Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-07-31
2004-02-24
Vo, Peter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S846000, C029S854000, C257S738000, C257S752000, C257S762000
Reexamination Certificate
active
06694611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin-film structure in which an insulating layer is formed on an electrically conductive layer, a bump formed on the surface of the electrically conductive layer is exposed at the surface of the insulating layer, and the surfaces of the bump and the insulating layer are flush with each other so as to form a flat face, and more particularly, relates to a thin-film structure in which an oxide layer formed on the bump exposed at the surface of the insulating layer can be reliably removed.
2. Description of the Related Art
FIG. 9
is a cross-sectional view of a conventional thin-film structure. In this thin-film structure, for example, an insulating layer
3
composed of Al
2
O
3
or SiO
2
is formed on an electrically conductive layer
2
, such as an elevating layer, composed of copper or the like and in contact with a lead layer extending from a coil layer of an inductive magnetic head, and a bump
1
is formed on the surface of the electrically conductive layer
2
. The bump
1
is exposed at the surface of the insulating layer
3
, and the surfaces of the bump
1
and the insulating layer
3
are flush with each other so as to form a flat face.
The bump
1
constructing a conventional thin-film structure is a single-layer structure formed by an isotropic plating of copper or an electrically conductive material containing copper. An electrode layer
4
electrically contacting the bump
1
is formed on a flat face
1
a
of the bump
1
. The electrode layer
4
is made of gold.
A thin-film device, such as an inductive magnetic head, is connected to a wiring member (not shown) which transmits signals at the electrode layer
4
of the thin-film structure. Recording signals inputted via the electrode layer
4
are transmitted through the bump
1
and the electrically conductive layer
2
.
The thin-film structure can be used in the construction of an inductive head of a magnetoresistive (MR)/inductive hybrid head shown in
FIGS. 10 and 11
.
FIG. 10
is a plan view showing a so-called MR/inductive hybrid head in which a recording inductive head H
2
is disposed on a reading MR thin-film magnetic head H
1
.
FIG. 11
is a cross-sectional view of the MR/inductive hybrid head taken along the line XI—XI in FIG.
10
.
As shown in
FIG. 11
, the recording inductive head H
2
of the MR/inductive hybrid head is composed of a lower core layer
5
, a gap layer
6
, a coil layer
7
, an insulating layer
8
, an upper core layer
9
, a lead layer
10
, and an insulating layer
3
composed of Al
2
O
3
in a laminated structure.
The coil layer
7
induces a recording magnetic field to the lower core layer
5
and the upper core layer
9
. In
FIG. 10
, for ease of illustration in the figure, the coil layer
7
is drawn as concentric circles instead of as a coil.
The coil layer
7
is in electrical contact with the lead layer
10
at an central edge
7
a
of the coil layer
7
, and the lead layer
10
is connected to a bump
1
via the electrically conductive layer
2
at the other edge of the lead layer
10
opposite to the edge thereof contacted with the central edge
7
a
of the coil layer
7
. The electrically conductive layer
2
, which is an elevating layer, is simultaneously formed, when the coil layer
7
is formed, by plating using the same material as is used for the coil layer
7
.
In the conventional thin-film structure shown in
FIG. 9
, the bump
1
formed on the electrically conductive layer
2
is exposed at the surface of the insulating layer
3
, and the electrode layer
4
in electrical contact with the bump
1
is used as an external electrode.
FIGS. 12
to
14
are cross-sectional views of the thin-film structures in
FIG. 9
in a manufacturing method therefor.
First, a resist layer
50
for forming the bump is formed on the electrically conductive layer
2
, and an opening is formed in the resist layer
50
at an area at which the bump is to be formed. In the opening, the single-layer bump
1
, as shown in
FIG. 12
, composed of copper, or composed of an electrically conductive material containing copper, is formed by isotropic plating. The height hi of the bump
1
is, for example, 40 &mgr;m. After forming the bump
1
, the resist layer
50
for forming the bump is removed.
After forming the bump
1
, as shown in
FIG. 13
, the insulating layer
3
composed of Al
2
O
3
or SiO
2
is formed on the electrically conductive layer
2
and the bump
1
.
Next, the insulating layer
3
is polished so that the surface of the bump
1
is exposed, for example, to the level indicated by the line A—A in FIG.
13
. The exposed face of the bump
1
is flush with the surface
3
a
of the insulating layer
3
so as to form the flat face
1
a
, as shown in FIG.
14
.
Finally, the electrode layer
4
is formed on the flat face
1
a
of the bump
1
, whereby the thin-film structure shown in
FIG. 9
is completed.
However, in the step shown in
FIG. 14
, the flat surface
1
a
of the bump
1
is exposed to the air, and an oxide layer may form thereon. In particular, when heat is applied in a rinsing/drying process or the like after a polishing process for planarizing the surface
3
a
of the insulating layer
3
, the flat face
1
a
of the bump
1
is susceptible to forced oxidation.
When the flat face
1
a
of the bump
1
is oxidized, an oxide layer forms on the flat face
1
a
. In the case in which the electrode layer
4
is formed on the surface of the flat face
1
a
with the oxide layer thereon, the cohesion and the electrical conduction between the bump
1
and the electrode layer
4
are degraded, so that electrical contact failure readily occurs, and direct current resistance of the thin-film device becomes unstable, and as a result, the recording/reading characteristics are degraded.
When the oxide layer forms on the flat face
1
a
of the bump
1
, there are methods for removing the oxide layer by using ion-milling, sputter etching, and the like. However, in the case in which the bump
1
is the single layer structure composed of copper or an electrically conductive material containing copper, the thickness of the oxide layer formed by exposure to the air varies in accordance with the conditions when the oxide layer was formed, and as a result, the thickness of the oxide layer on the flat face
1
a
of the bump
1
cannot be predicted.
Consequently, when the conditions for ion-milling are determined so as to remove a predetermined thickness of the oxide layer formed on the flat face
1
a
of the bump
1
, the oxide layer may not be reliably removed since a predetermined thickness to be removed is too small, or conversely, an area of the bump
1
, which is not oxidized, may be removed. Accordingly, there is a problem in that the characteristics of the thin-film structures vary from product to product.
SUMMARY OF THE INVENTION
In order to solve the conventional problems described above, it is an object of the present invention to provide a thin-film structure and a manufacturing method therefor, in which an oxide layer formed on a bump constructing the thin-film structure of the thin-film device can be reliably removed, and cohesion and electrical conduction between the bump and an electrode layer are improved, whereby electrical contact defects therebetween can be reduced.
A thin-film structure of the present invention comprises an electrically conductive layer, an insulating layer formed on the electrically conductive layer, and the bump formed on the surface of the electrically conductive layer, in which the bump is exposed at the surface of the insulating layer and the surface of the bump is flush therewith so as to form a flat face. The bump comprises an electrically conductive material layer and a protective layer, in which the protective layer covers the surface the electrically conductive material layer, is composed of a material which is not as easily oxidized as the electrically conductive material layer, and is on the flat face.
In a process for forming the thin-film structure of the prese
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Nguyen Donghai D.
Vo Peter
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