University of Twente Student Theses


Electrical measurement method and test structures for determining continuity of ultra-thin conducting or insulating films.

Velde, F.J. van der (2016) Electrical measurement method and test structures for determining continuity of ultra-thin conducting or insulating films.

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Abstract:Ultra-thin films can be used for many interesting new applications in the field of micro-electronics. The thickness of ultra-thin films ranges from sub-nanometer to a few tens of a nanometer. The various new applications require either discontinuous, percolated (almost continuous) or continuous ultra-thin films. Therefore it is critical to know the continuity of the deposited ultra-thin film. Currently there are no standard methods or test structures to determine the continuity of an ultra-thin film. The goal of this project is to design a methodology and corresponding test structures, to determine the closure point of conducting or insulating ultra-thin films. The established methodology for determining the continuity for conducting ultra-thin films is a combination of two methods. The first method is to look at the conduction mechanism of the film by measuring the I-V characteristics. Continuous conducting ultra-thin films have an ohmic conduction mechanisms, wherea discontinuous conducting ultra-thin films have non-ohmic conduction. The two conduction mechanisms can be distinguished by analyzing the I-V characteristics of the film. When the conduction mechanisms goes from non-ohmic to ohmic, the film is expected to become continuous. The second method is a method proposed by Maroof and Evans. They state that the minimum value in the Rt2 vs thickness plot is the onset of a continuous film, where R is the resistance and t is the thickness of the film. The continuity of insulating ultra-thin films can also be determined by measuring the I-V characteristics of the film. The film is sandwiched between two electrodes. When the film is discontinuous the conduction mechanism is ohmic, the two electrodes are in contact. When the film is continuous the conduction mechanism is non-ohmic, the current has to tunnel through the continuous insulating film. During this project test structures for both the conducting and the insulating ultra-thin films are designed, keeping the chosen methodologies in mind. Masks are designed to be able to fabricate the structures in the MESA+ nanolab of the University of Twente. During this project tungten (W) and aluminium nitride (AlN) are used as a conducting and insulating material respectively, to show the effectiveness of the methodologies and corresponding test structures. Two process flows are composed, one for the conducting and one for the insulating films. Measurements of 6 W ultra-thin films and 4 AlN ultra-thin films, with different thicknesses, are done. Both of the methods for the conducting ultra-thin films indicate that the W film becomes continuous between 1.3 and 2.2nm. The method for the insulating ultra-thin films indicates that the AlN film becomes continuous between 4 and 11nm. The drawn conclusions are compared to SE measurements done during the deposition of the films. The SE measurements of the W films show a sharp increase, caused by an incorrect model at this point. It is speculated that the incorrectness of the model is related to the change from a discontinuous to a continuous film. Interpreted in terms of film thickness this change falls in the same range as for the electrically found closure points of the W films. The growth rate of the AlN films becomes constant when the substrate is completel covered. The growth is no longer in fluenced by the substrate. For AlN films constant growth rate was established in the same range as the electrically found closure points of the films. This proves that the designed methodologies and corresponding test structures can be used to determine the closing point of conducting or insulating ultra-thin films.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:51 materials science, 53 electrotechnology
Programme:Electrical Engineering MSc (60353)
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