4H-SiC chemical mechanical polishing slurry enhanced with Mn oxides based on the KMnO4-Al2O3 system

Abstract

This invention relates to a chemical mechanical polishing slurry for 4H-SiC based on a KMnO4-Al2O3 system, enhanced with Mn oxide. The polishing slurry comprises an oxidant KMnO4, Al2O3 abrasive particles, Mn oxide, a pH adjuster, and deionized water. The concentration of KMnO4 is 0.01–0.1 mol / L, the concentration of Al2O3 abrasive particles is 0.01 wt.%–10 wt.%, the particle size of the Al2O3 abrasive particles is 100 nm–500 nm, the concentration of Mn oxide is 0.01 wt.%–1 wt.%, and the pH value of the 4H-SiC polishing slurry is 7–11. The Mn oxide is one or more of MnO2, Mn2O3, and Mn3O4. This invention solves the problems of low material removal rate, poor surface quality after polishing, and severe corrosion of equipment caused by traditional silicon carbide polishing slurries on 4H-SiC wafers.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide polishing slurries, specifically relating to a Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system and its preparation method. Background Technology

[0002] As the material foundation of the integrated circuit industry, silicon carbide benefits from its wide bandgap (3.26 eV) and high thermal conductivity (4.9 W·cm⁻¹). -1 ·℃ -1 ), larger breakdown electric field (3*10) 6 / V*cm) and a relatively fast electron saturation drift velocity (2.7*10 7 With its superior material properties such as high temperature resistance, high pressure resistance, high frequency resistance, and low energy loss, silicon carbide (SiC) has significant advantages in semiconductor devices requiring high temperature resistance, high pressure resistance, high frequency resistance, and low energy loss. It is widely used in smart grids, rail transportation, photovoltaic power generation, 5G communications, and new energy vehicles. CMP, a polishing technology in semiconductor processing, achieves global wafer planarization through the synergistic effect of chemical etching and mechanical polishing, and has a very important impact on the manufacturing of silicon carbide devices.

[0003] As a typical hard and brittle material, single-crystal silicon carbide has extremely high hardness and strong chemical inertness. In order to meet the manufacturing standards of semiconductor devices and the actual needs of industrial production, extremely high requirements are placed on the processing efficiency and surface quality of silicon carbide substrates. Liang et al. (DOI:10.16553 / j.cnki.issn1000-985x.2015.07.005) used the strong oxidant KMnO4 to perform chemical mechanical polishing on 4H-SiC wafers. The study found that an appropriate concentration of potassium permanganate improved the polishing effect on both the Si and C surfaces of 4H-SiC wafers. Under the condition of pH 3, when the concentration of KMnO4 was 0.3wt%, the roughness Ra of the Si surface of the 4H-SiC wafer after polishing was 0.0946 nm, which achieved atomic-level surface flatness. However, the removal rate of the Si surface of the 4H-SiC wafer was only 0.5 μm / h. Wang Weilei et al. (DOI:10.1149 / 2162-8777 / ac9f66) found that under pH 2.5 conditions, adding ferric nitrate to KMnO4-Al2O3 as a catalyst can increase the material removal rate of 4H-SiC wafers to 1.148 μm / h and reduce the surface roughness Ra from 0.123 nm to 0.110 nm. However, under strongly acidic conditions, polishing 4H-SiC wafers using the KMnO4-Al2O3 system will have a significant corrosive effect on the polishing equipment, seriously affecting its service life. Summary of the Invention

[0004] This invention addresses the shortcomings of current technologies by providing a Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system and its preparation method. Specifically, under weakly alkaline conditions, Mn oxide is added to the KMnO4-Al2O3 system either alone or in combination, achieving a material removal rate of over 1.2 μm / h and a surface roughness Sq of less than 0.3 nm. This solves the problems of low material removal rate, poor surface quality after polishing, and severe corrosion of equipment caused by traditional silicon carbide polishing slurries on the surface of 4H-SiC wafers.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A chemical mechanical polishing slurry for Mn oxide-enhanced 4H-SiC based on the KMnO4-Al2O3 system, wherein the 4H-SiC polishing slurry comprises oxidant KMnO4, Al2O3 abrasive particles, Mn oxide, pH adjuster and deionized water;

[0007] The concentration of the oxidant KMnO4 is 0.01–0.1 mol / L, the concentration of Al2O3 abrasive particles is 0.01 wt.%–10 wt.%, the particle size of Al2O3 abrasive particles is 100 nm–500 nm, the concentration of Mn oxide is 0.01 wt.%–1 wt.%, and the pH value of the 4H-SiC polishing solution is 7–11.

[0008] The Mn oxide is one or more of MnO2, Mn2O3, and Mn3O4;

[0009] Preferably, the molar concentration of the oxidant KMnO4 is 0.025 mol / L.

[0010] Preferably, the Al2O3 abrasive particle content is 2 wt.%.

[0011] Preferably, the particle size of the Al2O3 abrasive particles is 300 nm.

[0012] Preferably, the content of Mn oxide is 0.3 wt.%.

[0013] Preferably, the pH of the 4H-SiC polishing solution is 8.

[0014] Preferably, the pH adjuster is HNO3 or KOH. The present invention does not have any special limitation on the pH adjuster, as long as it can ensure that the pH of the 4H-SiC polishing solution meets the above requirements.

[0015] The preparation method of the Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system includes the following steps:

[0016] Weigh out fixed amounts of oxidant KMnO4, Al2O3 abrasive particles, and Mn oxide, and uniformly disperse them in a fixed amount of deionized water. Adjust the pH value to 7-11 using HNO3 or KOH to obtain the 4H-SiC polishing solution.

[0017] The application of the Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system is used for polishing 4H-SiC substrate materials required in the manufacture of power electronic devices, optoelectronic devices or radio frequency microwave devices.

[0018] The polishing process parameters of the Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system are as follows: polishing machine: SSP-500; polishing slurry flow rate: 10ml / min; polishing head speed: 50r / min; polishing disc speed: 50r / min; pressure: 5.2psi; polishing time: 1h; temperature: 25℃.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] The 4H-SiC polishing slurry of this invention fully utilizes the strong oxidizing power of KMnO4 and the high grinding ability of Al2O3. Simultaneously, it fully leverages the activation characteristics of Mn oxide on KMnO4 and its catalytic properties for redox reactions, further improving the material removal rate of 4H-SiC wafers and enhancing the surface quality of the polished wafers. Specifically, under pH 8 conditions, when MnO2 and Mn3O4 are added to the KMnO4-Al2O3 system in a 3:1 ratio, the polishing effect of the 4H-SiC wafers reaches its optimal level. Compared to the KMnO4-Al2O3 system without additives, the polishing rate of the 4H-SiC wafers increases by 33%, and the surface roughness Sq decreases to below 0.3 nm. This improves processing efficiency, reduces costs, and the improved wafer surface quality further enhances the yield. The 4H-SiC polishing fluid of this invention fully utilizes the relatively mild corrosive ability of the oxidant KMnO4 under weakly alkaline conditions, thereby slowing down the corrosive effect of the oxidant KMnO4 on the equipment, extending the service life of the equipment, and reducing the cost of maintenance and equipment replacement. Attached Figure Description

[0021] Figure 1 The images show the polishing rates and surface roughness results of different 4H-SiC polishing solutions in Examples 1, 2, 3, 4, 5, 6, 7 and Comparative Example 1.

[0022] Figure 2 Images show the surface morphology of different 4H-SiC polishing solutions used in Examples 1, 2, 3, and Comparative Example 1; wherein, Figure 2 (a) is a surface morphology image of Comparative Example 1 after polishing; Figure 2 (b) is an image of the surface morphology after polishing in Example 1; Figure 2 (c) is an image of the surface morphology after polishing in Example 2; Figure 2 (d) is an image of the surface morphology after polishing in Example 3;

[0023] Figure 3 Images show the surface morphology of different 4H-SiC polishing solutions used in Examples 4, 5, 6, and 7; among them, Figure 3 (a) is an image of the surface morphology after polishing in Example 4; Figure 3 (b) is an image of the surface morphology after polishing in Example 5; Figure 3 (c) is an image of the surface morphology after polishing in Example 6; Figure 3 (d) is an image of the surface morphology after polishing in Example 7;

[0024] Figure 4 Images of surface scratches and pits after polishing with different 4H-SiC polishing slurries in Comparative Examples 2 and 3 are shown; among them, Figure 4 (a) is a surface morphology image of Comparative Example 2 after polishing; Figure 4 (b) is a surface morphology image of Comparative Example 3 after polishing; Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0026] Example 1

[0027] The Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system in this embodiment is prepared as follows: 100g of 20wt.% Al2O3 suspension (particle size approximately 300nm) is added, along with 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4), and stirred until homogeneous. Then, 3g of MnO2 is added, and deionized water is added to bring the solution to 1000g. The mixture is stirred until homogeneous, and the pH is adjusted to 8 using 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing slurry.

[0028] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of 4-inch 4H-SiC wafers. The mass of the 4H-SiC wafers before polishing was measured using a Mettler Toledo precision electronic balance (accurate to 0.1 mg). The mass was determined using the formula MRR = (m1 - m2) / (ρ × S × t) × 10. 7 Calculate the polishing rate MRR (nm / h) of the 4H-SiC wafer, where m1 and m2 are the masses (g) of the 4H-SiC wafer before and after polishing, respectively, and ρ is the density of 4H-SiC (3.2 g / cm³). 3 S is the area of ​​the 4H-SiC wafer (81.073 cm²). 2 ),t represents the polishing time (h); the surface morphology of the polished 4H-SiC wafer was tested using atomic force microscopy (AFM, Agilent 5600LS), and the surface roughness Sq (nm) was used as the evaluation standard for the surface quality of the 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was 1176 nm / h, and the surface roughness Sq was 0.258 nm.

[0029] Example 2

[0030] The preparation method of the Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system in this embodiment is as follows: Take 100g of 20wt.% Al2O3 suspension (particle size of about 300nm), add 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4), and stir evenly; then, add 3g of Mn2O3, add deionized water to make the solution to 1000g, stir evenly, and then adjust the pH value to 8 with 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing slurry.

[0031] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was 992 nm / h, and the surface roughness Sq was 0.401 nm.

[0032] Example 3

[0033] The Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system in this embodiment is prepared as follows: 100g of 20wt.% Al2O3 suspension (particle size approximately 300nm) is added, along with 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4), and stirred until homogeneous. Then, 3g of Mn3O4 is added, and deionized water is added to bring the solution to 1000g. The mixture is stirred until homogeneous, and the pH is adjusted to 8 using 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing slurry.

[0034] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was 1030 nm / h, and the surface roughness Sq was 0.342 nm.

[0035] Example 4

[0036] The preparation method of the Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system in this embodiment is as follows: Take 100g of 20wt.% Al2O3 suspension (particle size of about 300nm), add 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4), and stir evenly; then, add 3g MnO2 and 1g Mn3O4, add deionized water to make the solution to 1000g, stir evenly, and then adjust the pH value to 8 with 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing slurry.

[0037] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was 1257 nm / h, and the surface roughness Sq was 0.281 nm.

[0038] Example 5

[0039] The preparation method of the Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system in this embodiment is as follows: Take 100g of 20wt.% Al2O3 suspension (particle size of about 300nm), add 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4), and stir evenly; then, add 3g MnO2 and 1.5g Mn3O4, add deionized water to make the solution to 1000g, stir evenly, and then adjust the pH value to 8 with 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing slurry.

[0040] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was 1141 nm / h, and the surface roughness Sq was 0.295 nm.

[0041] Example 6

[0042] The preparation method of the Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system in this embodiment is as follows: Take 100g of 20wt.% Al2O3 suspension (particle size of about 300nm), add 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4), and stir evenly; then, add 3g MnO2 and 3g Mn3O4, add deionized water to make the solution to 1000g, stir evenly, and then adjust the pH value to 8 with 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing slurry.

[0043] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was 1219 nm / h, and the surface roughness Sq was 0.32 nm.

[0044] Example 7

[0045] The Mn oxide-enhanced 4H-SiC chemical mechanical polishing slurry based on the KMnO4-Al2O3 system in this embodiment is prepared as follows: 100g of 20wt.% Al2O3 suspension (particle size approximately 300nm) is added, along with 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4), and stirred until homogeneous. Then, 3g of MnO2 and 6g of Mn3O4 are added, and deionized water is added to bring the solution to 1000g. The mixture is stirred until homogeneous, and the pH is adjusted to 8 using 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing slurry.

[0046] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was 1292 nm / h, and the surface roughness Sq was 0.452 nm.

[0047] Comparative Example 1

[0048] The 4H-SiC polishing solution of this embodiment is prepared as follows: Take 100g of 20wt.% Al2O3 suspension (particle size of about 300nm), add 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4), and stir evenly; then add deionized water to make the solution 1000g, stir evenly, and then adjust the pH value to 8 with 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing solution.

[0049] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was 941 nm / h, and the surface roughness Sq was 0.567 nm.

[0050] Comparative Example 2

[0051] The 4H-SiC polishing solution of this comparative example is prepared as follows: 100g of 20wt.% Al2O3 suspension (particle size of about 300nm) is taken; then deionized water is added to make the solution 1000g, stirred evenly, and then the pH value is adjusted to 8 with 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing solution.

[0052] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was only 103 nm / h, and the surface of the 4H-SiC wafer had obvious scratches and pits, with a surface roughness Sq of 1.29 nm.

[0053] Comparative Example 3

[0054] The 4H-SiC polishing solution of this comparative example is prepared as follows: Take 80g of 5wt.% KMnO4 solution (containing 0.025mol KMnO4); then add deionized water to make the solution 1000g, stir evenly, and then adjust the pH value to 8 with 30wt.% HNO3 or 30wt.% KOH solution to obtain the 4H-SiC polishing solution.

[0055] The prepared 4H-SiC polishing slurry was used for polishing the Si surface of a 4-inch 4H-SiC wafer. The test results showed that the material removal rate of the 4H-SiC wafer was only 125 nm / h, and the surface roughness Sq was 0.86 nm.

[0056] Based on the above experimental results, it can be found that the synergistic effect of potassium permanganate and alumina is the key to achieving good polishing results for 4H-SiC wafers. Furthermore, the addition of Mn oxides improved the polishing effect of 4H-SiC wafers to varying degrees. The order of the gain effect of the three Mn oxides on the chemical mechanical polishing of 4H-SiC wafers from largest to smallest is: MnO2 > Mn3O4 > Mn2O3. In particular, the addition of MnO2 enabled the 4H-SiC wafers to achieve the best polishing rate (1176 nm / h) and surface roughness (0.258 nm), representing a 24% increase in polishing rate compared to Comparative Example 1 (polishing rate of 941 nm / h). This is because permanganate ions in the solution chemically adsorb with MnO2, and the activated potassium permanganate promotes the redox reaction. In addition, some MnO2 reacts with OH- and O2 in alkaline solution to generate permanganate ions, which to some extent replenishes the consumption of the oxidant potassium permanganate and increases the formation rate of oxidation products on the 4H-SiC wafer surface. These oxidation products lower the chemical bond energy of Si-C, making it a softer layer with much lower hardness than 4H-SiC, which can be more easily removed during chemical mechanical polishing, thus increasing the polishing rate of the 4H-SiC wafer. Simultaneously, some MnO2 hydrolyzes to generate Mn(OH), which reacts with the SiO2 hydrolysis product Si(OH) to form Mn-O-Si-C, forming a protective film on the 4H-SiC wafer surface. This protective film prevents further oxidation of the pits on the 4H-SiC wafer, allowing for uniform removal of surface material and improving the surface quality of the 4H-SiC wafer after polishing. Mn2O3 and Mn3O4 have relatively weak oxidation and catalytic activity; therefore, their addition does not significantly enhance the chemical mechanical polishing (CMP) effect on 4H-SiC wafers compared to MnO2. Furthermore, when MnO2 and Mn3O4 are added to the KMnO4-Al2O3 polishing slurry system in a compound manner, on the one hand, Mn3O4 itself possesses a certain catalytic oxidation ability and can react with O2 in the solution, generating MnO2 that promotes the oxidation reaction of 4H-SiC wafers. However, as the Mn3O4 content increases, it competes with MnO2 for oxidation during the polishing process. Since Mn3O4's oxidation ability and catalytic activity are inferior to MnO2, the polishing rate of 4H-SiC wafers decreases. On the other hand, Mn3O4 enhances the mechanical grinding ability of the polishing slurry, thereby increasing the polishing rate of 4H-SiC wafers, but also leading to a deterioration in the surface quality of the 4H-SiC wafers.Taking into account both the polishing rate and surface quality of 4H-SiC wafers, in Example 4, the MnO2 to Mn3O4 composite ratio of 3:1 resulted in the best polishing effect for the 4H-SiC wafers, with a removal rate of 1257 nm / h and a surface roughness of 0.281 nm.

[0057] The above description is only considered as a preferred embodiment of the present invention. The present invention is not limited to the above embodiments. It should be noted that for those skilled in the art, the present invention can have various changes and modifications without departing from the principles and scope of the present invention, and all such changes and modifications should fall within the scope of the present invention as claimed.

[0058] Matters not covered in this invention are common knowledge.

Claims

1. A Mn oxide synergistic 4H-SiC chemical mechanical polishing liquid based on KMnO4-Al2O3 system, characterized in that, KMnO4 0.5-5.0 g / L Al2O3 0.5-5.0 g / L H2O 100-1000 mL / L pH 2-10 The polishing liquid comprises oxidant KMnO4, Al2O3 abrasive particles, Mn oxide and deionized water, and has a pH value of 7-11; the pH regulator is HNO3 or KOH; The concentration of the oxidant KMnO4 is 0.01-0.1 mol / L, the concentration of the Al2O3 abrasive particles is 0.01 wt.%-10 wt.%, the particle size of the Al2O3 abrasive particles is 100 nm-500 nm, and the concentration of the Mn oxide is 0.01 wt.%-1 wt.%. The Mn oxide is MnO2 and Mn3O4.

2. The Mn oxide synergized 4H-SiC chemical mechanical polishing liquid based on KMnO4-Al2O3 system according to claim 1, characterized in that, The molar concentration of the oxidant KMnO4 is 0.025 mol / L, the content of the Al2O3 abrasive particles is 2 wt.%, the particle size of the Al2O3 abrasive particles is 300 nm, the content of the Mn oxide is 0.3 wt.%, and the pH value of the 4H-SiC polishing liquid is 8.

3. The method for preparing the Mn oxide synergistic 4H-SiC chemical mechanical polishing liquid based on KMnO4-Al2O3 system according to claim 1, characterized in that, The method comprises the following steps: A fixed content of oxidant KMnO4, Al2O3 abrasive particles and Mn oxide are weighed and dispersed in deionized water, and the pH value is adjusted to 7-11 by using HNO3 or KOH to obtain the 4H-SiC chemical mechanical polishing liquid.

4. The use of KMnO4-Al2O3 system based Mn oxide synergistic 4H-SiC chemical mechanical polishing liquid according to claim 1, characterized in that, The 4H-SiC substrate material is used for polishing power electronic devices, optoelectronic devices or radio frequency microwave devices.

5. The use of KMnO4-Al2O3 system based Mn oxide synergistic 4H-SiC chemical mechanical polishing liquid according to claim 4, characterized in that, The polishing process parameters are as follows: a polishing machine: SSP-500; a polishing liquid flow rate: 10 ml / min; a polishing head rotation speed: 50 r / min; a polishing disc rotation speed: 50 r / min; a pressure: 5.2 psi; a polishing time: 1 h; and a temperature: 25 DEG C.

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