Ichizo Kobayashi

RuO2 Bottom Electrodes for Ferroelectric (Pb, La)(Zr, Ti)O3 Thin Films by Metalorganic Chemical Vapor Deposition

RuO2 thin films were grown on various substrates by metalorganic chemical vapor deposition (MOCVD) using Ru(C11H19O2)3. The films produced at 350° C in O2 had a tetragonal rutile structure and a resistivity of 60 µΩ cm with excellent adhesion. From the viewpoint of integrated device applications, lanthanum-modified lead zirconate titanate (PLZT) films were also prepared by MOCVD. The RuO2 films were found to serve as effective diffusion barriers for PLZT and MgO. Significant interdiffusion at RuO2/Si and RuO2/SiO2 interfaces occurred during the deposition of PLZT films, and annealing of RuO2 film considerably depressed the interface reactions. Ta2O5 film served as an excellent barrier against the interface reaction between RuO2 and Si. The dielectric and ferroelectric properties of PLZT thin films on the RuO2/MgO and RuO2/Ta2O5/Si substrates were superior compared to those observed with RuO2/Si and RuO2/SiO2/Si substrates.

Preparation of (111)-Oriented β-Ta2O5 Thin Films by Chemical Vapor Deposition Using Metalorganic Precursors

Tantalum pentaoxide thin films with orthorhombic structure have been grown on quartz and Si(100) substrates at 600~700°C under reduced pressure of 5 Torr by metalorganic chemical vapor deposition. Ta(OC2H5)5 and Ta(DPM)4Cl were used as the source materials, and were compared with each other with respect to deposition behavior, crystal structure and orientation of Ta2O5 films. When the Ta(DPM)4Cl precursor was used, fine (111)-oriented Ta2O5 films were obtained on quartz and Si(100) substrates in a temperature range of 625~675°C.

Preparation of SrTiO3 Thin Films by Metalorganic Chemical Vapor Deposition

Strontium titanate ( SrTiO3) thin films were grown by means of the metalorganic chemical vapor deposition (MOCVD) method using dipivaloylmethane (DPM) chelate of strontium (II) [ Sr(DPM)2] and titanium tetraisopropoxide as source materials. In the preliminary experiments, the deposition behaviors of SrO and TiO2 films from respective sources were examined separately. As-grown perovskite single-phase SrTiO3 films were obtained at the substrate temperature of 750° C under the reduced pressure of 530 Pa. The films deposited on the MgO (100) substrate showed high (100) orientation and good optical transmission spectra, with the refractive index of 2.35. The dielectric constant and dielectric loss were 150–250 and 0.01–0.04, respectively. The leakage current density of the 0.38 µ m-thick films was approximately 3×10-8 A/cm2 at 3 V.

Preparation of SrTiO3 Films on 8-Inch Wafers by Chemical Vapor Deposition

SrTiO 3 films were grown on 8-inch-diameter Si substrates by chemical vapor deposition [CVD] using bis(dipivaloylmethanato) strontium [Sr(DPM) 2 ], titanium tetraisopropoxide [Ti(OiPr) 4 ] and O 2 . We have developed an oil-circulating showerhead-type nozzle to prevent condensation and decomposition of source materials. Conditions of supplying Sr(DPM) 2 were investigated with respect to cylinder pressure and the charge in the cylinder, using a simple vapor transport system. The deposition rate of SrTiO 3 films on 8-inch wafers was improved to 2nm/min by increasing the charge in the source cylinder and decreasing the cylinder pressure. A thickness uniformity of 3.4% and a composition uniformity of 4.6% were obtained by complete mixing of gases. A step coverage of 85% was obtained using Sr(DPM) 2 , titanyl bis(dipivaloylmethanato) [TiO(DPM) 2 ] and N 2 O.

Preparation of Pb(Zr, Ti)O3 thin films using all dipivaloylmethane source materials by metalorganic chemical vapor deposition

Pb-bis-dipivaloylmethane [Pb(DPM)2], Zr(DPM)4 and Ti(DPM)2(i-OC3H7)2 are developed as the new chemical vapor deposition (CVD) sources for lead zirconate titanate (PZT) thin film. The growth rate of each of the single metal oxides PbO, ZrO2 and TiO2, was studied as a function of oxygen partial pressure. The growth rates of ZrO2 and TiO2 were independent of the input oxygen partial pressure, while the growth rate of PbO increased with increasing input oxygen partial pressure. PZT films were grown on (100) MgO substrates at 2.0 Torr by metalorganic chemical vapor deposition (MOCVD). The film grown at 500°C was amorphous. The film grown at 550°C was a mixed phase of a-axis- and c-axis-oriented perovskite. The film grown at 600°C was a single-phase c-axis-oriented perovskite.

Metal Complexes for Preparing Ferroelectric Thin Films by Metalorganic Chemical Vapor Deposition

Recently, metal β-diketonato complexes have been used as a gas source for preparing ferroelectric thin films by metalorganic chemical vapor deposition (MOCVD). Since we have synthesized highly purified metal dipivaloylmethanato (DPM) complexes such as Pb(DPM)2, Sr(DPM)2 and Ba(DPM)2 for ferroelectric thin films, we have investigated several properties of these chelate compounds related to depositing thin films. Their volatility and toxicity have also been investigated. As a result, it has been found that these chelate compounds have low vapor pressure, but present the advantages of easy handling because of the low toxicity and the possibility of forming thin films at lower temperature.

Effect of Substrate Temperature on Electrical Characteristics of (Pb, La)(Zr, Ti)O3 Ultrathin Films Deposited by Metalorganic Chemical Vapor Deposition

Lanthanum-modified lead zirconate titanate (PLZT) thin films (50-200 nm) were deposited on Pt/SiO 2 /Si substrates by metalorganic chemical vapor deposition (MOCVD). The electrical properties of the films were investigated as functions of the La content and substrate temperature. Ferroelectric PZT films were obtained at a substrate temperature as low as 500°C, and their electric characteristics were improved with increasing substrate temperature. La was adequately solid-dissolved into the PZT above 650°C. PLZT(15/45/55) films having a thickness of 100 nm were found to have good properties for application to capacitors of dynamic random access memory (DRAM), i.e., effective charge density of 80 fF/μm 2 , dielectric constant of 1000, SiO 2 equivalent thickness of 0.4 nm and leakage current density of 5 x 10 -8 A/cm 2 . La addition to PZT was effective in reducing the leakage current with an increase in the registration rate.

Synthesis of Ti(DPM)2(OCH3)2 and Evaluation of the TiO2 Films Prepared by Metal-Organic Chemical Vapor Deposition

Highly pure Ti(DPM) 2 (OCH 3 ) 2 was synthesized by an exchange reaction of Ti(DPM) 2 (i-OC 3 H 7 ) 2 with CH 3 OH. The Ti(DPM) 2 (OCH 3 ) 2 is a white crystalline material with a melting point of 80.1°C, having a high vapor pressure the source temperature of 90°C, which enable its stable supply for a long time. At the film deposition temperatures of PZT and BST (500°C-650°C), no gas phase nucleation reaction was observed. The order of the performance of the step coverage for several titanium source materials was Ti(DPM) 2 (OCH 3 ) 2 > Ti(DPM) 2 (i-OC 3 H 7 ) 2 > Ti(DPM) 2 Cl 2 > Ti(i-OC 3 H 7 ) 4 . In the case of Ti(DPM) 2 (OCH 3 ) 2 , the step coverage for the Si substrate with an aspect ratio of 1.0 was 80% under the TiO 2 film deposition conditions of 650°C and 1 Torr.