F. R. McFeely

Liner materials for direct electrodeposition of Cu

We identified a family of materials which can be directly electroplated with Cu in acidic plating baths commonly found in the microelectronics industry. Details are presented illustrating a number of important properties of the electroplated Cu/linear material system. These include the adhesion of the plated film to liner material, the recrystallization behavior of the plated film, the texture of the plated film, and the resistivity of the plated film after high-temperature anneals. Finally, an example is presented illustrating the direct plating of Cu across an 8 in. wafer without the use of a Cu seed layer.

Impact ionization in silicon

The electron dynamics for electron energies up to 5 eV has been studied by soft x‐ray photoemission spectroscopy. Monte Carlo simulations have been performed to derive the energy dependence of the pair‐production rate using these results in combination with published data on the ionization coefficient and on the quantum yield for pair production. The obtained ionization rate shows a very soft threshold at 1.2 eV, approaching the results by Kane [Phys. Rev. 159, 624 (1967)] at higher energies. Several published models have been found to be inconsistent with the full set of experimental data we have considered.

The chemisorption of chlorosilanes and chlorine on Si(111)7 × 7

Abstract The chemisorption of SiCl4, Si2Cl6, and chlorine on Si(111)7 × 7 has been characterized using soft X-ray photoemission with synchrotron radiation, thermal desorption spectroscopy, and Auger electron spectroscopy. SiCl4 dissociatively chemisorbs on room temperature Si(111)7 × 7 with an extremely low sticking coefficient, with only SiCl remaining on the surface. In contrast, Si2Cl6 chemisorbs with ∼ 500 times greater probability and then partly dissociates into SiClx (x = 1, 2, 3) fragments. A monolayer of Cl deposited directly also contains SiCl, SiCl2, and SiCl3 surface species, but they are created via reaction with substrate Si atoms and have lower Si2p core level binding energies. Upon heating the surface all the adsorbed Cl is removed via desorption of silicon chlorides, primarily SiCl2, indicating that SiCl4, Si2Cl6, and chlorine will etch Si(111)7 × 7 if an additional reactant is not avail to remove the surface Cl. Interestingly, the different reactivities of SiCl4 and Si2Cl6 upon adsorption can be explained by the dynamics of different adsorption mechanisms.

Microscopic Structure Of The SiO2/Si Interface

The bonding of Si atoms at the SiO2/Si interface is determined via high-resolution core level spectroscopy with synchrotron radiation. For oxides grown in pure O2, the SiO2/Si interface is found to contain Si atoms in intermediate oxidation states with a density of 1.5 ± 0.5 × 1015 cm−2. From the density and distribution of intermediate oxidation states, models of the interface structure are obtained. The interface is not abrupt, as evidenced by the non-ideal distribution of intermediate oxidation states and their high density (about 2 monolayers of Si). The finite width of the interface is explained by the bond density mismatch between SiO2 and Si. Annealing in H2 is found to influence the electrical parameters by removing the Pb centers that pin the Fermi level. The distribution of intermediate oxidation states is not affected.

Soft X-ray photoemission study of the silicon-fluorine etching reaction

High resolution soft X-ray photoemission spectra of Si(111) surfaces subjected to steady-state etching are reported. The reaction is shown to proceed via the formation of a thick, highly fluorinated reaction layer, dominated by trifluorosilyl moieties. In addition, SiF4, the major reaction product has been observed in the spectra, indicating that it may be trapped within the reaction layer. The implications of these measurements for previously proposed reaction mechanisms are discussed.

Fabrication of midgap metal gates compatible with ultrathin dielectrics

A process has been described which can produce a midgap tungsten gate compatible with the current and future complementary metal–oxide–semiconductor technology. The tungsten was deposited directly onto a 3.0 nm SiO2 gate dielectric without measurable degradation of any of its electrical properties. The tungsten deposition process yields no reactive or corrosive by-products that affect the gate dielectric integrity. The tungsten film is found to be pure within the limits of several analytical techniques and the resistivity of the tungsten films was found to be within a factor of 2 of the bulk value.

Atomic layer epitaxy of silicon by dichlorosilane studied with core level spectroscopy

The chemisorption and reaction of dichlorosilane (SiH2Cl2) with Si(111) and Si(100) surfaces is investigated with core‐level soft x‐ray photoelectron spectroscopy employing synchrotron radiation, in order to ascertain the surface chemistry involved in atomic layer epitaxy (ALE). Exposures to 8 kL of SiH2Cl2 were performed as a function of sample temperature in the range from room temperature to 800 °C. At all temperatures, SiH2Cl2 chemisorbs dissociatively forming silicon monochloride surface species. The coverage of monochloride displays a maximum for exposures at ∼600 °C. Under all conditions studied, larger chlorine coverages are observed on Si(100) than on Si(111). A Si surface that was first saturated with SiH2Cl2 at 600 °C was subsequently exposed to H2 at 600 °C, and no reaction occurred. These results indicate that recent models for silicon ALE are incorrect. An alternative method for low‐temperature ALE of Si is proposed, in which SiH2Cl2 is adsorbed onto Si at 600 °C and Cl is removed via reaction with atomic H.

Core‐level photoemission and the structure of the Si/SiO2 interface: A reappraisal

Photoemission spectroscopy of spherosiloxane cluster derived Si/SiOx interfaces has allowed the direct assignment of observed spectral features to specific chemical moieties. The implications of these assignments for structural models of the Si/SiO2 interface are explored. Models specifically constructed to be consistent with photoemission data are shown to be incorrect after reanalysis of core‐level shifts based on the recently synthesized model systems. A new model for the Si/SiO2 interface is proposed which is consistent with the current understanding of photoemission for Si/SiOx interfaces as well as with results from numerous other experiments.

Synchrotron photoemission investigation: Fluorine on silicon surfaces

High resolution core level photoemission spectroscopy has been used to obtain the first direct identification of the chemical species remaining on silicon surfaces after exposure to fluorine. Both Si(111) 2×1 and Si(111) 7×7 were exposed to fluorine via the dissociative chemisorption of XeF2. For fluorine coverages in the monolayer regime, SiF1, SiF2, and SiF3 were all present although their relative abundance varied significantly between the two surfaces. No evidence for the existence of unreacted interestitial fluorine was found. These results suggest the need for modification of current models describing plasma and reactive ion etching of silicon.

Role of oxygen vacancies in V FB /V t stability of pFET metals on HfO 2

We demonstrate experimentally that the flatband/threshold voltages (V/sub FB//V/sub t/) of pFET metal gates are strongly dependent on the post-deposition annealing conditions of the gate stacks. By varying the temperature and the O/sub 2/ partial pressure during post-deposition N/sub 2//O/sub 2/ and/or forming gas annealing (FGA) with Re, Ru and Pt, the gate stack V/sub FB/ can change by as much as 750 mV. However, using Re as an example, it is shown that conditions can be optimized and V/sub FB//V/sub t/-tuning for pFETs can be achieved for aggressively scaled stacks. It is proposed that charge transfer from oxygen vacancies to the gate electrode, possible only for high workfunction metal gates, leads to the formation of a dipole layer near the gate which can shift V/sub FB//V/sub t/. The results indicate that V/sub FB//V/sub t/ control remains a formidable processing challenge with high workfunction metals on HfO/sub 2/.