Crystal-pulling

The process of growing a pure crystal is sensitive to a host of process parameters that impact the iacorporation of impurities ia the crystal, the quality of the crystal stmcture, and the mechanical properties of the crystal rod. For example, the crystal-pulling mechanism controls the pull rate of the crystallisa tion, which affects the iacorporation of impurities ia the crystal, and the crystal rotation, which affects the crystal stmcture. 

Crystal Growth of Borides e.7.4.2. Liquid-Phase Methods 6.7.4.2.1. Crystal Pulling. 

Figure 1. Schematic diagram of the cold metal crucible system used for synthesis, zone melting and crystal pulling crystal growth (from ref. 5).

Figure 2. Schematic diagram of a tri-arc furnace for crystal pulling.

In a crystal-pulling procedure using a tri-arc furnace (Fig. 2), a resistor box, a d.c. power supply (300 A, 80/40 V) and a set of water-cooled power cables are used to bring power and water to the electrodes. The upper part of the furnace is equipped with three equally spaced copper cathodes, to which are fixed W-Rh electrodes. The upper part (cathode) is separated from the lower part (anode) by a transparent quartz glass tube. In the bottom of the furnace there is a tapered opening for a water-cooled copper hearth containing the boride melt. All parts of the furnace are also water... 

The next most importtmt parameters in Czochralski growth of crystals are the heat flow and heat losses in the system. Actually, aU of the parameters (with the possible exception of 2 and 9) are strongly ciffected by the heat flow within the crystal-pulling system. A tj pical heat-flow pattern in a Czochralski sjretem involves both the crucible and the melt. The pattern of heat-flow is important but we will not expemd upon this topic here. Let it suffice to point out that heat-flow is set up in the melt by the direction of rotation of the cr5rstal being pulled. It is also ctffected by the upper surface of the melt and how well it is thermally insulated from its surroundings. The circular heat flow pattern causes the surface to radiate heat. The crystal also absorbs heat and re-radiates it... 

Silicon single-crystal pulling electromagnets, 23 857 Silicon smelting, environmental impact of, 22 521... 

The system is usually evacuated to a suitable characteristic pressure before the actual working process begins. This happens, for example, in plants tor evaporative coating, electron-beam welding, and crystal pulling in particle accelerators, mass spectrometers, electron microscopes and others. 

Evaporative coating, crystal pulling, mass spectrometers, tube production, electron microscopes, electron beam plants, and particle accelerators. 

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 19 shows sample isotherms and interface shapes predicted by the QSSM for calculations with decreasing melt volume in the crucible, as occurs in the batchwise process. Because the crystal pull rate and the heater temperature are maintained at constant values for this sequence, the crystal radius varies with the varying heat transfer in the system. Two effects are noticeable. First, decreasing the volume exposes the hot crucible wall to the crystal. The crucible wall heats the crystal and causes the decrease in... 

Process Stability and Control. Operationally, automatic control of the crystal radius by varying either the input power to the heater or the crystal pull rate has been necessary for the reproducible growth of crystals with constant radius. Techniques for automatic diameter control have been used since the establishment of Czochralski growth. Optical imaging of the crystal or direct measurement of the crystal weight has been used to determine the instantaneous radius. Hurle (156) reviewed the techniques currently used for sensing the radius. Bardsley et al. (157,158) described control based on the measurement of the crystal weight. 

Figure 1.8 (a) Czochralski crystal pulling technique (b) commercial Czochralski crystal... 

Fig. 3.4-4. Czochralski crystal pulling unit for the manufacture of silicon single crystals.

Hurle, D.T.J. Crystal Pulling from the Melt Springer-Verlag Berlin, 1993. 

Fig. 3 Czochralski crystal pulling and watering. (Courtesy of UNSW Centre for Photovoltaic Engineering Image Library.)...

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