Junji Tanimura

Dielectric Properties of (Ba, Sr)TiO3 Thin Films Deposited by RF Sputtering

Thin films of (Ba0.65Sr0.35)TiO3 (BST) have been prepared by an rf-sputtering method at substrate temperatures of 500 to 700°C. The dielectric constant of these films ranges from 190 to 700 at room temperature. This value changes with the grain size rather than the film thickness. The dielectric constant of about 300 and leakage current density of about 1×10-8 A/cm2 are obtained in the 65-nm-thick film deposited at a substrate temperature of 600°C. This shows the BST film can be applied to dielectrics of dynamic random access memory (DRAM) capacitors.

Structure of stacking faults formed in pairs in a ZnSe epitaxial layer on a GaAs(001) buffer layer

Structure of stacking faults formed in pairs in a ZnSe epitaxial layer grown by gas source molecular beam epitaxy on a GaAs(001) buffer layer was determined with transmission electron microscopy. Extrinsic type stacking faults were formed on (111) and (111) planes with the same polarity, which was determined by convergent‐beam electron diffraction. The two stacking faults meet at a point which is a few atomic layers away from the interface between ZnSe and GaAs. Partial dislocations at the edge of the stacking faults were found to be the Shockley type ones with a Burgers vector of 1/6〈211〉. Probable formation processes of the stacking faults have been discussed.

XPS study of H-terminated silicon surface under inert gas and UHV annealing

We have investigated the changes of chemical bonding states of an H-terminated silicon surface under inert gas (Ar,N 2 ) and ultrahigh vacuum (UHV) annealing using X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). SiC is formed (corresponding to ∼0.1 monolayer) under inert gas and UHV annealing at around 500°C, which is coincident with the temperature of the dangling bonds formation at the silicon surface by hydrogen desorption, whereas SiC is not formed under O 2 annealing. From the precise analysis using a combination of XPS and TDS, the SiC formation is related to the reaction between the silicon surface and the organic contamination that is unavoidably adsorbed during air exposure. We also studied the electrical properties of metal oxide semiconductor capacitors with a chemical vapor deposited silicon oxide gate insulator formed on Ar- and O 2 -annealed silicon surfaces. Ar preannealing increases the leakage current by approximately 10 - 4 times compared with O 2 annealing.

In-plane orientation and coincidence site lattice relation of (001) Bi2Sr2CaCu2Ox formed on (001) MgO

Abstract A (001) Bi 2 Sr 2 CaCu 2 O x thin film fabricated on a (001) MgO substrate has been found to consist of two kinds of domain with in-plane orientation of Bi 2 Sr 2 CaCu 2 O x [100]∥MgO [510] and Bi 2 Sr 2 CaCu 2 O x [100] ∥MgO [5 1 0]. It is shown that near coincidence site lattice theory supports the occurence of this in-plane orientation. The dependence of the in-plane orientation on the substrate temperature was also investigated.

Study of plasma–surface interactions during overetch of polycrystalline silicon gate etching with high-density HBr/O2 plasmas

Plasma–surface interactions occurring during overetch of polycrystalline silicon (poly-Si) gate etching with high-density HBr/O2 plasmas have been investigated by x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The temporal variation of the gate oxide thickness measured by XPS indicates that both deposition of etch by-products SiBrxOy and oxidation of Si substrate underlying thin SiO2 occur during exposure to HBr/O2 plasmas. In particular, significant deposition of SiBrxOy, presumably coming from reactor walls, was observed at the beginning of the overetch step. Furthermore, TEM observations revealed that the profile evolution of oxide-masked poly-Si gates during overetch is limited by a sidewall deposition layer, which acts as an oxide mask for etching of poly-Si.

Low thermal budget surface cleaning after dry etching for selective silicon epitaxial growth

We studied the influence of plasma etching damage on epitaxial Si growth using ultrahigh vacuum chemical vapor deposition. The damaged layer induced on substrate surface had an amorphous structure that had some carbon, oxygen, and fluorine in its composition. The damaged layer was removed by in situ preheating above 850°C, before the growth, or by chemical dry etching (CDE). We found that CDE has the effect of decreasing the preheating temperature by 200°C as compared to the case without CDE. Furthermore, the dependence of the surface roughness of grown films on post-etching treatments is also discussed.

Angle resolved X-ray photoelectron spectroscopic study of ultrathin oxynitrides

Abstract We studied nitrogen distribution, concentration and chemical state in NO- and N2O-exposed silicon oxide films, to understand the relationship between nitridation and suppression of stress-induced leakage current (SILC) resulting from Fowler–Nordheim (F–N) stress. We applied angle resolved X-ray photoelectron spectroscopy (ARXPS) and electron energy loss spectroscopy (EELS) to obtain information at less than 2-nm thick film-substrate interface layers. Si3N4-like layer is formed only at the film-substrate interface in NO oxynitride. Nitrogen atoms in N2O oxynitride are broadly distributed in the oxynitride film near the interface because the interface moves deeper from the surface during N2O nitridation due to both oxidation and nitridation proceed simultaneously. SILC of both NO and N2O oxynitride decrease exceedingly. It is clear that both NO and N2O nitridation is effective in suppressing SILC in spite of the quite difference in the distribution, concentration and chemical state of nitrogen atoms.

Influence of Buffer Layers and Barrier Metals on Properties of (Ba, Sr)TiO3 Films Prepared by Liquid Source Chemical Vapor Deposition

The characteristics, especially the electrical properties, of (Ba, Sr)TiO 3 [BST] films obtained by a two-step process of liquid source chemical vapor deposition (CVD) on two types of substrates or Ru/Si and Ru/TiN/Ti/Si structures have been investigated. First, the studies on the best deposition conditions for BST buffer layers on Ru/Si substrates indicated that more crystallized buffer layers improved the electrical properties of the two-step-deposited BST films. The reproducibility of the measured thicknesses was 1.5% (1σ) and that for t eq -values of equivalent SiO 2 thicknesses was 5.4% (1σ) for seven consecutive two-step runs on Ru/Si substrates. Moreover, the insertion of the barrier metals TiN/Ti between Ru and Si, which was stable enough for back-end processing at high temperatures, increased the degree of some crystal orientations of BST and Ru films; however, it hardly changed the electrical properties of the BST films deposited in two-steps.

(01n)-Oriented BiSrCaCuO Thin Films Formed on CeO2 Buffer Layers

With the use of RF magnetron sputtering, (01n)-oriented BiSrCaCuO superconducting films were first formed using MgO(110) substrates with CeO2(110) buffer layers. The film obtained using the just MgO(110) substrate had (01n)- and (0n)-preferred orientations with the c-axis tilted 45° against the surface of the CeO2 buffer layer. Moreover, with the use of an off-oriented MgO(110) substrate, a uniquely oriented BiSrCaCuO film with the c-axis not perpendicular to the substrate surface was obtained without twin boundaries.

BiSrCaCuO Thin Film Grown on SrTiO3 Substrate with Off-Oriented (110) Surface

A Bi2(Sr, Ca)3Cu2Ox thin film with the (117) orientation was formed on a slightly off-oriented (110) SrTiO3 substrate by single-target sputtering. The (110) substrate off-oriented by 5° is considered to have limited film growth in one direction. From RHEED and cross-sectional TEM observations, it was found that the c-axis of the film tilts against the substrate surface by 46-47° and the SrTiO3(110) plane by 41-42°. Also, the surface morphology observed by SEM has been much improved.