Yoshiharu Inoue

Oxygen precipitation in nitrogen-doped Czochralski-grown silicon crystals

Oxygen precipitate behavior of nitrogen-doped Czochralski-grown silicon (CZ-Si) crystals is investigated. It is found that nitrogen doping enhances oxygen precipitation after heat treatment. The oxygen precipitate volume density in nitrogen-doped crystals after heat treatment does not change regardless of the heat treatment temperature, while the oxygen precipitate volume density of crystals which are not nitrogen doped decreases as the heat-treatment temperature increases. The characteristics of precipitation behavior in nitrogen-doped CZ-Si crystals are due to the “grown-in” oxygen precipitates, which already exist in an as-grown state with a high volume density. The oxygen precipitation growth of nitrogen-doped crystals is found to be an oxygen diffusion limited process, the same as in the case of the oxygen precipitation growth of crystals which are not nitrogen doped. The formation mechanism of grown-in oxygen precipitates will also be discussed in this article.Oxygen precipitate behavior of nitrogen-doped Czochralski-grown silicon (CZ-Si) crystals is investigated. It is found that nitrogen doping enhances oxygen precipitation after heat treatment. The oxygen precipitate volume density in nitrogen-doped crystals after heat treatment does not change regardless of the heat treatment temperature, while the oxygen precipitate volume density of crystals which are not nitrogen doped decreases as the heat-treatment temperature increases. The characteristics of precipitation behavior in nitrogen-doped CZ-Si crystals are due to the “grown-in” oxygen precipitates, which already exist in an as-grown state with a high volume density. The oxygen precipitation growth of nitrogen-doped crystals is found to be an oxygen diffusion limited process, the same as in the case of the oxygen precipitation growth of crystals which are not nitrogen doped. The formation mechanism of grown-in oxygen precipitates will also be discussed in this article.

Microvoid defects in nitrogen- and/or carbon-doped Czochralski-grown silicon crystals

Microvoid defects in nitrogen- and/or carbon-doped Czochralski-grown silicon crystals grown under various growth conditions were investigated by transmission electron microscopy. The morphology and volume of the void defects depended strongly on the nitrogen concentration and the cooling rate. With increasing nitrogen concentration, the shape of the voids changed from {111} octahedron to {111} parallelepiped-plate or -rod via an unfaceted structure. The average volume of the voids decreased exponentially with the increase in nitrogen concentration. On the other hand, multiple voids consisting of octahedral segments, whose average volume is small, were observed in carbon-doped crystals. In nitrogen- and carbon-codoped crystals, multiple voids consisting of plate and rod segments were observed, whose average volume was very small. The thickness of the inner oxide layers of voids was influenced by the cooling rate, and not by nitrogen and carbon. From these results, it was assumed that nitrogen and carbon play different roles in the void formation. The change of void morphology by nitrogen-doping is discussed in terms of anisotropic void growth.

Enhancement of the formation of Fe16N2 on Fe films by Co additions (invited)

Effects of Co additions on the formation of Fe16N2 have been investigated by observing nitrides formed on thin‐film surfaces. Thin films of Fe‐Co alloys with a (100) surface sputter‐deposited on MgO(100) substrates are exposed to a mixed gas of NH3 and H2. The 16:2 nitride was observed to form on a surface of Fe‐10 at. % Co film at a nitriding temperature of 500 °C. The formation temperature is 50 °C higher than for pure iron. The amount of the formed 16:2 nitride has been found to be 3× larger for Fe‐10 at. % Co than for pure iron.