Deep Silicon Etching Processing with SF₆/O₂/C₄F₈ Mixtures Using an Ultra-Low Cost Tool for Flexible, Small Volume Manufacturing AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY19030021

Chinese Library Classification Number:TN305.7

Citation Information:

In this paper，the non-BOSCH ternary gas etching process was investigated through a micro-desktop deep silicon etching system. The researchers aimed to understand the impact of different gas combinations on silicon etching and to develop a more efficient etching process. The study compared the effects of three etching gas mixtures：SF₆/O₂，SF₆/C₄F₈，and SF₆/O₂/C₄F₈. These mixtures were evaluated in terms of their influence on the etching rate，etching profile，selectivity，and surface roughness during the silicon etching process. Eventually，a deep silicon etching process based on the SF₆/O₂/C₄F₈ ternary mixed gas was successfully developed. To analyze the results of the etching，advanced equipment was employed. An optical microscope was used to obtain a general view of the etched silicon trenches. The scanning electron microscope （SEM） provided high-resolution images，allowing for detailed examination of the side-wall and bottom-surface features. A three-dimensional optical profilometer was utilized to accurately measure the etching depth，side-wall verticality，selectivity，and bottom-surface roughness. The experimental results revealed distinct characteristics of each gas mixture. When O₂ was added to SF₆，it had a catalytic effect on the SF₆ plasma，facilitating the generation of fluorine radicals. These radicals played a crucial role in the etching process. At the same time，O₂ reacted with silicon to form Si_xO_yF_x polymers. These polymers were deposited on the side-walls of the silicon trenches，acting as a protective layer and preventing SF₆ from etching the side-walls. This led to anisotropic etching，which was highly desirable in many semiconductor manufacturing applications. However，the selectivity of this gas combination was relatively low. A low selectivity meant that the etching process was not very specific to silicon，and it also etched other materials or the underlying layers to some extent. As a result，it was difficult to achieve deep etching with this mixture. When C₄F₈ was added to SF₆，the situation was different. This combination significantly improved the selectivity and the etching profile. The polymers formed by C₄F₈ were more effective in protecting the side-walls，resulting in better-defined etching profiles. However，the major drawback of this gas mixture was the extremely low etching rate. The deposition of polymers on the etching surface seemed to slow down the reaction between the etching gas and silicon，making the overall process very time-consuming. The most promising results were obtained with the SF₆/O₂/C₄F₈ ternary gas etching process. By adding a small amount of C₄F₈ to the SF₆/O₂ mixture at room temperature，the advantages of both previous combinations were combined. This process not only enhanced the etching selectivity，which was crucial for precise etching in semiconductor manufacturing，but also reduced the bottom-surface roughness，leading to a smoother and more uniform etching result. Moreover，it managed to increase the etching rate compared to the SF₆/C₄F₈ combination. This ternary gas etching process provided a more balanced and efficient solution for deep silicon etching，meeting the requirements of high-performance semiconductor device fabrication. In conclusion，this research provided valuable insights into the non-BOSCH ternary gas etching process. The development of the SF₆/O₂/C₄F₈ ternary gas etching process offered a significant improvement in silicon etching technology，which could have a wide range of applications in the semiconductor industry.