SIMS2015 Session DI-TuP: Depth Profiling/Inorganics Poster Session

The downscaling of semiconductor confronts the metallization technology with a large number of challenges. The line resistance of Cu deposited by electro-plating (EP) remarkably rises due to the size effect on the resistivity of the metal film [1].

One possible solution is to maximize the portion of the EP-Cu volume in the dual damascene structure with the thin and conformal diffusion barrier and a seed layer, respectively. The portion of Cu in the dual damascene structures can be increased further by direct plating if the EP of Cu can be achieved on a diffusion barrier without a seed layer. Ru has excellent properties such as low resistivity (7.1 μΩ∙cm), chemical/thermal stability, and immiscibility with Cu. It was also known that Ru adheres well with Cu [2,3], making Ru as a most promising material in the back end of line Cu-wiring as a seed layer or adhesion layer and even as a Cu direct-plateable diffusion barrier.

In this study, Ru films were deposited on a Si wafer using a showerhead-type PEALD reactor (Lucida-M100, NCD Technology), with IMBCH Ru [IMBCH = (η6-1-isopropyl-4-methylbenzene)(η4-cyclohexa-1,3-diene)] as a precursor.

We investigated the compositional characterization of Ru-based thin films using secondary ion mass spectrometry (SIMS). Composition of the films was characterized by SIMS depth profiling whose results were calibrated by RBS. These results will be presented.

Silicon carbide (SiC) is a promising material in nuclear engineering due to its high strength, good chemical stability and small neutron cross section. In nuclear reactors, extreme radiation condition may lead to degradation of material properties, including volume swelling. The volume swelling of SiC induced by slow heavy ion irradiations at room temperature has been extensively studied in the past decades, but the experimental data are considerably scattered, ranging from 8% to 25% depending on the irradiation conditions and the techniques used for the swelling determination.

Backside SIMS is an effective method to investigate the low concentration of dopant and impurities in the semiconductor materials. In particular, Backside SIMS is useful to examine the surface diffusion of dopant without knock-on effect. The samples for Backside SIMS were mounted onto a supporting substrate using a resin as an adhesive and then the samples were polished. The samples were irradiated with an electron beam for the charge neutralization during SIMS measurements. This often causes the destruction of the samples by the adhesive (resin) used for the bonding. To avoid this problem, we developed the new sample preparation method without using the resin. As a result, this method enabled us to analyze more easily insulators and improve the depth resolution using backside SIMS analysis. Recently, we employed a room-temperature direct bonding method (RTDBM).

The RTDBM was used for various materials including semiconductors (MEMS, LED, Power devices etc.). In this method called the surface activated bonding (SAB), oxide film and absorption layer are removed from the wafer surface irradiated with atoms or ions in a high vacuum and dangling bond is generated on the activated surfaces. These activated surfaces which have dangling bond immediately bond only by touching each other.

In this work, we investigated the depth profiling of insulating samples, which were stacked the dielectric films (SiN/SiO₂) on a silicon wafer, with/out the RTDBM using a magnetic sector SIMS(CAMECA 6f or 7f).

Zirconium-based alloys are widely used in nuclear industry mainly as cladding for nuclear fuel in power plants. Due to, both coolant and irradiation effects an outer oxide layer is formed on the cladding and modifies its mechanical and thermal properties and behaviour. These modifications can generate a risk for the exploitation of the nuclear fuel and then necessitate to be investigated. During the oxide growth process, boron and lithium, present in the cooling water for neutron absorption control and cladding corrosion control respectively, are trapped in the oxide layer and diffuse through it.

In this work, SIMS depth profiles have been performed using the shielded ATOMIKA 4000 SIMS installed in the Hot Lab Division of the Paul Scherrer Institute. Both lithium and boron profiles have been investigated using Ga⁺ and Cs⁺ primary ions through the cladding oxide layer (average thickness about 4 μm) of M5™ cladding material. The crater depths have been measured using an optical interferometer.

The obtained profiles indicate that the oxide layer is divided in two sub-layers. In particular an 800 nm-1μm thick layer, at the metal oxide interface, is strongly Li and B depleted and may play a protective role against lithium and boron diffusion through the oxide layer. This sub-layer also shows electrical properties widely different from the rest of the oxide layer.

Nickel-chromium-molybdenum alloys exhibit exceptional corrosion resistance and are widely used in the chemical processing industry. This resistance is generally attributed to the passive film whose properties appear dominated by the Cr/Mo contents of the alloys.

We have been studying the properties of these films as a function of applied potential, pH, temperature and solution composition using a range of electrochemical and surface analytical techniques. These techniques include polarization and voltammetric experiments, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In addition, we have used the measurement of oxygen reduction currents as an indicator of surface reactivity and as a probe to detect the redox transformations which occur in the oxide.

Using these techniques, it is possible to clarify the changes in the oxide film which could eventually lead to its breakdown and a susceptibility to localized corrosion. While passivity is generally attributed to the presence of a Cr(III)-dominated barrier layer, ToF SIMS shows that the segregation of oxidized Mo (and, to a lesser degree, W) to the outer regions of the film is an essential feature maintaining passivity when exposure conditions become particularly aggressive at positive potentials, low pH and high temperatures.