Synthesis of siloxane resins

Details Synthesis of siloxane resins Synthesis of siloxane resins

2000-02-16

2004-06-01

Robertson, Jeffrey B. (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C528S010000, C528S012000, C528S021000, C528S031000, C525S478000, C556S446000, C556S487000

Reexamination Certificate

active

06743856

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the preparation of substrates used in the manufacture of integrated circuits. In particular, the invention provides new and improved methods for preparing siloxane resins, including hydridosiloxanes and organohydridosiloxanes, that are free of the many disadvantages that previously attended the preparation of such materials. More particularly, the invention pertains to synthetic methods that employ phase transfer catalysts that avoid the disadvantages of previously employed catalytic systems that required hazardous catalytic reagents. The invention also pertains to synthetic methods that avoid the need for additional washing and purification steps that have heretofore been believed to be required to produce such resins.
2. Description of the Prior Art
It is known in the art that siloxane based resins are useful in the electronic and semiconductor fields to coat silicon chips and other similar components. Such coatings protect the surface of substrates and form dielectric layers between electric conductors on integrated circuits. Such coatings can be used as protective coatings, interlevel dielectric layers, doped dielectric layers to produce transistor like devices, pigment loaded binder systems containing silicon to produce capacitor and capacitor like devices, multilayer devices, 3-D devices, silicon on insulator devices, coatings for superconductors, superlattice devices and the like. These resins include hydridosiloxanes and organohydridosiloxanes containing a significant portion of organic moieties.
The production of siloxane resins, such as silsesquioxane resins, is well known in the art. For example, U.S. Pat. No. 5,486,564 describes the production of polyhydrogensilsesquioxane resins for electronic coatings. However, the process employs dangerous fuming sulfuric acid/sulfuric acid as a catalyst to produce polyhydrogensilsesquioxane. The product was contaminated with significant levels of trace metals despite washing in multiple steps with water containing decreasing percentages of sulfuric acid, followed by removal of all traces of water by azeotropic distillation. In an attempt to remedy these shortcomings, U.S. Pat. No. 5,416,190 describes fractionation of the silsesquioxane product using polar and nonpolar solvents. Other attempts to remedy these deficiencies in the production of silsesquioxane compounds employed supercritical fluid extraction in the purification process, as described by U.S. Pat. No. 5,063,267 and employed fuming/concentrated sulfuric acid but with CaCO
3
neutralization, as described by U.S. Pat. No. 5,010,159.
It is also known that the dielectric constant of such insulating films is an important factor where integrated circuits or IC's with low power consumption, cross-talk, and signal delay are required. As IC dimensions continue to shrink this factor increases in importance. As a result, siloxane based resin materials, and methods for making such materials, that can provide insulating films with dielectric constants below 3.0 are very desirable. In addition, it would be desirable to have siloxane-based resins, and methods for making the resins, that provide such low dielectric constant films and which additionally have a high resistance to cracking. It would also be desirable for such films to have low stress when formed in thickness of approximately 1.0 micron (&mgr;m) or greater. Additionally, it would be desirable for such siloxane-based resins, and methods for making, to provide low dielectric constant films via standard processing techniques. In this manner curing processes that require an ammonia or ammonia derivative type of atmosphere (See, U.S. Pat. No. 5,145,723, Sep. 8, 1992, Ballance et al.), an ozone atmosphere (See, U.S. Pat. No. 5,336,532, Haluska et al.), or other non-standard type of semiconductor process, are avoided.
Thus, it would be desirable to produce useful siloxane coating compositions, such as hydridosiloxane and organohydridosiloxane resins, by methods which are both efficient and which do not employ toxic catalytic reagents. It has now surprisingly been found that a reaction employing a phase transfer catalyst will produce the desired siloxane resins while avoiding all of the above described shortcomings of previous methods.
SUMMARY OF THE INVENTION
The processes of the invention provide for production of siloxane resins such as, for example, hydridosiloxanes and hydridosilsesquioxanes as well as organohydridosilsesquioxanes and organohydridosiloxanes, in high yield, by catalyzing the hydrolysis and condensation of a monomer precursor having the general formula of R
1
SiX
3
. In this formula, X is a halogen or OR
2
, and R
1
and R
2
are independently H or an alkyl or aryl functional group. When R
1
and/or R
2
is not H, either or both is independently a substituted or unsubstituted, straight or branched alkyl group, cycloalkyl group and/or aryl group, or a combination thereof. Thus, one, or optionally more than one, kind of phase transfer catalyst is employed in the hydrolysis and condensation of the above-described starting compounds, or monomeric precursors, to form desired siloxane resins.
The processes of the invention therefore include the steps of contacting a silane monomer with a phase transfer catalyst in the presence of a reaction mixture comprising a nonpolar, e.g., hydrocarbon, solvent, a polar solvent, e.g., alcohol and water, under conditions effective to catalytically convert said silane monomer into hydridosiloxanes and organohydridosiloxanes; and thereafter recovering the produced hydridosiloxanes and organohydridosiloxanes.
The processes of the invention are preferably conducted employing a dual phase solvent system. Further, the process is preferably conducted while protected from atmospheric oxygen, e.g., the reaction is conducted in a container that has been purged of oxygen and that is maintained in a flow of an inert gas, e.g., nitrogen gas (N
2
). In particular, the process is conducted by adding one or more monomer precursors, as described above, such as, trichlorosilane and/or one or more organotrichlorosilanes, or other art-known silane monomers, to a mixture that includes, but is not limited to, a phase transfer catalyst, a hydrocarbon solvent, alcohol and water. Once the reaction is complete, the reaction mixture is e.g., filtered, settled or centrifuged to remove any filterable impurities or precipitants and the phase transfer catalyst is removed by phase separation, e.g., by separation of the aqueous phase. The remaining hydrocarbon solvent, e.g., hexane, is then dried and evaporated to leave the product, typically a white solid. Thereafter, the recovered solid may optionally be slurried in a suitable hydrocarbon solvent to remove residual low molecular weight components, and then the solvent evaporated to leave desired product. The resulting product can be formulated in a suitable solvent for use as a spin-on polymer by methods well known to the art.
The weight average molecular weight (“Mw”) of the produced polymer can range from about 400 to about 300,000 atomic mass units (“amu”). In another embodiment, the Mw of the produced polymer can range from about 10,000 to about 80,000 amu, depending on the reaction conditions. In a more particular embodiment, the Mw of the produced polymer can range from about 4,500 to about 75,000 amu. Simply by way of example and with no limitation intended, it has been confirmed that materials produced by the methods of the invention having, e.g., Mw's of about 20,000, about 40,000 and about 60,000 amu have good coating properties.
Thus, the invention provides methods for producing useful siloxanes, such as hydridosiloxanes and organohydridosiloxanes, using suitable starting materials and solvents. In particular, it has surprisingly been discovered that the processes of the invention are efficiently catalyzed by a phase transfer catalyst. Catalysts according to the invention include quaternary ammonium salts (R
4
N
+
X
−
). Advantageously, quat

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