Field of the Invention
The invention relates to a method of forming a fine conductive pattern, such as forming a coil winding on the upper surface of a substrate at the time of fabricating a thin-film magnetic head.
Related Art
To form a coil pattern of a thin-film magnetic head, a frame plating method or an ion milling method have principally been used heretofore as ordinary processes. Generally known fine conductive pattern preparing methods include a wet-etching method and a lift-off method. The wet-etching method is not suitable because of its too large side etching in the case where the required thickness of a conductive film is relatively large and where a fine conductive pattern whose thickness is about the same as or less than the conductive film is required, such as in the case of a coil pattern of a thin-film magnetic head.
The above-mentioned fine conductive pattern forming methods address the following problems.
Since the frame plating method uses an electroplating bath, not only many kinds of chemical solutions are used, but also bath composition fluctuations during the plating process are caused. This means that a number of process steps must be under control, thereby imposing the problem that the obtained conductive film is not stable nor is it less reproducible. Further, it is difficult to confine the grain size of a deposited substance to 1 .mu.m or less. When the width of the conductive pattern is several micron meters or less, the problem of migration is inevitably encountered. Particularly, in the case of plating with copper that is generally employed as a coil conductor of a thin-film magnetic head, problems such as having high specific resistance and undergoing changes in profile due to heat treatment-induced fluctuations in volume are caused.
On the other hand, in the frame plating method, it is difficult to obtain a uniformly distributed thickness over the entire surface of the substrate. Particularly, it is more difficult to obtain a consistently distributed thickness on a fine pattern such as a coil portion and a comparatively large pattern such as a pad portion within the same chip.
Further, while it is inevitably necessary to remove undesired plated ground layer since the frame plating method is an electroplating method, the process of removing the fine pattern portion involves sophisticated techniques. Therefore, it is difficult to improve operating efficiency.
Since the etching ratio of the masking resist to the conductive film is almost 1:1 in the above-mentioned ion milling method, a resist thicker than the etching depth is required. That is, the conductive film having a relatively large thickness of about 3 to 5 .mu.m is required. This makes it difficult to process a fine conductive pattern whose inter-coil distance is 2 .mu.m or less.
Since the etching process, the re-depositing process, and the injected ion scattering process are so interrelated not only is etching profile control is difficult, but also the conductive film is ejected out by ion bombardment. Therefore, re-deposition of the conductor onto the sidewalls of the resist or the like causes defective insulation of a product, thereby imposing the problem of product reliability.
The above-mentioned lift-off method is designed to have such process steps, e.g., as shown in FIG. 3. That is, in FIG. 3, a coil portion 1 of a thin-film magnetic head is prepared by forming an insulating layer 3 on the upper surface of a substrate 2; and forming a masking pattern resist 4 thereon. The pattern resist 4 has groove portions 4a on which to form a coil pattern (see FIG. 3 (A)), and by depositing a conductor thereon, a conductive film 5 is formed inside the groove portions 4a (see FIG. 3 (B)). As a result, the coil portion of the thin-film magnetic head 1 is prepared.
A coil pattern can be formed easily according to such a method. However, during the deposition of the conductor, the trapezoidal profile of each pattern resist portion 4 is broken due to thermal deformation, thereby causing the overhang profile to be lost (see FIG. 3 (B)). As a result, out of the conductive film 5, pattern portions 5a to be left unetched inside the groove portions 4a and lift-off portions 5b to be removed which extend on the pattern resist 4 are fused together to be inseparable. This imposes the problem of not being able to form a predetermined pattern.