A modified cerium oxide polishing liquid for shallow trench isolation and a preparation method thereof

Abstract

The present invention provides a modified cerium oxide polishing liquid for shallow trench isolation and a preparation method thereof. The polishing liquid is mainly prepared from the following raw materials in terms of mass percentage: modified cerium oxide abrasive: 2% - 5%; deionized water: 95% - 98%; wherein the modified cerium oxide abrasive includes cerium oxide abrasive and a sulfonic acid ligand; the sulfonic acid ligand is one or more of L-camphorsulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid or cyclohexane-2-sulfonic acid. In the polishing liquid of the present invention, the polishing liquid is prepared by modifying cerium oxide with a sulfonic acid ligand. The introduction of the sulfonic acid ligand increases the surface activity of cerium oxide, ensures the uniform distribution of the polishing liquid, and greatly improves the selectivity ratio of the polishing liquid to the silicon oxide layer and the silicon nitride layer. Moreover, the introduction of the sulfonic acid ligand can significantly enhance the dispersion of cerium oxide particles in the solution and prevent aggregation.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth materials, and more particularly, relates to a modified cerium oxide polishing liquid for shallow trench isolation and a preparation method thereof. Background Art

[0002] As the semiconductor device manufacturing process shrinks to 3 nm and below nodes, the requirements for process precision and material compatibility in integrated circuit (IC) manufacturing have reached an unprecedented level. In this context, chemical mechanical polishing (CMP) and shallow trench isolation (STI), as the core process steps in chip manufacturing, their technological innovation is directly related to device performance, yield, and cost control. Among them, CMP technology realizes global or local planarization of the wafer surface through the synergistic action of mechanical and chemical effects, providing a uniform substrate for subsequent processes such as lithography and metal wiring; while STI technology forms insulating trenches between devices to isolate leakage current and improve device reliability, especially becoming a key support in three-dimensional architectures such as FinFET and GAA transistors.

[0003] However, traditional polishing liquids used in STI technology can easily cause nano-scratches, increased surface roughness, and lattice defects on silicon wafers due to the synergistic action of mechanical stress and chemical corrosion during the polishing process. At the same time, during the polishing process, both silicon nitride and silicon oxide contained on the silicon wafer surface are removed, thus affecting the performance of the silicon wafer. Therefore, it has become a hot topic to propose a polishing liquid that can balance the removal rates of the silicon oxide layer and the silicon nitride layer and improve the selectivity.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a modified cerium oxide polishing liquid for shallow trench isolation. This polishing liquid modifies cerium oxide with a sulfonic acid ligand, so that the cerium oxide modified by the sulfonic acid ligand can excellently protect silicon nitride in the silicon wafer during the polishing process, so that it can be retained in the silicon wafer as much as possible while removing the silicon oxide contained in the silicon wafer. Furthermore, the selectivity of the polishing liquid for the silicon oxide layer and the silicon nitride layer is improved, and the introduction of the sulfonic acid ligand can enhance the dispersion of cerium oxide particles in the solution, so that the polishing liquid can prevent agglomeration without adding stabilizers, etc., thereby ensuring the uniform distribution of the polishing liquid and improving the polishing effect.

[0006] The second object of the present invention is to provide a preparation method of the above-mentioned modified cerium oxide polishing liquid for shallow trench isolation. The polishing liquid prepared by this preparation method has high stability, is suitable for polishing high-precision components such as semiconductors or optical components, and its preparation process is simple while reducing the use of harmful substances and reducing environmental pollution.

[0007] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0008] A modified cerium oxide polishing liquid for shallow trench isolation is mainly prepared from the following raw materials by mass percentage:

[0009] Modified cerium oxide abrasive; 2% - 5%;

[0010] Deionized water; 95% - 98%;

[0011] Wherein the modified cerium oxide abrasive includes cerium oxide abrasive and a sulfonic acid ligand;

[0012] The sulfonic acid ligand is one or more of L-camphorsulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid or cyclohexane-2-sulfonic acid.

[0013] In the present invention, the cerium oxide is modified by introducing a sulfonic acid ligand, so that it is adsorbed on the surface of the cerium oxide through electrostatic action and effectively changes its surface properties. The modification of the cerium oxide by the sulfonic acid ligand realizes the precise regulation of the CMP polishing performance. Among them, as a functional ligand, the sulfonic acid ligand enhances the dispersibility of the cerium oxide particles in the solution after being introduced into the cerium oxide, prevents aggregation, makes the prepared polishing liquid evenly distributed, and thus improves the polishing effect; moreover, the introduction of the sulfonic acid ligand improves the chemical stability of the polishing liquid and can also extend the service life of the polishing liquid. At the same time, the activity of the surface of the modified cerium oxide particles increases, and the polishing efficiency and quality are significantly improved; and the introduction of the sulfonic acid ligand can significantly increase the dissolution rate of silicon dioxide, so that it can be separated from the silicon wafer as much as possible while protecting the silicon nitride in the silicon wafer well, so as to retain the silicon nitride in the silicon wafer to the greatest extent while removing the silicon dioxide of the silicon wafer as much as possible, so that the silicon wafer can be well applied in the shallow trench isolation technology.

[0014] The effects achieved by the above polishing liquid are due to the fact that the sulfonic acid ligand can form a weak chemical adsorption with the silicon-oxygen bond (Si-O) through its strong polarity, significantly enhancing the interaction between cerium oxide and the surface of silicon dioxide (SiO2). Thus, without damaging the silicon nitride film, the polishing rate of SiO2 is greatly improved. At the same time, after the sulfonic acid ligand binds to cerium oxide, it increases the activity of the polishing liquid towards silicon dioxide while reducing its chemical activity towards silicon nitride, thereby achieving selective polishing well and preferentially removing silicon dioxide in the silicon wafer. Meanwhile, the sulfonic acid ligand is negatively charged, and the combination of the two makes the surface of cerium oxide particles also negatively charged, generating electrostatic repulsion with the negatively charged silicon nitride surface, thus reducing its physical contact and damage to silicon nitride. In addition, the introduction of the sulfonic acid ligand can also significantly increase the polishing rate of the polishing liquid towards silicon dioxide. By adjusting the chemical reaction activity of cerium oxide through the sulfonic acid ligand, its corrosion rate towards silicon dioxide is relatively high while that towards silicon nitride is relatively low, thereby balancing the polishing rates of the two and further retaining silicon nitride in the silicon wafer. Moreover, the polymer chain or steric hindrance effect of the sulfonic acid group can effectively stabilize cerium oxide particles, prevent their agglomeration in the polishing liquid, ensure the uniform dispersion of abrasives and their continuous action on the polishing surface, and effectively reduce local over-polishing or depression defects caused by particle agglomeration. In addition, the sulfonic acid group enhances the chemical stability of cerium oxide through charge repulsion or hydrogen bond interaction, inhibits the dissolution or passivation of cerium oxide particles during the polishing process, and prolongs the service life of the abrasives.

[0015] Preferably, as a further specific embodiment, the ligand is a mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid.

[0016] Preferably, as a further specific embodiment, the mass ratio of the L-camphorsulfonic acid to the cyclohexane-2-sulfonic acid is (1 - 5):(2 - 3).

[0017] Preferably, as a further specific embodiment, the mass ratio of the L-camphorsulfonic acid to the cyclohexane-2-sulfonic acid is 2:3.

[0018] In the present invention, the selection of the sulfonic acid ligand is limited. When the sulfonic acid ligand is selected from one or more of L-camphorsulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid or cyclohexane-2-sulfonic acid, and preferably when the sulfonic acid ligand is a mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid, the achieved effect is excellent. This is because when L-camphorsulfonic acid and cyclohexane-2-sulfonic acid are selected as the sulfonic acid ligand, the synergistic effect of the two can make the sulfonic acid ligand more evenly distributed on the surface of cerium oxide, thereby enhancing the dispersibility. Moreover, both L-camphorsulfonic acid and cyclohexane-2-sulfonic acid are negatively charged on the surface. The mixed use can more effectively adjust the surface charge of cerium oxide particles, enhance the electrostatic repulsion, prevent agglomeration, and the mixture of the two can improve the dispersibility of cerium oxide particles in polar solvents, making the prepared polishing liquid more evenly dispersed and enhancing the polishing effect of the polishing liquid. And the synergistic effect of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid can better improve the surface performance of cerium oxide. In addition, the mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid can more finely adjust the chemical reactivity of cerium oxide, increasing its reactivity to silicon oxide while decreasing its reactivity to silicon nitride. Thus, the modified polishing liquid can selectively remove silicon oxide to protect silicon nitride while significantly increasing the dissolution rate of silicon oxide, enabling it to be separated from the silicon wafer as much as possible while also providing good protection for silicon nitride in the silicon wafer. As a result, silicon nitride in the silicon wafer is retained to the greatest extent while silicon oxide on the silicon wafer is removed as much as possible, enabling the silicon wafer to be well applied in shallow trench isolation technology. And through a series of creative efforts by the inventor, it is found that when a mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid is selected as the sulfonic acid ligand and introduced onto the surface of cerium oxide, the prepared polishing liquid exhibits higher efficiency and better surface quality during the polishing process, and is particularly suitable for shallow trench isolation technology.

[0019] In the present invention, there are certain limitations on the mass ratio between levocamphorsulfonic acid and cyclohexane-2-sulfonic acid. When the mass ratio of the levocamphorsulfonic acid to the cyclohexane-2-sulfonic acid is (1 - 5):(2 - 3), preferably when the mass ratio of the levocamphorsulfonic acid to the cyclohexane-2-sulfonic acid is 2:3, the achieved effect is excellent. This is because the mass ratio between the two can affect their distribution density on the surface of cerium oxide. An appropriate range of ratios can ensure their uniform distribution on the surface of cerium oxide, and the chiral structure of levocamphorsulfonic acid and the cyclic structure of cyclohexane-2-sulfonic acid can achieve good complementarity to optimize the surface modification effect. Too high or too low a mass ratio between the two will affect this effect and thus the modification effect of cerium oxide. At the same time, an appropriate ratio can enhance the selective removal of silica while protecting silicon nitride. Therefore, when the proportion of levocamphorsulfonic acid is too high, it will lead to too high a charge density, which will affect the interaction between the polishing liquid and the surface of the silicon wafer and weaken its protective effect on silicon nitride, affecting the polishing effect; while if the proportion of cyclohexane-2-sulfonic acid is too high, it will reduce the chemical stability of the polishing liquid, causing precipitation and stratification, and will also reduce the overall reaction activity of the polishing liquid, thus affecting the polishing efficiency.

[0020] Preferably, as a further specific embodiment, the mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is (50:1)-(130:1).

[0021] Preferably, as a further specific embodiment, the mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is (50:1)-(100:1).

[0022] Preferably, as a further specific embodiment, the mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is 50:1 or 70:1.

[0023] In the present invention, the mass ratio between the cerium oxide abrasive and the sulfonic acid ligand is limited to a certain extent. When the mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is (50:1)-(130:1), preferably the mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is (50:1)-(100:1), and more preferably the mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is 50:1 or 70:1, the effect that can be achieved is excellent. This is because the mass ratio between the cerium oxide abrasive and the sulfonic acid ligand has an important influence on the modification effect. This ratio determines the distribution density, distribution uniformity and performance of the sulfonic acid ligand on the surface of cerium oxide. The appropriate mass ratio can ensure that the sulfonic acid ligand is evenly distributed on the surface of cerium oxide to avoid local over-density or over-sparseness. The appropriate mass ratio can optimize the charge on the particle surface and increase Strong electrostatic repulsion improves dispersibility and improves interaction with the polishing surface, and an appropriate mass ratio can balance chemical corrosion and mechanical grinding to improve polishing selectivity and efficiency. Therefore, if the mass ratio is too high, that is, there are too many sulfonic acid ligands, it may cause multi-layer adsorption of sulfonic acid ligands on the surface of cerium oxide, and even cause agglomeration between ligand molecules. Too many sulfonic acid ligands may cause uneven charge distribution on the surface of the particles, affecting its interaction with the polishing surface. At the same time, it may also cause the chemical reaction activity of cerium oxide to be too strong, thereby excessive chemical corrosion of the surface of the silicon wafer, affecting the polishing quality; if the mass ratio is too low, that is, there are too few sulfonic acid ligands, the distribution density on the surface of cerium oxide is insufficient, making it unable to effectively cover the surface of cerium oxide, affecting the modification effect, and at the same time causing insufficient chemical reaction activity of cerium oxide, thereby affecting the polishing efficiency.

[0024] In the present invention, since cerium oxide can achieve excellent dispersibility in deionized water after being modified with sulfonic acid ligands, the cerium oxide abrasive in the polishing liquid can achieve better dispersibility without adding additional auxiliary raw materials such as stabilizers, thereby preventing it from agglomerating in the polishing liquid, ensuring that the abrasive is evenly dispersed and continuously acts on the polishing surface, thereby improving the polishing efficiency of the polishing liquid.

[0025] The present invention also provides a method for preparing the modified cerium oxide polishing liquid for shallow trench isolation, comprising the following steps:

[0026] Add cerium nitrate and ammonia water in sequence, stir magnetically for 24-26 hours, react under high temperature and high pressure for 8-10 hours, centrifuge, wash, and freeze-dry to obtain an intermediate;

[0027] The intermediate was then calcined at 600°C for 8 hours to obtain cerium oxide abrasive;

[0028] The cerium oxide abrasive, the sulfonic acid ligand and the deionized water are added in sequence, mixed and stirred evenly, and then ultrasonically dispersed to obtain the product.

[0029] Preferably, as a further specific embodiment, the temperature in the high temperature and high pressure is 120 - 150 °C, and the pressure is 3 MPa - 3.5 MPa.

[0030] In the preparation method of the present invention, through the directional modification of sulfonic acid groups, the surface chemical properties and reactivity of cerium oxide are significantly improved without adding auxiliary raw materials such as stabilizers. This enables it to exhibit stronger targeted adsorption ability for silicon dioxide during the CMP process, thereby achieving a high removal rate of silicon dioxide while maintaining low damage to the silicon nitride film, and ultimately effectively improving the polishing efficiency; the sulfonic acid groups form a stable steric hindrance layer with the surface of cerium oxide through the charge repulsion effect, significantly reducing the van der Waals force between particles, effectively inhibiting the agglomeration phenomenon, and promoting the formation of a uniform dispersion system of cerium oxide abrasives in the polishing liquid, thereby improving the selectivity ratio of silicon dioxide to silicon nitride. The strongly polar hydroxyl groups introduced by the sulfonic acid groups enhance the hydrophilicity of the particle surface, significantly increase the Zeta potential of the dispersion system by forming a dynamic hydration film, effectively delay the particle sedimentation, and further extend the suspension stability time through steric hindrance protection to ensure the continuous high efficiency of the polishing process.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) The present invention provides a modified cerium oxide polishing liquid for shallow trench isolation. This polishing liquid modifies cerium oxide with sulfonic acid ligands, enabling the cerium oxide modified by sulfonic acid ligands to excellently protect silicon nitride in the silicon wafer during the polishing process, so that it can be retained in the silicon wafer as much as possible while removing the silicon dioxide contained in the silicon wafer. Furthermore, the selectivity ratio of the polishing liquid for the silicon dioxide layer and the silicon nitride layer is improved, and the introduction of sulfonic acid ligands can enhance the dispersion of cerium oxide particles in the solution, enabling the polishing liquid to prevent agglomeration without adding stabilizers, etc., thereby ensuring the uniform distribution of the polishing liquid and improving the polishing effect.

[0033] (2) The present invention provides a preparation method of a modified cerium oxide polishing liquid for shallow trench isolation. The polishing liquid prepared by this preparation method has high stability, is suitable for polishing high-precision components such as semiconductor or optical components, and its preparation process is simple while reducing the use of harmful substances and reducing environmental pollution. Description of the Drawings

[0034] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components.

[0035] Wherein, Figure 1: Dynamic light scattering distribution image of a modified cerium oxide polishing liquid for shallow trench isolation;

[0036] Figure 2 : Zeta potential curve image of a modified cerium oxide polishing liquid for shallow trench isolation;

[0037] Figure 3 : Full spectrum distribution image of a modified cerium oxide polishing liquid for shallow trench isolation;

[0038] Figure 4 : S spectrum distribution image of a modified cerium oxide polishing liquid for shallow trench isolation;

[0039] Figure 5 : Ce spectrum distribution image of a modified cerium oxide polishing liquid for shallow trench isolation;

[0040] Figure 6 : X-ray diffraction image of a modified cerium oxide polishing liquid for shallow trench isolation;

[0041] Figure 7 : Dispersion photo image of a modified cerium oxide polishing liquid for shallow trench isolation. Detailed implementation manners

[0042] The technical solutions of the present invention will be clearly and completely described below in conjunction with the detailed implementation manners. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0043] In order to more clearly elaborate on the technical solutions in the present invention, the following will be described in the form of specific embodiments.

[0044] Example 1

[0045] Step 1: Prepare cerium oxide abrasive

[0046] Dissolve cerium nitrate in deionized water. After magnetic stirring for 24 h, cerium nitrate is completely dissolved. Then transfer it to a peristaltic pump, slowly add ammonia water, transfer the solution to a hydrothermal reaction kettle, seal it, and react at 120 °C and 3 MPa for 8 h. After the reaction is completed, centrifuge, wash, and freeze-dry to obtain an intermediate. Then calcine the intermediate at 600 °C for 8 h to obtain the cerium oxide abrasive;

[0047] Step 2: Prepare modified cerium oxide abrasive

[0048] Subsequently, cerium oxide abrasive and L-camphorsulfonic acid were added successively according to the mass ratio of cerium oxide abrasive to sulfonic acid ligand of 50:1, and reacted for 8 h to obtain modified cerium oxide abrasive;

[0049] Step 3: Prepare the polishing liquid

[0050] Mix the above 2 g of modified cerium oxide abrasive and 98 g of deionized water, stir evenly and then disperse ultrasonically to obtain the product.

[0051] Example 2

[0052] Step 1: Prepare cerium oxide abrasive

[0053] Dissolve cerium nitrate in deionized water, stir magnetically for 26 h until cerium nitrate is completely dissolved, then transfer it to a peristaltic pump, slowly add ammonia water, transfer the solution to a hydrothermal reaction kettle, seal it and react at 150 °C and 3.5 MPa for 10 h. After the reaction is completed, centrifuge, wash and freeze-dry to obtain an intermediate, and then calcine the intermediate at 600 °C for 8 h to obtain cerium oxide abrasive;

[0054] Step 2: Prepare modified cerium oxide abrasive

[0055] Subsequently, cerium oxide abrasive and L-camphorsulfonic acid were added successively according to the mass ratio of cerium oxide abrasive to sulfonic acid ligand of 130:1, and reacted for 8 h to obtain modified cerium oxide abrasive;

[0056] Step 3: Prepare the polishing liquid

[0057] Mix the above 5 g of modified cerium oxide abrasive and 95 g of deionized water, stir evenly and then disperse ultrasonically to obtain the product.

[0058] Example 3

[0059] Step 1: Prepare cerium oxide abrasive

[0060] Dissolve cerium nitrate in deionized water, stir magnetically for 25 h until cerium nitrate is completely dissolved, then transfer it to a peristaltic pump, slowly add ammonia water, transfer the solution to a hydrothermal reaction kettle, seal it and react at 120 °C and 3.5 MPa for 8 h. After the reaction is completed, centrifuge, wash and freeze-dry to obtain an intermediate, and then calcine the intermediate at 600 °C for 8 h to obtain cerium oxide abrasive;

[0061] Step 2: Prepare modified cerium oxide abrasive

[0062] Subsequently, cerium oxide and sulfonic acid ligand were added according to the mass ratio of cerium oxide to sulfonic acid ligand of 70:1 and reacted for 8 h to obtain modified cerium oxide abrasive, wherein the sulfonic acid ligand is a mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid in a mass ratio of 2:3;

[0063] Step 3: Prepare the polishing liquid

[0064] Mix the above 5 g of modified cerium oxide abrasive and 95 g of deionized water, stir evenly, and then disperse ultrasonically to obtain the product.

[0065] Subsequently, measure the polishing liquid obtained in this example, and the measurement results are as Figure 1-7 shown, which are respectively the dynamic light scattering distribution image, Zeta potential curve image, full spectrum distribution image, S spectrum distribution image, Ce spectrum distribution image, X-ray diffraction image, and dispersibility comparison image of the polishing liquid;

[0066] Among them, it can be clearly seen from Figure 1 and Figure 2 that the modified cerium oxide abrasive after modification of cerium oxide by sulfonic acid ligand shows excellent dispersibility in deionized water. It can be seen from Figure 1 that compared with the particle size of unmodified cerium oxide, the particle size of cerium oxide modified by sulfonic acid ligand in this invention is significantly smaller in deionized water, and Figure 2 its potential is significantly larger in

[0067] which indicates that it can be evenly dispersed in deionized water and continuously act on the polishing surface; Figures 3-6 From

[0068] Figure 7 it can be seen that during the modification of cerium oxide by sulfonic acid ligand, the structure of cerium oxide itself does not change. The two are mainly connected by charge adsorption above, so that the sulfonic acid ligand is connected to cerium oxide to modify cerium oxide;

[0069] Experimental Example 1 Influence of the selection of sulfonic acid ligand on the performance of the polishing liquid

[0070] The specific implementation steps are the same as those in Example 1, and the difference is to change the type of sulfonic acid ligand;

[0071] Among them, a control group and experimental groups 1-8 are set respectively. The control group is a polishing liquid sample obtained without modifying cerium oxide with sulfonic acid ligand;

[0072] The sulfonic acid ligand used in experimental group 1 is L-camphorsulfonic acid;

[0073] The sulfonic acid ligand used in experimental group 2 is o-toluenesulfonic acid;

[0074] The sulfonic acid ligand used in experimental group 3 is p-toluenesulfonic acid;

[0075] The sulfonic acid ligand used in experimental group 4 is cyclohexane-2-sulfonic acid;

[0076] The sulfonic acid ligands used in Experimental Group 5 were a mixture of L-camphorsulfonic acid and o-toluenesulfonic acid;

[0077] The sulfonic acid ligands used in Experimental Group 6 were a mixture of o-toluenesulfonic acid and p-toluenesulfonic acid;

[0078] The sulfonic acid ligands used in Experimental Group 7 were a mixture of p-toluenesulfonic acid and cyclohexane-2-sulfonic acid;

[0079] The sulfonic acid ligands used in Experimental Group 8 were a mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid;

[0080] Subsequently, the polishing liquids obtained from the control group and Experimental Groups 1-8 were used to chemically mechanically polish silicon oxide and silicon nitride wafers on a CMP polishing table under the same parameters, and the final experimental results are shown in Table 1 below.

[0081] Table 1: Influence of different sulfonic acid ligands on the polishing performance of the polishing liquid

[0082] 。

[0083] As can be seen from the above table, the polishing liquid prepared by modifying cerium oxide by introducing sulfonic acid ligands has excellent effects. This is because the sulfonic acid ligands can form weak chemical adsorption with the silicon-oxygen bond (Si-O) through their strong polarity, significantly enhancing the interaction between cerium oxide and the surface of silicon oxide (SiO2). Thus, without damaging the silicon nitride film, the polishing rate of SiO2 is greatly improved. At the same time, after the sulfonic acid ligands are combined with cerium oxide, the activity of the polishing liquid towards silicon oxide is increased while the chemical activity towards silicon nitride is decreased, thus achieving selective polishing well and preferably removing silicon oxide in the silicon wafer. Meanwhile, the sulfonic acid ligands are negatively charged, and their combination makes the surface of cerium oxide particles also negatively charged, generating electrostatic repulsion with the negatively charged silicon nitride surface, thereby reducing its physical contact and damage to silicon nitride. In addition, the introduction of sulfonic acid ligands can also significantly improve the polishing rate of the polishing liquid for silicon oxide. By adjusting the chemical reaction activity of cerium oxide through sulfonic acid ligands, its corrosion rate for silicon oxide is higher while that for silicon nitride is lower, thus balancing their polishing rates and further retaining silicon nitride in the silicon wafer. Moreover, the polymer chain or steric hindrance effect of the sulfonic acid group can effectively stabilize cerium oxide particles, prevent their agglomeration in the polishing liquid, ensure the uniform dispersion of abrasives and their continuous action on the polishing surface, and effectively reduce local over-polishing or depression defects caused by particle agglomeration. In addition, the sulfonic acid group enhances the chemical stability of cerium oxide through charge repulsion or hydrogen bond action, inhibiting the dissolution or passivation phenomenon of cerium oxide particles during the polishing process and prolonging the service life of the abrasives.

[0084] For the present invention, the selection of the sulfonic acid ligand is limited. When the sulfonic acid ligand is selected from one or more of L-camphorsulfonic acid, o-toluenesulfonic acid, p-toluenesulfonic acid, or cyclohexane-2-sulfonic acid, and preferably when the sulfonic acid ligand is a mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid, the achieved effect is excellent. This is because when L-camphorsulfonic acid and cyclohexane-2-sulfonic acid are mixed as the sulfonic acid ligand, the synergistic effect of the two enables the sulfonic acid ligand to be more evenly distributed on the surface of cerium oxide, thereby enhancing the dispersibility. Moreover, both L-camphorsulfonic acid and cyclohexane-2-sulfonic acid carry negative charges on their surfaces. The mixed use can more effectively adjust the surface charge of cerium oxide particles, enhance the electrostatic repulsion, prevent agglomeration, and the mixture of the two can improve the dispersibility of cerium oxide particles in polar solvents, making the prepared polishing liquid more evenly dispersed and enhancing the polishing effect of the polishing liquid. And the synergistic effect of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid can better improve the surface properties of cerium oxide. In addition, the mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid can more finely adjust the chemical reactivity of cerium oxide, increasing its reactivity with silicon oxide while decreasing its reactivity with silicon nitride. As a result, the modified polishing liquid can selectively remove silicon oxide to protect silicon nitride while significantly increasing the dissolution rate of silicon oxide, enabling it to be separated from the silicon wafer as much as possible while also providing good protection for silicon nitride in the silicon wafer. Thus, silicon nitride in the silicon wafer is retained to the greatest extent while silicon oxide on the silicon wafer is removed as much as possible, enabling the silicon wafer to be well applied in the shallow trench isolation technology. And through a series of creative efforts by the inventors, it is found that when a mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid is selected as the sulfonic acid ligand and introduced onto the surface of cerium oxide, the prepared polishing liquid exhibits higher efficiency and better surface quality during the polishing process, and is particularly suitable for the shallow trench isolation technology.

[0085] Experimental Example 2 Exploration of the mass ratio between L-camphorsulfonic acid and cyclohexane-2-sulfonic acid

[0086] Select Experimental Group 8 in Experimental Example 1 for refinement, and set Experimental Groups 9 - 16 respectively;

[0087] Among them, the mass ratio of L-camphorsulfonic acid to cyclohexane-2-sulfonic acid in Experimental Group 9 is 1:9;

[0088] The mass ratio of L-camphorsulfonic acid to cyclohexane-2-sulfonic acid in Experimental Group 10 is 1:7;

[0089] The mass ratio of L-camphorsulfonic acid to cyclohexane-2-sulfonic acid in Experimental Group 11 is 1:5;

[0090] The mass ratio of L-camphorsulfonic acid to cyclohexane-2-sulfonic acid in Experimental Group 12 is 1:4;

[0091] The mass ratio of levocamphorsulfonic acid to cyclohexane-2-sulfonic acid in experimental group 13 is 1:2;

[0092] The mass ratio of levocamphorsulfonic acid to cyclohexane-2-sulfonic acid in experimental group 14 is 2:3;

[0093] The mass ratio of levocamphorsulfonic acid to cyclohexane-2-sulfonic acid in experimental group 15 is 4:5;

[0094] The mass ratio of levocamphorsulfonic acid to cyclohexane-2-sulfonic acid in experimental group 16 is 1:1;

[0095] Subsequently, the polishing liquids obtained from control group and experimental groups 9 - 16 were used to chemically mechanically polish silicon oxide and silicon nitride wafers on a CMP polishing table under the same parameters. The final experimental results are shown in Table 2 below.

[0096] Table 2 Influence of sulfonic acid ligands with different mass ratios on the polishing performance of the polishing liquid

[0097] 。

[0098] From the data in the above table, it can be seen that when the sulfonic acid ligand is selected as a mixture of levocamphorsulfonic acid and cyclohexane-2-sulfonic acid, the mass ratio between them is also quite important. When the mass ratio of the levocamphorsulfonic acid to the cyclohexane-2-sulfonic acid is (1 - 5):(2 - 3), preferably when the mass ratio of the levocamphorsulfonic acid to the cyclohexane-2-sulfonic acid is 2:3, the achieved effect is excellent. This is because the mass ratio between them can affect their distribution density on the surface of cerium oxide. An appropriate range of ratios can ensure their uniform distribution on the surface of cerium oxide. Moreover, the chiral structure of levocamphorsulfonic acid and the cyclic structure of cyclohexane-2-sulfonic acid can achieve good complementarity, thereby optimizing the surface modification effect. If the mass ratio between them is too high or too low, it will affect this effect and thus affect the modification effect of cerium oxide. At the same time, an appropriate ratio can enhance the selective removal of silicon oxide while protecting silicon nitride. Therefore, when the proportion of levocamphorsulfonic acid is too high, it will lead to too high charge density, which will affect the interaction between the polishing liquid and the silicon wafer surface and weaken its protective effect on silicon nitride, affecting the polishing effect; while if the proportion of cyclohexane-2-sulfonic acid is too high, it will reduce the chemical stability of the polishing liquid, causing precipitation and stratification, and will also reduce the overall reaction activity of the polishing liquid, thus affecting the polishing efficiency.

[0099] Experimental Example 3 Exploration of the mass ratio between sulfonic acid ligand and cerium oxide

[0100] Experimental group 14 in Experimental Example 2 was selected for refinement. Experimental group 14 was used as the control group, and the mass of cerium oxide in Example 14 was 20 g. Experimental groups 17 - 24 were set up;

[0101] In experimental group 17, the mass ratio of cerium oxide to sulfonic acid ligand is 30:1;

[0102] In experimental group 18, the mass ratio of cerium oxide to sulfonic acid ligand is 40:1;

[0103] In experimental group 19, the mass ratio of cerium oxide to sulfonic acid ligand is 50:1;

[0104] In experimental group 20, the mass ratio of cerium oxide to sulfonic acid ligand is 70:1;

[0105] In experimental group 21, the mass ratio of cerium oxide to sulfonic acid ligand is 100:1;

[0106] In experimental group 22, the mass ratio of cerium oxide to sulfonic acid ligand is 120:1;

[0107] In experimental group 23, the mass ratio of cerium oxide to sulfonic acid ligand is 130:1;

[0108] In experimental group 24, the mass ratio of cerium oxide to sulfonic acid ligand is 150:1;

[0109] Subsequently, chemical mechanical polishing of the silicon oxide and silicon nitride wafers was carried out using a CMP polishing table under the same parameters, and the experimental results are shown in Table 3.

[0110] Table 3: Influence of different mass ratios of cerium oxide to sulfonic acid ligand on polishing performance

[0111] .

[0112] As can be seen from the above table, there is a certain limit to the mass ratio between cerium oxide and the sulfonic acid ligand. When the mass ratio of the cerium oxide to the sulfonic acid ligand is (50:1)-(130:1), preferably the mass ratio of the cerium oxide to the sulfonic acid ligand is (50:1)-(100:1), and more preferably the mass ratio of the cerium oxide to the sulfonic acid ligand is 50:1 or 70:1, the effect that can be achieved is excellent. This is because the mass ratio between cerium oxide and the sulfonic acid ligand has an important influence on the modification effect. This ratio determines the distribution density, distribution uniformity and performance of the sulfonic acid ligand on the surface of cerium oxide. The appropriate mass ratio can ensure that the sulfonic acid ligand is evenly distributed on the surface of cerium oxide to avoid local over-density or over-sparseness. The appropriate mass ratio can optimize the charge on the particle surface and enhance the electrostatic discharge. Repellent can improve the dispersibility and improve the interaction with the polishing surface, and the appropriate mass ratio can balance the chemical corrosion and mechanical grinding, and improve the polishing selectivity and efficiency. Therefore, if the mass ratio is too high, that is, there are too many sulfonic acid ligands, it may cause multi-layer adsorption of sulfonic acid ligands on the surface of cerium oxide, and even cause agglomeration between ligand molecules. Too many sulfonic acid ligands may cause uneven charge distribution on the surface of the particles, affecting its interaction with the polishing surface. At the same time, it will also cause the chemical reaction activity of cerium oxide to be too strong, thereby excessive chemical corrosion of the surface of the silicon wafer, affecting the polishing quality; if the mass ratio is too low, that is, there are too few sulfonic acid ligands, the distribution density of sulfonic acid ligands on the surface of cerium oxide will be insufficient, making it impossible to effectively cover the surface of cerium oxide, affecting the modification effect, and at the same time causing insufficient chemical reaction activity of cerium oxide, thereby affecting the polishing efficiency.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified cerium oxide polishing liquid for shallow trench isolation, characterized in that, It is mainly prepared from the following raw materials by mass percentage: Modified cerium oxide abrasive: 2% - 5%; Deionized water: 95% - 98%; Wherein the modified cerium oxide abrasive includes cerium oxide abrasive and sulfonic acid ligand; The sulfonic acid ligand is a mixture of L-camphorsulfonic acid and cyclohexane-2-sulfonic acid; The mass ratio of the L-camphorsulfonic acid to the cyclohexane-2-sulfonic acid is 2:

3.

2. The modified cerium oxide polishing liquid for shallow trench isolation according to claim 1, wherein The mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is (50:1) - (130:1).

3. The modified cerium oxide polishing liquid for shallow trench isolation according to claim 2, wherein The mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is (50:1) - (100:1).

4. The modified cerium oxide polishing liquid for shallow trench isolation according to claim 3, wherein The mass ratio of the cerium oxide abrasive to the sulfonic acid ligand is 50:1 or 70:

1.

5. A method for preparing a modified cerium oxide polishing liquid for shallow trench isolation according to any one of claims 1-4, characterized in that, It includes the following steps: Add cerium nitrate and ammonia water in sequence, magnetically stir for 24 - 26 h, react at high temperature and high pressure for 8 - 10 h, centrifuge, wash, and freeze-dry to obtain an intermediate; Subsequently, calcine the intermediate at 600 °C for 8 h to obtain cerium oxide abrasive; Add the cerium oxide abrasive, sulfonic acid ligand and deionized water in sequence, mix and stir evenly, and then perform ultrasonic dispersion to obtain the product.

6. The preparation method according to claim 5, characterized in that, In the high temperature and high pressure, the temperature is 120 - 150 °C and the pressure is 3 MPa - 3.5 MPa.

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