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Selective Activation of Metal Salt Loaded Polyimide by Exposure to Plasma

IP.com Disclosure Number: IPCOM000050747D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 28K

Publishing Venue

IBM

Related People

Romankiw, LT: AUTHOR

Abstract

In the past, polyimide containing metal salt particles was deposited upon a substrate by spinning a solution of a polar solvent, polyimide and a metallic salt upon the substrate. Then a photoresist mask stencil was formed upon the polyimide film produced. Next, the structure was heated to remove some of the polyimide. Finally, the structure was dipped into an electroless bath. The process was slowed by the reduction of the salt particles by the reducing agent in the electroless plating bath. Here, plasma etching is used to remove the outer surface of polyimide and simultaneously reduce the metal salts to yield an immediate plating base for an electrolessly deposited metallic layer.

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Selective Activation of Metal Salt Loaded Polyimide by Exposure to Plasma

In the past, polyimide containing metal salt particles was deposited upon a substrate by spinning a solution of a polar solvent, polyimide and a metallic salt upon the substrate. Then a photoresist mask stencil was formed upon the polyimide film produced. Next, the structure was heated to remove some of the polyimide. Finally, the structure was dipped into an electroless bath. The process was slowed by the reduction of the salt particles by the reducing agent in the electroless plating bath. Here, plasma etching is used to remove the outer surface of polyimide and simultaneously reduce the metal salts to yield an immediate plating base for an electrolessly deposited metallic layer.

It is possible to dissolve PdCl(2), nickel chloro palladate, ammonium salts of Pd with SO(4), acetates of Pd and similar salts of Cu, Ni, Co, Fe, Au and Ag in a number of polar organic solvents, which solutions are then mutually soluble with polyimides.

Very dilute solutions of such metal salts combined with a very dilute solution of polyimide can be applied by spinning onto partially cured or dried polyimide. The solution forms a 1,000 to 3,000 Angstroms thick film which adheres to the polyimide below very well. Since the size of the metal salt particles is only about 50 Angstroms and since they have a very sparse population density, the surface conductivity of the polyimide remains nearly identical with the surface conductivity of polyimide.

The polyimide surface is activated for electroless deposition by exposing the surface to heat to burst the partially encapsulated salt seeds. When surfaces loaded with Pd, Ni, Cu or other metal salts are dipped in electroless Cu after a short induction period, electroless Cu is plated and good adhesion to a very smooth polyimide surface results.

Under certain conditions, the activated surface is covered with a positive photoresist which is exposed and developed. Selective plating is provided in the resist openings.

In this article, solutions of metal salt are provided in NMP (Normal Methyl Perylydon), DMF (Di Methyl Formamide) , acetone, alcohol or other polar solvents. This solution is merged with polyimide. Then the resulting mixture is applied to partially cured polyimide insulation (i.e., after curing polyimide only to below 175 degrees C). The polyimide is fully cured. A positive resist of a photoactive polyimide resist is then applied. After exposing and developing the desired pattern in the resist, the sample is exposed for a few minutes to a plasma of forming gas or some other reducing or inert atmosphere in a plasma etcher or a diode system. This would be the critical step in the process because it is desired just to open up the metal salt seeds in the underlying surface without otherwise affecting the lithography. After this step, the part is fully cured in an inert atmosphere and is then plated in electroless Cu to form unattached...