A new generation of dry etching gas hexafluoro-1,3-butadiene C4F6, which can be used for etching of Silicon Dioxide (SiO2) and Silicon Nitride (Si3N4) and as an electronic specialty gas belongs to the electronics industry system. At present, the electronics industry has become the main pillar of the national economy and guarantees national strategic security. Electronic specialty gas is one of the key raw materials for many applications such as military defense, aerospace, new types of solar cells, and electronic products.
The No. 67 document issued by the State Council on November 26, 2016, “National Thirteenth Five-Year Plan” for the development of strategic emerging industries, pointed out that we need to improve the core hardware supply capability, the design level of key chip’s technology, development chips of new applications and accelerate the Industrialization of 16/14-nm process and the construction of memory production line. The R&D and industrialization of special electronic gas has become a core part of China’s integrated circuit manufacturing equipment and complete sets of processes and it’s obviously supported by policies.
In silicon-wafer manufacturing plant, a silicon wafer needs to complete 450 or more processes to obtain chips with various circuit patterns. This process includes extension, film formation, doping, etching, cleaning, packaging, and other processes. Fluorine etchants are widely used in semiconductor or LCD beginning process, mainly for dry etching. The fluorine etching gas mainly includes: CF4, CHF3, CH2F2, CH3F, C2F6, c-C4F8, C4F6, C5F8 and so on. The use of various etching gases and features are summarized in Table 1.
Table 1. Fluorine-containing etching gasses
|hexafluoroethane||C2F6||Silicon oxide||Anisotropy, it produces an ideal aspect ratio in silicon and silicon oxide etching and protects the sidewall of the polymer film (photoresist) by etching.|
|Hexafluoro-1,3-butadiene||C4F6||Silicon oxide||Anisotropy, it produces an ideal aspect ratio in silicon and silicon oxide etching and protects the sidewall of the polymer film (photoresist) by etching.|
|Octafluorocyclopentene||C5F8||Silicon oxide||Anisotropy, it produces an ideal aspect ratio in silicon and silicon oxide etching and protects the sidewall of the polymer film (photoresist) by etching.|
|Octafluorocyclobutane||C4F8||Silicon oxide||Anisotropy, it produces an ideal aspect ratio in silicon and silicon oxide etching|
|Trifluoromethane||CHF3||Silicon metal oxide||Anisotropy, it produces an ideal aspect ratio in silicon and silicon oxide etching|
|Sulfur hexafluoride||SF6||Polysilicon||Anisotropy, it produces an ideal aspect ratio in silicon and silicon oxide etching|
|Nitrogen trifluoride||NF3||Polysilicon||Anisotropy, it produces an ideal aspect ratio in silicon and silicon oxide etching|
Hexafluorobutadiene (C4F6) and octafluorocyclopentene (C5F8) are considered as new generation etching gases and considered to have a competitive advantage, especially C4F6.
Market demand for C4F6 as a semiconductor-grade fluorine-containing gas is in a overall growth. It can replace CF4 for dry process of KrF laser sharp etching of semiconductor capacitor patterns. C4F6 has many etching advantages at the 0.13um technology level. C4F6 has higher selectivity to photoresist and silicon nitride selectivity than C4F8 which are important two advantages because as the device size increases to 0.13um, the CD (key size) of the hole is 30% smaller than 0.18um. Around, the choice of the key film layer is higher than that, so that the etching window can be enlarged and the etching stability can be improved. Increased etching rate will reduce the amount of time required so the production efficiency can be increased. Increased etching uniformity and CDbias (critical size bias) will increase the stability of the CD and the device reliability, thus improving the good product rate.
In addition, environment is also a very important factor needs to be considered. The use of environment-friendly gas etching equipment and process technology with a low green house effect coefficient will be policy oriented and will be rapidly developed. The GWP of C4F6 is almost 0, it replaces C4F8 and C5F8 in oxide film etching process, C4F6 can reduce greenhouse gas emissions. The semiconductor etching experts provide data on the use of PFC (Perfluorocompound) during etching process and point out that replacing C4F8 with C4F6 has considerable performance in the etching of oxides and can reduce emissions of 65%-82% PFC, the experts say so far, C4F6 may be the only alternative to provide the required etching conditions and reduce emissions.