Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-10-29
2003-11-25
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S098000, C521S134000, C521S139000
Reexamination Certificate
active
06653358
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a composition that contains a cross-linkable matrix precursor and a poragen, and a porous matrix prepared therefrom.
As semiconductor devices become smaller and smaller, and chip packing densities increase correspondingly, undesirable capacitatance related delays and cross-talk between metal interconnects are more acutely manifested. Since capacitance related delays and cross-talk relate to the dielectric constant of the insulator, attention has focused on the creation of ultra-low dielectric constant materials (that is, dielectric materials having dielectric constants of ≦2.0). Such efforts include creating porous inorganic (for example, silicon dioxide) or thermoplastic polymeric (for example, polyimide) materials.
Silicon dioxide, which has been the dominant inter-level dielectric material (ILD) for the past 40 years, can be made porous by well-developed sol-gel techniques such as those disclosed in
Proc. Mat. Res. Soc.
381, 261 (1995);
Proc. Mat. Res. Soc.
443, 91 (1997); and
Proc. Mat. Res. Soc.
443, 99 (1997), which teachings are incorporated herein by reference. Although the introduction of pores into silicon dioxide causes a reduction of dielectric constant from 4.2 to less than 2.0, the resultant porous material is significantly weakened. Thus, porous silicon dioxide is impractical as a low dielectric constant material.
Porous thermoplastic polymers, particularly thermally stable polymers such as polyimides, have also been investigated for use as ultra-low dielectric materials. See, for example, U.S. Pat. Nos. 5,895,263 and 5,776,990. Although these porous thermoplastic materials can be made to have acceptable dielectric constants, the pores tend to collapse during subsequent high temperature processing, thereby precluding the use of these materials for the applications of interest.
In view of the deficiencies in the art, it would be desirable to have an ultra-low dielectric material that is stable to the severe processing conditions required in fabricating semiconductors.
SUMMARY OF THE INVENTION
The present invention addresses the problems of the prior art by providing a composition comprising a) a hydrocarbon-containing matrix precursor; and b) a poragen; wherein the matrix precursor is selected to form upon curing a cross-linked, hydrocarbon-containing material having a T
g
of greater than 300° C. The cross-linked hydrocarbon-containing material preferably has a thermal stability of at least 400° C.
In a second embodiment, the present invention is a low dielectric constant material comprising a porous cross-linked hydrocarbon-containing matrix having a T
g
of greater than 300° C. The material is preferably in the form of a thin film on a substrate.
In a third embodiment, the present invention is a method of making a porous film on a substrate comprising:
coating on a substrate, a solution comprising a matrix precursor which cures to form a matrix material having a Tg of at least 300° C., a poragen, and a solvent;
removing the solvent;
reacting the matrix precursor to form the matrix material; and
degrading the poragen to form pores in the matrix.
The removing, reacting, and degrading steps are performed by one or more heating steps as will be more thoroughly described below.
In a fourth embodiment, the present invention is an integrated circuit article comprising an active substrate containing transistors and an electrical interconnect structure containing patterned metal lines separated, at least partially, by layers or regions of a porous dielectric material, wherein the dielectric material comprises a cross-linked hydrocarbon-containing matrix having a T
g
of greater than 300° C.
The present invention solves a problem in the art by providing a low dielectric constant, porous matrix material that is suitable as an interlayer dielectric for microelectronics applications and stable to processing temperature of greater than 300° C.
DEFINITIONS
B-Staged—refers to a partially polymerized monomer, or a mixture of monomer and partially polymerized monomer. A b-staged product is usually synonymous with “prepolymer” or “oligomer.”
Cross-linkable—refers to a matrix precursor that is capable of being irreversibly cured, to a material that cannot be reshaped or reformed. Cross-linking may be assisted by UV, microwave, x-ray, or e-beam irradiation. Often used interchangeably with “thermosettable” when the cross-linking is done thermally.
Matrix precursor—a monomer, prepolymer, or polymer, or mixtures thereof which upon curing forms a cross-linked Matrix material.
Monomer—a polymerizable compound or mixture of polymerizable compounds.
Functionality—refers to the number of groups in a monomer available for polymerization. For example, a biscyclopentadienone and a bis-acetylene each have a functionality of 2, while the monomer 1,1,1-tris(4-trifluorovinyloxyphenyl)ethane has a functionality of 3.
Hydrocarbon-containing—refers to a matrix or matrix precursor that contains carbon and hydrogen, but may contain other elements. The matrix or matrix precursor preferably contains not more than 50 weight percent silicon, more preferably not more than 30 weight percent silicon, and most preferably not more than 20 weight percent silicon.
Poragen—a solid, liquid, or gaseous material that is removable from a partially or fully cross-linked matrix to create pores or voids in a subsequently fully cured matrix, thereby lowering the effective dielectric constant of the resin.
Thermal stability temperature—the maximum temperature, T, at which the weight loss of a sample maintained at that temperature in an inert environment is less than 1 percent per hour.
Matrix—a continuous phase surrounding dispersed regions of a distinct composition. In the final article, the matrix is a solid phase surrounding dispersed voids or pores.
DETAILED DESCRIPTION OF THE INVENTION
The porous matrix of the present invention can be prepared from a mixture of a poragen and a cross-linkable hydrocarbon-containing matrix precursor. The poragen may be reactive, so that the poragen becomes chemically bonded into the polymer matrix, or it may be non-reactive.
Matrix Precursors
Suitable matrix precursors are those that form cross-linked resins having a T
g
of greater than 300° C. and more preferably greater than 350° C.
Preferably, the matrix precursors are further characterized in that they experience either no decrease or only relatively small decreases in modulus during cure. If the material experiences large modulus drops during cure, especially if the low modulus occurs at temperatures near the degradation temperature of the poragen, pore collapse may occur.
One preferred class of matrix precursors include thermosettable benzocyclobutenes (BCBs) or b-staged products thereof, such as those described in U.S. Pat. No. 4,540,763 and U.S. Pat. No. 4,812,588, which teachings are incorporated herein by reference. A particularly preferred BCB is 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethynyl)-1,1,3,3-tetramethyldisiloxane (referred to as DVS-bisBCB), the b-staged resin of which is commercially available as CYCLOTENE™ resin (from The Dow Chemical Company).
Another second preferred class of matrix materials include polyarylenes. Polyarylene, as used herein, includes compounds that have backbones made from repeating arylene units and compounds that have arylene units together with other linking units in the backbone, e.g. oxygen in a polyarylene ether. Examples of commercially available polyarylene compositions include SiLK™ Semiconductor Dielectric (from The Dow Chemical Company), Flare™ dielectric (from Allied Signal, Inc.), and Velox™ (Poly(arylene ether)) (from AirProducts/Shumacher). A preferred class of polyarylene matrix precursor is a thermosettable mixture or b-staged product of a polycyclopentadienone and a polyacetylene, such as those described in WO 98/11149, which teachings are incorporated herein by reference. Examples of the thermosetting compositions or cross-linkable polyarylenes that may be used in the composition of this
Bouck Kevin J.
Bruza Kenneth J.
Godschalx James P.
Niu Qing Shan J.
Shaffer, II Edward O.
Dow Global Technologies Inc.
Foelak Morton
Zerull Susan Moeller
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