Formation of Low-resistivity Germanosilicide Contacts to Phosphorus Doped Silicon-germanium Alloy Source/drain Junctions for Nanoscale CMOS PDF Download

Author: Hongxiang Mo
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Languages : en
Pages : 131

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Keywords: SiGe, germanosilicide, contact reistance, silicide, silicon germanium, MOSFET, source drain.

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Languages : en
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Conventional source/drain junction and contact formation processes can not meet the stringent requirements of future nanoscale complimentary metal oxide silicon (CMOS) technologies. The selective Si[subscript 1-x]Ge[subscript x] source/drain technology was proposed in this laboratory as an alternative to conventional junction and contact schemes. The technology is based on selective chemical vapor deposition of in-situ boron or phosphorus doped Si[subscript 1-x]Ge[subscript x] in source/drain areas. The fact that the dopant atoms occupy substitutional sites during growth make the high temperature activation anneals unnecessary virtually eliminating dopant diffusion to yield abrupt doping profiles. Furthermore, the smaller band gap of Si[subscript 1-xGe[subscript x] results in a smaller Schottky barrier height, which can translate into significant reductions in contact resistivity due to the exponential dependence of contact resistivity on barrier height. This study is focused on formation of self-aligned germanosilicide contacts to phosphorous-doped Si[subscript 1-x]Ge[subscript x] alloys. The experimental results obtained in this study indicate that self-aligned nickel germanosilicide (NiSi[subscript 1-x]Ge[subscript x]) contacts can be formed on Si[subscript 1-x]Ge[subscript x] layers at temperatures as low as 350 & deg;C. Contacts can yield a contact resistivity of 1E-8 ohm-cm2 with no sign of germanosilicide induced leakage. However, above a threshold temperature determined by the Ge concentration in the alloy, the NiSi[subscript 1-x]Ge[subscript x]/Si[subscript 1-x]Ge[subscript x] interface begins to roughen, which affects the junction leakage. For phosphorus doped layers considered in this study, the threshold temperature was around 500 & deg;C, which is roughly 100 & deg;C higher than the threshold temperature for NiSi[subscript 1-x]Ge[subscript x contacts formed on boron doped Si[subscript 1-x] Ge[subscript x] layers with a Ge percentage of ~ 50%. Nickel and.

Author: Jing Liu
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Category :
Languages : en
Pages : 154

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Keywords: germanosilicide, silicide, silicon germanium, contact resistance, ultra-shallow junction, source drain, CMOS.

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Category :
Languages : en
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State-of-the-art p-channel metal oxide semiconductor field effect transistors (MOSFETs) employ Si(1-x)Ge(x) source/drain junctions to induce uniaxial compressive strain in the channel region in order to achieve hole mobility enhancement. It is also know that the elec- tron mobility can be enhanced if the MOSFET channel is under uniaxial tension, which can be realized by replacing Si(1-x)Ge(x) with Si(1-y)C(y) epitaxial layers in recessed source/drain regions of n-channel MOSFETs. This dissertation focuses on epitaxy of Si(1-y)C(y) layers and low resistivity contacts on Si, Si(1-x)Ge(x), and Si(1-y)C(y) alloys. While these contacts are of particular importance for future MOSFETs, other devices based on these semiconductors can also benefit from the results presented in this dissertation. The experimental work on Si(1-y)C(y) epitaxiy focused on understanding the impact of various process parameters on carbon incorporation, substitutionality, growth rate, phosphorus incorporation and activation in order to achieve low resistivity Si(1-y)C(y) films with high substitutional carbon levels. It was shown, for the first time, that phosphorus lev- els above 1.3x10^(21) cm^( -3) can be achieved with 1.2% fully substitutional carbon in epitaxial layers. Specific contact resistivity (C) on strained Si(1-x)Ge(x) layers was evaluated using the existent results from the band structure calculations. Previous work on this topic mainly focused on barrier height and the doping density at the interface. In this work, the impact of the tunneling effective mass on specific contact resistivity was calculated for the first time for strained Si(1-x)Ge(x) alloys. It was shown that due to the exponential dependence of contact resistivity on this parameter tunneling effective mass may have a strong impact on contact resistivity. This is especially important for strained alloys in which the tunneling effective mass is dependent on the strain. The contact resistivity was found to decrease with Ge.

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Category : Dissertations, Academic
Languages : en
Pages : 820

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Author: Emre Alptekin
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Languages : en
Pages : 92

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Keywords: silicon carbon, silicide, barrier height, contact resistance, MOSFET, source drain junction.

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Languages : en
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As CMOS integrated circuits are scaled beyond the 50nm regime, conventional source/drain junction and contact technologies can no longer satisfy the requirements of MOSFETs, which require super-abrupt doping profiles and extremely low contact resistivities. To address these challenges, selective Si1-xGex source/drain technology was proposed by this laboratory. In this approach, in-situ doped Si1-xGex layers are selectively deposited in recessed source/drain regions. Since the dopants occupy substitutional sites during epitaxial growth, high temperature annealing is not required for dopant activation, which eliminates diffusion and provides abrupt doping profiles. Furthermore, smaller bandgap of Si1-xGex reduces the metal-semiconductor barrier height, an essential requirement for achieving a substantial reduction in contact resistivity. This thesis focuses on selective rapid thermal chemical vapor deposition of in-situ phosphorus doped Si1-xGex alloys intended for this application. Experiments were carried out to study electrical properties of the in-situ doped layers with emphasis on maximizing the active carrier concentration. Active phosphorus levels in the range of 2 -- 5 x 1020 cm-3 were obtained. The deposited layers were used to fabricate pn junctions with excellent reverse leakage characteristics. Junctions fabricated on lightly doped substrates exhibited behavior equivalent to best junctions in spite of the lattice mismatch between the Si substrate and the phosphorus doped Si1-xGex. Junctions fabricated on heavily doped substrates suffered from band to band tunneling, which is expected regardless of the junction formation technique. Deposition selectivity of the process was studied and determined that high flows of PH3 could degrade the selectivity. An alternative deposition process based on alternating periods of deposition and etching was developed, which provided substantial improvements in deposition selectivity.

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Languages : en
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As metal-oxide semiconductor field effect transistors (MOSFETs) are scaled for higher speed and reduced power, new challenges are imposed on the source/drain junctions and their contacts. Future junction technologies are required to produce ultra-shallow junctions with junction depths as low as 4 nm, above-equilibrium dopant activation, super-abrupt doping profiles and specific contact resistivity values below 1x10− & 8312; &!cm2. Recently, selectively deposited, boron doped Si1−[subscript x]Ge[subscript x] junctions have been proposed to overcome these challenges. Success of technology relies on selective chemical vapor deposition of the process and satisfying stringent requirements for process integration. In the present work, the effects of process conditions on selective deposition of heavily boron doped Si1−[subscript x]Ge[subscript x] is investigated using Si2H6 and GeH4 as the precursors. It was found that addition of large amounts of diborane resulted in selectivity degradation. Addition of chlorine improved selectivity for both doped and undoped Si1−[subscript x]Ge[subscript x] depositions. It was shown that addition of chlorine to the undoped Si1−Ge[subscript x] deposition chemistry resulted in reduced surface roughness. It is proposed that chlorine preferentially segregates to the surface of the deposited films, and act as the surfactant. However, it was also found that addition of chlorine did not significantly impact the surface morphology of heavily boron doped Si1−Ge[subscript x]. It was shown that addition of chlorine strongly interfered with Ge and B incorporation. Furthermore, it was found that chlorine resulted in enhanced Ge but reduced B incorporation. It is proposed that chlorine adsorption on the growing surfaces reduced the available sites for boron while promoting SiCl2 desorption at lower temperatures. Increase in deposition temperature for a.

Author: Nemanja Pešović
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ISBN:
Category :
Languages : en
Pages : 149

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Keywords: selective, epitaxy, sige, source, drain, MOSFET, transistor.

Author: Astha Tapriya
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Category : Phosphorus
Languages : en
Pages : 176

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"Controlled doping of semiconductor material with high atomic accuracy and minimum defects in silicon is needed for next generation nanoscale and solar devices. The molecular monolayer doping (MLD) strategy is a novel technique based on the formation of self-assembled monolayer of dopant –containing molecule on surface of crystalline silicon, followed by rapid thermal annealing. MLD helps to form damage free junctions which are conformal. It is capable of nanometer scale control of dopant introduction and formation of ultra-shallow diffused profile. MLD can be used for conventional planar devices, FinFETs and nanowires, since both bottom-up and top-down approaches are feasible making it highly versatile. It also finds applications in solar cell industry, to fabricate selective emitters and increases the efficiency of the crystalline silicon solar cell along with reduced contact resistance. Phosphorus MLD on p-type silicon is formed using diethyl 1-propylphosphonate (DPP) as dopant source in this work. It involved demonstrating the formation of monolayer on silicon piece and 6-inch wafer. The setup is designed, assembled and implemented successfully to achieve monolayer formation on full wafer. The presence of phosphorous on the surface is detected by Auger electron spectroscopy and confirmed by X-ray photoelectron spectroscopy on the same silicon sample. The phosphorous monolayer on the surface is diffused in the silicon surface using rapid thermal anneal at 1000oC for 180 seconds. The diffusion profile is characterized by Secondary ion mass spectrometry (SIMS), spreading resistance profile and sheet resistance measurements. The result show successful creation of diffusion profile with high surface concentration, junction depth of 20 nm extracted at 1 x 1018 cm-3 base doping and sheet resistance is 920 [ohms]/sq. The total dose of phosphorous in the silicon is dependent on the number of bonds formed using DPP and dose is increased by multiple rounds of MLD and annealing, sheet resistance for double MLD is reduced to 670 [ohms]/sq. N+P junctions are fabricated using MLD and current-voltage characteristics are measured and analyzed using unified model. It is found that the specific contact resistivity of MLD doped wafer is lower than the implanted wafer. It is also reported that MLD doping can be masked by a thin oxide layer giving a possibility of patterned doping."--Abstract.