Formation mechanism of sidewall striation in high-aspect-ratio hole etching

Abstract

We investigated the formation mechanism of sidewall striations in etched holes with high aspect ratios, with focus on the roles of energetic ions and fluorocarbon radicals. Striations were observed on the sidewalls of holes with high aspect ratios in stacked dielectric films, despite the smooth sidewall of the mask. Argon plasma treatment increased the degree of striation on the carbon mask, while striation was prevented with a cyclic process consisting of a fluorocarbon deposition step and an argon plasma treatment step. The blanket films were irradiated with oblique ion beams in order to simulate the surface reactions on the sidewalls of high aspect ratio holes. Argon ion beams oriented 85° from the surface normal formed severe striations on the blanket fluorocarbon film surface, despite the low roughness of the SiO2 film surface. A thicker fluorocarbon film was observed in regions with striations than deeper regions with smooth sidewalls. The striations formed on the fluorocarbon films at the sidewalls of high aspect ratio holes and transferred to the dielectric films laterally as the hole diameters increased. In addition, as etching proceeded, striations began to form at the deeper regions, depending on the aspect ratios.

Mass spectroscopic measurement of time-varying ion composition in a pulse-modulated Ar/C4F8/O2 dual-frequency capacitively coupled plasma

“…The technique for creating HAR structures is the reactive ion etching (RIE) process. However, various issues such as insufficient mask selectivity, 2) shape bowing, 3) bending, 4) striation, 5) and aspect ratio-dependent etching rate reduction by RIE-lag 6) frequently occur in this process. Some of these phenomena are caused by charging-up on the sidewall of the hole 7,8) due to the angular broadening of incident-positive ions on the wafer.…”

Progress report on high aspect ratio patterning for memory devices

“…Experimental results confirmed that mask morphology plays a role in hole shape, but a literature survey suggests that stochastic ion scattering can also affect the hole shape. [12][13][14][15]24) Figure 10 shows a simplified HAR etch simulation where the hard mask shape stays constant. That is, the hard mask is perfectly circular, and hard mask shadowing species should not contribute to any hole distortions.…”

Topographically-selective atomic layer etching of SiO2 using radical fluorination of the surface followed by Ar ion bombardment

“…16) Silicon dioxide (SiO 2 ) is a key material for gate oxides, interlayer dielectrics, and spacer applications. 6,17) Considering its use in next-generation devices and the increasing complexity of design structures, plasma-assisted ALE processes for SiO 2 are continuously investigated for various targets. Among them, the periodic exposure of SiO 2 to C 4 F 8 /Ar plasma followed by low energy argon (Ar) ion bombardment that leads to a few nanometer etching of SiO 2 per cycle is popularly demonstrated by the group of Oehrlein.…”