M. L. Lucía

Optical spectroscopic study of the SiN∕HfO2 interfacial formation during rf sputtering of HfO2

High-k stacks formed by chemical-vapor-deposited SiN and high-pressure sputtered HfO2 in either O2 or Ar atmosphere have been studied. The introduction of a SiN layer is proposed to prevent the uncontrollable SiO2 growth while sputtering. The formation of Si–O bonds after the sputtering of the HfO2 film in O2 atmosphere was observed by infrared spectroscopy. Optical diagnosis of the plasma demonstrated a high density of O radicals in the system when working with O2. The small radius and high reactivity of these O radicals are the source of the SiN oxidation. However, the structure of the SiN film is preserved during Ar sputtering.

Chalcopyrite CuGaxIn1−xSe2 semiconducting thin films produced by radio frequency sputtering

CuGaxIn1−xSe2 thin films have been deposited by rf sputtering from three targets with different (Ga,In) content (x=0.25, x=0.5, and x=0.75). A structural, compositional, optical, and electrical study has been carried out for films grown at substrates temperatures higher than 350 °C. We have successfully obtained chalcopyrite single phase stoichiometric films. Very sharp absorption edges are obtained, with band gaps of 1.12, 1.35, and 1.51 eV for x=0, x=0.5, and x=0.75, respectively.

Optical spectroscopic study of the growth dynamics of radio‐frequency‐sputtered YBa2Cu3O7−x thin films

An optical spectroscopic study of the plasma produced during rf sputtering of an YBa2Cu3O7−x target was performed to analyze two basic properties of the deposition process: resputtering effects and oxidation mechanisms. Strong emissions of all the species above a value of the target voltage were found. These observations are associated to a strong secondary electron emission of the target which originates a negative self‐bias of the substrate and a subsequent resputtering by argon cations. The addition of different amounts of oxygen to the discharge reveals that preoxidation in the gas phase may decrease the oxygen content in the films: the oxidation of the films is dominated by atomic oxygen.

Scandium oxide deposited by high-pressure sputtering for memory devices: Physical and interfacial properties

Scandium oxide (ScO(x)) thin layers are deposited by high-pressure sputtering (HPS) for physical and electrical characterization. Different substrates are used for comparison of several ScO(x)/Si interfaces. These substrates are chemical silicon oxide (SiO(x)), H-terminated silicon surface and silicon nitride (SiN(x)), obtained by either electron-cyclotron-resonance chemical vapor deposition or plasma enhanced nitridation of the Si surface. Transmission electron microscopy images show that a 1.7 nm thick SiO(x) layer grows when ScO(x) is deposited on H-terminated silicon surface. We demonstrate that interfacial SiN(x) has some advantages over SiO(x) used in this work: its permittivity is higher and it presents better interface quality. It also avoids Si oxidation. An improvement of one order of magnitude in the minimum of interface trap density is found for SiN(x) with respect to the SiO(x), reaching values below 2 x 10(11) cm(-2) eV(-1). HPS deposited ScO(x) films are polycrystalline with no preferential growth direction for the used deposition conditions and their properties do not depend on the substrate. This material could be a candidate for high-k material in flash memory applications.

Optimization of in situ plasma oxidation of metallic gadolinium thin films deposited by high pressure sputtering on silicon

Gadolinium oxide thin films were deposited on silicon by a two-step process: high pressure sputtering from a metallic gadolinium target followed by an in situ plasma oxidation. Several plasma conditions for metal deposition and oxidation were studied in order to minimize the growth of a SiOx layer at the interface between the high permittivity dielectric and the silicon substrate and to avoid substrate damage. Plasma emission was studied with glow discharge optical spectroscopy. The films were structurally characterized by Fourier transform infrared spectroscopy. Metal–insulator–semiconductor capacitors were fabricated with two different top metals (titanium and platinum) to analyze the influence of deposition conditions and the metal choice. Pt gated devices showed an interfacial SiOx regrowth after a forming gas annealing, while Ti gates scavenge the interface layer.

Electrical and chemical characterization of high pressure sputtered scandium oxide for memory applications

Scandium oxide was deposited by means of high pressure sputtering in the same conditions on differently prepared (100) Si substrates: chemical oxide, nitrided Si and deposited silicon nitride. Time-of-flight secondary ion mass spectroscopy and X-ray photoemission spectroscopy show that polycrystalline Sc2O3 films were grown with a composition which is constant with depth. According to Capacitance-Voltage hysteresis measurements, nitrided Si or deposited SiNx proved to present a lower density of defects in the interface as compared to RCA native oxide.

Fiske steps and hysteresis in YBa2Cu3O7 grain boundary Josephson junctions: Structural information of the barrier by means of a nondestructive approach

A deep analysis of the current-voltage (I-V) characteristics of YBa2Cu3O7 grain boundary Josephson junctions (GBJJs) allows us to go much farther than the usual calculus of the transport parameters. It is possible to construct a structural image of the barrier by an exhaustive and complementary analysis of both transport and electromagnetic parameters obtained from I-V curves. For such an approach, we have chosen the following three representative bicrystalline geometries: 24 degrees [001] asymmetric, 45 degrees [100] asymmetric, and 24 degrees [001] symmetric +45 degrees [100] asymmetric. The dependence of the product ICRN on the junction normal resistance is of the ICRN-1 type pointing to a SNINS model (S denotes superconductor, I denotes insulator, and N denotes normal metal) for all our GBJJs. A satisfactory explanation of the discrepancy of the capacitance of the barrier estimated from Fiske resonance positions and hysteresis in the I-V curves needs of such a model. Moreover an estimation of the length of the normal regions adjacent to the crystallographic barrier can be made. This comparative analysis is presented in order to extract interesting information about the particular transport mechanisms involved in these GBJJs.

Interface engineering by metal electrode scavenging of Gd 2 O 3 films sputtered on Si

Amorphous Gd2O3 thin films were grown on Si by high-pressure sputtering (HPS). In order to minimize the uncontrolled interfacial SiOx, a metallic Gd film was deposited in Ar atmosphere, and afterwards it was in situ plasma oxidized in an Ar/O2 plasma. For postprocessing interfacial SiOx reduction several top metal electrodes were studied: platinum, aluminum and titanium. It was found that Pt did not react with the electrode or interface. On the other hand, Al reacted with the dielectric reducing capacitance. Finally, Ti was effective in reducing the SiO2 interface thickness without severely compromising gate dielectric leakage.

Growth of Silicon Nitride on Silicon by Electron Cyclotron Resonance Plasma Nitridation

In this work we report the formation of silicon nitride films on silicon substrates by N2 Electron Cyclotron Resonance plasma nitridation. An absorption band located around 860-890 cm-1 was observed in the infrared spectra, which is slightly above the wave number of the characteristic silicon nitride band. According to ellipsometry measurements performed at ¿= 532 nm, the thickness of the films ranged from 1.2 nm to 3.6 nm for nitridation times between 0.5 min. and 60 min. An empirical exponential law for the thickness as a function of nitridation time was found. The obtained refractive index values were higher than the expected for stoichiometric silicon nitride, which indicates that the films may be slightly silicon rich. Cross section Transmission Electron Microscopy showed the formation of a thin layer on top of the silicon with thickness consistent with the values obtained by ellipsometry. Energy Dispersive X-ray analysis confirmed the presence of N in this layer.