Study of high-k materials deposited by liquid source misted chemical deposition (LSMCD) method for advanced gate dielectric applications

Considerable efforts to replace conventional SiO₂ gate dielectric with alternative high-k dielectrics for sub-0.1 μm geometry CMOS technology are underway. Among several possible materials considered of prime interests are metal oxides which feature k substantially higher than that of SiO₂ (∼3.9), are thermodynamically stable with silicon, can be obtained as low-leakage films in the 4∼5 nm thickness regime, and maintain their structural integrity during post-deposition annealing cycles. Currently, a wide range of materials and deposition techniques are being explored to identify those producing gate dielectrics suitable for next generation CMOS devices. As a part of these efforts, the Liquid Source Misted Chemical Deposition (LSMCD) method is employed in this work to deposit metal oxides on silicon substrates. The LSMCD method is routinely utilized in memory device manufacturing industry to deposit up to 100 nm thick ferroelectric films. The goal of this investigation was to evaluate the feasibility of LSMCD method in depositing ultrathin high-k dielectrics for next generation CMOS devices. In this work, the LSMCD module is integrated into a commercial cluster which also includes gas-phase cleaning module, and Rapid Thermal Processing (RTP) module.; This work investigates fundamental material properties and electrical characteristics of mist-deposited high-k dielectrics including La₂O ₃, Al₂O₃, ZrO₂, HfO₂, Y ₂O₃, LaAlO₃, LaScO₃, ZrSiO₄, HfSiO₄, SrTiO₃ and SrTa₂O₆. A novel scheme which integrates surface preparation and high-k dielectric deposition is also proposed and investigated. Overall, the results obtained in this work indicate that mist-deposited oxides of hafnium and zirconium, and even more so, hafnium silicate as well as SrTa₂O₆ materials show promise in MOS gate applications. As it is the case in other methods of high-k gate dielectric deposition the problem here is a control of the formation of an interfacial oxide (SiO_x) sandwiched between Si substrate and high-k dielectric. This problem is among the key issues addressed in this investigation.; In the final stage of this study the focus was on HfSiO₄ which was found to be well compatible with mist-deposition. A thorough investigation of the Si-SiO_x-HfSiO₄ system was carried out using electrical methods as well as TEM, XPS, AFM, and XRD.; Overall, a potential of mist-deposition in MOS gate stack technology was demonstrated. The method is capable of forming ultrathin uniform films of high-k dielectrics on Si substrate in the cost and time effective fashion. The results obtained in this work identify additional tasks which must be pursed in order to develop the LSMCD method into manufacturing technology compatible with CMOS process requirements.