Success in Clarifying Behavior of Impurities in Silicon Nanowire with Diameter of 1/50,000mm

Toward Realization of Next-Generation Type Transistors and Nanowire Photovoltaic Cell Materials

2011.02.04

National Institute for Materials Science
Japan Science and Technology Agency
University of Tsukuba

The National Institute for Materials Science and the University of Tsukuba succeeded in non-destructive, non-contact detection of the states of impurities introduced as dopants for carrier control in silicon nanowires (diameter:

Abstract

  1. The National Institute for Materials Science (President: Sukekatsu Ushioda; hereinafter, NIMS) and the University of Tsukuba (President: Nobuhiro Yamada) succeeded in non-destructive, non-contact detection of the states of impurities introduced as dopants for carrier control in silicon nanowires (diameter: <20nm), which have attracted attention as a next-generation semiconductor material, and also succeeded in clarifying the behavior of those impurities. The result was achieved by a group led by Dr. Naoki Fukata, an Independent Scientist at the NIMS International Center for Materials Nanoarchitectonics (Director-General: Masakazu Aono), and a group under Prof. Koichi Murakami of the University of Tsukuba.
  2. The main stream in current-generation semiconductor transistor materials is silicon. Although their size has been progressively reduced to achieve higher performance, this is now approaching the limit for satisfying both integration and improved performance due to problems such as increased leakage current, heat generation, and the like. As a solution, the 1-dimensional nanowire structure has attracted attention.
  3. In order to use silicon nanowires with a 1-dimensional structure as transistor materials, doping with impurities for carrier control (pn control) is critical. Therefore, techniques for investigating the states and behaviors of doped impurities were an important issue for practical application. The development of next-generation high efficiency photovoltaic cell materials using nanowires has also attracted considerable attention in recent years, lending increased urgency to clarifying the states and behavior of impurities in nanostructures.
  4. In this work, the researchers succeeded for the first time in detecting the behavior of dopant impurities introduced in silicon nanowires for carrier control by using a state assessment method for impurities in semiconductor nanostructures. This research revealed that the behaviors of boron, which is a p-type impurity, and phosphorus, which is an n-type impurity, are completely different, and boron segregates preferentially to the oxide film, which is an insulating film. This work also showed that stress can be used to control behavior.
  5. The behaviors of the impurities which were clarified in this research, and particularly the phenomenon in which boron segregates to the insulating film, are problems that must be solved in order to apply nanowires with a high surface area ratio to next-generation transistors. This research clarified the fact that control of the stress on the nanowire is one key, and thus is a step toward the realization of next-generation transistors. The assessment method is also considered a promising approach for assessment of photovoltaic cells.
  6. This research was carried out as part of the research topic “Development of Semiconductor Nanowires for Realization of Vertical Three-Dimensional Devices (Research Representative: Naoki Fukata)” in the Precursory Research for Embryonic Science and Technology (PRESTO) Individual Type Research area “Materials and Processes for Innovative Next-generation Devices” (Research Adviser: Katsuaki Sato) of the Japan Science and Technology Agency (JST). These research results will be published in the near future in NANO Letters, a publication of the American Chemical Society.