| AVS 56th International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS2+MN-WeA |
| Session: | High Aspect Ratio and Deep Etching for 3D Integration and Memory |
| Presenter: | H. Mochiki, Tokyo Electron AT Ltd., Japan |
| Authors: | H. Mochiki, Tokyo Electron AT Ltd., Japan K. Yatsuda, Tokyo Electron Ltd., Japan S. Okamoto, Tokyo Electron AT Ltd., Japan F. Inoue, Tokyo Electron AT Ltd., Japan |
| Correspondent: | Click to Email |
It is required to fabricate capacitors with aspect ratio of from 40:1 to 60:1 for DRAM at hp 3x nm and beyond generation, and etching such ultra high aspect cylindrical shapes without distortion and/or twisting is the most difficult challenge. Recently, it has been reported that distortion and twisting were caused by electron shading effects, electrical potential difference between the top and bottom of dielectric during plasma etching. In this paper, we report how distortion and twisting are enhanced, and how they can be minimized.
First of all, electron shading effects are results of electrostatic charge on the surface of etched dielectric material – silicon dioxide, and organic capacitor mask is negatively charged where silicon dioxide surface is positively charged. At these generations, DRAM devices are so largely scaled that their capacitors need to be fabricated very close to each other. Consequently, incident positively charged ions in a cylinder, accelerated by plasma sheath, receive repulsive force from not only the cylinder surface itself but also neighboring cylinder surfaces. We confirmed that grad of distortion and twisting changed by altering the layout of capacitors.
On the other hand, we found that distortion and twisting could also be generated from the very beginning of etching at the low aspect ratio portion by observing the top view of a cylinder every 100 nm-deep from the wafer surface. Moreover, we affirmed that distortion strongly correlated with capacitor etch mask profile when varying it on purpose by changing mask etch conditions. Thus, we clarified that another enhancement mechanism of distortion existed apart from electron shading effects.
Therefore, there are several enhancement mechanisms of distortion and twisting, and it is necessary to address each solution. We divided the enhancement mechanisms of distortion and twisting into two modes, which are generated at low and high aspect ratio, and examined their solutions from the etching point of view, respectively. We conclude that the optimization of capacitor etch mask profile was the most effective solution at the low aspect ratio mode, and higher dissociation plasma with relatively higher plasma density and superimposed DC on CCP (capacitively coupled plasma) improved distortion and twisting at the high aspect ratio mode.