Study on fabrication method for ultra-small transistors by means of selective atomic-layer deposition

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The purpose of this study is to develop a new method for fabrication of ultrasmall transistors, which is impossible by the conventional lithography method, by means of the selective atomic-layer deposition of silicon (Si). At the edge of the stacked layered structures consisting of different materials, if the selective deposition of Si occurs only on the specific material, the gate length of the MOS transistors can be controlled by the thickness of the deposited film. In this study, this method is developed. The summary of the obtained results is listed below.1. The selective atomic-layer deposition method of silicon nitride is developed, which is the basis of this study.2. The selective atomic-layer deposition method for Si is developed, in which the Si film is deposited only onto the silicon nitride and very small amount deposition on SiO_2, by means of the intermittent exposure of Si_2H_6 gas.3. By using the above method, very narrow Si wires (21 nm wide and 28 nm thick) is fabricat … More ed. The resistivity of the Si wires is about 1/5 compared with that fabricated by the conventional method using lithography and dry etching.4. Atomic-layer deposition method of Si with very smooth surface is developed by using the alternative supply of Si_2H_6 and SiCl_4, in which the deposition rate is two mono-layers per one deposition cycle.5. As the preliminary study for the evaluation of the narrow Si wires, the polycrystalline (poly-) Si wires (minimum width of 95 nm and minimum thickness of 7 nm) were fabricated by using the low-pressure chemical vapor deposition of SiH_4, followed by the electron-beam lithography and dry etching. And the electrical characteristics were measured. As the result the Coulomb blockade effect was observed at low temperatures (5〜80 K) and the electronic conduction mechanism in the narrow poly-Si wires were proposed.1. The current suppression phenomenon at the low-voltage region, which might be caused by the coulomb blockade effect, was observed for the Si narrow wires fabricated by the selective atomic-layer deposition. Less