Paul Merchant

Titanium disilicide formation on heavily doped silicon substrates

Titanium disilicide formation on heavily doped silicon substrates was investigated with sheet resistance measurements, elemental depth profiling, and transmission electron microscopy. As found in a previous study [H.K. Park, J. Sachitano, M. McPherson, T. Yamaguchi, and G. Lehman, J. Vac. Sci. Technol. A 2, 264 (1984)], the TiSi2 growth rate depended on the dopant concentration. The growth rate was highest on undoped substrates, intermediate on heavily phosphorus‐doped substrates, and lowest on heavily arsenic‐doped substrates. However, the critical dopant concentration effect reported by Park et al. was not observed. The uniformity of the titanium‐silicon reaction was not seriously affected by heavy substrate doping. For heavily arsenic‐doped substrates (3.0×1021 As/cm3), TiAs precipitates formed at C49 TiSi2 grain boundaries, and the C49‐to‐C54 transformation temperature increased to 850 °C. For heavily phosphorus‐doped substrates (1.0×1021 P/cm3), no phosphides were unambiguously detected, and the C49‐...

Surface resistance of epitaxial YBa2Cu3O7 thin films on CeO2 diffusion barriers on sapphire

Epitaxial thin films of YBa2Cu3O7 (YBCO) have been deposited by off‐axis sputtering onto substrates of r‐plane sapphire coated with a CeO2 diffusion barrier which had been previously deposited by metalorganic chemical vapor deposition process. The YBCO films display excellent superconducting properties, with critical current densities and microwave surface resistances comparable to state of the art YBCO films deposited directly onto LaAlO3 or MgO substrates. The volume fraction of YBCO with large‐angle in‐plane misalignment relative to the underlying layers is comparable to, or smaller than that obtained for YBCO directly deposited onto MgO substrates.

Oxygen redistribution during sintering of Ti/Si structures

We have used helium backscattering spectroscopy (RBS) to trace the evolution of oxygen depth profiles after UHV sintering, in 1430 A titanium films, sputter deposited onto single crystal silicon substrates. The as‐deposited films exhibit a roughly exponential oxygen distribution, decreasing from the titanium film surface. After sintering at 350 °C, 30 min the oxygen has moved into the film and after 450 °C, 20 min the oxygen is uniformly distributed in the titanium. At higher temperatures, as silicide formation progresses, the oxygen is snowplowed back toward the surface and is completely driven from the TiSi2 film after sintering at 800 °C, 30 min. The low temperature oxygen redistribution in titanium correlates well with increases in the sheet resistance of the unreacted films, as has been suggested earlier from x‐ray diffraction results which revealed an increase in the titanium c axis after sintering at 500 °C [S. P. Murarka and D. B. Fraser, J. Appl. Phys. 51, 342 (1980)]. The sheet resistance reache...

Electrostatic surface drives: theoretical considerations and fabrication

Micromachined actuators with large travel, highly precise position control, and low actuation voltage are essential for atomic resolution storage, micro-optical stages, microwave devices, and control surfaces for a variety of sensors. We describe the characteristics and limitations of a novel electrostatic surface drive. A prototype, fabricated with two-level metallization, deep silicon etching, and a dry release process, has demonstrated 8 /spl mu/m travel at 4 V applied bias.

Arsenic out‐diffusion during TiSi2 formation

The behavior of implanted As atoms during high‐temperature (800–900 °C) TiSi2 formation was investigated by helium backscattering. A significant As loss was observed during TiSi2 formation by vacuum furnace annealing. The main factors influencing the As loss were the initial As profiles and Ti film thickness. Most of the As loss was caused by rapid As out‐diffusion through the TiSi2 layer; the remaining As atoms were only observed in the Si substrate after TiSi2 formation. As long as the As distribution was deeper than the TiSi2 layer, the loss of As atoms was kept to a minimum. Careful selection of the As implantation energy and the Ti film thickness can achieve high As concentration at the TiSi2/Si interface.

Dopant redistribution during titanium silicide formation

For advanced metal‐oxide‐semiconductor structures it is highly desirable to have a self‐aligned silicide structure on source and drain regions as well as on the gate in order to simplify lithography while reducing parasitic resistances. The reproducible formation of metal silicides on highly doped n+ and p+ regions with shallow junctions is required for those structures. Therefore, it is essential to understand the dopant behavior, silicide phase formation, and grain growth during high‐temperature annealing. Titanium silicides were formed on arsenic and boron difluoride implanted and annealed Si substrates. Arsenic atoms showed a significant redistribution and loss during titanium silicide formation. Arsenic atoms diffused out of the silicide surface with an activation energy of 0.95 eV. Boron atoms segregated to the silicide surface, and some boron atoms were lost from the surface; on the other hand, fluorine atoms were retained in the silicide layer. After prolonged 900 °C annealing, the thin titanium d...

HPSAC—A silicided amorphous-silicon contact and interconnect technology for VLSI

A high-performance silicided amorphous-silicon contact and interconnect technology (HPSAC) for VLSI is presented. In this novel scheme, a patterned silicide layer is used to form self-aligned contacts to the source/drain regions, as well as to interconnect devices. The fabrication procedures and some key processing techniques are described, Experimental results on n-and p-channel MOSFETs fabricated with HPSAC technology are presented. The performance improvement due to reduction of parasitic capacitance and resistance is discussed.

A new device interconnect scheme for sub-micron VLSI

A new device interconnect scheme for sub-micron VLSI has been developed. In this technology N+ and P+ diffusions and N+ and P+ gates of a CMOS process can be directly connected in any combination desired without the use of contacts or aluminum. This provides much improved packing density over conventional processes. Since the source/drain (S/D) contacts can extend over the field oxide regions, minimum sized S/D diffusion areas can be used. This leads to a significant decrease in parasitic diffusion capacitances relative to other processes. Several devices can share one contact when they need to communicate, and so the total number of contacts can be greatly reduced. Since the contacts do not have to be limited to minimum dimensions a relaxation of sub-micron contact processing is achieved. In addition the use of a self-aligned silicide reduces interconnect and other device parasitic resistances. NMOS and PMOS devices have been successfully fabricated using this process.

Thermal stability of diffusion barriers for aluminum alloy/platinum silicide contacts

Thin metal films of Cr, Ti, Mo, and W–Ti (10 wt.%) have been investigated for their effectiveness in preventing the Al–PtSi reaction which occurs during the post‐metallization alloy treatment of Ohmic contacts and Schottky diodes on integrated circuits. The metal films were deposited by two different dc magnetron sputtering systems. The processed structures were compared for their electrical and metallurgical stability as a function of alloy temperature up to 550 °C for 30 min, as well as for effects of a sputter‐etch versus a wet chemical dip prior to the barrier metal and aluminum alloy deposition. Degradation of the electrical behavior of the contact structures at the higher alloying temperatures is correlated with structural alterations of the layered structures by MeV He ion backscattering and Auger electron spectroscopy with Ar ion sputter‐depth profiling. Conditions under which each barrier metal is useful are presented.

Similarity of scanning tunneling microscopy and atomic force microscopy images of YBa2Cu3O7 thin‐film spiral growth patterns

The surface morphology of highly oriented c‐axis YBa2Cu3O7 films grown by off‐axis sputtering on MgO has been examined by scanning tunneling microscopy (STM) and atomic force microscopy (AFM) at room temperature. Spiral growth patterns were well resolved by both techniques, and the shape of the structures is qualitatively and semiquantitatively similar. The terraces tend to be uneven, with troughs near the steps. The mean height of the steps is close to a multiple of the unit cell, but individual step heights are often not. We conclude that the observed surface topography is not artifactual. The YBa2Cu3O7 appears to be covered by a thin layer (of unknown composition or structure) whose thickness may vary by several A, and whose electrical properties are temperature dependent.