Paper PS-TuP17
Reaction Mechanisms and Profile Evolution for HfO₂ High-K Gate-stack Etching: Integrated Reactor and Feature Scale Modeling*

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

To minimize leakage currents resulting from the thinning of the insulator of the gate-stack of field effect transistors, high-k metal oxides, and HfO₂ in particular, are being implemented as a replacement for SiO₂. To speed the rate of processing, it is desirable to etch the gate stack (e.g., metal gate, anti-reflection layers, dielectric) in a single process while having selectivity to the underlying Si. Plasma etching using Ar/BCl₃/Cl₂ mixtures have been shown to effectively etch HfO₂ while having a good selectivity with respect to Si. In this talk, we discuss results from integrated reactor and feature scale modeling of gate stack etching in chlorine plasmas. The stack consists of an erodible photoresist mask, metal gate and HfO₂ with underlying Si (and possibly anti-reflection layers). Reactant fluxes were obtained from reactor scale modeling of inductively and capacitively coupled plasma tools using the Hybrid Plasma Equipment Model. Surface reaction mechanisms were developed using its Surface Kinetics Module. The mechanisms were implemented in the Monte Carlo Feature Profile Model with which etch profiles are predicted. We found that BCl_x species produced by electron impact in the plasma react with HfO₂ which, under ion impact, form volatile etch products such as B_xOCl_y and HfCl_x. Selectivity to Si is achieved by boron creating Si-B bonding as a precursor to the deposition of BCl_x polymer, which slows the etch rate relative to HfO₂. The low ion energies required to achieve this selectivity then challenge one to obtain highly anisotropic profiles in the metal gate portion of the stack. Validation was performed with data from the literature. Results will be discussed from parametric studies of process variables (e.g., gas mixture, power, bias) on etch rate and profile.

*Work supported by the Semiconductor Research Corp.