Multilevel Modeling of Thin High-k Dielectric Film Growth
Goals and Requirements
High integration of components in microelectronics demand the replacement of SiO2 used as a gate dielectric material with materials with higher k values. Unfortunately, unlike the ideal «Si/SiO2» interface, «Si/high-k» interfaces possess more bad properties, therefore the fundamental understanding of the chemistry and kinetics of interface processes is very important for optimizing the conditions of the development of high-quality interfaces. Zirconia and hafnia films were considered as candidates for the replacement of SiO2, and atomic layer deposition (ALD) was taken as technique for film deposition on a silicon substrate. Experimental studies have shown that the properties of the growing film, such as impurity number density, crystallinity, growth rate, and others, strongly depend on various external and internal parameters. Therefore, the development of an integrated approach is required for the description of the film growth mechanism. This approach should predict film properties based on the characteristics of atomic processes.
Kintech Solution
Kintech Lab by request of Digital DNA Laboratories, MOTOROLA (now FreescaleTM) has performed a multilevel modeling of the macroscopic processes of ZrO2 и HfO2 film deposition based on calculations of gas-surface elementary processes. The family of Kintech Lab software Chemical Workbench, Khimera, and MD-kMC was used. Properties of elementary processes and reactions were calculated using state-of-the-art ab initio methods. The kinetics of film growth was investigated in the framework of two approaches, a surface site formalism and a kinetic Monte Carlo method with dynamic relaxation (MD-kMC). The last method allows not only the description of the growth kinetics but also the determination of the structure of the grown film and its phase composition. As a result, the best external parameters (temperature, pressure, mass flow rate) were predicted, which ensure the highest rate of film growth and the lowest chlorine contamination and film roughness.
Procedure of Mechanism Construction and Verification using Chemical Workbench®, Khimera® and MD-kMC®
Quantum chemical & microkinetic analysis of a gas-surface reaction and development of a film growth mechanism
The calculated energies and structures of reagents, transition states and products were used in statistical theory to calculate rate constants of gas-surface elementary reactions using special models with relaxation of the substrate and freezing some degrees of freedom on the surface. The rate constants obtained were used for the development of a film growth mechanism.
- Reaction path
- Surface structure formed
Surface site formalism simulation
The results of film growth modeling on the basis of the proposed mechanism using Chemical Workbench agree with the available experimental data. The modeling permits the determination of the optimum conditions of film growth.
- Growth rate at different temperatures
- Film mass change in one cycle
Kinetic Monte Carlo simulation
The Kinetic Monte Carlo model of film growth based on the proposed mechanism describes the structure and phase composition of the growing film and the observed temperature dependence of the residual chlorine concentration in the film subject to the steric factor of the chemisorbed surface groups and the adsorbed MCl4 (M = Zr, Hf) molecules.
- Structure of ZrO2 film grown on Si
- Residual Cl in the film
Thus, the multilevel approach proposed by Kintech Lab allows the construction of heterogeneous mechanisms of the growth of new phase, the determination of the optimum conditions of phase growth, and the prediction of the structural parameters of the grown phase.
The details of mechanism see in M. Deminsky еt al. Surface Science 549 (2004) 67–86.
Presentation on ALD thin film growth modeling
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