Clean SiO2 atomic layer etching based on physisorption of high boiling point perfluorocarbon.

This study aimed to evaluate the SiO2 atomic layer etching (ALE) process that is selective to Si3N4 based on the physisorption of high boiling point perfluorocarbons (HBP PFCs; C5F8, C7F14, C6F6, and C7F8 have boiling points above room temperature). The lowering of the substrate temperature from 20 °C to -20 °C not only increased SiO2 etch depth per cycle (EPC) but also increased etch selectivity of SiO2/Si3N4 to near infinity. Due to the differences in fluorocarbon adsorption at a temperature during the physisorption depending on boiling points of PFCs, the desorption time and ion bombardment energy during the desorption step needed to be optimized, and higher ion bombardment energy and longer desorption time were required for higher HBP PFCs. Even though near infinity etch selectivity of SiO2/Si3N4 was obtained, for the SiO2 etching masked with Si3N4 patterns, due to the adsorption of PFC on the sidewall of the Si3N4 layer, the difficulty in anisotropic etching could be observed. By adding an O2 descumming step in ALE processes, an anisotropic SiO2 etch profile could be obtained with no adsorption of fluorocarbon on the chamber wall. Therefore, it is believed that the HBP ALE processes can be applicable for achieving high selective SiO2/Si3N4 with more stability and reliability.

Investigation of SiO2 Etch Characteristics by C6F6/Ar/O2 Plasmas Generated Using Inductively Coupled Plasma and Capacitively Coupled Plasma.

The etching properties of C6F6/Ar/O2 in both an inductively coupled plasma (ICP) system and a capacitively coupled plasma (CCP) system were evaluated to investigate the effects of high C/F ratio of perfluorocarbon (PFC) gas on the etch characteristics of SiO2. When the SiO2 masked with ACL was etched with C6F6, for the CCP system, even though the etch selectivity was very high (20 ~ infinite), due to the heavy-ion bombardment possibly caused by the less dissociated high-mass ions from C6F6, tapered SiO2 etch profiles were observed. In the case of the ICP system, due to the higher dissociation of C6F6 and O2 compared to the CCP system, the etching of SiO2 required a much lower ratio of O2/C6F6 (~1.0) while showing a higher maximum SiO2 etch rate (~400 nm/min) and a lower etch selectivity (~6.5) compared with the CCP system. For the ICP etching, even though the etch selectivity was much lower than that by the CCP etching, due to less heavy-mass-ion bombardment in addition to an adequate fluorocarbon layer formation on the substrate caused by heavily dissociated species, highly anisotropic SiO2 etch profiles could be obtained at the optimized condition of the O2/C6F6 ratio (~1.0).

Radio Frequency Induction Welding of Silver Nanowire Networks for Transparent Heat Films.

Transparent heat films (THFs) are attracting increasing attention for their usefulness in various applications, such as vehicle windows, outdoor displays, and biosensors. In this study, the effects of induction power and radio frequency on the welding characteristics of silver nanowires (Ag NWs) and Ag NW-based THFs were investigated. The results showed that higher induction frequency and higher power increased the welding of the Ag NWs through the nano-welding at the junctions of the Ag NWs, which produced lower sheet resistance, and improved the adhesion of the Ag NWs. Using the inductive welding condition of 800 kHz and 6 kW for 60 s, 100 ohm/sq of Ag NW thin film with 95% transmittance at 550 nm after induction heating could be decreased to 56.13 ohm/sq, without decreasing the optical transmittance. In addition, induction welding of the Ag NW-based THFs improved haziness, increased bending resistance, enabled higher operating temperature at a given voltage, and improved stability.