Czochralski


The Gzochralski Technique. Pulling from the melt is known as the Czochralski technique. Purified material is held just above the melting point in a cmcible, usually of Pt or Ir, most often powered by radio-frequency induction heating coupled into the wall of the cmcible. The temperature is controlled by a thermocouple or a radiation pyrometer. A rotating seed crystal is touched to the melt surface and is slowly withdrawn as the molten material solidifies onto the seed. Temperature control is used to widen the crystal to the desired diameter. A typical rotation rate is 30 rpm and a typical withdrawal rate, 1—3 cm/h. Very large, eg, kilogram-sized crystals can be grown.  [c.215]

Lithium Niobate. Lithium niobate [12031 -64-9], LiNbO, is normally formed by reaction of lithium hydroxide and niobium oxide. The salt has important uses in switches for optical fiber communication systems and is the material of choice in many electrooptic appHcations including waveguide modulators and sound acoustic wave devices. Crystals of lithium niobate ate usually grown by the Czochralski method foUowed by infiltration of wafers by metal vapor to adjust the index of refraction.  [c.226]

Fabrication. Although CCDs have been fabricated in many semiconducting materials such as Ge (49), InP (50), and HgCdTe (51), by far the most readily available devices are those which utilize Si as the semiconductor. There are several common types of siUcon CCDs. AH share certain processing steps, and most utilize -type siUcon as the semiconducting material. SiUcon single crystals ate grown (52) in conventional Czochralski vertical pullers using a single-crystal siUcon seed dipped and rotated in a siUcon melt. The large boules of siUcon are sawed into wafers. The following fabrication discussion describes a process for the creation of a genetic four-phase CCD in -type siUcon (53).  [c.430]

Cu, Au, Zn, Cd, Hg, and some of the elements of Groups 13 (HI) and 15 (V) have been used in detectors. Germanium and siUcon, which are used in the preparation of detectors, must be of high purity before they are doped with the desired activator impurity in order to avoid unwanted compensation by impurities with smaller ionization energies than the activator. The required purity can be achieved by zone refining in which a short molten zone is repeatedly passed from end to end of an ingot of impure Ge or Si. Impurities having distribution coefficients larger than unity collect near the seed. The concentration of electrically active residual impurities in the center portion of the ingot can be reduced to 10 —10 /cm. Single crystals can be grown using the Czochralski method, in which an oriented seed crystal is brought into contact with the melt and then is withdrawn slowly while being rotated, or using a horizontal zone melting method, in which a seed crystal is melted onto one end of a polycrystaUine ingot. A molten zone is produced at the junction of the ingot and seed and is moved slowly along the ingot, leaving behind a single crystal. AH of these operations must be carried out in an inert or reducing atmosphere in order to prevent oxidation of the germanium or siUcon.  [c.435]

Electric Heating Elements. Machined graphite shapes are widely used as susceptors and resistor elements to produce temperatures up to 3300 K ia apphcations utilizing nonoxidizing atmospheres. The advantages of graphite ia this type of appHcation iaclude its very low vapor pressure (lower than molybdenum), high black body emissivity, high thermal shock resistance, and increasing strength at elevated temperatures with no iacrease ia brittleness. Graphites covering a broad range of electrical resistivity are available and can be easily machined iato complex shapes at lower cost than refractory metal elements. Flexible graphite cloth is also used widely as a heating element siace its low thermal mass permits rapid heating and cooling cycles. Typical apphcations iaclude molten-iron or steel-hoi ding furnaces, continuous casting tundishes, Hquid—steel degassiag units, chemical reaction chambers, quartz-fusion apparatus, ziac-vaporization chambers, sintering furnaces, vapor deposition units (qv) (60,61), and siagle-crystal siUcon ingot growing furnaces (Czochralski method). In the furnaces that use vacuum or iaert gas atmospheres, porous carbon or graphite, flexible carbon or graphite felts, and rigid fibrous graphite thermal iasulation materials are extensively used.  [c.522]

An example of an analysis done on polysilicon and single-crystal Czochralski silicon (CZ) is shown in Table 1. As can be seen, polysilicon, which was used to grow the crystal, is dirtier than the CZ silicon. This is expected, since segregation coefficients limit the incorporation of each element into the crystal boule during the crystal growth process. All values shown in the table are from bulk analysis. Table 2 shows NAA data obtained in an experiment where surface analysis was accom-  [c.676]

Aside from Czochralski, the other name always associated with growth of metal crystals from the melt is that of Percy Bridgman (1882-1961), an American physicist who won the Nobel Prize for his extensive researches on high-pressure phenomena (see below). For many of his experiments on physical properties of metals (whether at normal or high pressure) - for instance, on the orientation dependence of thermoelectric properties - he needed single crystals, and in 1925 he published a classic paper on his own method of doing this (Bridgman 1925). He used a metal melt in a glass or quartz ampoule with a constriction, which was slowly lowered through a thermal gradient the constriction ensured that only one crystal, nucleated at the end of the tube, made its way through into the main chamber. In a later paper (Bridgman 1928) he showed how, by careful positioning of a glass vessel with many bends, he could make crystals of varied orientations. In the 1925 paper he recorded that growing a single crystal from the melt sweeps dissolved impurities into the residual melt, so that most of the crystal is purer than the initial melt. He thus foreshadowed by more than 20 years the later discovery of zone-refining.  [c.164]

Czochralski, J. (1917) Z. Phys. Chem. 92, 219.  [c.183]

B. Bridgman and Czochralski growth  [c.852]

B. Bridgman and Czochralski Growth  [c.903]

In Bridgman growth [155], a boat or vessel filled with the melt is slowly cooled from one side, so that the crystal forms from that side. In Czochralski growth [156,157] a cylindrical crystal sits on the surface of the melt and is slowly pulled upward. In both cases the hydrodynamical flow of the melt is an important factor in the chemical composition and fine structure of the resulting crystal.  [c.904]

N. Miyazaki, S. Okuyama. Development of finite element computer program for dislocation density analysis of bulk semiconductor single crystals during Czochralski growth. J Cryst Growth 183 S, 1998.  [c.926]

Y.-S. Lee, C.-H. Chun. Experiments on the oscillatory convection of low Prandtl number hquid in Czochralski configuration for crystal growth with cusp magnetic field. J Cryst Growth 180 411, 1997.  [c.928]

Alexandrite. Alexandrite [12252-02-7] is chrysoberyl [1304-50-3] BeAl20 when pure. The Cr-containing alexandrite form has a psychooptic color change, appearing blue-to-green when viewed in daylight or fluorescent-tube lighting, and red in the light from a candle or an incandescent light bulb. It is grown as a luxury synthetic from the flux and also more recently by the Czochralski technique.  [c.217]

Corundum. Crystalline AI2O2, comndum [1302-74-5], is called mby [12174 9-1] when colored red by about 1% Cr, and sapphire [1317-82 ] for other colors, particularly when blue from charge transfer (2,11) between about 0.01% each of Fe " and Ti . A wide range of other colors can be grown, including colorless (pure), yellow (containing Ni), orange (Ni + Cr), green (Co), alexandrite-hke green/purple (V), and so on. Synthetic mby is grown (/) for high optical-quaUty laser use by the Czochralski technique (2) together with many colors of sapphire as a low cost synthetic by the Vemeuil technique and (J) together with blue sapphire as luxury synthetics by the flux technique. The hydrothermal technique has also been used. The colorless material has been used as a poor diamond imitation (Table 3), called Brillite, Diamondite, ThriUiant, etc. Synthetic mby and variously colored sapphires are used in class rings as imitations of various gemstones, as well as for other jewelry uses.  [c.217]

InSb Photodiode Detectors and Arrays. Sensitive photodiodes (68,69) have been fabricated from single-crystal InSb using cadmium or zinc to form a -type region in bulk n-ty e material. High quahty InSb crystals can be grown by the infinite-melt process (70) where an InSb film is grown epitaxially (from the hquid phase) on a shce of InSb which was prepared in a conventional Czochralski vertical puller. The diode formation process typically is a closed-tube diffusion. Cleaned and etched samples of InSb ate placed in a quartz ampul with a limited amount of zinc or cadmium. After evacuation and sealing, the ampul is heated to ca 50°C below the crystal melting point. The metal vaporizes partially or completely, depending on the amount, volume of ampul, and temperature, and diffuses into the crystal after a few hours. The impurity-diffusion profile approximates the error-function law and the p—n junction is 1—5 p.m below the surface. Diode arrays (16) are formed by etching mesas ca 50 p.m square. Typical performance of InSb detectors is given in Table 1 and the spectral sensitivity is shown in Figure 9c. Up to 480 x 640 matrix arrays of InSb photodiodes in a mesa configuration have been demonstrated. Commercial units of 256 x 256 ate available. The mesa detector array is mated to a siUcon chip having an array of amplifiers and multiplex circuitry. Each diode is coimected to an amplifier input. The hybridization process consists of forming indium bumps on each diode mesa and on each amplifier input, using a photohthographic process and In evaporation and pressing the detector array chip to the siUcon integrated circuit chip. The infrared must pass through the InSb chip to reach the photodiode junction. To improve quantum efficiency the InSb is grown on GaAs or GaAsSb substrates as a thin layer. Quantum efficiency is greater than 50% for wavelengths greater than 2 p.m and less than the cutoff of InSb, 5.3 p.m. A protective coating (passivation) of the InSb photodiode for stable operation over several hours without frequent signal normalizations has not been found. However, infrared imaging cameras using hybrid InSb focal planes are a commercial reaUty. In a real-time imaging configuration the scene sensitivity is ca 0.04°C using an InSb infrared camera.  [c.432]

Crystal Growth. Most high purity siUcon is used in the manufacture of semiconductor devices, and most such devices are made from single-crystal siUcon. Thus the process of growing single crystals of siUcon has been studied extensively since the 1950s. A number of processes are available, but the most common is the pulling technique first described by Teal and Litde in 1950 (13). This is an adaptation of a much eadier crystal growing method for studying the speed of crystallisation of metals (14), called the Csochralski method. The pulling process is shown schematically in Figure 4. SiUcon, surrounded by an inert gas atmosphere, is first melted in a fused siUca container. Then, the bottom end of a single-crystal siUcon seed, capable of being both rotated and pulled up from the melt, is dipped into the melt and slowly withdrawn as siUcon freeses on it. The freesing (growth) rate, normally on the order of cm/h, is controlled by a combination of melt temperature, radiation from the growing crystal, and conductive heat losses through the seed. Crystals as small as a few mm in diameter and as large as 300 mm in diameter have been grown by this process. Lengths vary according to equipment design and crystal diameter, but maybe as much as >2 m for 100-mm diameter crystals and as Htde as 50—60 cm for 300-mm diameter crystals.  [c.528]

Most semiconductor appHcations require thin, flat sections of crystal having damage-free surfaces for subsequent processing. Both the Czochralski and float zone methods produce long rods from which sHces must be cut and subsequendy lapped and poHshed. In an attempt to circumvent these steps, various modifications of melt growth have been proposed in order to grow single-crystal ribbons direcdy. The work started in the eady 1960s concentrated on dendrites and on growth in a (211) direction through a shaped orifice (15). Neither the dendrites nor the dendrite webs that followed were of sufficient quahty for most uses, and shaped crystals could not be grown thin enough to be of practical use. In the mid-1970s, the realization that reasonably efficient solar cells could be made from poorer quaHty siHcon material than was usable for transistors and integrated circuits, combined with a renewed search for low cost cells, led to renewed studies of sheet growth (see Solarenergy). One of the more promising approaches has been edge-defined growth, where a siHcon carbide die having a cross section equal to that of the desired crystal is used. The lower end of the die is immersed in molten siHcon in such a way that surface tension can draw molten siHcon to the top of the die. The crystal is then pulled from that small reservoir and can grow no larger in cross section than the siHcon supply at the top of the die.  [c.528]

TJItrahigh (99.999 + %) purity tellurium is prepared by zone refining in a hydrogen or inert-gas atmosphere. Single crystals of tellurium, tellurium alloys, and metal teUurides are grown by the Bridgman and Czochralski methods (see Semiconductors).  [c.386]

If the ceramic of interest melts congmenfly, eg, LiNbO and BaTiO, crystals can be grown using the Czochralski method. In this technique a seed crystal suspended from a rotating mount is slowly withdrawn from a melt causing the material on the seed to crystallize as its temperature falls below the melting point. Eventually a large boule is pulled from the melt, from which crystals may be cut. If the ceramic melts incongmenfly, eg, KTiOPO, or is a phase not stable at the composition s melting point, eg, Si02, crystals may sometimes be grown hydrothermally, or from a nonaqueous flux.  [c.338]

Siagle-crystal pyroelectrics are geaeraHy prepared by Czochralski growth. PolycrystaUine materials are frequeafly prepared by hot pressiag, followed by subsequeat thinning and polishing to prepare sections 10-30 fim ia thickness. Multielement arrays are prepared from these sectioas by selective etching, electrodiag, and connection to siUcon microcircuitry usiag solder-bump technology. Developments ia the sol-gel processiag of ferroelectric thin films and sacrificial etching techniques may allow for more straightforward, direct iategration of pyroelectric detectors onto siUcon devices.  [c.344]

The other method of growing large metal crystals is controlled freezing from the melt. Two physicists, B.B. Baker and E.N. da C. Andrade, in 1913-1914 published studies of plastic deformation in sodium, potassium and mercury crystals made from the melt. The key paper however was one by a Pole, Jan Czochralski (1917), who dipped a cold glass tube or cylinder into a pan of molten Pb, Sn or Zn and slowly and steadily withdrew the crystal which initially formed at the dipping point, making a long single-crystal cylinder when the kinetics of the process had been judged right. Czochralski s name is enshrined in the complex current process, based on his discovery, for growing huge silicon crystals for the manufacture of integrated circuits.  [c.162]

However, physicists alone could never have produced a reliable, mass-produ-cable transistor. We have seen that in the run-up to the events of 1947, Scaflf and Theuerer had identified p- and n-regions and performed the delicate chemical analyses that enabled their nature to be identified. There was much more to come. The original transistor was successfully made with a slice of germanium cut out of a polycrystal, and early pressure to try single crystals was rebuffed by management. One Bell Labs chemist, Gordon Teal, a natural loner, pursued his obsession with single crystals in secret until at last he was given modest backing by his manager eventually the preferred method of crystal growth came to be that based on Czochralski s method (Section 4.2.1). Ft soon became clear that for both germanium and silicon, this was the essential way forward, especially because intercrystalline boundaries proved to be electrically active . It also became clear that dislocations were likewise electrically active and interfered with transistor action, and after a while it transpired that the best way of removing dislocations was by carefully controlled single crystal growth to simplify, the geometry of the crystal was so arranged that dislocations initially present grew out laterally, leaving a crystal with fewer than 100 dislocation lines per square centimetre, contrasted with a million times that number in ordinary material. This was the achievement of Dash (1958, 1959), whom we have already met in relation to Figure 3.14, an early confirmation of the reality of dislocations. Indeed, the work done at Bell Labs led to some of the earliest demonstrations of the existence of these disputed defects. Later, the study and control of other crystal defects in silicon, stacking-faults in particular, became a field of research in its own right.  [c.260]

It is a reflection on present-day priorities in industry that the research laboratory of a great company, Metallgesellschaft in Frankfurt-am-Main, Germany, where Hansen began work on his epoch-making book, was closed down a few years ago to save money. This laboratory was initially directed, from 1918 onwards, by Jan Czochralski, the Pole whom we met in Section 4.2.1 and who gave his name to the present-day process for growing silicon crystals, and subsequently by Georg Sachs and, after he had been driven from Germany by the Nazis in 1935, by Erich Schmid, all highly distinguished figures. The manifold achievements of the laboratory are described in a book issued on the occasion of the company s centenary, when the laboratory was still going strong (Wassermann and Wincierz 1981).  [c.497]

M. Mihelcic, K. Wingerath. Threedimensional simulations of the Czochralski bulk flow in a stationary transverse magnetic field and in a vertical magnetic field Effects on the asymmetry of the flow and temperature distribution in the Si-melt. J Cryst Growth S2 318, 1987.  [c.923]

S. lida, Y. Aoki, K. Okitsu, Y. Sugita, H. Kawata, T. Abe. Microdefects in an as-grown Czochralski silicon crystal studied by synchrotron radiation section topography with aid of computer simulation. Jpn J Appl Phys Ptl 57 241, 1998.  [c.926]

T. Sinno, R. A. Brown, W. Van Ammon, E. Dornberger. Point defect dynamics and the oxidation-induced stacking-fault ring in Czochralski-grown silicon crystals. J Electrochem Soc 145 302, 1998.  [c.927]

H. Takeno, T. Otogawa, Y. Kitagawara. Practical computer simulation technique to predict oxygen precipitation behavior in Czochralski silicon wafers for various thermal processes. J Electrochem Soc 144 4340, 1997.  [c.927]

D. Givoli, J. E. Flaherty, M. S. Shephard. Simulation of Czochralski melt flows using parallel adaptive finite element procedures. Model Simul Mater Sci Eng 4 623, 1996.  [c.930]

Zhang Weihan, Yan Shuxia, Ji Zhijiang. Effective segregation coefficient and steady state segregation coefficient of germanium in Czochralski silicon. J Cryst Growth 169 598, 1996.  [c.931]


See pages that mention the term Czochralski : [c.275]    [c.275]    [c.275]    [c.276]    [c.333]    [c.163]    [c.545]    [c.903]    [c.923]    [c.928]   
Computational methods in surface and colloid science (2000) -- [ c.852 , c.903 , c.904 ]