Semiconductor device manufacturing: process – Chemical etching – Liquid phase etching
Reexamination Certificate
1999-04-30
2001-01-23
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Chemical etching
Liquid phase etching
C438S106000, C438S783000, C438S780000, C438S784000, C438S781000
Reexamination Certificate
active
06177357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention provides a process for making flexible circuits comprising the step of etching polymer films by masking portions thereof with UV curable 100% active liquid photoresist and dissolving unmasked portions thereof with concentrated aqueous base. The crosslinked photoresist is then removed by mild base solution.
2. Description of the Related Art
A typical step in the fabrication of electronic circuitry on polymeric carrier films is to etch through the polymeric film to allow for subsequent connection through the backside to other devices or, where applicable, connection of frontside and backside circuitry. The selective etching or milling is necessary to allow electrical connections to be made between the differing conductive layers. Those portions of the polymeric film for which etching is not desired must be masked with a protective coating. The masking process can be satisfactorily done with the art of photolithography whereby an etch-insensitive material is applied and patterned using normal lithographic methods, i.e., exposure and development.
Solvent processible, water-insoluble or water-insensitive photoresists are ideal for masking where the subsequent etching process is aqueous based. Solvent processible resists are both developed and stripped using solvents and remain intact during such a process and thus protect any covered areas of the polymeric film while allowing etching of areas not protected by resists. However, solvent processible resists are less desirable from environmental and economic perspectives, and thus aqueous processible resists are preferred.
However, aqueous processible resists are stripped using dilute bases. Therefore, they have not been used as masks in processes involving aqueous base chemical etching of polymers.
U.S. Pat. No. 4,039,371 discloses a composition for etching polyimide based polymers comprising a tetraalkyl ammonium hydroxide and acetic acid, tartaric acid or oxalic acid. The resists disclosed to be useful as masks are positive resists; those resists specifically mentioned are all solvent processible and coated by spin-coating techniques.
U.S. Pat. No. 3,871,930 discloses the use of a commercial solvent processible photomask for use with an etching solution comprising a suitable base in a nonaqueous solvent such as dimethylsulfoxide.
U.S. Pat. No. 3,395,057 discloses the use of solvent processible photoresists and copper foils to mask those areas not to be etched.
U.S. Pat. No. 4,857,143 discloses a process for etching a fully or substantially fully cured polyimide layer which comprises contacting such layer with an aqueous solution at least about 3 molar of a metal hydroxide and at least about 0.5 molar of a metal carbonate, metal sulfate or metal phosphate. It is specifically disclosed that copper is used as the etching mask for the polyimide film.
It has now been discovered that the etching step may be done with hot, concentrated, e.g., 35% potassium hydroxide, using a crosslinked UV-curable 100% active liquid processible photoresist as a mask. The photoresist protects the masked area such that etching of the polymer film is completed only where desired without significantly swelling or delaminating the photoresist. This process avoids use of a solvent processible resist, while also eliminating processing steps and the need for copper masks.
SUMMARY OF THE INVENTION
The invention provides a process for etching a fully cured or substantially fully cured polymeric film which comprises contacting said polymeric film with a concentrated base at a temperature of from about 50° C. to about 120° C., wherein portions of said polymeric film are protected with a mask comprising a UV-curable 100% active liquid photoresist, the photoresist exhibiting substantially no swelling or delamination from said polymeric film during the etching.
The invention further provides a process for making flexible circuits wherein the step of etching of a polymeric film is accomplished by dissolving portions thereof, using a UV-curable 100% active liquid photoresist as an etching mask, comprising the steps of
a) aminating said photoresist on a polymeric film,
b) xposing at least a portion of said photoresist, thereby crosslinking said exposed portions thereof,
c) developing said photoresist with a dilute aqueous solution until desired image is obtained,
d) etching portions of the polymeric film not covered by the crosslinked photoresist with a concentrated base at a temperature of from about 50° C. to about 120° C.,
e) stripping said crosslinked photoresist off said polymeric film with a dilute aqueous basic solution.
The invention also provides a preferred process wherein the concentrated aqueous base used to etch the polymeric film is 35% or stronger potassium hydroxide.
As used herein the terms “resist” and “photoresist” are synonymous and interchangeable. Also, the terms “pattern” and “image” are used interchangeably to mean the configuration which is formed by the exposure and development of a photoresist.
DETAILED DESCRIPTION OF THE INVENTION
The processes of the present invention are concerned with the etching of substantially fully cured polymeric films, including such films as polyester, e.g., poly(ethylene terephthalate), polycarbonates, and polyimide. Polyimides are preferred polymeric films, including unmodified polyimides as well as modified polyimides such as polyester imides, polyimide-imide-esters, polyamide-imides, polysiloxane-imides, and other mixed imides. Especially preferred is a polyimide polymer made from the anhydride of pyromellitic acid and 4,4 diamino-diphenyl ether represented by the general formula:
wherein n ranges from about 150 to about 650, available from E.I. DuPont de Nemours and Company, (DuPont), under the tradename Kapton™, e.g., Kapton™ V, Kapton™ E and Kapton™ H, and also available from Kaneka Chemical Industries under the trade name Apical™. Other commercially available polyimide precursors include those available from DuPont under the trade name Pyralin™.
The UV-curable liquid photoresists useful in processes of the invention include one or more ethylenically unsaturated, photopolymerizable, low molecular weight compound, one or more addition-polymerizable monomers, and one or more initiators.
Such photoresists typically consist of one or more &agr;, &bgr;-unsaturated carboxyl-containing acrylates or methacrylates. Examples of monomers used in such photoresists include cinnamic acid, crotonic acid, sorbic acid, acrylic acid, methacrylic acid, itaconic acid, propionic acid, maleic acid, fumaric acid and half-esters and anhydrides of such acids, and the like. Such monomers are typically present in an amount of from about 10% to about 60%, based on the total composition.
Also typically included in such photoresists is at least one addition polymerizable noncarboxyl-containing monomers. Typical monomers include alklylene or polyalkylene glycol diacrylates; glycerol triacrylate; 1,3-propandiol di(meth)acrylate; 1,2,4-butanetriol trimethacrylate; 1,4-benzenediol di(meth)acrylate; 1,3-cyclohexanediol diacrylate; pentaerythritol tri- and tetra-(meth)acrylates; tetraethylene glycol dimethacrylate, trimethylolpropane methacrylate; triethylene glycol diacrylate; tetraethylene glycol diacrylate; 1,6-hexanediol diacrylate, 1,5-pentanediol dimethacrylate, and the bis-(meth)acrylates of polyethylene glycols, polypropylene glycols, bisphenol epoxy, and copolymers thereof having molecular weights of from about 100 to about 750. Such monomers are typically present in an amount of from about 35% to about 85%.
The free-radical photoinitiator useful with the liquid photoresist is a one activatable by actinic radiation. Examples include aromatic ketones such as benzophenone, and dimethoxyphenyl acetophenone, Michler's ketone, 4,4′-bis(diethylamino)benzophenone, 2-ethylanthroquinone, thioxanthones, benzoin alkyl ethers and benzyl ketals. Useful photoinitiators are discussed in U.S. Pat. No. 4,268,619, the disclosure of which is incorporated herein by reference.
Use
3M Innovative Properties Company
Anya Igwe U.
Fonseca Darla P.
Smith Matthew
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