Polymer synthesis

Details Polymer synthesis Polymer synthesis

2001-09-22

2004-09-07

Cheung, William K. (Department: 1713)

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...

C524S847000

Reexamination Certificate

active

06787601

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to the field of polymer synthesis. In particular, the present invention relates to the field of emulsion polymer synthesis.
Polymers have been prepared by a variety of means such as solution polymerization and emulsion polymerization. Emulsion polymerization is advantageous in that polymer particles having small particle sizes and particle size polydispersities approaching 1 can be prepared. Typically, such emulsion polymerizations are performed using ionic surfactants.
For many polymer applications, such as paints, ionic surfactants used during emulsion polymerization pose no problems. However, for other applications, such as those in the electronics industry, such ionic surfactants are problematic.
One application of polymers in the electronics industry is in the formation of porous interlayer dielectric materials used in the manufacture of integrated circuits. As electronic devices become smaller, there is a continuing desire in the electronics industry to increase the circuit density in electronic components, e.g., integrated circuits, circuit boards, multichip modules, chip test devices, and the like without degrading electrical performance, e.g., crosstalk or capacitive coupling, and also to increase the speed of signal propagation in these components. One method of accomplishing these goals is to reduce the dielectric constant of the interlayer, or intermetal, insulating material used in the components. A method for reducing the dielectric constant of such interlayer, or intermetal, insulating material is to incorporate within the insulating film very small, uniformly dispersed pores or voids. Preferred are pores or voids having a diameter of less than or equal to 100 nm.
One known process of making a porous dielectric involves dispersing thermally removable solid particles, i.e. porogens, in a B-staged dielectric precursor, polymerizing the dielectric precursor without substantially removing the particles, followed by heating the dielectric material to substantially remove the particles and thereby leaving voids or free spaces in the dielectric material. Such voids reduce the dielectric constant of the dielectric material. See, for example, U.S. Pat. No. 5,895,263 (Carter et al.).
Emulsion particles are particularly suited for preparing porous dielectric materials due to their controlled particle size range and narrow particle size distribution. See, for example, Antonietti et al.,
Synthesis and Size Control of Polystyrene Latices via Polymerization in Microemulsion, Macromolecules,
vol. 24, 1991, pp 6636-6643. One problem with such decomposable polymer approach is that some of the polymeric material may remain in the pores after the polymers have been removed. This is particularly true of ionic material which is typically less volatile and more likely to remain in the pores. As the dielectric layers become smaller, the presence of even small amounts of ionic material can lead to cross-talk or shorts. Thus, conventional emulsion polymers, prepared with an ionic surfactant, are not suitable for use in the manufacture of porous dielectric materials.
While other methods of preparing porous dielectric materials are known, they suffer from broad distributions of pore sizes, too large pore size, such as greater than 20 microns, or technologies that are too expensive for commercial use, such as liquid extractions under supercritical conditions.
It is known that ionic surfactants can be removed from small emulsion polymer particles by treatment with ion-exchange resins or by successive washing of the isolated particles as described by Krieger. However, these approaches are cumbersome and time consuming.
Emulsion polymerizations using only ethoxylated alcohol surfactants, a nonionic surfactant, are known. Such emulsion polymerizations are typically inefficient, requiring high soap levels and low solids content. The particles produced by such polymerizations have a particle size in the range of several hundreds of nanometers. U.S. Pat. No. 5,502,105 (Revis) discloses a method of making a silicone emulsion by dispersing a siloxane in water by forming a mixture of water, a cyclic siloxane and an ethoxylated alcohol nonionic surfactant; adding an organosilanolate polymerization initiator, and heating the mixture to polymerize the cyclic siloxane. This patent does not disclosed cross-linked emulsion particles.
There is thus a need for a method of producing cross-linked emulsion polymer particles that are substantially free of ionic surfactants, particularly for use in electronics applications, and do not require extensive post polymerization treatments.
SUMMARY OF THE INVENTION
It has been surprisingly found that emulsion polymers having small particle sizes can be prepared in a non-ionic surfactant. Non-ionic surfactants are surprisingly capable of producing extremely small polymer particles less than 100 nm in size. Such polymers have a much lower level of ionic contaminants than conventionally produced emulsion polymers.
In one aspect, the present invention provides a process for preparing polymer particles including the step of: polymerizing one or more monomers in an aqueous emulsion including one or more surfactants, the one or more surfactants consisting of nonionic surfactants, wherein at least one of the nonionic surfactants is an amine-N-oxide surfactant, and wherein the polymer particles have a mean particle size of less than or equal to 100 nm.
In a second aspect, the present invention provides an emulsion of polymer particles including one or more surfactants, the one or more surfactants consisting of nonionic surfactants, wherein at least one of the nonionic surfactants is an amine-N-oxide surfactant, and wherein the polymer particles have a mean particle size of less than or equal to 100 nm.
In a third aspect, the present invention provides an emulsion of polymer particles including one or more surfactants, wherein the polymer particles have a mean particle size of less than or equal to 100 nm, and wherein the emulsion is substantially free of ionic surfactants.
In a fourth aspect, the present invention provides a composition including a B-staged dielectric material and an emulsion polymeric porogen particle wherein the polymer particles have a mean particle size of less than or equal to 100 nm, and wherein the polymer particles are substantially free of ionic surfactants.
In a fifth aspect, the present invention provides a method of manufacturing an electronic device including the steps of: a) depositing on a substrate a layer of a composition including B-staged dielectric material having a plurality of emulsion polymeric porogen particles dispersed therein, wherein the porogen particles have a mean particle size of less than or equal to 100 nm, and wherein the porogen particles are substantially free of ionic surfactants; b) curing the B-staged dielectric material to form a dielectric matrix material without substantially removing the porogen particles; c) subjecting the dielectric matrix material to conditions which at least partially remove the porogen particles to form a porous dielectric material layer without substantially degrading the dielectric material; d) patterning the dielectric layer; e) depositing a metallic film onto the patterned dielectric layer; and f) planarizing the film to form an electronic device.
DETAILED DESCRIPTION OF THE INVENTION
As used throughout this specification, the following abbreviations shall have the following meanings, unless the context clearly indicates otherwise: ° C.=degrees centigrade; nm=nanometer; g=gram; wt %=weight percent; L=liter; mL=milliliter; w/w=weight per weight basis; SLS=sodium lauryl sulfate; ALS=ammonium lauryl sulfate; A-MSTY=alpha-methylstyrene; and MMA=methyl methacrylate.
The term “(meth)acrylic” includes both acrylic and methacrylic and the term “(meth)acrylate” includes both acrylate and methacrylate. Likewise, the term “(meth)acrylamide” refers to both acr

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