Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2001-04-27
2003-11-04
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S313000, C430S270100, C430S170000, C430S905000, C029S603070, C029S603160, C360S313000
Reexamination Certificate
active
06641984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of frame plating and a method of forming a magnetic pole of a thin-film magnetic head through the use of the method of frame plating.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading.
It is required to increase the track density on a magnetic recording medium in order to increase recording density among the performance characteristics of a write head. To achieve this, it is required to implement a write head of a narrow track structure wherein the track width, that is, the width of top and bottom magnetic poles sandwiching the write gap layer on a side of the air bearing surface (medium facing surface) is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to implement such a structure.
For example, frame plating is used as a method for forming the magnetic poles that define the track width. In a conventional method of frame plating, as disclosed in Published Unexamined Japanese Patent Application Sho 50-95147, an electrode film is formed on a base layer, a resist layer is formed on the electrode film, and this resist layer is patterned through a photolithography process to form a frame to be used for plating. Using this frame, plating is performed through the use of the electrode film previously formed as a seed layer. A patterned plating pattern is thereby formed.
According to the conventional method of frame plating, a resist layer is patterned using optical measures and a patterned plating layer is formed using the resulting frame, and therefore it is theoretically impossible to form a plating layer patterned more finely than a dimension determined by an optical limit. Consequently, it has been impossible, by means of frame plating, to form a magnetic pole finer than the dimension determined by an optical limit.
For example, a method of forming a finely patterned resist layer is disclosed in Published Unexamined Japanese Patent Applications Hei 6-250379, Hei 10-73927 and Hei 11-204399 as follows. Specifically, in this method, a first resist containing a material generating an acid is used to form a first patterned resist layer and this first patterned resist layer is coated with a second resist that is water-soluble and capable of entering into a crosslinking reaction in the presence of an acid, to allow the acid to be generated in the first patterned resist layer, thereby forming a crosslinking film in a portion of the second resist near the boundary that touches the first patterned resist layer, followed by peeling off the non-crosslinked portion of the second resist to form a second patterned resist layer. In the present application, this method is hereinafter called a finely patterned resist layer-forming method.
The finely patterned resist layer-forming method described above was developed for a dry step such as dry etching used in usual technologies concerning production of semiconductors as shown in Published Unexamined Japanese Patent Applications Hei 10-73927 and Hei 11-204399.
The inventor of the present invention thought of using the patterned resist layer obtained by the above-mentioned finely patterned resist layer-forming method as a frame for frame plating in order to form a plating layer patterned more finely than the dimension determined by an optical limit.
However, through an experiment the inventor found that no finely patterned plating layer was obtainable by simply using the patterned resist layer formed by the finely patterned resist layer-forming method as the frame for frame plating to form a patterned plating layer.
Here, reference is made to
FIG. 23
to
FIG. 33
to describe the method used in the experiment for forming the patterned plating layer, and, at the same time, the fact that no finely patterned plating layer is obtainable by this method will be explained.
In this method, as shown in
FIG. 23
, a base film
152
for plating is first formed using a conductive material as necessary on a layer
151
which will be a base of a plating layer to be formed.
Next, as shown in
FIG. 24
, a first resist containing a material generating an acid is applied and then prebaked to form a first resist layer
153
.
Then, as shown in
FIG. 25
, the first resist layer
153
is subjected to an exposure step, a baking step in succession to the exposure step, a developing step, a washing step and a drying step in this order to form a first patterned resist layer
153
A having an isolated trench. However, the aforementioned drying step may be omitted.
Thereafter, as shown in
FIG. 26
, a second resist that is water-soluble and capable of entering into a crosslinking reaction in the presence of an acid is applied to cover the first patterned resist layer
153
A, thereby forming a second resist layer
154
.
Next, as shown in
FIG. 27
, heat treatment for the first patterned resist layer
153
A and the second resist layer
154
is carried out to generate an acid in the first patterned resist layer
153
A and to diffuse the acid to the second resist layer
154
. A crosslinked film
154
A is thereby formed in a portion of the second resist layer
154
near the boundary that touches the first patterned resist layer
153
A.
Here, the crosslinked film
154
A grows only from the surface of the first patterned resist layer
153
A and therefore the adhesion of the crosslinked film
154
A to the base film
152
is weakened. Also, if the heat resistance of the first patterned resist layer
153
A is low (low glass transition temperature), the first patterned resist layer
153
A is strained when the first patterned resist layer
153
A and the second resist layer
154
are heat-treated. As a result, the crosslinked film
154
A having weak adhesion to the base film
152
is peeled off from the base film
152
, leading to the occurrence of a clearance between the crosslinked film
154
A and the base film
152
.
Next, as shown in
FIG. 28
, in succession to washing with an aqueous isopropanol solution, a washing step and a drying step are carried out in this order to peel off the non-crosslinked portion of the second resist layer
154
thereby forming a second patterned resist layer
154
B consisting of the crosslinked film
154
A. In this manner, a frame having a narrowed trench is formed by the first patterned resist layer
153
A and the second patterned resist layer
154
B. At this time, there is a clearance between the second patterned resist layer
154
B and the base film
152
.
Next, as shown in
FIG. 29
, plating is carried out using the base film
152
as a seed layer by using a frame consisting of the first patterned resist layer
153
A and the second patterned resist layer
154
B to form plating layers
155
A and
155
B. Here, the symbol
155
A represents an object patterned plating layer formed in the trench, and the symbol
155
B represents a plating layer formed in other portions.
When the above plating layer is formed, a plating solution enters the clearance between the second patterned resist layer
154
B and the base film
152
, which causes the clearance to be plated, too. Also, the plating layer grows while it intends to spread and therefore the clearance is forcedly extended. As a result, the width of the bottom of the patterned plating layer
155
A becomes greater than a desired width by the width of the second patterned resist layer
154
B.
Next, as shown in
FIG. 30
, the frame is removed using an organic solvent. Then, as shown in
FIG. 31
, the base film
152
at the portion where the frame existed is removed by dry etching such as ion milling and reactive ion etching, or by wet
Chacko-Davis Daborah
Huff Mark F.
Oliff & Berridg,e PLC
TDK Corporation
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