Simultaneous Etching and Deposition Processes during the Etching of Silicon with a Cl₂/O₂/Ar Inductively Coupled Plasma

Abstract

In this article, surface processes occurring during the etching of Si with a Cl2/O2/Ar plasma are investigated by means of experiments and modeling. Cl2‐based plasmas are commonly used to etch silicon, while a small fraction of O2 is added to protect the sidewalls from lateral etching during the shallow trench isolation process. When the oxygen fraction exceeds a critical value, the wafer surface process changes from an etching regime to a deposition regime, drastically reducing the etch rate. This effect is commonly referred to as the etch stop phenomenon. To gain better understanding of this mechanism, the oxygen fraction is varied in the gas mixture and special attention is paid to the effects of oxygen and of the redeposition of non‐volatile etched species on the overall etch/deposition process. It is found that, when the O2 flow is increased, the etch process changes from successful etching to the formation of a rough surface, and eventually to the actual growth of an oxide layer which completely blocks the etching of the underlying Si. The size of this etch stop island was found to increase as a function of oxygen flow, while its thickness was dependent on the amount of Si etched. This suggests that the growth of the oxide layer mainly depends on the redeposition of non‐volatile etch products. The abrupt change in the etch rate as a function of oxygen fraction was not found back in the oxygen content of the plasma, suggesting the competitive nature between oxidation and chlorination at the wafer. Finally, the wafer and reactor wall compositions were investigated by modeling and it was found that the surface rapidly consisted mainly of SiO2 when the O2 flow was increased above about 15 sccm.

Concurrent effects of wafer temperature and oxygen fraction on cryogenic silicon etching with SF6/O2 plasmas

“…After this critical temperature the SF 6 gas starts to condense on the wafer (i.e., it forms a liquid layer on the surface), effectively limiting the etch rate to a value close to zero (i.e., denoted in Figure as “X”). This phenomenon, where the etch rate abruptly drops to a value near zero, either caused by a too low wafer temperature or by too much oxygen in the SF 6 /O 2 mixture, is called the “etch stop” phenomenon …”

Feature profile evolution during shallow trench isolation etching in chlorine-based plasmas. III. The effect of oxygen addition

“…6 Since ions are directional and dominate the etching process for chlorine-based plasmas, desirable anisotropic etch profiles can be achieved. This is consistent with the experimental observation reported by Guha et al 8 Tinck et al [9][10][11] studied the gas phase chemistry, surface kinetics, and plasma-surface interactions using numerical simulation in a series of publications. Due to its process importance, Cl 2 /O 2 plasma has been widely studied.…”

Science-based, data-driven developments in plasma processing for material synthesis and device-integration technologies

“…In plasma etching, multiscale models have been developed to simulate both the gas-phase reactions and transportation phenomena in Cl 2 /Ar plasma chambers, as reported by Osano and Ono, [154][155][156][157][158] Kushner et al, [159][160][161][162] Chang and Sawin, [163][164][165] Graves, et al, 166,167) Hamaguchi et al, [168][169][170] and Tinck and Bogaerts. [171][172][173] Kuboi et al modeled the surface reactions and plasmainduced damage on SiO 2 and Si 3 N 4 with fluorocarbon plasma using the voxel-slab model developed by Kuboi. [174][175][176][177][178] Vanraes reviewed the standardized computational methods to be used for multiscale modeling in a case study of Si and SiO 2 etching by fluorocarbon plasmas.…”