WO2001078869A1

WO2001078869A1 - A process for the purification of organometallic compounds or heteroatomic organic compounds with a palladium-based catalyst

Info

Publication number: WO2001078869A1
Application number: PCT/IT2001/000186
Authority: WO
Inventors: Giorgio Vergani; Marco Succi
Original assignee: Saes Getters S.P.A.
Priority date: 2000-04-19
Filing date: 2001-04-13
Publication date: 2001-10-25
Also published as: AU5255001A; WO2001078869A9

Abstract

A process is described for the purification of organometallic compounds or heteroatomic organic compounds from oxygen, water and from the compounds deriving from the reaction of water and oxygen with the organometallic or heteroatomic compounds whose purification is sought, comprising the operation of contacting the organometallic or heteroatomic compound to be purified, in the liquid state or in the form of vapor, pure or in a carrier gas, with a catalyst based on palladium deposited on a porous support, and optionally also with one or more gas sorbing materials selected among hydrogenated getter alloys and a mixture of iron and manganese supported on zeolites.

Description

"A PROCESS FOR THE PURIFICATION OF ORGANOMETALLIC COMPOUNDS OR HETEROATOMIC ORGANIC COMPOUNDS WITH A PALLADIUM-BASED CATALYST"

The present invention relates to a process for the purification of organometallic compounds or heteroatomic organic compounds with a palladium- based catalyst.

Organometallic compounds are characterized by the presence of a bond between one metal atom (also arsenic, selenium or tellurium being included among metals) and one carbon atom being part of an organic radical such as, for example, aliphatic or aromatic, saturated or unsaturated hydrocarbon radicals; by extension, with the definition of organometallic compounds also the compounds including metal atoms bound to organic radicals by means of an atom other than carbon, such as for instance the alcoholic radicals (-OR) or of esters (-0-CO-R) are meant. The heteroatomic organic compounds (also simply defined heteroatomic in the following) are those organic compounds comprising, in addition to carbon and hydrogen, also atoms such as oxygen, nitrogen, halides, sulfur, phosphorus, silicon and boron.

Many of these compounds have been used for a long time in traditional chemical applications. Reagents having very high purity are not generally requested in this field, and their purification is carried out by techniques such as distillation (optionally at reduced pressure, in order to reduce the boiling temperature and therefore the risks of thermal decomposition of the compounds) or recrystallization from solvents. However, these compounds have been recently used in high technology applications, particularly in the semiconductor industry. In these applications, the organometallic compounds and the heteroatomic compounds are used as reagents in the processes of chemical deposition from the gaseous state (known in the field with the definition "Chemical Vapor Deposition" or with the acronym CVD). In these techniques, a gas flow of one or more organometallic or heteroatomic compounds (or a flow of a earner gas containing a known concentration thereof) is conveyed into a process chamber; then, inside the chamber the compounds are decomposed or reacted, so that materials containing metal atoms or heteroatoms are formed in situ (generally in the form of thin layers on a substrate). The organometallic or heteroatomic compounds can be already in the gaseous form, but they can also be in the liquid form. In this second case, the gaseous flow of the compound is obtained either by evaporating the compound, in which case the flow- is composed only of the compound of interest, or by bubbling a gas in the container for the liquid, in which case the flow contains vapors of the compound in the earner gas. The main organometallic gases used in these applications are hafnium tetra- t-butoxyde, trimethylaluminum, triethylaluminum, tri-t-buthylaluminurn, di-i- buthylaluminum hydride, trim ethoxy aluminum, dimethylaluminum chloride, di ethyl aluminum ethoxyde, dimethylaluminum hydride, trimethylantimony, triethylantimony, tri-i-propyl antimony, tris-dimethylaminoantimony, trimethylarsenic, tris-dimethylaminoarsenic, t-buthylarsine, phenylarsine, barium bis-tetramethyleptandionate, bismuth tris-tetramethyleptandionate, dimethyl cadmium, diethylcadmium, iron pentacarbonyl, bis-cyclopentadienyl- iron, iron tris-acetylacetonate, iron tris-tetramethyleptandionate, trimethylgallium, triethylgallium, tri-i-propylgallium, tri-i-buthylgallium, triethoxygallium, trimethylindium, triethylindium, ethyldimethylindium, yttrium tris- tetramethyleptandionate, lanthanum tris-tetramethyleptandionate, bis- cyclopentadienyl-magnesium, bis-methylcyclopentadienyl-magnesium, magnesium bis-tetramethyleptandionate, dimethylmercury, niobium pentaethoxyde, niobium tetraethoxydimethylaminoethoxyde, dimethylgold acetilacetonate, lead bis-tetramethyleptandionate, bis-esafluorocopper acetilacetonate, copper bis-tetramethyleptandionate, scandium tris- tetramethyleptandionate, dimethylselenium, diethylselenium, tetramethyltin. tetraethyltin, tin tetra-t-butoxide, strontium bis-tetramethyleptandionate, tantalum pentoxide, tantalum tetraethoxydimethylaminoethoxyde, tantalum tetraethoxytetramethyleptandionate, tantalum tetramethoxytetramethyleptan- dionate, tantalum tetra-i-propoxytetramethyleptandionate, tantalum tri- diethylamido-t-buthylimide, dimethyltellurium, diethyltellurium, di-i- propyltellurium, titanium bis-i-propoxy-bis-tetramethyleptandionate, titanium bis- i-propoxy-bis-dimethylaminoethoxyde, titanium bis-ethoxy-bis- dimethylaminoethoxyde, titanium tetradimethylamide, titanium tetradiethylamide, titanium tetra-t-butoxide, titanium tetra-i-propoxyde, vanadyl i-propoxyde, dimethylzinc, diethylzinc, zinc bis-tetramethyleptandionate, zinc bis- acetylacetonate, zirconium tetra-t-butoxyde, zirconium tetra- tetramethyleptandionate and zirconium tri-i-propoxy-tetramethyleptandionate.

The principal heteroatomic compounds used in these applications are trimefhylborane, asymmetric dimethylhydrazine (that is, wherein both methyl groups are bound to the same nitrogen atom), t-buthylamine, phenylhydrazine, trimethylphosphorus, t-buthylphosphine and t-buthylmercaptane.

Some typical examples of application of these methods are the production of the semiconductors of type III-V, such as GaAs or InP, or of type II- VI such as ZnSe; the use for p doping (for instance with boron) or n doping (for instance with phosphorus) of traditional silicon-based semiconductor devices; the production of materials having a high dielectric constant (for example compounds such as PbZr_xTiι-_x0₃) used in ferroelectric memories; or the production of materials having a low dielectric constant (such as Si0 ) for insulating electric contacts in semiconductor devices.

For these applications reagents having an extremely high purity are required, with levels of the order of 10^"1, 10^"2 ppm, whereas the traditional chemical techniques do not allow to obtain levels of impurities lower than about ten ppm. Further, even in the case that organometallic or heteroatomic compounds of very high purity are produced, the storage is source of contamination due to gas release from the container walls, which anyway makes necessary to use a purifier immediately before the application (so-called "point-of-use" purifiers).

Patent US 5,470,555 describes the removal from organometallic compounds of oxygen gas which is present as an impurity, by using of a catalyst formed of copper or nickel metals, or the relevant oxides activated by reduction with hydrogen, deposited on a support such as alumina, silica or silicates. According to the patent, by this method the removal of oxygen gas from a flow of the organometallic compound can be obtained, down to values of 10^"" ppm.

However, oxygen is not the only impurity that has to be removed from the organometallic or heteroatomic compounds. Other harmful impurities in the CVD processes are for example water and, particularly, the species deriving from the alteration of the same organometallic or heteroatomic compound, following to undesired reactions generally with water or oxygen. For instance, in the case of a generic organometallic compound MR_n, wherein M represents the metal, R an organic radical and n the valence of the metal M, contamination from MR_n-χ(-OR)_x species can occur, wherein x is an integer varying between 1 and n. These oxygenated species are harmful in the CVD processes because they introduce oxygen atoms into the material being formed, thus sensibly altering the electric properties thereof.

Object of the present invention is providing a process for the purification of organometallic compounds or heteroatomic organic compounds from oxygen, water and from the compounds derived from the reaction of water and oxygen with organometallic or heteroatomic compounds whose purification is sought.

This object is obtained according to the present invention with a process wherein the organometallic or heteroatomic compound to be purified is contacted with a catalyst based on palladium deposited on a porous support. The purification can be carried out on the organometallic or heteroatomic compound either in the liquid or in the vapor state.

It is also possible to use, in addition to the palladium-based catalyst, other materials, such as a hydrogenated getter alloy or a mixture of iron and manganese supported on zeolites.

The invention will be described in the following with reference to the drawings, wherein:

- figure 1 shows a cutaway view of a purifier by which it is possible to put into practice a first embodiment of the process of the invention; - figure 2 shows a cutaway view of a purifier by which it is possible to put into practice a second embodiment of the process of the invention. In one embodiment thereof, the process of the invention consists m contacting the palladium-based catalyst with the compound to be purified m the liquid state This can be earned out simply by mtioducmg the catalyst into the container of the liquid compound, from which the same will be e\ aporated by heating or with a carrier gas

However, m a preferred embodiment the purification is carried out by contacting the palladium-based catalyst with vapors, pure or m a earner gas, of the organometallic or heteroatomic compound In the following, the invention will be described with particular reference to the purification at the vapor state, since this is the condition most commonly used in the industry

Preferably, the quantity of palladium varies from 0,3 to 4% by weight with respect to the catalyst At lower values of palladium content, the activity of impunty removal is limited, whereas palladium quantities higher than 4% by weight bnng about a great increase of the catalyst cost without notable increases of the punfication yield

The support may be any porous matenal normally used m the catalysis field, such as, e g , ceramics, molecular sieves, zeolites, porous glass or others Catalysts based on palladium on a porous support are available on the market, and are sold for the catalysis of chemical reactions (for example, hydrogenation reactions) from the companies Sud Chemie, Degussa and Engelhard Alternatively, the catalyst can be produced by impregnation m solution of the porous support with a quantity of a palladium salt or complex, for example palladium chlonde, PdCl , calculated on the basis of the desired quantity of palladium m the final catalyst, drying of the so impregnated porous support, decomposition (for example, thermal) of the precursor, optional calcination, for example at temperatures of about 400-500°C of the product so obtained

The support of the catalyst is generally m the form of pellets or small cylinders, having size between 1 and 3 mm

The range of the useful temperatures for the purification of organometallic or heteroatomic compounds with the palladium-based catalyst is between about

-20°C and 100°C, at lower temperatures the oxygen removal is limited, whereas at temperatures higher than about 100°C decomposition reactions of the gas to be purified could take place. The range of the preferred temperatures is within room temperature and about 50°C.

The flow of the gas to be purified can vary between about 0,1 and 20 slpm (liters of gas, measured in standard conditions, per minute) at absolute pressures preferably comprised between about 1 and 10 bars.

This flow can be fonned only of the vapors of the compound to be purified, or of said vapors in a flow of carrier gas. The carrier gas can be any gas interfering neither with the palladium-based catalyst (or with the other possibly used gas sorbing materials) nor with the deposition process wherein the organometallic or heteroatomic compound is used. Argon, nitrogen or even hydrogen are commonly used.

Figure 1 shows a cutaway view of a possible purifier to be used in the first embodiment of the process according to the invention. The purifier 10 is formed of a body 11, generally cylindrical; at the two ends of body 11 there are provided a piping 12 for the inlet of the gas into the purifier, and a piping 13 for the gas outlet. The palladium-based catalyst 14 (the type with the support of cylindrical shape is exemplified) is contained inside body 11. The inlet 12 and the outlet 13 of the gas are preferably provided with standard connections of the VCR type, known in the field (not shown in the figure) for coimection with the gas lines upstream and downstream the purifier. The purifier body can be made with various metal materials; the preferred material for this purpose is steel AISI 316. The internal surfaces of the purifier body, which come in contact with the gas, are preferably electropolished until a surface roughness lower than about 0,5 μm is obtained. In order to prevent traces of the catalyst powder from being carried downstream of the purifier by the outlet gas flow, inside the purifier body at outlet 13 can be arranged means for retaining the particulate, such as nets or porous septa generally metallic having size of the "gaps" or of the pores suitable for retaining particles without causing an excessive pressure drop in the gas flow; the size of these openings can generally vary between about 10 and 0,003 μm.

The gas flow to be purified can be contacted, not only with the palladium- based catalyst, but also with at least one additional matenal, selected among a hydrogenated getter alloy or a mixture of iron and manganese supported on zeolites, or both

The use of hydrogenated getter alloys for the purification of gases m the microelectronic field is known by patent EP-B-470936, but restricted to the purification of simple hydndes, such as SιH , PH^ and AsH^

The getter alloys useful for the invention are the alloys based on titanium or zirconium with one or more elements selected among the transition metals and aluminum, and mixtures of one or more of these alloys with titanium and/or zirconium In particular, useful for the invention are the alloys ZrM₂, wherein M is one or more of transition metals Cr, Mn, Fe, Co or Ni, descnbed m patent US 5,180,568, the alloys Zr-V-Fe described m patent US 4,312,669 and particularly the alloy having weight percent composition Zr 70% - V 24,6% - Fe 5,4% manufactured and sold by the Applicant under the name St 707, the alloys Zr-Co- A, wherein A means any element selected among yttrium, lanthanum, Rare Earths or mixtures of these elements, descnbed m patent US 5,961,750, the alloys Ti-Ni, and the alloys Ti-V-Mn described in patent US 4,457,891

The loading with hydrogen of the above mentioned alloys is earned out at a hydrogen pressure lower than 10 bars, and preferably higher than the atmosphenc pressure, at temperatures comprised between room temperature and about 400°C Greater details on the method of loading the getter alloys with hydrogen can be found m the above mentioned patent EP-B-470936 The optimal temperature range for use of the hydrogenated getter alloys in this application is compnsed between room temperature and about 100°C The material formed of the mixture of iron and manganese on zeolites has preferably a weight ratio between iron and manganese compnsed between 7 1 and 1 1 , even more preferably this ratio is about 2 1 This matenal can be produced according to the modalities descnbed patent US 5,716,588 m the Applicant's name The optimal temperatuie range for using this material is compnsed between about -20 and 100°C, and preferably between room temperature and 50°C

The additional material (or the additional matenals) can be positioned indifferently upstream or downstream the palladium-based catalyst along the direction of the gas flow It is also possible, when both the cited additional materials are used, that one of them is upstream ad the other one downstream the palladium-based catalyst The additional material (or the additional matenals) can be provided m a separate body, connected to body 11 of the punfier containing the palladium based catalyst by means of pipings and fittings, for instance of the above mentioned VCR type Also this second body will be preferably made of the matenals and with the finishing level of the surfaces as descnbed for body 11 Piefeiably, the additional material (or the additional matenals) is arranged in the same punfier body wherein the palladium-based catalyst is provided In this case, the different materials can be mixed, but preferably they are separated m the punfier body

Figuie 2 shows a cutaway view of a possible purifier containing more than one matenal (the case of two matenals is exemplified), in particular, it shows a purifier made according to the preferred mode wherein the different mateπals are kept separated mside the punfier body The purifier 20 is formed of a body 21, a gas inlet 22 and a gas outlet 23, the palladium-based catalyst 24 is arranged on the side of inlet 22 inside body 21, and, on the side of the outlet 23, a matenal 25 selected between a hydrogenated getter alloy or a mixture of iron and manganese supported on zeolites, preferably, a mechanical member 26 which is easily permeable to gases, such as a metal net, is arranged between the two matenals in order to help maintaining the separation and the original geometrical arrangement of the materials In the case that two different matenals are present at the same time in the same body (the situation exemplified m figure 2), the punfier must be kept at a temperature compatible with the working temperature of all the present matenals, and consequently pieferably between room temperature and about 50°C

Finally, it is also possible to add to the vanous cited matenals also a water chemical sorber, for example calcium oxide or boron oxide, this latter prepared accoidmg to the teachings of patent application EP-A-960647 m the Applicant's name.

The invention will be further illustrated in the following example. This example does not limit the scope of the invention and is useful for illustrating a possible embodiment intended to teach those skilled in the art how to put the invention into practice and to represent the way that is considered the best for carrying out the invention.

EXAMPLE 1 A purifier of the type shown in figure 1 is made. The purifier has a body made of steel AISI 316 and an internal volume of about 50 cm". The catalyst, formed of small cylinders of γ-alumina (total volume 20 cm ) on which 2% by weight of metal palladium is provided, is introduced into the purifier. The purifier is then connected, by means of VCR connections, upstream to a nitrogen cylinder containing 40 ppm by volume (ppmv) of water and 100 ppmv of oxygen, and downstream to a mass spectrometer of the APIMS type (atmospheric pressure ionization mass spectrometer) mod. TOF 2000 of the company Sensar, that has a sensing threshold of 10^"4 ppmv both for water and for oxygen. The test is carried out in nitrogen instead of in a flow of an organometallic compound vapor, because the analyzing instrument used (APIMS) has a reduced sensibility in the vapors of these compounds, such that a test with an organometallic compound would not enable to obtain significant results. The gas to be purified is passed at 5 bars in the purifier maintained at room temperature, with a flow of 0,1 slpm. At the beginning of the test the quantity of water and oxygen in the gas outlet from the purifier is under the analyzer sensibility threshold, indicating the functionality of the palladium-based catalyst in the removal of these species. The test is continued until the analyzer senses in the gas output from the purifier a quantity of contaminant of 10^"3 ppmv; this contamination value of the output gas is adopted as indicator of the purifier depletion. From the knowledge of the test data, it is obtained that the purifier has a capacity of 3 1/1 (liters of the gas measured in standard conditions per liter of the getter alloy) for oxygen, and 15 1/1 for water.

Claims

1. A process for the purification of organometallic compounds or heteroatomic organic compounds from oxygen, water and from the compounds derived from the reaction of water and oxygen with the compounds whose purification is sought, comprising the operation of contacting the organometallic or heteroatomic organic compound to be purified with a catalyst formed of metal palladium deposited on a porous support.

2. A process according to claim 1 wherein the palladium-based catalyst is contacted with the organometallic or heteroatomic organic compound in the form of vapor, pure or in a carrier gas.

3. A process according to claim 1 wherein the weight of palladium is between 0,3% and 4% of the total weight of the catalyst.

4. A process according to claim 2 wherein said operation is carried out at a temperature between about -20 and 100°C.

5. A process according to claim 4 wherein said operation is carried out at a temperature between room temperature and 50°C.

6. A process according to claim 2 wherein said operation is carried out with a flow of the gas to be purified between about 0,1 and 20 slpm, at absolute pressures comprised between about 1 and 10 bars.

7. A process according to claim 1 wherein the organometal compound is selected among hafnium tetra-t-butoxyde, trimethylaluminum, triethylaluminurn, tri-t- buthylaluminum, di-i-buthylaluminum hydride, trimethoxyaluminum, dimethylaluminum chloride, diethylaluminum ethoxyde, dimethylaluminum hydride, trimethylantimony, triethylantimony, tri-i-propylantimony, tris- dimethylaminoantimony. trimethyl arsenic, tris-dimethylaminoarsenic, t- buthylarsine, phenylarsine, barium bis-tetramethyleptandionate, bismuth tris- tetramethyleptandionate, dimethylcadmium, diethylcadmium, iron pentacarbonyl, bis-cyclopentadienyl-iron, iron tris-acetylacetonate. iron tris- tetramethyleptandionate, trimethylgallium, triethylgallium, tri-i-propylgallium, tri- i-buthylgallium, triethoxygallium, trimethylindium, triethylindium, ethyldimethylindium, yttrium tris-tetramethyleptandionate, lanthanum tris- tetramethyleptandionate, bis-cyclopentadienyl-magnesium, bis- methylcyclopentadienyl-magnesmm, magnesium bis-tetramethyleptandionate, dimethylmercury, niobium pentaethoxyde, niobium tetraethoxydimethylam oethoxyde, dimethylgold acetilacetonate, lead bis- tetramethyleptandionate, bis-esafluorocopper acetilacetonate, copper bis- tetramethyleptandionate, scandium tns-tetramethyleptandionate, dimethylselemum, diethylselemum, tetramethyltm, tetraethyltm, tm tetra-t- butoxide, strontium bis-tetramethyleptandionate, tantalum pentoxide, tantalum tetraethoxydimethylammoethoxyde, tantalum tetraethoxytetramethyleptandionate, tantalum tetramethoxytetramethyleptan-dionate, tantalum tetra-i- propoxytetramethyleptandionate, tantalum tn-diethylamido-t-buthyhmide, dimethyltelluπum, diethyltellunum, di-i-propyltellunum, titanium bis-i-propoxy- bis-tetramethyleptandionate, titanium bis-i-propoxy-bis-dimethylammoethoxyde, titanium bis-ethoxy-bis-dimethylaminoe hoxyde, titanium tetradimethylamide, titanium tetradiethylamide, titanium tetra-t-butoxide, titanium tetra-i-propoxyde, vanadyl l-propoxyde, dimethylzmc, diethylzmc, zmc bis-tetramethyleptandionate, zinc bis-acetylacetonate, znconium tetra-t-butoxyde, zirconium tetra- tetramethyleptandionate and zirconium tn-i-propoxy-tetramethyleptandionate A process according to claim 1 wherein the heteroatomic organic compound is selected among tnmethylborane, asymmetric dimethylhydrazine, t-buthylamme, phenylhydrazme, tnmethylphosphorus, t-buthylphosphme and t-buthylmercaptan A process according to claim 1 further compnsmg the operation of contacting the organometal or organic heteroatomic compound to be purified with at least a second matenal selected between a hydrogenated getter alloy and a mixture of iron and manganese supported on zeolites A process according to claim 9 wherein the organometallic or heteroatomic compound is m the form of vapor, pure or in a earner gas A process according to claim 9 wherein the second matenal is a hydrogenated getter alloy selected among the alloys based on titanium and/or zirconium with one or more elements selected among transition metals and aluminum, and mixtures among one or moie of these alloys with titanium and/or zirconium

12. A process according to claim 11 wherein the getter alloy is selected among ZrM₂ alloys, wherein M is one or more among transition metals Cr, Mn, Fe, Co or Ni; the alloys Zr-V-Fe and particularly the alloy having weight percent composition Zr 70%-V 24,6%-Fe 5,4%; the alloys Zr-Co-A, wherein A means any element selected among yttrium, lanthanum, Rare Earths or mixtures of these elements; the alloys Ti-Ni; and the alloys Ti-V-Mn.

13. A process according to claim 10 wherein the contact between the vapor to be purified and the hydrogenated getter alloy occurs at a temperature between room temperature and about 100°C.

14. A process according to claim 9 wherein the second material is formed of a mixture of iron and manganese supported on zeolites, and wherein the weight ratio between iron and manganese is between 7:1 and 1 :1.

15. A process according to claim 14 wherein said weight ratio is about 2:1.

16. A process according to claim 10 wherein the contact between the vapor to be purified and the mixture of iron and manganese on zeolites occurs at a temperature between about -20 and 100°C.

17. A process according to claim 16 wherein the temperature is between room temperature and 50°C.

18. A process according to claim 1 further comprising the operation of contacting the organometal or heteroatomic organic compound to be purified, in the form of vapor, pure or in a earner gas, with a chemical water sorber.