1. Field of the Invention
The present invention relates in general to wire etching devices and methods, and more particularly to a wire etching device and method wherein an etching operation is performed only once to etch a wire, thereby controlling a curvature radius and aspect ratio of the wire and reducing the amount of surface oxide of the wire.
2. Description of the Prior Art
At the present time, microscopes are required to observe materials up to a very fine unit. Scanning probe microscopes (SPMs) have been developed to meet such requirements. These SPMs are third-generation microscopes, next to first-generation light microscopes and second-generation electron microscopes, which have broken a common idea that atoms are so small in size (0.1-0.5 nm) as to be unable to be observed through even the best microscope. Whereas the light microscopes have a maximum of thousands of magnifications and the electron microscopes have a maximum of hundreds of thousands of magnifications, the SPMs have a maximum of tens of millions of magnifications to observe atoms individually.
Among the SPMs, an atomic force microscope (AFM) and a scanning tunneling microscope (STM) each comprise a tip formed by etching a thin wire such that it is sharply pointed at its end. The AFM or STM observes a sample using a tunneling effect, gravitation and repulsive force occurring between the tip and the sample under the condition that the tip is in close proximity to the surface of the sample at a distance (xcx9c0.5 nm) of the size of one or two atoms.
Until now, there have been reported many techniques and methods for manufacturing tips using wires. Among them, methods based on an electrochemical etching process have been often used in that they are relatively simple. However, these etching-based tip manufacturing methods are mostly empirical methods with little reproducibility.
The tip is of particular importance in its shape and a curvature radius at its end for special use. However, in the case where the above-mentioned empirical electrochemical etching process is performed to manufacture the tip, it is not easy to observe the shape of the tip with the naked eye during the manufacturing process, resulting in the manufacturing of the tip being very difficult. Further, it is hard to manufacture tips of the same shape while minimizing curvature radius thereof.
In order to overcome the above problems, there has been proposed an electrochemical etching process-based tip manufacturing method, which is disclosed in U.S. Pat. No. 4,375,396. This is a basic method for manufacturing a tip using a wire. This method is adapted to measure the amount of etching current and interrupt the etching current when the amount thereof reaches a threshold value.
In addition, a mechanism for controlling the position of a wire during an etching process is shown in U.S. Pat. No. 5,286,355. In this mechanism, at the moment that the amount of etching current reaches a threshold value set through pre-experiments, the etching current is interrupted, thereby reducing a curvature radius at the end of a tip.
However, the above-mentioned conventional techniques can desirably reduce the curvature radius at the end of the tip, but are disadvantageous in that they cannot control another important factor, or an aspect ratio, in applying the tip to an atomic force microscope or scanning tunneling microscope.
In other words, in the case where the above-mentioned electrochemical etching process is performed to manufacture a tip, the manufactured tip is reduced in aspect ratio but increased in surface oxide amount when the etching current is larger in amount, whereas it is smoother in surface and smaller in curvature radius but greater in aspect ratio when the etching current is smaller in amount.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a wire etching device and method which can control a curvature radius and aspect ratio of a tip in manufacturing the tip using a wire.
It is another object of the present invention to provide a wire etching device and method which can reduce the amount of oxide on the surface of a tip to smooth the surface, in manufacturing the tip using a wire.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a wire etching device comprising a signal generator for generating a voltage signal; a voltage generator for generating an etching voltage in response to the voltage signal from the signal generator; an etching unit for etching a wire with the etching voltage from the voltage generator; a current measurement unit for measuring the amount of etching current generated by the etching unit; and a controller for changing the level of the voltage signal to be generated by the signal generator, in accordance with the etching current amount measured by the current measurement unit, so as to change the level of the etching voltage to be generated by the voltage generator.
In accordance with another aspect of the present invention, there is provided a wire etching method comprising the first step of generating a voltage signal for determining the level of a wire etching voltage; the second step of applying the etching voltage of the level determined depending on the voltage signal to a wire to primarily etch it; the third step of measuring the amount of etching current generated while the wire is primarily etched at the above second step; the fourth step of changing the level of the voltage signal according to the etching current amount measured at the above third step to change the level of the etching voltage; the fifth step of applying the etching voltage of the level changed at the above fourth step to the wire to secondarily etch it; and the sixth step of measuring a variation of the etching current generated while the wire is secondarily etched at the above fifth step and completing the etching operation if the measured etching current variation is greater than or equal to a predetermined value.