The Czochralski (CZ) process is a highly productive and cost-effective method for manufacturing silicon, but it does have certain limitations. For that reason, the FZ method was developed to produce high-purity float zone wafers with better electrical properties.
Here, we’ll explain how the FZ method emerged—and why it became so important in silicon manufacturing.
The float-zone technique was developed by Henry Theurer at Bell Labs in 1955, based on earlier work on zone refining by William G. Pfann, also at Bell Labs, in 1951.
Pfann’s work on zone refining—a method for purifying metals by moving a molten zone through a solid material—laid the foundation for float-zone crystal growth.
In float-zone processing, a molten zone is created and moved along a vertically held silicon rod. The solidifying crystal rejects impurities and pushes them along with the molten zone, leaving behind extremely pure single-crystal silicon.
Zone refining exploits the principle that impurity atoms have different solubilities in solid and liquid phases. Most impurities are more soluble in the liquid than the solid, as indicated by the segregation coefficient (also known as k, the ratio of impurity concentration in the solid vs. the liquid), which is typically less than 1.
Float-zone processing avoids contact with a crucible (unlike the CZ method), reducing contamination. This helps produce silicon with very low oxygen and carbon content, which is ideal for high-power and high-frequency, power, and radiation-hardened electronic devices.
While they may be more expensive than CZ wafers, they offer superior electrical properties due to their purity. If you’re not sure which option is better for your project, Wafer World can help. Contact us today for more information about our products!
