Hideaki Machida

HfO2 growth by low-pressure chemical vapor deposition using the Hf(N(C2H5)2)4/O2 gas system

HfO2 thin film was deposited on a Si substrate by low pressure chemical vapor deposition using the Hf(N(C2H5)2)4 (tetrakis- diethylamido-hafnium)/O2 gas system. Hf(N(C2H5)2)4 is liquid at room temperature and has a moderate vapor pressure for the chemical vapour deposition process. The precursor was translated to the deposition chamber by a bubbling system, and the HfO2 films were deposited as functions of the deposition temperature and O2 gas flow rate. Typical deposition temperature was 300–450°C. Although the source gas has N in the molecule, the amount of residual N was small. The residual C amount was reduced by increasing the injected O2 gas flow rate. On the other hand, the amount of the residual N was almost constant independent of O2 gas flow rate, and was decreased by increasing the deposition temperature.

Synthesis of Novel Sr Sources for Metalorganic Chemical Vapor Deposition of SrTiO3

Novel Sr source materials for metalorganic chemical vapor deposition (MOCVD) of SrTiO3 have been developed. They were synthesized by adding amine, triethylenetetramine (trien) or tetraethylenepentamine (tetraen), to bis-dipivaloylmethanato strontium ( Sr(DPM)2, or strontium-bis-2,2,6,6-tetramethyl-3,5-heptanedionate). The new sources, Sr(DPM)2-trien2 and Sr(DPM)2-tetraen2, have a low melting point (43–75° C), and are liquid in phase when they are vaporized at 120–130° C. SrTiO3 thin films were prepared on Pt/Ta/ SiO2/Si substrates by MOCVD using the new Sr sources. The dielectric constant of films prepared with Sr(DPM)2-trien2 was 215 for 125 nm thick SrTiO3 films, and leakage current densities were below 10-6 A/cm2 at 1.5 V for 80 nm thick SrTiO3 films. The new Sr sources did not change in quality after 20-time heat cycles between room temperature and 130° C in Ar atmosphere at 40 Torr.

Using tetrakis-diethylamido-hafnium for HfO2 thin-film growth in low-pressure chemical vapor deposition

Abstract We synthesized very pure tetrakis-diethylamido-hafnium {Hf[N(C 2 H 5 ) 2 ] 4 :Hf(NEt 2 ) 4 } that can be used as a precursor for depositing Hf-related materials in chemical vapor deposition (CVD). Hf(NEt 2 ) 4 is liquid at room temperature and has a moderate vapor pressure (1 torr at 80 °C). It is stable, and not pyrophoric in the air. HfO 2 film was deposited by low-pressure CVD using the Hf(NEt 2 ) 4 /O 2 gas system. The amounts of residual N and C in the deposited film were decreased when the substrate temperature was increased. Increasing the temperature also improved the step coverage quality of the film deposited on the substrate with a trench. When the film was deposited with Hf(NEt 2 ) 4 and O 2 at 450 °C, the resulting stoichiometric HfO 2 film is polycrystalline with a low impurity concentration and has good step-coverage quality.

Hf1-xSixO2 deposition by metal organic chemical vapor deposition using the Hf(NEt2)4/SiH(NEt2)3/O2 gas system

Abstract Hf1−xSixO2 thin film was deposited on a Si substrate by low pressure chemical vapor deposition using the tetrakis-diethylamido-hafnium {Hf[N(C2H5)2]4}/Tris–diethylamino-silane {SiH[N(C2H5)2]3}/O2 gas system. During the HfO2 deposition, SiH[N(C2H5)]3 vapor was injected and Hf1−xSixO2 film was deposited. By increasing the amount of the supplied SiH[N(C2H5)2]3, the ratio of Si to Hf in the film increased and the refractive index of the film decreased. While the deposited HfO2 film was polycrystalline, Hf1−xSixO2 was amorphous. The step-coverage quality was slightly degraded as a result of the SiH[N(C2H5)2]3 injection. No residual C was detected in the film by XPS measurement indicating that the residual C amount was less than 1%. On the other hand, the amount of residual N increased with an increase in the supply of SiH[N(C2H5)2]3.

Self-Organized CdSe Quantum Dots on (100)ZnSe/GaAs Surfaces Grown by Metalorganic Molecular Beam Epitaxy

II–VI semiconductor low-dimensional structures, quantum dots, have been grown on GaAs substrates by metalorganic molecular beam epitaxy (MOMBE). Before the heteroepitaxial growth, atomically flat, As-stabilized GaAs surfaces were prepared by high-temperature As cleaning using tris-dimethylamino-arsenic (TDMAAs). CdSe thin films deposited on (100)ZnSe/GaAs surfaces have been investigated with atomic force microscopy (AFM) and were found to form three-dimensional islands with rather uniform size distribution. A large mismatch (~7%) of lattice constants between CdSe and ZnSe pseudomorphically grown on GaAs possibly results in the Stranski-Krastanov growth mode. CdSe quantum dots with a diameter of 97±11 nm were successfully formed at 350°C.

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.

N–H related defects in GaAsN grown through chemical beam epitaxy

The local vibration modes of N–H related defects in GaAsN are studied using isotopes. When GaAsN is grown through chemical beam epitaxy (CBE) using triethylgallium/tris(dimethylamino)arsenic/monomethylhydrazine gas, there are several local vibration modes (LVMs) in Fourier transform infrared (FTIR) spectra. Signals with stretching mode peaks at 2952, 3098, and 3125 cm−1 are reported, along with new wagging and stretching mode peaks at 960 and 3011 cm−1, which exist only in crystals grown through CBE. When the film is grown using deuterated MMHy as a nitrogen source, new peaks at 2206, 2302, 2318, 2245, and 714 cm−1 appear. This suggests that D related defects are created because of the deuterated MMHy. The ratios of frequencies of these new peaks to those obtained from crystals grown using MMHy are nearly 1.34. This suggests that all defects in GaAsN grown through CBE, which appear as LVMs, are N–H related defects. Especially, those with LVMs at 960 and 3011 cm−1 are new N–H defects only found in GaAsN grown through CBE.

Effect of Solvent on MOCVD of Pb ( Zr , Ti ) O 3 Films with Liquid-Delivery Source Supply Method

We investigated the effect of a solvent on the metallorganic chemical vapor deposition (MOCVD) of Pb(Zr, Ti)O 3 (PZT) films by comparing conventional bubbling and sublimation delivery methods with one using liquid delivery where the source materials were dissolved in a solvent and vaporized in separate vaporizers. A Pb(C 11 H 19 O 2 ) 2 -Zr(O.t-C 4 H 9 )-Ti(O.i-C 3 H 7 ) 4 -O 2 system was used as the source, while C 8 H 18 was used as the solvent together with C 4 H 8 O. The deposition rates of all constituent oxides decreased with the liquid-delivery method. Moreover, the process window to obtain stoichiometric PZT films [Pb/(Pb + Zr + Ti) = 0.5], irrespective of the supply rate of the Pb source, was diminished with the liquid delivery method, suggesting the contribution of the solvent on the deposition mechanism of PZT film. These phenomena were observed not only with C 8 H 18 but also when C 4 H 8 O was used as a solvent.

Effects of deposition conditions on step-coverage quality in low-pressure chemical vapor deposition of HfO2

Abstract Hafnium dioxide thin film is deposited on a Si substrate with trenches by LPCVD using the Hf(NEt2)4/O2 gas system. When the deposition temperature is 300°C, poor-quality step-coverage is obtained. The step-coverage quality improves as the deposition temperature increases, and the good-quality step coverage is achieved at 450°C. By analyzing the profile of the film thickness in the trench, it is suggested that there are at least two types of important reactants that contribute to the film deposition. One is an active reactant. The contribution of this adsorbate to the film deposition decreases as the substrate temperature increases. On the other hand, the other reactant is a slightly active reactant. When a film is deposited at 450°C, most of the film is deposited from this slightly active adsorbate and good-quality step coverage is obtained.

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.