Method for detecting and quantifying compounds of boron and / or aluminium

Abstract

The invention relates to a method for trace analytical detection and quantification of compounds of boron and / or aluminium in a gas or liquid flow containing at least one chlorosilane, comprising the steps of a) removing a sample from the gas flow and mixing with an inert gas to form a gaseous sample or removing a liquid sample from the liquid flow, 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) into the reaction chamber of a mass spectrometer, wherein electrons generated in an ion source by means of plasma discharge react with the chlorosilane to form chloride ion species and wherein the chloride ion species react with the compounds of boron and / or aluminum via chemical ionization to form boron and / or aluminum chloride ion species; c) separating and detecting the boron and / or aluminum chloride ion species.

Description

[0001] Wa12240P / Be

[0002] Methods for the detection and quantification of boron and / or aluminum compounds

[0003] The invention relates to a method for the trace-analytical detection and quantification of compounds of boron and / or aluminium in a gas or liquid stream containing at least one chlorosilane.

[0004] Polycrystalline silicon (polysilicon) serves as the starting material in the production of single-crystal silicon, for example by crucible pulling (Czochralski (CZ) process) or by zone melting (float zone process). The single-crystal silicon can be sawn into wafers and, after numerous further processing steps, used in the semiconductor industry to manufacture electronic components (e.g., resistors, diodes, bipolar transistors, and MOS transistors). These processing steps generally involve the targeted and localized doping of the single-crystal silicon with dopants. These include, in particular, atoms with three or five valence electrons, such as the elements of groups 3 and 5 of the periodic table.Therefore, a prerequisite for the production of these semiconductor components is that the silicon used is of the highest purity (no foreign doping) and is present as a perfect single crystal, because grain boundaries and lattice defects also lead to unwanted current paths.

[0005] Furthermore, polysilicon is used to produce multicrystalline silicon, for example, by means of the block casting process. The multicrystalline silicon obtained in block form can be used to manufacture solar cells. However, the purity requirements for this solar silicon are not as high as those for the previously described Wa12240P / Be

[0006] 2

[0007] Semiconductor silicon, and in general the CZ process for the production of single-crystal solar cells dominates the market.

[0008] In principle, impurities (e.g., boron, phosphorus, and arsenic) in the ppt range (parts per trillion, I²C) can already be present. -12) alter the desired performance of silicon semiconductors. Besides dopant atoms, other trace metal and non-metal impurities can also contribute to defects. Examples include the non-metals carbon and chlorine, and metallic impurities such as iron, chromium, nickel, or copper.

[0009] The reaction gases used in the production of polysilicon are already a possible source of the aforementioned impurities.

[0010] Polysilicon is usually produced using the Siemens process – a chemical vapor deposition (CVD) process. In this process, support structures are heated in a reactor, and a reaction gas containing a silicon-containing component and hydrogen is introduced. The silicon-containing component is typically monosilane (SiH₄) or a halosilane with the general composition SiH₄. n X4- n(n = 0, 1, 2, 3; X = Cl, Br, I) . It is usually a chlorosilane or a chlorosilane mixture.

[0011] Typical impurities that may be present in the reaction gases include boron (e.g., in the form of boron hydrides or boron trichloride), phosphorus compounds (e.g., in the form of PHa, PCla), aluminum, and arsenic compounds. These impurities can lead to the aforementioned problems during single-crystal production from polysilicon. Monitoring the type and quantity of these impurities in Wa12240P / Be is essential for quality control.

[0012] 3

[0013] Trace area (ppbx or even pptx area, where x = a (by atoms ) , v (by volume ) or w (by weight ) ) necessary .

[0014] WO 2015 / 6217 Al describes a laboratory-scale method in which the content of dopants in trichlorosilane (TCS) and hydrogen is determined indirectly by sample depositing a small amount of polysilicon in a quartz tube, followed by ICP-MS analysis (inductively coupled plasma mass spectrometry).

[0015] US 2022 / 0381761 describes a method for determining metallic impurities in a polysilicon rod obtained by test deposition. The impurities are carried along and concentrated in the molten polysilicon rod by zone melting (zone pulling). The cooled section containing the concentrated impurities is separated and dissolved in an aqueous acid. This solution is then analyzed by atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), or inductively coupled plasma optical emission spectrometry (TCPE-DES). Such an analysis typically takes one to two days.

[0016] Besides the significant time investment, a disadvantage of these methods based on test deposition is that the detected dopant content generally cannot be attributed to any of the reactant gases involved. Such an attribution is particularly desirable given that the reactant gases used increasingly originate from recycling processes and must be constantly tested for impurities. While attribution is fundamentally possible, it is only feasible if all reactant gases except the one being analyzed are present in highly pure form. The production of Wa12240P / Be

[0017] Producing highly purified chlorosilanes is, however, very time-consuming and expensive, as it requires complex, multi-stage distillation processes. Furthermore, maintaining a contamination-free storage environment for such highly purified chlorosilanes is technically demanding.

[0018] Furthermore, the quantities determined by means of test separation are only average values, since potentially contaminated reaction gas must be supplied for a test separation over several hours.

[0019] W. Lindinger et al. describe an online analysis of volatile organic compounds at pptv levels in ambient air using proton transfer reaction mass spectrometry (Lindinger et al. Proton-transf er-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 method, a gaseous analyte (ambient air) is chemically ionized by a proton transfer reaction, which generally does not result in unwanted dissociation of the analyte components. In an analyzer, the analyte components are then spatially (e.g., quadrupole) or temporally (time-of-flight (TOF)) separated according to their mass-to-charge ratio (m / z ratio) or, in the case of TOF, according to their flight time, by the influence of electric fields. For TOF, the flight time still needs to be calibrated to m / z using known support masses.In a mass spectrometer, masses are not measured directly, but only the ratio of mass (m) to charge (z). It must be taken into account that a particle can also be multiply charged. The previously separated masses are then quantified at the detector. A PTR mass spectrometer is described, for example, in US 2021 / 0057203 Al. Wa12240P / Be.

[0020] 5

[0021] However, PTR-MS relies on the generation of positive ions, which is why its application for the detection of the aforementioned impurities in chlorosilane streams is not yet possible. Since PTR-MS typically uses water as the ionizing agent, its application to chlorosilane streams would lead to the formation of silica and hydrogen chloride within the instrument. Due to the chemical properties of boron compounds (strong Lewis acids), they cannot be selectively ionized by proton transfer.

[0022] In view of the described disadvantages, the object underlying the invention was to provide a trace analytical detection method for impurities in chlorosilanes with high temporal resolution.

[0023] This problem is solved by a method for the trace-analytical detection and quantification of boron and / or aluminum compounds in a gas or liquid stream containing at least one chlorosilane. The method comprises the following steps: a) taking a gaseous sample from the gas stream and mixing it with an inert gas to form a gaseous sample, or taking 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 into the 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 react with the boron compounds Wa12240P / Be

[0024] 6 and / or of the aluminium react by chemical ionization to boron and / or aluminium chloride ion species; c) Separation and detection of the boron and / or aluminium chloride ion species.

[0025] Anions with lone pairs of electrons, such as Cl⁻, SF⁻, and SiHClA⁻, are hard Lewis bases that react efficiently with hard Lewis acids, such as boron compounds (e.g., BCla⁻, BHCl₂) and aluminum compounds (e.g., AIDS⁻, AIHCl₂), to form stable anions. Surprisingly, these stable anions could be detected in chlorosilane streams using a modified PTR-MS in the ppbv to pptv range. "Modified PTR-MS" means that this instrument was specifically designed for anions.

[0026] The electrons (e, equations (1) below) generated from the inert gas in the ion source (e.g., corona discharge ion source) by energy input (e.g., plasma discharge) are accelerated in an electric field to kinetic energies in the range of a few electron volts (0.1 to 10 eV, especially 0.5 to 3 eV) and collide with chlorosilane molecules from the gaseous sample obtained in step a) in the ion source and / or the reaction chamber. A small portion of this gaseous sample may also flow from the reaction chamber towards the ion source. This process ionizes the chlorosilane through electron attachment and dissociative electron attachment (DEA), resulting primarily in silicon chloride ions (SiH₄²⁻). n Cl x“, with n = 0 or 1 and x = 3 or 4) as well as CI” (chloride ion species ) are formed, whereby a neutral atom or molecule is eliminated in this reaction. The addition can also occur in the space between the discharge and the inlet to the reaction chamber, where the inert gas is pumped out from the ion source. The negative chloride ion species then serve in Wa12240P / Be

[0027] 7

[0028] Process step c) as primary ions for boron and

[0029] Aluminum verification.

[0030] Preferably, the method according to the invention is used for the detection of boron compounds.

[0031] The reaction pathway of chemical ionization is shown below using the example of TCS and BCI3 and argon as an inert gas.

[0032] (1) Ar + e~ Ar+ + 2e (electron generation)

[0033] (2) e“ + SiHCls SiHCl2+ Cl" (DEA)

[0034] (3) e“ + SiHCls SiCl3' + H (DEA)

[0035] (4) CI“ + BCla BClA (chemical ionization)

[0036] The inert gas can also be any other noble gas or nitrogen; argon is preferred. The purity is preferably at least 6N.

[0037] The boron compounds contained in the gas or liquid stream are preferably selected from the group consisting of boron chlorides, boron oxides, silicon chloroboroxides, borohydrides and mixtures thereof.

[0038] Typical borohydrides are BHa and B₂He. The ion species formed by chemical ionization are, for example, BHaCl and B₂H₆C₁.

[0039] Typical boron chlorides are BCI3, BOC1, BHC12 and BH2C1. The ion species formed by chemical ionization are, for example, BCI4", BOC12", BHCI3 and BH2C12".

[0040] Typical boron oxides are B₂O₅, B₃O₄Cl, and B₃O₄SiCl₂H. Ionic species formed by chemical ionization include, for example, B₂O₃Cl₁, B₂O₃SiCl₂H, B₃O₄CIA, and B₃O₄SiCl₃H. (Possibly Wa12240P / Be)

[0041] The eight existing boron oxide rings can be fragmented by evaporation or by reaction in the reaction chamber. The resulting fragments (BO2 and BOC12) could also be detected using the method according to the invention.

[0042] Typical silicon chloroboroxides (X-Si-OBY, where X and Y can be independent of each other, either Gl or H) are SiCl4HBO, Si2CleHBO, SisClsHBO, and SiCl2HBO2. The ion species formed by chemical ionization are, for example, SiClsHBO, Si2Cl7HBO, SisClgHBO, and SiCl3HBO2-.

[0043] The aluminium compounds contained in the gas or liquid stream are preferably selected from the group consisting of aluminium chlorides, aluminium oxides, aluminium hydrides and mixtures thereof.

[0044] A typical aluminum chloride is AlCl. The ion species formed by chemical ionization is AICI4.

[0045] The chlorosilane is preferably selected from the group consisting of tetrachlorosilane, TCS, dichlorosilane, monochlorosilane, organochloromonosilane, and mixtures thereof. The organochloromonosilane is preferably selected from the group consisting of dichloromethylsilane, trichloromethylsilane, dichlorodimethylsilane, and mixtures thereof.

[0046] The products resulting from the chlorosilane in step b)

[0047] The chloride ion species can therefore be:

[0048] (2) e~ + SiCl4SiCl3 + Eq" (DEA)

[0049] (3) e~ + SiCl4SiCl4' (DEA)

[0050] (4) e~ + SiH2Cl2SiH2Cl + Eq" (DEA)

[0051] (5) e~ + SiH2Cl2SiHCl2" + H (DEA)

[0052] (6) e~ + SiHsCl SiH3+ Eq" (DEA)

[0053] (7) e~ + SiHsCl SiH2Cl" + H (DEA) Wa12240P / Be

[0054] 9

[0055] Preferably, the liquid or gas stream, in particular a liquid stream, contains TCS and / or silicon tetrachloride (STC). This stream may consist substantially of TCS and / or STC. "Substantially" means that the liquid or gas stream may contain further chlorosilanes in a proportion of less than 5 wt.%, preferably less than 3 wt.%.

[0056] The concentration of the boron and / or aluminum compounds in the liquid or gas stream can be 10 pptv to 1 ppmv, preferably 250 pptv to 500 ppbv, and particularly preferably 500 pptv to 250 ppbv. The detection limit of the method is typically 10 pptv. Accordingly, 1 pptv means that one molecule of the boron or aluminum compound is present per 10 12The number of molecules in the sample is present. It can be assumed to a good approximation that the ideal gas law applies. Then the number of molecules is proportional to the volume. This assumption is generally well met and justified at the low pressure in a mass spectrometer.

[0057] If the sample is a liquid stream, it is completely evaporated in the evaporator unit. Evaporation in step a) preferably takes place at a temperature of 15 to 190°C, particularly preferably 20 to 150°C, and especially 20 to 100°C. The temperature is preferably set and controlled at the evaporator unit.

[0058] The pressure in the evaporator unit can be 1.5 to 5 bar, preferably 2 to 4 bar, particularly preferably 2.5 to 3 bar. The pressure is measured with a suitable pressure gauge (e.g., electronic transmitter) and displayed on the Wa12240P / Be

[0059] The set value is regulated by 10. All pressure readings are absolute pressure (bar ( a ) ).

[0060] The vaporization process is primarily an aerosol vaporization. The sample is mixed with an inert gas, forming droplets which are then vaporized, for example, using a heating rod. The aerosol formation lowers the boiling point of the liquid sample, allowing for particularly gentle vaporization at a lower temperature, thus preventing destructive damage (no fragmentation of the analyte). The sample typically remains gaseous at room temperature (20-25 °C). To avoid the introduction of unnecessary foreign gases, the same inert gas used in the ion source of the mass spectrometer is generally employed. The purity of the inert gas is preferably at least 6N.

[0061] Preferably, the sample is taken from a bypass line parallel to the gas or liquid flow, wherein the bypass line has a lower pressure than the gas or liquid flow. A bypass line is not strictly necessary for gaseous samples.

[0062] The transfer of the gaseous sample obtained in step a) into the reaction chamber of the mass spectrometer (step b)) can then be carried out via the bypass line, whereby the mass spectrometer automatically draws in a fixed amount of sample.

[0063] If it is a liquid flow, the evaporator unit is usually located upstream of the bypass line. Wa12240P / Be

[0064] 11

[0065] Preferably the pressure in the bypass line is 0.1 to 1 bar, preferably 0.3 to 0.9 bar, particularly preferably 0.5 to 0.8 bar.

[0066] Surprisingly, it was found that particularly low concentrations of boron and aluminum compounds could be detected at this pressure gradient (pressure reduction) between the evaporator unit and the bypass line.

[0067] The volume ratio of the liquid sample supplied after evaporation (conversion of the mass of the liquid, e.g., via the ideal gas law, to the volume of the gas) to the inert gas in the gaseous sample after the evaporator unit is preferably 1:0.5 to 1:20, particularly preferably 1:0.75 to 10, and especially 1:1 to 1:5.

[0068] Sample collection is preferably carried out continuously in online measurement mode. This offers the particular advantage of real-time measurement with maximum temporal resolution.

[0069] For sampling, a suitable flow meter, preferably with a control unit (e.g. with float or Coriolis mass flow measurement and mass flow control), can be used to remove the desired sample quantity from the bypass line.

[0070] Preferably, the reaction chamber and the ion source are separated from each other, with the generation of the chloride ion species taking place in the ion source.

[0071] The generation of electrons in the ion source can be achieved, for example, with a direct current plasma discharge. Neutral and positively charged byproducts that are also produced are typically extracted. Byproducts with positive Wa12240P / Be

[0072] 12

[0073] Charges are generally prevented from progressing further into the reaction chamber by electric fields. Neutral byproducts can largely be removed by an extraction system located in the ion source.

[0074] The separation (in other words, the singulation) of the boron and / or aluminum chloride ion species in step c) is preferably carried out using a method selected from the group consisting of magnetic sector field, quadrupole, electromagnetic ion trap, electric ion trap, time-of-flight analyzer, Orbitrap and combinations thereof.

[0075] The detection in step d) is preferably carried out with a detector selected from the group consisting of conversion dynode with secondary ion multiplier, Faraday cup, microchannel plate, inductive detection (in the case of Orbitrap) and combinations thereof.

[0076] Another aspect of the invention relates to the use of the inventive method for the analysis, in particular online analysis, of gas or liquid streams in the production of polysilicon and / or the production of chlorosilanes, in particular TCS.

[0077] In particular, this is a liquid or gas stream containing TCS, preferably a liquid stream. Most preferably, the liquid stream consists essentially of TCS.

[0078] A typical application is the determination of the boron content in distillation. This application of the method according to the invention makes it possible to control the distillation process more cost-effectively. Measurements can be taken at several critical points in the distillation process. If predetermined boron concentrations are exceeded or fall below specified limits (Wa12240P / Be), a measurement is taken.

[0079] 13. Suitable measures can be taken, e.g. increasing or decreasing the amount of steam supplied.

[0080] Another example is the determination of boron and / or aluminum content during the commissioning of equipment, pipelines, tanks, etc. New or refurbished plant components typically introduce dopants. However, these vary in type and amount. To ensure cost-effective yet high-quality commissioning, measurements with high temporal resolution at these points are appropriate.

[0081] For analysis, PTR-MS instruments from companies such as lonicon or Tofwerk can be modified. These modifications are necessary to enable operation with corrosive gases (TCS) and the detection of anions.

[0082] The production of polysilicon and halosilanes typically generates a gas consisting of unreacted hydrogen and halosilanes. Treating this gas is important for cost reasons. The treatment of the gas generated during polysilicon production is described, for example, in US 2013 / 0011558 Al.

[0083] Typically, the exhaust gas is fed into a multi-stage condensation unit, where the condensate is separated into low-boiling and high-boiling components by distillation. The gaseous components of the exhaust gas remaining after condensation are then subjected to adsorption. Here, hydrogen is separated from the other components of the gas stream and can be reused as recycled hydrogen. Wa12240P / Be

[0084] 14

[0085] In addition to TCS, which is the main component, smaller amounts of other chlorosilanes may be present. For example, the reaction gas may consist of hydrogen and TCS, with the TCS containing small amounts of dichlorosilane as an impurity. Furthermore, the boron and / or aluminum compounds mentioned earlier may be present in trace amounts. The gas after condensation typically contains TCS, dichlorosilane, and HCl. The exhaust gas before condensation typically contains HCl, methylchlorosilane, dichlorosilane, TCS, STC, and high-boiling elements.

[0086] Fig. 1 shows the determination of a boron concentration according to the method according to the invention.

[0087] Fig. 2 shows the determination of a boron concentration in a chlorosilane stream for polysilicon production according to the inventive method in comparison to the determination of the boron concentration after test deposition of a single crystal.

[0088] Fig. 3 shows a percentage distribution of different boron species according to the inventive method.

[0089] Example

[0090] Construction :

[0091] In the purification process of chlorosilanes, particularly TCS, a modified PTR-TOF (Proton Transfer Reaction - Time-Of-Flight) MS (Family lonicon) was installed for the online analysis of boron and aluminum compounds according to the inventive method. The PTR-MS was positioned between two distillation columns. The TCS, as the measuring medium, typically has a dopant content of less than 100 ppbx (x = a, v, w), with boron being the predominant dopant, as other dopants such as Al, P, As, and Sb are present in amounts of less than 500 ppbx. Wa12240P / Be

[0092] 15

[0093] Samples were taken from the liquid TCS stream (20°C, 1.3 bar, 20-30 L / h) via a bypass line. Using a solenoid valve, a sample volume of 300 g / h (corresponding to 0.2 L / h liquid volume) was first transferred into an aerosol vapor and mixed there with argon (30 L / h) at approximately 1.5 bar(a). Vaporization took place at 40°C. TCS has a boiling point of 32°C under normal conditions. This is lowered to approximately 12°C by aerosol vaporization. In this case, vaporization was carried out at 40°C to evaporate any high-boiling compounds (whose boiling point is higher than that of TCS) from the silane and siloxane groups. The gaseous sample obtained at a rate of 60 L / h was routed from the evaporator through a further bypass line at a pressure of 0.75 bar past the PTR-TOF-MS. The PTR-TOF-MS extracted the required quantity of approximately 3 L / h from this line.The ion species formed by plasma discharge (electron generation in argon) with subsequent chemical ionization were separated via TOF and detected on a microchannel plate (MCP).

[0094] The TCS stream from which the sample for the modified PTR-TOF-MS was taken was also used for the deposition of polysilicon in a Siemens reactor (test deposition). In general, a modified PTR-TOF-MS for online analysis of boron and aluminum compounds can also be installed on the feed line to the Siemens reactor (before mixing with hydrogen).

[0095] The volume flows were determined using a flow meter (variable area flow meter or Coriolis mass flow controller).

[0096] Validation of the modified PTR-TOF-MS: Wa12240P / Be

[0097] 16

[0098] A test gas (argon with a defined proportion of boron trichloride) was introduced directly into the gaseous TCS argon stream (originating from the aerosol vapor). High-purity TCS with a boron content below the detection limit (corresponding to 10 ppta and less) was used for this purpose. The test gas contained a defined amount of boron, e.g., 25 ppbv. Using a defined flow rate, e.g., 0.6 L / h (10 ml / min), a boron content of 5 ppbv was obtained in the sample medium, which was introduced into the PTR-TOF-MS. The test gas was diluted by a factor of 1:5 by the sample medium. The boron content in the sample medium was not taken into account.

[0099] The combination of test gas and measuring medium enabled reliable verification of the concentrations. Using a pure test gas would not yield the same results because the TCS can influence the concentration or ionization. A separate inlet for the test gas was installed on the measuring gas line, allowing different quantities of test gas to be metered in using a flow regulator.

[0100] The ions measured at the MCP are displayed in a spectrogram. There, the individual masses (actually m / z) at which a molecule or its isotope is located are represented as a Gaussian curve. The Gaussian curve results from the resolution of the instrument. With infinite resolution, there would only be one peak at exactly one mass. The area under this curve represents the counts, i.e., the number of ions of a given mass detected at the MCP. These counts can be converted into a theoretical concentration using a known formula (see W. Lindinger, A. Hansel and A.

[0101] Jordan, Int. J. Mass Spectrom. Ion Processes, 1998, 173, Issue 3, p. 191, ISSN 0168-1176). This theoretically determined value Wa12240P / Be

[0102] 17. The concentration is checked and adjusted using the concentration supplied during calibration.

[0103] Comparative measurement (test deposition): For the comparative measurement, a single crystal was produced from polysilicon manufactured using the Siemens process. Deposition in the Siemens reactor was stopped after 9 hours. The diameter of the resulting polysilicon rods was approximately 18 mm. One of these polysilicon rods was then used as a sample for further analysis.

[0104] The analysis was performed using the zone melting method, which produces a single-crystal silicon rod. This method is described, for example, in US 2022 / 0381761 Al. Determining the B and / or Al content by low-temperature photoluminescence spectroscopy and / or low-temperature infrared spectroscopy can generally only be done using a single crystal.

[0105] In general, dopant concentrations in single-crystal silicon samples can be determined by photoluminescence spectroscopy up to a detection limit of approximately 1 ppta (detection limit applies to B, P, Al, As) and by low-temperature infrared spectroscopy up to a detection limit of 10 ppta based on B and Al (see SEMI MF1630 - Test Method for Low Temperature FT-IR Analysis of Single Crystal Silicon for III-V Impurities).

[0106] The detection limits for boron and phosphorus by ICP-MS are approximately 20 pptw and 17 pptw, respectively, based on the sample solution. The detection limits for aluminum and arsenic are < 1 pptw, also based on the sample solution (see J. Takahashi and K. Kasahara, Analysis of metallic components in Wa12240P / Be).

[0107] 18 hydrocarbon fuels by ICP-MS, Agilent Application Note, Dec. 2013: 5991-3264EN).

[0108] Determination of B and / or Al using low-temperature photoluminescence spectroscopy:

[0109] A slice approximately 3 mm thick was cut from the single-crystal silicon rod using a saw (e.g., Accutom-5 with a diamond cutting disc, Struers). The surface of the slice was etched with a mixture of hydrofluoric and nitric acid to remove crystal defects. The concentration of boron and aluminum, and possibly other dopants, was determined on the etched silicon slice using low-temperature photoluminescence spectroscopy according to SEMI MF1389-00 (Test Methods for Photoluminescence Analysis of Single Crystal Silicon for III-V Impurities).

[0110] In Figure 1, the boron concentration in the measuring medium was determined over approximately 62 days (from May 19th to July 20th) (curve: real-time analysis). The measurement interval was 5 minutes. The individual measured values ​​are shown as points in gray. For better comparability, a moving average (20 values) is shown in black. The boron concentrations from the test deposits are indicated by diamonds. The width of the diamonds corresponds approximately to a period of about 9 hours (duration for obtaining the polysilicon rods from which the single crystal is obtained using the float zone (FZ) process). The boron concentration value assigned to the diamond is therefore an average over this period.

[0111] The boron concentration (y-axis) is generally given in [ppbx]. It should be noted that in the test deposition, the values ​​refer to atoms [ppba], while in the process according to the invention, they refer to volume [ppbv]. Wa12240P / Be

[0112] In general, the agreement between the boron concentrations obtained from the test deposition and those obtained according to the inventive method is clearly visible in Figure 1. However, a discrepancy was also observed. In the inventive method, boron molecules are measured, while in the test deposition, the boron atom in the silicon lattice is measured. During the deposition process, the various boron compounds likely incorporate into the silicon at different rates and to varying degrees. These incorporation rates, which have not yet been fully investigated, were determined by factors in an empirical comparison of both values ​​(from test deposition and PTR-TOF-MS). Using these factors (Table 1), there is good agreement between the two measured values. The theoretically determined values ​​were used and compared with the test deposition values ​​over a longer period (May 19 to May 31).The best match was determined by adjusting the factors listed in Table 1. For the remaining period, the concentration was calculated using these factors. As shown in Figure 1, there is a good match for the period from June 1st to July 20th.

[0113] This measurement enabled the online detection of various boron species for the first time. This knowledge allows not only for estimating the incorporation rate but also for adjusting the purification processes. This can be achieved by selectively removing low-boiling (e.g., BCla) or high-boiling (e.g., boron oxide compounds) substances from the process. Wa12240P / Be

[0114] 20

[0115] Table 1

[0116] In Figure 2, the boron concentration in the measuring medium was determined over approximately 6 days and 9 hours (from April 27th to May 4th) (curve: real-time analysis). The measurement interval in the method according to the invention was 5 minutes. The boron concentrations from the test deposits are marked by diamonds.

[0117] The horizontal error bar belonging to the rhombuses corresponds to a period of approximately 9 h (duration for obtaining the polysilicon rods from which the single crystal is obtained using the FZ process).

[0118] The boron peak 1 marked in Figure 2 (at approximately 3 a.m. on April 29, approximately 56 ppb boron) occurred precisely between two test depositions and therefore could not be detected using conventional methods (test deposition). Such inaccuracies can no longer occur with the method according to the invention.

[0119] The marked boron peak 2 (at approximately 18 h on May 2nd, about 35 ppb boron) lies roughly in the middle of a test precipitation. Since the values ​​determined by test precipitation are always averages, this boron peak 2 was not detected using conventional methods.

[0120] The method according to the invention also allows, with particular advantage, a differentiation between different boron and aluminium species.

[0121] Figure 3 shows a percentage distribution (based on the total boron content of the measuring medium) of four boron species over a period of approximately 4.5 days. Wa12240P / Be

[0122] 21

[0123] Point 1, marked in Figure 3 (approximately hour 12 of May 17), corresponds to a change in the composition of the boron molecules. At this point 1, the proportion of molecule C (HBCtSiCls) and molecule D (BCI4) decreases, while the proportion of molecule A (BOCI2) and molecule B (BO2) increases. The increase in molecule 2 is only temporary, and its proportion returns to its previous level (around May 19). The proportion of molecule B remains elevated until the end (at approximately 60%).

[0124] Molecules A and B could be fragments of boron oxide rings (e.g., a boroxine with chlorine instead of hydrogen). Molecule C could have been formed by the hydrolysis of BCla with oxygen on a TCS molecule. In this case, the boroxine would be a high-boiling compound and BCI3 a low-boiling compound. From point 1 marked in Figure 3 onward, only the proportion of high-boiling compounds (molecule A: BOCI2; molecule B: BO2) has increased, while the proportion of low-boiling compounds (molecule C: HBCtSiCls; molecule D: BCI4) has decreased.

[0125] This knowledge enables targeted column control to selectively remove additional boron. This would correspond to separation via the bottom of the column. Without this knowledge, boron would also have to be separated via the top, which requires more energy.

Claims

Wa12240P / Be 22 Patentansprüche 1. A method for the trace-analytical detection and quantification of boron and / or aluminum compounds in a gas or liquid stream containing at least one chlorosilane, comprising the steps of: a) taking a sample from the gas stream and mixing it with an inert gas to form a gaseous sample, or taking 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) into the 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 react with the boron and / or aluminum compounds by chemical ionization to form boron and / or aluminum chloride ion species;c) Separation and detection of the boron and / or aluminum chloride ion species.

2. Method according to claim 1, characterized in that the boron compounds are selected from the group consisting of boron chlorides, boron oxides, boron hydrides, silicon chloroboroxides and mixtures thereof.

3. Method according to claim 1 or 2, characterized in that the aluminium compounds are selected from the group consisting of aluminium chlorides, aluminium oxides, aluminium hydrides and mixtures thereof. Wa12240P / Be 23 4. Method according to one of the preceding claims, characterized in that the chlorosilane is selected from the group consisting of tetrachlorosilane, trichlorosilane, dichlorosilane, monochlorosilane, organochloromonosilane, and mixtures thereof.

5. Method according to one of the preceding claims, characterized in that the concentration of the boron and / or aluminium compounds is 10 pptv to 1 ppmv, preferably 250 pptv to 500 ppbv, particularly preferably 500 pptv to 250 ppbv.

6. Method according to one of the preceding claims, characterized in that the evaporation of the liquid sample in step a) takes place at a temperature of 15 to 190°C, preferably of 20 to 150°C, particularly preferably of 20 to 100°C.

7. Method according to one of the preceding claims, characterized in that the pressure in the evaporator unit is 1.5 to 5 bar, preferably 2 to 4 bar, particularly preferably 2.5 to 3 bar.

8. Method according to one of the preceding claims, characterized in that the sample is taken from a bypass line parallel to the gas or liquid flow, wherein the bypass line has a lower pressure than the gas or liquid flow.

9. Method according to one of the preceding claims, characterized in that the pressure in the bypass line is 0.1 to 1 bar, preferably 0.3 to 0.9 bar, particularly preferably 0.5 to 0.8 bar. Wa12240P / Be 24 10. Method according to one of the preceding claims, characterized in that the reaction chamber and the ion source are separated from each other, wherein the generation of the chloride ion species takes place in the ion source.

11. Method according to one of the preceding claims, characterized in that the generation of electrons in step b) is carried out with a direct current plasma discharge, wherein the resulting neutral and positive by-products are extracted.

12. Method according to one of the preceding claims, characterized in that the separation in step c) is carried out using a method selected from the group consisting of magnetic sector field, quadrupole, electromagnetic ion trap, electric ion trap, time-of-flight analyzer, Orbitrap and combinations thereof.

13. Method according to one of the preceding claims, characterized in that the detection in step c) is carried out with a detector selected from the group consisting of conversion dynode with secondary ion multiplier, Faraday cup, microchannel plate, inductive detection and combinations thereof.

14. Use of a method according to at least one of claims 1 to 15 for the analysis of gas or liquid flows in the production of polysilicon and / or the production of chlorosilanes.

15. Use according to claim 14, characterized in that it is a trichlorosilane stream.

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