Semiconductor device manufacturing: process – Semiconductor substrate dicing – Beam lead formation
Reexamination Certificate
2001-08-06
2004-03-30
Coleman, W. David (Department: 2823)
Semiconductor device manufacturing: process
Semiconductor substrate dicing
Beam lead formation
C360S110000
Reexamination Certificate
active
06713368
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an etching mask used for micromachining, a method of making the same, an etching method using the etching mask, a magnetic head device and a method of manufacturing the same, which are used for making writing poles and so on of a composite thin-film magnetic head device having a reading head and a writing head, for example.
2. Description of the Related Art
Demands have been increasing for techniques that achieve finer patterns as a reduction has been sought in size and film thickness of a magnetic head device such as a magnetoresistive (MR) head device used for a hard disk unit and various semiconductor devices. Fabrication of a micropattern includes an etching process. Anisotropic etching is required for achieving high etching accuracy in the etching process. Anisotropic etching has such orientation that a sidewall surface of a complete pattern is orthogonal to the surface of a base layer. An example that requires anisotropic etching is a composite thin-film magnetic head device having an inductive reading head and a magnetoresistive writing head. In order to achieve steady performance of the writing head of the magnetic head device, anisotropic etching is required to be performed orthogonally to the substrate for processing the writing pole (top pole) of the head.
As anisotropic etching, dry etching is preferred compared to wet etching achieved through a complete chemical reaction. Dry etching is to evaporate and remove an object, using reactive gas plasma or ion beams thereof A photoresist is generally used as an etching mask for forming a pattern by dry etching.
One of problems found in such an etching process is that not only the workpiece to be etched but also the mask itself is etched. In the case of dry etching using ion beams, in particular, a photoresist mask is easily deformed since the etching speed of the mask by ion beams is high and the photoresist is sensitive to heat. The photoresist film may be made thick in order to prevent such deformation. However, an increased film thickness makes it difficult to maintain anisotropy of etching, which is not desirable for fine pattern fabrication.
To overcome the foregoing problem, a mask utilizing a metal such as copper (Cu) has been fabricated instead of a heat-sensitive photoresist film.
However, if a metal mask is used, a problem still remains, that is, the top and sidewall surface of the mask are removed together with the workpiece through an ion beam application although the etching speed of the mask is decreased.
FIG. 14A
to
FIG. 14C
illustrate such a state. As shown in
FIG. 14A
, a metal mask
101
is formed on a workpiece
100
and ion beam etching is performed. As shown in FIG.
14
B and
FIG. 14C
, not only the surface of the workpiece
100
but also the top and sidewall surface of the metal mask
101
are removed by ion beams
102
. As a result, a sidewall surface
101
A of the patterned workpiece
100
is not perpendicular but has a cross section having the shape of a trapezoid whose top width is wider than the bottom width as shown in FIG.
14
C. The interface between the sidewall surface
101
A and the base layer takes a round shape.
In a composite thin film magnetic head device as mentioned above, in particular, if the cross section of a writing pole formed on a gap layer takes the shape of a trapezoid or the interface between the pole and the gap layer takes a round shape, leakage of magnetic flux results and affects data reading and writing. It is therefore desirable that the top surface of the writing pole layer is horizontal and sidewall surface is perpendicular, that is, the cross section is rectangular.
To achieve such a structure, a method is disclosed in Japanese Patent Application Laid-open Hei 3-252907 (1991) wherein a mask made of a metal (such as a nickel-iron alloy) whose etching speed is nearly similar to that of a workpiece is used. However, it is difficult to maintain sufficient anisotropy in this method, too, since the mask itself is removed through dry etching and part of the removed mask redeposits on the mask, and the mask thickness is required to be substantially thick (3 to 7 &mgr;m) and so on.
SUMMARY OF THE INVENTION
It is a first object of the invention to provide an etching mask and a method of making the same for precisely performing anisotropic etching through dry etching and forming a pattern on a workpiece, the cross section of the pattern being rectangular in shape.
It is a second object of the invention to provide an etching method for forming a pattern whose cross section is rectangular in shape on a workpiece through dry etching using such an etching mask.
It is a third object of the invention to provide a magnetic head device fabricated through the use of such an etching mask, for suppressing flux leakage in a writing pole and achieving stability of writing, and a method of manufacturing such a magnetic head.
An etching mask of the invention is used for selectively etching a workpiece. The mask is made of a metal and has a cross-sectional shape including a rectangular first region that determines a pattern width of the workpiece and a second region that intercepts an application of etching beams to a sidewall of the first region while etching is performed. To be specific, the etching mask is T-shaped in cross section. To be more specific, the cross section includes a vertical bar an end of which comes to contact with a surface of the workpiece and a lateral bar placed on the other end of the vertical bar whose width is greater than that of the vertical bar. The pattern width of the workpiece is determined by the width of the vertical bar. The lateral bar is not necessarily placed on the other end of the vertical bar but may be anywhere along the vertical bar as long as the lateral bar is closer to the other end of the vertical bar.
According to the etching mask, when dry etching such as ion beam etching is performed, the region of the workpiece not covered with the mask is removed by the application of ion beams and the like. At the same time, the beams are applied to the mask itself. However, the beams are not directly applied to the region of the wall of the vertical bar (the first region) obstructed by the lateral bar (the second region). The beams impinge on the region of the vertical bar other than the region obstructed by the lateral bar, and the metal material scatters. Part of the scattered metal redeposits on the region immediately above the point of application of the beam. The redeposit portion intercepts the application of beams to the wall below the redeposit portion. A change in width of the vertical bar is thereby suppressed.
A first method of the invention is provided for making an etching mask made of a metal and having a T-shaped cross section including a vertical bar and a lateral bar. The method includes the steps of: forming a film for mask formation on a workpiece and forming an opening in the film for mask formation, the opening reaching the workpiece and having a specific width; and forming a metal film in the opening and over a region around the opening to form the etching mask and removing the film for mask formation.
In the first method, the thickness of the film for mask formation may be made equal to the height of the vertical bar of the mask, and the width of the opening may be made equal to the width of the vertical bar. The etching mask whose vertical bar has a width and a height as desired is thereby obtained.
A second method of making an etching mask of the invention includes the steps of: forming a film for mask formation having a specific thickness on a workpiece and performing a first exposure on a region of a specific width in the film by such an exposure amount that reaches the workpiece; after the first exposure, forming a T-shaped exposed region by performing a second exposure on a region having a width greater than that of the region exposed through the first exposure by an exposure amount smaller than that of the first exposure; selective
Coleman W. David
TDK Corporation
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