With increasing miniaturization of the components in integrated circuits, the resistance associated with the current crossing from a metallically conductive zone into highly doped semiconductor material, that is to say the ohmic contact resistance, makes up an ever greater proportion of the total resistance of an electrically conductive connection. Many of these integrated circuits use thin film transistors, such as metal-oxide-semiconductor field effect transistors (MOSFETs). The MOSFETs contain a semiconductor, at least some of whose regions are doped, a gate electrode separated from a channel region of the semiconductor by a gate oxide, and electrodes that make ohmic contact with source and drain regions of the semiconductor.
If all the dimensions in the integrated circuit arrangement are decreased linearly, the dopant concentrations being adapted in a suitable manner, then the ratio of the width to the length of the transistor remains the same. Decreasing the dimensions also leads to decreasing the gate oxide thickness. By virtue of the decreased gate oxide thickness, the resistance of the transistor when on (the on resistance) decreases. The ohmic contact, on the other hand, is characterized by a sheet resistivity dependent on the conductor material of the electrodes and the dopant concentration in the semiconductor. Acceptable values of ohmic contact resistance lie for example in the range of 10−7 to 10−6 Ωcm2 (ohm times square centimeter) or 10 to 100 Ωμm2. A contact resistance of 10 to 100Ω would thus require an area of 1 μm2. If the dimensions are decreased, however, the contact resistance increases quadratically with the linear scaling factor. Accordingly, it is difficult to decrease the size of the integrated circuit arrangement without substantially increasing the contact resistance between the source/drain electrodes and the semiconductor.
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