C. Urban

Ultrathin Ni Silicides With Low Contact Resistance on Strained and Unstrained Silicon

Ultrathin Ni silicides were formed on silicon-on-insulator (SOI) and biaxially tensile strained SOI (SSOI) substrates. The Ni layer thickness crucially determines the silicide phase formation: With a 3-nm Ni layer, high-quality epitaxial NiSi2 layers were grown at temperatures > 450°C, while NiSi was formed with a 5-nm-thick Ni layer. A very thin Pt interlayer, to incorporate Pt into NiSi, improves the thermal stability and the interface roughness and lowers the contact resistivity. The contact resistivity of epitaxial NiSi2 is about one order of magnitude lower than that of a NiSi layer on both As- and B-doped SOI and SSOI.

Radio-Frequency Study of Dopant-Segregated n-Type SB-MOSFETs on Thin-Body SOI

We present a detailed direct current and radiofrequency study of fully depleted dopant-segregated Schottky barrier (SB) MOSFETs on thin-body Silicon-on-Insulator. On-wafer scattering-parameter measurements of n-type NiSi source/drain SB-MOSFETs provide an in-depth understanding of key device parameters (transconductances and capacitances) as a function of the implanted arsenic dose, i.e., different SB height. Devices with 80-nm-channel length show a high ON current of 1150 mA/mm and exhibit a unity-gain cutoff frequency of fT = 140 GHz.

High-frequency performance of dopant-segregated NiSi S/D SOI SB-MOSFETs

In this paper, we present fully-depleted Schottky barrier MOSFETs with dopant-segregated NiSi source and drain junctions. Schottky barrier MOSFETs with a channel length of 80nm show high on-currents of 900 µA/µm for n-type devices with As segregation and 427 µA/µm for p-type devices with B segregation, respectively. A detailed high-frequency characterization proves the high performance of the devices with cut-off frequencies fT of 117 GHz for n-type and 63 GHz for p-type Schottky barrier MOSFETs and clearly elucidates the effects of extrinsic and intrinsic device parameters as a function of gate length.

Schottky barrier height modulation by Arsenic Dopant segregation

High performance Schottky barrier MOSFETs require metallic source/drain contacts with very low Schottky barrier heights. This investigation focuses on barrier lowering via silicidation induced dopant segregation at the NiSi/Si interface with particular emphasis on the influence of dopant activation prior to Ni-silicidation. Diodes with activated dopants reveal significantly lower Schottky barrier heights than diodes made without dopant activation. The electrical measurements in combination with secondary-ion mass spectroscopy allowed the determination of the effective Schottky barrier heights resulting in minimum barrier heights of around 0.1 eV. Moreover, we present an n-type SB-MOSFET with dopant segregation on thin body SOI which shows an intrinsic performance comparable to a conventional MOSFET.

Improving the performance of band-to-band tunneling transistors by tuning the gate oxide and the dopant concentration

For the first time, we investigated the impact of varying doping concentration and gate oxide thickness on the performance of band-to-band tunneling transistors. The output saturation current revealed a strong dependence on both parameters. Consequently, we were able to improve the saturation current by nearly a factor of 50.

High performance Schottky barrier MOSFETs on UTB SOI

This paper presents fully-depleted short-channel Schottky barrier (SB) MOSFETs with silicidation induced dopant segregation of B at a low temperature of 450°C. The integration of nickel silicide combined with either As or B segregation significantly improves the switching performance of dopant-free SB-MOSFETs. The implantation dose dependence of the device characteristics is studied on long channel p- and n-type SB-MOSFETs. An enhanced device performance with higher oncurrents and a strong suppression of the ambipolar behaviour, which is typical for SB-MOSFETs, is observed with increasing implantation dose. Short channel p-type SB-MOSFETs with a channel length of 80nm show an on-current of 525 μA/μm at an Ion/Ioff-ratio of 104, becoming competetive with state-of-the-art SB-MOSFETs.

Formation and characterization of ultra-thin Ni silicides on strained and unstrained silicon

Ultra thin Ni-silicides were formed on silicon-on-insulator (SOI) and biaxially tensile strained Si-on-insulator (SSOI) substrates. Epitaxial NiSi<inf>2</inf> layers were formed with a 3 nm Ni layer at T>400°C, while a polycrystalline NiSi layer was with a 5nm thick Ni layer. The NiSi<inf>2</inf> layer quality advances with increasing temperature. A very thin Pt interlayer, to incorporate Pt into NiSi, forming Ni<inf>1-x</inf>Pt<inf>x</inf>Si, improves the thermal stability, the interface roughness and lowers the contact resistivity. The Schottky barrier heights (SBH) of these silicides were measured on n-Si(100). Ni<inf>1-x</inf>Pt<inf>x</inf>Si shows the highest SBH. The SBH of NiSi<inf>2</inf> layers decreases by improving the layer interface. Surprisingly, the contact resistivity of epitaxial NiSi<inf>2</inf> is about one order of magnitude lower than that of NiSi on both, As and B doped SOI and SSOI, The lowest value of 7×10⁻⁸ Ω cm² was measured on B doped SSOI.

Epitaxial growth of NiSi2 induced by sulfur segregation at the NiSi2/Si(100) interface

Epitaxial growth of a NiSi 2 layer was observed on S + ion-implanted Si(100) at a low temperature of 550 °C. Depending on the S + dose and the Ni thickness, we identified different nickel silicide phases. High quality and uniform epitaxial NiSi 2 layers formed at temperatures above 700 °C with a 20-nm Ni on high dose S + implanted Si(100), whereas no epitaxy was observed for a 36-nm Ni layer. We assume that the presence of sulfur at the silicide/Si(100) interface favors the nucleation of the NiSi 2 phase. The S atom distributions showed ultrasteep S depth profiles (3 nm/decade) in the silicon, which results from the snow-plow effect during silicidation and the segregation of S to the interface due to the low solubility of S in both Si and the silicide.

Non-linear analysis of n-type Schottky-Barrier MOSFETs

In the last few years, many efforts have been made looking for the improvement of the DC and RF performance of MOS transistors. In this scope, Schottky-Barrier transistors appear as very interesting alternative to conventional devices. In this paper we present the non-linear behavior of dopant segregated n-type SB-MOSFETs with 180 nm channel length.