Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2002-01-29
2003-01-07
Quach, T. N. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S759000, C438S623000
Reexamination Certificate
active
06504248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin film circuit substrate for use in the microwave and millimeter wave regions, and a manufacturing method therefor. In particular, the present invention relates to a thin film circuit substrate using an organic insulating film as an insulating film that is located between an upper thin film electrode and a lower thin film electrode, and a manufacturing method therefor.
2. Description of the Related Art
In recent years, wireless communication application industries have been facing increased requirements of miniaturization, lower price, and higher performance for high-frequency devices used in high frequency regions such as the microwave region and the millimeter wave region.
Also, for the above-described high-frequency devices, transmission lines having low transmission loss and a high efficiency are required. While electrode materials having a low resistance are used for wiring lines (electrodes) to connect the transmission lines, it is believed that dielectric materials having a low dielectric constant and a low dielectric loss tangent are necessary for insulating films provided between the wiring lines.
In complying with such requirements, various wiring substrates have been developed, in which low-resistance materials such as Au, Cu, Ag, and Al are used as electrode materials, and organic resins having a low dielectric constant and a low dielectric loss tangent such as a polyimide resin, an epoxy resin, a benzocyclobutene resin, and a bismaleimide triazine resin are used as insulating films provided between the wiring lines.
One example of such a wiring substrate is a thin film circuit substrate as shown in
FIG. 6
, including a substrate
51
composed of a ceramic such as alumina, lower thin film electrodes
52
provided on the substrate
51
, an organic insulating film
53
provided over the lower thin film electrodes
52
, and upper thin film electrodes
55
that are provided on the organic insulating film
53
and are connected to the lower thin film electrodes
52
by via holes
54
provided in the organic insulating film
53
.
In the thin film circuit substrate shown in
FIG. 6
, a problem arises in that the adhesion strength between the organic insulating film
53
, which is an organic resin, and the upper thin film electrodes
55
, which are made of an electrode material, is not sufficiently strong which causes delamination of the films in the process of forming wiring lines and in the wire bonding step of the wiring lines.
Furthermore, there is a problem in that the reliability of electroconductivity between the upper thin film electrodes
55
and the lower thin film electrodes
52
is decreased due to the fact that the surface of the lower thin film electrodes
52
is oxidized.
Accordingly, to improve the adhesion strength between the organic resin and an electrode material, various methods have been proposed, including:
(1) a method for improving the adhesion strength between the organic resin and an electrode material by surface-treating the surface of the organic resin with an oxygen plasma, as described in Japanese Unexamined Patent Application Publication No. 8-134639; and
(2) a method for improving the adhesion strength by providing a polar polymer on the organic resin, as described in Japanese Unexamined Patent Application Publication No. 9-219586.
However, in method (1) wherein the surface of the organic resin is treated with an oxygen plasma, although the adhesion strength between the electrode material and organic resin is improved, there is a problem in that the electrical properties of the organic resin, such as dielectric constant and dielectric loss tangent, are degraded due to oxidization of the surface of the organic insulating film, making it impossible to obtain the desired high-frequency module characteristics.
Furthermore, in method (2) wherein the adhesion strength between the organic resin and the electrode material is improved by providing a polar polymer on the organic resin, although the adhesion between the electrode material and organic resin is improved, there is a problem in that a step for polymerizing a polar monomer is needed after a step for activating the surface of the organic resin which increases the processing time, and results in increased production costs.
There are other possible methods for improving the reliability of electroconductivity between the upper thin film electrode and lower thin film electrode, such as removing the oxidized surface film on the lower thin film electrode by a wet etching method or a dry etching method including an RIE (Reactive Ion Etching) method.
However, when the oxidized surface film on the lower thin film electrode is removed by wet etching after the surface treatment of the organic insulating film, which is an organic resin, although it is possible to improve the reliability of electroconductivity between the upper thin film electrode and the lower thin film electrode, there is a problem in that the adhesion between the upper thin film electrode and the organic insulating film, which is an organic resin, is decreased due to the fact that the surface-treated layer of the organic insulating film in the case of (1) above and the polar polymer provided on the surface of the organic insulating film in the case of (2) above are combined with H
2
O.
Furthermore, when the oxidized surface film on the lower thin film electrode is removed by a dry etching method, such as an RIE method, after the surface treatment of the organic insulating film, which is an organic resin, there is a problem in that the surface-treated layer of the organic insulating film as well as the polar polymer provided on the surface of the organic insulating film are etched at the same time. Thus, it is not possible to improve the adhesion strength between the upper thin film electrode and the organic insulating film. In addition, the thickness of the organic insulating film is decreased because the organic insulating film itself is etched.
Furthermore, when the oxidized surface film on the lower thin film electrode is removed before the surface treatment of the organic insulating film, there is a problem in that during the oxygen plasma treating step and the polar polymer forming step in the process of surface-treating the organic insulating film after the removal of the oxidized film, an oxidized film is formed again on the surface of the lower thin film electrode. Thus, the reliability of electroconductivity between the upper thin film electrode and the lower thin film electrode is decreased.
Furthermore, in the above-described methods, the manufacturing process is complicated and production costs are substantially increased because the surface treatment step of the organic insulating film and the step for removing the oxidized surface film on the lower thin film electrode are two separate steps.
SUMMARY OF THE INVENTION
To overcome the above-described problems, preferred embodiments of the present invention provide a method for manufacturing a thin film circuit substrate, in which the surface treatment of an organic insulating film and the removal of an oxidized surface film on a lower thin film electrode are performed at the same time. Therefore, a thin film circuit substrate having excellent adhesion strength between the organic insulating film and the upper thin film electrode, as well as excellent reliability of electroconductivity between the upper thin film electrode and the lower thin film electrode is efficiently manufactured.
Additionally, a thin film circuit substrate having excellent adhesion strength between its organic insulating film and its upper thin film electrode as well as excellent reliability of electroconductivity between the upper thin film electrode and its lower thin film electrode is provided.
A preferred embodiment of the present invention provides a method for manufacturing a thin film circuit substrate including the steps of forming a lower thin film electrode or electrodes on a substrate, forming an or
Tose Makoto
Yoshida Koji
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Quach T. N.
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