Kazuki Komaki

Chemical Vapor Deposition of Low Hydrogen Content Silicon Nitride Films Using Microwave-Excited Hydrogen Radicals

The chemical vapor deposition method using hydrogen radicals excited by microwave plasma has been applied to obtain silicon nitride (SiN) films of low hydrogen content. In this method, silane and monomethylamine were used as source gases. Various properties of deposited films such as the composition of SiN, the residual contents of carbon and oxygen, and the deposition rate were influenced by growth conditions. In the growth conditions, the distance between the center of the waveguide and the substrate was the most critical parameter because the distribution of the H radical strongly depended upon it in our experiment. For a suitable substrate position, carbon and oxygen contents could be reduced to a small value. On the other hand, residual hydrogen content was less than ~1×1022 cm-3. This value was a quarter of that in the films grown by silane and ammonia gases under similar conditions.

Ferroelectric Properties of (Na0.5K0.5)NbO3-Based Thin Films Deposited on Pt/(001)MgO Substrate by Pulsed Laser Deposition with NaNbO3 Buffer Layer

(Na0.52K0.44Li0.04)(Nb0.84Ta0.10Sb0.06)O3 (NKLNTS) thin films with a thickness of about 1.4 µm were fabricated on Pt/(001)MgO substrate, on which an NaNbO3 buffer layer was introduced, by pulsed laser deposition (PLD). The X-ray diffraction pattern (XRD) showed that the 001 orientated NKLNTS thin films were grown on Pt/(001)MgO substrate. A rocking curve measurement revealed that the fluctuation of the crystalline orientation of the 001 orientated NKLNTS thin films is very small. The lattice parameters of the 001 orientated NKLNTS thin films were a=0.3911 nm and c = 0.3942 nm, determined by reciprocal space map. The dielectric constant, er, and the dielectric loss, tan δ, of the NKLNTS thin film were 398 and 0.22 at 1 kHz, respectively. The large tan δ is due to NKLNTS having a morphotropic phase boundary region around room temperature. The P–E hysteresis loops of the NKLNTS thin films showed clear ferroelectricity. The remanent polarization, Pr, and coercive electric field, Ec, were 26.3 µC/cm2 and 28.6 kV/cm, respectively. The NKLNTS thin films exhibited larger Pr value than NKLNTS ceramic.

Preparation of Pyroelectric Pb1-xLaxTi1-x/4O3 Thin Films from Ceramic Target by RF Magnetron Sputtering

Pyroelectric Pb1-x Lax Ti1-x /4O3 thin films of high quality have been obtained reproducibly by rf magnetron sputtering using a ceramic target. The effects of sputtering parameters on film composition and structure have been studied and related to plasma emission spectroscopy. By controlling the relative intensities of Pb* (406 nm) and Ti* (396 nm) emissions of the plasma, the sputtering conditions were optimized to produce stoichiometric and highly c-axis-oriented filins. Under stabilized conditions, use of the ceramic target offered stability of the plasma and a high deposition rate of 2 A/s. The PLT film exhibited good pyroelectric parameters with a dielectric constant of 290 and a pyroelectric coefficient of 4.2×10-8 C/cm2 K.

Development of Pt/MgO(100) Buffer Layers for Orientation Control of Perovskite Oxide Thin Films

(100)-oriented MgO thin films can be effectively grown at a substrate temperature of room temperature (RT) on Fe seed layers by the facing-targets sputtering (FTS) method. Pt(100) orientation was observed when the Pt layer was deposited on MgO(100)/Fe buffer layers at a substrate temperature above 350 ?C. Pt thin films can be grown effectively with (100) orientation and with smaller strain when they are prepared at a substrate temperature above 500 ?C. Also, Ba1-xSrxTiO3 (BST) thin films with (100) preferential orientation can be grown on Pt(100)/MgO(100)/Fe buffer layers when Pt and BST films are deposited at a substrate temperature of 500 ?C. Pt(100)/MgO(100)/Fe buffer layers are very effective for attaining BST(100) orientation.

Preparation of La-Modified Lead Titanate Thin Films by Rf-Magnetron Sputtering Method and Their Pyroelectric Properties

High-quality La-modified lead titanate (PLT) films were grown on MgO substrates by an rf-magnetron sputtering method. In this method, intermittent deposition was realized by periodical repetition of deposition and nondeposition processes with rotation of the substrate holder. The difference between intermittent and continuous methods was examined in terms of the crystal structure and the pyroelectric properties of the films. Intermittent deposition was found to enhance the horizontal grain growth of the films. Excellent PLT films with a high pyroelectric coefficient of 5.0×10-8 C/cm2·K and low dielectric constant of 185 were reproducibly obtained by this method.

Fabrication of Lead-Free (Na0.5K0.5)NbO3–BaZrO3–(Bi0.5Li0.5)TiO3 Ferroelectric Thin Films on (111)Pt/Ti/SiO2/(100)Si Substrate by Pulsed Laser Deposition

0.92(Na0.5K0.5)NbO3–0.06BaZrO3–0.02(Bi0.5Li0.5)TiO3 (NKN–BZ–BLT) thin films were fabricated on a (111)Pt/Ti/SiO2/(100)Si substrate by pulsed laser deposition (PLD). The quality of the NKN–BZ–BLT thin films was improved by introducing an NKN–BZ–BLT buffer layer, which was deposited at a high substrate temperature of 850 °C. An X-ray diffraction pattern (XRD) showed that the 100pt preferential-oriented NKN–BZ–BLT thin films [on the basis of a pseudotetragonal perovskite (pt) structure] were obtained without and with buffer layers. From the rocking curves, the crystallinity of the film was slightly improved by introducing the buffer layer. SEM images showed that the grain size was increased and cracks were eliminated by introducing the buffer layer. The dielectric constant of the films was comparable to that of NKN–BZ–BLT ceramics. The P–E hysteresis loops showed that the remanent polarization and spontaneous polarization of the films increased with the increase in the thickness of the buffer layer. The NKN–BZ–BLT film with a 0.8-µm-thick buffer layer exhibited a remanent polarization of 6.7 µC/cm2 and a spontaneous polarization of 28.0 µC/cm2. This improvement of the ferroelectric properties would be due to the relaxation of the tensile stress in the presence of the buffer layer.

Growth of amorphous SiN films by chemical vapor deposition using monomethylamine

Chemical vapor deposition of silicon nitride film has been studied by using SiH4 and NH2CH3 as source gases for the deposition temperature region of 700~900°C. The deposition rate was somewhat larger than that of the case using SiH4 and NH3 gases. The film deposited at 900°C had a particularly smooth specular surface.