AVS 45th International Symposium
    Plasma Science and Technology Division Monday Sessions
       Session PS-MoM

Paper PS-MoM10
Effect of Residual Chlorine (Cl) Atoms for Notching Formation in a High Density Plasma Reactor

Monday, November 2, 1998, 11:20 am, Room 318/319/320

Session: Feature Evolution
Presenter: H.C. Lee, IMEC vzw, Belgium
Authors: H.C. Lee, IMEC vzw, Belgium
Y.-B. Kim, IMEC vzw, Belgium
S. Beckx, IMEC vzw, Belgium
S. Vanhaelemeersch, IMEC vzw, Belgium
Correspondent: email address not available
Notching at the bottom corner of the etched polysilicon feature has been known as charging problem due to the electron shading effect,@footnote 1@ especially at the outermost line of the nested lines. Most of the experiments@footnote 2@ and simulations@footnote 3@ were conducted in a high density plasma reactor using Cl@sub 2@ chemistry. However, notching still occurs in the RIE reactors with symmetrical shape. We believe that notching can be formed due to the combination of plasma charging and preferable reaction between Si and Cl atoms. In this study, notching was investigated in terms of polymerization and chemical reaction between Si and Cl or Br atoms in a TCP 9400 high density plasma reactor. Mixed chemistry of HBr/Cl@sub 2@ and HBr/He-O@sub 2@ was used as a main etch step and over etch step respectively. From the TEM inspection of etched polysilicon profiles, the thickness of polymer which deposited on the sidewall decreases along down the sidewall. Much thicker polymer was detected at the top portion of the sidewall than the ones at the bottom. Thus, bottom sidewall exposed to the plasma without the protection layer against Cl atoms. Sidewall polymer was analyzed by angle resolved XPS in order to understand the polymer composition. TOA (Take of Angle) was varied from 15° to 90° which is normal to the horizontal gate oxide surface. Cl2p peaks were detected from the TOA35° to TOA65° which means most of Cl bonds are located at the sidewall of the feature. Si was also detected in the form of SiO@sub 2@ at the same TOA regime. At the TOA90°, however, intensity of Cl2p was very low, which explains that no Cl residues are on the etched gate oxide surface. It can be concluded that a lot of Cl atoms still remain on the sidewall even if it is not used during the over etch. In the meantime, Br3d peaks were detected whole range of TOA. With very low reaction probability of Br to Si, Br in the sidewall polymer also works as a protection layer. Consequently, notching has not been found in one step etching using HBr/He-O@sub 2@. Without the protection layer, 50nm thick SiO@sub 2@ was used as a mask material instead of photoresist, notching was increased dramatically. Residual Cl atoms play a major role in notching formation with combination of very thin polymer layer at the bottom corner of the features. @FootnoteText@ @footnote 1@K. Hashimoto: JJAP, 32, P6109, 1993. @footnote 2@T. Nozawa et al.: JJAP, Vol. 34, P2107, 1995. @footnote 3@G.S. Hwang and K.P. Giapis, Proceeding of P2ID, P63, 1997.