Nobuyoshi Kobayashi

Carbon-Doped Silicon Oxide Films with Hydrocarbon Network Bonds for Low-k Dielectrics: Theoretical Investigations

We have computationally explored the chemical structures of carbon-doped silicon oxide (SiOCH) films that give the smallest dielectric constant (k) under the required mechanical strength for low-k dielectrics. The focus of this study is on the SiOCH structures that have hydrocarbon components in the polymer network as cross-links. It has been found that SiOCH films of small dielectric constants can have improved mechanical strengths if the hydrocarbon components form cross-links, instead of the terminal methyl groups in the conventional structure. The calculated results suggest that SiOCH films of ideal structures can have substantially smaller dielectric constants than films of current interconnect technology with the same mechanical strengths.

Tuning depth profiles of organosilicate films with ultraviolet curing

This study demonstrates that ultraviolet (UV) radiation curing can control depth profiles of organosilicate films. Striking differences between the effects of monochromatic and broadband UV irradiation were observed. For the same as-deposited organosilicate film and cure duration, monochromatic radiation has a greater impact on film structure, elastic modulus, and fracture resistance, but also results in a greater degree of depth dependent properties. Oscillating elastic modulus through the film thickness was observed with force modulation atomic force microscopy. We present a new standing wave model that accurately predicts the resulting depth dependent stiffness variations considering changes in film shrinkage and refractive index in terms of curing time, and can further be used to account for initial film thickness dependence of UV curing and film absorption. Promising applications of the depth dependent UV curing to produce multifunctional ultralow-k layers with a single postdeposition curing process ...

Ultraviolet-Curing Mechanism of Porous-SiOC

Utilizing the structure of porous SiOC determined in our previous study, we investigated a mechanism for improving the properties of porous SiOC film by ultraviolet irradiation (UV curing). The generation of a Si–O–Si cross link from an OH group and its adjacent CH3 group is the primary process in UV curing. This cross-link generation enhances mechanical strength of the material and lowers the dielectric constant. Decrease in the number of CH3 groups and increase in the number of Si–H bonds, both due to UV curing, cause slight increases in mass density and dielectric constant of the film.

Paramagnetic Defect Spin Centers in Porous SiOCH Film Investigated Using Electron Spin Resonance

On the basis of electron spin resonance (ESR) measurements, we observed a unique paramagnetic center (Tb center, g=2.003) in porous low-dielectric-constant (low-k) carbon-doped silicon oxide (SiOCH) film after annealing the film in vacuum. Fourier transform infrared spectroscopy (FT-IR) spectra indicated that the number of Si–CH3 bonds in the SiOCH film decreased with increased Tb-center absorbance. Molecular calculations indicate that this paramagnetic center differs from an E center and has a microstructure with carbon atoms in its backbond. A Tb center was also observed after annealing using ultraviolet (UV) light or an electron beam (EB), which both increase film leakage current.

UV/EB Cure Mechanism for Porous PECVD/SOD Low-k SiCOH Materials

The mechanism of UV and EB cure processes for porous low-k SiCOH materials was investigated by using experimental results obtained using PECVD and SOD films as well as simulated results. Both UV and EB cures induced dielectric constant change and Youngs modulus improvement because Si-OH elimination (moisture removal) and cross-link formation occurred during film shrinkage. Excess UV curing, however, caused defects in the porous SiCOH film, as indicated by ESR analysis. The mechanism discussed in this work is applicable to most UV/EB cure systems and PECVD/SOD SiCOH materials for 45-nm-node Cu interconnects

First-principle molecular model of PECVD SiOCH film for the mechanical and dielectric property investigation

The microstructure of PECVD carbon-doped oxide (SiOCH) film has been obtained for the first time by using a theoretical method to create molecular models of amorphous polymers with cross-links. This method generates atomic coordinates of chemically possible SiOCH film structures from a given atomic composition. We have confirmed that this method creates reasonable SiOCH film structures that explain the experimental results of IR spectrum, dielectric constant, and Youngs modulus. Consequently, this method gives us a guideline for decreasing the density of PECVD SiOCH films having acceptable mechanical properties for interconnect applications.

Impacts of UV cure for reliable porous PECVD SiOC integration [IC interconnect applications]

An ultra violet (UV) cure was investigated to improve the mechanical and electrical properties of porous carbon-doped PECVD (plasma enhanced chemical vapor deposition) oxide film (k<2.4) for the 45 nm node technology and beyond. Drastic improvement in the film modulus and leakage current between Cu interconnects was observed. The formation of Si-O chemical bonds by breaking Si-CH/sub 3/ bonds after UV irradiation is thought to be an origin for the results of Si-O-C-H networks in p-SIOC films.

Surface-Reaction-Controlled Tungsten CVD Technology for 0.1-µm Low-Resistive, Encroachment-Free CMOS-FET Applications

A reliable and manufacturable tungsten (W) stacked source/drain (S/D)-and-gate technology has been developed which is applicable to conventional 0.1 μm complementary metal-oxide-semiconductor field-effect transistors (CMOS-FETs). A low-resistive (2-3 Ω/sq.) and encroachment-free S/D has been achieved. This technology has overcome two major problems in the selective chemical vapor deposition (CVD) of W. First, the difference in the thickness of W films grown on p + and n + silicon (Si) is reduced by Si-light-etching treatment. Second, encroachment during W-CVD is suppressed by a tungsten hexafluoride (WF6) high-pressure process. Excellent electrical characteristics have been obtained in 0.1 μm CMOS-FETs using the W stacked S/D-and-gate technology.

Atomic layer etching of SiO2 by alternating an O2 plasma with fluorocarbon film deposition

This work demonstrated a process for the atomic-scale etching of SiO2 films, consisting of alternating nanometer-thick fluorocarbon film deposition with O2 plasma irradiation in a capacitively coupled plasma reactor. Ar plasma etching after fluorocarbon film deposition tends to suffer from nanometer- or subnanometer-thick carbon films deposited on the SiO2 surface and chamber walls. These carbon films cause various problems, such as reductions in the etching rate per cycle and degradation of the SiO2 quality. In contrast, in our two-step process, O2 plasma removes carbon atoms in such fluorocarbon films. This process therefore allows the atomic scale etching of SiO2 films without any residue or surface contamination. Additionally, since the etching rate per cycle plateaus as both the etching time and deposition time are extended, it is unnecessary to uniformly deposit a fluorocarbon film over the wafer.

Plasma enhanced ALD pore sealing for highly porous SiOCH films with k = 2.0

In order to implement highly porous PECVD SiOCH films with k = 2.0 in ILD integration, the UV-assisted restoration to remove plasma damages related with dry etch and pore sealing by plasma enhanced ALD (PEALD)-SiN formation to prevent the metal penetration into the film during subsequent metallization process was investigated. Sequential application of the restoration and pore sealing processes was proved to be the best solution enabling successful sealing capability with preserving pristine k-value of the porous SiOCH films.