Float-Zone Silicon (FZ-Si) wafers are the high purity and newer alternative to to Czochralski (CZ-Si) wafers. These wafers have high temperature capabilities and a low concentration of light impurities, such as carbon and oxygen, which can be prevalent in Czochralski (CZ-Si), are extremely low with FZ-Si wafers. However, Float-Zone silicon’s (FZ-Si) mechanical strength can be improved by deliberately adding nitrogen to it in the growth process, which also helps to control microdefects.
Float-Zone silicon (FZ-Si) wafers are generally, not greater than hundred and fifty millimeters. That is due to surface tension effects during the growth process. Float-Zone silicon’s (FZ-Si) impurity enables it to undergo a lighter doping process. In some cases, Float-Zone silicon produce high resistivity measurements that reach high heights.
Float-zone silicon is obtained by the Float-Zone (FZ) method, based in the vertical zone-melting principle that was invented by Theuerer in 1962 at Bell Labs as a modification of a method developed by William Gardner Pfann for germanium.
The Float-Zone (FZ) growth process starts with passing a polycrystalline rod of silicon through a heating element by simultaneously rotating the ingot, which creates a localized molten zone. A segment of an ingot is partially melted, as the molten zone is moving along the polycrystalline rod from which the ingot grows. Because the most impurities are less soluble in the crystal than in silicon, the molten zone carries the impurities away with it, simultaneously purifying the material as it solidifies. The impurities concentrate near the end of the crystal and can simply be cut away. The necking process, which is carried before the neck, is allowed to increase in diameter, allowing for establishing the dislocation of free crystal. After the entire ingot passes through the heating coil, doping of crystals is realized by adding the doping gas phosphine (PH3) or diborane (B2H6) to the inert gas for n- and p-type, respectively, depending on the end user’s application. The silicon molten zone is not in contact with any other substances but ambient gas that may only contain doping gas, unlike Czochralski (CZ) growth process. Thus enabling Float-Zone Silicon (FZ-Si) to achieve much higher purity and resistivity. Then the ingot is cooled and sliced. The production takes place either in a vacuum, or in an inert gaseous atmosphere, allowing for the ingot to grow in an environment with very minimal contamination.
FZ-Si wafers offer a major advantage for high power devices and unique properties for optical and sensor devices, which cannot be achieved with CZ-Si wafers.
Applications of FZ-Si wafers:
- FZ-Si wafers are used in manufacturing of discrete power devices.
- FZ-Si wafers are used in high efficiency solar devices.
- FZ-Si wafers are used in RF circuits.
- FZ-Si wafers are used in sensors and detectors.
- FZ-Si wafers are used senses and windows for terahertz applications.
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