UCLA

In this work, a comprehensive framework for predicting etching behavior is developed using the test case of hafnium lanthanate (Hf_xLa_yO_z) in Cl₂/BCl₃ chemistry, starting from detailed thermodynamic analysis in the form of volatility diagrams. Through these calculations, it was predicted that at typical plasma reactor operating pressures, the reactions of molecular Cl₂ and Cl radicals with La₂O₃ and HfO₂ could generate sufficiently high partial pressures of O_xCl_y for measurable material removal to occur.

The etch rate of Hf_0.25La_0.12O_0.63 as a function of ion energy was characterized in situ using a quartz crystal microbalance. The etch rate data was found to exhibit a dual ion energy dependence with a maximum etch rate of ~27 Å/min at E_ion = 175 eV. The overall etch rate was found to be approximately half that of a pure HfO₂ film etched at the same conditions, due to the formation of non-volatile LaCl_x compounds.

QMS measurements of HfLaO in Cl₂ chemistry showed LaOCl and LaCl as the primary La-containing etch products. XPS analysis of pure La₂O₃ films provided further evidence of this hypothesis, showing significant Cl retention (~10%) compared to HfLaO and also revealing the presence of Cl-O-La bonding. A kinetics-based bulk scale (TML) model was fit to the aforementioned experimental data and good agreement was shown between the TML model's simulated results and etch rate data. An additional degree of validation was provided through a comparison of the model's predicted composition of the surface mixing layer and the XPS-measured film compositions after plasma exposure.

The final validation of this approach was to assess the fitted kinetic parameters for complex oxide etching in Cl-based chemistry (such as reaction rate coefficients, threshold energies and sticking probabilities) at feature scale levels. The results from the TML model were coupled to a Monte Carlo based feature profile simulator and used to predict the variation of the etched feature profiles of Hf_0.25La_0.12O_0.63 films for varying aspect ratios (1.5, 3 and 6) and ion energies (75, 100 and 175 eV). In order to compare to experimental results, features of varying aspect ratio were achieved using an e-beam tool to pattern a ZEP520A photoresist mask on HfLaO followed by etching in Cl₂ . Good agreement was achieved with the etched profile at 100 eV and AR = 5. As a test of the model's ability to handle variations in gas chemistry with a material system besides that of high-k dielectrics, this methodology was also applied to the shallow trench isolation process (Si etching in Cl₂2/O₂ chemistry). The model showed good fitting of the major process parameters (etch rate, etch product ratios and surface composition) and showed an ability to predict the profile variation with 0, 2, 6 and 8% oxygen addition to a pure Cl₂ plasma for the etching of Si.