Method for detecting content of trace metal ions in electronic-grade tetramethoxysilane

Abstract

The invention relates to a method for detecting the content of trace metal ions in electronic-grade tetramethoxysilane, which comprises the following steps of: a) removing a silicon substrate in the electronic-grade tetramethoxysilane by adopting a pretreatment method to prepare a sample solution; b) preparing at least six groups of standard solutions with different ion concentrations of metal elements to be detected by adopting the reagent obtained in the step a); c) determining the standard solution obtained in the step b) by using an inductively coupled plasma tandem mass spectrometer to obtain a CPS count value corresponding to each ion concentration of the standard solution; d) fitting a standard curve of'ion concentration-CPS count value 'of the metal element to be measured; and e) determining the sample solution treated in the step a) by using an inductively coupled plasma tandem mass spectrometer to obtain a CPS count value of each metal ion to be detected, and calculating the concentration of each metal ion in the sample to be detected according to the standard curve fitted in the step d). The method is high in analysis speed, good in accuracy and high in precision.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of detection, and particularly relates to a method for detecting content of trace metal ions in electronic-grade tetramethoxysilane. BACKGROUND

[0002] Electronic-grade tetramethoxysilane is an important silicon-based precursor material, which is used to form a silicon dioxide deposition film by a chemical vapor deposition process (CVD) to block pollutants and impurities from entering a semiconductor element, and can also play a role of an insulation layer, a temporary blocking etching, etc., and is widely applied to a semiconductor manufacturing process. The trace metal ion impurity pollution will affect the yield of the semiconductor process. Generally, the metal impurity content in the electronic-grade tetramethoxysilane is controlled at a ppt level. Therefore, accurate detection of the metal impurity content in the electronic-grade tetramethoxysilane has important significance in the semiconductor industry.

[0003] At present, the detection method for the content of trace metal ions mainly adopts an inductively coupled plasma mass spectrometer (ICP-MS). However, the ICP-MS is only equipped with a single quadrupole, and is easily interfered by a complex matrix during detection of electronic-grade organic reagents, so that the detection limit is high. Therefore, an inductively coupled plasma tandem mass spectrometer (ICP-MS / MS) is needed to detect the electronic-grade tetramethoxysilane, and most of the interference can be eliminated.

[0004] At present, the inductively coupled plasma tandem mass spectrometer sold on the market includes five modes: cool plasma-ammonia (Cool-NH3), no gas (No Gas), oxygen reaction (O2), hydrogen reaction (H2) and helium collision (He) five detection modes.

[0005] At present, the ICP-MS / MS detection of the trace metal ions in the electronic-grade tetramethoxysilane is not very mature, and related instrument parameters need to be further optimized. For example, the electronic-grade tetramethoxysilane itself contains silicon, and cannot be directly sampled and detected by the ICP-MS / MS. Therefore, a suitable pretreatment method is needed to remove the silicon matrix before sampling and testing. However, metal ion pollution is easily introduced in the pretreatment process, and the experimental process of the pretreatment scheme needs to be strictly designed. In addition, in the detection process of the ICP-MS / MS, the flow rates of hydrogen and helium introduced into the collision reaction cell directly affect the degree of removal of mass spectrum interference in the detection process, thereby causing different detection results. Therefore, it is necessary to study how to remove the background interference and select appropriate instrument parameters. SUMMARY

[0006] In order to overcome the deficiencies of the prior art, the application provides a method for detecting the content of trace metal ions in electronic-grade tetramethoxysilane, which has fast analysis speed, good accuracy and high precision.

[0007] The technical scheme adopted by the application to solve the technical problems is that:

[0008] A method for detecting trace metal ion content in electronic-grade tetramethoxysilane, comprising the following steps:

[0009] a) removing the silicon matrix in electronic-grade tetramethoxysilane using a pretreatment method to prepare a sample solution;

[0010] b) using the reagent obtained in a) to configure at least 6 groups of standard solutions with different ion concentrations of the metal elements to be detected;

[0011] c) using an inductively coupled plasma tandem mass spectrometer to determine the standard solutions obtained in b) to obtain the CPS count values corresponding to the ion concentrations of the standard solutions;

[0012] d) fitting a standard curve of the ion concentration-CPS count value of the metal elements to be detected;

[0013] e) using the sample solution treated in a), using an inductively coupled plasma tandem mass spectrometer to determine the sample solution to obtain the CPS count values of each metal ion to be detected, and calculating the concentration of each metal ion in the sample to be detected according to the standard curve fitted in d).

[0014] Further, in a), the pretreatment method is to remove the silicon matrix by heating and evaporating at 150°C, and to fully dissolve the metal ions on the PFA beaker using a 2% electronic-grade nitric acid solution. In this scheme, all pretreatment operations are completed in a hundred-level clean room, and the experimenters operate in standard dustproof clothes throughout the process.

[0015] The nitric acid and tetramethoxysilane are single metal ion <100ppt electronic-grade reagents.

[0016] In b), the metal elements to be detected are selected from one or more of Li, Be, Na, Mg, Al, K, Ca, Ti, Zn, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Rb, Sr, Ag, Sn, Sb, Cs, Ba, Pt, Pb, Bi, U.

[0017] In c), the inductively coupled plasma tandem mass spectrometer includes five detection modes: cool plasma-ammonia (Cool-NH3), no gas (No Gas), oxygen reaction (O2), hydrogen reaction (H2), and helium collision (He);

[0018] Wherein, the cool plasma-ammonia (Cool-NH3) mode is used to determine the standard solutions of Li, Na, Mg, Al, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Sr, Ag, Cs, Ba;

[0019] wherein the standard solution of Be, Bi is determined by the No Gas mode;

[0020] wherein the standard solution of Ti, V is determined by the O2 mode;

[0021] wherein the standard solution of Se, Rb, Sb is determined by the H2 mode;

[0022] wherein the standard solution of Sn, Pt, Pb, U is determined by the He mode.

[0023] The Cool-NH3 mode for determining the standard solution further comprises the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 800 W; sampling depth: 19 mm; helium flow rate: 1 mL / min; deflection voltage: -9 V; energy discrimination voltage: -6 V.

[0024] Preferably, the No Gas mode for determining the standard solution further comprises the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 1500 W; sampling depth: 8 mm; deflection voltage: -9 V; energy discrimination voltage: 2 V.

[0025] Preferably, the O2 mode for determining the standard solution further comprises the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 1550 W; sampling depth: 8 mm; deflection voltage: -7 V; energy discrimination voltage: -6 V.

[0026] Preferably, the H2 mode for determining the standard solution further comprises the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 1500 W; sampling depth: 8 mm; helium flow rate: 2 mL / min; hydrogen flow rate: 6.5 mL / min; deflection voltage: -16 V; energy discrimination voltage: -2 V.

[0027] Preferably, the He mode for determining the standard solution further comprises the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 1550 W; sampling depth: 8 mm; helium flow rate: 4.3 mL / min; deflection voltage: -19 V; energy discrimination voltage: 1 V.

[0028] Preferably, the inductively coupled plasma tandem mass spectrometer is Agilent ICP-MS / MS 8900.

[0029] The beneficial effects of the present application mainly manifest in that different reaction gas modes are preferred for different to-be-tested metal elements, preferred detection reagents are used, the interference of background elements on metal ions is reduced, a suitable pretreatment process is used to remove the influence of silicon matrix, the introduction of metal ion pollution is controlled, and a suitable reaction gas flow is preferred to reduce background interference while improving the signal intensity of corresponding metal ions. The detection method provided by the present application has high detection sensitivity and precision. In addition, the present method can accurately determine the content of 28 kinds of metal ions at the same time, and the operation is simple, which greatly improves the detection efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the influence of H2 flow on the signal intensity of the corresponding detection element, i.e. the CPS count value in Comparative Example 1.

[0031] Figure 2 is the influence of He flow on the signal intensity of the corresponding detection element, i.e. the CPS count value in Comparative Example 1. DETAILED DESCRIPTION

[0032] The present application will be further described below in conjunction with the drawings.

[0033] A detection method for the content of trace metal ions in electronic-grade tetramethoxysilane, which adopts an inductively coupled plasma tandem mass spectrometer (ICP-MS / MS) to test the content of metal ions in electronic-grade tetramethoxysilane.

[0034] Example 1

[0035] The detection method for the content of trace metal ions in electronic-grade tetramethoxysilane of the present embodiment comprises the following steps:

[0036] a) preparing a sample solution;

[0037] 10 g of tetramethoxysilane sample was weighed into a 100 ml polytetrafluoroethylene (PFA) open beaker (accurate to 0.0001 g), the beaker was placed on a temperature-controlled hot plate for heating at 150℃, and the sample was completely volatilized to remove the silicon matrix. After cooling to room temperature, the PFA beaker was thoroughly washed with 2% HNO3 to dissolve the cations in the sample into the HNO3 solution to prepare a sample solution.

[0038] b) preparing a standard solution;

[0039] An appropriate amount of 28 kinds of metal ion standard solutions was precisely measured, and 2% nitric acid was used to prepare standard working solutions with concentrations of 0 ppb, 10 ppb, 20 ppb, 50 ppb, 100 ppb and 200 ppb, respectively.

[0040] c) detecting the standard solution;

[0041] The standard solution obtained in b) was detected by inductively coupled plasma tandem mass spectrometer ICP-MS / MS, and 28 kinds of metal ion standard solutions were precisely measured and tested by sampling to obtain the signal intensity of each ion concentration in the standard solution, i.e. CPS count value.

[0042] The inductively coupled plasma tandem mass spectrometer ICP-MS / MS used was Agilent ICP-MS / MS 8900 equipped with a PFA self-suction atomizer. The manufacturer was Agilent, USA, and the model was 8900.

[0043] The metal ion contents of Li, Na, Mg, Al, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Sr, Ag, Cs, Ba were determined by cool plasma-ammonia (Cool-NH3) mode. The detection parameters of cool plasma-ammonia (Cool-NH3) mode were set as: RF power: 800 W; sampling depth: 19 mm; helium flow rate: 1 mL / min; deflection voltage: -9 V; energy discrimination voltage: -6 V;

[0044] The metal ion contents of Be and Bi were determined by gas-free (No Gas) mode. The detection parameters of gas-free (No Gas) mode were set as: RF power: 1500 W; sampling depth: 8 mm; deflection voltage: -9 V; energy discrimination voltage: 2 V;

[0045] The metal ion contents of Ti and V were determined by oxygen reaction (O2) mode. The detection parameters of oxygen reaction (O2) mode were set as: RF power: 1550 W; sampling depth: 8 mm; deflection voltage: -7 V; energy discrimination voltage: -6 V;

[0046] The metal ion contents of Se, Rb and Sb were determined by hydrogen reaction (H2) mode. The detection parameters of hydrogen reaction (H2) mode were set as: RF power: 1500 W; sampling depth: 8 mm; helium flow rate: 2 mL / min; hydrogen flow rate: 6.5 mL / min; deflection voltage: -16 V; energy discrimination voltage: -2 V;

[0047] The metal ion contents of Sn, Pt, Pb and U were determined by helium collision (He) mode. The detection parameters of helium collision (He) mode were set as: RF power: 1550 W; sampling depth: 8 mm; helium flow rate: 4.3 mL / min; deflection voltage: -19 V; energy discrimination voltage: 1 V;

[0048] The plasma gas used by the ICP-MS / MS instrument was 20% argon-oxygen mixed gas.

[0049] d) determination of linear relationship standard curve and detection limit;

[0050] According to the detection results of c), linear regression equations of "ion concentration-CPS count value" of each metal element to be detected were drawn; see Table 1. The detection limits of 28 elements were in the range of 0.02-2.73 ng·L -1 Table 1 is the linear regression equation and detection limit of each metal ion;

[0051]

[0052]

[0053]

[0054] e) detecting the sample solution to be detected;

[0055] The sample solution was determined in five detection modes of cool plasma-ammonia (Cool-NH3), no gas (No Gas), oxygen reaction (O2), hydrogen reaction (H2) and helium collision (He), and the CPS count value obtained by detection was substituted into the regression equation standard curve of the corresponding element to calculate the metal ion content in the electronic grade tetramethoxysilane. The sample preparation process avoided cross contamination as much as possible. The nitric acid and tetramethoxysilane used were single metal ion <100 ppt electronic grade reagents.

[0056] Under the determined analysis conditions, 6 times of continuous sample injection were determined, the entire detection process was carried out in a hundred-level clean room, and the test results of the sample are shown in Table 2. Table 2 shows the recovery rate and precision of each metal ion;

[0057]

[0058]

[0059] Table 1 shows that the linear correlation coefficient of 28 elements in the method is ≥0.9990, the linearity is good, and Table 2 shows that the relative standard deviation RSD of the repeatability test metal ion in the method is ≤6.8%, the precision is good. Within the linear range, the method can accurately measure the content of metal ions in the sample.

[0060] Comparative Example 1

[0061] Reference Figure 1 and Figure 2, Cool-NH3 is less suitable for Be, Ti, Zn, V, As, Se, Rb, Sn, Sb, Pt, Hg, Pb and U, and has low sensitivity, and different modes need to be considered for optimization. Be and Bi are suitable for No Gas mode and do not need to be connected to the reaction gas. The oxygen reaction (O2) mode eliminates interference by mass transfer reaction principle and is suitable for the determination of Ti and V. Se, Rb and Sb are suitable for hydrogen reaction (H2) mode. In H2 mode, H2 reacts with interfering ions to form neutral Ar ions, and Se + has low reactivity with H2 and can retain most of the ions to be measured. H2 can also undergo chemical reduction with ZrO + , eliminating the interference of oxides on Sb+(m / z=121). Sn, Pt, Pb and U are suitable for helium collision (He) mode determination. He collision mode reduces interference by collision-induced dissociation (CID) principle, which is manifested as He atoms colliding with interfering ions (such as MoO2 + , PbO + ) to form neutral molecules, and He gas is inert and does not participate in chemical reactions, which is suitable for heavy metals that form oxides (such as Pb and U). The flow rates of H2 and He reaction gas have a greater impact on the removal of interference and the response of metal ion signal intensity. The present application studies the effects of different H2 and He reaction gas flow rates on the signal intensity (CPS) of Zn, Se, Rb, Sb, Sn, Pt, Pb and U elements, as shown in Figure 1 、 2 .

[0062] As shown in Figure 1 、 Figure 2 , at low flow rate, with the increase of H2 flow rate, the chemical reduction reaction between H2 and interfering ions is enhanced, effectively reducing the matrix effect and improving the sensitivity. When the flow rate exceeds a certain value, excessive H2 molecules lead to a decrease in the signal intensity of the ions to be measured, which is manifested as the signal intensity of Se, Rb and Sb ions first increasing and then decreasing, and reaching a maximum at 6.5, 7.0, 6.0 ml·min -1 . In He gas mode, due to the inertness and low mass number of He gas, the signal intensity of Zn, Sn, Pt, Hg, Pb and U ions changes gently with the change of He gas flow rate, and the optimal value appears at 3.7-4.7 ml·min -1 . In order to ensure the detection sensitivity of each element at a high level, the H2 flow rate of 6.5 ml·min -1 is selected as the optimal value of hydrogen reaction (H2) mode, and the He flow rate of 4.3 ml·min -1 is selected as the optimal value of helium collision (He) mode.

[0063] The selection of each parameter in the hydrogen reaction (H2) mode and the helium collision (He) mode is the optimal parameter selected by comprehensively considering the background interference and the element ion response.

[0064] The embodiments of the present specification are merely a list of implementation forms of the inventive concept, and are only for the purpose of illustration. The protection scope of the present application should not be regarded as being limited to the specific forms presented in the embodiments, and the protection scope of the present application also extends to equivalent technical means that can be thought of by those skilled in the art according to the inventive concept.

Claims

1. A method for detecting trace metal ion content in electronic-grade tetramethoxysilane, characterized in that, The method includes the following steps: a) The silicon matrix in electronic-grade tetramethoxysilane was removed using a pretreatment method to prepare a sample solution; b) Prepare at least 6 standard solutions of different ion concentrations for the metal element to be tested using the reagents obtained in a); c) The CPS count values ​​corresponding to the concentrations of each ion in the standard solution obtained in b) were determined using an inductively coupled plasma tandem mass spectrometer. d) Fit the standard curve of "ion concentration - CPS count value" of the metal element to be tested; e) Using the sample solution treated in a), the CPS count value of each metal ion to be tested is obtained by inductively coupled plasma tandem mass spectrometry. The concentration of each metal ion in the sample is calculated according to the standard curve fitted in d).

2. The method for detecting trace metal ion content in electronic-grade tetramethoxysilane as described in claim 1, characterized in that, In a), the pretreatment method is as follows: the silicon substrate is removed by heating at 150°C to dry, and the metal ions on the PFA beaker are fully dissolved by using 2% electronic grade nitric acid solution.

3. The method for detecting trace metal ion content in electronic-grade tetramethoxysilane as described in claim 2, characterized in that, The nitric acid and tetramethoxysilane are electronic-grade reagents with a single metal ion concentration of <100 ppt.

4. A method for detecting trace metal ion content in electronic-grade tetramethoxysilane as described in any one of claims 1 to 3, characterized in that, The metal element to be tested is selected from one or more of the following: Li, Be, Na, Mg, Al, K, Ca, Ti, Zn, V, Cr, Mn, Fe, Co, Ni, Cu, Se, Rb, Sr, Ag, Sn, Sb, Cs, Ba, Pt, Pb, Bi, and U.

5. A method for detecting trace metal ion content in electronic-grade tetramethoxysilane as described in any one of claims 1 to 3, characterized in that, In c), the inductively coupled plasma tandem mass spectrometer includes five detection modes: cold plasma-ammonia, gas-free, oxygen reaction, hydrogen reaction, and helium collision. The standard solutions of Li, Na, Mg, Al, K, Ca, Cr, Mn, Fe, Co, Ni, Cu, Sr, Ag, Cs, and Ba were determined using the aforementioned cold plasma-ammonia mode. The standard solutions for determining Be and Bi were used in the gas-free mode. The standard solutions for determining Ti and V were used in the oxygen reaction mode described above. Among them, the standard solutions for determining Se, Rb, and Sb were used in the hydrogen reaction mode described above; The standard solutions for Sn, Pt, Pb, and U were determined using the helium collision mode.

6. The method for detecting trace metal ion content in electronic-grade tetramethoxysilane as described in claim 5, characterized in that, The cold plasma-ammonia mode determination of the standard solution also includes the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 800W; sampling depth: 19mm; helium flow rate: 1mL / min; deflection voltage: -9V; energy discrimination voltage: -6V. The gas-free mode determination of the standard solution also includes the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 1500W; sampling depth: 8mm; deflection voltage: -9V; energy discrimination voltage: 2V; The oxygen reaction mode determination standard solution also includes the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 1550W; sampling depth: 8mm; deflection voltage: -7V; energy discrimination voltage: -6V. The hydrogen reaction mode determination of the standard solution also includes the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 1500W; sampling depth: 8mm; helium flow rate: 2mL / min; hydrogen flow rate: 6.5mL / min; deflection voltage: -16V; energy discrimination voltage: -2V. The helium collision mode determination standard solution also includes the step of setting the inductively coupled plasma tandem mass spectrometer to the following detection parameters: RF power: 1550W; sampling depth: 8mm; helium flow rate: 4.3mL / min; deflection voltage: -19V; energy discrimination voltage: 1V.

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