S. Gennaro

Bendable Ultra-Thin Chips on Flexible Foils

This paper presents ultra-thin silicon chips (flex-chips) on flexible foils, realized through post-processing steps such as wafer thinning, dicing, and transferring the thinned chips to flexible polyimide foils. The cost effective chemical etching is adopted for wafer thinning and the transfer printing approach, to transfer quasi 1-D structures such as micro/nanoscale wires and ribbons, that is adapted for transferring large ultra-thin flex-chips (widths 4.5-15 mm, lengths 8-36 mm, and thickness ≈ 15 μm). The post-processing capability is demonstrated with passive structures such as metal interconnects realized on the flex-chips before carrying out the chip thinning step. The resistance values of metal interconnects do not show any appreciable change because of bending of chips for the tested range viz., radius of curvature 9 mm and above. Further, the bending mechanics of silicon membranes on foil is investigated to evaluate the bending limits before a mechanical fracture/failure occurs. The distinct advantages of this paper are: attaining bendability through post-processing of chips, cost effective fabrication process, and easy transfer of chips to the flexible substrates without using conventional and sophisticated equipment such as pick and place set up.

Vacancy-engineering implants for high boron activation in silicon on insulator

The formation of boron interstitial clusters is a key limiting factor for the fabrication of highly conductive ultrashallow doped regions in future silicon-based device technology. Optimized vacancy engineering strongly reduces boron clustering, enabling low-temperature electrical activation to levels rivalling what can be achieved with conventional preamorphization and solid-phase epitaxial regrowth. An optimized 160keV silicon implant in a 55∕145nm silicon-on-insulator structure enables stable activation of a 500eV boron implant to a concentration ∼5×1020cm−3.

Correlation of local structure and electrical activation in arsenic ultrashallow junctions in silicon

The understanding of the behavior of arsenic in highly doped near surface silicon layers is of crucial importance for the formation of N-type ultrashallow junctions in current and future very large scale integrated technology. This is of particular relevance when studying recently developed implantation and annealing methods. Past theoretical as well as experimental investigations have suggested that the increase in As concentration, and therefore the reciprocal proximity of several As atoms, leads to a drastic increase in electrically inactive defects giving only marginal reduction in sheet resistance. Monoclinic SiAs aggregates as well as various arsenic-vacancy clusters contribute to the deactivation of arsenic. This study aims to correlate between the results of electrical activation measurements and x-ray absorption fine structure measurements. Samples were doped with a nominal fluence of 1×1015–3×1015 atoms/cm2, implanted at 2 keV, and annealed by rapid thermal treatments, laser submelt treatments, ...

Highly Sensitive Detection of Inorganic Contamination

As the detection of inorganic contaminants is of steadily increasing importance for the improvement of yields in microelectronic applications, the aim of one of the joint research activity within the European Integrated Activity of Excellence and Networking for Nano- and Micro-Electronics Analysis (ANNA, site: www.ANNA-i3.org) is the development and assessment of new methodolo¬gies and metrologies for the detection of low concentration inorganic contaminants in silicon and in novel materials. A main objective consist in the benchmarking of various analytical techniques avail¬able in the laboratories of the participating ANNA partners, including the improvement of the res¬pective detection limits as well as the quantitation reliablity of selected analytical techniques such as total-reflection x-ray fluorescence (TXRF) analysis.

Deactivation of submelt laser annealed arsenic ultrashallow junctions in silicon during subsequent thermal treatment

The use of nonequilibrium annealing approaches can produce very high levels of arsenic electrical activation in Si. However, subsequent thermal treatments between 500 and 800°C easily deactivate the dopant to a level one order of magnitude below the solid solubility. In this work, the authors study the deactivation of laser annealed (LA) ultrashallow arsenic distributions in silicon using Hall effect measurements, extended x-ray absorption fine structure spectroscopy, and secondary ion mass spectrometry. Single crystal Si (100) wafers implanted with As ions at 2keV energy and different doses were activated with a millisecond LA at 1300°C using a scanning diode laser annealing system under nonmelt conditions. The samples were then thermally treated in a furnace at 300–900°C in a N2 atmosphere for 10min. Electrical deactivation has been observed for all the implanted doses but for the lowest one. In particular, it was observed that the higher the As dose the easier the deactivation, in particular, after the...

Ultralow energy boron implants in silicon characterization by nonoxidizing secondary ion mass spectrometry analysis and soft x-ray grazing incidence x-ray fluorescence techniques

Boron ultralow energy (0.2–3 keV) high dose (1×1015 cm−2) implants in single crystalline Si (100) were characterized by secondary ion mass spectrometry using an ultralow energy (0.35–0.5 keV) O2+ ion primary beam and collecting positive secondary ions. In particular, the not fully oxidizing approaches (primary beam oblique incidence and ultrahigh vacuum analysis atmosphere) were investigated because they are expected to provide better accuracy on the profile shape, especially in the region between the surface and the native oxide/substrate interface. The main drawback represented by an early formation of roughness on the crater bottom has been overcome by combining the ion sputtering with the rotation of the sample during the analysis. The reduced formation of roughness ensures more stable sputtering conditions and a more stable erosion rate with a more accurate depth calibration. The measured dose values were then cross-checked comparing them with results of soft x-ray synchrotron radiation grazing incid...

Surface proximity and boron concentration effects on end-of-range defect formation during nonmelt laser annealing

The effects of surface proximity and B concentration on end-of-range defect formation during nonmelt laser annealing in preamorphized silicon have been studied. These effects were analyzed by observing the activation and diffusion of an ultrashallow B implant, using Hall effect and secondary ion mass spectrometry measurements. By adjusting the preamorphizing implant and laser annealing conditions, B deactivation and diffusion were minimized, resulting in a sheet resistance of ∼600Ω∕sq with a 16nm junction depth. This is attributed to a combination of enhanced dissolution of end-of-range defects and preferential formation of B-interstitial clusters due to the surface proximity and high B concentration, respectively.

Formation of arsenic rich silicon oxide under plasma immersion ion implantation and laser annealing

Samples produced by plasma immersion ion implantation of Arsenic in Silicon using a non-pulsed plasma source and subsequent laser annealing were investigated with respect to As depth distribution, oxide thickness, and As local order using SIMS, XPS, INAA and EXAFS analysis. A surface layer (∼10 nm), was identified as an As-rich Si oxide formed after implantation. The thickness of this layer was found to be larger for samples annealed using a low thermal budget up to a threshold where probably melting occurred. Dopant depth profile was re-distributed whereas the final oxide film of these samples showed thicknesses of a few nm. The retained As dose exhibited an apparent drastic increase. A hypothesis for the processes involved is presented based on experimental evidence.

Junction Stability of B Doped Layers in SOI Formed with Optimized Vacancy Engineering Implants

Forming highly stable, low resistive, ultra shallow p‐type junctions is well known to be a challenge for future transistor devices. This paper investigates the junction stability of boron layers formed with an optimized 160keV silicon vacancy engineering implant in SOI. It is demonstrated that when the electrical activation is well above the solid solubility a combination of diffusion and possible boron precipitation, during prolonged annealing at 850°C, drives the boron to return to an equilibrium level of electrical activation, which is compensated by the carrier mobility to maintain a constant Rs. Reducing the anneal temperature to 700°C shows it is possible to create highly stable p‐type junctions in terms of diffusion and sheet resistance.

Arsenic redistribution after solid phase epitaxial regrowth of shallow pre-amorphized silicon layers

The behavior of ultra shallow ion implants of arsenic in Si following solid phase epitaxial re-growth process is reported. A 16 nm amorphous layer was created by ion implantation of Si+ at energy 5 keV and a dose 1×1015 at/cm2. As ion were implanted at 2 keV using 3 different doses: 1×1014, 5×1014 and 1×1015 at/cm2. The resulting As distributions, confined in the amorphous layer, were thermally treated at 550°C for 5-300 s in order to electrically activate dopant atoms. Crystal re-growth and As redistribution was investigated by secondary ion mass spectrometry and medium energy ion scattering. A growth rate depending on the As concentration was observed, the rate being slower for higher As content. Arsenic re-distribution to the surface and at the end-of-range defects was observed and a segregation model was developed. Finally, the substitutional fraction of As atoms was related to sheet resistance measurements revealing a higher fraction of electrically active dopant atoms in pre-amorphized samples compa...