Bulk crystal growth

We discuss the application of atomic scale computer models to bulk crystal growth and the formation of thin films. The structure of the crystal-fluid interface and the mobility of the material at this interface are discussed in some detail. The influence of strain on thin film perfection and stability is also examined. 

Overview of Unit Operations. To maximize the electron or hole (carrier) mobility and thus device speed, ICs are built in single-crystal substrates. Methods of bulk crystal growth are therefore needed. The most common of these methods are the Czochralski and float-zone techniques. The Czochralski technique is a crystal-pulling or melt-growth method, whereas the float-zone technique involves localized melting of a sintered bar of the material, followed by cooling and, thus, crystallization. 

FIGURE 2 Single crystal AIN grown using a high pressure. RF, bulk crystal growth technique. 

Bulk Crystal Growth Czochralski Bridgman Float zone... 

Artificially-grown materials can be contaminated by FAs for several reasons. The first one is the initial purity of the starting material for instance, the LHeT spectra of high-purity intrinsic silicon samples with RT resistivities 104flcm show the presence of residual boron and phosphorus at concentrations x 1012 cm 3 (see Fig. 7.7). Polycrystalline silicon also contains carbon as a residual impurity, which is transferred into the single crystal [45]. In bulk crystal growth, the impurities can come from the growth atmosphere,... 

The studies of growth by the sandwich method have provided a better understanding of the sublimation growth peculiarities and they have formed the basis of the new approach to the bulk crystal growth of silicon carbide. The first successful results in this direction were reported by Tairov and Tsvetkov [7,8]. Currently, similar studies are being performed by a number of research groups and rather impressive progress has been achieved thus far see Datareview 8.1. 

FIGURE 4 The types of growth cavities employed for bulk crystal growth (a) for the modified Lely process,... 

Aluminium contamination is seldom observed for low temperature vacuum sublimation. Aluminium has a low capture coefficient at low temperatures and it does not form refractory carbides with a low vapour pressure. Therefore, traces of aluminium can be easily removed by annealing the furnace in vacuum even if contamination occurs. However, if the material source is insufficiently pure, it can result in noticeable aluminium contamination, especially at elevated growth temperatures. For the bulk crystal growth, aluminium contamination is always observed when abrasive silicon carbide is used as source material [20,22]. The abrasive material usually is highly contaminated [1,22]. 

Alternatively, boron contamination can cause serious problems. Unintentional boron doping is observed both for epitaxial layer growth and for bulk crystal growth. Boron forms a highly stable carbide with a very low vapour pressure. Once introduced into the furnace, it is difficult to remove. Boron contamination can result from the graphite parts of the furnace, from the source material and from evaporation from the reverse side of the substrate as well as from occasional sources. The boron content can be decreased by long anneals at elevated temperatures, although this method is not always effective. 

Hurle, D.T.J., Ed. (1994) Handbook of Crystal Growth, Vol. 2, Bulk Crystal Growth, North-Holland, Amsterdam. 

I 8 Modelingof Semitransparent Bulk Crystal Growth Table 8.1 Properties of Crystals and Their Melts. 

---