| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS-WeA |
| Session: | Atomic Layer Etching and Low Damage Processing |
| Presenter: | Shuichi Noda, Tohoku University, Japan |
| Authors: | E.T. Lee, Tohoku University, Japan S. Noda, Tohoku University, Japan W. Mizubayashi, AIST K. Endo, AiST S. Samukawa, Tohoku University, Japan |
| Correspondent: | Click to Email |
Germanium Fin-FET has becoming a promising candidates for highly scaled CMOS FETs to solve the limitation of device scaling of Si CMOS FET due to large carrier mobility of Ge itself. However, it seems that the etching mechanisms of Ge and optimization of etching method have not investigated deeply in spite of its importance forming basic channel structures in FET devices. Since we have already succeeded to apply a neutral beam etching (NBE) method to damage-free Si Fin-FET fabrication process and shown excellent device performances1), much more advantages in the low-damage NBE can be expected for Ge fin etching because thermal annealing is difficult due to a heat resisting property of Ge.
The NBE characteristics of Ge Fin were evaluated using pure Cl2 gas chemistry which is the same for the Si Fin etching and compared results each other. The NBE system consists of an inductive coupled plasma (ICP) source and a carbon aperture plate where energetic negative ions are effectively converted to the neutral beam utilizing a pulse time modulated plasma. Ge Fin structure were etched with TEOS-CVD SiO2 hard masks which were patterned by an EB lithography and a conventional ICP RIE. The sample substrate was set on the cooled stage at -15°C. The Ge profile was optimized by adjusting the beam energy which was controlled by changing the RF bias power to the carbon aperture.
The Ge Fin was etched at the etch rate of more than three times larger than Si. However, the large bottom tails were observed with different profile from the Si Fin structure. The etch rate difference can be explained due to the different etch yield and chlorination density on the surfaces2). The large bottom tails of Ge Fin structure are considered to be caused by lower evaporation pressure of GeCl4 than that of SiCl4. The profile optimization was made by controlling RF bias power on the aperture plate. The bottom tail was reduced with increasing the bias power. The side-etching under the SiO2 hard mask hardly increased during long over etch period. Conversely, the etch rate of Ge was almost constant regardless of the RF bias power. This results indicate that the etching reaction is limited by Cl supply, which chlorinates adsorption site on the Ge surface. The lateral etching is limited because the Cl radical density is low and the samples are cooled down to -15°C. The bottom tails seemed to be reduced in according to beam divergence narrowing. High magnification TEM images showed extremely smooth side wall surface in the substantially atomic revel.
1) K. Endo et al., IEDM Tech. Dig. (2005) pp. 840-843. 2)J-Y Choe, et al., J. Vac. Sci. Technol. A, 16, 3266 (1998).