Kimiaki Shimokawa

Low Dielectric Constant Interlayer Using Fluorine-Doped Silicon Oxide

A new interlayer dielectric film using fluorine-doped silicon oxide (SiOF) for multilevel interconnection of very large scale integration (VLSI) has been fabricated. The film is deposited by a simple technique, which is hexafluoroethane ( C2F6) addition to conventional tetraethoxysilane (TEOS)-based plasma-enhanced chemical vapor deposition (PE-CVD). Si–F bond formation in the film is detected by chemical bonding structural studies using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Low dielectric constants caused by Si–F bond formation and good gap-filling ability due to in situ etching by C2F6 plasma are obtained. Therefore, SiOF film has very high applicability as an interlayer dielectric film for advanced VLSI devices.

Interaction between water and fluorine-doped silicon oxide films deposited by plasma-enhanced chemical vapor deposition

The interaction between water and fluorine-doped silicon oxide (SiOF) films has been studied using Fourier transform infrared spectroscopy and thermal desorption spectroscopy. The effects of the interaction on the relative dielectric constant of films were also studied using capacitance–voltage measurements. It was found that SiOF films with high fluorine concentration have three absorption bands attributable to Si–Fn stretching vibration, however, the SiOF films have only one absorption band after humidification. The residual band is assumed to be attributable to silicon monofluoride [Si(O–)3F] sites and the disappearing bands are attributable to silicon difluoride [Si(O–)2F2] sites. Si(O–)2F2 sites are hydrided during humidification and generate Si–OH bonds and HF in the film. In addition, Si(O–)2F2 sites increase the water absorbed in film. The relative dielectric constant of SiOF films capped by silicon nitride decreased steadily with increased fluorine concentration, from 4.5 (SiO2) to less than 2.8 [11.5 at. % (F)], however, that of uncapped SiOF films saturated the decrease at about 3.6 in films having 7.6 at. % (F) or more. This saturation is caused by the increase of Si(O–)2F2 sites in film because the ratio of Si(O–)2F2 sites to total fluorine bonding sites increases markedly at a fluorine concentration above 7.6 at. % (F). Si(O–)2F2 sites increase Si–OH bonds and water absorbed in film, and both, in turn, increase the film dielectric constant.The interaction between water and fluorine-doped silicon oxide (SiOF) films has been studied using Fourier transform infrared spectroscopy and thermal desorption spectroscopy. The effects of the interaction on the relative dielectric constant of films were also studied using capacitance–voltage measurements. It was found that SiOF films with high fluorine concentration have three absorption bands attributable to Si–Fn stretching vibration, however, the SiOF films have only one absorption band after humidification. The residual band is assumed to be attributable to silicon monofluoride [Si(O–)3F] sites and the disappearing bands are attributable to silicon difluoride [Si(O–)2F2] sites. Si(O–)2F2 sites are hydrided during humidification and generate Si–OH bonds and HF in the film. In addition, Si(O–)2F2 sites increase the water absorbed in film. The relative dielectric constant of SiOF films capped by silicon nitride decreased steadily with increased fluorine concentration, from 4.5 (SiO2) to less than 2.8 ...

Structure of fluorine-doped silicon oxide films deposited by plasma-enhanced chemical vapor deposition

The Fourier transform infrared (FTIR) spectra and Raman spectra of fluorine-doped silicon oxide films capped by silicon nitride thin film to prevent water absorption from the air were measured as a function of the fluorine concentration in the films. It was found that fluorine doping diminishes the Si–OH bonds in films. Films without fluorine show a clear OH band attributable to Si–OH bonds, but films with 7.6 at % (F) or more exhibit no OH band in FTIR spectra. The FTIR spectra also show that fluorine in films forms new absorption bands at frequencies ranging from 990 to 920 cm−1. These absorption bands are assigned as silicon monofluoride sites (940 cm−1) and as silicon difluoride sites (925 and 985 cm−1). While the silicon difluoride sites increase linearly with increasing fluorine source gas flow, the increase in silicon monofluoride sites saturate at a certain fluorine source gas flow [i.e., a fluorine concentration in film of about 7.6 at % (F)]. The Raman spectra show that fluorine doping reduces t...

Effects of helium dilution of TEOS–O2–C2F6 gas mixture on plasma-enhanced chemical vapor deposition of fluorine-doped silicon oxide film

It was found that helium dilution in reactant gas on plasma-enhanced chemical vapor deposition of fluorine-doped silicon oxide film increases the film deposition rate while decreasing hygroscopicity and dielectric constant. He dilution has also been found to decrease the intensity of the infrared absorption band at 980 and 923 cm−1, but affected band intensity only negligibly at about 948 cm−1. Absorption bands at 980 and 923 cm−1 are due to silicon difluoride sites, while that at 948 cm−1 is due to silicon monofluoride sites. He presumably plays an active role in chemical vapor deposition, not acting only as a dilution gas, increasing film deposition rate and reducing fluorine at silicon difluoride sites. The selective reduction of fluorine at silicon difluoride sites is also assumed to decrease the film hygroscopicity and dielectric constant.

Interaction between water and fluorine-doped silicon oxide film deposited by PECVD

The interaction between water and fluorine-doped silicon oxide (SiOF) films has been studied focusing on the relation between the fluorine bonding configuration in the film and film hygroscopicity. SiOF films with a high fluorine concentration have three IR absorption bands between 985 cm/sup -1/ and 920 cm/sup -1/. These bands are assumed to be attributable to silicon monofluoride and silicon difluoride sites. It was found that silicon difluoride sites interact with H/sub 2/O more easily than silicon monofluoride sites. Silicon difluoride sites are hydrided during humidification. The hygroscopicity of SiOF film with a high fluorine concentration is assumed to be due to an increase in the silicon difluoride sites in the film, because the ratio of silicon difluoride sites to total fluorine bonding sites increases markedly above a certain fluorine concentration. Plasma-enhanced chemical vapor deposition of SiOF film with excess helium dilution in the reactant gas was also studied to reduce the hygroscopicity of SiOF film. It was found that helium dilution decreases the number of silicon difluoride sites, and simultaneously increases the number of silicon monofluoride sites. Film having a high fluorine concentration deposited with helium dilution exhibited lower hygroscopicity and a lower relative dielectric constant than the film deposited without He. It is essential to reduce the silicon difluoride sites in SiOF film to obtain highly reliable film.

Experimental Demonstrations of Superior Characteristics of Variable Body-Factor (γ) Fully-Depleted SOI MOSFETs with Extremely Thin BOX of 10 nm

The superior characteristics of variable body-factor (γ) FD SOI MOSFETs which we have recently proposed are experimentally demonstrated. Devices were fabricated on a SOI wafer with BOX thickness of 10 nm by using the 140 nm technology. Their advantages, small leakage-current in the standby-state and improved delay in the active-state, are clearly validated by the measurements. This scheme is expected to be promising for future low-power, high-performance VLSIs