The Influences of Non-Volatile Surface Compound Layer on the Dry Etching of Borosilicate Glass

• Published in: Journal of microelectromechanical systems Vol. 30; no. 5; pp. 733 - 743
• Main Authors: Lee, Seungmok, Hasegawa, Masashi, Nishizono, Kazuhiro
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.10.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Borosilicate glass; Chemicals; CMUT; Compounds; Etchants; Etching; Gas composition; Gas plasmas; Glass; Ion bombardment; Ions; Morphology; non-volatile compound layer; Plasma etching; Plasmas; Quartz; Silicon; Substrates; Thickness; Volatile compounds
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2021.3095568

In the dry etching of borosilicate glass (BSG), the process gas reacts with the impurities of borosilicate glass and forms a non-volatile compound layer on the surface. This surface compound layer (SCL) makes it difficult to control the surface morphology and device structure dimension with precision and significantly influences the etch rate. We examined the influence of SCL on the etch rate of quartz and BSG and discussed its etching mechanism depending on the thickness of the SCL. The formation of SCL was dominated by both the plasma gas composition and substrate material, and the etching regime can be defined by the thickness of the SCL. A thin SCL was formed on the BSG by CF 4 /Ar gas plasma etching, and the etch rate was suppressed by the SCL. A significantly thin SCL was formed on the quartz specimens under in same etching conditions, and a direct etching reaction was occurred. As the ratio of physical etching gas (Ar) increased, both the ion energy flux and the physical ion bombardment increased and consequently improved the etch rate. The SCL plays the role of an F radical supplier, while the thick SCL reduces the etch rate because it takes time for the etchants to transit from the surface to the interface. The SCL acts as a barrier in the etching reaction, which could be adjusted by the regulation of the etching gas composition or the plasma parameters, such as the inductive power and the bias power of the RIE reactor. [2021-0071]