Multi-component mixtures for manufacture of semi-conductors

Details Multi-component mixtures for manufacture of semi-conductors Multi-component mixtures for manufacture of semi-conductors

1999-12-30

2001-05-08

Brunsman, David (Department: 1755)

Compositions: coating or plastic

Coating or plastic compositions

Silicon containing other than solely as silicon dioxide or...

Reexamination Certificate

active

06228159

ABSTRACT:

BACKGROUND OF INVENTION
This invention generally pertains to multicomponent liquid mixtures including tetraethylorthosilicate, triethylborate, and triethylphosphorus compound.
In the manufacture of semiconductor devices, it is often desirable to dope a silicon layer or structure with boron and phosphorus. Historically, such doping has been performed from separate high purity containers and by co-deposition of boron and phosphorus oxides. More recently, there have been efforts to combine a typical source of silicon, such as tetraethylorthosilicate (TEOS) with trimethylborate and trimethylphosphite to provide a mixture used as a reactant source to directly form borophosphosilicate glass. This mixture had several problems, including transesterification of the components and significant depletion effects, as described by R. A. Levy et al.,
J. Electrochem. Soc.,
Volume 134, Number 7, pages 1744-1749 (July, 1987). It was reported that the depletion effects resulted in a fairly rapid decrease in thickness and phosphorus content of the films along the length of the reaction chamber. The authors of this article proposed moving away from TEOS as a reactant, instead employing diacetoxyditertiarybutoxysilane (DADBS) as the reactive component for silicon. However, TEOS continues to be the most commonly used compound for silicate deposition.
Furthermore, other industry trends that promote the use of cocktail mixtures include the growing need for single wafer deposition systems and the use of liquid mass flow controllers (LMFC) for 300 millimeter wafers. LMFCs are used instead of bubblers and simple vapor delivery systems for the transport of the needed dopants to the deposition chamber. Cocktail mixtures are not feasible in bubbler or vapor delivery systems due to the differences in vapor pressures of the individual components of the mixture. The composition of the vapor flow will vary in concentration as the cocktail is consumed and will not result in a repeatable, manufacturable process. Several other issues make bubblers and vapor delivery less desirable and expensive, namely, the poor performance of vapor MFCs due to temperature dependency and condensation issues; temperature controllers for each individual source; expensive “hot boxes” that are required; temperature control of all delivery lines, valves, MFCs, and the like. Similarly, a syringe pump and a controlled leak methodology are not as accurate, have moving parts (particle generator), require frequent maintenance for seal replacement, and have no feedback controls for automation.
On the other hand, LMFCs have been found to be simpler and more controlled. The pure liquid or cocktail mixture is transported to the LMFC where the exact flow is controlled. The use of cocktails in an LMFC is desirable since they are not boiling point dependent, LMFCs do not produce particles during operation, and since LMFCs are considered to be more accurate than syringes. The liquid is then flash vaporized very near to the chamber and delivered via a “transport” gas to the wafer surface. The flash vaporizer is capable of handling multi-component mixtures with no known problems. Accordingly, choice of dopant is not determined by its boiling point, but instead on reactivity and stability. It is expected that use of LMFCs will continue to expand as the film requirements become more strict. The film requirements are a function of the need for thinner films as well as the need to provide repeatability and uniformity for 300 mm wafer processes.
The inventor herein has recognized that a need exists for a multicomponent mixture to serve as a feed stock for borophosphosilicates during semiconductor fabrication. This need is particularly timely given the recent trend toward use of LMFCs during semiconductor fabrication. Such a multicomponent mixture would provide a number of benefits such as simplified delivery systems requiring a single channel for doped silicon oxide production; reduction of process variables due to the simplified system; improved system reliability (i.e., mechanical pumps not being exposed to pure trimethylborate and trimethylphosphite flow during wafer transport), fixed stoichiometry of the reactants which makes the chemical source less dependent on exact calibration of flow controllers, pressures, and efficiency of mixing, and less chemicals to handle.
SUMMARY OF INVENTION
This invention provides a solution to one or more of the needs, disadvantages, and shortcomings described above.
In one broad respect, this invention is a composition useful in the manufacture of semiconductors, comprising a liquid mixture of: tetraethylorthosilicate, triethylborate, and a triethylphosphorus compound. The tetraethylorthosilicate, triethylborate, and triethylphosphorus compound may be present in amounts effective to provide a borophosphosilicate that is formed on a substrate by plasma deposition that contains boron and phosphate in a percentage ratio of about 5/5, about 5/3, about 3/3, about 4/4, or about 3/6. In one embodiment of this invention, the components of the liquid mixture each have a purity of at least 99.99%. In one embodiment of this invention, the liquid mixture comprises (a) from about 60% to about 80% tetraethylorthosilicate, (b) from about 15% to about 30% triethylborate, and (c) from about 4% to about 10% triethylphosphorus compound, and wherein the percentages are measured by weight and total 100% for components (a), (b), and (c). In another embodiment of this invention, the liquid mixture may further comprise a triethoxyarsenic compound, such as triethoxy arsenate.
In a second broad respect, this invention is a composition useful in the manufacture of semiconductors, comprising a liquid mixture of: (a) from about 60% to about 80% tetraethylorthosilicate, (b) from about 15% to about 30% triethylborate, and (c) from about 4% to about 10% triethylphosphate, wherein the percentages are measured by weight and total 100% for components (a), (b), and (c).
In a third broad respect, this invention is a method useful for the preparation of a liquid mixture useful in the manufacture of semiconductors, comprising the steps of: obtaining (a) tetraethylorthosilicate, (b) triethylborate, and (c) a triethylphosphorus compound; combining components (a), (b), and (c) and mixing the components to form the liquid mixture. In one embodiment, the mixing step occurs prior to adding the components to the container.
In yet another broad respect, this invention is a stainless steel canister containing tetraethylorthosilicate, triethylborate, and a triethylphosphorus compound. In one embodiment of this invention, the canister has a capacity of from about 1 to about 50 liters. These canisters may be shipped in approved shipping crates.
Advantageously, the liquid mixture of this invention is stable, and does not undergo transesterification or form by-products during proper storage. Furthermore, this composition does not suffer the depletion effects of the aforementioned TEOS, trimethylborate, and trimethylphosphite mixture. This invention, therefore, provides a single mixture effective in the manufacture of in situ doped borophosphosilicate during semiconductor manufacture, unlike the prior art. This invention thus overcomes the difficulties and problems inherent in the prior art. This invention, moreover, enables use of simplified delivery systems resulting in a reduction in process variables and reduced dependence on calibration of flow controllers, pressures, and efficiency of mixing compared to the prior art.
DETAILED DESCRIPTION OF THE INVENTION
The tetraethylorthosilicate, Si(OC
2
H
5
)
4
,employed in this invention is a well known compound which is available commercially. For example, high purity TEOS is available from a variety of sources such as Advanced Delivery and Chemical Systems, Ltd. in Austin, Tex. In the practice of this invention, it is generally desirable to use TEOS at least 95% pure, with 99.99% or more pure TEOS being more preferable.
Triethylborate is also a well known, commercially available material. High purity triethylborate is ava

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