Continuous titration method for determining the ammonium nitrate content of a silicon etching solution

Abstract

This application provides a continuous titration method for the sulfuric acid and ammonium nitrate content of silicon etching solution. The continuous titration method includes the following steps: weigh m grams of silicon etching solution sample into a sample bottle, add phenolphthalein indicator, titrate with a first sodium hydroxide standard solution of concentration C1 until a pink color is achieved, and record the volume consumed V1. Calculate the sulfuric acid content. Add neutral formaldehyde solution to the same solution and let it stand for a first preset time to generate a free acid solution. Continue titrating the free acid solution with a second sodium hydroxide standard solution of concentration C2 until the solution turns pink. Gently heat the solution to a preset temperature and maintain this temperature for a second preset time. If the pink color persists, the titration endpoint is determined, and the volume consumed V2 is recorded. Calculate the ammonium nitrate content. This method achieves continuous titration of two components with a single sample, eliminates mutual interference between components, optimizes the endpoint determination method, and thus achieves a simple operation, high accuracy, low sample consumption, and high detection efficiency.

Description

Technical Field

[0001] This application belongs to the field of chemical analysis and detection technology, and in particular relates to a continuous titration method for the content of sulfuric acid and ammonium nitrate in silicon etching solution. Background Technology

[0002] Silicon etching solution is a key chemical in semiconductor manufacturing, mainly composed of sulfuric acid, ammonium nitrate, and water. The content of sulfuric acid and ammonium nitrate directly determines the etching rate and etching effect. Accurate measurement of the content of these two components is crucial for the stability of semiconductor manufacturing processes. In the quality control stage of semiconductor manufacturing, rapid and accurate detection of the component content of silicon etching solution is necessary to ensure product yield.

[0003] Currently, the traditional method for determining the content of sulfuric acid and ammonium nitrate in silicon etching solution is to take samples separately and measure them individually. When determining sulfuric acid, the acid-base neutralization titration method using sodium hydroxide standard solution is often used, with phenolphthalein as an indicator to titrate to the endpoint. When determining ammonium nitrate, the formaldehyde method is mainly used, which utilizes the reaction of ammonium nitrate with formaldehyde to generate free acid, and then titrates it with sodium hydroxide standard solution.

[0004] However, this type of method requires multiple sampling, pretreatment, and separate titration of the silicon etching solution. This not only results in cumbersome operation and low detection efficiency, but also increases sample consumption due to multiple sampling. In particular, when sulfuric acid and ammonium nitrate coexist in the solution, the hydrogen ions ionized by sulfuric acid, a strong acid, will cause ionic interference to the formaldehyde method for the determination of ammonium nitrate. The presence of ammonium nitrate will also slightly affect the potential change of acid-base titration, thus interfering with the determination of sulfuric acid.

[0005] In view of this, it is necessary to design a continuous titration method for the sulfuric acid and ammonium nitrate content of silicon etching solution to solve one of the above problems. Summary of the Invention

[0006] This application provides a continuous titration method for the content of sulfuric acid and ammonium nitrate in silicon etching solution. This continuous titration method facilitates the detection of sulfuric acid and ammonium nitrate in silicon etching solution, achieving the effects of simple operation, high accuracy, low sample consumption, and high detection efficiency.

[0007] To achieve the above objectives, the technical solution provided in this application is as follows: This application provides a continuous titration method for determining the sulfuric acid and ammonium nitrate content in a silicon etching solution, wherein the continuous titration method includes the following steps: Weigh m grams of silicon etching solution sample into a sample bottle, add phenolphthalein indicator, titrate with a first sodium hydroxide standard solution of concentration C1 until the solution turns pink, and record the volume V1 of the first sodium hydroxide standard solution consumed. Calculate the sulfuric acid content, and record the solution after titration as the first solution. Add a neutral formaldehyde solution to the first solution and let it stand for a first preset time to allow ammonium nitrate and formaldehyde to react fully to generate a free acid solution; The generated free acid solution is titrated with a second sodium hydroxide standard solution of concentration C2 until the solution turns pink. The solution is then gently heated to a preset temperature and maintained for a second preset time. If the pink color does not fade, the titration endpoint is determined, and the volume of the second sodium hydroxide standard solution consumed, V2, is recorded. The ammonium nitrate content is then calculated.

[0008] Furthermore, the concentration C1 of the first sodium hydroxide standard solution is greater than the concentration C2 of the second sodium hydroxide standard solution.

[0009] Furthermore, the concentration C1 of the first sodium hydroxide standard solution is 0.5 mol / L to 1.5 mol / L, and the concentration C2 of the second sodium hydroxide standard solution is 0.08 mol / L to 0.12 mol / L.

[0010] Furthermore, the added volume V of neutral formaldehyde solution f The ratio of the sample mass m to the sample mass m is (20-40) mL: 1 g.

[0011] Furthermore, the first preset duration is 20-40 minutes.

[0012] Furthermore, the preset temperature is 45℃-55℃, and the second preset duration is 25s-35s.

[0013] Furthermore, the mass m of the silicon etching solution sample was weighed to an accuracy of 0.0001 g, and the burette accuracy for titrating the sodium hydroxide standard solution was 0.01 mL. Furthermore, the formula for calculating the sulfuric acid content is: X1=[(C1*V1*M1) / (2*m*1000)]*100%, Where V1 is in mL, C1 is in mol / L, and M1 is the molar mass of sulfuric acid. Furthermore, the formula for calculating ammonium nitrate is: X2=[(C2*V2*M2) / (m*1000)]*100%, Where V2 is in mL, C2 is in mol / L, and M2 is the molar mass of ammonium nitrate.

[0014] Furthermore, the same silicon etching solution sample was measured twice independently. The relative deviation between the two measurements was no more than 0.1% for sulfuric acid and no more than 0.3% for ammonium nitrate. The arithmetic mean was taken as the final content result.

[0015] Compared with related technologies, the beneficial effects of this application are as follows: by using the continuous titration method of sulfuric acid and ammonium nitrate content in silicon etching solution of this application, the continuous titration of two components can be completed in one sampling, eliminating mutual interference between components and optimizing the titration endpoint determination method, thereby achieving the determination effect of simple operation, high accuracy, low sample consumption and high detection efficiency. Attached Figure Description

[0016] Figure 1 This is a flowchart of a detection method according to an embodiment of the continuous titration method for the content of sulfuric acid and ammonium nitrate in silicon etching solution of this application. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0018] This application provides a continuous titration method for determining the sulfuric acid and ammonium nitrate content in silicon etching solution. The conventional chemical analysis titration apparatus used in this continuous titration method includes: an electronic balance for accurately weighing the sample with an accuracy of 0.0001 g; an alkaline burette for titrating a sodium hydroxide standard solution with an accuracy of 0.01 mL; an Erlenmeyer flask for holding the sample and serving as a reaction vessel; a constant temperature water bath for micro-heating the final titrant; and a dropper for adding an indicator. like Figure 1 As shown, the continuous titration method includes the following steps: Weigh m grams of silicon etching solution sample into a sample bottle, add phenolphthalein indicator, titrate with a first sodium hydroxide standard solution of concentration C1 until the solution turns pink, and record the volume V1 consumed by the first sodium hydroxide standard solution. Calculate the sulfuric acid content, and record the solution after titration as the first solution. Add neutral formaldehyde solution to the first solution, and let it stand for a first preset time to allow ammonium nitrate and formaldehyde to fully react and generate a free acid solution. Continue titrating the generated free acid solution with a second sodium hydroxide standard solution of concentration C2 until the solution turns pink. Gently heat the solution to a preset temperature and maintain this temperature for a second preset time. If the pink color persists, the titration endpoint is determined, and the volume V2 consumed by the second sodium hydroxide standard solution is recorded. Calculate the ammonium nitrate content. This method achieves continuous titration of two components with a single sample, eliminates mutual interference between components, optimizes the titration endpoint determination method, and thus achieves a simple, accurate, low-sample-consumption, and high-detection-efficiency measurement effect.

[0019] Understandably, the contents of sulfuric acid and ammonium nitrate can be calculated uniformly after all titrations are completed, without affecting the overall design of the experiment.

[0020] Given that the etching solution contains a high concentration of sulfuric acid and a trace amount of ammonium nitrate, the concentration C1 of the first sodium hydroxide standard solution is greater than the concentration C2 of the second sodium hydroxide standard solution. Using a higher concentration of sodium hydroxide standard solution when determining sulfuric acid improves titration efficiency and avoids further dilution of ammonium nitrate in the first solution due to an excessively large volume V1 of the first sodium hydroxide standard solution. Using a lower concentration of sodium hydroxide standard solution when determining ammonium nitrate can improve the accuracy of trace component determination and reduce volume titration error.

[0021] In this application, the concentration C1 of the first sodium hydroxide standard solution is no more than five times the concentration C2 of the first sodium hydroxide standard solution, so that the titration volumes of both steps fall within the optimal reading range of the burette.

[0022] Preferably, the concentration C1 of the first sodium hydroxide standard solution is 0.5 mol / L to 1.5 mol / L, and the concentration C2 of the second sodium hydroxide standard solution is 0.08 mol / L to 0.12 mol / L, which improves the accuracy of trace components and the determination efficiency of main components. The specific concentration value is related to the weight of the silicon etching solution to be tested.

[0023] The ratio of the added volume Vf of the neutral formaldehyde solution to the sample mass m is (20-40) mL:1g. Sufficient formaldehyde ensures that the reaction between ammonium nitrate and formaldehyde is nearly complete, and free acid is quantitatively generated.

[0024] The first preset time is 20-40 minutes, preferably 30 minutes, which ensures complete reaction without excessively prolonging the detection cycle.

[0025] Because the free acid generated after the reaction of formaldehyde and ammonium nitrate has a narrow acid-base transition range, the color change of phenolphthalein indicator is not significant, and there is a lack of clear endpoint judgment criteria, which can easily cause human error and affect the accuracy of the test results. In this application, the generated free acid is slightly heated. The preset temperature for slight heating is 45℃-55℃, preferably 50℃, to eliminate false endpoints caused by dissolved carbon dioxide and avoid errors in visual judgment.

[0026] The second preset duration is 25s-35s, which is sufficient to avoid premature termination of titration due to the operator's eagerness to read the values, thus ensuring the reliability of the titration endpoint determination.

[0027] If the color fades or other issues occur after the second preset heating time, the titration will fail. A new sample should be taken and titrated again.

[0028] In this application, the silicon etching solution sample is weighed with a mass m accurate to 0.0001 g, and the burette for titrating the sodium hydroxide standard solution has an accuracy of 0.01 mL, which ensures accurate results. Moreover, the design of different concentrations for titrating the sodium hydroxide standard solution can meet the requirements for accurate titration of high-component sulfuric acid and low-component ammonium nitrate.

[0029] According to the neutralization reaction equation of sulfuric acid and sodium hydroxide: H2SO4 + 2NaOH → Na2SO4 + 2H2O, 1 mol of sulfuric acid consumes 2 mol of sodium hydroxide. Therefore, the formula for calculating the sulfuric acid content is: X1 = [(C1*V1*M1) / (2*m*1000)]*100%, where C1 is in mol / L, V1 is in mL, and M1 is the molar mass of sulfuric acid. Based on the reaction of ammonium nitrate with formaldehyde: 4NH4NO3 + 6HCHO → (CH2)6N4 + 4HNO3 + 6H2O, and the neutralization reaction of free acid: HNO3 + NaOH → NaNO3 + H2O, the formula for calculating ammonium nitrate is: X2 = [(C2*V2*M2) / (m*1000)]*100%, where C2 is in mol / L, V2 is in mL, and M2 is the molar mass of ammonium nitrate.

[0030] Furthermore, the same silicon etching solution sample was tested twice independently. The relative deviation between the two results was no greater than 0.1% for sulfuric acid and no greater than 0.3% for ammonium nitrate. The arithmetic mean was taken as the final content result. Using the average as the final result can reduce random errors and improve the accuracy of the results. If the relative deviation between the two results exceeds the limit, it indicates that there may be operational errors or sample inhomogeneity, and the test needs to be repeated.

[0031] In specific embodiment 1, 1.3919 g of the silicon etching solution to be tested was weighed into an Erlenmeyer flask using an electronic balance, and phenolphthalein indicator was added; a 1.0005 mol / L first sodium hydroxide standard solution was titrated into the etching solution in the Erlenmeyer flask using an alkaline burette until the solution turned pink and was recorded as the first solution, and the volume V1 consumed by the first sodium hydroxide standard solution was recorded as 17.40 mL. The content of sulfuric acid was calculated to be 61.34% using the formula, and the molar mass of sulfuric acid was 98.08 g / mol.

[0032] Add 40 mL of neutral formaldehyde solution to the first solution and let it stand for the first preset time of 30 min. Continue titrating the generated free acid solution with a second sodium hydroxide standard solution with a concentration of 0.1001 mol / L until the solution turns pink. Gently heat the solution to 50°C and hold for 30 seconds. The titration endpoint is when the pink color does not fade. Record the volume of the second sodium hydroxide standard solution consumed, V2, as 7.0 mL. Calculate the ammonium nitrate content according to the formula as 4.03%, where the molar mass of ammonium nitrate is 80.04 g / mol.

[0033] In specific embodiment 2, 1.4350g of the silicon etching solution to be tested was weighed into an Erlenmeyer flask using an electronic balance, and phenolphthalein indicator was added. A first sodium hydroxide standard solution with a concentration of 1.0005mol / L was titrated into the etching solution in the Erlenmeyer flask using an alkaline burette until the solution turned pink and was recorded as the first solution. The volume V1 of the first sodium hydroxide standard solution consumed was recorded as 17.93mL. The content of sulfuric acid was calculated to be 61.31% using the formula, and the molar mass of sulfuric acid was 98.08g / mol.

[0034] Add 40 mL of neutral formaldehyde solution to the first solution and let it stand for the first preset time of 30 min. Continue titrating the generated free acid solution with a second sodium hydroxide standard solution with a concentration of 0.0800 mol / L until the solution turns pink. Gently heat the solution to 50°C and hold for 30 seconds. The titration endpoint is when the pink color does not fade. Record the volume of the second sodium hydroxide standard solution consumed, V2, as 9.01 mL. Calculate the ammonium nitrate content according to the formula as 4.02%, where the molar mass of ammonium nitrate is 80.04 g / mol.

[0035] The results of the two sets of specific embodiments above show that the average sulfuric acid content was 61.33% with a relative deviation of 0.05%, and the average ammonium nitrate content was 4.03% with a relative deviation of 0.25%, which verifies the high accuracy and good repeatability of the continuous titration method of this application. In summary, the continuous titration method for sulfuric acid and ammonium nitrate content in silicon etching solution of this application enables continuous titration of both components with a single sample, eliminates mutual interference between components, and optimizes the determination method of titration endpoint, thereby achieving the determination effect of simple operation, high accuracy, low sample consumption, and high detection efficiency.

[0036] 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.

[0037] The detailed descriptions listed above are merely specific illustrations of feasible embodiments of this application and are not intended to limit the scope of protection of this application. All equivalent embodiments 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 continuous titration method for the sulfuric acid and ammonium nitrate content in a silicon etching solution, characterized in that, The continuous titration method includes the following steps: Weigh m grams of silicon etching solution sample into a sample bottle, add phenolphthalein indicator, titrate with a first sodium hydroxide standard solution of concentration C1 until the solution turns pink, and record the volume V1 of the first sodium hydroxide standard solution consumed. Calculate the sulfuric acid content, and record the solution after titration as the first solution. Add a neutral formaldehyde solution to the first solution and let it stand for a first preset time to allow ammonium nitrate and formaldehyde to react fully to generate a free acid solution; The generated free acid solution is titrated with a second sodium hydroxide standard solution of concentration C2 until the solution turns pink. The solution is then gently heated to a preset temperature and maintained for a second preset time. If the pink color does not fade, the titration endpoint is determined, and the volume of the second sodium hydroxide standard solution consumed, V2, is recorded. The ammonium nitrate content is then calculated.

2. The continuous titration method for the sulfuric acid and ammonium nitrate content of the silicon etching solution as described in claim 1, characterized in that, The concentration C1 of the first sodium hydroxide standard solution is greater than the concentration C2 of the second sodium hydroxide standard solution.

3. The continuous titration method for the sulfuric acid and ammonium nitrate content of the silicon etching solution as described in claim 1, characterized in that, The concentration of the first sodium hydroxide standard solution C1 is 0.5 mol / L to 1.5 mol / L, and the concentration of the second sodium hydroxide standard solution C2 is 0.08 mol / L to 0.12 mol / L.

4. The continuous titration method for the sulfuric acid and ammonium nitrate content of the silicon etching solution as described in claim 1, characterized in that, Volume V of neutral formaldehyde solution added f The ratio of the sample mass m to the sample mass m is (20-40) mL: 1 g.

5. The continuous titration method for the sulfuric acid and ammonium nitrate content of the silicon etching solution as described in claim 1, characterized in that, The first preset duration is 20-40 minutes.

6. The continuous titration method for the sulfuric acid and ammonium nitrate content of the silicon etching solution as described in claim 1, characterized in that, The preset temperature is 45℃-55℃, and the second preset duration is 25s-35s.

7. The continuous titration method for the sulfuric acid and ammonium nitrate content of the silicon etching solution as described in claim 1, characterized in that, The mass m of the silicon etching solution sample was weighed to an accuracy of 0.0001 g, and the burette accuracy for titrating the sodium hydroxide standard solution was 0.01 mL.

8. The continuous titration method for determining the sulfuric acid and ammonium nitrate content of silicon etching solution according to any one of claims 1 to 7, characterized in that, The formula for calculating sulfuric acid content is: X1=[(C1*V1*M1) / (2*m*1000)]*100%, Where V1 is in mL, C1 is in mol / L, and M1 is the molar mass of sulfuric acid.

9. The continuous titration method for the sulfuric acid and ammonium nitrate content of the silicon etching solution as described in claim 8, characterized in that, The formula for calculating ammonium nitrate is: X2=[(C2*V2*M2) / (m*1000)]*100%, Where V2 is in mL, C2 is in mol / L, and M2 is the molar mass of ammonium nitrate.

10. The continuous titration method for the sulfuric acid and ammonium nitrate content of the silicon etching solution as described in claim 9, characterized in that, Two independent measurements were performed on the same silicon etching solution sample. The relative deviation between the two measurements was no more than 0.1% for sulfuric acid and no more than 0.3% for ammonium nitrate. The arithmetic mean was taken as the final content result.

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