Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1999-10-22
2002-02-05
Moore, Margaret G. (Department: 1712)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S322000, C430S297000, C528S034000, C528S038000, C427S098300, C205S163000, C205S167000
Reexamination Certificate
active
06344309
ABSTRACT:
This invention relates to a polysilane composition for forming a coating suitable for bearing a metal pattern, and a metal pattern forming method using the same. It also relates to a method for preparing a wiring board.
BACKGROUND OF THE INVENTION
Substrates having metal patterns formed thereon are used in a variety of applications, for example, as printed circuit boards and comb-shaped electrode substrates for sensors. Metallization on such substrates is generally carried out by vapor phase methods such as CVD and wet methods as typified by plating methods. The metal is then patterned by a complex method which generally uses a resist material and involves exposure and development steps.
To eliminate such complication, Whiteside et al. proposed a novel metal patterning procedure. This procedure is to form a metal pattern by immersing a rubber material having an irregular surface in a dispersion of palladium colloid. The rubber material is then pressed against a substrate whereby the palladium colloid on raised portions is transferred to the substrate. The substrate is then immersed in an electroless or chemical plating bath whereby a metal deposits only on the palladium colloid- bearing areas. (See Langmuir 1996, 12, 1375-1380.)
Unfortunately, this procedure has the drawback that the palladium colloid is very unstable. Typically, a surfactant such as tetraammonium halide is added to the palladium colloid for stabilizing the colloid. An attempt to apply the palladium colloid by an imprinting, ink jet printing or lithographic process fails because of coagulation and precipitation of the palladium colloid. No uniform metal pattern is formed and the adhesion between the substrate and the metal is insufficient.
Printed circuit boards now encounter a strong need for higher density because of the widespread use of ultra-thin equipment. In prior art printed circuit boards, after a copper foil is bonded to a resin substrate with an adhesive, patterning is carried out using a resist (subtractive process). However, a proper adhesive must be used depending on a particular resin selected from among phenolic resins, polyester resins, epoxy resins, polyimide resins, and bismaleimide triazine resins. A complex bonding process is necessary. The bond strength is not fully high.
In recent years, a need to form a finer metal pattern promotes research efforts on the additive process of metallizing a resin substrate, rather than the subtractive process suffering from the thinning of a metal film by over-etching, so that the additive process may be employed on a commercially acceptable level. For the additive process, however, an improvement in the adhesion between the resin substrate and the metallization is of significance.
For logic devices and system LSI's, there is a strong need to increase the degree of integration and operational speed of circuits in order to realize high-speed electronic equipment. In this regard, an attention is paid to copper as a low resistance wiring material. In the prior art semiconductor device manufacture, aluminum is used as the material for forming fine metal circuits on semiconductor and a CVD process is used for its application. Copper is more difficult to work than aluminum. Then there is an urgent desire to establish a micro-wiring technique for copper. One solution to the above-described problem is electrolytic plating. It has been studied to apply electrolytic plating to the copper wiring process on a commercially acceptable level (see monthly Semiconductor World, February 1998, pp. 82-85).
However, the electrolytic plating has the drawback that the thickness of metal coating locally varies and is not reproducible, which becomes a neck to mass manufacture. When the electrolytic plating is combined with a resist material and resist process necessary to form a fine metal pattern in a mass scale, optimum conditions of the electrolytic plating have not been fully established.
Polysilane is an interesting polymer because of its UV absorption properties due to the metallic property and unique electron delocalization of silicon as compared with carbon, as well as its high heat resistance, flexibility, and good thin film forming properties. Active research efforts have been made on polysilane for the purpose of developing a photoresist capable of forming a micropattern at a high precision (see, for example, JP-A 6-291273 and 7-114188).
Finding that a palladium colloid forms when a polysilane is contacted with a solution of a palladium salt, and that UV irradiation causes the conversion of polysilane into polysiloxane, the inventors proposed a pattern forming method. The inventors also found that a metal pattern can be formed by combining such characteristics of a polysilane thin film with electroless plating catalyzed by palladium colloid (JP-A 10-325957). However, this method still requires the steps of light irradiation and exposure.
JP-A 5-72694 discloses the use of a polysilane in a method for preparing a semiconductor integrated circuit. This method is characterized in that a film of polysilane optionally doped with iodine is used as a conductive layer and a siloxane layer converted from polysilane by light irradiation is used as an insulating layer. It has thus been contemplated to apply the polysilane or polymer having a Si-to-Si bond as conductive material.
However, the semiconductor integrated circuit obtained by the above method has the problems that the conductive areas consisting solely of polysilane are not fully conductive and the use of potentially corrosive iodine becomes a serious obstacle to the application of polysilane to electronic material. Additionally, since the polysilane which is likely to convert into siloxane upon exposure to moisture, oxygen or light in the ambient atmosphere is used as conductive material, its application to electronic material requiring reliability encounters great difficulty.
JP-A 57-11339 discloses a method for forming a metal image by exposing a compound having a Si-to-Si bond to light and contacting it with a metal salt solution. When the compound having a Si-to-Si bond is contacted with the metal salt solution, the metal salt is reduced to the metal. Utilizing this phenomenon, a metal layer is formed in the unexposed area. To define a definite image by this method, the exposed area must be completely deprived of reducing property, which requires to irradiate a large quantity of light. Upon light exposure, the polysilane is converted into siloxane. Once a finely defined circuit is formed by UV irradiation, it becomes very difficult to further convert the siloxane into a polycarbosilane or polysilazane which is an insulating ceramic precursor having heat resistance and toughness.
There is a desire to have a technique of manufacturing a wiring board of high quality in an industrially advantageous manner.
SUMMARY OF THE INVENTION
One object of the invention is to provide a method of forming a metal pattern on a substrate by a simple step such as a conventionally employed imprinting, ink jet printing or lithographic process without a need for light irradiation and exposure. Another object is to provide a polysilane composition used in the method for forming a coating suitable for bearing a metal pattern.
A further object is to provide a method for preparing a wiring board having a pattern of highly conductive areas and insulating areas through simple and inexpensive steps so that the wiring board may have high heat resistance and pattern definition and be used in a variety of applications in the electric, electronic and communication fields.
In a first embodiment of the invention, there is provided a polysilane composition for forming a coating suitable for bearing a metal pattern thereon, comprising a polysilane, a carbon functional silane, and a solvent.
In a second embodiment of the invention, there is provided a metal pattern forming method comprising the steps of:
applying the above-defined polysilane composition onto a substrate by an imprinting, ink jet printing or lithographic process, to form a patterned
Fukushima Motoo
Ito Kunio
Mori Shigeru
Moore Margaret G.
Shin-Etsu Chemical Co. , Ltd.
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