Germanosilicide Contacts Research Articles

Ni(Pt) germanosilicide contacts formed on heavily boron doped Si1−xGex substrates for Schottky source/drain transistors

The electrical properties of Ni0.95Pt0.05-germanosilicide/Si1−xGex contacts on heavily doped p-type strained Si1−xGex layers as a function of composition and doping concentration for a given composition have been investigated. A four-terminal Kelvin-resistor structure has been fabricated by using the conventional complementary metal–oxide–semiconductor (CMOS) process to measure contact resistance. The results showed that the contact resistance of the Ni0.95Pt0.05-germanosilicide/Si1−xGex contacts slightly reduced with increasing the Ge fraction. The higher the doping concentration, the lower the contact resistivity. The contact resistance of the samples with doping concentration of 4 × 1019 cm−3 is nearly one order of magnitude lower than that of the samples with doping concentration of 5 × 1017 cm−3. In addition, the influence of dopant segregation on the contact resistance for the lower doped samples is larger than that for the higher doped samples.

Platinum Germanosilicide Contacts Formed on Strained and Relaxed $\hbox{Si}_{1 - x}\hbox{Ge}_{x}$ Layers

Contact resistivity is a key contributor to the parasitic series resistance of nanoscale MOSFETs. Since the contact resistivity is an exponential function of the Schottky barrier height, new contact materials that can provide smaller barrier heights to source-drain junctions are needed. Platinum germanosilicide (PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) is of interest as a contact material to the recessed Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> junctions of p-channel MOSFETs due to the large work function of platinum silicide (PtSi). In this paper, we explore the impact of in-plane biaxial compressive strain in Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layers on PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> formation and the impact of the PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> on the strain in Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> . The parameters considered in this paper include the Ge content, the thickness of the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> epitaxial layer, and the PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> thickness. The results show that the resistance, surface morphology, and the crystalline structure of the PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> films are independent of the strain in the original Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layer. The results also indicate that PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> does not influence the strain in the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layer. The barrier-height measurements suggest the presence of Fermi-level pinning, and the pinning position is independent of the strain in the alloy, and it is primarily determined by the Ge concentration. As a result of Fermi-level pinning, hole Schottky barrier height of PtSi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> contacts is 0.1-0.2 eV higher than that of the PtSi-Si contacts.

The effects of nickel germanosilicide contacts on the biaxial compressive stress in thin epitaxial silicon-germanium alloys on silicon

When a thin Si1−xGex epitaxial layer is grown on Si, it is under biaxial compression. In this letter, it is shown that a nickel germanosilicide (NiSi1−xGex) layer formed on Si1−xGex can significantly reduce the in-plane compressive strain in Si1−xGex. It is proposed that the observed reduction is due to the biaxial tensile stress applied by the NiSi1−xGex layer. Because the Si1−xGex bandgap is a strong function of the strain, this is expected to have a strong impact on the metal-semiconductor barrier height and the contact resistivity of the interface if the metal Fermi level is pinned near the Si1−xGex midgap.

The effects of nickel germanosilicide contacts on the biaxial compressive stress in thin epitaxial silicon-germanium alloys on silicon

The effects of nickel germanosilicide contacts on the biaxial compressive stress in thin epitaxial silicon-germanium alloys on silicon

Impact of Heavy Boron Doping and Nickel Germanosilicide Contacts on Biaxial Compressive Strain in Pseudomorphic Silicon-Germanium Alloys on Silicon

AbstractIn recent years, the semiconductor industry has increasingly relied on strain as a performance enhancer for both n and p-MOSFETs. For p-MOSFETs, selectively grown SiGe alloys in recessed source/ drain regions are used to induce uniaxial compressive strain in the channel. In order to induce compressive strain effectively using this technology, a number of parameters including recess depth, SiGe thickness (junction thickness), sidewall thickness, dopant density, dislocation density, and contact materials have to be optimized. In this work, we have studied the effects of heavy boron doping and self-aligned germanosilicide formation on local strain. Raman spectroscopy has been used to study the impact of heavy boron doping on compressive stress in SiGe films. Strain energy calculations have been performed based on Vegard's law for ternary alloys and the effect of boron on strain in SiGeB alloys modeled quantitatively. It will be shown that, owing to the smaller size of a boron atom, one substitutional boron atom compensates the strain due to 6.9 germanium atoms in the SiGeB film grown pseudomorphically on silicon. The critical thickness of SiGeB has been calculated for the first time based on kinetically limited critical thickness calculations for metastable SiGe films. It will be shown that the critical thickness of the alloy increases as the boron content in the alloy is increased, making boron concentration an additional parameter for optimizing strain in the MOSFET. Based on these conclusions, boron concentration can be used to preserve the strain for thicker SiGeB films (compared to SiGe films) while keeping the dislocation density low. Furthermore, we show that NiSiGe contacts can have a profound impact on the SiGe strain. Our results indicate that NiSiGe introduces additional stress in the underlying SiGe, which further affects the strain induced in the channel

Nickel Germanosilicide Contacts Formed on Heavily Boron Doped&amp;lt;tex&amp;gt;$rm Si_1-xrm Ge_x$&amp;lt;/tex&amp;gt;Source/Drain Junctions for Nanoscale CMOS

Formation of source/drain junctions with a small parasitic series resistance is one of the key challenges for CMOS technology nodes beyond 100 nm. A new source/drain technology based on selective deposition of heavily in situ doped Si/sub 1-x/Ge/sub x/ layers was recently developed in this laboratory. This paper presents formation and structural characterization of self-aligned nickel germanosilicide contacts formed on heavily boron doped Si/sub 1-x/Ge/sub x/ alloys. The results show that thin NiSi/sub 1-x/Ge/sub x/ contacts with a resistivity of /spl sim/25 /spl mu//spl Omega/-cm can be formed on Si/sub 1-x/Ge/sub x/ alloys at temperatures as low as 350/spl deg/C. However, the low resistivity and the structural integrity of the NiSi/sub 1-x/Ge/sub x/ films can be maintained up to a maximum temperature of 450/spl deg/C. At higher temperatures, Ge out-diffusion from NiSi/sub 1-x/Ge/sub x/ grains results in interface roughening and NiSi spikes. If the maximum processing temperature is kept within 400/spl deg/C, p/sup +/-n junctions with excellent leakage behavior can be formed. A minimum contact resistivity of 2/spl times/10/sup -8/ /spl Omega/-cm/sup 2/ is demonstrated for Ge concentrations above /spl sim/40%, which can be linked to the smaller semiconductor bandgap and high boron activation under the metal contact. The results suggest that NiSi/sub 1-x/Ge/sub x/ contacts formed on Si/sub 1-x/Ge/sub x/ junctions have the potential to satisfy the contact resistivity requirements of future CMOS technology nodes.

Low Resistivity Nickel Germanosilicide Contacts to Ultra-shallow Junctions Formed by the Selective Si1-xGexTechnology for Nanoscale CMOS

AbstractIn this paper, we present our recent results on nickel germanosilicide contacts formed on p+-n and n+-p junctions formed by selective deposition of in-situ doped Si1-xGexalloys. Our results show that ultra-thin, low resistivity NiSi1-xGexcontacts can be formed at temperatures as low as 300°C on both boron and phosphorus doped Si1-xGexlayers. Ultra-shallow junctions with excellent reverse leakage behavior and a contact resistivity ∼ of 10-8ohm-cm2were successfully demonstrated. The thermal stability of NiSi1-xGexwas found to be limited to 500°C on p+-Si1-xGexand 600°C onn+-Si1-xGex. It was found that by inserting a thin Pt interlayer between Ni and Si1-xGex, the quality of the NiSi1-xGexcontacts could be significantly improved. The Pt interlayer was found to improve the interface morphology, which was found to have a direct impact on the electrical properties of the contacts.

Nickel, Platinum and Zirconium Germanosilicide Contacts to Heavily Phosphorous Doped Silicon-Germanium Alloys for Advanced CMOS Source/Drain Junctions

ABSTRACTAs the MOSFET dimensions continue to shrink, source/drain contact resistance is emerging as the dominant component of the MOSFET parasitic series resistance. To meet the series resistance requirements of future MOSFETs, contact resistivity values near 10-8 ohm-cm2 are required. Selective Si1-xGex source/drain technology has been proposed as an alternative to ionimplantation to form the ultra-shallow junctions of future CMOS technology nodes. One of the key advantages of this technology is the smaller band gap of Si1-xGex, which provides a smaller contact barrier height, an essential requirement for reducing the contact resistivity. We have previously reported low-resistivity of Ni germanosilicide NiSi1-xGex and Pt germanosilicide PtSi1-xGex contacts to boron doped Si1-xGex alloys. In this work, Zr germanosilicide, Zr(Si1-xGex)2 was considered as an alternative material with a higher thermal stability than Ni and Pt germanosilicides. The contact resistivity values for different contact materials were measured using four-terminal Kelvin structures. The results from this work show that both Zr and Pt germanosilicides yield high contact resistivity values around 10-7 ohm-cm2. On the other hand Ni germanosilicide contacts can reach 10-8 ohm-cm2 with further improvements using a thin layer of Pt under Ni.

Nickel, Platinum and Zirconium Germanosilicide Contacts to Ultra-shallow, P+N Junctions Formed by Selective SiGe Technology for CMOS Technology Nodes Beyond 70nm

AbstractSelective SiGe source/drain technology based on selective deposition of in-situ doped SiGe alloys in recessed source/drain regions can provide junctions with low sheet and contact resistance as well as abrupt doping profiles. This paper examines properties of Ni, Pt and Zr germanosilicides on heavily boron doped SiGe junctions. Our results show that all three metals can form low resistivity germanosilicides on heavily boron doped SiGe alloys. The stability of Ni germanosilicide was found to be limited to about 400°C on undoped SiGe. On heavily boron doped SiGe thermal stability was found to be significantly better possibly due to boron strain compensation. Our findings indicate that on undoped SiGe, thermal stability of Ni germanosilicide could be much enhanced by using a thin Pt interlayer. According to X-ray diffraction analysis, with increasing formation temperature, both Ni and Pt germanosilicides moved toward Ni and Pt monosilicides with signs of excess Ge appearing outside the contact. Analysis of the Pt germanosilicide layers is suggestive of a Ge rich SiGe layer under the germanosilicide. Boron diffusion into Pt and Ni germanosilicides was not observed. On the other hand, a distinct boron peak was observed in Zr germanosilicide suggestive of a stable Zr-B compound. Ultra-shallow junctions with excellent reverse bias behavior were formed using both Ni and Zr germanosilicides.

Phase formation and strain relaxation during thermal reaction of Zr and Ti with strained Si1−x−yGexCy epilayers

Silicides are often used in Si technology for both their ohmic and rectifying properties. In this work, we have compared Zr and Ti germanosilicides as possible metallic contacts on SiGeC alloys in terms of phase formation and stability of the unreacted SiGeC alloy. The germanosilicides are obtained after rapid thermal annealings of Zr or Ti with strained SiGeC layers. The interactions of the metal films with these alloys have been investigated by sheet resistance measurements, x-ray diffraction (XRD), cross-sectional transmission electron microscopy (TEM), and energy dispersive spectroscopy in situ in the TEM. Four crystal x-ray diffraction was performed to measure the residual strain of the unreacted SiGeC epilayer after reaction. The analyses indicate that the final compounds are the C49–Zr(SiGe)2 and C54–Ti(SiGe)2 phases, respectively: In both cases, the compound is formed by monocrystalline grains with various orientations. Nevertheless, neither XRD, nor sheet resistance measurements give any clear information about the C incorporation in the phase, when the reaction occurs with a SiGeC layer. We have observed that the use of Zr completely avoids Ge segregation with an uniform layer formed, while in the case of the reaction with Ti, the grains do not form a continuous layer and Ge-segregation is evidenced: A Ge-rich Si1−z−yGez(Cy) alloy is detected in between the metallic grains. In addition, an early strain relaxation of the unreacted SiGe layer is observed after reaction, and it is much more important after reaction with Ti. During the reaction with nearly compensated SiGeC layers, Zr totally prevents the initial state of strain, while Ti strongly affects the unreacted SiGeC alloy and destroys its initial state. All these results indicate that Zr may be an interesting candidate for realizing germanosilicide contacts on IV–IV alloys, due to its good thermal stability.

Self-Aligned Formation of C54 Titanium Germanosilicide Using Rapid Thermal Processing and Application to Raised, Ultrashallow Junctions

ABSTRACTIn this paper we present results on solid state reactions between Ti and Si1−xGex alloys selectively deposited onto Si (100) substrates using rapid thermal annealing (RTA) for contact applications in novel device structures. Germanium concentrations of 0%, 30%, 50%, and 100% within the reacting Si1−xGex alloy are investigated. The Si1−xGex alloys (approximately 2500 ° thick) are deposited using rapid thermal chemical vapor deposition (RTCVD). Titanium is then deposited by evaporation. Sheet resistance measurements as a function of RTA temperature (10 second anneals) provide indications of various phases that occur during the reactions through the formation of constant sheet resistance plateaus. The RTA temperature required for the formation of a minimum resistivity phase is observed to increase for increasing Ge concentrations within the reacting Si1−xGex alloy. Using x-ray diffraction we have determined that for the reactions of Ti with Si the C49 TiSi2 metastable phase forms prior to the minimum resistivity C54 TiSi2 phase. For the reactions between Ti and Ge a minimum resistivity TiGe2 phase also with the C54 structure forms, however, this phase is preceeded not by a C49 TiGe2 structure, but by a Ti6Ge5 phase. The minimum resistivity phases for Ti reactions with 30% and 50% Ge Si1−xGex, alloy reactions also have a C54 structure with unit cell dimensions varying from that of TiSi2) to TiGe2 as the Ge concentration is increased. The grain structures for the reactions are investigated by cross-sectional transmission electron microscopy (XTEM). As the Ge concentration within the reacting alloy decreases the lateral grain size for the C54 structures increases. A self-aligned germanosilicide process is identified and used to fabricate raised, ultrashallow junctions with Ti(SiGe)2 (germanosilicide) contacts. Forward and reverse bias characterization of the junctions indicate that leakage current induced during silicidation can be eliminated using raised junctions with germanosilicide contacts.