R. De Keersmaecker

A reliable approach to charge-pumping measurements in MOS transistors

A new and accurate approach to charge-pumping measurements for the determination of the Si-SiO2interface state density directly on MOS transistors is presented. By a careful analysis of the different processes of emission of electrons towards the conduction band and of holes towards the valence band, depending on the charge state of the interface, all the previously ill-understood phenomena can be explained and the deviations from the simple charge-pumping theory can be accounted for. The presence of a geometric component in some transistor configurations is illustrated and the influence of trapping time constants is discussed. Furthermore, based on this insight, a new technique is developed for the determination of the energy distribution of interface states in small-area transistors, without requiring the knowledge of the surface potential dependence on gate voltage.

Determination of Si-SiO/sub 2/ interface recombination parameters using a gate-controlled point-junction diode under illumination

A novel method is presented to determine Si-SiO/sub 2/ interface recombination parameters. The device used is a polysilicon-oxide-semiconductor capacitor with a microscale central junction (a gate-controlled point-junction diode). Data analysis has been performed using a numerical scheme to find a quasi-exact solution for the current combining at the interface. It was found that the interface recombination parameters depend only weakly on trap energy in a wide range around midgap. The cross-section for capturing electrons was found to exceed the cross-section for capturing holes by a factor of 10/sup 2/ to 10/sup 3/. >

A self‐aligned cobalt silicide technology using rapid thermal processing

The feasibility of a self‐aligned silicide technology based upon cobalt has been investigated. Silicidation reactions were performed by means of rapid thermal processing. Phase sequence, layer morphology, and reaction kinetics were studied by XRD, SEM, RBS, AES, and TEM. Extremely smooth, highly conductive (16 μΩ cm) CoSi2 films were formed by direct reaction of Co on Si, without significant lateral silicide formation at oxide edges. Shallow arsenic junctions were successfully silicided and low contact resistances were obtained on n+ and p+ Si.

A self-aligned CoSi 2 interconnection and contact technology for VLSI applications

Cobalt silicide is investigated in view of possible application in a self-aligned technology. Extremely smooth, highly conductive CoSi2films are obtained using rapid thermal processing for silicide formation starting from deposited cobalt layers (on Si). The phase formation is studied by XRD and RBS. No lateral silicide formation is observed at contact edges. The influence of Si consumption and dopant behavior on diode performance is studied. Shallow arsenic (0.15 µm deep) and boron (0.3 µm deep) junctions are successfully silicided. Very low contact resistances are obtained between the silicide and n+ and p+ regions. MOS transistors were fabricated with CoSi2on the source, drain, and gate. An increase in current driving capability is noticed while no degradation of other electrical parameters due to the silicide processing steps is observed. At some critical points, comparison is made with the TiSi2process.

Observation of hot-hole injection in NMOS transistors using a modified floating-gate technique

A modified floating-gate technique for measuring small gate currents in MOSFETs with very high resolution (0.01 fA) is described. Using this technique, gate oxide currents due to hot-carrier injection are measured in n-channel MOSFETs. The conventional negative channel hot-electron gate oxide current is observed nearV_{g} = V_{d}and a small positive gate current occurs at low Vg. We argue that the dependencies of this small positive current on Vgand gate length, together with results from a separate floating-source experiment, are consistent only with hot-hole injection.

Stability of as-doped and b-doped si with respect to overlaying cosi2 and tisi2 thin-films

The thermodynamic equilibrium of structures consisting of a thin film silicide (TiSi2 or CoSi2) on doped Si (with As or B) is investigated. Isothermal sections of the ternary phase diagrams for Ti–Si–B, Co–Si–B, Ti–Si–As, and Co–Si–As have been evaluated, indicating the stability of high B concentrations in Si underneath a CoSi2 layer, the instability of high As concentrations in Si underneath a CoSi2 layer, and of B and As concentrations underneath a TiSi2 layer. The obtained thermodynamic predictions agree very well with experimental results (i) on the redistribution of dopants during silicide formation, (ii) on the diffusion of dopants from an ion implanted silicide, and (iii) on the stability of highly doped regions underneath the silicide, both for the case of TiSi2 and CoSi2. It is shown that even though the inaccuracy of reported thermodynamic data is substantial, thermodynamic calculations provide a useful guidance and are consistent with the experimental results.

Oxide field dependence of SiSiO2 interface state generation and charge trapping during electron injection

Abstract The oxide field dependence of both the interface state generation and electron trapping during electron injection are studied using transistor structures. Two field thresholds are observed for the generation of interface states, at 1.5 and 4 MV/cm, respectively. The threshold at 4 MV/cm is also found for the generation of electron traps. The 1.5 MV/cm threshold is related to the change in energy loss mechanism of the injected electrons. The threshold at 4 MV/cm is suggested to originate from the injection of holes from the anode.

Limitations of TiSi2 as a source for dopant diffusion

The application of TiSi2 as a dopant diffusion source for boron and arsenic was studied. The TiSi2 layers were formed by the usual salicide process and doped by ion implantation. Diffusion was carried out by various furnace and rapid thermal processing steps. Using secondary ion mass spectrometry, scanning electron microscopy, and x‐ray diffraction, clear evidence for compound formation between Ti and the two dopant species is found. This leads to low dopant concentrations at the silicide/silicon interface, very poor efficiency of the diffusion source, and unacceptably high contact resistivities.

Impact of Patterned Layers on Temperature Non-Uniformity during Rapid Thermal Processing for VLSI-Applications

The influence of patterned oxide layers on temperature non-uniformity during RTP is studied. It is shown that large temperature non-uniformities (up to 80 °C) can occur during RTP as a consequence of large scale patterns of thick oxides. The dependence of oxide thickness and pattern geometry on temperature non-uniformity over a wafer is studied. A set of simulation programs is developed to calculate the optical characteristics of a wafer inside a chamber and to calculate the time dependent temperature non-uniformities on patterned wafers. The calculated results agree very well with the experimental results. The simulation program was used to define the optimal optical conditions for RTP systems for minimal temperature non-uniformity due to patterned overlayers on Si.

Comparison between CoSi2 and TiSi2 as dopant source for shallow silicided junction formation

Abstract Self-aligned silicidation technologies, based upon TiSi2 (and CoSi2) have been widely investigated during recent years. Junction spiking and limited thermal stability of the dopant concentration at the silicide/Si interface are important limitations of the technique of conventional formation of silicided junctions. Therefore, the diffusion of dopants from implanted silicide is compared for CoSi2 and TiSi2. Excellent diode integrity and low contact and series resistances are obtained for diffusion from CoSi2, whereas the diffusion from TiSi2 is strongly restricted by metal-dopant compound (TiB2 and TiAs) formation.