To understand the NF3/NH3 dry cleaning mechanism, we have investigated the dry cleaning process with different Si-based materials, Si, SiO2, and Si3N4 using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS) in terms of surface modification. In this paper, we report that the NF3/NH3 dry cleaning process using down-flow plasma technique can cause significant surface modification on SiO2 depending on the NF3:NH3 ratio and plasma power of the plasma reaction before (NH4)2SiF6 by-product sublimation step. These results might provide empirical evidence that there are competing reaction pathways producing different intermediate species on SiO2 surface to form (NH4)2SiF6 by-product depending on the process conditions. A possible mechanism is presented.

HfO2 gate stack has been one of the most popular subjects of research in recent years due to its outstanding material properties, such as high-k (20~25), wide band gap (~5.68eV), and the compatibility with Si-based semiconductor process technology. However, the interfacial layer (IL) with a reduced k-value between HfO2 dielectric and Si channel is still a critical issue for future ultra large scale integration (ULSI) technology application of the HfO2 gate stack. Various ways have been studied to improve the IL properties of HfO2 gate stack and to achieve ~1nm-thick equivalent oxide thickness (EOT) of the gate stack. Recently, fluorine incorporations into the HfO2 gate stack have been suggested for improvement of the electrical properties of the gate stack by defect passivation.1,2 However, it was reported that the SiOx IL grows during the fluorine treatment of HfO2 film, which finally led to degradation of electrical characteristics.2 In this paper, we present interesting findings on the IL removal effect of fluorine incorporation into the HfO2 gate stack where a post-gate dry cleaning technique is used with the NF3/NH3 plasma.

In this paper, we present preliminary findings on the fluorine incorporation into the HfO2 gate stack using post-gate dry cleaning technique with the novel NF3/NH3 plasma as an engineering technique to improve the HfO2 gate stack. The NF3/NH3 dry cleaning process was carried out using an indirect down-stream CCP system after annealing HfO2 gate stack. The analysis of chemical composition of HfO2 gate stacks by XPS has been revealed that fluorine was incorporated into the HfO2 films and Si-O bonding of interfacial layer was decreased depending on the process condition of the NF3/NH3 dry cleaning. TEM results consistently showed the interfacial SiOx layer thickness of the HfO2 gate stack was decreased with the NF3/NH3 dry cleaning. Also we have found that its electrical properties were improved with the reduced gate leakage currents and EOT.

The effects of dry cleaning of a HfO2 gate stack using NF3 only and a NF3/NH3 gas mixture plasma were investigated. The plasma dry cleaning process was carried out after HfO2 deposition using an indirect down-flow capacitively coupled plasma (CCP) system. An analysis of the chemical composition of the HfO2 gate stacks by XPS indicated that fluorine was incorporated into the HfO2 films during the plasma dry cleaning. Significant changes in the HfO2 chemical composition were observed as a result of the NF3 dry cleaning, while they were not observed in this case of NF3/NH3 dry cleaning. TEM results showed that the interfacial layer (IL) between the HfO2 and Si thickness was increased by the plasma dry cleaning. However, in the case of NF3/NH3 dry cleaning using 150 W, the IL thickness was suppressed significantly compared to the sample that had not been dry cleaned. Its electrical properties were also improved, including the low gate leakage currents, and reduced EOT. Finally, the finding show that the IL thickness of the HfO2 gate stack can be controlled by using the novel NF3/NH3 dry cleaning process technique without any the significant changes in chemical composition and metal-oxide-semiconductor (MOS) capacitor characteristics.