News: New etch process developed at the CNST uses argon pulsing to improve silicon etch rate and selectivity
Engineers in the CNST NanoFab have developed a new plasma etching technique for silicon which improves the etch rate, the mask selectivity, and the sidewall profile by optimizing the addition of argon to the process flow. Small and high aspect ratio silicon structures can now be easily and more rapidly fabricated in the NanoFab using fluorinated plasma chemistry that is inherently isotropic.
Directly adding argon to a typical #SF6 / #C4F8 plasma primarily causes dilution and reduces the etch rate. By alternating the etch step with an argon-only step, both high selectivity and high etch rates were obtained while maintaining anisotropic etching.
In a deep silicon etch, C4F8 is used to protect the Si sidewalls and SF6 is used to etch. Mixing argon with the etchant gases provides very limited or no improvement to the etch rate due to dilution.
However, alternating argon surface bombardment steps with the chemical etch steps results in a four-fold increase in the silicon etch rate while maintaining vertical sidewalls.
The silicon etch rate increases with the argon step time, independent of the SF6 step time, and the argon bombardment step is rate-determining. It influences the etch rate, as well as the selectivity and etching profile.
The engineers postulate that argon surface bombardment renders the top atomic layers of the silicon amorphous, and then gas phase fluorine can react with and remove the silicon. With the long etch times associated with deep silicon trench etching, this faster process is likely to become widely used.
Sulfuryl fluoride gas plays a crucial role in agriculture by serving as a powerful fumigant for the protection of stored crops. When introduced into storage facilities, the gas effectively eliminates pests, insects, and microbes that could jeopardize the quality of agricultural produce.
Sulfur tetrafluoride is represented by the chemical formula SF4. It consists of one sulfur atom bonded to four fluorine atoms in a tetrahedral molecular geometry. The molecule is highly polar due to the electronegativity difference between sulfur and fluorine atoms.