Masaki Yoshimaru

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.

Highly reliable copper dual-damascene interconnects with self-formed MnSi/sub x/O/sub y/ barrier Layer

Copper (Cu) dual-damascene interconnects with a self-formed MnSi xOy barrier layer were successfully fabricated. Transmission electron microscopy shows that approximately 2-nm thick and continuous MnSixOy layer was formed at the interface of Cu and dielectric SiO2, and that no barrier was formed at the via bottom because no oxygen was at the via bottom during annealing. No leakage-current increase was observed, and electron energy loss analysis shows that no Cu was in SiO2, suggesting that MnSixOy layer has sufficient barrier properties for Cu, and that the concept of self-forming barrier process works in Cu dual-damascene interconnects. Via chain yield of more than 90% and 50% reduction in via resistance were obtained as compared with physical vapor deposited tantalum barrier, because there is no barrier at the via bottom. In addition, no failure in the stress-induced voiding measurement was found even after a 1600-h testing. No failure in electromigration (EM) testing was found, as the electron flow is from the lower level interconnects through via up to upper level interconnects even after 1000-h testing. At least, four times EM lifetime improvement was obtained in the case of electron flow from upper level interconnect through via down to lower level interconnects. Significant EM lifetime improvement is due to no flux divergence site at the via bottom, resulting from there being no bottom barrier at the via

Structure and Electrical Properties of Thin Ta2O5 Deposited on Metal Electrodes.

The structure and electrical properties of chemical vapor deposition (CVD)-Ta2O5 thin films on Pt, Ru and poly-Si electrode were studied. With 750°C annealing after Ta2O5 deposition, a 12-nm-thick Ta2O5 on Pt and Ru shows a SiO2 equivalent thickness (teq) of 0.9 nm. We found that Ta2O5 on Pt and Ru shows (110) and (001) orientation, respectively. There is no interaction between Ta2O5 and these electrodes with 750°C annealing. teq on Pt and Ru decreases with annealing temperature increase. On the other hand, Ta2O5 on poly-Si is randomly oriented and its teq does not change with annealing temperature increase. The relative dielectric constant of Ta2O5 on Pt and Ru, which is highly oriented with 750°C annealing, is estimated over 50. It is clear that the Ta2O5 electrical properties are strongly related with its crystallinity.

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...

Rugged surface polycrystalline silicon film deposition and its application in a stacked dynamic random access memory capacitor electrode

Rugged surface polycrystalline silicon (poly‐Si) films deposited by low‐pressure chemical vapor deposition have been studied and the films have been applied to a storage electrode for stacked dynamic random access memory capacitors. The surface morphology of the films was drastically affected by growth conditions and by the film thickness. However, the rugged surface poly‐Si was characterized by the growth of grains that have 〈311〉 preferred orientation. The grains had grown on the amorphous Si surface just after deposition in the low‐pressure chemical vapor deposition furnace. It was observed that the amorphous Si films deposited at the transition temperature between amorphous and polycrystalline Si have small crystalline particles in the films. We surmise that the nucleation sites of rugged surface poly‐Si grains are small crystalline particles in amorphous Si near the surface, because the amorphous Si films deposited at high SiH4 pressure and low temperature (less than 540 °C) that have no crystalline ...

Growth of [111]-Oriented Lead Zirconate Titanate Thin Film with Smooth Surface to Improve Electrical Properties

[111]-Oriented lead zirconate titanate (PZT) films with smooth surfaces were successfully grown on (111). oriented polycrystalline Pt substrates after in-situ Ar-plasma cleaning by low-temperature reactive sputtering and rapid thermal annealing. The Pb composition was stoichiometrically controlled not only for total composition but also in the depth direction by low-temperature reactive sputtering. A (111)-oriented perovskite-phase PZT film with a very smooth surface was then obtained by rapid thermal annealing. The leakage current of quasi-epitaxial PZT films was markedly reduced to 10 -7 A/cm 2 and the equivalent SiO 2 layer thickness of around 0.4 nm was obtained for the fatigue-free PZT films thinner than 100 nm.

Silicon nitride thin-film deposition by LPCVD with in situ HF vapor cleaning and its application to stacked DRAM capacitor fabrication

Silicon nitride film deposited by LPCVD with newly developed in situ HF vapor cleaning has been studied and applied to fabricate dielectric films for stacked DRAM capacitors. Using this method, an oxide-free surface of underlaid poly-Si can be obtained. Silicon nitride film deposited on this surface has been verified by FTIR measurement to have the stoichiometrically proper composition of Si/sub 3/N/sub 4/. However, the film was found to be selectively deposited on poly-Si electrodes. This selective deposition degrades the reliability of the stacked capacitor, because the silicon nitride can not completely cover the periphery of poly-Si electrodes on SiO/sub 2/. We propose a simple process that avoids the problem making it possible to apply silicon nitride film to stacked-capacitor fabrication. Stacked capacitors fabricated by this process exhibit very low leakage current and high electrical reliability even for ultra-thin silicon nitride films less than 5 nm thick. >

Texture and electromigration performance in damascene interconnects formed by reflow sputtered Cu film

We have investigated the Cu texture in damascene interconnect structures formed by the reflow method of sputtered Cu film and electromigration (EM) performance in Cu damascene interconnects. The texture of reflowed Cu film depends on Cu deposition temperature and line width. Improved 〈111〉 texture in blanket films is obtained when Cu is deposited at temperatures over 200 °C. However, Cu films form voids in the trench patterns at deposition temperatures of 350 °C or more, and the voids cannot be filled even after the reflow process. Thus, it is necessary to choose the optimum deposition temperature to fabricate void-free Cu damascene interconnects. It was found that the Cu (111) peak intensity in reflowed Cu lines measured by using x-ray diffraction decreases as trench width decreases. This can be explained by aspect ratio changes of Cu lines in trenches, which affect the dominating Cu texture components originating from sidewall or bottom nucleations. Underlayer metals at sidewalls affect the Cu texture. ...

Electrical and Crystallographic Properties of Sputtered-Pb(Zr, Ti)O3 Films Treated by Rapid Thermal Annealing

Pyrochlore-phase lead-zirconate-titanate (PZT) films were prepared by rf-magnetron sputtering using a multi-element metal target at 400°C. These films were crystallized to the perovskite phase by rapid thermal annealing (RTA) at 600°C for a few minutes. The RTA-treated PZT films had not only extremely smooth surfaces but also tenfold stronger X-ray diffraction peak intensities of the perovskite structure than those of furnace-annealed films which had with rough undulation. The electrical properties of RTA-treated films indicated good ferroelectric properties. The remanent polarization and coercive field of the 100 nm-thick RTA-treated film were 15 µC/cm2 and 67 kV/cm, respectively. Fatigue measurements with alternating ±3 V pulses showed that the film was stable up to 109 cycles.