JPH0537151A - Thin film multilayer circuit formation method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for forming a thin film multilayer circuit having an insulating film which is free from pinholes and which causes less insulation short circuit and leakage by performing vacuuming in the third step. [Structure] (First Step) The conductor 9 is formed on the substrate 8,
(Second step) The conductor 9 is patterned, (third step) a polyimide resin solution is applied, and a vacuum is drawn. (Fourth step) Cure and via hole opening are performed, and (Fifth step)
Step) Embedding a conductor to repeat the above steps to form a thin film multilayer circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thin film multilayer circuit on a circuit board, which enables miniaturization and high density mounting.

[0002]

2. Description of the Related Art In recent years, thin-film multilayer circuit boards using polyimide as an insulating film have been used in large-scale computers for the purpose of high-speed signal processing. Hereinafter, a method of forming the above-mentioned thin film multilayer circuit will be described with reference to the drawings. Figure 2
1 illustrates a conventional method for forming a thin film multilayer circuit.

The first step is to form a conductor film 2 on an alumina substrate 1.
This is a step of forming (for example, a film in which a chromium film 500Å, a copper film 5 μm, and a chromium film 500Å are laminated) by a sputtering method. The second step is a step of patterning the film formed in the first step, for example, a photolithography method (a method of applying a resist of about 1 μm, and patterning through a series of steps of exposure, development, etching, and resist removal). Patterning is performed. The third step is a step of applying the polyimide resin solution 3 as an insulating film. For example, the photocurable polyimide resin solution 3 is applied and formed on the substrate 1 to a thickness of about 20 μm by a spin coating method. The fourth step is a step of forming the via holes 4 in the polyimide resin solution 3. After the polyimide resin solution 3 is applied and formed in the third step, pre-cure is performed at about 80 ° C. for 2 hours, and the polyimide on the substrate 1 is exposed through a photomask. The resin solution 3 is exposed and developed to form a via hole 4. After development, curing is performed at about 400 ° C. to form a polyimide film 5. The fifth step is a step of embedding the conductor 6 (copper film) in the via hole 4 in order to connect the wiring conductors above and below the via hole 4, for example, by embedding the conductor 6 by electroless plating or electrolytic plating. The thin film multilayer substrate 7 is formed by repeating the first to fifth steps described above.

[0004]

However, in the method of the third step, when the polyimide resin solution 3 is applied onto the alumina substrate 1 by, for example, the spin coating method, the solution may contain bubbles. Therefore, when cured after coating, air bubbles remain trapped in the polyimide film 3, failing to function as an insulating film, and cause a short circuit or a leak between the upper and lower wiring conductors of the polyimide film 3.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a method for forming a thin film multilayer circuit which prevents the generation of bubbles in a polyimide film.

[0006]

In order to achieve the above object, in the thin film multilayer circuit forming method of the present invention, the resin solution is applied onto the substrate by spin coating in the third step, and the pressure is reduced in a vacuum container. A method of pre-curing after exposing to the state, and then performing final exposure by developing and exposing through a photomask is adopted.

[0007]

Function The bubbles in the resin film are eliminated by the reduced pressure, and the occurrence of insulation short circuit or leak is reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A thin film multilayer circuit forming method according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a process diagram of a method for forming a thin film multilayer circuit in an embodiment of the present invention. First
The step is a step of forming a conductor film 9 (for example, a chromium film 500Å, a copper film 5 μm, a chromium film 500Å) on the alumina substrate 8 by a sputtering method. The second step is the first
This is a step of patterning the conductor film 9 formed in the step by a photolinography method. In the third step, a polyimide resin solution 10 (using a photocurable polyimide resin solution in this embodiment) as an insulating film is applied on the alumina substrate 8 by a spin coating method to a thickness of about 20 μm,
It is a step of placing in a vacuum container, evacuating, and exposing to reduced pressure for about 1 Torr for 1 minute.

In the fourth step, the via holes 11 are formed in the polyimide resin solution 10 and the polyimide resin 12 is cured.
Is a step of forming. After the polyimide resin solution 10 was applied and formed in the third step, it was exposed to a reduced pressure and then heated to about 80 ° C.
Precure is performed for 2 hours, and the polyimide resin solution 10 on the alumina substrate 8 is exposed and developed through a photomask to form a via hole 11. After development, curing is performed at about 400 ° C. to form the polyimide film 12. The fifth step is a step of embedding the conductor 13 (copper film) in the via hole 11 in order to connect the wiring conductors above and below the via hole 11, and the conductor 13 is embedded by, for example, electroless plating or electrolytic plating. The thin film multilayer substrate 14 is formed by repeating the first to fifth steps described above.

As described above, according to the present embodiment, after the polyimide resin solution 10 is applied and formed on the alumina substrate 8 by the spin coating method, the pressure is set to about 1 Torr in the vacuum container at about 1 Torr.
By holding under reduced pressure for a minute, air bubbles in the polyimide resin solution 10 formed by the spin coating method are released to the outside, so that after curing, there are no air bubbles in the polyimide film, and the upper and lower wirings of the polyimide film 12 are eliminated. It is possible to reduce the occurrence of insulation short circuit or leakage between them.

In the above embodiment, the substrate is an alumina substrate, but a silicon substrate, a glass substrate or a metal (for example, aluminum) substrate having an insulating film formed thereon may be used.
Further, although the polyimide resin solution 10 is made to be photo-curable in the above-mentioned embodiment, the same effect can be obtained by using a thermosetting polyimide resin solution. In addition, although the polyimide resin solution is used as the insulating film in the above-described embodiment, the same effect can be obtained with other curable resin solutions. Further, in the above embodiment, the vacuuming in the third step was set to 5 Torr for 1 minute, but it is not particularly limited to this, and the more the vacuum is pulled,
The time may be short, or conversely, if the degree of vacuum is bad, it is necessary to lengthen the time.

[0012]

As is apparent from the above description, according to the present invention, after the resin solution is applied onto the substrate and then kept under reduced pressure, the bubbles in the applied resin solution are released to the outside. . Therefore, after the curing, there are no bubbles in the resin film (insulating film), and it is possible to reduce the occurrence of insulation short circuit or leak between the upper and lower wirings in the insulating film.

[Brief description of drawings]

FIG. 1 is a diagram showing steps of a thin film multilayer circuit forming method of the present invention.

FIG. 2 is a diagram showing steps of a conventional thin film multilayer circuit forming method.

[Explanation of symbols]

 8 substrate 9 conductor 10 polyimide resin solution (insulating coating film) 11 via hole 12 insulating film 13 conductor (conductor embedded in via hole)

Claims (1)

Claims: 1. A first step of forming a conductor on a substrate, a second step of patterning the conductor, and a third step of forming an insulating film on the substrate on which the conductor is formed. A fourth step of forming a via hole in this insulating film, and a fifth step of embedding a conductor in this via hole. In the third step, the insulating coating film formed by coating on the substrate is evacuated and then cured. And an insulating film is formed, and a thin film multilayer circuit forming method is performed by repeating the above steps.