine dicarboxylate, and di-tert-butyl hydrazine dicarboxylate, all achieving significant optimization of MRR and Ra. This indicates that the alkyl chain length in the hydrazine dicarboxylate ester structure has a limited impact on CeO2 surface modification, while its core role mainly stems from the electron transfer effect induced by the hydrazine group and the carboxyl ester structure, as well as the stabilizing effect of oxygen vacancies.

[0041] 4. Determination of optimal conditions and mechanism analysis Comparing the experimental results of eight embodiments, the optimal performance was determined to be achieved when the molar ratio of hydrazine dicarboxylate to Ce source was 0.25:1. At this ratio, the oxygen vacancy concentration and dispersibility on the CeO2 surface reached equilibrium, resulting in the highest polishing rate and the lowest surface roughness. The hypothesized mechanism is that the nitrogen- and oxygen-containing coordination fragments generated during the decomposition of hydrazine dicarboxylate during calcination interact with Ce... 4+ Local reduction reactions occur, inducing the formation of stable oxygen vacancy structures, thereby enhancing the surface reactivity and mechanochemical synergy of CeO2.

[0042] In summary, this invention achieves precise control over the oxygen vacancies and interfacial electronic structure of CeO2 surface by introducing an appropriate amount of hydrazine dicarboxylate, resulting in abrasives exhibiting high material removal rate, low surface roughness, and excellent stability during K9 glass chemical mechanical polishing. This method provides a simple, controllable, and environmentally friendly new approach for preparing high-performance oxygen-vacancy-rich CeO2 abrasives, with broad industrial application prospects.

Claims

1. A method for synthesizing hydrazinedicarboxylate modified ceria abrasives, characterized in that, The method comprises the following steps: (1) reacting cerium nitrate solution with ammonium carbonate solution to prepare cerium carbonate precursor; (2) mixing the cerium carbonate precursor with hydrazine dicarboxylate compound and grinding thoroughly; (3) calcining the obtained mixture at 450-650 °C in inert atmosphere for 2-4 hours, and obtaining hydrazine dicarboxylate modified ceria abrasive, i.e. ceria abrasive rich in oxygen vacancies after cooling.

2. The method of claim 1, wherein, The hydrazine dicarboxylate compound comprises hydrazine dimethyl dicarboxylate, hydrazine diethyl dicarboxylate, hydrazine diisopropyl dicarboxylate, hydrazine dibenzyl dicarboxylate, hydrazine di-t-butyl dicarboxylate or mixture thereof; the molar ratio of cerium carbonate precursor to hydrazine dicarboxylate compound is 0.05-0.

50.

3. The method of claim 1, wherein, The grinding to the mixture fineness reaches D 90 ≤ 10 μm and the powder color is uniform.

4. The method of claim 1, wherein, The mixed powder is dried at 60-80°C for 6-12 hours to remove adsorbed water before calcination in step (3), and the inert atmosphere during calcination is nitrogen or argon; the obtained CeO2 powder has a particle size distribution of D 50 =0.2-0.5 μm after grinding.

5. A ceria abrasive enriched with oxygen vacancies, prepared by the method of any one of claims 1 to 4, characterized in that, The particle size distribution D of the abrasive 50 is 0.2-0.5 μm, and the oxygen vacancy concentration is represented by Ce 3+ / Ce 4+ The ratio is not less than 0.

15.

6. A chemical mechanical polishing liquid characterized by comprising: The polishing liquid comprises the following components by weight percentage: (1) 5-15 wt% of the ceria abrasive of claim 5; (2) 0.1-2 wt% of dispersant; (3) the balance being deionized water and pH adjuster; (4) the pH of the polishing liquid is 8-10.

7. A process for polishing the surface of optical glass, silicon wafers or crystalline materials, characterized in that, The chemical mechanical polishing liquid of claim 6 is used to polish for 5-10 minutes under the conditions of load 2 psi, lower disc rotation speed 50-60 rpm and upper disc rotation speed 50-80 rpm, and a polishing effect of surface roughness Ra≤0.5 nm is obtained.

8. The polishing process of claim 7, wherein, The polishing object is K9 glass, silicon wafer or sapphire substrate.

9. Use of the method of any one of claims 1-4 in the preparation of ceria abrasive for chemical mechanical polishing.

10. Use of the ceria abrasive of claim 5 in the ultra-precision polishing of optical elements, semiconductor wafers or crystal materials.

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