Hexafluoro-1,3-butadiene (C4F6) for high aspect ratio chip etching

February 25th 2022

Hexafluoro-1,3-butadiene (C4F6, also known as perfluorobutadiene, HFBD) is used as an environmentally friendly etching gas with a low greenhouse effect, mainly in dry etching processes for semiconductors. With the use of technologies such as the Internet of Things, cloud computing and artificial intelligence, the volume of data worldwide will increase dramatically in the future, and with it, the demand for storage capacity will become higher and higher, while 2D planar structures have reached their technical limits and 3D structures are the inevitable trend for future development. With the development of 3D NAND technology, the consumption of C4F6 on a single wafer will be more than 6 times higher than before in the process of moving from 2D to 3D NAND FLASH.
The use of hexafluoro-1,3-butadiene for etching purposes has the following excellent properties: a high C/F ratio of 67%, higher etch rates and selection ratios can be obtained with C4F6 compared to C4F8 and C5F8; C4F6 has a higher selection ratio for photoresist and silicon nitride compared to C4F8. These two etch advantages improve etch stability and productivity, and therefore product yield and reliability, because as the device size advances to 0.13um, the CD of the hole (critical size) is about 30% smaller than 0.18um and the selection ratio of the bond film layer has to be high so that the etch window can be expanded. In addition, C4F6 has a low GWP, produces a small greenhouse effect and has better environmental characteristics. The use of C4F6 instead of C4F8 can reduce PFC emissions by 65%-82%.
C4F6 can replace CF4 in dry etching processes for KrF laser etching of semiconductor capacitor patterns (Patterns). C4F6 is anisotropic and produces ideal aspect ratios in silicon and silicon oxide etching, and the polymer film (photoresist) formed during the etching process protects the sidewalls.

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