Method for determining content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy

Abstract

The invention relates to the technical field of gas analysis and detection, in particular to a method for determining the content of trace silicon tetrafluoride in boron trifluoride through infrared spectroscopy, and the method specifically comprises the following steps: pretreating high-purity boron trifluoride: removing carbon tetrafluoride in the high-purity boron trifluoride; then establishing a standard curve: performing infrared spectrum scanning on the silicon tetrafluoride standard gases with different concentrations, selecting infrared characteristic absorption peaks of the silicon tetrafluoride, and drawing the standard curve according to the absorbance of the silicon tetrafluoride standard gases with different concentrations; and finally, determining the spectrum of the high-purity boron trifluoride sample, and calculating the content of silicon tetrafluoride in the sample according to the absorbance and the standard curve. The method provided by the invention is high in reproducibility, low in danger coefficient and convenient to operate, and the content of silicon tetrafluoride in boron trifluoride can be rapidly and accurately measured.

Description

Technical Field

[0001] The present application belongs to the technical field of gas analysis and detection, and in particular relates to a method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy. Background Art

[0002] High-purity boron trifluoride is an important raw material in the semiconductor field. It is mainly used in processes such as ion implantation, etching and doping. It is one of the important gases in advanced chip manufacturing processes.

[0003] In the process production of boron trifluoride, since silicon tetrafluoride is difficult to remove, once the silicon tetrafluoride content exceeds the standard, it will affect the quality of electronic devices in integrated circuits. Therefore, the detection of silicon tetrafluoride in high-purity boron trifluoride is particularly important. "Boron Trifluoride Gas for Electronic Industry" GB / T14603-2009 stipulates that the index requirement for silicon tetrafluoride in 5N grade boron trifluoride is 5ppm, and it adopts the silicon molybdenum blue photometry. However, this analysis method has the following disadvantages: 1. It involves the absorption sampling of boron trifluoride solution, which is cumbersome and time-consuming, and has a high risk factor; 2. It involves the weighing and preparation of various reagents, which is cumbersome and has poor repeatability in manual operation; 3. The detection limit of the spectrophotometric method is not high, which cannot meet the quantitative analysis of low-content impurities.

[0004] Chinese patent CN113884600B discloses a device and a method for determining the content of carbonyl fluoride and silicon tetrafluoride in a fluorine-containing mixed gas. The connecting pipeline and the instrument are set up. After the carbonyl fluoride and silicon tetrafluoride standard gases of each content are respectively introduced, the silicon tetrafluoride spectrum is first scanned at a high resolution, and then the carbonyl fluoride spectrum is scanned at a low resolution to obtain the addition spectrum of the carbonyl fluoride and silicon tetrafluoride standard gases, and a standard curve is established; by measuring the fluorine-containing mixed gas sample to be tested, the accurate content of carbonyl fluoride and silicon tetrafluoride in the fluorine-containing mixed gas sample to be tested is obtained by the least squares method. However, in this method, carbonyl fluoride and silicon tetrafluoride have characteristic responses in the same wave number range, and different characteristic absorption peaks need to be found to quickly and accurately determine the content of silicon tetrafluoride. Therefore, it is urgent to propose a method that can quickly and accurately measure the trace silicon tetrafluoride content in boron trifluoride. Summary of the invention

[0005] In view of the problems in the prior art of inaccurate measurement of trace silicon tetrafluoride content in boron trifluoride and waste of time, the purpose of the present application is to provide a method for determining the trace silicon tetrafluoride content in boron trifluoride by infrared spectroscopy, which can quickly and accurately determine the content of silicon tetrafluoride.

[0006] In order to achieve the purpose of this application, the specific technical solutions provided by this application are as follows:

[0007] A method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy comprises the following steps:

[0008] Step S1. Pretreatment of high-purity boron trifluoride: passing high-purity boron trifluoride into a reactor containing an adsorbent to remove carbon tetrafluoride from the high-purity boron trifluoride to obtain pretreated high-purity boron trifluoride for standby use;

[0009] Step S2. Establishing a standard curve: Scanning the infrared spectrum of silicon tetrafluoride standard gas with different concentrations, selecting the infrared characteristic absorption peak of silicon tetrafluoride, and drawing a standard curve according to the absorbance of silicon tetrafluoride standard gas with different concentrations;

[0010] The infrared spectrum scanning conditions are: the infrared spectrum scanning conditions are: the window is BaF2; the resolution is 4cm -1 ; Detector: MCT; Scan times: 32; Scan wave number: 500-40004cm -1 ; The optical path of the gas cell is 10m; the injection pressure is -50kPa;

[0011] Step S3. Measurement of high-purity boron trifluoride sample: Under the same test conditions as those of silicon tetrafluoride standard gas, the pretreated high-purity boron trifluoride sample is tested, and the content of silicon tetrafluoride in the sample is calculated based on the absorbance of the same infrared characteristic absorption peak of silicon tetrafluoride in the infrared spectrum of the pretreated high-purity boron trifluoride sample according to the standard curve.

[0012] Preferably, the adsorbent in step S1 is an activated carbon / nano-alumina adsorbent; its preparation method is: the raw carbon is washed with nitric acid, then deoxidized at 50-250°C for 3-5h, and then the temperature is raised to 700-900°C for carbonization for 2-3h, and then inert gas, carbon dioxide and water vapor are introduced, and the temperature is maintained at 700-900°C for activation for 3-4h to obtain activated carbon, and finally the nano-alumina and activated carbon are mixed in a mass ratio of 1:(3.6-5.8) to obtain activated carbon / nano-alumina.

[0013] Preferably, the washing is carried out in a ratio of (50-100 mL) nitric acid per 1 g of raw carbon, the mass ratio of raw carbon to nitric acid is 1 g: (50-100 mL), the concentration of nitric acid is 4 mol / L; the volume ratio of inert gas, carbon dioxide and water vapor is 3:2:2, and the flow rates of inert gas, carbon dioxide and water vapor are all 100-500 mL / min.

[0014] Preferably, before performing infrared spectrum scanning, the standard gas or the sample to be tested is connected to the infrared spectrum through a pipeline, and pressure-maintaining leak detection is performed, and then the pipeline is evacuated and replaced with nitrogen.

[0015] Preferably, choose 1026cm -1 The peak at is taken as the characteristic absorption peak for quantitative analysis of silicon tetrafluoride.

[0016] Preferably, the concentration of silicon tetrafluoride standard gas is not higher than 10 ppm, and the balance gas is nitrogen.

[0017] Preferably, the calculation formula for the content of silicon tetrafluoride is: Y=AX-C, where X is the absorbance, Y is the concentration of silicon tetrafluoride in ppm, A is the slope of the drawn standard curve, and C is the intersection value of the drawn standard curve and the ordinate axis.

[0018] Beneficial effects of this application:

[0019] (1) Since high-purity boron trifluoride contains carbon tetrafluoride, and the C-Si stretching vibration in silicon tetrafluoride measured in this application is similar to the CF stretching vibration in carbon tetrafluoride, which may affect the accurate determination of the silicon tetrafluoride content. Therefore, this application removes carbon tetrafluoride from high-purity boron trifluoride by pretreating high-purity boron trifluoride; increases the specific surface area of ​​the adsorbent by carbonizing and activating the raw carbon by multiple heating, and the increase in the specific surface area provides more adsorption sites for CF4 molecules, thereby improving the adsorption efficiency; and by mixing activated carbon with nano-alumina, CF4 is fixed by the active Al sites of the effective anti-bonding orbitals on the surface of alumina, thereby preventing CF4 from desorbing from the activated carbon and affecting subsequent detection.

[0020] (2) The present application can accurately convert the absorbance obtained by infrared spectroscopy scanning into the specific content of silicon tetrafluoride by configuring a standard curve established by silicon tetrafluoride standard gas. Very low concentrations of silicon tetrafluoride (trace level) in boron trifluoride can be detected. The steps of this method are relatively simple and clear, including the establishment of a standard curve and the measurement of high-purity boron trifluoride samples. It does not involve complex chemical reactions or cumbersome pretreatment steps, and is conducive to rapid and batch sample analysis. The method provided in this application is highly reproducible and can quickly and accurately determine the content of silicon tetrafluoride in boron trifluoride. It has a low risk factor and is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of a device used in the method of the embodiment of the present application;

[0022] Figure 2 This is a standard curve diagram obtained in the examples of this application;

[0023] Figure 3 This is the infrared spectrum of the standard gas and boron trifluoride sample in the examples of this application.

[0024] Attached figure identification: 1. Gas cylinder to be tested; 2. First valve; 3. Pressure reducer; 4. Second valve; 5. Third valve; 6. Infrared spectrometer. DETAILED DESCRIPTION

[0025] In order to further explain the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present application are described in detail below in combination with the preferred embodiments.

[0026] Device Embodiment

[0027] like Figure 1 As shown, the schematic diagram of the device of the present application includes a gas cylinder 1 to be tested, and a first valve 2, a pressure reducer 3, a second valve 4, a third valve 5 and an infrared spectrometer 6 are arranged in sequence along the flow direction of the gas, wherein the first valve 2 is used to control the outflow of the gas in the gas cylinder 1 to be tested; the pressure reducer 3 is used to control the flow direction of the gas in the gas cylinder 1 to be tested, and the pressure reducer 3 can ensure that the pressure of the gas released from the cylinder is stable and moderate, thereby avoiding the impact or damage of the internal components of the infrared spectrometer 6 by the high-pressure gas. In infrared spectroscopy analysis, the pressure reducer 3 also controls the pressure of the gas to ensure that the sample is analyzed under stable environmental conditions, thereby improving the accuracy and reliability of the measurement; the second valve 4 is a vacuum valve, and the third valve 5 is a nitrogen purge gas valve. Before sampling, the entire pipeline needs to be replaced by nitrogen-vacuum through the second valve 4 and the third valve 5, so that the entire pipeline is filled with nitrogen to ensure the cleanliness of the pipeline, and there is no impurity that affects the accuracy of the test; the infrared spectrometer 6 is used to detect the sampled gas and measure the corresponding absorbance. The infrared spectrometer 6 of this embodiment is IS50 of Thermo Fisher.

[0028] Adsorbent Preparation Example 1:

[0029] This preparation example provides a method for preparing an activated carbon / nano-alumina adsorbent:

[0030] 10 g of raw carbon was added to 100 mL of 4 mol / L nitric acid, magnetically stirred for 1 h, centrifuged to remove the upper liquid, and then the solid was washed with deionized water until the pH of the upper clear liquid was 7, followed by deoxygenation at 100 °C for 5 h, and then heated to 800 °C for carbonization for 2.5 h, and then helium, carbon dioxide and water vapor were introduced at a flow rate of 300 mL / min, 200 mL / min, and 200 mL / min, respectively, and activated at 800 °C for 3 h to obtain activated carbon. Finally, 2 g of nano-alumina and 9 g of activated carbon were mechanically mixed to obtain activated carbon / nano-alumina.

[0031] Adsorbent Preparation Example 2:

[0032] This preparation example provides a method for preparing an activated carbon / nano-alumina adsorbent:

[0033] 10 g of raw carbon was added to 50 mL of 4 mol / L nitric acid, magnetically stirred for 1 h, centrifuged to remove the upper liquid, and then the solid was washed with deionized water until the pH of the upper clear liquid was 7, followed by deoxygenation at 50 °C for 3 h, and then the temperature was raised to 700 °C for carbonization for 3 h, and then helium, carbon dioxide and water vapor were introduced at a flow rate of 300 mL / min, 200 mL / min, and 200 mL / min, respectively, and activated at 700 °C for 4 h to obtain activated carbon. Finally, 2 g of nano-alumina and 9 g of activated carbon were mechanically mixed to obtain activated carbon / nano-alumina.

[0034] Adsorbent Preparation Example 3:

[0035] This preparation example provides a method for preparing an activated carbon / nano-alumina adsorbent:

[0036] 10 g of raw carbon was added to 90 mL of 4 mol / L nitric acid and stirred magnetically for 1 h. The upper liquid was removed by centrifugation and the solid was washed with deionized water until the pH of the upper clear liquid was 7. It was then deoxidized at 250 °C for 4 h and continued to be carbonized at 900 °C for 2 h. Helium, carbon dioxide and water vapor were then introduced at a flow rate of 150 mL / min, 100 mL / min and 100 mL / min, respectively, and activated at 900 °C for 3.5 h to obtain activated carbon. Finally, 2 g of nano-alumina and 9 g of activated carbon were mechanically mixed to obtain activated carbon / nano-alumina.

[0037] Examples 1 to 3 are based on the apparatus of the device example and the adsorbent provided in adsorbent preparation example 1. Due to objective factors such as experimental conditions, only the adsorbent prepared in adsorbent preparation 1 was selected to detect the trace silicon tetrafluoride content in boron trifluoride.

[0038] Example 1

[0039] This embodiment provides a method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy, comprising the following steps:

[0040] Step S1. Pretreatment of high-purity boron trifluoride: passing high-purity boron trifluoride into a reactor containing the adsorbent prepared in Adsorbent Preparation Example 1, removing carbon tetrafluoride from the high-purity boron trifluoride to obtain pretreated high-purity boron trifluoride for standby use;

[0041] Step S2. Establishment of standard curve: Before infrared spectrum scanning, connect the test gas to the infrared spectrum through a pipeline, perform pressure maintenance and leak detection, then evacuate the pipeline and replace it with nitrogen to use nitrogen as the balance gas, and perform infrared scanning with silicon tetrafluoride standard gas with concentrations of 0ppm, 1ppm, 5ppm, and 10ppm. The infrared spectrum scanning conditions are: the window is BaF2; the resolution is 4cm -1; Detector: MCT; Scan times: 32; Scan wave number: 500-40004cm -1 ; The optical path of the gas cell is 10m; the injection pressure is -50kPa, and 1026cm is selected -1 The peak at is taken as the characteristic absorption peak of the quantitative analysis of silicon tetrafluoride. A standard curve is drawn according to the absorbance of 0ppm, 1ppm, 5ppm, and 10ppm silicon tetrafluoride standard gas. Each corresponding concentration is tested 3 times and the average value is taken. The absorbance values ​​corresponding to different concentrations are shown in Table 1, and the standard curve is shown in the following figure. Figure 2 shown.

[0042] Table 1

[0043]

[0044] Step S3. Measurement of high-purity boron trifluoride sample: Under the same test conditions as the silicon tetrafluoride standard gas, the boron trifluoride sample is tested, and the content of silicon tetrafluoride in the sample is calculated on the standard curve according to the absorbance of the same characteristic infrared absorption peak of silicon tetrafluoride in the infrared spectrum of the obtained boron trifluoride sample. Here, three boron trifluoride samples are selected to measure the absorbance of each sample, and each sample is measured three times to take the average value as the absorbance of the corresponding sample. Since the vibration peaks of samples 1, 2 and 3 are similar, the difference lies in the difference in intensity, so this embodiment only shows the spectrum of sample 1 and the standard curve with a concentration of 5ppm silicon tetrafluoride standard gas, as shown in FIG. Figure 3 As shown; According to the standard curve in step 1, the content of silicon tetrafluoride in sample 1, sample 2 and sample 3 is calculated, and the results are shown in Table 2.

[0045] Table 2

[0046] <![CDATA[BF3 sample]]> Absorbance <![CDATA[SiF4 content / ppm]]> Sample 1 0.0064 3.28 Sample 2 0.0008 0.62 Sample 3 0.0037 2.00

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that the high-purity boron trifluoride is not pretreated, and the content of silicon tetrafluoride in the obtained BF3 sample is shown in Table 3.

[0049] Table 2

[0050] <![CDATA[BF3 sample]]> Absorbance <![CDATA[SiF4 content / ppm]]> Sample a 0.0070 4.03 Sample b 0.0012 0.97 Sample c 0.0045 2.51

[0051] The above is only a preferred embodiment of the present application and does not constitute any form of limitation to the present application. Although the present application has been disclosed as a preferred embodiment as above, it is not intended to limit the present application. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present application. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application are still within the scope of the technical solution of the present application.

Claims

1. A method for determining trace silicon tetrafluoride content in boron trifluoride by infrared spectroscopy, characterized in that: The following steps are involved: Step S1. Pretreatment of high-purity boron trifluoride: passing high-purity boron trifluoride into a reactor containing an adsorbent to remove carbon tetrafluoride from the high-purity boron trifluoride to obtain pretreated high-purity boron trifluoride for standby use; Step S2. Establishing a standard curve: Scanning the infrared spectrum of silicon tetrafluoride standard gas with different concentrations, selecting the infrared characteristic absorption peak of silicon tetrafluoride, and drawing a standard curve according to the absorbance of silicon tetrafluoride standard gas with different concentrations; The infrared spectrum scanning conditions are: the infrared spectrum scanning conditions are: the window is BaF2; the resolution is 4cm -1 ; Detector: MCT; Scan times: 32; Scan wave number: 500-40004cm -1 ; The optical path of the gas cell is 10m; the injection pressure is -50kPa; Step S3. Measurement of high-purity boron trifluoride sample: Under the same test conditions as those of silicon tetrafluoride standard gas, the pretreated high-purity boron trifluoride sample is tested, and the content of silicon tetrafluoride in the sample is calculated based on the absorbance of the same infrared characteristic absorption peak of silicon tetrafluoride in the infrared spectrum of the pretreated high-purity boron trifluoride sample according to the standard curve.

2. The method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy according to claim 1, characterized in that: The adsorbent in step S1 is an activated carbon / nano-alumina adsorbent; its preparation method is: the raw carbon is washed with nitric acid, then deoxidized at 50-250°C for 3-5h, and then the temperature is raised to 700-900°C for carbonization for 2-3h, and then inert gas, carbon dioxide and water vapor are introduced, and the temperature is maintained at 700-900°C for activation for 3-4h to obtain activated carbon, and finally the nano-alumina and activated carbon are mixed in a mass ratio of 1:(3.6-5.8) to obtain activated carbon / nano-alumina.

3. The method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy according to claim 2, characterized in that: The washing is carried out in a ratio of 1g of raw carbon to (50-100mL) of nitric acid, the mass ratio of raw carbon to nitric acid is 1g:(50-100mL), the concentration of nitric acid is 4mol / L; the volume ratio of inert gas, carbon dioxide and water vapor is 3:2:2, and the flow rates of inert gas, carbon dioxide and water vapor are all 100-500mL / min.

4. The method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy according to claim 1, characterized in that: Before performing infrared spectrum scanning, the standard gas or the sample to be tested is connected to the infrared spectrum through a pipeline, and pressure is maintained to detect leaks. The pipeline is then evacuated and replaced with nitrogen.

5. The method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy according to claim 1, characterized in that: Select 1026cm -1 The peak at is taken as the characteristic absorption peak for quantitative analysis of silicon tetrafluoride.

6. The method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy according to claim 1, characterized in that: The concentration of silicon tetrafluoride standard gas is not higher than 10ppm, and its balance gas is nitrogen.

7. The method for determining the content of trace silicon tetrafluoride in boron trifluoride by infrared spectroscopy according to claim 1, characterized in that: The calculation formula for the content of silicon tetrafluoride is: Y=AX-C, where X is the absorbance, Y is the concentration of silicon tetrafluoride in ppm, A is the slope of the drawn standard curve, and C is the intersection value of the drawn standard curve and the ordinate axis.

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