Johan Seger

Morphological and phase stability of nickel–germanosilicide on Si1−xGex under thermal stress

Continuous and uniform Ni(Si,Ge) layers are formed on polycrystalline Si and Si0.42Ge0.58 substrate films at 500 degreesC by rapid thermal processing. The germanosilicide is identified as NiSi0.42G ...

Increased nucleation temperature of NiSi2 in the reaction of Ni thin films with Si1−xGex

The formation of a ternary solid solution NiSi1−xGex, instead of a mixture of NiSi and NiGe, is found during solid-state interactions between Ni and various Si1−xGex films ranging from pure Si to pure Ge. The lattice parameters of the solid solution of orthorhombic structure increase linearly with Ge content (x) as: a=5.24+0.19x A, b=3.25+0.16x A, and c=5.68+0.15x A. The specific resistivity increases from 17 μΩ cm for NiSi to 21 μΩ cm for NiSi0.71Ge0.29 and NiSi0.42Ge0.58. Although the Ge content rapidly drops from 30–60 to about 10 at. % in the solid solutions formed above 600 °C, the crystallographic structure remains unchanged and no NiSi2 [or Ni(Si,Ge)2] is found in the Si1−xGex samples even after annealing at 850 °C. Without Ge, the NiSi completely disappears at 750 °C. These results indicate a strong effect of the entropy of mixing in NiSi–NiGe on the nucleation of NiSi2.

Lateral encroachment of Ni-silicides in the source/drain regions on ultrathin silicon-on-insulator

Lateral growth of Ni silicide towards the channel region of metal-oxide-semiconductor transistors (MOSFETs) fabricated on ultrathin silicon-on-insulator (SOI) is characterized using SOI wafers with a 20-nm-thick surface Si layer. With a 10-nm-thick Ni film for silicide formation, p-channel MOSFETs displaying ordinary device characteristics with silicided p+ source/drain regions were demonstrated. No lateral growth of NiSix under gate isolation spacers was found according to electron microscopy. When the Ni film was 20 nm thick, Schottky contact source/drain MOSFETs showing typical ambipolar characteristics were obtained. A severe lateral encroachment of NiSix into the channel region leading to an increased gate leakage was revealed, while no detectable voiding at the silicide front towards the Si channel was observed.

Morphological instability of NiSi1-uGeu on single-crystal and polycrystalline Si1-xGex

The morphological stability of NiSi1−uGeu ternary alloy films formed by reacting Ni with single-crystal (sc) and polycrystalline (poly) Si1−xGeu is studied (u can be different from x). The agglomeration of NiSi1−uGeu films on Si0.7Ge0.3 occurs at 550°C after rapid thermal processing for 30 s, independently of the crystallinity of the Si1−xGeu. This behavior distinctly different from NiSi: NiSi films on poly-Si display a poorer morphological stability and degrade at lower temperatures than NiSi on sc-Si. On strained Si1−xGex, the presence of Ge simultaneously gives rise to two effects of different origin: mechanical and thermodynamic. The main driving forces behind the agglomeration of NiSi1−uGeu on sc-Si1−xGex are found to be the stored strain energy in the Si1−xGex and the larger (absolute) free energy of formation of NiSi compared to NiGe. The latter constitutes the principal driving force behind the agglomeration of NiSi1−uGeu on poly-Si1−xGex and is not affected by the degree of crystallinity of Si1−x...

Control of Self-Heating in Thin Virtual Substrate Strained Si MOSFETs

This paper presents the first results and analysis of strained Si n-channel MOSFETs fabricated on thin SiGe virtual substrates. Significant improvements in electrical performance are demonstrated compared with Si control devices. The impact of SiGe device self-heating is compared for strained Si MOSFETs fabricated on thin and thick virtual substrates. This paper demonstrates that by using high-quality thin virtual substrates, the compromised performance enhancements commonly observed in short-gate-length MOSFETs and high-bias conditions due to self-heating in conventional thick virtual substrate devices are eradicated. The devices were fabricated with a 2.8-nm gate oxide and included NiSi to reduce the parasitic series resistance. The strained layers grown on the novel substrates comprising 20% Ge did not relax during fabrication. Good on-state performance, off-state performance, and cross-wafer uniformity are demonstrated. The results show that thin virtual substrates have the potential to circumvent the major issues associated with conventional virtual substrate technology. A promising solution for realizing high-performance strained Si devices suitable for a wide range of applications is thus presented

Enhanced phase stability and morphological stability of Ni(Si,Ge) on strained Si0.8Ge0.2

Abstract NiSi 0.8 Ge 0.2 film formed on a strained Si 0.8 Ge 0.2 layer epitaxially grown on a Si(100) substrate wafer is morphologically stable up to 750 °C. The NiSi 0.8 Ge 0.2 film is found to be strongly oriented along its 〈010〉 direction. This remarkable stability is thus possibly caused by the tendency of an epitaxial alignment between the NiSi 0.8 Ge 0.2 film and the Si 0.8 Ge 0.2 layer. The presence of Ge in NiSi forming the ternary solution NiSi 0.8 Ge 0.2 hinders the formation of NiSi 2 even at 850 °C.

Cross-sectional transmission electron microscopy study of the influence of niobium on the formation of titanium silicide in small-feature contacts

The influence of a Nb layer between Si and Ti on the formation of TiSi2 in small-feature contacts and of the substrate doping level has been studied using transmission electron microscopy in combination with convergent-beam electron diffraction. For an As dose of 2.5×1016 cm−2, a mixture of C49 and partially agglomerated C54 TiSi2 grains was found in some of the 5×5 μm2 contact windows, while only C49 existed in the 0.7×0.7 μm2 windows. Agglomeration is shown to lead to possible C49−C54 coexistence, as well as erroneous interpretation of the C54 nucleation density. Decreasing the As dose to 5×1015 cm−2 leads to a thicker TiSi2 layer, but does not have a major influence on phase formation in the small windows, although only C54 TiSi2 was found in the large ones. In the presence of a thin Nb layer between Ti and poly-Si, C40 (Ti,Nb)Si2 was consistently found in all contacts, indicating that formation does not depend on the contact size at least down to 0.5 μm2. Surprisingly, Ti was found on both sides of th...

A novel strained Si0.7Ge0.3 surface-channel pMOSFET with an ALD TiN/Al2O3/HfAlOx/Al2O3 gate stack

Proof-of-concept pMOSFETs with a strained-Si/sub 0.7/Ge/sub 0.3/ surface-channel deposited by selective epitaxy and a TiN/Al/sub 2/O/sub 3//HfAlO/sub x//Al/sub 2/O/sub 3/ gate stack grown by atomic layer chemical vapor deposition (ALD) techniques were fabricated. The Si/sub 0.7/Ge/sub 0.3/ pMOSFETs exhibited more than 30% higher current drive and peak transconductance than reference Si pMOSFETs with the same gate stack. The effective mobility for the Si reference coincided with the universal hole mobility curve for Si. The presence of a relatively low density of interface states, determined as 3.3 /spl times/ 10/sup 11/ cm/sup -2/ eV/sup -1/, yielded a subthreshold slope of 75 mV/dec. for the Si reference. For the Si/sub 0.7/Ge/sub 0.3/ pMOSFETs, these values were 1.6 /spl times/ 10/sup 12/ cm/sup -2/ eV/sup -1/ and 110 mV/dec., respectively.

Low‐frequency Noise in SiGe Channel pMOSFETs on Ultra‐Thin Body SOI with Ni‐Silicided Source/Drain

The low‐frequency noise in buried SiGe channel pMOSFETs fabricated on ultra‐thin body silicon‐on‐insulator (SOI) substrates is investigated. The total thickness of the Si/SiGe/Si body structure, which is fully depleted (FD), is 20 nm. The low‐frequency noise properties are compared with FD SOI pMOSFETs with a 20 nm Si body. The effect of the Ni‐silicide used in the Source/Drain were also studied, especially the case of Schottky‐Barrier (SB) MOSFETs when the Ni‐silicide is formed at the edges of the channel.

Influence of a Si layer intercalated between Si0.75Ge0.25 and Ni on the behavior of the resulting NiSi1−uGeu film

The interaction of Ni films with epitaxially grown Si-capped and not capped Si0.75Ge0.25 layers on Si(100) at 500°C leads to the formation of NiSi1−uGeu films as a bilayer NiSi on NiSi0.75Ge0.25 with a rather clear compositional boundary. In the absence of a Si cap at the surface, NiSi0.75Ge0.25 is formed on NiSi. Epitaxy of NiSi on NiSi0.75Ge0.25, and vice versa, occurs across the compositional boundary. The crystallographic orientation of the NiSi1−uGeu films is strongly affected by the initial layer thicknesses and the layer sequence. Without a Si cap, the NiSi1−uGeu films show an increased fiber texture with increasing Si0.75Ge0.25 thickness. In the presence of a Si cap, on the other hand, the texture collapses into a random orientation already for thin caps. Rapid diffusion of Ge at 500°C results in the presence of some Ge at the NiSi∕Si interface for a NiSi0.75Ge0.25∕NiSi∕Si structure. This diffusion is accompanied by an increased roughness at the NiSi∕Si interface, as compared to the quite flat NiS...