JPH07297590A - Method of forming wiring of coaxial structure - Google Patents

Abstract

PURPOSE:To provide a method of forming a wiring of coaxial structure higher in density and less in number of processes than usual. CONSTITUTION:A dielectric structure 23x having a recess 23a is formed, and a first conductor thin film 27 used for forming a part of a shielding conductor is provided onto the dielectric structure 23x. A dielectric film 29 to serve as a part of an insulating film is formed in the recess 23a of the dielectric structure 23x where the first conductor thin film 27 has been formed. A conductor core 37 is formed on the dielectric film 29. A dielectric film 39a to serve as the rest of the insulating film of a wiring of coaxial structure is formed on a specimen where conductor core 37 has been formed. A second conductor thin film 43 serving as the rest of the shielding conductor is formed on the surface of the dielectric film 39a coming into contact with the first, conductor thin film 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming wiring having a coaxial structure for transmitting high frequency signals.

[0002]

2. Description of the Related Art As a wiring structure suitable for transmitting high frequency signals and reducing crosstalk between adjacent wires,
Coaxial structure wiring is known. As shown in the cross-sectional view of FIG. 5D, this is a structure in which a core conductor 11 is covered with an insulating film 13 and the insulating film 13 is covered with a shield conductor 15 to form a coaxial structure on a substrate 17. Of the wiring structure. As a conventional method for forming a wiring having a coaxial structure, for example, reference I (Thin Film Multichip Modules), (199
2), especially on page 36 of FIG. There was a disclosed method in the left corner of each figure of 23.1). This method will be described with reference to FIGS. First, the lower wiring 15 that is a part of the shield conductor 15 is formed on the base substrate 17.
a is formed (FIG. 5A). This lower layer wiring 15a becomes a grounding wiring. Next, the lower half portion 15 of the shield wall, which is a part of the shield conductor, is contacted with the lower layer wiring 15a.
b is formed (FIG. 5 (B)). Next, the lower wiring 15a
An insulating film (an insulating film between the core conductor 11 and the shield conductor 15) in the recess surrounded by the lower half portion 15b of the shield wall.
Resin 13a which is a part of 13 is embedded (FIG. 3).
(C)). Next, the core conductor 11 is formed on the resin 13a. Next, the upper half portion 15c of the shield wall is formed. Next, the resin 13b which is the rest of the insulating film 13 is embedded in the recess surrounded by the upper half portion 15c of the shield wall. Next, the upper layer wiring 15d which is a part of the shield conductor 15 is formed on the embedded resin upper portion 13b in contact with the upper half portion 15c of the shield wall, and the coaxial wiring 19 is obtained (see FIG. D)). Note that in FIG. 5D, 15x
Is a conductor portion formed on the lower half portion 15b of the shield wall when the core conductor 11 is formed.

[0003]

However, in the above-mentioned conventional method, the lower layer wiring 15a and the lower half portion 1 of the shield wall are formed.
5b, the conductor portion 15x, the upper half portion 15c of the shield wall, and the upper layer wiring 15d must be sequentially laminated in a predetermined positional relationship. Therefore, in consideration of these lamination deviations, each of the shield walls 15b, 15c, and 15x is It cannot be thin. Therefore, there is naturally a limit to the high-density wiring. In addition, the conductor 15a for the shield conductor,
Since the manufacturing process is complicated such that 15b, 15x, 15c and 15d are sequentially laminated and the resin needs to be embedded twice, it is considered that there is also a problem in yield.

[0004]

Therefore, according to the present invention,
The following steps (a) to (f) are included in forming a coaxial wiring having a structure in which a core conductor is covered with an insulating film and the insulating film is covered with a shield conductor on a base substrate. And

(A) A step of forming a dielectric structure having a recess.

(B) A step of forming a first conductor thin film for forming a part of the shield conductor on the dielectric structure having the recess.

(C) A step of forming a dielectric film, which will be a part of the insulating film, in the recess of the structure on which the first conductor thin film has been formed.

(D) A step of forming a core conductor on the dielectric film formed in the recess.

(E) A step of forming a dielectric film to be the remaining portion of the insulating film on the sample on which the core conductor has been formed.

(F) On the surface of the dielectric film to be the remaining portion,
A step of forming a second conductor thin film which is in contact with the first conductor thin film and becomes the remaining portion of the shield conductor.

[0011]

According to the structure of the present invention, the lower half of the coaxial wiring can be formed in a self-aligned manner on the recess of the dielectric structure having the recess. Further, when forming a dielectric film which is the remaining portion of the insulating film in the coaxial wiring on the sample on which the core conductor has been formed, this dielectric film and the dielectric film already formed in the concave portion The alignment accuracy with the and can be looser compared to the prior art in which it was necessary to align the shield wall. Further, the shield conductor is completed by forming the second conductor metal on the dielectric film formed so as to cover the core conductor.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. Here, these drawings are process diagrams showing the state of the sample in the main process of the forming process of the embodiment by a cross-sectional view taken in a direction orthogonal to the longitudinal direction of the wiring. However, these drawings schematically show the dimensions, shapes, and positional relationships of the respective constituents so that the present invention can be understood. Further, in each drawing used for the explanation, the same constituents are denoted by the same reference numerals, and the duplicated explanation may be omitted.

First, a dielectric structure having a recess is formed. In this embodiment, this structure is formed as follows. First, the base substrate 21 is prepared, and the base substrate 2
A dielectric layer 23 is formed on the substrate 1 (FIG. 1 (A)). The base substrate may be various substrates such as a ceramic substrate, a glass epoxy substrate, or a semiconductor substrate on which wiring having a coaxial structure is desired to be formed. Further, the dielectric layer 23 is composed of a layer of a negative dielectric material having photosensitivity in this embodiment. Examples of the dielectric material having photosensitivity include photosensitive polyimide resin and photosensitive epoxy resin. The dielectric material layer having such photosensitivity can be formed by any suitable method such as a spin coating method, a bar coating method, and a spray coating method.

Next, the dielectric layer 23 is exposed through a photomask 25 having a predetermined portion (a portion corresponding to a portion where a concave portion is to be formed) as a light shielding portion 25a. next,
The exposed dielectric layer 23 is developed. Then, the remaining dielectric layer is cured. As a result, a dielectric structure 23x having the recess 23a is obtained. Here, the recess 23a
The depth, width, and planar shape of the are determined according to the specifications of the wiring of the coaxial structure to be formed. The term “dielectric structure having a recess” as used in the present invention means that when the bottom and the wall of the recess are both made of a dielectric, a part of the recess, for example, the bottom is made of a conductor or a semiconductor. It is meant to include both cases. As a concrete example of the former,
When a groove is formed in the dielectric substrate itself to obtain a recess, a concrete example of the latter is, for example, forming a dielectric layer on a semiconductor substrate and removing a part of this dielectric layer until the semiconductor substrate is exposed. The case where the removal trace is formed as a recess (the case where a part of the dielectric layer is left in a ridge shape and the ridge is formed as a recess) is exemplified.

Next, a first conductor thin film 27 for forming a part of the shield conductor is formed on the dielectric structure 23x having the recess 23a (FIG. 1C). The first conductor thin film 27 can be a thin film of any material according to the design, but is preferably a metal thin film having a low resistivity. Although not limited to this, for example, a copper thin film is suitable as the first conductor thin film 27. Further, the method of forming the first conductor thin film 27 can be any suitable method. For example, an electroless plating method, a vapor deposition method, a sputtering method or the like can be cited as a method for forming the first conductor thin film 27. In addition, in order to mainly improve the adhesion strength of the first conductor thin film 27 to the structure 23x and the base substrate 21, a suitable surface treatment may be performed on the structure 23x and the base substrate 21.

Next, in the recess 23a of the structure 23x on which the first conductor thin film 27 has been formed, the dielectric film 2 which is a part of the insulating film (insulating film between the core conductor and the shield conductor).
9 is formed (FIGS. 2A and 2B). The dielectric film 29 is preferably a flat surface that is continuous with the surface around the recess 23a. This is because it is possible to easily form the core conductor later, and moreover, the first conductor around the recess 23 is formed.
Since the conductor thin film 27 is exposed, the second conductor thin film to be formed later can easily come into contact with the first conductor thin film and the shield conductor can be easily formed. Therefore, in this embodiment, the recess 23a is sufficiently filled on the entire surface of the structure 23x on which the first conductor thin film 27 has been formed by any suitable method such as spin coating, bar coating, and spray coating. Further, the dielectric film 29 is formed so that the surface thereof is as flat as possible (FIG. 2A), and then this dielectric film is etched back by oxygen plasma, for example (FIG. 2B). The end point of this etch back is the time when the surface of the first conductor thin film 27 portion around the recess 23a is exposed.

When the first conductor thin film 27 is made of a material that is etched back by etch back, an arbitrary film (with good plasma etching resistance) is formed on the surface of the first conductor thin film 27. It is desirable to pre-form (not shown). Further, in forming the dielectric film 29, the dielectric film may be applied a plurality of times to obtain a dielectric film having a desired thickness and surface condition. Further, depending on the type of resin forming the dielectric film 27, the surface may not be flattened easily. For example, a resin having a large shrinkage during curing is likely to fall under this. In that case, a flattening sacrificial layer (not shown) may be provided on the dielectric film 29.

Next, a core conductor is formed on the dielectric film 29. In this embodiment, this is done according to the following procedure. First, a thin film 31 for current supply of electrolytic plating is formed on a sample that has been etched back (FIG. 2C). At this time, a suitable surface treatment may be performed on this sample in order to mainly improve the adhesion strength of the current supply thin film 31 to the dielectric film 29 and the first conductor thin film 27. Next, the current supply thin film 31
Apply a resist, for example, a positive type resist, and then,
With respect to this resist, a photomask 33 in which a portion other than the portion corresponding to the portion where the core conductor is to be formed is the light shielding portion 33a
Exposure is performed, and then the resist is developed to obtain a resist pattern 35 (FIG. 3A). The resist pattern 35 exposes a predetermined portion (a portion corresponding to the core conductor formation planned region) of the current supply thin film 31 and covers the other portion. Next, this sample is placed in an electrolytic plating solution, and the current supply thin film 31 is energized. Current supply thin film 3
Since the portion not covered with the resist pattern 35 of No. 1 is plated, the desired core conductor 37 is formed (FIG. 3 (B)). The material for forming the core wire conductor 37 may be any material according to the design, but a metal having a low resistivity is preferable. Although not limited to this, for example, copper is suitable as a constituent material of the core conductor.

After removing the resist pattern 35, unnecessary portions of the current supply thin film 31 are removed by, for example, a suitable etching means (FIG. 3C). At this time, the core conductor 3
7 may be etched to some extent, but this is not a problem because the thickness of the core conductor 37 is sufficiently thicker than the thickness of the current supply thin film 31.

The method of forming the core conductor 37 is not limited to the electrolytic plating method described above, and may be any suitable method such as an electroless plating method or a method combining a vapor deposition method and a lithography technique.

Next, a dielectric film to be the remaining portion of the insulating film between the core conductor and the shield conductor is formed on the sample on which the core conductor 37 has been formed (FIGS. 4A and 4B). ).
This is done as follows in this embodiment. First, the dielectric layer 39 is formed on the sample on which the core conductor 37 has been formed (FIG. 4A). In this embodiment, the dielectric layer 39 is
Like the dielectric layer 23, it is composed of a layer of a negative dielectric material having photosensitivity. Next, this dielectric layer 39 is exposed through a photomask 41 in which a predetermined portion (a portion of the dielectric layer 39 other than a portion corresponding to a portion to be left as an insulating film in the coaxial structure) serves as a light shielding portion 41a. To do.
Next, the exposed dielectric layer 39 is developed. Then, the dielectric layer remaining after development is cured. As a result, the dielectric film 39a, which is the remaining portion of the insulating film between the core conductor and the shield conductor, is obtained (FIG. 4).
(B)).

Next, on the surface of the dielectric film 39a, a second conductor thin film 43, which is the second conductor thin film in contact with the first conductor thin film 27 and is the remaining portion of the shield conductor, is formed (FIG. 4 (C)). Of course, the formation area of the second conductor thin film 43 may extend to a portion other than the surface of the dielectric film 39a. In the structure of FIG. 4 (C), each part indicated by I corresponds to one coaxial structure wiring. The second conductive thin film 43 can be formed by an arbitrary film forming method such as an electroless plating method, a vapor deposition method, or a sputtering method and a lithographic method. In addition, the second conductor thin film 4
In order to increase the adhesion strength of the dielectric film 39, etc.
Surface treatment may be performed on the dielectric film 39a and the first conductor thin film 27. The second conductor thin film 43 can be made of any suitable material, but is preferably the same as the constituent material of the first conductor thin film 27 in view of the thermal expansion coefficient and the like.
However, a metal having a different function is used for the first conductor thin film and the second conductor thin film.
There may be a case where the function of the wiring is enhanced by selectively using the conductor thin film.

Although the embodiment of the method for forming the wiring having the coaxial structure of the present invention has been described above, the present invention is not limited to the above embodiment.

For example, in the above-described embodiment, the material for forming the dielectric structure 23x having the recess is the same as the material for forming the dielectric films 29, 39a serving as insulating films between the core conductor and the shield conductor. An example was given. But structure 23
The dielectric material forming x and the dielectric films 29 and 39a serving as insulating films between the core conductor and the shield conductor may be made of different materials. For example, two types of dielectric materials having different dielectric constants are used. This is because doing so may improve the transmission characteristics of the wiring in some cases.
However, in that case, the dielectric film 2 inside the shield conductor
The material is selected so that the dielectric outside the shield conductor, that is, the structure 23x, is not deformed by the heat when the 9, 39a is cured, and the reaction between the dielectric inside and outside the shield conductor does not occur. .

Further, a dielectric structure 23x having a recess is formed.
Of course, the dielectric for forming the insulating film between the core conductor and the shield conductor may not have photosensitivity. In this case, the formation of the recess and the selective leaving of the dielectric film on the core conductor may be performed by a known lithography technique and a known dry etching or wet etching technique.

In the above embodiment, the dielectric formed in the recess is flattened by the etch back method.
The flattening technology is not limited to this. For example, flattening may be performed by a physical polishing method.

Further, although the above-mentioned embodiment has explained the example of forming the wiring of the coaxial structure of one layer, the method of the present invention can of course be applied to the formation of a multilayer wiring structure having a plurality of wirings of the coaxial structure.

[0028]

As is apparent from the above description, according to the coaxial wiring forming method of the present invention, a dielectric structure having a recess is formed and a shield conductor is formed on the structure. A first conductor thin film for forming a part is formed, and a dielectric film which will be a part of the insulating film is formed in the recess of the structure in which the first conductor thin film has been formed. A core conductor is formed on the core, a dielectric film that is the remaining portion of the insulating film is formed on the sample on which the core conductor has been formed, and then a second conductor thin film that is the remaining portion of the shield conductor. To form. Therefore, the lower half of the coaxial wiring can be formed on the recess in a self-aligned manner. Further, when forming a dielectric film which is the remaining portion of the insulating film in the coaxial wiring on the sample on which the core conductor has been formed, this dielectric film and the dielectric film already formed in the concave portion The alignment accuracy with the and can also be looser compared to the prior art in which it was necessary to align the shield wall. Then, by forming a second wiring metal on the dielectric film, the shield conductor is completed. Therefore, the thickness of the shield conductor can be made smaller (thinner than the thickness of a general wiring metal film) as compared with the conventional technique in which the shield walls are sequentially laminated, and thus wiring can be formed with high density. Further, as compared with the conventional method, the wiring of the desired coaxial structure can be formed under the condition that the mask alignment accuracy is loose and the simple process, so that the wiring of the coaxial structure with a small change in the characteristic impedance can be stably formed.

[Brief description of drawings]

FIG. 1A to FIG. 1C are process drawings for explaining an example.

2A to 2C are diagrams for explaining the embodiment.
FIG.

3A to 3C are diagrams for explaining an embodiment.
FIG.

4A to 4C are diagrams for explaining the embodiment.
FIG.

FIG. 5 is a diagram for explaining a conventional technique.

[Explanation of symbols]

21: Base Substrate 23a: Recess 23: Dielectric Layer (Photosensitive and Negative Dielectric Material Layer) 23x: Dielectric Structure Having Recess 25a: Light-Shielding Part 25: Photomask 27: First Conductor thin film 29: Dielectric film 31: Electrolytic plating current supply thin film 33a: Light-shielding portion 33: Photomask 35: Resist pattern 37: Core conductor 39: Dielectric layer (photosensitive and negative dielectric material Layer) 41a: Light-shielding part 41: Photomask 43: Second conductor thin film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Iguchi 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (3)

[Claims] 1. A dielectric structure having a recess is formed on a base substrate for forming a wiring having a coaxial structure in which a core conductor is covered with an insulating film and the insulating film is covered with a shield conductor. A step of forming a first conductor thin film for forming a part of a shield conductor on the dielectric structure having the recess, and a structure in which the first conductor thin film has been formed In the recess of the body,
A step of forming a dielectric film that becomes a part of the insulating film, a step of forming a core conductor on the dielectric film formed in the recess, and a step of forming the core conductor on the sample on which the core conductor has been formed. A step of forming a dielectric film to be the remaining portion, and a second film to be the remaining portion of the shield conductor, which is in contact with the first conductor thin film on the surface of the dielectric film to be the remaining portion.
And a step of forming the conductor thin film, the method for forming a wiring having a coaxial structure. 2. The method for forming a wiring having a coaxial structure according to claim 1, wherein the dielectric film is provided between the step of forming a dielectric in the recess and the step of forming a core conductor. A method of forming a wiring having a coaxial structure, further comprising the step of flattening so as to be a surface continuous with a surrounding surface. 3. The method of forming a wiring having a coaxial structure according to claim 1, wherein a constituent material of a dielectric structure having a recess and a constituent material of a dielectric film forming the insulating film are different from each other. A method for forming a wiring having a coaxial structure, which is characterized by the above.