Method for preparing silicon nitride from silicon wafer cutting waste

Abstract

The invention provides a method for preparing silicon nitride from silicon wafer cutting waste, which comprises the following steps: acid washing: adding waste silicon sludge generated by silicon wafer cutting into a mixed acid solution, stirring, filtering, and washing with water to be neutral; drying: drying the silicon sludge subjected to acid pickling to constant weight to obtain a silicon powder raw material; and nitriding: mixing the silicon powder raw material, silicon nitride and a diluent, introducing nitrogen-containing non-oxidizing gas under the condition of oxygen isolation, and heating for nitriding to obtain the silicon nitride powder. The method comprises the following steps: pickling silicon sludge to remove most impurities, drying to obtain a silicon powder raw material, mixing the silicon powder raw material with silicon nitride and a diluent, providing a nucleation point by silicon nitride, reducing the nitridation temperature by the diluent as a nitrogen source, and nitriding by using a nitrogen-containing non-oxidizing gas as a nitrogen source to obtain high-purity silicon nitride powder.

Description

Technical Field

[0001] This application relates to the field of silicon nitride preparation technology, and in particular to a method for preparing silicon nitride from silicon wafer cutting waste. Background Technology

[0002] Silicon nitride (Si3N4) is an important engineering ceramic material with excellent mechanical, thermal, and chemical properties. It possesses high strength, high toughness, and good wear resistance, and can operate stably at temperatures exceeding 1000°C. Furthermore, silicon nitride is an excellent electrical insulator and exhibits high resistance to chemical corrosion. Due to its multifunctional properties, silicon nitride is widely used in ceramic bearings, burners, semiconductor manufacturing, and other fields, making it an indispensable material in industry and technology.

[0003] Currently, the main methods for synthesizing silicon nitride powder include thermal decomposition, gas-phase reaction, sol-gel method, co-precipitation, and mechanical synthesis. Thermal decomposition utilizes high temperatures to decompose nitrogen- and silicon-containing compounds to generate silicon nitride powder. This method often requires high-temperature reaction conditions, resulting in high energy consumption, and controlling particle size and distribution is difficult. Gas-phase reaction involves the reaction of a silicon source in a nitrogen atmosphere at high temperatures to generate silicon nitride; however, it requires strict reaction conditions and has high equipment costs. The sol-gel method involves forming a silicon nitride sol in solution through a chemical reaction, followed by gelation and calcination to obtain silicon nitride powder. This method has a complex preparation process, requires precise control of the gelation process and calcination conditions, and is costly. The co-precipitation method involves the simultaneous precipitation of nitrogen and silicon sources in solution to form silicon nitride precipitate, which is then further processed to obtain silicon nitride powder. This reaction has high requirements for reaction conditions and solution treatment, making it difficult to control the quality and particle size distribution of the silicon nitride powder. Mechanical synthesis refers to the mixing and reaction of silicon nitride precursor powder using high-energy ball milling or mechanical force to form silicon nitride powder. This process may introduce impurities into the powder and may take a long time, making it unsuitable for large-scale production. Therefore, choosing a suitable method to obtain high-purity silicon nitride powder is of great significance.

[0004] The manufacturing process of photovoltaic silicon wafers typically generates cutting waste—silicon sludge. This waste is often of poor quality and has a low silicon content, and is mostly sold as waste. However, through some purification processes, the purity of the silicon sludge can be improved, making it usable as a raw material for producing high-purity silicon nitride powder. This not only yields a high-value product but also recycles the waste, achieving two goals at once. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing silicon nitride from silicon wafer cutting waste. The method involves adding silicon sludge to a mixed acid solution for acid washing to remove some impurities, drying the sludge, and then mixing the dried silicon powder raw material with silicon nitride and a diluent for nitriding. This method solves the problems of difficult silicon nitride synthesis and the need for repeated use of silicon wafer cutting waste in the prior art.

[0006] To achieve one of the above-mentioned objectives, one embodiment of this application provides a method for preparing silicon nitride from silicon wafer cutting waste, comprising the following steps:

[0007] Pickling: Add the waste silicon sludge generated from silicon wafer cutting to a mixed acid solution, stir, then filter and wash with water until neutral;

[0008] Drying: The acid-washed silica mud is dried to constant weight to obtain silica powder raw material;

[0009] Nitriding: Silicon powder raw material, silicon nitride and diluent are mixed, and nitriding is carried out by heating with a nitrogen-containing non-oxidizing gas in the absence of oxygen to obtain silicon nitride powder.

[0010] As a further improvement of one embodiment of this application, the mixed acid solution includes a hydrofluoric acid solution, the hydrofluoric acid solution accounting for 5 to 10% of the total volume of all substances in the mixed acid solution, and the mass percentage of hydrofluoric acid in the hydrofluoric acid solution is 40%.

[0011] As a further improvement of one embodiment of this application, the mixed acid solution also includes a nitric acid solution, which accounts for 20-40% of the total volume of all substances in the mixed acid solution, with the remainder being water; wherein, the mass percentage of nitric acid in the nitric acid solution is 68%.

[0012] As a further improvement of one embodiment of this application, the diluent is selected from one or more of ammonium acetate, ammonium carbonate, ammonium bicarbonate, ammonia, and ammonium chloride.

[0013] As a further improvement of one embodiment of this application, the amount of the diluent added is 1 to 10% of the silicon powder raw material by weight percentage.

[0014] As a further improvement of one embodiment of this application, the nitriding temperature is 1000-1500°C and the nitriding time is 8-24 hours.

[0015] As a further improvement of one embodiment of this application, the amount of silicon nitride added is 2 to 10% of the silicon powder raw material by weight percentage.

[0016] As a further improvement of one embodiment of this application, the nitrogen-containing non-oxidizing gas is selected from one or two of nitrogen and ammonia.

[0017] As a further improvement of one embodiment of this application, the nitrogen-containing non-oxidizing gas is a mixture of nitrogen and ammonia, and the volume percentage of nitrogen is 70-90%.

[0018] As a further improvement of one embodiment of this application, in the drying step, the drying atmosphere is a vacuum or an inert atmosphere, the drying temperature is 60-100°C, and the drying time is 5-10 hours.

[0019] One or more technical solutions provided in this application have at least the following technical effects or advantages:

[0020] The method for preparing silicon nitride from silicon wafer cutting waste provided in this application involves adding silicon sludge to a mixed acid solution for acid washing to remove some impurities from the silicon sludge, drying it, and then mixing the dried silicon powder raw material with silicon nitride and a diluent. The silicon nitride provides nucleation sites, and the nitrogen source in the diluent and the nitrogen source in the nitriding atmosphere are used for nitriding to obtain high-purity silicon nitride powder. Detailed Implementation

[0021] The present invention will be described in detail below with reference to specific embodiments, but these embodiments do not limit the present invention. Any changes in reaction conditions, reactants or raw material amounts made by those skilled in the art based on these embodiments are included within the protection scope of the present invention.

[0022] This application provides a method for preparing silicon nitride from silicon wafer cutting waste, including the following steps:

[0023] Pickling: Add the waste silicon sludge generated from silicon wafer cutting to a mixed acid solution, stir, then filter and wash with water until neutral;

[0024] Drying: The acid-washed silica mud is dried to constant weight to obtain silica powder raw material;

[0025] Nitriding: Silicon powder raw material, silicon nitride and diluent are mixed, and nitriding is carried out by passing a nitrogen-containing non-oxidizing gas in the absence of oxygen to obtain silicon nitride powder.

[0026] The silica sludge produced during silicon wafer cutting typically has a moisture content of 40-45%. Before drying, the silica sludge is first added to a mixed acid solution for acid washing to remove some impurities. It is then washed with water until neutral to prevent the acid in the mixed acid solution from adhering to the silicon surface during drying and introducing new impurities. Adding silicon nitride to the mixture participating in the nitriding reaction provides nucleation sites for silicon nitride in the silicon powder raw material, thus facilitating the nitriding process. Nitriding is performed in the absence of oxygen to prevent silicon oxidation and the formation of silicon oxide. Both the diluent and nitrogen-containing non-oxidizing gases serve as nitrogen sources, and the diluent also lowers the nitriding temperature, saving energy.

[0027] In some embodiments, the mixed acid solution includes a hydrofluoric acid solution, which accounts for 5-10% of the total volume of all substances in the mixed acid solution, and the mass percentage of hydrofluoric acid in the hydrofluoric acid solution is 40%. Hydrofluoric acid can react with silicon oxide in the silica sludge to form water-soluble silicon tetrafluoride, which is carried away with the water during washing, thus removing the silicon oxide from the silica sludge. Furthermore, some metallic impurities in the silica sludge can also be removed by reacting with hydrofluoric acid.

[0028] In some embodiments, the mixed acid solution further comprises a nitric acid solution, which accounts for 20-40% of the total volume of all substances in the mixed acid solution, with the remainder being water; wherein the mass percentage of nitric acid in the nitric acid solution is 68%. That is, the mixed acid solution is a mixture of hydrofluoric acid and nitric acid, with the nitric acid primarily used to remove metal elements from the silica sludge. Of course, in addition to hydrofluoric acid, the acid in the mixed acid solution can also be one or more selected from nitric acid, hydrochloric acid, and sulfuric acid.

[0029] In some embodiments, the diluent is selected from one or more of ammonium acetate, ammonium carbonate, ammonium bicarbonate, ammonia, and ammonium chloride. The diluent serves as a nitrogen source and also lowers the nitriding temperature, thereby reducing energy consumption. Besides nitrogen, ammonium acetate, ammonium carbonate, ammonium bicarbonate, ammonia, and ammonium chloride contain elements such as carbon and hydrogen, which allows them to decompose at high temperatures, preventing the diluent from introducing new impurities.

[0030] In some embodiments, the amount of diluent added is 1 to 10% of the silicon powder raw material by weight percentage. The diluent is not the main nitrogen source, and its proportion does not need to be very high. Among the silicon powder raw material, silicon nitride and diluent, the silicon powder raw material is the main raw material, silicon nitride is the nucleation site, and the diluent and nitrogen-containing non-oxidizing gas are used as nitrogen sources to synthesize silicon nitride powder.

[0031] In some embodiments, the nitriding temperature is 1000–1500°C and the nitriding time is 8–24 h.

[0032] In some embodiments, the amount of silicon nitride added is 2 to 10% of the silicon powder raw material by weight. Since silicon nitride forms nucleation sites during the nitriding reaction of silicon powder raw material, its content can be relatively low.

[0033] In some embodiments, the nitrogen-containing non-oxidizing gas is selected from one or both of nitrogen and ammonia. Nitrogen and ammonia, as nitrogen-containing gases, can serve as excellent nitrogen sources to participate in nitriding reactions.

[0034] In some embodiments, the nitrogen-containing non-oxidizing gas is a mixture of nitrogen and ammonia, with nitrogen accounting for 70-90% of the volume. Since nitrogen contains no other impurity elements, using a mixture with a higher nitrogen content is beneficial for the nitriding reaction.

[0035] In some embodiments, during the drying step, the drying atmosphere is a vacuum or an inert atmosphere, the drying temperature is 60–100°C, and the drying time is 5–10 hours. Drying in a vacuum or inert atmosphere can prevent silicon oxidation or other reactions that generate new impurities.

[0036] The technical solution of this application will be further described below with reference to some specific embodiments.

[0037] Example 1

[0038] Acid washing: Add 2.5 kg of silica mud to a mixed acid solution of 10 L of nitric acid solution and hydrofluoric acid solution, wherein the volume ratio of nitric acid solution, hydrofluoric acid solution and water is 4:1:15, the hydrofluoric acid solution contains 40% hydrofluoric acid by mass, and the nitric acid solution contains 68% nitric acid by mass. Stir for 2 hours, filter, and wash with water until neutral.

[0039] Drying: The acid-washed silica mud is placed in a vacuum drying oven and dried at 80°C for 8 hours to obtain silica powder raw material.

[0040] Nitriding: Take 1 kg of silicon powder raw material, 20 g of silicon nitride powder and 50 g of ammonium acetate, mix them evenly and put them into a reaction furnace. Then, evacuate the furnace to 1 Pa and perform multiple nitrogen purgings. Finally, introduce nitrogen gas to a pressure of 150 kPa, raise the temperature to 1200℃, react for 10 h, and cool to room temperature to obtain silicon nitride powder.

[0041] The obtained silicon nitride powder has an average particle size of 20 μm, a purity of over 99.9%, and an α phase content of over 98%.

[0042] Example 2

[0043] Acid washing: Add 2.5 kg of silica mud to a mixed acid solution of 10 L of nitric acid solution and hydrofluoric acid solution, wherein the volume ratio of nitric acid solution, hydrofluoric acid solution and water is 4:1:15, the hydrofluoric acid solution contains 40% hydrofluoric acid by mass, and the nitric acid solution contains 68% nitric acid by mass. Stir for 2 hours, filter, and wash with water until neutral.

[0044] Drying: The acid-washed silica mud is placed in a vacuum drying oven and dried at 80°C for 8 hours to obtain silica powder raw material.

[0045] Nitriding: Take 1 kg of silicon powder raw material, 20 g of silicon nitride powder and 50 g of ammonium bicarbonate, mix them evenly and put them into a reaction furnace. Then, evacuate the furnace to 1 Pa and perform multiple nitrogen purgings. Finally, introduce nitrogen gas to a pressure of 150 kPa, raise the temperature to 1350℃, react for 10 h, and cool to room temperature to obtain silicon nitride powder.

[0046] The obtained silicon nitride powder has an average particle size of 20 μm, a purity greater than 99.9%, and a β phase content greater than 85%.

[0047] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0048] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing silicon nitride from silicon wafer cutting waste, characterized in that, Includes the following steps: Pickling: Add the waste silicon sludge generated from silicon wafer cutting to a mixed acid solution, stir, then filter and wash with water until neutral; Drying: The acid-washed silica mud is dried to constant weight to obtain silica powder raw material; Nitriding: Silicon powder raw material, silicon nitride and diluent are mixed, and nitriding is carried out by heating with a nitrogen-containing non-oxidizing gas in the absence of oxygen to obtain silicon nitride powder.

2. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 1, characterized in that, The mixed acid solution contains a hydrofluoric acid solution, which accounts for 5-10% of the total volume of all substances in the mixed acid solution, and the mass percentage of hydrofluoric acid in the hydrofluoric acid solution is 40%.

3. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 2, characterized in that, The mixed acid solution also contains nitric acid solution, which accounts for 20-40% of the total volume of all substances in the mixed acid solution, with the remainder being water; among which, the mass percentage of nitric acid in the nitric acid solution is 68%.

4. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 1, characterized in that, The diluent is selected from one or more of ammonium acetate, ammonium carbonate, ammonium bicarbonate, ammonia, and ammonium chloride.

5. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 4, characterized in that, The amount of the diluent added is 1 to 10% of the silicon powder raw material, by weight percentage.

6. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 5, characterized in that, The nitriding temperature is 1000–1500℃, and the nitriding time is 8–24 hours.

7. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 1, characterized in that, The amount of silicon nitride added is 2 to 10% of the silicon powder raw material by weight percentage.

8. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 1, characterized in that, The nitrogen-containing non-oxidizing gas is selected from one or both of nitrogen and ammonia.

9. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 8, characterized in that, Nitrogen-containing non-oxidizing gases are a mixture of nitrogen and ammonia, with nitrogen accounting for 70-90% of the volume.

10. The method for preparing silicon nitride from silicon wafer cutting waste according to claim 1, characterized in that, During the drying process, the drying atmosphere is a vacuum or inert atmosphere, the drying temperature is 60–100℃, and the drying time is 5–10 hours.