Organohydridosiloxane resins with low organic content

Details Organohydridosiloxane resins with low organic content Organohydridosiloxane resins with low organic content

1998-03-20

2001-04-17

Wu, David W. (Department: 1713)

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

Synthetic resins

From silicon reactant having at least one...

C528S021000

Reexamination Certificate

active

06218497

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to siloxane based resins, and more specifically to a caged conformation organohydridosiloxane composition, methods for the synthesis thereof, and low dielectric constant films formed therefrom.
2. Description of the Related Art
Semiconductor devices often have one or more arrays of patterned interconnect levels that serve to electrically couple the individual circuit elements thus forming an integrated circuit (IC). These interconnect levels are typically separated by an insulating or dielectric film. Previously, a silicon oxide film formed using chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD) techniques was the most commonly used material for such dielectric films. However, as the size of circuit elements and the spaces between such elements decreases, the relatively high dielectric constant of such silicon oxide films is problematic.
In order to provide a lower dielectric constant than that of silicon oxide, dielectric films formed from siloxane based resins are becoming widely used. One such family of films formed from siloxane based resins are the films derived from hydrogen siloxane (HSQ) resins (See, U.S. Pat. No. 3,615,272, Oct. 19, 1971, Collins et al.; and U.S. Pat. No. 4,756,977, Jul. 12, 1988, Haluska et al.) However, while such films do provide lower dielectric constants than CVD or PECVD silicon oxide films and also provide other benefits such as gap filling and surface planarization, it has been found that typically the dielectric constants of such films are limited to approximately 3.0 or greater (See, U.S. Pat. No. 5,523,163, Jun. 4, 1996, Ballance et al.).
As known, the dielectric constant of such insulating films is an important factor where 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 a siloxane based resin, and method for making the resin, that provides such low dielectric constant films which additionally have a high resistance to cracking. It would also be desirable for such films to have low stress when formed in thicknesses of approximately 1.0 micron (&mgr;m) or greater. It would also be desirable for such a siloxane based resin, and method 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, or other non-standard type of semiconductor process, are avoided.
SUMMARY
In accordance with the present invention, organohydridosiloxane resins, and methods for making such resin, are provided. Solutions of such organohydridosiloxane resins are employed for forming caged siloxane polymer films useful in the fabrication of a variety of micro-electronic devices, particularly semiconductor integrated circuits.
The organohydridosiloxane resins of the present invention have the general formulas:
(HSiO
1.5
)
n
(RSiO
1.5
)
m
  Formula (1)
(H
0.4-1.0
SiO
1.5-1.8
)
n
(R
0.4-1.0
SiO
1.5-1.8
)
m
  Formula (2)
(H
0-1.0
SiO
1.5-2.0
)
n
(RSiO
1.5
)
m
  Formula (3)
(HSiO
1.5
)
x
(RSiO
1.5
)
y
(SiO
2
)
z
  Formula (4)
wherein:
the sum of n and m, or the sum or x, y and z is from about 8 to about 5000, and m or y is selected such that carbon containing constituents are present in an amount of less than about 40 percent, that is between about 0.1 and about 40 percent; R is selected from substituted and unsubstituted, normal and branched alkyls, cycloalkyls, aryls, and mixtures thereof; and wherein the specific mole percent of carbon containing substituents is a function of the ratio of the amounts of starting materials. In some embodiments, particularly favorable results are obtained with the mole percent of carbon containing substituents being in the range of between about 15 mole percent to about 25 mole percent.
Polymers in accordance with the present invention have a polymer backbone encompassing alternate silicon and oxygen atoms. In contrast with previously known organosiloxane resins, polymers of the present invention have essentially no hydroxyl or alkoxy groups bonded to backbone silicon atoms. Rather, each silicon atom, in addition to the aforementioned backbone oxygen atoms, is bonded only to hydrogen atoms and/or R groups as defined in Formulae 1, 2, 3 and 4. By attaching only hydrogen and/or R groups directly to backbone silicon atoms in the polymer, unwanted chain lengthening and cross-linking is avoided. Consequently, the shelf life of organohydridosiloxane resin solutions in accordance with the present invention is enhanced as compared to previously known organosiloxane resins. Furthermore, since silicon-carbon bonds are less reactive than silicon hydrogen bonds, the shelf life of the organohydridosiloxane resin solutions in accordance with the present invention is enhanced as compared to previously known hydridosiloxane resins.
In some embodiments, the polymer backbone conformation is a cage configuration. Accordingly, there are only very low levels or reactive terminal moieties in the polymer resin of this invention. This also ensures that no unwanted chain lengthening polymerization will occur in solution, resulting in an extended shelf life. Each silicon atom of the polymer is bonded to at least three oxygen atoms. Moieties bonded to the polymer backbone include hydrogen and organic moieties.
The organic moiety of the organotrichlorosilane monomer is alkyl or aryl and includes, but is not limited to, methyl, ethyl; linear and branched propyl, butyl, pentyl hexyl; and cyclic compounds such as cyclohexyl and phenyl. In some embodiments of the present invention, more than two of the aforementioned staring materials are employed.
In accordance with the method of this invention, synthesis of the organohydridosiloxane composition of this invention includes a dual phase solvent system using a catalyst. In some embodiments of the present invention, the starting materials encompass trichlorosilane and an organotrichlorosilane, for example either an alkyl or an aryl substituted trichlorosilane. The relative ratios of the trichlorosilane and the organotrichlorosilane determine the mole percent carbon-containing substituents in the polymer.
In some embodiments, the method of this invention includes:
1) mixing a solution of hydridotrihalosilanes and organic-substituted trihalosilanes (e.g. trichlorosilane and alkyl or aryltrichlorosilane) to provide a mixture,
2) combining the mixture with a dual phase solvent including a non-polar solvent, and a polar solvent to provide a dual phase reaction mixture,
3) adding a solid phase catalyst to the silane/solvent reaction mixture,
4) reacting the silanes to produce organohydridosiloxanes, and
5) recovering the organohydridosiloxane from the organic portion of the dual phase solvent system.
Additional steps may include washing the recovered organohydridosiloxane to remove any unreacted monomer, and fractionating the organohydridosiloxane product to thereby classify the product according to molecular weight.
In other embodiments, the catalyst is a phase transfer catalyst including, but not limited to, tetrabutylammonium chloride, and benzyltrimethylammonium chloride. The phase transfer catalyst is introduced into the reaction mixture and the reaction is allowed to proceed to the desired degree of polymerization.
In accordance with one aspect of the method of this invention, a dual phase solvent system includes a continuous phase non-polar solvent and a polar solvent. The non-polar solvent includes, but is not limited to, any suitable alkyl or aryl compounds or a mixture of any or all such suitable compounds, the operational definition of “suitable” in the present context includes the functional characteristics of:
1) solubilizing

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