Masaji Yoshida

Structural and electrical characterization of SrTiO3 thin films prepared by metal organic chemical vapor deposition

SrTiO3 thin films were prepared on Si and Pt/TaOx/Si substrates by Sr(DPM)2/Ti(i-OC3H7)4/O2/Ar chemical vapor deposition (CVD), using a simple vaporizing-and-transport source delivery system. A thickness uniformity of ±5.6% and a composition uniformity of ±2.7% were obtained. The dielectric constant was 210 for 110 nm thick SrTiO3 films (Sr/(Sr+Ti)=0.5) annealed at 600°C for 2 hours. An SiO2 equivalent thickness of 1.1 nm was obtained for 40 nm thick SrTiO3 films, and leakage current densities were 6×10-8 A/cm2 at 1.0 V and 5×10-7 A/cm2 at 1.65 V. The structural and electrical properties were affected by the film composition.

RuO2/TiN-based storage electrodes for (Ba, Sr)TiO3 dynamic random access memory capacitors

Sputtered (Ba, Sr)TiO 3 (BST) thin film capacitors have been fabricated with thick RuO 2 /TiN-based storage electrodes and poly-Si contact plugs, and the electrical properties of the storage electrodes have been studied. The electrode height was higher than 450 nm and the contact size was 0.8 x 0.8 μm 2 . Resistance of the storage electrodes including contact plugs can be evaluated from the dispersion observed in capacitance-frequency measurements. TiN oxidation at the RuO 2 /TiN interface and native oxide at the TiN/Si contact contribute to the electrode resistance of RuO 2 /TiN electrodes. With increasing BST deposition temperature, the thickness of oxidized TiN in RuO 2 /TiN electrbdes increases and the electrode resistance increases correspondingly. A Ru layer inserted at the RuO 2 /TiN interface, a TiN/TiSi 2 /Si junction and rapid thermal annealing in N 2 ambient of the TiN layer are effective ways to reduce the resistance of RuO 2 /TiN-based electrodes.

GaAs growth by atomic layer epitaxy using diethylgalliumchloride

GaAs is grown by metalorganic atomic layer epitaxy (MOALE) using diethylgalliumchloride (DEGaCl) as a new MO source material for ALE and AsH3 in a horizontal, low‐pressure metalorganic chemical vapor deposition system. Monolayer‐unit growth has been obtained over a wide range of growth conditions, including growth temperature and the time of substrate exposure to DEGaCl. This ALE process is called ‘‘digital epitaxy,’’ and its advantages may be seen in its successful application here to extremely uniform GaAs growth on a 3‐in. GaAs wafer. The digital nature of GaAs growth is well explained here using a Langmuir monolayer adsorption model for GaCl, a stable decomposition product of DEGaCl. Growth at higher temperatures leads to a reduction of carbon contamination; and at 600 °C, n‐type layers with a 77 K mobility of 22 400 cm2/V s are obtained.

Chemical Vapor Deposition of ( Ba , Sr ) TiO3

SrTiO 3 and (Ba, Sr)TiO 3 thin films were fabricated on Si and Pt/TaO 2 /Si substrates by chemical vapor deposition (CVD) using Sr(DPM) 2 , Ba(DPM) 2 , Ti(O-i-C 3 H 7 ) 4 , and O 2 where DPM is dipivaloylmethanate or formally 2,2,6,6-tetramethyl-3,5-heptanedionate. The deposition system was operated in both thermal CVD mode and electron cyclotron resonance (ECR) plasma CVD mode. Variations in individual Sr and Ti deposition rates with differing deposition conditions were investigated. The SrTiO 3 and (Ba, Sr)TiO 3 films were characterized with a view to discussing the step-coverage, crystal structure, and electrical properties. The step-coverage over the 300 nm wide SiO 2 lines, with 500 nm height and 500 nm spacing, was 30 to 40%. The 40 to 100 nm SrTiO 3 films, through the postdeposition annealing process, showed dielectric constants >140 with a leakage current density level <10 -7 A/cm at 1 V. The prospects for applying the CVD (Ba, Sr)TiO 3 films to giga-bit dynamic random access memory storage capacitors are discussed

A stacked capacitor technology with ECR plasma MOCVD (Ba,Sr)TiO/sub 3/ and RuO/sub 2//Ru/TiN/TiSi/sub x/ storage nodes for Gb-scale DRAMs

A Gb-scale DRAM stacked capacitor technology with (Ba,Sr)TiO/sub 3/ thin films is described, The four-layer RuO/sub 2//Ru/TiN/TiSi/sub x/, storage node configuration allows 500/spl deg/C processing and fine-patterning down to the 0.20 /spl mu/m size by electron beam lithography and reactive ion etching. Good insulating (Ba/sub 0.4/Sr/sub 0.6/)TiO/sub 3/ (BST) films with an SiO/sub 2/ equivalent thickness of 0.65 nm on the electrode sidewalls and leakage current of 1/spl times/10/sup -/6 A/cm/sup 2/ at 1 V are obtained by ECR plasma MOCVD without any post-deposition annealing, A lateral step coverage of 50% for BST is observed on the 0.2 /spl mu/m size storage node pattern, and the BST thickness on the sidewalls is very uniform, thanks to the ECR downflow plasma. Using this stacked capacitor technology, a sufficient cell capacitance of 25 fF for 1 Gb DRAMs can be achieved in a capacitor area of 0.125 /spl mu/m/sup 2/ with only the 0.3 /spl mu/m high-storage electrodes.

SrTiO3 thin films by mocvd for 1 gbit DRAM application

Abstract Three important aspects of the preparation of SrTiO3 thin films by MOCVD are discussed in detail in view of the application of these films as the capacitor dielectric of Gbit-scale DRAMs: CVD reactions in the Sr(DPM)2-Ti(i-OC3H7)4-O2 system, step coverage and relations between microstructure and electrical properties. The effect of the substrate temperature on the Sr and Ti deposition rates was first investigated for thermal and ECR CVD SrTiO3 films. SrO and TiO2 deposition by thermal CVD above 550°C were found to be controlled by the surface reaction and gas transport, respectively, whereas both SrO and TiO2 deposition are controlled by gas transport for ECR CVD at 450 to 600°C. The influence of the Sr and Ti deposition regimes on the step coverage of SrO, TiO2 and SrTiO3 were then assessed. SrO films prepared by thermal CVD at 600°C exhibited the best step coverage, indicating that a relation exists between reaction controlled deposition and good step coverage. The effect of the film compositio...

Epitaxial growth of Bi‐Sr‐Ca‐Cu‐O superconducting thin films by metalorganic chemical vapor deposition

The epitaxial growth of Bi‐Sr‐Ca‐Cu‐O thin films was achieved by metalorganic chemical vapor deposition. The film‐MgO substrate interface has been examined and discussed using the cross‐sectional transmission electron microscopy. On the smooth surface of the MgO substrate, the lattice of the film was ordered from the first atomic layer on the surface of the substrate, and the misfit dislocations caused by the large lattice mismatch between the film and the MgO substrate appeared every four or five lattices. The first Bi2O2 layer on the substrate surface was found to be regularly arranged regardless of the roughness of the substrate surface. The x‐ray diffraction patterns of the films as a function of the growth time showed that the high Tc phase (Bi2Sr2Ca2Cu3Ox) was not formed in the early stage of the growth while its amount increased as the growth was prolonged. These results suggest that the high Tc phase is not directly grown but formed via the low Tc phase (Bi2Sr2CaCu2Ox) or semiconducting phase (Bi2...

Heavily Si‐doped GaAs grown by metalorganic chemical vapor deposition

Heavily Si‐doped GaAs layers were grown by a metalorganic chemical vapor deposition method using disilane (Si2H6) as a silicon dopant source gas. The grown layers were characterized by the van der Pauw, secondary ion mass spectroscopy, and low‐temperature Fourier transformation infrared spectroscopy (FTIR) method. The carrier concentration has no growth temperature dependence from 550 to 700 °C temperature range. However, it has temperature dependence below 550 °C and above 700 °C. The carrier concentration of Si‐doped GaAs is usually saturated at 6×1018 cm−3 level. Further, Si doping makes the carrier concentration decrease. By using the low‐temperature FTIR method, absorption bands for SiGa, SiAs, SiGa‐SiAs pair, and lower energy bands (374 and 369 cm−1) were observed in heavily Si‐doped GaAs. The peak intensity for SiGa is smaller than that for SiAs, and the peak heights at 374 and 369 cm−1 are relatively larger than that for the other peaks. These facts suggest that, in heavily Si‐doped GaAs, a part o...

Low temperature deposition of (Ba, Sr)TiO3 films by electron cyclotron resonance plasma chemical vapor deposition

(Ba, Sr)TiO 3 films deposited by electron cyclotron resonance plasma chemical vapor deposition at 450°C and 500°C are investigated. The crystallinity, evaluated by X-ray diffraction and by measuring grain size, and electrical properties of films were evaluated for changes in deposition temperature, deposition rate, and Ba content, without a post-deposition annealing. Slower deposition rates as well as higher deposition temperatures were found to improve film crystallinity. Evaluation of electrical properties and film crystallinity revealed that the optimum Ba content of a film deposited at 500°C was 0.4. A 27nm thick film deposited on a Pt substrate at 500°C and at 1.1 nm/min with a Ba content of 0.4 exhibited a SiO 2 equivalent thickness of 0.65 nm and a leakage current density of 4.6 x 10 -7 A/cm 2 at 1V. The film composition was found to be sufficiently uniform throughout, i.e., from the top to the side of the films on a stacked bottom electrode.

Preparation of SrTiO 3 Thin Films by Ecr and Thermal Mocvd

SrTiO 3 thin films were prepared by ECR and thermal MOCVD. In thermal-CVD mode, Sr content and Ti content were at a maximum at 0.56 Torr. Results showed that SrO deposition is a surface reaction limited process between 500 and 650°C, whereas TiO 2 deposition is surface reaction limited between 500 and 600 °C, and diffusion limited above 600 °C. At a low pressure of 8 mTorr, ECR oxygen plasma was found to help decompose Ti(i-OC 3 H 7 ) 4 . In ECR-CVD mode, the deposition temperature could be lowered to 400 °C. TEM and SEM analyses showed that SrTiO 3 thin films have a columnar structure. The size of the grains depends on film thickness, and their shape on film composition (Sr/Ti ). Films prepared by thermal-CVD had a lateral step coverage of 50 %. 40 nm SrTiO 3 thin films (Sr/Ti = 1.0) prepared by thermal-CVD on Pt/TaO x /Si and annealed for 2 hours in O 2 had a maximum dielectric constant of 139 (Cs = 31 fF/μm 2 and teq = 1.1 nm) and a leakage current density of 6x10 −8 A/cm 2 at 1.0 V.