Tadamitsu Kanekiyo

Effects of Mask and Necking Deformation on Bowing and Twisting in High-Aspect-Ratio Contact Hole Etching

The effects of mask characteristics on high-aspect-ratio contact hole (HARC) etching profiles were investigated. The evaluation of etching profiles produced with different taper angle masks confirmed that the bowing amount and mask selectivity worsened with decreasing mask taper angle. The relationship between mask taper angle and distribution of scattered ion flux on the sidewall of a tapered mask was calculated. The scattered ion flux was heavily concentrated in the upper part of the sidewall in the case of a tapered mask, and this was considered to be the main cause of the bowing formation. Direct observation of an etched sidewall by atomic force microscopy (AFM) revealed that the roughness of the necking was strongly related to the roughness of the bottom part of the etched sidewall. To evaluate the dependence of twisting on nonuniform necking, the incident ion flux in a circular hole was calculated. As a result, in the case of nonaxisymmetric necking, an imbalance of ion flux in the bottom of the hole appeared and broke the etching symmetry in the bottom part of the hole, causing twisting. In addition, the probability of twisting was found to increase with increasing necking growth rate irrespective of mask electrification. Therefore, mask deformation and nonuniform necking in the upper part of the sidewall during HARC etching are considered the main factors causing bottom degradation. Accordingly, a vertical and nondeformed mask is very important for a smaller critical dimension (CD) and HARC etching.

A Novel Plasma Etching Tool with RF-Biased Faraday-Shield Technology: Chamber Surface Reaction Control in the Etching of Nonvolatile Materials

A novel electro-magnetically coupled plasma (EMCP) etching tool for nonvolatile materials has been developed. The EMCP etcher is based on inductively coupled plasma generation and has a function for controlling surface reactions by supplying RF bias to a Faraday shield which covers a ceramic discharge dome. We investigated plasma controllability and chamber surface reaction controllability of the EMCP etcher and found that the RF-biased Faraday shield effectively keeps the internal surface of the dome clean in the etching processes of nonvolatile materials. Because of this feature, the EMCP etcher can be applied to the etching processes of various nonvolatile materials such as Pt, Ru, Ir, NiFe, Au, Mo, Ta, Al2O3, HfO2, ZrO2, and indium tin oxide (ITO).

Thermal cyclic etching of silicon nitride using formation and desorption of ammonium fluorosilicate

Novel selective cyclic etching of SiN over SiO2 via the formation and desorption of ammonium fluorosilicate was developed. The formation of ammonium fluorosilicate was observed using X-ray photoelectron spectroscopy after hydrofluorocarbon-based radical exposure. Etching of SiN was observed after ammonium fluorosilicate was removed by thermal annealing. Cyclic etching tests were carried out by repeated radical exposure and thermal annealing. The etching depth increased on increasing the number of cycles. It was found that the cyclic etching is self-limiting because the etching depth does not depend on the radical exposure time but on the number of cycles.

Impact of low-potential plasma on long-term stability in low-k via etching

We have developed an ESC (electrostatic chuck) damage-less plasma-cleaning technique for a UHF-ECR dielectric etching apparatus. The degradation of the surface of the ESC in wafer-less plasma-cleaning was suppressed by lowering the ion energy incident on the ESC surface. We have confirmed long-term stability of the etching performance and a long MTBC (mean time between wet cleaning) of over 400 hrs in low-k via etching. We have also estimated that the ESC lifetime was over 12,000 hr.

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

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 masks 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 ...