Preparation method of superfine aluminum oxide abrasive for sapphire CMP (chemical mechanical polishing)

Abstract

The invention discloses a preparation method of a superfine aluminum oxide abrasive for sapphire CMP (chemical mechanical polishing). The preparation method comprises the following steps: step 1, putting an aluminum hydroxide precursor into a crucible; 2, putting the crucible into a muffle furnace for calcining; 3, putting the calcined aluminum oxide into a crusher for crushing, taking out the crushed aluminum oxide, mixing the crushed aluminum oxide with water to obtain aluminum oxide slurry, dropwise adding nitric acid to enable the aluminum oxide slurry to be in an acidic environment, and adding zirconium beads into the slurry by using a nylon wet grinding tank for grinding; and 4, adding water and potassium hydroxide into the ground slurry to obtain the polishing solution of the aluminum oxide abrasive. Compared with the prior art, the method has the advantages that when the prepared aluminum oxide abrasive is used for sapphire polishing, the removal rate is high, the polishing service life is long, and the polished surface quality is good.

Description

Technical Field

[0001] The invention relates to the technical field of ultrafine aluminum oxide abrasives, in particular to a method for preparing ultrafine aluminum oxide abrasives used for sapphire CMP. Background Art

[0002] In the chemical mechanical polishing of sapphire, it is necessary to select suitable abrasives according to its ultra-high hardness (Mohs hardness 9) and processing efficiency requirements. Commonly used polishing abrasives include aluminum oxide, silicon dioxide, cerium oxide, diamond, silicon carbide, and nano-composite abrasives. Silicon dioxide (SiO2) achieves ultra-low roughness (<0.1nm) through chemical softening reaction, but its insufficient hardness (Mohs 7) leads to low polishing efficiency and requires the assistance of strong corrosive reagents. It is only suitable for LED substrate polishing; cerium oxide (CeO2) can achieve atomic-level smooth surface (Ra<0.05nm) by chemical adsorption, but it is expensive and has a narrow process window (needs a neutral to weakly acidic environment), making it difficult to apply on a large scale; although diamond has the highest hardness (Mohs 10) and outstanding material removal rate (MRR), it has serious residual scratches and requires additional polishing repair, which is only suitable for initial processing of ingots; silicon carbide (SiC) has strong mechanical removal ability, but the risk of subsurface damage is high, and nano-scale particles and chemical additives need to be synergistically optimized, and the process complexity is significantly increased.

[0003] Traditional abrasives have obvious shortcomings in efficiency, cost or surface quality, while alumina (Al2O3) has become the best choice for sapphire polishing because of its hardness close to sapphire (Mohs 9), low cost and wide process adaptability.

[0004] Alumina (Al2O3) abrasives are the core material for sapphire polishing, mainly composed of high-purity α-phase alumina particles and surface modifiers. A technology for preparing nano-alumina abrasives by ball milling, using hydroxylation surface treatment to improve particle dispersibility, and adding phosphate as a dispersant. Although this technology reduces particle agglomeration through modification, the abrasive hardness is still close to sapphire (Mohs 9), which can easily cause micro scratches during polishing, resulting in subsurface damage (SSD) depth of 50-100nm, affecting the light transmission performance of optical devices.

[0005] General aluminum oxide abrasives are obtained by calcining at a relatively low temperature (900℃-1200℃). The calcined precursors are mostly monohydrated aluminum oxide (boehmite), which will be transformed into α-phase aluminum oxide particles at 1100℃. After a certain period of constant temperature calcination, the required aluminum oxide abrasives are obtained. Traditional aluminum oxide abrasives are rosin and shellac dissolved in alcohol solvents. Since the purity of the precursor itself affects its performance in various aspects, calcination at a relatively low temperature will lead to incomplete phase transformation. The hardness and other properties of the calcined aluminum oxide abrasives cannot achieve a good polishing effect. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the above technical defects.

[0007] To solve the above problems, the technical solution of the present invention is: a preparation method of ultrafine alumina abrasive for sapphire CMP, the preparation method comprising the following steps:

[0008] Step 1: Put the aluminum hydroxide precursor into a crucible;

[0009] Step 2: Put the crucible into a muffle furnace for calcination;

[0010] Step 3: Put the calcined alumina into a crusher for crushing, take out the crushed alumina and mix it with water to obtain an alumina slurry, drop nitric acid into it to make it in an acidic environment, and grind the slurry with a nylon wet grinding tank and zirconium beads;

[0011] Step 4: Add water and potassium hydroxide to the ground slurry to obtain a polishing liquid of alumina abrasive.

[0012] Further, the grinding equipment includes a crusher, a nylon wet grinding tank and zirconium beads, and the diameter of the zirconium beads is 1 mm to 2 mm.

[0013] Further, the calcination temperature is 1200 °C to 1400 °C, the holding time is 1 h to 2.5 h, and wet grinding with a nylon ball milling tank is used to control the particle size (D50 = 1 - 3 μm).

[0014] The advantages of the present invention compared with the existing technology are as follows:

[0015] The present invention uses high-purity aluminum trihydroxide (aluminum hydroxide) as a precursor. The precursor removes crystal water at 300 °C and has a transition temperature above 1200 °C. The high transition temperature can obtain alumina abrasive with higher hardness, enhance the polishing rate of the alumina abrasive, and then control the particle size of the alumina abrasive within a certain range through wet grinding technology. That is, when the surface roughness of the sapphire is guaranteed to be 0.2 - 0.3 nm, the removal rate can be increased to 2.5 μm / h without increasing the cleaning difficulty. Description of the Drawings

[0016] Figure 1 It is a broken line graph of the particle diameter of the preparation method of the ultrafine alumina abrasive for sapphire CMP of the present invention. Detailed Embodiments

[0017] The following further describes the detailed embodiments of the present invention with reference to the drawings.

[0018] It should be noted that the terms "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to the directions in the attached drawings, and the terms "inner" and "outer" refer to the directions towards or away from the geometric center of a specific component respectively.

[0019] In order to make the content of the present invention easier to be clearly understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0020] As Figure 1 shown, a preparation method of ultrafine alumina abrasive for sapphire CMP, the preparation method includes the following steps:

[0021] Step 1: Put the aluminum hydroxide precursor into a crucible;

[0022] Step 2: Put the crucible into a muffle furnace for calcination;

[0023] Step 3: Put the calcined alumina into a crusher for crushing, take it out after crushing and mix it with water to obtain an alumina slurry, drop nitric acid into it to make it in an acidic environment, and grind the slurry with a nylon wet grinding tank added with zirconium beads;

[0024] Step 4: Add water and potassium hydroxide to the ground slurry to obtain a polishing liquid of alumina abrasive.

[0025] The grinding equipment includes a crusher, a nylon wet grinding tank and zirconium beads, the diameter of the zirconium beads is 1 mm to 2 mm, the calcination temperature is 1200 °C to 1400 °C, the heat preservation time is 1 h to 2.5 h, and the particle size is controlled by wet grinding with a nylon ball milling tank (D50 = 1 - 3 μm).

[0026] In specific use, the synthesis of ultrafine alumina abrasive includes the following steps: calcination conditions (calcination temperature 1200 °C to 1400 °C, heat preservation time 1 h to 2.5 h), and the particle size is controlled by wet grinding with a nylon ball milling tank (D50 = 1 - 3 μm).

[0027] The present invention uses aluminum trihydroxide (aluminum hydroxide) as the precursor of ultrafine alumina abrasive. Due to its high phase transition point, the structural integrity and hardness and other properties after phase transition of aluminum trihydroxide meet the requirements of CMP. And because the purity of aluminum trihydroxide that can be achieved in industry is relatively high, the problems of performance caused by impurities can be reduced from the raw materials, thereby optimizing the polishing performance of alumina abrasive. The described aluminum hydroxide as the calcination precursor of alumina abrasive has properties such as high phase transition temperature and high purity. Under the synergistic action of a specific calcination temperature and calcination time, the prepared alumina abrasive can have high hardness and long service life during sapphire CMP. By controlling its particle size distribution, an alumina abrasive with high removal rate and good surface quality after polishing can be obtained.

[0028] As a preferred embodiment of the present invention, the aldehyde resin is a thermoplastic aldehyde resin, and the chemical formula of the aluminum trihydrate is Al2O3·3H2O. It is usually a white solid, insoluble in water but soluble in strong acids or strong alkalis. As a calcination precursor, it decomposes upon heating to form aluminum oxide (Al2O3) and water, and different crystal forms of aluminum oxide are formed depending on the calcination temperature.

[0029] The present invention and its embodiments have been described above. Such description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention. Generally speaking, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural forms and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. Preparation method of ultrafine alumina abrasive for sapphire CMP, characterized in that: The preparation method includes the following steps: Step 1: Put the aluminum hydroxide precursor into a crucible; Step 2: Put the crucible into a muffle furnace for calcination; Step 3: Put the calcined alumina into a crusher for crushing. After crushing, take it out and mix it with water to obtain an alumina slurry. Drop nitric acid into it to make it in an acidic environment, and add zirconium beads to the slurry with a nylon wet grinding tank for grinding; Step 4: Add water and potassium hydroxide to the ground slurry to obtain a polishing liquid of alumina abrasive.

2. The preparation method of the ultra-fine alumina abrasive for sapphire CMP according to claim 1, characterized in that: The grinding equipment includes a crusher, a nylon wet grinding tank and zirconium beads, and the diameter of the zirconium beads is 1 mm to 2 mm.

3. The preparation method of the ultra-fine alumina abrasive for sapphire CMP according to claim 1, characterized in that: The calcination temperature is 1200°C to 1400°C, and the heat preservation time is 1 h to 2.5 h. The particle size is controlled by wet grinding with a nylon ball milling tank (D50 = 1 - 3 μm).

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