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The Czochralski process
The Czochralski process

The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors (e. In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating A single crystal, also called monocrystal, is a Crystalline Solid in which the Crystal lattice of the entire sample is continuous and unbroken A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that g. silicon, germanium and gallium arsenide), metals (e. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Germanium (dʒɚˈmeɪniəm is a Chemical element with the symbol Ge and Atomic number 32 Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. g. palladium, platinum, silver, gold), salts, and synthetic gemstones. Palladium (pronounced \pəˈleɪdiəm\ is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the Platinum (ˈplætɪnəm is a Chemical element with the Atomic symbol Pt and an Atomic number of 78 Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash The process is named after Polish scientist Jan Czochralski, who discovered the method in 1916 while investigating the crystallization rates of metals. Jan Czochralski (pronounced cho-HRAL-skee ( October 23, 1885 - April 22, 1953) was a Polish chemist who invented the Year 1916 ( MCMXVI) was a Leap year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Leap year

The most important application may be the growth of large cylindrical ingots, or boules, of single crystal silicon. An ingot is a material usually metal that is cast into a shape suitable for further processing A boule is a single-crystal Ingot produced by synthetic means A single crystal, also called monocrystal, is a Crystalline Solid in which the Crystal lattice of the entire sample is continuous and unbroken Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Other semiconductors, such as gallium arsenide, can also be grown by this method, although lower defect densities in this case can be obtained using variants of the Bridgman-Stockbarger technique. Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. The Bridgman-Stockbarger technique is a method of growing Single crystal Ingots or boules.

Contents

Process

A puller rod with seed crystal for growing single-crystal silicon by the Czochralski process
A puller rod with seed crystal for growing single-crystal silicon by the Czochralski process

High-purity, semiconductor-grade silicon (only a few parts per million of impurities) is melted down in a crucible , which is usually made of quartz. A seed crystal is a small piece of Single crystal material from which a large Crystal of the same material typically is to be grown A single crystal, also called monocrystal, is a Crystalline Solid in which the Crystal lattice of the entire sample is continuous and unbroken Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that A crucible is a cup-shaped piece of laboratory object Laboratory equipment used to contain Chemical compounds when heating them to very high Temperatures Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Dopant impurity atoms such as boron or phosphorus can be added to the molten intrinsic silicon in precise amounts in order to dope the silicon, thus changing it into n-type or p-type extrinsic silicon. Boron (ˈbɔərɒn is a Chemical element with Atomic number 5 and the chemical symbol B. Phosphorus, (ˈfɒsfərəs is the Chemical element that has the symbol P and Atomic number 15 This influences the electrical conductivity of the silicon. Electrical conductivity or specific conductivity is a measure of a material's ability to conduct an Electric current. A seed crystal, mounted on a rod, is dipped into the molten silicon. A seed crystal is a small piece of Single crystal material from which a large Crystal of the same material typically is to be grown The seed crystal's rod is pulled upwards and rotated at the same time. By precisely controlling the temperature gradients, rate of pulling and speed of rotation, it is possible to extract a large, single-crystal, cylindrical ingot from the melt. Occurrence of unwanted instabilities in the melt can be avoided by investigating and visualizing the temperature and velocity fields during the crystal growth process. [1] This process is normally performed in an inert atmosphere, such as argon, and in an inert chamber, such as quartz. In English to be inert is to be in a state of doing little or nothing This article pertains to the chemical element For other uses see Argon (disambiguation. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in

Size of crystals

While the largest silicon ingots produced today are 400 mm in diameter and 1 to 2 metres in length, 200 mm and 300 mm diameter crystals are standard industrial processes. The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Thin silicon wafers are cut from these ingots (typically about 0. A wafer is a thin slice of Semiconductor material such as a Silicon crystal used in the fabrication of Integrated circuit and other microdevices 2 - 0. 75 mm thick) and can be polished to a very high flatness for making integrated circuits, or textured for making solar cells. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside A solar cell or photovoltaic cell is a device that converts Solar energy into Electricity by the photovoltaic effect.

Impurity incorporation

When silicon is grown by the Czochralski method the melt is contained in a silica (quartz) crucible. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in During growth the walls of the crucible dissolve into the melt and Czochralski silicon therefore contains oxygen impurities with a typical concentration of 1018cm − 3. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Oxygen impurities can have beneficial effects. Carefully chosen annealing conditions can allow the formation of oxygen precipitates. Precipitation is the formation of a Solid in a Solution during a Chemical reaction. These have the effect of trapping unwanted transition metal impurities in a process known as gettering. In Chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings It commonly refers to any element in Getters are reactive materials used for removing traces of gas from vacuum systems Additionally, oxygen impurities can improve the mechanical strength of silicon wafers by immobilising any dislocations which may be introduced during device processing. In Materials science, a dislocation is a Crystallographic defect, or irregularity within a Crystal structure. It has experimentally been proved in the 1990s that the high oxygen concentration is also beneficial for radiation hardness of silicon particle detectors used in harsh radiation environment ( eg. Radiation hardening is a method of designing and testing electronic components and systems to make them resistant to damage or malfunctions caused by high-energy Subatomic particles In experimental and applied Particle physics and Nuclear engineering, a particle detector, also known as a radiation detector, is a device used to CERN's LHC/S-LHC projects)[2][3][4] Therefore, radiation detectors made of Czochralski- and Magnetic Czochralski-silicon are considered to be promising candidates for many future high-energy physics experiments. The European Organization for Nuclear Research (Organisation Européenne pour la Recherche Nucléaire known as CERN Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them [5][6] However, oxygen impurities can react with boron in an illuminated environment, such as experienced by solar cells. This results in the formation of an electrically active boron–oxygen complex that detracts from cell performance. Module output drops by approximately 3% during the first few hours of light exposure. [7]

Mathematical expression of impurity incorporation from melt

The impurity concentration in the solid crystal that results from freezing an incremental amount of volume can be obtained from consideration of the segregation coefficient. [8]

kO: Segregation coefficient
V0: Initial volume
I0: Number of impurities
C0: Impurity concentration in the melt
VL: Volume of the melt
IL: Number of impurities in the melt
CL: Concentration of impurities in the melt
VS: Volume of solid
CS: Concentration of impurities in the solid

During the growth process, volume of melt dV freezes, and there are impurities from the melt that are removed.

dI = -k_O C_L dV\;
dI = - k_O \frac{I_L}{V_O - V_S} dV
\int_{I_O}^{I_L} \frac{dI}{I_L} = -k_O \int_{0}^{V_S} \frac{dV}{V_O - V_S}
\log \left ( \frac{I_L}{I_O} \right ) = \log \left ( 1 - \frac{V_S}{V_O} \right )^{k_O}
I_L = I_O \left ( 1 - \frac{V_S}{V_O} \right )^{k_O}
C_S = - \frac{dI_L}{dV_S}
 C_S = C_O k_O (1-f)^{k_o - 1}
f = V_S / V_O\;

Gallery

Crucibles used in Czochralski method

Crucible after being used

Silicon ingot

References

  1. ^ J. Aleksic et al. , Ann. of NY Academy of Sci. 972 (2002) 158.
  2. ^ Z. Li et al. , IEEE Trans Nucl. Sci. 39 (6) (1992) 1730
  3. ^ A. Ruzin et al. , IEEE Trans Nucl. Sci. 46 (5) (1999) 1310
  4. ^ G. Lindström et al. , Nucl. Instr. and Meth. A 466 (2001) 308 and cited literature therein.
  5. ^ CERN RD50 Status Report 2004, CERN-LHCC-2004-031 and LHCC-RD-005 and cited literature therein
  6. ^ J. Härkönen et al. , Nucl. Instr. and Meth. A 541 (2005)202.
  7. ^ Eikelboom, J. A. , Jansen, M. J. , 2000. Characteristion of PV modules of new generations; results of tests and simulations. Report ECN-C-00-067, 18.
  8. ^ James D. Plummer, Michael D. Deal, and Peter B. Griffin, Silicon VLSI Technology, Prentice Hall, 2000, p. 126-27

See also

External links

The Bridgman-Stockbarger technique is a method of growing Single crystal Ingots or boules. Float-zone silicon is a high-purity alternative to Silicon grown by the Czochralski process.
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