Application of Parametric Modeling in Atomic Layer Deposition

Atomic Layer Deposition (ALD) is sequential and conformal process that provides precise thickness control due to its self-limiting nature even in high aspect ratio structures. The exponential growth in the use of ALD is due the availability of hundreds of precursor chemistries for diverse technological applications beyond just semiconductors and microelectronics. However, one of recurring challenges is the problem of results disparity, and errors that underline the causes of disparity, primarily may be due to lack of consistency in process optimization and reproducibility. In this research, a Design of Experiment (DoE) approach is adopted for parametric optimization for synthesis of Al 2 O 3 thin films using ALD. The objective of this work is to adopt DoE for reproducible ALD synthesis processes within statistical reliability. Briefly, the precursors used for Al 2 O 3 ALD (Ultratech Veeco Thermal ALD) were Trimethylaluminum (TMA) and H 2 O with Ozone. The effect of four parameters, namely pulse duration of TMA and water, number of cycles, and temperature were evaluated for the response parameter of Al 2 O 3 thickness on Si with 300 nm of SiO 2 . E-Chip DoE software was chosen for data modeling. E-Chip considers multivariate analysis to provide the parametric relationship for Analysis of Variances (ANOVA) and predictive surface response analysis, thus eliminating the need for extensive process optimization experiments that are required for full factorial design. Initially, screening experiments were conducted to determine the levels of input parameters. The pulse duration for TMA and H 2 O were 0.01-0.02 sec, the number of cycles were varied between 50 and 100, the temperature range was 100-200 0 C. For each sample, five thickness and roughness readings were measured on an ex-situ ellipsometer and Atomic Force Microscope (AFM). The stoichiometry of Al 2 O 3 thin films were evaluated using XPS. The data analysis reveals that the influential parameters are number of cycles, pulse duration, and temperature in the order of their significance. The direct relationship between number of cycles and Al 2 O 3 thickness infers that flux available is effectively used for layer growth. The consistency of layer thickness is related not just to the conformality but also to the adsorption of reactive species effectively. Uneven pulse duration also contributes to the linear growth of layer thickness, which supports the effectiveness of reactive species saturation and purgin