IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Plasma Science Tuesday Sessions
       Session PS1-TuA

Paper PS1-TuA8
Characterization of Hydrofluorocarbon Reactants for Selective Silicon Nitride Plasma Etch Applications

Tuesday, October 30, 2001, 4:20 pm, Room 103

Session: Dielectric Etch I
Presenter: E.A. Hudson, Lam Research Corp.
Authors: E.A. Hudson, Lam Research Corp.
H. Zhu, Lam Research Corp.
D. Pirkle, Lam Research Corp.
J. Luque, Lam Research Corp.
J.P. Booth, Ecole Polytechnique, France
Correspondent: Click to Email
Certain dielectric etch applications require the removal of silicon nitride films with high selectivity to silicon dioxide. An important example is found in dual-damascene integration schemes using organic low-k dielectric materials and nitride diffusion barriers. At the completion of the via etch, the nitride at the via bottom must be removed without penetrating the oxide hardmask which protects the top surface of the low-k dielectric film. Nitride-to-oxide etch rate selectivities of >10:1 are desirable. To understand how this selectivity may be achieved, and to compare the effects of different hydrofluorocarbon feed gases, a series of processes have been evaluated using a dual-frequency, capacitively-coupled, dielectric etch system. The feed gases for the processes are Ar and O@sub 2@, combined with a hydrofluorocarbon from the series CH@sub x@F@sub y@, where x ranges from 0 to 4, and y=4-x. Selectivity trends were determined from blanket nitride and oxide etch rates. Trends in the plasma chemistry were characterized using broad-band UV absorption spectroscopy. CF, CF@sub 2@, and CH@sub 3@ densities were measured using absorption bands in the 200-270nm range. This method directly measures absolute densities of ground state radicals in the plasma. Best selectivity results were obtained using CH@sub 3@F, which produced selectivities >20:1 for blanket films and for patterned wafers. The CF@sub 2@ density was found to be relatively high for processes using CHF@sub 3@, and very low for processes using CH@sub 3@F. In contrast, the CF density followed a more linear trend through the hydrofluorocarbon series. Also the production of CH@sub 3@ radical from CH@sub 3@F reactant was much less than from CH@sub 4@ reactant, suggesting that the direct removal of atomic F from CH@sub 3@F is not a favorable dissociation pathway. These results and others are interpreted to understand the mechanism for high nitride-to-oxide selectivity.