Current requirements of nonvolatile memory (NVM) are the high density cells, low-power consumption, high-speed operation and good reliability for next-generation NVM application. However, all of the charges stored in the floating gate will leak into the substrate if the tunnel oxide has a leakage path in the conventional NVM during endurance test. Therefore, the tunnel oxide thickness is difficult to scale down in terms of charge retention and endurance characteristics. Nanocrystals (NCs) NVMs are one of the promising candidates to substitute for conventional floating gate memory since the discrete storage nodes as the charge storage media can effectively enable the improvement of data retention for the scaling down device. In this thesis, we try to overcome the limitation of conventional NVMs during the scaling down process and further increase the retention time by means of changing the structure of Nanocrystals NVMs. Firstly, we deposit a NiSi2 layer as the nanocrystal self-assembled layer and thereby apply it to Nanocrystals NVMs. In room temperature, we bombard NiSi2 target to form single layer and double layer charge trapping layer through sputtering system layer by layer, and the two charge trapping layers are separated by 30 Å silicon-oxide (SiO2). Next, we also deposit silicon oxide as control oxide. According to rapid thermal anneal (RTA) mix oxide gas, we improve the oxide quality and supply NiSi2 sufficient energy to reach the smallest Gibbs free energy so as to form uniform and high density NiSi nanocrystal. On account of the increasing of trapping center and the coulomb repulsion power, the double layer structure NiSi Nanocrystals NVMs has better memory window and retention than the single layer one. In the similar process, we sputter NiSi2 target with Ar gas mixes NH3 gas to form silicon-nitride compound layers. Then, we use the same RTA process to form nanocrystal and improve the oxide quality. In the light of TEM and XPS analysis, we may infer that the nanocrystal is formed by NiSi2 and SiNX compound. Further, based on our electronic analysis, we can observe that the retention of NiSi2/SiNX compound Nanocrystal NVMs after 104 sec rises from 50% to 72% in comparison with the traditional one due of the quantum well band structure contributes by NiSi2 and SiNX compound nanocrystals. The retention of NiSi2/SiNX compound Nanocrystal NVMs after 104 sec is even better than the double layer without NH3 mixed one, 68%. Furthermore, the threshold voltage of NiSi2/SiNX compound Nanocrystal NVMs has not been subject to change after endurance with 104 programming and erasing cycles continuously. Thus, by means of depositing nanocrystal charge trapping layer mixed with NH3 gas, we achieve the objective of simplifying the fabrication process. These fabrication techniques for the application of nonvolatile nanocrystal memory can also be applicable to the current manufacture process of the integrated circuit manufacture.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Im Rahmen dieser Arbeit wurden erste Untersuchungen zur Herstellung dünner NiSi(2-x)Al(x)- bzw. NiSi(2-x)Ga(x)-Schichten auf Si(001) erbracht. Dazu wurden Ni-Si-Al-Schichten mittels DC-Magnetron-Sputtern sowie Ni-Si-Ga-Schichten mittels Molekular-Strahl-Epitaxie (MBE) abgeschieden und anschließend in Abhängigkeit von der Herstellungsprozedur in einer RTA-Anlage thermisch behandelt. Die so entstandenen Reaktionsschichten wurden anschließend mittels RBS charakterisiert, wobei zusätzlich REM-, TEM-, AES-Tiefenprofil- und XRD-Untersuchungen ergänzend genutzt wurden. Es zeigt sich, dass unabhängig von der Abscheideprozedur bei ausreichend hoher Temper- bzw. Substrattemperatur die thermodynamisch stabilen Endphasen NiSi(2-x)Al(x) bzw. NiSi(2-x)Ga(x) gebildet werden. Während die Bildungstemperatur bei Festphasenreaktionen ohne Al- bzw. Ga-Zugabe für NiSi2 etwa 700°C beträgt, reduziert sich diese unter Anwesenheit von Al- bzw. Ga-Atomen auf 500°C und darunter. Dabei scheinen bereits eine Al- bzw. Ga-Konzentration von unter einem Atomprozent als notwendiger Stoffmengenanteil auszureichen. Befindet sich der Ort der Keimbildung der NiSi(2-x)Al(x)- bzw. NiSi(2-x)Ga(x)-Kristallite an der Grenzfläche zum Si(001)-Substrat, so ist eine Änderung der bevorzugten Wachstumsorientierung von NiSi(2-x)Al(x)(001)[100] || Si(001)[100] bzw. NiSi(2-x)Ga(x)(001)[100] || Si(001)[100] (A-Typ) zu einer NiSi(2-x)Al(x)(220) || Si(001)- bzw. NiSi(2-x)Ga(x)(220) || Si(001)-Vorzugsorientierung festzustellen. Die dafür notwendige Konzentration von Al- bzw. Ga-Atomen scheint jedoch höher zu sein als die, die für die Erniedrigung der Bildungstemperatur notwendig ist.

Les siliciures métalliques constituent un élément crucial des contacts électriques des transistors que l'on retrouve au coeur des circuits intégrés modernes. À mesure qu'on réduit les dimensions de ces derniers apparaissent de graves problèmes de formation, liés par exemple à la limitation des processus par la faible densité de sites de germination. L'objectif de ce projet est d'étudier les mécanismes de synthèse de siliciures métalliques à très petite échelle, en particulier le NiSi, et de déterminer l’effet de l’endommagement du Si par implantation ionique sur la séquence de phase. Nous avons déterminé la séquence de formation des différentes phases du système Ni-Si d’échantillons possédant une couche de Si amorphe sur lesquels étaient déposés 10 nm de Ni. Celle-ci a été obtenue à partir de mesures de diffraction des rayons X résolue en temps et, pour des échantillons trempés à des températures critiques du processus, l’identité des phases et la composition et la microstructure ont été déterminées par mesures de figures de pôle, spectrométrie par rétrodiffusion Rutherford et microscopie électronique en transmission (TEM). Nous avons constaté que pour environ la moitié des échantillons, une réaction survenait spontanément avant le début du recuit thermique, le produit de la réaction étant du Ni2Si hexagonal, une phase instable à température de la pièce, mélangée à du NiSi. Dans de tels échantillons, la température de formation du NiSi, la phase d’intérêt pour la microélectronique, était significativement abaissée. / Currently metal silicide constitutes a crucial component in the formation of electrical contacts for transistors that forms the heart of modern day integrated circuits. As we reduce the dimensions of the latter, we are faced with serious problems of formation, related for example to the process limitation due to the weak density of germination sites. The objective of this project is to study at small scale the synthesis mechanisms of metal silicide, in particular NiSi, and to determine the effect of Si implantation damage on the phase sequence. We have determined the different phase sequences of the Ni-Si system for samples composed of a 10 nm Ni surface layer deposited on a-Si. These were obtained by time resolved x-ray diffraction (TR-XRD) measurements. As for samples quenched at critical temperatures we identified the different phases, their composition and their microstructure were determined by pole figures, Rutherford back scattering (RBS) spectrometry and transmission electron microscopy (TEM). We noted that for approximately half the samples, a spontaneous reaction happened before annealing. The result of the reaction was hexagonal Ni2Si, a phase unstable at room temperature, mixed with NiSi. In theses samples, the temperature of formation for the phase of interest, the NiSi, was lower.

No description available.

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. / QC 20101005

NiSi is an attractive material in the production of CMOS devices. The problem with the utilization of NiSi, is that there is no proper method of cleaning the oxide on the surface. Sputtering is the most common method used for the cleaning, but it has its own complications. Dry cleaning methods include the reactions with radicals and these processes are not well understood and are the focus of the project. Dissociated NF3 and NH3 were used as an alternative and XPS is the technique to analyze the reactions of atomic fluorine and nitrogen with the oxide on the surface. A thermal cracker was used to dissociate the NF3 and NH3 into NFx+F and NHx+H. There was a formation of a NiF2 layer on top of the oxide and there was no evidence of nitrogen on the surface indicating that the fluorine and hydrogen are the reacting species. XPS spectra, however, indicate that the substrate SiO2 layer is not removed by the dissociated NF3 and NiF2 growth process. The NiF2 over layer can be reduced to metallic Ni by reacting with dissociated NH3 at room temperature. The atomic hydrogen from dissociated ammonia reduces the NiF2 but it was determined that the atomic hydrogen from the ammonia does not react with SiO2.

NiSi and Ni(Pt)Si, and of the effects of dissociated ammonia on oxide reduction was carried out under controlled ultrahigh vacuum (UHV) conditions. X-ray photoelectron spectroscopy (XPS) has been used to characterize the evolution of surface composition. Vicinal surfaces on NiSi and Ni(Pt)Si were formed in UHV by a combination of Ar+ sputtering and thermal annealing. Oxidation of these surfaces in the presence of either O+O2 or pure O2 at room temperature results in the initial formation of a SiO2 layer ~ 7 Å thick. Subsequent exposure to O2 yields no further oxidation. Continued exposure to O+O2, however, results in rapid silicon consumption and, at higher exposures, the kinetically-driven oxidation of the transition metal(s), with oxides >35Ǻ thick formed on all samples, without passivation. The addition of Pt retards but does not eliminate oxide growth or Ni oxidation. At higher exposures, in Ni(Pt)Si surface the kinetically-limited oxidation of Pt results in Pt silicate formation. Substrate dopant type has almost no effect on oxidation rate. Reduction of the silicon oxide/metal silicate is carried out by reacting with dissociated NH3 at room temperature. The reduction from dissociated ammonia (NHx+H) on silicon oxide/ metal silicate layer shows selective reduction of the metal oxide/silicate layer, but does not react with SiO2 at ambient temperature.

Im Rahmen dieser Arbeit wurden erste Untersuchungen zur Herstellung dünner NiSi(2-x)Al(x)- bzw. NiSi(2-x)Ga(x)-Schichten auf Si(001) erbracht. Dazu wurden Ni-Si-Al-Schichten mittels DC-Magnetron-Sputtern sowie Ni-Si-Ga-Schichten mittels Molekular-Strahl-Epitaxie (MBE) abgeschieden und anschließend in Abhängigkeit von der Herstellungsprozedur in einer RTA-Anlage thermisch behandelt. Die so entstandenen Reaktionsschichten wurden anschließend mittels RBS charakterisiert, wobei zusätzlich REM-, TEM-, AES-Tiefenprofil- und XRD-Untersuchungen ergänzend genutzt wurden. Es zeigt sich, dass unabhängig von der Abscheideprozedur bei ausreichend hoher Temper- bzw. Substrattemperatur die thermodynamisch stabilen Endphasen NiSi(2-x)Al(x) bzw. NiSi(2-x)Ga(x) gebildet werden. Während die Bildungstemperatur bei Festphasenreaktionen ohne Al- bzw. Ga-Zugabe für NiSi2 etwa 700°C beträgt, reduziert sich diese unter Anwesenheit von Al- bzw. Ga-Atomen auf 500°C und darunter. Dabei scheinen bereits eine Al- bzw. Ga-Konzentration von unter einem Atomprozent als notwendiger Stoffmengenanteil auszureichen. Befindet sich der Ort der Keimbildung der NiSi(2-x)Al(x)- bzw. NiSi(2-x)Ga(x)-Kristallite an der Grenzfläche zum Si(001)-Substrat, so ist eine Änderung der bevorzugten Wachstumsorientierung von NiSi(2-x)Al(x)(001)[100] || Si(001)[100] bzw. NiSi(2-x)Ga(x)(001)[100] || Si(001)[100] (A-Typ) zu einer NiSi(2-x)Al(x)(220) || Si(001)- bzw. NiSi(2-x)Ga(x)(220) || Si(001)-Vorzugsorientierung festzustellen. Die dafür notwendige Konzentration von Al- bzw. Ga-Atomen scheint jedoch höher zu sein als die, die für die Erniedrigung der Bildungstemperatur notwendig ist.