Float Zone Silicon
January 14, 2010
P-type boron doped and N-type phosphorous doped silicon approaching from 1000 ohm-cm to 10000 ohm-cm in 1-1-1 and 1-0-0 orientations up to 100 mm diameter is now available, frequently from stock.
Float Zone Silicon is in the Galileo spacecraft now orbiting Jupiter; it is in the Hubble Space Telescope in orbit around the Earth; it will be in the Genesis solar wind sampling project and etc., etc…
CISMarket.net is compiling possibly the most complete stock list of Float Zone Silicon in ingot form, as-cut wafers, etched wafers, lapped, and single and double sided polished wafers.
Zone refining of crystals in order to increase the purity of the crystals has been known for more than 50 years. The purification method takes advantage of the concentration change by segregation for most impurities during the liquid –solid transition. Many different purification techniques exists but one of the most fascinating is the freely floating zone refining method, where the floating zone is suspended between the melting and the freezing interfaces. The Float Zone technology has been perfected for the growth of silicon monocrystals. Being freely floating with no contact to crucibles and other possible contaminant sources make it possible to grow monocrystalline silicon with the highest purity which is important for a number of Electronic and Optoelectronic Applications. Float Zone monocrystalline growth starts from a high purity, small diameter seed crystal. The seed crystal is prepared in the right crystalline direction in order to grow pure silicon with no crystalline defects.
Float Zone technology for growing silicon monocrystals is by far the most pure method and results in silicon with unique properties as opposed to any other growth technology. Float Zone silicon can be grown with resistivities exceeding 100.000 ohm-cm because of the intrinsic process purity. Czochralski silicon does not have this high level of purity and it is difficult to grow Czochralski silicon with resistivities exceeding 1.000 ohm-cm. Also, performance degrading impurities such as oxygen is much lower by three orders of magnitude in Float Zone silicon in comparison with Czochralski silicon where crucibles needed for suspending the liquid silicon gives high and unpredictable levels of oxygen in the bulk of the silicon.
Perhaps the most important feature of the Float Zone technology is the ability to exactly control the resistivity throughout the whole of the crystal. This is in particular important for applications using the bulk of the silicon wafers in the making of devices. There are two pracitcal ways of obtaining the very good resistivity control. One is by doping the crystals when they are pulled by introducing conrollable amounts of gaseous dopants into the growth chamber. This technique is called in-situ doping or gas phase doping. The other technique is by doping the crystal after it has been pulled. This technique is called ex-situ doping and it is done in neutron irradiating reactors. The starting material for ex-situ doping is high resistivity silicon that after being irradiated with a controllable dose of neutrons changes it resistivity by transforming silicon atoms to dopant atoms.
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