Silicon carbide is slowly replacing silicon as a potential material for fabricating micro-electro-mechanical system (MEMS) devices, especially in extreme temperatures. To enhance the performance of SiC MEMS devices, researchers have majorly focused on processing and manufacturing of different types of silicon carbide-based microstructures and nanostructures. However, the high stability of Silicon carbide (SiC) remains a challenge to overcome. Among the available MEMS fabrications techniques, etching process and particularly inductively coupled plasma etching is widely preferred due to controllable high plasma density. Unfortunately, the current inductively coupled plasma etching rate cannot meet the desired practical demand and, therefore, needs to be improved. This requires the knowledge of both performance enhancement of the etching machines as well as increasing the etching rate of the existing machines by pre-treatment of silicon carbide that is currently underexplored.
Ultrafast lasers have been recently proposed as effective micromachining tools. The femtosecond laser has been particularly used to study the effects of laser on silicon. As such, Tsinghua University researchers: Yigang Huang, Professor Fei Tang, Zheng Guo and Xiaohao Wang proposed an ultrafast etching of single crystal 6H-SiC by integrating inductively coupled plasma etching and femtosecond laser modification. The main objective was to investigate the effects of single pulse energy and scanning rate of femtosecond laser on the inductively coupled plasma etching rate of 6H-SiC. The work is published in the journal, Applied Surface Science.
Briefly, the research team started their work by first treating the 6H-SiC substrate by femtosecond laser to produce irradiated region. Next, inductively coupled plasma etching was then performed on the sample to determine any changes in the etching rate. Additionally, the change in the chemical structure and surface roughness of the 6H-SiC sample was compared before treatment, after femtosecond laser irradiation, and after ICP etching. Finally, the reasons behind the increase in the inductively coupled plasma etching rate after laser irradiation were analyzed.
A higher modification degree on the 6H-SiC was effectively achieved with a femtosecond laser with a slower scanning rate and single pulse energy. This was favorable for increasing the inductively coupled plasma etching rate and reducing the etching time. Unlike the untreated one, a sample irradiated by femtosecond laser with a scanning rate of 20µm/s and single pulse energy of 25µJ recorded an increase in the inductively coupled plasma etching rate by 117%. It was necessary to analyze the accelerated etching process based on various techniques including X-ray diffraction and energy dispersive spectrum. The findings revealed that the primary cause of the accelerated etching was the femtosecond laser-induced SiO2 on top of the 6H-SiC substrate. Additionally, a roughened surface observed during the irradiation also contributed to the enhancement of the etching rate.
In summary, the Tsinghua University research team demonstrated the feasibility of accelerated inductively coupled plasma etching of 6H-SiC by femtosecond laser modification. The method significantly improved the etching rate and reduced the overall etching time as compared to conventional etching methods. Thus, it can be applied in the manufacturing of SiC-based MEMS devices to enhance production efficiency. In a statement to Advances in Engineering, Professor Fei Tang highlighted that their study is will pave way for further technological development of SiC-based electronic components.
Huang, Y., Tang, F., Guo, Z., & Wang, X. (2019). Accelerated ICP etching of 6H-SiC by femtosecond laser modification. Applied Surface Science, 488, 853-864.