Comparison of surface morphology and structure of Al2O3 thin films deposited by sol-gel and ALD methods

Abstract

Purpose: of this research was examination Al2O3 thin film obtained with two different method, by sol-gel and ALD, and comparison the surface morphology and structure of deposited thin films. The films deposited on the monocrystalline silicon were tested for their suitability for use in silicon solar cells. Design/methodology/approach: Trimethylaluminum (TMA) was used as a precursor of Al2O3 which is reacted with water enabled the deposition of thin films by ALD method. By the sol-gel method the aluminium tri-sec butoxide (TBA) was used as a precursor to obtain Al2O3 thin films. The aluminium oxide solutions prepared by sol-gel method were deposited by spin coating technique. Examination of the structure and morphology of the surface of the Al2O3 thin films deposited by sol gel and ALD method were performed using atomic force microscope and transmission electron microscope. For the analysis of surface topography deposited thin films atomic force microscope XE-100 from Park Systems was used. Qualitative analysis of the chemical composition was carried out using an energy dispersion spectrometer (EDS). The detailed structural studies were conducted using a Titan 80-300 scanning-transmission electron microscope S/TEM from the FEI Company. Detailed research on the structure of the deposited Al2O3 thin films were performed. The HRTEM images and diffraction SAED were recorded. Findings: The small atoms clusters of a width less than 20 nm were documented. The thin film deposited by spin-coating technique on silicon substrate with 3000 rpm is characterized by RMS and Ra values of, respectively, 0.26 and 0.2 nm. RMS was defined as rough mean square parameter and Ra was defined as the arithmetic mean deviation of the profile from the mean line. An analysis of the frequency histograms of irregularities of the thin film obtained by the spin coating on a silicon substrate at 3000 rpm shows that a large part of them does not exceed 0.5 nm, and the single irregularities reach up to 2.2 nm. When comparing the AFM pictures with the thin films deposited by ALD technique and spin-coating it has been found that the thin films obtained on polished silicon substrates are similar in morphology. The EDS spectra shows the characteristic for oxygen (0.525 keV) and aluminum (1.486 keV) reflections derived from the thin film. In Al2O3 thin film obtained by ALD method the occurrence of α phase of aluminum oxide with a hexagonal structure was identified, just like in the case of thin film deposited by sol-gel. Practical implications: Known aluminium oxide properties and the possibility of obtaining a uniform thin layer show that it can be good material for different application. Precise description of the properties of Al2O3 is very important, since this material is one of the most frequently used in catalyst industry, in medicine, electronics and photovoltaics, as well as a protective layer. The Al2O3 thin film can act as passive and anti-reflective layer simultaneously in silicon solar cell. Using this thin film can simplify the technology of manufacturing silicon solar cells Originality/value: The paper presents researches of aluminium oxide thin films deposited by sol-gel and atomic layer deposition method on monocrystalline silicon.