Method of detecting and quantifying compounds of boron and / or aluminum and use of the same

Abstract

This invention provides a method for trace analysis, detection, and quantification of boron and / or aluminum compounds in a gas stream or liquid stream containing at least one chlorosilane, comprising the following steps: a) removing a sample from the gas stream and mixing it with an inert gas to form a gaseous sample, or removing a liquid sample from the liquid stream, wherein the liquid sample is mixed with an inert gas in an evaporator unit and evaporated to form a gaseous sample; b) transferring the gaseous sample obtained in step a) to the reaction chamber of a mass spectrometer, wherein electrons generated in the ion source by plasma discharge react with chlorosilane to form chloride ion species, and wherein the chloride ion species reacts with boron and / or aluminum compounds by chemical ionization to obtain boron chloride and / or aluminum chloride ion species; c) separating and detecting the boron chloride and / or aluminum chloride ion species.

Description

[Technical Field]

[0001] This invention relates to a method for trace analysis, detection and quantification of compounds of boron and / or aluminum in a gas stream or liquid stream containing at least one chlorosilane. [Previous Technology]

[0002] In the production of single-crystal silicon, for example by crucible pulling (Czechsky process (CZ process)) or zone melting (floating zone process), polycrystalline silicon (polysilicon) is used as the starting material. Single-crystal silicon can be sawn into wafers and, after many further processing steps, can be used in the semiconductor industry to manufacture electronic components (e.g., resistors, diodes, bipolar transistors, and MOS transistors). The aforementioned processing steps generally involve controlled and locally confined contamination of the single-crystal silicon with dopants. These dopants include, in particular, atoms with trivalent or pentavalent electrons, i.e., elements of Group 3 and Group 5 of the periodic table. Therefore, a prerequisite for manufacturing these semiconductor devices is that the silicon used is of ultra-high purity (free from external doping) and in a perfect single-crystal form, because grain boundaries and lattice defects also lead to undesirable current paths.

[0003] In addition, polycrystalline silicon is used to produce multicrystalline silicon, for example by ingot casting. Multicrystalline silicon obtained in ingot form can be used to manufacture solar cells. However, the purity requirements for this solar silicon are not as high as those for the semiconductor silicon mentioned above, and the CZ method for producing monocrystalline solar cells generally dominates the market.

[0004] In principle, impurities (such as boron, phosphorus, and arsenic) can alter the desired properties of silicon semiconductors even within the ppt range (parts per trillion, 10⁻¹²). Besides dopant atoms, other trace metallic and nonmetallic impurities can also cause defects. Examples of these impurities include nonmetallic carbon and chlorine, as well as metallic contaminants such as iron, chromium, nickel, or copper.

[0005] The possible sources of the impurities mentioned even include reaction gases used in the production of polycrystalline silicon.

[0006] Polycrystalline silicon is typically produced using the Siemens process—chemical vapor deposition (CVD). This involves heating support bodies in a reactor and introducing a reaction gas containing silicon-containing components and hydrogen. The silicon-containing components are typically monosilanes (SiH4) or halosilanes with a general composition of SiHnX4-n (n = 0, 1, 2, 3; X = Cl, Br, I). They are usually chlorosilanes or mixtures of chlorosilanes.

[0007] Typical impurities that may be present in the reactant gases are, for example, boron (e.g., in the form of boron-hydride compounds or boron trichloride), phosphorus compounds (e.g., in the form of PH3, PCl3), aluminum compounds, and arsenic compounds. These impurities can cause the problems mentioned in the production of single crystals from polycrystalline silicon. In the context of quality control, it is necessary to monitor the type and amount of these impurities in trace amounts (ppbx or even pptx, where x can be a (atomic), v (volume), or w (weight)).

[0008] WO 2015 / 6217 A1 describes a laboratory-scale method in which the content of dopants in trichlorosilane (TCS) and hydrogen is indirectly determined by experimentally depositing a small amount of polycrystalline silicon in a quartz tube and then performing ICP-MS (inductively coupled plasma mass spectrometry) analysis.

[0009] US 2022 / 0381761 A1 describes a method, in particular, for determining metallic impurities in polycrystalline silicon rods obtained by test deposition. The impurities are thus entrained and enriched in the melt of the polycrystalline silicon rod by zone melting (zone pulling). The cooled block containing the enriched impurities is separated and dissolved in a water-soluble acid. The solution is then analyzed by atomic absorption spectrometry (AAS), ICP-MS, or inductively coupled plasma optical emission spectrometry (ICP-OES). This analysis typically takes 1 to 2 days.

[0010] Besides being time-consuming, these test-deposition-based methods have the following drawbacks: the amount of dopant found cannot usually be attributed to one of the reactant gases involved. However, such attribution is desirable, especially since the reactant gases used are increasingly derived from recycling processes and impurities must be constantly checked. In principle, attribution is possible, but only if all reactant gases, except the gas being analyzed, are of high purity. However, the separation of high-purity chlorosilanes is very time-consuming and expensive, as complex multi-stage distillation processes must be run. Furthermore, the contamination-free storage of such high-purity chlorosilanes requires sophisticated equipment.

[0011] Furthermore, the variables determined by the test deposition are merely average values, because for the test deposition, the potentially contaminated reaction gas must be supplied within several hours.

[0012] W. Lindinger et al. described the analysis of volatile organic compounds at pptv levels in ambient air via proton-transfer-reaction mass spectrometry (Lindinger et al.: Proton-transfer-reaction mass spectrometry (PTR-MS): on-line monitoring of volatile organic compounds at pptv levels, Chemical Society Reviews, 1998, vol. 27, 347-354). In this case, the gaseous analyte (ambient air) is chemically ionized via a proton transfer reaction, which typically does not lead to undesirable dissociation of the analyte components. In the analyzer, the effect of the electric field then causes the analyte components to be spatially (e.g., quadrupole) or time-of-flight (TOF) separated according to their mass / charge ratio (m / z ratio), or, in the case of TOF, according to their time of flight. In the case of TOF, the time of flight must still be calibrated to m / z with a known reference mass. The mass spectrometer does not directly measure mass, but only the ratio of mass (m) to charge (z). It is necessary to consider that particles can also have multiple charges. The detector then quantifies the previously separated mass. As for the apparatus, a PTR mass spectrometer is described, for example, in US 2021 / 0057203 A1.

[0013] However, PTR-MS is based on the formation of positive ions, and therefore it has not been possible to use it to detect impurities mentioned in chlorosilane streams until now. Since PTR-MS is typically operated with water as the ionizing agent, when applied to chlorosilane streams, this would result in the formation of silica and hydrogen chloride in the measuring instrument. Due to the chemical properties of boron compounds (strong Lewis acids), these cannot be selectively ionized by proton transfer. [Summary of the Invention]

[0014] In view of the above-mentioned disadvantages, the object of the present invention is to provide a trace analysis and detection method for impurities in chlorosilane with high time resolution.

[0015] This objective is achieved by a method for trace analysis to detect and quantify compounds of boron and / or aluminum in a gas stream or liquid stream containing at least one chlorosilane. The method comprises the following steps: a) removing a gaseous sample from the gas stream and mixing it with an inert gas to form a gaseous sample, or removing a liquid sample from the liquid stream, wherein the liquid sample is mixed with an inert gas in an evaporator unit and evaporated to form a gaseous sample; b) transferring the obtained gaseous sample to the reaction chamber of a mass spectrometer, wherein electrons generated in the ion source by plasma discharge react with chlorosilane to form chloride ion species, and wherein the chloride ion species react with compounds of boron and / or aluminum by chemical ionization to obtain boron chloride and / or aluminum chloride ion species; c) separating and detecting the boron chloride and / or aluminum chloride ion species.

Implementation Method

[0019] Anions with free electron pairs, such as Cl-, SF5-, and SiHCl4-, are hard Lewis bases that react efficiently with hard Lewis acids such as boron compounds (e.g., BCl3, BHCl2) and aluminum compounds (e.g., AlCl3, AlHCl2) to form stable anions. Surprisingly, these stable anions in the chlorosilane stream can be detected in the range of ppbv to pptv using a modified PTR-MS. "Modified PTR-MS" should therefore be understood as meaning that the device is specifically designed for anions.

[0020] By supplying energy (e.g., plasma discharge), electrons (e-, equation (1) below) formed by an inert gas in an ion source (e.g., a corona discharge ion source) are accelerated in an electric field to a kinetic energy in the range of several electron volts (0.1 to 10 eV, particularly 0.5 to 3 eV), and in the ion source and / or reaction chamber, they encounter chlorosilane molecules from the gaseous sample obtained in step a), a small fraction of which may also flow out of the reaction chamber in the direction of the ion source. This results in the chlorosilane being ionized by electron attachment and dissociation electron attachment (DEA), resulting in the formation of mainly silicon chloride ions (SiHnClx-, where n=0 or 1 and x=3 or 4) and Cl- (chloride ion species), in which uncharged atoms or molecules are eliminated. Attachment may also occur in the space between the discharge and the entry into the reaction chamber, where the inert gas is pumped out of the ion source. The negative chloride ion species then serves as the main ion for the detection of boron and aluminum in method step c).

[0021] The method of the present invention is preferably used for detecting boron compounds.

[0022] The reaction pathways for chemical ionization are shown below using TCS and BCl3, as well as argon as an inert gas. (1) Ar + e- → Ar+ + 2e- (electron production) (2) e- + SiHCl3 → SiHCl2 + Cl- (DEA) (3) e- + SiHCl3 → SiCl3- + H (DEA) (4) Cl- + BCl3 → BCl4- (chemical ionization)

[0023] The inert gas may also be any other rare gas or nitrogen, preferably argon. The purity is preferably at least 6 N.

[0024] The boron compounds present in the gas stream or liquid stream are preferably selected from the group consisting of boron chlorides, boron oxides, silicon chloride boron oxides, borohydrides and mixtures thereof.

[0025] Typical borohydrides are BH3 and B2H6. Ionic species formed by chemical ionization are, for example, BH3Cl- and B2H6Cl-.

[0026] Typical boron chlorides are BCl3, BOCl, BHCl2, and BH2Cl. Ionic species formed by chemical ionization are, for example, BCl4-, BOCl2-, BHCl3-, and BH2Cl2-.

[0027] Typical boron oxides are B2O3, B3O4Cl, and B3O4SiCl2H. Ionic species formed by chemical ionization are, for example, B2O3Cl-, B2O3SiCl2H-, B3O4Cl2-, and B3O4SiCl3H-. Any boron oxide rings present can be broken by evaporation or by reaction in a reaction chamber. The resulting fragments (BO2- and BOCl2-) can also be detected by the method of the present invention.

[0028] Typical silicon boron chloride oxides (X-Si-OBY, where X and Y can be Cl or H independently) are SiCl4HBO, Si2Cl6HBO, Si3Cl8HBO, and SiCl2HBO2. Ionic species formed by chemical ionization are, for example, SiCl5HBO-, Si2Cl7HBO-, Si3Cl9HBO-, and SiCl3HBO2-.

[0029] The aluminum compounds present in the gas stream or liquid stream are preferably selected from the group consisting of aluminum chlorides, aluminum oxides, aluminum hydrides and mixtures thereof.

[0030] A typical aluminum chloride is AlCl3. The ionic species formed by chemical ionization is AlCl4-.

[0031] Chlorosilanes are preferably selected from the group consisting of tetrachlorosilanes, TCS, dichlorosilanes, monochlorosilanes, organochlorine monosilanes, and mixtures thereof. Organochlorine monosilanes are preferably selected from the group consisting of dichloromethylsilanes, trichloromethylsilanes, dichlorodimethylsilanes, and mixtures thereof.

[0032] Therefore, the chloride ion species formed from chlorosilane in step b) can be: (2) e- + SiCl4 → SiCl3 + Cl- (DEA) (3) e- + SiCl4 → SiCl4- (DEA) (4) e- + SiH2Cl2 → SiH2Cl + Cl- (DEA) (5) e- + SiH2Cl2 → SiHCl2- + H- (DEA) (6) e- + SiH3Cl → SiH3 + Cl- (DEA) (7) e- + SiH3Cl → SiH2Cl- + H- (DEA)

[0033] Liquid or gas streams containing TCS and / or silicon tetrachloride (STC) are preferred, especially liquid streams. This can consist essentially of TCS and / or STC. "Essentially" here means that the liquid or gas stream can contain additional chlorosilane in a proportion of less than 5% by weight, preferably less than 3% by weight.

[0034] The concentration of boron and / or aluminum compounds in the liquid or gas stream can be from 10 pptv to 1 ppmv, preferably from 250 pptv to 500 ppbv, and more preferably from 500 pptv to 250 ppbv. 10 pptv is generally the detection limit of this method. Therefore, 1 pptv means that there is one molecule of boron or aluminum compound per 10¹² molecules of sample. In this case, the ideal gas law can be approximated well. The number of molecules is proportional to the volume. Under the low pressure in the mass spectrometer, this assumption is generally satisfactorily satisfied and proven to be reasonable.

[0035] In the case of a liquid flow, the sample taken from the liquid flow is completely evaporated in the evaporator unit. The evaporation in step a) is preferably carried out at a temperature of 15°C to 190°C, more preferably 20°C to 150°C, and most preferably 20°C to 100°C. The temperature is preferably fixed and controlled in the evaporator unit.

[0036] The pressure in the evaporator unit can be 1.5 to 5 bar, preferably 2 to 4 bar, and even more preferably 2.5 to 3 bar. The pressure is detected using a suitable pressure gauge (e.g., an electronic transmitter) and regulated to the set value by closed-loop control. All pressure values ​​are absolute pressures (bars (a)).

[0037] Evaporation, especially aerosol evaporation. Here, the sample is mixed with an inert gas, which results in the formation of evaporating liquid, such as droplets evaporating through a heating rod. Aerosol formation lowers the boiling point of the liquid sample and allows evaporation to occur at lower temperatures in a particularly gentle, i.e., non-destructive (without analyte breakage) manner. Typically, the sample remains gaseous at room temperature (20-25°C). To avoid introducing unwanted exogenous gases, the same inert gas as the free gas in the ion source of the mass spectrometer is typically used. The purity of the inert gas is preferably at least 6 N.

[0038] The sample is preferably taken out from a bypass conduit parallel to the gas or liquid flow, wherein the bypass conduit is at a lower pressure than the gas or liquid flow. In the case of a gaseous sample, the bypass conduit is not absolutely necessary.

[0039] The gaseous sample obtained in step a) can then be transferred to the reaction chamber of the mass spectrometer via a bypass conduit (step b) in which case the mass spectrometer automatically draws in a fixed amount of sample.

[0040] In the case of liquid flow, the evaporator unit is typically located upstream of the bypass duct.

[0041] The pressure in the bypass catheter is preferably 0.1 to 1 bar, more preferably 0.3 to 0.9 bar, and even more preferably 0.5 to 0.8 bar.

[0042] Surprisingly, it was found that particularly low concentrations of boron and aluminum compounds could be detected under this pressure gradient (pressure reduction) between the evaporator unit and the bypass duct.

[0043] The volume ratio of the liquid sample supplied after evaporation (the mass of the liquid, for example, the volume converted into gas by means of the ideal gas law) to the volume of the inert gas in the gaseous sample downstream of the evaporator unit is preferably 1:0.5 to 1:20, more preferably 1:0.75 to 10, and particularly 1:1 to 1:5.

[0044] In online measurement operations, sampling is preferably continuous. Therefore, this is particularly advantageous for instantaneous measurements with maximum time resolution.

[0045] Sampling can be accomplished using a suitable flow meter, preferably a flow meter with a control unit (e.g., a float flow meter or a Coriolis mass flow meter and mass flow controller), which discharges the required amount of sample from a bypass conduit.

[0046] The reaction chamber and the ion source are preferably separated from each other, wherein chloride ion species are generated in the ion source.

[0047] Electrons can be generated in an ion source, for example, through direct current (DC) plasma discharge. The resulting uncharged and positively charged byproducts are typically removed by suction filtration. An electric field is usually used to prevent positively charged byproducts from further entering the reaction chamber. Most of the uncharged byproducts can be removed by an attraction device within the ion source.

[0048] Boron chloride and / or aluminum chloride ion species are preferably separated (or in other words, isolated) in step c) by a method selected from the group consisting of: fan-shaped magnetic field, quadrupole, electromagnetic ion trap, electro-ion trap, time-of-flight analyzer, orbital trap and combinations thereof.

[0049] The detection in step d) is preferably performed using a detector selected from the group consisting of: a converted denier electrode with a secondary ion multiplier, a Faraday cup, a microchannel plate, inductive detection (in the case of an orbital trap), and combinations thereof.

[0050] Another aspect of the present invention relates to the use of the method of the present invention for analysis in the production of polycrystalline silicon and / or chlorosilanes, particularly TCS, especially for the online analysis of gas or liquid streams.

[0051] More particularly, the flow is a liquid or gas flow containing TCS, preferably a liquid flow. More preferably, the liquid flow is essentially composed of TCS.

[0052] A typical application example is the determination of boron content in distillation. This application of the method of the present invention allows for more cost-effective control of the distillation process. Measurements can be taken at several key points during distillation. If the boron concentration is higher or lower than a set level, appropriate measures can be taken, such as increasing or decreasing the amount of steam supplied.

[0053] Another example is the determination of boron and / or aluminum content during the commissioning of equipment, conduits, tanks, etc. Typically, new or refurbished factory parts result in the introduction of dopants. However, these vary in type and concentration. A suitable means of ensuring high-quality commissioning at these points, while remaining cost-effective, is to perform measurements with high time resolution.

[0054] For analysis, PTR-MS from Ionicon or Tofwork can be modified, for example. These modifications are necessary for operation with corrosive gases (TCS) and detection of anions.

[0055] In the production of polycrystalline silicon and halosilanes, waste gas consisting of unconverted hydrogen and halosilanes is typically obtained. Treatment of this waste gas is important due to cost considerations. Treatment of waste gas generated in the production of polycrystalline silicon is described, for example, in US 2013 / 0011558 A1.

[0056] Typically, the waste gas is fed into a multiple condensation unit, where the condensate is separated into low-boiling-point and high-boiling-point fractions by distillation. The remaining gaseous fraction of the waste gas after condensation is sent to an adsorption unit. Here, hydrogen is separated from the other components of the gas stream and can be reused as recovered hydrogen.

[0057] In addition to TCS, which is the main component, other chlorosilanes may be present in small amounts. For example, the reactant gas may be hydrogen and TCS, wherein the TCS contains a small amount of dichlorosilane as an impurity. Furthermore, the boron and / or aluminum compounds mentioned earlier may be present in trace amounts. The condensed gas typically contains TCS, dichlorosilane, and HCl. The exhaust gas before condensation typically contains HCl, methylchlorosilane, dichlorosilane, TCS, STC, and high-boiling-point substances.

[0058] Example

[0059] Settings:

[0060] In the purification of chlorosilanes, especially TCS, a modified PTR-TOF (proton transfer reaction-time of flight) MS (from Ionicon) was installed for online analysis of boron and aluminum compounds using the method of the present invention. The PTR-MS was installed between two distillation columns. The TCS used as the test medium typically has a dopant content of less than 100 ppbx (x = a, v, w), and is mostly composed of boron, as other dopants such as Al, P, As, and Sb are present in amounts of less than 500 pptx.

[0061] Samples were taken from the liquid TCS stream (20°C, 1.3 bar, 20-30 l / h) via a bypass conduit. First, a sample of 300 g / h (corresponding to a liquid volume of 0.2 l / h) was transferred to an aerosol evaporator via a solenoid valve and mixed therewith with argon (30 l / h) at approximately 1.5 bar (a). Evaporation was carried out at 40°C. TCS has a boiling point of 32°C under standard conditions. Aerosol evaporation lowers the boiling point to approximately 12°C. In this case, evaporation was carried out at 40°C to evaporate potentially high-boiling-point compounds from the silane and siloxane groups (whose boiling points are higher than the TCS's boiling point). The resulting gaseous sample of 60 l / h downstream of the evaporator was guided through a PTR-TOF-MS at a reduced pressure of 0.75 bar via another bypass conduit. The PTR-TOF-MS obtained the required amount of approximately 3 l / h from this conduit. Ionic species formed by plasma discharge (electrons generated in argon gas) and subsequent chemical ionization are separated by TOF and detected on a microchannel plate (MCP).

[0062] The TCS stream from which samples for the modified PTR-TOF-MS are obtained is also used for the deposition of polycrystalline silicon in the Siemens reactor (test deposition). Generally, the modified PTR-TOF-MS for online analysis of boron and aluminum compounds can also be installed on the feed gas duct leading to the Siemens reactor (before mixing with hydrogen).

[0063] The volumetric flow rate is determined by a flow meter (float flow meter or Coriolis mass flow controller).

[0064] Validation of the improved PTR-TOF MS:

[0065] The test gas (argon gas with a defined proportion of boron trichloride) is directly introduced into a gaseous TCS argon flow (from an aerosol evaporator). For this purpose, a high-purity TCS with a boron content below the detection limit (corresponding to 10 ppta or less) is used. The test gas contains a defined amount of boron, for example, 25 ppbv. Using a defined volumetric flow rate, for example, 0.6 l / h (10 ml / min), a boron content of 5 ppbv is obtained in the test medium introduced into the PTR-TOF-MS. The test gas is diluted with the test medium at a ratio of 1:5. The proportion of boron in the test medium is not considered.

[0066] The combination of test gas and test medium allows for reliable verification of concentration. Using pure test gas will not yield the same results, as TCS may affect concentration or ionization. In terms of equipment, a separate inlet for the test gas is installed in the measuring gas conduit, which can be used to meter the addition of different amounts of test gas via a flow controller.

[0067] The ions measured in the MCP are presented in the spectrum. The masses (actually m / z) of the molecules or their isotopes are presented here as Gaussian curves. The Gaussian curves are derived from the resolution of the apparatus. At infinite resolution, there will be only one peak at exactly one mass. The area under the curve represents the count, i.e., the number of ions of the mass detected in the MCP. These counts can be converted to theoretical concentrations using known formulas (see W. Lindinger, A. Hansel and A. Jordan, Int. J. Mass Spectrom. Ion Processes, 1998, 173, Issue 3, p. 191, ISSN 0168-1176). The theoretically determined value or concentration is verified and adjusted by the concentration provided in the calibration.

[0068] Comparative Measurement (Test Deposition):

[0069] For comparative measurements, single crystals were produced using polycrystalline silicon manufactured via the Siemens process. For this purpose, deposition in the Siemens reactor was terminated after 9 hours. The resulting polycrystalline silicon rods had a diameter of approximately 18 mm. One of these polycrystalline silicon rods was then used as a sample for further analysis.

[0070] Analysis is performed using zone melting, which forms single-crystal silicon rods. This method is described, for example, in US 2022 / 0381761 A1. The content of B and / or Al can usually be determined by low-temperature photoluminescence spectroscopy and / or low-temperature infrared spectroscopy using only single crystals.

[0071] Typically, the dopant concentration in a single crystal silicon sample can be determined by photoluminescence spectroscopy with a detection limit as low as about 1 ppta (the detection limit applies to B, P, Al, and As), and by low-temperature infrared spectroscopy with a detection limit as low as 10 ppta for B and Al (see SEMI MF1630 - Test Method for Low Temperature FT-IR Analysis of Single Crystal Silicon for III-V Impurities).

[0072] When measured by ICP-MS, the detection limits for boron and phosphorus, based on the test solution, are approximately 20 pptw and 17 pptw, respectively. Also based on the test solution, the detection limits for Al and As are <1 pptw (see J. Takahashi and K. Kasahara, Analysis of metallic components in hydrocarbon fuels by ICP-MS, Agilent Application Note, Dec. 2013: 5991-3264EN).

[0073] Determination of B and / or Al by low-temperature photoluminescence spectroscopy:

[0074] A wafer with a thickness of approximately 3 mm was cut from a single-crystal silicon rod using a saw (e.g., an Accutom-5 with a diamond cutting disc, from Struers). The surface of the wafer was etched with a mixture of hydrofluoric acid and nitric acid to remove crystal defects. The concentrations of B and Al, and other dopants as needed, were determined on the etched silicon wafer by low-temperature photoluminescence spectroscopy according to SEMI MF1389-00 (Test Method for Photoluminescence Analysis of III-V Impurities in Single-Crystal Silicon).

[0075] In Figure 1, the boron concentration in the test medium was measured over approximately 62 days (from May 19 to July 20) (curve: real-time analysis). Measurements were taken at 5-minute intervals. Each measurement is shown as a gray dot. For better comparability, the moving average (20 values) is shown in black. The boron concentration from the test deposition is identified by a rhombus. The width of the rhombus roughly corresponds to a time period of approximately 9 hours (the duration for which the polycrystalline silicon rod was obtained; the single crystal was obtained from the polycrystalline silicon rod using the float zone (FZ) method). Therefore, the boron concentration value assigned to this rhombus is the average value over that time period.

[0076] Boron concentration (y-axis) is usually expressed as [ppbx]. It should be noted that in test deposition, these values ​​involve atoms [ppba], and in the method of the present invention, they involve volume [ppbv].

[0077] Generally, the correlation between the boron concentration obtained from the test deposition and the boron concentration obtained by the method of the present invention is evident from Figure 1. However, differences can also be observed. In the method of the present invention, boron molecules are measured; in the test deposition, boron atoms in the silicon lattice are measured. During the deposition process, various boron compounds may be incorporated into silicon at different rates and with different efficiencies. These incorporation rates, which have not yet been finalized, are determined by factors in an empirical comparison of two values ​​(from the test deposition and PTR-TOF-MS). Using these factors (Table 1), there is good agreement between the two measurements. Theoretically determined values ​​are taken, and these values ​​are compared with the test deposition values ​​over a relatively long period of time (May 19 to May 31). The optimal correlation is determined by adjusting the factors referenced in Table 1. Concentrations are calculated using these factors for the remaining time period. As shown in Figure 1, good agreement is observed during the period from June 1 to July 20.

[0078] In this measurement, different boron species can be identified online for the first time. This knowledge means that not only can the installation rate be estimated, but the cleaning process can also be adjusted. This can be achieved by selectively removing low-boiling-point substances (e.g., BCl3) or high-boiling-point substances (e.g., boron oxide compounds) from the process.

[0079] Table 1 molecular Factors BO2 - 2.2 BOCl2 - 4.5 BCl4 - 2 HBO2SiCl3 - 2 SiOBCl5H - 2

[0080] In Figure 2, the boron concentration in the test medium was measured over approximately 6 days and 9 hours (from April 27 to May 4) (curve: real-time analysis). The measurement interval in the method of this invention is 5 minutes. The boron concentration from the test deposition is identified by a diamond. The horizontal error bars belonging to the diamond correspond to the time period of approximately 9 hours (used to obtain the duration of the polycrystalline silicon rod, from which the single crystal was obtained by the FZ method).

[0081] The boron peak 1 marked in Figure 2 (approximately 56 ppb boron at approximately 3:00 AM on April 29th) falls exactly between the two test depositions and therefore cannot be detected in the conventional way (test deposition). The method of the present invention will no longer exhibit this inaccuracy.

[0082] The marked boron peak 2 (approximately 35 ppb boron at approximately 6 PM on May 2nd) is roughly in the middle of the test deposition. Since the values ​​measured by the test deposition are always averages, this boron peak 2 cannot be identified in the conventional way.

[0083] The method of the present invention is also particularly advantageous in that it can distinguish between different types of boron and aluminum.

[0084] Figure 3 shows the percentage distribution of the four boron species over a period of approximately 4.5 days (based on the total boron content of the test medium).

[0085] Point 1 marked in Figure 3 (around noon on May 17) corresponds to the change in the composition of boron molecules. At point 1, the proportions of molecules C (HBO2SiCl3-) and D (BCl4-) decrease, while the proportions of molecules A (BOCl2-) and B (BO2-) increase. For molecule 2, the increase is only temporary, and its proportion decreases back to its previous level (around May 19). The proportion of molecule B remains elevated until the end (approximately 60%).

[0086] Molecules A and B can be segments of boron oxide rings (e.g., cycloboroxanes in which hydrogen is replaced by chlorine). Molecule C can be formed by the hydrolysis of BCl3 with oxygen in the TCS molecule. In this case, the cycloboroxane will be a high-boiling-point compound, and BCl3 will be a low-boiling-point compound. Starting from point 1 marked in Figure 3, only the high-boiling-point fraction (molecule A: BOCl2; molecule B: BO2-) increases, while the low-boiling-point fraction (molecule C: HBO2SiCl3-; molecule D: BCl4-) decreases.

[0087] This knowledge enables specific tower control to specifically remove additional boron. This corresponds to removal via the bottom of the tower. Without this knowledge, additional boron removal at the top of the tower would be required, meaning higher energy consumption. [Simplified Explanation of the Diagram]

[0016] Figure 1 shows the determination of boron concentration by the method of the present invention.

[0017] Figure 2 shows the boron concentration in the chlorosilane stream used for polycrystalline silicon production determined by the method of the present invention, compared with the boron concentration determined after testing the deposition of a single crystal.

[0018] Figure 3 shows the percentage distribution of various boron species by means of the method of the present invention.

Claims

1. A method for trace analysis to detect and quantify boron and / or aluminum compounds in a gas stream or liquid stream containing at least one chlorosilane, the method comprising the steps of: a) removing a sample from the gas stream and mixing it with an inert gas to form a gaseous sample, or removing a liquid sample from the liquid stream, wherein the liquid sample is mixed with an inert gas and evaporated in an evaporator unit to form a gaseous sample; b) transferring the gaseous sample obtained in step a) to a reaction chamber of a mass spectrometer, wherein electrons generated in an ion source by plasma discharge react with the chlorosilane to form chloride ion species, and wherein the chloride ion species reacts with the boron and / or aluminum compounds by chemical ionization to yield boron chloride and / or aluminum chloride ion species; c) separating and detecting the boron chloride and / or aluminum chloride ion species.

2. The method of claim 1, wherein the boron compound is selected from the group consisting of boron chloride, boron oxide, boron hydride, silicon chloride boron oxide, and mixtures thereof.

3. The method as claimed in claim 1 or 2, wherein the aluminum compound is selected from the group consisting of aluminum chlorides, aluminum oxides, aluminum hydrides, and mixtures thereof.

4. The method as claimed in claim 1 or 2, wherein the chlorosilane is selected from the group consisting of tetrachlorosilane, trichlorosilane, dichlorosilane, monochlorosilane, organochloromonosilane, and mixtures thereof.

5. The method as claimed in claim 1 or 2, wherein the concentration of the boron and / or aluminum compound is from 10 pptv to 1 ppmv.

6. The method as claimed in claim 1 or 2, wherein the liquid sample is evaporated at a temperature of 15°C to 190°C in step a).

7. The method as described in claim 1 or 2, wherein the pressure in the evaporator unit is 1.5 to 5 bar.

8. The method as claimed in claim 1 or 2, wherein the sample is removed from a bypass conduit parallel to the gas or liquid flow, wherein the bypass conduit is at a lower pressure than the gas or liquid flow.

9. The method as described in claim 8, wherein the pressure in the bypass conduit is 0.1 to 1 bar.

10. The method as claimed in claim 1 or 2, wherein the reaction chamber and the ion source are separated from each other, wherein the chloride ion species is generated in the ion source.

11. The method as claimed in claim 1 or 2, wherein electrons are generated by plasma discharge of direct current in step b), wherein uncharged byproducts and positively charged byproducts are removed by suction.

12. The method as claimed in claim 1 or 2, wherein the separation system in step c) is performed by a method selected from the group consisting of: a sector magnetic field, a quadrupole, an electromagnetic ion trap, an electric ion trap, a time-of-flight analyzer, an orbital trap, and combinations thereof.

13. The method as described in claim 1 or 2, wherein, The detection in step c) is performed using a detector selected from the group consisting of: a converted denier electrode with a secondary ion multiplier, a Faraday cup, a microchannel plate, inductive detection, and combinations thereof.

14. Use of the method as described in any one of claims 1 to 13 for analyzing gas or liquid flows in polycrystalline silicon production and / or chlorosilane production.

15. The use as described in claim 14, wherein the gas stream or liquid stream is a trichlorosilane stream.

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