10/22/13 Czochralski process - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Czochralski_process 1/5

The Czochralski process

Crystallization

Concepts

Crystallization · Crystal growth

Recrystallization · Seed crystal

Protocrystalline · Single crystal

Fundamentals

Nucleation · Crystal

Crystal structure · Solid

Methods and technology

Boules · Bridgman-Stockbarger

Czochralski process · Fractional crystalliz. · Frac. freezing · Hydroth. synthesis ·

LHPG · Iodide process

V · T · E (//en.wikipedia.org/w/index.php?title=Template:Crystallization&action=edit)

Czochralski processFrom Wikipedia, the free encyclopedia

The Czochralski process is a method ofcrystal growth used to obtain single crystals ofsemiconductors (e.g. silicon, germanium andgallium arsenide), metals (e.g. palladium,platinum, silver, gold), salts and syntheticgemstones. The process is named after Polish

scientist Jan Czochralski,[1] who invented themethod in 1916 while investigating thecrystallization rates of metals.

The most important application may be thegrowth of large cylindrical ingots, or boules, ofsingle crystal silicon.Other semiconductors,such as gallium arsenide,can also be grown bythis method, althoughlower defect densities inthis case can beobtained using variantsof the Bridgman-Stockbarger technique.

Contents

1 Production ofCzochralski

silicon2 Size of crystals

3 Impurity

incorporation

3.1

Mathematical expression of impurity incorporation from melt

4 Gallery5 See also

6 References

7 External links

10/22/13 Czochralski process - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Czochralski_process 2/5

A puller rod with seed crystal for

growing single-crystal silicon by the

Czochralski process

Production of Czochralski silicon

High-purity, semiconductor-grade silicon (only a few parts per millionof impurities) is melted in a crucible, usually made of quartz. Dopantimpurity atoms such as boron or phosphorus can be added to themolten silicon in precise amounts to dope the silicon, thus changing itinto p-type or n-type silicon, with different electronic properties. Aprecisely oriented rod-mounted seed crystal is dipped into the moltensilicon. The seed crystal's rod is slowly pulled upwards and rotatedsimultaneously. 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 unwantedinstabilities in the melt can be avoided by investigating and visualisingthe temperature and velocity fields during the crystal growth

process.[2] This process is normally performed in an inert atmosphere,such as argon, in an inert chamber, such as quartz.

Size of crystals

Due to the efficiencies of common wafer specifications, the semiconductor industry has used wafers withstandardized dimensions. In the early days, the boules were smaller, only a few inches wide. With advancedtechnology, high-end device manufacturers use 200 mm and 300 mm diameter wafers. The width is controlledby precise control of the temperature, the speeds of rotation and the speed the seed holder is withdrawn. Thecrystal ingots from which these wafers are sliced can be up to 2 metres in length, weighing several hundredkilogrammes. Larger wafers allow improvements in manufacturing efficiency, as more chips can be fabricated oneach wafer, so there has been a steady drive to increase silicon wafer sizes. The next step up, 450 mm, is

currently scheduled for introduction in 2012.[3] Silicon wafers are typically about 0.2–0.75 mm thick, and canbe polished to great flatness for making integrated circuits or textured for making solar cells.

The process begins when the chamber is heated to approximately 1500 degrees Celsius, melting the silicon.When the silicon is fully melted, a small seed crystal mounted on the end of a rotating shaft is slowly lowereduntil it just dips below the surface of the molten silicon. The shaft rotates counterclockwise and the cruciblerotates clockwise. The rotating rod is then drawn upwards very slowly, allowing a roughly cylindrical boule tobe formed. The boule can be from one to two metres, depending on the amount of silicon in the crucible.

The electrical characteristics of the silicon are controlled by adding material like phosphorus or boron to thesilicon before it is melted. The added material is called dopant and the process is called doping. This method isalso used with semiconductor materials other than silicon, such as gallium arsenide.

Monocrystalline silicon grown by the Czochralski process is the basic material in the production of the large-

scale integrated circuit chips used in computers, TVs, mobile phones and all types of electronic equipment.[4]

Impurity incorporation

When silicon is grown by the Czochralski method, the melt is contained in a silica (quartz) crucible. Duringgrowth, the walls of the crucible dissolve into the melt and Czochralski silicon therefore contains oxygen at a

typical concentration of 1018

cm−3

. Oxygen impurities can have beneficial effects. Carefully chosen annealingconditions can allow the formation of oxygen precipitates. These have the effect of trapping unwanted transitionmetal impurities in a process known as gettering. Additionally, oxygen impurities can improve the mechanical

10/22/13 Czochralski process - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Czochralski_process 3/5

strength of silicon wafers by immobilising any dislocations which may be introduced during device processing. Itwas experimentally shown in the 1990s that the high oxygen concentration is also beneficial for radiationhardness of silicon particle detectors used in harsh radiation environment (such as CERN's LHC/S-LHC

projects).[5][6] Therefore, radiation detectors made of Czochralski- and Magnetic Czochralski-silicon are

considered to be promising candidates for many future high-energy physics experiments.[7][8] It has also beenshown that presence of oxygen in silicon increases impurity trapping during post-implantation annealing

processes.[9]

However, oxygen impurities can react with boron in an illuminated environment, such as experienced by solarcells. 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.[10]

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.[11]

: Segregation coefficient

: Initial volume: Number of impurities

: Impurity concentration in the melt

: Volume of the melt: Number of impurities in the melt

: Concentration of impurities in the melt

: Volume of solid: Concentration of impurities in the solid

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

10/22/13 Czochralski process - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Czochralski_process 4/5

Gallery

Crucibles used inCzochralski method

Crucible after being used

Silicon ingot

See also

Monocrystalline silicon

Bridgman–Stockbarger techniqueFloat-zone silicon

Laser-heated pedestal growth

Micro-Pulling-Down

References

1. ^ (Polish), (English), Paweł Tomaszewski, ""Jan Czochralski i jego metoda" (ang.Jan Czochralski and hismethod), Oficyna Wydawnicza ATUT, Wrocław–Kcynia 2003, ISBN 83-89247-27-5

2. ^ Aleksic, J.; et al. (2002). "Temperature and Flow Visualization in a Simulation of the Czochralski Process

Using Temperature-Sensitive Liquid Crystals". Ann. of NY Academy of Sci. 972: 158.Bibcode:2002NYASA.972..158A (http://adsabs.harvard.edu/abs/2002NYASA.972..158A). doi:10.1111/j.1749-6632.2002.tb04567.x (http://dx.doi.org/10.1111%2Fj.1749-6632.2002.tb04567.x).

3. ^ Intel, Samsung, TSMC Reach Agreement for 450mm Wafer Manufacturing Transition(http://www.physorg.com/news129301282.html). Physorg.com. May 6, 2008. Retrieved on 2011-12-06.

4. ^ Czochralski Crystal Growth Method (http://www.bbc.co.uk/dna/h2g2/A912151). Bbc.co.uk. 30 January2003. Retrieved on 2011-12-06.

5. ^ Li, Z.; Kraner, H.W.; Verbitskaya, E.; Eremin, V.; Ivanov, A.; Rattaggi, M.; Rancoita, P.G.; Rubinelli, F.A. etal. (1992). "Investigation of the oxygen-vacancy (A-center) defect complex profile in neutron irradiated high

resistivity silicon junction particle detectors". IEEE Transactions on Nuclear Science 39 (6): 1730.Bibcode:1992ITNS...39.1730L (http://adsabs.harvard.edu/abs/1992ITNS...39.1730L). doi:10.1109/23.211360(http://dx.doi.org/10.1109%2F23.211360).

6. ^ Lindström, G (2001). "Radiation hard silicon detectors—developments by the RD48 (ROSE) collaboration".Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and

Associated Equipment 466 (2): 308. Bibcode:2001NIMPA.466..308L(http://adsabs.harvard.edu/abs/2001NIMPA.466..308L). doi:10.1016/S0168-9002(01)00560-5(http://dx.doi.org/10.1016%2FS0168-9002%2801%2900560-5).

7. ^ CERN RD50 Status Report 2004, CERN-LHCC-2004-031 and LHCC-RD-005 and cited literature therein

8. ^ Harkonen, J; Tuovinen, E; Luukka, P; Tuominen, E; Li, Z; Ivanov, A; Verbitskaya, E; Eremin, V et al.(2005). "Particle detectors made of high-resistivity Czochralski silicon". Nuclear Instruments and Methods in

Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 541: 202.

10/22/13 Czochralski process - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Czochralski_process 5/5

Bibcode:2005NIMPA.541..202H (http://adsabs.harvard.edu/abs/2005NIMPA.541..202H).doi:10.1016/j.nima.2005.01.057 (http://dx.doi.org/10.1016%2Fj.nima.2005.01.057).

9. ^ Custer, J. S.; Polman, A.; Van Pinxteren, H. M. (1994). "Erbium in crystal silicon: Segregation and trapping

during solid phase epitaxy of amorphous silicon". Journal of Applied Physics 75 (6): 2809.Bibcode:1994JAP....75.2809C (http://adsabs.harvard.edu/abs/1994JAP....75.2809C). doi:10.1063/1.356173(http://dx.doi.org/10.1063%2F1.356173).

10. ^ Eikelboom, J.A., Jansen, M.J., 2000. Characteristion of PV modules of new generations; results of tests andsimulations (http://www.ecn.nl/docs/library/report/2000/c00067.pdf). Report ECN-C-00-067, 18.

11. ^ James D. Plummer, Michael D. Deal, and Peter B. Griffin, Silicon VLSI Technology, Prentice Hall, 2000,ISBN 0-13-085037-3 pp. 126–27

External links

Czochralski doping process (http://www.articleworld.org/index.php/Czochralski_process)

Silicon Wafer Processing Animation (https://www.youtube.com/watch?v=LWfCqpJzJYM) on YouTube

Retrieved from "http://en.wikipedia.org/w/index.php?title=Czochralski_process&oldid=553025829"

Categories: Industrial processes Semiconductor growth Crystals Science and technology in Poland

Polish inventions

This page was last modified on 1 May 2013 at 11:38.

Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may

apply. By using this site, you agree to the Terms of Use and Privacy Policy.

Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.