Analysis of high-purity alkyl tin compounds

Abstract

A method is provided for determining the purity of a sample containing monoalkyltin triamide compounds and optionally dialkyltin diamide compounds, tetraalkyltin compounds, and tetrakis(dialkylamido)tin compounds using gas chromatography. The total content of dialkyltin diamide compounds, tetraalkyltin compounds, and tetrakis(dialkylamido)tin compounds detectable by the present method may be less than about 40 ppm.

Description

Background Technology

[0001] This application claims priority to U.S. Provisional Application No. 63 / 619,796 filed January 11, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] As semiconductor manufacturing technology continues to advance, feature sizes are shrinking, and consequently, the need for new process methods is increasing. Certain organotin compounds are known to be useful for the deposition of tin oxide hydroxide coatings in applications such as extreme ultraviolet (EUV) lithography. For example, alkyltin compounds provide radiation-sensitive Sn-C bonds, which can be used to pattern structures by lithography.

[0003] Materials used in microelectronic manufacturing require extremely high purity, to the extent that strict limits are applied to organic contaminants (e.g., reaction byproducts), metal contaminants, and particulate contaminants. Purity requirements are generally very stringent, and even more so in lithography applications, because chemicals come into contact with semiconductor substrates and organometallic impurities within compounds such as diisopropylbis(dimethylamino)tin [(iPr)₂Sn(NMe₂)₂] can affect the properties of the films formed. While precise purity targets are determined by various factors, including performance indicators, a general minimum purity target is 3N+. Residual metals within chemicals can degrade the electrical performance of devices fabricated by deposition on semiconductor substrates. Typical metal specifications require less than 10 ppb for individual metals, and the total metal content should not exceed approximately 100 ppb.

[0004] The process and performance of semiconductor materials can also be sensitive to dialkyltin contaminants. Dialkyltin impurities, such as R₂Sn(NMe₂)₂ where R is an alkyl group, cause gas emissions after vapor deposition or spin coating processes because the inclusion of dialkyl groups in the film lowers the density of the oxostanate cluster film. To manufacture microelectronic products using EUV lithography, it is necessary to properly control dialkyltin contaminants. Accordingly, achieving the high purity required in the monoalkyltin precursor manufacturing process becomes a challenge.

[0005] The main method currently used to analyze the purity of monoalkyltin amides is 119 It is to use Sn NMR spectroscopy. 119 Sn NMR spectroscopy is highly suitable for the quantitative analysis of monoalkyltin compounds due to its high sensitivity to small structural changes, broad spectral range of 6500 ppm, and ease of sample preparation (cf. Davies et al., Eds.; Tin Chemistry: Fundamentals, Frontiers, and Applications; Wiley (2008)). As a result 119 Since Sn resonance signals are very well separated, monoalkyltin compounds and their impurities can be easily identified and quantified. However, 119 Sn NMR is GC, HPLC, or 1 It has the disadvantage of low sensitivity compared to other analytical methods such as ¹H NMR. To improve sensitivity, monoalkyltin compounds are generally analyzed undiluted, and a large number of spectra (over 2,000) are collected to measure low levels of impurities (<0.1%). Because such a large number of spectra are required, 119 Analysis by Sn NMR can take several hours to obtain a single spectrum with sufficient sensitivity to measure low levels of impurities.

[0006] Gas chromatography (GC) and high-performance liquid chromatography (HPLC) are two commonly used techniques for analyzing the purity of compounds due to their low cost, high sensitivity, wide dynamic range, and broad applicability to various types of compounds. However, direct analysis of alkyltin amides by GC and / or HPLC is difficult because the tin-nitrogen bond is extremely sensitive to water and these compounds have low vapor pressures. Direct analysis by reverse-phase HPLC is also challenging because alkyltin amides react with most commonly used mobile phases. Normal-phase HPLC has the potential to directly analyze alkyltin amides because commonly used mobile phases are not reactive to the tin-nitrogen bond. However, the choice of stationary phase is limited because silica, the most widely used stationary phase in normal-phase HPLC, reacts with alkyltin amides. Additionally, normal-phase HPLC presents reproducibility issues, as trace amounts of water in the mobile phase can cause significant shifts in retention time and sensitivity coefficients.

[0007] Direct analysis by GC presents different challenges and difficulties compared to HPLC. For example, consumables such as inlet liners and GC columns used for the analysis of alkyltin amides must be highly inert, as free silanol can react and degrade chromatographic results. Additionally, there is an additional problem in GC where these compounds tend to decompose thermally during injection due to their low vapor pressure, and their decomposition temperature is often nearly equal to or lower than their boiling point.

[0008] Species analysis of trace organotin compounds is a field that has been actively researched for years due to the environmental impact of organotin compounds (e.g., Cole et al., “Trends in the analysis and monitoring of organotins in the aquatic environment,” Trends in Environmental Analytical Chemistry (2015). For example, tributyltin was widely used as a marine antifouling agent until it was found to be problematic for aquatic organisms even at concentrations below 1 ng / L. GC and HPLC are two techniques frequently used for the species analysis of organotin compounds. When used in conjunction with detectors such as MS, FPD, FAAS, or ICP-MS, these techniques can identify and detect organotin compounds at sub-ppb levels due to their high sensitivity and selectivity for tin. While these detectors possess high sensitivity, they are considerably expensive and are not readily available in most laboratories.

[0009] Species analysis by HPLC has the advantage of being able to directly detect these alkyltin compounds within a short analysis time. On the other hand, GC has the advantage of often being more sensitive than HPLC because it can generate sharper peaks and separate more compounds in a single analysis (Wahlen, A Comparison of GC-ICP-MS and HPLC-ICP-MS for the Analysis of Organotin Compounds, Agilent Application Note (2002). However, species analysis by GC generally requires an alkylation process to ensure the sample has sufficient volatility for analysis. Sodium tetraethylborate is the most commonly used alkylation reagent because it can be used under aqueous conditions, which facilitates the analysis of environmental samples. Additionally, derivatization methods using Grignard reagents are also used, but often an additional analysis step is required to confirm whether the sample has been derivatized.

[0010] Although the analysis of trace organotin compounds using GC is commonly performed, no method for analyzing the purity of these compounds using GC has been reported. A method capable of analyzing the purity of monoalkyltin amides faster and with higher sensitivity than NMR would be very attractive for ensuring the quality of these compounds for use in the microelectronics industry.

[0011] A method for determining the purity of a sample comprising at least one impurity selected from a monoalkyltin triamide compound having chemical formula (1) and optionally a dialkyltin diamide compound having chemical formula (2), a tetraalkyltin compound having chemical formula (3), and a tetrakis(dialkylamido)tin compound having chemical formula (4):

[0012] RSn(NR'2)3(1)

[0013] R2Sn(NR'2)2(2)

[0014] R4Sn (3)

[0015] Sn(NR'2)4(4)

[0016] Here, R is a primary, secondary, or tertiary linear, branched, or cyclic alkyl group having about 1 to 10 carbon atoms, and R' is an alkyl group having about 1 to about 5 carbon atoms;

[0017] Includes the following steps:

[0018] (a) reacting a sample with an alkylating agent solution containing an alkyl group R'' to form a solution comprising a mixed tetraalkyltin compound having formula (5) and optionally at least one compound selected from a tetraalkyltin compound having formula (3), a mixed tetraalkyltin compound having formula (6), and a tetraalkyltin compound having formula (7).

[0019] RR''3Sn (5)

[0020] R2R''2Sn (6)

[0021] R''4Sn (7)

[0022] Here, R'' is a primary, secondary, or tertiary alkyl group having about 1 to 10 carbon atoms different from R, and

[0023] (b) a step of determining the relative amount of compounds having chemical formulas (3), (5), (6) and (7) in the solution using gas chromatography, and thereby determining the relative amount of impurities having chemical formulas (2), (3) and (4) in the sample.

[0024] The steps of the above method are explained in more detail below.

[0025] Advantageous improvements of the present invention that can be implemented alone or in combination are described in dependent claims.

[0026] In summary, the following embodiments are proposed as particularly preferred embodiments within the scope of the present invention.

[0027] Embodiment 1:

[0028] A method for determining the purity of a sample comprising at least one impurity selected from a monoalkyltin triamide compound having chemical formula (1) and optionally a dialkyltin diamide compound having chemical formula (2), a tetraalkyltin compound having chemical formula (3), and a tetrakis(dialkylamido)tin compound having chemical formula (4):

[0029] RSn(NR'2)3(1)

[0030] R2Sn(NR'2)2(2)

[0031] R4Sn (3)

[0032] Sn(NR'2)4(4)

[0033] Here, R is a primary, secondary, or tertiary linear, branched, or cyclic alkyl group having about 1 to 10 carbon atoms, and R' is an alkyl group having about 1 to about 5 carbon atoms, and comprises the following steps:

[0034] (a) reacting a sample with an alkylating agent solution containing an alkyl group R'' to form a solution comprising a mixed tetraalkyltin compound having formula (5) and optionally at least one compound selected from a tetraalkyltin compound having formula (3), a mixed tetraalkyltin compound having formula (6), and a tetraalkyltin compound having formula (7).

[0035] RR''3Sn (5)

[0036] R2R''2Sn (6)

[0037] R''4Sn (7)

[0038] Here, R'' is a primary, secondary, or tertiary linear, branched, or cyclic alkyl group having about 1 to 10 carbon atoms different from R, and

[0039] (b) a step of determining the relative amount of compounds having chemical formulas (3), (5), (6) and (7) in the solution using gas chromatography, and thereby determining the relative amount of impurities having chemical formulas (2), (3) and (4) in the sample.

[0040] Example 2: A method according to Example 1, wherein the total content of a dialkyl tin diamide compound having formula (2), a tetraalkyl tin compound having formula (3), and a tetrakis(dialkylamido) tin compound having formula (4) in a sample is less than about 500 ppm.

[0041] Example 3: A method according to Example 2, wherein the total content of a dialkyltin diamide compound having formula (2), a tetraalkyltin compound having formula (3), and a tetrakis(dialkylamido)tin compound having formula (4) in a sample is less than about 200 ppm.

[0042] Example 4: A method according to Example 3, wherein the total content of a dialkyltin diamide compound having formula (2), a tetraalkyltin compound having formula (3), and a tetrakis(dialkylamido)tin compound having formula (4) in a sample is less than about 100 ppm.

[0043] Example 5: A method according to Example 4, wherein the total content of a dialkyltin diamide compound having formula (2), a tetraalkyltin compound having formula (3), and a tetrakis(dialkylamido)tin compound having formula (4) in a sample is less than about 50 ppm.

[0044] Embodiment 6: A method according to Embodiment 1, wherein a sample is dissolved in a solvent to form a solution, and the solution further comprises an internal standard.

[0045] Example 7: A method according to Example 1, wherein the alkylating agent is a Grignard reagent or an alkyllithium reagent comprising an alkyl group R''.

[0046] Example 8: A method according to Example 7, wherein the alkylating agent is R''MgBr or R''Li.

[0047] Example 9: A method according to Example 1, wherein the compound having the chemical formula (1) is isopropyl tris(dimethylamino)tin. Specific details for implementing the invention

[0048] One aspect of the present disclosure relates to a method for determining the purity of a sample comprising at least one impurity selected from a monoalkyltin triamide compound having formula (1), optionally a dialkyltin diamide compound having formula (2), a tetraalkyltin compound having formula (3), and a tetrakis(dialkylamido)tin compound having formula (4):

[0049] RSn(NR'2)3(1)

[0050] R2Sn(NR'2)2(2)

[0051] R4Sn (3)

[0052] Sn(NR'2)4(4)

[0053] In chemical formulas (1), (2), (3) and (4), R is a primary, secondary, or tertiary linear, branched, or cyclic alkyl group having about 1 to 10 carbon atoms, and R' is an alkyl group having about 1 to about 5 carbon atoms. More preferably, R has 1 to about 6 carbon atoms, most preferably about 3 to about 5 carbon atoms, and is a primary alkyl group including, for example but not limited to, methyl, ethyl, n-propyl, and n-butyl; a secondary alkyl group including isopropyl, isobutyl, sec-butyl, isopentyl, sec-pentyl, cyclohexyl, cyclopentyl, cyclobutyl, and cyclopropyl; and a tertiary alkyl group including t-butyl, t-amyl, etc.; and R is preferably isopropyl or cyclopentyl. R′ is preferably methyl, ethyl, n-propyl, n-butyl, n-pentyl, and most preferably methyl or ethyl.

[0054] The above method includes the following steps:

[0055] (a) reacting a sample with an alkylating agent solution containing an alkyl group R'' to form a solution comprising a mixed tetraalkyltin compound having formula (5) and optionally at least one compound selected from a tetraalkyltin compound having formula (3), a mixed tetraalkyltin compound having formula (6), and a tetraalkyltin compound having formula (7):

[0056] RR''3Sn (5)

[0057] R2R''2Sn (6)

[0058] R''4Sn (7)

[0059] Here, R'' is a primary, secondary, or tertiary linear, branched, or cyclic alkyl group having about 1 to 10 carbon atoms different from R, preferably having about 2 to about 5 carbon atoms, and currently preferred examples include ethyl and pentyl; and

[0060] (b) a step of determining the relative amounts of compounds having chemical formulas (3), (5), (6) and (7) in the solution using gas chromatography, and thereby determining the relative amounts of impurities having chemical formulas (2), (3) and (4) in the sample. The above method step is described in more detail below.

[0061] By using the method described herein, a dialkyltin diamide compound having formula (2), a tetraalkyltin compound having formula (3), and a tetrakis(dialkylamido)tin compound having formula (4) can be detected and quantified (for each compound) to impurity levels of about 500 ppm, about 200 ppm, about 100 ppm, about 50 ppm, about 40 ppm, or lower, which may vary depending on a specific alkyl group R''. The minimum detection limit is correlated with a specific R'' group, because sensitivity increases as the number of CH bonds included in the R'' group increases.

[0062] Unless otherwise specified, all figures should be understood as being modified by the term "approximately" in all cases. Accordingly, figures generally include ±10% of the stated value. For example, a temperature specification such as "10°C" or "approximately 10°C" includes 9°C and 11°C and all temperatures in between.

[0063] All numerical ranges described herein explicitly include all possible sub-ranges within the range, all individual numbers within the range, and integer, fractional, and decimal values ​​within the range, unless otherwise clearly indicated by the context. Accordingly, in some embodiments, the impurity levels of compounds having formulas (2), (3) and (4) may each independently be less than about 40 ppm, less than about 30 ppm, less than about 20 ppm, less than about 10 ppm, or lower. Additionally, alkyl groups having one to about four carbon atoms may be understood to include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl, cyclopropyl, and cyclobutyl, even if not all possible functional groups are specifically listed.

[0064] In a preferred embodiment, the total content of the dialkyltin diamide compound having formula (2), the tetraalkyltin compound having formula (3), and the tetrakis(dialkylamido)tin compound having formula (4) in the sample is less than about 500 ppm, less than about 200 ppm, less than about 100 ppm, less than about 50 ppm, or lower than that.

[0065] In a preferred embodiment, the sample to be analyzed is dissolved in a suitable solvent, including but not limited to THF, to form a solution of a desired concentration, for example, about 8 to about 12% w / v, for example, about 10% w / v. An internal standard is preferably added to the solution. Internal standards suitable for GC analysis are well known in the art, and, for example, tetraalkyltin compounds containing four identical alkyl groups different from R and R″ are most preferred. Ideally, the standard is a tetraalkyltin compound that can be chromatographically separated from the sample and all impurities. For example, when R is isopropyl and R″ is ethyl, tetrabutyltin can be a suitable internal standard. The standard may be added in an amount of about 500 ppm, or in an amount understood to be appropriate as an internal standard for GC analysis.

[0066] Subsequently, the solution containing the sample reacts with an alkylating agent in the solution, for example, a Grignard reagent containing an alkyl group R'' or an alkyllithium reagent (R'' or R''), to form a solution containing a mixed tetraalkyltin compound RR''3Sn having formula (5) from the reaction of the alkylating agent with the monoalkyltin triamide RSn(NR'2)3 having formula (1). Additionally, the reaction of the dialkyltin diamide impurity having formula (2) and the alkylating agent produces a mixed tetraalkyltin compound R2R''2Sn having formula (6), and the reaction of the tetrakis(dialkylamido)tin compound having formula (4) and the alkylating agent produces a tetraalkyltin compound having formula (7) as follows:

[0067]

[0068]

[0069]

[0070] In the above alkylating agent, R'' is a primary, secondary, or tertiary alkyl group having about 1 to 10 carbon atoms different from R. Preferably, R'' is ethyl or pentyl, and accordingly, preferred alkylating agents include ethyl Grignard reagents, ethyl lithium, pentyl Grignard reagents, and pentyl lithium compounds. In a preferred embodiment, the alkylating agent is added dropwise, for example, at a temperature of about 0°C to about 25°C, and then stirred for a sufficient time, for example, about 10 minutes, so that the dialkylamido (NR'₂) group is completely reacted and converted to the R'' alkyl group.

[0071] The resulting solution now contains a mixed tetraalkyltin compound having the chemical formula (5), optionally contains a tetraalkyltin compound having the chemical formula (3) if present as an impurity in the original sample, optionally contains a mixed tetraalkyltin compound having the chemical formula (6) if dialkyltin diamide impurity having the chemical formula (2) is present in the sample, and optionally contains a tetraalkyltin compound having the chemical formula (7) if tetrakis(dialkylamido)tin compound having the chemical formula (4) is present in the original sample.

[0072] After the reaction, the reaction mixture is treated by a known method to separate the tin compounds present. For example, excess alkylating agent is removed by washing, for example, with an aqueous solution of sulfuric acid or acetic acid, and then the organic layer is separated and dried using a drying agent such as sodium sulfate.

[0073] Finally, an aliquot of the organic layer is injected into a gas chromatograph equipped with a flame ionization detector calibrated for a monoalkyl tin triamide compound having chemical formula (2) and possible impurities having chemical formulas (3), (4), and (5), and the purity of the sample and the level of impurities contained therein can be quantified using the calibration data of the equipment. In other words, by determining the relative amounts of compounds (3), (5), (6), and (7) that are easily separated by GC in the solution, the relative amounts of compounds (1), (2), (3), and (4) in the original sample are determined, and accordingly, the level of impurities present in the original sample is determined.

[0074] The present invention will be described below through the following non-limiting embodiments.

[0075] Example 1: Conversion of Isopropyl Tris(Dimethylamino)tin to Triethyl Isopropyltin

[0076] In a glove box, 1 mL of isopropyl tris(dimethylamino)tin and 30 mL of anhydrous ether were added to a 100 mL flask. After cooling the mixture to 0°C, 3.01 eq of ethyl magnesium chloride (2 M) was added. The mixture was heated to room temperature and stirred for an additional 2 hours, after which a work-up with water was performed. After extraction, the organic layer was recovered and used directly as a GC sample.

[0077] Those skilled in the art will understand that various modifications can be made to the embodiments described above without departing from the broad concept of the invention. Accordingly, the invention should be understood not to be limited to the specific embodiments disclosed, but to include all variations that fall within the spirit and scope of the invention as defined by the appended claims.

Claims

Claim 1 A method for determining the purity of a sample containing at least one impurity selected from a monoalkyltin triamide compound having formula (1) and optionally a dialkyltin diamide compound having formula (2), a tetraalkyltin compound having formula (3) and a tetrakis(dialkylamido)tin compound having formula (4): R(n)(NR'2)3(1)R(2)Sn(NR'2)2(2)R(4)Sn(3)Sn(NR'2)4(4) where R is a primary, secondary, or tertiary linear, branched, or cyclic alkyl group having about 1 to 10 carbon atoms, and R' is an alkyl group having about 1 to about 5 carbon atoms; comprising the following steps: (a) reacting the sample with an alkylating agent solution containing the alkyl group R'' to produce a mixed tetraalkyltin compound having formula (5) and optionally a tetraalkyltin compound having formula (3), and formula (6). (a) forming a solution comprising at least one compound selected from a mixed tetraalkyltin compound having formula (7), RR''3Sn (5), R2R''2Sn (6), R''4Sn (7), wherein R'' is a primary, secondary, or tertiary alkyl group having about 1 to 10 carbon atoms different from R, and (b) determining the relative amount of compounds having formulas (3), (5), (6) and (7) in the solution using gas chromatography, thereby determining the relative amount of impurities having formulas (2), (3) and (4) in the sample. Claim 2 A method according to claim 1, wherein the total content of the dialkyltin diamide compound having formula (2), the tetraalkyltin compound having formula (3), and the tetrakis(dialkylamido)tin compound having formula (4) in the sample is less than about 500 ppm. Claim 3 A method according to claim 2, wherein the total content of the dialkyltin diamide compound having formula (2), the tetraalkyltin compound having formula (3), and the tetrakis(dialkylamido)tin compound having formula (4) in the sample is less than about 200 ppm. Claim 4 A method according to claim 3, wherein the total content of the dialkyltin diamide compound having formula (2), the tetraalkyltin compound having formula (3), and the tetrakis(dialkylamido)tin compound having formula (4) in the sample is less than about 100 ppm. Claim 5 A method according to claim 4, wherein the total content of the dialkyltin diamide compound having formula (2), the tetraalkyltin compound having formula (3), and the tetrakis(dialkylamido)tin compound having formula (4) in the sample is less than about 50 ppm. Claim 6 A method according to claim 1, wherein the sample is dissolved in a solvent to form a solution, and the solution further comprises an internal standard. Claim 7 A method according to claim 1, wherein the alkylating agent is a Grignard reagent or an alkyllithium reagent comprising an alkyl group R''. Claim 8 In claim 7, the method wherein the alkylating agent is R''MgBr or R''Li. Claim 9 A method according to claim 1, wherein the compound having the chemical formula (1) is isopropyl tris(dimethylamino)tin.

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