The Tungsten Probe in Electrical Test Preparation Method

With the improvement of the integration of semiconductor integrated circuits, the size of the device has been reduced. At present, the mainstream semiconductor transistors have reached the size of 22 nanometers or smaller. In order to measure the electrical characteristics of a single small size device, the diameter of the tungsten metal probe needed to contact the device is small enough.

The transistor is a four terminal device. In a very small area, the four metal probes still have enough space to move freely in a very small area. This requires that the length / diameter ratio (length / diameter) of the metal probe is large enough. For example, a probe with small length to diameter ratio (3:1), in the process of cell migration, other metal probes will be encountered, resulting in short circuiting, so that normal electrical measurement can not be carried out.

At present, the main method of preparing tungsten tip is electrochemical etching. The electrochemical corrosion technology is usually dependent on the immersion of the probe tungsten wire to the electrolyte, and the voltage is applied between the cathode electrode (usually stainless steel) and the tungsten wire in the electrolyte. When the voltage is applied, the boundary layer between the electrolyte and the air gradually falls off as time goes on, until the part of the electrolyte is very thin, the tungsten wire still soaked in the electrolyte is too heavy to fall off. Then, the current flowing through tungsten and electrolyte solutions is rapidly disconnected, thus preventing continuous corrosion of tungsten wires. The left top tungsten wire can be used as a probe. In another corrosion method, a very small ring electrode is used and tungsten wire passes through the ring electrode. The electrolyte is dripped on the inner surface of the ring electrode so that only the electrolyte film area will corrode. After a period of time, the tungsten wire in the electrolyte film area will become very thin, the lower end of the tungsten wire due to gravity will fall off, the lower end of the tungsten wire can be used as a probe.

The method described above is used to fabricate atomic-scale tips, where only a few microns of the electrolyte interface are corroded and the cone angle changes abruptly. In order to fabricate tungsten probe with large aspect ratio, a new method is needed to corrode the longer region of tungsten wire, and the taper angle should be kept continuously.

Recently, some scholars have proposed a better method for improving the tungsten tip. A tungsten wire is obtained by electrochemical corrosion of tungsten wire. The tungsten wire is used as the anode and soaked in the electrolyte. When the current of tungsten wire is reduced to 20mA, the tungsten wire is raised. When the tungsten wire is broken, the reverse current makes the tungsten wire as the cathode. The tungsten probe is removed from the electrolyte and the tungsten probe is obtained.

Compared with the existing technology, the new technology can prepare a tungsten probe with large length to diameter ratio. At the same time, the tip cone angle of tungsten probe can be estimated by detecting the reverse current when the tungsten wire is disconnected, thus saving the time and cost of the traditional subsequent need of electronic scanning microscope.

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