Paper PS1-ThM9
Control of Selectivity and Profile for HfO₂ Etching in BCl₃-Containing Plasmas

Thursday, November 12, 2009, 10:40 am, Room A1

Selective etching of high dielectric constant (high-k) films over the underlying Si (and/or SiO₂) is indispensable in the fabrication of high-k gate stacks. In practice, the selectivity is usually not so high, owing to highly volatile halogen compounds of Si, and also to strong metal-oxygen bonds of high-k dielectrics and less volatile metal-halogen compounds. Profile control is also indispensable during etching of high-k: anisotropic profiles are required for high-k, and also profiles of gate electrodes on high-k are required to remain unchanged. This paper presents the control of selectivity and profile for high-k HfO₂ etching under low ion-energy conditions in BCl₃-containing plasmas, with emphasis being placed on a better understanding of the etching mechanisms concerned. Experiments were performed in both electron cyclotron resonance (ECR) and inductively coupled (ICP) plasmas, by varying pressure, additive concentration of O₂, Cl₂, and Ar, rf bias power, and also substrate temperature. Samples for etching were blanket HfO₂ and TaN films, and separate Si and SiO₂ substrates were also employed for reference. Samples of TaN/HfO₂ stack as well as separate HfO₂ and TaN masked with line-and-space patterns were also employed to examine the etched profile. We examined substrate surfaces by x-ray photoelectron spectroscopy, and investigated reactant and product species in the plasma during etching by optical emission spectroscopy and quadrupole mass spectrometry. A transition from deposition to etching regimes was found to be caused on all substrate surfaces, by varying pressure, by using additives such as O₂ and Cl₂, and by increasing rf bias power. In practice, surface inhibitor deposition was less significant for HfO₂ than for Si, SiO₂, and TaN; and the threshold bias power or ion energy for HfO₂ etching was in the range 10-20 eV, while the threshold was more than 20 eV for the other. A difference in pressure, additive concentration, and bias power for the transition between HfO₂ and Si (and/or SiO₂) gave rise to high or infinite selectivity of high-k over Si (and/or SiO₂), together with vertical high-k profiles. The difference for the transition between HfO₂ and TaN also gave no significant distortion of TaN profiles during HfO₂ etching, owing to passivation layers deposited on TaN sidewalls. Plasma and surface diagnostics indicated that inhibitor species for deposition are primarily boron-chloride polymers produced in the plasma, whose concentration largely depends on pressure, additive concentration, and plasma reactor (ECR and ICP), which in turn leads to a marked difference in etching characteristics.