Relation to manufacture of masks and electronic parts

Details Relation to manufacture of masks and electronic parts Relation to manufacture of masks and electronic parts

1999-12-27

2003-05-06

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Including a second component containing structurally defined...

C428S327000, C428S457000, C428S458000, C428S461000, C430S296000, C430S311000, C430S312000

Reexamination Certificate

active

06558787

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to positive working precursors which may be used in masks and electronic parts, and to methods of making such precursors using imagable compositions, and to masks and electronic parts made using such precursors.
BACKGROUND
Thermally imageable compositions suitable for use as imagable coatings on masks and on precursors for printed circuit and other electronic parts are described in WO99/08879 and are effective. However there are some situations where these compositions are not optimal. For example they may not be sufficiently physically robust for some applications, particularly when coated on both sides of a thin, flexible substrate. Although there are available other compositions which are more physically robust, these generally require more imaging energy for a given dissolution rate in a given developer.
Accordingly, there remains a need for technological advances in relation to thermally imagable articles for use in mask and electronic part manufacture; and in particular there remains a need for articles which have a coating which is both physically robust and of good image forming characteristics.
The types of electronic parts whose manufacture may use an imagable coating include printed wiring boards (PWBs), thick- and thin-film circuits, comprising passive elements such as resistors, capacitors and inductors; multichip devices (MDCs); integrated circuits (ICs); and active semiconductor devices. The electronic parts may suitably comprise conductors, for example copper board; semiconductors, for example silicon or germanium; and insulators, for example silica as a surface layer with silicon beneath, with the silica being selectively etched away to expose portions of the silicon beneath (a step in the manufacture of e.g. field effect transistors). In relation to masks, a required pattern may be formed in the coating on the mask precursor, which is then used as a mask in a later processing step, in forming a pattern on, for example, a printing or electronic part substrate.
SUMMARY OF THE INVENTION
The present invention provides a positive working precursor comprising:
A. a substrate; and
B. a thermally sensitive composite layer structure having an inner surface contiguous to the substrate and an outer surface, the composite layer structure comprising:
(a) a first layer having the inner surface, the first layer comprising a first polymeric material, wherein the first polymeric material is soluble or dispersible in an aqueous solution; and
(b) a second layer having the outer surface, the second layer comprising a second polymeric material, wherein the second layer is insoluble in the aqueous solution; wherein, upon heating the composite layer structure, the heated composite layer structure has an increased rate of removal in the aqueous solution.
A further embodiment of this invention provides a method of making a mask or an electronic part, the method comprising the steps of:
I) providing a precursor for the mask or electronic part, the precursor comprising:
A. a substrate; and
B. a thermally sensitive composite layer structure having an inner surface contiguous to the substrate and an outer surface, the composite layer structure comprising:
(a) a first layer having the inner surface, the first layer comprising a first polymeric material, wherein the first polymeric material is soluble or dispersible in an aqueous solution; and
(b) a second layer having the outer surface, the second layer comprising a second polymeric material, wherein the second layer is insoluble in the aqueous solution;
II) imagewise exposing the composite layer structure to thermal energy to provide exposed portions and complimentary unexposed portions in the composite layer structure, wherein the exposed portions of the composite layer structure are selectively removable by the aqueous solution; and
III) applying the aqueous solution to the outer surface to remove the exposed portions of the composite layer structure to produce an imaged article having uncovered areas of the substrate and complimentary remaining regions of the composite layer structure.
In each of the embodiments of this invention the aqueous solution preferably has a pH of about 6 or greater. The second polymeric material is preferably soluble in an organic solvent; the first polymeric material is preferably insoluble in that organic solvent; and the first layer preferably contains a photothermal conversion material particularly when the element is imagewise exposed with the radiant source of energy such as an infrared emitting laser. Preferably, the second layer is free of the photothermal conversion material.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to precursors which can be imaged with thermal energy. More particularly, this invention relates to precursors for masks and, especially, for electronic parts, which can be imaged by thermal energy typically by imagewise exposure with an infrared emitting laser, a thermal printing head, or the like. The mask or electronic part precursors described in this invention are made up of a substrate, which may comprise an insulating, semiconductor or conductive surface, and which need not be hydrophilic, and adhered thereto, a thermally sensitive composite layer structure typically composed of two layer coatings. An aqueous developable polymeric mixture typically containing a photothermal conversion material is coated onto the substrate to form the first layer. The second layer is composed of one or more non-aqueous soluble polymeric materials which are soluble or dispersible in a solvent which does not dissolve the first layer or cause detrimental intermixing of the two layers. In the positive-working thermal imaging element of this invention, the term “photothermal conversion material” is intended to be one or more thermally sensitive components which absorb incident radiation and convert the radiation to thermal energy. Typically, the photothermal conversion material is an “infrared absorbing” compound. As used herein, the term “thermally sensitive” is intended to be synonymous with the term “heat sensitive”. The precursor is exposed, typically with an infrared laser or a thermal print head. Upon aqueous development of the imaged precursor, the exposed portions are developed away thus exposing regions of the surface of the substrate which are receptive to conventional aqueous developer solutions. The second layer protects the underlying aqueous-soluble coating areas from the aqueous solution. In one embodiment of this invention, only the first layer contains a photothermal conversion material. In another embodiment of the invention the second layer contains a photothermal conversion material. In this instance, imaging exposure may result in at least partial removal of exposed areas of the second layer from the underlying coating. Any remaining exposed areas of the second layer are removed during development of the imaged precursor. In the following description, the invention will be illustrated using infrared radiation, and infrared absorbing material as the photothermal conversion material, but is not intended to be limited thereby. In another embodiment both layers contain a photothermal conversion material; the photothermal material in the first layer may be the same as or different from the photothermal conversion material of the first layer.
Precursor Construction
The precursor of the present invention includes a composite layer structure supported by a substrate. The composite layer structure contains at least an aqueous-insoluble second layer overlying an aqueous-soluble layer which contains an infrared absorber, the composite layer being adhered to the surface of the substrate. The composite structure may additionally contain intermediate layers such as substrate subbing layers to enhance adhesion to the composite structure, or an adhesion promoting interlayer between the second layer and the infrared absorbing layer.
The electronic part may, for example, be any of the electronic parts mentioned in this specification.

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