Fenton reagent, polishing solution, polishing method of diamond substrate, and polished diamond wafer

Abstract

The invention provides a Fenton reagent, a polishing solution, a polishing method of a diamond substrate and a polished diamond wafer. The invention provides a Fenton reagent. The Fenton reagent comprises a hydrogen peroxide solution and a composition containing ferrite, the ferrite-containing composition comprises ferrite, a host molecule and a guest molecule, the host molecule is provided with a hydrophobic cavity for accommodating the guest molecule; the guest molecule has a conjugated pi bond that coordinates with Fe. The Fenton reagent and abrasive particles are adopted as a polishing solution, diamond is polished under irradiation of visible light, stability of the concentration of Fe < 2 + > in the polishing solution can be guaranteed, stable supply of hydroxyl radicals is achieved, and the high-quality diamond surface can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of diamond polishing, and specifically relates to a Fenton reagent, a polishing solution, a polishing method for a diamond substrate, and a diamond polishing sheet. Background Art

[0002] Diamond has excellent thermal conductivity, band gap width, high breakdown voltage, and stable chemical properties. Therefore, it is considered to be the most promising candidate material for next-generation power devices. Low subsurface damage and an ultrasmooth diamond surface are the prerequisites for realizing various excellent properties of diamond. However, as a typical difficult-to-machine material, diamond has extremely high hardness and chemical inertness, which greatly increases the polishing difficulty.

[0003] Currently, the polishing methods for diamond include thermal polishing, dynamic friction polishing, energy beam-assisted polishing methods, and chemical mechanical polishing, etc. However, thermal polishing, dynamic friction polishing, and energy beam-assisted polishing methods have problems such as easy volatilization of the polishing solution and thermal deformation, which are difficult to ensure the machining accuracy and machining quality, and the equipment cost is relatively high. And chemical mechanical polishing technology, as the only technology that can achieve global planarization of the wafer surface in integrated circuit manufacturing currently, can achieve atomic-level flatness. Diamond has extremely high chemical stability, and common oxidants are difficult to chemically react with diamond at room temperature. Currently, Fenton reagent is often used for diamond polishing. The Fenton reagent uses H2O2 to generate hydroxyl radicals (·OH), whose oxidation potential is as high as 2.8V, having strong oxidation ability, and the reaction conditions are mild and can be carried out at room temperature and normal pressure.

[0004] However, in the Fenton reagent, the oxidation rate of Fe 2+ and H2O2 is extremely fast. When it is used for diamond polishing, first, the oxidation rate in the initial stage of the reaction is extremely fast, making it impossible for the polishing process to match the oxidation rate and unable to achieve uniform polishing; second, with the rapid consumption of Fe 2+ , the reaction is difficult to maintain for a long time, making it difficult for polishing to be effectively carried out. The above two situations both make the surface of the diamond substrate uneven, the polishing effect is poor, and it is difficult to control the atomic-level roughness of the diamond surface. In addition, the trivalent iron generated during the reaction can catalyze the decomposition of hydrogen peroxide, accelerating the consumption of hydrogen peroxide, and Fe 3+ will also precipitate in the form of iron hydroxide, thus destroying the stability of the polishing solution. Therefore, in the Fenton reagent, how to better promote the reduction of the generated Fe 3+ to Fe 2+ , ensure the stability of the Fe 2+ concentration in the polishing solution, and achieve a stable supply of hydroxyl radicals is the difficulty in the process of polishing diamond with the Fenton reagent. Summary of the Invention

[0005] To solve the above problems in the prior art, the present invention provides a Fenton reagent, a polishing liquid, a polishing method for a diamond substrate, and a diamond polishing sheet. The present invention provides a Fenton reagent which, in addition to conventional hydrogen peroxide and ferrous salts, further comprises a host molecule and a guest molecule, wherein the guest molecule can catalyze Fe 3+ to be reduced to Fe 2+ . The host molecule has a hydrophobic cavity structure and can serve as a catalyst container for the guest molecule. Under the irradiation and catalysis of a light source, the conversion of Fe 3+ to Fe 2+ is completed through the cavity confinement effect of the host molecule, maintaining the stability of the Fe 2+ concentration in the system. The present invention uses a polishing liquid formed by a Fenton reagent as an oxidant and abrasive particles. The modified Fenton reagent can effectively control the stability of the Fe 2+ concentration in the polishing liquid system, realizing a stable and continuous supply of hydroxyl radicals, so that when the polishing liquid polishes diamond, a high-quality diamond surface can be obtained.

[0006] In a first aspect, the present invention provides a Fenton reagent, which includes a hydrogen peroxide solution and a composition containing a ferrous salt; The composition containing a ferrous salt includes: a ferrous salt, a host molecule, and a guest molecule; The host molecule has a hydrophobic cavity for accommodating the guest molecule; The guest molecule has a conjugated π bond for coordinating with Fe.

[0007] Specifically, in the present invention, the diameter of the hydrophobic cavity is greater than the diameter of the guest molecule.

[0008] Specifically, the solvent of the Fenton reagent in the present invention is water.

[0009] The Fenton reagent provided by the present invention contains a host molecule with a cavity structure and a guest molecule that can catalyze the reduction of Fe 3+ to Fe 2+ . The hydrophobic cavity of the host molecule can accommodate the guest molecule. Under the irradiation and catalysis of a light source, through the cavity confinement effect of the host molecule, the hydroxyl radicals generated by hydrogen peroxide are prevented from attacking the guest molecule, and the process of the guest molecule catalyzing Fe 3+ to Fe 2+ is completed. Specifically, the Fenton reagent uses H2O2 to react with Fe 2+ to generate hydroxyl radicals. Under the excitation of light source irradiation, the guest molecule forms a radical intermediate through the conjugated π bond. The radical intermediate coordinates with iron, and then the radical intermediate, as an electron donor, transfers an electron to Fe³⁺ in the form of forming a complex, reducing Fe 3+ to Fe 2+. However, the hydroxyl radicals generated by the Fenton reagent have strong oxidizing effects, which will attack the guest molecules and inactivate them, thus affecting their reduction of Fe 3+ to Fe 2+ . Therefore, it is necessary to introduce a host molecule with a cavity structure, and the cavity size should be slightly larger than the size of the guest molecule, so as to coat the guest molecule to form a host-guest complex, providing a micro-reaction space for the reduction of Fe 3+ . The generation of hydroxyl radicals occurs in the bulk solution, and their lifetime in the liquid phase is extremely short (nanosecond level), and they are quenched before diffusing into the cavity.

[0010] As a specific embodiment of the present invention, the molar ratio of ferrous salt, host molecule and guest molecule in the composition containing ferrous salt is (1:0.1~10:0.1~10), preferably (1:0.5~5:0.5~5).

[0011] As a specific embodiment of the present invention, in the Fenton reagent, the molar ratio of hydrogen peroxide to ferrous salt in the hydrogen peroxide solution is 1~100:1, preferably 3~20:1.

[0012] As a specific embodiment of the present invention, the content of hydrogen peroxide in the hydrogen peroxide solution is 7wt%~30wt%.

[0013] As a specific embodiment of the present invention, the ferrous salt is selected from one or more of ferrous chloride, ferrous nitrate, ferrous acetate, ferrous sulfate, ferrous carbonate, ferrous oxalate, ferrous phosphate, ammonium ferrous sulfate.

[0014] As a specific embodiment of the present invention, the composition containing ferrous salt includes a promoter, and the promoter is selected from transition metal salts other than ferrous salts. The promoter is preferably selected from one or more of copper salts, manganese salts, chromium salts, cobalt salts, nickel salts, vanadium salts, molybdenum salts.

[0015] In the Fenton reagent of the present invention, the promoter can cooperate with the ferrous salt to accelerate the generation of hydroxyl radicals, thereby improving the polishing efficiency when polishing diamond.

[0016] As a specific embodiment of the present invention, the molar ratio of ferrous salt, promoter, host molecule and guest molecule in the composition containing ferrous salt is (1:0.1~1:0.1~10:0.1~10), preferably (1:0.5~1:0.5~5:0.5~5).

[0017] As a specific embodiment of the present invention, the host molecule is selected from one or more of cyclodextrin, calixarene, pillararene, crown ether, cucurbituril, zeolite, metal-organic framework material, covalent organic framework material, porous organic cage, mesoporous material.

[0018] As a specific embodiment of the present invention, the guest molecule is selected from one or more of catechol, hydroquinone, naphthol, gallic acid, chrysophanol, 2,5-dihydroxy-1,4-benzoquinone, 1,4-dihydroxyanthraquinone, 2-hydroxy-1,4-naphthoquinone, 1,8-dihydroxyanthraquinone, 5,8-dihydroxy-1,4-naphthoquinone, 1,2-dihydroxyanthraquinone, and 1,4,5,8-tetrahydroxyanthraquinone.

[0019] In a second aspect, the present invention provides a polishing liquid, which comprises abrasive particles and the Fenton reagent provided in the first aspect of the present invention. The Fenton reagent provided by the present invention ensures the stability of the Fe 2+ concentration in the polishing liquid, realizes the stable supply of hydroxyl radicals, and can obtain a high-quality diamond surface when polishing diamond.

[0020] As a specific embodiment of the present invention, the polishing liquid comprises liquid A and liquid B. Liquid A comprises abrasive particles and a composition containing ferrous salt, and liquid B is a hydrogen peroxide solution. The volume ratio of liquid A to liquid B is 90-110:5, preferably 95-105:5.

[0021] As a specific embodiment of the present invention, liquid A further comprises one or more of a dispersant, a suspending agent, a lubricant, and an antifoaming agent.

[0022] As a specific embodiment of the present invention, based on the total mass of liquid A, liquid A comprises: 0.01 wt% - 10 wt% of abrasive particles, 0.01 wt% - 10 wt% of the composition containing ferrous salt, 0.01 wt% - 5 wt% of the dispersant, 0.01 wt% - 5 wt% of the suspending agent, 0.01 wt% - 5 wt% of the lubricant, 0.01 wt% - 5 wt% of the antifoaming agent, and the balance is water.

[0023] As a specific embodiment of the present invention, the particle size of the abrasive particles is 30 nm - 800 nm.

[0024] As a specific embodiment of the present invention, the oxidation-reduction potential (OPR value) of the polishing liquid is 550 - 650 mV.

[0025] As a specific embodiment of the present invention, the pH value of the polishing liquid is 2 - 6, preferably 3 - 5.

[0026] As a specific embodiment of the present invention, the abrasive particles are selected from any one of diamond, alumina, silica, cerium oxide, zirconium oxide, silicon nitride, and boron nitride.

[0027] As a specific embodiment of the present invention, the dispersant is selected from one or more of sodium citrate, sodium lactate, triethanolamine, alkyl ammonium oxide, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, alkyl alcohol amide, sodium hexametaphosphate, sodium phosphate, sodium polyphosphate, and silicate.

[0028] As a specific embodiment of the present invention, the suspending agent is selected from one or more of hydroxyethyl cellulose, sodium carboxymethyl cellulose, bentonite, sodium alginate, sodium polyacrylate, polyacrylamide, polyurethane resin, carbomer resin, and modified polyurea.

[0029] As a specific embodiment of the present invention, the lubricant is selected from one or more of methanol, ethanol, ethylene glycol, glycerol, diethylene glycol, polyethylene glycol, polyvinylpyrrolidone, polyethylene oxide, and glycerin.

[0030] As a specific embodiment of the present invention, a pH regulator is used to adjust the pH value of the polishing liquid, and the pH regulator is selected from one or more of sulfuric acid, nitric acid, hydrochloric acid, formic acid, oxalic acid, citric acid, or salts that hydrolyze to be acidic.

[0031] Specifically, the salts that hydrolyze to be acidic are selected from one or more of aluminum sulfate, aluminum nitrate, and aluminum chloride.

[0032] As a specific embodiment of the present invention, the defoaming agent is an organosilicon defoaming agent.

[0033] In a third aspect, the present invention provides a method for polishing a diamond substrate, which uses a polishing pad in cooperation with a polishing liquid and performs polishing under the irradiation of a light source, and the polishing liquid is the polishing liquid provided in the second aspect of the present invention.

[0034] As a specific embodiment of the present invention, the polishing conditions include: pressure: 0.01~1 MPa, preferably 0.05~0.1 MPa; polishing liquid feed rate: 10~500 mL / min, preferably 30~80 mL / min; wavelength of the light source: 300~700 nm, light intensity of the light source: 10~300 mW / cm².

[0035] As a specific embodiment of the present invention, the polishing pad is located on the polishing disc, and the rotational speed of the polishing disc is 80~120 rpm.

[0036] As a specific embodiment of the present invention, the rotational speed of the grinding head is 20~60 rpm.

[0037] As a specific embodiment of the present invention, the polishing pad is PO-3000.

[0038] In a fourth aspect, the present invention provides a diamond polishing sheet prepared by using the polishing method provided in the third aspect of the present invention.

[0039] As a specific embodiment of the present invention, the roughness of the polishing sheet is 0.08~0.15 nm.

[0040] In the present invention, MRR is also used to characterize the polishing process. MRR refers to the material removal rate, specifically, the amount of material removed from the surface of the workpiece per unit time during the polishing process.

[0041] Compared with the prior art, the present invention has the following beneficial effects.

[0042] The present invention provides a Fenton reagent, which contains a host molecule and a guest molecule. The guest molecule can catalyze the reduction of Fe 3+ to Fe 2+ , and the hydrophobic cavity of the host molecule can accommodate the guest molecule. Under the irradiation and catalysis of a light source, through the cavity confinement effect of the host molecule, the attack of hydroxyl radicals generated by hydrogen peroxide on the guest molecule can be avoided, and the conversion of Fe 3+ to Fe 2+ can be completed, thus solving the problems of too fast consumption of Fe 2+ in the Fenton reagent and non-uniform oxidation rate before and after the reaction.

[0043] The Fenton reagent provided by the present invention, when used as a polishing liquid, can ensure the stability of the Fe 2+ concentration in the polishing liquid and realize the stable supply of hydroxyl radicals. Furthermore, when using the polishing liquid to polish diamond, a smooth, flat and good-polished diamond surface can be obtained.

[0044] The present invention provides a diamond polishing method, which uses the polishing liquid provided by the present invention in combination with a polishing pad for polishing. During the polishing process, the oxidation rate of the polishing liquid is stable and the polishing efficiency is high. Moreover, the polishing method provided by the present invention has a simple and economical scheme and low requirements for equipment.

[0045] Using the polishing liquid and polishing method of the present invention to polish a diamond substrate, the obtained diamond polishing sheet has a flat surface and good polishing effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a surface roughness diagram of the polished diamond in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The present invention will be further described below in conjunction with specific embodiments, but it does not constitute any limitation to the present invention.

[0048] The raw materials used in each embodiment of the present invention are all commercially available. Among them, the abrasive particles are purchased from Nanjing Tianxing New Materials Co., Ltd.; β-cyclodextrin, 2,5-dihydroxy-1,4-benzoquinone, ammonium ferrous sulfate, copper chloride, aluminum sulfate, fatty alcohol polyoxyethylene ether, polyethylene glycol, and glycerol are purchased from Energy Chemical; sodium carboxymethyl cellulose is purchased from Green Micro Nano; The silicone defoamer was purchased from Datian Chemical The hydrogen peroxide solution was purchased from Shanghai Titan Scientific Co., Ltd. Example 1 The polishing liquid comprises the following components: Liquid A: Abrasive particles: polycrystalline diamond abrasive grains with a size of 150 - 250 nm, and the proportion of abrasive particles in Liquid A is 0.5 wt%; Ferrous salt - containing composition: ammonium ferrous sulfate, copper chloride, β - cyclodextrin, 2,5 - dihydroxy - 1,4 - benzoquinone. The molar ratio of ammonium ferrous sulfate, copper chloride, β - cyclodextrin, and 2,5 - dihydroxy - 1,4 - benzoquinone is 1:1:2:2, and the proportion of the ferrous salt - containing composition in Liquid A is 8 wt%; Dispersant: fatty alcohol polyoxyethylene ether, and the proportion of the dispersant in Liquid A is 2.5 wt%; Suspending agent: sodium carboxymethyl cellulose, and the proportion of the suspending agent in Liquid A is 3 wt%; Lubricant: polyethylene glycol, glycerol. The proportion of polyethylene glycol in Liquid A is 2 wt%, and the proportion of glycerol is 3 wt%; Defoamer: silicone defoamer, and the proportion of the defoamer in Liquid A is 0.1 wt%; pH regulator: aluminum sulfate, adjusting the pH value of Liquid A to 4; Balance: deionized water; Liquid B: 7 wt% H2O2 solution, adjusting the pH of Liquid B to 4; In the polishing liquid, the volume ratio of Liquid A to Liquid B is 100:5; The OPR value of the polishing liquid is 650 mV; The diamond substrate was polished using a polishing pad and the polishing liquid. Under the irradiation of visible light, the polishing parameters were a pressure of 50 kPa, a grinding wheel rotation speed of 100 rpm, a grinding head rotation speed of 30 rpm, and a liquid feed rate of 60 mL / min.

[0049] Example 2 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the ferrous salt - containing composition was ammonium ferrous sulfate, copper chloride, β - cyclodextrin, 2,5 - dihydroxy - 1,4 - benzoquinone, and the molar ratio of ammonium ferrous sulfate, copper chloride, β - cyclodextrin, and 2,5 - dihydroxy - 1,4 - benzoquinone was 1:1:1:1, and the OPR value of the polishing liquid was 642 mV. The other conditions were the same as in Example 1.

[0050] Example 3 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the ferrous salt-containing composition was ammonium ferrous sulfate, copper chloride, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone, and the molar ratio of ammonium ferrous sulfate, copper chloride, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone was 1:0.5:0.5:0.5, and the OPR value of the polishing liquid was 638 mV. The remaining conditions were the same as in Example 1.

[0051] Example 4 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the ferrous salt-containing composition was ammonium ferrous sulfate, copper chloride, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone, and the molar ratio of ammonium ferrous sulfate, copper chloride, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone was 1:0.3:2:2, and the OPR value of the polishing liquid was 645 mV. The remaining conditions were the same as in Example 1.

[0052] Example 5 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the ferrous salt-containing composition was ammonium ferrous sulfate, copper chloride, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone, and the molar ratio of ammonium ferrous sulfate, copper chloride, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone was 1:1:2:1, and the OPR value of the polishing liquid was 622 mV. The remaining conditions were the same as in Example 1.

[0053] Example 6 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the ferrous salt-containing composition was ammonium ferrous sulfate, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone, and the molar ratio of ammonium ferrous sulfate, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone was 1:8:8, and the OPR value of the polishing liquid was 560 mV. The remaining conditions were the same as in Example 1.

[0054] Example 7 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the ferrous salt-containing composition was ammonium ferrous sulfate, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone, and the molar ratio of ammonium ferrous sulfate, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone was 1:1:2, and the OPR value of the polishing liquid was 563 mV. The remaining conditions were the same as in Example 1.

[0055] Example 8 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the composition containing ferrous salt was ammonium ferrous sulfate, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone. The molar ratio of ammonium ferrous sulfate, β-cyclodextrin, and 2,5-dihydroxy-1,4-benzoquinone was 2:1:1, and the OPR value of the polishing liquid was 564 mV. Other conditions were the same as in Example 1.

[0056] Comparative Example 1 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the composition containing ferrous salt was ammonium ferrous sulfate, and the OPR value of the polishing liquid was 310 mV. Other conditions were the same as in Example 1.

[0057] Comparative Example 2 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the composition containing ferrous salt was ammonium ferrous sulfate and copper chloride, and the molar ratio of ammonium ferrous sulfate and copper chloride was 1:1, and the OPR value of the polishing liquid was 342 mV. Other conditions were the same as in Example 1.

[0058] Comparative Example 3 The diamond substrate was polished using the same method as in Example 1, except that in the polishing liquid used, the composition containing ferrous salt was ammonium ferrous sulfate, copper chloride, and 2,5-dihydroxy-1,4-benzoquinone, and the molar ratio of ammonium ferrous sulfate, copper chloride, and 2,5-dihydroxy-1,4-benzoquinone was 1:1:2, and the OPR value of the polishing liquid was 280 mV. Other conditions were the same as in Example 1.

[0059] Test Example The surface roughness of the diamond substrates polished in the examples and comparative examples was detected using an atomic force microscope. The roughness results are shown in Table 1, and the removal rate was calculated by weighing the mass before and after polishing. The results are shown in Table 1.

[0060] Table 1 Test Results of Examples and Comparative Examples

[0061] In summary, when using the polishing liquid formed by the Fenton reagent provided by the present invention as an oxidant and abrasive particles to polish diamond, the surface roughness of the polished diamond can reach 0.089 nm. When polishing diamond without using the Fenton reagent of the present invention in Comparative Examples 1 to 3, the roughness of the polished diamond is 0.3 to 0.4 nm. It can be seen that when using the Fenton reagent of the present invention as a polishing liquid to polish diamond, a smooth and flat diamond surface with good polishing effect can be obtained. And when the polishing liquid in Examples 1 to 5 contains a promoter, the MRR in the polishing stage is 750 to 820 nm / min, and the polishing efficiency is relatively high. When the Fenton reagent in the polishing liquid in Examples 6 to 8 does not contain a promoter, the MRR in the polishing stage drops to 420 to 632 nm / min. This shows that using a promoter in the Fenton reagent of the polishing liquid can improve the polishing efficiency. However, even if the polishing liquid provided by the present invention does not use a promoter and is used to polish diamond, the polishing efficiency is still much higher than that without using the Fenton reagent of the present invention.

[0062] It should be noted that the above-described embodiments are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described by referring to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words rather than limiting words. Modifications can be made to the present invention within the scope of the claims of the present invention as provided by regulations, and the present invention can be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein. On the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A Fenton reagent, characterized in that, The Fenton's reagent includes a hydrogen peroxide solution and a composition containing ferrous salts; The composition containing ferrous salts includes: ferrous salts, host molecules and guest molecules; The host molecules have hydrophobic cavities for accommodating guest molecules; The guest molecules have conjugated π-bonds coordinated with Fe; 2. The Fenton's reagent according to claim 1, characterized in that, In the composition containing ferrous salts, the molar ratio of ferrous salts, host molecules and guest molecules is (1: 0.1-10: 0.1-10); And / or, in the Fenton's reagent, the molar ratio of hydrogen peroxide to the ferrous salts in the hydrogen peroxide solution is 1-100: 1; And / or, the hydrogen peroxide content in the hydrogen peroxide solution is 7 wt% - 30 wt%; 3. The Fenton's reagent according to claim 1 or 2, characterized in that, The ferrous salts are selected from one or more of ferrous chloride, ferrous nitrate, ferrous acetate, ferrous sulfate, ferrous carbonate, ferrous oxalate, ferrous phosphate, ammonium ferrous sulfate; And / or, the composition containing ferrous salts further includes a promoter, and the promoter is selected from transition metal salts other than ferrous salts; And / or, in the composition containing ferrous salts, the molar ratio of ferrous salts, promoter, host molecules and guest molecules is (1: 0.1-1: 0.1-10: 0.1-10); And / or, the host molecules are selected from one or more of cyclodextrin, calixarene, pillararene, crown ether, cucurbituril, zeolite, metal-organic framework material, covalent organic framework material, porous organic cage, mesoporous material; And / or, the guest molecules are selected from one or more of catechol, hydroquinone, naphthol, gallic acid, chrysophanol, 2,5-dihydroxy-1,4-benzoquinone, 1,4-dihydroxyanthraquinone, 2-hydroxy-1,4-naphthoquinone, 1,8-dihydroxyanthraquinone, 5,8-dihydroxy-1,4-naphthoquinone, 1,2-dihydroxyanthraquinone, 1,4,5,8-tetrahydroxyanthraquinone; 4. A polishing liquid, characterized in that, The polishing liquid includes: abrasive particles and the Fenton's reagent according to any one of claims 1-3; 5. The polishing liquid according to claim 4, characterized in that, The polishing liquid includes liquid A and liquid B. Liquid A includes abrasive particles and a composition containing ferrous salts, and liquid B is a hydrogen peroxide solution. The volume ratio of liquid A to liquid B is 90-110: 5; 6. The polishing liquid according to claim 5, characterized in that, Liquid A further includes one or more of a dispersant, a suspending agent, a lubricant, and an antifoaming agent; 7. The polishing liquid according to claim 6, wherein Based on the total mass of liquid A, liquid A includes: 0.01 wt% - 10 wt% of abrasive particles, 0.01 wt% - 10 wt% of a composition containing ferrous salts, 0.01 wt% - 5 wt% of a dispersant, 0.01 wt% - 5 wt% of a suspending agent, 0.01 wt% - 5 wt% of a lubricant, 0.01 wt% - 5 wt% of an antifoaming agent, and the balance is water; 8. The polishing liquid according to any one of claims 5 to 7, characterized in that, The particle size of the abrasive particles is 30 nm - 800 nm; And / or, the redox potential of the polishing liquid is 550-650 mV; And / or, the pH value of the polishing liquid is 2-6; 9. The polishing liquid according to claim 6 or 7, wherein The abrasive particles are selected from any one of diamond, alumina, silica, cerium oxide, zirconium oxide, silicon nitride, and boron nitride; And / or, the dispersant is selected from one or more of sodium citrate, sodium lactate, triethanolammonium, alkyl ammonium oxide, fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, alkyl alcohol amide, sodium hexametaphosphate, sodium phosphate, sodium polyphosphate, and silicate; And / or, the suspending agent is selected from one or more of hydroxyethyl cellulose, sodium carboxymethyl cellulose, bentonite, sodium alginate, sodium polyacrylate, polyacrylamide, polyurethane resin, carbopol resin, and modified polyurea; And / or, the lubricant is selected from one or more of methanol, ethanol, ethylene glycol, glycerol, diethylene glycol, polyethylene glycol, polyvinylpyrrolidone, polyethylene oxide, and glycerin; And / or, the pH of the polishing liquid is adjusted using a pH adjuster, and the pH adjuster is selected from one or more of sulfuric acid, nitric acid, hydrochloric acid, formic acid, oxalic acid, citric acid, or salts that hydrolyze to be acidic; And / or, the defoaming agent is a silicone defoaming agent.

10. A polishing method for a diamond substrate, characterized in that, Polishing is carried out using a polishing pad in combination with the polishing liquid under the irradiation of light from a light source, and the polishing liquid is the polishing liquid according to any one of claims 4 to 9.

11. The polishing method according to claim 10, wherein The conditions for the polishing include: pressure: 0.01~1 MPa; The liquid feed rate of the polishing liquid: 10~500 mL / min; The wavelength of the light source is: 300~700 nm; The light intensity of the light source: 10~300 mW / cm²; And / or, the polishing pad is located on a polishing disc, and the rotational speed of the polishing disc is 80~120 rpm.

12. A diamond polishing disc, characterized in that, Prepared by using the polishing method according to claim 10 or 11.

13. The diamond polishing sheet according to claim 12, wherein, The roughness of the diamond polishing sheet is 0.08~0.15 nm.

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