Takeshi Kada

Fabrication of refractive index distributions in polymer using a photochemical reaction

We demonstrate that a photochemical reaction can create various distributions of refractive index in polymer. When the polymer containing a photochemically active material is irradiated by UV light, the photochemical reaction which breaks the π-conjugated system in the material and decreases its linear polarizability can reduce refractive index of the polymer. We prepared a PMMA film added DMAPN ((4-N,N-dimethylaminophenyl)-N′-phenylnitrone) with a rate of 23 wt % by use of spin coating. Electronic structural change of DMAPN and refractive indices of the film before and after UV irradiation were evaluated by UV absorption spectra and m-line method, respectively. The UV irradiation decreased λmax at 380 nm in the absorption spectra, which is attributed to nitrone, and the refractive indices exponentially with irradiation time. The change of refractive indices reached 0.028. The refractive index profile upon depth of the film was investigated by measuring refractive indices of stacked DMAPN/PMMA films. When...

Ni Precursor for Chemical Vapor Deposition of NiSi

Nickel thin film is an attractive material for use as electrodes or contacts of metal oxide semiconductor field effect transistors (MOSFETs), and numerous studies have focused on Ni monosilicide (NiSi). Bis-methylcyclopentadienyl-nickel [(MeCp)2Ni] is a dark green solid at room temperature, which becomes liquid at 36°C. Thermogravimetric differential thermal analysis (TGDTA) measurements revealed that most of the (MeCp)2Ni is vaporized without thermal decomposition and it decomposes from 200°C to 250°C. (MeCp)2Ni has a low viscosity and a high vapor pressure (1 Torr at 73°C), and its transportability is sufficiently good for it to be used as a chemical vapor deposition (CVD) precursor. Ni was deposited at 300°C by CVD using a (MeCp)2Ni/H2 gas system. Ni reacted with the Si substrate, and X-ray diffraction (XRD) analysis showed that a part of the silicides had formed on the Si substrate. Si3H8 injection prevents the Si substrate from being consumed by the silicide reaction, and a conformal NiSi film with a flat interface on the Si substrate was obtained.

Novel Precursor for Development of Si–C2H4–Si Networks in SiCH for Application as a Low-k Cap Layer beyond 22 nm Nodes

SiCH films are a potentially very useful low-k cap layer for covering Cu trenches in ultralarge-scale integration (ULSI) devices. To induce Si–C2H4–Si networks in SiCH film structures, 1,1-divinyl silacyclopentane (DVScP) and 5-silaspiro-[4,4]-nonane (SSN) were designed and prepared. Isobutyl trimethyl silane (iBTMS) and diisobutyl dimethyl silane (DiBDMS) were also designed to form Si–CH2–Si networks in the SiCH molecular structure. SiCH films were formed by plasma-enhanced chemical vapor deposition (PECVD), for use as a low-k cap layer and a Cu diffusion barrier on top of the Cu trenches. We demonstrated additional Si–C2H4–Si networks that can effectively suppress Cu diffusion in SiCH low-k barrier films with a reduced k-value of 3.1.

Vapor Pressure of Hf and Si Precursors for HfxSi1-xO2 Deposition Evaluated by a Saturated Gas Technique

The vapor pressure of the precursor is an important parameter, which is correlated with supply amount and deposition rate during chemical vapor deposition (CVD). Tetrakis(ethylmethyl)hafnium, tetrakis(diethylamido)hafnium, tetraethoxysilane, tetraisocyanatosilane and tri(diethylamino)silane are promising precursors for CVD. HfxSi1-xO2 films deposited using these precursors have been studied for applications in high-k gate insulators. The vapor pressure values are required for estimating adequate deposition conditions. Therefore, Clausius–Clapeyron equations for the precursors were systematically determined using a saturated gas technique.

Fabrication of Refractive Index Profiles in Poly (Methyl Methacrylate) using Ultraviolet Rays Irradiation

We demonstrated that the refractive index of poly(methyl methacrylate) (PMMA) increased by simple ultraviolet rays irradiation. The index change, +1.0% was due to the change of chemical structure including elimination of the carbonyl group, followed by olefin formation, which were determined by Fourier-transform infrared rays and UV absorption spectra. A refractive index profile for 15-µm-thick PMMA was realized by irradiation for 4 h. Therefore, it is considered that the graded index (GI) profile of PMMA can be applied to microdevices such as a microspherical lens, single-mode waveguide and so on.

Ni Thin Film Deposition from Tetrakistrifluorophosphine-Nickel

The inorganic molecule Ni(PF3)4 is a candidate as a Ni chemical vapor deposition (CVD) precursor, which is an alternative to organometal sources. We develop a new method of synthesizing Ni(PF3)4 from Cp2Ni and PF3 with a high yield. Ni(PF3)4 is liquid at room temperature and has a vapor pressure (215 Torr at 30°C) sufficiently high for CVD. CVD using MeCp2Ni or CpAllyNi as a Ni precursor does not produce a Ni film on a Si surface, but CVD using the Ni(PF3)4/He gas system deposits a continuous Ni film on a Si surface at low temperatures below 200°C.

Tris-diethylamino-silane Decomposition due to Tetrakis-diethylamido-hafnium in Hf1-xSixO2 Chemical Vapor Deposition

Tris-diethylamino-silane SiH(NEt2)3 is stable and does not decompose by itself below 550?C. However, it easily decomposes even at 150?C with the addition of tetrakis-diethylamido-hafnium (Hf(NEt2)4). This enhancement of silicon source decomposition determined the properties of Hf1-xSixO2 film, when the Hf1-xSixO2 film is deposited by CVD using the Hf(NEt2)4/SiH(NEt2)3/O2 gas system. Then 550?C, the Si concentration is almost constant and the ratio of N to Si is almost one independent of the deposition temperature. However, above 550?C, the Si concentration increases and the ratio of N to Si decreases, since SiH(NEt2)3 is thermally decomposed by itself.

Novel Precursors for SiCH Low-k Caps beyond the 22 nm Node: Reactions of Silacyclopentane Precursors in the Plasma-Enhanced Chemical Vapor Deposition Process and Structural Analyses of SiCH Films

To form SiCH films with high carbon content using plasma-enhanced chemical vapor deposition (PECVD), 1,1-divinylsilacyclopentane (DVScP) and 5-silaspiro[4,4]nonane (SSN) were designed as novel precursors for the low-k cap layer and Cu diffusion barrier at the top of Cu lines. We elucidated the relationship between the structure of low-k SiCH films made from these newly developed precursors and their barrier properties against copper and oxygen diffusion. We also studied the relationship between the structure of SiCH and the deposition process under various RF plasma powers. A Monte Carlo simulation was employed to estimate the deposition profile using an overhang test structure. Fourier transform infrared (FT-IR) spectroscopy was used to analyze the molecular structures. Our novel silacyclopentanes formed SiCH films with high carbon content and good barrier properties at high RF powers due to the specific reactions of silacyclopentanes designed according to our quantum chemical calculations. Precursor design is thus an important factor in forming SiCH with high carbon content that achieves both lower k and good barrier properties.

Isobutyl Silane Precursors for SiCH Low-

To form SiCH films with a high carbon content using plasma-enhanced chemical vapor deposition (CVD), isobutyl trimethylsilane (iBTMS) and diisobutyl dimethylsilane (DiBDMS) were examined as precursors for a low-k cap layer and Cu diffusion barrier at the top of Cu lines. We elucidated the relationship between the structure of low-k SiCH films made from these newly developed precursors and their barrier properties against copper and oxygen diffusion. We also studied the relationship between the structure of SiCH and the deposition process under various RF plasma powers. A Monte Carlo simulation was employed to estimate the deposition profile in an overhang test structure. Fourier transform infrared spectroscopy (FT-IR) was used to analyze molecular structures. Our studies indicate that deposition conditions cannot dictate carbon content, but can control porosity/density. Precursor selection is thus an important factor in forming SiCH with a high carbon content that achieves both lower k and good barrier properties.

k

We propose new precursors for bulk low-k films with plasma damage resistance. Our newly designed precursors contain long-chain hydrocarbon groups such as i-butyl and n-propyl groups. Using these precursors, we successfully produced films containing Si–CH2–Si groups by plasma-enhanced chemical vapor deposition (PECVD). The plasma damage resistance of these films under NH3 plasma treatment was studied. It was found that the increase in the k-value (Δk) is smaller in films with more Si–CH2–Si groups.