The FZ wafer is an alternative to the CZ wafer or a silicon wafer grown through the Czochralski process. The routine that creates a float zone wafer has several significant differences from the CZ method. Below is a summary of how the float zone approach to growing silicon crystals works, what its advantages are and what setbacks it has.
The float zone method passes silicon crystals through a feedstock heated via radio frequency. Operators insert argon gas into the rod so the crystal can float freely through the heating and molten areas and into a heated cone.
Once inside the cone, the silicon crystal is purified into a monocrystal. After purification, the cleansed crystal goes back up to the cone for the growing and doping process.
The seed crystal never interacts with any part of the feed rod throughout the entire process. This feature sets it apart from the Czochralski method, which involves a crucible that eventually dissolves and mixes with the molten silicon.
The FZ method produces silicon crystals with fewer impurities than those made through the CZ procedure. The technique minimizes the carbon and oxygen content in the final product by preventing contact between the crystal and the environment. FZ wafers theoretically promise better performance.
The inert gases used for the operation often contain the doping gas required to enhance the finished product’s conductivity. This system increases the speed and efficiency of the manufacturing operation, which means more wafers can be produced in a specific duration.
The float zone method is very limited in the size of crystals that the system can grow. FZ wafers can only grow to 200 millimeters in diameter due to surface tension in the molten silicon. This limitation also confines the resulting wafers into specific applications.
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