Bottom profile degradation mechanism in high aspect ratio feature etching based on pattern transfer observation

Abstract

The hypothetical mechanism of bottom profile degradation, such as distortion and twisting in high aspect ratio feature etching, was verified based on the pattern transfer observation of etched pattern. The authors mainly focused on trench pattern sample to make the investigation easier, that is, direct observation of the sidewall roughness, using an atomic force microscope, as well as analysis of the depth dependence of pattern deformation in high aspect ratio trench etching. Using Fourier transformation analysis for the trench sidewall roughness, it was found that lower spatial frequency component of the mask's sidewall roughness is amplified at the bottom region of the trench and that higher spatial frequency component of over 10 μm−1 disappears. However, the higher spatial frequency component is transferred directly to the upper sidewall of the trench. The observation of the pattern deformation profile, as a function of etch depth, revealed that the ratio of line width roughness to line edge roughness decreases linearly with increasing etch depth. This indicates that the deformation mode changes from “roughness” to “wiggling” as a function of etch depth. Also, the twisting depth, as determined by the cross section images, was found to be shallower when using lower wafer bias etching condition. Based upon these results, and previously proposed mechanisms, the authors conclude that the mask deformation should be considered as one of the root causes when bottom deformation occurs. This is due to the imbalance between ion flux and deposition amount created by mask asymmetric profile. In addition, the etching profile and etching direction should be affected by this phenomenon under polymer-rich process condition. In order to verify our assumed mechanism, the relationship between mask deformation degree, and bottom distortion and twisting amount was also evaluated by using different pitch hole patterns. As a result, the authors determined that the distortion is improved by 22% and the twisting is improved by 20% when the mask deformation is reduced by 50% with using a wider pitch pattern.

High-aspect-ratio amorphous carbon mask etch profile control through plasma and surface chemistry optimization

“…At suppressed isotropic etching (Figure 5a, the same condition as Figure 4b), profile twisting / roughness deteriorates toward the bottom of the feature. Similar trends of depth dependence have also been observed by Negishi et al [19]. In addition, at the same depth, the roughness is improved by longer etching time.…”

Plasma etching of high aspect ratio features in SiO2 using Ar/C4F8/O2 mixtures: A computational investigation

“…If E th and E r have nonzero values, the reaction has an energy dependent probability [Eq. (1)]. When the probability of reaction is less than unity, the remaining probability is allocated to nonreactive reflection.…”

“…Plasma etching of high aspect ratio (HAR) features in SiO 2 and Si 3 N 4 with aspect ratios (ARs) exceeding 100 is being challenged to maintain critical dimensions (CDs) and achieve high selectivity while etching stacks of materials for high capacity three-dimensional memory. [1][2][3] Controlling and mitigating phenomena such as aspect ratio dependent etching (ARDE), bowing, and contact edge roughness (CER) are necessary to obtain anisotropic features and better critical dimension uniformity (CDU). ARDE refers to a decrease in the etch rate for features having larger ARs for otherwise identical conditions.…”

“…35 A model addressing pattern deformation and experimental measurements by atomic force microscopy indicated that the ratio of line width roughness to line edge roughness decreases with increasing etch depth, and the depth at which twisting occurs is shallower for a lower bias power. 1 In this paper, results are discussed from integrated reactor and feature scale models for investigating the etching of HAR features in SiO 2 using a tri-frequency capacitively coupled plasma (TF-CCP) sustained in Ar/C 4 F 8 /O 2 mixtures at several tens of mTorr. Reactor scale modeling was performed using the two-dimensional hybrid plasma equipment model (HPEM), from which the fluxes, energy, and angular distributions of ions and neutrals to the wafer surface were obtained.…”

Ion and Radical Characteristics (Mass/Energy Distribution) of a Capacitively Coupled Plasma Source Using Plasma Process Gases (CxFy)

“…Furthermore, the RF bias power applied to substrates generates a self-bias voltage and affects the energy of ions entering the substrate. Recently, the high aspect ratio contact (HARC) etching process has increasingly gained importance as an etching process [8][9][10]. The high ionic energy required in the HARC etching process is generated according to the RF bias power.…”