Ultra-smooth magneto-rheological polishing slurry for inhibiting surface defects of monocrystalline silicon and polishing method

Abstract

The invention discloses ultra-smooth magneto-rheological polishing slurry for inhibiting surface defects of monocrystalline silicon and a polishing method. The ultra-smooth magneto-rheological polishing slurry comprises the following components: nano cerium oxide with the particle size of 50nm, a dispersing agent, a dispersion stabilizer, a surfactant and a pH regulator, the ultra-smooth magnetorheological polishing slurry comprises the following components in percentage by mass: 1-3 wt% of nano cerium oxide, 0-1 wt% of a dispersing agent, 0.1-2.0 wt% of a dispersion stabilizer, 0-0.5 wt% of a surfactant, 0.1-2 wt% of a pH regulator and the balance of water. The spherical cerium oxide with the size of 50 nm is used as the grinding material, the particle size is small, the sphericity degree is high, meanwhile, sodium gluconate and / or potassium gluconate are / is used as the dispersing agent, and the dispersion stabilizer and the surfactant are added, so that the dispersity of the small-size cerium oxide grinding particles with the size of 50 nm in the polishing solution can be improved; good roughness of the surface of the monocrystalline silicon can be achieved, meanwhile, surface damage can be restrained, and defects caused to the surface of the monocrystalline silicon in the polishing process are avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precision and ultra-precision machining, in particular to an ultra-smooth magnetorheological polishing slurry for inhibiting defects on a monocrystalline silicon surface and a polishing method. BACKGROUND

[0002] Monocrystalline silicon has high hardness, good thermal conductivity, and low expansion rate, and has been widely used in aerospace, high-energy lasers, and semiconductors. Among them, magnetorheological polishing is a key process for achieving excellent surface quality of monocrystalline silicon and plays an important role in the processing of ultra-precision monocrystalline silicon optical elements.

[0003] Existing monocrystalline silicon polishing methods are prone to cause damage on the surface of the silicon wafer. For example, Chinese patent CN202311471871.7 discloses a monocrystalline silicon magnetorheological polishing liquid and its application, which includes silica sol, surface adhesive, and deionized water. Through the adsorption selectivity of isopropyl alcohol molecules on the surface of monocrystalline silicon, a difference in material removal rate is formed between different regions, reducing the size of the topography. However, isopropyl alcohol in this formula has certain toxicity, and there is no corresponding solution to the surface damage caused by polishing. Chinese patent CN202510524354.4 discloses that magnetorheological polishing can solve the rainbow lines generated by diamond turning, but does not disclose the specific formula and scratch defects.

[0004] In view of this, the present application is proposed. SUMMARY

[0005] The existing monocrystalline silicon polishing liquid is prone to cause damage on the surface of the silicon wafer. To solve the above problem, the present application provides an ultra-smooth magnetorheological polishing slurry for inhibiting defects on a monocrystalline silicon surface and a polishing method. By using 50 nm spherical cerium oxide as an abrasive, which has a small particle size and high sphericity, it can achieve good roughness on the surface of monocrystalline silicon, while inhibiting surface damage and avoiding defects on the surface of monocrystalline silicon during the polishing process.

[0006] The present application is achieved by the following technical solutions: In a first aspect, the present application provides an ultra-smooth magnetorheological polishing slurry for inhibiting defects on a monocrystalline silicon surface, comprising the following components: Nano cerium oxide with a particle size of 50 nm, a dispersing agent, a dispersion stabilizer, a surfactant, and a pH adjuster.

[0007] In a certain specific embodiment, the mass fraction of each component of the ultra-smooth magnetorheological polishing slurry is as follows: The composition consists of 1-3 wt% nano-cerium oxide, 0-1 wt% dispersant, 0.1-2 wt% dispersion stabilizer, 0-0.5 wt% surfactant, 0.1-2 wt% pH adjuster, and the balance being water.

[0008] This invention uses spherical cerium oxide with a size of 50 nm as an abrasive. Its small particle size and high sphericity enable it to achieve good surface roughness of single-crystal silicon, while suppressing surface damage and avoiding defects on the surface of single-crystal silicon during the polishing process.

[0009] In one specific embodiment, the dispersant is sodium gluconate and / or potassium gluconate.

[0010] This invention optimizes the slurry composition by using sodium gluconate and / or potassium gluconate as dispersants, along with dispersing stabilizers and surfactants. Gluconic acid organic matter can be adsorbed onto the surface of abrasive cerium oxide particles, thereby improving the dispersibility of 50 nm small-sized cerium oxide particles in the polishing slurry and preventing agglomeration of cerium oxide particles. The addition of surfactants further promotes this behavior, improving agglomeration through steric hindrance and electrostatic repulsion, and reducing the actual size of cerium oxide particles acting on the monocrystalline silicon surface during polishing. This results in lower surface roughness, fewer defects, and less surface damage on the monocrystalline silicon surface.

[0011] In a specific embodiment, the dispersant stabilizer is often a polyphosphate and / or citrate, preferably a polyphosphate. This invention uses a polyphosphate as a dispersant stabilizer, which has a long-chain structure that can wrap around the abrasive grains, providing steric hindrance between the grains and preventing abrasive grain aggregation. Under the combined effect of the electrostatic repulsion provided by the gluconic acid organic matter and the steric hindrance provided by the polyphosphate, a more superior dispersion effect of the abrasive grains can be achieved, thereby improving the polishing effect.

[0012] In one specific embodiment, the surfactant is one or more of sodium lauryl sulfate, sodium stearate, and sodium dodecylbenzene sulfonate. By adding a surfactant, this invention can reduce the solid-liquid interfacial tension, improve the wettability of the liquid on the surface of nano-cerium oxide abrasive particles, thereby enhancing the adsorption effect between gluconic acid organic matter and polyphosphates and the abrasive particles.

[0013] In one specific embodiment, the pH adjuster is one or more selected from glycine, citric acid, sodium hydroxide, and potassium hydroxide. By adding a pH adjuster, this invention adjusts the slurry pH to 9-9.5, thus avoiding excessively high pH levels that could lead to overly vigorous hydrolysis of the monocrystalline silicon, causing surface damage and affecting the final surface processing effect.

[0014] Secondly, the present invention provides an ultra-smooth magnetorheological polishing method for suppressing defects on the surface of single-crystal silicon, comprising the following steps: S1, the polishing slurry and carbonyl iron powder are mixed by rolling and stirring at a mass ratio of 1:5 to obtain a polishing liquid; S2, add the polishing liquid to the magnetorheological polishing machine tool, and perform magnetorheological polishing on the fixed single crystal silicon surface until an ultra-smooth silicon wafer is obtained.

[0015] In one specific embodiment, the polishing wheel of the polishing machine rotates at a speed of 100-200 rpm; more preferably, the polishing wheel rotates at a speed of 120 rpm.

[0016] In one specific embodiment, the flow rate of the polishing fluid is 1000~1500 mL / min, the immersion depth is 0.2~0.4 mm, and the travel speed of the polishing wheel is 1000~2000 mm / min.

[0017] In one specific embodiment, the polishing fluid flow rate is 1200 mL / min, the immersion depth is 0.25 mm, and the polishing wheel travel speed is 1500 mm / min.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The ultra-smooth magnetorheological polishing slurry and polishing method for suppressing surface defects of single crystal silicon provided in the embodiments of the present invention use spherical cerium oxide with a size of 50 nm as abrasive. Its small particle size and high sphericity can achieve good surface roughness of single crystal silicon, while suppressing surface damage and avoiding defects on the surface of single crystal silicon during the polishing process. 2. The ultra-smooth magnetorheological polishing slurry and polishing method for suppressing surface defects of monocrystalline silicon provided in this embodiment of the invention optimizes the slurry composition formula, uses sodium gluconate and / or potassium gluconate as dispersants, and adds dispersing stabilizers and surfactants. Gluconic acid organic matter can be adsorbed on the surface of abrasive cerium oxide, thereby improving the dispersibility of 50nm small-sized cerium oxide abrasive particles in the polishing liquid and avoiding agglomeration of cerium oxide abrasive particles. The addition of surfactants can further promote this behavior, improve the abrasive particle agglomeration through steric hindrance and electrostatic repulsion, and reduce the actual size of cerium oxide abrasive particles acting on the surface of monocrystalline silicon during polishing, thereby achieving lower surface roughness, fewer defects, and less surface damage on the monocrystalline silicon surface. 3. The ultra-smooth magnetorheological polishing slurry and polishing method for suppressing surface defects of monocrystalline silicon provided in the embodiments of the present invention have excellent water solubility and are non-toxic in the added chemical reagents in the water-based slurry. The cleaning process is convenient, requires less time, and is cleaner and more thorough, avoiding the residue of organic reagents on the surface of monocrystalline silicon. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This refers to the surface roughness of single-crystal silicon after magnetorheological polishing provided in Embodiment 1 of the present invention. Figure 2 The image is taken by a white light interferometer on the single-crystal silicon surface after magnetorheological polishing, as provided in Embodiment 1 of the present invention. Figure 3 The damage condition of the single-crystal silicon surface after magnetorheological polishing provided in Embodiment 1 of the present invention; Figure 4 This refers to the surface roughness of single-crystal silicon after magnetorheological polishing provided in Comparative Example 1 of the present invention. Figure 5 The image is taken by a white light interferometer on the single-crystal silicon surface after magnetorheological polishing, as provided in Comparative Example 1 of this invention. Figure 6 The actual particle size of cerium oxide abrasive particles in the magnetorheological polishing slurry provided in Embodiment 1 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0022] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known materials or methods have not been specifically described in order to avoid obscuring the invention.

[0023] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this document; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0025] Example 1 This invention provides an ultra-smooth magnetorheological polishing slurry for suppressing surface defects in monocrystalline silicon, which is composed of the following raw materials in weight percentage: 2 wt% abrasive, 0.5 wt% dispersant, 0.5 wt% dispersion stabilizer, 0.1 wt% surfactant, and the balance being deionized water; and the pH value of the polishing slurry is adjusted to 10 using a pH adjuster.

[0026] Example 2 This invention provides an ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon, which is composed of the following raw materials in weight percentage: 2 wt% abrasive, 0.4 wt% dispersant, 2 wt% dispersion stabilizer, 0.1 wt% surfactant, and the balance being deionized water; and the pH value of the polishing slurry is adjusted to 10 using a pH adjuster.

[0027] Example 3 This invention provides an ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon, which is composed of the following raw materials in weight percentage: 2 wt% abrasive, 0.2 wt% dispersant, 1 wt% dispersion stabilizer, 0.1 wt% surfactant, and the balance being deionized water; and the pH value of the polishing slurry is adjusted to 10 using a pH adjuster.

[0028] Comparative Example 1 The present invention provides an ultra-smooth magnetorheological polishing slurry for suppressing defects on the surface of single-crystal silicon, which is composed of the following raw materials by weight percentage: 2 wt% abrasive, 0 wt% dispersant, 0 wt% surfactant, and the balance being deionized water; and the pH value of the polishing slurry is adjusted to 10 using a pH adjuster.

[0029] Comparative Example 2 The present invention provides an ultra-smooth magnetorheological polishing slurry for suppressing defects on the surface of single-crystal silicon, which is composed of the following raw materials by weight percentage: 2 wt% abrasive, 0 wt% dispersant, 0.1 wt% surfactant, and the balance being deionized water; and the pH value of the polishing slurry is adjusted to 10 using a pH adjuster.

[0030] Comparative Example 3 This invention provides a comparative example of an ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon, composed of the following raw materials by weight percentage: The abrasive is 2 wt%, the dispersant is 0.5 wt%, the surfactant is 0 wt%, and the balance is deionized water; and the pH value of the polishing solution is adjusted to 10 using a pH adjuster.

[0031] The polishing slurries prepared in Examples 1-3 and Comparative Examples 1-3 were used to polish the surface of single-crystal silicon. The specific methods are as follows: S1: Polishing liquid is prepared by rolling and stirring the slurry and carbonyl iron powder at a mass ratio of 1:5.

[0032] S2: Add polishing fluid to the magnetorheological polishing machine and perform magnetorheological polishing on the fixed single crystal silicon surface. The flow rate of the polishing fluid is 1200 mL / min, the immersion depth is 0.25 mm, the rotation speed of the polishing wheel is 120 rpm, and the travel speed of the polishing wheel is 1500 mm / min until an ultra-smooth silicon wafer is obtained.

[0033] Figures 1-3 The images show the surface roughness of single-crystal silicon after magnetorheological polishing using the polishing slurry prepared in Example 1, images captured by a white light interferometer, and damage conditions. It can be seen that the surface roughness of the polishing slurry prepared in Example 1 did not deteriorate significantly after multiple polishing cycles, and the depth of the polishing scratches gradually decreased with the increase of polishing cycles.

[0034] Figure 4 and Figure 5 The images shown are the surface roughness of single-crystal silicon after magnetorheological polishing using the polishing slurry prepared in Comparative Example 1 and images taken by a white light interferometer. It can be seen that the surface roughness of the polishing slurry prepared in Comparative Example 1 deteriorates significantly after multiple polishing cycles, and with the increase of polishing cycles, obvious scratches appear on the surface, indicating severe surface damage.

[0035] Figure 6 The actual particle size of the cerium oxide abrasive particles in the magnetorheological polishing slurry of Example 1 and Comparative Examples 1-4 is shown. It can be seen that in Example 1 of the present invention, due to the addition of dispersant gluconic acid compound, dispersant stabilizer, and surfactant, effective dispersion of small-sized cerium oxide abrasive particles is achieved. Therefore, the actual particle size of the cerium oxide abrasive particles in the polishing slurry is much larger than that of Examples 1-3. Combined with... Figures 1-5 The data shows that the polishing slurry prepared in the embodiments of the present invention can significantly reduce the number of scratches and pits, reduce surface damage, obtain better roughness, and thus effectively improve the polishing effect.

[0036] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon, characterized in that, It includes the following components: Nano-cerium oxide with a particle size of 50 nm, dispersant, dispersion stabilizer, surfactant and pH adjuster.

2. The ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon according to claim 1, characterized in that, The mass fractions of each component are as follows: The composition consists of 1-3 wt% nano-cerium oxide, 0-1 wt% dispersant, 0.1-2 wt% dispersion stabilizer, 0-0.5 wt% surfactant, 0.1-2 wt% pH adjuster, and the balance being water.

3. The ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon according to claim 1, characterized in that, The dispersant is sodium gluconate and / or potassium gluconate.

4. The ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon according to claim 1, characterized in that, The dispersion stabilizers are often polyphosphates and / or citrates.

5. The ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon according to claim 1, characterized in that, The surfactant is one or more of sodium lauryl sulfonate, sodium stearate, and sodium dodecylbenzene sulfonate.

6. The ultra-smooth magnetorheological polishing slurry for suppressing surface defects in single-crystal silicon according to claim 1, characterized in that, The pH adjuster is one or more of glycine, citric acid, sodium hydroxide, and potassium hydroxide.

7. A method for ultra-smooth magnetorheological polishing to suppress surface defects in single-crystal silicon, characterized in that, Includes the following steps: S1, a polishing liquid is prepared by rolling and stirring the polishing slurry according to any one of claims 1 to 6 and carbonyl iron powder; S2, add the polishing liquid to the magnetorheological polishing machine tool, and perform magnetorheological polishing on the fixed single crystal silicon surface until an ultra-smooth silicon wafer is obtained.

8. The ultra-smooth magnetorheological polishing method for suppressing surface defects in single-crystal silicon according to claim 7, characterized in that, In polishing machines, the polishing wheel rotates at a speed of 100~200 rpm.

9. The ultra-smooth magnetorheological polishing method for suppressing surface defects in single-crystal silicon according to claim 7, characterized in that, The flow rate of the polishing fluid is 1000~1500 mL / min, the immersion depth is 0.2~0.4 mm, and the travel speed of the polishing wheel is 1000~2000 mm / min.

10. The ultra-smooth magnetorheological polishing method for suppressing surface defects in single-crystal silicon according to claim 9, characterized in that, The polishing fluid flow rate is 1200 mL / min, the immersion depth is 0.25 mm, and the polishing wheel travel speed is 1500 mm / min.

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