AVS 52nd International Symposium
    Plasma Science and Technology Monday Sessions
       Session PS-MoP

Paper PS-MoP10
Effects of Non-Volatility of Etch Products on Surface Roughness during Etching of Advanced Gate Stack Materials

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Plasma Science and Technology Poster Session
Presenter: W.S. Hwang, National University of Singapore
Authors: W.S. Hwang, National University of Singapore
W.J. Yoo, National University of Singapore
Correspondent: Click to Email
As device dimensions continue to shrink, it becomes very crucial to understand evolution of surface roughness of device structures during etching. Until now, the mechanism on roughness evolution of Si surface from which volatile etch products are generated has been studied by various researchers. However, surface properties of new conducting materials such as TaN, TiN, HfN, and IrO@sub 2@ have rarely reported, although several reports on etching properties of advanced gate electrodes have been reported. In this work, we investigate the effects of the plasma parameters of ion energy (E), ion current density (J@sub i@) and ratio of ion flux over neutral flux (J@super +@ / J@sub n@) on the evolution of surface properties of these materials during etching. Etch rates of all samples are seen to obey the following empirical relation of ER(t)=C@sub 1@ E J@sub i@ (J@super +@/J@sub n@) (t) where ER is etch rate. The same approach was made to understand the evolution of surface roughness. It was found that surface roughness and etch rate are inversely related each other when volatile byproducts are formed, as shown in the following relation of @sigma@(t)=C@sub 2@ 1/E 1/J@sub i@ (J@sub n@ / J@super +@) t where @sigma@ is roughness value, in that surface roughness is proportional to pressure but inversely proportional to bias voltage. This relation implies that anisotropic profile can be attained without sacrificing the surface roughness. On the other hand, it is found that surface roughness and etch rate are proportional each other when non-volatile byproducts are formed, as expressed in the relation of @sigma@(t)=C@sub 3@ E J@sub i@ (J@super +@ / J@sub n@) t. That is, the formation of nonvolatile residues promotes surface roughening during ion induced chemical etching. In addition, results show that the average lateral distance between peak to peak increases with increasing surface roughness due to the redeposition and agglomeration of nonvolatile byproducts.