Shi-Li Zhang

Effects of Carbon on Schottky Barrier Heights of NiSi Modified by Dopant Segregation

The presence of carbon at the interface between NiSi and Si has been found to participate in the process of modification of effective Schottky barrier heights using the dopant segregation (DS) method. Carbon alone results in an increased phibn from 0.7 to above 0.9 eV. Boron diffusion in NiSi is inhibited by carbon, and no B-DS at the NiSi/Si interface occurs below 600degC. Above this temperature, B-DS at this interface is evident thus keeping phibn high. The presence of interfacial carbon leads to an increased interfacial As concentration resulting in beneficial effects in tuning phibp above 1.0 eV by As-DS.

Advances in the formation of C54-FiSi 2 with an interposed refractory metal layer some properties

The influence of the interposed refractory metal layer on the properties of the TiSi/sub 2/ formed is studied. The substrates used were either polycrystalline or monocrystalline Si. Three different metal depositions were done, one with only 60 nm Ti, the two others with 60 nm Ti on top of a 0.5 nm thick Mo or Ta layer. A rapid thermal anneal in N/sub 2/ was carried out for the silicide formation. Very smooth TiSi/sub 2/ films with sharp TiSi/sub 2//Si interface were obtained with the interposed layer.The influence of the interposed refractory metal layer on the properties of the TiSi/sub 2/ formed is studied. The substrates used were either polycrystalline or monocrystalline Si. Three different metal depositions were done, one with only 60 nm Ti, the two others with 60 nm Ti on top of a 0.5 nm thick Mo or Ta layer. A rapid thermal anneal in N/sub 2/ was carried out for the silicide formation. Very smooth TiSi/sub 2/ films with sharp TiSi/sub 2//Si interface were obtained with the interposed layer.

Surface morphology study of titanium silicide formed on polycrystalline silicon

TiSi2 can be used as a shunting layer to decrease the resistance of the poly-Si lines used as interconnections in integrated Si technology. In this work the correlation between the silicide thickness, the silicide surface roughness, the silicide grain size, the dopants in Si, and the crystallinity of Si was investigated on unpatterned wafers. The results will be used as reference in a further study of silicide formation on sub-micron poly-Si lines. After silicide formation at 700°C, the surface roughness has been found to be strongly dependent on the thickness of the silicide layer formed. The dopants in the Si did not only retard the formation of the C49 phase, but also hindered the transformation of TiSi2 from the C49 to the low resistive C54 phase. The surface roughness did not change when a second annealing step at 850°C was used to transform the silicide from the C49 phase to the C54 phase.

Schottky Barrier Height Tuning via the Dopant Segregation Technique through Low-Temperature Microwave Annealing

The Schottky junction source/drain structure has great potential to replace the traditional p/n junction source/drain structure of the future ultra-scaled metal-oxide-semiconductor field effect transistors (MOSFETs), as it can form ultimately shallow junctions. However, the effective Schottky barrier height (SBH) of the Schottky junction needs to be tuned to be lower than 100 meV in order to obtain a high driving current. In this paper, microwave annealing is employed to modify the effective SBH of NiSi on Si via boron or arsenic dopant segregation. The barrier height decreased from 0.4–0.7 eV to 0.2–0.1 eV for both conduction polarities by annealing below 400 °C. Compared with the required temperature in traditional rapid thermal annealing, the temperature demanded in microwave annealing is ~60 °C lower, and the mechanisms of this observation are briefly discussed. Microwave annealing is hence of high interest to future semiconductor processing owing to its unique capability of forming the metal/semiconductor contact at a remarkably lower temperature.

Design of a Novel Capacitorless DRAM Cell with Enhanced Retention Performance

A novel capacitorless DRAM cell with enhanced retention performance is investigated. The write / read mechanisms, speed, retention performance are studied with numerical simulations. Further, the manufacturing method of this device is briefly discussed.

Variation of Contact Resistivity with Ge in TiW/P + SiGe Contacts

The dependence of contact resistivity on the Ge content in Si1-xGex is examined for TiW/p(+) Si1-xGex interfaces. Measurements are made on contacts with epitaxial Si1-xGex layers either at the surf ...

Schottky barrier height tuning via nickel silicide as diffusion source dopant segregation scheme with microwave annealing

In this work, microwave annealing is explored to tune the Schottky barrier height between NiSi and Si via boron and arsenic dopant segregation using silicide as diffusion source scheme. The microwave annealing is found to be able to obtain equivalent electron and hole Schottky barrier heights at significantly lower temperature (>100 °C) compared with conventional rapid thermal annealing. A plausible interpretation has been further proposed to explain the impact of low temperature microwave annealing on formation of dopant segregated Schottky junctions. The effectiveness of Schottky barrier height tuning below 400 °C by microwave annealing paves the way to form advanced source/drain and contact structures for future ultra-scaled MOSFETs and monolithic 3D sequential integration.

Investigation of resistivity dependent microwave annealing on Si substrates

Heating of silicon substrates featuring different resistivity values by microwave annealing is investigated. The absorption of microwave energy for silicon wafers is found to be consistent with ohmic conduction loss theory. The strongest absorption occurs when the resistivity was around 10 Ω·cm. As the carrier concentration and the conductivity of silicon increase with temperature, the absorption of microwave energy also varies during the annealing processes. Furthermore, it is found that the electric field density around the annealed silicon wafer is stronger for higher conductive silicon substrates at fixed microwave power.

On Epitaxy of Ultrathin Ni1 − x Pt x Silicide Films on Si(001)

Epitaxial Ni(Pt)Si2-y (y < 1) films readily grow upon thermal treatment of 2 nm thick Ni and Ni0.96Pt0.04 films deposited on Si(001). For annealing at 500 degrees C, the films are 5.4-5.6 nm thick with 61-70 mu cm in resistivity. At 750 degrees C, the epitaxial Ni(Pt)Si2-y films become 6.1-6.2 nm thick with a resistivity of 42-44 mu cm. Structural analysis reveals twins, facet wedges, and thickness inhomogeneities in the films grown at 500 degrees C. For higher temperature, an almost defect-free NiSi2-y film with a flat and sharp interface is formed. The presence of Pt makes the aforementioned imperfections more persistent.

Different strain relaxation mechanisms in strained Si/Si1-xGex/Si heterostructures by high dose B+ and BF2+ doping

Strained Si/Si0.8Ge0.2/Si heterostructures are implanted at room temperature with 7.5 keV B+ and 33 keV BF2+ ions to a high dose of 2×1015 ions/cm2, respectively. The samples are subsequently subjected to three-step anneals (spacer anneal, oxidation anneal and rapid thermal anneal), which are used to simulate a real fabrication process of SiGe-based MOSFET devices. The damage induced by implantation and its recovery are characterized by 2 MeV 4He+ RBS/channeling spectrometry. A damage layer on the surface is induced by B+ implantation, but BF+2 ion implantation amorphizes the surface of Si/Si0.8Ge0.2/Si heterostructure. Channeling angular scans along the 〈110〉 axial direction demonstrate that the strain stored in the SiGe layer could be nearly completely retained for the B+ implantated and subsequently annealed sample. However, the strain in the BF2+ implanted/annealed SiGe layer has decreased drastically.