Characteristics of Silicon Nitride Reaction to Vapor-phase HF Gas Treatment

The gas-phase etching of SiO2 was examined using HF and methanol vapor at low temperature below 0 °C and at low pressure. The etching rate of SiO2 increased with decreasing temperature and showed a maximum around –30 °C. The obtained etching rate was maximum 40 nm/min at plasma-enhansed CVD SiO2. The etching rate of SiN examined for comparison was less than 10 times smaller than that of SiO2 in this condition. As a result, the etching selectivity of SiO2 to SiN was found to be over 20 at –40 °C. Utilizing low temperature less than –30 °C, gas-phase etching of SiO2 which shows high etching rate and selectivity was achieved.

Section: Residue On Pe-sin and Removalsupporting

confidence: 92%

Highly selective isotropic gas-phase etching of SiO₂ using HF and methanol at temperatures –30 °C and lower

Hattori

Kobayashi

Ohtake

et al. 2023

“…Figure 8 shows SEM photographs of the blanket PE-SiN surface after HF and methanol etching at -20 °C with and without 50 s IR exposure at different etching pressures. As previously reported, 46) x-ray photoelectron spectroscopy analysis identified this residue as ammonium hexafluorosilicate (NH 3 ) 2 SiF 6 , which is a reaction product of SiN in the HF 50) and methanol process 51) The decomposition temperature of (NH 3 ) 2 SiF 6 is known to be 100 °C-145 °C52,53) which means it is effective to remove the deposition on PE-SiN by IR lamp heating at around 150 °C. The residue at the PE-SiN blanket is without IR lamp exposure at all pressures examined and is completely removed with IR lamp heating (Fig.…”

Section: Effect Of Pressure On the Etching Of Pe-sin And The Selectivitymentioning

confidence: 76%

Etching selectivity of SiO₂ to SiN using HF and methanol at higher pressures up to 900 Pa

Hattori,

Kobayashi,

Ohtake

et al. 2024

The isotropic gas-phase etching of SiO2 was examined using HF and methanol vapor while changing the pressure from 300 Pa to 900 Pa. The temperature dependence of the etching rate of SiO2 showed a broad maximum around –30 °C, and the rate increased with increasing the pressure. The etching rate of plasma-enhanced chemical vapor deposition (PE-CVD) SiO2 became more than 60 nm/min at 900 Pa at –30 °C. When the pressure was increased from 300 Pa to 900 Pa, the temperature range that indicates the SiO2 etching was shifted to a higher temperature. The etching of SiO2, which did not proceed at 300 Pa, was found to proceed even at 0 °C at 900 Pa. The etching rate of PE-CVD SiN was also found to slightly increase with the pressure. At the higher pressure of 900 Pa, the formation of ammonium hexafluorosilicate, which is byproduct of SiN, was found to increase. As a result, the high selectivity of more than twenty was obtained at the lower pressure of less than 600 Pa and the lower temperature of less than –40 °C.

“…This indicates that the SiO x residue was removed from the gold surface by this process. Since it is known that the HF vapor does not etch Si or gold, [28][29][30] HF-vapor exposure is an effective way to remove SiO x residue without damaging Si and gold, which are often used in MEMS structures.…”

Section: Residue-removal Processmentioning

confidence: 99%

Selective Removal of Dry-Etching Residue Derived from Polymer Sacrificial Layer for Microelectromechanical-System Device Fabrication

Takagahara¹,

Kuwabara²,

Sakata³

et al. 2012

A selective removal of dry-etching residue using hydrofluoric acid (HF) vapor is described in relation to the fabrication of microelectromechanical-system (MEMS) devices. Auger electron spectroscopy (AES) analysis of residue after dry etching of polymer sacrificial layers reveals that the residue is mainly composed of silicon oxides. HF vapor removes the dry-etching residue, and raising the vapor temperature enables the selective removal of the residue without damaging silicon dioxide (SiO2), which is often used as the insulator for MEMS devices. Direct-contact-type MEMS switches with SiO2 insulators fabricated using polymer sacrificial layers demonstrate the effectiveness of removing the dry-etching residue selectively.