Czochralski-Grown Silicon Crystals for Microelectronics

Abstract

In the era of semiconductor electronics, monocrystalline silicon remains a basic and widely used material [1 4]. It will probably continue to dominate in the world of electronics for many years to come. The rst material in history, though, on the basis of which the invention of a transistor was made (1948) was germanium (Ge). In order to produce a germanium single crystal, the molten germanium was held in a graphite crucible, and the crystal grew from a seed initially immersed in the liquid and later slowly pulled upwards. This method of crystallization was described in 1916 by Jan Czochralski, a scientist and inventor (for his life and scienti c achievements, see [5]). During the rst years after invention, Czochralski focused his studies on determination of the rate of metal crystallization. In later investigations, he proved that materials produced using this method are single crystals. They were not single crystals in today understanding, though, they were threads of such metals as zinc, tin and lead. At the time there was no need whatsoever for monocrystaline materials, as all materials industrially exploited at that time were polycrystalline. Properties were studied such as textures, martensitic structures; recrystallization, mostly in order to improve the mechanical properties. Returning to the subject of this article, it must be pointed out that despite technological progress and development in the examination of semiconductor devices, the Czochralski crystallization method applied to semiconductor materials, in particular to silicon, remained essentially the same since the 1950s. It is commonly called the Czochralski method (for a detailed description of the method see, e.g. [6 8]). On the following pages, the characteristics of the method, contributing to its success are discussed, taking into consideration the mechanisms of crystallization and technological progress observed in the last decades. The discussion is focused on crystallization of silicon, a material which became irreplaceable in electronics and microelectronics. At the present time, silicon crystals are produced in tens of thousands of tons, annually. The broad use of silicon is due to both, its physical and technological characteristics as well as availability of resources (the primary resource of silicon is SiO2). Silicon has a unique characteristics of forming, on its surface, an ultrathin passivating oxide lm. Thermal conductivity of silicon (140 163 W/(mK)) is higher in comparison to other semiconductors (GaAs 46 55 W/(mK), SiC 16 55 W/(mK)). This property is of particular signi cance as it leads to (advantageous) heat dissipation at semiconductor junctions. Silicon became a leading material in electronics due to its energy gap (1.1 eV at 300 K) which guarantees the work of semiconductor devices at high temperatures.