High purity ethylenediamine for semiconductor applications

Abstract

Disclosed are ethylenediamine (EDA) compositions and methods for making EDA suitable for thin film semiconductor processing applications. The EDA is purified to remove water and trace metals. Water content below about 50 ppm by weight is achieved by passing the liquid through 3A molecular sieves in a packed bed. Metal impurities are removed by distillation and the resulting product is packaged in specially dried and optionally pre-conditioned containers.

Description

[0001] This application claims priority interests in U.S. Application Serial No. 15 / 649,271, filed July 13, 2017, and U.S. Provisional Application No. 62 / 364,959, filed July 21, 2016, the disclosures of which are incorporated herein by reference in their entirety. Background Technology

[0002] Ethylenediamine (EDA) is commonly used in the chemical industry. New applications for this chemical in semiconductor processing are under development (see, for example, US2016060754A, US2016020091A, US2016024647A, US2016035542A, and US2017114459A). However, this chemical must be delivered to the process without carrying metallic or oxygen-containing impurities, such as water, which could adversely affect the quality of films grown or processed with this reagent. EDA forms adducts with water (1:1 and 1:2), making it difficult to dry. One complexity is that it forms a high-boiling azeotrope containing approximately 15% by weight of water, making dehydration by conventional fractionation impossible. Furthermore, it is a very effective chelating agent for many metallic elements such as iron, sodium, nickel, and aluminum. This property makes it difficult to transport or contain this chemical using metal components typically used for semiconductor chemicals without the risk of significant contamination.

[0003] Ethylenediamine (EDA) is most commonly synthesized in the presence of water. This water must be removed in many applications. Because EDA forms a high-boiling azeotrope with water, it cannot be dried by conventional fractionation alone. Benzene or other dehydrating agents have been successfully used to break down this azeotrope. For example, Creamer and Chambers (doi: 10.1149 / 1.2781223 J. Electrochem. SOC. 1954, 101(3), 162) were able to reduce the water content to below 0.5% (5000 ppm by weight) and the conductivity to below 10 using various dehydrating agents (preferably benzene). -5 ohm -1 cm -1 .

[0004] In U.S. Patent No. 3,394,186, Muhlbauer describes a method for producing substantially anhydrous ethylenediamine, comprising the steps of: (A) contacting dichloroethane with a molar excess of an aqueous ammonia solution at a temperature ranging from about 75°C to about 175°C to provide a crude reaction mixture containing ethylenediamine dihydrochloride; (B) contacting the crude reaction solution with an aqueous caustic soda solution of about 50 to about 75 wt% in a combined neutralization distillation zone at a temperature of about 80°C to about 100°C to neutralize the ethylenediamine dihydrochloride and to flash headspace water and amine azeotrope; (C) contacting the azeotrope in a liquid solution with an aqueous caustic soda solution of about 0.5 to about 1.5 parts per part of the azeotrope of about 60 to 80 wt% per part to selectively and partially remove water from the azeotrope; and (D) fractionating the partially dehydrated azeotrope at a subatmospheric pressure of about 100-500 mmHg absolute to obtain an anhydrous distillate ethylenediamine product.

[0005] In German Patent No. 1,955,827A (1971), Adam and Merkel taught that ethylenediamine could be dehydrated by distillation with piperidine. Thus, 500 parts of an 80% aqueous EDA solution and 280 parts of piperidine were distilled in a column of 20 theoretical plates at 1 atm and with a reflux ratio of 2:1 to give 371 parts of EDA with an H2O content of <0.1%.

[0006] All these methods produce products with excessively high residual water content and other impurities (such as entrainers), making them unsuitable for semiconductor processing. Furthermore, the requirements for recycling entrainers and the complex integration of recirculating flows make such processes undesirable for the manufacture of specialty chemicals.

[0007] The preparation of nominally anhydrous EDA using chemical drying agents has been disclosed. Mukherjee and Bruckenstein, in their report on the preparation of anhydrous ethylenediamine (Pure Appl. Chem. 1966, 13, 421), recommended a multi-step procedure that begins with a) pre-drying by shaking 98% EDA and 5A molecular sieves for 12 hours and then decanting, followed by b) shaking a mixture of calcium oxide and potassium hydroxide for 12 hours, then c) fractionation from the newly activated 5A molecular sieves at a reflux ratio of 1:20, and d) a second distillation from metallic sodium under nitrogen. This method yields EDA with a water content of ~0.015 mol / L (0.27 g / L or about 300 ppm by weight).

[0008] Even when EDA is distilled to remove metallic impurities, it can dissolve many metals upon exposure to surfaces containing metal oxides. While not wishing to be bound by theory, it is believed that metal oxides or metal hydroxides dissolve to form soluble EDA complexes. It is further believed that this process is accelerated and enhanced by the presence of water (free water or water complexed with EDA or water adsorbed on the inner surface of the metal container holding the EDA). Furthermore, the presence of halides (especially chlorides) in the EDA can increase metal dissolution and raise the concentration of metal-EDA complexes by promoting corrosion.

[0009] Other conventional methods for processing EDA are disclosed by Mukherjee in Pure Appl. Chem. 1966, 13, 421; US4,273,621A and JP7278064A.

[0010] The publications, patents and patent applications identified above are incorporated herein by reference. Summary of the Invention

[0011] This invention addresses problems associated with conventional methods and provides an improved ethylenediamine (EDA) composition, as well as methods for processing EDA and containers for handling and storing EDA to provide EDA suitable for thin-film semiconductor processing applications. Using the methods of this invention to remove water (and water fractions) from EDA and storing the EDA of this invention in a dry and pretreated container reduces the corrosion rate of the container and thus allows for relatively long storage times of EDA while maintaining specified purity.

[0012] In one aspect of the invention, the EDA is purified to remove water and trace metals. A water content of less than about 50 ppm by weight is achieved by passing the liquid through a type 3A molecular sieve (zeolite) in a packed bed. Metallic impurities are removed by distillation, and the resulting product is packaged in a particularly dry and generally pre-conditioned container.

[0013] For semiconductor applications, low levels of metallic element impurities are required to avoid electrical failures in devices.

[0014] The present invention also provides a container that has been pretreated to reduce water and metal elements leaching from the container into the EDA.

[0015] Another aspect of the invention is that a large amount of metallic sodium is not required during the distillation process. Sodium metal is highly flammable and air-sensitive, and may potentially introduce undesirable sodium contamination into the product.

[0016] Various aspects of the present invention can be used individually or in various combinations thereof. Detailed Implementation

[0017] The EDA compositions of the present invention are EDA with a purity of about 99% to about 99.99%, about 99.8% to about 99.95%, typically about 99.8% to about 99.9% by weight, and in some cases, greater than 99.9% by weight. When measured by gas chromatography with discharge ionization detection, the EDA of the present invention contains less than about 50 ppm of water, typically less than about 20 ppm of water, and in most cases less than about 10 ppm of water, or 5 ppm of water, or 1 ppm of water, down to an undetectable water content. The EDA of the present invention contains less than about 100 ppb of each of the following trace metals: aluminum, chromium, copper, iron, magnesium, manganese, molybdenum, nickel, titanium, and zinc. In particular, by inductively coupled plasma mass spectrometry (ICP / MS), the EDA of the present invention contains less than about 20 ppb of each trace metal, typically less than about 10 ppb, and in most cases less than about 1 ppb, reduced to an undetectable level. The compositions of the present invention are analyzed by GC / TCD or GC / PDID to confirm the amount of EDA and water, and by ICP / MS to determine the amount of trace metals. The EDA compositions of the present invention may also contain less than about 10 ppm, typically less than about 5 ppm, and in most cases less than about 1 ppm of halides, particularly chlorine. The content of halides (particularly chloride ions) in the EDA compositions of the present invention can be analyzed by ion chromatography of aqueous solutions. The EDA compositions of the present invention may also contain less than 100 ppb, less than 50 ppb, less than 20 ppb, less than 10 ppb, less than 1 ppb, and in most cases less than 0.5 ppb of each of alkali metals (e.g., sodium, potassium, magnesium, calcium), aluminum, and stainless steel elements, particularly aluminum, chromium, iron, molybdenum, and nickel. The content of alkali metals, aluminum, and stainless steel elements (particularly sodium, aluminum, chromium, iron, manganese, molybdenum, and nickel) in the EDA compositions of the present invention can be analyzed by ICP / MS.

[0018] The EDA of this invention can be stored in any container or delivery system suitable for supplying the EDA to a semiconductor manufacturing system. Examples of suitable containers and delivery systems are disclosed in U.S. Patent Nos. 7,334,595; 6,077,356; 5,06,9244; and 5,465,766, the disclosures of which are incorporated herein by reference. Containers may comprise glass (borosilicate or quartz glass) or 316, 316L, 304, or 304L type stainless steel alloys (UNS designations S31600, S31603, S30400, S30403).

[0019] Before introducing the EDA of the present invention into the container, the container and / or delivery system are pretreated by: 1) drying by circulating a dry inert gas (e.g., dry air, dry nitrogen, dry helium, or dry argon, or a combination thereof) or by periodically applying a vacuum for a period of time to achieve a pressure below about 1 Pa to about 10 kPa (or a combination of both), wherein drying is facilitated by applying heat from about 60°C to about 210°C to the dry inert gas or the container or both; then 2) filling the pre-dried system with purified EDA (e.g., the EDA of the present invention) and exposing the surfaces to the liquid for about 1 hour to about 1 week to remove any remaining adsorbed water molecules on the inner surface of the container. In one embodiment, the container may also be filled with a water-soluble solvent, such as tetrahydrofuran (THF), acetonitrile, or other organic amines, to help remove adsorbed water molecules on the inner surface of the container prior to step 1 or 2 above.

[0020] A preferred method involves heating the system to approximately 180°C for approximately 24 hours while maintaining a pressure below 10 Pa. The container is filled with EDA prepared according to the invention to the maximum safe fill level and stored at approximately 23°C for approximately 48 hours before removing the liquid and refilling with the desired amount of high-purity EDA (e.g., the EDA of the present invention).

[0021] The pure ethylenediamine of this invention is prepared by a two-step method. The first step of the method involves passing commercially available ethylenediamine as a liquid through a packed bed containing a molecular sieve and collecting the material in a container. While any molecular sieve that preferentially removes water relative to EDA can be used, the preferred molecular sieve comprises 3A molecular sieve (UOP 3A type zeolite, CAS Registry No. 308080-99-1, having an approximate formula K). n Na 12-n [(AlO2)) 12 (SiO2) 12 [·x H2O, where n ranges from about 6 to 10, typically about 8). The pressure applied to the EDA when passing it through the sieve ranges from about 1 psi to about 15 psi, and the temperature ranges from about 10°C to about 35°C, to achieve a time of 0.1 to 10 h. -1 Preferably 0.2 to 5 hours -1 And usually 0.5 to 1 hour -1The EDA weight time space velocity (WHSV) is important. 3A molecular sieves have particle sizes of 4-8 mesh, but smaller mesh sizes may be advantageous if a higher space velocity is used. The sieve bed should be long enough to accommodate the mass transfer zone. For 4-8 mesh particles, a bed length of at least 1 meter is preferred when the WHSV is approximately 0.5. The detection of water flowing from the column can be determined by monitoring the conductivity of the liquid leaving the column using an Emerson / Rosemount 1056 conductivity analyzer with a Type 404 flow cell sensor.

[0022] The material thus treated with 3A molecular sieves is then distilled to remove metallic impurities. Distillation can be carried out in a batch distillation apparatus equipped with a packed column or sieve plate column and an externally heated reboiler and overhead condenser. Preferably, if pretreatment is performed according to the method disclosed herein, the distillation system is constructed of glass with flanges sealed with polytetrafluoroethylene (PTFE) gaskets, although other materials, such as stainless steel, can also be used. Distillation is carried out at overhead pressures in the range of 10 kPa to 110 kPa absolute pressure. Reflux ratios in the range of 60:1 to 1:1 can be used, with reflux rates of up to 1 kg / h / cm³. 2 Column cross-sectional area. Such a method can produce the EDA of the present invention (e.g., less than about 50 ppm of water and less than about 100 ppb of each trace metal element).

[0023] The distilled material is stored in a dry container, preferably an electropolished stainless steel container pretreated with dry EDA. The container is pretreated by filling it with dry EDA and immersing it at ambient temperature until the Fe and water concentrations reach a plateau (reaching an asymptote) and no longer increase significantly over time. Immersion times ranging from one hour to several weeks are possible, typically requiring about one week to achieve this. By providing high-purity EDA with reduced water content to the dry and pretreated container, the rate of metal leaching from the container is reduced. The high purity of the EDA stored under a headspace of an inert gas (e.g., helium, nitrogen, argon, or any mixture thereof) can be maintained for extended periods, thereby enhancing the suitability of the stored EDA for semiconductor manufacturing.

[0024] The following examples illustrate certain aspects of the invention and do not limit the scope of the appended claims.

[0025] Example

[0026] Example 1a - Method for preparing high-purity EDA

[0027] A 2” x 40” stainless steel column, equipped with a stainless steel sanitary flange and PTFE gasket, is prepared for use by inserting a stainless steel fine mesh support, followed by approximately 2” of quartz wool filler, and then a stainless steel coarse mesh support. The bottom of the column is then sealed with the sanitary flange and gasket. 1.2 kg of 3A molecular sieve (Sigma Aldrich 208574) is loaded into the column. The column is gently tapped with a rubber mallet to aid in material settling. The top support is prepared by inserting a stainless steel fine mesh at the sieve bed surface, followed by approximately 2” of quartz wool filler, and then a stainless steel coarse mesh. The column is then sealed with a PTFE gasket and sanitary flange.

[0028] The molecular sieve was then activated by placing the column under a dynamic vacuum of <0.050 Torr, slowly heating it from 20°C to 70°C over 1 hour, immersing it at 70°C for 4 hours, then heating it from 70°C to 300°C over 2.5 hours, and immersing it at 300°C for 4 hours. Heat was applied externally using a heating belt controlled by a digital temperature controller. The column was then cooled from 300°C to 20°C under dynamic vacuum over 8 hours.

[0029] A stainless steel source container was filled with 32.68 kg of ethylenediamine (supplied by Dow Chemical Company) and connected to a nitrogen supply line to pressurize the headspace. The container's pick-up tube was connected to the bottom inlet of the adsorption column. A 38 L thoroughly dried, electropolished stainless steel receiver container was placed on a balance and connected to the top outlet of the column. The receiver was also connected to a nitrogen purge vent. The balance under the receiver was then tare to record the mass of the collected material.

[0030] To start collection, open the following valves in sequence: Adjust the nitrogen supply pressure to 12.5 ± 0.5 psi to the source material container headspace valve, source material sucker valve, bottom valve at the column base, top valve at the column top, needle valve flow control valve, vent valve, receiver headspace valve, receiver vent valve, and vent system valve. Record a pressure of 7.5–8.5 psig at the top of the column. The flow rate is controlled by the needle valve and maintained at 650 ± 25 g / hr. The water content of the EDA collected in the receiver should be <7 ppm by weight.

[0031] When the moisture content of the material from the column discharge exceeds system specifications, the bed is regenerated. The flow is stopped by sequentially closing the following: nitrogen source valve, source vessel headspace valve, column bottom diverter valve, column top diverter valve, and regulating needle valve. The line below the needle valve is then purged with nitrogen to remove free liquid. The receiver is then sealed by sequentially closing the following: receiver vent valve, vent connector valve, and receiver headspace valve. The column is then purged and dried by applying nitrogen pressure through the column top diverter valve and draining it into the column discharge receiver through the column bottom vent valve. Once all free liquid (approximately 0.6 kg) has been drained into the column discharge receiver, the column discharge receiver is removed and replaced with a solid CO2 cooling trap.

[0032] A dynamic vacuum was then applied to the cooling trap, eventually generating a pressure of <0.050 Torr. The molecular sieve was then reactivated by placing the column under a dynamic vacuum of <0.050 Torr and then gently heating the heat applied via the heating band using a digital temperature controller. The heater cycled from 20°C to 70°C over 1 hour, followed by immersion at 70°C for 4 hours to remove adsorbed liquid from the bead surface, then heating from 70°C to 300°C over 2.5 hours, followed by immersion at 300°C for 4 hours to remove water from the sieve. After immersion at 300°C, the column was cooled from 300°C to 20°C under vacuum over 8 hours. The column was then plugged into the pump and the seal was checked using vacuum decay. Once integrity was confirmed, the column was backfilled with nitrogen, making it ready for dehydration.

[0033] Example 1b - Distillation Method

[0034] The 15L of dry, oxygen-free EDA collected in a stainless steel receiver was transferred to a 20L glass reboiler heated by a 2200W zone 3 heating hood. The reboiler was connected to a 66-inch long, 2-inch ID glass column filled with approximately 5 feet of 0.16-inch stainless steel ProPak distillate packing, and topped with a glass condenser with a coolant coil connected to a 500W cooler and an atmospheric pressure vent for nitrogen purging.

[0035] Fractional distillation was performed by applying heat to the reboiler and refluxing for 1 hour, followed by collecting 500 ml of pre-fraction at a rate of 0.4 L / h. A total of 13.8 L of pure EDA was collected at a rate of 1.8 L / h on a surface roughness <0.8 μm. a The high-purity EDA produced is placed in a pre-dried 38L electropolished stainless steel container. The resulting high-purity EDA contains <1 ppb of Fe, Cr, Ni, and Mo as measured by inductively coupled plasma mass spectrometry, and <10 ppm of water as measured by gas chromatography with thermal conductivity detection. The Cl content, measured by ion chromatography, is <10 ppm.

[0036] Example 2 - Method for processing containers

[0037] Internal surface finish <0.8μm R a The electropolished stainless steel containers were dried by heating at 4-6 L / min, purging with purified nitrogen, and simultaneously baking in a 110°C oven for 8 hours (e.g., electropolishing to a surface roughness of about 25-40 μin R according to US Patent No. 8,590,705). a (Incorporated herein). After such drying, the container was further treated by filling it with EDA produced according to Example 1. The container was immersed in the dried EDA at ambient temperature, and EDA samples were periodically removed from the container and the moisture and iron concentrations were analyzed. Daily samples showed an increase in moisture and iron concentrations until they reached asymptotic values ​​(where the concentrations no longer increased over time). The leaching rate appeared to stabilize as the storage time in the unpassivated container increased. At t=0 day, Fe=0.69 ppb. At t=2 day, Fe=1.61 ppb. At t=7 day, Fe=1.22 ppb. The iron leaching rate was 0.46 ppb / day at 2 days and decreased to 0.08 ppb / day at 7 days. The time to reach the asymptotic values ​​was therefore 1 week.

[0038] Example 3 - Leaching rate of the treated container

[0039] The EDA prepared according to Example 1 was placed in a container pretreated according to Example 2. The rate of leaching of trace metals from the container into the EDA was determined as follows: EDA samples were periodically collected from the container during the study period. Trace metals in the samples were analyzed by inductively coupled mass spectrometry. The leaching rate is the slope of a linear fit of the trace metal concentration versus time during the study period. The analytical results of this example are listed in Table 1. This example demonstrates that when the EDA of the present invention is stored in the pretreated container of the present invention, the rate of metal leaching from the container can be reduced.

[0040] Table 1

[0041]

[0042] Example 4

[0043] The 19L stainless steel container was dried at 120°C, purged, purged with nitrogen, and cooled to achieve an internal surface moisture content of <500 ppb H2O. The container was then heated using a belt heater placed around the external area of ​​the container. The internal surface was untreated before being filled with EDA containing 59 ppm H2O. After 244 days of storage at ambient temperature, the water content increased to 1646 ppm, indicating residual moisture on the container surface prior to filling. The container exhibited a corrosion rate of 0.288 ppb / day of Fe. Therefore, with an impurity specification of 1 ppb Fe, the shelf life is 3 days.

[0044] Example 5

[0045] A 19L stainless steel container was dried to <500 ppb H2O using a belt heater according to Example 4. The inner surface was untreated before filling with EDA containing 68 ppm H2O. After 176 days of storage at ambient temperature, the water content increased to 130 ppm, indicating that the container surface had residual moisture before filling. The container exhibited a corrosion rate of 0.025 ppb / day of Ni. Therefore, the shelf life is 40 days at an impurity specification of 1 ppb Ni.

[0046] Example 6

[0047] A 19L stainless steel container was dried to <500 ppb H2O using a belt heater according to Example 4. The inner surface was passivated by immersion in the dried EDA of the present invention for 48 hours, and then removed before filling the container with the dried EDA of the present invention containing 17 ppm H2O. After storage at ambient temperature for 350 days, the water content increased to 25 ppm, indicating that the container surface had less residual moisture than the untreated surface before filling. The container exhibited a corrosion rate of 0.02 ppb / day Ni. Therefore, the shelf life was 50 days at an impurity specification of 1 ppb Ni.

[0048] Example 7

[0049] A 38L stainless steel container was dried in an oven dryer to <100 ppb H2O, wherein the entire container was placed inside the oven to uniformly heat the entire container. The inner surface was passivated by immersion in the dry EDA of the present invention for 48 hours, and then removed before filling the container with the dry EDA of the present invention containing 8 ppm H2O. After storage at ambient temperature for 330 days, the water content increased to 22 ppm. It is not intended to be bound by any theory or interpretation, but it is believed that the container surface had even less residual moisture before filling than the passivated, dried container in Example 3. The container exhibited a corrosion rate of 0.00043 ppb / day Ni. Therefore, at an impurity specification of 1 ppb Ni, the shelf life was 2300 days.

[0050] The leaching rate was determined according to Example 3. Detailed analytical results for Examples 4-7 are listed in Table 2.

[0051] Table 2 - Stainless steel corrosion rate as a function of EDA moisture content and container surface treatment

[0052] Corrosion rate (ppb / day)

[0053]

[0054]

[0055] The comparison of Examples 4 and 5 illustrates that variations in the effectiveness of container drying can affect the amount of water adsorbed on the surface, which in turn affects the amount of water released into the EDA, and consequently the corrosion rate of the container (as measured by metal leaching rate).

[0056] A comparison of Examples 4 and 5 with Examples 6 and 7 illustrates that introducing EDA treated according to Example 1a into a dried and pretreated container resulted in a reduced corrosion rate (as measured by metal leaching rate). The corrosion rate was reduced by removing water from the EDA and water adsorbed on the inner surface of the container. The reduced corrosion rate, in turn, imparts improved stability or shelf life to the EDA within the container.

[0057] A comparison of Examples 6 and 7 illustrates that uniform container drying (which can be achieved through an oven) further reduces the amount of water adsorbed on the surface, thereby reducing corrosion and increasing the shelf life of the EDA.

[0058] Comparative example

[0059] This embodiment compares a method for contacting EDA with molecular sieves. A 5-gallon plastic carboy filled with ethylenediamine was treated with activated 3A molecular sieves such that solid pellets covered the bottom of the container by 1-2 inches. The container was rotated to mix, then stored in a dry package and sampled periodically. The moisture content of the liquid was determined over several weeks to obtain the following results, listed in Table 3 as moisture content measured in ppm using GC / TCD. Processing times to achieve less than 10 ppm moisture (for the static contact process in this embodiment) are impractical for large-scale production.

[0060] Table 3 - Moisture content in EDA relative to static contact time

[0061]

[0062] While the invention has been described with reference to certain embodiments, those skilled in the art will understand that various changes can be made and elements can be substituted in an equivalent manner without departing from the scope of the invention. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of the invention without departing from the essential scope of the invention. Therefore, it is intended that the invention be limited to the specific embodiments disclosed as the best mode for carrying out the invention, but rather that the invention encompass all embodiments falling within the scope of the appended claims.

Claims

1. A method for treating ethylenediamine, the method comprising contacting the ethylenediamine with a molecular sieve comprising type 3A zeolite under conditions sufficient to reduce the amount of water in the ethylenediamine to less than 50 ppm; and distilling the ethylenediamine under conditions sufficient to reduce the amount of trace metals to less than 100 ppb, wherein the trace metals are selected from aluminum, chromium, copper, iron, magnesium, manganese, molybdenum, nickel, titanium, and zinc.

2. The method according to claim 1, wherein the ethylenediamine is more than 99.9% by weight pure.

3. The method of claim 1, wherein the contact comprises passing ethylenediamine through a bed of molecular sieves comprising type 3A zeolite.

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