Material Characterization and Chemical-Mechanical Polishing of Low-Dielectric Constant Fluorinated Silicon Dioxide Films

Nanohardness, modulus, and bonding structure of fluorinated silicon dioxides are characterized in order to evaluate their correlations with chemical-mechanical polishing (CM[P) performance. Alkaline-based slurry with adjusted pH is used for polishing in an attempt to delineate the chemical erosion from mechanical abrasion effects during CMIP of fluorinated oxides. The increase in CMIP removal rate and the reduction in refractive index with increasing fluorine content in the fluorinated oxides are related to the change in bonding configuration. The enhanced moisture absorption is due to the presence of fluorine in the oxide network.

Enhanced Gate Oxide Reliability through Fluorine Incorporation and the Influence of Polysilicon Process Variations

ABSTRACTThere has been some uncertainty as to the impact of fluorine (F) on SiO2 quality and reliability. Several laboratories have shown greatly enhanced quality and reliability with fluorinated oxides, while others have been unable to repeat the results. In addition, the laboratories which have shown enhanced reliability with the fluorinated oxides have differed in their interpretation of the mechanism by which the enhancement occurs. X-ray diffraction stress measurements, partial time dependent dielectric breakdown (TDDB) measurements, SIMS depth profiling, transmission electron microscopy, standard high/low frequency C-V measurements, and hot-carrier aging of variously processed MOSFETs have been used to investigate a variety of fluorinated films. We believe that the apparent lack of consistency of the effects of fluorine on MOSFET reliability between laboratories may be explained by slight variations in the gate polysilicon processing which result in variations in polysilicon morphology. The polysilicon morphology determines both mechanical stress and F diffusion which ultimately impacts interface state density and thus hot carrier reliability.

The Investigation of Fluorine Effects on Charge Trapping and Interface State Generation in Mos Structures

ABSTRACTThe bulk and interface charge trapping phenomena of fluorinated oxides have been studied by various electronic measurements. Fluorine is introduced into dry oxides by low energy (25kev) implantation followed by a 1000°C N2 ambient anneal to remove physical damage. Both the flat band and the mid gap voltage shifts of such MOS devices are measured during avalanche electron injection. We have developed techniques to separate effects due to interface state generation from bulk trapping effects. The bulk electron traps in the fluorinated oxides have a different cross section from the known water-related traps in conventional oxides. The generation of fast and slow interface states for different dosages of fluorine implantation is discussed based on Q-V and C-V measurements. The fast interface donor states, generated during avalanche injection, are charged at flat band but discharged at mid gap and beyond. An optimum dosage of fluorine implantation is found to suppress the so called turn-around effect during avalanche injection due to the formation of slow donor states. Finally, injection under high temperature (120°C-150°C) anneals out most of these donor states.