Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2000-03-31
2002-10-01
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C436S072000, C423S335000
Reexamination Certificate
active
06458984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method for purifying silanes such as tetraethylorthosilicate (TEOS) to remove boron impurities therefrom, as well to as a method of analysis of analyzing boron impurities in such silanes.
2. Description of the Related Art
In the fabrication of microelectronic devices, current thin-film fabrication techniques require ultra-high purity precursors for depositing specific films. As device densities increase and critical dimensions decrease, electrical requirements of constituent thin-films become increasingly critical.
For example, dielectric films used to insulate gate and multi-level interconnect structures are commonly formed of silicon dioxide (SiO
2
) and must possess specific electrical properties. To reliably and reproducibly achieve such electrical properties, the precursors used to deposit the corresponding silicon dioxide thin-films must be of ultra-high purity.
Such precursors include tetraethoxysilane or tetraethylorthosilicate (TEOS). A common impurity in TEOS is triethylborate (TEB). Boron can form oxides of differing electrical properties relative to SiO
2
. Boron is also a dopant species that is extensively used to influence the charge carrier properties of silicon. In ultra-thin gate dielectrics, the diffusion of boron impurities can change the dopant concentration in silicon and thus, alter the performance of a specific transistor junction.
For this reason, the presence of excess boron in the SiO
2
layer can be problematic. In fact, it has been shown that boron impurities ranging from 40-80 parts per billion (ppb) can result in boron concentrations in the deposited film of 10
17
atoms/cc as determined by SIMS (see R. K. Laxman, A. K. Hochberg and M. J. Jahl, “Boron Determination in TEOS and Reduction of Boron in SIMOX-SOI Process”).
For these reasons, integrated circuitry (IC) manufacturers require boron concentration to be <10
15
atoms/cc in the SiO
2
film for optimized performance.
Since the film growth conversion efficiency for boron-containing molecules in TEOS is relatively high (R. K. Laxman, A. K. Hochberg and M. J. Jahl, “Boron Determination in TEOS and Reduction of Boron in SIMOX-SOI Process”), the concentration of boron impurities typically must be less than 10 ppb in the TEOS starting material to realize good device quality characteristics in the final product.
SUMMARY OF THE INVENTION
The present invention relates to removal and analysis of boron impurities present in silane materials, e.g., TEOS, in connection with the use of such silanes as chemical reagents.
In one aspect, the invention relates to a process for purification of a silane material containing a boron impurity, comprising contacting the silane material with a multifunctional chelating reactant (MCR) for reaction of the boron impurity therewith, to yield an organoborate chelate as a reaction product, and separating the organoborate chelate from the silane material to recover a purified silane material.
Another aspect of the invention relates to a method of determining the amount of boron impurity in a sample of a silane material containing same, comprising the steps of: contacting the silane material with an MCR for reaction of the boron impurity therewith, to yield an organoborate chelate as a reaction product; separating the organoborate chelate from the silane material to recover a purified silane material; and quantitatively assaying the amount of the organoborate chelate to identify the amount of boron impurity in the sample.
As used herein, the term “multifunctional chelating reactant” or “MCR” refers to a chemical agent that is (1) reactive with boron species having the formula B(RR′R″), wherein each of R is same or different and selected from the group consisting of hydroxyl, C
1
-C
8
alkoxy and C
1
-C
8
alkyl, and (2) reactive with such R, R′ and R″ groups to form protonated reaction by-products.
In one aspect of the invention the MCR is reactive with TEB to form a donor acceptor complex and alcohol as a reaction by-product.
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.
DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF
Although described hereinafter primarily in reference to TEOS, it will be appreciated that the method of the invention is not thus limited, but rather is broadly applicable to the purification and analysis of other alkoxysilanes, as well as alkylsilanes, and mixtures of the foregoing. The ensuing discussion relating to TEOS should therefore be understood to encompass such other silane materials, as variant feedstocks to which the purification/analysis methodology of the invention is usefully applied.
The present invention provides a method for obtaining high levels of TEOS purity, suitable for semiconductor device manufacturing applications, in which the TEOS is useful to form SiO
2
films of corresponding high purity.
The present invention also provides in one aspect a method of analyzing TEOS to determine the level of purity thereof, for applications such as integrated circuitry manufacturing requiring >99.999% and more preferably >99.99999 elemental purity of the TEOS reagent.
The present invention allows boron species having the formula B(RR′R″), wherein each of R is same or different and selected from the group consisting of hydroxyl, C
1
-C
8
alkoxy and C
1
-C
8
alkyl, to be chelated and removed from the TEOS. Common boron impurities such as triethylborate (TEB) may be greatly reduced in the purified TEOS product, e.g., to levels <10ppb boron.
The boron impurity that invariably is present in TEOS produced for microelectronics fabrication applications is triethylborate (TEB). The method of the present invention enables TEB to be reduced to levels <0.001% and more preferably to <0.00001 % in the purified TEOS product.
The purification and analysis reagent compositions useful in the practice of the invention may alternatively comprise, consist of, or consist essentially of any of the purification/analysis components hereinafter described, and such compositions may additionally, or alternatively, exclude or be substantially free of any components not specifically described herein as being included or includable in such compositions.
The purification/analysis compositions of the invention in one aspect comprise one or more multifunctional chelating reactants (MCRs) that react with boron to form an organoborate chelate, preferably a nitrogen-containing organoborate chelate, having a boiling point above that of TEOS, preferably at least 50° C. above that of TEOS, more preferably at least 80° C. and most preferably at least 100° C. above such boiling point of TEOS.
The MCRs of the invention that are employed to form a nitrogen-containing organoborate chelate as the reaction product of the MCR and the boron impurity, can be of any suitable type. Such MCRs correspondingly include nitrogen, preferably as an amine functionality of the MCR, or alternatively in the form of imine or nitrile functionality. In the chelated reaction product of the MCR and the boron impurity, the electron-rich nitrogen constituent deriving from the MCR coordinates to the electron-deficient boron central atom to form a highly stable chelate as the coordination complex reaction product. A preferred class of such MCRs includes multifunctional organoamines, such as alkylamines and aminoalkylamines. A highly preferred MCR of such type is tris(2-aminoethyl)amine.
The MCRs of the invention in one embodiment include oxygen-containing functionality that reacts with the boron impurities in the TEOS to form the organoborate chelate reaction product. The oxygen functionality of the MCR is preferably a hydroxyl functionality, or alternatively carboxyl or carboxamide functionality. A preferred class of such MCRs includes multifunctional organooxy compounds, such as multifunctional alcohols, glycols and other polyols.
A particularly preferr
Battle Scott L.
Baum Thomas H.
Benac Brian L.
Bernhard David Daniel
Hedges Frank R.
Advanced Technology & Materials Inc.
Chappuis Margaret
McLauchlan Robert A.
Shaver Paul F.
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