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Oligomeric Ketoester Precursors for Improved Polyimide Planarization and Gapfilling

IP.com Disclosure Number: IPCOM000039509D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 4 page(s) / 26K

Publishing Venue

IBM

Related People

Kent, JP: AUTHOR [+3]

Abstract

The ability to cover irregular topography with a flat (nonconformal) coating is limited by the viscosity and wettability of the polymer solution. That is, the surface tension of the solution must be sufficiently low so as to spontaneously wet the surface to which it is applied and, at a given temperature, the solvent, percent solute (solids), and molecular weight (MW) of the solute polymer must permit a viscosity low enough for flow. Both planarization and gapfilling require flowable polymer solution viscosity at relatively high solids concentrations. In polyamic acid solutions, this involves good flow of nearly solventless polymers near the solidification (cure) temperature. However, high solids content and low viscosity are competing parameters: an increase in solids content leads to higher viscosity.

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Oligomeric Ketoester Precursors for Improved Polyimide Planarization and Gapfilling

The ability to cover irregular topography with a flat (nonconformal) coating is limited by the viscosity and wettability of the polymer solution. That is, the surface tension of the solution must be sufficiently low so as to spontaneously wet the surface to which it is applied and, at a given temperature, the solvent, percent solute (solids), and molecular weight (MW) of the solute polymer must permit a viscosity low enough for flow. Both planarization and gapfilling require flowable polymer solution viscosity at relatively high solids concentrations. In polyamic acid solutions, this involves good flow of nearly solventless polymers near the solidification (cure) temperature. However, high solids content and low viscosity are competing parameters: an increase in solids content leads to higher viscosity. In addition to high solids content and low viscosity, gapfilling of small geometries also involves good wetting character of the polymer solution. A novel polyamic acid preparation technique using a specific class of hindered alcohols produces a thermally-curable oligomeric coating solution of good stability that remains flowable at higher concentrations and temperatures and cures to form a planar polyimide film. A novel polyamic acid precursor having terminal ketoester groups is produced. The ketoester terminal group allows chain extension at higher temperatures than normal amic acid imidization, which permits greater solvent evaporation with consequent higher solids concentration prior to viscosity increases due to chain extension. Planarization is improved, and the resulting film has enhanced mechanical and dielectrical properties. The present invention involves the synthesis and use of oligomeric polyamic acid precursors which incorporate end group ketoalcohol esters as wetting agents. The ketoalcohol ester has the general formula: where A = amic acid chain, R1 = an alkyl having from 1 to 10 carbon atoms, or cylcoalkyl,

phenyl, benzyl or substituted aryls,

R2 = the same as R1 or hydrogen,

R3 = (CH2)n where n = 0 to 8, and

R4 = alkyl, cylcoalkyl, aryl or benzyl. R1 may or may not equal R2 or R4, but R4 is not hydrogen. Preparation of the oligomeric polyamic acid precursor comprises the following steps. A monomeric anhydride-ester starting material is prepared through equilibration of an aromatic dianhydride with a moderately reactive alcohol. In this procedure, a molar equivalent of dianhydride is equilibrated in a suitable solvent with a molar equivalent (or a lesser or greater amount) of a hindered ketoalcohol. A single dianhydride or a mixture of dianhydrides may be used. Dianhydrides useful in conjunction with the present invention may be expressed by the following formula: where R5 = tetravalent organic radical containing at least two carbon atoms selected from susbtituted and unsubstituted

aliphatic,

cycloaliphatic, heterocylcic, aromatic a...