Studying the Etch Rates and Selectivity of SiO2 and Al in BHF Solutions

• Main Authors: Meow Yen Sim, Gleixner, S.
• Format: Conference Proceeding
• Language: English
• Subjects: Aluminum; Anti-freeze; Chemical technology; Fabrication; Hafnium; Microelectromechanical devices; Micromechanical devices; Silicon compounds; Sputter etching; Wet etching
• ISSN: 0749-6877; 2375-5350
• DOI: 10.1109/UGIM.2006.4286387

One limitation to fabricating MEMS devices in some academic labs is the lack of polysilicon deposition technology. This limits the devices that can be fabricated because polysilicon is a common structural material in MEMS devices. In order to enhance the MEMS fabrication capabilities, expanding the use of Al as a structural layer has been researched. The main difficulty is the lack of a selective wet etch between the Al structural layer and the SiO 2 sacrificial layer. In this study, seven etching solutions were studied on SiO 2 and Al for their etch rates and selectivity. Two were buffered hydrofluoric acid (BHF) solutions with different concentrations of NH 4 F. Four were BHF solutions with propylene glycol or glycerin at different concentrations. The seventh solution was a commercial solution, Pad Etch 4. Among the seven etching solutions, 5:1 BHF gave the best selectivity between SiO 2 and Al. Increasing the NH 4 F concentration from 5 to 7 parts did not increase the selectivity, but selectivity increased by adding NH 4 F in HF solution. Adding propylene glycol or glycerin to the 7:1 BHF solution did not increase the selectivity. When glycerin was added to 7:1 BHF solution it provided superior selectivity than was obtained from adding propylene glycol to 7:1 BHF. This paper will present the etch rates and selectivity of the 7 solutions along with comparisons with other published results.