Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-04-06
2002-09-17
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S910000
Reexamination Certificate
active
06451498
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to photosensitive compositions and their use as etching or galvano resist in the structuring of metal coatings on electrical circuit-substrates.
2. Brief Description of the Prior Art
In order to structure metal coatings, for example copper coatings on circuit board laminates, photosensitive lacquers or foils are used preferably, which cover the copper coatings during etching, so that the latter can be protected with respect to the etching solutions (Panel-Plating-Process, Print-and-Etch Process).
In this case these resists serve as etching protection. For this purpose, the circuit board surfaces or the laminates which serve as the circuit board inner coatings are coated with the resist film, then exposed with the conductive pattern, developed and the uncovered copper surfaces removed by etching. Subsequently the resist which is being used as an etching mask can be removed again.
In another type of method (Pattern-Plating-Process) the resists are applied, before the further metal application, on to the substrates which are to be coated (galvano resists) and then exposed with the conductive pattern and developed. After that, further metal can be deposited on to the uncovered copper surfaces.
In the past, in the construction of circuit conductor track structures, resist types were predominantly used which were developed after exposure with the metal structure about to be produced by means of organic solvents. In this process solvents, which besides water included esters, organic carbonates, ethers or acetates, were preferably used. Recently resist types have been introduced which can be developed by mean s of aqueous-alkaline solutions, since these developing solutions are easier to handle in effluent treatment. Moreover, they also offer advantages with respect to the protection of personnel since no volatile organic compounds, which are harmful to health, are contained in the solutions.
As a rule so-called negative resists are used, which are hardened by exposure so that after subsequent developing the resist regions, which were not exposed, can be removed. The disadvantage of negative resists lies in the fact that the protective effect of the resists only occurs after photo-hardening. For example, dust particles can prevent the photo-hardening during exposure at certain places, with the result that holes occur in the resist surface in these places during development. This susceptibility to error can be avoided by using larger resist coating thicknesses. Admittedly, the photographic resolution of the resist, for example, reduces then because of light scattering in the resist coating. Another possibility for avoiding the problem consists of increasing the purity of the ambient air. However this uses a lot of resources and is therefore costly. Therefore a certain proportion of circuit boards, which are produced with a negative resist, must be examined for error, possibly even within the manufacturing process after exposure and developing of the resist, in order to expose defects of this type.
Furthermore, negative resists for use in the Panel-Plating-Process are used only as foil and therefore protect the holes, which are contained in the circuit boards, against the copper etching solutions such that the resist foil covers the hole entrances (Tenting Process). An alternative type of method, in which the negative resist is deposited on to the hole walls directly and remains there for the protection of the copper coatings, even during the subsequent copper etching procedure, is by comparison not practicable, since the resist which is in the holes for this purpose would need to be exposed. This is however not possible on a reliable basis, particularly not in smallish holes with rough hole walls. In the Tenting Process it is essential that the resist foil regions which cover the holes, have an adequately large supporting area round the hole entrances for a copper ring to be placed round the hole entrances at these points even during subsequent etching, said copper ring however occupying unnecessary space on the circuit board.
When using a positive resist, in which the film, which is deposited on the surfaces about to be constructed, is at first insoluble in the developing solutions and only converted into a soluble state by exposure, the problems which have been mentioned exist to a far lesser extent.
In particular, it is possible by means of positive resists to metallize holes in circuit boards using the Panel-Plating-Process without residual rings being left round hole entrances. In this way considerably finer circuit patterns are made possible. Furthermore, it has emerged that, with positive resists, a better photographic resolution can be obtained by means of more precise definition of the structure edges.
The effect of negative and positive resists is depicted in greater detail in W. M. Moreau, Semiconductor Lithography, Plenum Press, 1988. Typical positive photoresists normally contain novolaks as polymers. For example, resists of this type are described in U.S. Pat. No. 5,266,440.
These photoresists are however not particularly light sensitive, so that long exposure times or high light intensities must be accepted. For example, in order to expose circuit boards which are coated with traditional positive resists, light intensities of about 350 mJ/cm
2
are required, while, when using negative resists, normally values of about 100 mJ/cm
2
suffice (c.f. Nakahara, Electronic Packaging & Production. 1992, pp. 66 ff).
In recent times positive resists are described, the photosensitivity of which depends on light-induced proton split-off in certain organic acids and consequent acid cleavage of side groups of the polymer consisting the resist generating soluble compounds in aqueous-alkaline solutions. The photosensitivity of these resist types is considerably higher that that of the previously mentioned types.
The principle of these resists described as in “Photoresiste mit chemischer Verstarkung” (Amplifikation-“chemically amplified photoresists”) is described in G. M. Wallraff et al., “Designing tomorrow's photoresists”, Chemtech, 1993, pp. 22 to 30. According to this, organic onium salts, for example, diphenyliodonium-hexafluoroantimonate are used as acid generators which are split by UV radiation. Polyacrylates are used preferably as acid-cleavable polymers, said polyacrylates containing tert.-butyl-groups as carbon acid ester side groups which are split off by acid catalysis. In this process polar carbon acid side groups emerge, which cause the higher solubility of the polymer in an aqueous solution.
In U.S. Pat. No. 4,491,628, a resist composition operating according to the previously mentioned principle is shown, said resist composition containing, as well as the acid generator, an acid-cleavable polymer. As a polymer, compounds with phenols or styrenes with tert-butylester-groups, for example poly-(tert-butoxycarbonyloxystyrene) are suggested. As acid generators, diaryliodonium- and triarylsulfonium-metal halogenides are used.
In EP O 445 058 A1 photoresists are described, which are catalyzed by acid cleavage and which, besides an acid generator, contain acid-cleavable polymers for example polystyrenes with tert-butoxycarbonyloxy groups. Organic onium salts for example aryldiazonium-, diaryliodonium-, and triarylsulfonium-metal halogenides are suggested as acid generators.
In EP O 568 827 A2, a pattern-forming composition is described which can also be deposited electrically and which, besides an acid generator, also contains polystyrenes as acid-cleavable polymers, namely phenolic resins, for example novolaks with tert-butoxycarbonyloxy-groups.
In U.S. Pat. No. 5,272,042 positive resists are described, which likewise contain polystyrenes with tert-butoxycarbonyl groups, as well as those which contain, as acid-cleavable polymers, polyacrylates with tert-butoxycarbonyl groups as side groups. N-hydroxyamides and N-hydroxyimides, for example N-trifluoromethyl sulfonyloxynaphthalimide are used as acid
Desmasion Gonzalo Urrutia
Meunier Gilles
Meyer Heinrich
Pirri Rosangela
Verzaro Francis
Atotech Deutschland GmbH
Clarke Yvette M.
Paul & Paul
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