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
2001-11-28
2004-11-16
Huff, Mark F. (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
C430S281100, C430S285100, C430S311000, C430S319000, C430S325000, C430S326000, C430S905000, C430S914000, C430S916000, C430S919000, C430S920000, C430S923000, C430S921000, C430S922000, C430S924000, C430S925000
Reexamination Certificate
active
06818375
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the field of photoresists. In particular, this invention relates to the field of photoresists having improved stripping properties, especially suitable for use in printed wiring board manufacture.
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or cross-link in a reaction between a photoactive compound and polymerizable agents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For positive-acting photoresists, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. In general, photoresist compositions include at least a resin binder component and a photoactive agent.
A wide variety of polymeric or resin binders may be used in photoresists. Such polymeric binders may include, as polymerized components, one or more acid functional monomers such as acrylic acid or methacrylic acid. For example, U.S. Pat. No. 5,952,153 (Lundy et al.) discloses photoimageable compositions containing as a polymeric binder having sufficient acid functionality to render the photoimageable composition developable in alkaline aqueous solution.
Photoresists may be either liquid or dry film. Liquid photoresists are dispensed on a substrate and then cured. Dry film photoresists are typically laminated to a substrate. Such dry film photoresists are particularly suitable for use in printed wiring board manufacture. One problem with conventional dry film photoresist compositions is that they are difficult to strip from electrolytically plated circuit boards using conventional alkaline aqueous stripping solutions, e.g. 3% sodium hydroxide solution. This problem arises from the demand of circuit board manufacturers to reduce the size of printed circuit boards, while increasing their functional capabilities. Consequently, the circuit lines and spaces on the circuit boards have continued to shrink, as more circuitry needs to be accommodated in smaller spaces. At the same time, metal plating heights have also increased above the thickness of the photoresist. This causes the metal to hang over the photoresist, resulting in a very narrow space containing the photoresist being virtually encapsulated by the overplated metal. The photoresist then becomes trapped by the plated overhang, making it difficult to attack and strip by conventional methods. If the photoresist is not completely stripped or removed, ragged copper circuit lines will result after etching which are unsuitable as they can cause short circuiting of the board.
Some circuit board manufacturers have tried thicker photoresists to accommodate the increasing plating heights, however, this approach is more expensive and limits resolution of the circuit lines. Typically, organic-based (amine- or organic solvent-containing) alkaline stripping solutions are used which produce a smaller stripped particle to facilitate stripping. While such organic-based strippers remove the resist better, they are expensive relative to inorganic-based strippers (e.g. sodium or potassium hydroxide) and have more waste treatment and environmental concerns associated with them. Solvent-strippable photoresists are much less desirable due to workplace regulations limiting or reducing solvent emissions.
It is thus desirable to provide photoresist compositions that are easily removed using alkaline aqueous inorganic-based stripping solutions.
A wide variety of trihalomethyl-substituted compounds are known, particularly as photoactive components. For example, U.S. Pat. No. 4,935,330 (Hofmann et al.) discloses trihalomethyl-substituted triazines as a photoactive component in the production of lithographic printing plates.
U.S. Pat. No. 5,668,080 (Cove et al.) discloses thermally responsive recording material including a support having provided thereon in substantially contiguous relationship an electron donating dye precursor and alpha-trichloromethylbenzyl acetate. Photoresist compositions are neither disclosed nor suggested in this patent.
SUMMARY OF THE INVENTION
It has been surprisingly found that the addition of one or more non-polymerizable photoresist strip enhancers provide photoimageable compositions having improved stripability or removability. Such photoresist strip enhancers are compounds containing one or more trihalomethyl-substituents in an alpha position relative to a group capable of stabilizing a negative charge. It has also been surprisingly found that such non-polymerizable photoresist strip enhancers do not adversely affect other properties of the photoresist binder such as chemical resistance. Thus, the present compositions show improved stripping with substantially no loss of chemical resistance, as compared to the same compositions free of non-polymerizable photoresist strip enhancers.
In one aspect, the present invention provides a photoresist composition including a polymeric binder, a photoactive component, a photoresist strip enhancer and optionally a cross-linking agent, wherein the photoresist strip enhancer is non-polymerizable with the polymeric binder, optional cross-linking agent or both and has the formula
wherein each X is independently chlorine, bromine, fluorine or iodine; Z=cyano, aryl, substituted aryl, C(Y)—R
1
, C≡C—R
2
and C(R
3
)═CR
4
R
5
; Y=oxygen or sulfur; R=Z, hydrogen, (C
1
-C
4
)alkyl, (C
1
-C
4
)alkoxy, substituted (C
1
-C
4
)alkyl, substituted (C
1
-C
4
)alkoxy; R
1
=(C
1
-C
8
)alkyl, (C
1
-C
8
)alkoxy, substituted (C
1
-C
8
)alkyl, substituted (C
1
-C
8
)alkoxy, aryl or substituted aryl; R
2
=hydrogen, (C
1
-C
8
)alkyl, substituted (C
1
-C
8
)alkyl, aryl or substituted aryl; and R
3
, R
4
and R
5
are independently selected from hydrogen, halogen or R
1
.
In a second aspect, the present invention provides a method of enhancing the removal of a photoresist composition from a substrate including the step of combining a photoresist strip enhancer with a photoresist composition including polymeric binder, a photoactive component and optionally a cross-linking agent, wherein the photoresist strip enhancer is non-polymerizable with the polymeric binder, optional cross-linking agent or both and has the formula
wherein each X is independently chlorine, bromine, fluorine or iodine; Z=cyano, aryl, substituted aryl, C(Y)—R
1
, C≡C—R
2
and C(R
3
)═CR
4
R
5
; Y=oxygen or sulfur; R=Z, hydrogen, (C
1
-C
4
)alkyl, (C
1
-C
4
)alkoxy, substituted (C
1
-C
4
)alkyl, substituted (C
1
-C
4
)alkoxy; R
1
=(C
1
-C
8
)alkyl, (C
1
-C
8
)alkoxy, substituted (C
1
-C
8
)alkyl, substituted (C
1
-C
8
)alkoxy, aryl or substituted aryl; R
2
=hydrogen, (C
1
-C
8
)alkyl, substituted (C
1
-C
8
)alkyl, aryl or substituted aryl; and R
3
, R
4
and R
5
are independently selected from hydrogen, halogen or R
1
.
In a third aspect, the present invention provides a method of manufacturing a printed wiring board including the steps of: a) disposing on a printed wiring board substrate a photoresist composition including a polymeric binder, a photoactive component, a photoresist strip enhancer and optionally a cross-linking agent, wherein t
Johnson Todd
Koes Thomas A.
Eternal Technology Corporation
Huff Mark F.
Lee Sin J.
Scully Scott Murphy & Presser
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