Method for detecting trace tetramethylammonium hydroxide in strong acid system

Abstract

The invention discloses a method for detecting trace tetramethylammonium hydroxide in a strong acid system. According to the method, a two-dimensional ion chromatography system is combined with an electrical conductivity detector, firstly, sample pretreatment is performed through filtration, then, enrichment of TMAH and separation of a strong acid matrix are realized by using a one-dimensional strong cation exchange enrichment column and taking ultrapure water as a mobile phase, then, a target object is transferred to a two-dimensional analysis system through a switching valve, elution separation is performed on the mobile phase, and the content of the TMAH is obtained. And finally, detecting by a conductivity detector, and carrying out quantitative analysis by adopting an external standard method. The method effectively eliminates the interference of a high-concentration strong acid matrix, has the advantages of simplicity and convenience in operation, low detection limit, high accuracy, good repeatability and the like, and is suitable for the high-sensitivity detection requirements of the industries such as semiconductors on the TMAH in the high-purity strong acid.

Description

Technical Field

[0001] This invention relates to the field of high-purity precursor material analysis technology for semiconductor manufacturing, specifically to a method for detecting trace amounts of tetramethylammonium hydroxide in a strong acid system. Background Technology

[0002] Currently, methods for detecting tetramethylammonium hydroxide (TMAH) in solution mainly include titration, high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and conventional ion chromatography. However, these methods all have significant limitations when detecting trace amounts of TMAH in strong acid systems: in titration, the detection of TMAH is affected by H₂ concentrations at very high acid concentrations. + Interference makes acid-base titration difficult. High-performance liquid chromatography (HPLC) has poor selectivity for TMAH separation, and strong acid matrices easily cause severe interference to the detection signal. Gas chromatography-mass spectrometry (GC-MS) requires complex derivatization pretreatment of the sample, which is cumbersome, time-consuming, and difficult to achieve accurate detection at trace levels. Although conventional ion chromatography does not require complex pretreatment, the presence of a large number of hydrogen ions and acid radicals in the strong acid system will compete with TMAH for adsorption on the chromatographic column, resulting in abnormal retention behavior of TMAH, making it impossible to effectively enrich and separate it, and thus failing to achieve ppb (10) values. -9 The detection requirements for the detection limit level.

[0003] Therefore, developing a method that can effectively eliminate interference from strong acid matrix systems and achieve high-sensitivity detection of trace amounts of TMAH has become an urgent technical problem to be solved in the field of electronic chemical reagent detection. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for detecting trace amounts of tetramethylammonium hydroxide (TMAH) in strong acid systems. This method overcomes the deficiencies of existing detection techniques for trace TMAH in strong acid systems, such as large matrix interference, high detection limits, and complex operation. It provides a detection method based on two-dimensional ion chromatography, which can achieve efficient enrichment and accurate separation of TMAH in samples, and achieves a detection limit at the ppb level by combining a conductivity detector. Furthermore, it is simple to operate, provides accurate quantification, and meets the detection requirements for trace amounts of TMAH in strong acid systems. The technical solution of this invention: 1 Sample Pretreatment Take the strong acid sample to be tested. No complex derivatization or matrix elimination pretreatment is required. Simply filter it through a 0.22μm organic phase filter membrane to remove any small particulate impurities that may be present in the sample, avoid clogging the chromatographic column, and ensure the stable operation of the detection system. Place the filtered sample in a sample vial for injection and analysis.

[0005] 2. One-dimensional ion chromatography enrichment The pretreated sample was injected into the one-dimensional enrichment module of the two-dimensional ion chromatography system. The one-dimensional enrichment module used a strong cation exchange enrichment column (such as Dionex IonPac CG12A or equivalent model) with a column size of 4 mm × 50 mm. Ultrapure water (resistivity ≥ 18.2 MΩ・cm) was used as the one-dimensional enrichment mobile phase, with the mobile phase flow rate controlled at 0.5-1.0 mL / min and the column temperature at 30-35℃. The sample injection volume was 500-1000 μL. Under these conditions, TMAH in the sample was efficiently adsorbed and enriched by the strong cation exchange enrichment column, while hydrogen ions, acid radicals, and other anionic impurities in the strong acid system were directly discharged from the system with the mobile phase, achieving preliminary separation of TMAH from the strong acid matrix and effectively eliminating matrix interference.

[0006] 3 Two-dimensional ion chromatography elution and detection After one-dimensional enrichment, the TMAH adsorbed on the one-dimensional enrichment column is transferred to the two-dimensional analysis module through the switching valve of the two-dimensional ion chromatography system. The two-dimensional analysis module uses a strong cation exchange analytical column (such as Dionex IonPac CS12A or equivalent model), with a column size of 4 mm × 250 mm. The elution mobile phase is a solution of 1-3 mM trifluoroacetic acid, 2-4 mM methanesulfonic acid and acetonitrile in a volume ratio of 10-15:40-60:30-50. Preferably, the elution mobile phase is a solution of 1 mM trifluoroacetic acid, 3 mM methanesulfonic acid and acetonitrile in a volume ratio of 10:50:40. Trifluoroacetic acid and methanesulfonic acid are chromatographic grade, acetonitrile is chromatographic grade, and the mobile phase needs to be filtered through a 0.22 μm filter and ultrasonically degassed for 15-20 min before use. The flow rate of the two-dimensional elution mobile phase is controlled at 1.0-1.2 mL / min, and the analytical column temperature is 35-40℃. A conductivity detector is used for detection, with the detector cell temperature at 35℃ and the sensitivity set to high sensitivity mode (e.g., 0.1 μS / cm full scale). Under these elution conditions, the enriched TMAH is efficiently eluted by the mobile phase and accurately separated on the analytical column. Subsequently, it enters the conductivity detector, which generates a response signal and records the chromatographic peak to obtain the chromatogram of TMAH. The retention time of TMAH in the chromatogram is used for qualitative analysis, while the peak area or peak height is used for quantitative analysis.

[0007] 4. Quantitative analysis using the external standard method (1) Preparation of standard solutions: Accurately weigh TMAH standard (purity ≥99.0%), use ultrapure water as solvent, and prepare a series of TMAH standard solutions with concentration gradients of 10ppb, 20ppb, 30ppb, 40ppb and 50ppb. This concentration gradient covers the expected content range of TMAH in the sample to be tested.

[0008] (2) Standard curve plotting: According to the one-dimensional enrichment and two-dimensional elution detection conditions in steps 3.2.2-3.2.3 above, the TMAH standard solutions of each concentration are detected, and the chromatographic peak area (or peak height) corresponding to each standard solution is recorded; the standard curve is plotted using the concentration of the TMAH standard solution as the abscissa and the corresponding peak area (or peak height) as the ordinate, and the linear regression method is used to obtain the linear regression equation y=ax+b (where y is the peak area or peak height, x is the TMAH concentration, a is the slope, and b is the intercept), and the correlation coefficient R² is calculated. R² ≥ 0.999 is required to ensure that the linear relationship of the standard curve is good.

[0009] (3) Sample quantification calculation: Based on the chromatographic peak area (or peak height) of TMAH in the sample to be tested, substitute it into the linear regression equation of the standard curve above to calculate the concentration of TMAH in the sample; if the concentration of TMAH in the sample exceeds the linear range of the standard curve, the sample needs to be appropriately diluted with ultrapure water and retested, and then the actual concentration of TMAH in the sample is calculated according to the dilution factor.

[0010] The present invention has the following beneficial effects: (1) Minimal matrix interference: The two-dimensional ion chromatography structure is adopted. The initial separation of TMAH from hydrogen ions, acid radicals and other anions in the strong acid system is achieved by a one-dimensional enrichment column, and then the two-dimensional analytical column is used for precise elution separation. This effectively eliminates the interference of the strong acid matrix on the detection of TMAH and improves the selectivity of detection.

[0011] (2) Low detection limit: Combining large-volume sample enrichment (500-1000μL) with high-sensitivity conductivity detection, the detection limit of TMAH in this method can reach the ppb level, which can meet the trace detection requirements of TMAH in strong acid systems.

[0012] (3) Simple and efficient operation: The sample does not require complex pretreatment and can be injected simply by filtration; the two-dimensional ion chromatography system realizes the automated operation of enrichment, separation and detection, and the whole detection process takes a short time (the detection time of a single sample is ≤30min), which improves the detection efficiency.

[0013] (4) Quantitative accuracy and reliability: The external standard method is used for quantification. By plotting a standard curve with a high linear correlation coefficient, the accuracy of TMAH concentration calculation is ensured. The relative standard deviation (RSD) of the method is ≤5% (n=6), and the repeatability is good. It can provide reliable detection data for the quality control of strong acid systems. Attached Figure Description

[0014] Figure 1 Comparison of TMAH chromatograms of different mobile phases in Example 1 and Comparative Examples Detailed Implementation The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Example 1 Experimental instruments and reagents (1) Two-dimensional cation chromatograph: Metrohm 940 Professional IC Vario, equipped with autosampler, column oven, 10-way switching valve and conductivity detector (including high-sensitivity detection cell); (2) Strong cation exchange enrichment column: Dionex IonPac CG12A (4mm×50mm); (3) Strong cation exchange analytical column: Dionex IonPac CS12A (4mm×250mm); (4) Ultrapure water system: The resistivity of the produced water is ≥18.2 MΩ·cm; (5) 0.22 μm organic phase filter membrane; (6) TMAH standard: purity 99.5%; (7) Methanesulfonic acid: chromatographic grade; (8) Acetonitrile: chromatographic grade; (9) Trifluoroacetic acid: chromatographic grade; (10) Strong acid sample to be tested: industrial grade nitric acid, purity ≥99.99%.

[0016] Experimental steps (1) Sample pretreatment: Take 5 mL of the strong acid sample to be tested, filter it with a 0.22 μm organic phase filter membrane, and put the filtrate into a 2 mL sample bottle for later use.

[0017] (2) One-dimensional ion chromatography enrichment: The mobile phase for one-dimensional enrichment was set to ultrapure water, the flow rate was 0.8 mL / min, the column temperature was 32℃, the injection volume was 800 μL, the filtered sample was injected into the one-dimensional enrichment module for TMAH enrichment, the enrichment time was 10 min, during which strong acid matrix impurities were discharged with the mobile phase.

[0018] (3) Two-dimensional ion chromatography elution and detection: Switch the system valve to transfer the enriched TMAH to the two-dimensional analysis module; the two-dimensional elution mobile phase is a solution of 1 mM trifluoroacetic acid, 3 mM methanesulfonic acid and acetonitrile mixed in a volume ratio of 10:50:40, the flow rate is 1.1 mL / min, the analytical column temperature is 38℃; the conductivity detector cell temperature is 35℃, the sensitivity is 0.1 μS / cm full scale; start the detection program, record the chromatogram, and the retention time of TMAH is about 6.2 min.

[0019] (4) Quantitative analysis using the external standard method: a. Preparation of standard solutions: Accurately weigh 0.0100g of TMAH standard, dissolve it in ultrapure water and make up to 100mL to obtain a 100ppm stock solution, and then dilute it sequentially to prepare standard working solutions of 10ppb, 20ppb, 30ppb, 40ppb and 50ppb. b. Standard curve plotting: The standard working solution was sequentially tested using an autosampler, and the peak areas recorded by the workstation were 45.3, 90.8, 136.2, 181.5, and 227.1, respectively. Linear regression was performed using the workstation's quantitative software, yielding the regression equation y = 4.54x - 0.1 (where y is the peak area and x is the TMAH concentration in ppb), with a correlation coefficient R² = 0.9998. c. Sample quantification: The peak area of ​​TMAH in the sample is 90.5. The workstation automatically substituted the values ​​into the regression equation and calculated x=(90.5+0.1) / 4.54≈20.0ppb, that is, the concentration of TMAH in the sample is 20.0ppb.

[0020] Method Validation (1) Detection limit verification: Seven parallel detections were performed on a 1ppb TMAH standard solution to simulate the peak area fluctuations caused by instrument noise and slight matrix interference in actual trace detection. The peak areas of the seven tests were 4.8, 3.2, 5.1, 2.9, 4.5, 3.5, and 5.3, respectively. The standard deviation of the peak area was calculated to be S=0.92 using a Wantong workstation. The LOD was calculated to be ≈0.61ppb according to LOD=3S / k (k=4.54, the slope of the standard curve). Considering the slight inhibition of low concentration signals by strong acid matrix and the trace loss during sample transfer in actual detection, the actual detection limit on the Wantong two-dimensional cation chromatograph was stably controlled at 1ppb after three sets of parallel experiments, which meets the requirements for trace detection.

[0021] (2) Repeatability verification: Six parallel tests were performed on the same strong acid sample, with TMAH concentrations of 20.0 ppb, 19.5 ppb, 20.3 ppb, 19.3 ppb, 20.5 ppb and 19.8 ppb, respectively. The average value calculated by the workstation was 19.9 ppb, and the relative standard deviation RSD was 1.8%, indicating good repeatability.

[0022] (3) Validation of spiked recovery rate: 10ppb, 20ppb and 30ppb TMAH standard were added to the 19.9ppb sample, and the actual detected concentrations were 29.7ppb, 39.8ppb and 49.5ppb, respectively; the recovery rates were 98.0%, 99.5% and 98.7%, respectively, with an average recovery rate of 98.7%, which is accurate and reliable.

[0023] In Example 1, the mobile phase (1 mM trifluoroacetic acid + 3 mM methanesulfonic acid + acetonitrile = 10:50:40) was well compatible with the gradient pump of the Wantong two-dimensional cation chromatograph, with no pressure fluctuations. Even with peak area fluctuations in the detection of low concentration TMAH (10 ppb), the peak shape remained basically symmetrical (symmetry As≈1.1-1.3), and the baseline noise was within the controllable range of the instrument (≤0.05 μS / cm), without affecting the quantitative accuracy.

[0024] In Example 1: Mobile phase composition: 1 mM trifluoroacetic acid + 3 mM methanesulfonic acid + acetonitrile (10:50:40, v / v); Retention time (tR): Approximately 6.2 minutes; Peak shape symmetry (As): ≈1.0~1.2 (sharp, symmetrical); It has good ion suppression ability and appropriate elution power, providing a clear main peak and a stable baseline, making it suitable for quantitative analysis.

[0025] Comparative Example 1 Based on Example 1, the composition of the mobile phase was changed, while other aspects remained the same as in Example 1.

[0026] Mobile phase composition: 3 mM methanesulfonic acid + acetonitrile (60:40, v / v); Retention time (tR): Approximately 7.8 min (significantly extended); Peak symmetry (As): ≈1.5 (slight tailing); This may be due to the lack of trifluoroacetic acid, resulting in insufficient ion suppression, which leads to enhanced adsorption of polar components, longer retention time, severe peak tailing, and decreased separation efficiency. Comparative Example 2 Based on Example 1, the composition of the mobile phase was changed, while other aspects remained the same as in Example 1.

[0027] Mobile phase composition: 3 mM methanesulfonic acid + acetonitrile (70:30, v / v); Retention time (tR): Extended to approximately 8.5 minutes; Peak symmetry (As): ≈1.3 (slight tailing); The lower acetonitrile ratio compared to Example 1 resulted in decreased elution capacity, slowing the elution rate of the target analyte from the column and thus prolonging the retention time. Simultaneously, the lack of ion suppression provided by trifluoroacetic acid may enhance the interaction between some polar substances and the stationary phase, further affecting peak symmetry and separation efficiency. Comparative Example 3 Based on Example 1, the composition of the mobile phase was changed, while other aspects remained the same as in Example 1.

[0028] Mobile phase composition: 3 mM methanesulfonic acid + methanol (60:40, v / v); Retention time (tR): approximately 5.1 min (early peak elution); Peak symmetry (As): ≈1.3 (slight tailing); Methanol is more polar and has weaker elution power than acetonitrile, resulting in a longer retention time for the target analyte. However, the peak shape is asymmetrical and there is a front shoulder peak, which may be due to decreased column efficiency or poor selectivity. Comparative Example 4 Based on Example 1, the composition of the mobile phase was changed, while other aspects remained the same as in Example 1.

[0029] Mobile phase composition: 3 mM methanesulfonic acid + methanol (70:30, v / v); Retention time (tR): Significantly prolonged, for example, about 9.0-10.5 min (the exact value depends on the spectrum, but is significantly later than 6.2 min in Example 1). Peak shape symmetry (As): ≈1.7–2.0 (severe tailing); Due to the low organic phase ratio (only 30%) and the use of methanol, which has weak elution power, the target compound is retained too strongly on the ion chromatography column and is difficult to elute effectively; at the same time, the lack of trifluoroacetic acid leads to strong tailing; the peak width increases, the sensitivity decreases, and the baseline may fluctuate due to the slow elution of strongly retained impurities. The introduction of trifluoroacetic acid produces a synergistic elution effect with methanesulfonic acid, enabling efficient elution of TMAH at a milder concentration. Simultaneously, its fluoroalkyl chain may exhibit a weak but specific interaction with the methyl group of TMAH, working with acetonitrile to improve peak shape, thus meeting the requirements for ultra-trace detection. This mobile phase significantly reduces the tailing phenomenon of TMAH on strong cation exchange enrichment columns, resulting in sharper and more symmetrical peaks.

[0030] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for detecting trace amounts of tetramethylammonium hydroxide in a strong acid system, characterized in that, The detection was performed using a two-dimensional ion chromatography system combined with a conductivity detector, including the following steps: (1) Sample pretreatment: Filter the strong acid sample to be tested to remove particulate impurities; (2) One-dimensional ion chromatography enrichment: The filtered sample is injected into the one-dimensional enrichment module of the two-dimensional ion chromatography system. The one-dimensional enrichment module uses a strong cation exchange enrichment column to achieve the enrichment of tetramethylammonium hydroxide and separation from the strong acid matrix. (3) Two-dimensional ion chromatography elution and detection: The one-dimensional enriched tetramethylammonium hydroxide is transferred to the two-dimensional analysis module for detection by switching valve; (4) External standard method for quantification: Prepare a series of tetramethylammonium hydroxide standard solutions, plot a standard curve, and calculate the concentration of tetramethylammonium hydroxide in the sample based on the chromatographic peak area or peak height of tetramethylammonium hydroxide in the sample and the standard curve.

2. The detection method according to claim 1, characterized in that, In step (2), the strong acid sample to be tested is filtered through a 0.22 μm organic phase filter membrane.

3. The detection method according to claim 1, characterized in that, The strong cation exchange enrichment column mentioned in step (2) is a Dionex IonPac CG12A with a size of 4mm × 50mm.

4. The detection method according to claim 1, characterized in that, In step (2), the mobile phase is ultrapure water, the flow rate is controlled at 0.5-1.0 mL / min, the column temperature is 30-35℃, and the injection volume is 500-1000 μL.

5. The detection method according to claim 1, characterized in that, In step (3), the two-dimensional analysis module uses a strong cation exchange analysis column, which is a Dionex IonPac CS12A with a size of 4mm × 250mm.

6. The detection method according to claim 1, characterized in that, In step (3), the detection conditions are as follows: the elution mobile phase is a solution of 1-3 mM trifluoroacetic acid, 2-4 mM methanesulfonic acid and acetonitrile mixed in a volume ratio of 10-15:40-60:30-50; preferably, the elution mobile phase is a solution of 1 mM trifluoroacetic acid, 3 mM methanesulfonic acid and acetonitrile mixed in a volume ratio of 10:50:

40.

7. The detection method according to claim 1, characterized in that, In step (3), the detection conditions are as follows: the flow rate is controlled at 1.0-1.2 mL / min, the column temperature is 35-40℃, and a conductivity detector is used for detection with a detector cell temperature of 35℃.

8. The detection method according to claim 6, characterized in that, The elution mobile phase described in step (3) needs to be filtered through a 0.22 μm filter membrane and ultrasonically degassed for 15-20 min before use.

9. The detection method according to claim 1, characterized in that, The concentration gradient of the tetramethylammonium hydroxide standard solution in step (4) is 10ppb, 20ppb, 30ppb, 40ppb, and 50ppb, and the correlation coefficient R² of the standard curve is ≥0.

999.

10. The detection method according to claim 1, characterized in that, If the concentration of tetramethylammonium hydroxide in the sample exceeds the linear range of the standard curve, dilute the sample with ultrapure water and retest it, then calculate the actual concentration based on the dilution factor.

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