Kimihiro Sasaki

Etching Effect of Hydrogen Plasma on Electron Cyclotron Resonance-Chemical Vapor Deposition and Its Application to Low Temperature Si Selective Epitaxial Growth

Si etching properties by H2 plasma generated using the ECR technique were investigated. The etch rate increases in the order of (111) < (110) < (100). This phenomenon is explained by the bond formation of the Si atoms and the number of the atomic layer for each orientation. Si epitaxial growth was examined by the ECR plasma CVD technique using a SiH4–H2 gas system. At the substrate temperature of 150°C, although the crystallinity degrades with an increase of the film thickness, we confirmed epitaxial growth. An appropriate etching process with H2 plasma, which enhances rearrangement of the Si atoms, is important for Si epitaxial growth at low temperatures. Si epitaxial films with excellent crystallinity and smooth surface morphology as determined by observation of the Kikuchi-lines were obtained at 450°C. Complete selective epitaxial growth was successfully realized at substrate temperature of 150°C by utilizing the etch rate difference for the crystallinity of deposited films. However, the epitaxial thickness was limited to approximately 40 nm. For the substrate temperatures higher than 150°C, the film polycrystallization on an SiO2 substrate degraded the selectivity.

Analysis of Sputter Process on a New ZrTi+PbO Target System and Its Application to Low-Temperature Deposition of Ferroelectric Pb(Zr,Ti)O3 Films

An rf reactive sputter deposition technique was adopted to deposit ferroelectric lead zirconate titanate (PZT) thin films from a ZrTi (50%/50%) alloy target combined with PbO pellets. Deposition characteristics including the effects of PbO area ratio were discussed. A new deposition mode called the near-metallic mode was observed. The crystallinity and the composition of the films prepared in the near-metallic mode were investigated as functions of PbO area ratio and substrate temperature. Excess Pb supply tended to enhance perovskite phase formation. Near-stoichiometric perovskite PZT films were obtained at a substrate temperature as low as 450° C. On the other hand, for a PZT+PbO target, perovskite PZT films were obtained only at temperatures higher than 540° C. Deposition rate of perovskite films from the ZrTi+PbO target was 2–3 times higher than that from the PZT+PbO target.

High-rate reactive deposition of indium oxide films on unheated substrate using ozone gas

Abstract The effectiveness of ozone incorporation in reactive gas of oxygen for producing indium oxide films by DC reactive magnetron sputtering employing a metal target has been investigated. It was found that 4% volume concentration of O 3 in addition to oxygen greatly enhanced the reactivity of the sputtered particles on the substrate of growing surface without substrate heating. The deposition rate of stoichiometric oxide film is found much greater in ozone added environment than that of growing in only oxygen environment.

Electrical Properties of Low-Temperature (450°C) Pb(Zr,Ti)O 3 Films Prepared in Quasi-Metallic Mode by RF Reactive Sputtering

Ferroelectric lead zirconate titanate (PZT) thin films were prepared on Pt/Ti/SiO 2 /Si substrates from a ZrTi (50%/50%) alloy target combined with PbO pellets using an rf reactive sputter deposition technique. Perovskite PZT films were obtained at a growth temperature as low as 450°C in the quasi-metallic mode. Crystalline structure, depth profiles, ferroelectric and dielectric characteristics of the films prepared from the (ZrTi+30%PbO) target were investigated. The interdiffusion between the PZT film and the Pt/Ti/SiO 2 /Si substrate was suppressed by the low-temperature sputtering. The remanent polarization, leakage current and dielectric constant decrease with increasing growth temperature. The perovskite films prepared at 450°C exhibit the remanent polarization of 20 μC/cm 2 , the coercive field of 150kV/cm, the leakage current smaller than 10 -6 A/cm 2 at the electric field lower than 235 kV/cm, and the dielectric constant as high as 561.

Growth and dielectric properties of tetragonal ZrO2 films by limited reaction sputtering

Recently, crystallized gate dielectrics have attracted considerable interest due to their high performance in dielectric properties. We investigated the growth of crystalline ZrO2 films prepared on Si (1 0 0) by the limited reaction sputtering system under different growth temperatures from 400 to 700 °C. The structural characteristics of the samples were studied by x-ray diffraction, reflection high-energy electron diffraction and atomic force microscopy, respectively, which provide a solid identification of the phase transformation from the monoclinic phase to the tetragonal phase. The dielectric properties were studied by C–V and I–V measurements on Au/ZrO2/Si (1 0 0) MIS structures, suggesting that the electrical properties are strongly influenced by the crystalline structures. Furthermore, the tetragonal ZrO2 thin film exhibits a high permittivity up to 32 as well as a negligible flatband voltage shift in C–V curves. The results indicate that the tetragonal ZrO2 dielectric appears to be a very promising high-k candidate for future ULSI devices.

Hall Mobility of Low-Temperature-Deposited Polysilicon Films by Catalytic Chemical Vapor Deposition Method.

Nondoped polysilicon films are deposited at temperatures as low as 260°C by the catalytic chemical vapor deposition (cat-CVD) method using a silane and hydrogen gas mixture. Electrical properties such as the Hall mobility are investigated for various measuring temperatures. It is found that the Hall mobility depends on the hydrogen flow rates during deposition and is larger than 20 cm2/Vs, and that the barrier height at the grain boundary appears to be lower than the thermal activation energy at room temperature.

Preparation of perovskite, Pb(Zr, Ti)O3 thin-films on YSZ( 111)/Si( 111) substrates by post-deposition annealing

Abstract Perovskite Pb(Zr, Ti)O 3 [PZT] thin-films on yttria-stabilized zirconia [YSZ] (111)/Si(111) substrates were prepared at various growth temperatures by quasi-metallic mode reactive sputtering (QMMRS) system using a (ZrTi+ x %PbO) composite target. The surface of the PZT film deposited on a YSZ(111)/Si(111) substrate, however, revealed many holes (no growth region of PZT film). These holes could be eliminated by using a post-deposition annealing process. Perovskite Pb(Zr, Ti)O 3 thin films were obtained by an annealing process at temperatures of approximately 600°C in an oxygen gas atmosphere for 1 h. Moreover, ferroelectric properties were observed on Pb(Zr, Ti)O 3 thin films/YSZ(111)/Si(111) structure.

Anomalous Large Thermoelectric Power on Heavily B-Doped SiGe Thin Films with Thermal Annealing.

The thermoelectric properties of heavily B-doped SiGe thin films were studied. The electrical resistivity in the high-temperature region was very low, which suggests the possibility of high-temperature use of heavily doped SiGe films. After thermal annealing, the low-temperature deposited samples showed collapse of the superlattice structure. As deposited condition, the samples might be in amorphous like SiGe thin films apart from good crystallinity. In these films, the anomalous large thermoelectric power was observed in the room temperature region. The power factor reached 4×100 W/mK2 at 400 K and 1×100 W/mK2 at 900 K.

Low-temperature fabrication of Pb(Zr,Ti)O3 films by RF reactive sputtering using Zr/Ti + PbO target

Pb(Zr,Ti)O 3 (PZT) films were grown on fused quartz substrates by reactive sputtering using a Zr/Ti (50%/50%) alloy target combined with PbO pellets under argon pressure of 10mTorr and O 2 /Ar flow rate ratio of 2.1%. Structure and deposition rate of the films have been investigated as functions of substrate temperature and PbO content. When films were grown in near metallic mode using a Zr/Ti + 41%PbO target, perovskite PZT films were successfully prepared at a temperature as low as 450°C, and in the wide range from 450°C to 570°C. It was impossible to obtain perovskite PZT films using only a stoichiometic Pb(Zr 0.5 Ti 0.5 )O 3 ceramic target, while perovskite PZT films could be obtained between 540°C and 570°C using a Pb(Zr 0.5 Ti 0.5 )O 3 + 15%PbO target. Deposition rate of perovskite films for the Zr/Ti + 41%PbO target was 2-3 times higher than that for the PZT + 15%PbO target.

Properties of indium tin oxide films with indium tin modulation layers prepared by nano-scale controlled reactive magnetron sputtering

Abstract A new preparation method for tin-doped indium oxide (ITO) films containing nano-scale indium tin (IT) sandwich layer(s) by the combined use of reactive and non-reactive d.c. magnetron sputtering is proposed. The film properties vary markedly with the number of IT layers and the thickness ratio m of the IT layer to the ITO layer. The lowest resistivity of a 100 nm film is 5.8 × 10−4 Ω cm with IT layers, but 9.8 × 10−4 Ω cm without IT layers. The transparency of the film is greater than 90% in the visible region.