| 1. |
- Chakraborty, S., et al.
(författare)
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Symbolic trajectory evaluation for word-level verification: theory and implementation
- 2017
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Ingår i: Formal Methods in System Design. - : Springer Science and Business Media LLC. - 1572-8102 .- 0925-9856. ; 50:2-3, s. 317-352
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Tidskriftsartikel (refereegranskat)abstract
- Symbolic trajectory evaluation (STE) is a model checking technique that has been successfully used to verify many industrial designs. Existing implementations of STE reason at the level of bits, allowing signals in a circuit to take values from a lattice comprised of three elements: 0, 1, and X. This limits the amount of abstraction that can be achieved, and presents limitations to scaling STE to even larger designs. The main contribution of this paper is to show how much more abstract lattices can be derived automatically from register-transfer level descriptions, and how a model checker for the general theory of STE instantiated with such abstract lattices can be implemented in practice. We discuss several implementation issues, including how word-level circuits can be symbolically simulated using a new encoding for words that allows representing X values of sub-words succinctly. This gives us the first practical word-level STE engine, called STEWord. Experiments on a set of designs similar to those used in industry show that STEWord scales better than bit-level STE, as well as word-level bounded model checking.
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| 2. |
- Isheden, Christian, et al.
(författare)
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Formation of Ni mono-germanosilicide on heavily B-doped epitaxial SiGe for ultra-shallow source/drain contacts
- 2003
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Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172 .- 1946-4274. ; 745, s. 117-122
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Tidskriftsartikel (refereegranskat)abstract
- The formation of Ni germanosilicides during solid-state interaction between Ni and heavily B-doped strained epitaxial Si1-xGex films with x=0.18, 0.32 and 0.37 is studied. No NiSi2 is found in these samples even after annealing at 850 degreesC, which can be compared to the formation of NiSi2 at 750 T on Si(I 00). Resistance and diffraction studies for the Si0.82Ge0.18 sample indicate that NiSi0.82Ge0.18 forms and the NiSi0.82Ge0.18/Si0.82Ge0.18 structure is stable from 400 to 700 degreesC. For the NiSi1-uGeu formed in all Si1-xGex samples, where u can be different from x, a strong film texturing is observed. When the Ge fraction is increased from 18 at.% to 32-37 at.%, the morphological stability of the film is degraded and a substantial increase in sheet resistance occurs already at 600 degreesC. The contact resistivity for the NiSi0.8Ge0.2/Si0.8Ge0.2 interface formed at 550 T is determined as 1.2x10(-7) Omegacm(2), which satisfies the ITRS contact resistivity requirement for the 70 nm technology node.
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| 3. |
- Jarmar, T., et al.
(författare)
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Germanium-induced texture and preferential orientation of NiSi1-xGex layers on Si1-xGex
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:23, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- NiSi1-xGex films on compressively strained as well as relaxed undoped Si1-xGex epitaxially grown substrates with x=0.06-0.30 on Si(001) wafers have been studied with respect to the relative orientation of film and substrate after annealing at temperatures in the range 400-850 degreesC. Using x-ray diffraction, transmission electron microscopy, and pole-figure measurements, it was found that only the monogermanosilicide phase formed above 450 degreesC and was the only phase still at 850 degreesC. New information regarding the effects of Ge on the silicidation of Ni was also found. Thus, the preferred plane parallel to the surface is (013). Compared to NiSi, Ge suppresses the development of the other planes parallel to the surface except (013). Within this plane, the orientations of the grains pile up in such a way that the configuration NiSi1-xGex[100]//Si1-xGex[100] is avoided, which in the pole-figures leads to broad peaks in-between the substrate [100] and [010]. In addition, peaks indicating the epitaxial alignment NiSi0.8Ge0.2(+/-21-1) or (+/-2-11)//Si0.8Ge0.2(+/-2+/-20) coupled with NiSi0.8Ge0.2(+/-100)approximate to//Si0.8Ge0.2(+/-100) or (0+/-10) were found. Fine structure in the broad peaks is found to be due to lateral epitaxial alignments between grains along their common grain boundary. Based on the nonexistence of NiGe2, the observations are interpreted in terms of Ge preventing the formation of certain Ni-Ge bonds at the interface between NiSi1-xGex and the Si1-xGex substrate.
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| 4. |
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| 5. |
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| 6. |
- Jarmar, T., et al.
(författare)
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Morphological and phase stability of nickel-germanosilicide on Si1-xGex under thermal stress
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:12, s. 7193-7199
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Tidskriftsartikel (refereegranskat)abstract
- 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 NiSi0.42Ge0.58, i.e., with the same Si-to-Ge ratio as in the substrate. The NiSi0.42Ge0.58 layer has agglomerated at 600 degrees C. This is accompanied by a diffusion of Ge out from the germanosilicide grains and the growth of a Ge-rich SiGe region in their close vicinity. These changes cause a slight variation in the atomic composition of Ni(Si,Ge) detectable for individual grains by means of energy dispersive spectroscopy. Above 600 degreesC, substantial outdiffusion of Ge from the Ni(Si,Ge) grains occurs concurrently with the migration of the grains into the substrate film away from the surface area leaving a Ge-rich SiGe region behind. These observations can be understood with reference to calculated Ni-Si-Ge ternary phase diagrams with and without the inclusion of NiSi2. When Ge is present, the Ni-based self-aligned silicide process presents a robust technique with respect to device applications.
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| 7. |
- Olsen, Sarah H., et al.
(författare)
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Control of self-heating in thin virtual substrate strained Si MOSFETs
- 2006
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 53:9, s. 2296-2305
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
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| 9. |
- Pope, Jeremy, 1991, et al.
(författare)
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Bifrodie;st: Creating Hardware with Building Blocks
- 2023
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Ingår i: Forum on Specification and Design Languages. - 1636-9874. ; 2023-September
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Konferensbidrag (refereegranskat)abstract
- Domain-specific hardware design has become increasingly attractive as single-Thread performance improvement has drastically slowed down. At the same time, it is clear that traditional hardware design approaches are difficult and error-prone. In this paper we describe a hardware design language, Bifrodie;st, aimed at allowing clear, correct, and modular specification of hardware. Bifrodie;st is tightly integrated into the Thor system, and thus a design in Bifrodie;st can be refined in a correctness-preserving way to a realistic hardware implementation. This paper gives both syntax and semantics of the language, highlights important design decisions, and illustrates its use in several projects. copy; 2023 IEEE.
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| 10. |
- Pope, Jeremy, 1991, et al.
(författare)
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Cephalopode: A custom processor aimed at functional language execution for IoT devices.
- 2020
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Ingår i: 2020 18th ACM-IEEE International Conference on Formal Methods and Models for System Design, MEMOCODE 2020.
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Konferensbidrag (refereegranskat)abstract
- The Internet of Things (IoT) conceives a future where "things"are interconnected by means of suitable information and communication technologies. Unfortunately, recent events have demonstrated the high vulnerability of IoT. One of the main reasons for this is the use of low-level programming languages. The Octopi project is developing technologies to easily and securely program IoT devices by the use of functional high-level languages. Unfortunately, a traditional implementation of a modern functional language that runs on traditional hardware is very resource demanding. So resource demanding that few, if any, IoT devices can run them.In the Cephalopode project (which is a subproject of Octopi) we are exploring the implementation of a very low power hardware device directly aimed at running a high-level functional language. By integrating many resource-heavy tasks into dedicated hardware, we aim at creating an execution engine for IoT devices that will allow secure programming.
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| 11. |
- Pope, Jeremy, 1991, et al.
(författare)
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Stately: An FSM Design Tool.
- 2020
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Ingår i: 2020 18th ACM-IEEE International Conference on Formal Methods and Models for System Design, MEMOCODE 2020.
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Konferensbidrag (refereegranskat)abstract
- Finite state machines (FSMs) are at the heart of many digital circuits, in particular microprocessors such as the IoT-oriented Cephalopode processor we are implementing as part of the Octopi project.We frequently encounter two practical difficulties with FSM design: first, in the case of Mealy machines state transitions and output logic can have complex and overlapping conditions, which are difficult to maintain and comprehend if separated; and second, there is a tension between clarity and clock cycles with respect to the insertion of intermediate states.To address these in the context of the Cephalopode processor we developed the open-source tool Stately, a visual environment for designing finite state machines. States are organized spatially, individually programmed in a simple domain-specific language, and the resulting machine can be compiled to HFL code for the VossII hardware design and simulation platform.In addition to allowing the intermingling of transitions and output declarations, Stately introduces a mechanism by which chosen states can be merged during compilation. While only a modest semantic extension, it resolves several clarity-efficiency tradeoffs while retaining a clear visual interpretation. Other features include lightweight simulation for rudimentary testing, and extensive error-checking.
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| 12. |
- Seger, Carl-Johan, 1961
(författare)
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Formal Verification of Complex Data Paths: An Industrial Experience
- 2021
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Ingår i: Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). - Cham : Springer International Publishing. - 1611-3349 .- 0302-9743. ; 13047 LNCS, s. 697-716
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Konferensbidrag (refereegranskat)abstract
- After caches, most transistors in a modern microprocessor are devoted to wide data-paths. Due to performance and power requirements, these data-paths often use complex implementations of sophisticated algorithms. As Intel experienced in 1994, a bug in a data-path can be extremely expensive and thus needs to be avoided at almost any cost. At the same time, simulation based verification is extremely poor at verifying data-paths due to the vast data space and thus formal verification is almost a requirement. In this paper a retrospective is given of the formal verification of complex data-paths that took place at Intel from the mid 1990 s until very recently. The technology that made the effort possible, the tools developed that made it feasible, and the methodology created that made it practical will all be discussed. Finally, a few examples that illustrates the approach will be presented as well as a concluding discussion on what the goal of using formal verification should be.
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| 13. |
- Seger, Johan, et al.
(författare)
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Enhanced phase stability and morphological stability of Ni(Si,Ge) on strained Si0.8Ge0.2
- 2003
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 429:02-jan, s. 216-219
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Tidskriftsartikel (refereegranskat)abstract
- NiSi0.8Ge0.2 film formed on a strained Si0.8Ge0.2 layer epitaxially grown on a Si(100) substrate wafer is morphologically stable up to 750 degreesC. The NiSi0.8Ge0.2 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 NiSi0.8Ge0.2 film and the Si0.8Ge0.2 layer. The presence of Ge in NiSi forming the ternary solution NiSi0.8Ge0.2 hinders the formation of NiSi2 even at 850 degreesC.
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| 14. |
- Seger, Johan, et al.
(författare)
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Increased nucleation temperature of NiSi2 in the reaction of Ni thin films with Si1-xGex
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:11, s. 1978-1980
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Tidskriftsartikel (refereegranskat)abstract
- 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 Angstrom, b=3.25+0.16x Angstrom, and c=5.68+0.15x Angstrom. The specific resistivity increases from 17 muOmega cm for NiSi to 21 muOmega 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 degreesC, 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 degreesC. Without Ge, the NiSi completely disappears at 750 degreesC. These results indicate a strong effect of the entropy of mixing in NiSi-NiGe on the nucleation of NiSi2.
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| 15. |
- Seger, Johan, et al.
(författare)
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Influence of a Si layer intercalated between Si0.75Ge0.25 and Ni on the behavior of the resulting NiSi1-uGeu film
- 2004
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:12, s. 7179-7182
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of Ni films with epitaxially grown Si-capped and not capped Si0.75Ge0.25 layers on Si(100) at 500degreesC 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 500degreesC 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 NiSi/Si interface in the absence of Ge. For thin Si caps, severe interface roughening with thick NiSi0.75Ge0.25 grains protruding deeply into the remaining Si0.75Ge0.25 is observed.
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| 16. |
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| 17. |
- Seger, Johan, 1975-
(författare)
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Interaction of Ni with SiGe for electrical contacts in CMOS technology
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the reactive formation of Ni mono-gernanosilicide, NiSi1-uGeu, for contact metallization of future CMOS devices where Si1-xGex can be present in the gate, source and drain of a MOSFET. Although the investigation has been pursued with a strong focus on materials aspects, issues related to process integration in MOSFETs both on conventional bulk Si and ultra-thin body SOI have been taken into consideration. The thesis work has taken a balance between experimental studies and theoretical calculations. The interaction between Ni films and Si1-xGex substrates, polycrystalline (poly) as in the gate or single-crystal (sc) as in the source/drain, leads to the formation of a ternary solid solution NiSi1-uGeu with the MnP structure in a wide range of temperature from 450 to 850oC. A linear variation of the lattice parameters of the NiSi1-uGeu with u is determined. A number of key observations are made: (1) the agglomeration of NiSi1-uGeu on Si1-xGex at a lower temperature compared to that of NiSi on Si, (2) the absence of NiSi2 up to 850 oC when Ge is present, and (3) a substantial Ge out-diffusion from the NiSi1-xGex and a precipitation of Ge-richer SiGe around the NiSi1-uGeu grains. These observations are interpreted referring to the ternary phase diagram for the Ni-Si-Ge system presented in this work. Possible factors influencing the morphological stability of NiSi1-uGeu films on Si1-xGex are discussed: (1) mechanical strain in the epitaxial Si1-xGex, (2) the favorable formation of NiSi at the expense of NiGe, (3) grain growth in poly-Si1-xGex, and (4) grain grooving in NiSi1-uGeu on sc-Si1-xGex. Energetically, the former two factors have been found to play a comparable, yet major role in the morphological instability of NiSi1-uGeu. The inter-diffusion of Si and Ge in NiSi1-uGeu and Si1-xGex provides the kinetic pathway for the morphological evolution. On Si1-xGex epitaxially grown on Si(100), a strong preferential orientation of the resulting NiSi1-uGeu film is found; NiSi films formed on Si show no specific film texturing. Furthermore, layer sequence and layer thickness of Si/SiGe or SiGe/Si are found to strongly affect the film texture in the resulting NiSi1-uGeu. Epitaxy of NiSi on NiSi1-uGeu, and vice versa, occurs across the compositional boundary, which confirms Ni as the dominant diffusion species during germanosilicide formation. The presence of Ge reduces the contact resistivity for NiSi1-uGeu on p-tyep Si1-xGex, as expected. For poly-Si1-xGex doped by B to 1020cm-3, a contact resistivity of 9x10-8 Ωcm2, 5 times lower than for the corresponding NiSi/Si contact, is obtained. On n-type Si1-xGex doped by As to 1020 cm-3, the opposite is true regarding the effect of Ge and a contact resistivity of 2x10-5 Ωcm2, 20 times higher than for the corresponding NiSi/Si contact, is obtained. When formed in the source/drain regions of a MOSFET fabricated on ultra-thin body SOI, a severe lateral growth of NiSi and Ni2Si into the channel region is revealed if the initial Ni thickness is too thick and if the silicidation conditions are not carefully controlled. This leads to a Schottky contact S/D MOSFET due to the consumption of the entire source/drain. In order to realize a low source/drain resistance for MOSFETs on ultra-thin SOI, satisfying the Roadmap recommendation for the 45-nm technology node, simplified calculations have been performed and an elevated source/drain structure is clearly shown to be advantageous.
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| 18. |
- Seger, Johan, et al.
(författare)
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Lateral encroachment of Ni-silicides in the source/drain regions on ultrathin silicon-on-insulator
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:25
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 19. |
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| 20. |
- Seger, Johan, et al.
(författare)
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Morphological instability of NiSi1-uGeu on single-crystal and polycrystalline Si1-xGex
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:4, s. 1919-1928
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Tidskriftsartikel (refereegranskat)abstract
- 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 550degreesC 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-xGex. The total free-energy change also includes terms corresponding to the entropy of mixing of Si and Ge in both Si1-xGex and NiSi1-uGeu. Calculations show that the strain energy and the total free-energy change can be 5-7 times (with 30 at.% Ge) the surface/interface and grain-boundary energies in a NiSi film or the grain-boundary energy in an underlying poly-Si. These latter energies are responsible for the agglomeration of NiSi on sc- and poly-Si. The agglomeration takes place primarily via the interdiffusion of Si and Ge between Si1-xGex and NiSi1-uGeu. A structure likely to improve the stability of NiSi1-uGeu/Si1-xGex is discussed.
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| 21. |
- von Haartman, Martin, et al.
(författare)
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Low-frequency noise in SiGe channel pMOSFETs on ultra-thin body SOI with Ni-silicided source/drain
- 2005
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Ingår i: Noise and Fluctuations. - : AIP. ; , s. 307-310
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Konferensbidrag (refereegranskat)abstract
- Thelow-frequency noise in buried SiGe channel pMOSFETs fabricated on ultra-thinbody silicon-on-insulator (SOI) substrates is investigated. The total thickness ofthe Si/SiGe/Si body structure, which is fully depleted (FD), is20 nm. The low-frequency noise properties are compared with FDSOI pMOSFETs with a 20 nm Si body. The effectof the Ni-silicide used in the Source/Drain were also studied,especially the case of Schottky-Barrier (SB) MOSFETs when the Ni-silicideis formed at the edges of the channel.
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| 22. |
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| 23. |
- Östling, Mikael, et al.
(författare)
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Novel integration concepts for sige-based rf-MOSFETs
- 2005
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Ingår i: Proc. Electrochem. Soc.. ; , s. 270-284
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Konferensbidrag (refereegranskat)abstract
- An overview of critical integration issues for future generation rf-MOSFETs is presented. The process requirements and implementation of selective epitaxy for the source and drain regions is given. In-situ doping of highly boron doped recessed SiGe S/D is demonstrated. Channel region engineering is discussed and 50 nm strained SiGe pMOSFETs are demonstrated. Implementation of high-κ gate dielectrics is presented and device performance is demonstrated for surface channel MOSFETs with a gate stack based on ALD-formed HfO2/Al 2O3. Low frequency noise properties for those devices are analyzed. Contact metallization issues are critical for ultra scaled devices and here the implementation of NiSi on SiGe(C) regions as well as on ultra thin body SOI MOSFETs are presented. Finally, a spacer pattering technology using optical lithography to fabricate sub-50 nm high-frequency MOSFETs is demonstrated.
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