A Study on the Al Doping Effect of HfO2 Thin Films Using PEALD

A memory semiconductor, a component that stores information, is an essential element in all electronic devices. There are many different types of memory semiconductors. Dynamic Random Access Memory (DRAM) and Flash Memory are widely used. Although DRAM has the advantage of processing data at high speed, it is a volatile memory that loses data when no power is supplied. Also, Flash memory has the advantages of being small, light, and robust against physical shocks, but the disadvantage is that the data processing speed is slow. They are reaching the limit of processing the lots of data generated by society.<br/>Research on new memories to replace these devices is continuously being done. FeRAM (Ferroelectric Random Access Memory) is a next-generation memory with only the advantages of DRAM and Flash Memory. It can preserve data even when power is not supplied and process information quickly. This device is one of the representative non-volatile memories using ferroelectrics. It has a memory function by distinguishing ‘0’ and ‘1’ according to the polarization direction, and it can be used as a non-volatile memory by using the characteristic of maintaining polarization even when the voltage is cut off.<br/>It is known that the initial ferroelectricity occurs in perovskites such as SrTiO3, KTaO3, and CaTiO3. However, recently, HfO2 and ZrO2 thin films have emerged as new types of ferroelectric materials, and many studies have been conducted. Also, HfO2-based ferroelectric materials are being researched by doping various materials such as Zr, Si, Y, and Al. Among the many dopants, HfO2 exists in a high dielectric constant structure at high temperatures, so changing the crystal structure with a high dielectric constant at room temperature is crucial.<br/>This study studied ferroelectricity by growing a tetragonal HfO2 thin film by doping with Al. In order to evaluate the non-volatile memory characteristics, a metal-ferroelectric-metal (MFM) structure was fabricated using an Al-doped HfO2 ferroelectric thin film. The Al:HfO2 thin film was fabricated using PE-ALD (Plasma Enhanced Atomic Layer Deposition), and the HfO2 thin film doped with 5-10 mol% Al was deposited by controlling the deposition ratio of HfO2 and Al2O3. TiN was deposited on the upper and lower electrodes to improve the ferroelectricity of HfO2 by sputtering. Annealing was performed between 500 and 700 degrees to generate crystallinity while removing organic matter. Transmission electron microscope (TEM) analysis was performed to confirm the structure of the thin film. In addition, X-ray photoelectron spectroscopy (XPS) was used to evaluate the Al:HfO2 doping concentration. The growth of the tetragonal phase according to the heat treatment temperature of Al:HfO2 was analyzed using XRD. To evaluate the electric properties of the thin film, the leakage current characteristics of Al doped HfO2 thin films were measured according to the applied voltage. In addition, Polarization (Pr) was measured to confirm the ferroelectric properties.