R. L. Opila

Properties of high κ gate dielectrics Gd2O3 and Y2O3 for Si

We present the materials growth and properties of both epitaxial and amorphous films of Gd2O3 (κ=14) and Y2O3 (κ=18) as the alternative gate dielectrics for Si. The rare earth oxide films were prepared by ultrahigh vacuum vapor deposition from an oxide source. The use of vicinal Si (100) substrates is key to the growth of (110) oriented, single domain films in the Mn2O3 structure. Compared to SiO2 gate oxide, the crystalline Gd2O3 and Y2O3 oxide films show a reduction of electrical leakage at 1 V by four orders of magnitude over an equivalent oxide thickness range of 10–20 A. The leakage of amorphous Y2O3 films is about six orders of magnitude better than SiO2 due to a smooth morphology and abrupt interface with Si. The absence of SiO2 segregation at the dielectric/Si interface is established from infrared absorption spectroscopy and scanning transmission electron microscopy. The amorphous Gd2O3 and Y2O3 films withstand the high temperature anneals to 850 °C and remain electrically and chemically intact.

Profiling nitrogen in ultrathin silicon oxynitrides with angle-resolved x-ray photoelectron spectroscopy

Angle-resolved x-ray photoelectron spectroscopy (AR–XPS) is utilized in this work to accurately and nondestructively determine the nitrogen concentration and profile in ultrathin SiOxNy films. With furnace growth at 800–850 °C using nitric oxide (NO) and oxygen, 1013–1015 cm−2 of nitrogen is incorporated in the ultrathin (⩽4 nm) oxide films. Additional nitrogen can be incorporated by low energy ion (15N2) implantation. The nitrogen profile and nitrogen chemical bonding states are analyzed as a function of the depth to understand the distribution of nitrogen incorporation during the SiOxNy thermal growth process. AR–XPS is shown to yield accurate nitrogen profiles that agree well with both medium energy ion scattering and secondary ion mass spectrometry analysis. Preferential nitrogen accumulation near the SiOxNy/Si interface is observed with a NO annealing, and nitrogen is shown to bond to both silicon and oxygen in multiple distinct chemical states, whose thermal stability bears implications on the relia...

Photoemission study of Zr- and Hf-silicates for use as high-κ oxides: Role of second nearest neighbors and interface charge

We show a systematic trend of x-ray photoelectron binding energy shifts for Zr- and Hf-silicates, which are related to the composition of the films. The binding energy for the core photoelectrons can shift by up to 2 eV, depending on the relative electronegativities of the second nearest-neighbor elements. Understanding these shifts helps determine the underlying local electronic and chemical nature of the silicate network. Furthermore, we explain how charge at the dielectric-semiconductor interface can lead to shifts in the measured Si 2p peak binding energy by as much as 1 eV. The direction and magnitude of the binding energy shift can be used to determine the sign and density of the charge at the interface.

Dielectric properties of electron‐beam deposited Ga2O3 films

We have fabricated high quality, dielectric Ga2O3 thin films. The films with thicknesses between 40 and 4000 A were deposited by electron‐beam evaporation using a single‐crystal high purity Gd3Ga5O12 source. Metal‐insulator‐semiconductor (MIS) and metal‐insulator‐metal structures (MIM) were fabricated in order to determine dielectric properties, which were found to depend strongly on deposition conditions such as substrate temperature and oxygen pressure. We obtained excellent dielectric properties for films deposited at substrate temperatures of 40 °C with no excess oxygen and at 125 °C with an oxygen partial pressure of 2×10−4 Torr. Specific resistivities ρ and dc breakdown fields Em of up to 6×1013 Ω cm and 2.1 MV/cm, respectively, were measured. Static dielectric constants between 9.93 and 10.2 were determined for these films. Like in other dielectrics, the current transport mechanisms are found to be bulk rather than electrode controlled.

An in-situ X-ray photoelectron study of the interaction between vapor-deposited Ti atoms and functional groups at the surfaces of self-assembled monolayers

X-ray photoelectron spectroscopy (XPS) was used to study in situ the interface chemistry and film morphology during titanium metal deposition on functionalized surfaces prepared by self-assembly of end-functional alkanethiols, X-(CH2)15-SH, on gold (X = COOCH3, OH, CN, and CH3). The high reactivity of Ti with the COOCH3, OH, and CN groups on the surface results in the consumption of all functional groups at about one monolayer coverage, and the formation of oxide or nitride species, accordingly. At higher coverage the Ti atoms form direct metal-carbon bonds with the surface without altering the structure of the monolayer. The data also support the formation of metal clusters during film growth, and indicate a strong dependence of the Ti film morphology during the early stages of growth on the strength of the Ti-surface interaction. The strongest Ti-surface interaction results in the smallest cluster size (COOCH3 ≈ CN < OH < CH3) as indicated by a larger surface core-level shift.

Thermal desorption of Xe from the W(110) plane

Abstract The thermal desorption of Xe from the (110) plane of W was investigated. Desorption could be followed layer by layer for three adsorbed layers, each containing equal amounts of Xe. In each case desorption rates were nearly coverage independent (i.e., of zero order) until θ =0.25−0.3 (in the layer under study), at which point a sharp transition to first order desorption occurred. If only one monolayer of Xe was adsorbed small amounts of preadsorbed oxygen led to first order desorption over the entire coverage regime. Possible mechanisms for the zero order regime in terms of desorption from the edges of islands with constant total island perimeter, or via more complicated mechanisms are given. The activation energies of desorption are shown to be less than the enthalpies of desorption for all layers and the meaning of this result is discussed. Results for Xe adsorbed on O/W layers preheated to 90 K and 900 K are also presented.

Comparison of the sputter rates of oxide films relative to the sputter rate of SiO2

There is a growing interest in knowing the sputter rates for a wide variety of oxides because of their increasing technological importance in many different applications. To support the needs of users of the Environmental Molecular Sciences Laboratory, a national scientific user facility, as well as our research programs, the authors made a series of measurements of the sputter rates from oxide films that have been grown by oxygen plasma-assisted molecular beam epitaxy, pulsed laser deposition, atomic layer deposition, electrochemical oxidation, or sputter deposition. The sputter rates for these oxide films were determined in comparison with those from thermally grown SiO2, a common reference material for sputter rate determination. The film thicknesses and densities for most of these oxide films were measured using x-ray reflectivity. These oxide films were mounted in an x-ray photoelectron or Auger electron spectrometer for sputter rate measurements using argon ion sputtering. Although the primary objec...

Passivation of GaAs using (Ga2O3)1−x(Gd2O3)x, 0⩽x⩽1.0 films

The Ga2O3(Gd2O3) dielectric film was previously discovered to passivate the GaAs surface effectively. We have investigated the systematic dependence of the dielectric properties of (Ga2O3)1−x(Gd2O3)x on the Gd (x) content. Our results show that pure Ga2O3 does not passivate GaAs. Films with x⩾14% are electrically insulating with low leakage current and high electrical breakdown strength. Furthermore, a low interfacial density of states was attained in films with x⩾14%. The results show the important role of Gd2O3 in the (Ga2O3)1−x(Gd2O3)x dielectric films for effective passivation of GaAs.

Role of hydrogen bonding environment in a-Si:H films for c-Si surface passivation

The search for an ideal surface passivation layer of crystalline silicon (c-Si) to be employed in a silicon heterojunction photovoltaic device has garnered much attention. The leading candidate is a few nanometers of intrinsic amorphous silicon ((i)a-Si:H) film. Reported dependencies of film surface passivation quality on substrate preparation, orientation, and deposition temperature have been extended in this work to include H2 to SiH4 dilution ratio and postdeposition annealing. Simple avoidance of the deposition regimes that lead to epitaxial growth of Si on the c-Si substrate produces decent lifetimes on the order of 500μs. Subsequent low temperature annealings cause an important restructuring of Si–H bonding at the a-Si:H∕c-Si interface increasing the amount of monohydride at the c-Si surface. This restructuring would reduce the c-Si surface defect density and cause an improvement of surface passivation as confirmed by effective lifetime measurements. Final effective carrier lifetimes up to 2550μs ar...

Thin films and interfaces in microelectronics: composition and chemistry as function of depth

The chemistry and physics of thin films and interfaces govern the behavior of microelectronic devices. In this review, we examine how different spectroscopies, in particular X-ray photoemission spectroscopy (XPS), have been used to determine the physics and chemistry of a variety of thin films and interfaces commonly found in microelectronic devices. Electron spectroscopies are particularly attractive because the electron escape depths are comparable to the thickness of the films, allowing one to probe the bulk of the film and the interfaces simultaneously. We also give examples of how one can use the maximum-entropy method, a relatively straightforward analysis technique, to derive composition depth profiles of thin films from angle-resolved XPS data. Two technologically important classes of thin films are discussed. First, we examine thin inorganic films that are important high dielectric constant materials for CMOS devices or DRAM applications. Second, we discuss metal/polymer interfaces that are important in low dielectric constant device packaging. We conclude by discussing future developments and applications.