Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

A BioFET array can be fabricated by post-processing of a standard CMOS chip if temperatures are kept below 450 ° and radiation or ion-bombardment damage is minimized. The processing starts with encapsulation by deposition of a low stress, electrolyte-impermeable silicon nitride layer by PECVD at 375 °C. Anisotropic reactive ion etching with an inductively coupled plasma using C4F8 and Ar was used to remove the silicon nitride and oxide layers above the poly-silicon gates. The poly-silicon was then etched off using a selective wet etch. The effect of the processing was characterized by making current-voltage and capacitance-voltage measurements with MOS capacitor structures at each stage of processing and results showed that trapped charges or interface states could be annealed out at low temperatures. Scanning electron microscopy was used to examine the cross-section of the gate areas after the etching. The results of current-voltage measurements with a Ag/AgCl reference electrode on devices in electrolyte solutions were compared to the results of charge-sheet model calculations including the effect of amphoteric charging sites on the oxide and the potential drops in the electrolyte. Measurements showing the threshold shifts subsequently produced by DNA probe attachment and hybridization will also be presented.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

In recent years, electron energy loss spectroscopy has provided high spatial resolution information on the elemental composition of interfacial reactions. with the use of field emission guns in conventional TEM or STEM, additional information on the chemical, structural and electronic state at grain boundaries and interfaces can also be obtained (e.g. Ref. 1 and 2). in the study of new types of materials for semiconductor applications such as high-K dielectrics, high spatial resolution information of this type is of critical importance as the dimensions of the structures are reduced and the ultimate electronic properties become size dependent. This paper discusses the analysis of near edge structure information obtained at the Si-Gd2O3 interface, a system with great potential for the next generation of gate material.

The preparation of the thin films and the sample preparation details are given elsewhere3 and only a summary of the characterization method and results are described here.

Silicon nitride was deposited in-situ by electron-cyclotron resonance plasma chemical-vapour deposition (ECR-CVD) on (110) surfaces formed by cleaving GaAs and InP(100) substrates in an ultra-high vacuum processing system. Capacitors formed by depositing Al gates on the facet surfaces were analyzed by the high-low frequency capacitance-voltage (CV) technique. The minimum interface-state densities obtained for the cleaved GaAs (110) surfaces were 1–2 × 1012 eV−1cm−2. For cleaved InP facets the measured minimum interface state densities were a factor of two higher; however, they exhibited a smaller hysteresis in the CV characteristics and a smaller modulation in the surface potential. The interface state densities did not change significantly for the GaAs(110) facets if a Si interface control layer 0.8–2 nm thick was deposited prior to silicon nitride deposition; however, a larger effect was observed for the hysteresis and flatband voltage shift of the CV characteristics. The effect of annealing on the interfaces with Si was investigated and the performance compared with published results for GaAs(100) surfaces prepared by molecular-beam epitaxy.

A remote plasma enhanced chemical vapour deposition (RPECVD) process was used to deposit thin silicon dioxides on silicon substrates. The oxide properties were compared with thermal oxides with similar thicknesses (2.5–9 nm) using capacitance‐voltage (C‐V), current‐voltage (I‐V) and constant voltage stress measurements (I‐t). Post‐metallization annealing (PMA) showed different annealing dynamics as compared to the thermal oxides for anneal times below approximately 1000 s (at 260 °C) after which the dynamics were similar. The deposited oxides had a higher initial interface state density (Dit) than the thermal oxides, but after PMA they were found to be of the same quality as the thermal oxides. Positive charging of the deposited oxides during constant voltage stress was the same as for thermal oxides, showing that the stress endurance of the two are similar.

Silicon nitride films have been deposited with a single‐magnet electron‐resonance deposition system using nitrogen and silane as the reaction gases at substrate temperatures of 110°C and 300°C. The films are slightly nitrogen‐rich with no measurable Si‐H bonds measurable by Fourier Transform infrared spectroscopy and the concentration of hydrogen present as N‐H bonds increases with increasing SiH4/N2. The stress levels in the films can be controlled from tensile to compressive by decreasing the SiH4/N2 flow ratio and very low stress can be obtained with N‐H bond concentrations of 4 at. %. The optical bandgap for the layer with the lowest stress value (‐11.5 MPa), deposited at 300°C was 4.9 eV, as determined from a taue plot, and the waveguide loss at 632.8 nm was 2.3 dB/cm for 500 nm thick film deposited on fused silica.

We have prepared thin SiO2 layers on Si(100) wafers by electron cyclotron resonance chemical vapour deposition (ECR-CVD) in a multi-chamber ultra-high vacuum (UHV) processing system. The oxides were characterized in-situ by single wavelength ellipsometry (SWE) and x-ray photoelectron spectroscopy (XPS) and ex-situ by Fourier transform infra-red spectroscopy (FTIR), spectroscopic ellipsometry (SE) and capacitance-voltage (CV) electrical measurements. Films deposited at higher pressures, low powers and low silane flow rates had excellent physical and electrical properties. Films deposited at 400 °C had better physical properties than those of thermal oxides grown in dry oxygen at 700 °C. A 1 minute anneal at 950 °C reduced the fast interface state density from 1.2×1011 to 7×1010 eV−1cm−2

The effect of power on the properties of SiO2 films produced by direct plasma-enhanced chemical vapor deposition using nitrous oxide and silane with high helium dilution has been investigated. As the power increases the p-etch rate decreases while the frequency of the Si-O-Si stretching vibration measured by Fourier transform infra-red spectroscopy increases. However the refractive index of the films measured by ellipsometry is almost constant as is the electron density measured by low-angle x-ray reflection, indicating that the structural changes of the film with power do not relate to bulk density changes. The x-ray and ellipsometry measurements indicate the existence of a transitional layer with monolayer dimensions at the Si/SiO2 interface.

X-ray reflectivity has been used to study properties of thin SiO2 films on (100) Si prepared by plasma-enhanced chemical vapor deposition (PECVD) or by anodic oxidation. Reflectivity curves were analyzed to obtain information concerning the thickness, density (p) and interface roughness (σ) of these oxide films. We found that the PECVD films have typically a density of 0.98 psi with a sharp Si/SiO2 interface (σ < 0.2 nm) and a surface roughness of -0.5 nm. Anodic oxide films have a lower density (p = 0.88 psi) and larger interface and surface roughness σ - 0.5 nm. High temperature annealing of the anodic oxides up to 900 °C resulted in no appreciable densification but caused an increase in the interfacial roughness. Considerable variations were observed in the reflectivity curves from a PECVD oxide film annealed in the 650-1050 °C range.-Modeling of these results suggests the existence of a thin interfacial layer (-0.5 nm) of less density (∼0.9psi) at the original silicon/PECVD oxide interface.

Properties of ultrathin (— lOnm) silicon nitride films on single crystal Si, InP and GaAs have been studied using Raman spectroscopy, medium energy ion scattering (MEIS), variable-energy positron annihilation spectroscopy and x-ray photoelectron spectroscopy (XPS). The silicon nitride films were prepared by remote microwave plasma chemical vapour deposition (RPCVD). The results showed that oxidation of the film due to air exposure was restricted to the near surface with an oxygen penetration depth no greater than 2 nm. The residual stress in the as-grown films was substrate-dependent. For films on Si (100), the film induced residual stress was compressive with a value of 0.5GPa. Annealing at 500°C for 60 minutes resulted in a complete release of the residual stress. Vacuum annealing at a temperature below 500° C also led to changes of the electrical properties in the films but not the substrate.

In the context of this article, adhesion, friction, and wear are defined as follows: Adhesion is the resistance against separation of two bodies in a direction normal to the common interface. Friction is the resistance against motion of the contacting bodies in the direction of the common interface. Wear is the gradual change of geometry and loss of material due to the different contact processes that may occur in moving contacts.

Bowden and Tabor have shown convincingly that adhesion, friction and wear are interrelated at least to some extent. This article will review some of the current arguments that support this notion.

If surfaces are not separated by a viscous film, both friction and wear have their origin in the contact phenomena occurring at the roughness asperities of the sliding bodies.

Within one contact cycle, three primary events can be distinguished:

1. In order to obtain a (normal) load-carrying capacity, the contacting asperities must be compressed or indented (Figure 1), similar to a Brinell hardness test.

2. At the beginning of the contact cycle, the asperities interfere in the direction of sliding (Figure 2). Thus during the first half of the contact cycle, frontal loading of the asperities occurs (Figure 2b).

Particularly if the resulting deformation is plastic (as it will usually be for metals, see Reference 1), the net effect of this contributes to friction, the so-called “ploughing” effect.